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DNA provides the instructions and regulation of cell growth and survival. Mutations in DNA can cause uncontrolled and unregulated cell proliferation, resulting in cancer. Treatment of cancer involves physical removal of these cells through surgery or inducing cell death by causing irreversible damage to DNA through chemotherapy and radiotherapy. However, natural DNA repair mechanisms may interfere with therapy and may even be increased in cases of therapy resistant cancer. The use of chemotherapy and radiotherapy leads to increased recruitment of DNA repair proteins while aggressive, therapy resistant cancers show overexpression of DNA repair proteins. Rad51 is a protein involved in the homologous recombination (HR) DNA repair process. Rad51 is recruited to sites of DNA damage caused by double stranded breaks, often generated by chemotherapy and radiotherapy. It is expected that inhibition of Rad51 will impair the HR repair process while enhancing the effectiveness of chemotherapy and radiotherapy compared to conventional means. As a result, this literature review aims to identify and examine the drug inhibitors of Rad51 in order to demonstrate the potential viability of this novel treatment in a variety of cancers.

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De nombreuses études ont montré l'intérêt thérapeutique de molécules dérivant des microARN (inhibiteurs ou analogues) en cancérologie. Cependant avant d'espérer en faire de futurs médicaments, il est indispensable d'élaborer des systèmes permettant leur délivrance préférentielle dans les cellules cancéreuses. Dans ce travail, nous avons développé deux plateformes innovantes basées sur les microARN : la première utilise les propriétés optiques des quantum dots (QD) et est destinée à l'imagerie des microARN ; la seconde repose sur la sérum albumine humaine (SAH) et a une finalité de délivrance ciblée de microARN. La mise en place de ces plateformes a nécessité la synthèse d'une petite chimiothèque de bioconjugués lipidiques dérivés des microARN (inhibiteurs ou analogues), le but étant d'exploiter l'effet hydrophobe pour les fixer à la surface des QD (ancrage hydrophobe dans la paroi lipidique des QD) et de la SAH (interaction avec les sites de liaison aux acides gras). Dans les deux cas, différentes études incluant des caractérisations physico-chimiques (MET, DLS), des expériences in vitro (SPR) et in cellulo (microscopie de fluorescence, criblage fonctionnel, RTqPCR) ont montré la potentialité de ces nouvelles plateformes. / Exploitation of gene-silencing is a very promising strategy in human therapeutics. Several engineered small non coding RNAs (inhibitors or mimics) are already in preclinical and clinical trials. However a key impediment to the wider success of these approaches remains the specific delivery of RNA-derived molecules into cancerous cells. This work aimed at developing two innovative microRNA-based plateforms : the first one relying on quantum dots (QD) is dedicated to microRNA imaging and the second one based on human serum albumin (HSA) represents a new targeted delivery system. The implementation of both plateforms required the synthesis of a small library of microRNA derived lipidic bioconjugates (inhibitors or mimics), the aim being to exploit the hydrophobic effect for their loading on QD (hydrophobic anchoring in the hydrophobic QD surface) and on HSA (interaction with fatty acid binding sites). In both cases, different studies including physico-chemical caracterizations (TEM, DLS), in vitro (SPR) and in cellulo experiments (fluorescence microscopy, functional screening, RTqPCR) demonstrated the great promises held by these new plateforms.

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Au cours de chimiothérapies, les cellules cancéreuses parviennent fréquemment à échapper aux effets toxiques des médicaments en développant des mécanismes de chimiorésistance qui résultent souvent de la présence d’un système d’efflux de ces médicaments. Cette chimiorésistance est corrélée à un phénomène appelé « phénotype MDR » pour (MultiDrug Resistance) et associé à la surexpression d’ATPases membranaires appartenant aux transporteurs ABC (ATP Binding Cassette). Le transporteur ABCG2 fait partie de cette grande famille de protéines. Un alignement de séquence a permis l’identification chez ABCG2 une séquence spécifique (LSGGE) très semblable à la séquence signature (VSGGE) de tous les transporteurs ABC. La mutation ponctuelle des résidus de cette séquence en alanine a produit une perte importante de fonction des mutants L352A et S353A, observée au niveau du transport et de l’activité ATPasique. Des relations structure-activité établies à partir de différents composés de la famille des flavonoïdes ont permis d’identifier MBLI 97, boéravinone G, MHT et ABI comme des composés puissants et spécifiques, capables d’abolir la résistance à de multiples drogues et chimiosensibiliser la croissance cellulaire. Le ciblage de séquences spécifiques et l'utilisation d'inhibiteurs spécifiques de ces transporteurs constituent des stratégies destinées à contrer la chimiorésistance et augmenter l’efficacité des traitements chimiothérapeutiques. / During chemotherapy, cancer cells frequently succeed to escape the toxic effects of drugs by developing mechanisms of chemoresistance which often result from the presence of an efflux system of these drugs. Such a chemoresistance is correlated to the MDR (MultiDrug Resistance) phenotype and associated to overexpression of membrane ATPases belonging to the ABC (ATP-Binding Cassette) transporters. The ABCG2 transporter belongs to this large family of proteins. Sequence alignment allowed the identification of a specific (LSGGE) sequence in ABCG2, which is quite similar to the canonical sequence signature (VSGGE) of all ABC transporters. Point mutation of these residues into alanine produced a loss of function in L352A and S353A mutants, as observed in transport and on ATPase activity. Structure-activity relationships drawn from some compounds among the family of flavonoids allowed the identification of MBLI 97, boeravinone G, MHT and ABI as potent and ABCG2-specific inhibitors, able to revert multidrug resistance and chemosensitize cell growth. The study of specific sequences and use of specific inhibitors of these transporters constitute strategies to abolish cancer cell chemoresistance and to increase the efficiency of chemotherapeutic treatments.

