Le parasitisme est un des principaux problèmes dans les élevages des ruminants. Les nématodes parasites du tractus digestif des ovins et caprins sont responsables d’importantes baisses de rendement. La maîtrise de ces parasitoses a été longtemps basée sur l’utilisation de molécules anthelminthiques. Cependant, l’efficacité des traitements est fréquemment remise en cause par l’émergence d’isolats résistants à une ou plusieurs de ces molécules. Dans ce contexte, une meilleure connaissance des mécanismes impliqués dans l’installation et la survie des parasites dans leur hôte est essentielle pour le développement de méthodes de lutte efficaces. Les P-glycoprotéines sont des pompes membranaires de la superfamille des transporteurs ABC. Ces pompes transportent des molécules très variées qui ont en commun leur caractère hydrophobe. Nous avons émis l’hypothèse de l’implication de ces transporteurs dans l’interaction hôte-parasite. Dans le contexte de ce travail nous avons identifié des séquences partielles ou complètes d’ADNc de 9 Pgps du nématode parasite Haemonchus contortus. Une forte activation des Pgps des nématodes en présence des produits de dégranulation des éosinophiles de l’hôte a été observée, démontrant ainsi l’interaction entre les Pgps des nématodes et les produits issus de l’hôte. De plus, l’exposition in vitro des nématodes parasites aux produits de l’hôte montrent après analyse par PCR quantitative une induction significative de l’expression de deux Pgps (Hco-pgp-3, et Hco-pgp-16). Chez le nématode murin Heligmosomoides polygyrus bakeri 5 Pgps ont été identifiés. D’autre part, l’analyse du niveau d’expression des Pgps d’H. bakeri a permis de montrer que le gène Hba-pgp-2 est exprimé uniquement chez les stades en contact avec les produits de l’hôte (oeufs, L4 et adultes). De plus, une induction spécifique d’Hba-pgp-2 par le cholestérol a été observée suggérant ainsi l’implication d’Hba-pgp-2 dans la capture et/ou la distribution des stérols des cellules de l’hôte indispensable aux nématodes. Ce travail constitue la première mise en évidence de l’interaction entre les Pgps des nématodes parasites et des produits issus de leur hôte. Ces résultats constituent une base solide pour le développement d’une méthode efficace permettant de bloquer ces transporteurs et d’éliminer les nématodes parasites. / Gastrointestinal nematodes cause significant economic loses in goat and sheep livestocks. Control of these parasites is mainly based on anthelmintic treatments. However, the efficacy of these molecules is questioned by the emergence of isolates resistant to one or several antiparasitic drugs. In this context, a better understanding of the mechanisms involved in the nematode parasites establishment and survival in the host is essential for the development of an effective control methods. P-glycoproteins are membrane pumps belonging to the ABC transporter family. These pumps transport a wide range of hydrophobic molecules. In the present study, we hypothesized that in addition to their critical role in xenobiotic resistance, helminth ABC transporters such as P-glycoproteins (Pgps) may also be involved in the transport of host products. Using the sheep parasitic nematode Haemonchus contortus, we investigated the modulation and expression of parasite Pgps activity in response to host eosinophil granule products. These works allowed to identify nine partial or complete H. contortus Pgps. Using a rhodamine efflux assay, we provided functional evidence that host eosinophil granule products can activate Pgps from the parasite suggesting that granule products could act as potential modulators of the ABC transporters activity. We showed by quantitative RT-PCR that among nine different H. contortus Pgp genes; Hco-pgp-3, Hco-pgp-9.2, Hco-pgp-11 and, Hco-pgp-16 were specifically up-regulated in parasitical life stages suggesting a potential involvement of these Pgps during the host-parasite interaction. Using exsheated L3 larvae, we demonstrated that eosinophil granules induced in a dose response manner an overexpression of Hco-pgp-3 and the closely related Hco-pgp-16 gene highlighting the possible involvement of these Pgps in host product transport. . The mice parasitic nematode Heligmosomoides polygyrus bakeri was used for studying the involvement of Pgps in the cholesterol transport. These works allowed identifying five Pgps in H. bakeri. The analysis of the mRNA expression level of H. bakeri Pgps has shown that Hba-pgp-2 gene is expressed only in stages in contact with host products. In addition, a specific induction of Hba-pgp-2 by cholesterol was observed suggesting the involvement of Hba-pgp-2 in the capture and / or distribution of cholesterol from host cells. Taken together, our results provide the first evidence that a subset of helminth Pgps could be involved in the transport of host products. This opens the way for further studies aiming to explore the function of helminth Pgps in host-parasite interactions including host immune response evasion.

