RESUMO
Multidrug resistance (MDR) and induction of metastasis are some of the puzzles encountered during cancer chemotherapy. The MDR phenotype is associated with overexpression of ABC transporters, involved in drug efflux. Metastasis originates from the epithelial-mesenchymal transition (EMT), in which cells acquire a migratory phenotype, invading new tissues. ABC transporters' role during EMT is still elusive, though cells undergoing EMT exhibit enhanced ABCB1 expression. We demonstrated increased ABCB1 expression but no change in activity after TGF-ß-induced EMT in A549 cells. Moreover, ABCB1 inhibition by verapamil increased snail and fibronectin expression, an event associated with upregulation of ABCB1, evidencing coincident cell signaling pathways leading to ABCB1 and EMT-related markers transcription, rather than a direct effect of transport. Additionally, for the first time, increased ABCC1 expression and activity was observed after EMT, and use of ABCC1 inhibitors partially inhibited EMT-marker snail, although increased ABCC1 function translated into collateral sensibility to daunorubicin. More investigations must be done to evaluate the real benefits that the gain of ABC transporters might have on the process of metastasis. Considering ABCC1 is involved in the stress response, affecting intracellular GSH content and drug detoxification, this transporter could be used as a therapeutic target in cancer cells undergoing EMT.
Assuntos
Transição Epitelial-Mesenquimal , Neoplasias , Humanos , Subfamília B de Transportador de Cassetes de Ligação de ATP/genética , Transportadores de Cassetes de Ligação de ATP/metabolismo , Linhagem Celular Tumoral , Resistência a Múltiplos Medicamentos , Resistencia a Medicamentos Antineoplásicos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Neoplasias/tratamento farmacológico , Neoplasias/genética , Fator de Crescimento Transformador betaRESUMO
Recently, a link between the biological activity of CD73 in solid tumors and multidrug resistance protein (MRP) has been proposed. Cisplatin (CP) is the most widely used anticancer agent to treat advanced and recurrent cervical cancer (CC). However, multidrug resistance protein-1 (MRP1) is overexpressed in approximately 85% of these tumors and has been strongly associated with cisplatin resistance (CPR). In this study, we examine the involvement of CD73 and the interaction of adenosine (ADO) with its receptors (ARs) in MRP1 expression in CC cells. We found that ADO positively modulates MRP1 expression in CC cells in a dose-dependent manner. The inhibition of CD73 expression with a CD73-targeted siRNA and A2AR blockade with the selective antagonist ZM241385 significantly decreased MRP1 expression and the extrusive capacity of CC cells, making them significantly more sensitive to CP treatment than cancer cells treated with MK-751, a specific MRP1 inhibitor. These results suggest CD73 inhibition or blocking ADO signaling through A2AR could be strategies to reverse CPR in patients with advanced or recurrent CC, which is characterized by very low response rates to CP (10%-20%).
Assuntos
Neoplasias do Colo do Útero , Feminino , Humanos , Membro 1 da Subfamília B de Cassetes de Ligação de ATP , Cisplatino/farmacologia , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Neoplasias do Colo do Útero/tratamento farmacológicoRESUMO
The discovery of predictive biomarkers in metastatic colorectal cancer (mCRC) is essential to improve clinical outcomes. Recent data suggest a potential role of circulating tumor cells (CTCs) as prognostic indicators. We conducted a follow-on analysis from a prospective study of consecutive patients with mCRC. CTC analysis was conducted at two timepoints: baseline (CTC1; before starting chemotherapy), and two months after starting treatment (CTC2). CTC isolation/quantification were completed by ISET® (Rarecells, France). CTC expressions of drug resistance-associated proteins were evaluated. Progression-free survival (PFS) and overall survival (OS) were estimated by the Kaplan-Meier method. Seventy-five patients were enrolled from May 2012 to May 2014. A CTC1 cut-off of >1.5 CTCs/mL was associated with an inferior median OS compared to lower values. A difference of CTC2-CTC1 > 5.5 CTCs/mL was associated with a reduced median PFS. By multivariate analysis, CTC1 > 1.5 CTCs/mL was an independent prognostic factor for worse OS. Multi-drug resistance protein-1 (MRP-1) expression was associated with poor median OS. CTC baseline counts, kinetics, and MRP-1 expression were predictive of clinical outcomes. Larger studies are warranted to explore the potential clinical benefit of treating mCRC patients with targeted therapeutic regimens guided by CTC findings.
