Bien qu’au 11ème rang des cancers les plus fréquents et au 12ème rang des cancers les plus mortels, le mélanome reste un problème médical majeur préoccupant. En effet, cette pathologie, au stade métastatique, reste réfractaire à la chimiothérapie et aux thérapies ciblées. Un certain nombre d’arguments définissent la résistance à l’apoptose comme un point crucial dans l’échec aux traitements anti-cancéreux. Ces mécanismes de résistance et chimiorésistance spécifiques aux mélanomes, déclenchés en réponse aux traitements traditionnels, sont la conséquence d’une dérégulation des voies apoptotiques suite à l’activation des protéines anti-apoptotiques, l’inactivation des protéines pro-apoptotiques avec renforcement des signaux de survie (voies de survie PI3K/Akt, NF-κB et MAPK/ERK). Une étude effectuée sur la lignée murine de mélanome B16-F0 a introduit la mélanogenèse comme une forme de résistance à l’apoptose induite par l’acide ursolique (AU), un triterpène pentacyclique d’origine naturelle ; ainsi les cellules entrant en apoptose sont capables de déclencher une résistance qui se manifeste par une surproduction de la mélanine tout en retardant la mort cellulaire. D’autres études ont montré l’implication de la COX-2 dans un mécanisme de résitance à l’apoptose dans plusieurs types de cancers dans le but de retarder leur mort cellulaire. Dans cette optique, nous nous sommes intéressés à étudier l’implication de la mélanogenèse et de la voie COX-2/PGE2 dans la résistance à l’apoptose dans le mélanome et plus précisément dans un modèle d’apoptose induite par l’AU sur la lignée humaine de mélanome M4Beu. Par la suite, nous avons décrit une interaction probable entre ces deux voies distinctes, la mélanogenèse et la voie COX-2/PGE2. Dans un autre contexte, nous avons montré que l’AU inhibe les voies de survie PI3K/Akt et ERK1/2, ce qui favorise ses effets pro-apoptotique et anti-prolifératif. Notre étude permet de mieux explorer les mécanismes de résistance spécifiques aux mélanomes tout en suggérant l’effet bénéfique de l’AU comme adjuvant naturel aux traitements chimio-thérapeutiques traditionnels. / Despite the deployment of targeted therapies, the incidence and mortality rates of cutaneous melanoma is increasing very fast making it a pre-eminent public health threat. Previously, we had showed that B16-F0 murine melanoma cells undergoing apoptosis are able to delay their own death induced by ursolic acid (UA), a natural pentacyclic triterpenoid compound. We had demonstrated that tyrosinase and TRP-1 up-regulation in apoptotic cells and the subsequent production of melanin were implicated in an apoptosis resistance mechanism. Several resistance mechanisms to apoptosis have been characterized in melanoma such as hyperactivation of DNA repair mechanisms, drug efflux systems, and reinforcement of survival signals (PI3K/Akt, NF-κB and MAPK/ERK pathways). Otherwise, other mechanisms of apoptosis resistance involving different proteins, such as cyclooxygenase-2 (COX-2), have been described in many cancer types. In this study, we demonstrated the involvement of melanogenesis and COX-2/PGE2 pathway in resistance to UA-induced apoptosis in human M4Beu melanoma cells. Then, we established the evidence that an interaction exists between these two pathways by investigating on the one hand the effect of inhibiting melanogenesis by N-phenylthiourea (PTU) on COX-2 expression and its product PGE2, and on the other hand the effect of inhibiting COX-2 activity using NS-398 on tyrosinase expression and melanin production. Furthermore, we showed that anti-proliferative and proapoptotic effects of UA were mediated through modulation of multiple signaling pathways including Akt and ERK-1/2 proteins. Our study not only uncovers underlying molecular mechanisms of UA action in human melanoma cancer cells but also suggest its great potential as an adjuvant in treatment and cancer prevention.

