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Absorption of drug substances across the intestinal epithelium is a complex and dynamic process. Counter transport proteins are responsible for the efflux of specific drug molecules after they have been absorbed. One of the key counter transport efflux proteins, which is of importance in this study, is P–glycoprotein. The efflux pump P–glycoprotein plays a major role in altering the pharmacokinetics of a wide variety of drugs limiting their absorption and therefore also bioavailability. Many flavonoids have been shown to interact with P–glycoprotein mediated efflux in vitro studies. Numerous in vitro methods have been used to study drug absorption across the intestinal membranes, but it is often not possible to use only one in vitro model to accurately predict permeability characteristics. The purpose of this study was to determine the effect of four selected hydroxy– and methoxy– flavonoids on the in vitro transport of Rhodamine 123, a known P–gp substrate, across excised rat and pig intestinal tissue using the Sweetana–Grass diffusion apparatus. The results were further used to determine if the two different animal tissue models corresponded with regard to the flavonoids' effects on P–glycoprotein related efflux. Two control groups were included in the experimental design. In the negative control group, the transport of Rhodamine 123 was tested alone and no modulator was added. In the positive control group, the transport of Rhodamine 123 was determined in the presence of Verapamil, which is a known P–glycoprotein inhibitor. The experiments with the flavonoids Morin, Galangin, 6–Methoxyflavone and 7–Methoxyflavone were done in triplicate to determine repeatability of the results. The transport of Rhodamine 123 was evaluated in both the apical to basolateral (absorptive) and basolateral to apical (secretory) directions. The relative transport of Rhodamine 123, the apparent permeability coefficient (P app) values and flux (J) values in both directions as well as the efflux ratio (ER) and net flux (J net) were calculated. The concentration Rhodamine 123 present in the acceptor chamber was determined by means of a validated HPLC method. Statistical analysis was used to compare the results of the test groups with the control groups in order to indicate significant differences. It has been found that Morin, Galangin and 6–Methoxyflavone have a significant inhibitory effect on the Rhodamine 123 efflux (probably P–glycoprotein related) in both the rat and pig intestinal tissue models with p–values smaller than 0.05. On the other hand, 7–Methoxyflavone showed a significant effect on the efflux of Rhodamine 123 in the pig intestinal tissue model (p < 0.05) but not in the rat intestinal tissue model (p > 0.05). These flavonoids may increase the bioavailability of drugs that are substrates for P–glycoprotein and thereby cause clinically significant pharmacokinetic interactions, however, this should be confirmed with in vivo studies. On the other hand, these flavonoids may be used for drug absorption enhancement when applied under controlled circumstances. With regard to the different animal tissue models used it can be concluded that data obtained from the rat intestinal tissue model cannot be compared and extrapolated to data obtained from the pig intestinal tissue model. It is recommended that the in vitro results be correlated to in vivo findings to identify the most suitable model. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

Absorption of drug substances across the intestinal epithelium is a complex and dynamic process. Counter transport proteins are responsible for the efflux of specific drug molecules after they have been absorbed. One of the key counter transport efflux proteins, which is of importance in this study, is P–glycoprotein. The efflux pump P–glycoprotein plays a major role in altering the pharmacokinetics of a wide variety of drugs limiting their absorption and therefore also bioavailability. Many flavonoids have been shown to interact with P–glycoprotein mediated efflux in vitro studies. Numerous in vitro methods have been used to study drug absorption across the intestinal membranes, but it is often not possible to use only one in vitro model to accurately predict permeability characteristics. The purpose of this study was to determine the effect of four selected hydroxy– and methoxy– flavonoids on the in vitro transport of Rhodamine 123, a known P–gp substrate, across excised rat and pig intestinal tissue using the Sweetana–Grass diffusion apparatus. The results were further used to determine if the two different animal tissue models corresponded with regard to the