Au cours de ces années de Doctorat, nous avons étudié les effets ototoxiques de certains médicaments et les moyens de prévenir les surdités neuro-sensorielles quils peuvent induire. Parmi ces molécules, nous nous sommes concentrés sur les plus couramment utilisées en pratique clinique : les antibiotiques de la famille des aminoglycosides et le cisplatine, un agent anti-cancéreux. Lintroduction de notre travail replace la surdité dans son contexte de santé publique. En particulier, nous décrivons pourquoi les médicaments ototoxiques sont utilisés et dans quelles circonstances. Nous présentons la structure de loreille interne et nous tentons dexpliquer sa vulnérabilité aux molécules ototoxiques. Nous abordons ensuite les moyens de prévention et/ou de traitement de ces atteintes neuro-sensorielles pharmaco-induites. Outre les moyens classiques de prévention, que sont les facteurs trophiques et les antioxydants, nous décrivons de nouvelles voies dapproche que sont les voies de signalisation impliquant la protéine kinase C ou la cascade dactivation RhoA/ROCK. La présentation de notre travail original sarticule autour de deux parties. Dans la première partie, nous rapportons les résultats obtenus au cours de notre étude de la toxicité des aminoglycosides et du cisplatine chez la souris et le cobaye in vivo. Nous avons mis en évidence une différence de vulnérabilité significative entre ces deux espèces face à lagression ototoxique. Cette différence existe au niveau fonctionnel, mis en évidence par létude des potentiels évoqués auditifs, et au niveau anatomique, étudié en histologie et en immunohistochimie. Nous en discutons les implications en recherche et en pratique clinique. Dans la seconde partie, nous étudions les moyens de prévenir cette surdité in vivo et in vitro. Nous avons utilisé un modèle de surdité par aminoglycoside chez le cobaye. Nous avons testé et validé une technique de perfusion intra-cochléaire in vivo. Nous avons observé les effets de deux molécules expérimentales : la Bryostatine 1, un activateur de la protéine kinase C, et un inhibiteur de la voir RhoA-ROCK. Leffet protecteur de ces molécules est actuellement limité au ganglion spiral, dont la survie est essentielle à tout traitement dimplantation prothétique et de réadaptation. Nous discutons des perspectives en médecine humaine dans notre conclusion. In this work, we focused our attention on the effects of main ototoxic drugs i.e. aminoglycosides and cisplatin in mammals. We identified new avenues for the prevention of this toxicity. In the introduction, we described how and why ototoxic drugs are used. We then described potential otoprotective strategies in neurosensory deafness. Among them, trophic factors and antioxidant molecules have been widely used. New otoprotective approaches do exist, implying the protein kinase C or RhoA/ROCK signalling. Our original work was presented in two parts. In the first part, we reported the in vivo effects of aminoglycosides and cisplatin in two mammalian species: mice and guinea pigs. Contrarily to guinea pigs, evidence of mice resistance to ototoxicity was found at a functional level, assessed by auditory brainstem responses, and at an anatomical level, studied by immunohistochemistry. We discussed the implication of such differences in research and in clinical practice. In the second part, we studied the effect of two potential otoprotective molecules: Bryostatine 1, an activator of the protein kinase C, and Y-27632, a Rho kinase inhibitor. We showed that these molecules are protecting spiral ganglion neurons both in vitro and in vivo. Survival of spiral ganglion neurons is crucial in the management and rehabilitation of deafness. The potential perspectives of these results in human medicine were discussed.