Made available in DSpace on 2016-05-02T13:54:42Z (GMT). No. of bitstreams: 1 DISSERTACAO COMPLETA ERICA SILVA BIANCHETTI.pdf: 401322 bytes, checksum: d859a5d12a9b16ecd28ee0fecfa86d09 (MD5) Previous issue date: 2006-06-01 / Conselho Nacional de Desenvolvimento Cientifico e Tecnologico / Etoricoxib is a new medicine expected to lead the next generation of selective inhibitors of COX-2 Presently the focus of many clinical assays it is a potent fast-action second generation coxib and the most selective of all The purpose of this study was to evaluate the interference of different nutritional diets in the anti-inflammatory and analgesic actions of etoricoxib and also the interactions of this NSAID plus different diets and their gastric and hematological side effects The following assays were carried out a) paw edema induced by carrageenin b) granuloma test c) dermatitis induced by croton oil d) vascular permeability in rats e) writhing test in mice f) formalin test g) gastric ulcers by stress and h) evaluation of the hematological parameters after sub-chronic treatment With regard to edema by carrageenin the etoricoxib-treated group showed a maximum peak of edema 49.04% (1.061 +- 0.1886) the other groups showed the following percentages of inhibiton etoricoxib + hyperproteic diet 30.2% (1.4537 +- 0.0955) etoricoxib + hyperlipidic diet 35.96% (64.04 +- 0.0578) etoricoxib + hyperglicidic diet 35.35% (1.346 +-0.0423) etoricoxib + standardized diet 33% (1.2968+-0.047) all of them in relation to the control group (2.0825+-0.1886) and the results were statistically significant (p < 0.01) However when the groups treated with etoricoxib associated to different diets were compared there was no statistically significant difference In the granuloma test the daily oral administration of 1 mg/kg of etoricoxib during 6 days significantly (p < 0.01) inhibited the formation of granulomatous tissue 57.02% (153.2 +- 21.908) the other groups showed the following percentages of inhibition etoricoxib + hyperlipidic diet 59% (144.98 +- 9.632) etoricoxib + hyperproteic diet 47.5% (185.575 +- 26.043) etoricoxib + hyperglicidic diet 38.5% (217.4 +- 21.318) etoricoxib + standardized diet 47.13% (166.583 2 +- 2.229) all of them in relation to the control group (353.475 +- 37.692) In the croton oil-induced dermatitis the edema of the control group had 10.33 mg The treatment with etoricoxib (1 mg/kg) associated with different nutritional diets showed inhibition of the edema but not significantly when compared to the control group The inhibition percentages were etoricoxib-treated group 7.86% (9.525 +- 1.345) etoricoxib + hyperproteic diet 31.43% (7.0875 +- 1.160) etoricoxib + hyperlipidic diet 35.6% (6.6625 +- 1.523) etoricoxib + hyperglicidic diet 39.5% (6.2571 +- 1.362) etoricoxib + standardized diet 30.7% (7.1875 +- 1.130) *p < 0.05 (Student s t test) when compared to the control group (10.3375 +- 1.462) In the vascular permeability by histamine etoricoxib (1 mg/kg) etoricoxib + hyperproteic diet etoricoxib + hyperlipidic diet etoricoxib + hyperglicidic diet and etoricoxib + standardized diet exhibited the following inhibition percentages 5.29% -31.4% -31.3% 4.05% and 15.82 respectively These results were not significant when compared to the control group (527.862 +- 66.869) In the writhing test the administration of etoricoxib (1mg/kg) inhibited the algogenic process in 9.32% (49.86 +- 4.166) When associated with different nutritional diets the inhibition percentages were hyperproteic diet 29.27% (38.9 +- 6.166) hyperlipidic diet 11.36% (48.75 +- 5.384) hyperglicidic diet 9.81% (49.6 +- 6.775) standardized diet -7.3% (59 +- 4.946) In the formalin test both in the acute and late phase all the treatments caused significant (p < 0.05) inhibitions of the hyperalgesic process etoricoxib (1mg/kg) 47.74% (62.71 +- 8.462) etoricoxib + hyperproteic diet 74.64% (30.428 +- 5.163) etoricoxib + hyperglicidic diet 68.61% (37.67 +- 5.308) etoricoxib + hyperlipidic diet 46.46% (64.25 +- 5.662) etoricoxib + standardized diet 68.2% (38.17 +- 5.528) when compared to the control group (120 +- 5.021) In the late phase the percentages of inhibition were 84.4% (10.142 +- 2.98) for etoricoxib 82.65% (11.28 +- 2.705) for etoricoxib + hyperproteic diet 66.16% (22 +- 11.781) for etoricoxib + hyperlipidic diet 98.72% (0.18 +- 0.0) for etoricoxib + hyperglicidic diet and 99.74% (0.16 +- 0.1667) for etoricoxib + standardized diet in comparison with the control group (65 +- 4.167) In the test of stress-induced ulcer the animals treated with etoricoxib (1mg/kg) + standardized diet showed the highest lesion index when compared to the other groups The lowest lesion index was shown by the group treated with etoricoxib + hyperlipidic diet whose significance was p < 0.01 (Student s t test) when compared to the control group The hematological parameters in the groups treated with etoricoxib (1mg/kg) + hyperlipidic diet (19.637 +- 3.879) and etoricoxib + hyperglicidic diet (19.3 +- 4.562) showed statistically significant differences