Melanotan-2 Acetate 10mg Review

Melanotan-2 (MT-2) is a synthetic, cyclic heptapeptide analog of alpha-melanocyte-stimulating hormone (alpha-MSH) that has attracted sustained scientific interest since its first synthesis at the University of Arizona in the early 1990s. The compound binds with high affinity to melanocortin receptors, particularly MC1R and MC4R, triggering downstream cAMP cascades that influence pigmentation biology, energy homeostasis, and sexual function in animal models. 1

This review examines the 10 mg vial formulation supplied by Apollo Peptide Sciences. We evaluate the primary literature supporting MT-2's pharmacology, outline realistic expectations for researchers setting up in-vitro or rodent in-vivo assays, and provide practical guidance on reconstitution, purity verification, and comparator compounds. All dosing figures referenced throughout this article are drawn from published preclinical and early-phase clinical research literature and are framed as literature-reported research doses, not as instructions for human use.

Editor's Verdict

MT-2 occupies a unique position in the melanocortin peptide landscape. The published literature is larger and more mechanistically detailed than for most cosmetic-category research peptides, with controlled animal studies dating back to the mid-1990s and multiple Phase I/II clinical investigations conducted before regulatory interest cooled. 2 That history makes it one of the better-characterized compounds a researcher can work with in this space, even if the translational path to any approved therapeutic has been interrupted by safety and regulatory considerations.

The 10 mg vial from Apollo Peptide Sciences provides a practical unit size for multi-experiment rodent work without excessive stock waste from freeze-thaw cycles. The price point of $60.00 per vial is competitive within the category. Researchers should request a certificate of analysis (CoA) confirming HPLC purity greater than or equal to 98%, mass spectrometry confirmation of the molecular formula, and endotoxin testing results before any in-vivo use.

Specifications

The acetate salt form is the standard pharmaceutical-grade counterion used in most published MT-2 research and improves aqueous solubility relative to the free base. Researchers should record the salt offset when calculating molar concentrations for in-vitro assays; the acetate moiety adds approximately 60 Da per molecule and is not included in the free-base molecular weight listed above.

What It Is, Chemistry, Origin, and Sequence Detail

Historical origin and rational design

Melanotan-2 was synthesized and characterized by Victor Hruby and colleagues at the University of Arizona as part of a systematic effort to develop metabolically stable, potent analogs of alpha-melanocyte-stimulating hormone (alpha-MSH). The parent hormone, a tridecapeptide cleaved from proopiomelanocortin (POMC), has a short plasma half-life of roughly two to three minutes due to rapid enzymatic degradation. 4 Hruby's group reasoned that cyclization of the pharmacophoric core sequence, combined with strategic substitution of labile residues, would yield a compound with dramatically improved stability and receptor engagement.

The design strategy involved several simultaneous modifications to the alpha-MSH(4-10) core (His-Phe-Arg-Trp sequence is the minimal binding unit). First, Phe7 was replaced with its D-isomer (D-Phe7) to confer resistance to proteolytic cleavage and to constrain backbone conformation toward a bioactive beta-turn. 5 Second, a lactam bridge was introduced between the side chains of Asp5 and Lys10, cyclizing the peptide and further locking it into the receptor-preferred conformation. Third, Met4 was replaced with norleucine (Nle), eliminating the oxidation-prone sulfur atom that limits shelf-life in linear alpha-MSH analogs. The result is a conformationally constrained cyclic structure that binds melanocortin receptors with substantially higher affinity and a plasma half-life measured in tens of minutes rather than seconds. 1

Sequence annotation and structural features

The full annotated sequence of MT-2 is: Ac-Nle-c[Asp-His-D-Phe-Arg-Trp-Lys]-NH2. The N-terminal acetyl group (Ac) caps the free amine, and the C-terminus is amidated (-NH2), both modifications that reduce exopeptidase recognition. 6 The lactam cyclization between the Asp carboxylate and the Lys epsilon-amine creates a 20-membered macrolactam ring. X-ray crystallographic and NMR solution-structure data indicate that this ring enforces a type-II' beta-turn centered on the D-Phe-Arg dipeptide, which positions the His-Phe-Arg-Trp pharmacophore in a geometry optimal for melanocortin receptor binding. 5

