Research Brief S25KX Strategies for Extending the Half-Life of Vasoactive Intestinal Peptide (VIP)

Kamil Khoury
0 comments

Prepared by: Kamil Khoury

Date: September 30, 2025
Intended Use: Research‑use only; not medical advice.

Disclaimer: Educational content for research‑use only. This document does not provide medical advice, diagnosis, treatment, or dosing guidance.

Executive Summary

Why VIP is short‑lived. Vasoactive intestinal peptide (VIP; 28 aa) is rapidly inactivated in plasma (human IV discontinuation t½ ≈ 1 min, MCR ≈ 9 mL·kg⁻¹·min⁻¹, Vd ≈ 14 mL·kg⁻¹), driven by proteolysis (notably neprilysin, NEP) and organ extraction, not distribution. Dipeptidyl‑peptidase‑4 (DPP‑4) prefers X‑Pro/X‑Ala; VIP’s N‑terminus is His‑Ser, so DPP‑4 is not the primary driver. Class‑B GPCR activation by VPAC1/VPAC2 requires unhindered N‑terminal access for the peptide to engage the receptor core. [Domschke, Gut, 1978; PMID 730072/PMC1412244] [Suzuki, Circ Res, 1996; PMID 8770140] [Mentlein, FEBS J, 1993; PMID 8100523] [Couvineau, Front Endocrinol, 2012; PMC3499705]

Most promising extension strategies.

  1. Conformational constraint (cyclic analogs) such as RO 25‑1553 → strong functional persistence and potency in airway models. [O’Donnell, JPET, 1994; PMID 7932180; Gourlet, Br J Pharmacol, 1997; PMID 9145428]

  2. PEGylation ≤5 kDa (C‑terminal/site‑specific) → stability ↑ with ~30× affinity penalty; 24 h PD shown in sensitized rats. [Onoue, EJPS, 2013; DOI 10.1016/j.ejps.2013.04.011]

  3. Pulmonary liposomal delivery → most VIP‑specific formulation evidence; protects against airway proteolysis. [Hajós, Int J Pharm, 2008; PMID 18328650; Stark, J Aerosol Med, 2008; PMID 18555674]

Top 3 recommendations (research‑use only).

  • Advance a cyclic VIP panel (RO‑like) — strong lung efficacy + manageable CMC.

  • Bracket PEGylation at 2–5 kDa — quantify potency–PK trade space using the Onoue 5 kDa benchmark.

  • Pair best chemotype with liposomal inhalation (DPI/nebulized) — most mature VIP‑specific formulation dataset.

Abbreviations

VIP: vasoactive intestinal peptide · VPAC1/VPAC2: VIP/PACAP receptors 1/2 · NEP: neprilysin · DPP‑4: dipeptidyl‑peptidase‑4 · FcRn: neonatal Fc receptor · HSA: human serum albumin · ELP: elastin‑like polypeptide · XTEN: unstructured hydrophilic polypeptide tag · ISFI/ISFD: in‑situ forming implant/depot · QbD: quality by design · COGs: cost of goods · CMC: chemistry, manufacturing and controls · PD: pharmacodynamics · PK: pharmacokinetics · DPI: dry‑powder inhaler · NHP: non‑human primate · SPPS: solid‑phase peptide synthesis · SEC‑MALS: size‑exclusion chromatography–multi‑angle light scattering · DLS: dynamic light scattering.

Refined Full Brief 

1) Mechanistic Basis for VIP’s Short Half‑Life

PK profile. After IV discontinuation in humans, plasma VIP decays mono‑exponentially (t½ ≈ 1 min; MCR ≈ 9 mL·kg⁻¹·min⁻¹; Vd ≈ 14 mL·kg⁻¹), supporting rapid metabolic inactivation rather than extensive distribution. [Domschke, Gut, 1978; PMID 730072/PMC1412244]

Proteolysis. NEP (EC 3.4.24.11) modulates VIP responses in vascular/lung tissues; NEP inhibition potentiates VIP effects. DPP‑4 removes X‑Pro/X‑Ala from P1′; VIP begins His‑Ser, thus not a canonical DPP‑4 substrate. [Suzuki, Circ Res, 1996; PMID 8770140] [Mentlein, FEBS J, 1993; PMID 8100523]

