<p><strong>A growing body of evidence suggests that most human tumors, including those of the breast, are organized as cellular hierarchies. Positioned at the apex of these hierarchies are tumor-initiating cells (TICs), which are capable of limitless self-renewal and also differentiate, to give rise to various populations of non-tumorigenic cells that make up the bulk of the tumor. Importantly, recent findings have demonstrated that TICs are refractory to current best practice therapies, and thus likely account for high rates of tumor recurrence following remission. Therefore, it will likely be important to identify novel means of targeting TICs in order to achieve durable cancer cures.</strong></p> <p><strong>Using a highly sensitive transplantation assay, our laboratory previously showed that mammary tumors arising in various strains of transgenic mice comprise a very high fraction of TICs, and that when cells from these tumors are propagated in serum-free medium as tumorspheres, the high frequency of TICs is maintained. We therefore sought to use mouse mammary tumorspheres as an <em>in vitro</em> system with which to identify TIC-targeted agents and carried out a high-throughput screen of nearly 32,000 small molecules. To eliminate compounds showing general toxicity, we employed mouse mammospheres, which primarily comprise normal mammary epithelial stem and progenitor cells, in a secondary screen. Using this platform, we identified a small molecule that selectively targeted tumorsphere-derived cells <em>in vitro</em> and led to tumor growth arrest and tumor cell death <em>in vivo</em>. This study illustrates the utility of mouse models and high throughput screening to identify compounds which may target TICs but spare untransformed stem cells.</strong></p> / Master of Science (MSc)

Selective killing of tumor cells requires the identification of drug targets critical to pathways that drive or support cancer progression. Protein kinases are an important class of intracellular enzymes involved in the regulation of biochemical pathways, deregulation of these kinases has been strongly implicated in cancer progression. To identify possible oncogenic kinases to which tumor cells might be selectively addicted, we screened the ON108 series of ATP-mimetic small molecule inhibitors in various triple negative breast cancer (TNBC) and normal cell lines. This approach led us to the identification of a novel kinase inhibitor, ON108600. We first examined the in vitro and in vivo effects of ON108600. ON108600 was found to be a potent inhibitor of Casein Kinase 2 (CK2) and the Dual-Specificity-Tyrosine (Y)-Phosphorylation-Regulated-Kinase (DYRK) family of serine-threonine kinases, both of which have been implicated in cancer progression. ON108600 showed broad-spectrum anti-proliferative and cytotoxic activity in multiple TNBC cell lines whilst having little or no effect on normal cells. Treatment of cancer cells with ON108600 resulted in inhibition of downstream signaling mediated by substrates of CK2. Further, ON108600 selectively arrested cancer cells in the mitotic phase of the cell cycle and activated the caspase-signaling cascade. We next performed x-ray crystallographic studies of ON108600-CK2 to determine the structural basis of ON108600-CK2 interaction. The co-crystal structure of ON108600-CK2 revealed that ON108600 binds in the active site pocket of CK2&alpha; wherein it mimics the binding of ATP and GTP in the CK2 active site. Notably, ON108600 mimics not only the shape and electrostatics of ATP/GTP, but also their hydration patterns in the CK2 active site pocket. Structural studies further revealed that ON108600 induces a conformational change in the &beta;4-&beta;5 loop of the catalytic subunit, which is known to interact with the &beta;-regulatory subunit of CK2 and is critical for substrate recognition and activation. Lastly, we examined the efficacy of ON108600 in Triple Negative Breast Cancer (TNBC) and its ability to target and eliminate chemo-resistant Tumor-Initiating Stem Cells (TI-SCs) in TNBC. Clonogenic survival and sphere forming ability of purified CD44high CD24-/low TI-SCs from MDAMB-231 and Hs578t cells was potently inhibited by ON108600 treatment. We also observed that paclitaxel-resistant MDAMB-231 cells had increased levels of the CD44high CD24-/low stem cell- like population that correlated with increased expression of kinases CK2&alpha;2, DYRK1A and DYRK1B and these cells were sensitive to ON108600 treatment. Significantly, ON108600 showed robust antitumor efficacy as a single agent in a highly aggressive orthotopic TNBC xenograft model showing ~60% tumor growth inhibition. Immunohistochemical analysis of ON108600 treated tumors showed that a significant percentage of cells were apoptotic, indicating that activation of caspase mediated apoptosis contributes to the mechanism of action of ON108600 in vivo. Taken together, our results demonstrate that ON108600 is a novel and potent inhibitor of the CK2&alpha;1, CK2&alpha;2, DYRK1A and DYRK1B kinases. ON108600 binds in the active site pocket of CK2&alpha; and mimics ATP-GTP binding. ON108600 inhibits CK2-mediated signaling; arrests cancer cells in mitosis and induces apoptotic cell death via activation of caspases. Importantly, ON108600 is able to effectively kill the CD44high CD24-/low breast-cancer stem cell like population from TNBC cells. Finally, taxol-resistant MDAMB-231 TNBC cells express high levels of CD44, CK2&alpha;2, DYRK1a and DYRK1b and are sensitive to ON108600 treatment. Our study represents the first attempt to associate protein kinase CK2, DYRK1A and DYRK1B with TNBC and TI-SCs in TNBC and identifies a novel kinase inhibitor, ON108600 which effectively kills TI-SCs and taxol-resistant cells in TNBC. / Molecular Biology and Genetics