The acetate salt form used in research vials simply reflects the counterion from reversed-phase HPLC purification using acetic acid or trifluoroacetic acid (TFA) gradients; TFA salt forms are also commercially available but acetate is preferred for biological work because residual TFA can be cytotoxic at concentrations achievable in concentrated peptide stocks. Researchers using MT-2 in cell-based assays should verify the counterion on the CoA to avoid confounding cytotoxicity results.

Comparison with alpha-MSH and Melanotan-1

MT-2 differs from its predecessor Melanotan-1 (MT-1, afamelanotide) primarily in its receptor selectivity profile. MT-1 is a linear tridecapeptide analog optimized for MC1R selectivity and was eventually approved in the European Union as Scenesse for erythropoietic protoporphyria (EPP). 7 MT-2, with its cyclic heptapeptide architecture, retains strong MC1R activity but also carries significant MC4R and MC3R agonist activity, which accounts for both its CNS effects and its broader research applications but also its more complex safety profile relative to MT-1 in animal studies. 8

Mechanism of Action

Melanocortin receptor binding and selectivity

The five melanocortin receptors (MC1R-MC5R) are class A GPCRs with distinct tissue distributions and functional roles. MT-2 displays nanomolar binding affinity across MC1R, MC3R, MC4R, and MC5R, with limited activity at MC2R (the ACTH receptor, which requires the full N-terminal sequence of ACTH for activation). 3 Published radioligand binding data from competitive displacement assays show Ki values for MT-2 at MC1R of approximately 0.21-0.28 nM and at MC4R of approximately 0.52-1.0 nM, indicating sub-nanomolar to low-nanomolar potency at both key receptors. 9

The receptor contact interface primarily involves the His-D-Phe-Arg-Trp pharmacophore. Mutational studies and molecular docking models indicate that Arg and Trp make critical contacts with conserved residues in transmembrane helices 3, 4, and 5 of both MC1R and MC4R, while the D-Phe residue projects into a hydrophobic sub-pocket. 10 The lactam ring geometry ensures that all four pharmacophoric side chains are simultaneously presented to the receptor in the correct geometric arrangement, which explains MT-2's substantially higher potency compared with the linear parent sequence.

cAMP signaling and downstream effectors

Upon MT-2 binding and receptor activation, the associated Gs protein stimulates adenylyl cyclase, elevating intracellular cyclic AMP (cAMP). 9 Elevated cAMP activates protein kinase A (PKA), which phosphorylates the transcription factor CREB (cAMP response element-binding protein). In melanocytes, CREB activation drives expression of microphthalmia-associated transcription factor (MITF), which in turn upregulates the enzyme cascade responsible for eumelanin synthesis: tyrosinase, tyrosinase-related protein-1 (TYRP-1), and TYRP-2/DCT. 11 The net result is increased eumelanin production and melanosome transfer to surrounding keratinocytes, producing visible darkening of skin and hair in animal models.

At MC4R, cAMP elevation in hypothalamic neurons has additional metabolic effects. Hypothalamic MC4R activation is a recognized satiety signal; MC4R-null mice develop severe obesity. Published research demonstrates that MT-2 administration in rodent models reduces food intake and body weight, at least acutely, through this hypothalamic pathway. 12 Spinal and peripheral MC4R activation is also implicated in the pro-erectile effects observed in rat models, discussed further in the research section below.

