Cytostatic and cytotoxic properties of the marine product bistratene A and analysis of the role of protein kinase C in its mode of action.
Bistratene A is a polyether which was isolated from the marine ascidian Lissoclinum bistratum Sluiter. The hypothesis has been tested that the cytostatic effect of bistratene A is mediated by modulation of protein kinase C (PKC). Human-derived A549 lung and MCF-7 breast adenocarcinoma cells are extremely sensitive to growth inhibition induced by activators of PKC. Therefore, the effect of bistratene A on these cell lines was compared with that of the known PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA). The ability of bistratene A to modulate PKC activity in cellular cytosol was assessed to determine the involvement of PKC in the induction of cytostasis. Bistratene A inhibited the growth of both cell lines and initial seeding density determined its cytostatic potency. IC50 values were between 1.0 and 2.9 nM. Bistratene A also had a profound effect on the colony forming ability of A549 cells, preventing clonal growth at 5 nM. Using the incorporation of [3H]thymidine into cells to assess DNA synthetic activity and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay to define cytotoxicity, the compound was found to have both cytostatic and cytotoxic properties. Bistratene A decomposed by 50% after only 2.8 hr in cell culture medium. TPA induced rapid motility and the formation of a network of branched colonies in both cell lines grown on Matrigel, whereas bistratene A did not cause the same effect. Cell cytosol was analysed for phorbol ester binding sites after treatment with bistratene A or TPA. Incubation with TPA (10 nM) caused a reduction in binding sites to 57% of binding in control cells after 30 min and to 35% after 24 hr. Bistratene A did not cause a significant change in binding sites. Assays of PKC activity in cellular cytosol revealed that bistratene A was unable to activate or inhibit the enzyme at concentrations of up to 10 microM. The results suggest that bistratene A is an exquisitely potent cytostatic agent in the two cell lines studied, but modulation of PKC is not involved in the mode of action by which it elicits this effect.
Stanwell
C
C
Department of Pharmaceutical Sciences, Aston University, Birmingham, U.K.
Gescher
A
A
Watters
D
D
D000081:Acetamides; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D004988:Ethers, Cyclic / Q000633:toxicity*; D006801:Humans; D008387:Marine Toxins / Q000633:toxicity*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011714:Pyrans; D015398:Signal Transduction / Q000187:drug effects; D013141:Spiro Compounds; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects
D000081:Acetamides; D004988:Ethers, Cyclic; D008387:Marine Toxins; D011714:Pyrans; D013141:Spiro Compounds; C059975:bistratene A; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate