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.

Lipidation of NOD2 Agonists with Adamantane and Stearoyl Moieties Differentially Regulates Their In Vivo Adjuvant Activity

NOD2 is an innate immune receptor that constitutes an important target for the development of small molecule immunopotentiators with great potential to be used as vaccine adjuvants. We report here the results of an in vivo study of the adjuvant properties of a desmuramylpeptide NOD2 agonist SG29 and its lipidated analogs featuring an adamantyl moiety or a stearoyl group. These compounds have been synthesized, incorporated into liposomes, and evaluated for their in vivo adjuvant activity. The characterization of liposome formulations of examined compounds revealed that their size increased in comparison to that of empty liposomes. The introduction of a stearoyl or an adamantane lipophilic anchor into the structure of SG29, to produce SG115 and ZSB63, respectively, substantially improved the in vivo adjuvant activity. Of note, the attachment of the stearoyl moiety produced a Th2-biased immune response, while the incorporation of the adamantyl moiety greatly enhanced the production of total IgG but mostly augmented the production of IgG2a antibodies, which indicated a shift toward a Th1 immune response. The identified bona fide capacity of ZSB63 to initiate a cellular immune response thus highlights its untapped potential as an alternative vaccine adjuvant.

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.

Production of fever mediator PGE2 in human monocytes activated with MDP adjuvant is controlled by signaling from MAPK and p300 HAT: Key role of T cell derived factor

Fever and inflammatory responses were observed in some subjects in early clinical trials of vaccines adjuvanted with muramyl dipeptide (MDP), a NOD2 agonist. Biosynthesis of Prostaglandin E2 (PGE₂) that transmits febrile signals to the brain is controlled by an inducible enzyme, Cyclooxygenase 2 (COX-2). MDP alone was not sufficient to induce expression of COX-2 and PGE₂ production in vitro. Conditioned medium prepared from Peripheral Blood Mononuclear Cells (PBMCs)-derived CD3-bead purified human T cells (TCM) dramatically increased COX2 gene transcription, COX-2 protein expression, and PGE₂ production in MDP-treated monocytes. We explored epigenetic changes at the COX2 promoter using Chromatin Immunoprecipitation assay (ChIP). Increase in COX2 transcription correlated with increased recruitment of RNA polymerase II (Pol II) and p300 histone acetyl transferase (HAT) to the COX2 promoter in monocytes activated with MDP and TCM. The role of p300 HAT was confirmed by using C646, an inhibitor of p300, that reduced binding of acetylated H3 and H4 histones at the COX2 promoter, COX2 transcription, and PGE₂ production in monocytes. Binding of p300, Nuclear Factor Kappa B (NF-κB), and Pol II to the COX2 promoter was also sensitive to inhibitors of Mitogen-Activated Protein Kinase (MAPK) pathway and to antibodies against Macrophage-1 (Mac-1) integrin in MDP/TCM-treated monocytes. Importantly, recombinant Glycoprotein Ib alfa (GPIbα), the recently identified factor in TCM, increased binding of NF-κB, p300, and of Pol II to the COX2 promoter and COX2 transcription in MDP-treated monocytes. Our findings suggest that a second signal through Mac-1 and MAPK is triggered by a T cell derived soluble GPIbα protein leading to the assembly of the transcription machinery at the COX2 promoter and production of PGE₂ in human monocytes in response to MDP/NOD2 activation.

Structural requirements of acylated Gly-l-Ala-d-Glu analogs for activation of the innate immune receptor NOD2

The fragment of bacterial peptidoglycan muramyl dipeptide (MDP) has long been known for its adjuvant activity, however the underlying mechanism of this action has only recently been elucidated. It is ascribed to its agonist action on the nucleotide-binding oligomerization domain-containing protein 2 (NOD2). In spite of the pressing need for novel adjuvants for human use, this discovery is hampered, by not knowing the structural requirements underlying the immunostimulatory activity. We have investigated how minor modifications of hit compound acyl Gly-L-Ala-D-Glu derivative I modulate the molecular recognition by NOD2. A series of novel desmuramyldipeptides has been designed and synthesized leading to the identification of compound 16, in which the sugar moiety is replaced by a 6-phenylindole moiety, that exhibits the strongest NOD2 activation to date sans the carbohydrate moiety. The results have enabled a deeper understanding of the structural requirements of desmuramylpeptides for NOD2 activation.