Oncogenic Kras-mediated resistance to chemotherapy via increased ADAM17 activity and ligand shedding in colorectal cancer.

Abstract

e14104 Background: Oncogenic mutations in the small GTPase c-Kirsten (K)-ras occur in 40%-45% of patients with advanced colorectal cancer (CRC) and are challenging in development of anti-cancer therapeutics. Clear understanding of the vulnerabilities of Kras mutant (MT) CRC is important, and identification of druggable targets uniquely required by KrasMT CRC cells has the potential to fill a gap in the therapeutic armamentarium of advanced CRC. In this study, we examined the role of mutant Kras in determining response to chemotherapy using isogenic KrasMT HCT116 and Kras wild type (WT) HKH-2 cells. Methods: In vitro and in vivo models of CRC were assessed. ADAM-17 activity was measured using a fluorometric assay. Ligand shedding was assessed by ELISA or Western blotting. Apoptosis was assessed by flow cytometry and Western blotting. Results: HKH-2 cells showed enhanced sensitivity to 5-FU compared to HCT116 cells. Furthermore, oncogenic Kras was associated with increased Erk1/2 activity, ligand shedding and this correlated with increase in ADAM17 activity. Treatment of CRC cells with Kras siRNA, MEK1/2 or Erk1/2 inhibition resulted in inhibition of ligand shedding and ADAM17 activity following chemotherapy treatment and led to a potent increase in apoptosis when combined with chemotherapy in KrasMT cells. In addition, MEK1/2 inhibition resulted in significant decrease in tumour ADAM17 activity and serum ligand shedding and suppressed the growth of HCT116 xenografts. Importantly, we found that apoptosis induced by MEK1/2 inhibition was dependent on ADAM17 activity and ligand shedding. Conclusions: Taken together, our findings indicate that oncogenic Kras regulates chemotherapy resistance via increase in ADAM17 activity and ligand shedding. Furthermore, KrasMT CRC tumours are vulnerable to MEK1/2 inhibitors whose sensitivity is dependent on ADAM17 activity. Moreover, serum ligand levels may be a surrogate marker for response to MEK1/2 inhibition in combination with chemotherapy in Kras MT CRC tumours. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration AstraZeneca