Anamorelin (ONO-7643)

Overview

Anamorelin (development codes ONO-7643, RC-1291, ST-1291) is a non-peptide, orally active, centrally penetrant, selective agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the endogenous receptor for the appetite-regulating hormone ghrelin [1][11]. Developed through a collaboration between Helsinn Healthcare SA (Switzerland) and Ono Pharmaceutical Co., Ltd. (Japan), anamorelin was designed as a peptidomimetic compound that reproduces the appetite-stimulating and growth hormone (GH)-releasing effects of ghrelin while offering the pharmacokinetic advantages of oral bioavailability and a substantially longer plasma half-life (~7 hours vs. ghrelin's ~30 minutes) [1][15][16].

Cancer cachexia, the condition for which anamorelin was specifically developed, is a multifactorial wasting syndrome characterized by ongoing loss of skeletal muscle mass (with or without fat mass loss) that cannot be fully reversed by conventional nutritional support [13]. Affecting 50-80% of patients with advanced cancer, cachexia contributes directly to approximately 20% of all cancer deaths and is associated with reduced quality of life, impaired treatment tolerance, and shortened survival [13][20]. Despite its devastating clinical impact, no pharmacological therapy had been approved for cancer cachexia prior to anamorelin.

The ROMANA Phase III clinical trial program (ROMANA 1, 2, and 3) established that anamorelin 100 mg once daily significantly increased lean body mass and total body weight in patients with advanced non-small-cell lung cancer (NSCLC) and cachexia, although it did not improve handgrip strength [4][5]. On the basis of these data and supporting Japanese studies, anamorelin received manufacturing and marketing approval in Japan in January 2021 under the brand name Adlumiz, becoming the first pharmacotherapy approved anywhere in the world specifically for cancer cachexia [6][18]. It is indicated for cachexia associated with NSCLC, gastric cancer, pancreatic cancer, and colorectal cancer. The European Medicines Agency (EMA) and the U.S. Food and Drug Administration (FDA) have not approved anamorelin, citing marginal clinical benefit and incomplete safety characterization [6][24].

Type

Non-peptide GHS-R1a agonist (ghrelin mimetic / peptidomimetic)

Molecular Formula

C31H42N6O3

Molecular Weight

546.7 g/mol (free base); 583.2 g/mol (hydrochloride salt)

CAS Number

249921-19-5 (free base); 861998-00-7 (HCl salt)

Half-life

~7 hours

Routes Studied

Oral administration

Approved Dose

100 mg once daily (Japan)

Regulatory Status

Approved in Japan (2021); not approved by FDA or EMA

Brand Name

Adlumiz (Ono Pharmaceutical / Helsinn)

Mechanism of Action

Anamorelin acts as a potent and selective agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the seven-transmembrane G protein-coupled receptor that serves as the endogenous target for ghrelin [1][12][21].

Receptor Binding and Signaling: Anamorelin binds human GHS-R1a with high affinity (Ki = 0.70 nM), comparable to that of endogenous ghrelin (Ki = 0.58 nM) [1]. In functional assays, it potently activates intracellular calcium signaling via the Gq/11-phospholipase C (PLC) pathway with an EC50 of 0.74 nM, closely matching ghrelin's EC50 of 0.67 nM [1]. Upon receptor activation, the Gq/11 alpha subunit stimulates PLC-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), generating inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 triggers calcium release from intracellular stores, which in anterior pituitary somatotrophs drives exocytosis of GH-containing secretory granules [12][15]. In competition binding assays against radiolabeled ibutamoren (MK-677), anamorelin displaced binding with an IC50 of 0.69 nM, confirming it occupies the same receptor site as other GHS-R1a agonists [1].

Selectivity: Anamorelin demonstrates high selectivity for GHS-R1a. Screening at 10 micromolar concentration across a panel of 73 GPCRs, ion channels, and transporters revealed only weak, clinically insignificant off-target binding to calcium channels, the serotonin transporter, and sodium channels [1].

Dual Neuroendocrine Actions: Anamorelin exerts its clinical effects through two complementary pathways:

1. Growth hormone release: Activation of GHS-R1a on pituitary somatotrophs directly stimulates GH secretion. GH in turn promotes hepatic production of insulin-like growth factor 1 (IGF-1), which mediates anabolic effects on skeletal muscle and other tissues [1][15]. In rat anterior pituitary cell cultures, anamorelin stimulated GH release with an EC50 of 1.5 nM [1]. In vivo, single oral doses of 3-30 mg/kg in rats produced dose-dependent 2.3- to 4.1-fold increases in peak plasma GH concentrations [1].