Glioblastoma (GBM) is a very aggressive and invasive tumour that relapses within nine months of diagnosis and remains incurable despite advances in multimodal therapy including surgical resection, chemotherapy and radiation. Poor patient outcome has been correlated to specific markers of brain tumour initiating cells (BTIC) and intratumoural heterogeneity (ITH), which have also been associated with treatment resistance and tumour recurrence. ITH can be explained at the cellular level by the existence of multiple populations of cancer cells, including some which have acquired stemness properties like self-renewal, proliferation, and multilineage differentiation, also known as cancer stem cells (CSCs). In brain tumours, CSCs or BTICs, have been shown to be resistant to both chemotherapy and radiation treatment, allowing them to escape therapy and consequently generate for tumour recurrence. As a result, therapies that focus on targeting the BTIC compartment within the bulk GBM tumour would provide better treatment and prognosis for patients. To profile GBM BTICs we conducted two transcriptomic screens. The first compared GBM BTICs to neural stem cells (NSCs), their healthy counterparts, and for the second we developed a pipeline utilizing a dynamic BTIC patient-derived xenograft (PDX) model of human GBM recurrence allowing for the profiling of GBM BTICs at engraftment, after chemoradiotherapy delivery in a phase we have termed "minimal residual disease" (MRD), and at tumour recurrence. In this study, Dickkopf-1 (DKK1) was identified as a potential therapeutic target for GBM from each transcriptomic screen and was studied using short hairpin knockdowns, blockade with monoclonal antibodies, and subsequent functional stem cell assays. / Thesis / Master of Science (MSc) / Glioblastoma (GBM) is a very aggressive tumour that relapses within nine months of diagnosis and remains incurable despite chemotherapy, radiation, and surgery. Relapse is believed to be caused by the presence of a wide variety of cell types, including cancer stem cells (CSCs), which have been shown to be resistant to both chemotherapy and radiation in GBM. As a result, therapies that focus on targeting the CSCs within the bulk GBM tumour would provide better treatment for patients. In this study, we analyzed this cell population by conducting two screens. The first compared the level at which genes are expressed in GBM CSCs in comparison to how they are expressed in their healthy counterparts, neural stem cells, whereas the second compared the primary patient GBM tumour to its relapsed form in a mouse model of the disease. In this study, the protein Dickkopf-1 (DKK1) was identified and validated as a potential therapeutic target of GBM using well established molecular and stem cell functional assays.

Yes / A sub-population of cells named cancer stem cells (CSCs) that initiate and promote tumour growth have been demonstrated to exist in several malignancies including colon carcinoma. The objective of our pilot study was to isolate CD133+CD26+CD44+ CSCs from patient colon tumours, culture spheres or organoids and observe their proliferation in primary cultures. Parallel cultures of non-cancer controls from colon normal lining and nonadenomatous polyps were set up. Magnetic activated cell sorting was used to isolate CD133+CD26+CD44+ cell populations followed by primary cell culturing under stem cell culture conditions. Number, cells/organoid and daughter generations of organoids were calculated using phase contrast microscope. Trypan blue exclusion method was used to test the viability of the cells. Both colon tumour and colon non-adenomatous polyp formed floating organoids in suspension; however non-adenomatous polyp cultures did not show self-renewal properties for more than 1 passage. Normal colon singlecell suspension did not create organoids. Metastatic colon tumours rapidly produce cancer cell organoids in less than 24 hours in larger numbers compared to non-metastatic colon tumours (1-3 weeks). Metastatic colon tumour organoids have the ability for proliferation for upto five daughter generations in primary culture compared to three generations for those grown from non-metastatic tumours. This in vitro CSC organoid model will help study colon cancer biology, in particular providing a valuable source of primary cell-derived tissue for studying personalized molecular profiling using ‘omics strategies to direct therapeutic intervention.

