Effects of plasmid-mediated growth hormone-releasing hormone supplementation on LL-2 adenocarcinoma in mice

Oncology Update: Anamorelin

Background:

Cancer cachexia is a catabolic syndrome associated with uncontrolled muscle breakdown. There may be associated fat loss. Occurring in high frequency in advanced cancer, it is an indicator of poor prognosis. Besides weight loss, patients experience a cluster of symptoms including anorexia, early satiety, and weakness. The 3 stages of cachexia include stages of precachexia, cachexia, and refractory cachexia. Refractory cachexia is associated with active catabolism or the presence of factors that make active management of weight loss no longer possible. Patients with refractory cachexia often receive glucocorticoids or megasterol acetate. Glucocorticoid effect is short and responses to megasterol are variable. Anamorelin is a new agent for cancer anorexia-cachexia, with trials completed in advanced lung cancer. Acting as an oral mimetic of ghrelin, it improves appetite and muscle mass. This article reviews the pharmacology, pharmacodynamics, and effect on cancer cachexia.

Methods:

A PubMed search was done using the Medical Subject Headings term anamorelin. Articles were selected to provide a pharmacologic characterization of anamorelin.

Results:

Anamorelin increases muscle mass in patients with advanced cancer in 2-phase 3 trials.

Conclusions:

Anamorelin improves anorexia-cachexia symptoms in patients with advanced non–small-cell lung cancer.

Anamorelin HCl (ONO-7643), a novel ghrelin receptor agonist, for the treatment of cancer anorexia-cachexia syndrome: preclinical profile

BACKGROUND

Anamorelin HCl (ANAM) is a novel, orally active, ghrelin receptor agonist in clinical development for the treatment of cancer cachexia. We report in vitro and in vivo studies evaluating the preclinical pharmacologic profile of ANAM.

METHODS

Fluorescent imaging plate reader and binding assays in HEK293 and baby hamster kidney cells determined the agonist and antagonist activity of ANAM, and its affinity for the ghrelin receptor. Rat pituitary cells were incubated with ANAM to evaluate its effect on growth hormone (GH) release. In vivo, rats were treated with ANAM 3, 10, or 30 mg/kg, or control orally, once daily for 6 days to evaluate the effect on food intake (FI) and body weight (BW), and once to assess GH response. In pigs, single (3.5 mg/kg) or continuous (1 mg/kg/day) ANAM doses were administered to assess GH and insulin-like growth factor (IGF-1) response.

RESULTS

ANAM showed significant agonist and binding activity on the ghrelin receptor, and stimulated GH release in vitro. In rats, ANAM significantly and dose-dependently increased FI and BW at all dose levels compared with control, and significantly increased GH levels at 10 or 30 mg/kg doses. Increases in GH and IGF-1 levels were observed following ANAM administration in pigs.

CONCLUSION

ANAM is a potent and highly specific ghrelin receptor agonist with significant appetite-enhancing activity, leading to increases in FI and BW, and a stimulatory effect on GH secretion. These results support the continued investigation of ANAM as a potential treatment of cancer anorexia-cachexia syndrome.

Effect of ghrelin and anamorelin (ONO-7643), a selective ghrelin receptor agonist, on tumor growth in a lung cancer mouse xenograft model

Purpose

Anamorelin (ONO-7643) is an orally active ghrelin receptor agonist in development for non-small cell lung cancer (NSCLC)-related anorexia/cachexia. It displays both orexigenic and anabolic properties via ghrelin mimetic activity and transient increases in growth hormone (GH). However, increasing GH and insulin-like growth factor-1 in cancer patients raises concerns of potentially stimulating tumor growth. Therefore, we investigated the effect of ghrelin and anamorelin on tumor growth in a murine NSCLC xenograft model.

Methods

Female nude mice (15–21/group) with established A549 tumors were administered ghrelin (2 mg/kg i.p.), anamorelin (3, 10, or 30 mg/kg p.o.), or vehicle controls daily for 28 days. Tumor growth, food consumption, and body weight were monitored. Murine growth hormone (mGH) and murine insulin-like growth factor-1 (mIGF-1) were measured in plasma.

Results

Tumor growth progressed throughout the study, with no significant differences between treatment groups. Daily food consumption was also relatively unchanged, while the percentage of mean body weight gain at the end of treatment was significantly increased in animals administered 10 and 30 mg/kg compared with controls (p < 0.01). Peak mGH levels were significantly higher in ghrelin- and anamorelin-treated animals than in controls, while peak mIGF-1 levels were slightly elevated but not statistically significant. All regimens were well tolerated.

Conclusions

These findings demonstrate that neither anamorelin nor ghrelin promoted tumor growth in this model, despite increased levels of mGH and a trend of increased mIGF-1. Together with anamorelin’s ability to increase body weight, these results support the clinical development of ghrelin receptor agonist treatments for managing NSCLC-related anorexia/cachexia.

