PACAP38
Also known as: ADCYAP1 peptide, ADCYAP1 peptide (38aa form), PACAP, PACAP-38, PACAP‑38, Pituitary Adenylate Cyclase-Activating Polypeptide 38, Pituitary adenylate cyclase‑activating polypeptide
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Summary
Pituitary adenylate cyclase‑activating polypeptide 38 (PACAP38) is a 38‑amino‑acid neuropeptide that acts as a hormone, neurotransmitter and trophic factor. It binds to three related G‑protein‑coupled receptors (PAC1, VPAC1, VPAC2) and is implicated in neuroendocrine regulation, vascular tone and migraine pathophysiology. In research, PACAP38‑derived radioligands are explored for PET imaging of tumors that overexpress its receptors, and the peptide itself is used to provoke migraine attacks in human models, highlighting its potential as a therapeutic target.
Mechanism of Action
PACAP38 engages three class‑B GPCRs—PAC1 (high affinity) and VPAC1/VPAC2 (shared with VIP). Receptor activation stimulates adenylate cyclase, raising intracellular cAMP, and can also activate phospholipase C, generating IP3 and DAG. These cascades modulate neuronal excitability, hormone release, vasodilation and neurotrophic signaling. Overexpression of VPAC receptors on many cancers provides a binding site for PACAP‑based imaging agents, while PACAP‑driven signaling in trigeminal pathways contributes to migraine initiation.
What the Research Shows
Preclinical studies have produced radiolabeled PACAP/VIP analogues such as 64Cu‑TP3939, which bind VPAC receptors with nanomolar affinity and enable PET imaging of prostate and breast cancer xenografts. Clinical migraine research shows that intravenous PACAP38 reliably triggers migraine‑like attacks in susceptible individuals; a 2025 randomized trial demonstrated that blocking CGRP with eptinezumab did not reduce PACAP‑induced attacks, indicating a CGRP‑independent pathway. Reviews identify PACAP38 as a promising biomarker and therapeutic target, though an anti‑PAC1 monoclonal antibody trial reported negative results. Ongoing proof‑of‑concept trials are evaluating PAC1 antagonism for migraine prevention.
Reported Benefits
In the diagnostic arena, PACAP‑based PET probes have shown specific tumor uptake in animal models, suggesting a non‑invasive method to visualize VPAC‑expressing cancers. For migraine, PACAP38 provocation studies clarify disease mechanisms and support the development of PAC1‑targeted therapies, which could complement existing CGRP‑focused treatments. The peptide’s broad physiological actions also make it a valuable tool for studying neuroendocrine and vascular biology.
Limitations of the Evidence
Evidence for tumor imaging is limited to preclinical experiments; human safety, optimal dosing and regulatory approval remain untested. Migraine provocation data demonstrate variability in individual response, and the negative outcome of a PAC1 antibody trial raises questions about therapeutic efficacy. Overall, clinical translation is pending, and the peptide’s pleiotropic effects complicate interpretation of outcomes.
Safety Considerations
Intravenous infusion of PACAP38 can induce migraine attacks, headache, and vasodilatory changes such as increased superficial temporal artery diameter and facial skin blood flow. In the cited trial, no serious adverse events were reported, but the provoked symptoms underscore the need for careful monitoring. As a vasoactive peptide, potential hypotension or flushing may occur, especially with systemic administration.
How It Is Administered
Research protocols have employed intravenous infusion of PACAP38 (e.g., 10 pmol/kg/min for 20 minutes) to provoke migraine, and intravenous injection of radiolabeled analogues for PET imaging. Other experimental routes include intracerebroventricular, intranasal and subcutaneous delivery, typically using sterile peptide solutions formulated for short‑term use.
