A combined adjuvant and carrier system for enhancing synthetic peptides immunogenicity utilising lipidic amino acids

Liposomes as Adjuvants and Vaccine Delivery Systems

The review considers liposomes as systems of substantial interest as adjuvant carriers in vaccinology due to their versatility and maximal biocompatibility. Research and development on the use of liposomes and lipid nanoparticles to create subunit vaccines for the prevention and treatment of infectious diseases has been going on for several decades. In recent years, the area has seen serious progress due to the improvement of the technology of industrial production of various high-grade lipids suitable for parenteral administration and the emergence of new technologies and equipment for the production of liposomal preparations. When developing vaccines, it is necessary to take into account how the body’s immune system (innate and adaptive immunity) functions. The review briefly describes some of the fundamental mechanisms underlying the mobilization of immunity when encountering an antigen, as well as the influence of liposome carriers on the processes of internalization of antigens by immunocompetent cells and ways of immune response induction. The results of the studies on the interactions of liposomes with antigen-presenting cells in function of the liposome size, charge, and phase state of the bilayer, which depends on the lipid composition, are often contradictory and should be verified in each specific case. The introduction of immunostimulant components into the composition of liposomal vaccine complexes—ligands of the pathogen-associated molecular pattern receptors—permits modulation of the strength and type of the immune response. The review briefly discusses liposome-based vaccines approved for use in the clinic for the treatment and prevention of infectious diseases, including mRNA-loaded lipid nanoparticles. Examples of liposomal vaccines that undergo various stages of clinical trials are presented.

Dendrimers in vaccine delivery: Recent progress and advances

Dendrimers are well-defined, highly branched, multivalent and monodisperse molecules which host a range of attractive, yet functional, chemical and biological characteristics. A dendrimers accessible surface groups enable coupling to different functional moieties (e.g., antibodies, peptides, proteins, etc), which is further assisted by the dendrimers tailored size and surface charge. This adaptability allows for the preparation of molecularly precise vaccines with highly specific and predictable properties, and in conjunction with a dendrimers immune stimulating (adjuvanting) property, makes dendrimers attractive substrates for biomedical applications, including vaccines. This review highlights the structural and synthetic evolution of dendrimers throughout history, detailing the dendrimers role as both an adjuvant and carrier system for vaccine antigens, in addition to reviewing the development of commercially available vaccines for use in humans.

Lipids as Activators of Innate Immunity in Peptide Vaccine Delivery

BACKGROUND

Innate immune system plays an important role in pathogen detection and the recognition of vaccines, mainly through pattern recognition receptors (PRRs) that identify pathogen components (danger signals). One of the typically recognised bacterial components are lipids in conjugation with peptides, proteins and saccharides. Lipidic compounds are readily recognised by the immune system, and thus are ideal candidates for peptide- based vaccine delivery. Thus, bacterial or synthetic lipids mixed with, or conjugated to, antigens have shown adjuvant properties. These systems have many advantages over traditional adjuvants, including low toxicity and good efficacy for stimulating mucosal and systemic immune responses.

METHODS

The most recent literature on the role of lipids in stimulation of immune responses was selected for this review. The vast majority of reviewed papers were published in the last decade. Older but significant findings are also cited.

RESULTS

This review focuses on the development of lipopeptide vaccine systems including application of palmitic acid, bacterial lipopeptides, glycolipids and the lipid core peptide and their routes of administration. The use of liposomes as a delivery system that incorporates lipopeptides is discussed. The review also includes a brief description of immune system in relation to vaccinology and discussion on vaccine delivery routes.

CONCLUSION

Lipids and their conjugates are an ideal frontrunner in the development of safe and efficient vaccines for different immunisation routes.

The application of self-assembled nanostructures in peptide-based subunit vaccine development

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Smaller polymer-peptide conjugates-based nanoparticles are often more immunogenic.

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Lipid-antigen conjugates-based nanoparticles can interact with immune receptors.

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Peptides with β-sheet conformation usually form nanofibers.

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α-Helical and random coil peptides tend to self-assemble into nanoparticles.

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Peptide-based nanostructures are usually poorer inducers of immune responses.

