Mutant PIK3CA As a Negative Predictive Biomarker for Treatment with a Highly Selective PIM1 Inhibitor in Human Colon Cancer

Significant improvement in targeted therapy for colorectal cancer (CRC) has occurred over the past few decades since the approval of the EGFR inhibitor cetuximab. However, cetuximab is used only for patients possessing the wild-type oncogene KRAS, NRAS, and BRAF, and even most of these eventually acquire therapeutic resistance, via activation of parallel oncogenic pathways such as RAS-MAPK or PI3K/Akt/mTOR. The two aforementioned pathways also contribute to the development of therapeutic resistance in CRC patients, due to compensatory and feedback mechanisms. Therefore, combination drug therapies (versus monotherapy) targeting these multiple pathways may be necessary for further efficacy against CRC. In this study, we identified mutant ( MT) as a determinant of resistance to SMI-4a, a highly selective PIM1 kinase inhibitor, in CRC cell lines. In CRC cell lines, SMI-4a showed its effect only in wild type ( WT) cell lines, while MT cells did not respond to SMI-4a in cell death assays. xenograft and PDX experiments confirmed that MT is responsible for the resistance to SMI-4a. Inhibition of MT by PI3K inhibitors restored SMI-4a sensitivity in MT CRC cell lines. Taken together, these results demonstrate that sensitivity to SMI-4a is determined by the genotype and that co-targeting of PI3K and PIM1 in MT CRC patients could be a promising and novel therapeutic approach for refractory CRC patients.