RESUMO
Lung cancer is the most common neoplasm and the primary cause-related mortality in developed and in most of nondeveloped countries. Epidemiological studies have demonstrated that even at low arsenic doses, the lungs are one of the main target organs and that chronic arsenic exposure has been associated with an increase in lung cancer development. Among the risk factors for cancer, arsenic methylation efficiency (As3MT) and the clearance of arsenic from cells by two members of the ATP-binding cassette (ABC) transporter family (multidrug resistance protein 1 [MRP1] and P-glycoprotein [P-gp]) play an important role in processing of arsenic and decreasing its intracellular levels. This study aimed to evaluate the association between chronic exposure to arsenic with polymorphism of three proteins involved in arsenic metabolism and efflux of the metalloid in subjects with lung cancer. Polymorphism in As3MT, MRP1, and P-gp modified the arsenic metabolism increasing significantly the AsV urinary levels. A significant association between MRP1 polymorphisms with an increase in the risk for cancer was found. The high inorganic arsenic urinary levels registered in the studied subjects suggest a reduction in the efficiency of As3MT, MRP1, and P-gp firstly because of gene polymorphisms and secondarily because of high internal inorganic arsenic levels. MRP1 polymorphism was associated with a twofold increase in the risk of lung cancer.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/genética , Arsênio/metabolismo , Neoplasias Pulmonares/induzido quimicamente , Neoplasias Pulmonares/genética , Metiltransferases/genética , Proteínas Associadas à Resistência a Múltiplos Medicamentos/genética , Polimorfismo Genético/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Arsênio/análise , Arsênio/urina , Estudos de Coortes , Estudos Transversais , Água Potável/análise , Exposição Ambiental , Feminino , Genótipo , Humanos , Neoplasias Pulmonares/epidemiologia , Masculino , Metilação , México/epidemiologia , Pessoa de Meia-Idade , Fatores de Risco , Inquéritos e Questionários , Adulto JovemRESUMO
Cancer stem cells show epigenetic plasticity and intrinsic resistance to anti-cancer therapy, rendering capable of initiating cancer relapse and progression. Transcription factor OCT-4 regulates various pathways in stem cells, but its expression can be regulated by pseudogenes. This work evaluated how OCT4-PG1 pseudogene can affect OCT-4 expression and mechanisms related to the multidrug resistance (MDR) phenotype in FEPS cells. Considering that OCT-4 protein is a transcription factor that regulates expression of ABC transporters, level of gene expression, activity of ABC proteins and cell sensitivity to chemotherapy were evaluated after OCT4-PG1 silencing. Besides we set up a STRING network. Results showed that after OCT4-PG1 silencing, cells expressed OCT-4 gene and protein to a lesser extent than mock cells. The gene and protein expression of ABCB1, as well as its activity were reduced. On the other hand, ALOX5 and ABCC1 genes was increased even as the activity of this transporter. Moreover, the silencing cells become sensitive to two chemotherapics tested. The network structure demonstrated that OCT4-PG1 protein interacts directly with OCT-4, SOX2, and NANOG and indirectly with ABC transporters. We conclude that OCT4-PG1 pseudogene plays a key role in the regulation OCT-4 transcription factor, which alters MDR phenotype in the FEPS cell line.
Assuntos
Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Fator 3 de Transcrição de Octâmero/genética , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Transportadores de Cassetes de Ligação de ATP/genética , Araquidonato 5-Lipoxigenase/metabolismo , Linhagem Celular Tumoral , Resistência a Múltiplos Medicamentos , Resistencia a Medicamentos Antineoplásicos , Células-Tronco Embrionárias/metabolismo , Expressão Gênica , Inativação Gênica/fisiologia , Humanos , Células K562 , Leucemia Mielogênica Crônica BCR-ABL Positiva/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Células-Tronco Neoplásicas/metabolismo , Fenótipo , Pseudogenes , Fatores de Transcrição SOXB1/metabolismoRESUMO
BACKGROUND: Proteins that belong to the ATP-binding cassette superfamily include transporters that mediate the efflux of substrates from cells. Among these exporters, P-glycoprotein and MRP1 are involved in cancer multidrug resistance, protection from endo and xenobiotics, determination of drug pharmacokinetics, and the pathophysiology of a variety of disorders. OBJECTIVE: To review the information available on ATP-binding cassette exporters, with a focus on Pglycoprotein, MRP1 and related proteins. We describe tissue localization and function of these transporters in health and disease, and discuss the mechanisms of substrate transport. We also correlate recent structural information with the function of the exporters, and discuss details of their molecular mechanism with a focus on the nucleotide-binding domains. METHODS: Evaluation of selected publications on the structure and function of ATP-binding cassette proteins. CONCLUSIONS: Conformational changes on the nucleotide-binding domains side of the exporters switch the accessibility of the substrate-binding pocket between the inside and outside, which is coupled to substrate efflux. However, there is no agreement on the magnitude and nature of the changes at the nucleotide- binding domains side that drive the alternate-accessibility. Comparison of the structures of Pglycoprotein and MRP1 helps explain differences in substrate selectivity and the bases for polyspecificity. P-glycoprotein substrates are hydrophobic and/or weak bases, and polyspecificity is explained by a flexible hydrophobic multi-binding site that has a few acidic patches. MRP1 substrates are mostly organic acids, and its polyspecificity is due to a single bipartite binding site that is flexible and displays positive charge.