Indiana University-Purdue University Indianapolis (IUPUI) / Many cancers, including breast cancer, often develop resistance to chemotherapeutic drugs over a course of treatment. Many factors, including ABC transporter-mediated drug efflux, have been shown to play a role in acquired drug resistance. Fatty acid synthase (FASN), the key enzyme of lipid synthesis pathway, was found to be over-produced in an Adiamycin resistant breast cancer cell line MCF7/AdrVp3000, compared to its parental drug sensitive MCF7 cell line. Inhibition of FASN expression increased the drug sensitivity in breast cancer cells (MCF7/AdrVp3000 and MDA-MB-468), but not in the normal breast epithelia cell line MCF10A1. Enforced overexpression of FASN in MCF7 breast cancer cells decreased its drug sensitivity. These results indicated that FASN overexpression can induce drug resistance in breast cancers. Ectopic overexpression of FASN in MCF7 cells did not affect cell membrane permeability, transporter activity, nor did it affect cell proliferation rate. However, FASN overexpression protects cancer cells from drug-induced apoptosis by decreasing caspase-8 activation. In FASN over-expressing MCF7 cells, I discovered the positive feedback relationship between FASN and activation of Akt as previously reported. However, activation of Akt did not mediate FASN-induced drug resistance. Together with the findings that FASN expression associates with poor prognosis in several types of cancers, my investigations suggest that FASN overexpression is a novel mechanism of drug resistance in breast cancer chemotherapy. Inhibitors of FASN can be used as sensitizing agents in breast cancer chemotherapy.

La résistance des cellules tumorales à la chimiothérapie constitue une cause majeure d’échec des traitements anticancéreux. Des études précliniques montrent que les acides gras polyinsaturés oméga-3 à longues chaînes (AGPIn-3LC), apportés par l’alimentation, améliorent l’efficacité des chimiothérapies sans majorer les effets secondaires. Cette thèse a eu pour but d’identifier les mécanismes moléculaires impliqués dans l’augmentation de la sensibilité des cellules tumorales mammaires au docétaxel. Nous avons montré que le docétaxel induit un mécanisme de résistance via l’activation des voies de signalisation PKC/ERK et Akt impliquées dans la prolifération et la survie cellulaires. La modification de l’environnement lipidique membranaire par la supplémentation en AGPIn-3LC inhibe ces voies de signalisation et augmente l’efficacité du docétaxel dans des lignées tumorales mammaires et dans un modèle préclinique de tumeurs mammaires autochtones chez le rongeur. De plus, dans ce modèle in vivo, nous avons identifié une autre cible moléculaire régulée par les AGPIn-3LC : l’épiréguline, membre de la famille EGF. Les AGPIn-3LC bloquent l’induction de l’épiréguline par le VEGF dans les cellules endothéliales et induisent un remodelage de la vascularisation tumorale. Outre un effet direct des AGPIn-3LC sur les cellules tumorales, les AGPIn- 3LC agissent sur le microenvironnement tumoral. Ces travaux de thèse apportent des arguments supplémentaires pour l’utilisation des AGPIn-3LC comme molécules adjuvantes pour lutter contre la résistance des tumeurs mammaires aux agents anticancéreux. / Chemotherapy-resistant tumor cells are a major cause of cancer treatment failure. Preclinical studies show that polyunsaturated omega-3 long chain fatty acids (AGPIn-3LC), provided by food, improve the efficacy of chemotherapy without increasing side effects. AGPIn-3LCs are incorporated in cancer and stromal cells. This thesis aimed to identify molecular mechanisms involved in the increased sensitivity of mammary tumor cells to docetaxel. We have shown that docetaxel induces a resistance mechanism via activation of PKC/ERK and Akt pathways involved in cell proliferation and survival. Modification of the membrane lipid environment by AGPIn-3LCs supplementation inhibits these signaling pathways and increases the efficacy of docetaxel in mammary tumor cell lines and in a preclinical rodent model of native mammary tumors. Moreover, in this mammary tumor model we have found another molecular target regulated by AGPIn-3LCs: epiregulin, a member of the EGF family. AGPIn-3LCs inhibit epiregulin-VEGF induced in endothelial cells and induce a remodeling of tumor vasculature. Furthermore, AGPIn-3LCs act on the tumor microenvironment directly. This thesis work provides additional arguments for the use of AGPIn-3LCs as adjuvant molecules to reduce the resistance of breast tumors to anticancer agents.