Synthesis and structure-activity relationship study of novel quinazolin-4(3H)-one derivatives as Toll-like receptor 7 and 8 agonists with immunomodulatory activity

Toll-like receptors (TLRs) 7 and 8 are intracellular pattern recognition receptors that play a crucial role in the innate immune system, making them promising targets for the treatment of viral infections, autoimmune diseases and cancer. In this study, we present the synthesis and biological evaluation of quinazolin-4(3H)-one derivatives as a new class of dual TLR7/8 agonists. In a comprehensive structure-activity relationship (SAR) study, different substitutions on the quinazoline ring and modifications of the aliphatic side chain were investigated. Several compounds showed significantly improved potency compared to the original hit compound, with EC₅₀ values in the nanomolar and low micromolar range for TLR7 and TLR8, respectively. The most potent compounds significantly increased the secretion of the proinflammatory cytokines TNF-α, IL-1β, IL-8 and interferon γ in peripheral blood mononuclear cells (PBMCs). In addition, increased secretion of TNF-α and upregulated CD86 expression in dendritic cells were also observed, indicating their immunomodulatory properties. Notably, the most potent compound 69 significantly suppressed tumor growth in vivo in the CT26 mouse tumor model after intratumoral administration. These results highlight the potential of quinazolinone-based compounds as promising candidates for further development of new immunomodulatory agents targeting TLR7 and TLR8.