in the hematocrit (HCT) in relation to the group treated only with etoricoxib (40.5375 +- 2.410) for p < 0.01 (Student s t test) There was a significant difference in the group treated with etoricoxib + hyperglicidic diet (8.9 +- 1.940) in relation to the group treated with etoricoxib (19.9 +- 2.134) (Student s t test) In the erythrocyte dosage the group etoricoxib + hyperglicidic diet (3.82125 +- 0.893) showed a significant difference when compared to the group treated with etoricoxib (9.4037 +- 1.027) (p < 0.01 Student s t test) No statistically significant differences were observed in the other hematological parameters The evaluation of the ponderal development of the animals treated with etoricoxib (1mg/kg) and etoricoxib assiciated with different kinds of nutritional diets showed no significant differences between the treated and control groups however the group treated with etoricoxib + hyperglicidic diet revealed lower ponderal development than the other groups With regard to diuresis there were variations in all the groups For water and feed consumption variations were practically similar in all the experimental groups The weight of the organs from different groups of animals treated with etoricoxib (1mg/kg) and etoricoxib associated with different nutritional diets showed no significant differences when compared to the control group The mean weight of the organs are within the normal parameters for rats The results suggest that a) the association of etoricoxib to different kinds of diets did not change the anti-inflammatory effect in the present assays b) the association of different types of diets potentialized the analgesic effect mainly when associated to hyperproteic diet for peripheral pain and hyperglicidic diet for central pain c) the association of etoricoxib to hyperglicidic diet decreases the gastric lesion index d) the use of etoricoxib alone did not interfere with the hematological parameters e) the association of etoricoxib to hyperglicidic diet interfered with the hemoglobin and erythrocyte index f) the treatment of the sub-chronic phase (30 days) with etoricoxib alone and etoricoxib associated to different nutritional diets caused no changes on the ponderal development diuresis and water and feed consumption / O etoricoxib (Arcóxia®) um medicamento novo posicionado para liderar a próxima geração de inibidores seletivos de COX-2 é um coxib de segunda geração potente e de ação rápida sendo motivo atualmente de muitos ensaios clínicos É o mais seletivo de COX-2 de todos os coxibs O objetivo deste estudo foi estudar em modelos in vivo a interferência sobre a atividade antiinflamatória e analgésica do etoricoxib antiinflamatório inibidor seletivo de COX-2 associado a diferentes tipos de dietas nutricionais observando as possíveis interações entre este AINE com as dietas empregadas e observar possíveis efeitos adversos ao nível gástrico e hematológico com o uso da associação do etoricoxib com as dietas nutricionais Para tanto foram utilizados os seguintes ensaios a) edema de pata por carragenina b) teste do granuloma c) dermatite induzida por óleo de croton d) permeabilidade vascular em ratos e) contorções em camundongos f) teste da formalina g) úlcera por estresse e h) avaliação dos parâmetros hematológicos após tratamento sub-crônico No edema por carragenina o grupo tratado com etoricoxib produziu inibição no pico máximo do edema de 49,04% (1.061 +- 0.1886) no tratado com etoricoxib + dieta hiperprotéica a inibição foi de 30,2% (1.4537 +- 0.0955) no tratado com etoricoxib + dieta hiperlipídica a inibição foi de 35,96% (64.04 +- 0.0578) no tratado com etoricoxib + dieta hiperglicidica a inibição foi de 35,36% (1.346 +- 0.0423) e no grupo tratado com etoricoxib + dieta padrão a inibição foi de 33% (1.3968 +- 0.047) todos em relação ao grupo controle (2.0825 +- 0.1886) apresentando resultados significativos estatisticamente (p < 0,01) Entretanto quando comparados entre si os grupos tratados com etoricoxib associado às diferentes dietas não houve diferença estatística significativa No teste do granuloma a administração diária de 1 mg/kg/v.o de etoricoxib durante 6 dias inibiu de forma significativa a formação do tecido granulomatoso (p < 0,01) em 57,02% (153.2 +- 21.908) e 59% (144.98 +- 9.632) pelo grupo tratado com etoricoxib + dieta hiperlipídica respectivamente no grupo tratado com etoricoxib + dieta hiperprotéica a inibição foi de 47,5% (185.575 +- 26.043) no tratado com etoricoxib + dieta hiperglicídica a inibição foi de 38,5% (217.4 +- 21.318) e no tratado com etoricoxib + dieta padrão foi 47,13% (166.583 2 +- 2.229) todas em relação ao grupo controle (353.475 +- 37.692) Na dermatite por óleo de cróton o edema no grupo controle foi de 10,33 mg Neste experimento observou-se que o tratamento dos animais com etoricoxib (1mg/kg) associado aos diferentes tipos de dietas nutricionais apresentou inibição do processo edematogênico mas não de forma significativa quando comparado com o grupo controle Para o grupo tratado com etoricoxib a inibição foi de 