Le tissu tumoral comprend, outre les cellules cancéreuses, une matrice extra-cellulaire modifiée, les cellules endothéliales des vaisseaux sanguins et lymphatiques, immunes et inflammatoires et des fibroblastes actives associés au cancer (CAFs). La podoplanine (PDPN), glycoprotéine transmembranaire de type mucine, y est exprimée dans les cellules cancéreuses et les CAFs. Elleaidea la métastase comme montré dans le carcinome mammaire envahissant les ganglions lymphatiques. Ce travail montre que PDPN module l’interaction chimiokine/récepteur de l’axe CCL21/CCR7 et dépend de l’hypoxie. La progression tumorale est aidée par le stroma ou les CAFs ont des propriétés particulières par rapport aux fibroblastes normaux. Ils promeuvent la croissance tumorale, le recrutement des précurseurs endothéliaux et l’angiogenèse. Dans le carcinome mammaire, 80% des fibroblastes ont un phénotype CAF. Un modèle de CAFs exprimant la PDPN a permis de démontrer l’implication de CCL21/CCR7 dans la reconnaissance entre cellules tumorales et CAFs via la liaison CCL21/PDPN. Les CAFsPDPN+ secrètent des microARNs qui contrôlent des gènes des cellules cancéreuses. MiR-21 est un régulateur oncogène fondamental, par son action sur le suppresseur de tumeur PTEN. Nous avons analysé l’effet de miR-21, ainsi que de miR-210 et miR-29b sur PDPN dans les fibroblastes en hypoxie pour mimer le microenvironnement intratumoral et mis en évidence les différences biologiques comparativement à la normoxie ainsi que l’effet de la podoplanine sur l’angiogenèse par les cellules endothéliales en colocalization avec les CAFs exprimant la podoplanine et sur l’expression des facteurs proangiogéniques. / Tumor is a pathologic tissue including cancer cells, a modified extracellular matrix, endothelial cells, blood and lymphatic vessels, immune and inflammatory cells and activated fibroblasts called cancer-associated fibroblasts (CAFs). Podoplanin (PDPN), mucin-type transmembrane glycoprotein is expressed in tumor cells and CAFs, helps metastasis. Its role in metastaticprocess has been demonstrated for breast cancer cells into lymph nodes. Here we show that PDPN modulates the CCL21/CCR7 chemokine/receptor axis in a hypoxia-dependent manner. Cancer progression depends on the tumour stroma in which CAFs differ from normal fibroblasts. CAFs promote tumour growth, recruitment of endothelial progenitor cells and angiogenesis. In breast cancer up to 80% of fibroblasts display the CAF phenotype. Here a PDPN expressing model of CAFs made it possible to demonstrate the involvement of CCL21/CCR7 axis in the tumor cell-to-CAF recognition through podoplanin binding of CCL21. PDPN positive CAFs secrete microRNAs, which control gene expression at post-transcriptional level and influence cancer cells. MiR-21 is a key regulator of the oncogenic process, through its downstream target proteins among which the tumor suppressor, PTEN. We analyzed the effect of miR-21, but also oncogenic and hypoxia dependent miRs: miR-210 and miR-29b, on PDPN expression in fibroblasts in conditions mimicking the intra tumor microenvironment, i.e. in hypoxia. This points to crucial differences as compared to normoxia. Moreover we uncover the effect of podoplanin on angiogenesis by endothelial cells colocalizing with CAFs expressing podoplanin and on the expression of most prominent proangiogenic factors.

<p dir="ltr">Metastatic breast cancer (BC) remains a dauting therapeutic challenge due to the heterogeneity and cellular plasticity that exists. Because of these, BC resistance to targeted therapies and immune checkpoint blockade (ICB) present major challenges in the clinical setting. As a result, incomplete clearance of BC during a therapeutic regimen can lead to the persistence of minimal residual disease (MRD) which greatly contributes to tumor relapse. Here we develop a powerful in vivo model of lung metastasis in which we can achieve robust pulmonary tumor regression in response to the fibroblast growth factor receptor (FGFR) inhibitor, pemigatinib.</p><p dir="ltr">To enhance the efficacy of ICB, tumors must first be converted from an immune “cold” environment to an immune “hot” environment. Using our in vivo model of lung metastasis, we demonstrated that pemigatinib can significantly increase the presence of infiltrating T-cells into the lungs while suppressing the presence of MDSCs both locally in the lungs and systemically. Taken together, pemigatinib is an ideal candidate to prime these immune “cold” tumors for combination with ICB.</p><p dir="ltr">Upon establishment of MRD by pemigatinib in our in vivo model we observe upregulation of an alternate growth factor receptor, platelet-derived growth factor receptor (PDGFR). Functionally, upon FGFR inhibition, there is increased response to pulmonary fibroblast derived PDGF ligand, fueling survival of MRD. We demonstrated that knockdown of PDGFR significantly delayed tumor growth reinitiation in an in vitro 3D culture following pemigatinib as well as delayed tumor relapse in our pulmonary metastasis model.</p><p dir="ltr">To limit cellular plasticity and reduce survival of MRD, we propose a novel dual-targeted approach utilizing pemigatinib, in conjunction with inhibition of DNMT1 using the reversible inhibitor GSK3484862. We used our in vivo model of lung metastasis after treatment with pemigatinib as a model of cellular plasticity to targeted therapy. This combination therapy prevented growth factor plasticity and delayed tumor recurrence. Through prevention of PDGFR upregulation induced by pemigatinib.</p><p dir="ltr">In the present dissertation works, our study demonstrates pemigatinib’s robust ability to increase infiltrating T-cells in addition to its strong antitumor effects on pulmonary tumors. Despite the robust effects of pemigatinib, acquired mechanism of resistance through upregulation of PDGFR allows survival of MRD and are supported by PDGF secreting fibroblasts. Using an approach of limiting cellular plasticity through DNA methylation inhibition combined with pemigatinib, we achieved a more durable therapeutic response. Our findings underscore the significance of understanding adaptive responses to targeted therapies and provide a tangible therapeutic strategy to prolong treatment response in metastatic breast cancer.</p>