Abstract A091: Crosstalk between tumor vasculature and ovarian cancer stem cells: the role of L1CAM

Abstract Ovarian cancer is the most lethal gynaecologic tumor, mainly due to relapse and chemoresistance, two events fuelled by ovarian cancer stem cells (OCSC). The tumor microenvironment (TME) is thought to act as a niche for OCSC, preserving stem cells properties and sustaining tumor recurrence. The close contact between neoplastic and non-malignant cells can rely, besides physical cell-cell interactions, on soluble ligands and receptors. Therefore, studying the crosstalk between TME and OCSC may unveil new targets and mechanisms to overcome the limitations of current treatments. We identified L1CAM, a cell adhesion molecule expressed both in tumor endothelium and epithelial cancer cells, as a mediator of the interaction between the vascular TME (vTME) and OCSC. Our previous work implicated L1CAM in OC cell proliferation and chemoresistance, which reflected the correlation of L1CAM expression with metastatic spread and poor outcome. Furthermore, we reported that L1CAM is expressed in tumor-associated endothelial cells (EC), where it promotes vessels permeability and neo-angiogenesis. Notably, EC express an alternatively spliced isoform of L1CAM, L1-DTM, that is released as a soluble factor. To gain insights into the functional role of L1-DTM in the crosstalk between EC and OCSC, we genetically manipulated its expression, generating gain-of-function models. Conditioned media (CM) were used to investigate the impact of L1-DTM-regulated secretome in the crosstalk. Through a series of sphere formation assays, a proxy for stemness-related features, I found that the CM from L1-DTM-expressing EC enhances stem-like properties in OCSC, an effect that was abolished upon depletion of the ectopic protein. To deeply study the functional role and the mechanism of action, we took advantage of purified recombinant L1-DTM which, indeed, recapitulated the effect of the CM. Interestingly, we found that L1-DTM drives OC sphere initiation and proliferation via the activation of IL6/JAK2/STAT3 signaling pathway, thus implying a paracrine axis that links endothelial L1-DTM to OCSC STAT3. Furthermore, L1-DTM induced the upregulation of pluripotency-associated genes and a hybrid epithelial-mesenchymal phenotype in OCSC. Finally, an RNA-seq analysis revealed that L1-DTM confers a proinflammatory phenotype on OCSC, which may contribute to support cancer initiation, proliferation, and progression. To assess if L1-DTM- expressing endothelium can give rise to a perivascular niche, we have set up microfluidics chips, co-culturing EC and OCSC. This “niche-on-a-chip” model confirmed the capability of L1-expressing vessels to foster OCSC proliferation and spreading. Notably, we also obtained evidence that L1-DTM influences the response of OCSC to chemotherapy, promoting resistance to treatments. Our approach highlighted L1-DTM as a druggable target in the crosstalk between vTME and OCSC. Indeed, our findings could provide the rationale for exploring novel L1CAM-based therapeutic approaches aimed at the eradication of OC through the elimination of its stem cell compartment. Citation Format: Micol Baronio. Crosstalk between tumor vasculature and ovarian cancer stem cells: the role of L1CAM abstract. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84 (5 Suppl₂): Abstract nr A091.