Mode of cell death induced in Chinese hamster cells by sequence-selective DNA minor groove binding nitrogen mustards: comparison with untargeted mustards and with Hoechst 33342.

Abstract

The clinical antitumor efficacy of nitrogen mustards such as chlorambucil may relate to their ability to cause programmed cell death (apoptosis), probably through their DNA cross-linking properties. In contrast, bisbenzimidazoles such as Hoechst 33342 interact noncovalently with the minor groove of DNA, and appear to cause apoptosis in a fundamentally different way, which may involve the inhibition of topoisomerase (topo) I enzymes. A series of DNA minor groove binding nitrogen mustards with selective DNA affinity and in vivo antitumor activity in animal models was studied. Although two examples of such compounds proved to inhibit topo I enzymes in vitro, they were equally toxic towards topo I-proficient and- deficient strains of yeast, suggesting that topo I inhibition was not involved in cell killing. Flow cytometric analysis of Chinese hamster cells highlighted the differences in the propensity to cause apoptosis by chlorambucil compared with Hoechst 33342, revealing two distinct apoptotic populations in cells treated with the latter drug. Unexpectedly, the bisbenzimidazole mustards showed a novel peak of apoptotic activity, distinct from that shown by either parent drug. Exploring these different mechanisms of apoptosis may provide new directions for the development of antitumor drugs.