Novel 1,2,3-triazole-tethered Pam3CAG conjugates as potential TLR-2 agonistic vaccine adjuvants

Synthesis, evaluation and molecular dynamics study of human toll-like receptor 2/6 specific monoacyl lipopeptides as candidate immunostimulants

TLR2 agonists typified by the S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-R-cysteinyl-S-serine (Pam2CS) motif have exhibited powerful immunostimulatory activities. Based on simplified monoacyl lipopeptide (Carbamate-linked N-Ac PamCS), we describe interesting SAR investigations where modifications are done to alter the size of substituents on the cysteine amine, introduce ionizable groups to the terminal and insert aromatic substitutions to the aliphatic chain. Our structural modifications have led to a highly specific human TLR2/6 agonist 14a (EC50 = 0.424 nM), which behaves like Pam2CSK4 by inducing NF-κB activation to trigger downstream signaling pathways, such as subsequent phosphorylation of related proteins (p65, p38) and production of key inflammatory cytokines (IL-6, IL-1β, TNF-α). Importantly, the ability to stimulate enhanced T cell response compared to Carbamate-linked N-Ac PamCS makes compound 14a a further potential candidate immunostimulant.

Design, synthesis and biological evaluation of novel lipophilic 2, 5-disubstituted tetrazole analogues of muramyl dipeptide as NOD2 agonists

A focused library of six new 2, 5-disubstituted tetrazole (2, 5-DST) analogues of N-acetylmuramyl-l-alanyl-d-isoglutamine (MDP) as potential immunomodulators were synthesized by the bioisosteric replacement of α-amide of d-isoglutamine with 5-substituted tetrazole (5-ST). Another parameter 'lipophilicity' was also considered to improve the pharmacological properties of MDP through the alkylation of 5-substituted tetrazole during synthesis. In total, six 2, 5-DST analogues of MDP were synthesized and bio-evaluated for the study of human NOD2 stimulation activity in the innate immune response. Interestingly, among the varied lengths of the alkyl chain in 2, 5-disubstituted tetrazole derivatives, the tetrazole analogues 12b bearing the -Butyl (C4) and 12c having -Octyl (C8) chain showed the best NOD2 stimulation potency equivalent with reference compound MDP. These analogues were evaluated for their adjuvanticity against dengue antigen and analogues 12b and 12c have elicited a potent humoral and cell mediated response.

Synthesis and immunopharmacological evaluation of novel TLR7 agonistic triazole tethered imidazoquinolines

Toll-like receptors-7 and -8 are expressed abundantly on antigen-presenting cells, and their agonists make potential adjuvant candidates for the development of new efficacious vaccines. In view of the importance of new efficacious imidazoquinoline based adjuvants, herein we have synthesized a focused library of a new class of imidazoquinolines retaining the N-isobutyl substitution of an imidazole moiety as in imiquimod and introduced a 1,2,3-triazolyl moiety upon alkyl substitution at the imidazolemethyne carbon employing triazolyl click chemistry. All the novel analogues were characterized using various spectroscopic techniques and the target specificity of these molecules was determined using HEK TLR7/8 transfected cell lines. TLR7/8 activity and also the molecular docking results correlated primarily to the position of the substituent for aromatic groups and also to the chain length in alkyl substitutions. The immunomodulatory properties of these analogues were evaluated using murine DC activation and also with hPBMC activation markers, cytokines which revealed that these analogues after modification were able to target the TLR7 receptors and also had a pro-inflammatory immune response.

Identification and immunological evaluation of novel TLR2 agonists through structural optimization of Diprovocim

As an important family member of Toll-like receptors (TLRs), TLR2 can recognize various pathogen-associated molecular patterns (PAMPs) such as bacteria and viral components. Accumulating evidence demonstrates that TLR2 agonists play a critical role in cancer immunotherapy and infectious diseases. Diprovocim is the most potent small molecule TLR2 agonist known, showing remarkably immune adjuvant activity in mice. However, the further clinical research and development of Diprovocim was hampered because of its structural complexity as well as high molecular weight. Here, we designed and synthesized 21 structurally simplified derivatives of Diprovocim, performed their TLR2 agonistic activities by HEK-Blue hTLR2 SEAP assay, and evaluated the toxicity in two human normal cell lines. Compounds B3-B4 and B9-B12 with excellent TLR2 agonistic activity were found through the structure-activity relationship study. Among them, diastereomer B10 and B12 substituted (S)-2-phenylcyclopropylamide side chain of Diprovocim with simple (R)- and (S)-n-butyl groups exhibited comparable TLR2 agonistic activities with EC₅₀ values of 35 nM and 39 nM, respectively. ELISA and western blot experiments on THP-1 cells showed that B10 and B12 displayed remarkable immunostimulatory activity in the release of various inflammatory cytokines through activating MyD88-dependent NF-κB and MAPK signaling pathways. Importantly, B10 and B12 have less structural complexity and better safety compared to Diprovocim, and the chiral center of right pyrrolidine ring has negligible influence on TLR2 activition. Our study provides simplified Diprovocim derivatives with high agonistic activity, providing a clue to further optimize Diprovocim.

Synthesis and biological evaluation of novel 2-azido muramyl dipeptide as NOD2 agonistic adjuvants

Novel 2-Azido muramyl dipeptide was synthesized by the bio-isosteric replacement of the N-acetyl group of the muramic acid fragment with the azide functionality at the C2 position. In order to examine the effect of hydrophilic-lipophilic balance on the adjuvant activity, derivatives were synthesized by removing protecting groups sequentially to tune the polarity. Amongst five novel azido derivatives of MDP studied here, di- and mono-benzylated azido derivatives 10 and 11 exhibited good DENV specific antibody(IgG) response with Th1 polarization compared to parent compound Muramyl dipeptide (MDP) whereas all five new derivatives responded positively to NOD2 agonistic assays with compound 10 showing highest stimulation.