Cone Snail Venom–Derived Peptide Shows Potential as Nonopioid Treatment for Inflammatory Pain

A peptide derived from cone snail venom reduced inflammatory pain–associated behavior in mice without causing sedation or motor impairment, according to preclinical findings published in Nature Structural & Molecular Biology. The peptide, χ-conotoxin AoIA, selectively inhibits the norepinephrine transporter (NET), offering a potential foundation for developing a novel class of nonopioid analgesics.¹

These findings are especially notable because AoIA demonstrated antinociceptive activity following subcutaneous administration. Other conotoxin-based analgesics, including FDA-approved ziconotide (Prialt; TerSera Therapeutics), require intrathecal administration, limiting their use to carefully selected patients with severe chronic pain.¹˒² Although AoIA remains in the earliest stages of development, its systemic activity may support the investigation of less invasive conotoxin-derived pain therapies.

AoIA Demonstrates Potent, Selective NET Inhibition

Cone snails produce venom containing biologically active peptides known as conotoxins, which can act with high selectivity on receptors, transporters, and ion channels in the nervous system. This selectivity has made conotoxins valuable as pharmacologic research tools and potential therapeutic agents.¹

AoIA was originally isolated from the venom of Conus araneosus. Investigators identified it as a member of the χ-conotoxin family based on its amino acid sequence, disulfide connectivity, and structural similarities to other χ-conotoxins. Members of this family target NET, which removes norepinephrine from the synaptic cleft and helps regulate noradrenergic signaling.¹˒³

Norepinephrine plays an important role in pain modulation. Increasing synaptic norepinephrine can suppress nociceptive transmission through descending inhibitory pathways and α₂-adrenergic receptor signaling. This mechanism contributes to the analgesic effects of certain medications that inhibit norepinephrine reuptake, including some agents used for chronic and neuropathic pain.³

In laboratory testing, AoIA inhibited human NET activity with a half-maximal inhibitory concentration (IC₅₀) of 1.06 ± 0.48 μM. It was approximately 10 times more potent than MrIA, a previously characterized χ-conotoxin, which had an IC₅₀ of 10.9 ± 4.6 μM in the same assay.¹

AoIA also demonstrated marked selectivity. It did not inhibit the serotonin or dopamine transporters at concentrations up to 100 μM, despite the structural similarities among the 3 monoamine transporters.¹

Investigators additionally tested AoIA against several targets involved in pain signaling. The peptide did not bind to μ-, δ-, or κ-opioid receptors and did not directly affect transient receptor potential ankyrin 1, transient receptor potential vanilloid 1, voltage-gated calcium channels, or the voltage-gated sodium channels NaV1.7 and NaV1.8.¹

Suzetrigine (Journavx), a selective NaV1.8 inhibitor, was used as a positive control during the sodium-current experiments. However, the investigators did not compare the analgesic efficacy of AoIA and suzetrigine. The assay instead helped demonstrate that AoIA’s activity was not attributable to direct NaV1.8 inhibition.¹

Collectively, these findings support selective NET inhibition—rather than opioid receptor activation or direct sodium-channel inhibition—as the primary mechanism underlying AoIA’s observed effects.

Structural Analysis Reveals an Unusual Binding Mechanism

Using cryogenic electron microscopy, the investigators resolved the structure of AoIA bound to human NET at 2.77-Å resolution. AoIA displayed an atypical binding pattern that encompassed the transporter’s outer vestibule and extended into its central substrate-binding site.¹

The peptide effectively acted as a molecular wedge, stabilizing NET in an outward-open configuration and interfering with norepinephrine transport. Structural differences among NET and the dopamine and serotonin transporters also helped explain AoIA’s selectivity. Larger amino acid residues within the corresponding regions of the dopamine and serotonin transporters would be expected to interfere with AoIA binding.¹

Identifying these interactions may help researchers determine which structural features are necessary for potency and selectivity. The findings could therefore inform the development of synthetic AoIA analogs with improved stability, pharmacokinetic properties, or suitability for clinical administration.

