Les inhibiteurs de tyrosine kinases (ITKs) sont une nouvelle classe thérapeutique ayant connu un grand essor ces dix dernières années. Inhibiteurs compétitifs de l’adénosine triphosphate (ATP), ils sont utilisés dans le traitement de nombreux cancers dans lesquels une dérégulation de tyrosine kinases a été mise en évidence. Malgré une efficacité prouvée, des cas de résistance sont rapportés, en particulier avec l’exemple de la leucémie myéloïde chronique (LMC) et le traitement par ITK. Cette variabilité inter-individuelle peut être due à des mécanismes de résistance propre de la cellule tumorale ou à des variations dans les paramètres pharmacocinétiques de la molécule. De nombreuses études ont analysé l’impact de polymorphismes (SNPs) dans des gènes codants pour les déterminants pharmacocinétiques et pharmacodynamiques des ITKs. Nous avons analysé l’impact de SNPs sur l’obtention de la réponse moléculaire majeure à 1 an dans 2 cohortes de patients atteints de LMC et traités par imatinib. C1236T, G2677T/A et C3435T, 3 SNPs du gène MDR-1 codant pour la glycoprotéine P et les SNPs de la région codante du gène SLC22A1 à l’origine du transporteur d’influx hOCT1. L’impact bénéfique de l’allèle 1236T ou haplotype *4 et l’impact péjoratif de l’allèle 2677G ou haplotype *1, retrouvés dans la 1ère cohorte n’ont pas été retrouvés dans la 2ième cohorte suggérant un impact mineur voire nul de ces derniers sur la réponse à l’imatinib. L’impact des SNPs de SLC22A1 observés dans la 2ième cohorte nécessite d’être confirmé. Des travaux supplémentaires à plus grande échelle, selon des critères nécessitant d’être harmonisés, sont nécessaires avant d’espérer pouvoir aboutir à une «médecine personnalisée» pour l’imatinib mais également de façon générale pour l’ensemble des ITKs. / Tyrosine kinases inhibitors (TKIs) are a new class of drugs having bloomed over the past decade. As competitive inhibitors of the adenosine triphosphate, they are used in the treatment of many cancers in which deregulation of tyrosine kinases has been demonstrated. In spite of dramatic efficacy, cases of resistance have been reported particularly with chronic myeloid leukemia (CML) and TKI treatment. This inter-individual variability may be due to mechanisms of intrinsic resistance of tumor cells or changes in the pharmacokinetic parameters of the molecule. Numerous studies have analyzed the impact of polymorphisms (SNPs) in genes coding for pharmacokinetic and pharmacodynamic determinants. We analyzed the impact of SNPs on major molecular response at 1 year in 2 cohorts of patients with CML treated with imatinib. C1236T, G2677T/A, C3435T, three SNPs in the MDR-1 gene encoding P-glycoprotein and SNPs in the coding region of the SLC22A1 gene encoding hOCT1. The protective impact of the 1236T allele or haplotype*4 and the pejorative impact of the 2677G allele or haplotype*1, found in the 1st cohort, were not replicated in the 2nd cohort, suggesting minor or no impact on the response to imatinib. The impact of SLC22A1 SNPs observed in the 2nd cohort needs to be confirmed. Further works on a larger cohort, according to criteria that need to be harmonized, are necessary before we reach a “personalized medicine” for imatinib but also for all TKIs

La chimiorésistance des cancers est caractérisée par une résistance pléïotropique à de multiples médicaments. Ce mécanisme est en partie causé par la surexpression des transporteurs à «ATP binding cassette» (Pgp, MRP1, BCRP…). Les inhibiteurs connus de ces transporteurs comme la cyclosporine A, le vérapamil et le RU486 sont toxiques à doses élevées. Dans cette étude, de nombreux dérivés stéroïdiens synthétisés au laboratoire à base de progestérone ou d’acides biliaires ont été évalués pour leur capacité à inhiber les transporteurs ABC et plus spécifiquement les fonctions de transport par la Pgp ou la BCRP. Plusieurs de ces dérivés synthétisés se sont avérés capables de restaurer complètement la sensibilité des cellules résistantes d’une manière plus importante que la cyclosporine A in vitro. De plus, le meilleur des nos dérivés testés s’est avéré capable in vivo de diminuer significativement la progression tumorale de xénogreffe sur les souris et d’augmenter la durée de survie des souris. Cette étude a ainsi permis d’ouvrir la voie au développement de nouveaux dérivés stéroïdiens peu toxiques ayant la capacité d’inhiber le phénotype MDR et de restaurer la sensibilité des cellules cancéreuses vis-à-vis des agents chimiothérapeutiques utilisés, avec un perspective d’application clinique / The chemoresistance of cancer is characterized by a pleitropic resistance to multiple drugs. This mechanism is partly caused by the overexpression of “ATP Binding Cassette” transporters (Pgp, MRP1, BCRP…). Known inhibitors of these transporters such as cyclosporin A, verapamil and RU486 rather toxic at high doses. In this study, many steroid derivatives synthesized in the laboratory (from progesterone or bile acid precursor) to bind and inhibit ABC transporters, specifically the transport by Pgp or BCRP. Several of these synthetic derivatives were able to completely restore the sensivity of the resistant cells compared to cysclosporine A in vitro. In addition, the efficient of these derivatives could, in vivo significantly reduce tumor growth of xenografts on mice and increase survival time of mice. This study opens a route for development of new steroid derivatives with low toxicity, having the ability to reverse the MDR phenotype and restore sensitivity of cancer cells to the chemotherapeutic agents use, with a perspective at clinical use

Au cours des dernières décennies, une augmentation non négligeable du phénomène de résistance aux antibiotiques des bactéries a été observée. Ces bactéries possèdent plusieurs mécanismes de résistance parmi lesquels l’utilisation de transporteurs de type MDR (MultiDrug Resistance) dont certains appartiennent à la famille des transporteurs ABC (ATP-Binding Cassette). Les transporteurs ABC sont des protéines membranaires et ubiquitaires qui possèdent une topologie commune avec deux domaines transmembranaires et deux domaines cytoplasmiques. Les transporteurs ABC de type exportateur permettent le transport de molécules à l’extérieur de la cellule en utilisant l’énergie fournie par l’hydrolyse de l’ATP. PatA-PatB est un transporteur ABC de Streptococcus pneumoniae, un pathogène humain responsable de pneumonies et de méningites. Cette protéine est impliquée dans la résistance de ce pathogène à des antibiotiques de types fluoroquinolones. Pour étudier son mécanisme moléculaire, nous avons optimisé la surexpression fonctionnelle de ce transporteur chez Escherichia coli. Ainsi, nous avons pu caractériser son activité de transport de drogues et son activité d’hydrolyse de nucléotides. Ces expériences ont révélé que PatA-PatB a la particularité d’utiliser préférentiellement le GTP comme source d’énergie, contrairement aux autres membres de cette famille. Afin d’identifier l’origine de cette propriété au niveau moléculaire, des expériences de mutagénèse dirigée ont été effectuées et nous avons ainsi identifié deux simples mutants qui transportent les drogues aussi bien avec du GTP que de l’ATP / The excessive use of antibiotics during the past decades led to the amplification of multidrug resistance in pathogenic bacteria. Bacteria have developed several mechanisms of antibiotic resistance. One of them involves the antibiotic efflux by MDR (MultiDrug Resistance) transporters, some of which belong to the ABC (ATP-Binding Cassette) transporter family. ABC transporter are ubiquitous membrane proteins with a conserved topology comprising four domains : two «TransMembrane Domain» and two cytoplasmic domains named « Nucleotide-Binding Domain ». ABC exporters expel drugs outside the bacteria using the energy of ATP hydrolysis. PatA-PatB is an ABC transporter from Streptococcus pneumoniae, a human pathogen bacterium responsible for pneumonia and meningitis. This protein is involved in S. pneumoniae resistance against fluoroquinolone antibiotics. To study the molecular mechanism, we optimized the functional expression of this transporter in Escherichia coli. Then, we characterized its drug transport activity and its nucleotide hydrolysis activity. These experiments showed that PatA-PatB, in contrast to other members of the ABC superfamily, preferentially uses GTP as energy supply. To identify the origin of this property at a molecular level, mutagenesis experiments were performed and we identified two mutants capable of an even drug transport with ATP and GTP

Drug resistant bacteria pathogen poses a severe threat to human health. Bacterial drug efflux pumps are transporter proteins involved in the export of antibiotics out of cells. Efflux by transporters is one of the major drug resistant mechanisms. Multidrug efflux pumps can transport multiple classes of antibiotics and are associated with bacteria multiple drug resistance (MDR). Overproduction of these pumps reduces susceptibility of bacteria to a variety of antibiotics. MDR regulators are cytoplasmic proteins that control the expression level of MDR transporters in response to the cellular concentration of antibiotics. This thesis research focuses on three main directions in the area of bacteria drug resistance: the structural and functional study of a MDR transporter, the characterization of a novel MDR regulator protein, and the development of a