Pharmacologic inhibition of HO-1 suppresses growth of CML cell. (A,B) K562 cells were treated with PEG-ZnPP (left panel) or SMA-ZnPP (right panel) (5 μM each) for various time periods as indicated. Thereafter, cellular uptake of the compounds expressed as μM ZnPP incorporated in 10⁶ input cells (A), and the HO-1 activity in treated cells (B) were determined as described in “Methods.” HO-1 activity is expressed as nanomoles of bilirubin formed per milligram of protein per hour (nmol Bilirubin/mg/hr). Results represent the mean (± SD) of 3 independent experiments. *P < .05 compared with untreated cells (timepoint 0). (C) Time-dependent inhibition of growth of K562 cells by SMA-ZnPP. K562 cells were incubated with SMA-ZnPP (10 μM; gray bars) or control medium (black bars) at 37°C for various time periods as indicated. Proliferation was measured by ³H-thymidine incorporation. Results are expressed as percent of medium control and represent the mean (± SD) of triplicates of one representative experiment. (D-G) K562 cells (D,E) or KU812 cells (F, G) were incubated with various concentrations of PEG-ZnPP (D,F) or SMA-ZnPP (E, G) as indicated for 48 hours. After incubation, growth of cells was determined by ³H-thymidine incorporation. Results represent the mean (± SD) of 3 independent experiments. *P < .05 compared with control.