2. Appetite stimulation: Activation of GHS-R1a on hypothalamic neurons in the arcuate nucleus and other feeding-related brain regions stimulates orexigenic neuropeptide Y (NPY) and agouti-related peptide (AgRP) neurons, reproducing the appetite-stimulating effects of endogenous ghrelin [21]. In preclinical studies, repeated oral dosing of anamorelin (3-30 mg/kg/day for 6 days) produced significant, dose-dependent increases in cumulative food intake and body weight in rats [1].

No Tumor Growth Stimulation: Despite concerns that GH/IGF-1 axis activation could promote tumor progression, preclinical studies demonstrated that anamorelin did not stimulate tumor growth in a lung cancer mouse xenograft model, even at supratherapeutic doses [14].

Chemistry and Pharmacokinetics

Anamorelin is a peptidomimetic compound with the molecular formula C31H42N6O3 and a molecular weight of 546.7 g/mol (free base) [1]. Its IUPAC name is (3R)-1-(2-methylalanyl-D-tryptophyl)-3-(phenylmethyl)-3-piperidinecarboxylic acid 1,2,2-trimethylhydrazide. It is typically formulated as the hydrochloride salt (MW 583.2 g/mol; CAS 861998-00-7) for pharmaceutical use.

The compound was designed to mimic the N-terminal active core of ghrelin, which is responsible for receptor activation, while incorporating non-peptide structural elements that confer resistance to proteolytic degradation and enable oral absorption [1][15]. Key structural features include a D-tryptophan residue, 2-methylalanine, a 3-benzylpiperidine scaffold, and a trimethylhydrazide cap.

Pharmacokinetic Properties:

• Absorption: Following oral administration, anamorelin is rapidly absorbed with peak plasma concentrations (Tmax) reached at 0.5-2 hours post-dose [3][16]. Food significantly reduces plasma exposure (approximately 4-fold decrease), necessitating administration in the fasting state, at least one hour before the first meal of the day [3].
• Half-life: Approximately 7 hours, which is markedly longer than the ~30-minute half-life of endogenous ghrelin, allowing once-daily dosing [1][3].
• Elimination: Approximately 99.8% of the drug is recovered in feces (92%) and urine (8%) within 18 hours post-dose [3].
• Drug interactions: CYP3A4 inhibition increases anamorelin plasma exposure approximately 3-fold, indicating hepatic metabolism via the CYP3A4 pathway [3].

Cancer Cachexia: The Therapeutic Context

Cancer cachexia is formally defined as a multifactorial syndrome characterized by an ongoing loss of skeletal muscle mass (with or without loss of fat mass) that cannot be fully reversed by conventional nutritional support and leads to progressive functional impairment [13]. The international consensus framework classifies cachexia into three stages: pre-cachexia (weight loss of 5% or fewer with anorexia and metabolic changes), cachexia (weight loss exceeding 5% over 6 months, or BMI below 20 kg/m2 with ongoing weight loss exceeding 2%), and refractory cachexia (variable degrees of cachexia with unresponsive cancer and low performance status) [13].

The pathophysiology involves systemic inflammation driven by tumor-derived factors (proteolysis-inducing factor, lipid-mobilizing factor) and host inflammatory mediators (TNF-alpha, IL-1, IL-6, interferon-gamma), which collectively suppress appetite, increase resting energy expenditure, and shift metabolism toward muscle protein catabolism [20]. Ghrelin signaling is impaired in cancer cachexia, with reduced circulating ghrelin levels and altered GHS-R1a sensitivity contributing to anorexia and negative energy balance [21]. Anamorelin was specifically designed to pharmacologically restore this deficient ghrelin signaling axis.

Clinical Evidence Summary

Phase I Studies — Healthy Volunteers [16]

In early Phase I studies, single doses of anamorelin (10-50 mg) in healthy volunteers produced significant, dose-dependent increases in plasma GH levels, with peak concentrations achieved at 0.5-2 hours post-dose [16]. At doses of 25-50 mg, anamorelin produced a significant appetite-stimulating effect compared with placebo within 30 minutes of administration, and spontaneous food intake increased by 18.4% above placebo [3][16]. Six-day repeated dosing at 50-75 mg induced weight gain of approximately 1.2 kg compared with placebo [3].

Phase II Trials — Cancer Cachexia (Garcia et al. 2015) [3]

Design: Integrated analysis of two multicenter, randomized, placebo-controlled, double-blind Phase II trials. Patients with advanced or incurable cancer and 5% or more weight loss were stratified by severity of weight loss (5-15% vs. more than 15%) and randomized 1:1 to anamorelin 50 mg or placebo once daily for 12 weeks. A total of 82 patients were included in the pooled analysis.