Le cancer de l’ovaire est un cancer ayant un taux de décès particulièrement élevé. Les patientes répondent habituellement bien aux traitements chimiothérapeutiques mais la majorité connaîtront une rechute. Plusieurs mécanismes ont été identifiés comme partiellement responsables du développement de la résistance clinique à la chimiothérapie, dont la réparation plus efficace de l’ADN par la réparation par excision de nucléotides (NER). L'un des agents communément utilisés pour traiter ce cancer est le cisplatine, qui induit des dommages à l'ADN réparés par le NER. Une étude précédente de notre laboratoire a démontré qu'une déficience uniquement en phase S de la réparation par le NER peut se produire. Cette déficience est aussi dépendante de la kinase ATR. Nous avons choisi de déterminer si cette déficience est présente dans certains cas de cancer de l’ovaire et si cette déficience joue un rôle sur la résistance à la chimiothérapie. Nos objectifs sont donc : (i) vérifier la présence de cette déficience dans diverses lignées isolées du cancer de l’ovaire ; (ii) vérifier si le traitement chimiothérapeutique par des agents à base de platine peut favoriser la survie de cellules ayant une meilleure capacité de réparation par le NER; (iii) mesurer la sensibilité de ces lignées au cisplatine et vérifier si ceci corrèle avec leur capacité de réparation par le NER en phase S; (iv) déterminer si cette déficience est causée par la kinase ATR dans ces lignées. Nous avons déterminé qu’une déficience importante de la réparation par le GG-NER en phase S est présente dans de nombreuses lignées. De plus, des lignées isolées d’une même patiente pré-chimiothérapie et post-chimiothérapie montrent une augmentation significative de leur capacité de réparation par le GG-NER en phase S, suggérant un rôle de ce processus dans la résistance à la chimiothérapie. Nous avons aussi démontré qu’il y a une corrélation entre la capacité de réparation en phase S par le GG-NER et la sensibilité des lignées au cisplatine. Toutefois, nos résultats suggèrent que cette déficience n’est pas causée par ATR dans ces lignées puisque la phosphorylation de H2AX en réponse aux UV est similaire dans toutes les lignées. En plus d’un important apport fondamental, cette étude permettra d’étudier un potentiel mécanisme de résistance aux traitements chimiothérapeutiques dans le cancer de l’ovaire humain. / Ovarian cancer is one of the most lethal cancers. Patients usually respond very well to chemotherapy but most will eventually relapse. Many molecular processes have already been shown to influence chemotherapy resistance, including more efficient DNA repair by nucleotide excision repair. One commonly used drug for the treatment of ovarian cancer is cisplatin, a drug inducing lesions on DNA that can be repaired by NER. A previous study in our lab has shown that NER can be deficient specifically in S-phase. This effect is dependent on the kinase ATR. Thus, we chose to explore the possibility that this deficiency has an impact on resistance to cisplatin. Our objectives are: (i) to study the repair profile by NER in S-phase in ovarian cancer cell lines; (ii) to test if chemotherapeutic treatment can modulate nucleotide excision repair in cell lines by selecting cells that repair damage by NER more efficiently; (iii) to measure the sensitivity of these cell lines to cisplatin; (iv) to test if this deficiency can be attributed to ATR signalling. We show in this study that many ovarian cancer cell lines have an important defect in GG-NER specifically in S-phase. Pairs of cell lines that were isolated before and after chemotherapeutic treatment show an increase in their GG-NER efficiency in S-phase, suggesting a role for this enzymatic process in chemotherapy resistance. Also, we have found a correlation between the efficiency of GG-NER in S-phase and the sensitivity to cisplatin in the cell lines used in our study. However, the defect in GG-NER in S-phase in these ovarian cancer cell lines doesn’t seem to be due to ATR because the phosphorylation of H2AX in response to UV is equivalent between the different cell lines. This study will have an impact on our understanding of the fundamental aspects of DNA repair but could also provide insights on a potential novel mechanism of resistance to chemotherapy.

