Pharmacological exploration of the role of Acid-Sensing Ion Channels in pain – PharmASIC

We use the complementary expertise of both partners (Partner # 1 IPMC-UMR7275 and partner # 2 NEURO-DOL U1107), including :
- Molecular Biology, Biochemistry and Cell Biology (Partner # 1 and # 2).
- Electrophysiology (two-electrode voltage-clamp in Xenopus oocytes, patch-clamp, ex vivo skin-nerve recordings, in vivo extracellular recordings in the spinal cord) (Partner # 1).
- Pharmacology: animal toxins including the identification, purification and characterization of new specific toxins for ASIC channels (Partner # 1 and # 2).
- Pain models and behavior (Partner # 1 and # 2).

- Mambalgins are pain-relieving peptides that we recently discovered, which act through specific inhibition of Acid-Sensing Ion Channels (ASICs). ASICs form excitatory ion channels activated by protons. Mambalgins bind into the pH sensor (acidic pocket) of ASICs and block them through a pH-sensor trapping mechanism.
- The first full stepwise solid-phase peptide synthesis of mambalgin-1 allows us to solve its 3D crystal structure and to perform structure-activity studies to map the pharmacophore for ASIC channel inhibition. This work and the previous one open the way for the development of new optimized peptide variants.
- Mambalgins have an opioid-independent analgesic effect on both thermal and mechanical inflammatory pain upon systemic intravenous (i.v.) administration and are effective against neuropathic pain, demonstrating the participation of ASICs in neuropathic pain.
- Tissue acidification, which activates ASIC channels, is often associated with painful conditions. We have demonstrated, in collaboration with the rheumatology department of the Nice University Hospital and the STIM laboratory in Poitiers, that joint pain in humans would not necessarily be linked to an extracellular acidification, since non-acidic joint effusions from patients with pain constitutively activate ASIC3. This activation is lipid-dependent and the joint effusions contain high levels of lipids (especially lysophosphatidylcholine and arachidonic acid), which are primarily responsible for ASIC3 activation at resting pH 7.4 and evoke ASIC3-dependent pain behaviour in rodents. These data reinforce the therapeutic value that ASIC3 channels may have in the treatment of joint pain, and they open up new perspectives on the role of ASIC channels in the absence of tissue pH variation in pain and beyond.

Ongoing experiments involved:
- Identification and characterization from animal venoms of new specific peptide blockers of ASIC channels that can be used as pharmacological tools and may also have therapeutic value.
- Study of the properties and of the structure-function relationships of ASIC channels.
- Explore the physiological and pathophysiological role of ASIC channels in the peripheral and central nervous system in pain of different etiologies.

Papers:
1. Diochot et al. Pain. 2016 Mar;157:552-9. [ARTICLE]
2. Marra et al. EMBO J. 2016 Feb 15;35:414-28. [ARTICLE]
3. Mourier et al. J Biol Chem. 2016 Feb 5;291:2616-29. [ARTICLE]
4. Baron and Lingueglia. Neuropharmacology 2015 Jul;94:19-35. [REVUE]
5. Deval and Lingueglia. Neuropharmacology 2015 Jul;94:49-57. [REVUE]
6. Salinas et al. J Biol Chem, 2014, 289:13363-73. [ARTICLE]
7. Lingueglia, E. Biologie Aujourdhui 2014, 208:13-20. [REVUE]
8. Baron et al. Toxicon, 2013, 75:187-204. [REVUE]

International lectures :
1. 2015, 5th SFICT Workshop, Lisbon, Portugal.
2. 2014, 4th Biannual International Multidisciplinary Pain Congress, Eindhoven, Netherlands.
3. 2014, XXIII International Symposium on Medicinal Chemistry, Lisbon, Portugal.
4. 2014, Gordon Research Conference on Ion Channels, South Hadley, MA, USA.
5. 2014, Annual Meeting of the Danish Pain Society, Horsens, Denmark.