Le neuroblastome (NB) est la tumeur solide extracranienne la plus fréquente chez le jeune enfant. En dépit de plusieurs avancements thérapeutiques, seulement 60% survivront à long terme. Cette résistance aux traitements est possiblement due, en partie, à la présence des cellules souches cancéreuses (CSC). PARP-1 joue un rôle important dans la chimiorésistance de certaines tumeurs et son inhibition a montré une potentialisation des agents anticancéreux conventionnels. De plus, Bcl-2 est surexprimé dans le NB et son expression accrue contribuerait à la résistance à la chimiothérapie. Le but de notre travail était de déterminer les effets in vitro d’un PARP inhibiteur, AG-014699 (AG), et d’un inhibiteur de Bcl-2, Obatoclax (Obx), in vitro et in vivo, en monothérapie ou en combinaison avec de la Doxorubicine (Doxo) ou du Cisplatin (Cis), deux agents anticancéreux classiquement utilisés dans le traitement du NB. Afin de déterminer l’expression de PARP-1 dans les tumeurs de NB, nous avons analysé une cohorte de 132 tumeurs. Nous avons utilisé le test MTT afin d’évaluer la sensibilité de 6 lignées cellulaires de NB et des CSC à un traitement avec AG seul ou en combinaison avec de la Doxo ou du Cis. Nous avons déterminé l’étendue de la mort cellulaire par Annexin-V et caractérisé les dommages à l’ADN à l’aide d’un marquage γH2aX. De plus, les modulations des voies de signalisation intracellulaire ont été analysées par Western Blot. La sensibilité des cellules à l’Obx a été analysée par MTT sur 6 lignées cellulaires de NB et sa combinaison avec le Cis a également été déterminée dans 2 lignées cellulaires. Le marquage Annexin-V et des combinaisons avec ZVAD-FMK ont aussi été utilisés pour caractériser les effets d’Obx sur l’apoptose. Des expériences in vivo ont également été faites. Nos résultats démontrent que l’expression de PARP-1 est associée aux tumeurs moins agressives. AG n’a peu ou pas effet sur la croissance tumorale et ne potentialise pas significativement les effets de la Doxo ou de Cis. AG combiné à la Doxo semble sensibiliser les CSC dans une lignée cellulaire. L’Annexin-V et le marquage γH2aX ne révèlent pas d’effets synergiques de cette combinaison et les dommages à l’ADN et la mort cellulaire observés sont attribués à la Doxo. Cependant, on observe une augmentation d’apoptose et de bris d’ADN dans une lignée cellulaire (SK-N-FI) lorsqu’AG est utilisé en monothérapie. On observe une surexpression de pAKT et pERK suite à la combinaison Doxo et AG. Les cellules de NB sont sensibles à l’Obx à des concentrations à l’échelle nanomolaire. De plus, Obx active la mort cellulaire par apoptose. Aussi, Obx a un effet synergique avec le Cis in vitro. In vivo, l’Obx diminue significativement la taille tumorale. Nous concluons que l’Obx présente une avenue thérapeutique prometteuse dans le traitement du NB alors que l’utilisation d’AG ne semble pas être aussi encourageante. / Neuroblastoma (NB) is the most common extracranial solid tumour of childhood. In spite of many therapeutic improvements, only 60% survive long term. Presence of cancer stem cell (CSCs) is thought to mediate such resistance. PARP-1 plays an important role in the chemoresistance of certain tumours and its inhibition is shown to potentiate cells to routinely used anticancer agents. Moreover, Bcl-2 is over-expressed in NB and that its increased expression would contribute to chemotherapy resistance. Our goal was to determine the efficacy in vitro of a PARP inhibitor, AG-014699 (AG), and a Bcl-2 inhibitor, Obatoclax (Obx), in vitro and in vivo, in monotherapy or in combination to Doxorubicine (Doxo) and Cisplatine (Cis), classical chemotherapeutic agents used in NB treatment. In order to determine PARP-1 expression in NB tumours, 132 tumours were analyzed. We used an MTT test to evaluate 6 NB cell line and CSC sensitivity to AG alone or in combination to Doxo and Cis. We investigated the extent of cell death by Annexin-V and determined the degree of DNA damage by γH2aX staining. Also, signalling pathway modulations were analyzed by Western Blots. Obx sensitivity was determined by MTT test on 6 NB cell lines and its combination to Cis was also examined in 2 NB cell lines. Annexin-V and combinations to ZVAD-FMK also evaluated its effect on apoptosis. In vivo experiments