This is a working overview of MC4R, written for readers who want more than a one-paragraph summary but less than a textbook.
This page was last updated on 2026-07-14 and is reviewed periodically as new material appears.
Handling procedures emphasize minimizing moisture uptake, since the dried solid is hygroscopic and can draw water when warmed to room temperature before a vial is opened. Laboratories record lot number, purity, counter-ion content, and residual solvent data supplied by the producer. Impurity profiles are compared run to run, and any shift in retention time or peak shape prompts re-verification against a reference standard. Certificates of analysis are treated as claims to be checked rather than accepted at face value.
Identity and purity testing for this peptide typically relies on reversed-phase high-performance liquid chromatography with ultraviolet detection, reported as area-percent purity. Mass spectrometry, usually in tandem mode, confirms molecular mass and supports quantification in biological matrices. Sequence confirmation may use peptide mapping after enzymatic digestion, while nuclear magnetic resonance and circular dichroism supply supplementary structural detail. No single technique establishes identity alone, so laboratories compare retention time, mass, and fragment pattern against a verified reference standard.
The lactam ring that closes the peptide backbone improves resistance to exopeptidase attack, but the molecule stays susceptible to hydrolysis and oxidation once dissolved. Degradation accelerates with temperature, extreme pH, and light exposure, and repeated freeze-thaw cycles promote aggregation and material loss. Lyophilized powder held desiccated at or below minus twenty degrees Celsius is the common way to keep reference material. Reconstituted solutions are generally kept cold and used within a short window because their stability is far lower than that of the dry solid.
Across literature and commercial listings, the substance appears under several names, including bremelanotide, PT-141, and various brand designations. A CAS registry number provides a unique identifier for the compound, aiding retrieval from chemical databases. Synonym lists may also contain early development codes and descriptive chemical names. When consulting sources, researchers need to confirm that the cited names refer to the same molecular structure to avoid confusion. Naming consistency matters especially when comparing analytical data across publications.
PT-141 is a synthetic cyclic heptapeptide whose development code is bremelanotide. It belongs to the class of melanocortin receptor agonists and acts by mimicking endogenous peptide hormones. The compound originated from research on melanotan II, where investigators exploring derivatives found distinct pharmacological features. Unlike the parent compound, PT-141 showed effects on pathways related to sexual desire and function in early studies, prompting its development as a separate candidate. Its molecular design aimed to separate receptor activity from pigmentary effects.
The molecular backbone consists of seven amino acid residues joined into a ring through a disulfide bridge. This cyclic conformation is critical for receptor binding. The sequence includes an acetylated N-terminus and an amidated C-terminus, modifications that improve resistance to enzymatic breakdown. One residue is in the D-configuration, a feature that further stabilizes the peptide against protease activity. Together, the ring structure and specific stereochemistry determine selectivity among melanocortin receptor subtypes.
| Property | Value | Notes |
|---|---|---|
| Appearance | White to off-white solid | Lyophilized powder form |
| Solubility class | Freely soluble in water | Also dissolves in polar organic solvents |
| Typical storage temperature | Minus 20 degrees Celsius or lower | Desiccated and protected from light |
| Typical analytical method | Reversed-phase HPLC with UV detection | Purity reported by area normalization |
| Common synonyms | PT-141; bremelanotide | Research code and assigned generic name |
Early research on PT-141 grew out of work on melanotan II, a related cyclic peptide studied for pigmentation. Investigators observed that centrally acting melanocortin agonists also influenced sexual behaviour in animal models, and the programme shifted toward that endpoint. A nasal formulation was evaluated in clinical trials but showed inconsistent absorption, and later studies used subcutaneous administration instead. Regulatory approval in the United States followed in 2019 for a defined population of premenopausal women with acquired, generalised hypoactive sexual desire disorder. That approval was specific to that group rather than a broad indication.
Bremelanotide acts as a non-selective agonist at melanocortin receptors, with reported activity at MC1R, MC3R, MC4R and MC5R. The proposed basis for its central effects is activation of MC4R populations in the hypothalamus, a region associated with appetite and reproductive signalling. Because the peptide carries a net positive charge and polar side chains, it does not cross biological membranes freely, which is one reason oral administration is not the standard route. Effects generally appear within an hour of parenteral administration and are described as centrally mediated rather than peripheral.
Bremelanotide, developed under the code PT-141, is a synthetic cyclic heptapeptide analogue of alpha-melanocyte-stimulating hormone. Its structure is Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH, with a lactam bridge joining the aspartate and lysine side chains. The molecule has the formula C50H68N14O10 and a monoisotopic mass near 1025 daltons. It is commonly prepared as the acetate salt and appears as a white to off-white lyophilised powder in solid form. The free acid is the pharmacologically relevant species, while the counter-ion improves handling and dissolution.
