Approximately 60% of patients with breast cancer require radiotherapy. With significant advances in breast cancer outcomes, an increasing focus is being placed on cancer survivorship, including the reduction of the late effects from radiotherapy. The aim of this review article is to highlight the potential of particle therapy in ensuring comprehensive radiotherapy for patients with breast cancer while reducing normal tissue exposure that can lead to subsequent impairments in quality of life. We review the latest literature in this space for both proton and carbon therapy and highlight opportunities for future study.Particle therapy has received increasing attention in the treatment of breast cancer due to its unique physical properties that may enhance patient quality of life and reduce the late effects of therapy. In this review, we will examine the rationale for the use of proton and carbon therapy in the treatment of breast cancer and highlight their potential for sparing normal tissue injury. We will discuss the early dosimetric and clinical studies that have been pursued to date in this domain before focusing on the remaining open questions limiting the widespread adoption of particle therapy. Advances in multi-disciplinary care have led to improvement in overall outcomes for women diagnosed with breast cancer, with a 40% decline in breast cancer mortality seen over the last 28 years . With imParticle therapy, by virtue of its physical properties, can better spare normal tissue, or OARs, in proximity to the radiation target, compared to conventional radiation. Specifically, both proton therapy and carbon therapy exhibit a narrow area of high energy deposition with a sharp dose fall off, called a Bragg peak. This distribution of radiation, in contrast, to conventional X-rays, permits more precise dose shaping, particularly distal to the radiation beam, resulting in greater sparing of low dose to normal tissue beyond the target . In the Much attention has been paid to the cardiac sparing properties of proton therapy given the well-described association between mean cardiac dose exposure and subsequent major cardiac events. In the oft-cited study by Darby and colleagues of greater than 2100 women with breast cancer receiving radiation therapy, a linear relationship was demonstrated between the risk of ischemic cardiac events and estimated mean radiation dose exposure to the heart, wherein each increase in 1 Gy of mean radiation dose exposure to the heart corresponded to a 7.4% increase in major coronary events (MCE), with no minimum threshold for events . More moCardiac sparing holds particular value when considering target coverage to the internal mammary nodes (IMN). Coverage of the IMN with breast radiotherapy has been shown to improve overall and disease-free survival for women with high-risk breast cancer, both in a population-based trial and in the meta-analysis of the EORTC 22922 and MA.20 trials ,14,15,16When considering proton therapy’s cardiac sparing properties, some have also posed the advantage of combining other cardiac sparing approaches, including deep inspiration breathhold techniques (DIBH), with proton delivery with the goal of furthering limiting cardiac exposure. However, many institutions do not utilize DIBH with proton therapy, despite widespread use of DIBH with photon therapy because of the additional technical requirements of DIBH and because of the modest additional dosimetric benefits suggested when DIBH is paired with proton dosimetry . HoweverProton therapy can also be effective at limiting both high- and low-dose exposure to the ipsilateral and contralateral lungs. Taking advantage of the steep dose fall-off of the Bragg peak, the dose gradient is sharp, allowing for reduction of lung tissue in the treatment field. While modern estimates of grade 2 or higher radiation pneumonitis (1–3%) and pulmonary fibrosis (4–5%) after photon-based RNI are modest ,24, furtMusculoskeletal sparing including relative sparing of the intrinsic muscles of the shoulder has been posited as potentially beneficial to reduce arthritis and/or extremity symptoms. Upper limb disability is a common problem after breast cancer therapy . Women uImportantly, as a consequence of pre-existing shoulder or arm conditions or as a result of axillary dissection, shoulder abduction and/or external rotation may be limited at the time of radiation planning. In these women, proton therapy  can be used to spare normal tissues of the arm and shoulder while treating patients in an arms-down or akimbo position without limiting therapeutic doses to target tissues . Photon-As proton beam therapy is not reliant on tangential fields to avoid normal tissue, the contralateral breast does not receive meaningful radiation exposure, resulting in a lower estimated risk of contralateral breast cancer, compared to other photon-based radiation techniques ,25,33,34Geometric challenges may arise in those undergoing standard intact breast or post-mastectomy radiotherapy with photons for a number of reasons. For those undergoing mastectomy, reconstruction is increasingly pursued by women. Target coverage may be compromised, or doses to OARs may be higher, particularly among those with bilateral reconstruction with permanent implants ,37 as thOther underlying anatomic variations can lead to considerable geometric challenges for photon radiation. For example, when larger than typical target volumes are required, such as those with inflammatory breast cancer, deep nodal boosts, or extensive skin involvement, photon radiotherapy target coverage may be compromised. Yet, these are often the scenarios in which such compromise could be most detrimental, and the recurrence risk highest, suggesting that improved target coverage using proton therapy may meaningfully reduce risk for recurrence a. In addPectus excavatum (PEx) also often results in anatomic distortion of the cardiac position, making appropriate cardiac sparing with typical photon approaches challenging. Compared with optimal VMAT-BH plans, proton therapy reduced mean heart dose, lung dose, and contralateral breast dose in a planning study of women with PEx . DosimetIn scenarios under which comprehensive target coverage is desired and particle therapy is utilized for breast cancer radiotherapy, some normal tissue exposure may be counterintuitively higher than when using three-dimensional conformal radiotherapy. For example, the medial portion of the supraclavicular fossa is typically omitted from the radiation field when using three-dimensional conformal radiotherapy due to concerns of spinal cord and spinal nerve root exposure. With particle therapy, more complete target coverage of the supraclavicular fossa can be achieved due to the precise dose shaping of the beam, but with the trade-off of slightly higher exposures to the esophagus and thyroid gland, similar to what can be observed with volumetric arc therapy, or other inverse planned photon techniques . TherefoThe unique dosimetric advantages of proton therapy may offer particular benefit in scenarios in which reduction of normal tissue exposure is of heightened importance. For example, the risk for contralateral breast cancer is high among those with underlying genetic mutations . Such paFor those undergoing reconstruction with tissue flaps, particle therapy offers the unique ability to dose paint, allowing for potential advantages such as sparing of the vascular anastomosis. This sharper dose fall-off could result in other anatomic regions outside of historically delineated CTVs receiving a lower dose than what was delivered with photon-based treatments; however, whether or not this reduction results in a clinically meaningful recurrence risk in these regions remains unknown. For example, intentional sparing of the dissected levels I/II when deemed appropriate has been associated with lower risk for lymphedema, and proton therapy could further enhance sparing of the dissected axilla. Further investigations into defining the highest risk regions may yield opportunities for customization or dose painting within the CTV, as the updated ESTRO contouring guidelines suggest that deep and lateral tissue may be spared .There are presently few data that report on reconstructive results following radiotherapy with particles; however, early findings have been encouraging. In a prospective trial of 69 patients treated with proton therapy, 83% pursued breast reconstruction and while approximately one-third experienced some form of unplanned surgical re-intervention at 5 years, only 4% experienced reconstructive loss attributable to radiation . ImportaModerately hypofractionated radiotherapy, using doses of approximately 2.65–2.67 Gy per day, is established as the current standard of care for women undergoing adjuvant whole breast radiotherapy, based on equivalent oncologic outcomes, with similar or reduced toxicity reported in long term follow-up ,49. HypoThe use of ultrahypofractionated whole breast and regional nodal irradiation, using 5.2–5.7 Gy per day, is also receiving increasing attention based on equivalent oncologic outcomes with similar toxicity reported in short-term follow-up from the UK FAST FORWARD trial . One cliAccelerated partial breast radiotherapy (APBI) has emerged as an appropriate form of adjuvant radiotherapy following lumpectomy in women with favorable early-stage breast cancer, such as those with small, hormone receptor positive, lymph node negative disease. The data have consistently demonstrated that, in select populations, APBI enables more convenient, efficient therapy with similar oncologic outcomes ,58,59,60Radiotherapy techniques utilizing carbon ions offer many similar physical advantages to those achieved using proton therapy, albeit with less prospective literature to date to provide support for use in breast cancer  Table 1Table 1. With the goal of harmonizing the unique characteristics of carbon ion therapy, a few studies have begun to demonstrate encouraging findings across diverse disease sites. For instance, the COSMIC study prospectively explored a combination of carbon ion therapy (24 Gy RBE) followed by 50 Gy IMRT for patients with malignant salivary gland tumors, with an encouraging three-year local control of 81.9%, and moderate acute and late toxicity . Other, In breast cancer, utilization of carbon ion therapy is nascent, but has shown potential utility in early clinical case reports . For insUnfortunately, cost and resource barriers prevent widespread use of carbon ion radiation therapy for breast cancer. For example, while carbon ion treatment centers are open and treating patients in at least five countries, no carbon ion center has yet been built in the United States. In addition, the optimal clinical scenarios to justify the use of carbon therapy are not fully understood. Combining carbon ion radiation therapy with existing modalities, as in the COSMIC trial, could offer a novel approach to explore its utility, but for the reasons above, utilization is likely