by To Siu Hang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 84-92). / Abstract also in Chinese. / Declaration --- p.i / Abstract --- p.ii / Acknowledgement --- p.vi / Abbreviations --- p.vii / List of Figures --- p.viii / List of Tables --- p.xii / Content --- p.xiv / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 1.1. --- Osteosarcoma --- p.1 / Chapter 1.1.1. --- Incidence / Chapter 1.1.2. --- Age and Sex Distribution / Chapter 1.1.3. --- Clinical Features / Chapter 1.1.4. --- Treatment / Chapter 1.2. --- Adriamycin --- p.9 / Chapter 1.2.1. --- Drug Action / Chapter 1.2.2. --- Pharmacology / Chapter 1.3. --- Multidrug Resistance --- p.11 / Chapter 1.4. --- P-glycoprotein --- p.13 / Chapter 1.4.1. --- Nature / Chapter 1.4.2. --- Tissue Distribution / Chapter 1.4.3. --- Relation with MDR / Chapter 1.5 --- Multidrug Resistance Protein --- p.16 / Chapter 1.6. --- Reactive Oxygen Species --- p.17 / Chapter 1.6.1. --- Problems Arising from ROS / Chapter 1.6.2. --- Oxidative Stress and Diseases / Chapter 1.6.3. --- Defense System / Chapter 1.6.4. --- Antioxidative Enzymes / Chapter 1.6.5. --- Relation with MDR / Chapter 1.7. --- Topoisomerase II --- p.22 / Chapter 1.8. --- Methods to Detect MDR --- p.24 / Chapter 1.8.1. --- P-glycoprotein Immunohistochemistry / Chapter 1.8.2. --- Adriamycin Binding Assay / Chapter 1.9. --- Aims of Study --- p.25 / Chapter 2. --- MATERIALS AND METHODS --- p.27 / Chapter 2.1. --- Clinical Study --- p.27 / Chapter 2.1.1. --- Patients Recruitment / Chapter 2.1.2. --- Adriamycin Binding Assay / Chapter 2.1.3. --- P-glycoprotein Immunohistochemistry / Chapter 2.1.3.1. --- Sample and Control Preparation / Chapter 2.1.3.2. --- Immunohistochemical Procedure / Chapter 2.1.4. --- Tumour Necrosis Assessment / Chapter 2.2. --- Effect of Adriamycin on Osteosarcoma Cells --- p.32 / Chapter 2.2.1. --- Establishment of Adriamycin Adapted Osteosarcoma Cells / Chapter 2.2.1.1. --- Maintenance and Subculture of SaOS-2 Cell Line / Chapter 2.2.1.2. --- Storage of Cell Line / Chapter 2.2.1.3. --- Adriamycin Treatment / Chapter 2.2.2. --- KB-V1 Cell Culture / Chapter 2.2.3. --- Adriamycin Binding Assay / Chapter 2.2.4. --- P-glycoprotein Immunohistochemistry / Chapter 2.2.4.1. --- Sample and Control Preparation / Chapter 2.2.4.2. --- Immunohistochemical Procedures / Chapter 2.2.5. --- Thymidine Incorporation Assay / Chapter 2.2.5.1. --- Assay Procedures / Chapter 2.2.6. --- Catalase Assay / Chapter 2.2.6.1. --- Assay Procedures / Chapter 2.2.6.2. --- Unit Calculation / Chapter 2.2.7. --- Glutathione Peroxidase Assay / Chapter 2.2.7.1. --- Assay Procedures / Chapter 2.2.7.2. --- Unit Calculation / Chapter 2.2.8. --- Protein Determination / Chapter 2.3. --- Statistical Analysis --- p.45 / Chapter 3. --- RESULTS --- p.46 / Chapter 3.1. --- Clinical Study --- p.46 / Chapter 3.1.1. --- Patients Recruitment / Chapter 3.1.2. --- Correlation of Adriamycin Sensitivity to Tumour Necrosis / Chapter 3.1.3. --- Correlation of P-glycoprotein Expression to Tumour Necrosis / Chapter 3.1.4. --- Correlation of P-glycoprotein Expression to Adriamycin Sensitivity / Chapter 3.2. --- Effect of Adriamycin on Osteosarcoma Cells --- p.63 / Chapter 3.2.1. --- Adriamycin Sensitivity and P-glycoprotein Expression / Chapter 3.2.2. --- Thymidine Incorporation Rate / Chapter 3.2.3. --- Intracellular Concentration of Catalase / Chapter 3.2.4. --- Intracellular Concentration of Glutathione Peroxidase / Chapter 4. --- DISCUSSIONS --- p.71 / Chapter 4.1. --- Clinical Study --- p.71 / Chapter 4.1.1. --- Patients Recruitment / Chapter 4.1.2. --- Correlation