Targeting neuroinflammatory pathways with novel and existing compounds for the development of analgesic therapeutics

B. J. Moore, B. Islam, P. C. McHugh. Centre for Biomarker Research, University of Huddersfield, Huddersfield, United Kingdom.

Introduction: A clinical need for novel approaches in the treatment of chronic neuropathic pain (NP) is essential to address an emerging issue in modern pain treatment, with a severe lack of effective pharmacological interventions comprising of antidepressants, opioids and anticonvulsants. Inflammatory pathways mediated by cells such as microglia and astrocytes in the central nervous system (CNS) contribute to the pathogenesis of several neurodegenerative diseases. These occur through the release of potent regulatory mediators including cytokines, chemokines and other secreted molecules, and are affiliated with symptoms of NP in diseases such as Alzheimer’s disease and multiple sclerosis (MS). Efforts to elucidate inflammatory pathways such as the tetrahydrobiopterin (BH4) pathway have shown promising analgesic drug targets; the de novo enzymatic pathway is of interest in neuroinflammation and NP research as it is significantly increased in response to damaged or hyperactive peripheral nociceptors (1).

Method: A library of ∼50 compounds including novel small molecules and FDA approved drugs have been assessed in their potential to alleviate the inflammatory response through use of an in vitro IFN-gamma induced inflammation model in THP-1 monocytic cells. This was performed through quantification of the pharmacological effects on pathway markers in BH4 production (GCH1/SPR activity) and their effect on cell metabolism and cytotoxicity after 24 hours of cytokine stimulation and drug treatment, using 5 or 6-point dose response curves covering the typical therapeutic dosage range. Various markers of neuroinflammation and precursors to the IFN-gamma pathway activation upstream of, and including GCH1/GCHFR have been assessed through gene expression analysis by qPCR.

Results: Several small molecules have shown promise in alleviating inflammatory pathway activity in cytokine-stimulated THP-1 cell line after pharmacological and molecular analysis. Dose response curves exhibited quantifiable IC₅₀concentrations for inflammatory pathway markers of neopterin production and SPR activity in the BH4 pathway, with most compounds exhibiting no significant detrimental effect to cell health or viability (p≤0.05, n=3). Pharmacological inhibition through targeting the BH4 pathway could offer a unique repurposing role of existing therapeutics or the identification of novel small molecule analgesics.

Conclusion: These results show several of the analysed drugs from the compound library assessed as having a possible inhibitory effect in neuroinflammation. Further pharmacological analysis will be performed to build up compound profiles of each compound of interest to assess their suitability as potential novel analgesics in the treatment of neuroinflammatory diseases and NP.

References:

(1) Tegeder I et al (2006). Nature Medicine 12, 1269 - 1277.