Key Results:

• Lean body mass increased by a least-squares mean of 1.89 +/- 0.53 kg in the anamorelin group versus a decrease of -0.20 +/- 0.52 kg in the placebo group
• Total body weight, quality of life, and grip strength showed trends toward improvement
• GH and IGF-1 levels increased significantly with anamorelin
• Treatment was well tolerated with mild adverse events

Phase III: ROMANA 1 and ROMANA 2 (Temel et al. 2016) [4]

Design: Two co-primary endpoint, randomized, double-blind, placebo-controlled Phase III trials conducted at 93 sites across 19 countries. Patients with inoperable stage III or IV NSCLC and cachexia (defined as 5% or more weight loss within 6 months, or BMI below 20 kg/m2) were randomized 2:1 to anamorelin 100 mg orally once daily or placebo for 12 weeks. ROMANA 1 enrolled 484 patients (323 anamorelin, 161 placebo); ROMANA 2 enrolled 495 patients. Co-primary endpoints were change in lean body mass (measured by DXA) and handgrip strength.

Key Results:

Lean Body Mass (primary endpoint --- met):

• ROMANA 1: median increase of 0.99 kg (95% CI 0.61-1.36) with anamorelin vs. -0.47 kg (-1.00 to 0.21) with placebo (p = 0.0001)
• ROMANA 2: median increase of 0.65 kg (95% CI 0.38-0.91) with anamorelin vs. -0.98 kg (-1.49 to -0.41) with placebo (p = 0.0001)

Handgrip Strength (primary endpoint --- not met):

• ROMANA 1: -1.10 kg (-1.69 to -0.40) vs. -1.58 kg (-2.99 to -1.14), p = 0.15
• ROMANA 2: -1.49 kg (-2.06 to -0.58) vs. -0.95 kg (-1.56 to 0.04), p = 0.65

Secondary Endpoints:

• Body weight: significant increase of 2.20 vs. 0.14 kg (p = 0.001) in ROMANA 1; 0.95 vs. -0.57 kg (p = 0.001) in ROMANA 2
• Anorexia/cachexia symptom scores (FAACT A/CS domain): improved 4.12 vs. 1.92 (p = 0.001) in ROMANA 1; 3.48 vs. 1.34 (p = 0.002) in ROMANA 2
• Median overall survival was not different between treatment arms

Phase III: ROMANA 3 Safety Extension (Currow et al. 2017) [5]

Design: Open-label safety extension study. Patients completing ROMANA 1 or 2 could continue or cross over to anamorelin 100 mg daily for an additional 12 weeks (24 weeks total treatment for original anamorelin recipients).

Key Results:

• Body weight improvements observed during the initial 12 weeks were maintained over 24 weeks of treatment
• Anorexia-cachexia symptom improvements were sustained
• No new safety signals emerged with extended treatment
• Anamorelin continued to be well tolerated

Japanese Phase II Trial (ONO-7643-04) [7][9]

Design: Multicenter, randomized, double-blind, placebo-controlled trial in Japanese patients with NSCLC and cachexia. Patients received anamorelin 50 mg, 100 mg, or placebo once daily for 12 weeks.

Key Results:

• Dose-dependent increases in lean body mass and body weight were observed
• The 100 mg dose was selected for further development based on the benefit-risk profile
• Safety profile was consistent with global trials

Japanese Phase III GI Cancer Trial (ONO-7643-05) [8]

Design: Multicenter, open-label, single-arm study in patients with advanced gastrointestinal cancer (gastric, pancreatic, or colorectal) and cancer cachexia. Patients received anamorelin 100 mg daily.

Key Results:

• Lean body mass increased by 1.89 +/- 0.36 kg from baseline (by DXA)
• Body weight increased by 1.41 +/- 0.61 kg
• Treatment response rate was 63.3% (95% CI 48.3-76.6%)
• This study provided the efficacy data for the expanded Japan approval covering GI cancers

Post-Marketing Surveillance in Japan (Takayama et al. 2024) [10]

Design: Interim analysis of a prospective post-marketing surveillance study including 6,016 patients who started anamorelin between April 2021 and January 2023.

Key Results:

• Real-world improvements in body weight and appetite were consistent with clinical trial findings
• Overall safety profile raised no new concerns
• Hyperglycemia and nausea remained the most notable adverse events
• Continued caution was recommended for glucose monitoring

Osteosarcopenia Trial (Bala et al. 2024) [17]

Design: Randomized, placebo-controlled, 12-month trial investigating anamorelin 100 mg/day in 26 adults with osteosarcopenia (combined sarcopenia and osteoporosis) at Tufts University.

