Abstract LB231: Overcoming KRAS G12C inhibitor resistance with a chaperone-mediated protein degrader (CHAMP)

Abstract KRAS is the most frequently mutated oncogene in cancer and is particularly common in lung, pancreatic and colorectal cancers. While KRAS has been undruggable, covalent KRAS G12C inhibitors, sotorasib and adagrasib, that bind preferentially to GDP-bound KRAS and prevent exchange for GTP and interaction with downstream effectors, have been approved for use in NSCLC. While these reagents show promising efficacy and are well-tolerated by patients, acquired drug resistance rapidly develops. The drug resistance landscape of G12C inhibitors is complex, with several mechanisms of resistance already described, ranging from reactivation of mutated RAS or other RAS isoforms, acquisition of new KRAS mutations, and genetic alterations of pro-growth signaling pathways. Thus, an ideal approach to overcoming drug resistance will need to target multiple different mechanisms. We exposed NSCLC and pancreatic cell lines (NCI-H358, NCI-H1373 and MIA PaCa-2, respectively) to increasing doses of sotorasib or adagrasib until the resulting cells grow normally in the presence of 10 µM of each inhibitor. Sotorasib-resistant cells, designated as S-R, remarkably remain sensitive to adagrasib, suggesting that the resistant cells continue to be dependent on mutant KRAS for survival. In contrast, adagrasib-resistant cells, designated as A-R, are resistant to both inhibitors. Treatment of innate and acquired adagrasib-resistant cells with 500 nM adagrasib attenuated RAS activity; however, this is compensated for by increased KRAS, HRAS and NRAS mRNA and restored p-ERK levels, a surrogate marker of RAS activity. Moreover, analysis of RTK activation in drug-resistant cells reveals that adagrasib treatment induces the activity of specific RTKs in a cell-line specific manner. Interestingly, during the acquisition of adagrasib resistance, several RTKs are strongly induced to escape drug inhibition. These results indicate the need to simultaneously reduce both KRAS G12C and compensating RTK activity to effectively treat KRAS G12C NSCLC. The majority of oncogenic RTKs are known to be dependent on the molecular chaperone HSP90 for their proper folding and stability. Therefore, a heterobifunctional chaperone-mediated protein degrader (CHAMP), RNK07421, was designed to specifically target both KRAS G12C and HSP90. RNK07421 induces an artificial ternary complex with KRAS G12C and HSP90, while also inhibiting the activity of both proteins and promoting proteasomal degradation of KRAS G12C via HSP90-associated E3-ligases. Treatment of adagrasib-resistant NSCLC cells and PDOs with RNK07421 resulted in decreased levels of KRAS G12C, p-ERK and RTKs. Furthermore, in vivo treatment with RNK07421 demonstrated dramatic tumor growth inhibition as compared to adagrasib treatment alone. Together, these observations indicate that the novel mechanisms of action of RNK07421 may provide several advantages over G12C inhibitors and possibly other targeted protein degradation agents to effectively treat KRAS G12C-dependent NSCLC. Citation Format: Ines Pulido Endrino, Qiyue Luan, Jennifer Graeber, Brianna Borger, Chenghao Ying, Jinhua Li, Zimo Yang, Zhiyong Wang, Yaya Wang, Yuetong Sun, Yan Dai, Ian Papautsky, Thomas L. Prince, Guoqiang Wang, Kevin P. Foley, Weiwen Ying, Takeshi Shimamura. Overcoming KRAS G12C inhibitor resistance with a chaperone-mediated protein degrader (CHAMP) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB231.