to progress slowly. Alternatively, carbon ion therapy may have a potential role involving definitive radiotherapy for breast cancer, as opposed to adjuvant therapy. However, such a substantial paradigm shift would also require further study.As particle therapy offers more precise dose shaping and treatment delivery, it is inherently more sensitive to changes in immobilization and daily set-up variations. This is true among women with reconstructed breasts because the implant and/or tissue expander can shift in position during treatment. It can also be identified in women with intact breasts who experience inflammatory changes and edema over the course of treatment. Consequently, daily set-up surface imaging in combination with X-ray and cone-beam CT is typically employed and in circumstances where shifts exceed institutional tolerance based on robustness calculations, it should prompt re-planning to ensure fidelity of the intended dose delivery ,80.While the central advantage of particle therapy has focused on its beneficial physical properties, there is emerging data to indicate that particle therapy may also hold unique biologic properties with implications for both normal tissue toxicity and cancer control. For example, while it is assumed that the average radiobiologic equivalent dose (RBE) of protons relative to photon beams is approximately 1.1, it has been supported through multiple studies that the acute RBE values may be higher, particularly at the end of range ,82. NormDespite the rapid increase in indications for, and the availability of, particle therapy across the world, it remains a limited resource . AccordiFuture comprehensive cost-effectiveness analysis could also consider individual risk profiles. Separate cost analyses may be warranted for additional scenarios in breast cancer radiotherapy, including those with altered fractionation. For instance, partial breast irradiation has historically been offered for carefully-selected elderly patients with favorable tumor characteristics; however, providing a 3-fraction proton-based PBI treatment may also provide cost-effective treatment to a young patient by minimizing secondary malignancies and cardiac risk . DespiteExploring the full utility of particle therapy for breast cancer is still required in many domains. Suboptimal patient selection is a potential concern, as particle therapy may be maximally beneficial only in specific clinical situations. Further, particle therapy remains a limited resource not available to all patients, so judicious use is required for equitable healthcare ,97. PartParticle therapy offers a radiobiologically distinct modality for the delivery of radiotherapy, and its use may improve patient outcomes and minimize toxicity in specific clinical situations in breast cancer. Future research is required to optimize patient selection for particle therapy . We awai


The serendipitous discovery of ketamine’s antidepressant effects represents one of the major landmarks in neuropsychopharmacological research of the last 50 years. Ketamine provides an exciting challenge to traditional concepts of antidepressant drug therapy, producing rapid antidepressant effects seemingly without targeting monoaminergic pathways in the conventional way. In consequence, the advent of ketamine has spawned a plethora of neurobiological research into its putative mechanisms. Here, we provide a brief overview of current theories of antidepressant drug action including monoaminergic signaling, disinhibition of glutamatergic neurotransmission, neurotrophic and neuroplastic effects, and how these might relate to ketamine. Given that research into ketamine has not yet yielded new therapies beyond ketamine itself, current knowledge gaps and limitations of available studies are also discussed. The purpose of this mini-review is, therefore, to provide an overview of current thinking on ketamine’s putative mechanisms of action within the context of antidepressant drug discovery and development.®), was serendipitously identified as possessing antidepressant characteristics  occur within a few hours while conventional antidepressants typically require several days to weeks to take effect. Neurobiological research into the mechanisms underpinning the antidepressant response has therefore pivoted to longer-term adaptive changes downstream of the acute effects on biogenic amines.N-methyl-D-aspartate (NMDA) receptor antagonist. However, in a manner somewhat reminiscent of clozapine, ketamine is a “dirty” drug. Multiple off-target effects including on monoamine systems need to be considered. In vitro, ketamine displays affinity to dopamine D2 and serotonin 5-HT2 receptors in the same range as its affinity for the NMDA receptor -HNK. From a broader view, however, the prospect of discovering other molecules, not directly related to ketamine itself but tapping into the same neurobiological mechanisms, remains uncertain, at least for the time being. So far, the principle of NMDA antagonism has, unfortunately, not translated into tangible new drugs. Also, side-effects beyond psychotic symptoms have to be considered. Merck & Co’s dizocilpine (commonly referred to as MK-801 in the lab), a strong NMDA receptor antagonist, was shown to produce acute pathomorphological lesions in specific populations of neurons when administered acutely to adult rats in comparatively low doses . MK-801 Moving beyond neurotoxicity, which may represent a class effect, investigations of NMDA receptor antagonists other than ketamine in depression have, so far, failed to produce clinically relevant outcomes. Memantine proved ineffective as an antidepressant in two double-blind placebo-controlled trials . SimilarThe possibility of still other modes of action should also not be overlooked. It has long been known that ketamine possesses certain anti-inflammatory properties, which may especially benefit patients undergoing major surgery or septic patients requiring sedation . IntriguOpioid effects have also been implicated in ketamine’s clinical profile. Both S- and R-ketamine bind to and activate mu and kappa opioid receptors . FurtherIn the aggregate, ketamine represents the first major breakthrough in antidepressant development in the last half-century. As described above, it engages novel mechanisms beyond monoaminergic neurotransmission, resulting in a much faster onset of action than conventional monoamine-based therapeutics. Although much remains to be elucidated, the advent of ketamine signals exciting new opportunities to extend and refine our knowledge of the neurobiological mechanisms underlying the antidepressant response. Given the accruing evidence of ketamine’s therapeutic effects in TRD, it seems that the time has arrived to assign a central position to ketamine as an augmentation in the treatment algorithms for TRD patients.GK drafted the manuscript with substantive input from all authors. All authors contributed to the article and approved the submitted version.The authors are conducting a study of oral ketamine in TRD funded by Ketabon GmbH. ES serves on advisory boards of Janssen.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Variations in headgroup and acyl chains influence phospholipid physicochemical properties and consequently the membrane behavior. Flaviviruses interact with cellular membranes at every step of their cellular cycle. Recent evidence demonstrates that flaviviruses reconfigure the phospholipidome in mosquitoes by regulating phospholipid syntheses to increase virus multiplication. Identifying the phospholipids involved and understanding how flaviviruses regulate these in mosquitoes is required to design new interventions.Mosquito-borne flaviviruses, such as dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses, threaten a large part of the human populations. In absence of therapeutics and effective vaccines against each flaviviruses, targeting viral metabolic requirements in mosquitoes may hold the key to new intervention strategies. Development of metabolomics in the last decade opened a new field of research: mosquito metabolomics. It is now clear that flaviviruses rely on mosquito lipids, especially phospholipids, for their cellular cycle and propagation. Here, we review the biosyntheses of, biochemical properties of and flaviviral interactions with mosquito phospholipids. Phospholipids are structural lipids with a polar headgroup and apolar acyl chains, enabling the formation of lipid bilayer that form plasma- and endomembranes. Phospholipids are mostly synthesized through the  Flaviviruses like dengue (DENV), Zika (ZIKV), yellow fever (YFV), West Nile (WNV), and Japanese encephalitis (JEV) viruses threaten almost the whole human population . They caThere is no effective means to control all flaviviruses . Rare exRecent technical developments enabled the study of metabolic interactions in flavivirus infection [methodology of metabolomics was extensively reviewed in Aedes or Culex mosquitoes (Mosquito-transmitted flaviviruses such as the four DENV serotypes (DENV 1–4), ZIKV, YFV, JEV, and WNV are genetically related and primarily transmitted by either squitoes . FlaviviViruses collected during a blood meal on an infected host first infect the mosquito midgut epithelium . While bThroughout infection in mosquito, flaviviruses are confronted to different barriers . After iPhospholipids (PL) are composed of one hydrophilic head group, a glycerol backbone and two hydrophobic fatty acyl chains . DependiPhospholipid biosynthesis is intimately connected with the tricarboxylic (TCA) cycle and glycolysis . CarbohyThe fatty acyl chains of PL can have different carbon number and degree of saturation, both of which are generated during fatty acid biosynthesis. Fatty acid synthesis starts with the formation of malonyl-CoA from acetyl-CoA, via acetyl-CoA carboxylase . In the Mono-unsaturated fatty acids are produced by oxidative desaturation by desaturases to form a double bond. The first double bond introduced is generally in carbon at position 9 (Δ9) . In mostde novo biogenesis is initiated by two types of acyl-transferases that sequentially add two acyls to one glycerol-3-phosphate  or cytidine diphosphate (CDP)-DAG (CDP)-DAG . SynthesDe novo PC and PE synthesis is conducted through the Kennedy pathway  calcium-independent PLA2; and (iv) platelet activating factor lipoprotein-associated PLA2. There exist other types of phospholipases that can hydrolyze PL  are produced . As the As steric hindrance of PL varies with the headgroup size and the acyl chains, PL composition influences membrane shape . PC and Membrane asymmetry refers to an asymmetric distribution of lipid species in lipid bilayers. Asymmetry induces biophysical properties that promote certain cellular functions . A well-Phospholipid asymmetry is maintained by lipid transporters . FlippasElectrostatic charges of membranes depend on negatively charged lipids, i.e., PS and phosphoinositides (PIPs) . PS and Lipid packing defects refer to heterogeneous lipid arrangements, which