PT-141

Overview

PT-141, international nonproprietary name bremelanotide, is a synthetic cyclic heptapeptide. Its structure is derived from α-melanocyte-stimulating hormone (α-MSH), an endogenous neuropeptide, and traces back to the earlier melanocortin analogue melanotan II. What makes it interesting is its route of action: rather than acting peripherally on blood vessels, as most well-known agents for sexual function do, bremelanotide engages the central nervous system, binding melanocortin receptors expressed largely in the brain.

The compound has an unusually mature research history for a peptide in this catalogue. In June 2019 the U.S. FDA granted approval to bremelanotide (brand name Vyleesi) for acquired, generalized hypoactive sexual desire disorder (HSDD) in premenopausal women. That places it among the few melanocortin peptides with a completed clinical trajectory. In the EU it holds no EMA registration.

At Peptalis, PT-141 is available strictly for research use only, intended for in-vitro laboratory research, not for human or animal use.

Mechanism of action

Bremelanotide is an agonist at the melanocortin receptors, with the greatest affinity for MC3R and MC4R. Both are expressed primarily in the central nervous system, and MC4R in particular is linked to the regulation of sexual response. Human MC4R binding affinity is in the order of 10 nM. The mechanism is convincing in animal models and receptor pharmacology, but has not been confirmed with a direct biomarker in humans.

MC4R activation in the hypothalamus

• Non-selective agonist across the melanocortin receptors (MC1R, MC3R, MC4R); at the relevant doses MC4R is the operative target
• MC4R in the medial preoptic area (mPOA) of the hypothalamus is the central site of action
• In rats, systemic PT-141 raises c-Fos immunoreactivity in the hypothalamus, a marker of neuronal activation (Molinoff et al., 2003)

A central, not peripheral, route

• The mPOA connects through neural pathways to the peripheral genitalia
• Downstream dopaminergic transmission in motivational circuits is engaged
• This distinguishes bremelanotide from the vasodilation on which PDE5 inhibitors rely: it requires blood-brain-barrier passage

What the human data can and cannot show

• Human studies measured behavioural and experiential outcomes, not a molecular mechanistic marker
• The central mechanism is therefore inferred from animal models and receptor pharmacology
• The broader melanocortin biology (metabolism, energy balance) that MC4R governs remains clinically little explored

Research findings

• In rats and non-human primates, administration of PT-141 produces erections (Molinoff et al., 2003)
• Early proof of concept (Diamond et al., 2006): 18 premenopausal women with an arousal disorder, single intranasal 20 mg dose vs placebo; significantly more reported moderate or high desire after bremelanotide (P = 0.0114)
• Phase 3 RECONNECT (Kingsberg et al., 2019): two identical randomized placebo-controlled trials (301, 302) of bremelanotide 1.75 mg subcutaneously as needed over 24 weeks in premenopausal women with HSDD; desire rose and related distress fell versus placebo (both P < 0.001), effect modest in absolute terms
• FDA approval in June 2019 as Vyleesi; no EMA registration in the EU
• Reported observations were largely mild to moderate: nausea (≈40%), flushing (≈20%), headache (≈11%)

Animal & in-vitro data

• In rats and non-human primates, administration of PT-141 produces erections (Molinoff et al., 2003)
• In female rats, precopulatory behaviours regarded as analogous to sexual arousal have been evoked (Shadiack et al., 2007)
• Systemic dosing raises c-Fos in the hypothalamus; together with the known receptor distribution this forms a consistent picture of a centrally acting melanocortin agonism

Human studies

• Early proof of concept (Diamond et al., 2006): in a double-blind crossover study, 18 premenopausal women with an arousal disorder received a single intranasal 20 mg dose or placebo; significantly more reported moderate or high desire after bremelanotide (P = 0.0114), while measured vaginal vasocongestion did not change significantly. A subjective outcome thus moved where a physiological one did not. Doses are reported as facts about the study, not directions for use.
• Phase 3 RECONNECT (Kingsberg et al., 2019): two identical randomized, double-blind, placebo-controlled trials (301 and 302) evaluated bremelanotide 1.75 mg subcutaneously, as needed, over 24 weeks in premenopausal women with HSDD; of 1,267 randomized, 1,202 formed the efficacy population. Sexual desire (FSFI-desire) rose and related distress fell versus placebo (integrated +0.35 desire, −0.33 distress; both P < 0.001).
• A critical appraisal (Mayer & Lynch, 2020) notes the statistically significant outcomes pair with a clinically modest effect