Organ extraction & receptor cycling. Pulmonary/hepatic extraction accelerates loss (animal data). Class‑B GPCR binding requires N‑terminal access; steric bulk near the VIP N‑terminus can impair potency or alter receptor bias/internalization. [Couvineau, Front Endocrinol, 2012; PMC3499705; Lu, IJMS, 2022; DOI 10.3390/ijms23158069]

Readout distinction. Several analogs report functional persistence (sustained bronchodilation/PD) without measured plasma t½; where absent, PD duration is cited and plasma PK is marked [Verify].

2) Modification Strategies (Peptide‑Level Engineering)

2.1 Sequence substitution & terminal protection. Reduce endo/exopeptidase cleavage while preserving the N‑terminal pharmacophore. Example: IK312532 ([R15,20,21,L17]‑VIP‑GRR) retained structure and served as a 5 kDa PEG handle with improved stability. [Ohmori, Regul Pept, 2004; DOI 10.1016/j.regpep.2004.04.029] [Onoue, EJPS, 2013]

2.2 Conformational constraint (cyclization/stapling). RO 25‑1553 shows 24–89× potency vs VIP and long‑acting bronchodilation; plasma t½ typically not reported (functional persistence dominates). [O’Donnell, JPET, 1994; PMID 7932180; Gourlet, Br J Pharmacol, 1997; PMID 9145428]

2.3 Polymer conjugation (PEGylation). 5 kDa PEG‑VIP (C‑terminal) preserved secondary structure but showed ~30×affinity weakening (IC₅₀ 2.8 nM → ~82 nM) with substantial stability gains; 24 h in‑vivo activity in sensitized rats (DPI). Potency–PK trade‑off quantified. [Onoue, EJPS, 2013]

2.4 Lipidation & albumin‑binding motifs. Attach C16–C18 chains via spacers at non‑pharmacophoric sites to confer albumin binding and reduce filtration/proteolysis (GLP‑1 precedent). Stearyl‑norleucine‑VIP (SNV) improved persistence/activity. Place away from the N‑terminus to maintain VPAC fidelity. [Eger, Front Pharmacol, 2021; PMID 34025407/PMC8131842]

2.5 Long‑lived fusion scaffolds.

  • Fc/HSA fusions leverage FcRn/albumin recycling (class precedents ~5 days t½). For VIP, steric shielding of the N‑terminus is the key risk—use long, flexible linkers. [FDA Trulicity label, 2020; FDA Albiglutide Clin Pharm]

  • XTEN/ELP fusions extend exposure to multi‑day timeframes; ELP may form in situ depots. N‑terminal display remains critical. [Despanie, ADDR, 2015/2016; PMC5767577]

3) Delivery Approaches (Formulation/Device)

3.1 Liposomes & inhalable carriers (VIP‑specific). Nano‑liposomal VIP (nebulizable/DPI) protects against proteolysis and prolongs lung effect; this is the most mature VIP‑specific formulation evidence base. [Hajós, Int J Pharm, 2008; Stark, J Aerosol Med, 2008]

3.2 Polymeric depots: PLGA microspheres & ISFI/ISFD. PLGA supports weeks→months release; ISFI/ISFDprovides simpler manufacturing with FDA‑mapped gaps. Track deamidation/oxidation/acylation under release. [Wan, J Control Release, 2023; FDA ISFI Gap, 2021]

3.3 Targeted carriers (considerations). VIP as a targeting ligand is feasible, but for self‑delivery, co‑display risks self‑competition and complex PK. Favor generic stabilization (liposomes/depots) unless a strong tissue‑targeting rationale exists. [Verify]

Strategy Comparison — Table (T1)

Evidence Strength: A robust human/strong multi‑model preclinical; B moderate preclinical or strong platform analogy; C preliminary/in vitro.

Feasibility Plan 

Phase 0 — Liability mapping (4–6 weeks). Incubate native VIP in human plasma and NEP‑rich membranes ± NEP inhibitors; map scissile bonds by LC‑MS/MS to guide substitutions/cyclization. [Suzuki, Circ Res, 1996]

Phase 1 — Parallel chemotype panels.

