demecolcine and tubulazole

1. Evidence exists that associations of adrenal nicotinic acetylcholine receptors (nAChRs) with the cytoskeleton play an important role in signal transduction pathways by maintaining these receptors in a functional state. These studies were designed to explore this possibility and elucidate the mechanism by which antimitotic agents inhibit activation of adrenal nAChRs. 2. Functional studies demonstrated that vincristine, tubulozole, podophyllotoxin, and demecolcine inhibited nAChR-stimulated catecholamine release noncompetitively and in a concentration-dependent manner, with IC50 values of 3 (1-10), 5 (2-10), 8 (4-15), and 19 (9-39) microM, respectively. 3. Detergent extraction experiments indicated that approximately 36% of adrenal nAChRs were associated with the detergent-insoluble cytoskeletal fraction. When chromaffin cells were first treated with antimitotic agents and then detergent solubilized, a significant reduction occurred in the population of adrenal nAChRs associated with the detergent-insoluble cytoskeleton. 4. These studies support an association of adrenal nAChRs with microtubules and suggest that the mechanism by which the antimitotic drugs interfere with the signal transduction pathway is by inducing dissociation of nAChRs from the microtubular network.

Topics: Adrenal Glands; Animals; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Catecholamines; Cattle; Cell Division; Cells, Cultured; Chromaffin Cells; Cytoskeleton; Demecolcine; Detergents; Dioxolanes; Diphenylacetic Acids; Mecamylamine; Microtubules; Nicotine; Nicotinic Agonists; Nicotinic Antagonists; Parasympatholytics; Podophyllotoxin; Receptors, Nicotinic; Vincristine

At low concentrations, both isomers of tubulozole (C, T) inhibit Plasmodium falciparum but only tubulozole C inhibits mammalian cells. Since tubulozole C prevents polymerization of mammalian tubulin whereas tubulozole T does not, the antimalarial action of tubulozoles may not involve microtubules. The present study concerns the inhibition of parasite protein synthesis by the tubulozoles. While tubulozoles took 3-4 h to kill parasites in erythrocytic culture, they inhibited protein synthesis within 10 min. The concentrations of the drug required were, however, too high for this to account for their antimalarial action. The microtubule inhibitor colcemid inhibited protein synthesis rapidly and at relevant concentrations, but vinblastine did not inhibit protein synthesis. Tubulozole T and colcemid inhibited protein synthesis posttranscriptionally since they had little effect on RNA synthesis. Analysis of labelled parasite proteins by two-dimensional gel electrophoresis showed that while it inhibited synthesis of most proteins to the same degree, tubulozole T super-inhibited the synthesis of certain proteins. This may cause its antimalarial effect at low concentrations.

Topics: Animals; Antimalarials; Antineoplastic Agents; Cycloheximide; Demecolcine; Dioxolanes; Drug Resistance; Electrophoresis, Gel, Two-Dimensional; Erythrocytes; Humans; Kinetics; Methionine; Microtubules; Plasmodium falciparum; Protozoan Proteins; RNA, Protozoan; Vinblastine

The mode of action of the tubulozole isomers, recently recognized as a new class of potential antimalarial agents, was investigated. Whereas neither glycolysis, protease activity, or nucleic acid biosynthesis was primarily affected, protein biosynthesis decreased soon after addition of the drug. Inhibitors of protein biosynthesis, however, did not show synergistic activity with tubulozole. Colcemid, on the other hand, had an effect on protein synthesis similar to that seen with the tubulozoles. Furthermore, combinations of the tubulozole isomers with compounds known to interact with tubulin inhibited malaria in a synergistic or antagonistic fashion. Therefore, the inhibition might be elicited by interaction with tubulin or some other component of the microtubules. This is remarkable insofar as only one of the tubulozole isomers affects mammalian cells by binding to tubulin.

Topics: Animals; Antineoplastic Agents; Benzimidazoles; Cell Line; Demecolcine; Dioxolanes; DNA; Dose-Response Relationship, Drug; Drug Synergism; Endopeptidases; Erythrocytes; Hypoxanthines; Lactates; Methionine; Plasmodium falciparum; Protease Inhibitors; Protein Biosynthesis; Sulfur Radioisotopes

The effects of nine different tubulin-binding substances and of one actin-binding compound, cytochalasin B, upon the intraerythrocytic development of the malaria parasite Plasmodium falciparum were investigated in vitro. From the data obtained, plasmodial tubulins seem to be quite different from the mammalian proteins on the molecular level. Tubulozole-T, a substance which is inactive in mammalian systems, appears to be a promising novel antimalarial drug.

Topics: Actins; Alkaloids; Animals; Benzimidazoles; Cytochalasin B; Demecolcine; Dioxolanes; Dioxoles; Drug Resistance; Plasmodium falciparum; Tubulin; Vinblastine; Vincristine

The effects of nine different tubulin-binding substances and of one actin-binding compound, cytochalasin B, upon the intraerythrocytic development of the malaria parasite Plasmodium falciparum were investigated in vitro. From the data obtained, plasmodial tubulins seem to be quite different from the mammalian proteins on the molecular level. Tubulozole-T, a substance which is inactive in mammalian systems, appears to be a promising novel antimalarial drug.

Topics: Actins; Albendazole; Animals; Anthelmintics; Antimalarials; Antineoplastic Agents; Benzimidazoles; Cytochalasin B; Cytoskeletal Proteins; Demecolcine; Dioxolanes; Drug Resistance; Erythrocytes; Humans; Mebendazole; Nocodazole; Plasmodium falciparum; Tubulin; Vinblastine; Vincristine