Impairment of TNF-α Production and Action by Imidazo[1,2- α] Quinoxalines,as Derivative Family Which Displays Potential Anti-Inflammatory Properties

In a previous study, we analysed the synthesis and properties of a series of imidazo[1,2-a]quinoxalines designed in our laboratory as possible imiquimod analogues. We found that these imidazo[1,2-a]quinoxalines were in fact potent inhibitors of phosphodiesterase 4 enzymes (PDE4). PDE4 inhibition normally results in an increase in intracellular cAMP which, in PBMC, induces the suppression of TNF-α mRNA transcription and thus cytokine synthesis. Such an effect is antagonistic to that of imiquimod. Furthermore, some TNF-α-induced activity, such as cell apoptosis which is dependent on the intracellular cAMP levels might also be affected. Therefore, by counteracting the properties of TNF-α and/or its production, the imidazo[1,2-a]quinoxalines could be considered as potential antiinflammatory drugs. The present study was performed to confirm or refute this hypothesis. For this, we characterized the effects of imidazo[1,2-a]quinoxalines both on TNF-α activity and synthesis in regard to their ability to act as inhibitors of PDE4 (IPDE4). We found that the imidazo[1,2-a]quinoxalines dose-dependently prevented the TNF-α-triggered death of L929 cells, with the 8-series (-NHCH3 in R4) being the most potent. Moreover, when the effect of the 8-series on TNF-α production was investigated using γ9δ2 T cells, it was observed that these compounds impaired the TCR:CD3-triggered TNF-α production. Structure-activity analysis revealed that these properties of the drugs did not coincide with their IPDE4 properties. This prompted further exploration into other signalling mechanisms possibly involved in TNF-α action and production, notably the p38 MAPK and the PI3K pathway. We demonstrate here that the imidazo[1,2-a]quinoxalines targeted these pathways in a different way: they activated the p38 MAPK pathway whilst inhibiting the PI3K pathway. Such effects on cell signalling could account for the imidazo[1,2-a]quinoxalines effects on 1) action and 2) production of TNF-α, which define these drugs as potential anti-inflammatory agents.