flavonoids' effects on P–glycoprotein related efflux. Two control groups were included in the experimental design. In the negative control group, the transport of Rhodamine 123 was tested alone and no modulator was added. In the positive control group, the transport of Rhodamine 123 was determined in the presence of Verapamil, which is a known P–glycoprotein inhibitor. The experiments with the flavonoids Morin, Galangin, 6–Methoxyflavone and 7–Methoxyflavone were done in triplicate to determine repeatability of the results. The transport of Rhodamine 123 was evaluated in both the apical to basolateral (absorptive) and basolateral to apical (secretory) directions. The relative transport of Rhodamine 123, the apparent permeability coefficient (P app) values and flux (J) values in both directions as well as the efflux ratio (ER) and net flux (J net) were calculated. The concentration Rhodamine 123 present in the acceptor chamber was determined by means of a validated HPLC method. Statistical analysis was used to compare the results of the test groups with the control groups in order to indicate significant differences. It has been found that Morin, Galangin and 6–Methoxyflavone have a significant inhibitory effect on the Rhodamine 123 efflux (probably P–glycoprotein related) in both the rat and pig intestinal tissue models with p–values smaller than 0.05. On the other hand, 7–Methoxyflavone showed a significant effect on the efflux of Rhodamine 123 in the pig intestinal tissue model (p < 0.05) but not in the rat intestinal tissue model (p > 0.05). These flavonoids may increase the bioavailability of drugs that are substrates for P–glycoprotein and thereby cause clinically significant pharmacokinetic interactions, however, this should be confirmed with in vivo studies. On the other hand, these flavonoids may be used for drug absorption enhancement when applied under controlled circumstances. With regard to the different animal tissue models used it can be concluded that data obtained from the rat intestinal tissue model cannot be compared and extrapolated to data obtained from the pig intestinal tissue model. It is recommended that the in vitro results be correlated to in vivo findings to identify the most suitable model. / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

Gene delivery for therapeutic purposes is quickly emerging as the best potential treatment option for inherited genetic diseases and cancer. Viral gene carriers have been the choice for this purpose due to their high efficiency, but harmful immunogenic and oncogenic host reactions have limited their in vivo use. Cationic polymers provide a safe alternative to viral carriers as they can be engineered to reduce immunogenic and toxic responses and serve therapeutic purposes in the body. Due to their strong positive charge, they are able to compact the negatively charged nucleotides to small nano-sized particles appropriate for cellular uptake. Additionally, they efficiently encapsulate the highly sensitive nucleotides, and protect them against degradation by the nucleases present at the physiological milieu. In this thesis work, I have used a novel approach for gene delivery by combining the critical properties of a cationic polymer (i.e., nucleotide condensing ability) with that of a fatty acid (i.e., lipid membrane compatibility). The resulting lipid modified polymer increased delivery of our gene of interest into target cells and resulted in increased siRNA delivery for cancer gene therapy. / Biomedical Sciences

Thesis (Ph.D.). / Written for the Institute of Parasitology. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Made available in DSpace on 2016-06-02T20:21:35Z (GMT). No. of bitstreams: 1 6279.pdf: 1318446 bytes, checksum: 3ea93c315d61578a7b50605db41ae915 (MD5) Previous issue date: 2014-02-28 / Financiadora de Estudos e Projetos / Among the sheep parasites, Haemonchus contortus is the most prevalent and pathogenic nematode in tropical areas, causing huge economic losses. Alterations in the gene encoding the membrane P-glycoprotein (PgP) have been associated with multidrug resistance. The goal of this study was to identify single nucleotide polymorphisms (SNPs) on the PgP gene in H. contortus by comparing two isolates with different status of anthelmintic resistance. For this purpose, two ewes were experimentally infected, one with a susceptible H. contortus isolate (McMaster, Australia) and the other with a multidrug-resistant isolate (Embrapa2010, Brazil). Feces from infected animals were submitted to coproculture in order to obtain larvae and, after the slaughter of the ewes, adults H. contortus were collected from abomasum and individually submitted to DNA