Design and discovery of BH-501242, a novel pan-KRAS on/off inhibitor targeting KRAS switch II pocket

KRAS mutations are involved in approximately 25% of all tumors and are frequent oncogenic drivers in lung (32%), colorectal (40%), and pancreatic cancers (85-90%). The most common KRAS driver mutations are on codon 12 and 13, including G12C, G12D, G12V, G12R, G13A, G13D, etc. The G12C mutation has been effectively targeted using a covalent strategy that exploits the unique reactivity of the cysteine residue. Other mutations, however, require inhibitors with high intrinsic binding affinity with KRAS to be effective in clinic. MRTX1133 was the first to demonstrate low single-digit nM cell potency for G12D mutation; however, the inhibitor lacked the ADME properties required for a successful oral drug. Since then, multiple KRAS inhibitors targeting G12D, G12V, or pan-KRAS mutations have advanced into clinical trials. Leveraging our structure-based drug design expertise, we designed a novel chemical scaffold targeting KRAS switch II pocket and identified the pan-KRAS inhibitor, BH-501242 after lead optimization on potency, ADME/PK, and safety properties. BH-501242 demonstrated excellent potency and target engagement across a broad spectrum of KRAS mutations and achieved sub-nM to low single-digit nM IC 50 values in cellular anti-proliferation assays and anti-phosphorylation assays against downstream kinase ERK. In a panel of 15 cell lines with KRAS G12D mutation, 10 cell lines with G12V, and 11 cell lines with G12C, BH-501242 showed superior anti-cell proliferation activity with median IC 50 s of 1.31 nM (0.40 nM for GP2D - 9.96 nM for SUIT-2), 3.55 nM (1.84 nM for SW620 - 19.7 nM for SW900), and 2.13 nM (0.68 nM for SW1463 - 5.79 nM for SW756) against KRAS G12D, G12V, and G12C mutant cells, respectively. BH-501242 also demonstrated outstanding cell potency against other KRAS mutations including G12S, G12F, G12A, G13D and K117N. Mechanistically, BH-501242 tightly binds with both active (GTP-bound or “on”) and inactive (GDP-bound or “off”) forms of mutant KRAS, effectively blocking its interaction with downstream effector c-RAF, and inhibiting the phosphorylation of ERK. Synergistic effects were observed in combination with EGFR antibody cetuximab in colony formation assays with KRAS mutant cells. PK profiling revealed oral bioavailability of BH-501242 in multiple species and dose dependent plasma exposures in mouse xenograft tumor models. BH-501242 demonstrated excellent anti-tumor activity in multiple CDX mouse models with various KRAS mutations, including GP2D and HPAC models with G12D mutation, H441 with G12V, and MiaPaca-2 with G12C, etc. In conclusion, the strong preclinical profile provides a strong rationale for the advancement of BH-501242 into further development.