7,86% (9.525 +- 1.354) etoricoxib + dieta hiperprotéica foi de 31,43% (7.0875 +- 1.160) etoricoxib + dieta hiperlipídica foi de 35,6% (6.6625 +- 1.523) etoricoxib + dieta hiperglicídica foi de 39,5% (6.2571 +- 1.362) e etoricoxib + dieta padrão foi de 30.7% (7.1875 +- 1.130) *p < 0.05 ( teste t de Student) quando comparado ao grupo controle (10.3375 +- 1.462) Na permeabilidade vascular por histamina o etoricoxib (1mg/kg) etoricoxib + dieta hiperprotéica etoricoxib + dieta hiperlipídica etoricoxib + dieta hiperglicídica e etoricoxib + dieta padrão apresentaram inibições de 5,29% -18.4% -31.3% 4,05% e 15,82% respectivamente não sendo significativas quando comparados ao grupo controle (527.862 +- 66.869) No teste de contorções a administração de etoricoxib (1mg/kg) produziu 9,32% (49.86 +- 4.166) de inibição do processo algogênico e quando associado as diferentes dietas nutricionais a inibição foi de dieta hiperprotéica 29,27% (38.9 +- 6.166) dieta hiperlipídica 11,36% (48.75 +- 5.384) hiperglicídica 9,81% (49.6 +- 6.775) e dieta padrão 7,3% (59 +- 4.946) No teste da formalina tanto na fase aguda quanto na fase tardia todos os tratamentos produziram inibições significativas do processo hiperalgésico (p < 0.05) cujas percentagens de inibições foram de 47,74% para etoricoxib (1mg/kg) (62.71 +- 8.462) 74,64% para etoricoxib (1mg/kg) + dieta hiperprotéica (30.428 +- 5.163) 68,61% para etoricoxib (1mg/kg) + dieta hiperglicídica (37.67 +- 5.308) 46,46% para etoricoxib (1mg/kg) + dieta hiperlipídica (64.25 +- 5.662) e 68,2% para etoricoxib (1mg/kg) + dieta padrão (38.17 +- 5.528) quando comparados ao grupo controle (120 +- 5.021) Na fase tardia as percentagens de inibições foram de 84,4% (10.142 +- 2.98) para etoricoxib 82,65% (11.28 +- 2.705) para etoricoxib + dieta hiperprotéica 66,16% (22 +- 11.781) para etoricoxib + dieta hiperlipídica 98,72% (0,18 +- 0.0) para etoricoxib + dieta hiperglicídica e 99,74% (0.16 +- 0.1667) para etoricoxib + dieta padrão em comparação com o grupo controle (65 +- 4.167) No teste de úlcera por estresse observou-se que o tratamento dos animais com etoricoxib (1mg/kg) + dieta padrão foi o grupo que apresentou maior índice de lesão comparado aos outros grupos de tratamentos Já o grupo tratado com etoricoxib (1mg/kg) + dieta hiperglicídica foi o que apresentou menor índice de lesão cuja significância quando comparado ao grupo controle foi de p < 0.01 (teste t de Student) Os parâmetros hematológicos nos grupos tratados com etoricoxib (1mg/kg) + dieta hiperlipídica (19.637 +- 3.879) e etoricoxib + dieta hiperglicídica (19.3 +- 4.562) apresentaram diferenças estatisticamente significativas para o hematócrito (HCT) em relação ao grupo tratado apenas com etoricoxib (40.5375 +- 2.410) para p < 0.01 (teste t de student) Quanto à hemoglobina (HGB) foi significativa a diferença para o grupo tratado com etoricoxib + dieta hiperglicídica (8.9 +- 1.940) em relação ao grupo tratado com etoricoxib (19.9 +- 2.134) (p < 0.05, teste t de Student) Na dosagem de hemácias o grupo etoricoxib + dieta hiperglicídica (3.82125+- 0.893) apresentou diferença significativa quando comparada com o grupo tratado com etoricoxib (9.4037 +- 1.027) (p < 0.01, teste t de Student) Em relação aos outros parâmetros hematológicos não foram observadas diferenças significativas estatisticamente Na avaliação do desenvolvimento ponderal dos animais tratados com etoricoxib (1mg/kg) e etoricoxib associado aos diferentes tipos de dietas nutricionais não foram observadas diferenças significativas entre os grupos tratados e o controle entretanto o grupo tratado com etoricoxib + dieta hiperglicidica apresentou desenvolvimento ponderal menor que os outros grupos Em relação à diurese pôde-se observar ocorrência de variações em todos os grupos Para os consumos de água e ração houve variações praticamente semelhantes em todos os grupos experimentais Quanto ao peso dos órgãos dos diferentes grupos de animais tratados com etoricoxib (1mg/kg) e etoricoxib associado a diferentes dietas nutricionais não apresentaram diferenças significativas quando comparados ao grupo controle O peso médio dos órgãos encontram-se dentro dos parâmetros normais para a espécie animal (ratos) A partir dos resultados obtidos pode-se sugerir que a) A associação do etoricoxib aos diferentes tipos de dietas empregadas não alterou o efeito antiinflamatório nos ensaios empregados b) A associação do etoricoxib aos diferentes tipos de dietas empregadas potencializou o efeito analgésico principalmente quando associado à dieta hiperprotéica para dor periférica e dieta hiperglicídica para dor central c) A associação do etoricoxib à dieta hiperglicídica diminui o índice de lesão gástrica d) O tratamento com etoricoxib isolado não interferiu sobre os parâmetros hematológicos avaliados e) A associação do etoricoxib à dieta hiperglicídica provocou interferência sobre a taxa de hemoglobina e hemácias f) O tratamento em fase sub-crônica (30 dias) com etoricoxib e etoricoxib associado às diferentes dietas nutricionais não produziu alterações sobre o desenvolvimento ponderal diurese consumo de água e ração

