Triptorelin
Triptorelin is a synthetic decapeptide analogue of gonadotropin-releasing hormone with D-tryptophan at position 6. It is an FDA-approved GnRH agonist (Trelstar and others) used in long-acting formulations to suppress gonadal sex-steroid production.
Overview
Triptorelin is one of the GnRH agonists developed after the structure of native gonadotropin-releasing hormone was determined. Replacing glycine 6 of the native decapeptide with D-tryptophan produced an analogue that resists enzymatic cleavage and binds the GnRH receptor with higher affinity, giving much greater and longer-lasting activity than gonadorelin. The compound emerged from work associated with Andrew Schally's laboratory and has been developed into several commercial products worldwide.
Like other GnRH agonists, triptorelin initially stimulates release of LH and FSH, producing a transient rise in sex steroids, but sustained exposure then desensitizes the pituitary and suppresses gonadotropin and sex-steroid output. This suppression is the basis of its approved use in advanced prostate cancer and, in various countries, in other hormone-dependent conditions. Clinical products use depot formulations, such as microspheres, that release the peptide over weeks to months.
Structure
Triptorelin is a decapeptide with the sequence pGlu-His-Trp-Ser-Tyr-D-Trp-Leu-Arg-Pro-Gly-NH2. It differs from native GnRH only by the substitution of D-tryptophan for glycine at position 6, which stabilizes a receptor-favored turn conformation and protects the Gly6-Leu7 bond from enzymatic cleavage. It retains the N-terminal pyroglutamate and C-terminal glycinamide. Pharmaceutical forms include triptorelin pamoate (embonate) and triptorelin acetate, which differ substantially in solubility and are used in different formulations; research material is usually the acetate or TFA salt.
Mechanism
Triptorelin is an agonist of the GnRH receptor on pituitary gonadotrophs. Its initial action mirrors native GnRH, stimulating LH and FSH release through Gq/11-coupled signaling and causing a transient rise in testosterone or estradiol, often called a flare. With continued exposure, the receptor becomes desensitized and downregulated, gonadotropin secretion falls, and gonadal sex-steroid production is suppressed to castrate or postmenopausal-like levels. The suppression is reversible after exposure ends, although recovery time varies.
Research
Advanced prostate cancer
The principal US approved indication of triptorelin is the palliative treatment of advanced prostate cancer, where suppression of testosterone is the therapeutic goal. Clinical trials of depot formulations assessed the proportion of patients reaching and maintaining castrate testosterone levels. Triptorelin is one of several GnRH agonists with this indication, and comparative questions between agonists, and between agonists and antagonists, have been studied in the oncology literature. Regional labels and formulations differ, so details vary by product.
Other hormone-dependent conditions
In various countries, triptorelin formulations are approved or studied for central precocious puberty, endometriosis, uterine fibroids and as part of assisted reproduction protocols, where it is used to control the timing of ovulation. Indications differ between jurisdictions and products, so researchers should consult the relevant national labeling rather than assume that an indication approved in one country applies elsewhere. Pediatric and gynecological uses carry their own monitoring considerations described in local labeling.
Receptor pharmacology
Triptorelin is widely used as a reference GnRH agonist in receptor-binding and signaling studies, and in work on GnRH receptors expressed outside the pituitary, including in some tumor cell lines. In-vitro studies have explored whether GnRH analogues have direct effects on such cells. These investigations are mechanistic and do not themselves establish clinical effects beyond the hormonal suppression on which approved uses rest.
Formulation science
Because triptorelin requires sustained exposure to suppress the axis, much pharmaceutical research has focused on depot formulations, particularly biodegradable polymer microspheres that release the peptide over defined periods. Studies of these systems examine release kinetics, initial burst release and polymer degradation. These formulation characteristics, rather than the peptide alone, largely determine the clinical behavior of each product. Different products are therefore not interchangeable without regard to their formulation.
Regulatory status
Triptorelin is FDA-approved, marketed as Trelstar and under other names, in long-acting formulations; check current labeling for approved US indications. It is also approved in many other countries under various brand names, with indications that vary by jurisdiction. WADA prohibits GnRH analogues such as triptorelin under class S2 in males; check the current WADA Prohibited List for the exact wording.
Status changes often. See the regulatory tracker for dated updates.
Quality and identity testing
A certificate of analysis should confirm identity by mass spectrometry, with the observed mass matching the expected mass shown on this page, and report HPLC purity with the chromatogram. The salt form is especially important for triptorelin because the pamoate and acetate salts have very different molecular weights per unit of peptide and different solubility, so net peptide content must be stated. Diastereomeric impurities, such as the L-Trp6 epimer, should be resolved by the HPLC method. With two tryptophan residues, the peptide is prone to oxidation, and oxidized species should be reported among related substances.
For a walkthrough of each section of a certificate, see how to read a COA.
Storage and stability
Store lyophilized triptorelin sealed at -20 °C or in refrigerated conditions as indicated on its documentation, protected from light and moisture, and let vials reach room temperature before opening. Its two tryptophan residues make it light- and oxidation-sensitive. Acetate salts dissolve readily in water, whereas the pamoate salt is poorly water-soluble and is intended for suspension formulations. Aliquot solutions for lab use, store them at -20 °C or below, and avoid repeated freeze-thaw cycles.
Download the Triptorelin data sheet (PDF): sequence, masses, expected MS ions and handling on one printable page.
Latest research
The newest PubMed-indexed papers that mention Triptorelin in their title or abstract, retrieved through Europe PMC and refreshed automatically. Inclusion is not an endorsement of a paper's findings.
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Frequently asked questions
Is triptorelin FDA approved?
Yes. Triptorelin is FDA-approved and marketed in the United States as Trelstar and under other names, in long-acting depot formulations. It is also approved in many other countries. Approved indications differ by product and jurisdiction, so the current label for a specific product should be consulted.
Is triptorelin an agonist or an antagonist?
Triptorelin is a GnRH receptor agonist. It first stimulates LH and FSH release, then, with sustained exposure, desensitizes the receptor and suppresses gonadotropin and sex-steroid production. GnRH antagonists, by contrast, block the receptor directly without an initial stimulatory phase. This flare is a known feature of agonists.
What is the difference between triptorelin pamoate and triptorelin acetate?
Both contain the same triptorelin peptide but with different counter-ions. The pamoate (embonate) salt is poorly soluble in water and suited to sustained-release suspensions, while the acetate salt is water-soluble. Because the counter-ions differ in mass, the amount of peptide per milligram of powder also differs. Peptide content per vial therefore depends on the salt used.
Related compounds
- Gonadorelin
Gonadorelin is the synthetic form of native gonadotropin-releasing hormone (GnRH), a 10-amino-acid hypothalamic peptide that stimulates release of LH and FSH. It was previously approved in the US as a diagnostic agent and is used in veterinary products.
- Kisspeptin-10
Kisspeptin-10 is the C-terminal decapeptide of kisspeptin, the product of the KISS1 gene. It activates the kisspeptin receptor (KISS1R, also called GPR54) and is studied as a regulator of gonadotropin-releasing hormone and reproductive hormones.
- Oxytocin
Oxytocin is a nine-amino-acid peptide hormone made in the hypothalamus and released from the posterior pituitary, with a disulfide-bridged ring structure. It regulates uterine contraction and milk ejection, and synthetic oxytocin (Pitocin) is FDA-approved.
References
- PubMed: all indexed literature on Triptorelin
- ClinicalTrials.gov: registered studies mentioning Triptorelin
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