Inhibition of caspase activity delays apoptosis in a transfected NS/0 myeloma cell line

The productivity of NS/0 myeloma batch cultures is:often compromised by the premature induction of apoptosis, now established to be the predominant me thod df cell death du ri ng cu Itu re decline. Caspase proteases have recen tly been shown to play a major role in the transmission of signals for apop totic cell death. Using a specific:inhibitor that targets a range of caspas es (Z-VAD-fmk) we assessed whether inhibition of caspase activity could pro long the viability of NS/0 cells under conditions that cause apoptotic cell death in batch cultures. Z-VAD-fmk was found to significantly reduce apopt otic cell death (by similar to 50%) induced by cytotoxins and to preserve m embrane integrity to a similar extent. In conditions of low serum, Z-VAD-fm k reduced certain features:bf: apoptosis (e.g., DNA fragmentation), but onl y marginally:improved viability. In medium-depleted batch cultures, Z-VAD-f mk afforded a delay of between 24 and 48h in both the induction of apoptosi s and loss of viability. Despite:an apparent increase in viability in Z-VAD -fmk-treated NS/0 cultures, no improvement in productivity could be demonst rated, suggesting that at least some normal pathways for protein production are shut down upstream df caspase activation. An examination of mitochondr ial membrane potential (Delta psi m) in Z-VAD-fmk-treated and :untreated NS /0 cells revealed only a small initial difference (5%) in the levels of Del ta psi m depolarization. Similar levels of mitochondrial dysfunction, despi te caspase inactivity, may therefore be responsible for the comparable prod uctivity in untreated and Z-VAD-fmk-treated cultures. Thus, this study sugg ests that, while a delay in cell death due to caspase inhibition may reduce problems associated with cellular disintegration, it does not permit produ ctivity improvements in this type of culture. (C) 2000 John Wiley & Sons, I nc.