Molecular modeling and in vivo imaging can identify successful flexible XXXX dendrimer-based siRNA delivery systems.

@entity7482 @entity21750 @entity137 @entity8681
This study aimed to identify suitable siRNA delivery systems based on flexible generation 2-4 @entity21750 dendrimers by correlating physico-chemical and biological in vitro and in vivo properties of the complexes with thermodynamic parameters calculated using molecular modeling. The siRNA binding properties of the dendrimers and @entity8681 25 kDa were simulated, binding and stability were measured in SYBR Gold assays, and hydrodynamic diameters, zeta potentials, and @entity137 were quantified. These parameters were compared with cellular uptake of the complexes and their ability to mediate RNAi. Radiolabeled complexes were administered intravenously, and pharmacokinetic profiles and biodistribution of these polyplexes were assessed both invasively and non-invasively. All flexible @entity21750 dendrimers formed thermodynamically more stable complexes than @entity8681 . While @entity8681 and the generation 4 dendrimer interacted more superficially with siRNA, generation 2 and 3 virtually coalesced with siRNA, forming a tightly intertwined structure. These dendriplexes were therefore more efficiently charge-neutralized than @entity8681 complexes, reducing agglomeration. This behavior was confirmed by results of hydrodynamic diameters (72.0 nm-153.5 nm) and zeta potentials (4.9 mV-21.8 mV in 10 mM HEPES) of the dendriplexes in comparison to @entity8681 complexes (312.8 nm-480.0 nm and 13.7 mV-17.4 mV in 10 mM @entity7482 ). All dendrimers, even generation 3 and 4, were less toxic than @entity8681 . All dendriplexes were efficiently endocytosed and showed significant and specific luciferase knockdown in HeLa/Luc cells. Scintillation counting confirmed that the generation 2 @entity21750 complexes showed more than twofold prolonged circulation times as a result of their good thermodynamic stability. Conversely, generation 3 complexes dissociated in vivo, and generation 4 complexes were captured by the reticulo-endothelial system due to their increased surface charge. Molecular modeling proves very valuable for rationalizing experimental parameters based on the dendrimers' structural properties. Non-invasive molecular imaging predicted the in vivo fate of the complexes. Therefore, both techniques effectively promote the rapid development of safe and efficient siRNA formulations that are stable in vivo.
