Inhibition of drug-induced DNA fragmentation, but not cell death, of glioma cells by non-caspase protease inhibitors.

The role of non-caspase protease activation in drug-induced cell death of glioma cells was examined. Neither calpain inhibitors I or II, phenylmethylsulfonyl fluoride (PMSF), Nalpha -p-tosyl-L-lysine chloromethyl ketone (TLCK), N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), E64, leupeptin nor pepstatin inhibit the cytotoxicity of vincristine, cisplatin, doxorubicin, cytarabine, camptothecin, BCNU or VM26 in two malignant glioma cell lines, T98G and LN-229. However, DNA fragmentation induced by VM26 is inhibited by calpain inhibitor I, PMSF, TLCK and TPCK, and that induced by camptothecin by calpain inhibitors I and II and TPCK. Moreover, protease inhibitors fail to abrogate CD95 ligand-induced apoptosis even though DNA fragmentation is attenuated by calpain inhibitor II and TPCK. Thus, non-caspase protease activation is not required for drug-induced apoptosis of glioma cells. Protease inhibitor-mediated inhibition of DNA fragmentation operates downstream of the commitment point for cell death.