(W1030-04-19) Beyond Voltage-Gated Sodium Channel (Na_v1.7): Exploring the Dual Role of GX201 and Sulfamethoxazole in Itch Management

Purpose: Pruritus, or itch is a common symptom in dermatological conditions, involves Na_V1.7, a key subtype of voltage-gated sodium channels crucial for transmitting itch signals from sensory neurons to the central nervous system. Pharmacological inhibition of Na_V1.7, notably with GX201 under investigation for neuropathic pain, can alleviate histamine-dependent itch triggered by allergies and inflammation [1, 2]. Conversely, sulfamethoxazole, a sulfonamide antibiotic, inhibits bacterial dihydrofolic acid production but can induce itching through hypersensitivity reactions. These reactions, involving histamine release and T-cell-mediated responses, manifest as immediate symptoms like itching, hives, and swelling, or delayed symptoms such as skin inflammation and rashes [3]. This study aims to elucidate whether sulfamethoxazole binds to Na_V1.7 receptors and shares binding sites with GX201. While Na_V1.7 inhibition theoretically reduces itching, sulfamethoxazole's histamine receptor stimulation suggests Na_V1.7 blockade alone may not fully alleviate itching.

Methods: Protein Structure Acquisition and Optimization: The protein structure of Na_V1.7 (PDB ID: 8I5B) was acquired from the Protein Data Bank (PDB) and refined using Chimera software to enhance accuracy and energetically favorable states. Acquisition and Optimization of GX 201 Structure: The chemical structure of GX 201 was obtained from PubChem, and its 3D structure was optimized using Avogadro, a molecular modeling tool, for geometry optimization. Molecular Docking: Molecular docking simulations were performed using AutoDock 4.2 to analyze the binding interactions between Na_V1.7 and GX 201, generating binding energy data. Binding Pocket and Binding Site Analysis: The binding pockets and sites on Na_V1.7 were analyzed to identify specific amino acid residues involved in interactions with GX 201 and Sulfamethoxazole, crucial for understanding their binding mechanisms.

Results: Both GX201 and Sulfamethoxazole share the same binding site, however with binding energies of -9.29 kcal/mole and -7.31 kcal/mol respectively. The binding site amino acid residues for GX201 include the following: The 2-D interaction for GX201 is shown in Figure 1 and the binding pocket details are shown in Figure 2. Hydrogen bonds between specific amino acid residues in the Na_V1.7-GX201 complex create a stable interaction, enhancing selectivity and complex strength (Figure 2A). Aromatic rings further stabilize the complex through pi-stacking and edge-to-face interactions, bolstering binding affinity and stability (Figure 2B). GX201's binding to the hydrophobic Na_V1.7 pocket minimizes water contact, optimizing interaction energetics (Figure 2C). This hydrophobic environment supports Na_V1.7's preference for GX201 over hydrophilic molecules. Solvent accessible surface area (SASA) of the Na_V1.7 pocket does not significantly influence GX201 binding, indicating minimal impact on protein-ligand interactions (Figure 2D). These structural and environmental factors collectively contribute to the robust and specific binding of GX201 to Na_V1.7, crucial for its modulation of receptor activity and therapeutic potential in managing pruritus and related conditions.

Conclusion: Both GX201 and Sulfamethoxazole bind to the same site on the Na_V1.7 receptor, but they exhibit different binding energies, with GX201 showing a stronger affinity with a binding energy of -9.29 kcal/mol compared to Sulfamethoxazole's -7.31 kcal/mol. This difference underscores GX201's superior interaction with the Na_V1.7 binding pocket, facilitated by multiple hydrogen bonds, favourable aromatic interactions, and hydrophobic contacts, which collectively enhance complex stability and specificity. Despite sharing the binding site, Sulfamethoxazole induces itching through H1 receptor activation, highlighting that Na_V1.7 inhibition alone is insufficient to alleviate itching. Histamine-mediated pathways contribute significantly to itch induction, necessitating comprehensive management strategies that address both Na_V1.7 modulation and histamine receptor activation for effective relief. Exploring these differential binding energies and mechanisms is crucial for developing targeted therapies that address the multifaceted nature of pruritus and related conditions, aiming for more comprehensive and effective treatment approaches in clinical settings.

References: 1) Bankar G, Goodchild SJ, Howard S, Nelkenbrecher K, Waldbrook M, Dourado M, Shuart NG, Lin S, Young C, Xie Z et al: Selective NaV1.7 Antagonists with Long Residence Time Show Improved Efficacy against Inflammatory and Neuropathic Pain. Cell Reports 2018, 24(12):3133-3145.
2) Wang JT, Zheng YM, Chen YT, Gu M, Gao ZB, Nan FJ: Discovery of aryl sulfonamide-selective Nav1.7 inhibitors with a highly hydrophobic ethanoanthracene core. Acta Pharmacol Sin 2020, 41(3):293-302.
3. Kocak Z, Hatipoglu CA, Ertem G, Kinikli S, Tufan A, Irmak H, Demiroz AP: Trimethoprim–sulfamethoxazole induced rash and fatal hematologic disorders. Journal of Infection 2006, 52(2):e49-e52.

Figure 1. The binding site amino acid residues for GX201 include the following: VAL-1751, VAL-1752, PHE-1745, SER-1747, SER-1697, ILE-1744, CYS-1328, PHE-1452, TRP-1332, LEU-1329, VAL-1741, TYR-1396, GLN-360, THR-1693, THR-1404, SER-1445, PHE-391, LEU-1449, ALA-1403, ILE-1745, LEU-1400, LEU-1325

Figure 2. Binding pocket features in NaV1.7 receptor for GX201. (a) Hydrogen Bonds, (b) Aromatic edges, (c) Hydrophobicity, (d) Solvent accessible Surface Area.

Figure 3. The binding site amino acid residues for Sulfamethoxazole include the following: ALA-1403, THR-1404, LEU-1400, ILE-1745, ILE-1744, SER-1445, LEU-1449, THR-1448, PHE-1748, PHE-1452, TRP-1322, LEU-1325, CYS-1328, TYR-1396, LEU-1329.