BBIQ, a pure TLR7 agonist, is an effective influenza vaccine adjuvant

Abstract

Better adjuvants are needed for vaccines against seasonal influenza. TLR7 agonists are potent activators of innate immune responses and thereby may be promising adjuvants. Among the imidazoquinoline compounds, 1-benzyl-2-butyl-1H-imidazo[4,5-c]quinolin-4-amine (BBIQ) was reported to be a highly active TLR7 agonist but has remained relatively unexplored because of its commercial unavailability. Indeed, in silico molecular modeling studies predicted that BBIQ had a higher TLR7 docking score and binding free energy than imiquimod, the gold standard TLR7 agonist. To circumvent the availability issue, we developed an improved and higher yield method to synthesize BBIQ. Testing BBIQ on human and mouse TLR7 reporter cell lines confirmed it to be TLR7 specific with significantly higher potency than imiquimod. To test its adjuvant potential, BBIQ or imiquimod were admixed with recombinant influenza hemagglutinin protein and administered to mice as two intramuscular immunizations 2 weeks apart. Serum anti-influenza IgG responses assessed by ELISA 2 weeks after the second immunization confirmed that the mice that received vaccine admixed with BBIQ had significantly higher anti-influenza IgG1 and IgG2c responses than mice immunized with antigen alone or admixed with imiquimod. This confirmed BBIQ to be a TLR7-specific adjuvant able to enhance humoral immune responses.

Structure–Activity Relationships toward the Identification of a High-Potency Selective Human Toll-like Receptor-7 Agonist

“…The ipso-displacement of a chloro functionality with 4chlorobenzylamine (for compound 8a), 4-methoxybenzylamine (for compound 8b), and 4-hydroxybenzylamine (for compound 8c) was carried out as described previously. 37 The nitro reduction was achieved using 1% palladium on activated charcoal (10% Pd basis) using a rubber bladder filled with hydrogen gas. The volatilities were removed by passing the reaction mixture through a bed of Celite to obtain an intermediate amino derivative that without further purification was reacted with trimethylorthovalerate in toluene to furnish 1H-imidazo [4,5-c]quinoline derivatives (8a−8c).…”

“…30,34,35 Vesatolimod (4) with 30-fold selectivity for hTLR7 over hTLR8 was tested in clinical trials to treat chronic hepatitis B virus (HBV) infection. 36 BBIQ (5), a TLR7 selective agonist, has been explored as a vaccine adjuvant 37 and as an immuno-chemotherapeutic agent against Plasmodium berghei. 21 Most recently, a whole virion inactivated SARS-COV-2 vaccine (BBV152) adjuvanted with a TLR7 agonist adsorbed to an alum adjuvant has been approved in India.…”

Role of toll-like receptor 7/8 pathways in regulation of interferon response and inflammatory mediators during SARS-CoV2 infection and potential therapeutic options

“…These TLR7/8 ligands either bind to both TLR7/8 receptors or selectively interact with either one to initiate a signaling cascade. For example, imiquimod activates TLR7, whereas CL097 induces TLR7/8 mediated responses [90] . Small structural modifications in TLR7/8 agonists may result in variable TLR7/8 pathway specific responses and selective induction of IFNs and inflammatory mediators [91] .…”

Promising Adjuvants and Platforms for Influenza Vaccine Development

“…Administration of TLR3, TLR9, TLR7, or TLR7/8 agonists resulted in viral inhibition and improved mouse survival [ 27 ]. Recent publications have further demonstrated that the combinations of synthesized TLR4, TLR7, and TLR7/8 ligands were potent adjuvants for recombinant influenza HA vaccines in different animal models [ 28 , 29 , 30 , 31 ]. Significantly, the TLR4 and TLR7 ligands—such as MPL/R837, TRAC-478, and 1Z105/1V270—synergistically increased antigen-specific, long-lasting humoral immune responses, Th1 cell-mediated or Th1/Th2-balanced immunity, and protection against homologous, heterologous, and heterosubtypic viral challenges [ 6 , 28 , 30 ].…”