Au cours des études de survie, certains facteurs ayant un rôle pronostique peuvent être inobservés ou indisponibles. Dans le cadre des essais cliniques randomisés où deux groupes de traitement sont comparés par un modèle de Cox, « l’oubli » de tels facteurs dans le modèle entraîne une sous-estimation en valeur absolue de l’effet du traitement. L’objectif de la thèse est de préciser le rôle de différents déterminants de ce biais et de suggérer l’utilisation de méthodes pouvant le réduire, avec un intérêt particulier pour les essais de prévention à l'infection VIH où de tels facteurs peuvent exister. L’effet des principaux facteurs pouvant influencer le biais est précisé dans une première partie de la thèse. Si certains facteurs sont connus de longue date, d’autres, comme la durée de l’essai n’ont, à notre connaissance, pas été étudiés. L’approche utilisée repose sur l’utilisation d’un « vrai » modèle de type à risques proportionnels. Dans ce modèle, l’effet des covariables « oubliées » est résumé par l’introduction dans l’expression du risque instantané d’un terme aléatoire de « fragilité » propre à chaque sujet. Le biais cherché est calculé comme la limite asymptotique, sous le modèle marginal correspondant au « vrai » modèle, du rapport des risques instantanés déduit du modèle de Cox n’incluant pas la fragilité. Les résultats montrent une nette augmentation du biais, en valeur absolue, avec la durée de l’essai. Cette augmentation est particulièrement marquée pour des distributions de fragilité continues comme celles pouvant être rencontrées en pratique, par rapport à des fragilités binaires. Par ailleurs, les résultats antérieurs de la littérature sont confirmés et précisés. Dans un second temps, les conséquences d’une variation de la fragilité au cours du temps sur le biais sont recherchées. Plus précisément, la situation envisagée est celle qui est rencontrée dans les essais de prévention contre le VIH effectués auprès de populations « instables » vis-à-vis du risque, comme les jeunes ou les prostituées en Afrique sub-saharienne. Ces populations montrent une hétérogénéité comportementale liée aux changements de partenaires sexuels dont le statut VIH est par ailleurs inconnu. Il s’agit d’évaluer le biais en présence d’une telle fragilité « intermittente » au moyen de simulations reflétant les situations réelles. Les résultats montrent que le biais dû à l’omission de la fragilité dans l’analyse, bien qu’inférieur au biais obtenu dans le cas d’une fragilité constante au cours du temps, reste significatif et doit être considéré. Les différentes fragilités générées au cours du suivi sont soit indépendantes entre elles, soit corrélées. Enfin, dans le cas d’une fragilité supposée constante au cours du temps, l’intérêt de l’utilisation d’un essai en « cross-over » est recherché. Dans un tel essai, les sujets exempts d’évènement après un temps de suivi donné changent de groupe de traitement. Dans le cadre des essais de prévention VIH, Auvert & al [2011] ont montré en particulier une diminution du biais avec un schéma en cross-over comparativement à un schéma parallèle classique, en utilisant une fragilité catégorielle dans une étude de simulation. Buyze & Goetghebeur [2011] ont également montré les avantages du cross-over, en particulier concernant l’efficacité relative d’un test de comparaison des deux groupes, en utilisant une fragilité de distribution gamma ou log-normale. Ces résultats sont précisés en calculant formellement le biais asymptotique dans l’estimation du risque relatif pour les différentes distributions possibles de la fragilité omise, continue ou catégorielle. Les résultats obtenus sont nettement en faveur du cross-over, avec une diminution du biais entre 60% et 90% et une amélioration de l’efficacité du test. Le temps de changement de groupe optimal est également recherché. Il apparaît que celui-ci dépend essentiellement de la durée le l'essai et de la valeur de l'effet traitement. / In survival analysis, some prognostic factors can be unobserved or unavailable. In randomized clinical trials framework where two treatment groups are compared in the Cox model setting, the omission of such factors in the model leads to an under-estimation in absolute value of the treatment effect. The aim of the project is to better understand the determinants of this bias and to suggest the use of methods that could reduce it, with a particular interest in HIV prevention trials where such factors are likely to exist. In a first step, the role of the main determinants of the bias is highlighted. While some of them have long been identified, others like trial duration have never been considered to our knowledge. The bias was calculated as the asymptotic limit of the maximum likelihood estimator of the treatment effect when the analysis is done following a proportional hazard model which no takes into account the frailty. The results show a clear increase of the bias in absolute value with the trial duration. This