Key Results:

• No significant change in the primary endpoint of appendicular lean mass
• Secondary analyses showed significant improvements in leg strength, body weight, the bone formation marker P1NP, and IGF-1 levels
• These findings suggest potential utility beyond oncology, warranting further investigation in larger trials

Dosing in Published Research

The following doses have been used in clinical research or approved for clinical use. This information is provided for educational reference only and does not constitute medical advice.

| Protocol | Dose | Frequency | Route | Duration | Source | |---|---|---|---|---|---| | Cancer cachexia (Japan approved) | 100 mg | Once daily, fasting | Oral | Continuous | Adlumiz PI [6][18] | | ROMANA 1/2 Phase III | 100 mg | Once daily | Oral | 12 weeks | Temel et al. 2016 [4] | | ROMANA 3 extension | 100 mg | Once daily | Oral | Up to 24 weeks | Currow et al. 2017 [5] | | Phase II cancer cachexia | 50 mg | Once daily | Oral | 12 weeks | Garcia et al. 2015 [3] | | Phase I (healthy volunteers) | 10-50 mg | Single or repeated | Oral | Up to 6 days | Garcia et al. 2009 [16] | | Osteosarcopenia | 100 mg | Once daily | Oral | 12 months | Bala et al. 2024 [17] |

The approved dosage in Japan is anamorelin hydrochloride 100 mg (two 50 mg tablets) taken orally once daily on an empty stomach, at least one hour before the first meal. Food substantially reduces bioavailability and should be avoided around the time of dosing [6].

Safety and Side Effects

Common Adverse Effects

The following adverse effects have been consistently observed across clinical trials and post-marketing surveillance:

Hyperglycemia: The most frequent drug-related adverse event in clinical trials, occurring in approximately 4-5% of anamorelin-treated patients compared with less than 1% receiving placebo [4][5]. This reflects ghrelin's known role in glucose metabolism: GHS-R1a activation stimulates GH release, which antagonizes insulin action, and ghrelin directly suppresses insulin secretion from pancreatic beta cells [21]. In the Japanese post-marketing surveillance, patients with pre-existing diabetes were at higher risk for hyperglycemic events and showed reduced weight gain benefit [10]. Glycated hemoglobin (HbA1c) elevations were also observed.

Nausea: Reported in approximately 2.5-3.8% of patients across the ROMANA program [4][5].

Cardiac Conduction Effects: The Adlumiz prescribing information in Japan notes that anamorelin depresses the cardiac conduction system and may cause prolongation of the PR interval, QRS complex, or QT interval [6]. First-degree atrioventricular block and prolonged QRS complex have been reported. Anamorelin is contraindicated in patients with congestive heart failure, recent myocardial infarction or angina pectoris, and severe conduction defects [6].

Other Reported Adverse Effects

• Elevated gamma-glutamyltransferase (GGT)
• Mild peripheral edema (consistent with GH-mediated fluid retention)
• Transient increases in cortisol (within physiological range)

Serious Adverse Events

Grade 3 or higher adverse events were rare in clinical trials (0.9-2.7%) [4]. The overall incidence of serious adverse events was similar between anamorelin and placebo groups in the ROMANA trials, with no increase in treatment-emergent deaths [4][5].

Contraindications and Precautions (Japan Label)

• Congestive heart failure, myocardial infarction, or angina pectoris
• Severe cardiac conduction defects
• Pre-existing diabetes or glucose intolerance requires close monitoring
• Caution with concurrent CYP3A4 inhibitors (increased anamorelin exposure)

Effect on Tumor Growth

A key safety consideration for any anabolic agent in oncology is the potential to promote tumor growth. Preclinical studies specifically addressed this concern: anamorelin did not stimulate tumor growth in lung cancer xenograft models, and tumor volumes were comparable between treated and control animals [14]. In the ROMANA trials, median overall survival did not differ between anamorelin and placebo groups, providing clinical reassurance [4].

Regulatory History and Development

Anamorelin was originally discovered by Elixir Industry (later acquired by Ardea Biosciences) and initially developed by Rejuvenon Corporation under the code RC-1291. Helsinn Healthcare SA subsequently acquired global rights and advanced the compound through Phase III development. In accordance with a licensing agreement, Ono Pharmaceutical holds exclusive development and commercialization rights in Japan, South Korea, and Taiwan, while Helsinn retains rights in the rest of the world [6][18].

Key Regulatory Milestones:

• 2014-2015: ROMANA 1 and 2 Phase III results published, demonstrating efficacy on lean body mass but failing the co-primary endpoint of handgrip strength [4]
• 2017: The EMA Committee for Medicinal Products for Human Use (CHMP) issued a negative opinion, concluding that the effect on lean body mass was marginal and that there was no proven benefit on handgrip strength or quality of life, with inadequately characterized safety [6]
• 2018-2019: Japanese Phase II (ONO-7643-04) and Phase III (ONO-7643-05) trials completed [8][9]
• January 2021: Ono Pharmaceutical received manufacturing and marketing approval from Japan's Ministry of Health, Labour and Welfare for Adlumiz (anamorelin hydrochloride) 50 mg tablets [6]
• April 2021: Commercial launch of Adlumiz in Japan [18]
• 2019-present: Helsinn initiated two additional global Phase III trials (ANAMORA studies) in broader cancer cachexia populations, seeking potential regulatory submissions in Western markets [24]

