MK-1775, a small molecule Wee1 inhibitor, enhances antitumor efficacy of various DNA-damaging agents, including 5-fluorouracil

MK-1775 is a potent and selective small molecule Wee1 inhibitor. Previously we have shown that it abrogated DNA damaged checkpoints induced by gemcitabine, carboplatin and cisplatin and enhanced the antitumor efficacy of these agents selectively in p53-deficient tumor cells. MK-1775 is currently in Phase I clinical trial in combination with these anti-cancer drugs. In this study, the effects of MK-1775 on 5-fluorouracil (5-FU) and other DNA-damaging agents with different modes of action were determined. MK-1775 enhanced the cytotoxic effects of 5-FU in p53-deficient human colon cancer cells. MK-1775 inhibited CDC2 Y15 phosphorylation in cells, abrogated DNA damaged checkpoints induced by 5-FU treatment, and caused premature entry of mitosis determined by induction of Histone H3 phosphorylation Enhancement by MK-1775 was specific for p53-deficient cells since this compound did not sensitize p53-wild type human colon cancer cells to 5-FU in vitro. In vivo, MK-1775 potentiated the antitumor efficacy of 5-FU or its prodrug, capecitabine, at tolerable doses. These enhancements were well correlated with inhibition of CDC2 phosphorylation and induction of Histone H3 phosphorylation in tumors. In addition, MK-1775 also potentiated the cytotoxic effects of pemetrexed, doxorubian, camptothecin and mitomyan C in vitro. These studies support the rationale for testing the combination of MK-1775 with various DNA-damaging agents in cancer patients.