eleutherobin and discodermolide

Microtubule stabilization by chemotherapy is a powerful weapon in the war against cancer. Disruption of the mitotic spindle activates a number of signaling pathways, with consequences that may protect the cell or lead to its death via apoptosis. Taxol, the first microtubule stabilizing drug to be identified, has been utilized successfully in the treatment of solid tumors for two decades. Several features, however, make this drug less than ideal, and the search for next generation stabilizing drugs with increased efficacy has been intense and fruitful. Microtubule stabilizing agents (MSAs), including the taxanes, the epothilones, discodermolide, laulimalide, and eleutherobin, form an important and expanding family of chemotherapeutic agents. A strong understanding of their molecular signaling consequences is essential to their value, particularly in regard to their potential for combinatorial chemotherapy - the use of multiple agents to enhance the efficacy of cancer treatment. Here we present a critical review of research on the signaling mechanisms induced by MSAs, their relevance to apoptosis, and their potential for exploitation by combinatorial therapy.

Topics: Alkanes; Animals; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Carbamates; Cyclooxygenase 2; Diterpenes; Epothilones; Humans; Inhibitor of Apoptosis Proteins; Interleukin-1; Interleukin-8; Lactones; Macrolides; MAP Kinase Kinase 1; MAP Kinase Signaling System; Maturation-Promoting Factor; Microtubule-Associated Proteins; Microtubules; Neoplasm Proteins; Neoplasms; NF-kappa B; Phosphatidylinositol 3-Kinases; Proto-Oncogene Proteins c-akt; Pyrones; Signal Transduction; Survivin; Taxoids; Tumor Suppressor Protein p53

Topics: Alkaloids; Alkanes; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Carbamates; Diterpenes; Lactones; Macrolides; Materia Medica; Microtubules; Molecular Structure; Paclitaxel; Pyrones; Structure-Activity Relationship; Taxoids

The xanthophylls-lutein, zeaxanthin, and meso-zeaxanthin (L&Z)-are found in the central region of the primate retina, which is called the macula lutea (yellow spot). How they are anchored there and what their function is has been debated for over 50 years. Here, we present evidence that they may be bound to the paclitaxel (Taxol) binding site of the beta-tubulin subunit of microtubules and that a major function may be to modulate the dynamic instability of microtubules in the macula. Also, we compare nucleic acid and amino acid sequences of tubulins that are in human brain with those we have isolated from human-retina and monkey-macula cDNA libraries. In so doing, we suggest that in primates, class I beta-tubulin consists of at least two subtypes (beta(Ia) and beta(Ib)). Alignment analysis of the sequences of the genes for beta(Ia) and beta(Ib) indicates that the corresponding mRNAs may have other functions in addition to that of coding for proteins. Furthermore, we show that there are at least five different types of beta-tubulin in the macula lutea of rhesus monkey.

Topics: Alkaloids; Alkanes; Animals; Antineoplastic Agents, Phytogenic; Binding Sites; Carbamates; Carotenoids; Diterpenes; Epothilones; Epoxy Compounds; Haplorhini; Humans; Lactones; Ligands; Lutein; Models, Molecular; Molecular Sequence Data; Paclitaxel; Pyrones; Retina; Thiazoles; Tubulin

Recently, three natural products have been identified, the epothilones, eleutherobin, and discodermolide, whose mechanism of action is similar to that of Taxol in that they stabilize microtubules and block cells in the mitotic phase of the cell cycle. In this report, we have compared and contrasted the effects of these new agents in Taxol-sensitive and -resistant cell lines. We also have taken advantage of a human lung carcinoma cell line, A549-T12, that was isolated as a Taxol-resistant cell line and found to require low concentrations of Taxol (2-6 nM) for normal cell division. This study then examined the ability of these new compounds to substitute for Taxol in sustaining the growth of A549-T12 cells. Immunofluorescence and flow cytometry have both indicated that the epothilones and eleutherobin, but not discodermolide, can substitute for Taxol in this Taxol-dependent cell line. In A549-T12 cells, the presence of Taxol significantly amplified the cytotoxicity of discodermolide, and this phenomenon was not observed in combinations of Taxol with either the epothilones or eleutherobin. Median effect analysis using the combination index method revealed a schedule-independent synergistic interaction between Taxol and discodermolide in four human carcinoma cell lines, an effect that was not observed between Taxol and epothilone B. Flow cytometry revealed that concurrent exposure of A549 cells to Taxol and discodermolide at doses that do not induce mitotic arrest caused an increase in the hypodiploid population, thereby indicating that a possible mechanism for the observed synergy is the potentiation of apoptosis. Our results suggest that Taxol and discodermolide may constitute a promising chemotherapeutic combination.

Topics: Alkaloids; Alkanes; Animals; Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily B; Carbamates; Cell Count; Cell Division; Cell Line; Cytoskeleton; Diterpenes; Dose-Response Relationship, Drug; Drug Synergism; Epothilones; Epoxy Compounds; Flow Cytometry; Humans; Lactones; Lung Neoplasms; Microtubules; Mitosis; Paclitaxel; Pyrones; Thiazoles; Tumor Cells, Cultured

Taxol (paclitaxel), a complex diterpene obtained from the Pacific yew, Taxus brevifolia, is arguably the most important new drug in cancer chemotherapy. The mechanism of cytotoxic action for paclitaxel-i.e., the stabilization of microtubules leading to mitotic arrest-is now shared by four recently identified natural products, eleutherobin, epothilones A and B, and discodermolide. Their ability to competitively inhibit [3H]paclitaxel binding to microtubules strongly suggests the existence of a common binding site. Recently, we have developed nonaromatic analogues of paclitaxel that maintain high cytotoxicity and tubulin binding (e.g., nonataxel). We now propose a common pharmacophore that unites paclitaxel, nonataxel, the epothilones, eleutherobin, and discodermolide, and rationalizes the extensive structure-activity relationship data pertinent to these compounds. Insights from the common pharmacophore have enabled the development of a hybrid construct with demonstrated cytotoxic and tubulin-binding activity.

Topics: Alkaloids; Alkanes; Antineoplastic Agents, Phytogenic; Carbamates; Computer Graphics; Diterpenes; Epothilones; Epoxy Compounds; Lactones; Magnetic Resonance Spectroscopy; Microtubules; Models, Molecular; Molecular Conformation; Molecular Structure; Paclitaxel; Pyrones; Thiazoles