sensing method for the detection of glycopeptide antibiotics. Acriflavine resistance protein B (AcrB) in Escherichia coli belongs to resistance nodulation division (RND) superfamily of efflux transporters. It plays an important role in confering multidrug resistance in Gram-negative bacteria. The functional unit of AcrB is a trimer in vivo. However, the relationship between AcrB trimer stability and functionality remains elusive. In chapter 2, a residue that is critical for AcrB trimerization, Pro 223, was identified. The replacement of Pro 223 by other residues destabilized AcrB trimer, and thus decreased its activity. The loss of transport activity could be partially recovered when the AcrB trimer was stabilized by the introduction of a pair of inter-subunit disulfide bond. In chapter 3, a systematically alanine-scanning study of the producing loop (amino acid residues 211-240) was conducted. Five residues in the loop were found to be important for AcrB activity. These residues form a collar or belt in the loop close to the tip. These mutation studies revealed new insight into the conformation of the loop during AcrB trimerization. In chapter 4, residue Arg 780 was identified to be crucial for the pump function of AcrB. The study results indicated that Pro 223 serves as a “wedge” and Arg 780 as a “lock” via hydrogen bonding between the backbone carbonyl oxygen of Pro 223 and side chain of Arg780. Similar as Pro 223, replacement of Arg 780 by other residues drastically decreased the activity of AcrB. Dissociation of the AcrB trimer also contributed to the decrease of activity. However, the introduction of inter-subunit disulfide bond could not restore the function of the mutant, indicating that Arg 780 plays multiples roles in the operation of AcrB. In chapter 5, a MDR regulator ST1710 from the archaeon Sulfolobus tokodaii, homologous to the multiple-antibiotic resistance repressor (MarR) family bacterial regulators, was characterized in vitro. The binding affinities of ligands and double strand (ds) DNA for ST1710 were measured. The presence of substrates suppressed the interaction between ST1710 and dsDNA, which indicated that ST1710 functioned as a repressor in vivo. Finally, in chapter 6, a direct fluorescence polarization based method for the detection of glycopeptide antibiotics is developed. Briefly, the acetylated tripeptide L-Lys-D-Ala-D-Ala was labeled with a fluorophore (fluorescein isothiocyanate or AlexaFluor 680) to create a peptide probe. The fluorescence polarization signal of the peptide probe increased upon binding with glycopeptide antibiotics in a concentration dependent manner. The detection is highly selective toward glycopeptide antibiotics. The designed method is expected it to have broad applications in both research and clinical settings.

L’objet de ces recherches était de trouver de nouveaux EPIs du système d’efflux AcrAB-TolC dans les groupes de dérivés d’amine de la 5-arylidenehydantoine et de la 5-arylideneimidazolone. Dans la première étape de recherche, 32 nouveaux dérivés ont été obtenus après modification de la structure lead P2.Un screening théorique du risque toxique et la prédiction des propriétés médicamenteuses des composés ont été réalisés en utilisant le programme OSIRIS qui calcule différentes propriétés médicamenteuses pertinentes basées sur la structure planaire de la molécule.Dans l’étape suivante de la recherche, l’activité des composés a été évaluée par des études microbiologiques sur souches d’Enterobacter aerogenes avec différentes expressions de la pompe d’efflux AcrAB. La première étude effectuée était un test de sensibilité pour déterminer les CMI des composés afin de trouver une concentration à laquelle les utiliser avec des antibiotiques sans avoir l’influence de leur activité intrinsèque. Puis l’effet des composés sur la sensibilité des antibiotiques tels que l’acide nalidixique, le chloramphénicol, la doxycycline et l’érythromycine a été étudié. Après, le type de coopération avec les antibiotiques a été déterminé par la construction d’isobologrammes et le calcul de l’index de FIC. Les dernières études microbiologiques réalisées sont des tests d’efflux en temps réel qui utilisent un colorant fluorescent 1,2’-dinaphthylamine et ont permis de suivre directement le fonctionnement de la pompe. L’étude des relations structure-activité souligne le rôle essentiel de la nature amphiphile des EPIs dérivés de groupes arylidene de l’hydantoine et de l’imidazolone. / The purpose of this research was to find new EPIs of the AcrAB-TolC efflux system in groups of amine derivatives of 5-arylidenehydantoin and 5-arylideneimidazolone. In the first stage of the research 32 new derivatives of 5-arylidenehydantoin