Abstract B027: Bioluminescence resonance energy transfer (BRET) as a tool for assessing mutant KRAS-effector affinity and drug efficacy
Authors: Rigby Megan , Columbus John , Wall Vanessa , Esposito Dominic , Turbyville Thomas , Simanshu Dhirendra , Nissley Dwight , McCormick Frank , Maciag Anna 
Published: May 2023

Abstract
KRAS mutations occur in roughly 15% of cancer patients, with KRAS G12D, KRAS G12V, and KRAS G12C substitutions constituting the majority of these cases. Cancer types also display puzzling preferences for certain RAS mutations; for instance, 49% of pancreatic ductal carcinomas (PDAC) are driven by KRAS G12D substitutions compared to 35% of colon adenocarcinomas (COAD) and 17% of lung adenocarcinomas (LUAD)1. In contrast, KRAS G12C mutations drive only 3% of PDAC and 10% of COAD, but 41% of LUAD cases1. Some of this discrepancy can be explained by mutagen exposure, as there is evidence that tobacco smoke carcinogens drive the predominance of KRAS G12C mutations in lung cancer. However, it is possible that inherent functional differences between the mutant proteins also contribute to such preferences across cancer types. These oncogenic substitutions do endow subtle and unique differences in biochemical properties, but it is unknown whether this translates to differences in cellular signaling potential. KRAS activates the MAPK and PI3K signaling pathways by binding directly to RAF1 or the p110 catalytic subunit of PI3K. These interactions are important signaling nodes that result in cellular proliferation, survival, movement, differentiation, and immune evasion, and therefore drive cancer when constitutively activated by mutant KRAS. Biochemical assessments of relative effector affinity between KRAS mutants lack crucial elements present in a cellular environment, such as GDP/GTP ratios, membrane interactions, subcellular localization, and engagement with other proteins. Here, we optimize a cell-based Bioluminescent Resonance Energy Transfer (BRET) system in HEK293T cells using NanoLuc- and mVenus-tagged proteins to quantify relative effector affinities between KRAS mutants. We assess the affinities of KRAS4b G12C, KRAS4b G12D, and KRAS4b WT for effectors p110α and RAF1(52-188), along with RAS binding deficient control mutants p110α T208D/K227A and RAF1(52-188)R89L, and show statistical differences in effector engagement between the wildtype and mutant proteins. We also demonstrate the efficacy of this optimized system as a drug screening tool by assessing compounds in clinical development for their ability to disrupt mutant KRAS-effector interactions within a cellular environment. 1Prior IA, Hood FE, Hartley JL. The frequency of Ras mutations in cancer. Cancer Research 2020.
Citation Format: Megan Rigby, John Columbus, Vanessa Wall, Dominic Esposito, Thomas Turbyville, Dhirendra Simanshu, Dwight Nissley, Frank McCormick, Anna Maciag. Bioluminescence resonance energy transfer (BRET) as a tool for assessing mutant KRAS-effector affinity and drug efficacy [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr B027.