Comparison with Other Ghrelin Receptor Agonists

Anamorelin belongs to a class of growth hormone secretagogues (GHS) that target GHS-R1a. Several other compounds in this class have been studied clinically, each with distinct pharmacological profiles:

Endogenous Ghrelin: The 28-amino acid acylated peptide hormone produced primarily by gastric oxyntic cells [11]. While potent at GHS-R1a, ghrelin requires intravenous or subcutaneous administration and has a very short half-life (~30 minutes), making it impractical for chronic therapy. Anamorelin was designed to overcome these limitations while preserving ghrelin's dual appetite-stimulating and GH-releasing activities [1][21].

MK-677 (Ibutamoren): Another non-peptide GHS-R1a agonist developed by Merck, with a longer half-life (~24 hours) than anamorelin [15][22]. MK-677 has been extensively studied in aging, obesity, and bone metabolism but was never advanced to Phase III for any indication. Unlike anamorelin, which was developed specifically for cancer cachexia, MK-677 clinical trials focused primarily on somatopause and body composition in elderly populations [22]. MK-677 remains unapproved by any regulatory authority.

Macimorelin: An oral GHS-R1a agonist approved by the FDA in 2017 solely as a diagnostic agent for adult growth hormone deficiency (Macrilen) [23]. Unlike anamorelin, macimorelin is not used therapeutically; it is administered as a single dose to provoke GH release for measurement in a stimulation test. Its therapeutic applications have not been developed.

Peptide GH Secretagogues (GHRP-6, GHRP-2, Hexarelin, Ipamorelin): These are injectable peptide agonists of GHS-R1a with varying selectivity profiles [15]. They require subcutaneous or intravenous administration, have short half-lives (minutes to 1-2 hours), and none have received regulatory approval for any therapeutic indication. Ipamorelin is notable for its high selectivity (minimal effects on cortisol, prolactin, and ACTH) but lacks clinical data in cancer cachexia.

Key Differentiating Features of Anamorelin:

• Only GHS-R1a agonist approved for a therapeutic indication (cancer cachexia, Japan)
• Oral bioavailability combined with an intermediate half-life (~7 hours) suitable for once-daily dosing
• Extensive Phase III clinical evidence in cancer cachexia (ROMANA program, more than 1,400 patients)
• Confirmed lack of tumor growth stimulation in preclinical models [14]

The Lean Body Mass vs. Function Paradox

A central challenge highlighted by the ROMANA trials is the discordance between anamorelin's significant effects on lean body mass and body weight versus the absence of improvement in handgrip strength or physical function [4]. This dissociation raises several important considerations:

Muscle quality vs. quantity: Increases in lean body mass detected by DXA do not necessarily reflect gains in functional contractile muscle tissue. DXA measures total fat-free mass, which includes water, connective tissue, and organ mass in addition to skeletal muscle. GH-mediated fluid retention may contribute to measured lean mass gains without improving muscle function [4][24].

Cachexia pathophysiology: Cancer cachexia involves not only muscle wasting but also qualitative changes in muscle tissue, including mitochondrial dysfunction, impaired protein synthesis, and altered myofiber composition [20]. Restoring muscle mass alone may be insufficient to restore function if these intracellular defects persist.

Multimodal intervention hypothesis: Current expert opinion suggests that effective cachexia management will likely require multimodal approaches combining pharmacological appetite and anabolic stimulation (such as anamorelin) with structured exercise, nutritional optimization, and anti-inflammatory therapy [24]. Clinical trials evaluating anamorelin in combination with exercise programs or myostatin inhibitors are being explored.

This was the primary reason cited by the EMA for its negative opinion: the clinical relevance of lean body mass gain without functional improvement was deemed uncertain [6].

Pharmacokinetics

Absorption

Anamorelin is rapidly absorbed following oral administration, with time to maximum plasma concentration (Tmax) of approximately 0.5-2 hours post-dose [3][16]. The compound was specifically designed as a non-peptide peptidomimetic to achieve oral bioavailability, incorporating a D-tryptophan residue, 2-methylalanine, a 3-benzylpiperidine scaffold, and a trimethylhydrazide cap that collectively confer resistance to gastrointestinal proteolysis and enable intestinal absorption [1][15].

Food effect: Food substantially reduces anamorelin plasma exposure, with an approximately 4-fold decrease in area under the curve (AUC) when administered with a meal [3]. This necessitates administration in the fasting state, at least one hour before the first meal of the day. The magnitude of the food effect is clinically significant and represents an important compliance consideration in the cachectic oncology population.

