title: Biochemical and cellular effects of didemnins A and B.
abstract: Didemnins are a new class of cyclic depsipeptides in which didemnin A is the major component, didemnin B the minor component, and a trace of didemnin C is present. Didemnin B was more potent than was didemnin A against B16 melanoma and P388 leukemia in vivo, and B was also approximately 20 times more cytotoxic than was didemnin A in vitro. Therefore, didemnin B was studied in greater detail for its biochemical and cellular effects. Didemnin B inhibited the in vitro growth of B16 greater than L1210 greater than V-79 cells = human foreskin fibroblast = 9L greater than Chinese hamster ovary cells. Didemnin B was more lethal to exponentially growing B16 cells (50% lethal dose for a 2-hr exposure, 17.5 ng/ml) than to plateau-phase cells (50% lethal dose for a 2-hr exposure, 100 ng/ml). After a 24-hr exposure, the 50% lethal dose for exponential- and plateau-phase B16 cells was 8.8 and 59.6 ng/ml, respectively. Chinese hamster ovary cells were not killed even at 25,000 ng/ml. Mitotic cells were the least sensitive to didemnin B, and cells became more sensitive as they progressed into G1 and S phase. However, since cells in all phases were killed, didemnin B cannot be considered a phase-specific agent. Didemnin B inhibited the synthesis of protein more than that of DNA, with much less inhibition of RNA synthesis. Cell progression studies showed that high doses (300 ng/ml for 2 hr or 100 ng/ml for 24 hr) of didemnin B "froze" the cells in their respective phases with complete inhibition of cell progression or growth. At low doses (10 ng/ml for 2 hr or 3 ng/ml for 24 hr), the cells were blocked at the G1-S border thereby increasing the percentage of G1 cells and decreasing the percentage of S-phase cells. Cells continued to progress from S phase to G2 + M and from G2 + M to G1. The cytotoxicity to different cell lines and inhibition of macromolecule synthesis by didemnin A is also reported.
mesh_terms: D000818:Animals; D001932:Brain Neoplasms / Q000503:physiopathology*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D047630:Depsipeptides; D005260:Female; D007700:Kinetics; D007939:Leukemia L1210 / Q000503:physiopathology*; D008168:Lung; D008545:Melanoma / Q000503:physiopathology*; D051379:Mice; D010053:Ovary; D010456:Peptides, Cyclic / Q000633:toxicity; D051381:Rats; D013997:Time Factors
chemical_list: D047630:Depsipeptides; D010456:Peptides, Cyclic; C030051:didemnins