Melanotan 2 is a synthetic cyclic heptapeptide (Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-NH₂) that functions as a potent nonselective melanocortin receptor agonist. It is employed in receptor binding and signal transduction studies exploring MC1R–MC5R-mediated cAMP activation and GPCR desensitization mechanisms. MT-II provides a research model for peptide–receptor pharmacology and neuroendocrine signaling dynamics.

Sequence:Cys(1)-Tyr-Ile-Gln-Asn-Cys(1)-Pro-Leu-Gly
MolecularFormula: C50H69N15O9
Molecular Weight: 1024.2 g/mol
PubChem CID: 92432
CAS Number: 50-56-6

Melanotan II (MT-II) is a synthetic cyclic heptapeptide analog of α-melanocyte-stimulating hormone (α-MSH). It is primarily studied for its ability to activate melanocortin receptors (MC1R–MC5R), a receptor family involved in pigmentation, metabolism, inflammation, and neuroendocrine signaling.

1. Pigmentation & Melanogenesis Research

• Investigated as a tool compound to stimulate melanin synthesis in melanocytes

• Used to study:

  • MC1R activation pathways

  • Tyrosinase expression

  • Eumelanin vs pheomelanin balance

• Frequently applied in in-vitro skin models and animal studies examining UV-induced pigmentation responses

Why researchers care:
Understanding melanin regulation has implications for photobiology, oxidative stress, and skin cell signaling.

2. Melanocortin Receptor Signaling Studies

Melanotan II is non-selective, activating multiple melanocortin receptors:

Used to:

• Map receptor-ligand affinity

• Compare agonist vs antagonist behavior

• Study downstream cAMP signaling cascades

3. Metabolic & Energy Homeostasis Models

• Studied in animal models examining:

  • Appetite signaling

  • Energy expenditure

  • Hypothalamic melanocortin pathways

• MT-II is frequently referenced in obesity and metabolic research as a benchmark melanocortin agonist

Important note:
These studies are mechanistic and exploratory, not clinical treatment models.

4. Neuroendocrine & Behavioral Research

Because MT-II crosses the blood–brain barrier in animal models, it is studied for:

• Central melanocortin signaling

• Hypothalamic-pituitary interactions

• Neurochemical pathway mapping

Researchers use it to:

• Probe CNS receptor distribution

• Study peptide-based neuromodulation

• Evaluate structure-activity relationships of cyclic peptides

5. Inflammation & Immunomodulation Studies

α-MSH and its analogs, including MT-II, are explored for:

• Anti-inflammatory signaling pathways

• Cytokine modulation

• Melanocortin-mediated immune regulation

Primarily conducted in:

• Cell culture models

• Rodent inflammation paradigms

6. Peptide Stability & Drug Design Research

Melanotan II is frequently cited in peptide engineering literature because:

• Its cyclic structure improves enzymatic stability

• It serves as a reference scaffold for designing longer-acting peptide analogs

• Useful for studying:

  • Cyclization effects

  • Receptor selectivity tuning

  • Half-life extension strategies

1. Ligand–Receptor Interaction

Melanotan II (MT-II) is a synthetic cyclic analog of α-melanocyte-stimulating hormone (α-MSH).
It functions as a non-selective agonist at melanocortin receptors:

• MC1R (predominant in melanocytes)

• MC3R / MC4R (central energy balance, hypothalamic signaling)

• MC5R (exocrine and peripheral signaling)

MT-II binds the extracellular domain of these G-protein–coupled receptors (GPCRs) with high affinity.

2. Primary Signal Transduction: Gs → cAMP

Upon receptor binding:

1. MC receptor activates Gs protein

2. Adenylyl cyclase is stimulated

3. Intracellular cAMP levels increase

4. Protein kinase A (PKA) is activated

This Gs–cAMP–PKA axis is the central signaling pathway for MT-II.

3. Downstream Nuclear Signaling (MC1R Focus)

In melanocytes (MC1R-dominant context):

• PKA phosphorylates CREB (cAMP response element-binding protein)

• Activated CREB increases transcription of MITF

  • MITF = master regulator of melanocyte function

MITF upregulates melanogenic enzymes:

• Tyrosinase (TYR)

• TYRP-1

• TYRP-2

➡ Result: Increased melanin synthesis (eumelanin bias)

4. Secondary Pathways & Crosstalk

Beyond cAMP, MT-II signaling has been shown to interact with:

• MAPK / ERK pathways

• PI3K–Akt signaling

• NF-κB modulation (context-dependent)

These pathways are often studied in:

• Oxidative stress models

• UV-response research

• Inflammatory signaling systems

5. Central Nervous System (MC3R / MC4R)

In neuroendocrine research models:

• MT-II activates hypothalamic melanocortin circuits

• Modulates:

  • Energy balance signaling

  • Neuroendocrine output

  • Behavioral response pathways

Mechanistically:

• GPCR activation → cAMP signaling → neuronal firing pattern changes

• Used experimentally to map melanocortin tone in CNS circuits

6. Structural Contribution to Mechanism

Melanotan II’s cyclic peptide structure contributes to:

• Increased proteolytic resistance

• Enhanced receptor binding stability

• Prolonged signaling duration vs linear α-MSH

This makes MT-II a reference agonist in:

• Structure-activity relationship (SAR) studies

• Peptide cyclization research

• Melanocortin receptor pharmacology

Mechanism Summary (Concise Flow)

MT-II → MC receptor binding → Gs activation → ↑ cAMP → PKA activation → CREB phosphorylation → gene transcription changes (MITF, melanogenic enzymes)