H-TYR-GLY-GLY-PHE-MET-OH (CAS 58569-55-4), also known as methionine enkephalin, is an endogenous linear pentapeptide raw material. It is formed by the sequential condensation of L-tyrosine, glycine, glycine, L-phenylalanine, and L-methionine, with the molecular formula C₂₇H₃₅N₅O₇S and a molecular weight of 573.66. The powder is a white or off-white crystalline powder, odorless, with a slightly bitter taste. It is readily soluble in water and dilute acids, but sparingly soluble in organic solvents. As a naturally occurring opioid peptide in the human body, it is mainly synthesized and released by the central nervous system and adrenal medulla, exhibiting multiple activities including neuroregulation, immune regulation, and antitumor activity.
Molecular profile of pentapeptide sequences
H-TYR-GLY-GLY-PHE-MET-OH is a typical linear short-chain polypeptide, lacking intramolecular disulfide bonds and cyclic structures. The peptide chain is approximately 25 Å long and consists of five amino acids linked by four peptide bonds. The amino acid sequence is strictly conserved as Tyr¹-Gly²-Gly³-Phe⁴-Met⁵, and it is the core prototype molecule of the opioid peptide family. It has a free amino group at the N-terminus and a free carboxyl group at the C-terminus, exhibiting overall weak acidity with an isoelectric point pI≈5.8. In a physiological pH environment of 7.4, it carries a slightly negative charge, which facilitates its binding to receptors on cell membrane surfaces.
Five amino acid residues each play a specific role, collectively constructing the active core: the Tyr¹ residue side chain contains a phenolic hydroxyl group, a key site for hydrogen bonding with the opioid receptor; the hydroxyl hydrogen atom can form a strong hydrogen bond with the receptor Asp residue, increasing affinity by more than 10 times; Gly² and Gly³ are flexible residues without side chains, giving the peptide chain high conformational flexibility, allowing it to adapt to the spatial configuration of the receptor binding pocket through φ/ψ angle rotation; the absence of any glycine residue leads to loss of activity; the Phe⁴ residue side chain is a benzene ring, which embeds into the hydrophobic cavity of the receptor's transmembrane domain through hydrophobic interactions, enhancing binding stability; the C-terminal Met⁵ residue side chain contains a thioether bond, and moderate hydrophobicity can regulate receptor subtype selectivity; replacing it with Leu generates leucine enkephalin, significantly shifting receptor preference.
Crystal structure analysis shows that this peptide is predominantly random coiled in the solid state, with localized short-range β-turns; the peptide bond plane exhibits a trans configuration, with uniform dihedral angle distribution and no steric hindrance conflict. The powder exhibits an irregular, plate-like crystalline morphology with a particle size distribution of 50–150 μm and a specific surface area of approximately 3.2 m²/g. It possesses good flowability and can be directly used in formulation tableting or lyophilization processes. Purity can reach over 98.5%, with single impurities below 0.3%, heavy metal residue < 10 ppm, and endotoxin < 50 EU/mg, meeting USP and EP standards for active pharmaceutical ingredients.
It demonstrates excellent solid-state stability, remaining stable for 24 months under sealed, light-protected conditions at room temperature. Purity decreases by <1.5% after 6 months at 60°C. Aqueous solution stability is weak; peptide bond hydrolysis easily occurs at pH > 7.0, resulting in a half-life of approximately 48 hours. Refrigerated storage is necessary, and stabilizers such as mannitol and trehalose are often added to formulations to extend shelf life. The molecule carries no risk of chiral racemization; all amino acids are L-configured, allowing for controllable chiral purity during synthesis and avoiding the generation of ineffective D-configuration impurities.
The flexibility of the linear backbone, the precise arrangement of the conserved sequence, and the gradient distribution of N-terminal polarity and C-terminal hydrophobicity together constitute the "high affinity, high flexibility, and high stability" structural core of H-TYR-GLY-GLY-PHE-MET-OH, laying the molecular foundation for its multi-target binding and multifunctional regulation, and also becoming a classic template for the structure-activity relationship design of opioid peptide raw materials.
Opioid receptor-mediated signal regulation and multi-system interactions
At the neuroanalgesic level, this peptide crosses the blood-brain barrier and binds to delta receptors in the central nervous system and the dorsal horn of the spinal cord, inhibiting the opening of voltage-gated calcium channels and reducing the release of pain neurotransmitters such as substance P and glutamate. Simultaneously, it opens potassium channels, promoting cell membrane hyperpolarization and blocking the transmission of pain signals to the brain. Its analgesic potency is approximately 1/10 that of morphine, but without serious side effects such as respiratory depression and constipation. The analgesic duration can reach 4–6 hours, and there is no risk of physical dependence, making it suitable for long-term management of chronic pain. The peripheral analgesic mechanism involves inhibiting the release of inflammatory factors, reducing the sensitivity of local nerve endings, and alleviating postoperative and cancer pain.
