Antihelicase action of CI-958, a new drug for prostate cancer.
CI-958, a new DNA-intercalating drug derived from a series of substituted 2H-[1] benzothiopyrano[4,3,2-cd]indazoles, is being tested in clinical trails because of its curative properties against murine solid tumor models and because it has demonstrated activity in a pilot phase II study of patients with hormone-refractory prostate cancer. However, the mechanism of anticancer action of CI-958 has not been established. Because CI-958 binds to DNA and DNA helicases are profoundly affected by DNA-binding drugs, we examined the effects of CI-958 on human DNA helicase action. DNA helicase activity was measured by strand dissociation of double-stranded (ds) DNA with a gel electrophoresis assay, and ATPase activities were determined on thin-layer chromatography by measurement of the conversion of ATP to ADP. For human helicase blockade, CI-958 is slightly more potent than doxorubicin (EC50 values 0.17 and 0.26 microM, respectively). We observed no difference in helicase-blockade EC50 values recorded for three helicase substrates containing A-T rich, G-C rich, and both types of oligonucleotide sequences. The effects of CI-958 helicase blockade and DNA-dependent ATPase activities were similar for the two reactions. The kinetics of the blockade by CI-958 of the human DNA helicase indicates that it involves a reversible ternary complex of helicase-drug-dsDNA. CI-958 produces potent blockade of human DNA helicases with no apparent strong DNA sequence-binding preference. Similar potency against helicase strand dissociation and DNA-dependent ATPase suggests that the mechanism against these reactions is the same. The blockade of DNA helicases by CI-958 may be central in its mechanism of action as an anticancer drug.
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University of Maryland Cancer Center, University of Maryland School of Medicine, Baltimore 21201, USA.
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D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001483:Base Sequence; D004265:DNA Helicases / Q000037:antagonists & inhibitors*; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D007191:Indazoles / Q000494:pharmacology* / Q000627:therapeutic use; D007700:Kinetics; D008297:Male; D011471:Prostatic Neoplasms / Q000188:drug therapy*
D000970:Antineoplastic Agents; D017931:DNA Primers; D004791:Enzyme Inhibitors; D007191:Indazoles; C054558:ledoxantrone; D004265:DNA Helicases