Lipidated Brartemicin Analogues Are Potent Th1-Stimulating Vaccine Adjuvants

Abstract

Effective Th1-stimulating vaccine adjuvants typically activate antigen presenting cells (APCs) through pattern recognition receptors (PRRs). Macrophage inducible C-type lectin (Mincle) is a PRR expressed on APCs and has been identified as a target for Th1-stimulating adjuvants. Herein, we report on the synthesis and adjuvanticity of rationally designed brartemicin analogues containing long-chain lipids and demonstrate that they are potent Mincle agonists that activate APCs to produce inflammatory cytokines in a Mincle-dependent fashion. Mincle binding, however, does not directly correlate to a functional immune response. Mutation studies indicated that the aromatic residue of lead compound 9a has an important interaction with Mincle Arg183. In vivo assessment of 9a highlighted the capability of this analogue to augment the Th1 response to a model vaccine antigen. Taken together, our results show that lipophilic brartemicin analogues are potent Mincle agonists and that 9a has superior in vivo adjuvant activity compared to TDB.

Identification and Biological Activity of Synthetic Macrophage Inducible C-Type Lectin Ligands

“…This was first demonstrated in studies with linear TDEs, with longer lipids leading to a stronger pro-inflammatory response in vitro ( 48 , 60 ). A similar trend was observed with lipidated brartemicin derivatives, whereby it was also demonstrated that π-cation interactions were essential for the activity of the lead compound ( 62 ). The effect of lipid length on the immunomodulatory potential of Mincle agonists other than trehalose derivatives has also been demonstrated with, for example, longer chain GMCM and β-gentiobiosyl diacylglycerides derivatives showing enhanced Mincle activity compared to their shorter-chain counterparts ( 50 , 87 ).…”

“…In another study, however, a glucosyl monomycolate derivate showed similar adjuvant activity to TDB in an in vivo OVA immunization model ( 27 ). Lipidated brartemicin derivatives have also shown enhanced in vivo adjuvant activity compared to TDB ( 62 ). In studies that identified the first endogenous ligand for Mincle, β-GlcCer, it was also demonstrated that ceramide, lactosyl ceramide and galactosyl ceramide were not Mincle agonists ( 91 ).…”

“… Non-branched trehalose diesters (TDEs), including linear TDEs ( 60 ), brartemicin derivatives ( 61 , 62 ), fluorescent TDE probes ( 63 ), and a trehalose based affinity probe ( 64 ). Of these derivatives, only the linear TDEs ( 7d–i ), the lipophilic brartemicin derivatives ( 9a–f ), and the fluorescent TDE probes ( 10a–d ) have been shown to be macrophage inducible C-type lectin agonists.…”

“…In more recent studies by our group, we synthesized a variety lipophilic brartemicin analogs (e.g., 9a–f ), including the natural product itself ( 8a ) and other non-lipidated derivatives ( 8c , d ), with the idea that a lipophilic tail would enhance Mincle binding ( 62 ). Surprisingly, we demonstrated that brartemicin ( 8a ) did not bind either human or murine Mincle, as determined via an enzyme-linked immunosorbent assay (ELISA) using soluble Mincle-Ig fusion-proteins, and moreover, that 8a did not activate NFAT-GFP reporter cells expressing mMincle or hMincle, or cause BMMs to produce IL-6, IL-1β, TNF-α, or MIP-2.…”

The coadministration of trehalose dibehenate and monosodium urate crystals promotes an antitumor phenotype in human‐derived myeloid cells

“…Thus, our findings further illustrate species‐specific differences that may exist with regard to Mincle expression 17,46 . Lastly, as functional changes to Mincle agonists can further enhance the type 1 helper immune response, 17,47,48 this highlights the potential of developing additional Mincle agonists as anticancer adjuvants.…”