between Adriamycin Sensitivity and Tumour Necrosis / Chapter 4.1.3. --- Correlation between P-glycoprotein Expression and Tumour Necrosis / Chapter 4.1.3.1. --- P-glycoprotein Is Induced During Chemotherapy / Chapter 4.1.3.2. --- P-glycoprotein Cannot Serve As a Prognostic Factor / Chapter 4.1.4. --- Correlation Between Adriamycin Sensitivity and P-glycoprotein Expression / Chapter 4.2. --- Effect of Adriamycin on Osteosarcoma Cells --- p.76 / Chapter 4.2.1. --- Adriamycin Sensitivity and P-glycoprotein Expression / Chapter 4.2.2. --- Proliferation Rate / Chapter 4.2.3. --- Antioxidative Enzymes Activities / Chapter 5. --- CONCLUSION --- p.82 / Chapter 6. --- FURTHER STUDY --- p.83 / Chapter 7. --- BIBLIOGRAPHY --- p.84 / Chapter 8. --- APPENDIX - SOLUTIONS PREPARATION --- p.93

Drug development is a long and expensive process. Potential drug candidates can fail clinical trials due to numerous issues, including metabolic stability and efficacy issues, wasting years of research effort and resource. This thesis detailed the development of in silico methods to predict the metabolic stability of structures and their bioavailability. Coralie Atom-based Statistical SOM Identifier (CASSI) is a site of metabolism (SOM) predictor which provides a SOM prediction based on statistical information gathered about previously seen atoms present in similar environments. CASSI is a real-time SOM predictor accessible via graphical user interface (GUI), allowing users to view the prediction results and likelihood of each atom to undergo different types of metabolic transformation. Fast Metabolizer (FAME)1 is a ligand-based SOM predictor developed around the same time by Kirchmair et al. In the course of the evaluation of CASSI and FAME performance, the two concepts were combined to produce FamePrint. FamePrint is a tool developed within the Coralie Cheminformatics Platform developed by Lhasa Limited. which can carry out SOM predictions, as well as bioisosteric replacement identification. Same as CASSI, this is available via the Coralie application GUI. The bioavailability issues caused by the metabolic enzyme, cytochrome P450 3A4, and transporter protein P-gylcoprotein are also investigated in this work, along with the potential synergistic relationship between the two systems. In silico classifiers to distinguish substrates against non-substrates of the two systems are produced and it was envisaged that these classifiers can be integrated into FamePrint as an additional layer of information available to the user when deciding on bioisosteric replacements to use when optimising a compound.

La surexpression de protéines d’efflux, et tout particulièrement la P-glycoprotéine, est impliquée dans la multidrug résistance. Dans cette thèse, nous démontrons que le vandetanib, inhibiteur de tyrosine kinase, est à la fois substrat et inhibiteur de la P-glycoprotéine et qu’il est capable de réverser in vitro la résistance à la doxorubicine liée à la surexpression de la P-glycoprotéine.Nous nous sommes également intéressés à l’étude du passage transplacentaire du vandetanib et nous montrons que ce médicament traverse la barrière placentaire. / Overexpression of ABC transporters, especially P-glycoprotein, is involved in multidrug resistance. In this study, we demonstrate that vandetanib, a tyrosine kinase inhibitor, is both substrate and inhibitor of P-glycoprotein and is able to reverse in vitro resistance to doxorubicin, linked to overexpression of P-glycoprotein.We also studied the placental transfer of vandetanib and we show that this drug crosses the placenta.

