Sequence selectivity, cross-linking efficiency and cytotoxicity of DNA-targeted 4-anilinoquinoline aniline mustards

We have investigated the sequence selectivity, DNA binding site characteris tics, interstrand cross-linking ability and cytotoxicity of four 4-anilinoq uinoline aniline mustards related to the AT-selective minor groove-binding bisquaternary ammonium heterocycles. The compounds studied include two full mustards that differ in alkylating power, a half mustard and a quaternary anilinoquinolinium bismustard. We have also compared their cytotoxitity wit h their precursor diols and their toxicity and cross-linking ability with t he classical alkylating agents melphalan and chlorambucil. We find that the anilinoquinaline aniline mustards weakly and non-specifically alkylate gua nines in the major groove and that they bind strongly to AT-rich sequences in the minor groove, where they alkylate both adenines and guanines at the N3 position. The most preferred sites are classical minor groove binder AT- tracts to which all four ligands bind equally well, The remaining sites are AT-rich, but include GC base pairs, to which the ligands bind with prefere nces depending on their structure, The full mustards alkylate at the 3' end s of the binding site in an orientation that depends on the spatial disposi tion of the purines within the two strands. Generally speaking guanines are found to be much less reactive than adenines, The anilinoquinoline aniline mustards are interstrand cross-linking agents that are 60- to 100-fold mor e effective than melphalan, with the quaternary compound being the most eff icacious. However, the type of binding site at which the cross-links occur is not clear, since distamycin challenge fails to antagonize them fully. Th e full mustards are 20- to 50-fold more cytotoxic than their diol precursor s, are more cytotoxic than the half mustard and are 20- to 30-fold more act ive than melphalan and chlorambucil, The quaternary ligand is the most pote nt. Given the evidence to hand, it appears that antitumour activity correla tes with capacity to cause interstrand cross-links at classical or near-cla ssical AT-minor groove binder sites, rather than with ability to discrimina te between the subsets of potential anilinoquinoline aniline mustard bindin g sites.