Abstract 3836: Novel conditionally active biologic anti-Axl antibody-drug conjugate demonstrates anti-tumor efficacy and improved safety profile

Abstract Axl is a TAM family receptor tyrosine kinase that has been implicated in the pathogenesis of many cancer types. The high level of expression on the cancer cell surface has made it an attractive target for antibody therapeutics. However, Axl is expressed on many normal tissues and has been implicated in wide ranging requisite biological processes including response of endothelial cells to vascular injury, hematopoiesis, and regulation of immune responses. This normal tissue expression may limit Axl as a target for antibody-drug-conjugates (ADC). Conditionally Active Biologics (CAB) technology is a proprietary platform that selects antibodies that bind to target antigen in the context of diseased tissues, but not normal tissues, by taking advantage of the unique cancer microenvironment that is produced largely as a result of the Warburg effect. Using our CAB technology, we have identified anti-Axl Abs that reversibly bind to recombinant Axl and Axl expressing cells under conditions that are present in the tumor microenvironment but not in normal tissues. CAB-Axl antibodies were then conjugated to a model toxin payload to generate CAB-Axl-ADCs. The CAB-Axl-ADCs were active against Axl positive human tumor xenografts with tumor stasis observed at 1mg/kg weekly and tumor regressions observed at 1 mg/kg twice a week dose levels. A non-specific IgG-ADC showed minimal efficacy at the same dose levels. Single dose studies in cynomolgus macaques have demonstrated that CAB-Axl-ADC has reduced liver toxicity and immune system effects compared to Axl-ADCs that bind to Axl under normal conditions. In conclusion, our data is consistent with our work on CAB-EGFR antibodies, and suggests that ADCs generated using the CAB technology provides biologics with increased therapeutic index. Specifically, the CAB-Axl-ADC is an excellent candidate for evaluation as a treatment for human cancers that are Axl positive. Citation Format: Cathy Chang, Gerhard Frey, William J. Boyle, Leslie L. Sharp, Jay M. Short. Novel conditionally active biologic anti-Axl antibody-drug conjugate demonstrates anti-tumor efficacy and improved safety profile. [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 3836.