Abstract 4704: Biochemical and cell-based assay platforms for development of RAF inhibitors against human cancers

Abstract The RAF protein kinases are key intermediates in cellular signal transduction, functioning as direct effectors of the RAS GTPases and as the initiating kinases in the ERK cascade. In human cancer, RAF activity is frequently dysregulated due to mutations in the RAF family members (ARAF, BRAF, and CRAF) or to alterations in upstream RAF regulators, including RAS and receptor tyrosine kinases. The first and second generations of RAF inhibitors have yielded dramatic responses in malignant melanomas containing BRAF mutations; however, their overall usefulness has been limited by both intrinsic and acquired drug resistance. In addition, cancers with hyperactive RAS exhibit intrinsic resistance to these drugs. In particular, issues related to the dimerization of the RAF kinases can impact the efficacy of these compounds and are a primary cause of drug resistance. We have established biochemical HotSpotTM kinase assay, NanoBRETTM and NanoBITTM cell assay platforms for High Through Screening of kinase inhibitors. Here, we demonstrate that the 3rd generation of pan-RAF inhibitors LY3009120, LXH254, and Belvarafenib inhibit ARAF, BRAF, CRAF, BRAF(V600E), and CRAF(R391W) kinase activity in biochemical HotSpotTM assay. Our NanoBRETTM target engagement and NanoBITTM cellular assay data show that LY3009120, LXH254, and Belvarafenib bind to KRAS(G12C) primed BRAF and CRAF, and block BRAF and CRAF dimerization. Furthermore, our results show these inhibitors can block the downstream ERK phosphorylation in cellular HTRF assay and induce caspase-3/7 activation in Western blot assay in the triple negative breast cancer MDA-MB-231 cells. Taken together, our results indicate the biochemical HotSpotTM kinase activity assay, and NanoBRETTM target engagement and NanoBITTM cellular assays can serve as great platforms to facilitate RAF drug discovery against human cancers. Citation Format: Jianghong Wu, Yong Wan, Shuguang Liang, Peter Gallagher, Li Liang, Christian Loch, Haiching Ma. Biochemical and cell-based assay platforms for development of RAF inhibitors against human cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4704.