A novel mechanism of irinotecan targeting MDM2 and Bcl-xL

Irinotecan is a strong anticancer drug whose mechanism of action has been reported only for the inhibition of DNA topoisomerase I (Topo I) through its active metabolite SN-38. In this study, we present a new mechanism of Irinotecan which inhibits the activities of MDM2, an E3 ligase of tumour suppressor p53, and Bcl-xL, an anti-apoptotic protein, through direct binding. In our structure modelling study, Irinotecan could fit to the binding sites of MDM2 and Bcl-xL for their known drugs, Nutlin-3 and ABT-737, with a better binding affinity than to Topo I. The direct binding of Irinotecan to both proteins was confirmed through a NMR study. We further showed that Irinotecan increased the amount of p53 only in the presence of MDM2 and inhibited the physical interaction of Bcl-xL with Bim, a core pro-apoptotic protein. In addition, we demonstrated that Irinotecan induced the down regulation of proliferation and strong G2/M arrest in HCT116 colon cancer cells shortly after treatment. Collectively, we suggest a new mechanism of action for Irinotecan as a dual target inhibitor of MDM2 and Bcl-xL facilitating the anticancer activities mediated by p53 and Bcl-xL interaction partners. •The direct binding of Irinotecan to MDM2 and Bcl-xL was confirmed in modelling and NMR.•The effects of Irinotecan in MDM2 were confirmed by cell cycle, proliferation, and p53 expression.•The effects of Irinotecan in Bcl-xL were confirmed by apoptosis and Bcl-xL-Bim binding.•Irinotecan regulates proliferation, apoptosis and induces strong G2/M arrest.