title: Cell-cycle specific cytotoxicity mediated by rearranged ent-kaurene diterpenoids isolated from Parinari curatellifolia.
abstract: Two structurally novel cytotoxic ent-kaurene diterpenoids, 13-methoxy-15-oxozoapatlin and 13-hydroxy-15-oxozoapatlin, were isolated from the root bark of Parinari curatellifolia, together with the known compound, 15-oxozoapatlin, on the basis of bioactivity-guided chromatographic fractionation and found to demonstrate broad-spectrum cytotoxic activity against a panel of cultured human cancer cell lines. The structures of these compounds were determined by analysis of their spectroscopic data. The presence of an alpha, beta-unsaturated carbonyl group in 13-methoxy-15-oxozoapatlin suggested that the cytotoxic potential of this compound could be mediated through reaction with cellular nucleophiles by means of a Michael-type addition. The compound 13-methoxy-15-oxozoapatlin reacted with the nucleophiles L-cysteine and beta-mercaptoethanol. The adduct with beta-mercaptoethanol was isolated, structurally characterized and found to be approximately 5-fold less cytotoxic than 13-methoxy-15-oxozoapatlin itself. The compound 13-methoxy-15-oxozoapatlin did not interact with DNA nor guanosine, and it was not mutagenic for Salmonella typhimurium strain TM677. The effects of 13-methoxy-15-oxozoapatlin on the growth of human cancer cells were analyzed utilizing cultured ZR-75-1 breast cancer cells. Biosynthesis of DNA, RNA and protein was reduced in treated cells, and accumulation at the G2/M phase of the cell cycle was observed. The compound 13-methoxy-15-oxozoapatlin did not mediate antimitotic activity with dibutyryl cAMP-treated cultured astrocytoma cells, suggesting that the cell cycle effect is G2 specific. No antitumor activity was observed when athymic mice carrying KB cells were treated with 13-methoxy-15-oxozoapatlin. These data indicate that the cytotoxic activity of 13-methoxy-15-oxozoapatlin is mediated in part by covalent reaction with a cellular component (such as sulfhydryl-containing protein) by means of a Michael-type addition, and this results in the blockage of cell-cycle progression.
authors.affiliation: Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago 60612, USA.
authors.forename: I S
authors.initials: IS
authors.lastname: Lee
authors.forename: L A
authors.initials: LA
authors.lastname: Shamon
authors.forename: H B
authors.initials: HB
authors.lastname: Chai
authors.forename: T E
authors.initials: TE
authors.lastname: Chagwedera
authors.forename: J M
authors.initials: JM
authors.lastname: Besterman
authors.forename: N R
authors.initials: NR
authors.lastname: Farnsworth
authors.forename: G A
authors.initials: GA
authors.lastname: Cordell
authors.forename: J M
authors.initials: JM
authors.lastname: Pezzuto
authors.forename: A D
authors.initials: AD
authors.lastname: Kinghorn
mesh_terms: D000349:Africa; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003545:Cysteine / Q000378:metabolism; D004224:Diterpenes / Q000302:isolation & purification / Q000494:pharmacology* / Q000633:toxicity; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008519:Medicine, Traditional; D008623:Mercaptoethanol / Q000378:metabolism; D015394:Molecular Structure; D009369:Neoplasms / Q000378:metabolism; D010944:Plants / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: C099329:13-hydroxy-15-oxozoapatlin; C099330:13-methoxy-15-oxozoapatlin; D004224:Diterpenes; D008623:Mercaptoethanol; D003545:Cysteine