increase is especially marked with continuous frailty distributions, such as those which can be encountered in practice, compared to binary frailties. Also, some previous results have been confirmed. In a second step, a frailty depending on time is considered, as it can be encountered in HIV clinical trials including “unstable” population about infection risk, as prostitutes or young people in sub-Saharan Africa. These populations present a behavioral heterogeneity linked to the change of partner whose the HIV status is unknown. The bias is estimated using a transient frailty with a simulation study reflecting real-life situations. The results show that when the frailty is regenerated during the follow-up, the bias caused by its omission, although lower than the bias obtained with a time-independent frailty, stays significant and has to be considered. The different frailties generated during the follow-up are independent or correlated. Finally, with a “stable” population whose the frailty can be supposed constant over time, the interest of the use of the “cross-over” is searched. In such trial, the subjects which have not presented the event after a given time of follow-up, change of treatment group. In HIV prevention trials framework, Auvert & al. (2011) have particularly shown a decrease of the bias with a cross-over design comparatively to a parallel design, using a categorized frailty in a simulation study. Buyze & Goetghebeur (2011) have also shown the advantages of the cross-over, particularly about the relative efficiency of the comparison test of the two treatment groups, using gamma or log-normal frailty distributions. These results are specified calculating explicitly the asymptotic bias of the hazard ratio estimate for different possible distributions of the omitted frailty, continuous or categorized. The obtained results are clearly in favor of the cross-over, with a decrease of the bias between 60% et 90% and a significant improvement of the efficiency of the comparison test. The optimal switch time and its prognostic factors are searched. It appears that it essentially depends on the trial duration and is little affected by the frailty distribution or the value of the treatment effect.

Mitochondria are the key source of vital ATP molecules, which are largely produced within cells by a system of oxidative phosphorylation (OXPHOS). Genetic defects affecting any of the components of the oxidative phosphorylation system or the structure and function of mitochondria lead to mitochondrial disorders, which occur at an incidence rate of 1 in 5000 live births. Cytochrome c oxidase (COX) is the terminal enzyme and electron acceptor of a respiratory chain that catalyses oxygen to produce a water molecule. In addition to complex I deficiency, isolated or combined COX deficiency is the most common respiratory chain defect in paediatric patients, and it can arise from mutations located either in mitochondrial DNA or in nuclear genes encoding the structural subunits or corresponding assembly factors of the enzyme complex. However, the molecular basis of COX deficiency remains elusive in many patients despite advances in the identification of an increasing number of mutations and genes involved in the disease. This thesis focuses on the identification of the genetic causes of mitochondrial diseases in a cohort of 60 unrelated Czech children with clinically and laboratory confirmed COX-deficiency. With the use of a high-resolution melting analysis mutation screen, four heterozygous sequence...

We have studied aspirin as a potential chemopreventive for colorectal cancer, completing Phase I studies on aspirin pharmacology and potential biomarker assays (prostaglandins, PGE2 and PGF(2α) and cyclooxygenase modulation) in normal human subjects. These studies have determined the optimal dose of aspirin for future Phase IIa and IIb chemopreventive trials in high-risk cohorts of patients for colon cancer. Aspirin's effects on rectal prostaglandins are prolonged, detectable even after aspirin and its metabolite are removed from the plasma. Aspirin-mediated inhibition of prostaglandin production in the human rectal epithelium may be related to direct suppression of cyclooxygenase transcription and not to enzyme inactivation by acetylation. A systematic method to monitor adherence (self- report, telephone contact, pill count, and microelectronic monitoring) has been established for future trials. Strategies to improve recruitment of high-risk cohorts have been developed. Phase IIa non-randomized studies with aspirin at 81 mg in high-risk cohorts (resected Duke's A colon cancer, Duke's C colon cancer treated with adjuvant therapy and disease-free at 5 years, history of colon adenomas > 1 cm, two or more first-degree relatives with colon cancer, and familial adenomatous polyposis and hereditary non-polyposis colorectal cancer syndromes) are currently being conducted for surrogate end- point biomarker (prostaglandins, cyclooxygenase, cellular mucins, and proliferation) modulation.