Para fármacos administrados por via oral, o controle da extensão e da velocidade de absorção depende basicamente de duas importantes etapas: solubilidade do fármaco nos líquidos fisiológicos e sua permeabilidade através das membranas biológicas. Assim, o Sistema de Classificação Biofarmacêutica (SCB) foi proposto como uma ferramenta para o desenvolvimento de novos fármacos, de novas formulações e para auxiliar nos processos de bioisenção. No entanto, outro fator relacionado à biodisponibilidade e que deve ser considerado nos estudos biofarmacêuticos é o metabolismo. Desta forma, o Sistema de Classificação Biofarmacêutica de Distribuição de Fármacos (SCBDF) foi proposto com a finalidade de classificar os fármacos de acordo com suas características de solubilidade e de metabolismo de modo que seja possível avaliar e predizer o comportamento do fármaco in vivo. O metabolismo tem sido amplamente investigado, sobretudo as enzimas do citocromo P450, as quais estão presentes também nos enterócitos. Além disso, o SCBDF oferece um suporte quanto à avaliação dos mecanismos de permeabilidade envolvidos nos processos de absorção, interações fármaco-fármaco e interações fármaco-alimento. Assim, o presente trabalho teve como objetivo elucidar os mecanismos envolvidos na permeabilidade de fármacos antirretrovirais por meio dos modelos ex vivo (câmaras de difusão vertical tipo Franz) e in vitro (PAMPA, MDCK-MDR1 e microssomas) considerando os aspectos relacionados ao metabolismo intestinal e ao efluxo destes fármacos. Dada a importância da utilização de fármacos antirretrovirais na terapia medicamentosa contra a Síndrome da Imunodeficiência Adquirida (SIDA) e que estes medicamentos são normalmente administrados cronicamente, a compreensão dos mecanismos envolvidos na permeabilidade é de suma importância, uma vez que estes não estão totalmente esclarecidos e poucas informações são encontradas na literatura. Além disso, a biodisponibilidade de fármacos como estavudina, lamivudina e zidovudina indica variação na permeabilidade, necessitando de uma investigação científica mais aprofundada dos processos absortivos. Assim, segmentos de jejuno provenientes de ratos machos Wistar foram utilizados para a avaliação da permeabilidade intestinal dos referidos antirretrovirais considerando a avaliação de efluxo pela glicoproteína-P e o metabolismo intestinal pela CYP3A. De maneira complementar, estudos in vitro com o emprego de membranas artificiais paralelas (PAMPA) e culturas celulares de MDCK-MDR1 foram realizados com a finalidade de auxiliar na elucidação dos mecanismos de permeabilidade dos fármacos antirretrovirais. Além disso, a avaliação do metabolismo dos referidos fármacos foi realizada com o emprego de microssomas a fim de verificar se tais substâncias são substratos de enzimas da família CYP3A e, assim, verificar o impacto do metabolismo intestinal na absorção. Os resultados de permeabilidade obtidos em PAMPA foram: 0,74±0,11 x 10-6 cm/s para a estavudina, 0,25±0,12 x 10-6 cm/s para a lamivudina e 1,14±0,25 x 10-6 cm/s para a zidovudina. Já no modelo ex vivo com o emprego de câmaras de difusão vertical tipo Franz, os resultados foram: 1,56±0,32 x 10-5 cm/s para a estavudina, 1,26±0,27 x 10-5 cm/s para a lamivudina e 2,54±0,49 x 10-5 cm/s para a zidovudina. Portanto, com base nos resultados obtidos a partir dos dois métodos empregados, sugere-se que 30 outro mecanismo de transporte que não envolva a permeabilidade por difusão transcelular passiva possa estar relacionado à permeabilidade dos fármacos antirretrovirais. Com relação aos estudos de efluxo, os resultados obtidos a partir dos experimentos realizados em câmaras de difusão vertical tipo Franz demonstraram o aumento significativo da permeabilidade dos três antirretrovirais quando o inibidor de P-gp foi empregado, sendo: de 15,6 x 10-6 para 42,5 x 10-6 cm/s para a estavudina, de 12,6 x 10-6 para 37,5 x 10-6 cm/s para a lamivudina e de 25,4 x 10-6 para 56,6 x 10-6 cm/s para a zidovudina. Em culturas celulares MDCK-MDR1, os resultados de permeabilidade foram utilizados para a obtenção das razões entre as direções B→A e A→B. Os valores de Papp na condição inibida para os fármacos estudados apresentaram razão menor do que 1. Já a razão B→A/A→B para cada fármaco nos ensaios sem inibidor apresentou-se igual ou maior que 