MEK inhibition does not induce apoptosis in Nras-mutant AML. (A) Cell-cycle analysis using in vivo BrdU incorporation comparing vehicle- (n = 2) and PD901- (n = 3) treated Nras^G12D AML #6730 after 24 hours. (B-C) The percentage of BM cells collected from recipients of AML #6695 after PD901 (n = 5) or control vehicle (n = 4) treatment expressing cleaved Caspase-3 (P = .43) and Annexin V/7-AAD (P = .18). (D) Induction of apoptosis in short-term ex vivo culture measured by percentage activated Caspase-3 in 3 independent Nras^G12D AML lines (n = 2 per AML) treated with control vehicle, staurosporine (STS), or PD901.