Assuntos
Membro 1 da Subfamília B de Cassetes de Ligação de ATP/metabolismo , Transportadores de Cassetes de Ligação de ATP/metabolismo , Subfamília B de Transportador de Cassetes de Ligação de ATP/metabolismo , Transportadores de Cassetes de Ligação de ATP/química , Sítios de Ligação , Humanos , Conformação Proteica , Relação Estrutura-AtividadeRESUMO
Multidrug resistance-associated proteins (MRP) 1 and 2 belong to the ABC (ATP-Binding Cassette) transporters. These transport proteins are involved in the removal of various drugs and xenobiotics, as well as in multiple physiological, pathological, and pharmacological processes. There is a strong correlation between different polymorphisms and their clinical implication in resistance to antiepileptic drugs, anticancer, and anti-infective agents. In our study, we evaluated exon regions of MRP1 (ABCC1)/MRP2 (ABCC2) in a Colombian cohort of healthy subjects to determine single nucleotide polymorphisms (SNPs) and to determine the allelic and genomic frequency. Results showed there are SNPs in our population that have been previously reported for both MRP1/ABCC1 (rs200647436, rs200624910, rs150214567) and MRP2/ABCC2 (rs2273697, rs3740066, rs142573385, rs17216212). Additionally, 13 new SNPs were identified. Evidence also shows a significant clinical correlation for polymorphisms rs3740066 and rs2273697 in the transport of multiple drugs, which suggests a genetic variability in regards to that reported in other populations.
RESUMO
Alteration of multidrug resistance-associated protein-1 (MRP1) expression has been associated with certain lung diseases, and this protein may be pivotal in protecting the lungs against endogenous or exogenous toxic compounds. The aim of this study was to evaluate and compare the expression of MRP1 in bronchoalveolar cells from subjects with and without lung cancer who had been chronically exposed to arsenic through drinking water. MRP1 expression was assessed in bronchoalveolar cells in a total of 102 participants. MRP1 expression was significantly decreased in those with arsenic urinary levels >50 µg/L when compared with the controls. In conclusion, chronic arsenic exposure negatively correlates with the expression of MRP1 in BAL cells in patients with lung cancer.
Assuntos
Arsênio/toxicidade , Líquido da Lavagem Broncoalveolar , Neoplasias Pulmonares/metabolismo , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Adulto , Idoso , Arsênio/urina , Estudos de Casos e Controles , Água Potável , Exposição Ambiental/efeitos adversos , Feminino , Humanos , Masculino , México , Pessoa de Meia-IdadeRESUMO
P-Glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) are efflux pumps responsible for the MDR phenotype (multidrug resistance). In this work, we will investigate the immunohistochemical expression of P-gp and MRP1 in 24 tissue samples from dogs with Leishmania infantum (syn. L. chagasi) and evaluate whether canine visceral leishmaniasis (CVL) induces MDR in dogs. The expectation is that the results obtained from this research may offer prospects for a safer and more effective therapeutic approach for this disease. Findings illustrated that the expression of P-gp in CVL affected tissue samples (p<0.05) was greater than those of the control group, with the exception of skin tissue samples which did not differ. However, only the adrenal gland samples affected by LVC expressed significantly more MRP1 (p<0.05) than the control group. The expressions of P-gp and MRP1 were lower (p<0.05) in LVC positive spleen and skin samples in comparison with other tissues. These results suggest that the lack of a parasitological cure could be due to the high expression of P-gp and MRP1 in the liver, adrenal glands, and kidneys, which block the action of parasitacidal drugs recommended in treatment.
