Abstract DD01-02: Targeting EGFR and HER3 with a “two-in-one antibody”

Abstract

Abstract Deregulation of the epidermal growth factor receptor (erbB, HER) family plays an important role in tumorigenesis. In particular, EGFR and HER2 are validated targets in cancer. Over the last decade numerous antibodies and small-molecule tyrosine kinase inhibitors (TKI) were developed against each receptor, many of which are now commercially available. HER3, the third member of the family, is also implicated in cancer and ongoing studies continue to elucidate its biological function. The lack of intrinsic kinase activity requires HER3 to heterodimerize with a fully functional kinase in order to signal. Because of HER3's unique ability to directly couple to the p85 subunit of PI3K it is a potent activator of cell survival pathways. HER3 is the preferred heterodimerization partner for HER2 and is also frequently co- activated when EGFR is overexpressed or mutated. Adding to its function as a ligand dependent signaling mediator, it was recently shown that HER2 amplified systems utilize and require HER3 in order to activate the PI3K/Akt pathway. Additional studies demonstrated that HER3 is a central mediator of resistance to HER targeted therapeutics. Collectively, these new findings established HER3 as a new drugable target in the HER family. Because of the observed extensive crosstalk among these receptors it is hypothesized that blocking the signaling potential of more than one of the receptors may be essential to effectively treat cancer or to avoid the development of drug resistance. Since HER3 lacks intrinsic kinase activity it cannot be targeted with a standard ATP competitive small molecule TKIs. We chose an antibody based approach that leveraged a recently developed technology that enables two members of the HER family to be targeted with one agent. This novel engineering strategy produces dual specific antibodies in a conventional IgG format. Also, each of the two antigen binding fragments (Fabs) is capable of binding two different antigens with high affinity. The first such “two-in-one” antibody was derived from trastuzumab, a HER2 binding antibody. Selected sites in the variable region of trastuzumab were altered in such a way as to enable binding to VEGF with high affinity while maintaining binding to HER2. The high affinity binding to VEGF and HER2 translated into potent inhibitory activity in vitro and in vivo (Bostrom, J et al., Variants of the antibody herceptin that interact with HER2 and VEGF at the antigen binding site. Science. 2009, 323:1610-1614). To further test the hypothesis that it would be valuable to target all of the important signaling HER pairs in cancer we generated a HER3/EGFR “two-in-one” antibody that was capable of binding HER3 and EGFR with high affinity. The dual specificity was recruited sequentially by first isolating and validating an EGFR specific antibody and then modifying it to add a second specificity to HER3 through mutation of the antigen-binding site. Structure and mutagenesis studies showed that each Fab of the HER3/EGFR dual specific antibody, called MEHD7945A (DL11f), interacted with HER3 or EGFR on distinct and non-homologous epitopes. The binding of MEHD7945A to its respective receptors resulted in the blockade of ligand binding to EGFR and HER3 and subsequent receptor activation. MEHD7945A ablated EGFR driven signaling and potently blocked the HER2/HER3 signaling pathway in various cancer cell lines. The dual specific antibody engaged immune effector functions in vitro and in vivo. MEHD7945A was efficacious in multiple tumor types, for example, squamous cell carcinoma of the head and neck, as well as non-small cell lung, colorectal, and pancreatic cancers. We detected superior potency in comparison to monospecific HER antibodies. Additionally, preliminary toxicology studies suggest a better safety profile than other EGFR targeting agents. Taken together, the dual action antibody platform enabled us to target EGFR and HER3 containing signaling pairs with one molecule thereby generating an agent with superior efficacy and tolerability compared to monospecific antibodies. The conventional IgG format of MEHD7945A enables streamlined protein production. We therefore believe MEHD7945A has the potential to be a novel and potent anticancer agent. Citation Format: Gabriele M. Schaefer. Targeting EGFR and HER3 with a “two-in-one antibody” [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr DD01-02