In Vitro and in Vivo Stability of Anthramycin-DNA Conjugate and Its Potential Application as an Anthramycin Prodrug

Anthramycin-DNA adducts, produced in vitro by reaction of anthramycin with calf thymus DNA, have been shown to be stable only as long as the secondary structure of DNA is maintained. Denaturation either by heat or enzymatic degradation of the DNA adduct, with DNase I and snake venom phosphodiesterase, leads to the release of significant amounts of the bound drug as unchanged anthramycin. These observations led us to suspect that the DNA adduct might be a suitable prodrug system for anthramycin, which might be more efficacious and less toxic than the administration of the free drug. In order to test this hypothesis, the ability of the adduct versus free drug to inhibit DNA synthesis and induce unscheduled DNA synthesis in a human cell line was evaluated. The results demonstrated that the anthramycin-DNA adduct was less potent than the free drug in these systems in both respects. The anthramycin and anthramycin-DNA conjugate were compared in mice for lethality, tissue levels, alteration of hexobarbital sleeping times, and efficacy against a mouse ascites tumor model. These results showed that the DNA adduct was three times more lethal and produced similar increases in sleeping times at equitoxic doses. The increase in lethality of the anthramycin-DNA adduct could be explained by elevated and more prolonged blood and tissue levels following administration of the DNA conjugate as compared to free anthramycin. When tested for efficacy against a mouse ascites tumor line, the anthramycin-DNA adduct was found to be less efficacious than the free drug.