loosen lipid bilayer and increase fluidity, facilitating protein insertion . Ratio bLipid phase relates to the fluidity of lipid membranes and how lipids can move within each layer. The liquid phase is characterized by lateral mobility of lipids within their layer, whereas in the solid phase, also called gel phase, lipids lose lateral mobility. Lipid phase depends on the lipid composition and extrinsic factors such as temperature, pressure, and composition of the aqueous phase . Most biMembrane lipids can also form non-lamellar transitory structures, known as hexagonal phases . HexagonProteins inserted in membranes drastically modify the behavior of lipid membranes. Insertion of proteins is influenced by the physicochemical parameters of the membrane, such as curvature, electrostatics, and lipid packing . Once inLipid droplets (LD) are essential for cell storage of carbons in the form of neutral lipids, triacylglycerol and sterol esters . These sLipids in LD are mobilized by lipases to provide substrates for PL synthesis, fatty acid pathway, and signaling lipid production . LD alsoFlavivirus virions are composed of three structural proteins, all of which interact with lipids. The envelope and membrane proteins form the outer layer of the virion and are anchored in a lipid bilayer membrane. The asymmetric charge distribution of the capsid enables interaction with lipid membranes  and LDs,Virus attachment occurs through interactions with cell surface factors, including, but not restricted to, lipids . There eAfter virus adsorption to cell surface, entry occurs mainly by clathrin-dependent endocytosis . As compCholesterol is a crucial lipid during flavivirus entry, playing a role both in the target cell and in the viral particle. Depletion of cellular cholesterol inhibits DENV and JEV entry , while sOnce released, the encapsidated genome is uncoated and recruited to ER-bound ribosomes for translation. The single open reading frame of the genome is translated into a multi-pass transmembrane polyprotein, which is processed by viral and host proteases into the three structural proteins  and seven non-structural proteins  . SuccessTo initiate genome replication, a negative single-strand RNA antigenome is produced from the entering positive-strand genome and then used as a template to duplicate the positive-strand genome . ReplicaSeveral of the non-structural viral proteins are required to rearrange ER membranes into replication complexes . VesicleFlavivirus assembly occurs within the ER membrane . The captrans-Golgi networks and requires an acidic environment , immune deficiency pathway (IMD), the Toll pathway, the Jun-N-terminal Kinase (JNK) pathway, and the RNA interference pathway (RNAi) have all been shown to reduce flavivirus infection . InteresD number . The intReconfiguration of the lipidome upon infection in mosquitoes may also modify lipid-mediated signaling. Prostaglandins that regulate immunity and inflammation  are reguBecause of the lack of treatment and of effective vaccines against all flaviviruses, there is a great need for new strategies to block flavivirus transmission. Targeting branches of lipid metabolism that are required for virus infection may hold the key to novel antiviral tools. While lipid-related anti-flaviviral strategies have already been reviewed , targetide novo PL biogenesis reduces virus load, disrupting PL biosynthesis may hinder viral multiplication. Induction of de novo PL biogenesis by supplementing the blood on which mosquitoes feed with a de novo PL precursor reduced mosquito midgut infection (de novo PL biogenesis could be activated by exogenous supply of PE. Moreover, flavivirus infection significantly modifies blood lipid composition (As PL remodeling promotes DENV infection in mosquitoes  whereas nfection . Harnessposition , which tposition . ChemicaLipid-targeted therapeutics have been identified for other viruses. Influenza virus infection is blocked by the fatty acid docosahexaenoic acid, which limits transport of viral transcripts . Supplemin vitro and in vivo metabolomic approaches. However, there remain much to understand. The importance of PL and its reconfiguration for DENV infection in mosquitoes is well established now but studies with multiple flavivirus species are required to determine the conservation of these lipid needs. Further mechanistic analyses will also help identify the PL species involved and understand how flaviviruses alter their concentrations. In the end, characterized PLs will provide ideal targets for novel transmission blocking strategies.Our understanding of the lipid interactions between mosquitoes and flaviviruses has expanded in recent years, thanks to innovative TV and JP wrote the original draft. TV, DM, GM, and JP edited the manuscript. All authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Exosomes are cell-secreted nano-sized vesicles which deliver diverse biological molecules for intercellular communication. Due to their therapeutic potential, exosomes have been engineered in numerous ways for efficient delivery of active pharmaceutical ingredients to various target organs, tissues, and cells. In vivo administered exosomes are normally delivered to the liver, spleen, kidney, lung, and gastrointestinal tract and show rapid clearance from the blood circulation after systemic injection. The biodistribution and pharmacokinetics (PK) of exosomes can be modulated by engineering various factors such as cellular origin and membrane protein composition of exosomes. Recent advances accentuate the potential of targeted delivery of engineered exosomes even to the most challenging organs including the central nervous system. Major breakthroughs have been made related to various imaging techniques for monitoring in vivo biodistribution and PK of exosomes, as well as exosomal surface engineering technologies for inducing targetability. For inducing targeted delivery, therapeutic exosomes can be engineered to express various targeting moieties via direct modification methods such as chemically modifying exosomal surfaces with covalent/non-covalent bonds, or via indirect modification methods by genetically engineering exosome-producing cells. In this review, we describe the current knowledge of biodistribution and PK of exosomes, factors determining the targetability and organotropism of exosomes, and imaging technologies to monitor in vivo administered exosomes. In addition, we highlight recent advances in strategies for inducing targeted delivery of exosomes to specific organs and cells. DNAs, RNAs), proteins, lipids, and carbohydrates. Of note, in vivo circulating exosomes isolated from body fluids (e.g. urine and blood) carry biological materials (e.g. proteins and nucleic acid) and represent current physiological conditions, which suggests the diagnostic value of exosomes as novel biomarkers for multiple pathophysiological conditions including cancer , 4544, 4One of the main factors that determine the biodistribution of exosomes is its cellular origin. Exosomes from different cellular sources were observed to have an asymmetric biodistribution , and subCellular or organ targeting of exosomes is influenced by various membrane compositions of exosomes, such as proteins, lipids, and glycans. Membrane protein composition of exosomes is determined by their cellular origin as well as the physiological state of parental cells during exosome biogenesis . For inse.g., CD9, CD63, CD81, CD82), integrins and MHC molecules, of which various composition of these proteins could influence organotropism of exosomes .–83.81–83The surface of exosomes can be directly engineered via various chemical or physical modifications for inducing targetability of therapeutic exosomes. There are two major modification approaches for directly introducing targeting moieties to the exosomal surface: one is utilizing covalent attachments of targeting moieties such as “click chemistry”, and the other utilizes non-covalent methods . Additiovβ3 which is expressed in reactive cerebral vascular endothelial cells after ischemia, was conjugated to the surface of MSC-derived exosomes by click chemistry for the treatment of stroke [Click chemistry utilizes covalent interactions between an alkyne and azide residue to form a stable triazole linkage, which can be applied to attach targeting moieties on the surface of exosomes in a variety of aqueous buffers including water, alcohols, and dimethyl sulfoxide (DMSO) –88. PEGyf stroke . c which is fused with exosomal membrane components such as tetraspanins, Lamp2b, and C1C2 domain of lactadherin . To deliver therapeutic exosomes to cancer cells, targeting moieties which could bind to specific integrins or receptors expressed on cancer cells, such as antibodies and peptides, could be expressed on the surface of therapeutic exosomes with genetic modification approach. For instance, fusion proteins of anti-EGFR nanobodies conjugated with glycosylphosphatidylinositol (GPI)-anchor signal peptide were utilized to induce targetability of exosomes to EGFR-expressing tumor cells [v integrin-specific iRGD peptide fused with Lamp2b was over-expressed on the surface of exosomes produced from immature dendritic cells (iDCs), and these exosomes were loaded with doxorubicin as API via electroporation. Compared to non-engineered exosomes, these exosomes exhibited threefold better cellular uptake by human breast cancer cells in vitro and showed better anti-tumor efficacy in vivo with threefold decrease of tumor volume compared to tumor volume of non-engineered exosome-treated mouse [vβ3 in an RGD (Arg-Gly-Asp) dependent manner, which could target αvβ3 overexpressing tumors such as melanoma, glioma and breast cancer [Recently, there has been considerable attentions in active targeting of therapeutic exosomes to various cancer cells  with high biocompatibility, high yield capacity for intercellular cargo delivery and low immunogenicity. Due to these biological and functional characteristics, exosomes can be utilized as novel therapeutic platform for delivering various API cargos with specific tissue/cell targetability via multiple exosome engineering technologies.Here, we reviewed the current knowledge for biodistribution and PK of systemically administered exosomes, factors influencing the targetability of exosomes, and technologies to determine administered exosomes’ in vivo fate. We also summarized technologies and strategies for inducing active targeting of exosomes to specific tissues/cells. These factors are essential for developing next-generation exosome therapeutics with clinical efficacy and safety. Although there are still significant technological huddles to overcome for developing clinical-grade exosomes, the efforts made by the leading companies developing exosome therapeutics will pave the way for conquering the scientific and technological challenges. In conclusion, we can position exosome as an attractive next-generation therapeutic platform to treat the various human diseases with medical unmet needs.


