Abstract CT133: Targeting BCL-2 and MCL-1 overcomes treatment resistance in relapsed and refractory non-Hodgkin lymphoma: Pre-clinical rationale and results from an open-label phase 1b study

Purpose: Treatment of patients with relapsed or refractory lymphoid neoplasms represents a significant clinical challenge, largely due to the genetic heterogeneity of these malignancies. Our study goal was to design a rational treatment strategy that simultaneously targets multiple disease drivers to provide safe, efficacious, and durable responses in patients with relapsed or refractory non-Hodgkin lymphoma (NHL). Experimental procedures and data summary: Venetoclax is a selective BCL-2 inhibitor that induces apoptosis and is efficacious in chronic lymphocytic leukemia; however, single-agent efficacy in other lymphoid neoplasms is limited. Using pharmacologic and genetic studies, we identified the pro-survival BCL-2 protein family member MCL-1 as a venetoclax resistance factor in NHL cell lines. We found that the monomethyl auristatin E (MMAE) payload of the antibody-drug conjugate polatuzumab vedotin promotes MCL-1 degradation via the ubiquitin/proteasome system, thus providing a strong rationale for combination with venetoclax. Mechanistically, polatuzumab vedotin combined with venetoclax promoted apoptotic NHL cell death. In NHL animal models, venetoclax, polatuzumab vedotin, and the anti-CD20 antibody obinutuzumab, that activates targeted antibody- and complement-dependent cell cytotoxicity, produced durable tumor regressions. In a phase 1b clinical trial, 33 patients with relapsed or refractory follicular lymphoma were evaluable for response over 6 dose levels with 19 complete responses and 6 partial responses (overall response rate 76%). All patients (8 of 8) treated with the recommended phase 2 regimen (venetoclax 800mg + polatuzumab vedotin 1.8mg/kg + obinutuzumab 1000mg) achieved complete responses at end of induction. The median duration of follow-up for all dose levels was 17.7 months. This triplet combination was well-tolerated by most patients and had an expected and acceptable safety profile. Conclusions: Our studies implicate MCL-1 as a key venetoclax resistance factor in NHL that can be overcome by polatuzumab vedotin, which promotes MCL-1 degradation. Pre-clinical NHL animal models and early clinical data confirmed that the combination of venetoclax, polatuzumab vedotin, and obinutuzumab is safe and promotes durable responses. Because MMAE and other anti-tubulin agents are likely not the only therapeutics that antagonize MCL-1, our study provides scientific rationale to pursue the broader strategy of identifying other therapeutics that similarly neutralize MCL-1 function. Such agents could be used in combination with venetoclax in other malignancies where MCL-1 is a venetoclax resistance factor. Our mechanism-based treatment regimen that directly targets oncogenic drivers in NHL patients may serve as a framework for treating other malignancies with complex etiologies. Citation Format: Dhara N. Amin, Rajat Bannerji, Raghuveer Singh Mali, Jason Oeh, Eva Lin, Anuradha Zindal, MaryAnn Go, Shang-Fan Yu, Maxwell Krem, Chris Arthur, Uwe Hahn, Anna M. Johnston, Vinit G. Karur, Nadia Khan, Paula Marlton, Tycel Phillips, Giuseppe Gritti, John F. Seymour, Monica Tani, Sam Yuen Yuen, Scott Martin, Matthew T. Chang, Christopher M. Rose, Victoria C. Pham, Elizabeth A. Lasater, Andrew G. Polson, YiMeng Chang, Jamie Hirata, Lisa Musick, Deepak Sampath, Christopher R. Flowers, Ingrid E. Wertz. Targeting BCL-2 and MCL-1 overcomes treatment resistance in relapsed and refractory non-Hodgkin lymphoma: Pre-clinical rationale and results from an open-label phase 1b study [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT133.