extraction. For the evaluation of potential molecular markers of geographic isolation, larvae originating from coprocultures of two other Brazilian isolates (Bahia and Pernambuco), with no determined resistance status, were also submitted to DNA extraction. After PCR amplification of DNA extracted from adults H. contortus, a fragment of the PgP gene was sequenced and six SNPs (position described in relation to the sequence of contig 004690 from the Wellcome Trust Sanger Institute) were identified : 508 (A> G in exon), 580 (G> A), 601 (G> C), 800 (G> A), 845 (G> T), and 878 (G> T), the last five in introns. The Fisher's exact test, applying the Bonferroni correction, revealed a significant association (P<0.01) between 508, 580, 601, 845 and 878 SNPs and the state of resistance to anthelmintics. Among these SNPs, 601 and 878 are in linkage disequilibrium and form the CC haplotype associated (P < 0.05) to resistance and the GG haplotype associated to susceptibility. Considering that there is considerable genetic differentiation between different continental areas in H. contortus, the frequencies of the SNPs were compared between the Brazilian isolates and the susceptible Australian one. It was found that the SNPs 580 and 845 may be associated with geographic isolation. We conclude that the 508, 601 and 878 SNPs in the P-glycoprotein gene can be molecular markers for multiple resistance to anthelmintics, and that the 580 and 845 SNPs can be candidate markers of geographical isolation in H. contortus. We developed software for Risk Analysis Development of Parasitic Resistance to Anthelmintics in Sheep (SARA) which will provide information that may guide the rational use of anthelmintics. / Among the sheep parasites, Haemonchus contortus is the most prevalent and pathogenic nematode in tropical areas, causing huge economic losses. Alterations in the gene encoding the membrane P-glycoprotein (PgP) have been associated with multidrug resistance. The goal of this study was to identify single nucleotide polymorphisms (SNPs) on the PgP gene in H. contortus by comparing two isolates with different status of anthelmintic resistance. For this purpose, two ewes were experimentally infected, one with a susceptible H. contortus isolate (McMaster, Australia) and the other with a multidrug-resistant isolate (Embrapa2010, Brazil). Feces from infected animals were submitted to coproculture in order to obtain larvae and, after the slaughter of the ewes, adults H. contortus were collected from abomasum and individually submitted to DNA extraction. For the evaluation of potential molecular markers of geographic isolation, larvae originating from coprocultures of two other Brazilian isolates (Bahia and Pernambuco), with no determined resistance status, were also submitted to DNA extraction. After PCR amplification of DNA extracted from adults H. contortus, a fragment of the PgP gene was sequenced and six SNPs (position described in relation to the sequence of contig 004690 from the Wellcome Trust Sanger Institute) were identified : 508 (A> G in exon), 580 (G> A), 601 (G> C), 800 (G> A), 845 (G> T), and 878 (G> T), the last five in introns. The Fisher's exact test, applying the Bonferroni correction, revealed a significant association (P<0.01) between 508, 580, 601, 845 and 878 SNPs and the state of resistance to anthelmintics. Among these SNPs, 601 and 878 are in linkage disequilibrium and form the CC haplotype associated (P < 0.05) to resistance and the GG haplotype associated to susceptibility. Considering that there is considerable genetic differentiation between different continental areas in H. contortus, the frequencies of the SNPs were compared between the Brazilian isolates and the susceptible Australian one. It was found that the SNPs 580 and 845 may be associated with geographic isolation. We conclude that the 508, 601 and 878 SNPs in the P-glycoprotein gene can be molecular markers for multiple resistance to anthelmintics, and that the 580 and 845 SNPs can be candidate markers of geographical isolation in H. contortus. We developed software for Risk Analysis Development of Parasitic Resistance to Anthelmintics in Sheep (SARA) which will provide information that may guide the rational use of anthelmintics. / Entre os parasitas de ovinos, Haemonchus contortus é o nematoide mais prevalente e patogênico em áreas tropicais, causando grandes perdas econômicas. As alterações no gene que codifica a glicoproteína-P de membrana (PgP) foram associadas com a resistência a múltiplas drogas. Assim, o objetivo deste estudo foi identificar polimorfismos de nucleotídeo único (SNPs) no gene PgP em H. contortus por comparação de dois isolados com diferentes status de resistência