Abstract 6053: Mechanism of action of tumor-selective, chaperone-mediated protein degraders (CHAMPs)

Abstract

Abstract HSP90 mediates the folding of many important cancer-associated proteins, but it can also direct its substrates towards degradation via the ubiquitin-proteasome system. Furthermore, in tumor tissues, HSP90 complexes are in an activated state relative to normal tissues, and small molecule HSP90 inhibitors display unique tumor-selective pharmacokinetics. To take advantage of these attributes, we have developed a novel targeted protein degradation technology, termed Chaperone-Mediated Protein Degradation (CHAMP), and present here an in-depth characterization of the CHAMP mechanism of action. Initially, from a chemical library of greater than 1000 linkered HSP90 binders, hetero-bifunctional CHAMPs were synthesized in which target protein binders and HSP90 binders were covalently coupled together by short linkers. The resulting compounds were screened for target protein degradation and cancer cell cytotoxicity to identify promising leads for further optimization. We found that CHAMPs can degrade a wide variety of target proteins. This included proteins that are known to be regulated by HSP90, such as transcription factor BRD4 or ERK5 kinase. However, proteins that are normally independent of HSP90 function can also be degraded, including mutated KRAS and SHP2 phosphatase. In vitro, CHAMP treatment of cells resulted in formation of a ternary complex between the target protein, CHAMP compound and HSP90. Moreover, an X-ray crystal structure was solved for a mKRAS-CHAMP-HSP90 ternary complex. CHAMP-mediated degradation required both the target- and HSP90-binding moieties to be covalently coupled and involved ubiquitination of the target protein. Multiple ubiquitin E3 ligases were present in ternary complexes, and depending on the target protein, NEDD8 inhibition or CRISPR knockouts of individual E3 ligases could suppress proteasome-dependent target degradation. In vivo, irrespective of target, CHAMPs displayed prolonged exposure in tumors relative to plasma and normal tissues, resulting in prolonged target degradation in tumors and strong tumor growth inhibition at well-tolerated doses. CHAMP technology can be applied to a diversity of cancer-associated targets and has potential advantages relative to other protein degradation approaches, including an improved safety margin due to preferential accumulation in tumor tissues. Citation Format: Xiangcai Yang, Yan Dai, Qinglin Ding, Feng Du, Jinhua Li, Chuhe Liu, Chunyang Lv, Liang Ma, Thomas L. Prince, Yuetong Sun, Mingkai Wang, Rong Wang, Yaya Wang, Zhiyong Wang, Min Wu, Mengmeng Xu, Zimo Yang, Long Ye, Wei Yin, Chenghao Ying, Haoxin Zhou, Guoqiang Wang, Weiwen Ying, Kevin P. Foley. Mechanism of action of tumor-selective, chaperone-mediated protein degraders (CHAMPs) [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 6053.