MEK1 inhibition sensitizes primary acute myelogenous leukemia to arsenic trioxide–induced apoptosis

We found that MEK1 inhibitor PD184352 strikingly increased apoptosis induced by arsenic trioxide (ATO) in 21 of 25 patients with primary acute myelogenous leukemia (AML). Isobologram analysis confirmed the synergistic (13 of 25 patients) or additive (8 of 25 patients) nature of this interaction. Moreover, we demonstrated that the p53-related gene p73is a molecular target of the combined treatment in AML blasts. Indeed, ATO modulates the expression of the p73gene by inducing the proapoptotic and antiproliferative TAp73 and the antiapoptotic and proproliferative ΔNp73 isoforms, thereby failing to elevate the TA/ΔNp73 ratio. Conversely, treatment with PD184352 reduces the level of ΔNp73 and blunts the arsenic-mediated up-regulation of ΔNp73, thus causing an increase in the TA/ΔNp73 ratio of dual-treated cells. High doses of ATO induced p53 accumulation in 11 of 21 patients. Combined treatment resulted in the induction of the proapoptotic p53/p73 target gene p53AIP1(p53-regulated apoptosis-inducing protein 1) and greatly enhanced the apoptosis of treated cells.