[Effect of quinine on the multiple drug resistance and intracellular distribution of pirarubicin in LR73 tumor cells: a comparative study with verapamil and S9788 by confocal laser microspectrofluorometry].

Effectiveness of chemotherapeutic treatment is limited by multidrug resistance (MDR) phenomenon mediated by the overexpression of P-glycoprotein 170 termed Pgp which serves as an efflux pump removing several types of cytostatic drugs from the MDR cells. Several small molecules, frequently lipophilic cations and weak bases, are able to reverse in vitro this resistance. Several studies have shown that MDR modulators interact with Pgp. However, some molecules do not interact with Pgp but are able to completely restore drug sensitivity (e.g., quinine). Bennis et al. (1995) have shown recently that in contrast to verapamil and S9788, quinine increases nuclear doxorubicin accumulation without modifying its intracellular concentration. From this work, the authors concluded that quinine has essentially intracellular targets involved in drug distribution (cytoplasm to nucleus) from sequestration compartments. Their results have been obtained using spectrofluorometry on cell populations and fluorescence microscopy. By using confocal laser microspectrofluorometry, we investigated restoration of nuclear THP-DOX accumulation and sensitivity by verapamil, S9788 and quinine in 2 variants of the Chinese hamster ovary cells LR73, selected for resistance to doxorubicin (LR73D) and transfected with the mdr1 gene (LR73R), as well as in the sensitive ones (LR73S). Results show that verapamil and S9788 were able to restore THP-DOX sensitivity in resistant cells by increasing nuclear THP-DOX accumulation. This restoration is the consequence of Pgp inhibition and redistribution of the anticancer drug from the cytoplasm to nucleus. Quinine, in contrast, restores the sensitivity of MDR cells to THP-DOX and decreased their resistance index, but has no effect on THP-DOX nuclear accumulation. This suggests that quinine modifies the molecular environment of anthracyclines and/or their binding to cytoplasmic targets involved in another mechanism of anthracycline action.