Growth hormone-releasing hormone: not only a neurohormone

Growth hormone-releasing hormone (GHRH) is mostly thought to act by stimulating the production and release of growth hormone from the pituitary. However, this neuropeptide emerges as a rather pleiotropic hormone in view of the identification of various extrapituitary sources for GHRH production, as well as the demonstration of a direct action of GHRH on several tissues other than the pituitary. Non-pituitary GHRH has a wide spectrum of activity, exemplified by its ability to modulate cell proliferation, especially in malignant tissues, to regulate differentiation of some cell types, and to promote healing of skin wounds. These findings extend the role of GHRH and its analogs beyond its accepted regulation of somatotropic activity and indicate new possibilities for therapeutic intervention.

Muscle and fat mass modulation in different clinical models

Studies described in the recent literature support the idea that gene therapy can lead to genuine clinical benefits when mediated by plasmid delivery in conjunction with electroporation. Plasmid-mediated muscle-targeted gene transfer offers the potential of a cost-effective pharmaceutical-grade therapy delivered by simple intramuscular injection. This approach is particularly appropriate for modulating muscle and fat mass and their intrinsic properties, from treatment of conditions such as cachexia associated with chronic diseases, autoimmune diseases, e.g., myasthenia gravis, to stimulation or suppression of appetite, and further to in vivo manipulation of glucose metabolism and fat deposition in patients with diabetes, or to basic studies of muscle-specific transcription factors and their impact in development. Recent innovations, including in situ electroporation, enabling sustained systemic protein delivery within the therapeutic range, are reviewed. Translation of these advances to human clinical trials will enable muscle- and fat-targeted gene therapy to become a viable therapeutic alternative.

Electroporation for targeted gene transfer

The utilisation of nonviral gene delivery methods has been increasing steadily, however, a drawback has been the relative low efficiency of gene transfer with naked DNA compared with viral delivery methods. In vivo electroporation, which has previously been used clinically to deliver chemotherapeutic agents, also enhances the delivery of plasmid DNA and has been used to deliver plasmids to several tissue types, particularly muscle and tumour. Recently, a large number of preclinical studies for a variety of therapeutic modalities have demonstrated the potential of electrically mediated gene transfer. Although clinical trials using gene transfer with in vivo electroporation have not as yet been realised, the tremendous growth of this technology suggests that the first trials will soon be initiated.

Growth hormone releasing hormone plasmid supplementation, a potential treatment for cancer cachexia, does not increase tumor growth in nude mice

Growth hormone releasing hormone (GHRH) is known to have multiple anabolic effects and immune-stimulatory effects. Previous studies suggest that treatment with anabolic hormones also has the potential to mitigate the deleterious effects of cancer cachexia in animals. We studied the effects of plasmid-mediated GHRH supplementation on tumor growth and the role of antitumor immune cells with two different human tumor cell lines, NCI-H358 human bronchioalveolar carcinoma and MDA-MB-468 human breast adenocarcinoma, subcutaneously implanted in nude mice. GHRH supplementation by delivery of human GHRH from a muscle-specific GHRH expression plasmid did not increase tumor progression in tumor-bearing nude mice. Male animals implanted with the NCI-H358 tumor cell line and treated with the GHRH-expressing plasmid exhibited a 40% decrease in the size of the tumors (P<.02), a 48% increase in white blood cells (P<.025) and a 300% increase in monocyte count (P<.0001), as well as an increase in the frequency of activated CD3+ and CD4+ cells in the tumors, compared to tumors of control animals. No adverse effects were observed in animals that received the GHRH-plasmid treatment. The present study shows that physiological stimulation of the GHRH-GH-IGF-I axis in mice with cancer does not promote tumor growth and may provide a viable treatment for cancer cachexia in humans.

Extrapituitary Effects of the Growth Hormone-Releasing Hormone

Growth hormone-releasing hormone (GHRH) is a neuropeptide secreted by the hypothalamus that stimulates the synthesis and release of growth hormone (GH) in the pituitary. Accumulating evidence suggests that in addition to GHRH's neuroendocrine action, GHRH is present in several extrahypothalamic tissues and is involved in a variety of cellular processes. Its function is related to the regulation of cell proliferation and differentiation of various nonpituitary cell types. In certain cases, ectopic production of GHRH has also been implicated in carcinogenesis. The mechanisms by which GHRH affects the peripheral extrapituitary tissues remain poorly understood, but it is likely that classic neuroendocrine action as well as paracrine and autocrine pathways are involved. Some headway has been made in the identification of extrapituitary receptors for GHRH and cDNA as splice variants of these GHRH receptors found in various tumors. The fact that the nonpituitary GHRH receptors are not fully identified, however, remains the major obstacle in studying, at a more mechanistic level, the action of local GHRH. This review summarizes the information available regarding the role of GHRH in the extrapituitary tissues with emphasis on its potential therapeutic and diagnostic applications.