L’hypoxie est une caractéristique majeure des glioblastomes (GB). Elle est la cause principale de la résistance aux traitements observée dans ces tumeurs. Les conséquences de la baisse en oxygène au niveau tumoral, sont médiées par les facteurs de transcription Hypoxia Inducible Factors (HIF). Ces facteurs sont des protéines hétérodimériques HIF-α/HIF-1β responsables de la transcription de nombreux gènes cibles. Certaines de ces cibles participent à la progression tumorale et à la mise en place d’un phénotype agressif. L’une des cibles de l’isoforme HIF-2α, est la βIII-tubuline (βIII-t). Cette protéine, qui compose les microtubules, est décrite comme surexprimée dans les gliomes de haut grade, comme les GB. Ces travaux de thèse s’intéressent au rôle de la βIII-t dans la progression tumorale ainsi qu’au développement de stratégies permettant d’inhiber l’expression de HIF-2α. Les résultats obtenus montrent que la βIII-t a une importance centrale dans le développement tumoral. En effet, les tumeurs issues de l’implantation de cellules humaines de GB invalidées pour la βIII-t, se développent significativement moins vite comparées aux tumeurs contrôles. In vitro, nous avons montré que cette protéine est impliquée dans la prolifération, la migration et l’invasion cellulaires. En revanche, nous n’avons pas pu confirmer que la βIII-t est impliquée dans la résistance aux traitements (chimio- ou radiothérapeutiques). Les deux composés testés comme inhibiteurs de HIF-2α (SR2933 et PT2385) ont montré des résultats prometteurs sur la βIII-t, gène cible spécifique de HIF-2α. Cependant, malgré les stratégies développées, nous n’avons pas pu évaluer l’efficacité directe de ces deux composés sur l’hétérodimérisation de HIF-2α avec HIF-1β. / Hypoxia is a major feature of glioblastoma (GB). It is the main cause of the resistance to treatments observed in these tumors. The consequences of the decrease in oxygen at the tumor level, is mediated by the Hypoxia Inducible Factors (HIF). These transcription factors are heterodimeric proteins HIF-α/HIF-1β responsible for the transcription of many target genes. Some of these targets are responsible for setting up an aggressive phenotype and in tumor progression. One of the targets of the HIF-2α isoform is βIII-tubulin (βIII-t). This protein, which is a constituent of microtubules, is described as overexpressed in high grade gliomas, such as GB. In the present thesis, we examined the role of βIII-t in tumor progression and we developed strategies to inhibit the expression of HIF-2α. Our results show that βIII-t is of central importance in tumor development. Indeed, tumors resulting from the implantation of GB human cells invalidated for βIII-t, developed significantly less rapidly compared to control tumors. In vitro, we have shown that this protein is involved in cell proliferation, migration and invasion. However, we could not confirm that βIII-t is involved in resistance to treatments (chemotherapeutic or radiotherapeutic).The two compounds tested as inhibitors of HIF-2α (SR2933 and PT2385) showed promising results on βIII-t, a specific target gene of HIF-2α. However, despite the different tested strategies, we could not evaluate the direct inhibitory action of these two compounds on the heterodimerization of HIF-2α with HIF-1β.