National lectures:
1. 2016, 12e symposium du Réseau Douleur Inserm, Nice.
2. 2015, mini-symposium, IGF Montpellier.
3. 2015, 2nd colloque du LabEx ICST, Montpellier.
4. 2015, 11e symposium du Réseau Douleur Inserm, Strasbourg.
5. 2014, 6e Colloque Toxine Botulinique & Douleurs, Lyon.
6. 2014, 2nd International Conference on Bioinspired and Biobased Chemistry & Materials, Nice.
7. 2014, 1er congrès Jeunes Chercheurs du LabEx ICST, Lille.
8. 2014, 25th Ion Channel Meeting, Oléron.
9. 2014, Séminaire INMED, Marseille.
10. 2014, 10e symposium du Réseau Douleur Inserm, Montpellier.
11. 2013, 1er colloque du LabEx ICST, Grenoble.
12. 2013, 13th Meeting SFETD, Paris.
13. 2013, Journée Claude Bernard 2013 de la Société de Biologie, Paris.

Review (general public):
1. Diochot S and Baron A.
Biofutur N° 355 (Juin 2014):pp.46-51.

Participation to public conferences and events:
1. Brain Awareness Week /Semaine du Cerveau sur la Côte d’Azur since 2014.
2. Science Festival/Fête de la Science 2015, Scientific animation, Antibes Juan les Pins.
3. Conference, Les Eucalyptus high school, Nice, in 2016.

The pathophysiology of pain remains poorly understood and there is clearly a need for new analgesics. ASICs (Acid-Sensing Ion Channels) have emerged as important players in the pain pathway. They form depolarizing cation channels activated by extracellular protons that are expressed in both sensory and central neurons. Our project aims to provide a better understanding of the mechanisms of pain by exploring with innovative pharmacological tools the role of ASICs in these processes, and to provide at the same time leads in the development of new analgesics.

We will use the complementary expertises of the two partners, i.e., ASICs, electrophysiology, toxins and pain behaviour (Team#1), animal pain models and behaviour (Team#2) to achieve the following objectives:

1 – Better characterize the in vivo effects on chronic pain of mambalgins and develop from animal venoms new specific peptide blockers of ASICs with therapeutic potential. Take advantage of these toxins to investigate the structure-function of ASIC channels.

Mambalgins are snake peptides recently identified by Team#1 in collaboration with Team#2 that block subtypes of central and peripheral ASIC channels to produce a potent analgesic effect in rodents in acute pain and inflammation. We propose to further characterize the in vivo analgesic activity of these peptides by exploring their effect via different delivery routes (i.t., i.c.v., i.pl., i.v.) on a variety of chronic pain models of clinical relevance like monoarthritis, neuropathy and migraine.

We propose in parallel to screen animal venoms for new peptide toxins against ASIC channels lacking a specific pharmacology and/or of potential clinical interest. The most interesting ones will be patented and licensed for further clinical development. In addition, analysis of the interaction of the toxins with the targeted channels and of their mechanisms of inhibition will help to better understand the relationship between ASIC channel structure and function.

2 – Combine toxins with the other available tools to explore the pathophysiological role of ASIC channels in the peripheral and the central nervous system in inflammatory and neuropathic pain.

We have previously shown the importance for inflammatory pain of peripheral ASIC channels in sensory neurons. However, a lot still remains to be understood in the regulation of these channels. We propose to explore the role of peripheral ASICs expressed in nociceptors in a context of inflammation and inflammatory pain by identifying new and/or pathology-specific modulators of these channels, and by evaluating the contribution of ASICs to the in vivo effects of these modulators. We will combine studies of the sensitivity of recombinant and native ASIC channels to specific inflammatory mediators (candidate approach) with a global translational approach through the effect of whole human inflammatory exudates isolated from different pathological conditions.

The role of central and peripheral ASIC channels in neuropathic pain has never been directly investigated. We propose to take advantage of the specific toxin inhibitors already available and developed in the course of this project, as well as of ASIC-deficient and ASIC knockdown animals to study this role in two models of neuropathic pain of different aetiology (oxaliplatin-induced neuropathy and chronic constriction injury of sciatic nerve).