Recent advances in our understanding of the stem cell potential in adult tissues have far-reaching implications for cancer research, and this creates new opportunities for the development of new therapeutic strategies. Here we outline changes in stem cell biology that characterize main gynaecological malignancies, ovarian, endometrial, and cervical cancer, and focus on specific differences between them. We highlight the importance of the local niche environment as a driver of malignant transformation in addition to mutations in key cancer-driving genes. Patient-derived organoids capture in vitro main aspects of cancer tissue architecture and stemness regulatory mechanisms, thus providing a valuable new platform for a personalized approach in the treatment of gynecological malignancies. This review summarizes the main achievement and formulates remaining open questions in this fast-evolving research field.Gynaecological malignancies represent a heterogeneous group of neoplasms with vastly different aetiology, risk factors, molecular drivers, and disease outcomes. From HPV-driven cervical cancer where early screening and molecular diagnostics efficiently reduced the number of advanced-stage diagnosis, prevalent and relatively well-treated endometrial cancers, to highly aggressive and mostly lethal high-grade serous ovarian cancer, malignancies of the female genital tract have unique presentations and distinct cell biology features. Recent discoveries of stem cell regulatory mechanisms, development of organoid cultures, and NGS analysis have provided valuable insights into the basic biology of these cancers that could help advance new-targeted therapeutic approaches. This review revisits new findings on stemness and differentiation, considering main challenges and open questions. We focus on the role of stem cell niche and tumour microenvironment in early and metastatic stages of the disease progression and highlight the potential of patient-derived organoid models to study key events in tumour evolution, the appearance of resistance mechanisms, and as screening tools to enable personalisation of drug treatments. Gynaecological malignancies represent a great medical burden for women’s health in general. Together, uterine, cervical, and ovarian cancer are responsible for approximately 30,000 deaths every year in the USA (CDC data) , with anAlthough the whole genital system functions within the hormonal milieu during reproductive years, in some cases, the same physiological stimuli have opposing effects on cancer risk depending on the cancer type. For example, while oral contraceptives significantly reduce the risk of ovarian and endometrial cancers, they increase the risk for cervical cancer ,4. MoreoEpithelial homeostasis in healthy tissue is maintained by the presence of long-lived progenitor cells that continuously give rise to differentiated progeny. Wnt pathway signalling gradients play a central role in the maintenance of homeostasis in all structures of Mullerian duct origin: fallopian tubes, uterus, and cervix. Active Wnt signalling is essential for the development of the genital tract, which is apparent in strong defects in female sex determination during embryogenesis caused by deleterious mutations of Wnt pathway components . While cA recent study in mice demonstrated that the Wnt gradient defines the border between endocervical columnar epithelium and squamous epithelium of the ectocervix, where likely two different populations of stem cells are regenerating epithelial compartments depending on the signalling received from the stroma . While eStill, more comprehensive molecular studies are necessary to understand how regeneration processes are regulated on the cellular level in response to different physiological environments in all regions of the genital tract.The intersection between intrinsic and extrinsic factors in tumour development occurs at the level of the stem-cell compartment, which is regulated by paracrine signalling. Epithelium regeneration has an intrinsic lineage hierarchy, but the stromal compartment can produce signals that directly influence stem cell differentiation . AlthougEpithelial ovarian cancer is a heterogeneous disease, classified based on the histologic types on high-grade serous, mucinous, endometrioid, clear cell cancer, and transitional cell carcinoma. While HGSOC likely originates from the epithelium of the distal fallopian tube, the phenotypic characteristics and molecular profile of mucinous tumours indicate that they could be metastasis from the intestinal tract, and endometrioid and clear cell are the rare malignant transformation of endometriotic tissue from the uterus .Secretory cell outgrowth is presumed to be an early step in HGSOC aetiology . Serous Lineage tracing studies in mice  and tempEndometrial cancer is a malignancy of the inner uterine lining and the most frequent gynaecological malignancy in industrialised countries. Endometrial cancer is broadly classified into two types: endometrioid cancer (75% of cases) and serous cancer (25%). Serous endometrial cancer shares some important genetic hallmarks with HGSOC, >90% prevalence of TP53 mutation and high copy number variations (CNV), while the more common endometrioid type has recurring PTEN, PIK3CA, and ARID1A mutations . ConditiEndometriosis is a prevalent uterine disease that affects up to 10% of women of active reproductive age and has a debilitating effect on the fertility and quality of life of the patients but is a generally benign condition. Its main manifestation is uncontrolled expansion of endometrial epithelium which can extend to extrauterine sites such as ovary or peritoneum. On the molecular level, it represents a very interesting example of extensive change in phenotype and great proliferative potential of the epithelium but without the invasive biology characteristic of malignancies. Subtle changes in growth requirements of endometrial organoids are reported ,29, whicThe cervix connects the uterine cavity with the vagina and consists of the endocervix, composed of a single layer of mucin-secreting columnar cells, and ectocervix, composed of stratified squamous epithelium projecting into the vagina. The squamocolumnar junction (SCJ) is formed from the transition of the columnar epithelium to the squamous epithelium also frequently termed the transformation zone . CervicaCancer stem cells (CSCs) have been widely investigated in different malignancies to better understand disease progression and recurrence. Although each cancer type has a unique group of stem cell markers, they share expression of stemness-related genes, notably SOX2, OCT4, and NANOG. These genes are responsible for maintaining the stem cell-like phenotype, including conserving self-renewal capacity and pluripotency.In endometrial cancer, cancer stem cell populations are characterised by cells expressing CD117 and CD133, both demonstrating increased tumourigenicity and reduced platinum sensitivity ,35,36. HAnalysis of cellular interactions of HPV oncoproteins E6 and E7 with host signalling networks is key for understanding of the progression from high risk HPV infection to cervical carcinoma. It was shown that they cause the degradation of tumour suppressors p53 and retinoblastoma-associated protein, which would normally repress stemness genes OCT4, SOX2, NANOG, and fibroblast growth factor 4 ,40. OCT4As with other gynaecological cancers, higher expression of CSC markers in ovarian cancer is associated with chemotherapy resistance and poor patient outcomes. A side population of cells expressing NANOG, OCT4 and ABCG2/BCRP1 was isolated from ovarian cancer cell lines and ascites of ovarian cancer patients, and was found to have increased tumourgenicity and chemoresistance . SimilarSeveral studies have also demonstrated mesenchymal stem cell populations that contribute to maintaining stemness and are associated with chemoresistance ,53. RaghA recent study by Robinson et al. aimed to characterize the roles of SOX2, OCT4, and NANOG in ovarian CSCs . FollowiA widely accepted postulate of molecular carcinogenesis is that the vast majority of solid cancers have a monoclonal origin, where a single event of cellular transformation is followed by a sequence of events and progression based on the competitive advantage of the cancer tissue at the expense of healthy tissue. Molecular divergence of malignant tumours during disease progression is extensive, and tumour heterogeneity is particularly prominent in aggressive and fast-growing types such as HGSOC. An increase in heterogeneity is thought to be driven by differences in selection pressures within local microenvironments at distinct sites. Moreover, treatments by chemotherapy agents foster the emergence of resistant clones, and disease recurrence is still an inevitable long-term outcome for most patients. Different growth requirements for evolving cancers can lead to a reversal of phenotypic characteristics at times, as metastatic cancer cannot be considered as a solely unidirectional process of loss of differentiation and continuous reduction in fidelity of cell functions. There are several examples of genomic alterations, which are essential for cell transformation, that are reverted at later stages of the disease. This phenomenon is well documented in the cases of recurrent chemoresistant ovarian cancer which has been shown to reacquire DNA repair proficiency by reversion of BRCA1/BRCA2 mutations or modification of epigenetic marks ,59. MoreA large genome-wide association study (GWAS) and meta-analysis of sporadic epithelial ovarian cancer cases , BRCA1 and BRCA2 carriers  and 30,845 healthy controls identified genomic variants of Wnt pathway components, Wnt4 and RSPO1 genes, as new susceptibility loci . AnalysiRegulation of the processes of differentiation at the SCJ in the cervix is central to the understanding of the carcinogenesis of this cancer type, which is an HPV-driven event, but occurs very rarely as the vast majority of viral infections are resolved without long-lasting impact. Which combination of intrinsic and broader microenvironmental factors triggers expansion of the latent HPV-infected cells requires further investigation, but in this case, it is also clear that selection and clonal evolution are likely dependent on the broader tissue context.Organoids are an attractive prospect for personalising patient treatments because it is now well established that patient-derived organoids (PDOs) resemble the parental tumour, as confirmed by genome sequencing and phenotypic analysis, and are applicable to drug screening . Tumour A recent study establishing HGSOC PDOs from chemo-naïve tumours identified a shift in required stem cell growth conditions for HGSOC, in contrast to healthy Fallopian tube organoids, and detected that key regulatory changes in markers of stemness and differentiation occur early in the development of HGSOC tumourigenesis . HoweverPropagation of PDOs to determine drug or radiotherapy efficacy is becoming more commonplace for different gynaecological malignancies. In particular, significant progress has been made for establishing drug treatment parameters and platforms for PDOs derived from EOC tumours, albeit currently at a low-medium throughput level. PDOs from EOC cases were treated with standard-of-care first-line chemotherapies  and relevant targeted therapeutic agents , and responses recorded correlated with the patient’s clinical responses ,70,71,72Studies which established human endometrial PDOs include the optimization and differentiation of hormone-responsive organoid cultures. Furthermore, upon exposure to pregnancy signals, endometrial organoids displayed characteristics of early pregnancy . OrganoiRecent comprehensive studies deriving PDOs from cervical cancer cells or normal cervical tissue have been described. Organoids have been developed from normal cervical cells from the SCJ region, and metastatic squamous cells from the transformation zone, providing models in which HPV-driven cervical carcinogenesis could be evaluated . FurtherIn addition to a necessary focus on cancer driving genes and developmental pathways which control epithelial homeostasis, it is becoming clear that micro-RNAs and noncoding RNAs could regulate CSC potential on a post-transcriptional level. Micro-RNA family miR-34 has been described in several malignancies as tumour-suppressive and thus could be a promising pharmacological therapeutic candidate . As TP53Potential mechanistic links between cell cycle regulation and DNA homologous recombination machinery and mechanisms which control stemness and differentiation warrant further investigation. Moreover, better insight into the involvement of chromatin remodelling complexes in the development of gynaecological malignancies is required. NGS studies revealed frequent mutations in ARID1A in the endometrioid type of ovarian cancer as well as in endometrioid adenocarcinoma of the uterus . ARID1A HGSOC, on the contrary, is driven by mutated TP53 gene, and in almost 50% of cases, homologous DNA repair is deficient, due to germline mutations, somatic mutations, or epigenetic inactivation of BRCA1/ BRCA2 genes. Tumours with impaired HR have a high sensitivity to platinum-based chemotherapies. Recent clinical studies have established the benefit of PARP inhibitor therapies in patients who have homologous recombination deficiency (HRD) even in the absence of BRCA1/2 mutations ,83,84, tBRCA test [Due to nearly half of HGSOC cases demonstrating deficiency in homologous recombination repair, screening for HRD status to inform on treatment options has entered clinical routine. For example, tests have been developed based on genomic footprints to identify HRD to predict the use of PARP inhibitors (PARPi) such as the myChoice CDx , ClassifRCA test . NeverthRCA test . A functRCA test ,92 and mRCA test , detectiRCA test . AnotherRCA test . These iclinicaltrials.gov (accessed on 10 May 2021) to evaluate PDOs as representative models of cancer for screening of different therapies, seven of which relate to gynaecological malignancies, mainly ovarian cancers. Prospective trials of colorectal cancer PDOs demonstrated a correlation of patient responses to chemotherapy and targeted agents with ex vivo PDO drug screening [At present, there are fifty-three clinical trials registered  with creening ,95. Nevecreening ,71,72,96creening . The broThe applications of human organoids are numerous from precision medicine to disease modelling . They prTo further recapitulate the in vivo physiology of the tumour and surrounding stroma and cell constituents, efforts have turned to incorporation of other important cell types to create co-culture organoids, with significant strides made in other cancer types developing co-cultures with immune cells  and/or cTaken together, recent advances in our understanding of changes in stem cell regulation and epithelial homeostasis during carcinogenesis and disease progression have opened promising new approaches in the research of gynaecological malignancies, with great translational potential. Cancer stem cells appear be able to modulate core signalling pathways in epithelial ovarian cancer and are believed to be responsible for disease progression, relapse, and drug resistance development . Hence, A further perspective for exploration is the field of early diagnosis and detection of CSCs. Many recent technologies have focused on the endoscopic or hysteroscopic examination of the fallopian tubes and/or uterine lavage fluid with clinical trials ongoing to test these devices . These tOverall, it can be concluded that complex 3D patient-derived organoid culture models provide new and versatile experimental platforms to study gynaecological malignancies. They create opportunities to identify central mechanisms of cancer biology, which remain poorly understood such as tissue hierarchy and clonal diversification, influence of microenvironment and interactions with immune system. This could lead to development of new, better-tailored therapeutic concepts that help towards achieving the long-term goal of improving detection and patient outcomes.


