title: Sensitization of human cervical carcinoma cells to cis-diamminedichloroplatinum(II) by bryostatin 1.
abstract: Bryostatins are an important class of protein kinase C (PKC) activators. We have investigated the effect of bryostatin 1 on the antiproliferative activity of cis-diamminedichloroplatinum(II) (CP). A 24-h pretreatment of HeLa cells with 1 nM bryostatin 1 increased cellular sensitivity to CP by 4-fold. The effect of bryostatin 1 on the IC50 of CP (concentration of drug required to inhibit cell proliferation by 50%) was concentration-dependent and biphasic; the maximum effect of bryostatin 1 was seen with 1 nM, but higher concentrations of bryostatin 1 (greater than or equal to 10 nM) produced less CP sensitization. Although bryostatin 1 and phorbol esters caused an equivalent stimulation of HeLa cell PKC in cell-free systems, bryostatin 1 was less effective than phorbol esters in sensitizing cells to CP. Additionally, higher concentrations of bryostatin 1 (greater than or equal to 10 nM) antagonized CP sensitization by phorbol esters. Bryostatin 1 was even more potent than 12-O-tetradecanoylphorbol-13-acetate in inducing PKC down-regulation, and the maximum down-regulation was achieved with 10 nM bryostatin 1. Bryostatin 1 also increased cellular sensitivity to a CP analogue, cis-dichloro(ethylenediamine)platinum(II). A 24-h pretreatment with 1 nM bryostatin 1 increased cellular cis-[3H]DEP by 60%. The concentration- and time-dependent enhancement in CP sensitivity by bryostatin 1 was related to the increase in cis-[3H]DEP level. Thus, cellular accumulation of CP may be regulated by a PKC-dependent phosphorylation event.
authors.affiliation: Department of Pharmacology, University of Pittsburgh School of Medicine, Pennsylvania 15261.
authors.forename: A
authors.initials: A
authors.lastname: Basu
authors.forename: J S
authors.initials: JS
authors.lastname: Lazo
mesh_terms: D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D054713:Bryostatins; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002945:Cisplatin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation; D006367:HeLa Cells; D006258:Head and Neck Neoplasms; D006801:Humans; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D007783:Lactones / Q000494:pharmacology*; D018942:Macrolides; D009944:Organoplatinum Compounds / Q000378:metabolism; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000302:isolation & purification / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000970:Antineoplastic Agents; D054713:Bryostatins; D007527:Isoenzymes; D007783:Lactones; D018942:Macrolides; D009944:Organoplatinum Compounds; C002892:platinum ethylenediamine dichloride; D015240:Phorbol 12,13-Dibutyrate; C046785:bryostatin 1; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002945:Cisplatin