were also done. Our results show that PARP-1 is associated to less aggressive tumors. AG has little to no effect on tumour growth when used alone and does not potentiate the effects of Doxo and Cis although more experiments will be needed. AG combined to Doxo seems to sensitize CSC in one cell line. Annexin-V and γH2aX staining reveal no effects of AG combination and Doxo mostly confers all cell damage and death. However, we do observe an increase in DNA damage and apoptosis in one cell line (SK-N-FI) when AG is used in monotherapy. pAKT and pERK are upregulated by Doxo and AG combination. NB cells are sensitized to Obx at nanomolar concentrations. Also, Obx activates apoptotic cell death. Moreover, Obx synergizes with Cis in vitro. In vivo, Obx significantly decreases tumor size. We conclude that Obx seems like a promising therapeutic approach in NB treatment whilst AG does not look so encouraging.

L’étude des mécanismes aboutissant à la tumorigénèse a permis de révéler, dans beaucoup de cancers, une amplification ou une mutation de divers oncogènes, avec pour conséquence des capacités de prolifération et de survie accrues pour la cellule tumorale. L’identification des protéines kinases comme étant des éléments centraux de ces processus en ont fait des cibles thérapeutiques prometteuses. Plusieurs inhibiteurs ciblant de façon plus ou moins spécifique les tyrosines kinases oncogéniques ont ainsi été développés. Parmi eux, l’imatinib mesylate (Gleevec®, Novartis) a constitué la première chimiothérapie ciblée. Il correspond aujourd’hui au traitement de première intention contre la LMC. Cependant, malgré sa très grande efficacité, il est apparu que certains mécanismes de résistances pouvaient être mis en place pour diminuer son effet pro-apoptotique. Le travail de cette thèse a consisté à mieux comprendre les mécanismes d’apoptose induits par les inhibiteurs de tyrosine kinases (ITK), et à rechercher quelles voies alternatives de survie devront être bloquées pour leur assurer une meilleure efficacité. Trois modèles ont été utilisés : la leucémie myéloïde chronique (LMC), les leucémies aiguës myéloïdes (LAM) et les glioblastomes (GBM). La LMC a été utilisé comme modèle et la démarche utilisé pour essayer d’augmenter l’efficacité des ITK, a été transposée aux modèles des LAM et des GBM. L’ensemble des résultats obtenus a démontré qu’une meilleure compréhension de la réponse apoptotique et des mécanismes de résistance permettait l’identification de nouvelles cibles thérapeutiques. Nous avons pu observer que, tout en favorisant la diminution des doses de molécules administrées, l’inhibition simultanée de plusieurs cibles apportait plusieurs bénéfices. Elle permet d’augmenter l’action pro-apoptotique des ITK, de contrer certains mécanismes de résistances, d’atteindre la cellule souche cancéreuse résistance et par conséquent de cibler simultanément des populations a plusieurs de stades de différenciation. / Protein kinases have been identified as playing fundamental roles in cancer development, suggesting that they could represent a promising therapeutic target. Several kinase inhibitors have been developed and the most successful of them, by far, is Gleevec® (imatinib, STI57; Novartis), a BCR-ABL inhibitor. It is currently used as the treatment of reference for chronic myeloid leukemia. However, despite a huge efficiency, some resistance mechanisms could be used to decrease its pro-apopototic effect. The global aim of my PhD was to understand the apoptotic mechanisms induced by tyrosine kinase inhibitors (TKI) to identify new potential therapeutic targets. I work on three different tumors: Chronic Myeloid Leukemia (CML), Acute Myeloid Leukemia (AML) and Glioblastomas (GBM). CML has been used as a model and the approach followed to increase TKI efficiency has been transposed to AML and GBM models. Altogether, our results showed that a better understanding of apoptotic response and resistance mechanisms could lead to the identification of new therapeutic targets. We observed that combination therapy brings several benefits. It allows to increase the TKI-induced apoptotic response, to counter some resistance mechanism, to reach the resistant cancer stem cells, and thus, to target simultaneously several populations in the tumour.

