In vitro DNA strand scission and inhibition of nucleic acid synthesis in L1210 leukemia cells by a new class of DNA complexers, the anthra[1,9-cd]pyrazol-6(2H)-ones (anthrapyrazoles)

Abstract

CI-937 and CI-942 belong to a new class of DNA complexers, the anthra[1,9-cd]pyrazol-6(2H)-ones (anthrapyrazoles), and are being further developed as antitumor drugs based on their curative properties against murine solid tumour models. The biochemical effects of these agents were studied in L1210 leukemia in relation to other clinically used intercalators. After a 1-hr exposure, CI-937 and CI-942 reduced the cloning efficiency of L1210 cells by 50% at 3.0 X 10(-8) and 1.5 X 10(-7) M respectively. Based on an ethidium displacement assay, these drugs bound strongly to DNA, reducing the fluorescence of an ethidium-DNA complex by 50% at concentrations of 23 and 33 nM for CI-937 and CI-942 respectively. This was comparable to mitoxantrone at 15 nM, but much more potent than Amsacrine which required over 1.3 microM. A distinct property of the anthrapyrazoles was a much more potent inhibitory effect on whole cell DNA synthesis than on RNA synthesis. After L1210 cells were exposed to drug for 2 hr the concentration needed to inhibit DNA synthesis by 50% was 0.33 and 0.57 microM for CI-937 and CI-942, respectively, whereas 2.0 and 11.3 microM were required to inhibit RNA synthesis by the same extent. This was in contrast to Adriamycin and mitoxantrone which inhibited both activities equally at similar concentrations. It was apparent that the inhibition of these processes was not due to substrate depletion since intracellular ribonucleoside and deoxyribonucleoside triphosphates either remained constant or were elevated after a 2-hr exposure to 1 or 10 microM drug. A similar discriminatory effect was observed on DNA and RNA polymerase in permeabilized cells, and the inhibition of nucleic acid synthesis in this system could be reversed by exogenously added DNA. Since the high incidence of cardiotoxicity associated with the administration of anthracyclines has been related to the formation of reactive oxygen species, the ability of the anthrapyrazoles to augment superoxide dismutase sensitive oxygen consumption was observed in a rat liver microsomal system. CI-937 and CI-942 induced 5- and 10-fold less oxygen consumption than Adriamycin, producing rates of 12.4, 24.2 and 138.9 nmoles/min/mg microsomal protein, respectively, at a drug concentration of 0.5 mM.(ABSTRACT TRUNCATED AT 400 WORDS)