were obtained as a result of modifications of the lead structure P2. Theoretical screening of the toxicity risk as well as the prediction of drug-like properties of hydantoins/imidazolones synthesised were performed by using the OSIRIS program which calculates various drug-relevant properties based on a planar structure of the molecule.In the next stage of the research the activity of compounds was evaluated in microbiological studies. Strains of Enterobacter aerogenes with different expressions of the AcrAB efflux pump were used. The first study carried out was a susceptibility test determining the MICs of compounds in order to find a concentration that could be used in combination with antibiotics without the influence of an intrinsic antibacterial activity of the compounds. Then the effect of the compounds on bacterial susceptibility to antibiotics such as nalidixic acid, chloramphenicol, doxycycline and erythromycin was examined. After, the type of cooperation with antibiotics was determined based on isobolograms and the FIC index calculated. The last of microbiological studies was the real-time efflux (RTE) assay which used the fluorescent dye 1,2’-dinaphthylamine and allowed the functioning of the pump to be monitored directly. The structure-activity relationship (SAR) analysis emphasized the essential role of the amphiphilic nature of the EPIs from the group of arylidene derivatives of hydantoin and imidazolone.

Background: Risk factors for acquired multidrug resistant tuberculosis (MDR TB) are well described but risk factors of primary MDR TB is understudied. We aimed to 1) assess risk factors for primary MDR TB, including diabetes, and 2) determine if diabetes reduced the rate of sputum culture conversion in patients with primary MDR TB. Methods: From 2011-2014 we conducted a prospective cohort study at the National Center for TB and Lung Disease in Tbilisi, Georgia. Adult (≥35 years) patients with primary TB were eligible. MDR TB was defined as resistance to at least rifampicin and isoniazid. Patients with HbA1c ≥6.5% were defined to have diabetes. Polytomous regression was used to estimate the association of patient characteristics with drug resistance. Cox regression was used to compare the hazard rate of sputum culture conversion in patients with and without diabetes. Results: Among 318 patients, 268 had drug susceptibility test results. Among patients with DST results, 19.4% was primary MDR TB and 13.4% had diabetes. In adjusted analyses, diabetes (aOR 2.51 95%CI 1.00 – 6.31) and lower socioeconomic status (aOR 3.51 95%CI 1.56 – 8.20) were associated with primary MDR TB. Among patients with primary MDR TB, 44 (84.6%) converted sputum cultures to negative. The hazard rate of sputum culture conversion was lower among patients with diabetes (aHR 0.34 95%CI 0.13 – 0.87) and among smokers (aHR 0.16 95%CI 0.04 – 0.61). Conclusions: We found diabetes to be associated with an increased risk of primary MDR TB; both diabetes and smoking were associated with a decreased rate of sputum culture conversion.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Student number:0312412A Faculty of Health Sciences School of Public Health / Management of multidrug-resistant tuberculosis (MDR-TB) is more expensive, lengthy and is associated with less favourable outcomes and more adverse reactions than management of susceptible tuberculosis. The aim of this study was to review the management and treatment outcomes of registered MDR-TB patients hospitalized at Sizwe hospital during a five-year period. A cross-sectional study with both descriptive and analytic features was done on 237 MDR-TB patients hospitalized from the beginning of June 1998 to the end of May 2003. Data were analysed using SPSS version 12 Software. Main outcome measures were interim treatment outcomes at the end of hospitalization period. These outcomes comprised culture conversion rates, time to culture conversion, transfer out, interruption, and death rates. Multiple logistic regression analysis was performed to determine risk factors for poor treatment outcomes. These poor outcomes were defined as treatment interruption, failure and mortality rates. The burden of institutional care for MDR-TB patients in this setting was found to involve high numbers of MDR-TB patients for whom the allocated hospital beds were insufficient. Patients with primary MDR-TB, who had no history of nonadherence to treatment, were paradoxically more likely to be hospitalized shortly after diagnosis. Acquired MDR-TB patients were mostly managed as outpatients immediately after diagnosis only to be hospitalized later due to persistent nonadherence or disease severity. Overall, acquired MDR-TB patients were hospitalized