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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 ...

BackgroundMultidrug resistance (MDR) is a major obstacle in cancer treatment and is often the result of overexpression of the drug efflux protein, P-glycoprotein (P-gp), as a consequence of hyperactivation of NFκB, AP1 and Nrf2 transcription factors. In addition to effluxing chemotherapeutic drugs, P-gp also plays a specific role in blocking caspase-dependent apoptotic pathways. One feature that cytotoxic treatments of cancer have in common is activation of the transcription factor NFκB, which regulates inflammation, cell survival and P-gp expression and suppresses the apoptotic potential of chemotherapeutic agents. As such, NFκB inhibitors may promote apoptosis in cancer cells and could be used to overcome resistance to chemotherapeutic agents.ResultsAlthough the natural withanolide withaferin A and polyphenol quercetin, show comparable inhibition of NFκB target genes (involved in inflammation, angiogenesis, cell cycle, metastasis, anti-apoptosis and multidrug resistance) in doxorubicin-sensitive K562 and -resistant K562/Adr cells, only withaferin A can overcome attenuated caspase activation and apoptosis in K562/Adr cells, whereas quercetin-dependent caspase activation and apoptosis is delayed only. Interestingly, although withaferin A and quercetin treatments both decrease intracellular protein levels of Bcl2, Bim and P-Bad, only withaferin A decreases protein levels of cytoskeletal tubulin, concomitantly with potent PARP cleavage, caspase 3 activation and apoptosis, at least in part via a direct thiol oxidation mechanism.ConclusionsThis demonstrates that different classes of natural NFκB inhibitors can show different chemosensitizing effects in P-gp overexpressing cancer cells with impaired caspase activation and attenuated apoptosis.