The Imidazoquinoline Toll-Like Receptor-7/8 Agonist Hybrid-2 Potently Induces Cytokine Production by Human Newborn and Adult Leukocytes.
BACKGROUND
Newborns and young infants are at higher risk for infections than adults, and manifest suboptimal vaccine responses, motivating a search for novel immunomodulators and/or vaccine adjuvants effective in early life. In contrast to most TLR agonists (TLRA), TLR8 agonists such as imidazoquinolines (IMQs) induce adult-level Th1-polarizing cytokine production from human neonatal cord blood monocytes and are candidate early life adjuvants. We assessed whether TLR8-activating IMQ congeners may differ in potency and efficacy in inducing neonatal cytokine production in vitro, comparing the novel TLR7/8-activating IMQ analogues Hybrid-2, Meta-amine, and Para-amine to the benchmark IMQ resiquimod (R848).


METHODS
TLRA-induced NF-κB activation was measured in TLR-transfected HEK cells. Cytokine production in human newborn cord and adult peripheral blood and in monocyte-derived dendritic cell cultures were measured by ELISA and multiplex assays. X-ray crystallography characterized the interaction of human TLR8 with Hybrid-2.


RESULTS
Hybrid-2 selectively activated both TLR7 and 8 and was more potent than R848 in inducing adult-like levels of TNF-α, and IL-1β. Consistent with its relatively high in vitro activity, crystallographic studies suggest that absence in Hybrid-2 of an ether oxygen of the C2-ethoxymethyl substituent, which can engage in unfavorable electrostatic and/or dipolar interactions with the carbonyl oxygen of Gly572 in human TLR8, may confer greater efficacy and potency compared to R848.


CONCLUSIONS
Hybrid-2 is a selective and potent TLR7/8 agonist that is a candidate adjuvant for early life immunization.
Division of Infectious Diseases, Boston Children's Hospital, Boston, MA, United States of America; Harvard Medical School, Boston, MA, United States of America.
Lakshmi
L
Ganapathi
Division of Infectious Diseases, Boston Children's Hospital, Boston, MA, United States of America; Harvard Medical School, Boston, MA, United States of America.
Simon
S
Van Haren
Division of Infectious Diseases, Boston Children's Hospital, Boston, MA, United States of America; Harvard Medical School, Boston, MA, United States of America.
David J
DJ
Dowling
Division of Infectious Diseases, Boston Children's Hospital, Boston, MA, United States of America.
Ilana
I
Bergelson
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, United States of America.
Nikunj M
NM
Shukla
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, United States of America.
Subbalakshmi S
SS
Malladi
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, United States of America.
Rajalakshmi
R
Balakrishna
Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan.
Hiromi
H
Tanji
Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan.
Umeharu
U
Ohto
Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan.
Toshiyuki
T
Shimizu
Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, United States of America.
Sunil A
SA
David
Division of Infectious Diseases, Boston Children's Hospital, Boston, MA, United States of America; Harvard Medical School, Boston, MA, United States of America.
Ofer
O
Levy
D000328:Adult; D016207:Cytokines / Q000378:metabolism*; D003713:Dendritic Cells / Q000187:drug effects / Q000378:metabolism; D005260:Female; D005312:Fetal Blood / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007231:Infant, Newborn; D007962:Leukocytes / Q000187:drug effects* / Q000378:metabolism*; D011247:Pregnancy; D011804:Quinolines / Q000494:pharmacology*; D011993:Recombinant Fusion Proteins / Q000494:pharmacology*; D051199:Toll-Like Receptor 7 / Q000819:agonists*; D051200:Toll-Like Receptor 8 / Q000819:agonists*; D015854:Up-Regulation / Q000187:drug effects
D016207:Cytokines; D007093:Imidazoles; D007166:Immunosuppressive Agents; D011804:Quinolines; D011993:Recombinant Fusion Proteins; D051199:Toll-Like Receptor 7; D051200:Toll-Like Receptor 8; C402365:resiquimod