Le stress oxydatif définit un phénomène cellulaire particulier caractérisé par un niveau élevé de molécules hautement réactives, essentiellement lié à l’utilisation de l’oxygène par les systèmes biologiques via la respiration. La dérégulation de l’état oxydatif de la cellule est à l’origine soit de processus d’adaptations efficaces (adaptation à l’altitude) soit de pathologies (AVC, infarctus). Ce travail de thèse s’est porté sur l’étude de deux nouvelles cibles pouvant induire une résistance/tolérance à la variation du stress oxydatif : la première est la protéine canal CFTR («Cystic Fibrosis Transmembrane conductance Regulator») et la seconde la voie d’activation d’eIF5A («eukaryotic Initiation translation Factor 5A»). Nous avons pu mettre en évidence que la protéine CFTR grâce à sa perméabilité au glutathion (l’antioxydant majoritaire cellulaire) est un modulateur de l’état oxydatif de la cellule, que ce soit lors de l’exposition à des agents cytotoxiques (cisplatine) ou lors de l’adaptation à des conditions hypoxiques chroniques. La deuxième cible identifiée est le facteur eIF5A qui est la seule protéine activée par la fixation d’un résidu hypusine. L’inhibition de cette modification post-traductionnelle protège les cellules d’une production d’espèces réactives induite par l’anoxie. Cette résistance à l’anoxie est accompagnée d’un profond remodelage métabolique et mitochondrial. Sur des modèles animaux d’ischémie (rein et cerveau), l’inhibition de l’activation d’eIF5A conduit à une protection des organes face à un manque d’oxygène. Ces études fondamentales ont des applications cliniques potentielles dans des pathologies humaines (infarctus, AVC, transplantation). / Oxidative stress represents a particular cellular condition, characterized by an intracellular increase in thereactive species level. These species are highly reactive towards biomolecules and result of oxygenconsumption by biological systems essentially through respiration. Deregulation of the cellular oxidativestate can initiate adaptive processes (as elevation adaptation) or several human pathologies (stroke,infarct). This thesis work has been devoted to the study of two news potential targets allowing atolerance/resistance towards disequilibrium of oxidative stress; the first one is CFTR, a channel protein(«Cystic Fibrosis Transmembrane conductance Regulator»), and the second one is the activation pathwayof the translation factor eIF5A («eukaryotic Initiation translation Factor 5A»). Based on the peculiaractivity of CFTR, consisting in the transport of glutathione, the major antioxidant of the cell, weevidenced the role of CFTR in the management of cellular oxidative state during cytotoxic drugexposure (cisplatin) or during adaptation to chronical hypoxia. The second target, eIF5A is the only oneprotein described as post-translationally modified by fixation of a hypusine residue. We demonstratedthat inhibition of eiF5A activation protect cells from reactive oxygen species generated during anoxia. Atcellular level, this protection is accompanied with deep metabolic and mitochondrial changes. Usinganimal models, we showed that inhibition of this eiF5A activation allows a tolerance against ischemicaccident in different organs (kidney and brain). These fundamentals results can have extensiveapplication in human clinical use (infarct, stroke, graft).

O objetivo da tese foi caracterizar a economia do Rio Grande de São Pedro na primeira metade do século XIX, a partir da análise da sua atividade mercantil e do padrão de investimento econômico. Investigou-se a atuação dos negociantes de grosso trato e de que modo as Guerras Cisplatinas e a Guerra dos Farrapos afetaram o comércio e a economia da região. Constatou-se que no período entre as duas guerras, parte dos investimentos anteriormente destinados aos empreendimentos rurais passou a ser aplicado na aquisição de bens urbanos e embarcações, indício da crescente urbanização vinculada à intensificação da atividade mercantil. Após a independência, o charque e os couros permaneceram como os principais produtos de exportação, mas a abertura dos portos em 1808 possibilitou que fossem estabelecidos negócios diretos com a Europa e os Estados Unidos e se amenizasse a dependência em relação ao Rio de Janeiro. Os homens de negócio (negociantes de grosso trato) diferenciavam-se dos demais agentes mercantis, ao se destacarem na importação e exportação de mercadorias e concentrarem parcelas significativas dos valores investidos nas transações envolvendo bens rurais e urbanos e no fornecimento de crédito. As principais fontes utilizadas foram os registros de entrada e saída de embarcações no porto de Rio Grande, mapas de importação e exportação e escrituras públicas de compra, crédito, sociedade e de procuração. / This thesis aimed to characterize the Rio Grande de São Pedro economy in the first half of the nineteen century through the analysis of its mercantile activity and investment pattern. It was investigated the businessmen (negociantes de grosso trato) acting and how the Cisplatine War and the Farrapos War affected the region trade and economy. It was established that during the period between the wars, part of the investments which used to be invested in rural undertakings started to be used in the acquisition of urban properties and vessels. It represents a trace of the growing urbanization linked to the increase in mercantile activity. After the Independency, the jerky and the leather remained as the main export products, but the opening of the Brazilian harbors in 1808 allowed business to be established directly with Europe and United States, reducing the dependence of Rio de Janeiro. The businessmen (negociantes de grosso trato) were different from the other merchant agents due to their highlight in the importation and exportation trade and because they concentrated significant amounts of the values invested on the transactions involving rural and urban properties and in providing credit. The main sources used were the registers of the vessels arrivals and departures from Rio Grande harbor, importations and exportation maps and public scriptures of purchase, credit, society and public authorization.