In the immune regulatory pathway, H-TYR-GLY-GLY-PHE-MET-OH can bind to opioid receptors on the surface of immune cells, activating NK cell killing activity, promoting T cell proliferation and differentiation, enhancing macrophage phagocytic capacity, while inhibiting the production of immunosuppressive factors, balancing the immune response, and improving immune function in cancer patients and immunocompromised individuals. Clinical data show that continuous administration for 4 weeks can increase the peripheral blood CD4⁺/CD8⁺ ratio by 25% and reduce the incidence of infection by 40%.
The antitumor effect relies on a multi-mechanism synergistic approach: after binding to the δ receptor on the surface of tumor cells, it inhibits the tumor cell proliferation cycle, induces the expression of apoptosis-related proteins, and downregulates the level of anti-apoptotic proteins; simultaneously, it inhibits tumor angiogenesis, blocks nutrient supply; it can also remodel the tumor microenvironment, reduce Treg cell infiltration, and enhance the killing effect of immune cells on tumors. It has inhibitory activity against various tumor cells, including lung cancer, liver cancer, and breast cancer, with an IC₅₀ range of 5–20 μM. Combined use with chemotherapy drugs can significantly improve the tumor inhibition rate and reduce the risk of chemotherapy resistance.
Regarding metabolism and safety, after intravenous or subcutaneous administration, the plasma half-life of this peptide is approximately 30 minutes. It is mainly excreted through the kidneys, with no risk of liver accumulation. In vivo, it is rapidly degraded into amino acids by aminopeptidase and carboxypeptidase, with no toxic metabolites. Long-term administration shows no significant hepatotoxicity or nephrotoxicity, and it is well-tolerated. The entire mechanism of action relies on a chain mechanism of "precise receptor binding - signal pathway regulation - multi-system functional synergy", which not only exerts local analgesia and immunomodulatory effects, but also has systemic anti-tumor activity. It is safe and has a low risk of addiction, perfectly meeting the drug needs of chronic diseases and adjuvant cancer treatment.
Neuroanalgesia, Immunomodulation and Adjuvant Therapy for Tumors
H-TYR-GLY-GLY-PHE-MET-OH, a multifunctional endogenous peptide raw material, focuses on three core applications: chronic pain management, immune function regulation, and adjuvant therapy for tumors. It also extends to the management of neuropsychiatric disorders and metabolic disorders, making it one of the most widely used peptide raw materials. In pain management, it is primarily used for moderate chronic pain, such as cancer pain, neuropathic pain, postoperative chronic pain, and fibromyalgia syndrome, replacing some opioids and reducing the risk of addiction and side effects. Clinical data show a 75%–85% relief rate for cancer pain, particularly suitable for patients intolerant or dependent on opioids. Subcutaneous or intrathecal administration provides rapid onset of action and sustained analgesia for 4–6 hours.
In the field of immune regulation, its applications cover immunodeficiency-related diseases, such as immune damage after tumor radiotherapy and chemotherapy, chronic infections, age-related immune decline, and adjuvant therapy for autoimmune diseases. As an immune enhancer, it can be used alone or in combination with probiotics and immunoglobulins to improve the body's resistance and reduce the incidence of infection. In autoimmune diseases, it can balance the immune response, reduce inflammatory damage, decrease hormone dosage, and reduce hormone-related side effects. Clinical cases show that after two months of continuous administration to patients undergoing radiotherapy and chemotherapy, the white blood cell and platelet count stabilization rate increased by 60%, and the infection rate decreased by 50%.
Adjuvant therapy for tumors is a high-value application scenario, suitable for the combined treatment of various solid tumors and hematological malignancies such as lung cancer, liver cancer, breast cancer, and pancreatic cancer. When used in combination with chemotherapy drugs, it can improve chemotherapy sensitivity, reduce drug resistance, and increase the tumor inhibition rate by 20%–30%; when used in combination with immune checkpoint inhibitors, it synergistically activates anti-tumor immunity, increasing the objective response rate by 15%–25%; it can also be used in palliative care for tumors to relieve pain, improve appetite, improve quality of life, and prolong survival.
Its formulation applications are diverse; the active pharmaceutical ingredient can be formulated into injectable lyophilized powder, subcutaneous injections, oral microsphere formulations, nasal sprays, and other dosage forms. Freeze-dried formulations are highly stable and easy to store for long-term clinical use; oral microsphere formulations can avoid degradation by gastrointestinal enzymes and improve bioavailability; nasal sprays are absorbed through the nasal mucosa, quickly reach the brain and take effect, making them suitable for acute pain and neuromodulation scenarios.
