Molecular Pharmacology of the Anthracycline Drug 9,10-Anthracenedicarbox-aldehyde Bis[(4,5-dihydro-1 H-imidazol-2-yl)hydrazone] Dihydrochloride (CI 216,942)¹

9,10-Anthracenedicarboxyaldehyde bis[(4,5-dihydro-1H-imidazol-2yl)hydrazone] dihydrochloride (CI 216,942) is a new anthracene bishydrazone derivative which has shown antitumor activity in Phase I trials against both hematological cancers and solid tumors. The effects of CI 216,942 on L1210 mouse leukemia cells were studied with the nucleoid sedimentation and alkaline elution assays. Evidence for CI 216,942 intercalation into cellular DNA was obtained in exponentially growing cells by comparing the L1210 nucleoid sedimentation behavior in neutral sucrose gradients of ethidium bromide with nucleoids from CI 216,942-treated cells. A 1-hr treatment of exponentially growing L1210 cells with CI 216,942 induced both protein-associated DNA single-strand breaks and DNA-protein cross-links as detected by the alkaline elution assay. The DNA strand break and DNA-protein cross-link frequencies were found to be within a factor of 2 of each other over a range of CI 216,942 concentrations. The dose response for the induction of DNA damage showed a linear increase up to 10 µg/ml, but this was followed by a decrease in damage at dose levels greater than 10 µg/ml. The biphasic dose response could not be explained by changes in the cellular uptake of CI 216,942. The kinetics of CI 216,942 induction of DNA damage after a 1-hr treatment showed that at the dose which gave maximum damage the degree of damage (10 µg/ml) decreased with further incubation, but at a higher dose (20 µg/ml) DNA damage increased with postincubation at 37°. The cytotoxicity produced by CI 216,942 at a given frequency of protein-associated strand breaks was low. CI 216,942 thus appeared to belong to a low-toxicity group of DNA intercalators.