Description
Summary Abstract
PT-141 (Bremelanotide; cyclic heptapeptide; C50H68N14O10; MW 1,025.2 g/mol; CAS 189691-06-3; PubChem CID 9941379) is a cyclic heptapeptide lactam derived as an active metabolite of Melanotan II, structurally stabilized by a lactam bridge between aspartic acid and lysine residues. Unlike peripherally acting phosphodiesterase-5 (PDE5) inhibitors that facilitate vascular engorgement, Bremelanotide engages the central nervous system melanocortin system — specifically the Melanocortin 4 Receptor (MC4R) in the hypothalamic Paraventricular Nucleus (PVN) and Medial Preoptic Area (mPOA) — to generate neurobiological sexual motivation and arousal signals de novo. This centrally initiated signal recruits dopaminergic pathways in the mPOA and oxytocinergic outputs from the PVN, producing both the appetitive (desire) and consummatory (performance) components of the sexual response. Bremelanotide received FDA approval in 2019 as Vyleesi for acquired, generalized HSDD in premenopausal women, based on the RECONNECT Phase 3 program (n=1,247). It has additionally demonstrated efficacy in Phase 2 clinical studies for male erectile dysfunction (ED) that is refractory to sildenafil, where 33.5% of previously non-responding men achieved adequate erection compared to 8.5% on placebo. Half-life is approximately 2.7 hours with ~100% subcutaneous bioavailability.
Clinical Indications
PT-141 targets the neurobiological root of sexual dysfunction, with validated and investigational applications:
- Hypoactive Sexual Desire Disorder (HSDD) — Premenopausal Women (FDA Approved): RECONNECT Phase 3 trials (n=1,247) demonstrated statistically significant improvements in the Female Sexual Function Index-Desire (FSFI-D) score and reductions in distress (FSDS-DAO Item 13), with sustained efficacy over 52 weeks without evidence of tachyphylaxis.
- Male Erectile Dysfunction — PDE5i Non-Responders: A randomized, double-blind study (n=342 sildenafil-refractory men) showed 33.5% vs. 8.5% placebo response rate; PT-141 bypasses the central inhibitory block that prevents PDE5 inhibitors from being effective in psychogenic or anxiety-driven ED.
- Male Orgasmic Disorder / SSRI-Induced Sexual Dysfunction: MC4R-driven dopaminergic activation in the mPOA may normalize the ejaculatory threshold blunted by SSRI-mediated serotonergic dampening of dopamine tone.
- Metabolic Syndrome (Investigational Adjunctive): MC4R governs both sexual function and energy balance; MC4R agonism reduces caloric intake and has been associated with weight loss in clinical and preclinical observations.
Contraindications
- Uncontrolled Hypertension and High-Risk Cardiovascular Disease: Bremelanotide produces transient pressor effects (mean +2–4 mmHg systolic, +1–2 mmHg diastolic, peak at 2–4 hours); use is contraindicated in patients with uncontrolled hypertension or significant cardiovascular comorbidity.
- Concurrent Naltrexone Use: Bremelanotide markedly slows gastric emptying, significantly reducing absorption and peak plasma levels of oral naltrexone; co-administration can result in naltrexone treatment failure in patients using it for alcohol or opioid dependence.
- Pregnancy: Contraindicated; no safety data and potential for teratogenic effects from central MC4R agonism during fetal development.
- Focal Hyperpigmentation Risk with Frequent Dosing: Off-target MC1R activation causes irreversible focal hyperpigmentation (face, gums, breasts) in ~1% of users; risk is dose-dependent and increases with >8 doses/month.
Mechanism of Action (MOA)
Bremelanotide’s centrally mediated mechanism is anatomically and neurochemically distinct from vascular PDE5 inhibitors:
MC4R Agonism — cAMP/PKA/CREB Signaling
Bremelanotide binds MC4R in the PVN and mPOA, activating Gαs and adenylyl cyclase to elevate intracellular cAMP. PKA phosphorylates CREB, altering gene expression profiles that enhance neuronal excitability. Simultaneously, MC4R activation closes potassium channels and opens non-selective cation channels, depolarizing hypothalamic neurons and lowering the threshold for sexual stimuli to generate action potentials. This is the foundational signal absent in patients with central sexual dysfunction.
mPOA Dopaminergic Activation — Desire and Motivation
MC4R activation in the Medial Preoptic Area (mPOA) stimulates release of dopamine, the primary neurotransmitter of the brain’s “seeking” and appetitive behavior system. Dopamine governs motivation, attention to erotic stimuli, and anticipation of reward. Microdialysis studies in animal models confirm this dopaminergic surge, explaining clinical observations of restored libido and sexual motivation rather than simply facilitating performance.
PVN Oxytocinergic Release — Performance and Bonding
MC4R neurons in the Paraventricular Nucleus (PVN) project to oxytocinergic neurons, stimulating endogenous oxytocin release. Oxytocin governs the consummatory phase of sexual activity, including orgasmic intensity, post-coital bonding, and tactile sensitivity. Prairie vole studies demonstrate that blocking oxytocin receptors ablates the pro-social and bonding effects of melanocortin activation, confirming oxytocin as a necessary downstream effector.
Spinal Erectile Pathway — Bypass of Psychogenic Inhibition
The hypothalamic cascade descends via spinal pathways to the pelvic cavernous nerves, increasing nitric oxide (NO) synthesis in the corpus cavernosum. Crucially, PT-141 can initiate this signal independent of psychogenic arousal, allowing it to overcome the cortical inhibition of the spinal erectile reflex that frustrates men with performance anxiety, where intact vascular machinery otherwise precludes PDE5 inhibitor failure.
Key Features & Specifications
Structural and pharmacological highlights of Bremelanotide:
Chemical Analysis
| Property | Specification Reference Data |
|---|---|
| IUPAC Name | (3S,6S,9R,12S,15S,23S)-15-amino-9-benzyl-6-[3-(diaminomethylideneamino)propyl]-12-(1H-imidazol-5-ylmethyl)-3-(1H-indol-3-ylmethyl)-2,5,8,11,14,17-hexaoxo-1,4,7,10,13,18-hexazacyclotricosane-23-carboxylic acid |
| CAS Number | 189691-06-3 |
| Molecular Formula | C50H68N14O10 |
| Molecular Weight | 1,025.2 g/mol |
| PubChem CID | 9941379 |
| Synonyms | Bremelanotide, Vyleesi, PT-141 |
| Form / Variation | 10 MG Lyophilized (P-030) |
Storage, Safety, and Handling
Storage Protocol
Store lyophilized Bremelanotide at −20 °C, protected from light and moisture; the cyclic lactam structure confers excellent chemical stability under these conditions. Once reconstituted, store at 2–8 °C and use within 14 days. The compound is metabolized via peptide-bond hydrolysis rather than cytochrome P450 pathways, making it compatible with a broad range of co-medications except those requiring intact oral naltrexone absorption.
Handling & Compliance
Handle under aseptic conditions with standard PPE. The FDA-approved autoinjector (Vyleesi) uses a 1.75 mg fixed dose; research applications use a broader titration range (0.5–2.0 mg subcutaneous). Cardiovascular monitoring is advisable in patients with borderline blood pressure, as a mean systolic increase of 2–4 mmHg peaks 2–4 hours post-dose. Maximum 8 doses per month is the approved clinical limit to mitigate cumulative focal hyperpigmentation risk (off-target MC1R). PT-141 is not classified as a WADA-prohibited substance for therapeutic use in approved indications.