Dolastatin 10, a
cytostatic peptide containing several unique
amino acid subunits, was isolated from the marine shell-less mollusk Dolabella auricularia (Pettit GR, Kamano Y, Herald CL, Tuinman AA, Boettner FE, Kizu H, Schmidt JM, Baczynskyj L, Tomer KB and Bontems RJ, J Am Chem Soc 109: 6883-6885, 1987). Since our preliminary studies demonstrated that
dolastatin 10 inhibited
tubulin polymerization and the binding of radiolabeled
vinblastine to
tubulin, an initial characterization of the properties of
dolastatin 10 included a comparison to other
antimitotic drugs interfering with vinca
alkaloid binding to
tubulin (
vinblastine,
maytansine,
rhizoxin, and
phomopsin A).
Dolastatin 10 inhibited the growth of L1210 murine
leukemia cells in culture, with a concordant rise in the mitotic index, and its IC50 value for cell growth was 0.5 nM. Comparable values for the other drugs were 0.5 nM for
maytansine, 1 nM for
rhizoxin, 20 nM for
vinblastine, and 7 microM for
phomopsin A. IC50 values were also obtained for the polymerization of purified
tubulin in
glutamate: 1.2 microM for
dolastatin 10, 1.4 microM for
phomopsin A, 1.5 microM for
vinblastine, 3.5 microM for
maytansine, and 6.8 microM for
rhizoxin.
Dolastatin 10 and
vinblastine were comparable in their effects on microtubule assembly dependent on
microtubule-associated proteins. Preliminary studies indicated that
dolastatin 10, like
vinblastine, causes formation of a cold-stable
tubulin aggregate at higher
drug concentrations. We confirmed that
rhizoxin,
phomopsin A, and
maytansine also inhibit the binding of radiolabeled
vinblastine and
vincristine to
tubulin.
Dolastatin 10 and
phomopsin A were the strongest inhibitors of these reactions, and
rhizoxin the weakest.
Dolastatin 10,
phomopsin A,
maytansine,
vinblastine, and
rhizoxin all inhibited
tubulin-dependent
GTP hydrolysis. The greatest inhibition of hydrolysis was observed with
dolastatin 10 and
phomopsin A, and the least inhibition with
rhizoxin.