DIFFERENTIAL-EFFECTS OF ACTIVE ISOMERS, SEGMENTS, AND ANALOGS OF DOLASTATIN-10 ON LIGAND INTERACTIONS WITH TUBULIN - CORRELATION WITH CYTOTOXICITY

Dolastatin 10 is a potent antimitotic peptide isolated from the marine mollusk Dolabella auricularia. Four of its five residues are modified amino acids (in sequence, dolavaline, valine, dolaisoleuine, dolaproi ne, dolaphenine). Besides inhibiting tubulin polymerization, dolastati n 10 non-competitively inhibits vinca alkaloid binding to tubulin, inh ibits nucleotide exchange and formation of the beta(s) cross-link, and stabilizes the colchicine binding activity of tubulin. To examine the mechanism of action of dolastatin 10 we prepared six chiral isomers, one tri- and one tetrapeptide segment, and one pentapeptide analog of dolastatin 10, all of which differ little from dolastatin 10 as inhibi tors of tubulin polymerization. However, only two of the chiral isomer s were similar to dolastatin 10 in their cytotoxicity for L1210 murine leukemia cells and in their effects on vinblastine binding, nucleotid e exchange, beta(s) cross-link formation, and colchicine binding. Thes e were isomer 2, with reversal of configuration at position C(19a) in the dolaisoleuine moiety, and isomer 19, with reversal of configuratio n at position C(6) in the dolaphenine moiety. The pentapeptides with r educed cytotoxicity and reduced effects on tubulin interactions with o ther ligands were all modified in the dolaproine moiety at positions C (9) and/or C(10). The tripeptide and tetrapeptide segments which inhib ited polymerization but not ligand interactions were the amino termina l tripeptide (lacking dolaproine and dolaphenine) and the carboxyl ter minal tetrapeptide (lacking dolavaline). We speculate that strong inhi bition of other ligand interactions with tubulin requires stable pepti de binding to tubulin (i.e. slow dissociation), but that inhibition of polymerization requires only rapid binding to tubulin.