Sotorasib Is a Pan-RASG12C Inhibitor Capable of Driving Clinical Response in NRASG12C Cancers

Abstract

KRASG12C inhibitors, like sotorasib and adagrasib, potently and selectively inhibit KRASG12C through a covalent interaction with the mutant cysteine, driving clinical efficacy in KRASG12C tumors. Because amino acid sequences of the three main RAS isoforms-KRAS, NRAS, and HRAS-are highly similar, we hypothesized that some KRASG12C inhibitors might also target NRASG12C and/or HRASG12C, which are less common but critical oncogenic driver mutations in some tumors. Although some inhibitors, like adagrasib, were highly selective for KRASG12C, others also potently inhibited NRASG12C and/or HRASG12C. Notably, sotorasib was five-fold more potent against NRASG12C compared with KRASG12C or HRASG12C. Structural and reciprocal mutagenesis studies suggested that differences in isoform-specific binding are mediated by a single amino acid: Histidine-95 in KRAS (Leucine-95 in NRAS). A patient with NRASG12C colorectal cancer treated with sotorasib and the anti-EGFR antibody panitumumab achieved a marked tumor response, demonstrating that sotorasib can be clinically effective in NRASG12C-mutated tumors.

Significance: These studies demonstrate that certain KRASG12C inhibitors effectively target all RASG12C mutations and that sotorasib specifically is a potent NRASG12C inhibitor capable of driving clinical responses. These findings have important implications for the treatment of patients with NRASG12C or HRASG12C cancers and could guide design of NRAS or HRAS inhibitors. See related commentary by Seale and Misale, p. 698. This article is featured in Selected Articles from This Issue, p. 695.

Figure 1.

Distinct RAS isoform selectivity profiles of KRAS^G12C inhibitors. A, Amino acid sequence aligments of the four RAS family isoforms, including KRAS4A and KRAS4B, NRAS, and HRAS. Amino acid differences are shown in red and blue. Regions involved in the switch-II binding pocket are shaded in green, and the hypervariable region is shaded in purple. B, Ba/F3 cells engineered to express either KRAS^G12C, NRAS^G12C, HRAS^G12C, or KRAS^G12D were treated for 72 hours in the absence of IL3 with various concentrations of the indicated inhibitors. Viable cell titer was measured using CellTiter Glo. C, Ba/F3 cells engineered to express the various mutant forms of KRAS, NRAS, and HRAS were treated for 72 hours with a range of concentrations of the indicated inhibitors, and viable cell titer was assessed as in B.

Figure 2.

Structural basis of RAS^G12C isoform selectivity. A, Crystal structures of sotorasib (6OIM) and adagrasib (6UT0) bound to KRAS^G12C are shown making distinct intractions with His95 (orange). Each inhibitor is colored magenta, GDP and a conserved Mg ion are shown in green, and the key hydrogen bond is shown in purple. B and C, Reciprocal mutagenesis studies were performed to explore the effects of substituting the four amino acid differences within the switch-II binding pocket, with NRAS amino acids substituted into KRAS^G12C (B) or KRAS amino acids substituted into NRAS^G12C. Constructs were expressed in Ba/F3 cells and treated for 72 hours in the absence of IL3 with various concentrations of the indicated inhibitors. Viable cell titer was measured using CellTiter Glo.

Figure 3.

Frequencies of NRAS^G12C, HRAS^G12C, and KRAS^G12C mutations in cancer. A, Percentage of HRAS^G12C, NRAS^G12C, and KRAS^G12C mutations observed in 148,268 cancers from the AACR GENIE database. B, Of all cases with HRAS, NRAS, or KRAS mutations, the percentage with G12C mutations, other mutations of glycine 12 (G12), or other mutations not involving G12 are shown. C, Frequencies of HRAS^G12C, NRAS^G12C, and KRAS^G12C mutations observed in specific cancer types. Actual numbers of cases with each mutation in specific diseases are indicated above each column.

Figure 4.

Clinical response in a patient with NRAS^G12C colorectal cancer treated with sotorasib and panitumumab. A, Graphical representation of the patient's treatment history. B, CT scans taken pretreatment and after 68 days of combined therapy with sotorasib and panitumumab with measurements of the dominant metastatic liver lesion shown. C, Serial serum CEA tumor marker measurements were obtained before and throughout treatment. The dotted horizontal line represents the upper limit of normal (3.5 ng/mL). D, The mutant allele fraction of NRAS^G12C was assessed in serial ctDNA speciments collected before and throughout therapy by ddPCR.