O trabalho se propõe a discutir o tema do recrutamento militar para a Guerra da Cisplatina, entre os anos de 1825 e 1828, na província do Rio Grande do Sul, pertencente ao Império do Brasil, e na Província Oriental, atual Uruguai, integrante das Províncias Unidas do Rio da Prata. Através do estudo de correspondências das autoridades militares dos dois lados do conflito e pautado pelas contribuições da “nova história militar” brasileira, se faz um estudo da legislação que regulava essa prática, a interpretação dos comandantes sobre estas, e o impacto causado na população pelos recrutadores. Enfoca-se, nessa última questão, na resistência oferecida pelas populações, de diferentes maneiras, para evitar que os homens fossem servir nos exércitos e milícias que combatiam pelo domínio da Banda Oriental. Para o caso do Brasil, se dá especial atenção à evolução da instituição militar desde o domínio português, através do estudo da legislação que regulava o serviço das armas. / The paper aims to discuss the issue of the military recruitment for the Cisplatine War between the years 1825 and 1828 in the province of Rio Grande do Sul, part of the Empire of Brazil, and in the Banda Oriental, now Uruguay, a member of the United Provinces of the Rio de la Plata. Through the study of correspondences from the military authorities on both sides of the conflict and guided by the contributions of the Brazilian "new military history", becomes a study of the legislation that regulated this practice, the interpretation of the commanders on these, and the impact on the population by recruiters. It is focused on that last question, the resistance offered by people, in different ways, to prevent men from serving in armies and militias who fought for dominance of the Banda Oriental. For the case of Brazil, it will be given particular attention to the evolution of the military institution since the Portuguese domination, through the study of legislation that regulated the military service.

L’objectif de cette thèse est de développer des nanoparticules mésoporeuses de silice (MSNs) capables de libérer un anticancéreux, le cisplatine, dans le milieu intracellulaire de tumeurs solides. Une étude paramétrique montre que les propriétés morphologiques, structurales et texturales des MSNs de type MCM-41, synthétisées par voie sol-gel à partir d’un mélange d’un précurseur de silice (TEOS) et de tensioactif (CTAB), dépendent du pH, de la vitesse d’agitation, de la température et du mode d’extraction du CTAB. La synthèse doit avoir lieu sous atmosphère contrôlée pour éviter la présence en solution d’ions carbonates et d’éthanol à l’origine de ponts entre les particules qui altèrent la stabilité colloïdale des MSNs.Les MSNs ont été fontionnalisées pour contrôler l’affinité chimique du cisplatine pour la surface des MSNs et pour améliorer la stabilité colloïdale des MSNs en milieu physiologique. Des organosilanes (APTES, TESP, MPTES, CEST) et des polymères neutres ou ionisés (PEG, PEI) ont été ajoutés par co-condensation ou par greffage post synthèse tout en préservant les propriétés structurales et texturales des MSNs. Les quantités de cisplatine encapsulées par imprégnation sont plus élevées que par adsorption et dépendent de la fonctionnalisation des MSNs. Les MSNs greffées en surface par la PEI permettent une libération progressive de l’anticancéreux ainsi qu’une cytotoxicité comparable à celle du cisplatine administré seul.Des tests in vitro montrent que les MSNs en l’absence de cisplatine ne présentent pas d’effet cytotoxique jusqu’à une concentration de 200 µg/mL. Une étude par microscopie confocale montre une internalisation des MSNs à partir de 2h de mise en contact avec les cellules. / The aim of this PhD thesis is to elaborate mesoporous silica nanoparticles (MSNs) able to sustain the release of cisplatin into the intracellular compartments of solid tumors. The parametric study shows that morphological, structural and textural properties of MSNs-MCM-41, synthesized by sol-gel reaction by using TEOS as a silica source and CTAB as a structure-directing agent, depend on pH, stirring speed, temperature and extraction process of CTAB. The synthesis atmosphere has to be controlled in order to avoid the presence of ethanol and carbonate species which are responsible of necks between particles generating unstable suspensions of MSNs.MSNs were functionalized in order to control the interactions between cisplatin and MSNs or to improve their colloidal stability in physiological media.Various silanated organic molecules (APTES, TESP, MPTES, CEST) and neutral or ionised polymers were grafted into the MSNs using a co-condensation approach or a postsynthetic functionalization method while keeping structural and textural properties of MSNs unchanged.The amount of cisplatin encapsulated by using impregnation are higher than those obtained by using adsorption and depend on MSNs fonctionalization. MSNs grafted by PEI allow a sustained drug release and cytotoxic effects similar to cisplatin. In vitro assays show that MSNs devoid of cisplatin are not cytotoxic up to 200 µg/mL. Confocal microscopy study reveals that MSNs internalization is efficient after about 2h of contact with cells.

