PMX-205

Summary

PMX‑205 is a cyclic hexapeptide that blocks the complement C5a receptor 1 (C5aR1), a G‑protein‑coupled receptor involved in inflammatory signaling. In pre‑clinical studies it has been used to explore treatment of radiation‑induced cognitive decline, neurodegenerative disease, inflammatory bowel disease, and glioblastoma. The compound is currently a research tool and has not received regulatory approval for any therapeutic indication.

Mechanism of Action

PMX‑205 binds to C5aR1 and prevents activation by the anaphylatoxin C5a. By antagonising this GPCR, downstream G‑protein signaling that drives production of pro‑inflammatory cytokines (IL‑1β, TNF‑α, IL‑6) and recruitment of microglia and neutrophils is reduced. In the brain this limits microglial activation, astrocyte gliosis, and complement‑mediated synaptic pruning. In tumor cells, C5aR1 inhibition lowers ERK1/2‑driven METTL3 activity, decreasing m6A‑stabilised GPX4 expression and thereby promoting ferroptotic cell death.

What the Research Shows

Multiple mouse studies have examined PMX‑205. Krattli et al. showed that oral, brain‑penetrant PMX‑205 reversed radiation‑induced cognitive decline, reduced microglial activation, and did not impair tumor control. Gomez‑Arboledas et al. reported that genetic or pharmacologic C5aR1 blockade rescued excessive synaptic pruning and improved long‑term potentiation in two Alzheimer models. Cui et al. encapsulated PMX‑205 in pH‑sensitive nanoparticles for colon delivery, demonstrating protection against DSS‑induced colitis comparable to C5aR1‑deficient mice. Meng et al. found that PMX‑205 promoted ferroptosis and slowed glioblastoma growth in intracranial xenografts via METTL3‑dependent GPX4 regulation. A recent review highlighted pre‑clinical efficacy of C5aR1 antagonists, including PMX‑205, in Alzheimer and ALS models. Across studies, the peptide was administered orally, subcutaneously, intracranially, or topically in experimental settings.

Reported Benefits

Pre‑clinical evidence suggests PMX‑205 can (1) protect cognition after cranial irradiation by dampening neuroinflammation, (2) reduce pathological synaptic loss and improve electrophysiological plasticity in Alzheimer mouse models, (3) alleviate experimental colitis when delivered to the colon via nanoparticle formulation, and (4) inhibit glioblastoma progression by inducing ferroptosis. In each case, the benefits were observed without compromising the primary therapeutic effect (e.g., tumor control after radiotherapy).

Limitations of the Evidence

All reported outcomes are derived from animal experiments; no human efficacy data exist for these indications. The peptide’s short half‑life and rapid metabolism limit oral use, prompting formulation strategies that have not yet been validated clinically. Safety data are limited to early‑phase trials in healthy volunteers, and adverse‑event profiles in disease states are unknown. Moreover, effects on plaque load in Alzheimer models were modest, indicating that C5aR1 blockade may need to be combined with other therapies.

Safety Considerations

PMX‑205 has been described as safe in early clinical testing with healthy participants, but detailed adverse‑effect information is not provided in the literature. In animal studies, no overt toxicity was reported for the dosing regimens used, including intracranial injection and oral nanoparticle administration. Potential risks include off‑target immunomodulation, given C5aR1’s role in host defense, and unknown effects of chronic complement inhibition. Caution is warranted when extrapolating to patients with compromised immunity.

How It Is Administered

Research use of PMX‑205 has employed several routes: intracranial injection for direct brain studies, subcutaneous injection, topical application, and oral delivery of a brain‑penetrant formulation. A colon‑targeted oral nanoparticle system has been developed to release the peptide in the distal gut. Formulations are typically peptide solutions or polymer‑based nanoparticles; no commercial dosage forms exist.

Routes of Administration

Goals & Uses

• Traumatic brain injury inflammationNeuroprotectionLow
• anti‑inflammatory therapyImmunomodulationModerate
• NeuroprotectionNeurologyModerate
• Inflammatory skin diseaseDermatology / Anti InflammatoryLow
• Sepsis mitigationInfectious DiseaseLow
• Complement-mediated inflammatory diseaseImmunomodulationLow
• Neuroinflammation reduction in Alzheimer's diseaseNeuroprotectionLow

Contraindications

• Known hypersensitivity to cyclic peptide componentsAllergyHigh
• Severe immunodeficiencyImmunologyModerate

Adverse Effects

• Injection site irritationLocal ReactionCommon
• Local irritation (topical)DermatologicalUnknown
• ImmunosuppressionImmunologicalUnknown

Drug Interactions

• Other complement inhibitors (e.g., eculizumab)Moderate
• Complement inhibitors (e.g., eculizumab)Moderate

Population Constraints

• Pediatric populationsAgeRelative
• pediatric subjectsAgeRelative
• Pregnant or lactating womenReproductiveRelative
• Immunocompromised individualsImmunologicalRelative

Regulatory Status

• European UnionUnapprovedResearch chemical only.
• United StatesUnapprovedInvestigational peptide; no IND filed for therapeutic use.
• United KingdomUnapprovedNo MHRA authorization; research use only.

Investigational research tool; not approved for clinical use in any jurisdiction.

Evidence & Sources

• C5aR1 Inhibition Alleviates Cranial Radiation-Induced Cognitive Decline
  Journal ArticleLowKrattli RP Jr, et al.2026-01-01T00:00:00.000000Z
• C5aR1 signaling promotes region- and age-dependent synaptic pruning in models of Alzheimer's disease
  Journal ArticleLowGomez-Arboledas A, et al.2024-01-01T00:00:00.000000Z
• Colon-targeted complement C5a(1) receptor inhibition using pH-sensitive nanoparticles ameliorates experimental colitis
  Journal ArticleLowCui CS, et al.2025-01-01T00:00:00.000000Z
• Intracellular C5aR1 inhibits ferroptosis in glioblastoma through METTL3-dependent m6A methylation of GPX4
  Journal ArticleLowMeng X, et al.2024-01-01T00:00:00.000000Z
• Targeting the C5-C5aR1 axis: A promising therapeutic strategy for Alzheimer's disease and amyotrophic lateral sclerosis by unlocking neuroprotection
  Journal ArticleModerateGe TQ, Wang P, Guan PP2026-01-01T00:00:00.000000Z
• C5aR1 antagonism suppresses inflammatory glial responses and alters cellular signaling in an Alzheimer's disease mouse model
  Journal ArticleLowSchartz ND, et al.2024-01-01T00:00:00.000000Z

Frequently Asked Questions