a anti-helmínticos. Para esse fim, uma ovelha foi infectada experimentalmente com o isolado suscetível (McMaster, Austrália) e outra ovelha com o isolado multirresistente (Embrapa2010, Brasil) de H. contortus. Fezes dos animais infectados foram submetidas à coprocultura para a obtenção de larvas e, após o abate das ovelhas, H. contortus adultos foram colhidos do abomaso e individualmente submetidos à extração de DNA. Para a avaliação de possíveis marcadores moleculares de isolamento geográfico, larvas oriundas de coprocultura de dois outros isolados brasileiros (Bahia e Pernambuco), com status de resistência não determinado, também foram submetidas à extração de DNA. Após amplificação por PCR do DNA extraído de H. contortus adultos, um fragmento do gene PgP foi sequenciado e foram identificados seis SNPs (posição descrita em relação à sequência do contig 004690 do Wellcome Trust Sanger Institute): 508 (A>G, em éxon), 580 (G>A), 601 (G>C), 800 (G>A), 845 (G>T) e 878 (G>T), os cinco últimos em íntrons. O teste exato de Fisher, por meio da correção de Bonferroni, revelou associação significativa (P<0,01) entre os SNPs 508, 580, 601, 845 e 878 e o estado de resistência a anti-helmínticos. Desses SNPs, o 601 e o 878 estão em desequilíbrio de ligação e formam os haplótipos CC, que está associado (P<0,05) à resistência, e GG, à suscetibilidade. Levando em consideração que em H. contortus há considerável diferenciação genética entre áreas continentais distintas, as frequências dos SNPs foram comparadas entre os isolados brasileiros e o isolado suscetível australiano e foi verificado que os SNPs 580 e 845 podem estar associados ao isolamento geográfico. Conclui-se que os SNPs 508, 601 e 878 no gene de glicoproteína-P podem ser marcadores moleculares para a resistência múltipla a anti-helmínticos, e os SNPs 580 e 845 candidatos a marcadores de isolamento geográfico em H. contortus. Nós desenvolvemos um software para Análise de Risco de Desenvolvimento de Resistência Parasitária a Anti- Helmínticos em Ovinos (SARA) que fornecerá informações que poderão orientar a utilização racional de anti-helmínticos. / Entre os parasitas de ovinos, Haemonchus contortus é o nematoide mais prevalente e patogênico em áreas tropicais, causando grandes perdas econômicas. As alterações no gene que codifica a glicoproteína-P de membrana (PgP) foram associadas com a resistência a múltiplas drogas. Assim, o objetivo deste estudo foi identificar polimorfismos de nucleotídeo único (SNPs) no gene PgP em H. contortus por comparação de dois isolados com diferentes status de resistência a anti-helmínticos. Para esse fim, uma ovelha foi infectada experimentalmente com o isolado suscetível (McMaster, Austrália) e outra ovelha com o isolado multirresistente (Embrapa2010, Brasil) de H. contortus. Fezes dos animais infectados foram submetidas à coprocultura para a obtenção de larvas e, após o abate das ovelhas, H. contortus adultos foram colhidos do abomaso e individualmente submetidos à extração de DNA. Para a avaliação de possíveis marcadores moleculares de isolamento geográfico, larvas oriundas de coprocultura de dois outros isolados brasileiros (Bahia e Pernambuco), com status de resistência não determinado, também foram submetidas à extração de DNA. Após amplificação por PCR do DNA extraído de H. contortus adultos, um fragmento do gene PgP foi sequenciado e foram identificados seis SNPs (posição descrita em relação à sequência do contig 004690 do Wellcome Trust Sanger Institute): 508 (A>G, em éxon), 580 (G>A), 601 (G>C), 800 (G>A), 845 (G>T) e 878 (G>T), os cinco últimos em íntrons. O teste exato de Fisher, por meio da correção de Bonferroni, revelou associação significativa (P<0,01) entre os SNPs 508, 580, 601, 845 e 878 e o estado de resistência a anti-helmínticos. Desses SNPs, o 601 e o 878 estão em desequilíbrio de ligação e formam os haplótipos CC, que está associado (P<0,05) à resistência, e GG, à suscetibilidade. Levando em consideração que em H. contortus há considerável diferenciação genética entre áreas continentais distintas, as frequências dos SNPs foram comparadas entre os isolados brasileiros e o isolado suscetível australiano e foi verificado que os SNPs 580 e 845 podem estar associados ao isolamento geográfico. Conclui-se que os SNPs 508, 601 e 878 no gene de glicoproteína-P podem ser marcadores moleculares para a resistência múltipla a anti-helmínticos, e os SNPs 580 e 845 candidatos a marcadores de isolamento geográfico em H. contortus. Nós desenvolvemos um software para Análise de Risco de Desenvolvimento de Resistência Parasitária a Anti- Helmínticos em Ovinos (SARA) que fornecerá informações que poderão orientar a utilização racional de anti-helmínticos.