in larger numbers than those with primary disease. This reflects the higher prevalence of acquired MDR-TB compared to primary MDR-TB. Page v Abstract Culture turnaround time was on average 19 days. The overall culture conversion rate of the hospitalized patients was low at 41.9 percent. This low culture conversion rate resulted in protracted hospitalization periods and high interim mortality rates. The mean duration of hospitalization, 3.52 months, correlated favourably with the time interval to the first culture conversion of 2.96 months. Hospitalization did not guarantee the expected adherence to treatment. Surgical interventions were done belatedly with resultant high mortality outcomes. The main reasons given by patients for refusing hospital treatment were visiting traditional healers, solving socioeconomic problems and attending to family matters. A large percentage of hospitalized patients were co-infected with HIV. HIV care and support was incomplete as antiretroviral drugs were not available at the hospital. Among the main findings of the study was the powerful influence HIV status had on poor hospitalization outcomes. Recommendations arising from the study include the need to provide ARVs at the Sizwe hospital. Admission and discharge guidelines aimed at ensuring adequate beds are reserved for deserving patients should be formulated. Continuing education for service providers must be encouraged and rewarded. Infection control procedures at both community and health institution level ought to be vigorously promoted. Patients known to be hopelessly non-adherent should at least be partially hospitalized in the interest of public health.

Após o surgimento e disseminação das β-lactamases de amplo espectro em membros da família Enterobacteriaceae, os antibióticos carbapenêmicos (imipenem, meropenemeertapenem) têm sido considerados a terapia de escolha devido à estabilidade apresentada contra estas enzimas. A desvantagem destes antibióticos é a sua capacidade de induzir resistência aos β-lactâmicos e a outros antibióticos quimicamente não relacionados. O imipenem tem favorecido a indução de cefalosporinases cromossômicas (AmpC) e também tem sido relacionado, in vivo, com a seleção de mecanismos intrínsecos de resistência, contribuindo com o perfil multi -droga resistente (MDR). Esse perfil é freqüentemente associado à diminuição da permeabilidade por alteração na síntese de porinas em conjunto com um aumento da atividade de bombas de efluxo, as quais não permitem o estabelecimento de uma concentração ativa do antibiótico no interior da célula bacteriana. O presente trabalho teve como objetivo avaliar o estabelecimento do perfil MDR em enterobactérias provenientes de isolados clínicos em função da exposição a diferentes concentrações de imipenemin vitro. A seleção do grupo das amostras estudadas foi feito por meio da determinação do perfil de sensibilidade dos isolados, tipagem molecular e ensaio de hidrólise de Imipenem. Nos isolados selecionados para a indução foi realizada numa etapa inicial (etapa basal) a análise de porinas de membrana externa por SDS-PAGE e o estudo de genes codificadores de β-lactamases pela técnica de PCR. O estudo do estabelecimento do perfil MDR foi feito por meio de passagens sucessivas das amostras em meio contendo concentrações sub-inibitórias de imipenem seguido de análise fenotípica (CIM e acúmulo do antibiótico intracelular e SDS-PAGE), e a análise da expressão gênica de genes associados a permeabilidade de membrana (ompC, ompF eAcrA) e genes reguladores(marA e ompR). Após a indução com o imipenem, 77% dos isolados induzidos aumentaram a CIM para os carbapenêmicos, mudando assim o perfil de resistência observado na etapa basal Também foi afetado o perfil de resistência para outros antibióticos não relacionados a β-lactámicos, porém numa percentagem menor. Com relação à alteração da permeabilidade, a perda de porina foi observada apenas para um isolado, no entanto a diminuição na expressão gênica de Omp36 foi significativa desde o começo da indução. A expressão da bomba de efluxoAcrAB foi afetada pela indução com imipenem, aumentando significativamente a expressão de AcrA, enquanto os reguladores estudados, MarA e OmpR tiveram a sua expressão induzida pelo imipenem. Foi possível observar também associação do nível de expressão gênica do regulador MarA com a expressão de AcrA,porém não foi possível observar uma associação estatisticamente significativa deste regulador com o perfil de expressão de OMPs. A indução de OmpR foi associado com um aumento da expressão de RNAm de Omp35, já para Omp36 foi possível observar apenas uma tendência na repressão deste gene. O estudo da resposta destes genes reguladores e determinantes