O trabalho se propõe a discutir o tema do recrutamento militar para a Guerra da Cisplatina, entre os anos de 1825 e 1828, na província do Rio Grande do Sul, pertencente ao Império do Brasil, e na Província Oriental, atual Uruguai, integrante das Províncias Unidas do Rio da Prata. Através do estudo de correspondências das autoridades militares dos dois lados do conflito e pautado pelas contribuições da “nova história militar” brasileira, se faz um estudo da legislação que regulava essa prática, a interpretação dos comandantes sobre estas, e o impacto causado na população pelos recrutadores. Enfoca-se, nessa última questão, na resistência oferecida pelas populações, de diferentes maneiras, para evitar que os homens fossem servir nos exércitos e milícias que combatiam pelo domínio da Banda Oriental. Para o caso do Brasil, se dá especial atenção à evolução da instituição militar desde o domínio português, através do estudo da legislação que regulava o serviço das armas. / The paper aims to discuss the issue of the military recruitment for the Cisplatine War between the years 1825 and 1828 in the province of Rio Grande do Sul, part of the Empire of Brazil, and in the Banda Oriental, now Uruguay, a member of the United Provinces of the Rio de la Plata. Through the study of correspondences from the military authorities on both sides of the conflict and guided by the contributions of the Brazilian "new military history", becomes a study of the legislation that regulated this practice, the interpretation of the commanders on these, and the impact on the population by recruiters. It is focused on that last question, the resistance offered by people, in different ways, to prevent men from serving in armies and militias who fought for dominance of the Banda Oriental. For the case of Brazil, it will be given particular attention to the evolution of the military institution since the Portuguese domination, through the study of legislation that regulated the military service.

O objetivo da tese foi caracterizar a economia do Rio Grande de São Pedro na primeira metade do século XIX, a partir da análise da sua atividade mercantil e do padrão de investimento econômico. Investigou-se a atuação dos negociantes de grosso trato e de que modo as Guerras Cisplatinas e a Guerra dos Farrapos afetaram o comércio e a economia da região. Constatou-se que no período entre as duas guerras, parte dos investimentos anteriormente destinados aos empreendimentos rurais passou a ser aplicado na aquisição de bens urbanos e embarcações, indício da crescente urbanização vinculada à intensificação da atividade mercantil. Após a independência, o charque e os couros permaneceram como os principais produtos de exportação, mas a abertura dos portos em 1808 possibilitou que fossem estabelecidos negócios diretos com a Europa e os Estados Unidos e se amenizasse a dependência em relação ao Rio de Janeiro. Os homens de negócio (negociantes de grosso trato) diferenciavam-se dos demais agentes mercantis, ao se destacarem na importação e exportação de mercadorias e concentrarem parcelas significativas dos valores investidos nas transações envolvendo bens rurais e urbanos e no fornecimento de crédito. As principais fontes utilizadas foram os registros de entrada e saída de embarcações no porto de Rio Grande, mapas de importação e exportação e escrituras públicas de compra, crédito, sociedade e de procuração. / This thesis aimed to characterize the Rio Grande de São Pedro economy in the first half of the nineteen century through the analysis of its mercantile activity and investment pattern. It was investigated the businessmen (negociantes de grosso trato) acting and how the Cisplatine War and the Farrapos War affected the region trade and economy. It was established that during the period between the wars, part of the investments which used to be invested in rural undertakings started to be used in the acquisition of urban properties and vessels. It represents a trace of the growing urbanization linked to the increase in mercantile activity. After the Independency, the jerky and the leather remained as the main export products, but the opening of the Brazilian harbors in 1808 allowed business to be established directly with Europe and United States, reducing the dependence of Rio de Janeiro. The businessmen (negociantes de grosso trato) were different from the other merchant agents due to their highlight in the importation and exportation trade and because they concentrated significant amounts of the values invested on the transactions involving rural and urban properties and in providing credit. The main sources used were the registers of the vessels arrivals and departures from Rio Grande harbor, importations and exportation maps and public scriptures of purchase, credit, society and public authorization.