Melanocortin receptors form a family of five G-protein-coupled proteins, labelled MC1R through MC5R, that respond to peptides derived from pro-opiomelanocortin. Alpha-melanocyte-stimulating hormone and adrenocorticotropic hormone are the best-known endogenous ligands. The receptors are distributed differently across tissues, so a single agonist can produce effects in the brain, skin, adrenal gland and vasculature. This distribution explains why one peptide can influence both pigmentation and motivated behaviour.
Bremelanotide is a cyclic heptapeptide that binds several melanocortin receptors rather than one. In vitro assays report agonist activity at MC1R, MC3R, MC4R and MC5R, with MC4R generally treated as the subtype most relevant to sexual effects. MC4R is expressed in hypothalamic nuclei involved in appetite, energy balance and motivated behaviour, which provides a plausible route for central action. Selective MC4R agonists studied in animals produce comparable behavioural changes, supporting that interpretation.
Bremelanotide is a moderately large peptide with a molecular mass near 1025 daltons. In lyophilised form it appears as a white to off-white powder and is freely soluble in water and other polar solvents. The intact lactam ring is essential for receptor affinity, while linearised fragments bind far more weakly. Solutions are sensitive to extremes of pH and to prolonged exposure to light and heat, so handling typically involves buffered conditions and cold storage. Its short plasma half-life reflects rapid distribution and clearance rather than chemical breakdown inside the vial.
Development of the peptide passed through several delivery formats, including an intranasal version tested in early trials and an injectable version that entered later clinical study. Regulatory approval for a subcutaneous product in the United States was granted in 2019 after review of controlled trials in premenopausal women. Outside the clinic, the compound circulates in research and non-pharmaceutical markets under its code name, where identity and purity vary considerably between suppliers. Synonyms appearing across technical literature include bremelanotide, PT-141, and Palatin 141.
PT-141 is the research designation for bremelanotide, a synthetic cyclic heptapeptide developed as a melanocortin receptor agonist. The peptide contains seven amino acids with an internal lactam bridge that constrains the backbone into a stable ring. Cyclisation of this kind improves resistance to enzymatic degradation relative to linear analogues. The compound was first explored for effects on melanin production, because several melanocortin receptors influence pigmentation. Its later association with sexual desire emerged from observations made during that early work, and the molecule became the subject of a separate development programme.
Melanocortin receptors form a family of five G-protein-coupled receptors designated MC1 through MC5. Bremelanotide binds most strongly at MC4R and MC1R, with weaker activity reported at MC3R and MC5R. MC4R is expressed in hypothalamic nuclei that coordinate energy balance and aspects of sexual behaviour. The prevailing interpretation is that central MC4R activation, rather than peripheral vascular effects alone, drives the reported changes in desire. This account remains partly inferential, since direct receptor-level measurement in living humans is not practical.
After subcutaneous administration, plasma concentrations rise within roughly thirty minutes and the elimination half-life is short, on the order of two to three hours. Reported physiological responses include transient increases in blood pressure and nausea, which tended to diminish with repeated dosing in trial settings. Because the peptide clears quickly, effects are not expected to persist long after a dose. Absorption from non-injected routes is poorly characterised, and nasal delivery produced variable plasma levels in older work.
Clinical research typically uses randomised, double-blind, placebo-controlled designs. The most common primary endpoint is the desire domain score of the Female Sexual Function Index, sometimes paired with a distress measure. Secondary outcomes include arousal, satisfaction, and event-based counts of satisfying sexual episodes. Across trials, average improvements are modest and individual responses vary widely. Whether benefits persist beyond a few months, and whether they depend on baseline hormone status, remain open questions rather than settled findings.
=== Cancers === NF-κB is widely used by eukaryotic cells as a regulator of genes that control cell proliferation and cell survival. As such, many different types of human tumors have misregulated NF-κB: that is, NF-κB is constitutively active. Active NF-κB turns on the expression of genes that keep the cell proliferating and protect the cell from conditions that would otherwise cause it to die via apoptosis. In cancer, proteins that control NF-κB signaling are mutated or aberrantly expressed, leading to defective coordination between the malignant cell and the rest of the organism. This is evident both in metastasis, as well as in the inefficient eradication of the tumor by the immune system. Normal cells can die when removed from the tissue they belong to, or when their genome cannot operate in harmony with tissue function: these events depend on feedback regulation of NF-κB, and fail in cancer. Defects in NF-κB results in increased susceptibility to apoptosis leading to increased cell death. This is because NF-κB regulates anti-apoptotic genes especially the TRAF1 and TRAF2 and therefore abrogates the activities of the caspase family of enzymes, which are central to most apoptotic processes. In tumor cells, NF-κB activity is enhanced, as for example, in 41% of nasopharyngeal carcinoma, colorectal cancer, prostate cancer and pancreatic tumors.
