A developmental model of paragangliar tumorigenesis highlights therapeutic targets

To identify genes and pathways commonly deregulated in head and neck paragangliomas (PGLs), we integrated genome-wide copy number variation (CNV) analysis with microRNA and immunomorphological studies. Gene-centric CNV analysis of 24 cases identified 104 genes most significantly targeted by PGL- associated alterations. A "NOTCH signaling pathway" implicated in vasculoangiogenesis was the most significantly enriched term (P = 0.002). Expression of the relevant proteins was confirmed in 47/47 head and neck PGLs, with no relationships to germline SDHx mutation status or SDHB immunostaining (1). Five microRNAs that control cell differentiation (miR-200a,b,c and miR-34b,c) were among those most downregulated in the PGLs. To understand the origin of PGLs, we developed a biobank comprising 77 cases, 18 primary cultures, 4 derived cell lines, 80 patient-derived xenografts and 11 cell-derived xenografts. We investigated these unique complementary materials using morphofunctional, ultrastructural and flow cytometric assays accompanied by microRNA studies (2). We found that PGLs contain stem-like cells with hybrid mesenchymal/vasculoneural phenotype, stabilized and expanded in the derived cultures. The cultures depended on the downregulation of the miR-200 and miR-34 families, which allowed high NOTCH1, PDGFRA and ZEB1 protein levels. PGL xenografts, both tissue- and cell culture- derived, recapitulated the typical vasculoneural tumor structure and arose from mesenchymal-like cells through a fixed developmental sequence. First, vasculoangiogenesis organized the microenvironment, building a perivascular niche that in turn supported neurogenesis. Neuroepithelial differentiation was associated with severe mitochondrial dysfunction, not present in cultured PGL cells, but acquired in vivo during xenograft formation. Imatinib, that targets endothelial-mural signalling, blocked PGL xenograft formation (11 xenografts from 12 cell transplants in the control group versus 2 out of 10 in the treated group, P = 0.0015). Overall our results were unaffected by the SDHx gene carrier status of the donor patient, characterized for 70 out of 77 cases. In conclusion, we explain the biphasic vasculoneural structure of PGLs and identify an early and pharmacologically actionable phase of PGL organization (2). Work supported by AIRC Grant IG 16932.