2, evidenciando a interação fármaco-transportador. Com base nisso, o modelo ex vivo com o emprego de segmentos intestinais em câmaras de difusão vertical tipo Franz apresentou-se adequado na avaliação do mecanismo de efluxo dos fármacos antirretrovirais, o que foi confirmado com os estudos realizados em MDCK-MDR1. Assim, os fármacos antirretrovirais estudados apresentaram interação significativa com a P-gp. Em relação aos estudos de metabolismo realizados em câmaras de difusão vertical tipo Franz, os resultados demonstraram grande variação na permeabilidade dos três antirretrovirais quando o inibidor de CYP3A foi empregado, sendo: de 15,6 x 10-6 para 23,5 x 10-6 cm/s para a estavudina, de 12,6 x 10-6 para 27,3 x 10-6 cm/s para a lamivudina e de 25,4 x 10-6 para 40,5 x 10-6 cm/s para a zidovudina. Já no modelo que emprega microssomas, os resultados de metabolização na ausência e na presença de inibidor de CYP3A foram: de 16,56% para 19,79% para a estavudina, de 14,56% para 15,55% para a lamivudina e de 17,85% para 16,48% para a zidovudina. Com base nisso, sugerese o emprego de microssomas para a determinação de metabolismo, uma vez que o método ex vivo empregado demonstrou grande variação entre os valores obtidos. Desta forma, observou-se que, para cada fármaco, não houve influência significativa no metabolismo pré-sistêmico relacionado às enzimas do complexo CYP3A, o que indica que a absorção oral das referidas substâncias não é limitada por tais enzimas. Portanto, a utilização dos diferentes métodos empregados no desenvolvimento do presente trabalho permitiu compreender os mecanismos envolvidos no transporte dos fármacos antirretrovirais, o que se torna de grande relevância nas etapas de desenvolvimento farmacêutico de novas moléculas e na compreensão de eventos clínicos ainda não esclarecidos atualmente. / For orally administered drugs, control of the extent and rate of absorption depends on two important steps: solubility of the drug in physiological liquids and their permeability across biological membranes. Thus, the Biopharmaceutics Classification System (BCS) has been proposed as a tool for the development of new drugs, new formulations and aid in the biowaiver processes. However, another factor related to bioavailability that should be considered in biopharmaceutic studies is the metabolism. Thus, the Biopharmaceutics Drug Disposition Classification System (BDDCS) has been proposed for drug classification according to their solubility and metabolism characteristics, so it is possible to evaluate and predict the in vivo behavior of a compound. Metabolism has been extensively investigated, especially cytochrome P450 enzymes, which are also expressed in enterocytes. Besides, BDDCS provides support in evaluating the permeability mechanisms involved in the absorption processes, drug-drug interactions and drug-food interactions. Thus, the present study aimed to evaluate the mechanisms of permeability of antiretroviral drugs through the ex vivo (Franz cells) and in vitro (PAMPA, MDCK-MDR1 and microsomes) models considering aspects related to the intestinal metabolism and efflux of these drugs. Given the importance of the use of antiretroviral drugs in drug therapy against Acquired Immune Deficiency Syndrome (AIDS) and that these drugs are usually administered in a long-term way, understanding the mechanisms involved in the permeability is of a great importance, since they are not totally elucidated and no information is found in the literature. In addition, drugs as stavudine, lamivudine and zidovudine indicate variation in the permeability, which require further scientific investigation of absorptive processes. Thus, jejunum segments from rats were used to evaluate the intestinal permeability of these antiretroviral drugs, considering the evaluation of efflux by P-glycoprotein and intestinal metabolism by CYP3A. In a complementary manner, in vitro studies using parallel artificial membranes (PAMPA) and cell cultures MDCK-MDR1 were performed to aid in the elucidation of the permeability mechanisms of antiretroviral drugs. Also, the evaluation of the metabolism was carried out using microsomes to verify if such substances are substrates of CYP3A, and verify the impact of the intestinal metabolism in the absorption. The permeability results obtained in PAMPA were: 