BFL-1/A1 is a BCL-2 family protein implicated in the progression and chemoresistance of melanoma, lymphoma, and other cancers, yet it remains undrugged. Anti-apoptotic BCL-2 family proteins block cell death by trapping the critical α-helical BH3 domains of pro-apoptotic members in a surface groove. Cancer cells hijack this survival mechanism by overexpressing a spectrum of anti-apoptotic members, mounting formidable apoptotic blockades that resist chemotherapeutic treatment. Drugging the BH3-binding pockets of anti-apoptotic proteins has become a highest-priority goal, fueled by the clinical success of venetoclax, a selective BCL-2 inhibitor, in reactivating apoptosis in BCL-2-dependent cancers. A natural juxtaposition of two unique cysteines at the binding interface of the NOXA BH3 helix and BFL-1/A1 pocket informed the development of stapled BH3 peptides bearing acrylamide warheads to irreversibly inhibit BFL-1/A1 by covalent targeting. Here, we describe the development and application of cysteine-reactive stapled peptides that, compared to their non-covalent analogs, trigger rapid mitochondrial cytochrome c release, caspase 3/7 activation, and apoptosis induction of BFL-1/A1 driven cancers such as melanoma. Mechanism of action studies demonstrated the exquisite BFL-1/A1 selectivity and mitochondrial localization of the in situ covalent reaction. Given the frequent proximity of native cysteines to regulatory binding surfaces, covalent stapled peptide inhibitors provide a new therapeutic strategy for targeting oncogenic protein interactions.

Citation Format: Rachel M. Guerra, Annissa J. Huhn, Edward P. Harvey, Gregory H. Bird, Loren D. Walensky. Reactivating apoptosis in BFL-1/A1 driven cancer with cysteine-reactive stapled peptide inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2024. doi:10.1158/1538-7445.AM2017-2024