Identification of High-Potency Human TLR8 and Dual TLR7/TLR8 Agonists in Pyrimidine-2,4-diamines

• Published in: Journal of medicinal chemistry 2017-03, Vol.60 (5), p.2084-2098
• Main Authors: Beesu, Mallesh, Salyer, Alex C. D, Brush, Michael J. H, Trautman, Kathryn L, Hill, Justin K, David, Sunil A
• Format: Article
• Language: English
• Subjects: Diamines - chemistry; Diamines - pharmacology; Humans; Pyrimidines - chemistry; Pyrimidines - pharmacology; Toll-Like Receptor 7 - agonists; Toll-Like Receptor 8 - agonists
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/acs.jmedchem.6b01860

The induction of toll-like receptor 7 (TLR7)-dependent type I interferons (IFN-α/β) from plasmacytoid dendritic cells as well as the production of TLR8-dependent type II interferon (IFN-γ), TNF-α, and IL-12 in myeloid dendritic cells are of importance in generating T helper-1 biased adaptive immune responses. In an effort to identify novel dual TLR7/TLR8-active compounds, we undertook structure–activity relationship studies in pyrimidine 2,4-diamines, focusing on substituents at C5. Several analogues substituted with aminopropyl appendages at C5 displayed dominant TLR8-agonistic activity. N 4-Butyl-6-methyl-5-(3-morpholinopropyl)­pyrimidine-2,4-diamine was found to be a very potent dual TLR7/TLR8 agonist. Employing novel cytokine reporter cell assays, we verified that potency at TLR7 correlates with IFN-α/β production in human blood, whereas IFN-γ and TNF-α induction is largely TLR8-dependent. Dual TLR7/TLR8 agonists markedly upregulate CD80 expression in multiple dendritic cell subsets, providing insight into the immunological basis for the superior adjuvantic properties of such innate immune stimuli.