0.74±0.11x10-6 cm/s for stavudine, 0.25±0.12x10-6 cm/s for lamivudine and 1.14±0.25x10-6 cm/s for zidovudine. In ex vivo method using the intestinal segments in Franz cells, the results were: 1.56±0.32x10-5 cm/s for stavudine, 1.26±0.27x10-5 cm/s for lamivudine and 2.54±0.49x10-5 cm/s for zidovudine. Thus, based on the results obtained from these two methods, it is suggested that the antiretroviral drugs present other transport mechanism that is different from transcellular passive diffusion. For efflux studies, results obtained from experiments performed in Franz cells shown the increase of the permeability of the three antiretroviral drugs when the P-gp inhibitor was used: from 15.6x10-6 to 42,5x10-6 cm/s for stavudine, from 12.6x10-6 cm/s to 37.5x10-6 cm/s for lamivudine, and 25.4x10-6 to 56.6x10-6 cm/s for zidovudine. In MDCK-MDR1, the permeability results were used for obtaining ratio values between the directions B→A and A→B. The Papp values obtained with 33 inhibitor shown a ratio less than 1. For ratio B→A/A→B for each drug in experiments without inhibitor, the values obtained was equal or greater than 2, which shows the interaction between drug and transporter. Based on that, the ex vivo model using intestinal segments in Franz cells seems to be adequate for evaluation of efflux mechanism of antiretroviral drugs, which was confirmed by MDCK-MDR1 studies. Thus, the antiretroviral drugs presented interaction with P-gp. For metabolism studies in intestinal segments in Franz cells, a wide range of standard deviation was observed for the three antiretroviral drugs when the CYP3A inhibitor was used: from 15.6x10-6 cm/s to 23.5x10-6 cm/s for stavudine, from 12.6x10-6 cm/s to 27.3x10-6 cm/s for lamivudine, and from 25.4x10-6 cm/s to 40.5x10-6 cm/s for zidovudine. In experiments in microsomes, the results of metabolization in the absence and presence of CYP3A inhibitor were: from 16.56 to 19.79% for stavudine, from 14.56 to 15.55% for lamivudine and from 17.85 to 16.48% for zidovudine. Based on that, it is suggested the use of microsomes for metabolism evaluation, since the ex vivo method presented high variability between the results obtained. For each drug, no significative influence in pre-systemic metabolism related to CYP3A enzymes was observed, which indicates that the oral absorption of the drugs is not limited by these enzymes. The use of different methods in this work allowed to understand the mechanisms involved in the transport of antiretroviral drugs, which is of a great relevance in drug development and in the understanding of clinical events currently not clarified.

Thesis (M.Sc. (Pharmacology))--North-West University, Potchefstroom Campus, 2009.

The phenomenon called multi drug resistance (MDR) is the resistance of cancer cells to anticancer drugs before or during chemotherapy. One of the mechanisms causing MDR is the upregulation of efflux pumps. The overexpression of MDR1 and MRP1 results in increased efflux of anticancer agents. The aim of this study was to reverse MDR1-mediated paclitaxel resistance in MCF7 breast cancer cell line by a chemical MDR modulator elacridar. In this study, cytotoxicity and the reversal effect of elacridar on sensitive and paclitaxel resistant cells were investigated. The effect of elacridar on MDR1 and MRP1 gene expressions were also determined. Results indicated MDR1 gene was highly overexpressed (208 fold) in MCF7/Pac cells compared to MCF7/S cells. Elacridar was not found to be cytotoxic in MCF7/Pac cells up to 30&micro / M. XTT results demonstrated 0.5&micro / M elacridar concentration was able to restore the antiproliferative effect of paclitaxel by 94% in MCF7/Pac cells. Complete MDR reversal was achieved at 5&micro / M elacridar concentration. qPCR results revealed dose dependent upregulations in MDR1 and MRP1 gene expression levels after elacridar treatment which did not prevent reversal of MDR by elacridar. Elacridar was shown to be very effective against paclitaxel resistance in MCF7/Pac cells at low concentrations. Therefore, it can be a suitable candidate for therapeutic applications in patients who developed paclitaxel resistance. Nevertheless, dose dependent upregulations in MDR1 and MRP1 gene expressions should be taken into consideration and overdose elacridar administration should be avoided.

