cactinomycin and ellipticine

DNA helicases unwind the duplex DNA in an ATP dependent manner and thus play an essential role in DNA replication, repair, recombination and transcription. Any DNA-interacting ligand which will modulate DNA helicase activity may interrupt practically all kinds of DNA transactions. There are no studies on the effect of various cytotoxic DNA-interacting ligands on organelle helicases. We have determined the effect of camptothecin, VP-16 (etoposide), ellipticine, genistein, novobiocin, m-AMSA, actinomycin C1, ethidium bromide, daunorubicin and nogalamycin on unwinding and ATPase activities of purified chloroplast DNA helicase from pea (Pisum sativum). Our study has shown that DNA-intercalating ligands actinomycin C1, ethidium bromide, daunorubicin and nogalamycin were inhibiting the DNA unwinding activity with an apparent Ki of 2.9 microM, 3.0 microM, 1.4 microM and 1.0 microM, respectively. These four inhibitors also inhibited the ATPase activity of pea chloroplast DNA helicase. These results indicate that the intercalation of the inhibitors into DNA generates a complex that impedes the translocation of chloroplast DNA helicase, resulting in both inhibition of unwinding activity and ATP hydrolysis. This study would be useful for understanding the mechanism of organelle DNA helicase unwinding and the mechanism by which these DNA-interacting ligands inhibit cellular function.

Topics: Adenosine Triphosphatases; Adenosine Triphosphate; Amsacrine; Camptothecin; Chloroplasts; Dactinomycin; Daunorubicin; DNA Helicases; Ellipticines; Ethidium; Etoposide; Genistein; Hydrolysis; Intercalating Agents; Ligands; Nogalamycin; Novobiocin; Pisum sativum

DNA helicases catalyze the unwinding of duplex DNA and thus play important roles in the processing of DNA, little is known about the effects of various cytotoxic or antitumor chemotherapeutic agents on purified human DNA helicases. We have determined the effect of actinomycin C1, VP-16, camptothecin, ethidium bromide, ellipticine, nogalamycin, novobiocin, genistein, m-AMSA, aphidicolin and daunorubicin on the enzymatic activities of purified human DNA helicase II which was identified as Ku autoantigen. Ku contains DNA helicase, ATPase and DNA end binding activities. Our data have shown that out of several chemotherapeutic agents tested ethidium bromide, actinomycin C1, daunorubicin and nogalamycin were inhibitors of DNA unwinding activity of human DNA helicase II with ID50 values of 8.44 microM, 11.68 microM, 6.23 microM and 0.42 microM respectively. These inhibitors also inhibited the ATPase activity but not the DNA binding activity of this helicase. This inhibition could be due to binding of these drugs to DNA, thereby impeding the movement of the helicase for unwinding action which may be their most important pharmacological function against cancer cells.

Topics: Adenosine Triphosphatases; Amsacrine; Antineoplastic Agents; Aphidicolin; Camptothecin; Dactinomycin; Daunorubicin; DNA; DNA Helicases; Ellipticines; Enzyme Inhibitors; Ethidium; Etoposide; Genistein; Humans; Isoflavones; Nogalamycin; Novobiocin; Topoisomerase I Inhibitors