Effect of the CED-3/ICE–like protease inhibitor Z-VAD.fmk on PARP proteolysis in B-CLL cells. (A) Dose response of the inhibitory effect of Z-VAD.fmk on PARP proteolysis. Cells from patient 6 were incubated without dexamethasone (○) and cells from patient 9 were incubated with 10 μmol/L dexamethasone (•), in the presence of various concentrations of Z-VAD.fmk for 48 hours. Western blots of PARP were performed as described in Materials and Methods and the inhibition of PARP cleavage was quantified by densitometric scanning of the immunoblots. (B) B lymphocytes from four B-CLL patients were incubated for 48 hours with 10 μmol/L dexamethasone in the presence or absence of 200 μmol/L Z-VAD.fmk. Z-VAD.fmk was added 1 hour before dexamethasone administration. Cells were lysed and analyzed by Western blot as described in Materials and Methods.