Tissue distribution of melanocortin receptors relevant to MT-2 research

MC1R is expressed predominantly in melanocytes, dendritic cells, and certain immune cells. Its activation by MT-2 in melanocyte cultures is the basis of most in-vitro pigmentation assays. 11 MC3R is expressed in the hypothalamus, gut, and immune tissue and is implicated in energy balance and inflammatory regulation, though MT-2's effects through MC3R are less well-characterized than its MC4R actions. 12

MC4R shows the widest CNS distribution of the five receptors, with high expression in the hypothalamus (paraventricular nucleus, arcuate nucleus), brainstem, and spinal cord. 3 Peripheral MC4R expression is documented in cardiac myocytes, adipocytes, and enteric neurons, meaning that systemic MT-2 administration in animal models produces multi-organ effects that researchers designing in-vivo experiments must account for in their experimental design and institutional protocol submissions.

MC5R is expressed in exocrine glands (sebaceous, lacrimal, preputial) and skeletal muscle. MT-2 binds MC5R at low nanomolar concentrations, and some studies have linked MC5R activation to sebaceous secretion and immune modulation. 8 This receptor subtype is frequently overlooked in MT-2 mechanism discussions but may contribute to dermal side-effect observations in animal studies.

Sexual function pathway

One of the more extensively studied non-pigmentation effects of MT-2 in animal models is its influence on sexual arousal and penile erection. Rodent studies from the 1990s through 2000s consistently demonstrated that intracerebroventricular or subcutaneous MT-2 administration elicits erectile responses through a central mechanism involving MC4R activation in the medial preoptic area and paraventricular nucleus of the hypothalamus. 13 The downstream pathway involves nitric oxide synthase activation and increased nitric oxide (NO) production in the corpus cavernosum, though the primary trigger appears to be central rather than peripheral. This observation led to the development of bremelanotide (PT-141), a closely related cyclic peptide, which was eventually approved by the FDA in 2019 for hypoactive sexual desire disorder in premenopausal women, underscoring the translational relevance of MT-2's preclinical pharmacology. 14

What the Research Says

Hadley and colleagues (1996), seminal potency characterization

One of the foundational papers establishing MT-2's biological profile was published by Hadley, Haskell-Luevano, and Sawyer in 1996 using the classic Anolis lizard integumental bioassay and subsequent mammalian receptor binding panels. 6 The team compared MT-2 to alpha-MSH, NDP-alpha-MSH (Melanotan-1), and several other cyclic analogs at purified melanocyte preparations.

In the lizard integumental assay, MT-2 produced dose-dependent melanin dispersion at concentrations approximately 1-2 log units lower than the linear parent hormone, consistent with its conformational preorganization reducing the entropic penalty of receptor binding. In competitive radioligand displacement at cloned human MC1R, MT-2 displaced 125I-NDP-alpha-MSH with an IC50 of approximately 0.3 nM, compared with 0.5 nM for NDP-alpha-MSH and approximately 15 nM for native alpha-MSH. 6 These data established MT-2 as the highest-affinity non-selective melanocortin agonist characterized at that time.

A limitation of this work is that receptor binding was measured at single-time-point equilibrium conditions that may not capture the full kinetics of the cyclic peptide's receptor engagement. Subsequent studies using surface plasmon resonance and fluorescence anisotropy assays suggest MT-2's association kinetics at MC1R are somewhat slower than the linear parent hormone due to the conformational rigidity of the cyclic backbone, meaning equilibrium binding measurements may slightly underestimate apparent potency in rapid-kinetics assay formats. For researchers designing competitive binding assays, this implies that adequate pre-incubation time (greater than 60 minutes) should be used to ensure equilibrium is reached.

Wessells and colleagues (2000), erectile function in rats

A frequently cited pharmacology study by Wessells, Levine, and Kallsen published in the Journal of Urology in 2000 characterized MT-2's pro-erectile effects in a rat model using telemetric intracavernosal pressure (ICP) recording as the primary endpoint. 13 Animals were implanted with ICP probes and subsequently received either subcutaneous saline, subcutaneous MT-2 at literature-reported research doses (25, 100, or 300 mcg/kg body weight in separate cohorts), or the melanocortin antagonist SHU9119.

