PT-141, also called bremelanotide, is a synthetic cyclic heptapeptide: Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH. A lactam bridge between the aspartic acid and the lysine closes most of the chain into a ring, the N-terminus is acetylated and the C-terminus is a free acid. It is a melanocortin receptor agonist, and chemically it is a close relative of Melanotan II, which differs only at that C-terminal end.
This reference collects what a laboratory needs to know about PT-141 as a material: how its ring and its seven residues behave in the vial, what it dissolves in, how it is handled at the bench and what to do when an order arrives. Each section below has its own page.
Molecular reference
| Name | PT-141 (bremelanotide) |
|---|---|
| Also known as | PT 141 |
| Sequence | Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-OH (lactam bridge between Asp2 and Lys7; Nle is norleucine) |
| Residues | 7 |
| Molecular formula | C50H68N14O10 |
| Molecular weight | 1025.2 g/mol |
| CAS number | 189691-06-3 |
Formula, molecular weight and CAS number are from PubChem (CID 9941379). The MedChemExpress data sheet gives the same formula and CAS number and a weight of 1025.16 (MedChemExpress, HY-18678). The same figures and the sequence appear in the specifications on our PT-141 10 mg product page. PubChem also holds a separate record for the acetate salt (CID 91971505, C52H72N14O12), which is a different formula and weight; our product page gives the free-acid figures.
Three features explain most of its behaviour. The lactam ring uses up both the aspartate side chain and the lysine side chain, so neither is available as a free charged group or as a reaction site, and the ring itself makes the chain hard for enzymes to cut. Its tryptophan is the one residue with a clear chemical weak point: tryptophan is among the residues most open to oxidation, and it absorbs ultraviolet light (Li et al., Biotechnology and Bioengineering, 1995); the histidine is a second, slower one. And what is left ionisable is a histidine, an arginine and the C-terminal carboxyl, which by our calculation puts the net charge close to zero at pH 7 and the isoelectric point near pH 9.2.
What it is studied for
PT-141 is a melanocortin receptor agonist. The MedChemExpress sheet records concentration-dependent binding at the melanocortin-3 and melanocortin-4 receptors and cAMP accumulation in cell-free assays with EC50 values of 0.4 nM at MC3R and 0.2 nM at MC4R (MedChemExpress, HY-18678). Melanocortin receptors are a family of G protein coupled receptors; the same family carries the pigmentation signalling that the related compound Melanotan II is studied for.
That family relationship is the clearest way to place PT-141 chemically. Melanotan II is the same cyclic heptapeptide with an amidated C-terminus instead of a free acid, and it came from a design programme that closed fragments of alpha-melanocyte-stimulating hormone into lactam rings. Its chemistry, including the same tryptophan and the same ring, is set out in the Melanotan II research reference.
Human pharmacokinetic work exists: in healthy male subjects, the median time to maximum concentration was 0.50 hours and the mean half-life ranged from 1.85 to 2.09 hours (Diamond et al., International Journal of Impotence Research, 2004). Our summaries of the wider research are in the PT-141 human studies page. This reference covers the material and its chemistry only.
Stability
Its ring resists enzymes and its aspartate and lysine side chains are tied up, so the routes that remain are oxidation of the tryptophan, which light drives, and slow hydrolysis. The PT-141 stability page covers those routes, freeze-thaw, light and what visible changes mean.
Solubility
A supplier gives water at 100 mg/mL with ultrasound, which is far above anything a research vial needs, though by our calculation PT-141 carries little net charge near neutral pH. The PT-141 solubility guide explains why, which concentrations dissolve cleanly and what causes haze.
Handling
Bench practice for PT-141 is mostly about keeping the solution cold, clean and labelled. The PT-141 handling page lists the steps and the common mistakes.
On arrival
What a sealed vial should look like, why it travels without an ice pack and where it and the ready-mixed spray go first are on the PT-141 on-arrival page.
Storage and reconstitution
Fridge and freezer windows, before and after mixing, are on how long PT-141 lasts. Water volumes and the concentration table for a 10 mg vial are on how much bacteriostatic water for a PT-141 10 mg vial.
FAQ
Short answers to the questions researchers ask most about storing, mixing and handling PT-141 are on the PT-141 FAQ.
Where to get it
Vistara Labs supplies PT-141 10 mg as a lyophilised vial for laboratory research, shipped within Canada by Canada Post Xpresspost. A ready-mixed PT-141 Nasal Spray is also available, in two bottle sizes. Certificates are on our lab reports page. Its closest chemical relative is covered in the Melanotan II research reference.
All products supplied by Vistara Labs are intended for laboratory research use only. They are not drugs, are not approved for human or veterinary use, and are not intended to diagnose, treat, cure or prevent any condition. Nothing on this page constitutes medical advice or guidance for use in humans.
