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Multidrug resistance (MDR) is a principle cause of failure in human drug treatment. MDR phenomena are intensively studied in anti-cancer, anti-bacterial, anti-paludism, and human immunodeficiency virus-1. [1][2][3][4][5] The MDR phenotype is characterized by a low free intracellular cytotoxic drug concentration in comparison with their corresponding drugsensitive cells. This is frequently associated with protein membrane transporters, such as P-glycoprotein and MRP1-protein, which ATP-dependently extrude cytotoxic agents out of cells, thus reducing their efficacy. To overcome MDR phenomena, the direct interaction between inhibitors and proteins has been researched by many groups. A variety of small molecules, such as verapamil, dihydropyridines, forskolin and cyclosporin were found to bind to P-glycoprotein and inhibit its ability to pump out antitumor drugs. 6-9) All compounds cited are difficult to use in vivo due to their toxicity. As a consequence, the clinical utility of non-toxic derivatives of these and other molecules as chemosensitizing agents has been extensively studied. 10,11) It was reported that in MDR plasmodium falciparum strains, the pfmdr-1 gene and pgh-1 were characterized, which has about 54% homology to mdr-1 gene of MDR cancer cells. [12][13][14][15] However, its function is still not clear. Recently, it was reported that qinghaosu is an effective compound against MDR plasmodium falciparum strains, 16,17) but studies regarding its effect on protein transporters have not been performed, neither in erythrocytes infected by MDR plasmodium falciparum strains nor in cancer MDR cells. Qinghaosu drugs such as artemisinin and artesunate are now in widespread use, particularly in Southast Asia, and are used as a prophylaxis in China. 18,19) In this study we have demonstrated that artemisinin, artesunate and dihydroartemisinin poorly inhibited P-glycoprotein and did not inhibit MRP1 protein function in multidrug resistant K562/adr cells, overexpression P-glycoprotein, or in GLC4/adr cells overexpression of MRP1-protein, respectively. However, they increased in cytotoxic effect induced by pirarubicin or doxorubicin only in MDR cell lines. We also demonstrated that these qinghaosu modulate mitochondrial function, leading to a decrease in intracellular ATP content in all cell lines tested. MATERIALS AND METHODS Cell Culture and Cytotoxicity AssayThe erythromyelogenous leukemic, K562, and its P-glycoprotein-overexpressing K562/adr, 20,21) and the human small cell lung cancer, GLC4 and its MRP1-overexpressing GLC4/adr, [22][23][24] were kindly provided by Professor Arlette Garnier-Suillerot, Laboratoire de Chimie Physique, Biomoleculaire et Cellulaire, UFR Sante Medecine Biologie Humaine, Universite de Paris Nord, France. These cells were routinely cultured in RPMI 1640 medium supplemented with 10% fetal calf serum (Gibco Biocult, Ltd.). The resistant K562/adr and GLC4/adr cells were cultured with 100 nM doxorubicin two weeks before the experiments. For the assays, a culture was initiated at 5ϫ10 5 cells ...

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The effect of low-density membrane domains on function of the plasma membrane transporter P-glycoprotéine (P-gp), involved in multidrug resistance (MDR) phenotype, has been investigated in K562/ADR cells. To this end we reversibly altered the cholesterol content of K562/ADR cells by using methyl-beta-cyclodextrin as a cholesterol chelator and conversely we repleted them through incubation with cholesterol in culture medium. We also used the cholesterol-binding fluorochrome filipin and cholesterol oxidase. Our data show that either cholesterol depletion or complex formation with filipin resulted in a strong decrease of P-gp activity. However, when cells were incubated with cholesterol oxidase that are known to disrupt rafts, no modification of the P-gp activity was observed. In addition, using a free-detergent methodology to separate by ultracentrifugation, "light," "heavy," and "extra heavy" fractions we show that no P-gp is found in the "light" fraction where rafts are usually detected. Altogether, our data strongly suggest that, in this cell line, P-gp is not localized in rafts.

The objective of this study was to determine the kinetics of nuclear factor-kappa B (NF-kappaB) activation and cytokine expression in bone marrow (BM) cells of exposed mice as a function of the dose rate of protons. The cytokines included in this study are pro-inflammatory [i.e., tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6] and anti-inflammatory cytokines (i.e., IL-4 and IL-10). We gave male BALB/cJ mice a whole-body exposure to 0 (sham-controls) or 1.0 Gy of 100 MeV protons, delivered at 5 or 10 mGy min(-1), the dose and dose rates found during solar particle events in space. As a reference radiation, groups of mice were exposed to 0 (sham-controls) or 1 Gy of (137)Cs gamma rays (10 mGy min(-1)). After irradiation, BM cells were collected at 1.5, 3, 24 h, and 1 month for analyses (five mice per treatment group per harvest time). The results indicated that the in vivo time course of effects induced by a single dose of 1 Gy of 100 MeV protons or (137)Cs gamma rays, delivered at 10 mGy min(-1), was similar. Although statistically significant levels of NF-kappaB activation and pro-inflammatory cytokines in BM cells of exposed mice when compared to those in the corresponding sham controls (Student's t-test, p < 0.05 or <0.01) were induced by either dose rate, these levels varied over time for each protein. Further, only a dose rate of 5 mGy min(-1) induced significant levels of anti-inflammatory cytokines. The results indicate dose-rate effects of protons.