Glicoproteína-P (gp-P) e proteína de resistência a múltiplas drogas (MRP1) são bombas de efluxo responsáveis pelo fenótipo MDR (resistência a múltiplas drogas). Neste trabalho, investigamos a expressão por imuno-histoquímica da gp-P e MRP1 em amostras de tecidos de 24 cães com Leishmania infantum (syn. L. chagasi), e avaliamos se a leishmaniose visceral canina (LVC) induz a MDR em cães, tendo a expectativa de que os resultados obtidos possam oferecer perspectivas de uma abordagem terapêutica mais segura e eficaz nesta doença. Os resultados mostraram que a expressão da gp-P nas amostras de cães com LVC foi maior (p<0,05) em todos os tecidos em comparação ao grupo controle, com exceção da pele, que não diferiu. Entretanto, apenas as glândulas adrenais nas amostras LVC, em comparação as controle, expressaram significativamente mais MRP1 (p<0,05). As expressões de gp-P e MRP1 foram menores (p<0,05) no baço e pele das amostras LVC positivas, em comparação aos demais tecidos. Os resultados sugerem que a falha da cura parasitológica poderia ser devido à alta expressão da gp-P e MRP1 no fígado, adrenal e rins, por impedir a ação parasiticida dos fármacos recomendados no tratamento.
Assuntos
Animais , Cães , Leishmania infantum , Leishmaniose Visceral/veterinária , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/isolamento & purificação , Proteínas Associadas à Resistência a Múltiplos Medicamentos/isolamento & purificação , Imuno-Histoquímica/veterináriaRESUMO
P-Glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) are efflux pumps responsible for the MDR phenotype (multidrug resistance). In this work, we will investigate the immunohistochemical expression of P-gp and MRP1 in 24 tissue samples from dogs with Leishmania infantum (syn. L. chagasi) and evaluate whether canine visceral leishmaniasis (CVL) induces MDR in dogs. The expectation is that the results obtained from this research may offer prospects for a safer and more effective therapeutic approach for this disease. Findings illustrated that the expression of P-gp in CVL affected tissue samples (p<0.05) was greater than those of the control group, with the exception of skin tissue samples which did not differ. However, only the adrenal gland samples affected by LVC expressed significantly more MRP1 (p<0.05) than the control group. The expressions of P-gp and MRP1 were lower (p<0.05) in LVC positive spleen and skin samples in comparison with other tissues. These results suggest that the lack of a parasitological cure could be due to the high expression of P-gp and MRP1 in the liver, adrenal glands, and kidneys, which block the action of parasitacidal drugs recommended in treatment.(AU)
Glicoproteína-P (gp-P) e proteína de resistência a múltiplas drogas (MRP1) são bombas de efluxo responsáveis pelo fenótipo MDR (resistência a múltiplas drogas). Neste trabalho, investigamos a expressão por imuno-histoquímica da gp-P e MRP1 em amostras de tecidos de 24 cães com Leishmania infantum (syn. L. chagasi), e avaliamos se a leishmaniose visceral canina (LVC) induz a MDR em cães, tendo a expectativa de que os resultados obtidos possam oferecer perspectivas de uma abordagem terapêutica mais segura e eficaz nesta doença. Os resultados mostraram que a expressão da gp-P nas amostras de cães com LVC foi maior (p<0,05) em todos os tecidos em comparação ao grupo controle, com exceção da pele, que não diferiu. Entretanto, apenas as glândulas adrenais nas amostras LVC, em comparação as controle, expressaram significativamente mais MRP1 (p<0,05). As expressões de gp-P e MRP1 foram menores (p<0,05) no baço e pele das amostras LVC positivas, em comparação aos demais tecidos. Os resultados sugerem que a falha da cura parasitológica poderia ser devido à alta expressão da gp-P e MRP1 no fígado, adrenal e rins, por impedir a ação parasiticida dos fármacos recomendados no tratamento.(AU)
Assuntos
Animais , Cães , Membro 1 da Subfamília B de Cassetes de Ligação de ATP/isolamento & purificação , Proteínas Associadas à Resistência a Múltiplos Medicamentos/isolamento & purificação , Leishmania infantum , Leishmaniose Visceral/veterinária , Imuno-Histoquímica/veterináriaRESUMO