La glycoprotéine P ou Pgp est une protéine de transport transmembranaire qui a pour rôle principal d'évacuer hors des cellules les xénobiotiques et les toxines. Elle agit comme une pompe à efflux et est surexprimée par certaines cellules cancéreuses. Ainsi, via ce mécanisme, les cellules tumorales peuvent devenir résistantes aux antitumoraux et conduire à l'échec des traitements lors de la chimiothérapie anticancéreuse. Aussi, la modulation de l'activité de cette protéine peut être un des moyens permettant l'amélioration des traitements anticancéreux. La Pgp possède plusieurs sites de fixation de substrats dont deux sont relativement proches spatialement : un site à stéroïdes et un site à ATP permettant d'hydrolyser l'ATP, source d'énergie nécessaire au fonctionnement de la Pgp. Notre objectif a été de synthétiser des modulateurs bivalents stéroïdes/bras/nucléosides. Pour cela, nous avons dans un premier temps préparé des analogues de bases puriques et plus particulièrement des didéazapurines, les 5- et 6-azaindoles et les trioxopyrrolopyridines correspondant puis effectué la glycosylation de ces derniers. Dans un second temps, des modulateurs stéroïdiens ont été synthétisés : plusieurs ont montré une bonne activité modulatrice de la Pgp. Enfin, des bras polyéthylènes glycols de longueurs variables ont été reliés à l'adénine pour être ensuite fixés aux stéroïdes via une fonction amide / P-glycoprotein Pgp is a transmembrane transporter protein that protects cells from potentially toxic exogenous compounds. This protein acts as a molecular pump and is overexpressed in cancer cells. So via that mechanism, tumor cells exhibit intrinsic or acquired cross-resistance to diverse chemotherapeutic agents, resulting in the failure of chemotherapy for some cancers. The modulation of the efflux activity of that protein can be one of the mean that could increase anticancer treatments efficiency. Pgp has different substrates sites, two of which are spatially close : the steroid site and the ATP site, the latter is in charge of ATP hydrolysis which give the required energy for the Pgp efflux activity. Our goal was to synthesize bivalent modulators steroids/linker/nucleosides. First we have obtained purine bases analogues and particularly didéazapurines such as 5- and 6-azaindoles and the corresponding trioxopyrrolopyridines, then we have carried out the glycosylation of those compounds. Then, steroids modulators have been synthesized : some of them have shown a good modulation activity toward Pgp. Finally, polyethylene glycols chains with different length have been grafted on adenine so that they could be attached to the steroids via an amide function

Frequency of occurrence of selected single nucleotide polymorphisms of CYP2C8 and MDR1 in the Czech population and their influence on the effect of amiodarone Introduction: Variability in drug response is sometimes conditioned by genetic differences in the metabolism and the transport of drugs. Interindividual differences are often caused by polymorphisms affecting biotransformation activity of enzymes and expression of transporters. In the thesis we paid attention to the cytochrome P450 CYP2C8 and MDR1. First, we described the frequency of occurrence of selected variant alleles CYP2C8 * 2, CYP2C8 * 3 (2 substitution in exon 3 and 8, CYP2C8 and CYP2C8 * 3G416A * 3A1196G), CYP2C8 * 4, CYP2C8 P404A in the healthy Czech population and MDR1 variant alleles in these exons: 26 C3435T, 21 G2677A/T, 12 C1236T a 17 T-76A. Subsequently, we studied the influence of these polymorphisms on effects of amiodarone in the selected group of patients. Methods: We determined genotypes MDR1 a CYP2C8 by PCR-RFLP by using restriction enzymes and specific primers. We determined the frequency of MDR1 genotypes in 189 healthy volunteers and CYP2C8 in 161 healthy subjects. Further we included into the study 63 patients treated with amiodarone for longer than two months. Their treatment was assessed from medical records and...

