Trastuzumab And C6.5 Diabody Armed With Debouganin Overcome Drug Resistance To Adcs Comprised Of Anti-Microtubule Agents

DeBouganin (deB) is a de-immunized form of bouganin, a Ribosome Inactivating Protein (RIP) that when internalized blocks protein synthesis thereby leading to cell death. When conjugated to trastuzumab (T-deB) or genetically attached to the C6.5 diabody, deBouganin was more potent than DM1 and unaffected by mechanisms of resistance to which DM1 is susceptible. To further highlight the differentiating mechanism of action of deBouganin, HCC1419 and BT-474 tumor cells that survived T-DM1 or trastuzumab-MMAE (T-MMAE) treatment in vitro were re-exposed to T-DM1, T-MMAE, or treated with T-deB or an anti-HER2 C6.5 diabody-deBouganin fusion protein. C6.5 diabody-deBouganin and T-deB were potent against HCC1419 and BT-474 cells surviving T-DM1 or T-MMAE treatment. However, the surviving cell populations were resistant to T-DM1, T-MMAE, DM1, MMAE and taxol treatment. In addition, cross-resistance was seen against trastuzumab-duocarmycin which contains a payload with a cell cycle independent mechanism of action. The contribution of multi-drug resistance, Bcl-2 family members and other survival pathways accounting for the resistant phenotype will be discussed. Overall, the data suggest that treatment with chemotherapeutics or ADCs comprised of small molecule compounds such as anti-microtubule agents, can lead to the outgrowth of tumor cells resistant to similar agents. In contrast, antibodies and antibody fragments armed with deBouganin can overcome these mechanisms of resistance and may therefore represent a more effective treatment option. Citation Format: Shilpa Chooniedass, Rachelle L. Dillon, Arjune Premsukh, Gregory P. Adams, Glen C. MacDonald, Jeannick Cizeau. Trastuzumab and C6.5 diabody armed with deBouganin overcome drug resistance to ADCs comprised of anti-microtubule agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 79. doi:10.1158/1538-7445.AM2017-79