BI-2865

KRAS is one of the most commonly mutated proteins in cancer, and efforts to directly inhibit its function have been continuing for decades. The most successful of these has been the development of covalent allele-specific inhibitors that trap KRAS G12C in its inactive conformation and suppress tumour growth in patients1–7. Whether inactive-state selective inhibition can be used to therapeutically target non-G12C KRAS mutants remains under investigation. Here we report the discovery and characterization of a non-covalent inhibitor that binds preferentially and with high affinity to the inactive state of KRAS while sparing NRAS and HRAS. Although limited to only a few amino acids, the evolutionary divergence in the GTPase domain of RAS isoforms was sufficient to impart orthosteric and allosteric constraints for KRAS selectivity. The inhibitor blocked nucleotide exchange to prevent the activation of wild-type KRAS and a broad range of KRAS mutants, including G12A/C/D/F/V/S, G13C/D, V14I, L19F, Q22K, D33E, Q61H, K117N and A146V/T. Inhibition of downstream signalling and proliferation was restricted to cancer cells harbouring mutant KRAS, and drug treatment suppressed KRAS mutant tumour growth in mice, without having a detrimental effect on animal weight. Our study suggests that most KRAS oncoproteins cycle between an active state and an inactive state in cancer cells and are dependent on nucleotide exchange for activation. Pan-KRAS inhibitors, such as the one described here, have broad therapeutic implications and merit clinical investigation in patients with KRAS-driven cancers.

KRASG12C selective inhibitors, such as sotorasib and adagrasib, have raised hopes of targeting other KRAS-mutant alleles in patients with cancer. We report that KRAS wild-type (WT)–amplified tumor models are sensitive to treatment with the small-molecule KRAS inhibitors BI-2493 and BI-2865. These pan-KRAS inhibitors directly target the “OFF” state of KRAS and result in potent antitumor activity in preclinical models of cancers driven by KRAS-mutant proteins. In this study, we used the high-throughput cellular viability Profiling Relative Inhibition Simultaneously in Mixtures assay to assess the antiproliferative activity of BI-2493 in a 900+ cancer cell line panel, expanding on our previous work. KRAS WT–amplified cancer cell lines, with a copy number >7, were identified as the most sensitive, across cell lines with any KRAS alterations, to our pan-KRAS inhibitors. Importantly, our data suggest that a KRAS “OFF” inhibitor is better suited to treat KRAS WT–amplified tumors than a KRAS “ON” inhibitor. KRAS WT amplification is common in patients with gastroesophageal cancers in which it has been shown to act as a unique cancer driver with little overlap to other actionable mutations. The pan-KRAS inhibitors BI-2493 and BI-2865 show potent antitumor activity in vitro and in vivo in KRAS WT–amplified cell lines from this and other tumor types. In conclusion, this is the first study to demonstrate that direct pharmacologic inhibition of KRAS shows antitumor activity in preclinical models of cancer with KRAS WT amplification, suggesting a novel therapeutic concept for patients with cancers bearing this KRAS alteration.