Functional profiling of somatostatin receptors identifies somatostatin receptor subtype 2 as a vulnerability in Succinate Dehydrogenase SDHB-deficient pheochromocytomas and paragangliomas.

Pheochromocytomas and Paragangliomas (PPGL) are rare neuroendocrine tumors with favorable prognosis, although a significant subset (20-25%) progress to metastasis, worsening patient prognosis. For metastatic cases, pharmacological interventions become essential, yet most tumors show poor response to treatment. While clinical trials are ongoing, there is no established treatment for metastatic PPGL. Like other neuroendocrine tumors, PPGL exhibit high membrane expression of somatostatin receptors, and despite Peptide Receptor Radionuclide Therapy, PRRT, strategies have successfully been implemented, trials with cold somatostatin analogs were abandoned prematurely due to inconsistent results. To investigate this issue and identify potential therapeutic tools, we widely profiled somatostatin receptors expression in PPGL and conducted a comprehensive functional screening on wild-type and SDHB knockdown PPGL cell lines of native and synthetic somatostatin analogs. Results revealed that pheochromocytomas and paragangliomas similarly display a predominant SSTR2 and SSTR1 expression regardless of molecular cluster. Treatment with somatostatin, cortistatin, octreotide or pasireotide did not exert clear antitumoral effects on model cell lines. Notably, the selective SST2 agonist BIM-23120 significantly reduced cell proliferation and induced apoptosis in an SST2-dependent manner, but only in SDHB knocked-down PPGL cells. Indeed, only SDHB KD cells showed stronger membrane-enriched SST2 and clear receptor internalization upon BIM-23120 treatment. Molecular analysis revealed a generalized dephosphorylation affecting key proliferation, growth and cell survival pathways in response to BIM-23120 (unlike when treating with octreotide). Altogether, our results provide novel information on the status of the somatostatin system in PPGL and identify new potential therapeutic tools selectively targeting somatostatin receptors on this refractory tumor.