Stents are a widely-used device to treat a variety of cardiovascular diseases. The purpose of this review is to explore the application of regenerative medicine principles into current and future stent designs. This review will cover regeneration-relevant approaches emerging in the current research landscape of stent technology. Regenerative stent technologies include surface engineering of stents with cell secretomes, cell-capture coatings, mimics of endothelial products, surface topography, endothelial growth factors or cell-adhesive peptides, as well as design of bioresorable materials for temporary stent support. These technologies are comparatively analyzed in terms of their regenerative effects, therapeutic effects and challenges faced; their benefits and risks are weighed up for suggestions about future stent developments. This review highlights two unique regenerative features of stent technologies: selective regeneration, which is to selectively grow endothelial cells on a stent but inhibit the proliferation and migration of smooth muscle cells, and stent-assisted regeneration of ischemic tissue injury. Cardiovascular diseases, a group of disorders of the heart or blood vessels, are considered to be the leading cause of mortality worldwide. An estimated 17.9 million people died from cardiovascular diseases in 2019 , with 85% due to heart attack and stroke . CoronarAngioplasty, a surgical procedure to open vessel blockages along with placement of a vascular stent, is a common treatment for heart attack and an option for stroke treatment or stroke prevention. More than 2 million people get a stent each year for coronary artery disease alone . CoronarNow is an important moment to examine regenerative approaches for this widely-used device in interventional cardiology and assess their benefits and risks for future stent therapies. We will start with a brief overview of the current status of stent uses in clinic, including stent types and uses in treating various cardiovascular diseases. Then, this review focuses on new methods emerging in recent stent research endeavors related to the regeneration concept. Comparative analyses of these methods include the regenerative effects, therapeutic effects and challenges faced. Lastly, thoughts about future perspectives in this subject area are provided in context of recent developments in relevant regenerative medicine.Vascular stents are a device to treat a partially clogged artery by holding the arterial wall open and preventing it from collapsing. The majority of stents within the coronary stent market are bare metal stent (BMS) and drug eluting stent (DES), with the latter holding a larger share and being accepted as a safer treatment . NeverthMajor clinical issues for stent usage are thrombosis and restenosis. Restenosis, re-narrowing of the stented vessel due to proliferation and migration of smooth muscle cells, is triggered by arterial injury during stenting. Widely-used DESs have a polymer coating blended with a drug or drug mixture that inhibit vascular smooth muscle cell growth. These anti-proliferative drugs are released over several months to help prevent restenosis. After that period, the stent may trigger platelet adhesion initiating thrombotic response. Controlled release of anti-proliferative agents inhibits neointimal growth but also delays arterial healing, thereby predisposing to a late risk of thrombosis. This high rate of late thrombosis (1–12 months post-implantation), demonstrated by the first generation stents, stimulated DES research for new generation stents in the last decade.Contemporary second or third generations of stents are superior to the first generation in a number of clinical measures, including late stent thrombosis and strut coverage , showingCovered stents have a fabric material component that covers a metal stent. The majority of covered stents use polytetrafluoroethylene and have various clinical applications in peripheral arterial disease management. Covered stents offer an effective strategy for the creation of transjugular intrahepatic portosystemic shunts , as wellRecently, covered stents have become a platform that offer a minimally invasive, safe, and effective solution for arterial emergencies, such as bleeding, pseudoaneurysm, dissection, or fistula . During Taken together, current stent-assisted therapies—BMS, DES and covered stents—are employed to combat a wide range of vascular diseases and emergencies. Despite low complication rates (approximately 2–3% per year after the first year), stent therapy is still associated with a risk of restenosis and thrombosis, which persists for over 20 years. Recent comparisons of stent therapy and non-stent therapy for treating different clinical conditions such as coronary artery disease and infrainguinal peripheral artery disease showed no difference between stent and non-stent therapies, while the stent procedure is more invasive and has a significantly higher cost . TherefoSimilar to the application of regenerative medicine concepts in other tissues or devices, regeneration-relevant approaches emerge in the stent technology in two forms: regenerative surface and biodegradable or bioresorable scaffolding materials. However, due to the presence of diseased artery tissue around a stent, major considerations of all stent technologies must include their therapeutic impact such as the inhibition of arterial recoil and smooth muscle proliferation. To this end, we review the two major types of approaches to stent design by comparing and evaluating their regenerative effects and therapeutic effects.inorganic coatings, including diamond-like carbon  e carbon , pyrolyte carbon , titaniue carbon , and care carbon ; 2) genecoating;  3) cell-or cells . The inoor cells . The genor cells . Neverthor cells .in situ re-endothelialization or to integrate critical endothelial functions. This is achieved through cell secretomes, cell-capture coatings, mimics of endothelial products , surface topography, endothelial growth factor, cell-adhesive peptides and other biologics. The root cause of stent pathology, as revealed by numerous studies on BMS and DES, , is endoselective regeneration”, which is to selectively grow endothelial cells on the stent surface but inhibit the proliferation and migration of smooth muscle cells. Therefore, multifunctional coatings in recent developments exhibit both regenerative effect on the endothelium and therapeutic effects on the smooth muscle. Second, stent-assisted regeneration of ischemic tissue injury is needed in certain applications such as myocardial infarction and renal ischemia, where narrowing of an artery is accompanied by the loss of distal vasculature and thus tissue injury. Stenting provides an opportunity to regenerate the tissues with biologics that regenerate stented artery and distal vasculature  combining cell-capture molecules with other prohealing/proregenerative molecules;  2) usingNO is one of the most potent molecules produced by healthy endothelial cells that play multiple essential roles in cardiovascular physiology . Vasculain vitro and in vivo. This is consistent with the results from recent graft study which employed NO-producing vascular graft on rodents for 12 weeks and found rapid endothelialization and hampered SMC proliferation , S-nitroso-N-acetylpenicillamine, and peptide amphiphiles , immobilferation . DespiteVEGF is a most potent, endothelial-specific growth factor to regenerate endothelial cells. Early attempts to incorporate it into stent coatings were made as early as 1990s . HoweverIn conclusion, VEGF-bound stents hold great promise in endothelial regeneration but the outcome using this regenerative molecule depends on: 1) co-grafting condition, such as drugs or other molecules coexisting on the stent and collaborating into action at the stent-artery interface; 2) the form of VEGF , and 3) the conjugation method of VEGF, for example eluting vs. polymer-bound.Specialized micro- and nano-patterns have been introduced on the stent surface to reduce the risk of blood clotting, expedite healing and improve endothelialization. The design of textures on the thin struts of a stent includes nanotubes, ridges, pores, diamonds, leafy structure, or even a pattern mimicking the shape of smooth muscle cells  Junkar . ImportaTwo major groups of other biologics used in stent coatings, often in combination with other approaches, are adhesive peptides and glycosaminoglycan (GAG) molecules such as heparin and hyaluronic acid or GAG-mimics such as chitosan.in vitro and in vivo, and reduced restenosis compared to BMS  is incompetent in terms of its integrity and function, showing poorly formed cell junctions, reduced expression of anti-thrombotic molecules , and decreased NO production . Drugs fTo mitigate the risk of restenosis and thrombosis in stent, it has long been envisioned that a fully bioresorbable polymer is used in replacement of metal. The first-generation, FDA-approved BVS product was created and launched by Abbott as Absorb BVS stent in September 2012. This type of products was characterized by a degradation rate, ranging from 6 months to 2 years, to avoid undesired long-term effects, but demonstrated worse clinical performances including in-stent thrombosis, restenosis, and target vessel myocardial infarction, when compared to BMS or DES . Thus, iNewer BVS technologies and devices mostly loaded with drugs are currently undergoing preclinical and clinical testing . A promiTo enhance therapeutic and regenerative performances of BVS, bioactive molecules can also coat the BVS surface or be integrated into the bulk polymer. Any regenerative molecules reviewed above  may be aFor a more detailed summary of BVS, please refer to additional reviews on the topic . In brieWith advancements in stent technologies and implantation techniques, the event-free survival rate for stent patients, in particular those with the new generation DES, has kept improving in the last decade. Based on the overall satisfactory results from the new generation DES, it can be extremely challenging for any new stent design or material to demonstrate better effectiveness while being safe and worth enormous investments into innovation and translation. An additional barrier that hampers the translation of the new design or material to clinical applications lies in the lack of sufficient understanding of mechanisms underlying the materials interactions. Further refinement of existing DES has an excellent benefit-risk ratio. Therefore, future developments of permanent metallic stents such as new functional coating or topography strategies may take the advantage of the current DES platform, based off it for design and performance analysis.To address the long-term concern about permanent metallic stents—an ongoing risk of restenosis or thrombosis arising from the implant site which persists for at least 20 years  occurrinin situ stent cellularization results can vary accordingly. In this case, custom design strategies may be necessary for a specific patient’s cohort. 2) Multiple signaling strategies with defined spatiotemporal regimes of regenerative signals.Finally, an amazing array of stent functionalization strategies are available in the literatures. However, translation efforts of them into clinical practices remain very limited if not futile. Future efforts in this area may fall into two categories: 1) Stent design according to specific needs of a patient’s cohort  for competitive efficacy and superior outcome. For example, the regeneration of distal vasculature is only desired in ischemic conditions. Another example is for cell-capture stents: the EPC quantity, quality and capability can vary greatly among patients, and thus