Distribution and Protein Binding

Specific data on volume of distribution and plasma protein binding in humans have not been extensively published. Based on preclinical data and the compound's moderate lipophilicity, anamorelin distributes beyond the intravascular compartment. The compound crosses the blood-brain barrier, as evidenced by its central appetite-stimulating effects mediated through hypothalamic GHS-R1a receptors [1][21].

Metabolism and Elimination

Anamorelin is primarily metabolized by CYP3A4 in the liver, with a clinically significant drug interaction potential [3]:

| Parameter | Value | |---|---| | Half-life | ~7 hours | | Primary metabolic pathway | Hepatic CYP3A4 | | Elimination (18 h) | ~92% feces, ~8% urine | | Total recovery | ~99.8% within 18 hours | | CYP3A4 inhibitor effect | ~3-fold increase in plasma exposure |

The 7-hour half-life represents a marked improvement over endogenous ghrelin (~30 minutes) and enables once-daily dosing, but is substantially shorter than MK-677's approximately 24-hour half-life [1][15][22].

Drug interaction considerations: Strong CYP3A4 inhibitors (ketoconazole, itraconazole, clarithromycin, ritonavir) increase anamorelin exposure approximately 3-fold and should prompt dose modification or avoidance. CYP3A4 inducers (rifampin, phenytoin, carbamazepine) may reduce efficacy. This CYP3A4 dependency is particularly relevant in the oncology population, where polypharmacy is common and antifungal agents (azoles) are frequently co-prescribed [3][6].

Pharmacokinetic Comparison with Endogenous Ghrelin

| Parameter | Endogenous Ghrelin | Anamorelin | |---|---|---| | Route | Endogenous (stomach) | Oral | | Half-life | ~30 minutes | ~7 hours (14x longer) | | Receptor affinity (Ki) | 0.58 nM | 0.70 nM (comparable) | | Functional potency (EC50) | 0.67 nM | 0.74 nM (comparable) | | Octanoyl modification required | Yes (Ser3) | No (non-peptide mimetic) | | CNS penetration | Yes | Yes | | Dosing feasibility | IV/SC only; impractical | Once-daily oral |

Dose-Response Relationships

GH Secretion Dose-Response

In Phase I studies in healthy volunteers, anamorelin produced dose-dependent increases in plasma GH levels [16]:

| Dose (mg, single oral) | Peak GH Response | Duration of GH Elevation | |---|---|---| | 10 mg | Modest increase above baseline | ~2-3 hours | | 25 mg | Significant increase; appetite stimulation within 30 min | ~4-6 hours | | 50 mg | Robust GH peak; 18.4% increase in spontaneous food intake vs. placebo | ~6-8 hours |

In preclinical studies (rat anterior pituitary cells), anamorelin stimulated GH release with an EC50 of 1.5 nM. In vivo in rats, single oral doses of 3-30 mg/kg produced dose-dependent 2.3- to 4.1-fold increases in peak plasma GH concentrations [1].

Lean Body Mass Dose-Response

The Japanese Phase II trial (ONO-7643-04) directly compared 50 mg and 100 mg daily doses in NSCLC patients with cachexia, providing a within-trial dose-response assessment [7][9]:

| Dose | Lean Body Mass Change (12 weeks) | Body Weight Change | GH/IGF-1 Response | |---|---|---|---| | Placebo | Decreased | Decreased | No change | | 50 mg daily | Increased (dose-dependent) | Modest increase | Moderate increase | | 100 mg daily | Greater increase than 50 mg | Greater increase; selected for Phase 3 | Robust, sustained increase |

The 100 mg dose was selected for Phase 3 development based on the superior lean body mass response and acceptable safety profile. In the pivotal ROMANA trials at 100 mg daily [4]:

• ROMANA 1: +0.99 kg lean body mass (anamorelin) vs. -0.47 kg (placebo) over 12 weeks
• ROMANA 2: +0.65 kg lean body mass (anamorelin) vs. -0.98 kg (placebo) over 12 weeks
• Body weight: +2.20 kg vs. +0.14 kg (ROMANA 1); +0.95 kg vs. -0.57 kg (ROMANA 2)

Appetite Stimulation Dose-Response

In healthy volunteers, anamorelin 25-50 mg produced appetite stimulation within 30 minutes of administration, with spontaneous food intake increasing by 18.4% above placebo at the 50 mg dose [3][16]. Six-day repeated dosing at 50-75 mg induced weight gain of approximately 1.2 kg compared with placebo [3]. In the ROMANA trials, appetite improvements were captured by the FAACT Anorexia/Cachexia Subscale (A/CS domain), which improved significantly with 100 mg daily: +4.12 vs. +1.92 (p = 0.001, ROMANA 1) and +3.48 vs. +1.34 (p = 0.002, ROMANA 2) [4].

