Melanotan II vs PT-141: Receptor-Binding Selectivity
Melanotan II vs PT-141: Receptor-Binding Selectivity
RESEARCH USE ONLY — NOT FOR HUMAN OR VETERINARY USE
This guide is for laboratory, analytical and procurement context. It does not provide human or veterinary administration, dosing, injection, tanning, sexual-function, treatment or personal-use guidance.
Melanotan II vs PT-141: Receptor-Binding
Selectivity
Melanotan II (MT-II)
and PT-141/bremelanotide are closely related cyclic melanocortin
peptides, but they are not analytically identical. MT-II is commonly
written as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2, while the
current bremelanotide drug label gives
Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys-OH]. The practical structural
difference is the C-terminal carboxamide versus free carboxylic acid.
That small terminal
change changes the molecular formula and mass, so batch identity
should be confirmed analytically. Receptor literature can then be
compared, but it should not be converted into clinical-selection or
administration guidance.
Figure
1. Melanotan II and PT-141 comparison showing shared cyclic
melanocortin scaffold, C-terminal amide versus free acid and
evidence-based receptor context.
Quick comparison
|
Attribute |
Melanotan |
PT-141 |
|
Shared |
Ac-Nle |
Closely |
|
C-terminus |
Carboxamide |
Free |
|
Receptor |
Broad |
Official |
|
Analytical |
Exact |
Exact |
|
What |
Clinical |
Drug |
The shared cyclic melanocortin scaffold
Both peptides use
the conformationally constrained MT-II-type lactam ring built around
the melanocortin pharmacophore. Primary structure-activity studies
show that changes around this cyclic scaffold can materially alter
affinity and selectivity across melanocortin receptor subtypes.
Because the scaffold
is shared, broad receptor activity can overlap. Because the terminal
chemistry differs, however, the two names should not be collapsed
into one analytical identity.
The cleanest structural distinction is the
C-terminus
MT-II literature
describes a C-terminal amide. The official Vyleesi label describes
bremelanotide as a synthetic cyclic heptapeptide with a free acid at
the carboxyl terminus and an acetylated amino terminus. The label
provides an authoritative current chemical identity for the regulated
bremelanotide active ingredient.
For an RUO batch,
this means expected mass and terminal chemistry are part of identity.
A supplier should not rely on “PT-141 is derived from MT-II” as a
substitute for an actual identity record.
Receptor selectivity: avoid a simplistic
single-receptor story
The current
bremelanotide label describes nonselective activation of multiple
melanocortin receptor subtypes, with a potency order of MC1R, MC4R,
MC3R, MC5R and MC2R. MT-II research likewise shows broad melanocortin
receptor activity, and structure-activity work demonstrates that
modest chemical modifications can shift subtype selectivity.
A research
comparison should therefore state the assay, receptor subtype and
ligand form when discussing potency. “Selective for MC4R” or
similar blanket claims are too strong unless the specific experiment
supports them.
Analytical verification matters because the
structures are so similar
A terminal
amide-to-acid difference is easy to blur in marketing prose and
important in mass spectrometry. Expected mass, ion assignment and
fragmentation should be interpreted against the stated chemical form.
HPLC can support purity/profile under a method but cannot by itself
establish which terminal group is present.
From Our Work: closely related names still
require separate batch evidence
Core Research’s
approved batch-review workflow treats analytical evidence as a linked
set rather than as a single purity number. The review checks HPLC
purity/profile, MS identity, product and batch match, appearance,
labelled amount/content, water or moisture where applicable,
counter-ion information, document completeness and storage/handling
status. Analytical testing is produced by the manufacturer and/or
third-party laboratories; Core Research reviews that evidence. If a
meaningful mismatch remains unresolved, the batch is held while
clarification and/or a justified retest is requested. This does not
imply in-house analytical testing or laboratory accreditation.
For MT-II and
PT-141, the review principle is to keep the chemical-form statement
coupled to the batch. A coherent CoA/label/MS record is more useful
than a generic receptor claim. If the stated terminal form and mass
evidence do not agree, that mismatch is resolved before the
literature comparison is used.
Regulated bremelanotide is not evidence for an
RUO batch
Vyleesi is an
approved prescription drug with its own manufacturing, formulation
and regulatory controls. Its label is useful here to establish the
bremelanotide molecule and official receptor description. It does not
validate an independently supplied RUO product, its purity, its
content or its intended use.
Frequently asked questions
Are Melanotan II and PT-141 the same peptide?
They share a very
similar cyclic scaffold, but the commonly described MT-II has a
C-terminal amide whereas bremelanotide has a free C-terminal
carboxylic acid. That makes them separate analytical identities.
Is PT-141 selective only for MC4R?
The current official
bremelanotide label does not describe it that way. It lists
nonselective activation of several melanocortin receptor subtypes,
with potency varying by receptor.
Can a high HPLC purity percentage prove PT-141
identity?
No. HPLC area
percentage is method-specific and does not establish the terminal
chemical form. Mass-spectrometric identity and batch/document linkage
are needed.
Why cite a prescription-drug label on an RUO
page?
Only to verify the
chemical identity and official receptor description of bremelanotide.
The regulated medicine is not being presented as equivalent to an
Core Research research product.
Key takeaway
MT-II and PT-141 are
close structural relatives, not interchangeable batch identities.
Resolve the C-terminal amide-versus-acid distinction analytically,
then interpret receptor data in the specific assay context without
turning it into clinical-selection guidance.
References
1. Dorr RT, et al.
Evaluation of melanotan-II, a superpotent cyclic melanotropic peptide
in a pilot phase-I clinical study. Life Sci. 1996. PMID: 8637402.
https://pubmed.ncbi.nlm.nih.gov/8637402/ (used here only for MT-II
chemical identity; clinical dosing content is not reproduced).
2. FDA/DailyMed
VYLEESI label. Bremelanotide is
Ac-Nle-cyclo-(Asp-His-D-Phe-Arg-Trp-Lys-OH); official label lists
nonselective melanocortin-receptor agonism with potency order MC1R,
MC4R, MC3R, MC5R, MC2R.
https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f1d0c1b5-2f39-4bad-a6a4-0066e3ad5dcf
3. Bednarek MA, et
al. Analogs of MTII, lactam derivatives of alpha-melanotropin,
modified at the N-terminus, and their selectivity at human
melanocortin receptors 3, 4, and 5. Biochem Biophys Res Commun.
1999;261(1):209-213. DOI: 10.1006/bbrc.1999.0981. PMID: 10405347.
https://pubmed.ncbi.nlm.nih.gov/10405347/
4. Schioth HB, et
al. Selectivity of cyclic [D-Nal7] and [D-Phe7] substituted MSH
analogues for the melanocortin receptor subtypes. Peptides. 1997.
DOI: 10.1016/S0196-9781(97)00079-X. PMID: 9357059.
https://pubmed.ncbi.nlm.nih.gov/9357059/
Publishing
notes — not visible article copy
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Field |
Instruction |
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SEO |
Melanotan |
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Meta |
Compare |
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Canonical |
/laboratory-guides/science-compliance/melanotan-ii-vs-pt-141-receptor-binding-selectivity/ |
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Schema |
Article |
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Journey |
Consideration |
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Priority |
P2 |
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Primary |
O27_MTII_vs_PT141_Structure_Receptor_Context.png |
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Image |
Melanotan |
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Image |
After |
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Internal |
C31 |
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Canonical |
Current |
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Implementation |
No |