Activity of the KRAS G12D Inhibitor MRTX1133 against the Mutant KRAS Triple-Negative MDA-MB-231 Breast Cancer Cell Line

Background: Although <2% of breast cancers exhibit Kirsten rat sarcoma virus (KRAS) mutations, KRAS activity plays a role in triple-negative breast cancer (TNBC)/basal-like tumors. TNBC accounts for approximately 15% of breast tumors and is associated with a poor prognosis. Mutant KRAS G12D-triggered activation of the Rat sarcoma virus-Mitogen activated protein kinase (RAS-MAPK) pathway promotes immune evasion in TNBC by remodeling the tumor immune microenvironment (TIME). Specifically, CD11b(+) myeloid suppressor cells promote KRAS G12D-driven cancer and enhance the infiltration of CD4(+)Gata3(+) Th2 regulatory T cells. Of the breast cancer cell lines, only MDA-MB231 cells carry the KRAS G13D mutation. In this study, the efficacy of the KRAS G12D inhibitor MRTX1133 in inhibiting KRAS-driven growth and the migration of the MDA-MB-231 cell line was evaluated. Methods: The proliferation, chemosensitivity and migration of the MDA-MB-231 KRAS G13D cell line in response to MRTX1133 was compared with those of the MDA-MB-436 KRAS wildtype cell line using 3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assays and scratch assays. Furthermore, phosphorylation of cellular proteins and alterations in protein expression in response to KRAS/Son of Sevenless 1 (SOS1) inhibitors was detected using protein profiler western blot arrays. Results: MRTX1133 significantly inhibited (p < 0.05) the proliferation of MDA-MB-231 cells but not that of MDA-MB-436 cells. Similarly, migration of MDA-MB-231 but not that of MDA-MB-436 was retarded by this inhibitor. Furthermore, the SOS1 inhibitors BAY-293, BI-3406 and MRTX0902 exhibited high antiproliferative activity against MDA-MB-231 cells. In case of lung cancer, MRTX1133 was highly active against the BH1194 KRAS G12D Non-small cell lung cancer (NSCLC) cell line but demonstrated low activity against the BH1338 KRAS G13D NSCLC cell line. In phosphoprotein arrays, the phosphorylation of Extracellular signal-Regulated Kinases 1/2 (ERK 1/2), cAMP-response Element Binding protein (CREB), Glycogen Synthase Kinase 3 Alpha/ Beta (GSK-3 alpha/beta), and stress kinases was downregulated and in protein arrays, Epithelial Cell Adhesion Molecule (EpCAM), Interleukin 6 (IL-6), Granulocyte Macrophage-Colony Stimulating Factor 2 (GM-CSF), Macrophage-Colony Stimulating Factor 1 (M-CSF) and Vascular Endothelial Growth Factor A (VEGF) showed reduced expression in response to MRTX1133. Conclusions: KRAS G12D inhibition reprogrammed the TIME in pancreatic cancer experimental models, reversed tumor growth, increased CD8(+) T cell infiltration, decreased myeloid infiltration and elicited sustained tumor regression in response to MRTX1133 combined with immune checkpoint inhibitors. The significant and selective activity of MRTX1133 against the KRAS G13C mutant MDA-MB-231 cell line appears to be linked to the presence of Cyclin Dependent Kinase Inhibitor 2A (CDKN2) deletions as well as of B-Raf Proto-Oncogene, Serine/Threonine Kinase (BRAF) and Tumor Protein P53 (TP53) mutations in contrast to NSCLC cell lines. Therefore, in selected cases of KRAS mutant TNBC, inhibition of KRAS G12D may be used synergistically with immunotherapy.