Positionnée en aval des voies PI3K/AKT et RAS/MAPK, la protéine kinase mTOR joue un rôle déterminant dans le développement et la progression tumorale des cancers colorectaux où elle est fortement surexprimée. Par ailleurs, les cancers colorectaux comme toutes les tumeurs solides, ont un microenvironnement hypoxique. L’adaptation des cellules tumorales à l’hypoxie est notamment régulée par la voie PI3K/AKT/mTOR ainsi que par les facteurs de transcription HIFs dont l’expression protéique et l’activité transcriptionnelle est en partie régulée par mTOR. Dans cette étude, nous avons montré que l’inhibition verticale et complète de l’axe PI3K/AKT/mTOR/HIF-1α par l’utilisation combinée d’irinotecan à faible dose et d’inhibiteurs catalytiques de mTOR inhibe significativement la prolifération cellulaire de lignées coliques humaines, la croissance tumorale et le développement de métastases de xénogreffes de tumeurs coliques dérivées de patients.En parallèle, une étude de cohorte de tumeurs coliques humaines de stade III par Tissue Micro Array montre que les facteurs HIFs sont fortement exprimés dans l’épithélium et le stroma de cancers du côlon de stade III, qu’une faible expression nucléaire de HIF-1α dans les cellules épithéliales confère une mauvaise survie aux patients et qu’elle a une valeur prédictive de moins bonne réponse au traitement 5-FU. / Downstream of the PI3K/AKT and RAS/MAPK pathways, mTOR protein kinase plays a decisive role in the development and tumor progression of colorectal cancers. Furthermore, the microenvironment of colorectal cancers is hypoxic. The adaptation of the tumor cells to hypoxia is regulated by the PI3K/AKT /mTOR pathway as well as by the HIFs transcription factors whose protein expression and transcriptional activity is partially regulated by mTOR. In this study, we showed that the vertical and complete inhibition of the PI3K / AKT / mTOR /HIF-1α axis by the combined use of low-dose irinotecan and mTOR catalytic inhibitors significantly inhibits human colon cancer cell proliferation, as well as the growth and metastatic development of xenografted human colon tumors. In parallel, a Tissue Micro Array study on a cohort of stage III human colic tumors shows that the HIFs are strongly expressed in the epithelium and stroma of the tumors and a low nuclear expression of HIF-1α in epithelial cells provides with poor survival to patients and has a predictive value of worse response to 5-FU treatment.

Background: Angiogenesis is recognised as a critical step in tumour progression. The angiogenic switch is activated by various trigger signals, such as hypoxia, low pH, and genetic mutations. Renal cell carcinoma (RCC) is often an aggressive tumour, and advanced disease has limited treatment options and bad prognosis. This study was focused on markers of angiogenesis in RCC: endoglin (CD105) and CD31 assessing microvessel density (MVD), and carbonic anhydrase (CA) IX and hypoxia-inducible factor (HIF)-2α expressed at hypoxia. Upregulation of HIF is also associated with inactivation of the von Hippel-Lindau (VHL) tumour suppressor gene, which is common in conventional/clear cell (c)RCC. Method: A tumour bank containing 308 tumours from patients operated 1982-2003 was used. The tumours were well characterised regarding tumour type, TNM stage, nuclear grade, tumour size, and patient survival. The tumours were prepared in tissue microarrays and fresh frozen in whole sections. To analyse the expression of endoglin, CD31, CA IX, and HIF-2α mRNA, immunohistochemistry and real-time PCR were used. Results: There was a higher endoglin expression in cRCC than in papillary (p)RCC and chromophobe (ch)RCC, and a higher CD31 expression in cRCC than in pRCC. MVD correlated inversely to TNM stage and nuclear grade in cRCC. There was also an inverse correlation between tumour diameter and CD31 expression in cRCCs. Patients with cRCC with high MVD had a more favourable prognosis than patients with lower MVD. Endoglin and CD31 were not independent prognostic factors. The CA IX expression was higher in cRCC than in pRCC and chRCC. Patients with cRCC expressing low CA IX had a significantly less favourable prognosis compared with those with higher expression. CA IX is an independent prognostic factor. There was a higher HIF-2α mRNA expression in cRCC than in pRCC and chRCC. In cRCC, there was a significant inverse correlation between HIF-2α mRNA expression, and TNM stage and nuclear grade. There was also an inverse correlation between HIF-2α mRNA expression and tumour size among patients with cRCC. HIF-2α was not an independent prognostic factor. Conclusion: In these studies, the factors related to hypoxia and vascularity were all inversely correlated to tumour aggressiveness in cRCC. MVD, CA IX, and HIF-2α expression were also higher in cRCC than in pRCC and chRCC. The relationship between angiogenesis, vascularity, and hypoxia is ambiguous. A line of reasoning including mutations increasing angiogenesis in advanced disease may also be applied to RCC. Measurements of individual angiogenic factors seem to provide prognostic information, and can potentially be combined in patient monitoring and treatment.