PHYSICAL-CHEMICAL PROPERTIES SHARED BY COMPOUNDS THAT MODULATE MULTIDRUG RESISTANCE IN HUMAN-LEUKEMIC CELLS

  • 1 April 1988
    • journal article
    • research article
    • Vol. 33  (4) , 454-462
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 multidrug-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 physicl 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.sbd.verapamil, quinacrine, indole alkaloids, and quinolines.sbd.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. Thus, we conclude that, although structural similarities may play a role in the ability of some compounds to modulate drug resistance, it appears that lipid solubility at physiological pH, cationic charge, and molar refractivity are important physical properties for modulators of MDR. Our studies provide direction for the development of new compounds that may be useful in understanding the mechanisms of MDR and may also suggest possible chemotherapeutic strategies for its circumvention.