title: Luteolin, an emerging anti-cancer flavonoid, poisons eukaryotic DNA topoisomerase I.
abstract: Luteolin, a naturally occurring flavonoid, is abundant in our daily dietary intake. It exhibits a wide spectrum of pharmacological properties, but little is known about its biochemical targets other than the fact that it induces topoisomerase II-mediated apoptosis. In the present study, we show that luteolin completely inhibits the catalytic activity of eukaryotic DNA topoisomerase I at a concentration of 40 microM, with an IC50 of 5 microM. Preincubation of enzyme with luteolin before adding a DNA substrate increases the inhibition of the catalytic activity (IC50=0.66 microM). Treatment of DNA with luteolin before addition of topoisomerase I reduces this inhibitory effect. Subsequent fluorescence tests show that luteolin not only interacts directly with the enzyme but also with the substrate DNA, and intercalates at a very high concentration (>250 microM) without binding to the minor groove. Direct interaction between luteolin and DNA does not affect the assembly of the enzyme-DNA complex, as evident from the electrophoretic mobility-shift assays. Here we show that the inhibition of topoisomerase I by luteolin is due to the stabilization of topoisomerase-I DNA-cleavable complexes. Hence, luteolin is similar to camptothecin, a class I inhibitor, with respect to its ability to form the topoisomerase I-mediated 'cleavable complex'. But, unlike camptothecin, luteolin interacts with both free enzyme and substrate DNA. The inhibitory effect of luteolin is translated into concanavalin A-stimulated mouse splenocytes, with the compound inducing SDS-K+-precipitable DNA-topoisomerase complexes. This is the first report on luteolin as an inhibitor of the catalytic activity of topoisomerase I, and our results further support its therapeutic potential as a lead anti-cancer compound that poisons topoisomerases.
authors.affiliation: Molecular Parasitology Laboratory, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Kolkata 700 032, India.
authors.forename: Arnab Roy
authors.initials: AR
authors.lastname: Chowdhury
authors.forename: Shalini
authors.initials: S
authors.lastname: Sharma
authors.forename: Suparna
authors.initials: S
authors.lastname: Mandal
authors.forename: Anindya
authors.initials: A
authors.lastname: Goswami
authors.forename: Sibabrata
authors.initials: S
authors.lastname: Mukhopadhyay
authors.forename: Hemanta K
authors.initials: HK
authors.lastname: Majumder
mesh_terms: D000677:Amsacrine / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000302:isolation & purification / Q000494:pharmacology*; D001483:Base Sequence; D002384:Catalysis; D002467:Cell Nucleus / Q000201:enzymology; D004278:DNA, Superhelical / Q000737:chemistry* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000302:isolation & purification / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D047311:Luteolin; D009691:Nucleic Acid Denaturation; D009838:Oligodeoxyribonucleotides; D053978:Pentacyclic Triterpenes; D018515:Plant Leaves / Q000737:chemistry; D011794:Quercetin / Q000494:pharmacology; D051381:Rats; D013050:Spectrometry, Fluorescence; D059004:Topoisomerase I Inhibitors; D014315:Triterpenes / Q000494:pharmacology; D000094062:Betulinic Acid
chemical_list: D000970:Antineoplastic Agents; D004278:DNA, Superhelical; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009838:Oligodeoxyribonucleotides; D053978:Pentacyclic Triterpenes; D059004:Topoisomerase I Inhibitors; D014315:Triterpenes; D000677:Amsacrine; D005047:Etoposide; D011794:Quercetin; D047311:Luteolin; D000094062:Betulinic Acid