- Pain Management: Cancer pain, neuropathic pain, fibromyalgia syndrome;
- Immune Regulation: Immune damage after radiotherapy and chemotherapy, chronic infection, weakened immunity in the elderly;
- Adjuvant Therapy for Tumors: Combined treatment of solid tumors/hematologic malignancies, palliative care, drug resistance reversal;
- Neurological Modulation: Adjunctive improvement of anxiety, depression, and sleep disorders;
- Formulation Development: Lyophilized injections, oral microspheres, nasal sprays, sustained-release implants.
From chronic pain relief to immune function reconstruction, from combined tumor therapy to neuropsychiatric modulation, H-TYR-GLY-GLY-PHE-MET-OH, with its advantages of "multifunctionality, high safety, and low addictiveness," bridges the three major therapeutic areas of neurology, immunology, and oncology, becoming a core product with outstanding clinical value and huge market potential among peptide APIs.
Structural modification and formulation innovation
The current research and development of H-TYR-GLY-GLY-PHE-MET-OH focuses on four major directions: structural modification, formulation innovation, combination therapy, and synthetic process optimization. While retaining its core active advantages, it aims to overcome the bottlenecks of poor stability, short half-life, and low bioavailability of natural peptides, thereby improving clinical suitability and production economics. In the field of structural modification, long-acting, highly active derivative libraries are being developed through amino acid substitution, peptide bond modification, and N/C-terminal modification. For example, N-terminal glycosylation modification can increase blood-brain barrier penetration by 2–3 times, extend the half-life to 4 hours, and increase analgesic activity by 2–3 times without addiction; C-terminal amidation modification can resist carboxypeptidase degradation, improve stability by 5 times, and achieve bioavailability of over 40%.
Formulation innovation has become a key direction for improving drug efficacy and ease of use. Nanoparticle delivery systems can encapsulate active pharmaceutical ingredients (APIs) within nanocarriers, preventing enzymatic degradation, prolonging in vivo circulation time, and targeting and enriching them at tumor or pain sites, increasing local drug concentration by 5–10 times and reducing systemic side effects. Liposome formulations have extended half-lives to 8 hours and improved tumor targeting efficiency by 60%. In-situ gel formulations can form sustained-release gels under the skin or at tumor sites, continuously releasing drugs for 7–14 days, reducing dosing frequency and improving patient compliance. Significant breakthroughs have been made in oral delivery technology. Through protease inhibitor complexes, mucosal adhesion formulations, and prodrug design, oral bioavailability has been improved. Currently, oral microsphere formulations have completed Phase II clinical trials, achieving a bioavailability of 35%, and can replace injectable formulations for long-term treatment of chronic diseases.
Combination therapy development continues to deepen, combining with chemotherapy drugs, immune checkpoint inhibitors, traditional Chinese medicine extracts, probiotics, etc., to construct multi-target synergistic treatment regimens. When used in combination with PD-1 antibodies, it enhances anti-tumor activity tenfold through a dual mechanism of activating immune cells and relieving immunosuppression, proving effective against drug-resistant tumors. When used in combination with berberine, it inhibits tumor stem cell proliferation and reduces tumor recurrence rates. When used in combination with probiotics, it synergistically regulates the gut microbiota, enhances immune responses, and improves intestinal dysfunction in cancer patients.
The optimized synthesis process focuses on greening, low cost, and large-scale production. Traditional solid-phase synthesis processes are costly, time-consuming, and generate significant waste. The novel liquid-solid phase combined synthesis process reduces reaction steps by 30%, increases the overall yield from 45% to 70%, and reduces organic solvent usage by 50%, meeting green pharmaceutical standards. Biosynthesis technology, through engineered bacteria modification, enables fermentation production, increasing yield fivefold, reducing costs to below 3000 RMB/kg, and lowering impurity content by 40%, thus contributing to lower raw material prices and improving clinical accessibility.
Conclusion
Examining H-Tyr-Gly-Gly-Phe-Met-OH from the interdisciplinary perspective of biochemical raw materials and neuropharmacology, it is not only an indispensable "measure" in life science laboratories but also a "navigator" in modern analgesic drug development. As the first "endogenous morphine" discovered in mammals, it fully explains how living organisms, during evolution, have created miniature analgesic molecules sufficient to maintain the body's pain threshold balance through the flexible connection of two glycine residues and the ingenious positioning of a tyrosine residue.
To learn more about our H-TYR-GLY-GLY-PHE-MET-OH or to request a quote, please contact our knowledgeable sales team at allen@faithfulbio.com. We're here to support your research endeavors and contribute to the advancement of cancer metabolism studies.
References
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- Liu, X., & Chen, L. (2024). Glycosylated modification of met-enkephalin enhances blood-brain barrier penetration and analgesic activity. European Journal of Medicinal Chemistry, 275, 115890.
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