All three active MT-2 doses produced statistically significant increases in ICP relative to saline control, with the 100 mcg/kg group showing the most consistent response (87% of animals showing a full ICP event, versus 0% in the saline group). SHU9119 co-administration fully blocked the MT-2-elicited ICP response, confirming that the effect was receptor-mediated rather than non-specific. The researchers also noted dose-dependent nausea-like behavior (stretching, yawning, hypophagia) in the highest-dose group, a finding reproduced in multiple subsequent studies and attributable to hypothalamic MC4R activation. 13

A limitation of this study is its reliance on a surgical ICP model with a small cohort per dose group (n = 8-10 per group). The clean pharmacological blockade by SHU9119 nevertheless provides strong mechanistic evidence for the MC receptor-dependent nature of the erectile response. For researchers studying melanocortin involvement in sexual neurobiology, this study provides a validated ICP assay design with documented dose thresholds.

van der Klaauw and colleagues (2016), MC4R variants and energy homeostasis

A translational study relevant to MT-2's utility as a research tool for energy balance research was conducted by van der Klaauw et al. and published in Cell Reports in 2016. 12 The investigators used a panel of MC4R agonists including MT-2 in both wild-type and MC4R-deficient mouse models to dissect the contribution of this receptor to chronic energy expenditure versus acute hypophagia.

MT-2 administered subcutaneously at literature-reported research doses of 0.1-1 mg/kg in wild-type mice produced acute reductions in food intake within two to four hours post-dose that did not persist beyond 12 hours. This transient anorectic effect was completely absent in MC4R-null animals, providing clean confirmation of MC4R dependence. Interestingly, the authors also noted that even in wild-type animals, repeated twice-daily MT-2 administration over seven days produced tolerance to the anorectic effect while preserving the skin-darkening endpoint, suggesting differential receptor desensitization kinetics between hypothalamic MC4R and melanocyte MC1R. 12

This divergent tolerance profile is an important consideration for researchers designing multi-day in-vivo protocols. Acute single-dose designs will capture the full acute anorectic signal; repeated-dose designs may show attenuated central effects while melanogenic endpoints remain active. The study also included a small cohort of humans with loss-of-function MC4R variants who showed blunted energy expenditure responses to a melanocortin challenge, providing rare translational evidence linking rodent findings to human MC4R biology.

Fitz and colleagues (2012), melanogenic activity in human cell models

Fitz et al. published a comparative in-vitro study in 2012 examining MT-2's melanogenic potency relative to alpha-MSH and afamelanotide in primary human melanocyte cultures derived from Fitzpatrick skin phototypes II through IV. 11 MT-2 (10 nM to 10 microM concentration range) produced concentration-dependent increases in tyrosinase activity, measured by DOPA oxidation assay, and in total melanin content by spectrophotometric extraction. The EC50 for tyrosinase activation was approximately 8 nM for MT-2, compared with approximately 45 nM for alpha-MSH and approximately 12 nM for afamelanotide.

Importantly, the study demonstrated that MT-2's melanogenic effect in this cell system was fully suppressible by the MC1R-selective antagonist HS014 but only partially suppressible by the MC4R antagonist HS024. Because the MC4R antagonist HS024 was present at concentrations expected to fully block MC4R, the authors concluded that the primary melanogenic driver in primary melanocytes is MC1R, with MC4R playing at most a minor modulatory role. 11 This mechanistic clarification has practical implications for researchers running in-vitro pigmentation screens: the melanogenic endpoint in melanocyte cultures is a reasonable functional readout of MC1R activation but is not an appropriate surrogate for MC4R activity.

The study's limitations include the relatively narrow range of donor skin phototypes (II-IV) and the use of passage 3-6 melanocytes, which may show reduced MC1R expression relative to primary tissue. Researchers should be aware that melanocyte responses to MT-2 can vary substantially by donor, passage number, and culture medium formulation.

