DRD2 Agonist Cabergoline Abolished the Escape Mechanism Induced by mTOR Inhibitor Everolimus in Tumoral Pituitary Cells

• Published in: Frontiers in endocrinology (Lausanne) 2022-06, Vol.13, p.867822-867822
• Main Authors: Mangili, Federica, Esposito, Emanuela, Treppiedi, Donatella, Catalano, Rosa, Marra, Giusy, Di Muro, Genesio, Barbieri, Anna Maria, Locatelli, Marco, Lania, Andrea G., Mangone, Alessandra, Spada, Anna, Arosio, Maura, Peverelli, Erika, Mantovani, Giovanna
• Format: Article
• Language: English
• Subjects: AKT phosphorylation; cabergoline; dopamine receptor type 2; Endocrinology; everolimus; mTOR inhibitors; pituitary neuroendocrine tumors
• ISSN: 1664-2392; 1664-2392
• DOI: 10.3389/fendo.2022.867822

The mammalian target of rapamycin (mTOR) inhibitor everolimus has been shown to display antiproliferative effects on a wide spectrum of tumors. In vitro studies demonstrated that everolimus inhibited pituitary neuroendocrine tumor (PitNET) cell growth in a subset of patients. Sensitivity to everolimus is reduced by an escape mechanism that increases AKT phosphorylation (p-AKT), leading to pro-survival pathway activation. Dopamine receptor type 2 (DRD2) mediates a reduction of p-AKT in a subgroup of non-functioning PitNETs (NF-PitNETs) and in prolactin-secreting tumor cells (MMQ cells) through a β-arrestin 2-dependent mechanism. The aim of this study was to investigate the efficacy of everolimus combined with DRD2 agonist cabergoline in reducing NF-PitNET primary cells and MMQ cell proliferation and to evaluate AKT phosphorylation and a possible role of β-arrestin 2. We found that 9 out of 14 NF-PitNETs were resistant to everolimus, but the combined treatment with cabergoline inhibited cell proliferation in 7 out of 9 tumors (-31.4 ± 9.9%, p < 0.001 vs . basal) and reduced cyclin D3 expression. In the everolimus-unresponsive NF-PitNET group, everolimus determined a significant increase of p-AKT/total-AKT ratio (2.1-fold, p < 0.01, vs . basal) that was reverted by cabergoline cotreatment. To investigate the molecular mechanism involved, we used MMQ cells as a model of everolimus escape mechanism. Indeed everolimus did not affect MMQ cell proliferation and increased the p-AKT/total-AKT ratio (+1.53 ± 0.24-fold, p < 0.001 vs . basal), whereas cabergoline significantly reduced cell proliferation (-22.8 ± 6.8%, p < 0.001 vs . basal) and p-AKT. The combined treatment of everolimus and cabergoline induced a reduction of both cell proliferation (-34.8 ± 18%, p < 0.001 vs . basal and p < 0.05 vs . cabergoline alone) and p-AKT/total-AKT ratio (-34.5 ± 14%, p < 0.001 vs . basal and p < 0.05 vs . cabergoline alone). To test β-arrestin 2 involvement, silencing experiments were performed in MMQ cells. Our data showed that the lack of β-arrestin 2 prevented the everolimus and cabergoline cotreatment inhibitory effects on both p-AKT and cell proliferation. In conclusion, this study revealed that cabergoline might overcome the everolimus escape mechanism in NF-PitNETs and tumoral lactotrophs by inhibiting upstream AKT activation. The co-administration of cabergoline might improve mTOR inhibitor antitumoral activity, paving the way for a potential combined therapy in β-arres