Vinca

Abstract: Summary A phytochemical investigation of the plant Vinca rosea Linn. has demonstrated that a number of alkaloidal substances can be obtained with antitumor activity. Over 30 alkaloids have been obtained, of which four—vinblastine, vinleurosine, vincristine, and vinrosidine—are known definitely to be active. Chemically these compounds are closely related to one another and to two monomeric alkaloids, vindoline and catharanthine. The structure of these latter two compounds has been determined, and partial structures for the biologically active alkaloids have been proposed. They represent a new class of large complex dimeric alkaloids containing both indole and dihydroindole moieties. Experimentally, a strain-specific, transplantable, acute, lymphocytic leukemia (P-1534) carried in DBA/2 mice served as a bioassay for obtaining these compounds and for predicting their clinical activity. Vinblastine, vincristine, and vinrosidine are capable of prolonging and/or “curing” mice of the P-1534 leukemia even when therapy is delayed until a near-terminal state of generalized disease. Resistance to an additional challenge of leukemic cells has been observed in these “cured” animals. Parenteral administration of vincristine has been demonstrated to “cure” mice given intracranial implants of the P-1534. The experimental tumor spectrum and toxicological studies are presented and discussed. Biochemical studies performed to date do not reveal any effect on cellular respiration, glycolysis, protein or nucleic acid synthesis. The mechanisms of action of these compounds, which may differ within the group as well as from those of other known agents, remain to be determined. Only two of these compounds, vinblastine and vincristine, have received extensive clinical evaluation. In spite of their close similarity, chemically, a somewhat different group of human neoplasms responds to these compounds, and there has been a singular lack of cross-resistance between these two drugs and any other oncolytic drug now in wide use. Vinblastine has proved effective in chorioepithelioma, Hodgkin9s disease, and other lymphomas, and a number of beneficial results have been obtained in carcinoma of the breast and bronchus. In addition, there have been smaller numbers of a variety of other neoplasias reported as responding to this compound. Vincristine has been striking in its ability to induce complete hematological remission of the acute leukemias of childhood, both lymphocytic and myelogenous in type. Responses have also been reported in a number of other malignancies. The problems and obstacles encountered in obtaining a full realization of the clinical efficacy of these new types of oncolytic compounds are discussed in addition to areas of clinical application other than those previously reported.

Abstract: We have used a structure-activity approach to investigate whether the Vinca alkaloids inhibit cell proliferation primarily by means of their effects on mitotic spindle microtubules or by another mechanism or by a combination of mechanisms. Five Vinca alkaloids were used to investigate the relationship in HeLa cells between inhibition of cell proliferation and blockage of mitosis, alteration of spindle organization, and depolymerization of microtubules. Indirect immunofluorescence staining of microtubules and 4,6-diamidino-2-phenylindole staining of chromatin were used to characterize the effects of the drugs on the distributions of cells in stages of the cell cycle and on the organization of microtubules and chromosomes in metaphase spindles. The microtubule polymer was isolated from cells and quantified using a competitive enzyme-linked immunoadsorbent assay for tubulin. We observed a nearly perfect coincidence between the concentration of each Vinca derivative that inhibited cell proliferation and the concentration that caused 50% accumulation of cells at metaphase, despite the fact that the antiproliferative potencies of the drugs varied over a broad concentration range. Inhibition of cell proliferation and blockage of cells at metaphase at the lowest effective concentrations of all Vinca derivatives occurred with little or no microtubule depolymerization or spindle disorganization. With increasing drug concentrations, the organization of microtubules and chromosomes in arrested mitotic spindles deteriorated in a manner that was common to all five congeners. These results indicate that the antiproliferative activity of the Vinca alkaloids at their lowest effective concentrations in HeLa cells is due to inhibition of mitotic spindle function. The results suggest further that the Vinca alkaloids inhibit cell proliferation by altering the dynamics of tubulin addition and loss at the ends of mitotic spindle microtubules rather than by depolymerizing the microtubules. The specific alterations of spindle microtubule dynamics appear to differ among the five Vinca congeners, and such differences may be responsible for differences in the antitumor specificities of the drugs.

