Ghrelin Agonists for Cancer Cachexia

Peptide Therapies for Chemo Side Effects

73.8% of studies show no link between ghrelin agonists and cancer risk

Cancer cachexia kills an estimated 20% of all cancer patients. Anamorelin, the first ghrelin receptor agonist approved for cachexia, increased lean body mass by 0.99 kg over placebo in 12-week trials.

Sever et al., Endocrine-Related Cancer, 2016

Sever et al., Endocrine-Related Cancer, 2016

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Cancer cachexia is not simply weight loss from eating less. It is a metabolic syndrome driven by tumor-derived inflammatory cytokines that reprogram the body's energy metabolism, catabolize skeletal muscle protein, suppress appetite through central nervous system signaling, and resist reversal by nutritional supplementation alone. An estimated 50-80% of advanced cancer patients develop cachexia, and it directly causes approximately 20% of all cancer deaths.^[1] Patients with cachexia tolerate chemotherapy poorly, experience more dose reductions and treatment delays, and have shorter survival than cancer patients without wasting. For the broader landscape of peptide-based chemotherapy supportive care, see the pillar article on peptide therapies for chemotherapy side effects.

Ghrelin agonists target this syndrome through the growth hormone secretagogue receptor 1a (GHSR-1a), the same receptor that endogenous ghrelin activates to stimulate appetite before meals. By activating GHSR-1a, ghrelin agonists simultaneously increase appetite, promote food intake, stimulate growth hormone release (which drives anabolic signaling in muscle), and may directly counteract the inflammatory pathways that drive muscle catabolism.^[2] Anamorelin, the most clinically advanced ghrelin agonist for cachexia, was approved in Japan in December 2020 for cancer cachexia in four tumor types.

The Biology of Cancer Cachexia

Cancer cachexia operates through multiple simultaneous pathways that distinguish it from starvation or simple malnutrition. Tumors secrete pro-inflammatory cytokines (TNF-alpha, IL-6, IL-1) that activate the ubiquitin-proteasome pathway in skeletal muscle, accelerating protein degradation beyond what reduced food intake alone would cause. Simultaneously, these cytokines suppress the hypothalamic appetite centers, creating anorexia that further compounds the catabolic state.^[3]

The result is a self-reinforcing cycle: inflammation drives muscle wasting, muscle wasting releases amino acids that fuel tumor growth, and the metabolic cost of this futile cycle depletes energy reserves. Unlike starvation (which primarily depletes fat stores and preserves muscle through adaptive hormone changes), cancer cachexia destroys skeletal muscle and fat simultaneously, reflecting a fundamentally different metabolic program. The distinction matters clinically: feeding a cachectic patient more calories does not stop muscle wasting because the inflammatory catabolic drive continues regardless of caloric intake.

The severity of cachexia correlates with tumor type. Pancreatic and gastric cancers produce cachexia in 80-85% of patients, while breast and hematologic cancers produce it less frequently. The degree of systemic inflammation, measured by C-reactive protein and IL-6 levels, predicts cachexia severity better than tumor size or stage.

Esposito et al. (2015) reviewed the mechanisms of cancer anorexia-cachexia syndrome and the rationale for selective ghrelin receptor agonists. Effective treatment requires addressing both the appetite suppression and the metabolic reprogramming, not just one or the other. Ghrelin receptor activation offers this dual-target approach because GHSR-1a is expressed in both the hypothalamus (appetite regulation) and peripheral tissues (anabolic signaling).^[2]

From Ghrelin Discovery to Cachexia Therapy

Ghrelin was identified in 1999 by Kojima et al. as a 28-amino-acid peptide secreted primarily by the stomach, with an unusual octanoyl modification at serine-3 that is essential for its growth hormone-releasing activity. The name "ghrelin" derives from "ghre," the Proto-Indo-European root of the word "grow." Its discovery revealed a new mechanism for growth hormone regulation distinct from hypothalamic GHRH.^[4]

The connection between ghrelin and cachexia emerged from observations that ghrelin levels were often altered in wasting conditions. DeBoer (2008) reviewed the emerging evidence that ghrelin receptor agonists could treat cachexia through a triple mechanism: appetite stimulation (reversing anorexia), growth hormone/IGF-1-mediated anabolism (opposing muscle wasting), and anti-inflammatory effects (countering cytokine-driven catabolism). This triple action made ghrelin agonists more comprehensive than single-target appetite stimulants or anabolic agents.^[1]

