AIP and the somatostatin system in pituitary tumours

Classic somatostatin analogues aimed at somatostatin receptor type 2, such as octreotide and lanreotide, represent the first-line treatment for acromegaly, which normally decrease hormone secretion and reduce tumour size; nevertheless, patients with a germline mutation in the aryl hydrocarbon receptor-interacting protein gene, AIP, develop young-onset acromegaly, poorly responsive to pharmacological therapy. In this review, we summarise the most recent studies on AIP-related pituitary adenomas, paying special attention to: the causes of the resistance to treatment in acromegaly; the somatostatin receptor profile in the somatotrophinoma, especially type 2, and type 5 and its truncated variants; the role of G proteins in this pathology; the use of pasireotide, a novel multi-ligand somatostatin analogues; and the role of ZAC1, a zinc-finger protein which, among other functions, acts as a key mediator in octreotide response in somatotrophinoma models and, interestingly, its expression is linked to AIP.

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