ABC drug transporter, MDR1, is a drug flippase that moves a variety of hydrophobic molecules from the inner to the outer leaflet of the plasma membrane. We have previously reported that MDR1 can function as a glycolipid flippase, being one of the mechanisms responsible for the translocation of glucosylceramide into the Golgi for neutral, but not acidic, glycosphingolipids (GSLs) synthesis. The interplay between GSLs and MDR1 could provide a whole new spectrum of innovative therapeutic options. We found that cell surface MDR1 partially co-localized with globotriaosyl ceramide (Gb3) in MDR1 transfected cells. Inhibition of GSL biosynthesis results in the loss of drug resistance and of cell surface MDR1. We speculated that an association of MDR1 and cell surface GSLs, in particular Gb3, may be functional at the cell surface, as MDR1 partitions into plasma membrane lipid rafts regulating MDR1 function. We therefore tested adamantyl Gb3 (adaGb3), a water soluble analog of Gb3, on MDR1 functions. AdaGb3 was able to inhibit MDR1-mediated rhodamine 123 drug efflux from MDR1 expressing cells, like cyclosporin A (CsA), a classical MDR1 inhibitor. AdaGb3 was also able to reverse vinblastine drug resistance in cell culture, whereas adamantyl galactosylceramide had no effect on drug resistance. The strong MDR1 reversal effects of adaGb3, as well as its favourable in vivo features make it a possible choice for inhibition of MDR1 to increase bioavailability of drugs across the intestinal epithelium (De Rosa et al., 2008). Thus, specific GSL analogs provide a new approach to MDR reversal. We have previously shown that MDR1 inhibitor CsA depletes Fabry cell lines of Gb3, the characteristic GSL accumulated in this disease, by preventing its de novo synthesis, and can also deplete Gaucher lymphoid cell lines of accumulated GlcCer (Mattocks et al., 2006). Liver and heart sections of Fabry mice treated with third generation MDR1 inhibitors showed significantly less Gb3 than liver and heart sections of untreated Fabry mice. Thus, MDR1 inhibition offers a potential alternative therapeutic approach not only for Fabry disease given the extraordinary cost of conventional enzyme replacement therapy, but also for other neutral GSL storage diseases, such as Gaucher disease.

Several families of highly effective anticancer drugs are selectively toxic to cancer cells because they interfere with nucleic acids synthesis. Many such drugs are pumped out of cells faster than they can reach their targets, which limits efficacy and renders many tumors drug-resistant. By delivering a drug to the mitochondria of mammalian cells – an organelle where nucleic acids synthesis also occurs – efflux could be prevented through sequestration. Doxorubicin, a topoisomerase II inhibitor, was used as proof-of-principle for this concept due to its susceptibility to resistance. When doxorubicin is attached to a peptide that specifically targets mitochondria, its efficacy is not attenuated by various resistance mechanisms to which doxorubicin is normally susceptible. These results indicate that targeting drugs to the mitochondria provides a means to evade the most common mechanism of drug resistance.

Several families of highly effective anticancer drugs are selectively toxic to cancer cells because they interfere with nucleic acids synthesis. Many such drugs are pumped out of cells faster than they can reach their targets, which limits efficacy and renders many tumors drug-resistant. By delivering a drug to the mitochondria of mammalian cells – an organelle where nucleic acids synthesis also occurs – efflux could be prevented through sequestration. Doxorubicin, a topoisomerase II inhibitor, was used as proof-of-principle for this concept due to its susceptibility to resistance. When doxorubicin is attached to a peptide that specifically targets mitochondria, its efficacy is not attenuated by various resistance mechanisms to which doxorubicin is normally susceptible. These results indicate that targeting drugs to the mitochondria provides a means to evade the most common mechanism of drug resistance.