  • Cyclic VIP (head‑to‑tail; lactam/stapled; RO‑like).

  • PEGylated VIP ≤5 kDa (C‑terminus or solvent‑exposed Lys) per Onoue.

  • Lipidated VIP (C16/C18 + spacer) tuned to avoid N‑terminal occlusion; quantify albumin binding.

  • ELP/XTEN fusions with long flexible linkers ensuring N‑terminal exposure.

Phase 2 — In‑vitro triage (2–4 weeks/iteration).
Stability in human plasma ± NEP (t½, intrinsic CL); VPAC1/VPAC2 binding (Kd/IC₅₀), Gs–cAMP efficacy, β‑arrestin recruitment, internalization/recycling (bias factors). Bioanalytics: ligand‑binding assay validated against fragment cross‑reactivity + LC‑MS/MS intact peptide.

Phase 3 — PK/PD (rodent → NHP as needed).
Routes: IV, SC, pulmonary (nebulized/DPI liposomes). Readouts: plasma/tissue concentrations (LC‑MS/MS), lung PD (airway resistance/vasorelaxation), safety telemetry.

Phase 4 — Formulation down‑selection.
Pulmonary: nano‑liposomal VIP/lead analog; nebulizer/DPI stress; post‑nebulization integrity. Systemic LAI: start ISFI(speed) in parallel with PLGA microspheres; build QbD risk registers from FDA ISFI gap analysis and PLGA analytics literature.

Phase 5 — Developability/CMC.
Track deamidation (Asn/Gln), oxidation (Met), acylation (PLGA). Analytics: SEC‑MALS, DLS, LC‑MS/MS peptide mapping; residual solvent; release integrity; DSC for lyophilized forms. Manufacture: SPPS, site‑specific PEG/lipidconjugation, recombinant ELP/XTEN/Fc/HSA.

Editorial Change Log 

  • Standardized abbreviations and SI units; definitions at first use.

  • Clarified that rapid loss reflects proteolysis/organ extraction (high MCR, small Vd), not distribution.

  • Made DPP‑4 X‑Pro/X‑Ala preference vs VIP His‑Ser explicit.

  • Added functional persistence vs plasma t½ distinction; marked missing t½ as [Verify].

  • Expanded Onoue 5 kDa PEG example (IC₅₀ 2.8→82 nM; 24 h PD) to show potency–PK trade‑off.

  • Elevated liposomal/inhalation as most VIP‑specific formulation evidence.

  • Emphasized N‑terminal access/steric constraints for class‑B GPCRs; linker guidance.

  • Rebuilt T1 with Evidence Strength, TRL, and CMC notes.

  • Added risk register and phase‑gated plan with analytics.

  • Normalized references; flagged gaps as [Verify].

Gaps & Verification List

  • Plasma t½ for RO 25‑1553 and other cyclic/stapled VIP analogs often not reported. [Verify] → Single‑dose IV/SC PK in rats with LC‑MS/MS intact‑peptide assay; parallel PD.

  • Human‑matrix cleavage map for VIP (dominant scissile bonds). [Verify] → LC‑MS/MS mapping ± NEPinhibitors.

  • VIP‑specific PLGA/ISFI integrity data (deamidation/oxidation/acylation). [Verify] → Accelerated and real‑time release with LC‑MS/MS + SEC‑MALS/DLS.

  • Quantitative albumin‑binding for lipidated VIP (SNV, C16/C18 variants). [Verify] → HSA binding by SPR/ITC; translate to in‑vivo t½.

  • XTEN/ELP‑VIP fusion primary data beyond review mentions. [Verify] → Reproduce VPAC pharmacology; rodent PK.

  • PEG site/size SAR vs VPAC1/VPAC2. [Verify] → 2/5/10 kDa; C‑term vs Lys; cAMP/β‑arrestin bias profiling.

