Mechanism of Action
Bombesin Receptor Activation
Litorin activates the gastrin-releasing peptide receptor (GRPR/BB2) and neuromedin B receptor (NMBR/BB1), which are Gq-coupled GPCRs. Receptor activation stimulates phospholipase C, increases intracellular calcium, and activates PKC. In the gastrointestinal tract this drives gastric acid secretion and pancreatic enzyme release. GRPR is overexpressed in many cancers, making bombesin-like peptides useful as cancer-targeting ligands.
Smooth Muscle Stimulation
Like bombesin, litorin causes smooth muscle contraction in the gallbladder, intestine, and urinary tract through BB2 receptor activation. It also stimulates gastric motility and has satiating effects through central GRPR receptors in the hypothalamus and brainstem, reducing food intake when administered centrally.
Research Summary
Receptor Pharmacology
PreclinicalLitorin has been used to characterize the binding properties and selectivity of bombesin receptor subtypes. Its slightly different N-terminal sequence compared to bombesin provides selectivity information useful in receptor subtype discrimination. Litorin analogs with radiolabels have been developed for tumor imaging studies.
Cancer Imaging and Targeting
PreclinicalBombesin-like peptides including litorin derivatives have been radiolabeled with technetium-99m and gallium-68 for PET/SPECT imaging of GRPR-overexpressing cancers (prostate, breast, small cell lung cancer). Litorin-based vectors show good tumor uptake and retention in preclinical models.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| GRPR receptor binding | 1-100 nM | Single | Receptor binding assay |
| Pancreatic secretion model | 0.1-1 nmol/kg IV | Single | IV bolus |
Research use only. Not used clinically. Bombesin analogs are in clinical oncology imaging trials.
Interactions
Safety Profile
Litorin causes transient gastrointestinal effects (nausea, gastric acid secretion) and smooth muscle contraction. Not used therapeutically in humans. Bombesin analogs used in clinical cancer imaging are generally well tolerated at tracer doses.
References
- [1]Erspamer V et al. (1972). New peptides related to bombesin in frog skin. Experientia, 28(2), 221-222.
- [2]Delle Fave G et al. (1994). Bombesin receptors: physiology and pharmacology. Digestive Diseases, 12(2), 107-114.