Au sein des tumeurs, y compris pour le carcinome hépatocellulaire (CHC), des sous-populations de cellules néoplasiques ont révélé une grande capacité à initier de nouvelles tumeurs et à induire des métastases. Les premières études sur ces cellules ont rapidement montré que la présence de ces cellules était déterminante dans le développement tumoral et elles ont donc été renommées « cellules souches cancéreuses » (CSCs). Malheureusement les mécanismes impliqués dans la maintenance de ces CSCs ne sont que partiellement compris. Par ailleurs dans le CHC un lien a été établi entre les signaux du facteur de croissance de transformation (Transforming Growth Factor, TGF-ß) provenant du microenvironnement tumoral et certaines populations de cellules cancéreuses dont la présence est corrélée à un faible pronostic. La façon dont TGF-ß peut ainsi établir et modifier un phénotype cellulaire dans le CHC reste néanmoins obscure. La méthylation de l’ADN étant un acteur majeur dans la mise en place des programmes cellulaires, notre but a été de caractériser le méthylome de CSCs hépatiques et son lien avec la capacité de TGF-ß à induire des CSCs. Nous nous sommes appuyés sur l’expression du marqueur CD133 pour définir la population de CSCs hépatiques. Afin comprendre l’importance des marques de méthylation de l’ADN dans les CSCs hépatiques, nous avons dans un premier temps déterminé quelle était la signature des cellules CD133+ au niveau de la méthylation de l’ADN en utilisant des puces de méthylation à grande échelle. Les sites CpG différentiellement méthylés ont montré un enrichissement pour d’une part des voies de signalisation déjà identifiées dans les CSCs et, d’autre part, pour des voies de signalisation associées au processus inflammatoire dont la voie TGF-ß/SMAD. Par la suite, nous avons montré que TGF-ß pouvait induire de façon permanente les cellules CD133+ contrairement à une autre cytokine influente dans le cancer du foie, l’interleukine 6. Cette augmentation de cellules CD133+ induite par TGF-ß est associée à des changements de méthylation de l’ADN sur l’ensemble du génome et qui sont, de plus, maintenus au cours des divisions cellulaires. La comparaison entre les deux méthylomes (liés aux cellules CD133+ et à l’action de TGF-ß) a exposé une signature commune significative indiquant que TGF-ß pourrait promouvoir le phénotype de CSC via le processus de méthylation de l’ADN. Mais nous avons également déterminé qu’une grande partie des effets sur la méthylation induits par TGF-ß était totalement indépendante de l’induction de cellules CD133+. Enfin, nous avons observé que les sites de méthylation sensibles au signal de TGF-ß étaient regroupés de façon significative au niveau de régions « enhancer » qui régulent la transcription des gènes. Par ailleurs, ces sites incluaient également des gènes précédemment identifiés comme cibles de TGF-ß mais aussi des gènes codant pour des acteurs épigénétiques de premier ordre comme les méthyltransférases de l’ADN. Ces résultats constituent la première description d’une signature de méthylation de l’ADN induite par TGF-ß permettant une reprogrammation stable vers un profil épigénétique de CSC hépatiques. / Distinct subpopulations of neoplastic cells within tumors, including hepatocellular carcinoma (HCC), display a pronounced ability to initiate new tumors and induce metastasis. Investigations on theses cells rapidly described them as essential for tumor growth and based on theses observations they have been named “cancer stem cells” (CSCs). Unfortunately, the mechanisms involved in sustaining their programs are only partially known. In HCC, there is an established link between microenvironmental signals from Transforming Growth Factor beta (TGF-ß) and survival of certain cell subpopulations which is results in a bad prognosis. However, how TGF-ß establishes and modifies cell behavior in HCC is not fully understood. As DNA methylation is involved in establishing cellular programs, our aim was to characterize the methylome of putative liver CSCs, and its link to the ability of TGF-ß to induce liver CSCs. We used CD133 expression as a positive marker for liver CSC. To understand the relevance of DNA methylation programs in liver CSCs, we first defined the methylome signature of CD133+ cells in liver cancer cells using methylation bead arrays. Differentially methylated CpG sites were enriched in known pathways related to CSC survival and to inflammation, including the TGF-ß/SMAD pathway. Next, we showed that TGF-ß persistently induces CD133+ cells in opposition to another cytokine related to HCC, interleukin 6. We observed that this increase is associated with genome-wide changes in the methylome induced by TGF-ß and that are perpetuated through cell division. We observed a significant overlap between the CD133+ methylome and the methylome induced by TGF-β, indicating that TGF-ß may induce CSC phenotype through DNA methylation reprogramming. Additionally, we observed genome-wide effects of TGF-ß that are independent of the induction of CD133. Finally, TGF-ß methyl-sensitive sites were significantly concentrated in enhancer regions of the genome, and include well-known targets of TGF-ß, and epigenetic players, such as de novo DNA methyl-transferases. In conclusion our results are the first indication of the ability of TGF-ß to induce genome-wide changes of DNA methylation, leading to a stable switch to a liver cancer stem cell epigenetic program.