Safety data from research

• Observations reported in the trials were largely mild to moderate and tolerability-related; most frequent were nausea (≈40%), flushing (≈20%) and headache (≈11%) (Kingsberg et al., 2019; Mayer & Lynch, 2020)
• The FDA-approved label additionally notes a transient rise in blood pressure after administration and focal hyperpigmentation with repeated use, and describes a maximum of one administration per 24 hours and no more than eight per month
• These points are recorded as facts about the trials and the approved label, not as a recommendation

Research context

For laboratories, PT-141 is valuable primarily as a pharmacological probe of central melanocortin signalling. MC4R is strongly expressed in the medial preoptic area (mPOA) of the hypothalamus, a region the central melanocortin system uses to regulate sexual response as well as energy balance, metabolism and stress response, making the compound a tool that reaches beyond its registered indication.

The regulatory picture belongs to the reading of the evidence. The FDA approval concerns one specific indication in premenopausal women in the United States; the reported effect sizes in the pivotal trials were statistically significant but modest in absolute terms, a point independent reviews have emphasised.

Open questions

The evidence for bremelanotide is stronger than for most peptides in this field, but its clinical reach is narrow and largely single-programme. Mechanistic work on MC4R signalling and central neuropeptide pathways is the natural next step.

• The clinical base derives largely from a single sponsor programme and predominantly U.S. sites; independent replication is limited
• The effect sizes in the phase 3 trials are statistically convincing but clinically modest
• The human mechanism is inferred from receptor pharmacology and animal models, not confirmed with a direct biomarker in humans
• Nearly all clinical work concerns sexual function; the broader melanocortin biology PT-141 engages is clinically almost unexplored
• No EMA registration; the European regulatory position differs from the U.S.

Research outlook

MC4R signalling in metabolism, energy balance and stress response, where PT-141 serves as a pharmacological tool

Central neuropeptide pathways from the hypothalamic mPOA to downstream dopaminergic circuits

Independent replication beyond the original sponsor programme

Scientific interest

Central melanocortin signalling via MC4R

Hypothalamic mPOA–dopaminergic circuitry

α-MSH-derived melanocortin pharmacology

MC4R biology beyond the registered indication

Specifications

References

1. PT-141: a melanocortin agonist for the treatment of sexual dysfunction. · Molinoff PB, Shadiack AM, Earle D, Diamond LE, Quon CY. · Annals of the New York Academy of Sciences · 2003
2. An effect on the subjective sexual response in premenopausal women with sexual arousal disorder by bremelanotide (PT-141), a melanocortin receptor agonist. · Diamond LE, Earle DC, Heiman JR, et al. · J Sex Med · 2006
3. Bremelanotide: an overview of preclinical CNS effects on female sexual function. · Pfaus J, Giuliano F, Gelez H. · Journal of Sexual Medicine · 2007
4. Bremelanotide: First Approval. · Dhillon S, Keam SJ. · Drugs · 2019
5. Bremelanotide for the Treatment of Hypoactive Sexual Desire Disorder: Two Randomized Phase 3 Trials. · Kingsberg SA, Clayton AH, Portman D, et al. · Obstetrics & Gynecology · 2019
6. Bremelanotide: New Drug Approved for Treating Hypoactive Sexual Desire Disorder. · Mayer D, Lynch SE. · Annals of Pharmacotherapy · 2020
7. The neurobiology of bremelanotide for the treatment of hypoactive sexual desire disorder in premenopausal women. · Pfaus JG, Sadiq A, Spana C, Clayton AH. · CNS Spectrums · 2021
8. Bremelanotide and flibanserin for low sexual desire in women: the fallacy of regulatory precedent. · Mintzes B, Tiefer L, Cosgrove L. · Drug Ther Bull · 2021
9. Targeting the central melanocortin system for the treatment of metabolic disorders. · Sweeney P, Gimenez LE, Hernandez CC, Cone RD. · Nature Reviews Endocrinology · 2023

Availability

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