The human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus associated with neoplasias and inflammatory diseases, such as adult T-cell leukemia/lymphoma and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-1-infected individuals present a spontaneous T lymphocyte proliferation. This phenomenon is related to the HTLV-1-proviral load and the persistence of the infection. Viral proteins induce many cellular mediators, which can be associated with the abnormal cellular proliferation. The intracellular levels of glutathione (GSH) are important to modulate the cellular proliferation. The aim of this study was to investigate the correlation between the modulation of intracellular GSH levels and the spontaneous lymphocyte proliferation during the HTLV-1 infection. Intracellular GSH level can be modulated by using dl-buthionine-[S,R]-sulfoximine (BSO, GSH synthesis inhibitor) and N-acetylcysteine (NAC, peptide precursor). Our results demonstrated that BSO was capable of inducing a decrease in the spontaneous proliferation of PBMC derived from HTLV-1 carriers. On the other hand, the GSH precursor induces an increase in mitogen-stimulated cellular proliferation in infected and uninfected individuals. Similar results were observed by the inhibition of ABCC1/MRP1 protein, augmenting the mitogen-induced proliferation. This effect can be related with an increase in the GSH levels since ABCC1/MRP1 transports GSH to the extracellular medium. There was a significant difference on the expression of CD69 and CD25 molecules during the lymphocyte activation. We did not observe any alterations on CD25 expression induced by BSO or NAC. However, our results demonstrated that NAC treatment induced an increase in CD69 expression on unstimulated CD8(+) T lymphocytes obtained from HTLV-1 infected individuals, healthy donors and HTLV carriers. Therefore, our results suggest that the cellular proliferation promoted by the infection with HTLV-1 and the activation phenotype of CD8(+) T lymphocytes can be regulated by changing the intracellular GSH levels; suggesting the modulation of these intracellular levels as a new approach for the treatment of pathologies associated with the HTLV-1 infection.
Assuntos
Linfócitos T CD8-Positivos/imunologia , Portador Sadio/imunologia , Glutationa/metabolismo , Infecções por HTLV-I/imunologia , Vírus Linfotrópico T Tipo 1 Humano/imunologia , Acetilcisteína/metabolismo , Adulto , Idoso , Linfócitos T CD8-Positivos/virologia , Proliferação de Células , Células Cultivadas , Feminino , Regulação da Expressão Gênica/imunologia , Humanos , Espaço Intracelular/metabolismo , Ativação Linfocitária , Masculino , Metionina Sulfoximina/análogos & derivados , Metionina Sulfoximina/metabolismo , Pessoa de Meia-Idade , Proteínas Associadas à Resistência a Múltiplos Medicamentos/metabolismo , Adulto JovemRESUMO
"A leucemia mielóide crônica (LMC) é caracterizada pela presença da translocação t(9:22) que codifica a proteína quimérica oncogênica BCR-ABL. Imatinibe é uma droga alvo-específica que inibe a atividade tirosina quinase (TK) da proteína BCR-ABL. Entretanto, os níveis intracelulares do imatinibe podem ser alterados pelas proteínas transportadoras de efluxo de drogas: glicoproteína P (Pgp), proteína da resistência em câncer de mama (BCRP) e proteína relacionada à resistência à múltiplas drogas (MRP1), assim como a proteína transportadora de influxo de drogas (OCT1). O objetivo do presente estudo foi analisar a participação dessas proteínas, isoladamente ou em associação, na resistência ao imatinibe em linhagens celulares e células de pacientes com LMC. Para análise da atividade das proteínas transportadoras de efluxo, foi utilizado o fluorocromo rodamina-123 associado ao modulador ciclosporina-A (Rho+CSA) e o pheophorbide A associado ao fumitremorgin C (PhA+FTC), ambos através de citometria de fluxo. A análise dos RNAm dos genes ABCB1, ABCG2 e SLC22A1 que codificam as proteínas Pgp, BCRP e OCT1, respectivamente, foi realizada por PCR em tempo real. A inibição da TK BCR-ABL foi mensurada através dos níveis de fosforilação de CrkL (pCrkL), seu principal alvo de ativação. Observamos uma maior positividade para o ensaio Rho+CSA nas amostras que expressavam Pgp comparada com as que expressavam MRP1, sugerindo menor atividade dessa proteína em pacientes com LMC, ou ainda que tal ensaio possa ser menos específico para a atividade da MRP1. O ensaio PhA+FTC foi capaz de identificar a atividade da proteína BCRP em linhagens celulares e células