O carcinoma hepatocelular (HCC) é uma neoplasia primária com mau prognóstico e alta taxa de recorrência. Estudos recentes demostram que o HCC pode ser classificado em três subtipos segundo o perfil molecular. Destes subtipos, o HCC pouco diferenciado apresenta pior prognostico. Neste sentido, torna-se de particular interesse o estudo de compostos com efeitos diferenciadores e citotóxicos nas células destas neoplasias pouco diferenciadas. O butirato, um ácido graxo de cadeia curta produzido pela fermentação microbiana da fibra alimentar no intestino, tem demonstrado atividade anti-neoplásica e capacidade moduladora da diferenciação celular em diversos tipos celulares, incluindo linhagens de HCC humano e células progenitoras hepáticas. Assim, objetivou-se neste estudo, caracterizar o efeito do butirato de sódio (NaBu) em duas linhagens de células neoplásicas de rato: uma pouco diferenciada (GP7TB) e a outra, uma linhagem derivada de um HCC diferenciado (JM-1). A linhagem GP7TB mostrou maior resistência ao NaBu (ED50= 7,7 mM) do que as células JM-1 (ED50= 5,2 mM). A redução na viabilidade celular após 72 h de tratamento com NaBu esteve relacionada com a diminuição na proliferação celular e no caso das células GP7TB, de um aumento na apoptose. O tratamento com NaBu induziu alterações morfológicas nas duas linhagens celulares, porém apenas nas células do tipo GP7TB, essas alterações sugerem um processo de diferenciação/transdiferenciação celular. O aumento na expressão de genes envolvidos no controle da pluripotência de células tronco, assim como de alguns marcadores de células tronco, sugere que o NaBu induziu uma reprogramação profunda das células GP7TB. Por outro lado, a redução na expressão de genes relacionados com migração e plasticidade celular assim como de proliferação celular apontam que estas células diminuíram seu potencial invasivo e a capacidade de autorenovação. Embora sejam necessárias análises adicionais para confirmar o efeito observado nos perfis de expressão gênica, os resultados deste estudo sugerem que o NaBu apresenta efeito antineoplásico por meio da redução da proliferação, aumento da apoptose e modulação da expressão de genes associados com a transição epitéliomesenquimal em células com características tronco tumorais. / Hepatocellular carcinoma (HCC) is a primary neoplasia with poor prognosis and high recurrence rate. Recent evidence suggests that HCC can be classified in three different subtypes based on their molecular profile. Among these subtypes, the poorlydifferentiated HCC has the worst prognosis. Therefore, the study of compounds with pro-differentiating and cytotoxic effects on poorly-differentiated neoplastic cells represents a matter of primary concern. Butyrate which is a short-chain fatty acid produced by microbial fermentation in the intestine, has demonstrated anti-neoplastic activity and pro-differentiating potential in several cell types, including, human HCC cell lines and liver progenitor cells. In this study, we aimed to characterize the effect of sodium butyrate (NaBu) on two neoplastic cell lines derived from rats: a poorlydifferentiated cell line (GP7TB) and, a cell line derived from a well-differentiated HCC. GP7TB showed increased resistance to NaBu treatment (ED50= 7.7 mM) compared to JM-1 (ED50= 5.2 mM). The reduction in cell viability observed after 72 h of treatment was explained by a reduction in cell proliferation and, in the case of GP7TB, by increased levels of apoptosis. The NaBu treatment induced morphological alterations in both cell lines. However, only in the case of GP7TB cells, the alterations suggested a differentiation/transdifferentiation process. The up-regulation of genes involved in pluripotency and genes expressing stem cell markers indicated that NaBu triggered a deep reprogramming of GP7TB cells. Besides, a down-regulation in the expression of genes related with cell migration and plasticity suggested that these cells reduced their invasive potential and their self-renewal capacity. Additional analyses are necessary to confirm the observed effect on gene expression profiles. However, the results of this study suggest that NaBu exert anti-neoplastic effects through apoptosis, reduction of cell proliferation and downregulation of genes associated with epithelial-mesenchymal transition of cancer stem-like cells.