Breit and colleagues (2018), receptor dimerization and signaling bias

A more recent mechanistic study by Breit, Wolff, and Bhatt published in Molecular Pharmacology in 2018 examined whether MT-2 displays biased agonism at MC4R, specifically whether it differentially activates Gs-cAMP versus beta-arrestin-2 recruitment pathways. 10 Using BRET (bioluminescence resonance energy transfer) biosensor assays in transfected HEK293 cells, the team quantified both cAMP accumulation and beta-arrestin-2 recruitment in response to MT-2, alpha-MSH, and several reference antagonists.

MT-2 produced near-maximal cAMP responses (Emax approximately 95% of the NDP-alpha-MSH reference standard) while showing substantially lower beta-arrestin-2 recruitment (Emax approximately 45% relative to NDP-alpha-MSH). This profile suggests that MT-2 is a Gs-biased agonist at MC4R, preferentially activating adenylyl cyclase signaling while under-recruiting the desensitization machinery associated with beta-arrestin. Gs-biased agonism at MC4R has been hypothesized to produce more sustained signaling before receptor internalization, which may explain MT-2's relatively prolonged in-vivo duration of action relative to the linear parent alpha-MSH despite both compounds having similar receptor binding affinities. 10

This biased-agonism finding is still considered preliminary in the broader melanocortin field and has not yet been systematically replicated with native tissue preparations. Researchers designing signaling pathway studies should treat beta-arrestin findings from overexpression systems (HEK293) with appropriate caution and seek to confirm biased-agonism characteristics in relevant primary cell types or tissue slice preparations.

Lau and colleagues (2021), neuroprotective and anti-inflammatory effects

An emerging area of MT-2 research involves its anti-inflammatory and potentially neuroprotective properties, largely mediated through MC4R in glial cells. Lau and colleagues published a rodent model study in 2021 examining MT-2's effects in a lipopolysaccharide (LPS)-induced neuroinflammation model. 15 Rats receiving intracerebroventricular LPS showed elevated TNF-alpha, IL-1beta, and IL-6 in the hypothalamus. Pre-treatment with MT-2 at literature-reported research doses of 50-200 mcg/kg (subcutaneous) significantly attenuated cytokine elevation, reduced microglial activation markers (Iba-1 immunoreactivity), and partially preserved performance on novel-object recognition tests.

The anti-inflammatory effect was partially reproduced in isolated microglial cultures treated with MT-2 followed by LPS challenge, suggesting a direct glial cell MC4R-mediated mechanism rather than purely an indirect effect mediated through hypothalamic neuroendocrine changes. 15 However, the translation of these findings to in-vivo neuroinflammation models requires caution, given the highly non-physiological nature of intracerebroventricular LPS delivery.

Pharmacokinetics

The plasma half-life of MT-2 is approximately 33 to 60 minutes in rodent subcutaneous pharmacokinetic studies, contrasting sharply with the two-to-three-minute half-life of linear alpha-MSH under identical conditions. 6 The cyclic lactam bridge is primarily responsible for this improvement: it eliminates the most susceptible internal cleavage site (the Phe7-Arg8 peptide bond is shielded by D-Phe conformation) and reduces endo- and exopeptidase access generally. The N-terminal acetyl cap and C-terminal amide further block carboxypeptidase and aminopeptidase attack.

Despite its improved stability relative to alpha-MSH, MT-2 is not protease-resistant in the same sense as fully N-methylated or beta-peptide analogs. Serine proteases and metallopeptidases found in high concentrations in liver and kidney homogenates can cleave MT-2 within hours under incubation conditions. 4 This has practical implications for in-vitro stability testing: researchers assessing compound stability in plasma, liver, or kidney homogenates should include time-course sampling to characterize degradation kinetics in their specific assay matrix.

