• Biomolecules & Therapeutics
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• v.24 no.5
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• pp.482-488
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• 2016

Cancer stem cells (CSCs) are a subset of tumor cells, which are characterized by resistance against chemotherapy and environmental stress, and are known to cause tumor relapse after therapy. A number of molecular mechanisms underlie the chemoresistance of CSCs, including high expression levels of drug efflux transporters. We investigated the role of the antioxidant transcription factor NF-E2-related factor 2 (NRF2) in chemoresistance development, using a CSC-enriched colonosphere system. HCT116 colonospheres were more resistant to doxorubicin-induced cell death and expressed higher levels of drug efflux transporters such as P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) compared to HCT116 monolayers. Notably, levels of NRF2 and expression of its target genes were substantially elevated in colonospheres, and these increases were linked to doxorubicin resistance. When NRF2 expression was silenced in colonospheres, Pgp and BCRP expression was downregulated, and doxorubicin resistance was diminished. Collectively, these results indicate that NRF2 activation contributes to chemoresistance acquisition in CSC-enriched colonospheres through the upregulation of drug efflux transporters.

• Biomolecules & Therapeutics
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• v.18 no.4
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• pp.375-385
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• 2010

Conventional cancer chemotherapy is seriously limited by tumor cells exhibiting multidrug resistance (MDR), which is caused by changes in the levels or activity of membrane transporters that mediate energy-dependent drug efflux and of proteins that affect drug metabolism and/or drug action. Cancer scientists and oncologists have worked together for some time to understand anticancer drug resistance and develop pharmacological strategies to overcome such resistance. Much focus has been on the reversal of the MDR phenotype by inhibition of ATP-binding cassette (ABC) drug transporters. ABC transporters are a family of transporter proteins that mediate drug resistance and low drug bioavailability by pumping various drugs out of cells at the expense of ATP hydrolysis. Many inhibitors of MDR transporters have been identified, and though some are currently undergoing clinical trials, none are in clinical use. Herein, we briefly review the status of MDR in human cancer, explore the pathways of MDR in chemotherapy, and outline recent advances in the design and development of MDR modulators.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.2
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• pp.107-122
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• 2001

A function of the kidney is elimination of a variety of xenobiotics ingested and wasted endogenous compounds from the body. Organic anion and cation transport systems play important roles to protect the body from harmful substances. The renal proximal tubule is the primary site of carrier-mediated transport from blood into urine. During the last decade, molecular cloning has identified several families of multispecific organic anion and cation transporters, such as organic anion transporter (OAT), organic cation transporter (OCT), and organic anion-transporting polypeptide (oatp). Additional findings also suggested ATP-dependent organic ion transporters such as MDR1/P-glycoprotein and the multidrug resistance-associated protein (MRP) as efflux pump. The substrate specificity of these transporters is multispecific. These transporters also play an important role as drug transporters. Studies on their functional properties and localization provide information in renal handling of drugs. This review summarizes the latest knowledge on molecular properties and pharmacological significance of renal organic ion transporters.

• Toxicological Research
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• v.31 no.2
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• pp.137-149
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• 2015

Human hepatocytes, with complete hepatic metabolizing enzymes, transporters and cofactors, represent the gold standard for in vitro evaluation of drug metabolism, drug-drug interactions, and hepatotoxicity. Successful cryopreservation of human hepatocytes enables this experimental system to be used routinely. The use of human hepatocytes to evaluate two major adverse drug properties: drug-drug interactions and hepatotoxicity, are summarized in this review. The application of human hepatocytes in metabolism-based drug-drug interaction includes metabolite profiling, pathway identification, P450 inhibition, P450 induction, and uptake and efflux transporter inhibition. The application of human hepatocytes in toxicity evaluation includes in vitro hepatotoxicity and metabolism-based drug toxicity determination. A novel system, the Integrated Discrete Multiple Organ Co-culture (IdMOC) which allows the evaluation of nonhepatic toxicity in the presence of hepatic metabolism, is described.