Psychiatric illness is a prevalent and highly debilitating disorder, and more than 50% of the general population in both middle- and high-income countries experience at least one psychiatric disorder at some point in their lives. As we continue to learn how pervasive psychiatric episodes are in society, we must acknowledge that psychiatric disorders are not solely relegated to a small group of predisposed individuals but rather occur in significant portions of all societal groups. Several distinct brain regions have been implicated in neuropsychiatric disease. These brain regions include corticolimbic structures, which regulate executive function and decision making , as well as striatal subregions known to control motivated behavior under normal and stressful conditions. Importantly, the corticolimbic neural circuitry includes the hippocampus, a critical brain structure that sends projections to both the cortex and striatum to coordinate learning, memory, and mood. In this review, we will discuss past and recent discoveries of how neurobiological processes in the hippocampus and corticolimbic structures work in concert to control executive function, memory, and mood in the context of mental disorders. A region of the brain called the hippocampus and its connections to other parts of the brain via what are called cortico-limbic structures are implicated in a variety of mental health disorders. These disorders can be accompanied by reduced hippocampal volume. Mi-Hyeon Jang, Doo-Sup Choi and colleagues at the Mayo Clinic College of Medicine and Science, Rochester, USA, review the role of hippocampal and cortico-limbic neurobiology in memory and mood in mental disorders. They focus particular attention on the role of neurogenesis, the production and growth of new nerve cells and connections. Disrupted neurogenesis in the adult hippocampus is implicated in conditions including addiction, depression, schizophrenia and related psychotic disorders. Learning more about neural regeneration in the hippocampus could yield insights into mental health conditions and open new avenues toward developing drug-based treatments. While there is still much to learn regarding the neural circuitry and molecular mechanisms that are affected by neuropsychiatric disease, dysregulation of the corticolimbic circuit, which includes the cortex, striatum, and hippocampus2, has been implicated in mental disturbances that negatively affect learning, memory, and mood3. The hippocampus has long been implicated in psychiatric disorders due to its enduring plasticity throughout life and sensitivity to environmental changes4. Reductions in hippocampal volume have been reported in patients suffering from a variety of psychiatric disorders, including depression, addiction, and schizophrenia. Moreover, lesions of the ventral hippocampus in preclinical models recapitulate the characteristics of schizophrenia and other mental disturbances5. The hippocampus is a brain region capable of continuously generating newborn progenitor cells throughout adulthood, thereby giving rise to new neurons , and the relatively sparse evidence for neurogenesis in adult humans obtained in subsequent years. Over time, however, the concept of adult hippocampal neurogenesis has garnered intense interest. By the late 1990s, this process was characterized in Eriksson et al.’s seminal report, in which the authors described how new neurons in the DG of the human hippocampus are functionally relevant to spatial memory, episodic memory, and other cognitive functions11. Although numerous clinical and preclinical animal investigations have since documented the existence of adult hippocampal neurogenesis15, a recent study suggested that hippocampal neurogenesis may be extremely rare in the adult human brain after young adolescence16. Such discrepancies and contradictory findings on the existence of human hippocampal neurogenesis can likely be attributed to technical issues related to postmortem tissue processing. For example, Sorrells et al.16 used doublecortin (DCX) and Polysialylated-neural cell adhesion molecule (PSA-NCAM) as marker proteins to detect neurogenesis but failed to detect DCX/PSA-NCAM+ cells in the DG of individuals between 18 and 77 years of age and patients with chronic epilepsy, concluding that neurogenesis does not occur in the adult human hippocampus. In contrast, Boldrini et al.12, Moreno-Jiménez et al.14, and Tobin et al.15, utilized the same markers but clearly demonstrated the existence of neurogenesis. The most critical step in accurately detecting marker proteins is a tightly controlled postmortem delay , given that DCX can rapidly breakdown after death. Other critical variables that may affect adult hippocampal neurogenic expression are the timing of fixation and the available tissue processing technology 14, which may explain the relative absence of this marker in the tissues analyzed by Sorrells et al.The discovery of adult hippocampal neurogenesis within the mammalian brain has long been controversial since Altman and Das’s19. Interestingly, subpopulations of patients with major depression disorder (MDD) show decreased hippocampal volume and cognitive deficits20. Along these lines, studies utilizing volumetric magnetic resonance imaging (MRI) have consistently shown lower hippocampal volume and reduced gyrification in patients with schizophrenia23. While deficits in neurogenic capacity resulting from depression and neurodegeneration have been reported for some time, more recent discoveries have also implicated drug addiction in these deficits. For example, chronic use of cocaine24 and alcohol25 suppresses neurogenesis in rodents. Supporting these preclinical findings, multiple neuroimaging studies have found reduced gray matter volumes in the prefrontal cortices of cocaine-dependent patients compared with those of healthy controls26.Although numerous studies have reported correlations between adult hippocampal neurogenesis and numerous pathophysiological conditions, including epilepsy, stroke, and neurodegenerative disorders, whether altered hippocampal neurogenesis contributes to psychopathology remains unclear and needs further study. An enduring question that underlies the study of adult neurogenesis in psychopathology is whether dysfunctional neurogenic changes occur as part of disease pathology or, alternatively, as an adaptive response that compensates for disease states generated by environmental stressors. Diminished cell proliferation within the DG and reduced hippocampal volume have been documented in the context of several psychiatric disorders 27. As such, we will review the role of adult neurogenesis within the context of alcohol addiction, depression, and schizophrenia, paying special attention to the molecular and cellular targets relevant to psychiatric disease and adult neurogenesis.These studies bring to light the possibility that dysregulation of the adult neurogenic process may itself play a seminal role in the symptomatology of psychiatric disorders. Therefore, experimental characterization of the neurogenic process can engender the discovery of novel therapeutic targets in psychiatric disorders. Additionally, intensely researching the interaction between neurogenesis and psychiatric disorders can provide critical insight into the effector systems involved, which may increase the likelihood of developing successful treatments for psychiatric disorders. Consequently, we posit that the generation of new neurons throughout life is imperative to overall mental health, which is supported from the fact that (1) behavioral abnormalities mimicking the symptoms of diseases inhibit neurogenesis; (2) certain pharmacological treatments or behavioral interventions alleviate mental illness and enhance neurogenesis; (3) certain circumstances or environmental contexts increase the probability of developing mental illness, thus inhibiting neurogenesis; and (4) neurogenic potential is changed in patients already diagnosed with a psychiatric illness28. NSCs and NPCs are multipotent, highly proliferative cells. In rodents, NSCs in the DG primarily reside in the SGZ, where four subtypes  differing in morphology, proliferation rate, and protein expression profiles have been characterized. Type I NPCs resemble glia and have radial processes. Additionally, these type I NPCs express the intermediate filament protein nestin and glial fibrillary acidic protein (GFAP) and have a lower proliferation rate than other NPC subtypes28. In contrast, type IIa cells do not express GFAP, are not radial, and exhibit a much higher proliferation rate than type I NPCs. Type IIa cells express Tbr2 (ref. 29) and nestin and do not exhibit a radial glia-like morphology. Type IIb cells are unique in that they maintain expression of Tbr2 while showing commitment to a neuronal lineage, as indicated by the expression of the microtubule-associated protein DCX  proliferation of neural stem cells (NSCs) and neural progenitor cells (NPCs), (2) NSC/NPC migration from a specific neurogenic niche to areas of integration, (3) differentiation of NPCs into mature neurons, and (4) integration of cells into synaptic networks that can affect behavior and cognitionDCX Fig. 29. Type 31. Type C cells are similar to type II cells in the SGZ, exhibiting no GFAP expression and a high proliferation rate. Interestingly, both cell types (A and B) are nestin+ and Sox2+, although type A cells  are neuroblasts with the capability of migrating along the rostral migratory stream to the olfactory bulb31. Although they originate from different locations, NSCs in both the DG and lateral ventricles can produce cells with the capacity to differentiate into neurons and astrocytes. Generally, neuroblasts from the SVZ preferentially differentiate into olfactory bulb interneurons, while NSCs of the DG migrate to the granular cell layer, allowing for the integration of granular cells into the hippocampal circuitry through the formation of glutamatergic synapses with other granular neurons, interneurons, and pyramidal cells.Neurogenesis in the SVZ within the lateral ventricles is similar to that in the DG, and only three cell types are implicated in the process . The cell types are analogous to those in the DG, with type B cells resembling type I cells in the SGZ with regard to morphology, protein expression profiles, and proliferation rate32. Additionally, the hippocampus is involved in the maintenance and acquisition of drug-taking behavior due to its ability to mediate associative memories of drug-taking, thereby regulating relapse upon re-exposure to drug-related contexts19. The anatomical location of the hippocampus allows this brain region to influence the brain reward pathways (dopaminergic reward circuitry) through afferent projections from the ventral striatum and ventral tegmental area (VTA). Further evidence of hippocampal involvement in the reward circuit was obtained from functional studies indicating that the hippocampal CA1, CA3, and DG subfields are manipulated after the firing of dopaminergic cells in the VTA and the discovery of a dedicated population of cells encoding reward in the hippocampus34.Historically, the hippocampus has been accepted as a critical constituent of the limbic system, playing roles primarily in learning and memory. However, more attention is being paid to the hippocampus due to its involvement in the behavioral adaptability of mood, the associations between drug context, and the rewarding