Molfino et al. (2014) traced the path from ghrelin's discovery to its therapeutic application in cancer cachexia, noting that while ghrelin's mechanisms of action were still being clarified, its effects on appetite and body composition were consistent across multiple preclinical and early clinical studies.^[3]

Anamorelin: The Clinical Evidence

Anamorelin is a non-peptide, orally active ghrelin receptor agonist with a molecular weight of 546 Da. It binds GHSR-1a with high affinity, stimulating appetite, food intake, growth hormone release, and lean body mass accumulation. Its oral bioavailability and once-daily dosing (100 mg) distinguish it from injectable ghrelin, which requires intravenous administration and has a plasma half-life of minutes.

Zhang et al. (2015) reviewed the clinical development of anamorelin for cancer anorexia-cachexia in NSCLC, summarizing results from the ROMANA phase III trials. In ROMANA 1, anamorelin increased lean body mass by a median of 0.99 kg compared to a loss of 0.47 kg in the placebo group over 12 weeks (p<0.0001). In ROMANA 2, the difference was similarly robust (0.65 kg gain vs. 0.98 kg loss, p<0.0001). Appetite scores improved and serum IGF-1 levels rose in both trials.^[5]

Graf et al. (2017) placed anamorelin in the broader therapeutic context for cancer cachexia, noting that while multiple drug candidates had entered clinical development, anamorelin was the first to demonstrate consistent lean mass improvement in large, multi-center phase III trials. The review emphasized that cancer cachexia had no approved treatment in most countries, making any measurable improvement relevant for a patient population with limited options.^[6]

Currow et al. (2014) provided an early assessment of anamorelin's clinical profile, identifying the dissociation between lean mass gains and functional outcomes as the central unresolved question. Patients gained measurable lean mass on DXA scans but did not improve on grip strength testing or the Stair Climb Power test. This gap became the primary reason the FDA and EMA did not approve anamorelin, despite the Japanese regulatory authority accepting the body composition endpoint as sufficient evidence of benefit.^[7]

Nishie et al. (2022) documented the post-approval landscape in Japan, where anamorelin was approved in December 2020 for cachexia in NSCLC, gastric cancer, pancreatic cancer, and colorectal cancer. Real-world data confirmed the lean mass and appetite improvements observed in clinical trials, with additional quality-of-life benefits reported by treated patients that grip strength measurements alone could not capture. Japanese oncologists have reported that patients on anamorelin maintain better nutritional status during chemotherapy, tolerate treatment with fewer dose reductions, and report improvements in energy and well-being.^[8]

The divergent regulatory outcomes between Japan, Europe, and the United States reflect a fundamental disagreement about what constitutes meaningful clinical benefit in a disease with no other approved treatment. Japan accepted that preventing further lean mass loss and improving appetite in terminally ill patients has inherent value, even without demonstrated strength improvement. Western regulators required proof that body composition changes translate to physical function. Neither position is unreasonable; the disagreement illuminates how different regulatory philosophies handle conditions where the evidence is real but incomplete.

The Function Gap: Why Lean Mass Did Not Equal Strength

The central question in cancer cachexia treatment is whether gaining lean mass translates to meaningful physical improvement. For anamorelin, the answer has been "not yet," and the reasons are more nuanced than simple drug failure.

Cancer cachexia degrades not just muscle quantity but muscle quality. Intramuscular fat infiltration, mitochondrial dysfunction, and neuromuscular junction impairment all reduce the force-generating capacity of remaining muscle fibers. Adding lean mass (which may include water and non-contractile protein) through hormonal stimulation does not automatically restore these qualitative deficits.

The 12-week trial duration may be too short to detect functional recovery. Muscle protein must be synthesized, assembled into myofibrils, integrated into the existing contractile apparatus, and innervated by motor neurons before it can generate force. This remodeling takes months in healthy adults undergoing resistance training and is almost certainly slower in cachectic patients whose anabolic signaling is compromised by ongoing inflammation.

