Short answer
What is PT-141 (Bremelanotide)? PT-141, also known as bremelanotide, is a synthetic cyclic heptapeptide in the same lactam family as Melanotan II. It is a melanocortin receptor agonist most commonly studied with respect to MC3R and MC4R, and it is used in laboratory research as a tool for probing central melanocortin neuroendocrine signaling. It is sold as a lyophilized research powder and is not for human use.
What is PT-141 (Bremelanotide)?
PT-141 is the research designation for bremelanotide, a synthetic cyclic heptapeptide developed as a melanocortin receptor agonist. It shares its molecular core with Melanotan II: both compounds carry the same cyclic lactam scaffold built around the His-Phe-Arg-Trp (HFRW) pharmacophore, the conserved message sequence of the melanocortin peptides [1][4]. The shared scaffold means the two molecules are structurally very close, but their research profiles differ in receptor emphasis and in the body of literature surrounding each one.
Bremelanotide is notable because it was advanced into an extensive program of controlled clinical research in the 2010s. Two identically designed, randomized, double-blind, placebo-controlled phase 3 trials, collectively known as the RECONNECT program, evaluated the compound in a large cohort and generated a substantial dataset for a melanocortin agonist [1]. A subsequent 52-week open-label extension study added longer-term data [2]. For a research reagent, this clinical-research background is valuable because it provides unusually detailed human pharmacokinetic and tolerability information that can inform the design of in vitro studies.
Chemical characterization: a cyclic lactam heptapeptide
Bremelanotide is a seven-residue peptide, structurally defined as a cyclic lactam heptapeptide in the same family as Melanotan II. The peptide is cyclized through a lactam bridge, and its C-terminus differs from the amide-capped Melanotan II in bearing a free carboxyl, a subtle but analytically important distinction when confirming identity by mass spectrometry.
Like other cyclic lactam melanocortin analogs, bremelanotide was designed to constrain the HFRW message sequence into its bioactive conformation. Conformational restriction increases receptor affinity and confers resistance to proteolytic degradation relative to linear alpha-MSH, the endogenous parent peptide [1][4].
The cyclic scaffold is central to the pharmacology of the molecule. In structure-activity studies of the melanocortin receptor family, small changes to the residues within the lactam ring can shift a compound between agonism and antagonism at specific subtypes, which is why the scaffold has been so productive as a platform for designing tool molecules [4].
This structural family illustrates a broader point about peptide design that is directly relevant to laboratory use: small modifications to a validated scaffold can be used to tune receptor selectivity without rebuilding the pharmacophore. Because bremelanotide, its agonist relative Melanotan II, and antagonist variants such as SHU-9119 all share the same ring geometry, the family is often studied as a matched set, with agonist and antagonist tools applied side by side in receptor panels to confirm that an observed response is mediated by the melanocortin pathway rather than an off-target mechanism [4].
MC3R and MC4R research pharmacology
The melanocortin receptor family consists of five G-protein-coupled receptors, MC1R through MC5R, activated by POMC-derived peptides such as alpha-MSH [3]. Bremelanotide is a non-selective agonist but is most commonly studied with respect to MC3R and MC4R, the two subtypes expressed in the central nervous system. MC4R in particular is one of the most intensively studied GPCRs in neurobiology because of its role in hypothalamic circuits that govern energy homeostasis and other neuroendocrine functions [3].
Bremelanotide is thought to act predominantly within the central nervous system. Because MC3R and MC4R are expressed in hypothalamic and limbic regions, a centrally acting melanocortin agonist provides a tool for probing melanocortin signaling in whole-cell preparations, receptor-transfected lines, and explant models of the hypothalamus [1][3].
Melanocortin receptors couple primarily to the Gs-adenylyl cyclase-cAMP pathway. In receptor assays, an agonist such as bremelanotide produces a measurable increase in intracellular cyclic AMP, which is the canonical readout used to compare potency across ligands and receptor subtypes. This makes bremelanotide a convenient positive control for MC3R/MC4R functional assays [3][4].
The practical consequence for experimental design is that PT-141 is a useful agonist for studies that aim to activate MC3R and MC4R signaling pathways, particularly where the experimenter wants a compound with documented blood-brain barrier penetration and a large clinical-research dataset behind it.
Research history and clinical-research background
The development of bremelanotide grew out of the cyclic lactam melanocortin program that produced Melanotan II. As the field mapped the physiological roles of central melanocortin receptors, bremelanotide emerged as a candidate that combined potent MC3R/MC4R agonism with the ability to act in the central nervous system [1][3][4].
The RECONNECT program consisted of two phase 3, randomized, double-blind, placebo-controlled trials that enrolled more than 1,200 participants. The trials met their coprimary endpoints, showing statistically significant changes from baseline on validated self-report instruments, and the reported safety profile was dominated by transient events such as nausea, flushing, and headache, with small, transient elevations in blood pressure that returned toward baseline within hours [1]. A long-term open-label extension that followed participants for up to 52 additional weeks reported no new safety signals and stable outcomes on the measured endpoints [2].
For laboratory researchers, this body of work is best read as pharmacology. It documents that bremelanotide engages central melanocortin circuits in humans and quantifies its tolerability and pharmacokinetics. Those data are directly useful when designing in vitro experiments, because they define concentration ranges and exposure windows that are relevant to the molecular pharmacology of MC3R and MC4R.
What research shows about PT-141 as a research tool
Several findings from the clinical-research literature translate into laboratory practice:
When designing a study, it can be instructive to compare bremelanotide with its close relative Melanotan II, which is a broad-spectrum agonist across four receptor subtypes. See our Melanotan II research peptide guide.
PT-141 compared with related research peptides
For a general overview of the peptide category, see what are peptides, and for the receptor family specifically, the melanocortin research category.
How to evaluate research-grade PT-141
When sourcing PT-141 for laboratory work, verify the same quality markers as for any research peptide:
For a detailed look at what a peptide COA should contain, see our peptide COA guide, and for a comparison of the analytical methods used to verify purity, our article on HPLC versus mass spectrometry for peptide purity.
Storage and handling
Lyophilized PT-141 is stable when stored correctly. Standard laboratory handling guidance applies:
For a step-by-step protocol, see our peptide reconstitution and laboratory handling guide, and for general storage recommendations, our how to store peptides guide.
Summary
PT-141 (bremelanotide) is a synthetic cyclic heptapeptide melanocortin receptor agonist sharing its lactam core with Melanotan II and most commonly studied with respect to MC3R and MC4R. Its clinical-research background, including randomized controlled trials and a long-term extension study, provides unusually detailed pharmacology for a research peptide, while its in vitro profile makes it a practical positive control for central melanocortin assays. Research-grade material should be verified for HPLC purity, mass-spectrometry identity, and batch-specific COA, and handled according to standard lyophilized-peptide protocols.
FAQ
What is PT-141 (Bremelanotide)?
PT-141 is the research designation for bremelanotide, a synthetic cyclic heptapeptide melanocortin receptor agonist in the same lactam family as Melanotan II.
How does PT-141 differ from Melanotan II?
Both share the cyclic lactam core, but PT-141 is most commonly studied with respect to MC3R and MC4R and carries an extensive clinical-research background.
What signaling pathway does the melanocortin receptor use?
Melanocortin receptors are G-protein-coupled receptors that primarily signal through the Gs-adenylyl cyclase-cAMP pathway.
What purity should research-grade PT-141 have?
At least 98-99% by HPLC, with identity confirmed by mass spectrometry and a batch-specific COA.