MRTX-1257

AMG 510 is the first‐in‐class KRASG12C inhibitor, currently in phase 2 clinical trials as an orphan drug to treat non‐small cell lung cancer patients. We developed and validated a sensitive, selective, and high‐throughput HPLC‐MS/MS method for the quantitation of AMG 510 in mouse plasma per the regulatory guideline of the US Food and Drug and Administration. AMG 510 and the IS (MRTX‐1257) were extracted from mouse plasma using tert‐butyl methyl ether and chromatographed using an isocratic mobile phase (0.2% formic acid:acetonitrile; 25:75, v/v) at a flow rate of 0.65 mL/min on an Atlantis dC18 column. AMG 510 and the IS eluted at ~0.95 and 0.73 min, respectively. AMG 510 and the IS were detected by positive electrospray ionization in multiple reaction monitoring using transition pair (Q1 → Q3) m/z 561.1 → 134.1 and m/z 566.5 → 98.2, respectively. Excellent linearity was achieved in the concentration range of 1.08–5040 ng/mL (r > 0.0996). No matrix effect and carryover were observed. Intra‐ and inter‐day accuracies and precisions were within the acceptance range. AMG 510 was demonstrated to be stable under the tested storage conditions. This novel method has been applied to a pharmacokinetic study in mice.

The KRAS(G12C) mutation is the most common genetic mutation in North American lung adenocarcinoma patients. Recently, direct inhibitors of the KRASG12C protein have been developed and demonstrate clinical response rates of 37-43%. Importantly, these agents fail to generate durable therapeutic responses with median progression-free survival of ~6.5 months.

To provide models for further preclinical improvement of these inhibitors, we generated three novel murine KRASG12C-driven lung cancer cell lines. The co-occurring NRASQ61L mutation in KRASG12C-positive LLC cells was deleted and the KRASG12V allele in CMT167 cells was edited to KRASG12C with CRISPR/Cas9 methods. Also, a novel murine KRASG12C line, mKRC.1, was established from a tumor generated in a genetically-engineered mouse model.

The three lines exhibit similar in vitro sensitivities to KRASG12C inhibitors (MRTX-1257, MRTX-849, AMG-510), but distinct in vivo responses to MRTX-849 ranging from progressive growth with orthotopic LLC-NRAS KO tumors to modest shrinkage with mKRC.1 tumors. All three cell lines exhibited synergistic in vitro growth inhibition with combinations of MRTX-1257 and the SHP2/PTPN11 inhibitor, RMC-4550. Moreover, treatment with a MRTX-849/RMC-4550 combination yielded transient tumor shrinkage in orthotopic LLC-NRAS KO tumors propagated in syngeneic mice and durable shrinkage of mKRC.1 tumors. Notably, single-agent MRTX-849 activity in mKRC.1 tumors and the combination response in LLC-NRAS KO tumors was lost when the experiments were performed in athymic nu/nu mice, supporting a growing literature demonstrating a role for adaptive immunity in the response to this class of drugs.

These new models of murine KRASG12C mutant lung cancer should prove valuable for identifying improved therapeutic combination strategies with KRASG12C inhibitors.