Since its introduction by Max Otto Lorenz, the Lorenz curve has been utilizedin several financial contexts. By using regression analysis to approximate theclaim cost of policyholders, a vector consisting of policyholder characteristics canbe obtained. The ordered Lorenz curve can subsequently be used to understandwhat commonalities are shared between profitable policyholders. This allows forbetter management of the insurance portfolio and thus better customer relationstowards both the policyholders and the insurer, which is important for an insuranceconsultancy agency. The aim of this thesis was to investigate which attributesapproximate the policyholder claim costs and consequently obtain insight into whatattributes are shared among profitable portfolio clients. The results presented inthis thesis show that a multi-linear regression model, transformed using the Box-Cox method is insufficient to approximate the claim costs in a convincing manner.The model obtained in the thesis was capable of identifying significant regressorsbut the overall result displayed uncertainties in regards to overall goodness of fit.This means that the variability explained by the regression model only represents4.95% of the variability in the claim cost data. Thus, the relativity measureintroduced in section 2.1.1 was deemed uninterruptible in a meaningful way.Consequently, the empirical distribution functions presented in section 1.1 wouldbe based on a faulty order statistic, and in turn the visualization of an orderedLorenz curve with such a relativity measure is unnecessary. / Sedan Lorenzkurvan introducerades av Max Otto Lorenz 1904 har den använtsinom flera finansiella sammanhang. Genom att använda regressionsanalys föratt approximera försäkringstagares skadekostnader kan en vektor som består avförsäkringstagarnas attribut erhållas. Den sorterade Lorenzkurvan kan i sin turanvändas för att förstå vilka gemensamma attribut som delas mellan lönsammaförsäkringstagare. Detta möjliggör bättre hantering av försäkringsportföljen ochdärmed bättre kundrelationer mot både försäkringstagarna och försäkringsbolaget,något som är viktigt för försäkringsförmedlare. Syftet med denna avhandling var attundersöka vilka egenskaper som approximerar försäkringstagarnas skadekostnaderoch därmed få insikt i vilka attribut som delas bland lönsamma portföljkunder.Resultaten som presenteras i denna avhandling visar att en multilinjär regressionsmodell,som transformeras med Box-Cox-metoden, är otillräcklig för att approximeraskadekostnader på ett övertygande sätt. Modellen som erhölls i avhandlingenkunde identifiera signifikanta regressorer, men det övergripande resultatet visadeosäkerheter när det gäller den generella anpassning. Detta innebär att variabilitetensom förklaras av regressionsmodellen bara representerar 4,95% av variabilitetenbland skadekostnadsdatan. Därmed ansågs relativitetsmåttet som introduceras iavsnitt 2.1.1 vara oanvändbart på ett meningsfullt sätt. Följaktligen ger de empiriskafördelningsfunktionerna som presenteras i avsnitt 1.1 ett felaktig sorteringsmåttsom i sin tur medför att visualiseringen av en sorterad Lorenzkurva baserad påovannämnda mått är onödigt.

Background Treatment of cancer patients in certified cancer centers, that meet specific quality standards in term of structures and procedures of medical care, is a national treatment goal in Germany. However, convincing evidence that treatment in certified cancer centers is associated with better outcomes in patients with pancreatic cancer is still missing. Methods We used patient-specific information (demographic characteristics, diagnoses, treatments) from German statutory health insurance data covering the period 2009–2017 and hospital characteristics from the German Standardized Quality Reports. We investigated differences in survival between patients treated in hospitals with and without pancreatic cancer center certification by the German Cancer Society (GCS) using the Kaplan–Meier estimator and Cox regression with shared frailty. Results The final sample included 45,318 patients with pancreatic cancer treated in 1,051 hospitals (96 GCS-certified, 955 not GCS-certified). 5,426 (12.0%) of the patients were treated in GCS-certified pancreatic cancer centers. Patients treated in certified and non-certified hospitals had similar distributions of age, sex, and comorbidities. Median survival was 8.0 months in GCS-certified pancreatic cancer centers and 4.4 months in non-certified hospitals. Cox regression adjusting for multiple patient and hospital characteristics yielded a significantly lower hazard of long-term, all-cause mortality in patients treated in GCS-certified pancreatic centers (Hazard ratio = 0.89; 95%-CI = 0.85–0.93). This result remained robust in multiple sensitivity analyses, including stratified estimations for subgroups of patients and hospitals. Conclusion This robust observational evidence suggests that patients with pancreatic cancer benefit from treatment in a certified cancer center in terms of survival. Therefore, the certification of hospitals appears to be a powerful strategy to improve patient outcomes in pancreatic cancer care.

Master of Science / Department of Statistics / James J. Higgins / The time for an event to take place in an individual is called a survival time. Examples include the time that an individual survives after being diagnosed with a terminal illness or the time that an electronic component functions before failing. A popular parametric model for this type of data is the Weibull model, which is a flexible model that allows for the inclusion of covariates of the survival times. If distributional assumptions are not met or cannot be verified, researchers may turn to the semi-parametric Cox proportional hazards model. This model also allows for the inclusion of covariates of survival times but with less restrictive assumptions. This report compares estimates of the slope of the covariate in the proportional hazards model using the parametric Weibull model and the semi-parametric Cox proportional hazards model to estimate the slope. Properties of these models are discussed in Chapter 1. Numerical examples and a comparison of the mean square errors of the estimates of the slope of the covariate for various sample sizes and for uncensored and censored data are discussed in Chapter 2. When the shape parameter is known, the Weibull model far out performs the Cox proportional hazards model, but when the shape parameter is unknown, the Cox proportional hazards model and the Weibull model give comparable results.

