Dopamine receptor expression and function in the normal and pathological hypothalamus-pituitary-adrenal axis

__Abstract__ Dopamine is the predominant catecholamine neurotransmitter in the human central nervous system, where it controls a variety of functions including cognition, emotion, locomotor activity, food intake and endocrine regulation. Dopamine also plays multiple roles in the periphery as a modulator of cardiovascular and renal function, gastrointestinal motility and the endocrine system (1). Dopamine exerts its functions via the binding with dopamine receptors (1). Dopamine receptors belong to the family of seven transmembrane domain G protein-coupled receptors and include five different receptor subtypes, named D1-Ds. The members of dopamine receptor family are encoded by genes localized on different chromosome loci, displaying a considerable homology in their protein structure and function. The analysis of dopamine receptor structure and function suggests the existence of two different groups of receptors: D1-like, including D1 and D5 receptors, associated to a stimulatory function, and Dz-like, including Dz, D3 and D4 receptors, associated to an inhibitory function. The D1 and Ds receptors are encoded by intronless genes and share an 80% homology in their transmembrane domains. The Dz receptor shares a 75% homology with the D3 and a 53% homology with the D4 transmembrane domains and all three receptor subtypes are encoded by genes, which are interrupted by introns. The Dz receptor exists in two main variants, called Dzlong and Dzshort, generated by an alternative splicing of an 87 base pairs exon. These two D2 receptor isoforms differ for the presence or absence of a stretch of 29 amino acids in the third cytoplasmic loop in their protein structure. Splicing variants of the D3 receptor encoding nonfunctional proteins have been also identified. The analysis of the D4 receptor reveals the existence of polymorphic variations within the coding sequence, being a 48 base pairs sequence existent as a direct repeat sequence (D4.1), fourfold (D4.4), sevenfold (D4.7) or eleven fold (D4.11) repeat sequence. Therefore, the D4 receptor isoforms differ for the length of the third cytoplasmic loop and have one, four, seven or eleven times the same insert of a stretch of 19 amino acids in their protein structure. The Ds receptor has two related pseudogenes, which share a 95% homology with the gene and encode for truncated non functional forms of the receptor (1). The molecular characteristics of human dopamine receptor family are summarized in Table 1. A schematic representation of the human dopamine receptor is shown in Fig. 1

Role of the mTOR pathway in normal and tumoral adrenal cells

The mammalian target of rapamycin (mTOR) is a kinase of the phosphoinositide 3-kinase (PI3Ks)/protein kinase B (PKB or AKT) signaling pathway, which is one of the most important intracellular mediators of the activity of growth factors receptors, including vascular endothelial growth factor (VEGF) and insulin-like growth factors (IGFs). Dysregulation of the mTOR pathway has been found in many human tumors. Therefore, the mTOR pathway is considered as a target for antineoplastic therapy in several malignancies. Presently, the role and functions of mTOR and its signaling pathway in the normal and pathological adrenal gland has not been clarified yet. However, many growth factors and growth factor receptors, which are considered to play a role in the pathogenesis of adrenal tumors, can at least in part exert their effects through the activation of PI3K/AKT/mTOR pathway. Dysregulation of AKT has been reported in adrenocortical carcinomas and adrenomedullary tumors, named pheochromocytomas. Adrenocortical carcinomas and malignant pheochromocytomas are aggressive tumors with poor prognosis and scant treatment options. Therefore, new treatment options are warranted for these malignancies. On the basis of the current knowledge, mTOR could play a role in the pathogenesis of both adrenocortical carcinomas and pheochromocytomas. Moreover, mTOR inhibitors, interfering with the activation of several mitogenic and angiogenic factors, could be considered as a novel treatment opportunity for the management of malignant adrenal tumors

Physiological and pathophysiological role of somatostatin receptors in the human thymus

This is a review summarizing the physiological and pathophysiological role of somatostatin receptors in the human thymus

The dual targeting of insulin and insulin-like growth factor 1 receptor enhances the mTOR inhibitor-mediated antitumor efficacy in hepatocellular carcinoma

