Bombesin and GRP

bombesin (BN); gastrin-releasing peptide (GRP, GRP(1-27)), its C-terminal fragment neuromedin C (GRP(18-27)); related mammalian peptide neuromedin B (NMB). Receptor-targeted tracers include 68Ga-RM2 (DOTA-RM2, BAY 86-7548), 68Ga-NeoBOMB1, 68Ga-RM26, 177Lu-AMBA

Oncology & imaging

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Summary

Class: Bombesin is a naturally occurring 14-amino-acid peptide from frog skin; GRP (27 amino acids) and neuromedin B (10 amino acids) are the endogenous mammalian members of the same family. The imaging agents are synthetic GRP-receptor ligands conjugated to a chelator and a radiometal
Mechanism: Act at the bombesin receptor family — principally GRP receptor (BB2/GRPR) and neuromedin B receptor (BB1) — which in normal physiology drives gastrin release, gut motility, satiety and itch, and which is heavily over-expressed on several common cancers, making it an imaging target
Routes studied: Intravenous infusion (human physiology studies and radiotracer imaging); intracerebroventricular and peripheral injection in animals; intrathecal in itch research
Half-life: Bombesin and GRP are cleared within minutes in plasma. Tracer imaging windows are dictated by the isotope (gallium-68, ~68 minutes physical half-life)
Storage: Not applicable to this profile — radiopharmaceuticals are prepared and used within hours in a licensed radiopharmacy
Regulatory status: No bombesin-family peptide or GRPR-targeted radiopharmaceutical is approved anywhere. All investigational

Doses are as reported in studies or by the community — never recommendations.

1What it is

Bombesin was isolated in 1971 by Vittorio Erspamer's group in Rome from the skin of the European fire-bellied toad, Bombina bombina — part of a remarkable run of discoveries from amphibian skin that also produced caerulein, the tachykinins and the dermorphins. Erspamer's approach was to extract frog skin, inject the fractions, and see what happened; bombesin's conspicuous effect was a rise in gastric acid secretion, which turned out to be mediated by gastrin release. Hence the name of its mammalian counterpart.

Humans do not make bombesin. We make gastrin-releasing peptide, a 27-amino-acid peptide whose C-terminal seven residues are nearly identical to bombesin's, and neuromedin B. GRP is released from enteric and central neurons and acts locally; it is a genuine endogenous signalling peptide, not a research compound.

The reason it appears in a peptide reference is oncology. The GRP receptor is expressed at high density on the great majority of prostate cancers, a large fraction of breast cancers, and small cell lung cancer — in some cases on tumours that have lost the markers used by current imaging agents. Attach a chelator and a radiometal to a GRPR-binding peptide and you have a PET tracer that lights up GRPR-positive tumour; attach a therapeutic isotope instead and you have a candidate radioligand therapy. That is the field this profile describes.

2How it's thought to work

Receptor pharmacology. GRP acts at GRPR (BB2); neuromedin B prefers NMBR (BB1); bombesin binds both. A third family member, BRS-3, has no identified natural ligand and is a separate metabolic target. All are G-protein-coupled receptors signalling mainly through Gq and phospholipase C.

Gut physiology. GRP released from enteric neurons stimulates gastrin secretion from G cells, gastric acid output, pancreatic enzyme secretion, gallbladder contraction and gut motility. This is the function the peptide was named for.

Satiety. Peripheral bombesin and GRP reduce food intake in animals and in human infusion studies, acting partly through vagal afferents. The effect is short-lived, which is one reason the family never became an obesity target.

Itch. GRP and GRPR in the dorsal spinal cord form a dedicated itch-transmission pathway, distinguishable from pain. This was shown by deleting GRPR in mice, which selectively abolished scratching responses while leaving pain intact (Sun & Chen 2007, Nature) — an important piece of basic neuroscience and the origin of current interest in GRPR antagonists for chronic itch.