Conte et al. (2017) demonstrated that growth hormone secretagogues prevented dysregulation of skeletal muscle calcium homeostasis in a cisplatin-induced cachexia model. The study showed that GH secretagogue treatment preserved the molecular machinery of muscle contraction (calcium channels, sarcoplasmic reticulum function) even when it did not fully prevent muscle mass loss. This suggests functional preservation may be a separate therapeutic target from mass preservation.^[9]

Do Ghrelin Agonists Promote Tumor Growth?

A reasonable concern with any appetite-stimulating, growth-hormone-releasing treatment in cancer patients is whether it could fuel tumor progression. Sever et al. (2016) addressed this question with a systematic review of 61 in vivo studies examining ghrelin, ghrelin receptor agonists, and ghrelin genetic variants in relation to cancer risk, presence, or growth.

The results were largely reassuring. Of the 61 studies, 45 (73.8%) reported either no significant association or an inverse association between ghrelin and cancer. All 11 studies involving exogenous ghrelin or ghrelin receptor agonist treatment showed null or inverse associations with cancer progression. Only 10 studies (16.7%) reported positive associations, and 6 (10%) reported mixed results. The review concluded that ghrelin-based treatment may have a favorable safety profile for use in cancer cachexia, though larger prospective trials were needed for definitive conclusions.^[10]

Anamorelin's phase III trial data supports this conclusion: overall survival was not compromised in anamorelin-treated patients compared to placebo across the ROMANA trials, and the growth hormone and IGF-1 elevations produced by the drug did not translate to measurable tumor growth acceleration.^[7] That said, most safety data comes from studies lasting 12-24 weeks. Whether chronic ghrelin agonist use over months or years carries different risks remains an open question, though the existing evidence does not raise specific red flags.

Beyond Anamorelin: Other Ghrelin-Based Approaches

Natural Ghrelin

Blum et al. (2021) reported outcomes from subcutaneous natural ghrelin in advanced cancer patients with cachexia. Six patients with metastatic solid tumors self-injected ghrelin twice daily for 4 days at escalating doses starting at 32 mcg/kg body weight, followed by a maintenance period. Ghrelin was safe without dose-limiting toxicity and well tolerated. Muscle mass was stable in two patients and increased in one; muscle strength was stable in three patients. Patients showed positive effects on nutritional intake and reported subjective improvement in narratives about their eating and well-being, though the trajectory was fluctuating. Median survival was 88 days (range 51-412).^[11]

HM01

Villars et al. (2017) tested HM01, a non-peptidergic oral ghrelin receptor agonist, in mice bearing colon-26 (C26) tumors. This model produces pronounced body weight loss and muscle wasting. HM01 treatment increased food intake, body weight, fat mass, muscle mass, and bone mineral density while decreasing energy expenditure. These effects appeared independent of the inflammatory cytokines IL-6 and MIC-1, which were not affected by HM01, suggesting the drug works through metabolic and appetite pathways rather than anti-inflammatory ones.^[12]

Z-505

Yoshimura et al. (2017) investigated Z-505, an oral GHSR-1a agonist with an EC50 of 0.45 nM (comparable to human ghrelin). In C26 tumor-bearing mice, Z-505 (300 mg/kg twice daily for 7 days) significantly increased food intake, inhibited weight loss progression, and attenuated muscle wasting and fat loss. The compound increased circulating insulin and IGF-1 levels without affecting the catabolic markers IL-6 and corticosterone, suggesting its anti-cachexia effects operate through enhanced anabolic signaling rather than inflammation suppression.^[13]

Anamorelin and Ipamorelin in Chemotherapy-Induced Wasting

Lu et al. (2024) compared anamorelin and ipamorelin for prevention of cisplatin-induced weight loss in ferrets. Both compounds inhibited cisplatin-induced weight loss by approximately 24% during the delayed phase (48-72 hours). Anamorelin administered centrally (intracerebroventricularly) reduced acute emesis by 60% and improved food and water consumption by 20-40%, an effect not seen with peripheral administration. This suggests brain penetration is important for the anti-emetic mechanism but not for the weight-sparing effect.^[14]

Emerging Peptide Approaches to Cachexia

The limitations of ghrelin receptor agonism alone have driven research into complementary peptide strategies that address cachexia's metabolic reprogramming.