Reference Normalization

  1. Domschke S, et al. Gut. 1978. “Vasoactive intestinal peptide in man: pharmacokinetics …” PMID 730072 / PMC1412244.

  2. Suzuki H, et al. Circulation Research. 1996. “Neutral endopeptidase modulates VIP‑induced dilation …” PMID 8770140.

  3. Mentlein R. FEBS Journal. 1993. “DPP‑IV hydrolyses GIP/GLP‑1; VIP (His‑Ser) not significantly degraded.” PMID 8100523.

  4. Couvineau A, et al. Front Endocrinol. 2012. “VPAC1 receptor: structure & function.” PMC3499705.

  5. Lu J, et al. Int J Mol Sci. 2022. “Targeting VIP and PACAP receptor signaling.” DOI 10.3390/ijms23158069 / PMC9331257.

  6. O’Donnell M, et al. JPET. 1994. “RO 25‑1553: long‑acting VIP analog.” PMID 7932180.

  7. Gourlet P, et al. Br J Pharmacol. 1997. “RO 25‑1553 selective for VPAC2.” PMID 9145428.

  8. Yin J, et al. PLoS One. 2013. “Inhaled RO 25‑1553: pulmonary effects.” DOI 10.1371/journal.pone.0075861.

  9. Onoue S, et al. Eur J Pharm Sci. 2013;49:382‑389. “PEGylated IK312532 (5 kDa): IC₅₀ shift; DPI feasibility.” DOI 10.1016/j.ejps.2013.04.011.

  10. Ohmori Y, et al. Regul Pept. 2004. “[R15,20,21,L17]‑VIP‑GRR (IK312532): lung pharmacology.” DOI 10.1016/j.regpep.2004.04.029.

  11. Eger M, et al. Front Pharmacol. 2021. “Stearyl‑Norleucine‑VIP (SNV).” PMID 34025407 / PMC8131842.

  12. Hajós F, et al. Int J Pharm. 2008;357:286–294. “Inhalable liposomal VIP.” PMID 18328650.

  13. Stark B, et al. J Aerosol Med Pulm Drug Deliv. 2008;21:361–368. “Polymer‑grafted liposomal VIP.” PMID 18555674.

  14. Wan B, et al. J Control Release. 2023. “PLGA microspheres: advances & analytics.” PMID 37149041.

  15. FDA (OCP). 2021. “Scientific Gap Analysis of Polymeric ISFI Products (GDUFA).” [Verify Doc ID/URL].

  16. Knudsen LB. Drug Des Devel Ther. 2019. “Discovery & development of liraglutide.” PMC6474072.

  17. EMA EPAR (Ozempic/semaglutide). 2017–2021. EPAR Ozempic.

  18. FDA Label (Trulicity/dulaglutide). 2020. t½ ~5 days.

  19. FDA Clin Pharm Review (Albiglutide). 2014. t½ ~5 days (NDA 125431).

Quality Gates — Confirmation

  • Numerical sanity: Human VIP t½, MCR, Vd align with metabolic inactivation, not distribution.

  • Mechanistic specificity: DPP‑4 preference (X‑Pro/X‑Ala) vs VIP His‑Ser explicitly stated.

  • Design constraints: Emphasized N‑terminal access; steric risks for PEG/fusions; linker guidance.

  • Potency vs PK trade‑off: Onoue 5 kDa PEG (IC₅₀ 2.8→82 nM; 24 h PD) made explicit.

  • Pulmonary evidence: Liposomal/inhalation identified as most VIP‑specific/mature evidence base.

  • No overclaiming: Where plasma t½ not reported, cite functional persistence and mark [Verify].

Decision Rationale 

Priority went to strategies with VIP‑specific data and class‑B GPCR constraints (N‑terminal access). Cyclic analogsprovide the strongest functional persistence with tractable CMC. PEGylation (≤5 kDa) quantifies the potency–PK trade‑off while enabling manufacturable exposure gains. Liposomal inhalation offers the most direct VIP formulation evidence for lung protection/persistence. Platform solutions (Fc/HSA, XTEN/ELP) can reach week‑scale PK but demand careful linker engineering to protect N‑terminal binding and should run in parallel once a potent, receptor‑faithful chemotype is selected. Regulatory and CMC readiness informed the phase‑gated plan and risk controls above.

Leave a comment