Antagonists of Growth Hormone-Releasing Hormone Inhibit the Growth of Pituitary Adenoma Cells by Hampering Oncogenic Pathways and Promoting Apoptotic Signaling

Pituitary adenomas (PAs) are intracranial tumors, often associated with excessive hormonal secretion and severe comorbidities. Some patients are resistant to medical therapies; therefore, novel treatment options are needed. Antagonists of growth hormone-releasing hormone (GHRH) exert potent anticancer effects, and early GHRH antagonists were found to inhibit GHRH-induced secretion of pituitary GH in vitro and in vivo. However, the antitumor role of GHRH antagonists in PAs is largely unknown. Here, we show that the GHRH antagonists of MIAMI class, MIA-602 and MIA-690, inhibited cell viability and growth and promoted apoptosis in GH/prolactin-secreting GH3 PA cells transfected with human GHRH receptor (GH3-GHRHR), and in adrenocorticotropic hormone ACTH-secreting AtT20 PA cells. GHRH antagonists also reduced the expression of proteins involved in tumorigenesis and cancer progression, upregulated proapoptotic molecules, and lowered GHRH receptor levels. The combination of MIA-690 with temozolomide synergistically blunted the viability of GH3-GHRHR and AtT20 cells. Moreover, MIA-690 reduced both basal and GHRH-induced secretion of GH and intracellular cAMP levels. Finally, GHRH antagonists inhibited cell viability in human primary GH- and ACTH-PA cell cultures. Overall, our results suggest that GHRH antagonists, either alone or in combination with pharmacological treatments, may be considered for further development as therapy for PAs.

Abstract 15998: Therapeutic Effectiveness Against Heart Failure With Preserved Ejection Fraction by the Activation of the Growth Hormone-releasing Hormone Receptor in a Murine Model

Introduction: Heart failure with preserved ejection fraction (HFpEF) accounts for ~50% of heart failure cases and is characterized by impaired relaxation, ventricular stiffening and fibrosis. Growth hormone releasing hormone-agonists (GHRH-As) reduce fibrosis in rat and swine models of ischemic myocardial injury. However, their therapeutic effect in HFpEF is unknown. Hypothesis: We hypothesized that activation of GHRH receptor signaling prevents pathological remodeling and targets cardio-myocyte (CM) excitation-contraction coupling, ameliorating the compromised myocardial performance associated with HFpEF. Methods: CD1 mice implanted with a mini-osmotic pump (Alzet) to deliver angiotensin-II (Ang-II) for 8 weeks, were randomized at week 4 to receive daily injections of either GHRH-A (MR-356; n=12) or vehicle (n=12). Echocardiographic data and pressure-volume loops were recorded. Biometric measurements and fibrosis were assessed. CMs were isolated and intracellular Ca2 + and sarcomere length acquired. Results: Ang-II-treated mice exhibited functional and morphologic features consistent with HFpEF. CMs exhibited reduced sarcomere length, indicating an inability to relax. The Ca2 + decay rate and sarcomere re-lengthening were delayed. MR-356 treatment reverted the structural remodeling, including fibrosis, improving diastolic function (Figure Top panel). This treatment also abrogated the HFpEF-associated delay in Ca2 + decay and further enhanced sarcomere re-lengthening rate (Figure Bottom panel). Conclusions: Our findings confirm that chronic infusion of Ang-II mediates functional changes in CMs consistent with HFpEF and demonstrate that activation of GHRH receptor signaling pathways targets mechanisms of excitation-contraction coupling, inflammation and fibrosis, thereby preventing HFpEF-associated dysfunctional CM relaxation and myocardial remodeling.

Activity of the GHRH Antagonist MIA602 and its Underlying Mechanisms of Action in sarcoidosis

Growth hormone releasing hormone (GHRH) is a potent stimulator of GH secretion from the pituitary gland. Although GHRH is essential for the growth of immune cells, the regulatory effects of its antagonist in granulomatous disease remains unknown. Here, we report expression of GHRH receptor (R) in human tissue with sarcoidosis granuloma and demonstrate the anti-inflammatory effects of MIA602 (a GHRH antagonist) in two in vitro human granuloma models and an in vivo granuloma model. MIA602 decreases levels of IL2, IL12, and IL17A in in vitro granuloma model.We show further that the anti-inflammatory effect of MIA602 appears to be mediated by reduction in CD45++CD68+ cells in granulomatous tissue and upregulation in PD-1 expression in macrophages.In analysis of expression of proteins involved in the mitochondrial stage of apoptosis, we show that MIA602 increases the levels of caspase 3, BCL-xL/BAK dimer, and MCl-1/Bak dimer in granuloma. These findings indicate that MIA602 may not induce apoptosis.The clinical relevance of our findings further suggest that HGRH-R is potentially a target for treatment of granulomatous disease and MIA602 possibly a novel therapeutic agent for sarcoidosis.