ABSTRACT/SUMMARY Background: The clinical efficacy of tamoxifen therapy may be modified by the drug-metabolizing enzymes and transporting molecules involved into the pharmacokinetics of tamoxifen. The aim of this study was to evaluate the association of CYP2D6, ABCB1 polymorhisms and comedication with efficacy and safety of tamoxifen treatment. Methods: Totally 258 women with hormonal positive breast carcinoma were retrospectively evaluated in relation to CYP2D6, ABCB1 polymorphisms and comedication. Results: CYP2D6 polymorphisms or co-medication affecting CYP2D6 activity demonstrated no statistically significant effect on the efficacy of tamoxifen therapy or adverse event incidence; there was only a trend towards shortening the time to event (TTE) in CYP2D6 poor metabolizers. ABCB1 polymorphism rs2032582 was not associated with clinical outcomes, while a trend towards an increase of TTE in variant allele carriers was noted. The ABCB1 polymorphism rs1045642 demonstrated statistical significance in premenopausal patients (p = 0.0012, HR 0.69 (95% CI 0.21 to 2.31), and its significant association was noted with gynaecological /vasomotor adverse events (p = 0.0221, HR = 1.0588), with no evidence of the influence on the incidence and onset of venous complications. Conclusions: Although this work did not show...

INTRODUÇÃO: O fenótipo de resistência a drogas é caracterizado pela superexpressão das proteínas da família ABC (ATP-Binding Cassette). A Pglicoproteína (P-gp), codificada pelo gene ABCB1, é uma das bombas de efluxo mais estudadas, como agente interferente no tratamento de diversos tipos de câncer, seguida pela proteína MRP1 (Multidrug Resistance-related Protein 1), transcrita pelo gene ABCC1. Estudos recentes relacionaram a atuação da proteína LRP (Lung Resistance Protein) a estas bombas, devido sua alta expressão em tumores com fenótipo resistente. Em contrapartida, estes transportadores também exercem funções fisiológicas contra metabólitos, compostos citotóxicos e teratogênicos, em diversos tecidos normais como rins, fígado, intestino e célulastronco. As proteínas ABC são consideradas marcadores específicos das célulastronco hematopoiéticas, porém, ainda são pouco descritas nas células-tronco mesenquimais (CTM). A medula óssea (MO) é a fonte mais bem descrita de CTM adultas, cujas propriedades são conhecidas e utilizadas na aplicação clínica. Entretanto, recentemente células-tronco de origem fetal têm criado expectativas e o líquido amniótico (LA) apontado como fonte promissora deste tipo celular, que por sua vez, é pouco estudada acerca da atuação das bombas ABC. Sendo assim, o presente estudo visou caracterizar a expressão da P-gp, MRP1 e LRP em célulastronco mesenquimais humanas do líquido amniótico e medula óssea. MÉTODOS: Foram isoladas CTM de amostras do LA e MO, caracterizadas através de citometria de fluxo, ensaios de diferenciação em tecidos mesenquimais in vitro e expressão dos genes de indiferenciação Oct-4 e Nanog por RT-PCR. Verificou-se também a presença da P-gp através da técnica de imunocitoquímica e a sua resistência frente a diferentes concentrações de doxorrubicina (DOX) através do ensaio de MTT, foram utilizadas como controles as células MES-SA e MES-DX (sarcoma uterino respectivamente sensível e sua variante resistente à DOX). Para avaliar o funcionamento da P-gp, foi feito ensaio de exclusão do corante Rhodamina 123 (Rh 123) por meio de citometria de fluxo, com ou sem bloqueio da P-gp utilizando verapamil. E por fim, foi verificada a expressão dos genes ABCB1/ABCC1/LRP por meio de PCR em tempo real, nas amostras pré e pós-diferenciações adipogênica, osteogênica e condrogênica. RESULTADOS: As CTM, tanto da MO