Abstract LB-243: The ErbB3-targeting antibody MM-121 (seribantumab) reverses heregulin-driven resistance to multiple chemotherapies on tumor cell growth
Authors: Masson Kristina , Grantcharova Viara , Burenkova Olga , Wainszelbaum Marisa , Iadevaia Sergio , Adams Sharlene , Raue Andreas , Czibere Akos , Schoeberl Birgit , MacBeath Gavin 
Published: August 2015

Abstract
Purpose: Heregulin-mediated activation of the human epidermal growth factor receptor 3 (HER3/ErbB3) is required for the growth and survival of many epithelial cancers. This signaling pathway is also emerging as a mechanism of resistance to targeted agents and chemotherapies. MM-121 (seribantumab) is an investigational human monoclonal anti-ErbB3 antibody that has previously been shown to effectively block ligand-dependent activation of ErbB3 in a range of tumors, and has demonstrated clinical activity in biomarker positive patients in several Phase II trials. The purpose of this study was to examine in three indications of interest, the ability of heregulin to induce resistance to standard chemotherapies and the reversal of this effect by MM-121. Such systematic evaluation of different combinations can serve as a guide for the future clinical development of MM-121.
Methods: To assess the effect of heregulin and MM-121 on chemotherapies in cancer cells, we conducted a high throughput proliferation screen in 3D cultures. A panel of 60 cell lines of relevant clinical indications (ovarian, breast and lung cancer) was selected and tested for the sensitivity to respective standard-of-care chemotherapies in the absence or presence of exogenously added heregulin. Using these data, we analyzed the rescuing capacity of heregulin and the MM-121 combination's sensitivity, and selected representative combinations for in vivo models.
Results: We show that in a large panel of cancer cell lines the presence of heregulin can induce resistance to multiple chemotherapies with very different mechanisms of action. The combination of MM-121 with any one of these chemotherapies can reverse the heregulin-meditated rescue and provide an additive treatment effect at therapeutically relevant doses achieved in the clinic. These results were further validated in xenograft mouse models of all three indications, using representative chemotherapies and doses. In addition, biomarker analysis revealed that ErbB3 receptor levels largely determine responsiveness to heregulin and MM-121.
Conclusions: MM-121 is an anti-ErbB3 antibody designed to block ligand-mediated signaling, and currently in clinical development. The results presented here demonstrate the role of heregulin in reducing the sensitivity of tumors to standard-of-care chemotherapies, and the effect of ErbB3 pathway inhibition across indications.
Citation Format: Kristina Masson, Viara Grantcharova, Olga Burenkova, Marisa Wainszelbaum, Sergio Iadevaia, Sharlene Adams, Andreas Raue, Akos Czibere, Birgit Schoeberl, Gavin MacBeath. The ErbB3-targeting antibody MM-121 (seribantumab) reverses heregulin-driven resistance to multiple chemotherapies on tumor cell growth. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-243. doi:10.1158/1538-7445.AM2015-LB-243