HIP-PA treatment sensitizes the hypoxia-resistant 8226, U266, and hypoxia-sensitive MM1S and OPM-2 cells to hypoxia-mediated apoptosis in vitro. (A) 8226 were cultured under normoxic or hypoxic (0.1% O2, 5% CO2) conditions with indicated concentration of HIF-PA or CO-PA for 72 hours. (B) U266 were cultured under normoxic or hypoxic (0.1% O2, 5% CO2) with indicated concentration of HIF-PA or CO-PA for 72 hours. (C) MMI.S cells were cultured under normoxic or hypoxic (0.1% O2, 5% CO2) with indicated concentration of HIF-PA or CO-PA for 48 hours. (D) OPM-2 cells were cultured under normoxic or hypoxic (0.1% O2, 5% CO2) with indicated concentration of HIF-PA or CO-PA for 24 hours. At the end of the treatment, cells were harvested and the percent apoptosis was measured by flow cytometry for cleaved caspase 3. Values are mean ± 1 standard deviation of 3 independent experiments. Bracket * indicates significant change (P<0.05) (ANOVA) of treatment compared to control.