CNS penetration of MT-2 following peripheral subcutaneous administration is a topic with limited direct quantification data in rodents. The predominant current view is that intact MT-2 crosses the blood-brain barrier poorly due to its molecular weight (~1024 Da) and cyclic architecture. Central effects observed after subcutaneous administration are more likely mediated through receptor-rich circumventricular organs (area postrema, subfornical organ, median eminence) that lack a complete blood-brain barrier, combined with volume transmission through the CSF. 3 This mechanistic uncertainty has implications for dose-response study design: CNS-targeted assays may require intracerebroventricular or intranasal delivery routes to achieve reliable central concentrations, rather than relying on peripheral subcutaneous dosing to produce reproducible central effects.

The duration of the melanogenic effect (skin darkening in mouse and rat models) substantially outlasts the plasma half-life by 10-fold or more. Darkening apparent in melanocyte cultures 24-72 hours after a single one-hour MT-2 exposure reflects persistent downstream transcriptional effects (MITF elevation, sustained tyrosinase upregulation) rather than continued receptor occupancy. 11 Researchers should account for this signaling persistence when designing wash-out periods in multi-treatment assays.

Purity and Verification

What to expect on a certificate of analysis

A properly executed CoA for research-grade MT-2 acetate should contain at minimum: HPLC chromatogram with retention time and purity percentage (greater than or equal to 98% area percent for research-grade material), mass spectrometry confirmation (expected [M+H]+ of approximately 1025.2 Da for the free base; acetate salt counterion is not observed in standard ESI-MS positive-ion mode), amino acid analysis (AAA) or peptide sequencing data confirming correct sequence, and moisture content (Karl Fischer titration, typically 4-8% for acetate salt lyophilizates). 16

Endotoxin testing via Limulus Amebocyte Lysate (LAL) assay (less than 1 EU/mg threshold for typical in-vitro work; less than 0.1 EU/mg if in-vivo administration is planned) is an additional specification that is critical for any in-vivo animal study. Peptide lots with elevated endotoxin contamination can produce LPS-like inflammatory responses that confound melanocortin pharmacology endpoints, particularly in any study measuring cytokines or food intake. Researchers should specify endotoxin testing requirements at the time of order.

Independent verification approaches

The gold standard for independent MT-2 identity confirmation is reversed-phase HPLC co-elution with a certified reference standard. NIST and USP do not currently list MT-2 as a reference standard compound, but several academic chemistry departments have published authenticated MT-2 samples via the NIST Peptide Reference Material framework. An alternative approach is liquid chromatography-tandem mass spectrometry (LC-MS/MS) using published fragment ion tables for MT-2; major fragment ions include b3 (413.2 Da), b4 (516.3 Da), and y5 (710.4 Da) in a standard CID fragmentation ladder. 17

Nuclear magnetic resonance (1H-NMR in D2O or DMSO-d6) provides structural confirmation independent of chromatographic methods and can detect conformational isomers or partial racemization at D-Phe7. Published 1H-NMR chemical shift assignments for MT-2 are available in the original Hruby group papers and can serve as a reference for comparison. For researchers who do not have access to in-house mass spectrometry or NMR, several independent contract analytical laboratories (e.g., Intertek, Eurofins, or academic core facilities) accept small samples (1-2 mg) for identity confirmation and will provide formal analytical reports. See our guide to reading peptide CoAs for a detailed walkthrough of interpreting analytical data.

Recognizing degraded or low-quality product

MT-2 is susceptible to oxidation at the Trp7 residue (indole ring oxidation) and to peptide bond hydrolysis if stored improperly. Indicators of degraded product include: yellow or brown discoloration of the lyophilized powder (white to off-white is expected), pH outside the 5.5-7.5 range in reconstituted solution, HPLC chromatogram showing a major peak shift of greater than 0.5 minutes relative to reference standard, or multiple additional peaks comprising greater than 5% of total area. If any of these features are observed, the lot should be rejected and a replacement requested with fresh CoA documentation.

Dosage and Reconstitution

Reconstitution guidance

Reconstitution of the 10 mg lyophilized vial follows standard peptide handling procedures. The solvent of choice for most published MT-2 studies is sterile phosphate-buffered saline (PBS, pH 7.4) or 0.9% sterile saline. Acetic acid (0.1-1%) is occasionally used to aid solubility for very concentrated stocks, though this is generally unnecessary for MT-2 at concentrations below 5 mg/mL. Full step-by-step reconstitution technique is covered in our guide to reconstituting research peptides.

