99mTechnetium- or Cy7-Labeled Fab(Tocilizumab) as Potential Multiple Myeloma Imaging Agents.
BACKGROUND
Multiple Myeloma (MM) is a malignant hematologic disorder and the second most common blood cancer. Interleukin-6 (IL-6) has been identified as a crucial factor for the proliferation and survival of MM cells and the overexpression of IL-6 receptor is being studied as a molecular target for therapeutic and diagnostic use in myelomas and other comorbidities. Tocilizumab is a humanized monoclonal antibody that binds IL-6R.


OBJECTIVE
We aim to label and evaluate Fab(Tocilizumab) with 99mTechnetium or Cy7 as potential MM imaging agents.


METHODS
IL-6R distribution was analyzed by Laser Confocal Microscopy (LCM) in MM cell lines. Fab(Tocilizumab) was produced by the digestion of Tocilizumab with papain for 24h at 37°C, derivatized with NHS-HYNIC-Tfa and radiolabeled with 99mTc. Radiochemical stability and in vitro cell assays were evaluated. Biodistribution and SPECT/CT were performed. Also, Fab(Tocilizumab) was labeled with Cy7 for in vivo fluorescence imaging up to 72h.


RESULTS
LCM analysis demonstrates IL-6R distribution on MM cell lines. Incubation with papain resulted in complete digestion of Tocilizumab and exhibited a good purity and homogeneity. Radiolabeling with 99mTc via NHS-HYNIC-Tfa was found to be fast, easy, reproducible and stable, revealing high radiochemical purity and without interfering with IL-6R recognition. Biodistribution and SPECT/CT studies showed a quick blood clearance and significant kidney and MM engrafted tumor uptake. Cy7-Fab(Tocilizumab) fluorescent imaging allowed MM1S tumor identification up to 72h p.i.


CONCLUSION
These new molecular imaging agents could potentially be used in the clinical setting for staging and follow-up of MM through radioactive whole-body IL-6R expression visualization in vivo. The fluorescent version could be used for tissue sample evaluation and to guide surgical excision, if necessary.
['Camacho|Ximena|X|', 'Perroni|Carolina|C|', 'Machado|Camila L|CL|', 'de Godoi Carneiro|Camila|C|', 'de Souza Junqueira|Mara|M|', 'Faria|Daniele|D|', 'García|María F|MF|', 'Fernández|Marcelo|M|', 'Oddone|Natalia|N|', 'Benech|Juan|J|', 'Buchpiguel|Carlos A|CA|', 'Cerecetto|Hugo|H|', 'Chammas|Roger|R|', 'Riva|Eloisa|E|', 'Cabral|Pablo|P|', 'Gambini|Juan P|JP|']
Fab(Tocilizumab) multiple myeloma IL-6R molecular imaging 99mTechnetium- or Cy7-lableled Fab(Tocilizumab).