11P - Therapeutic effects of MRTX1133 in KRAS G12D mutant appendiceal cancer: Insights from organoid and in vivo studies

Background

KRAS is the most frequently mutated gene in appendiceal adenocarcinoma (AA) (45.6%) with just over half (50.4%) being G12D. Unique to AA, KRAS mutant tumors are strongly enriched for co-mutation with GNAS(odds ratio 12.2; p = 7.8x10^-40, 45% of KRAS^mut have co-mutant GNAS). The KRAS-G12D inhibitor MRTX1133 has shown robust anti-cancer activity in pre-clinical models of pancreatic, lung and colon cancer (CRC). Here we explore MRTX1133 in orthotopic PDX models of KRAS^G12D AA.

Methods

Four AA and CRC organoid models were developed and treated with MRTX1133. Orthotopic AA PDX models with KRAS^G12D were established by intraperitoneal implantation (TM00351 from Jackson Laboratory) and were intraperitoneally treated with MRTX1133 (15 mg/kg) (N=3) or vehicle (10% Captisol/50 mM citrate pH 5.0) (N=3), BID for 28 days. Tumor samples were analyzed using H&E, IHC, and RNAseq.

Results

KRAS^G12D but not KRAS^G12V organoids were sensitive to treatment with single-agent MRTX1133 (IC50 4.1 nM vs 1.8 uM, F-test, p < 0.0001). In PDX models IP MRTX1133 significantly reduced tumor volume relative to control as measured by MRI (1.15 vs 2.39, p =0.04). MRTX1133-treated tumors displayed low cellularity, with few cells positive for Ki-67 and a marked reduction in pERK, consistent with reduced cell proliferation and inactivation of RAS-MAPK pathway. Gene Sets Enrichment Analysis (GSEA) confirmed significant downregulation of E2F targets (NES = -1.9, FDR = 0.06) and RAS/ERK upregulated (NES = -2.3, FDR = 0.06) gene sets in MRTX1133-treated tumors. Interestingly, overexpression of GNAS^R201C (but not GNAS^WT ) in C479T organoids (AA) conferred resistance to KRAS-G12D inhibition (IC50 2.1 vs 5.9 nM, p < 0.0001). LS174T (CRC) organoid models were 100 fold less sensitive to MRTX1133 relative to AA models, but similarly expressing GNAS^R201C conferred resistance (IC50 360 nM vs >5 uM, p < 0.0001).

Conclusions

To our knowledge, this is the first report of activity of a KRAS inhibitor in pre-clinical models of AA. AA Models with KRAS^G12D were highly sensitive to MRTX1133 monotherapy providing a clear rationale for clinical testing. However, the presence of GNAS^R201C appears to cause resistance, suggesting a combination strategy may be required in KRAS^G12D/GNAS^mut tumors.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

This work was supported by the Colonel Daniel Connelly Memorial Fund, the National Cancer Institute (grant No. K22 CA234406 to Dr Shen, Cancer Center Support grant No. P30 CA016672), the Cancer Prevention and Research Institute of Texas (CPRIT) (grant No. RR180035 to Dr Shen, who is a CPRIT Scholar in Cancer Research), and a Conquer Cancer Career Development Award.

Disclosure

J.P.Y. Shen: Financial Interests, Personal, Other, general consultation and expert testimony: ShenJPMD Inc; Financial Interests, Personal, Other, advisory board: Engine Biosciences, NaDeNo Nanosciences; Financial Interests, Institutional, Coordinating PI, research project: Celsius Therapeutics; Financial Interests, Institutional, Other, research funding for pilot project: BostonGene. All other authors have declared no conflicts of interest.