Investigation toward multi-epitope vaccine candidates using native chemical ligation

Peptide conjugation via CuAAC 'click' chemistry

The copper (I)-catalyzed alkyne azide 1,3-dipolar cycloaddition (CuAAC) or ‘click’ reaction, is a highly versatile reaction that can be performed under a variety of reaction conditions including various solvents, a wide pH and temperature range, and using different copper sources, with or without additional ligands or reducing agents. This reaction is highly selective and can be performed in the presence of other functional moieties. The flexibility and selectivity has resulted in growing interest in the application of CuAAC in various fields. In this review, we briefly describe the importance of the structural folding of peptides and proteins and how the 1,4-disubstituted triazole product of the CuAAC reaction is a suitable isoster for an amide bond. However the major focus of the review is the application of this reaction to produce peptide conjugates for tagging and targeting purpose, linkers for multifunctional biomacromolecules, and reporter ions for peptide and protein analysis.

Influence of conjugation chemistry and B epitope orientation on the immune response of branched peptide antigens

Multimeric presentation, a well-proven way of enhancing peptide immunogenicity, has found substantial application in synthetic vaccine design. We have reported that a combination of four copies of a B-cell epitope with one of a T-cell epitope in a single branched construct results in a peptide vaccine conferring total protection against foot-and-mouth disease virus in swine, a natural host (Cubillos et al. (2008) J. Virol. 82, 7223-7230). More recently, a downsized version of this prototype with only two copies of the B epitope has proven as effective as the tetravalent one in mice. Here we evaluate three approaches to bivalent platforms of this latter type, involving different chemistries for the conjugation of two B epitope peptides to a branching T epitope. Comparison of classical thioether, "reverse" thioether (Monsó et al. (2012) Org. Biomol. Chem. 10, 3116-3121) and thiol-ene conjugation chemistries in terms of synthetic efficiency clearly singles out the latter, maleimide-based strategy as most advantageous. We also examine how minor structural differences among the conjugates--including the N- or C-terminal attachment of the B epitope to the branching T epitope--bear on the immunogenicity of these vaccine candidates, with the maleimide-based conjugate again emerging as the most successful.

Reverse thioether ligation route to multimeric peptide antigens

Multimeric presentation, a rather effective way of enhancing peptide immunogenicity, is best exemplified by MAP (multiple antigenic peptide) dendrimers consisting of a branched Lys core on which several copies of the peptide epitope are displayed. While accessible by solid-phase synthesis, MAPs can also be conveniently made in solution, e.g., by linking the epitope (N-acetylated and with a C-terminal Cys) through a thioether bond onto the α and ε (haloacetyl-activated) positions of the Lys core. We now report the reverse version of this approach, whereby a chloroacetyl-derivatised epitope is tethered to a thiol-functionalised form of a Lys dendron core. This convergent approach can be carried out either in solution or in the solid phase and is advantageous because (i) in situ tris(2-carboxyethyl)phosphine (TCEP)-mediated reduction of disulfide bonds maintains the thiol platform reactive throughout the ligation process; (ii) the low amounts of TCEP used pose minimal risk to chloroacetyl groups in the peptide, resulting in (iii) significantly reduced byproduct formation, hence cleaner products. For the solid phase version of the method, an optimised procedure has been devised to convert the Lys core into a tetrathiol dendron.

Current status of multiple antigen-presenting peptide vaccine systems: Application of organic and inorganic nanoparticles

Many studies are currently investigating the development of safe and effective vaccines to prevent various infectious diseases. Multiple antigen-presenting peptide vaccine systems have been developed to avoid the adverse effects associated with conventional vaccines (i.e., live-attenuated, killed or inactivated pathogens), carrier proteins and cytotoxic adjuvants. Recently, two main approaches have been used to develop multiple antigen-presenting peptide vaccine systems: (1) the addition of functional components, e.g., T-cell epitopes, cell-penetrating peptides, and lipophilic moieties; and (2) synthetic approaches using size-defined nanomaterials, e.g., self-assembling peptides, non-peptidic dendrimers, and gold nanoparticles, as antigen-displaying platforms. This review summarizes the recent experimental studies directed to the development of multiple antigen-presenting peptide vaccine systems.

Lipid-core-peptide system for self-adjuvanting synthetic vaccine delivery

Disadvantages of classical vaccines, such as the risk of an autoimmune reaction, might be overcome by using a subunit vaccine containing the minimal microbial components necessary to stimulate appropriate immune responses. However, vaccines based on minimal epitopes suffer from poor immunogenicity and require the use of an additional immunostimulant (adjuvant). Only a few adjuvants have been permitted for use with vaccines intended for human administration. We have developed several vaccine candidates based on a lipid-core-peptide (LCP) system. This system has self-adjuvanting properties, and it can be used for the delivery of a variety of epitopes to produce vaccine candidates against a targeted disease. The LCP system is easily assembled by simple stepwise Boc solid-phase peptide synthesis.

Design and Synthesis of Lipopeptide - Carbohydrate Assembled Multivalent Vaccine Candidates Using Native Chemical Ligation

Development of a synthetic vaccine against group A streptococcal infection is increasingly paramount due to the induction of autoimmunity by the main virulent factor – M protein. Peptide vaccines, however, are generally poorly immunogenic, necessitating administration with carriers and adjuvants. One of the promising approaches to deliver antigenic peptides is to assemble peptides on a suitable template which directs the attached peptides to form a well defined tertiary structure. For self-adjuvanting human vaccines, the conjugation of immunostimulatory lipids has been demonstrated as a potentially safe method. This study describes the design and optimized synthesis of two lipopeptide conjugated carbohydrate templates and the assembling of peptide antigens. These lipopeptide–carbohydrate assembled multivalent vaccine candidates were obtained in high yield and purity when native chemical ligation was applied. Circular dichroism studies indicated that the template-assembled peptides form four α-helix bundles. The developed technique extends the use of carbohydrate templates and lipopeptide conjugates for producing self-adjuvanting and topology-controlled vaccine candidates.

Lipid Core Peptide System for Gene, Drug, and Vaccine Delivery

A vast number of biologically active compounds await efficient delivery to become therapeutic agents. Lipidation has been demonstrated to be a convenient and useful approach to improve the stability and transport across biological membranes of potential drug molecules. The lipid core peptide (LCP) system has emerged as a promising lipidation tool because of its versatile features. This review discusses the progress in the development of the LCP system to improve cell permeability of nucleotides, physicochemical properties of potential drugs, and vaccine immunogenicity. Emphasis was put on the application of the LCP system to deliver antigens for the prevention of group A streptococcus infection, novel techniques of conjugation of target molecules to the LCP, and new alterations of the LCP system itself.