SYNTHESIS, DNA-BINDING AND CYTOTOXIC PROPERTIES OF A BIS(NETROPSIN)-ANTHRACENEDIONE CONJUGATE

A combilexin molecule containing two netropsin moieties attached to th e aminoalkyl side chains of mitoxantrone has been synthesized and eval uated for cytotoxic activity towards murine L1210 leukaemia and human MCF7 carcinoma cells in vitro. It is marginally less cytotoxic than mi toxantrone but much more growth-inhibitory than netropsin. Various spe ctroscopic and biochemical techniques have been employed to characteri ze the interaction of the drug, NetMitox, with DNA. Circular dichroism (CD) and electric linear dichroism (ELD) data indicate that binding o f the netropsin moiety or moieties within the minor groove of the doub le helix impedes the intercalation of the adjacent anthracenedione rin g. ELD and footprinting experiments reveal a certain amount of mutual interference between the two functionalities of the conjugate molecule but the selective recognition of AT-rich sequences by netropsin large ly dominates the recognition pattern. The lack of interaction with GC- rich sequences is attributable to steric hindrance occasioned by the 2 -amino group of guanine which impedes access of the netropsin moiety i nto the minor groove, as is evident by the good binding of the hybrid to poly(dI-dC).poly(dI-dC) as well as by the redistribution of its bin ding sites on DNA molecules substituted with inosine and/or 2,6-diamin opurine. The difficulty of the anthracenedione system in intercalating : correlates with the lack of effect of the drug on cleavable complex formation with topoisomerase II as well as its diminished cytotoxicity compared to mitoxantrone. However, the finding that the drug retains significant toxicity towards leukaemia cells may suggest that DNA is p erhaps not the unique molecular target.