• Journal of Microbiology and Biotechnology
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• v.30 no.7
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• pp.982-995
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• 2020

A putative multidrug efflux gene, yddA, was cloned from the Escherichia coli K-12 strain. A drug-sensitive strain of E. coli missing the main multidrug efflux pump AcrB was constructed as a host and the yddA gene was knocked out in wild-type (WT) and drug-sensitive E. coliΔacrB to study the yddA function. Sensitivity to different substrates of WT E.coli, E. coliΔyddA, E. coliΔacrB and E. coliΔacrBΔyddA strains was compared with minimal inhibitory concentration (MIC) assays and fluorescence tests. MIC assay and fluorescence test results showed that YddA protein was a multidrug efflux pump that exported multiple substrates. Three inhibitors, ortho-vanadate, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and reserpine, were used in fluorescence tests. Ortho-vanadate and reserpine significantly inhibited the efflux and increased accumulation of ethidium bromide and norfloxacin, while CCCP had no significant effect on YddA-regulated efflux. The results indicated that YddA relies on energy released from ATP hydrolysis to transfer the substrates and YddA is an ABC-type multidrug exporter. Functional study of unknown ATP-binding cassette (ABC) superfamily transporters in the model organism E. coli is conducive to discovering new multidrug resistance-reversal targets and providing references for studying other ABC proteins of unknown function.

• Journal of Microbiology and Biotechnology
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• v.23 no.3
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• pp.430-435
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• 2013

Multidrug resistance, especially multidrug efflux mechanisms that extrude structurally unrelated cytotoxic compounds from the cell by multidrug transporters, is a serious problem and one of the main reasons for the failure of therapeutic treatment of infections by pathogenic microorganisms as well as of cancer cells. Streptococcus mutans is considered one of the primary causative agents of dental caries and periodontal disease, which comprise the most common oral diseases. A fragment of chromosomal DNA from S. mutans KCTC3065 was cloned using Escherichia coli KAM32 as host cells lacking major multidrug efflux pumps. Although E. coli KAM32 cells were very sensitive to many antimicrobial agents, the transformed cells harboring a recombinant plasmid became resistant to several structurally unrelated antimicrobial agents such as tetracycline, kanamycin, rhodamin 6G, ampicillin, acriflavine, ethidium bromide, and tetraphenylphosphonium chloride. This suggested that the cloned DNA fragment carries a gene encoding a multidrug efflux pump. Among 49 of the multidrug-resistant transformants, we report the functional gene cloning and characterization of the function of one multidrug efflux pump, namely MdeA from S. mutans, which was expressed in E. coli KAM32. Judging from the structural and biochemical properties, we concluded that MdeA is the first cloned and characterized multidrug efflux pump using the proton motive force as the energy for efflux drugs.

• Journal of Integrative Natural Science
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• v.5 no.2
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• pp.72-78
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• 2012

Multidrug resistance is a major obstacle in cancer chemotherapy. Cancer cells efflux chemotherapeutic drug out of cell by means of transporter and reduce the active concentration of it inside cell. Such transporters are member of the ATP binding cassettes (ABC) protein. It includes P-gp, multiple resistant protein (MRP), and breast cancer resistant protein (BCRP). These proteins are widely distributed in the human cells such as kidney, lung, endothelial cells of blood brain barrier etc. However, there are number of drugs developed for it, but most of them are getting transported by it. So, still there is necessity of a good modulator, which could effectively combat the transport of chemotherapeutic agents. Natural products origin modulators were found to be effective against transporter such as flavonoids, which belongs to third generation modulators. They have advantage over synthetic inhibitor in the sense that they have simple structure and abundant in nature. This review focuses on the P-gp structure its architecture, efflux mechanism, herbal inhibitors and their mechanism of action.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.9
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• pp.4807-4814
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• 2012