Ji et al. (2023) developed a peptide drug (Pen-X-ACIP) that restores AMPK and adipose tissue functionality in cancer cachexia. AMPK is a master metabolic sensor that is dysregulated in cachexia; restoring its function prevented cachexia progression, preserved body weight and adipose tissue mass, and had no effect on tumor growth. The peptide showed favorable uptake into adipose tissue upon intraperitoneal injection and exerted anti-lipolytic activity in human adipocytes, providing a platform for clinical development toward a first-in-class approach against cachexia that targets metabolic cause rather than symptoms.^[15]

For how ghrelin's role in appetite regulation extends beyond cancer, see ghrelin: the hunger hormone. For the digestive motility aspects of ghrelin signaling, see ghrelin and gut motility. For a sibling perspective on chemotherapy oral damage, see peptides for oral mucositis.

The Bottom Line

Ghrelin agonists represent the most clinically advanced peptide approach to cancer cachexia. Anamorelin, approved in Japan for four cancer types, consistently increases lean body mass and appetite in patients with cancer-related wasting. The central limitation is that lean mass gains have not translated to measurable improvements in grip strength or physical function in 12-week trials, a gap that prevented FDA and EMA approval. Safety data are broadly favorable: a systematic review of 61 studies found no evidence that ghrelin agonists promote tumor growth. Multiple next-generation ghrelin agonists (HM01, Z-505, ipamorelin) show distinct pharmacological profiles in preclinical models, and emerging AMPK-targeting peptides offer complementary mechanisms beyond appetite stimulation.

Frequently Asked Questions

What is cancer cachexia and how common is it?

Cancer cachexia is a metabolic syndrome characterized by involuntary loss of skeletal muscle mass driven by tumor-derived inflammatory cytokines. It affects 50-80% of advanced cancer patients and directly causes approximately 20% of all cancer deaths. Unlike simple weight loss from reduced eating, cachexia involves active muscle protein degradation through the ubiquitin-proteasome pathway that cannot be fully reversed by nutritional supplementation alone.

Is anamorelin FDA approved for cancer cachexia?

No. Anamorelin is approved only in Japan (since December 2020) for cachexia in NSCLC, gastric, pancreatic, and colorectal cancer. The FDA and EMA declined approval because anamorelin increased lean body mass in phase III trials (ROMANA 1 and 2) but did not improve grip strength or physical function. Japan accepted body composition improvement as sufficient evidence of benefit in a disease with no other approved treatment.

How does anamorelin work for cancer cachexia?

Anamorelin activates the ghrelin receptor (GHSR-1a), producing three simultaneous effects: stimulation of hypothalamic appetite centers (increasing food intake), growth hormone release from the pituitary (promoting anabolic muscle signaling via IGF-1), and possible direct anti-inflammatory effects that counter cachexia's catabolic pathways. It is taken orally at 100 mg daily, unlike injectable ghrelin which has a plasma half-life of minutes.

Do ghrelin agonists cause cancer to grow faster?

A 2016 systematic review by Sever et al. analyzed 61 in vivo studies and found that 73.8% showed no association or an inverse association between ghrelin/ghrelin agonists and cancer risk or progression. All 11 studies using exogenous ghrelin or ghrelin receptor agonist treatment reported null or inverse associations. The ROMANA trial data showed no compromise in overall survival. While long-term data beyond 24 weeks are limited, the existing evidence does not indicate that ghrelin agonists accelerate tumor growth.

Why did anamorelin increase lean mass but not muscle strength?

Cancer cachexia damages muscle quality as well as muscle quantity. Intramuscular fat infiltration, mitochondrial dysfunction, and impaired neuromuscular signaling reduce force generation even when total lean mass increases. The 12-week trial duration may also be insufficient for newly synthesized muscle protein to organize into functional contractile units. Conte et al. (2017) showed that GH secretagogues preserved muscle calcium homeostasis (function) even when they could not fully prevent mass loss, suggesting mass and function are partially separate targets.

What ghrelin agonists besides anamorelin are being studied for cachexia?

Several compounds are in preclinical development. HM01, a non-peptidergic oral agonist, increased muscle mass and bone mineral density in tumor-bearing mice (Villars et al., 2017). Z-505 attenuated muscle wasting via increased insulin and IGF-1 signaling (Yoshimura et al., 2017). Ipamorelin showed weight-sparing effects comparable to anamorelin in cisplatin-treated ferrets (Lu et al., 2024). Natural ghrelin administered subcutaneously was safe and tolerable in advanced cancer patients (Blum et al., 2021). None have reached phase III trials for cachexia.