properties of drug abuse35. This concept was confirmed by separate studies showing that abstinence from methamphetamine-related reward seeking increased aberrant hippocampal neurogenesis36. However, it is possible that addiction-related dysfunctional neurogenesis may be drug-dependent, as there is controversy regarding whether opiate seeking vs. opiate taking influences neurogenesis during abstinence from drugs of abuse38 , disruptions in the expectation of receipt of a natural sucrose reward foments impulsive response seeking behavior, which is associated with increased, albeit aberrant, neurogenesise38 Fig. .Additional research on how readily available substances, such as alcohol and, to a lesser extent, cannabis, are able to affect neurogenic potential is crucial. Furthermore, given that both alcohol and cannabis are legal or soon-to-be-legal substances that can be used recreationally, it is imperative to understand the neurobiological mechanisms of action to identify novel targets and treatment strategies for addiction to these compounds.39. Perturbations in NSC populations by alcohol may be associated with decrements in hippocampal volume in AUD patients since the production and turnover of these cells ultimately govern the total number of neurons and the subsequent volume of this brain region10. Despite this association, improved imaging techniques, perhaps in combination with cell-type specific optogenetic manipulation, will be helpful to identify the specific subregions of the hippocampus or specific cellular populations that are uniquely susceptible to alcohol abuse. Notably, recent clinical reports have shown that transmagnetic deep brain stimulation has promise in reducing nicotine consumption and cravings41. Therefore, it may soon be feasible to use a minimally invasive clinical optogenetic approach (perhaps in combination with deep brain stimulatory currents) to identify or manipulate the functional neurogenicity of specific hippocampal cell populations susceptible to alcohol damage in the future42.Ethyl alcohol, due to its ease of acquisition and cultural importance, is one of the most extensively studied substances with regard to addiction. Excessive alcohol consumption is a hallmark characteristic of alcohol use disorder (AUD). Studies on adult neurogenesis and alcohol consumption have generally indicated a negative correlation between the two, with reduced neurogenesis resulting from chronic alcohol abuse. However, as with other drugs of abuse, the effect of alcohol on adult neurogenic potential varies with dosage, duration of exposure, and intake pattern. Translational studies investigating neural adaptation associated with AUD have been integral to elucidating the effects of the disease. Due to greater advancements in technology used to assess brain function in vivo, a more consistent understanding of the effects of alcohol on the hippocampus has emerged. For instance, fMRI of adolescent AUD patients has shown a reduction in hippocampal volume, with early-onset alcohol consumption potentiating these deficits43. Paradoxically, long-term voluntary alcohol self-administration in the two-bottle choice test enhances NPC proliferation but had no effects on the differentiation or survival of these cells in mice44. Interestingly, numerous studies have suggested that alcohol may kill NSCs or NPCs in long-term alcohol exposure models. These studies suggest that neuronal cell death induced via alcohol is dose- and duration-dependent, as sustained blood alcohol concentrations (BACs) >200 mg/dl (0.20 g %) are known to induce neurodegeneration45. In line with these reports, hippocampi of controls with no history of alcohol consumption compared to hippocampi isolated from deceased donors with a known history of prolonged alcohol abuse showed decreases in granular cell number and granular cell layer volume46. Subsequent immunostaining for markers of cell proliferation (Ki67), stem/progenitor cells (Sox2), and immature neurons (DCX) revealed significant deficits in the expression of all markers in the DG in donors with a prolonged history of alcoholism compared with healthy controls47  and brain-derived neurotrophic factor (BDNF), both of which are important promotors of adult hippocampal neurogenesis49. In the DG, NPY is expressed in a subpopulation of GABAergic interneurons, and its receptor, Y1, is expressed in SGZ NPCs. BDNF promotes the survival and differentiation of NPCs, and some of the highest levels of BDNF are found in the hippocampus and DG. Multiple lines of evidence have shown that alcohol exposure has detrimental effects on hippocampal BDNF expression, reducing neurogenesis and promoting depressive-like behaviors51. Given the direct role of cAMP–CREB signaling in regulating adult hippocampal neurogenesis45, it is conceivable that alcohol adversely alters neurogenesis through CREB signaling.Several possible mechanisms underlying the effect of alcohol in disrupting the neurogenic process have been proposed. The cyclic adenosine monophosphate (cAMP)–responsive element binding (CREB) protein signaling pathway is known to be sensitive to alcoholCannabis sativa, endocannabinoids, and synthetic cannabinoids. The neural cannabinoid system constitutes a complex series of receptor–ligand and receptor–receptor interactions that include various signaling pathways, such as growth factor receptor and G-protein receptor signaling, which control a wide variety of physiological processes, including adult neurogenesis28. Cannabinoids exert their effects via activation of G protein-coupled cannabinoid receptors type 1 and type 2 , which are localized throughout the central nervous system (CNS), including on astrocytes, microglia, and neurons. Studies have suggested that various cannabinoid ligands control cell genesis and overall neurogenesis in the mammalian brain52. Therefore, NPCs expressly regulate endocannabinoid systems to produce endogenous cannabinoids53, highlighting the potential of the cannabinoid system to exert regulatory control over adult neurogenesis.Cannabis use is increasing widely as legalization of its recreational use increments worldwide. As approximately 2.5% of the world population consumes cannabis, it is important to consider the effects of prolonged use on the neurobiology of cognition and homeostatic brain function. Cannabinoids include the active components of the plant 52. Interestingly, the results of this study suggested that NPC proliferation in mice was unaffected by cannabis smoke, whereas the number of DCX+ cells in the DG was decreased, dendritic morphology was altered, and migration was perturbed in cannabis-exposed mice compared to untreated controls52. This finding is comparable to others indicating that the endocannabinoid system plays an important role in regulating cell proliferation, migration, and differentiation through differential activation of CB1/CB2 receptors54.A recent study in which stressed young adult mice voluntarily inhaled cannabis smoke for 2 months and hippocampal neurogenesis in the DG was assessed, demonstrated that smoking cannabis regulates adult hippocampal neurogenesis55. The neurogenesis hypothesis suggests that adult neurogenesis within the SGZ of the DG is negatively regulated by stressful stimuli and positively regulated by antidepressant drugs56. Additionally, it posits that perturbations in the rate of neurogenesis are critical in the pathology and treatment of depression, which is suspected to be multifaceted. The reduction in hippocampal volume (particularly gray matter volume) in patients diagnosed with depression highlights the potential for alteration of adult neurogenesis in the development of the disease20. A meta-analysis of 32 publications indicated that hippocampal volume is significantly reduced in individuals who experience a major depressive episode lasting more than 1 year or >2 years of overall illness in their lifetimes, suggesting that volume reductions are attributes of the disease rather than contributing risk factors57. While it is argued that many factors other than a decrease in the number of neurons may account for a decrease in hippocampal volume, the prevailing evidence suggests a role for neurogenesis in the etiology of depression  is a common diagnosis for people with MDD. Bidirectional cooccurrence is common for MDD and AUD60  potentiates depressive-like behavior and neurogenic impairments, both of which are rescued by tetracyclic triterpenes (found in sapogenins). Tetracyclic triterpene administration activates BDNF signaling and neurogenesis in the hippocampus55. Mechanistically, neurogenesis was recently shown to confer resilience to chronic stress by decreasing the neural activity of mature granule cells located in the ventral hippocampal DG, a brain region implicated in mood regulation65. This study also showed that chemogenetic inhibition or activation of adult neurogenesis in the ventral hippocampus DG causes susceptibility or resilience, respectively, to social defeat stress. Moreover, in vivo calcium imaging has revealed that neurogenesis leads to decreased activity of stress-responsive granule cells that are preferentially activated during stressful circumstances and that both of these effects within the DG are necessary for stress resilience65. In summary, this study emphasizes the importance of adult hippocampal neurogenesis in the etiology of depression.Despite the controversy related to the role of neurogenesis in depression, numerous preclinical studies support this concept, showing that neurogenic stimuli can be modulated via antidepressant medication and wheel running physical exercise60 Fig. . Interes66. A full summary describing in detail the contributions of Wnt signaling to adult hippocampal neurogenesis is not within the purview of this review and is discussed elsewhere66. However, it is sufficient to say that manipulation of members of the canonical Wnt pathway  has been shown to impact the target trajectory of newborn neurons within the DG66. Indeed, a genome-wide association study (GWAS) examining differentially expressed genes between patients diagnosed with MDD and healthy controls identified a key single-nucleotide polymorphism (SNP) (rs1969253) in DVL3, a component of the Wnt signaling pathway67. Accordingly, SNPs in DVL3 display the strongest association with MDD and are increased in patients currently experiencing MDD67.Recently, the role of the Wnt (wingless-related integration site) signaling pathway in mood disorders has garnered more attention, as unabated Wnt signaling is imperative for hippocampal neurogenesis68). These results are supported by more recent studies showing that the incidence of psychosis is related to sex and immigration status and that a higher incidence of psychosis is associated with lower socioeconomic level as well as exposure to traumatic experiences during childhood and adolescence70. Although psychosis is the most prominent “positive” symptom  of schizophrenia, it is one of the three main symptoms required for diagnosis, as “negative” emotional symptomatology  and cognitive dysfunction  are also diagnostic criteria for schizophrenia. This debilitating disease often strikes young individuals on the cusp of a promising future during a period where the developing brain encounters stressful social contexts , which in combination with a genetic predisposition, may tip the balance toward emergence of a first psychotic episode71. Given that intracranial brain volume stabilizes and is maintained in early- to mid-adolescence72, it is not illogical to assert that schizophrenia is a neurodevelopmental