Le médulloblastome (MB) est la plus fréquente des tumeurs cérébrales malignes pédiatriques qui représentent la première cause de mortalité par cancer chez l’enfant. Malgré les avancées des nouveaux traitements, les risques de récidive, séquelles et décès après traitement restent importants. Le récepteur de neuropiline-1 (NRP-1) a été récemment impliqué dans la progression tumorale des MBs et semble jouer un rôle important dans le phénotype des cellules souches cancéreuses (CSCs). Le ciblage de cette molécule pourrait ainsi présenter un intérêt thérapeutique dans le traitement des MBs. Nous avons sélectionné des cellules souches de MB capables de former des médullosphères (MS) à partir de 3 lignées cellulaires (DAOY, D283-Med et D341-Med). Ces modèles ont été caractérisés par l’expression de neuropilines (NRP-1 and NRP-2) et de marqueurs phénotypiques (CD133，CD15 et NF-M). Les résultats ont montré une augmentation significative de l’expression de NRP-1 par les cellules cultivées en médullosphères confortant notre stratégie de ciblage. L’impact du traitement de ces cellules par un composé innovant ciblant spécifiquement NRP-1, le MR438, a été ensuite évalué in vitro seul et association avec la radiothérapie notamment sur l’étude de la capacité d’auto-renouvellement des CSCs de MBs. Nous avons mis en évidence une diminution de la capacité d’autorenouvellement des cellules souches de MBs après exposition au MR438 avec une radiosensibilité augmentée pour les 3 modèles cellulaires. In vivo, le composé MR438 a été evalué sur des modèles de xénogreffes hétérotopiques chez la souris nude et montre un effet radiopotentialisant significatif pour les tumeurs issues de la lignée Daoy avec une tendance à la diminution de la progression tumorale pour les 2 autres lignées. De façon intéressante, le composé MR438 induit une diminution significative du nombre de cellules souches pour l’ensemble de nos modèles. Par conséquent, le composé semblerait induire les cellules souches vers un phénotype différencié au moins pour la lignée DAOY, même si les mécanismes n’ont pas pu être clairement élucidé. En conclusion, l’inhibition de NRP-1 via MR438 semble stimuler la différenciation des cellules souches cancéreuses pouvant à terme réduire la progression du MB et apporter un bénéfice en association avec la radiothérapie. L’evaluation du composé sur des modèles orthotopiques de MB permettrait d’obtenir des informations quant à son efficacité sur des modèles plus proche de la physiopathologie tenant compte de sa distribution au niveau cérébral / Medulloblastoma (MB) is the most common malignant pediatric brain tumors which is the leading cause of cancer death in children. Despite the progress of new treatments, the risk of recurrence, morbidity, and death after treatment remain important. The neuropilin-1 receptor (NRP-1) has recently been implicated in tumor progression of MBs, which seems to play an important role in the phenotype of cancer stem cells (CSCs). Targeting this molecule could thus present an interesting therapeutic value in the treatment of MB. We have selected cancer stem like cells of MBs in the form of medullospheres (MSs) from 3 cell lines (DAOY, D283-Med and Med-D341). These models were characterized by expression of neuropilins (NRP-1 and NRP-2) and phenotypic markers (CD133, CD15 and NF-M). Results showed a significant increase of the expression of NRP-1 by our CSCs models cultured in MSs that confirms our targeting strategy. The impact of the treatment of these cells with an innovative compound specifically targeting NRP-1, MR438, was then evaluated in vitro alone and in association with radiotherapy, especially on the study of the capacity for self-renewal. A decrease of self-renewal capacity for MB stem cells after exposition of MR438 with an increase of radiosensitivity for the 3 cell models in vitro was demonstrated. In vivo, MR438 was evaluated on heterotopic xenograft models in nude mice and showed a significant augmentation of radiosensitivity for DAOY tumors with a tendency to decrease tumor progression for the other 2 cell lines. Interestingly, the compound MR438 induced a significant decrease in the number of stem cells for all of our models. The compound appeared to induce CSCs to a differentiated phenotype at least for the DAOY cells, although mechanisms could not be clearly elucidated. In conclusion, inhibition of NRP-1 via MR438 seems to stimulate the differentiation of CSCs that may eventually reduce the progression of MB and bring a benefit in association with radiotherapy. Evaluation of this compound on orthotopic models of MB would provide information on its effectiveness on models closer to the physiopathology taking into account its distribution at the cerebral level