de resistência, em resposta à exposição ao com o imipenem in vitro, permitiu reportar o comportamento molecular da bactéria numa resposta adaptativa no estagio inicial do estabelecimento do fenótipo MDR. A utilização de isolados clínicos com diversos determinantes de resistência permitiu observar a variabilidade nas respostas adaptativas das enterobacterias, o que é fundamental para a compreensão dos mecanismos de adaptação da bactéria e sua contribuição na falha terapêutica. / After emergence and broad dissemination of extended spectrum β-lactamases into the Enterobacteriaceae family, the carbapenemic antibiotics (imipenem, meropenem and ertapenem) have been considered the chosen therapy in the treatment of nosocomial infections by the stability that these antibiotics show to these enzymes. The disadvantage of carbapenems is theirs capacity to induce resistance against β-lactamics and to other chemically unrelated antibiotics. The imipenem has been shown to induce chromosomal cephalosporinases (AmpC) and it was also related, in vivo, with the selection of intrinsic mechanism leading to multi-drug resistance profile (MDR). This profile is usually associated with membrane impermeability due to reduced outer membrane porin synthesis with an incremented activity of efflux pumps, which results in a reduced concentration of antibiotics inside the bacteria. This study aimed to evaluate the establishment of the MDR profile in Enterobacteriaceae from clinical isolates by exposure to different concentrations of imipenem in vitro. The selection of the study group was performed by determination of antibiotic susceptibility profile,molecular typing and hydrolysis assay of imipenem. In the selected isolates submitted to induction, in an initial step (baseline), was performed the outer membrane porin analysis by SDS-PAGE and the gene-specific amplification of B-lactamase enzymes by PCR. The study of the establishment of MDR was performed by progressive passages with subclinical concentrations of imipenem, followed each one by the evaluation of phenotypic profile (MIC, accumulation antibiotic in celland SDS-PAGE) and gene expression analysisof genes related to membrane permeability (ompC, ompF and acrA) and regulatory genes(MarA and ompR). After induction with imipenem, 77 % of the isolates increased the MIC for the carbapenems, changing the resistance profile at the baseline. In a lesser percentage, the resistance profile to other β-lactams-unrelated antibiotics was also affected. Loss of porin was observed only for an isolated, however a significantly decreased Omp36 mRNA expression was observed from the start of induction. The expression of the efflux pump AcrAB ,was also affected by the imipenem induction, significantly increasing the AcrA gene expression, whereas the studied regulatory genes,MarA and OmpR,were induced by the imipenem. It was also possible to observe an association between the expression of the regulator MarA and the expression of AcrA, nevertheless no association was observed between this regulator and OMPs . OmpR induction was associated with an increased Omp35mRNA expression, however only a trend for the repression of Omp36was observed. The study of the response of these regulatory genes and genetic determinants of resistance, in response to the imipenem exposure in vitro, allowed to report the molecular behavior of the bacteria in an adaptive response in the initial stage of the establishment of a MDR phenotype. The use of clinical isolates with diverse resistance determinants allowed observing the variability in adaptive responses in enterobacteria, which is important to understand the adaptive mechanisms of bacteria to this antibiotic, the involvement in the emergence of the MDR profile and its contribution to the treatment failure.

Resistance to various chemotherapeutic agents is a major problem in success of cancer chemotherapy. One of the primary reasons of development of multidrug resistance (MDR) is the overexpression of ATP binding cassette (ABC) transporter proteins. Breast cancer resistance protein (BCRP) belongs to ABC transporter family and encoded by ABCG2 gene. BCRP is mainly expressed in MDR1 (P-glycoprotein) lacking breast cancer cells. Overexpression of BCRP leads to efflux of chemotherapeutic agents at higher rates, therefore, decreased levels of intracellular drug accumulation. Despite the fact that several chemical modulators claim to restore BCRP-mediated increased drug efflux, these modulators were shown to display various side effects, precluding their clinical use. Therefore, to reverse BCRPmediated MDR phenotype by a modulator with minimum cytotoxicity may increase clinical benefits and minimize side effects.