Synthetic Growth Hormone-Releasing Hormone Agonist as Novel Treatment for Heart Failure with Preserved Ejection Fraction

ObjectiveTo test the hypothesis that the activation of the growth hormone-releasing hormone (GHRH) receptor signaling pathway within the myocardium both prevents and reverses heart failure with preserved ejection fraction (HFpEF).BackgroundHFpEF is characterized by impaired myocardial relaxation, fibrosis and ventricular stiffness. Despite the rapidly increasing prevalence of HFpEF, no effective therapies have emerged. Synthetic agonists of the GHRH receptors reduce myocardial fibrosis, hypertrophy and improve performance, independently of the growth-hormone axis.MethodsWe generated a HFpEF-like phenotype with continuous infusion of angiotensin-II (Ang-II) in CD1 mice. Mice were injected with either vehicle or a potent synthetic agonist of the growth hormone-releasing hormone, MR-356.ResultsAng-II treated animals had diastolic dysfunction, ventricular hypertrophy, and normal ejection fraction and isolated cardiomyocytes (ex vivo) exhibited incomplete relaxation, depressed contractile responses and altered myofibrillar protein phosphorylation. Calcium handling mechanisms were disturbed in cardiomyocytes from mice with HFpEF. MR-356 both prevented and reversed the development of the pathological phenotype in vivo and ex vivo.ConclusionThese findings indicate that the GHRH receptor signaling pathway represents a new molecular target to counteract HFpEF-associated cardiomyocyte dysfunction by targeting myofilament phosphorylation. Accordingly, activation of the GHRH receptor with potent synthetic GHRH agonists may provide a novel therapeutic approach to management of the HFpEF syndrome.Condensed abstractHeart failure with preserved ejection fraction (HFpEF) is characterized by a remodeled myocardium conferring ventricular stiffness and diastolic dysfunction. There are no effective therapies. Agonists of growth hormone-releasing hormone (GHRH) receptors have beneficial effects on the heart. We hypothesize that activation of GHRH receptors suppresses this HFpEF phenotype. Treatment with a synthetic agonist of GHRH, prevented the development of the pathological phenotype in a murine model of HFpEF-induced by chronic angiotensin-II infusion. These findings indicate that activation of GHRH receptors represents a novel molecular strategy to counteract HFpEF-associated cardiomyocyte dysfunction and provide a potential approach to management of HFpEF syndrome.HighlightsA synthetic growth hormone-releasing hormone agonist (GHRH-A) prevents and reverses the pathological remodeling in a mouse model of HFpEF induced by infusion of low dose Ang II.GHRH-A improves intracellular calcium handling by reducing the sarcoplasmic reticulum calcium leakage and enhancing phospholamban phosphorylation.GHRH-A treatment prevents and reverses diastolic dysfunction by enhancing the rate of sarcomere re-lengthening.Activation of the GHRH receptor with the GHRH-A, MR-356, leads to targeting myofibrillar proteins and desensitizing myofilaments in response to calcium.

Growth Hormone Deficiency: Health and Longevity

The important role of GH in the control of mammalian longevity was first deduced from extended longevity of mice with genetic GH deficiency (GHD) or GH resistance. Mice with isolated GHD (IGHD) due to GHRH or GHRH receptor mutations, combined deficiency of GH, prolactin, and TSH, or global deletion of GH receptors live longer than do their normal siblings. They also exhibit multiple features of delayed and/or slower aging, accompanied by extension of healthspan. The unexpected, remarkable longevity benefit of severe endocrine defects in these animals presumably represents evolutionarily conserved trade-offs among aging, growth, maturation, fecundity, and the underlying anabolic processes. Importantly, the negative association of GH signaling with longevity extends to other mammalian species, apparently including humans. Data obtained in humans with IGHD type 1B, owing to a mutation of the GHRH receptor gene, in the Itabaianinha County, Brazil, provide a unique opportunity to study the impact of severe reduction in GH signaling on age-related characteristics, health, and functionality. Individuals with IGHD are characterized by proportional short stature, doll facies, high-pitched voices, and central obesity. They have delayed puberty but are fertile and generally healthy. Moreover, these IGHD individuals are partially protected from cancer and some of the common effects of aging and can attain extreme longevity, 103 years of age in one case. We think that low, but detectable, residual GH secretion combined with life-long reduction of circulating IGF-1 and with some tissue levels of IGF-1 and/or IGF-2 preserved may account for the normal longevity and apparent extension of healthspan in these individuals.