Comparative Effectiveness

Anamorelin vs. MK-677 (Ibutamoren)

Both are non-peptide oral GHS-R1a agonists, but with distinct pharmacological and development profiles [1][15][22]:

| Parameter | Anamorelin | MK-677 (Ibutamoren) | |---|---|---| | Half-life | ~7 hours | ~24 hours | | Dosing | 100 mg once daily (fasting) | 25 mg once daily (with or without food) | | GHS-R1a affinity | Ki = 0.70 nM | Ki = 1.3 nM | | Food effect | 4-fold reduction (must fast) | Minimal (no fasting required) | | CYP3A4 metabolism | Yes (significant DDI risk) | CYP3A4 substrate but less DDI concern | | Phase 3 trials | Yes (ROMANA 1/2/3; 1,400+ patients) | No (never advanced to Phase 3) | | Cancer cachexia data | Extensive (Phase 3 evidence) | None (studied in aging/body composition) | | Regulatory status | Approved (Japan, cachexia) | Not approved anywhere | | Tumor safety data | Confirmed no tumor promotion [14] | Not assessed in oncology | | Key limitation | No handgrip strength improvement | Edema, insulin resistance with chronic use |

MK-677's longer half-life and lack of significant food effect offer practical advantages for patient compliance. However, anamorelin has vastly superior clinical evidence in its target indication (cancer cachexia) and is the only compound in its class with regulatory approval for any therapeutic use [6][22].

Anamorelin vs. Megestrol Acetate

Megestrol acetate (Megace) is a synthetic progestational agent that has been used off-label as an appetite stimulant in cachexia for decades, despite limited evidence of lean body mass preservation [13][24]:

| Parameter | Anamorelin | Megestrol Acetate | |---|---|---| | Mechanism | GHS-R1a agonist (ghrelin mimetic) | Progestational agent; appetite via hypothalamic mechanisms | | Effect on lean body mass | Significant increase (+0.65 to +0.99 kg) | No increase; weight gain primarily fat and fluid | | Effect on body weight | +0.95 to +2.20 kg (12 weeks) | +2-5 kg (variable, primarily fluid/fat) | | GH/IGF-1 effect | Increases both (anabolic) | No effect or suppressive | | Thromboembolic risk | No increased risk | Significant (DVT, PE) | | Adrenal suppression | None | Yes (clinically significant) | | Edema | Minimal | Common (fluid retention) | | Regulatory status | Approved (Japan, cachexia) | Not approved for cachexia; off-label use | | Quality of evidence | Phase 3 RCTs | Primarily older, smaller trials |

Anamorelin's ability to increase lean body mass (rather than just total body weight from fat and fluid) represents a qualitative advantage over megestrol acetate, though neither agent has demonstrated functional benefit (handgrip strength, physical performance) [4][24].

Anamorelin vs. Endogenous Ghrelin Infusion

Ghrelin infusions have been studied in cancer cachexia and other wasting conditions [11][21]:

| Parameter | Anamorelin | Ghrelin Infusion | |---|---|---| | Route | Oral (once daily) | IV or SC (multiple daily infusions) | | Half-life | ~7 hours | ~30 minutes | | Practicality | High (oral pill) | Low (IV/SC, short duration) | | Efficacy data | Phase 3 (1,400+ patients) | Small pilot studies only | | GH response | Robust, sustained | Potent but transient | | Appetite effect | Sustained over dosing interval | Brief (hours) | | Clinical development | Advanced (approved in Japan) | No advanced development for cachexia |

Positioning in Cachexia Management

| Agent | Mechanism | Weight Effect | LBM Effect | Functional Effect | Approval | |---|---|---|---|---|---| | Anamorelin | GHS-R1a agonist | +1-2 kg | +0.7-1.0 kg | No improvement | Japan (cachexia) | | Megestrol acetate | Progestational | +2-5 kg (fat/fluid) | No increase | No improvement | Off-label | | Dronabinol | Cannabinoid CB1 agonist | Modest | Minimal | No improvement | Off-label | | Corticosteroids | Anti-inflammatory | Transient appetite increase | Catabolic (worsens) | No improvement | Off-label (short-term) | | Ghrelin infusion | GHS-R1a agonist | Small studies | Limited data | Not assessed | Investigational |

Enhanced Safety Profile

Cardiac Conduction Effects

Anamorelin depresses the cardiac conduction system and may prolong the PR interval, QRS complex, or QT interval [6]. This is a class-specific concern for GHS-R1a agonists and represents the most clinically significant safety finding:

| Cardiac Effect | Incidence | Clinical Significance | |---|---|---| | First-degree AV block | Uncommon but reported | Monitor ECG in at-risk patients | | Prolonged QRS | Uncommon | Avoid in pre-existing bundle branch block | | QT prolongation | Potential risk | Avoid concurrent QT-prolonging drugs |

Contraindications (Japan label): Congestive heart failure, recent myocardial infarction or angina pectoris, and severe cardiac conduction defects [6].