Purpose: The chemoresistance of human hepatocellular carcinoma (HCC) to cytotoxic drugs, especially intrinsic or acquired multidrug resistance (MDR), still remains a major challenge in the management of HCC. In the present study, possible mechanisms involved in MDR of HCC were identified using a 5-fluorouracil (5-FU)-resistant human HCC cell line. Methods: BEL-7402/5-FU cells were established through continuous culturing parental BEL-7402 cells, imitating the pattern of chemotherapy clinically. Growth curves and chemosensitivity to cytotoxic drugs were determined by MTT assay. Doubling times, colony formation and adherence rates were calculated after cell counting. Morphological alteration, karyotype morphology, and untrastructure were assessed under optical and electron microscopes. The distribution in the cell cycle and drug efflux pump activity were measured by flow cytometry. Furthermore, expression of potential genes involved in MDR of BEL-7402/5-FU cells were detected by immunocytochemistry. Results: Compared to its parental cells, BEL-7402/5-FU cells had a prolonged doubling time, a lower mitotic index, colony efficiency and adhesive ability, and a decreased drug efflux pump activity. The resistant cells tended to grow in clusters and apparent changes of ultrastructures occurred. BEL-7402/5-FU cells presented with an increased proportion in S and G2/M phases with a concomitant decrease in G0/G1 phase. The MDR phenotype of BEL-7402/5-FU might be partly attributed to increased drug efflux pump activity via multidrug resistance protein 1 (MRP1), overexpression of thymidylate synthase (TS), resistance to apoptosis by augmentation of the Bcl-xl/Bax ratio, and intracellular adhesion medicated by E-cadherin (E-cad). P-glycoprotein (P-gp) might play a limited role in the MDR of BEL-7402/5-FU. Conclusion: Increased activity or expression of MRP1, Bcl-xl, TS, and E-cad appear to be involved in the MDR mechanism of BEL-7402/5-FU.

• Journal of Microbiology and Biotechnology
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• v.18 no.5
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• pp.845-851
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• 2008

TolC is an outer membrane porin protein and an essential component of drug efflux and type-I secretion systems in Gram-negative bacteria. TolC comprises a periplasmic $\alpha$-helical barrel domain and a membrane-embedded $\beta$-barrel domain. TdeA, a functional and structural homolog of TolC, is required for toxin and drug export in the pathogenic oral bacterium Actinobacillus actinomycetemcomitans. Here, we report the expression of the periplasmic domain of TdeA as a soluble protein by substitution of the membrane-embedded domain with short linkers, which enabled us to purify the protein in the absence of detergent. We confirmed the structural integrity of the TdeA periplasmic domain by size-exclusion chromatography, circular dichroism spectroscopy, and electron microscopy, which together showed that the periplasmic domain of the TolC protein family fold correctly on its own. We further demonstrated that the periplasmic domain of TdeA interacts with peptidoglycans of the bacterial cell wall, which supports the idea that completely folded TolC family proteins traverse the peptidoglycan layer to interact with inner membrane transporters.

• Natural Product Sciences
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• v.20 no.1
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• pp.1-6
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• 2014

P-glycoprotein (P-gp) is a permeability glycoprotein also known as multidrug resistance protein 1 (MDR1). P-gp is an ATP-binding cassette (ABC) transporter that pumps various types of drugs out of cells. These transporters reduce the intracellular concentrations of drugs and disturb drug absorption. The Caco-2 cell permeability assay system is an effective in vitro system that predicts the intestinal absorption of drugs and the functions of enzymes and transporters. Rhodamine-123 (R-123) and digoxin are well-known P-gp substrates that have been used to determine the function of P-gp. Efflux of P-gp substrates by P-gp has been routinely evaluated. To date, a number of herbal medicines have been tested with Caco-2 cell permeability assay system to assess bioavailability. There are growing efforts to find phytochemicals that potentially regulate P-gp function. The Caco-2 cell permeability assay system is a primary strategy to search for candidates of P-gp inhibitors. In this mini review, we have summarized the P-gp modulation by herbal extracts, decoctions or single components from natural products using Caco-2 cell permeability assays. Many natural products are known to regulate P-gp and herbal medicines could be used in combination with conventional drugs to enhance bioavailability.