de pacientes. Níveis reduzidos dos RNAm ABCB1 e SLC22A1, mas não do RNAm ABCG2, foram observados quando comparados com as amostras de indivíduos saudáveis. Não houve correlação entre os níveis da proteína Pgp e do RNAm ABCB1. A expressão de Pgp foi detectada na maioria das amostras de LMC, independente da fase da doença, e não foi associada com o prognóstico desfavorável. Variações nos níveis de expressão da Pgp foram observadas durante a evolução da LMC e relacionadas com o tratamento prévio. O imatinibe foi capaz de aumentar a expressão da Pgp, assim como os níveis do RNAm ABCB1 na linhagem K562-Lucena 1, Pgp+. Além disso, observamos uma maior redução de pCrkL e um maior percentual de morte celular nas células K562, Pgp-, quando comparadas à K562-Lucena 1, evidenciando um possível papel do imatinibe como substrato para a Pgp. Este fármaco também demonstrou ter potencial para funcionar como agente modulador da bomba de efluxo, uma vez que impediu o exporte de Rho das células K562-Lucena 1. Amostras de pacientes resistentes ao imatinibe exibiram altos níveis de atividade das proteínas transportadoras de efluxo de drogas (ensaio Rho+CSA). Nossos dados mostram que a atividade e/ou expressão dos transportadores de efluxo e influxo de drogas encontram-se alterados na maioria dos pacientes com LMC, porém não há correlação com a resposta ao imatinibe e o prognóstico na LMC. Entretanto, o conjunto dos resultados sugere um papel para a Pgp na resistência in vitro ao imatinibe"(AU)
"Chronic myeloid leukemia (CML) is characterized by the presence of the t(9:22) encoding the BCR-ABL chimeric oncogenic protein. Imatinib is a target specific drug that inhibits the activity of the tyrosine kinase (TK) protein BCR-ABL. However, imatinib intracellular concentration may be altered by transporter proteins. It was described that efflux proteins, P-glycoprotein (Pgp), breast cancer resistance protein (BCRP) and multidrug resistance related protein (MRP1), and the influx protein, the organic cation transporter protein (OCT1) may contribute for imatinib clinical resistance. The aim of this study was to evaluate the role of these proteins in imatinib resistance in cell lines and leukemic cells from CML patients. To analyze the activity of the efflux transporter proteins, fluorochrome rhodamine-123 associated with the modulator cyclosporin A (Rho+CSA) and pheophorbide A associated with fumitremorgin C (PhA+FTC) were used by flow cytometry. Analysis of ABCG1, ABCG2 and SLC22A1 genes, that encode the Pgp, BCRP and OCT1 proteins, respectively, was performed by real time PCR. The inhibition of BCR-ABL TK was measured by the levels of CrkL phosphorylation (pCrkL), its main target of activation. We observed a higher positivity for Rho+CSA assay in samples expressing Pgp, when compared with the ones expressing MRP1. These results suggest that patients with CML have lower activity of this protein, or this assay might be less specific to indicate the activity of MRP1. The PhA+FTC assay was able to identify BCRP activity in cell lines and cells from patients. Reduced levels of ABCB1 and SLC22A1, but not ABCG2 mRNA were observed when compared with samples from healthy individuals. There was no correlation between the levels of Pgp protein and ABCB1 mRNA. Pgp expression was detected in most samples of CML, regardless of disease stage and was not associated with poor prognosis. Changes in Pgp expression levels have been observed during the development of CML and were related to pretreatment. Imatinib was able to increase Pgp expression as well as ABCB1 mRNA levels in Pgp+ K562Lucena 1 cells. Moreover, we observed a greater pCrkL reduction and a higher percentage of cell death in Pgp- K562 cells compared to K562-Lucena 1, indicating a possible role of imatinib as a Pgp substrate. This drug has also been shown to have potential as an efflux pump modulating agent, once efflux of Rho was prevented in K562-Lucena 1. Imatinib resistant patient samples exhibited high levels of efflux transporter proteins activity (Rho+CSA assay). Our data show that the activity and / or expression of influx and efflux transporters of drugs are altered in most patients with CML, but no correlation with prognosis and response to imatinib in CML was observed. However, our results suggest a role for Pgp in imatinib resistance"(AU)