Subcutaneous AoIA Reduces Inflammatory Pain Behavior

Researchers evaluated subcutaneous AoIA in male mice using models of acute nociceptive and inflammatory pain. AoIA did not significantly increase withdrawal latency in a radiant-heat tail-flick test, indicating that the peptide did not reduce acute thermal nociception at the tested dose.¹

In the formalin model, AoIA did not alter pain behavior during phase I, which represents the initial nociceptive response following formalin injection. However, it produced dose- and time-dependent reductions during phase II, which is associated with sustained nociceptor activation, inflammation, and sensitization.¹

At doses of 7.6 and 19 μmol/kg, AoIA reduced pain-associated behaviors—including paw licking, biting, lifting, and flinching—by 55% ± 31% and 67% ± 39%, respectively, compared with saline. Its calculated median antinociceptive effective dose was 8.24 μmol/kg (95% CI, 3.06-22.2).¹

In comparison, MrIA did not demonstrate antinociceptive activity when administered subcutaneously at an equimolar dose of 19 μmol/kg. Earlier research into MrIA and its synthetic analog Xen2174 largely focused on intrathecal administration, making the systemic activity observed with AoIA particularly relevant.⁴

AoIA also did not impair motor performance in the rotarod test at its highest effective dose, suggesting that the reduction in pain behavior was not caused by sedation or motor dysfunction. Additionally, the peptide was undetectable in postmortem mouse brain samples. The investigators noted that this finding may indicate a peripheral mechanism, although AoIA’s precise site of action remains uncertain.¹

Further Research Needed Before Clinical Translation

The findings support AoIA as a possible starting point for developing selective, nonopioid NET inhibitors. However, the research remains preclinical and was limited to cellular experiments, structural analyses, and short-term behavioral testing in male mice.

AoIA did not demonstrate efficacy in the acute thermal pain model or the initial phase of the formalin test. Studies are still needed to evaluate its pharmacokinetics, duration of activity, long-term safety, cardiovascular effects, efficacy in female animals, and performance in additional inflammatory and neuropathic pain models.¹

Earlier experience with Xen2174 also illustrates the difficulty of translating conotoxin research into clinical pain therapies. Although Xen2174 demonstrated promising analgesic activity in preclinical studies, it did not produce a significant difference compared with placebo in a small phase 2 study.⁴˒⁵

Nevertheless, the combination of selective NET inhibition, structural specificity, subcutaneous activity, and an absence of observed sedation supports additional investigation of AoIA. The findings may ultimately help researchers develop a new mechanistic approach to nonopioid pain management.

REFERENCES

1. Belleza, O.J.V., Zhang, H., Schmidhammer, H. et al. Structural and functional basis of antinociceptive action of χ-conotoxin AoIA at the noradrenaline transporter. Nat Struct Mol Biol (2026). https://doi.org/10.1038/s41594-026-01838-z

2. Prialt—ziconotide acetate injection, solution. Prescribing information. DailyMed. Updated December 5, 2025. Accessed August 3, 2026. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=57376a5b-4530-9018-e063-6394a90a9afe&version=1

3. Pertovaara A. The noradrenergic pain regulation system: a potential target for pain therapy. Eur J Pharmacol. 2013;716(1-3):2-7. doi:10.1016/j.ejphar.2013.01.067

4. Brust A, Palant E, Croker DE, et al. chi-Conopeptide pharmacophore development: toward a novel class of norepinephrine transporter inhibitor (Xen2174) for pain. J Med Chem. 2009;52(22):6991-7002. doi:10.1021/jm9003413

5. Okkerse P, Hay JL, Sitsen E, et al. Pharmacokinetics and pharmacodynamics of intrathecally administered Xen2174, a synthetic conopeptide with norepinephrine reuptake inhibitor and analgesic properties. Br J Clin Pharmacol. 2017;83(4):751-763. doi:10.1111/bcp.13176