Background: The study examined the effects of the determinants of under-five mortality in Malawi. It therefore aimed to estimate the rate or prevalence of under-five mortality in Malawi and to examine differentials in infant and child mortality by socio-economic, demographic, environmental, health-seeking behaviour and nutritional value. Methods: This study involved a secondary data analysis of the 2010 Malawi Demographic and Health Survey (MDHS) data set of children under five years old and women who had given birth in the five years preceding the survey. The Kaplan-Meier survival analysis and multivariate hazard analysis were used to examine the relationship between under-five mortality and socio-economic. demographic, environmental, health-seeking behaviour and nutritional factors. Results: The results show that birth order, mother's education, place of residence. region and exclusive breastfeeding were significantly associated with under-five mortality. The results also show that there was no significant association between under-five mortality and other indicators of socio-economic. demographic. environmental, health-seeking behaviour. The results also show that more deaths of under-fives occurred during infancy than during childhood. Conclusion: The results show that more deaths occurred during the first months after birth than after 12 months of age. This showed that mother's education, birth order, place of residence, region and breastfeeding had a greater influence on the survival of the child. / Thesis (M.Soc.Sc. Population Studies) North-West University, Mafikeng Campus, 2014

In Sweden, all banks must report their regulatory capital in their reports to the market and their models for calculating this capital must be approved by the financial authority, Finansinspektionen. The regulatory capital is the capital that a bank has to hold as a security for credit risk and this capital should serve as a buffer if they would loose unexpected amounts of money in their lending business. Loss-Given-Default (LGD) is one of the main drivers of the regulatory capital and the minimum required capital is highly sensitive to the reported LGD. Workout LGD is based on the discounted future cash flows obtained from defaulted customers. The main issue with workout LGD is the incomplete workouts, which in turn results in two problems for banks when they calculate their workout LGD. A bank either has to wait for the workout period to end, in which some cases take several years, or to exclude or make rough assumptions about those incomplete workouts in their calculations. In this study the idea from Survival analysis (SA) methods has been used to solve these problems. The mostly used SA model, the Cox proportional hazards model (Cox model), has been applied to investigate the effect of covariates on the length of survival for a monetary unit. The considered covariates are Country of booking, Secured/Unsecured, Collateral code, Loan-To-Value, Industry code, Exposure-At- Default and Multi-collateral. The data sample was first split into 80 % training sample and 20 % test sample. The applied Cox model was based on the training sample and then validated with the test sample through interpretation of the Kaplan-Meier survival curves for risk groups created from the prognostic index (PI). The results show that the model correctly rank the expected LGD for new customers but is not always able to distinguish the difference between risk groups. With the results presented in the study, Nordea can get an expected LGD for newly defaulted customers, given the customers’ information on the considered covariates in this study. They can also get a clear picture of what factors that drive a low respectively high LGD. / I Sverige måste alla banker rapportera sitt lagstadgade kapital i deras rapporter till marknaden och modellerna för att beräkna detta kapital måste vara godkända av den finansiella myndigheten, Finansinspektionen. Det lagstadgade kapitalet är det kapital som en bank måste hålla som en säkerhet för kreditrisk och den agerar som en buffert om banken skulle förlora oväntade summor pengar i deras utlåningsverksamhet. Loss- Given-Default (LGD) är en av de främsta faktorerna i det lagstadgade kapitalet och kravet på det minimala kapitalet är mycket känsligt för det rapporterade LGD. Workout LGD är baserat på diskonteringen av framtida kassaflöden från kunder som gått i default. Det huvudsakliga problemet med workout LGD är ofullständiga workouts, vilket i sin tur resulterar i två problem för banker när de ska beräkna workout LGD. Banken måste antingen vänta på att workout-perioden ska ta slut, vilket i vissa fall kan ta upp till flera år, eller så får banken exkludera eller göra grova antaganden om dessa ofullständiga workouts i sina beräkningar. I den här studien har idén från Survival analysis (SA) metoder använts för att lösa dessa problem. Den mest använda SA modellen, Cox proportional hazards model (Cox model), har applicerats för att undersöka effekten av kovariat på livslängden hos en monetär enhet. De undersökta kovariaten var Land, Säkrat/Osäkrat, Kollateral-kod, Loan-To-Value, Industri-kod Exposure-At-Default och Multipla-kollateral. Dataurvalet uppdelades först i 80 % träningsurval och 20 % testurval. Den applicerade Cox modellen baserades på träningsurvalet och validerades på testurvalet genom tolkning av Kaplan-Meier överlevnadskurvor för riskgrupperna skapade från prognosindexet (PI). Med de presenterade resultaten kan Nordea beräkna ett förväntat LGD för nya kunder i default, givet informationen i den här studiens undersökta kovariat. Nordea kan också få en klar bild över vilka faktorer som driver ett lågt respektive högt LGD.