Routes of Administration
Goals & Uses
- Migraine prophylaxisNeurologyModerate
- NeuroprotectionNeurologyModerate
- CardioprotectionCardiovascularLow
- PTSD and stress modulationPsychiatry / ResearchModerate
- Regulation of insulin secretionEndocrinologyLow
- Migraine research and provocation modelNeurologyHigh
- Neuroprotection after ischemic strokeNeuroscienceModerate
- Anti-inflammatory effectsInflammationModerate
Contraindications
- Severe hypotension or cardiovascular instabilityCardiovascularHigh
- Known hypersensitivity to PACAP38 or related peptidesAllergyHigh
- Active migraine or severe headache disorder (provocative dosing)NeurologyModerate
- Known hypersensitivity to PACAP‑38ImmunologicHigh
- Severe hypotensionCardiovascularModerate
Adverse Effects
- Facial flushingCardiovascular/DermatologicCommon
- HeadacheNeurologicCommonPain in the head or upper neck
- HypotensionCardiovascularUncommonLow blood pressure
- FlushingVascularCommonWarmth and redness of the skin
- TachycardiaCardiovascularUncommonAbnormally fast heart rate
- NauseaGastrointestinalUncommonFeeling of sickness or urge to vomit
- Headache / migraine-like attackNeurologicalCommon
Drug Interactions
- Triptans / ErgotaminesLow
- CYP‑modulating agentsLow
- Antihypertensive agentsModerate
- Other vasodilators (e.g., nitrates)Moderate
Population Constraints
- PregnancyReproductive SafetyRelative
- Pediatric populationsAgeRelative
- Pediatric patientsAgeRelative
- Patients with cardiovascular diseaseComorbidityRelative
- Pregnant womenReproductiveRelative
Regulatory Status
- European UnionUnapprovedNo marketing authorization; used in clinical trials.
- United StatesUnapprovedInvestigational New Drug (IND) status for clinical studies only.
- United KingdomUnapprovedNo approved therapeutic use.
Not approved for any indication; has been evaluated in early‑phase clinical trials (Phase I/II) for migraine and neuroprotection.
Evidence & Sources
- Journal ArticleModerateCheng KT, Thakur ML2004-01-01T00:00:00.000000Z
- Journal ArticleModerateAl-Karagholi MA, et al.2025-01-01T00:00:00.000000Z
- Journal ArticleModerateYan BM, et al.2021-01-01T00:00:00.000000Z
- Journal ArticleModerateFahrenkrug J2006-01-01T00:00:00.000000Z
- Journal ArticleModerateMoreno-Ajona D, Villar-Martínez MD, Goadsby PJ2021-01-01T00:00:00.000000Z
- Journal ArticleModerateAshina H, et al.2017-01-01T00:00:00.000000Z
Frequently Asked Questions
What is the primary biological role of PACAP38?
PACAP38 is a neuropeptide that activates PAC1, VPAC1 and VPAC2 receptors, stimulating cAMP and phospholipase C pathways. This leads to hormone release, neuronal modulation, vasodilation and neurotrophic effects across the hypothalamic‑pituitary‑adrenal axis.
Can PACAP38 be used to diagnose cancer in patients?
Radiolabeled PACAP‑based agents have shown tumor‑specific uptake in animal models, but no human diagnostic studies have been published yet. Clinical use for cancer imaging remains experimental and unapproved.
Why does PACAP38 trigger migraines even when CGRP is blocked?
A 2025 randomized trial showed that eptinezumab, a CGRP‑blocking antibody, did not reduce PACAP38‑induced migraine attacks, suggesting that PACAP activates migraine pathways independently of CGRP, likely via PAC1‑mediated neuronal and vascular mechanisms.
Are there any approved medicines that target PACAP38?
No PACAP‑targeted drug has received regulatory approval. Anti‑PAC1 antibodies are in early clinical testing, and PACAP‑based imaging probes are still in preclinical development.
What safety concerns should be considered in research using PACAP38?
Intravenous PACAP38 can provoke migraine, cause vasodilation, and potentially lead to transient hypotension or flushing. In controlled studies, serious adverse events have not been reported, but monitoring of headache intensity and vascular signs is essential.
What is PACAP38 used for?
PACAP38 is educationally associated with: Migraine prophylaxis, Neuroprotection, Cardioprotection, PTSD and stress modulation, Regulation of insulin secretion, Migraine research and provocation model, Neuroprotection after ischemic stroke, Anti-inflammatory effects. Educational only — not medical advice.
How is PACAP38 administered?
Recorded routes of administration: Intracerebroventricular, Intranasal, Intravenous, Subcutaneous.
What are the potential side effects of PACAP38?
Reported adverse effects include: Facial flushing, Headache, Hypotension, Flushing, Tachycardia, Nausea, Headache / migraine-like attack. This list is not exhaustive — consult a qualified clinician.
Who should avoid PACAP38?
Recorded contraindications: Severe hypotension or cardiovascular instability, Known hypersensitivity to PACAP38 or related peptides, Active migraine or severe headache disorder (provocative dosing), Known hypersensitivity to PACAP‑38, Severe hypotension. Consult a qualified clinician before use.