O trabalho se propõe a discutir o tema do recrutamento militar para a Guerra da Cisplatina, entre os anos de 1825 e 1828, na província do Rio Grande do Sul, pertencente ao Império do Brasil, e na Província Oriental, atual Uruguai, integrante das Províncias Unidas do Rio da Prata. Através do estudo de correspondências das autoridades militares dos dois lados do conflito e pautado pelas contribuições da “nova história militar” brasileira, se faz um estudo da legislação que regulava essa prática, a interpretação dos comandantes sobre estas, e o impacto causado na população pelos recrutadores. Enfoca-se, nessa última questão, na resistência oferecida pelas populações, de diferentes maneiras, para evitar que os homens fossem servir nos exércitos e milícias que combatiam pelo domínio da Banda Oriental. Para o caso do Brasil, se dá especial atenção à evolução da instituição militar desde o domínio português, através do estudo da legislação que regulava o serviço das armas. / The paper aims to discuss the issue of the military recruitment for the Cisplatine War between the years 1825 and 1828 in the province of Rio Grande do Sul, part of the Empire of Brazil, and in the Banda Oriental, now Uruguay, a member of the United Provinces of the Rio de la Plata. Through the study of correspondences from the military authorities on both sides of the conflict and guided by the contributions of the Brazilian "new military history", becomes a study of the legislation that regulated this practice, the interpretation of the commanders on these, and the impact on the population by recruiters. It is focused on that last question, the resistance offered by people, in different ways, to prevent men from serving in armies and militias who fought for dominance of the Banda Oriental. For the case of Brazil, it will be given particular attention to the evolution of the military institution since the Portuguese domination, through the study of legislation that regulated the military service.

Résumé : Il est généralement admis que les cassures double-brin (CDB) de l’ADN sont parmi les lésions les plus toxiques induites par les radiations ionisantes (RI). Les CDBs non ou mal réparées peuvent conduire à une instabilité génomique et à la mort cellulaire. La chimioradiothérapie concomitante est l’une des modalités la plus efficace pour le traitement de certains cancers surtout en stade avancé. Le rendement des CDBs a augmenté quand l’ADN a été irradié en présence de cisplatine avec des électrons de basse énergie (EBEs). Notre étude a pour objectif de réévaluer la contribution des CDBs et d’autres lésions induites par les RI dans la létalité cellulaire. L'effet des RI sur la fonctionnalité de l’ADN plasmidique modifié ou non de façon covalente par le cisplatine a été étudié par mesure de l'efficacité de transformation du plasmide dans E. coli. Les complexes cisplatine-ADN ont été préparés de telle sorte qu’il y avait en moyenne deux adduits de cisplatine par plasmide tel que mesuré par ICP-MS. Nos échantillons ont été irradiés en solution avec des doses croissantes de rayonnements gamma (137Cs). La présence de cisplatine a augmenté la formation des CDBs par un facteur de 2.6 par comparaison avec l'ADN non modifié. Malgré cette augmentation, le rendement des CDBs reste très faible et ne peut pas expliquer la perte de fonctionnalité observée. Alors que, les dommages multiples localisés (LMDS) (non-DSB cluster damage) donnant naissance à des CDBs sous l’action des enzymes de réparation la formamidopyrimidine [fapy]-DNA glycosylase (Fpg) et l’endonuclease III (Nth) où leur rendement a été augmenté d’un facteur de 2.1 lorsque l’ADN a été irradié en présence de cisplatine, ont pu expliquer la perte de fonctionnalité observée. Ces résultats suggèrent que le cisplatine peut agir, non seulement comme un agent chimiothérapeutique, mais aussi