Endocrine Abstracts

JOINT1102

Non-functioning pituitary neuroendocrine tumors (NF-PitNETs) represent the most common subtype of PitNETs after prolactin-secreting ones and are still orphan of an effective pharmacological approach for persistent or recurrent cases. Lot of attention was given to dopamine receptor type 2 (DRD2) agonists (DAs), based on high DRD2 expression levels in NF-PitNETs, but their use in clinic is still controversial, since they efficacy on tumor growth’s control is not well demonstrated. β-arrestin2 has been recently identified as possible molecular determinant predicting DAs responsiveness in NF-PitNETs. In fact, its fundamental role in regulating DRD2 inhibitory effects on AKT phosphorylation and cell proliferation in NF-PitNETs has been unveiled, since it has been demonstrated that β-arrestin2 lack prevents the inhibitory effect of DRD2 on AKT pathway activation with a consequent resistance to the antimitotic action of DAs. The aim of this study was to investigate β-arrestin2 expression at both protein and transcript level in human NF-PitNETs, correlating it with their in vitro responsiveness to DAs in terms of cell proliferation inhibition. 65 primary cultured NF-PitNET cells have been treated for 72h with 100nM DAs and cell proliferation assay was performed. DAs treatment determined a significative inhibition of cell proliferation (-27.7(20.14),P < 0.001) in 26 samples (considered ‘responsive’ NF-PitNET, using a cut-off of at least 15% of cell proliferation inhibition). Then, RNA and proteins from NF-PitNETs frozen tissues have been extracted (n = 56 and n = 48 for proteins, respectively) have been extracted. β-arrestin2 relative expression of 23 NF-PitNET samples in vitro responsive to DAs treatment and 33 resistant ones has been evaluated by real-time PCR (qPCR). Our data revealed that there was no significative difference between the median of expression between the two groups (0.0037(0.0032) responsive vs 0.0033(0.0031) resistant). Moreover, β-arrestin2 protein expression was analysed in 24 responsive and 24 resistant NF-PitNETs by western blot. Our analysis revealed that the 83% of NF-PitNETs responsive to DAs were positive for β-arrestin2 expression, while only the 20% of resistant ones expressed it (P < 0.001). In addition, significative correlation (P < 0.05) between β-arrestin2 protein expression and DA responsiveness of NF-PitNET samples tested has been highlighted. β-arrestin2 mRNA levels were not correlated to protein expression nor with NF-PitNET cell proliferation inhibition after DAs treatment. In conclusion, our analysis demonstrated that β-arrestin2 protein expression positively correlated with NF-PitNETs in vitro sensitivity to DAs, paving the way for a potential role of β-arrestin2 as a biomarker predicting responsiveness to pharmacological treatment with DAs for NF-PitNETs.