Glycemic Effects

Hyperglycemia is the most frequently reported drug-related adverse event, occurring in approximately 4-5% of anamorelin-treated patients versus less than 1% on placebo [4][5]. The mechanism involves dual pathways:

1. GH-mediated insulin antagonism (indirect, via pituitary GH release)
2. Direct ghrelin-mediated suppression of pancreatic beta-cell insulin secretion [21]

In the Japanese post-marketing surveillance (6,016 patients), patients with pre-existing diabetes were at highest risk and showed attenuated weight gain benefit [10]. HbA1c monitoring is recommended throughout treatment.

Tumor Growth Safety

A critical concern for any GH-axis stimulating agent in oncology is potential tumor promotion. Key reassurance comes from:

• Preclinical: Anamorelin did not stimulate tumor growth in lung cancer xenograft models at supratherapeutic doses [14]
• Clinical: Median overall survival in ROMANA 1 and ROMANA 2 did not differ between anamorelin and placebo groups [4]
• Mechanistic: IGF-1 increases are moderate and within physiological ranges, unlike supraphysiological exogenous GH administration

Long-Term Safety (Post-Marketing)

The Japanese post-marketing surveillance (interim analysis, 6,016 patients, April 2021-January 2023) confirmed the clinical trial safety profile in real-world use [10]:

• Real-world adverse event rates consistent with clinical trials
• No new safety signals identified
• Hyperglycemia and nausea remained the most notable adverse events
• Continued glucose monitoring recommended for all patients

Adverse Event Summary Across Trials

| Adverse Event | Anamorelin (100 mg) | Placebo | Notes | |---|---|---|---| | Hyperglycemia | 4-5% | 0.5-1% | Most common drug-related AE | | Nausea | 2.5-3.8% | 1-2% | Mild in severity | | Elevated GGT | 1-2% | Similar | Monitor liver function | | Peripheral edema | Uncommon | Uncommon | GH-mediated fluid retention | | Cardiac conduction effects | Rare | -- | ECG monitoring in at-risk patients | | Grade 3+ adverse events | 0.9-2.7% | Similar | Low incidence | | Serious adverse events | No increase vs. placebo | Reference | Reassuring | | Treatment-emergent deaths | No increase vs. placebo | Reference | Reassuring [4] |

SCALA Phase 3 Program and Ongoing Development

SCALA-1 and SCALA-2 (Confirmatory Phase 3 Trials)

Between March 2019 and August 2022, Helsinn conducted two additional confirmatory Phase 3 studies (SCALA-1 and SCALA-2), enrolling a total of 636 patients with advanced cancer and cachexia who were randomized to anamorelin 100 mg or placebo once daily for 24 weeks. In both studies, anamorelin significantly increased body weight over 12 weeks compared to placebo, consistent with the ROMANA findings. These multinational trials were designed to support potential regulatory submissions in Western markets beyond Japan.

Urothelial Carcinoma Trial (2025)

A randomized controlled study published in The Oncologist in 2025 evaluated anamorelin in patients with metastatic urothelial carcinoma receiving systemic chemotherapy, representing an expansion of the clinical evidence base beyond NSCLC and GI cancers. Results demonstrated consistent body weight and appetite improvements in this new cancer population.

Ongoing Global Development

Helsinn continues to pursue global regulatory strategies for anamorelin. A 2025 review in Anticancer Research summarized the clinical efficacy, challenges, and future directions for anamorelin in cancer cachexia management, highlighting the need for multimodal approaches combining anamorelin with exercise and nutritional interventions to improve functional outcomes [24].

Related Peptides

See also: MK-677 (Ibutamoren), GHRP-6, Ipamorelin, Hexarelin

• MK-677 (Ibutamoren) --- Another non-peptide GHS-R1a agonist with a longer half-life (~24 hours). Studied primarily in aging and body composition but never advanced to Phase III. Not approved for any indication.

• GHRP-6 --- A synthetic hexapeptide GH secretagogue that also acts on GHS-R1a. Requires injection and has a shorter half-life. Stimulates appetite and GH release but with lower receptor selectivity than anamorelin.

• Ipamorelin --- A highly selective peptide GHS-R1a agonist with minimal effects on cortisol and prolactin. Requires subcutaneous injection and has not been studied in cancer cachexia.

• Hexarelin --- The most potent peptide GHS-R1a agonist, but subject to tachyphylaxis (receptor desensitization) with chronic use. Injectable only.

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