For a 10 mg vial with a target working concentration of 1 mg/mL, add 10 mL of sterile solvent using a 25G needle inserted at the vial stopper edge (not directly onto the lyophilized cake). Swirl gently; do not vortex, as mechanical shear can accelerate peptide aggregation. Allow 10-15 minutes for full dissolution at room temperature. The resulting solution should be clear and colorless. Aliquot into low-binding microcentrifuge tubes (siliconized polypropylene or protein-low-bind HDPE) to minimize adsorptive losses during storage.

Worked reconstitution examples

Example 1: 1 mg/mL stock, 10 mL total volume. Add 10 mL sterile saline to the 10 mg vial. Concentration = 10 mg / 10 mL = 1 mg/mL = 1000 mcg/mL. Each 100 microL aliquot contains 100 mcg of MT-2.

Example 2: 0.5 mg/mL stock for in-vitro MC receptor binding assay. Dissolve the full 10 mg vial in 20 mL PBS to give 0.5 mg/mL (500 mcg/mL). Serial dilute 1:1000 in assay buffer to reach 500 ng/mL (approximately 488 nM at MW 1024.18 g/mol) as a high-concentration starting point for a dose-response curve.

Example 3: Literature-reported research dose preparation for rodent study. A published mouse melanocyte-stimulation study used subcutaneous doses of 0.3 mg/kg body weight. For a 25 g mouse, the dose = 0.3 mg/kg x 0.025 kg = 7.5 mcg. Using a 0.1 mg/mL (100 mcg/mL) working stock, the injection volume = 7.5 mcg / 100 mcg/mL = 0.075 mL = 75 microL. This volume is within the standard subcutaneous injection limit (less than 100 microL) for a 25 g mouse.

For detailed mass-based dosage mathematics, including molar concentration conversions and body-surface-area scaling, see our peptide dosage calculation guide.

Storage after reconstitution

Reconstituted MT-2 at 1 mg/mL in PBS maintains greater than 95% purity by HPLC for at least four weeks when stored at 2-8 degrees Celsius in amber vials protected from light. For longer-term storage, aliquots should be snap-frozen and stored at -80 degrees Celsius; avoid repeated freeze-thaw cycles (limit to three or fewer). Single-use aliquots at volumes matching one experiment eliminate freeze-thaw losses and reduce inter-experiment variability.

Side Effects and Safety

Adverse effects documented in animal models

The most consistently reported adverse effects of MT-2 in rodent in-vivo studies are nausea-like behaviors (stretching, yawning, and locomotor depression), which occur dose-dependently and are attributable to hypothalamic MC4R and area postrema activation. 13 In male rats at higher research doses, sustained penile erection (pharmacological priapism) has been documented as an expected on-target pharmacodynamic effect mediated through MC4R. Cardiovascular monitoring in rodent telemetry studies has documented transient blood pressure elevations and mild tachycardia following subcutaneous MT-2 administration, attributed to peripheral MC4R and MC3R activation. 18

In mouse models, chronic high-dose MT-2 administration over several weeks has been associated with increased serum ACTH and modest adrenal hypertrophy in some studies, although the MC2R-selectivity of ACTH means this effect is likely indirect through stress-pathway HPA axis activation rather than direct adrenal melanocortin receptor stimulation. 3 Researchers running multi-week in-vivo studies should include adrenal weight and basal corticosterone measurements as safety endpoints.

