Interaction of cytocidal drugs and the inhibition of caspase-3 by 3-nitrosobenzamide

The effect of 3-nitrosobenzamide (NOBA) on the etoposide, staurosporine and dexamethason induced rapid (4-6 hr), caspase-dependent apoptosis was inves tigated in thymocytes and lymphoma cells by flow cytometric assay of DNA fr agmentation. When NOBA (ED50 = 4 mu M) was added to these cell systems, the rapid onset of apoptosis was prevented. Such apparent protection by NOBA w as related to the inactivation of caspase-3, by s-nitrosyltation of 1.3 mol -SH per enzyme molecule out of 7 -SH groups. Since NOBA by itself induces DNA fragmentation within 18 hr in lymphoma cells, our results indicate that at least two active cell death pathways exist with apparent dissimilar kin etics and molecular mechanisms. (C) 1999 Wiley-Liss, Inc.