Deregulation of mTOR and IGF pathways is frequent in hepatocellular carcinoma (HCC), thus mTOR and IGF1R represent suitable therapeutic targets in HCC. The aim of this study was to evaluate the effects of mTOR inhibitors (mTORi) and OSI-906, blocker of IGF1R/IR, on HCC cell proliferation, viability, migration and invasion, and alpha-fetoprotein (α-FP) secretion. In HepG2 and HuH-7 we evaluated, the expression of mTOR and IGF pathway components; the effects of Sirolimus, Everolimus, Temsirolimus and OSI-906 on cell proliferation; the effects of Sirolimus, OSI-906, and their combination, on cell secretion, proliferation, viability, cell cycle, apoptosis, invasion and migration. Moreover, intracellular mechanisms underlying these cell functions were evaluated in both cell lines. Our results show that HepG2 and HuH-7 present with the same mRNA expression profile with high levels of IGF2. OSI-906 inhibited cell proliferation at high concentration, while mTORi suppressed cell proliferation in a dose-time dependent manner in both cell lines. The co-treatment showed an additive inhibitory effect on cell proliferation and viability. This effect was not related to induction of apoptosis, but to G0/G1 phase block. Moreover, the co-treatment prevented the Sirolimus-induced AKT activation as escape mechanism. Both agents demonstrated to be differently effective in inhibiting α-FP secretion. Sirolimus, OSI-906, and their combination, blocked cell migration and invasion in HuH-7. These findings indicate that, co-targeting of IGF1R/IR and mTOR pathways could be a novel therapeutic approach in the management of HCC, in order to maximize antitumoral effect and to prevent the early development of resistance mechanisms

Dopamine receptor expression and function in corticotroph pituitary tumors

The role of dopamine agonist treatment in corticotroph pituitary tumors is controversial. The aim of this study was to evaluate D(2) receptor expression in 20 corticotroph pituitary tumors and to correlate it to the in vitro effect of dopamine agonists on ACTH secretion and the in vivo effect of short-term cabergoline treatment on cortisol secretion. D(2) expression was evaluated by receptor-ligand binding, immunohistochemistry, and RT-PCR. A 50% or more decrease in daily urinary cortisol levels was considered a significant clinical response. At receptor-ligand binding, specific binding of [(125)I]epidepride was found in 80% of cases. At immunohistochemistry, specific D(2) immunostaining was found in 75% of cases. D(2) expression was found in 83.3% of cases (D(2long) in 40%, D(2short) in 20%, and both in 40%) by RT-PCR. Significant in vitro inhibition of ACTH secretion was found in 100% of D(2)-positive cases, but not in 100% of D(2)-negative cases by either bromocriptine or cabergoline. A significant in vivo inhibition of cortisol secretion after 3-month cabergoline treatment was found in 60%, although a normalization of cortisol secretion was found in 40% of cases. All cabergoline-responsive cases were associated with D(2) expression, whereas all noncabergoline-responsive cases but one were not associated with D(2) expression. In conclusion, functional D(2) receptors were expressed in approximately 80% of corticotroph pituitary tumors. The effectiveness of cabergoline in normalizing cortisol secretion in 40% of cases supports its therapeutic use in the management of Cushing's disease

Levoketoconazole improves clinical signs and symptoms and patient-reported outcomes in patients with Cushing’s syndrome

Purpose: The efficacy of levoketoconazole in treating hypercortisolism was demonstrated in an open-label phase 3 study (SONICS) of adults with endogenous Cushing’s syndrome (CS) and baseline mean urinary free cortisol (mUFC) ≥ 1.5× ULN. Clinical signs and symptoms and patient-reported outcomes from the SONICS trial were evaluated in the current manuscript. Methods: Patients titrated to an individualized therapeutic dose entered a 6-month maintenance phase. Secondary endpoints included investigator-graded clinical signs and symptoms of CS during the maintenance phase, and patient-reported quality of life (CushingQoL questionnaire) and depression symptoms (Beck Depression Inventory II [BDI-II]). Results: Of 94 enrolled patients, 77 entered the maintenance phase following individualized dose titration. Significant mean improvements from baseline were noted at end of maintenance (Month 6) for acne, hirsutism (females only), and peripheral edema. These improvements were observed as early as Day 1 of maintenance for hirsutism (mean baseline score, 7.8; ∆ − 1.9; P < 0.0001), end of Month 1 for acne (mean baseline score, 2.8; ∆ − 1.2; P = 0.0481), and Month 4 for peripheral edema (mean baseline score, 1.0; ∆ − 0.5; P = 0.0052). Significant mean improvements from baseline were observed by Month 3 of maintenance for CushingQoL (mean baseline score, 44.3; ∆ + 6.9; P = 0.0018) and at Month 6 for BDI-II (mean baseline score, 17.1; ∆ − 4.3; P = 0.0043) scores. No significant mean improvement was identified in a composite score of 7 other clinical signs and symptoms. Conclusions: Treatment with levoketoconazole was associated with sustained, meaningful improvements in QoL, depression, and certain clinical signs and symptoms characteristic of CS. ClinialTrials.gov identifier: NCT01838551