Effect of protease inhibitors on IGFBP-3-induced growth inhibition of myeloid leukemia cells. HL-60 (A) and U937 (B) cells were cultured in the presence of IGFBP-3 (2 μg/mL) or protease inhibitors (5 μg/mL phenylmethysulfonyl fluoride, 1 μg/mL aprotinin, 0.5 μg/mL pepstatin, and 5 μg/mL leupeptin). Data represent the mean ± SD of triplicate cultures; and results represent 3 independent experiments. BP-3 indicates IGFBP-3; PIs, protease inhibitors.