A Cyclic Heptapeptide Derived from Melanotan II
PT-141, also designated bremelanotide (molecular formula C₅₀H₆₈N₁₄O₁₀; CAS 189691-06-3), is a cyclic heptapeptide structurally derived from Melanotan II (CAS 121062-08-6). Both compounds are melanocortin receptor agonists, but the structural relationship is specific: PT-141 was developed from the Melanotan II scaffold through modifications intended to alter receptor selectivity and central nervous system signaling.
The melanocortin system is the signaling context that defines the PT-141 research profile. It comprises five G-protein-coupled melanocortin receptors — MC1R through MC5R — each with a distinct tissue distribution and signaling readout. Agonist selectivity across these five receptors is the primary research variable in the melanocortin field.
MC3R and MC4R Receptor Selectivity
The defining research feature of PT-141 is its selective binding affinity for MC3R and MC4R:
- MC4R is highly expressed in the central nervous system (hypothalamus and other brain regions) and is studied for its role in appetite regulation, energy homeostasis, and — of particular research interest for this compound class — sexual behavior signaling in animal models.
- MC3R is also expressed centrally, with research interest in its role related to energy balance and feeding behavior.
The MC4R signaling axis is the most studied mechanistic hypothesis in the PT-141 literature. Where Melanotan II engages MC1R (the receptor associated with melanogenesis and skin pigmentation signaling) more broadly, PT-141's research profile is studied primarily through the MC3R/MC4R — central melanocortin — lens, with comparatively less emphasis on MC1R-driven peripheral signaling.
Central vs Peripheral Mechanism
A key distinction in the published literature is central versus peripheral mechanism. Melanotan II was historically studied across multiple melanocortin receptors, including MC1R in skin tissue — a peripheral target. PT-141's research framing centers on the central nervous system (CNS) mechanism through MC3R/MC4R.
This central mechanism distinction is studied through:
- Receptor distribution mapping in CNS tissue models
- Ligand penetration of the blood–brain barrier in laboratory models
- Downstream signaling readouts in hypothalamic tissue preparations
- Behavioral assay readouts in animal model systems
The research question is not whether PT-141 binds melanocortin receptors — it does — but where, in the body and in the nervous system, that binding is most informative to study. The CNS MC3R/MC4R framing distinguishes PT-141 from MC1R-dominant melanocortin research.
Comparison with Melanotan II
| Receptor | Melanotan II | PT-141 | | --- | --- | --- | | MC1R (peripheral, skin) | Broadly studied | Less emphasized | | MC3R (central) | Studied | Selectively studied | | MC4R (central, CNS) | Studied | Selectively studied (primary focus) |
The structural derivation is the point: PT-141 was engineered as a modified Melanotan II analog to investigate whether central MC3R/MC4R signaling could be studied more selectively, with reduced engagement of the MC1R-dependent peripheral melanogenesis pathway. In laboratory research, this selectivity profile is the experimental variable.
Kisspeptin-10 and the Broader Central Signaling Context
PT-141 research sits in a broader central-signaling research context. Kisspeptin-10 (CAS 374683-45-1) — a decapeptide fragment of the KISS1 gene product — is studied for hypothalamic-pituitary-gonadal (HPG) axis signaling upstream of GnRH. Where PT-141 is studied through melanocortin receptors, Kisspeptin-10 is studied through the kisspeptin/GnRH axis. Both are central signaling research tools, but they engage distinct receptor systems and signaling cascades. Researchers studying central endocrine or behavioral signaling often examine both peptide families in parallel.
Research Framing
PT-141 and the comparator melanocortin compounds are supplied for laboratory and scientific research use only. They are not for human consumption and are not approved by the FDA for any medical use. Receptor binding and CNS signaling readouts in laboratory and animal models do not translate to or imply effects in humans. Purchasers must be 21 years of age or older.