Tumour biology. GRP acts as an autocrine growth factor in small cell lung cancer and some other tumours, and GRPR over-expression is the basis of the imaging strategy. Notably, receptor antagonists have proved better tracers than : they bind without triggering signalling or internalisation, give cleaner images, and avoid the gastrointestinal effects that agonist tracers caused.

Proposed: bombesin, first found in frog skin, acting at the mammalian gastrin-releasing peptide receptor. It reduces food intake and triggers gastrin release; the same receptor drives growth in some tumours, which is why it is used as an imaging target.Schematic — not to scale

3What the research shows

Human gastrointestinal and satiety physiology

Intravenous bombesin and GRP infusions in healthy volunteers raise plasma gastrin and pancreatic polypeptide, stimulate gastric acid and pancreatic secretion, and reduce food intake at a subsequent meal (Gutzwiller 1994 and related human infusion studies). These are small, short, mechanistic studies in volunteers, not therapeutic trials, and they are the main source of human dose-response information for the native peptides.

GRPR PET imaging in prostate cancer

68Ga-RM2, a GRPR antagonist tracer, has been studied in biochemically recurrent and primary prostate cancer in several academic series, with detection of disease in a proportion of patients whose conventional imaging was non-contributory, and reports of complementarity with PSMA-targeted imaging — some lesions are PSMA-negative and GRPR-positive (Stanford and other academic series; ClinicalTrials.gov NCT03113617). Sample sizes are modest and the comparator standards vary. 68Ga-NeoBOMB1 has been evaluated similarly.

GRPR PET imaging in breast cancer and other tumours

Small series report GRPR tracer uptake in oestrogen-receptor-positive breast cancer, with uptake correlating with receptor expression. Gastrointestinal stromal tumours and glioma have also been imaged. Exploratory.

Graded B/C

GRPR-targeted radioligand therapy

Agonist-based therapeutic constructs such as 177Lu-AMBA entered early human study but were limited by gastrointestinal toxicity attributable to receptor activation in the gut and pancreas. Antagonist-based therapeutic constructs have been examined in early-phase work. No approved product.

Graded C/D

Chronic itch

The GRP–GRPR spinal pathway is well established in rodents. Translation to human antipruritic therapy remains preclinical and early-clinical †.

Graded C/D

Small cell lung cancer growth

Autocrine GRP signalling and anti-GRP antibody approaches were explored from the 1980s onward without producing a therapy.

4Reported side effects and interactions

Literature-reported

Literature (human infusion of native peptides). bombesin and GRP infusions in volunteer studies caused nausea, abdominal discomfort, a sensation of fullness, flushing and occasional vomiting — dose-related and short-lived. These effects are direct consequences of the gastrointestinal pharmacology.

Literature (radiotracers). GRPR antagonist tracers have generally been reported as well tolerated at the microgram peptide masses used, with the radiation dose being the main consideration. tracers and therapeutic agonist constructs produced the gastrointestinal effects above, which is the principal reason the field moved to antagonists.

Community-reported

Community use: essentially none documented. Self-administration would be pointless and unpleasant — the native peptides are cleared in minutes, their only reliable effects at tolerable doses are nausea and gastric acid secretion, and the imaging agents are radioactive products that do nothing observable without a PET scanner and a licensed radiopharmacy.

Radiation considerations. as with any radiopharmaceutical, the effective dose and the organs receiving the highest dose (pancreas is notable for GRPR ligands, given physiological receptor expression) are the relevant safety parameters, managed by dosimetry.

Theoretical. agonist activity at GRPR on a GRP-responsive tumour is a theoretical growth-stimulation concern and another argument for antagonists; pancreatic receptor expression limits deliverable therapeutic dose.

Interactions. none established. Proton pump inhibitors and other acid-suppressing drugs would confound any gastric acid endpoint.

