Role of DNA minor groove alkylation and DNA cross-linking in the cytotoxicity of polybenzamide mustards

Interstrand DNA cross-links have been considered essential to the activity of current clinical DNA-alkylating antitumour drugs, which generally alkyla te in the major groove, However, the relationship between cross-linking add ucts located in the minor groove of DNA with cytotoxicity and antitumour ac tivity has not been extensively investigated, Previous studies have shown t hat cross-linking ability is not correlated with cytotoxicity in a novel se ries of polybenzamide-linked nitrogen mustard compounds which alkylate DNA at adenines in the minor groove, In the present study the nature of these c ross-linking adducts was explored for a related pair of compounds which are both highly effective cross-linkers but which differ in antitumour potenti al. Both of these drugs effectively interact with adenines in the minor gro ove, although their sequence specificity differs. However, the cross-linkin g event was not inhibited by pre-treatment with Hoechst 33258, although thi s pre-treatment effectively prevented adenine alkylation, The primary cross -links detected may thus represent guanine N7 alkylations in the major groo ve. Whether minor groove cross-linking adducts can be formed is uncertain, since the effect of background guanine N7 alkylation may complicate analysi s. The cytotoxicity of the polybenzamides may therefore be related to other factors such as their interaction with cellular repair systems.