Induction of mitotic cell death by overriding G2/M checkpoint in endometrial cancer cells with non-functional p53

ObjectiveEndometrial tumors with non-functional p53, such as serous uterine endometrial carcinomas, are aggressive malignancies with a poor outcome, yet they have an Achilles' heel: due to loss of p53 function, these tumors may be sensitive to treatments which abrogate the G2/M checkpoint. Our objective was to exploit this weakness to induce mitotic cell death using two strategies: (1) EGFR inhibitor gefitinib combined with paclitaxel to arrest cells at mitosis, or (2) BI2536, an inhibitor of polo-like kinase 1 (PLK1), to block PLK1 activity.MethodsWe examined the impact of combining gefitinib and paclitaxel or PLK1 inhibitor on expression of G2/M checkpoint controllers, cell viability, and cell cycle progression in endometrial cancer cells with mutant p53.ResultsIn cells lacking normal p53 activity, each treatment activated CDC25C and inactivated Wee1, which in turn activated cdc2 and sent cells rapidly through the G2/M checkpoint and into mitosis. Live cell imaging demonstrated irreversible mitotic arrest and eventual cell death. Combinatorial therapy with paclitaxel and gefitinib was highly synergistic and resulted in a 10-fold reduction in the IC50 for paclitaxel, from 14 nM as a single agent to 1.3 nM in the presence of gefitinib. However, BI2536 alone at low concentrations (5 nM) was the most effective treatment and resulted in massive mitotic cell death. In a xenograft mouse model with p53-deficient cells, low dose BI2536 significantly inhibited tumor growth.ConclusionsThese findings reveal induction of mitotic cell death as a therapeutic strategy for endometrial tumors lacking functional p53.

► Therapeutic synergy between gefitinib and paclitaxel is achieved by abrogating the G2/M cell cycle checkpoint in p53-deficient endometrial cancer cells.
► Endometrial cancer cells lacking functional p53, but not cells with gain-of-function p53 mutation, undergo mitotic arrest and cell death.
► PLK1 inhibition decreases growth of p53-null xenograft endometrial tumors, identifying a new therapeutic strategy for this molecular phenotype.