Abstract P4-15-17: A novel targeted engineered toxin body for treatment of HER2 positive breast cancer

Abstract

Abstract The HER2 receptor is overexpressed in 20-30% of breast cancers. HER2 overexpression in breast cancer has been successfully targeted by both antibody and antibody-drug conjugate (ADC) approaches. The recently approved trastuzumab-emtansine (T-DM1, Kadcyla) ADC has shown promising clinical results in patients refractory to trastuzumab (Herceptin). Because DM1 is a chemotherapeutic and refractory breast cancer patients have typically progressed through several rounds of chemotherapy, we are developing a new targeted therapy approach utilizing a novel mechanism of action. MT-2H74 is an engineered toxin body comprised of the trastuzumab single chain variable fragment (scFv) and a modified ribosome-inactivating protein derived from Shiga-like toxin 1 A (SLT-1A). We have proprietarily modified SLT-1A for reduced immunogenic potential and increased stability. MT-2H74 selectively binds HER2-expressing breast cancer cells, and exerts a potent HER2-specific cytotoxic effect on several tested cell lines. MT-2H74 demonstrates effective cell kill at picomolar concentrations on cell lines expressing high levels of HER2 and is not cytotoxic to HER2 negative control cell lines. Multi-drug resistance transporter 1 (MDR1) has been reported to confer resistance to chemotherapeutic and ADC treatments, such as direct T-DM1 cell kill; however, MT-2H74 displays cytotoxic activity against HER2 transfected NCI/ADR-RES cells known to express MDR1. Murine models are under investigation to determine therapeutic efficacy in vivo. MT-2H74 is a promising HER2-targeted therapeutic agent against breast carcinomas with a unique mechanism of action and is currently under further development. Citation Format: Erin K Willert, Sangeetha Rajagopalan, Garrett L Robinson, Brigitte Brieschke, Jennifer Erdman, William Null, Jack P Higgins. A novel targeted engineered toxin body for treatment of HER2 positive breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-15-17.