Identification of a Human Toll-Like Receptor (TLR) 8-Specific Agonist and a Functional Pan-TLR Inhibitor in 2-Aminoimidazoles

Mallesh Beesu, Giuseppe Caruso, Alex C.D. Salyer, Nijunj M. Shukla, Karishma K. Khetani, Luke J. Smith, Lauren M. Fox, Hiromi Tanji, Umeharu Ohto, Toshiyuki Shimizu, Sunil A. David

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27 Scopus citations


Activation of human toll-like receptor-8 (TLR8), expressed in myeloid dendritic cells, monocytes, and monocyte-derived dendritic cells, evokes a distinct cytokine profile which favors the development of Type 1 helper T cells. Part-structures of the 2-aminobenzimidazole scaffold were examined with a view to identifying structural requisites corresponding to the smallest possible fragment of the benzimidazole core that would allow for retention of TLR8-agonistic activity. TLR8-specific agonistic activity was retained in 1-pentyl-4-phenyl-1H-imidazol-2-amine. The crystal structure of this compound bound to the TLR8 ectodomain displayed binding interactions that are common to other TLR8 agonists. This compound showed markedly attenuated proinflammatory properties in ex vivo human blood models. SAR studies revealed that 4-(2-(benzyloxy)phenyl)-1-pentyl-1H-imidazol-2-amine inhibited TLR signaling in a variety of TLR reporter cell lines, as well as in pharmacologically relevant human blood model systems. A kinase screen of this compound showed relative specificity for calmodulin kinases.

Original languageEnglish (US)
Pages (from-to)3311-3330
Number of pages20
JournalJournal of medicinal chemistry
Issue number7
StatePublished - Apr 28 2016

Bibliographical note

Funding Information:
This work was supported by NIH/NIAID contracts HSN272200900033C and HHSN272201400056C.


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