Most currently available genes used to engineer insect resistance come from the Bacillus thuringiensis bacterium and code for delta endotoxins. A few use the genes that encode for vegetative insecticidal proteins. The only gene commercially used to provide insect protection that does not originate from B. thuringiensis is the Cowpea trypsin inhibitor (CpTI). CpTI was first approved for use cotton in 1999 and is currently undergoing trials in rice. Less than one percent of GM crops contained other traits, which include providing virus resistance, delaying senescence and altering the plants composition.
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Nefopam by mouth and cannabis are not recommended as of 2012, as the risks of use appear to be greater than the benefits. Limited evidence suggests the use of weak oral opioids, but the adverse effects may outweigh the benefits. Alternatively, physical therapy has been tested and shown as an effective aid in reducing pain in patients with RA. As most RA is detected early and treated aggressively, physical therapy plays more of a preventive and compensatory role, aiding in pain management alongside regular rheumatic therapy.
Sources: en.wikipedia.org
=== Chronic toxicity === Ingestion of melamine may lead to reproductive damage, or bladder or kidney stones, which can lead to bladder cancer. A study in 1953 reported that dogs fed 3% melamine for a year had the following changes in their urine: (1) reduced specific gravity, (2) increased output, (3) melamine crystalluria, and (4) protein and occult blood. A survey commissioned by the American Association of Veterinary Laboratory Diagnosticians suggested that crystals formed in the kidneys when melamine combined with cyanuric acid, "don't dissolve easily. They go away slowly, if at all, so there is the potential for chronic toxicity."
== Beginnings of Genentech == A young Swanson now found himself unemployed. Swanson was interviewing almost daily, attempting to find a job. However, he was still fascinated by the potential of recombinant DNA technology, and decided to cold call scientists working on the technology, with the hope that one of them would be interested in commercializing it. One of the scientists he contacted, Herbert Boyer, expressed interest but was hesitant of meeting up with Swanson at first. Boyer was an academic scientist, and was not well versed on the matters of business. Swanson convinced Boyer to meet, for a short time, at his University of California, San Francisco lab. The short meeting was extended to three hours, and Boyer came out determined to commercialize the technology he had helped pioneer. He would deal with the science behind the product, whereas Swanson would work on obtaining funds, and managing the organization as a whole. The two agreed to form a partnership, and each put down $500 to cover legal fees. Swanson made the decision to pursue the creation of the company full-time, rather than obtain a job at an established institution or company. He explains his logic in an interview: "(I told myself) "Look, I think this is important. If I don't do this, I'm not going to like myself so much for not having given it a shot." So that was what made that decision." Swanson then set out to identify their first marketable product, and quickly focused on the human protein insulin.
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Sources: en.wikipedia.org
These failures suggested that either these are the wrong molecular targets to induce neovascularization, that they can only be effectively used if formulated and administered correctly, or that their presentation in the context of the overall cellular microenvironment may play a vital role in their utility. It may be necessary to present these proteins in a way that mimics natural signaling events, including the concentration, spatial and temporal profiles, and their simultaneous or sequential presentation with other appropriate factors.
Hohhot Baita International Airport (IATA: HET, ICAO: ZBHH) is an international airport serving Hohhot, the capital of Inner Mongolia, China. It is the largest airport in Inner Mongolia and lies 14.3 km (8.9 mi) east of downtown Hohhot. Its name Baita, meaning White Pagoda, derives from Wanbu Huayanjing Pagoda; one of the historical attractions in Hohhot which lies 5.6 km (3.5 mi) south-east of the airport. In 2025 it served 12,722,692 passengers.
The Six Million Dollar Man is an American science fiction and action television series, running from 1973 to 1978, about a former astronaut, USAF Colonel Steve Austin, portrayed by Lee Majors. After being seriously injured in a NASA test flight crash, Austin is rebuilt (at considerable expense, hence the title of the series) with bionic implants that give him superhuman strength, speed and vision. Austin is then employed as a secret agent by a fictional American government office titled OSI. The series was based on Martin Caidin's 1972 novel Cyborg, which was the working title of the series during pre-production. Following three television films intended as pilots, which all aired in 1973, The Six Million Dollar Man television series aired on the ABC network as a regular episodic series for five seasons from 1974 to 1978. Steve Austin became a pop culture icon of the 1970s.
Sources: en.wikipedia.org
Chemical degradation such as hydrolysis and oxidation proceeds more slowly as temperature falls. Cold storage also limits microbial growth in reconstituted material. Repeated warming should be avoided because thermal cycling stresses the peptide.
Retention time supports consistency but does not establish structure by itself. A different compound can elute at a similar time under one set of conditions. Mass spectrometry or comparison with a verified standard is normally required alongside the chromatographic result.
The lactam bridge constrains the peptide backbone and limits attack by some exopeptidases. It does not protect against hydrolysis of amide bonds inside the ring or against oxidative modification of susceptible residues. Stability therefore still depends heavily on storage conditions.
It belongs to the melanocortin receptor agonist family of peptides. Its cyclic structure distinguishes it from linear peptides and shapes its receptor binding profile.