Les cancers moléculaires apocrines sont un sous-groupe de cancer du sein caractérisé par l'expression du récepteur aux androgènes (RA), l'absence du récepteur aux oestrogènes (RE) et l'expression paradoxale de nombreux gènes typiquement exprimés dans les tumeurs RE positives. Une proportion significative de ces patientes va récidiver sous forme de métastases dont la prise en charge repose sur des traitements non spécifiques (chimiothérapies). En préclinique, la lignée cellulaire MDA-MB-453 a été identifiée comme ayant un profil transcriptomique similaire à ce sous-groupe tumoral. En clinique, les essais réalisés dans ce sousgroupe tumoral avec différents anti-androgènes, dont l’abiratérone (inhibiteur de la synthèse des androgènes), retrouvent un bénéfice clinique chez environ 25% des patientes. L’objectif de cette thèse est d’améliorer les connaissances et les prises en charge thérapeutiques spécifiques de ces tumeurs. Nos données précliniques comparatives montrent que l'ODM-201, nouvel antiandrogène, ne présente pas une efficacité supérieure par rapport aux antiandrogènes déjà étudiés. Afin de contourner les limites des lignées cellulaires identifiées dans ce premier projet, nous avons démontré la nécessité de développer de nouveaux modèles : les Patient-Derived-Xenograft orthotopiques. Notre deuxième projet est en faveur d’une meilleure sélection des patientes à traiter par abiratérone notamment basé sur des caractéristiques immunohistochimiques apocrines. Chez les patientes ne présentant pas ces caractéristiques, nous avons isolé CHEK1 comme une cible d’intérêt en combinaison thérapeutique pour majorer les taux de réponse de l’abiratérone en monothérapie. / Molecular apocrine cancers are a subgroup of breast cancer characterized by the expression of the androgen receptor (AR), the absence of the estrogen receptor (ER) and the paradoxical expression of many genes typically expressed in ER positive tumors. A significant proportion of these patients will recur in the form of metastases whose management is based on non-specific treatments (chemotherapy). In preclinical study, the MDA-MB-453 cell line was identified as having a transcriptomic profile similar to this tumor subgroup. Clinical trials in this tumor subgroup testing different antiandrogens, including abiraterone (inhibitor of androgen synthesis), found a clinical benefit in about 25% of patients. The aim of this thesis is to improve the knowledge and the specific therapeutic management of these tumors. Our comparative preclinical data show that ODM-201, a new anti-androgen, does not show superior efficacy compared to previously studied anti-androgens. In order to circumvent the limits of cell lines provided by this first project, we have shown the need to develop new models: orthotopic Patient-Derived-Xenograft. Our second project favors a better selection of patients to be treated with abiraterone, especially based on apocrine immunohistochemical characteristics. In patients without these characteristics, we isolated CHEK1 as a target of interest in combination therapy to increase response rates of abiraterone monotherapy.

DNA is wrapped around proteins called histones, whose modification regulates numerous cellular processes. Therefore it is not surprising that mutations in the genes that modify the histones are frequently associated with human cancer. For example, mutations in SETD2, encoding the sole enzyme that catalyses histone H3 lysine 36 trimethylation (H3K36me3), occur frequently in multiple cancer types. This identifies H3K36me3 loss as an important event in cancer development, and also as a potential therapeutic target. This thesis investigates the following questions: (1) how does the loss of H3K36me3 contribute to cancer development; and (2) what therapy can be used to kill cancers that have already lost H3K36me3. To answer the first question, this thesis shows that H3K36me3 facilitates the accurate repair of DNA double-stranded breaks (DSBs) by homologous recombination (HR). H3K36me3 promotes HR by recruiting CtIP to the site of DSBs to carry out resection, allowing the binding of HR proteins (such as RPA and RAD51) to the damage sites. Thus it is proposed that error-free HR repair within H3K36me3-decorated transcriptionally active genomic regions suppresses genetic mutations which could promote tumourigenesis. To answer the second question, this thesis reveals a clinically relevant synthetic lethal interaction between H3K36me3 loss and WEE1 inhibition. WEE1 inhibition selectively kills H3K36me3-deficient cells by inhibiting DNA replication, and subsequent fork stalling results in MUS81 endonuclease-dependent DNA damage and cell death. The mechanism is found to be synergistic depletion of RRM2 (ribonucleotide reductase small subunit), the enzyme that generates deoxyribonucleotides (dNTPs). This work reveals two pathways that regulate RRM2: one involves transcriptional activation of RRM2 by H3K36me3, and the other involves RRM2 degradation regulated by Cyclin-Dependent Kinase, CDK1 (which is controlled by WEE1, CHK1 and ATR). Based on this mechanism, the synthetic lethal interaction is expanded, from between two genes, to between two pathways. Supported by in vivo experiments, the study suggests that patients with cancers that have lost H3K36me3 could benefit from treatment with the inhibitors of WEE1, CHK1 or ATR.