disorder. In support of this hypothesis, several reports have demonstrated distinct deficits in hippocampal volume in young patients in mid-to-late adolescence following a first psychotic episode74. Unfortunately, during this critical juncture of adolescent neurodevelopment, when intracranial brain substructures are still undergoing maturation and development, hippocampal volume does not seem to be restored by antipsychotic drug treatment74. While the average age of onset of the initial psychosis episode occurs after early adolescence in females (early twenties to early thirties) and males (late teens to late twenties), clinical epidemiological investigations have revealed that psychosis manifestations are often preceded by poor academic performance76.Schizophrenia and related psychotic disorders are extremely debilitating neuropsychiatric conditions characterized by a loss of contact with reality, and the median incidence of these disorders in the general population in the United States is 3–5 per 1000 . Interestingly, observations of intracranial and hippocampal volume deficits in the postmortem brains of schizophrenia patients have given rise to the hypothesis that stressful life events and subsequent psychosis may in fact result in cell death74. Supporting this notion, a recent report examined the effects of poly (ADP-ribose) polymerase-1 (PARP-1) deletion in cultured NSCs and found impaired neuronal lineage cell differentiation with concomitant PI3K-Akt-ERK-FOXO1-dependent increases in astroglial differentiation. Importantly, the authors demonstrated that a mouse model of constitutive PARP-1 deletion recapitulates schizophrenia-like impairments in NSC proliferation, memory, and prepulse inhibition (PPI)78. Therefore, the observed intracranial deficits exhibited by schizophrenia patients may be due to abnormal cell death resulting from the aberrant psychosis that is characteristic of the disease.If schizophrenia patients have cognitive deficits along with psychotic symptoms, could impaired neurogenesis be a contributing factor to psychosis-associated cognitive dysfunction? Indeed, the postmortem brains of patients with schizophrenia exhibit distinct reductions in Ki6779. Notably, impaired axonal targeting and diminished synaptic contacts have also been observed in the postmortem hippocampi of schizophrenia patients80, suggesting that DISC1 is an important contributor to the etiology of schizophrenia. The atypical antipsychotic drug clozapine alleviates these aberrant alterations, and additional research on DISC1 has elucidated its potential to regulate neurogenic capacity and schizophrenia-like impairments in hippocampal-related cognitive tests82. Mechanistically, selective inducible expression of DISC1 in astrocytes was shown to result in decreases in the hippocampal expression of the NPC marker MCM2 and dendritic outgrowth of newborn neurons, both of which are restored by d-serine administration83. These findings suggest that astrocytes are instrumental in the metabolic regulation of neurogenic function and functional cognition, which are notoriously impaired in schizophrenia83. Surprisingly, the potential involvement of astrocytes in regulating neurobiological processes that are disrupted in schizophrenia highlights the involvement of glutamate neurotransmission in the etiology of schizophrenia and related psychotic disorders84. Recently, Provenzano and colleagues observed high hippocampal glutamate levels and a large degree of hippocampal atrophy in patients at clinically high risk of developing schizophrenia73.While much remains to be explored regarding adult neurogenic disruptions in patients with schizophrenia, animal models utilized in the study of this condition have revealed that disrupted in schizophrenia (DISC1) is critically involved in axonal targeting of mossy fiber projections and synaptic contact formation, as DISC1 knockdown disrupts these adult neurodevelopmental processesN-methyl-d-aspartate receptor (NMDAR) and plays an essential role in synaptic plasticity, neurogenesis, and adequate neuronal function via promoting metabolic homeostasis in the brain. Therefore, evidence for glutamate’s involvement in the etiology of schizophrenia suggests that dysfunctional glutamate neurotransmission can be a contributor to psychosis development. Consequently, kynurenic acid (KYNA), an endogenous NMDAR antagonist and metabolic product of tryptophan–kynurenine metabolism, was recently detected in the cerebrospinal fluid (CSF) of Alzheimer’s disease patients, linking hippocampal neurogenic disturbances to aberrant kynurenine metabolism85. In line with the neuroinflammatory hypothesis of schizophrenia, observation of inflammation-mediated increases in the expression of IL-1β, an inflammatory cytokine effector released by microglia, the brain’s immune surveyor and defender86, have been demonstrated to decrease the levels of neural lineage differentiation markers DCX and MAP1 in human cortical and hippocampal cultures while promoting the proliferation of astroglial cell types88. Moreover, following LPS-induced neuroinflammation, in situ hybridization of mRNA specific for the enzyme kynurenine aminotransferase II (KATII), which encodes KYNA, has revealed increased KATII expression in the rostral migratory stream, SVZ and hippocampal neurogenic niche89. It has been well established that neuroinflammation impairs cognitive function in animal models91. Therefore, it is hypothesized that neuroinflammatory mediators, which are uniquely involved in the neurodevelopment of schizophrenia92, seemingly include components of kynurenine metabolism86. Not surprisingly, the anti-inflammatory drug minocycline, which coincidentally is also an NMDAR antagonist, has shown promise in reversing excessive synaptic pruning and engulfment by microglia in schizophrenia patient-derived neuronal and microglial cocultures93. Importantly, microglia and their effectors  are pivotal cellular mediators of neuroinflammation and can contribute to adult hippocampal neurogenesis as well as homeostatic synaptic pruning. Therefore, microglia are important cells in the clinical development of schizophrenia and psychosis95.Glutamate is an excitatory neurotransmitter that binds the 81, including disruptions in neurogenic function, sensorimotor gating, and hippocampal-dependent attention and working memory96. Moreover, antipsychotic medications have been reported to have limited ability to reverse the aforementioned behavioral impairments observed in maternal immune activation animal models84. However, regarding the restorative effects of antipsychotic medications on neurogenic function, further research is warranted, as the neurogenic benefits of typical  vs. atypical  antipsychotic medications are inconclusive.The involvement of inflammation in schizophrenia and related psychoses has attracted increasing interest. Maternal immune activation animal models of schizophrenia can be generated by administering LPS or polyinosinic:polycytidylic acid (Poly I:C), which triggers a maternal immune response to bacterial or viral pathogens, respectively. Subsequent prenatal and postnatal cytokine-induced inflammatory mediators  are speculated to play a role in the development of schizophrenia-like behaviors in adult offspringIn summary, increasing evidence demonstrates that schizophrenia and psychosis-related conditions have a strong neurodevelopmental etiology, with adult neurogenic development and function being distinctly and aberrantly affected Fig. . ConsequRemarkable strides have been made in research on the application of NSCs and NPCs for the development of potential stem cell-based therapies for neuropsychiatric disorders, CNS injury, and neurodegenerative diseases. As such, regenerative medicine provides a new opportunity for psychiatric disorder treatment. For instance, in the CNS, under diseased or injured conditions, transplanted NPCs tend to differentiate into astrocytes. Application of small molecules to facilitate the differentiation of these progenitor cells toward the desired cell fate will be a feasible therapeutic option in the near future.97. Interestingly, BET proteins have been demonstrated to regulate the gene expression of multiple genes implicated in tumor cell growth, inflammatory responses, and cardiac hypertrophy98. Since BET proteins are strongly implicated in numerous disease states, selective98 small-molecule inhibitors of BET bromodomains can prevent the interaction between BET proteins and acylated histones. Accordingly, a small-molecule cocktail comprising BET-inhibiting compounds increased the direct conversion of fibroblasts into neurons98, suggesting that these compounds can efficiently reprogram other cell types into functional neurons, indicating that this cocktail may be a potential replacement therapy for neurological disorders. In addition, BET bromodomain inhibition was shown to promote neurogenesis while decreasing gliogenesis in NPCs98. Therefore, small molecules targeting BET family proteins may be useful for promoting endogenous neuronal regenerative capacity in the context of a broad range of mental disorders that are associated with impaired neurogenesis, such as depression and schizophrenia.Some of these novel small molecules are members of the bromodomain and extraterminal (BET) family of proteins, which consists of Brd2, Brd3, Brd4, and testis-specific BrdT, which are epigenetic readers of the acylated histone code of chromatin99. Moreover, utilization of these novel research models will help elucidate the molecular underpinnings and mechanisms underlying the modulation of adult neurogenesis and its involvement in psychiatric disorders. Recent developments in organoid technologies and strategies have enabled remarkable, although limited, recapitulation of human neurodevelopment. The ontology of human corticolimbic structures and function is highly complex, proceeding through cycles of NPC and NSC proliferation, differentiation, migration, and apoptosis, all of which organoid models are able to recapitulate. In line with this, comparison of the development of 3D cerebral organoids derived from adult schizophrenia patients with that of organoids derived from healthy controls has already been utilized to identify aberrations in NPC proliferation100. Despite the extraordinary promise brain organoids offer in recapitulating human-specific developmental phenotypes, epitomized by the generation of outer SVZ-like progenitor cells, these models are not without drawbacks. Hypoxia leading to cell death (diffusion limit) results in outer SVZ shrinkage and disruption of radial glial scaffolds in prolonged culture, which prevents the migration required for cortical lamination99. To overcome such hurdles, new methodologies have been developed, including sliced neocortical organoids (SNOs), which overcome diffusion limits and possess better resolution of the more superficial and deeper cortical layers101, thus enabling organoids to be used in prolonged culture. Additionally, the SNO system has demonstrated utility in the study of the molecular mechanisms that control human cortical neuron subtype fate in psychiatric disorders101.Undoubtedly, the emerging use of human brain organoids and pluripotent stem cells with the capability to self-organize and develop three-dimensional organ-like structures will likely prove to be useful in the discovery of therapeutics for neuropsychiatric diseaseMental health disorders encompass a wide variety of ailments, which include addictive, depressive, and psychotic behaviors, all of which are extremely debilitating Fig. . A broad