Repurposing of Tranilast for Potential Neuropathic Pain Treatment by Inhibition of Sepiapterin Reductase in the BH₄ Pathway

Abstract

Tetrahydrobiopterin (BH 4 ) is a cofactor in the production of various signaling molecules including nitric oxide, dopamine, adrenaline, and noradrenaline. BH 4 levels are critical for processes associated with cardiovascular function, inflammation, mood, pain, and neurotransmission. Increasing pieces of evidence suggest that BH 4 is upregulated in chronic pain. Sepiapterin reductase (SPR) catalyzes both the reversible reduction of sepiapterin to dihydrobiopterin (BH 2 ) and 6-pyruvoyl-tetrahydrobiopterin to BH 4 within the BH 4 pathway. Therefore, inhibition of SPR by small molecules can be used to control BH 4 production and ultimately alleviate chronic pain. Here, we have used various in silico and in vitro experiments to show that tranilast, licensed for use in bronchial asthma, can inhibit sepiapterin reduction by SPR. Docking and molecular dynamics simulations suggest that tranilast can bind to human SPR (hSPR) at the same site as sepiapterin including S157, one of the catalytic triad residues of hSPR. Colorimetric assays revealed that tranilast was nearly twice as potent as the known hSPR inhibitor, N -acetyl serotonin. Tranilast was able to inhibit hSPR activity both intracellularly and extracellularly in live cells. Triple quad mass spectrophotometry of cell lysates showed a proportional decrease of BH 4 in cells treated with tranilast. Our results suggest that tranilast can act as a potent hSPR inhibitor and therefore is a valid candidate for drug repurposing in the treatment of chronic pain.

Kynurenine and Tetrahydrobiopterin Pathways Crosstalk in Pain Hypersensitivity

“…We also demonstrated that SPRi reduced pain scores in mice submitted to a colitis experimental model, and that this effect was in part due to the absolute requirement of T cells for BH4 in order to expand and infiltrate tissues ( Cronin et al, 2018 ). Another FDA-approved drug, Tranilast – an anti-allergic agent, was also demonstrated to inhibit SPR in protein- and cell-based assays ( Moore et al, 2019 ) and to reduce pelvic pain caused by endometriosis in a clinical study ( Honda et al, 2013 ).…”

Novel Approaches, Drug Candidates, and Targets in Pain Drug Discovery

“…Other SPR inhibitors discovered include 109 , 110 , QM385 ( 111 ), and tranilast ( 112 ) licensed for use in bronchial asthma (Figure ). − Sulfasalazine, an FDA approved anti-inflammatory drug, was found to inhibit SPR activity through its metabolite sulfapyridine ( 113 ), which aided the discovery of some of the above-mentioned compounds (Figure ). Reducing BH4 levels by inhibiting SPR activity is a viable approach for alleviating neuropathic and inflammatory pain hypersensitivity.…”

Discovery of Novel Pleuromutilin Derivatives as Potent Antibacterial Agents for the Treatment of MRSA Infection

“…The dissociation rate constant (K d ) demonstrated the dissociate rate. The equilibrium dissociation constant (K D ) demonstrated the degree of dissociation of the compounds and the 50S ribosome in the equilibrium state [30]. A low K D value indicated that the binding affinity between the compound and the 50S ribosome was strong [31].…”