Certaines cellules cancéreuses sont méthionine dépendantes cependant les mécanismes de cette méthionine dépendance sont inconnus. Les cellules initiatrices de tumeur, qui représentent un faible pourcentage des cellules d’une tumeur, sont impliquées dans la récidive du cancer, phénocopient les cellules souches cancéreuses et forment des sphéroïdes 3D ou «tumor spheres (TS)» dans des conditions de culture non adhérentes. Nous montrons que, contrairement aux cellules monocouches adhérentes U251, les TS dérivées de cellules de glioblastome U251 ont besoin de méthionine exogène pour se développer. Cette méthionine-dépendance est caractérisée par une courbe en forme de cloche dans laquelle la croissance des TS est ralentie par des concentrations élevées de méthionine (> 0,01mM). Pendant la restriction en méthionine, le 5-méthyle-tétrahydrofolate restaure la formation des TS. Si les TS sont privées de méthionine pendant 24h, puis supplémentées en acide folique, elles présentent des concentrations d'isoformes des folates significativement inférieures à celles retrouvées dans les cellules adhérentes maintenues dans les mêmes conditions. Ceci suggère que le cycle des folates est réprimé dans les TS comparativement aux cellules adhérentes. L'annotation fonctionnelle des données ARN-Seq montre des changements nets dans plusieurs fonctions moléculaires et dévoile dans les TS un cycle cellulaire réduit, une augmentation du caractère « stemness » et une diminution du métabolisme des folates affectant particulièrement DHFR, SHMT et MTFHD. L'analyse du méthylome révèle des changements de méthylation dans le cycle cellulaire, la signature « stemness » et le cycle des folates, malgré des profils globaux de méthylation de l'ADN qui restent stables. Cependant, contrairement à la méthylation importante des promoteurs observée pour le cycle cellulaire et les gènes « stemness » (+ 25%), seuls 10 gènes du cycle des folates sur 139 gènes impliqués dans le métabolisme des mono-carbones sont significativement modifiés. En conclusion, un cycle des folates avec activité réduite fait partie de la reprogrammation métabolique qui déclenche la dédifférenciation en cellules souches cancéreuses et cette répression ne s'explique qu’en partie par la modification de méthylation des promoteurs / Some cancer cells are methionine dependent however little is known about the mechanisms of this dependency. Tumor initiating cells are a rare population of cancer cells, implicated in disease recurrence, that phenocopy cancer stem cells and form 3D spheroids or ‘tumor spheres (TS)» under non adherent conditions. We show that, unlike U251 adherent monolayer cells, TS derived from U251 glioblastoma cells need exogenous methionine to grow. This methionine dependency is characterized by a bell shape curve in which high methionine concentrations (>0.01mM) slow down TS growth. During methionine restriction, 5- methyltetrahydrofolate restores TS formation. When TS are deprived from methionine for 24h, then supplemented with folic acid, they exhibit lower levels of folate isoforms than adherent cells maintained in the same conditions, suggesting that folate cycle is repressed in TS relative to adherent cells. Functional annotation of the RNA-seq data shows clear changes in several molecular functions and reveals in TS a reduced cell cycle, an increased stemness and a diminished folate metabolism affecting particularly DHFR, SHMT and MTFHD. Methylome analysis shows methylation changes in cell cycle, stemness and folate cycle, despite global DNA methylation patterns remaining stable. However, unlike the important promoter methylation observed for cell cycle and stemness genes (+25%), only 10 folate cycle genes out of 139 genes involved in one-carbon metabolism are significantly altered. In conclusion, reduced folate cycle is part of the metabolic reprogramming triggering dedifferenciation into cancer stem cells and this repression is only partly explained by the alteration of promoter methylation