Structure-Based Design of Human TLR8-Specific Agonists with Augmented Potency and Adjuvanticity

Human Toll-like receptor 8 (hTLR8) is expressed in myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells. Engagement by TLR8 agonists evokes a distinct cytokine profile which favors the development of type 1 helper T cells. Crystal structures of the ectodomain of hTLR8 cocrystallized with two regioisomers of a dual TLR7/8-agonistic N1-substituted imidazoquinolines showed subtle differences in their interactions in the binding site of hTLR8. We hypothesized that the potency of a previously reported best-in-class pure TLR8 agonist, 3-pentylquinoline-2-amine, could be further enhanced by “designing in” functional groups that would mimic key intermolecular interactions that we had observed in the crystal structures. We performed a focused exploration of decorating the quinoline core with alkylamino groups at all possible positions. These studies have led to the identification of a novel TLR8 agonist that was ∼20-fold more potent than the parent compound and displays prominent adjuvantic activity in a rabbit model of immunization.

人类Toll样受体8（human Toll-like receptor 8，hTLR8）表达于髓系树突状细胞、单核细胞及单核细胞衍生树突状细胞中。TLR8激动剂与hTLR8结合后，可诱导独特的细胞因子谱，该谱有利于1型辅助性T细胞的分化发育。将hTLR8胞外域与双靶点TLR7/8激动性N1取代咪唑并喹啉类的两种区域异构体共结晶所获得的晶体结构显示，二者在hTLR8结合位点的分子相互作用存在细微差异。基于上述结构信息，我们提出假说：此前报道的同类最优纯TLR8激动剂——3-戊基喹啉-2-胺，可通过引入能够模拟我们在晶体结构中观察到的关键分子间相互作用的官能团，进一步提升其活性效力。我们针对在喹啉母核的所有可能位点引入烷基氨基基团开展了定向修饰研究。通过上述工作，我们成功鉴定得到一种新型TLR8激动剂，其效力约为母化合物的20倍，并且在兔免疫模型中展现出显著的佐剂活性。