Markers researchers commonly monitor

No compound-specific markers apply to self-directed use, because there is none. In the research settings the relevant measures are:

Marker	Why it's watched
Plasma gastrin and pancreatic polypeptide	the classical readouts of bombesin/GRP infusion, and the measures that gave the peptide its name.
Gastric acid output and food intake at a test meal	the physiological endpoints in the human volunteer studies.
Tumour GRPR expression by immunohistochemistry or autoradiography on biopsy tissue	the reference standard against which tracer uptake is validated.
Tracer uptake metrics (SUVmax, tumour-to-background ratio) and lesion detection rate	the actual imaging endpoints.
Dosimetry, with attention to pancreatic absorbed dose	because physiological receptor expression in the pancreas is the dose-limiting organ for therapeutic constructs.
PSA and conventional staging imaging	the clinical context in which prostate GRPR imaging is assessed.

Free for everyone. Safety information is never behind a paywall.

5Research context and safety notes

This profile covers an endogenous human peptide, a frog-skin peptide used as its pharmacological surrogate, and a family of investigational radiopharmaceuticals. The constraints differ by category: - GRP is endogenous, and that limits what exogenous dosing can achieve. It is released locally by neurons, acts over short distances, and is destroyed within minutes. Flooding the circulation with it produces gut effects, not physiological signalling. - The imaging agents are radioactive drugs. They are synthesised in a licensed radiopharmacy, assayed, and administered within hours because the isotope decays. They require a PET scanner to produce any result at all, and handling them involves radiation protection controls. There is no circumstance in which these exist outside that infrastructure. - versus antagonist matters. The same receptor, approached two ways, gives either a clean image or a patient vomiting. This is a useful general lesson about receptor-targeted peptides and worth knowing when reading the older literature. No preparation, concentration or storage guidance is given here.

6Commonly studied alongside

PSMA-targeted tracers and radioligand therapies (the direct comparator and complement in prostate cancer); somatostatin analogue radiopharmaceuticals such as the DOTATATE agents, which are the proven template this field is modelled on; cholecystokinin and gastrin analogues as the other gut-peptide imaging targets; caerulein and the tachykinins as the other Erspamer frog-skin discoveries.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	No bombesin-family peptide or GRPR-targeted radiopharmaceutical is FDA-approved. Investigational, under academic INDs and early-phase sponsorship
European Union	Not authorised; investigational
United Kingdom	Not licensed
Australia	Not approved by the TGA
South Africa	Not registered with SAHPRA
Sport	Not listed by WADA; no performance application. S0 would apply in principle to any non-approved substance

8Open questions

Does GRPR imaging change management in prostate cancer, and in which patients — those with PSMA-negative disease being the obvious candidates?
Can GRPR radioligand therapy achieve a useful therapeutic index given pancreatic receptor expression?
Is spinal GRPR a tractable target for chronic itch in humans?
Why has a receptor over-expressed on so many common tumours, known since the 1980s, produced no approved agent in four decades?

9References

1Erspamer V, Erspamer GF, Inselvini M (1971). Some pharmacological actions of alytesin and bombesin. J Pharm Pharmacol. PubMed · DOI
2McDonald TJ et al. (1979). Characterization of a gastrin releasing peptide from porcine non-antral gastric tissue. Biochem Biophys Res Commun. PubMed · DOI
3Jensen RT et al. (2008). International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states. Pharmacol Rev. PubMed · DOI
4Sun YG, Chen ZF (2007). A gastrin-releasing peptide receptor mediates the itch sensation in the spinal cord. Nature. PubMed · DOI
5Mansi R et al. (2011). Development of a potent DOTA-conjugated bombesin antagonist for targeting GRPr-positive tumours. Eur J Nucl Med Mol Imaging. PubMed · DOI
6Kähkönen E et al. (2013). In vivo imaging of prostate cancer using 68Ga-labeled bombesin analog BAY86-7548. Clin Cancer Res. PubMed · DOI
7Baratto L, Jadvar H, Iagaru A (2018). Prostate cancer theranostics targeting gastrin-releasing peptide receptors. Mol Imaging Biol. PubMed · DOI

† Being confirmed by our reviewers against current sources.

10Community

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11Page history

31 Oct 2026Profile published — awaiting medical review

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