quanto do LA, exibiram respostas semelhantes às células resistentes MES-DX e expressam a Pgp de forma homogênea nas suas populações. O ensaio de exclusão da Rh 123 demonstrou dinâmicas de efluxo do corante semelhantes entre as células-tronco do LA e as MES-DX, com e sem a presença de verapamil. No entanto, as células da MO apresentaram efluxo crescente e não responderam ao bloqueador verapamil como as outras linhagens. A distribuição da expressão gênica, o ABCB1 se mostrou menor que a do LRP nas amostras de LA indiferenciadas. No entanto a expressão do ABCB1 nas amostras de LA foi maior em comparação às amostras de MO indiferenciadas. Não houve seignificância estatística na comparação da expressão gênica antes e depois das diferenciações adipogênica e osteogênica. CONCLUSÃO: As CTM são resistentes ao quimioterápico doxorrubicina, mas, possuem baixa expressão do ABCB1. Portanto, as CTM podem possuir outro mecanismo, como a MRP1 e LRP, atuando no mecanismo de resistência à DOX, além da P-gp / BACKGROUND: The drug resistance phenotype is characterized by ABC (ATPBinding Cassette) family proteins overexpression. The P-glycoprotein (P-gp) codified by ABCB1 gene is one of the most studied efflux pumps such as interfering agent in cancer treatment followed by MRP1 (Multidrug Resistance-related protein 1) transcribed by ABCC1 gene. Recent studies have linked the LRP (Lung Resistance Protein) to these pumps activities because of its high expression in resistant cancers. Though these transporters also have physiological functions against metabolites, cytotoxic and teratogenic compounds in normal tissues as kidneys, liver, intestine and stem cells. ABC proteins are considered hematopoietic stem cells specific markers but are poorly described in mesenchymal stem cells (MSC). Bone marrow (BM) is the best characterized adult MSC source its properties are well known and used in clinical application. However recently fetal stem cells has raised expectations and amniotic fluid (AF) is a promising source of this cell type which in turn is scarce regarding about presence and activity of the ABC pumps. The aim of this study was characterize the P-gp, MRP1 and LRP expression in human mesenchymal stem cells from amniotic fluid and bone marrow. METHODS: Mesenchymal stem cells were isolated from AF and BM and characterized by flow cytometry, in vitro mesenchymal differentiation assays, Oct-4 and Nanog genes expression by RT-PCR. The P-gp presence were found over immunocytochemical technique and its activity against different concentrations of doxorubicin (DOX) by MTT assay which were used as control cells MES-DX and MES-SA (uterine sarcoma respectively resistant and susceptible to DOX). The P-gp was evaluated in Rhodamine 123 (Rh 123) dye exclusion through flow cytometry with or without blocking P-gp from verapamil. Finally was observed ABCB1/ABCC1/LRP genes expression by real time PCR after and before adipogenic, osteogenic and chondrogenic differentiation. RESULTS: BM and AF MSC showed the same response of the DOX resistant cells MES-DX and express P-gp homogeneously though their populations. The Rh 123 dye exclusion assay demonstrated that the AF stem cells efflux dynamics are similar to the MES-DX with and without the presence of verapamil. However BM MSC showed crescent efflux and no response to verapamil as the other cells. The ABCB1 gene was less expressed than LRP in undifferentiated AF MSC. No difference was found in gene expression before osteogenic and adipogenic differentiation. CONCLUSION: MSC have low expression of ABCB1 although are resistant to doxorubicin so other mechanisms such as MRP1 or LRP may be acting to these cells defense in addition to P-gp