comme un radiosensibilisateur efficace par addition d’autres lésions à l’ADN. Aussi, pour la première fois nous avons pu évaluer l’effet des EBEs sur la létalité cellulaire. Des films d'ADN ont été préparés en utilisant la méthode d’adsorption douce sur un substrat de graphite pyrolytique, en présence de 1,3- diaminopropane (Dap[indice supérieur]2+) et ont été irradiées avec des EBEs 10 eV. Nous avons pu conclure, qu’en plus des CSBs, CDBs et des dommages de base, les EBEs sont capables aussi d’induire des LMDS (non-DSB cluster damage) et induire la perte de fonctionnalité de l’ADN. Le rendement des CDBs est très faible d’où ils n’ont pas pu expliquer la perte de fonctionnalité de plasmide observée, après irradiation avec les EBEs. Le rendement très faible des LMDS (non-DSB cluster damage) ne peut pas expliquer la perte de fonctionnalité de l’ADN. Il semble que les EBEs sont capables d’induire des dommages très proches les uns des autres et qui ne peuvent pas être révélés par les enzymes de réparation Fpg et Nth. Plus les dommages sont proches les uns des autres, plus leur réparation est difficile, car une de ces lésions peut inhiber la réparation de l’autre la plus proche. // Abstract : It is generally accepted that DNA double-strand breaks (DSB) are among the most toxic lesions induced by ionizing radiation (IR). Unrepaired or misrepaired DSB can lead to genomic instability and cell death. It is known that concomitant chemoradiation therapy is one of the most preferred methods for the treatment of certain cancers especially in advanced stage. The yield of DSBs was increased when DNA was irradiated with low energy electron (LEEs). The aims of our study was to reassess the contribution of DSBs and other lesions induced by indirect and direct effect of IR in cell lethality. The effect of IR on the DNA functionality of the plasmid modified covalently with cisplatin was studied by measuring the transformation efficiency of the plasmid in E. coli. Cisplatin-DNA complexes were prepared such that there was an average of two cisplatin adducts per plasmid as measured by ICP-MS. Aqueous solutions of the samples were irradiated with 137Cs [gamma]-rays at various doses. Gel electrophoresis analysis shows that cisplatin enhances, by a factor of 2.6, the formation of DSB by [gamma]-rays relative to those in unmodified DNA. Despite this increase, the yield of DSBs is very low and cannot explain the loss of functionality observed after transformation with plasmids modified with cisplatin. While locally multiple damaged sites (LMDS) revealed by repair enzymes Fpg (Formamidopyrimidine [fapy]-DNA glycosylase) and Nth (Endonuclease III) as DSB (nonDSB cluster damage), where their yield was increased by a factor of 2.1 when DNA was irradiated in the presence of cisplatin were able to explain the observed loss of DNA functionality. These results suggest that cisplatin may act not only as a chemotherapeutic agent, but also as an effective radiosensitizer by addition of other DNA lesions. For the first time, we could also evaluate the effect of low energy electrons (LEEs) on DNA functionality. Highly ordered DNA films were prepared on pyrolytic graphite by molecular self-assembly using 1,3-diaminopropane ions (Dap[superscript]2+) to bind together the plasmids and irradiated with LEE (10 eV). We concluded that in addition to CSBs, DSBs and base damage, LEEs induced the formation of non-DSB cluster damage and also induced the loss of DNA functionality under LEE irradiation. The yields of DSBs and of non-DSB cluster damage are too low and so one unable to explain the loss of DNA functionality. It seems that LEEs are able to induce a high complex damage that cannot be revealed by repair enzymes Fpg and Nth. The high complex damage is difficult to repair possibly because the repair of one lesion, may inhibit the repair of another.