discodermolide and Adenocarcinoma

A Taxol-resistant cell line, K20T, which does not express P-glycoprotein, was selected with Taxol from human MDA-MB-231 breast adenocarcinoma cells and maintained in the presence of 20nM Taxol. K20T cells were approximately 18-fold resistant to Taxol, displayed cross-resistance to Taxotere and the epothilones, but little cross-resistance to discodermolide. Sequence analysis of the class I beta-tubulin indicated that it harbored an A593G mutation resulting in a change from glutamate to glycine at amino acid 198, which is near the intradimer interface within the alpha/beta-tubulin heterodimer. An HA-tagged wild-type class I beta-tubulin expression vector was transfected into the K20T cells. Immunofluorescence studies demonstrated that this exogenous tubulin was incorporated into cellular microtubules and Western blot analysis indicated that the K20T transfectants predominantly expressed the exogenous wild-type class I beta-tubulin. The transfected cells were only approximately 5-fold resistant to Taxol. Our results, plus the knowledge that Glu198 is the target for other anti-tubulin agents, suggest that glutamate198 in beta-tubulin is a critical determinant for microtubule stability and Taxol resistance.

Topics: Adenocarcinoma; Alkanes; Antineoplastic Agents, Phytogenic; Breast Neoplasms; Carbamates; Cell Line, Tumor; Cell Survival; Dimerization; Docetaxel; Drug Resistance, Neoplasm; Epothilones; Fluorescent Antibody Technique, Indirect; Glutamic Acid; Glycine; Humans; Lactones; Models, Molecular; Mutation, Missense; Paclitaxel; Protein Structure, Quaternary; Pyrones; Taxoids; Transfection; Tubulin; Tubulin Modulators

Discodermolide (1) and five new discodermolide analogues trivially named 2-epi-discodermolide (2), 2-des-methyldiscodermolide (3), 5-hydroxymethyldiscodermolate (4), 19-des-aminocarbonyldiscodermolide (5), and 9(13)-cyclodiscodermolide (6) have been isolated from marine sponges belonging to the genus Discodermia collected from the Caribbean Sea. The isolation, structure elucidation, and biological activities of 2-6 are described. The natural analogues, which were isolated in trace amounts, exhibited significant variation of cytotoxicity against the cultured murine P-388 leukemia and A-549 human adenocarcinoma cells and suggested the importance of the C(7) through C(17) moiety for potency against cultured tumor cell lines.

Topics: Adenocarcinoma; Animals; Caribbean Region; Drug Screening Assays, Antitumor; Humans; Lactones; Leukemia P388; Mice; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Porifera; Structure-Activity Relationship; Tumor Cells, Cultured

A series of 12 semisynthetic discodermolide analogues, 2-13, have been prepared using natural (+)-discodermolide (1) and evaluated for in vitro cytotoxicity against cultured murine P-388 leukemia and A-549 human adenocarcinoma cells. These semisynthetic analogues showed a significant variation of cytotoxicity and confirmed the importance of the C-7 through C-19 molecular fragment for potency. Specifically, these analogues suggested the importance of the C-11 and C-17 hydroxyl groups and the C-13 double bond for the potency of discodermolide. The preparation, structure elucidation, and biological activity of these new analogues are described.

Topics: Adenocarcinoma; Alkanes; Animals; Antineoplastic Agents; Carbamates; Drug Screening Assays, Antitumor; Humans; Lactones; Leukemia P388; Mice; Microtubules; Molecular Structure; Nuclear Magnetic Resonance, Biomolecular; Porifera; Pyrones; Structure-Activity Relationship; Tumor Cells, Cultured