Metnase protects cells from the cytotoxic effects of the clinically relevant Topo IIα inhibitor VP-16. (A) Proliferation was measured in THP-1 cells expressing Metnase shRNA or vector control using growth curves. (B) THP-1 cells expressing Metnase shRNA or a vector control were subjected to 24 hours of 0.5 μM VP-16 and then analyzed for apoptosis using annexin-V expression. (C-D) THP-1 cells transfected with control vector proliferate in the presence of 0.5 μM (C) or 1.0 μM (D) VP-16, but THP-1 cells expressing Metnase shRNA do not. Data are averages (± SEM) of triplicate experiments performed twice. *Student t test (P < .05); **Student t test (P < .01); ***Student t test (P < .005).