Abstract 379: Application of NanoBRET target engagement cellular assay for measurement of inhibitor binding to wild type and mutant RAS in live cells

Abstract

Abstract NanoBRET࣪ target engagement (TE) is the first biophysical technique that broadly enables the quantitative determination of protein inhibitor occupancy in live cells, without disruption of cellular membrane integrity. This quantitative capability is achieved in live cells via BRET with an optimized set of cell-permeable tracers, allow the measurement of compound binding to a selected cellular target protein. RAS is a well-known oncogene that is frequently mutated in most lung, pancreatic and colorectal cancers and is associated with poor disease prognosis. Mutated RAS is locked in the activated GTP bound state and facilitates enhanced RAS signaling in cancer cells. While being a desirable target, the absence of good druggable binding pockets has made modulator compound discovery challenging and unsuccessful. The recent discovery of a unique switch II binding pocket and successful inhibition of the KRAS (G12C) mutant by covalent inhibitors have led to the resurgence of interest in the design of inhibitors targeting RAS directly. Here, we performed NanoBRET࣪ TE cellular assay with RAS inhibitors against transfected RAS and its mutants. Our data demonstrate that NanoBRET࣪ TE cellular assay can measure the apparent affinity of RAS inhibitors by competitive displacement of a NanoBRET࣪ RAS switch I/II pocket tracer, reversibly bound to the LgBiT- and SmBiT- KRAS, KRAS (G12C), KRAS (G12D), KRAS (G12V), KRAS (G13D), KRAS (Q61H), KRAS (Q61L), KRAS (Q61R), or HRAS fusion constructs co-transfected in live HEK293 cells. Z factor analysis indicates the assay is High Throughput Screening (HTS) compatible and reproducible. In addition, we are able to confirm the signaling inhibition of downstream phospho-ERK1/2 by KRAS (G12C)-specific inhibitors AMG 510 (Sotorasib), ARS-1620, MRTX849, and MRTX1257 in MIA PaCa-2 pancreas and SW837 colon cancer cells bearing KRAS (G12C) mutation by Western blot assay. Our results suggest NanoBRET࣪ TE cellular assay can serve as a great tool to facilitate RAS pathway drug discovery against human cancers. Citation Format: Jianghong Wu, Shawn McGinley, Yuan Wang, Peter Gallagher, Haiching Ma. Application of NanoBRET target engagement cellular assay for measurement of inhibitor binding to wild type and mutant RAS in live cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 379.