Abstract 2963: VB7-756: a Her2-specific diabody armed with deBouganin, a plant toxin with a distinct MOA

Abstract

Abstract VB7-756 is Targeted Protein Therapeutic (TPT) comprised of a de-immunized form of bouganin (deBouganin), a potent, plant-derived, type I ribosome-inactivating protein (RIP), genetically linked to the C6.5 anti-Her2 diabody via a furin protease sensitive linker. To engineer the optimal diabody TPT format, several constructs were generated to assess the best diabody-deBouganin orientation. All constructs were expressed as a soluble protein in E. coli supernatant and compared with respect to expression level, stability and potency. The optimal configuration consisted of deBouganin genetically linked to the N-terminus of the VH-VL diabody via a furin protease-sensitive linker and was termed VB7-756. VB7-756 potency was analyzed against a panel of breast cancer cell lines with disparate levels of Her-2 expression and compared to that of Trastuzumab chemically linked to either DM1 (T-DM1) or MMAE (T-MMAE). Overall, VB7-756 was more potent than T-DM1 and T-MMAE with high Her-2 expressing tumor cell lines. In contrast to T-DM1, VB7-756 potency was unaffected by the Her2-Her3 dimerization mediated by heregulin. As opposed to T-DM1 and T-MMAE, which showed only minimal cytoxicity, VB7-756 was highly potent in vitro against tumor cells with cancer stem cell properties. To further differentiate the RIP mechanism of action of deBouganin from tubulin inhibitor reagents, tumor cells that escaped T-DM1 and T-MMAE treatment were incubated in the presence of VB7-756. Results revealed that, VB7-756 was cytotoxic against cancer cells surviving T-DM1 or T-MMAE treatment suggesting that deBouganin can overcome mechanisms of resistance developed by small molecule agents. Moreover, VB7-756 was also cytotoxic against tumor initiating cancer cells evading T-DM1 or T-MMAE toxicity by preventing tumorosphere formation. Overall these results demonstrate that deBouganin's distinct MOA could overcome mechanisms of resistance affecting the efficacy of small molecule drugs. Citation Format: Shilpa Chooniedass, Rachelle L. Dillon, Arjune Premsukh, Joycelyn Entwistle, Gregory P. Adams, Peter J. Hudson, Glen C. MacDonald, Jeannick Cizeau. VB7-756: a Her2-specific diabody armed with deBouganin, a plant toxin with a distinct MOA. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2963.