title: Semisynthesis, cytotoxicity, antiviral activity, and drug interaction liability of 7-O-methylated analogues of flavonolignans from milk thistle.
abstract: Silymarin, an extract of the seeds of milk thistle (Silybum marianum), is used as an herbal remedy, particularly for hepatoprotection. The main chemical constituents in silymarin are seven flavonolignans. Recent studies explored the non-selective methylation of one flavonolignan, silybin B, and then tested those analogues for cytotoxicity and inhibition of both cytochrome P450 (CYP) 2C9 activity in human liver microsomes and hepatitis C virus infection in a human hepatoma (Huh7.5.1) cell line. In general, enhanced bioactivity was observed with the analogues. To further probe the biological consequences of methylation of the seven major flavonolignans, a series of 7-O-methylflavonolignans were generated. Optimization of the reaction conditions permitted selective methylation at the phenol in the 7-position in the presence of each metabolite's 4-5 other phenolic and/or alcoholic positions without the use of protecting groups. These 7-O-methylated analogues, in parallel with the corresponding parent compounds, were evaluated for cytotoxicity against Huh7.5.1 cells; in all cases the monomethylated analogues were more cytotoxic than the parent compounds. Moreover, parent compounds that were relatively non-toxic and inactive or weak inhibitors of hepatitis C virus infection had enhanced cytotoxicity and anti-HCV activity upon 7-O-methylation. Also, the compounds were tested for inhibition of major drug metabolizing enzymes (CYP2C9, CYP3A4/5, UDP-glucuronsyltransferases) in pooled human liver or intestinal microsomes. Methylation of flavonolignans differentially modified inhibitory potency, with compounds demonstrating both increased and decreased potency depending upon the compound tested and the enzyme system investigated. In total, these data indicated that monomethylation modulates the cytotoxic, antiviral, and drug interaction potential of silymarin flavonolignans.
authors.affiliation: Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, NC 27402, USA.
authors.forename: Hanan S
authors.initials: HS
authors.lastname: Althagafy
authors.forename: Tyler N
authors.initials: TN
authors.lastname: Graf
authors.forename: Arlene A
authors.initials: AA
authors.lastname: Sy-Cordero
authors.forename: Brandon T
authors.initials: BT
authors.lastname: Gufford
authors.forename: Mary F
authors.initials: MF
authors.lastname: Paine
authors.forename: Jessica
authors.initials: J
authors.lastname: Wagoner
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Polyak
authors.forename: Mitchell P
authors.initials: MP
authors.lastname: Croatt
authors.forename: Nicholas H
authors.initials: NH
authors.lastname: Oberlies
mesh_terms: D000998:Antiviral Agents / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004347:Drug Interactions; D014453:Glucuronosyltransferase / Q000378:metabolism; D016174:Hepacivirus / Q000187:drug effects*; D006526:Hepatitis C / Q000188:drug therapy; D006801:Humans; D008745:Methylation; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D020944:Silybum marianum / Q000737:chemistry*; D012838:Silymarin / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D000998:Antiviral Agents; D012838:Silymarin; D003577:Cytochrome P-450 Enzyme System; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C473667:cytochrome P-450 CYP3A45; D014453:Glucuronosyltransferase