Percentage of cells in S phase at different times after release from lovastatin arrest.

K562 cells were treated for 24 hours with (A) none, (B) 1 nM IN-ODN, (C) 1 nM ASH-ODN+ASL-ODN, (D) ASH-ODN+ASL-ODN+10 μM DFO (added for the last 24 hours of incubation), (E) 50 μM DFO (added for the last 24 hours of incubation). Then the cells were growth arrested by 24-hour incubation with 10 μM lovastatin, washed, and resuspended in media containing 2 mM mevalonic acid, 20 μM leupeptin, and 0 (▪), 5 (○), 10 (▴), 25 (⋄), or 50 (X) μg/mL Tf-Fe. Percentage of cells in the S phase was analyzed 3, 6, and 10 hours later by flow cytometry, as described in “Materials and methods.” (F) Tf-Fe concentrations (μg/mL) producing half-maximal growth after 10-hour release from lovastatin arrest. Half-maximal concentrations were calculated using first-order dependence of cell cycle progression on Tf-Fe concentrations, as verified by analysis of variance for linear regression with the following levels of significance: untreated,P = .01; IN-ODN, P = .025; *ASH-ODN+ASL-ODN, half-maximal growth not obtained because without Tf-Fe, already 85% of the cells (out of the maximal) were in S phase. Tf-Fe concentration for 90% growth was 10 μg/mL, P = .07; ASH-ODN+ASL-ODN+DFO (10 μM), P = .025; DFO (50 μM), P = .01. Data are from a representative experiment.