BIOCHEMICAL AND CELLULAR EFFECTS OF DIDEMNINS-A AND DIDEMNINS-B

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 44  (5) , 1796-1801
Abstract
Didemins 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 [mouse] B16 melanoma and P388 leukemia in vivo, and B was also .apprx. 20 times more cytotoxic than was didemnin A in vitro. Didemnin B was studied in greater detail for its biochemical and cellular effects. Didemnin B inhibited the in vitro growth of B16 > [mouse leukemia] L1210 > [Chinese hamster lung] N-79 cells = human foreskin fibroblast = [rat brain tumor] 9L > Chinese hamster ovary cells. Didemnin B was more lethal to exponentially growing B16 cells (50% lethal dose for a 2-h exosure, 17.5 ng/ml) than to plateau-phase cells (50% lethal dose for a 2-h exposure, 100 ng/ml). After a 24-h 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. Since cells in all phases were killed, didemnin B cannot be considered a phase-specific agent. Didemnin B inhibited the synthesis of protein than that of DNA, with much less inhibition of RNA synthesis. Cell progression studies showed that high doses (300 ng/ml for 2 h or 100 ng/ml for 24 h) of didemin B froze the cells in their respective phases with complete inhibition of cell progression or growth. At low doses (10 ng/ml for 2 h or 3 ng/ml for 24 h), 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.