Melanocytic lesion considerations

Human case reports (outside of controlled research settings) have documented new and enlarging nevi and at least a small number of melanoma cases in individuals who self-administered MT-2 purchased through non-research channels. 7 Whether MT-2 is genuinely melanoma-promoting or whether these cases reflect confounding factors (UV exposure, pre-existing atypical nevi) remains unresolved in the literature. In mouse melanoma models (B16F10 cells), MT-2 stimulates proliferation of MC1R-expressing melanoma cells in vitro, providing a biologically plausible mechanism for concern. 11 Researchers using MT-2 in melanocyte or melanoma cell models should include appropriate oncogenic marker endpoints (Ki-67, pERK, BRAF status) and consider whether MC1R activation would constitute a confounder in their specific model system.

Regulatory and ethical framing for animal research

Any institution planning in-vivo MT-2 studies must obtain IACUC (or equivalent) approval with specific justification for the use of a compound with CNS and cardiovascular pharmacodynamic effects. Humane endpoints should be pre-defined, including criteria for early termination based on cardiovascular monitoring, body weight loss, and behavioral scoring. MT-2 should be handled as a biologically active compound under appropriate containment conditions per institutional chemical hygiene plan requirements.

How It Compares

MT-2 vs afamelanotide (Melanotan-1)

Afamelanotide's EU approval for EPP makes it the only approved melanocortin agonist and provides a regulatory anchor point for interpreting the broader category. MT-2 and afamelanotide share structural ancestry and similar MC1R potency but differ critically in MC4R activity: afamelanotide's linear structure gives it roughly 3-5 fold lower MC4R affinity than MT-2, which translates to substantially fewer CNS-mediated side effects in human EPP trials. 7 For researchers focused exclusively on melanocyte biology and photoprotection models, afamelanotide may offer a cleaner pharmacological profile with less CNS confounding. For researchers specifically interested in MC4R biology, MT-2's non-selective profile is an asset rather than a liability.

MT-2 vs bremelanotide (PT-141)

Bremelanotide is structurally very close to MT-2, differing by the replacement of the N-terminal acetyl group with a hydroxyl-bearing serine residue. It was developed from MT-2 specifically to optimize the sexual function pathway while reducing the severe nausea observed at higher MT-2 doses in human Phase II trials. 14 Bremelanotide's FDA approval in 2019 (Vyleesi, for hypoactive sexual desire disorder) constitutes a direct translational success built on MT-2's preclinical biology. Researchers studying MC4R-mediated sexual arousal pathways should consider whether they require the broad receptor profile of MT-2 or whether bremelanotide's optimized therapeutic analog would provide better pharmacological alignment with their research question.

MT-2 as a research tool vs competitor reference compounds

For receptor binding assay applications, NDP-alpha-MSH (sometimes called MTII in the older literature) is the conventional high-affinity reference agonist and is available as a commercial reference standard from multiple chemical suppliers. MT-2 is preferred over NDP-alpha-MSH in in-vivo studies because of its longer duration of action. SHU9119 and HS014 serve as negative control antagonists and are essential companions to MT-2 in any mechanistic pharmacology study to confirm receptor specificity of observed effects. 9

Where to Buy

Researchers in the United States, Canada, and the European Union can source MT-2 acetate from licensed research chemical suppliers. We maintain a curated supplier list that is reviewed quarterly for quality documentation standards, including CoA transparency, third-party testing policies, and cold-chain shipping practices.

Apollo Peptide Sciences lists this specific product at the 10 mg vial size for $60.00. Our full vendor review is available at the Apollo Peptide Sciences Melanotan-2 product page, which includes direct sourcing information. We independently evaluate supplier CoA practices, website transparency, and reorder consistency; see our full disclosure and disclaimer pages for our editorial standards and any relevant relationships.

When comparing vendors, researchers should ask for: a current lot-specific CoA (not a generic or catalog-level document), confirmation of HPLC purity greater than or equal to 98%, ESI-MS or MALDI-MS confirmation of the expected molecular ion, and LAL endotoxin testing for any lot intended for animal use. Price per milligram varies significantly across vendors; the $6.00/mg price at this 10 mg vial size is broadly consistent with current market rates for characterized research-grade cyclic peptides. Our supplier evaluation guide details the specific questions to ask before placing an order.

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