Abstract LB-068: From intracellular antibody fragments to small molecule inhibitors of mutant KRAS

Abstract

Abstract Our aim was to develop methods to employ intracellular antibody fragments as lead macromolecules for small compound selections. We have used this approach to identify small molecules binding to mutant RAS with potential to inhibit the RAS-effector interactions. Mutation in RAS family members is among the most frequent in human cancer and the mutant RAS proteins are tumour-specific proteins for therapy. We have previously selected an intracellular antibody single domain fragment that binds to mutant forms of KRAS and HRAS and used this antibody fragment to demonstrate that blocking RAS-effector interaction-dependent signal transduction prevents tumour initiation and overt tumour growth in mouse preclinical models. The antibody fragment binds to GTP-bound RAS with high pM affinity and we have used this property to isolate compounds from a fragment library using a competitive SPR method that places the compounds in the region of the binding site of the antibody fragment. Using a combination of X-ray crystallography and medicinal chemistry, we have obtained a family of compounds that bind adjacent to the KRAS switch I region with nM affinity and that inhibit the downstream phosphorylation of AKT and ERK that results from RAS signaling. The chemical evolution and interaction characteristics of the KRAS-binding compounds will be described and their biochemical and cell-based properties presented. We have validated our approach using an antibody fragment as a screening tool for the identification of small molecule inhibitors of the RAS-effector interaction. This approach has yielded small compound fragments that are currently being developed as potential RAS-effector inhibitors in our medicinal chemistry programme. Citation Format: Camilo E. Quevedo, Abimael Cruz, Hanna Tulmin, Carole J. Bataille, Tomoyuki Tanaka, Donna Petch, Angela J. Russell, Simon Phillips, Terence H. Rabbitts. From intracellular antibody fragments to small molecule inhibitors of mutant KRAS [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 LB-068. doi:10.1158/1538-7445.AM2017-LB-068