Pro-apoptotic interactions between XK469 and the peripheral benzodiazepine receptor.

XK469 (2-[4-(7-chloro-2-quinoxalinyloxy) phenoxy]propionic acid) is a new anti-tumor agent with substantial activity against several drug-resistant cell lines. Using murine leukemia L1210 cells in culture, we found the chiral R(+) form of XK469 to be substantially more cytotoxic than the S(-) form, while the herbicide analog 'Assure' was essentially inactive. The cytotoxic response to these agents was accompanied by apoptosis, and was found to be correlated with drug binding to the peripheral benzodiazepine receptor in cell culture, suggesting that receptor binding may be a factor in drug-induced cytotoxicity.