Unmasking a new prognostic marker and therapeutic targetfrom the GDNF-RET/PIT1/p14ARF/p53 pathway in acromegaly

Abstract

[ENG]Background:Acromegaly isproduced byexcessgrowthhormone secreted bya pituitary adenoma of somatotrophcells (ACRO). First-line therapy, surgery and adjuvant therapy with somatostatin analogs, fails in 25% of patients.There is no predictive factor of resistance to therapy. New therapies are investigated using few dispersed tumorcells in acute primary cultures in standard conditions where the cells do not grow, or using rat pituitary cell linesthat do not maintain the full somatotroph phenotype. The RET/PIT1/p14ARF/p53 pathway regulates apoptosis innormal pituitary somatotrophs whereas the RET/GDNF pathway regulates survival, controlling PIT1 levels andblocking p14ARF (ARF) and p53 expression.Methods:We investigated these two RET pathways in a prospective series of 32 ACRO and 63 non-functioningpituitary adenomas (NFPA), studying quantitative RNA and protein gene expression for molecular-clinical corre-lations and how the RET pathway might be implicated in therapeutic success. Clinical data was collected duringpost-surgical follow-up. We also established new'humanized’pituitary cultures, allowing 20 repeated passagesand maintaining the pituitary secretory phenotype, and testedfive multikinase inhibitors (TKI: Vandetanib,Lenvatinib, Sunitinib, Cabozantinib and Sorafenib) potentially able to act on the GDNF-induced RET dimeriza-tion/survival pathway. Antibody arrays investigated intracellular molecular pathways.Findings:In ACRO, there was specific enrichment of all genes in both RET pathways, especially GDNF. ARF andGFRA4 gene expression were found to be opposing predictors of response tofirst-line therapy. ARF cut-off levels,calculated categorizing by GNAS mutation, were predictive of good response (above) or resistance (below) totherapy months later. Sorafenib, through AMPK, blocked the GDNF/AKT survival action without altering theRET apoptotic pathway.Interpretation:Tumor ARFmRNA expression measured atthe time of thesurgery is a prognosis factor in acromeg-aly. The RET inhibitor, Sorafenib, is proposed as a potential treatment for resistant ACRO