Abstract: Starting with an established line of human leukemic lymphoblasts (CCRF-CEM), we have developed sublines with varying degrees of resistance to vinblastine by growth in the presence of sublethal concentrations of drug. The resistance of these sublines to vinblastine ranges from 10.6-fold to more than 2000-fold when compared with the sensitive parent cells. These vinblastine-resistant cells tend to form large aggregates in stationary suspension culture, suggesting the possibility of an alteration in the cell surface membrane. The surface glycoproteins of sensitive and vinblastine-resistant CCRF-CEM cells were examined by the galactose oxidase (with or without neuraminidase)-[ 3 H]borohydride procedure. It was found that a glycoprotein with a molecular weight of 170,000 to 190,000 is present on the surface of the drug-resistant cells. This prominent glycoprotein appears to be related to the degree of resistance in that it increases in amount with increased resistance to vinblastine. This relationship obtains with cells up to 269 times more resistant to this drug than is the sensitive parent line. Further increases in the degrees of resistance apparently do not lead to greater amounts of this glycoprotein, suggesting that the changes in the cell surface seen with resistance are not absolute or are not all detectable by the surface-labeling method used in this study. Finally, cells selected for high resistance to 1-β-d-arabinofuranosylcytosine have a cell surface glycoprotein pattern similar to that of the sensitive parent line, indicating that the altered glycoprotein profile shown here is not a characteristic of resistance in general but is rather associated with resistance to such Vinca alkaloids as vinblastine.

Abstract: Multidrug resistance (MDR), typified by resistance to Vinca alkaloids and anthracyclines, is a well characterized experimental phenomenon that may have some clinical correlates. Verapamil, chloroquine, and related drugs have been shown previously to be capable of enhancing anticancer drug cytotoxicity in multi-drug-resistant cells, but the mechanism(s) by which these agents do this is(are) unclear. Since these agents did not seem to have common features, we studied these and other compounds for their ability to "modulate" Vinca alkaloid resistance in order to determine whether they possessed any common chemical or physical features. In addition to verapamil, 24 compounds, consisting of indole alkaloids, lysosomotropic agents, and amines, were tested for their ability to enhance the cytotoxicity of vinblastine and/or vincristine in our human leukemic multidrug-resistant cell line, CEM/VLB100. Seventeen compounds that enhance the cytotoxicity of the Vinca alkaloids by more than 5-fold have been identified. These include quinolines (chloroquine, quinine, chinchonidine, and primaquine), acridines (acridine, acridine orange, and quinacrine), and indole alkaloids (yohimbine, corynanthine, reserpine, physostigmine, and the vindoline and catharanthine moieties of the Vinca alkaloids), as well as other alkaloids and amines (chlorpromazine, propranolol, atropine, and tryptamine). Vindoline, catharanthine, and quinacrine also enhanced the cytotoxicity of doxorubicin and teniposide in these cells, indicating that this "modulation" was not limited to Vinca alkaloids. We examined some well known lysosomotropic compounds (methylamine, epinephrine, suramin, and trypan blue) and found that they were not able to enhance the cytotoxicity of vincristine in the CEM/VLB100 cells, indicating that lysosomotropic activity per se is not required for modulator activity. Three-dimensional computer modeling permitted molecular comparisons of conformationally related congeners of vinblastine, vindoline, and verapamil and revealed three regions of structural homology. We measured the hydrophobicity (by oil/water partitioning) and calculated the molar refractivity (by the additive substituent constant method) of active and inactive compounds. We found that those cationic agents--verapamil, quinacrine, indole alkaloids, and quinolines--that were lipid soluble at physiologic pH and had similar molar refractivities were best able to enhance the cytotoxicity of the Vinca alkaloids in our multidrug-resistant cells.(ABSTRACT TRUNCATED AT 400 WORDS)