Peptide based-vaccines are becoming one of the most widely investigated prophylactic and therapeutic health care interventions against a variety of diseases, including cancer. However, the lack of a safe and highly efficient adjuvant (immune stimulant) is regarded as the biggest obstacle to vaccine development. The incorporation of a peptide antigen in a nanostructure-based delivery system was recently shown to overcome this obstacle. Nanostructures are often formed from antigens conjugated to molecules such as polymers, lipids, and peptide, with the help of self-assembly phenomenon. This review describes the application of self-assembly process for the production of peptide-based vaccine candidates and the ability of these nanostructures to stimulate humoral and cellular immune responses.

Lipid core peptide technology and group A streptococcal vaccine delivery

The antiphagocytic surface M protein of group A streptococcus has been widely studied as the major candidate antigen for a vaccine to prevent group A streptococcus infection. Approaches that have proven to be effective in animal models include the use of multi-epitope vaccines incorporating highly variable amino terminal serotypic determinants, those based on the carboxy terminal conserved region and combination vaccines incorporating both serotypic and conserved region determinants of the M protein. The use of lipid core peptide technology is at the forefront of this research in the quest to develop a broad-strain protective vaccine that can be delivered via the mucosal route, stimulating mucosal and systemic immunity. This review aims to cover the various strategies and technologies that have been investigated with regard to group A streptococcus vaccine design and development.

Synthesis of medicinally useful lipidicα-amino acids, 2-amino alcohols and diamines

The lipidicα-amino acids (LAAs) are non-naturalα-amino acids with saturated or unsaturated long aliphatic side chains. LAAs and their derivatives (lipid mimetics) together with the lipidic peptides represent a class of compounds which combine structural features of lipids with those of amino acids and peptides. Racemic LAAs may be prepared by classical methods and resolved by chemical or enzymatic methods. LAA amides and esters with saturated or unsaturated long chain amines and alcohols respectively, as well as lipidic dipeptide derivatives inhibit both pancreatic and human platelet phospholipase A2. Lipophilic peptide derivatives are inhibitors of human neutrophil elastase. LAAs and their oligomers have been used as drug delivery system. A Lipid-Core-Peptide system has been designed and used as a combined adjuvant-carrier-vaccine system. A variety of lipid mimetics such as lipidic 2-amino alcohols, lipidic 1,2- and 1,3-diamines have been prepared based upon LAAs. Some of them are potent inhibitors of phospholipase A2. A general approach to enantioselective synthesis of LAAs and lipid mimetics is based on the oxidative cleavage of 3-amino-1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols.

Activation of monocytic cells by immunostimulatory lipids conjugated to peptide antigens

Bacterial derived lipoproteins constitute potent macrophage activators in vivo and are effective stimuli, enhancing the immune response especially with respect to low or non-immunogenic compounds. In the present study we have prepared branched lipopeptide constructs in which different (B- and T-cell) epitopes of Herpes simplex virus type 1, derived from glycoproteins B (gB) and D (gD), are linked to a synthetic lipid core. The ability of the lipid core peptide (LCP) constructs (LCP-gB and LCP-gD) to induce cytokine expression and activate the mitogen-activated protein kinase cascade has been evaluated and compared with the behaviour of the isolated epitopes and the lipid core. In this respect, the use of LCP technology coupled with the use of three different gB or gD peptide epitopes in the same branched constructs could represent an interesting approach in order to obtain efficient delivery systems in the development of a synthetic multiepitopic vaccine for the prevention of viral infections.

Pro-apoptotic activity of lipidic α-amino acids isolated from Protopalythoa variabilis

Lipidic α-amino acids (LAAs) have been described as non-natural amino acids with long saturated or unsaturated aliphatic chains. In the continuing prospect to discover anticancer agents from marine sources, we have obtained a mixture of two cytotoxic LAAs (1a and 1b) from the zoanthid Protopalythoa variabilis. The anti-proliferative potential of 14 synthetic LAAs and 1a/1b were evaluated on four tumor cell lines (HCT-8, SF-295, MDA-MB-435, and HL-60). Five of the synthetic LAAs showed high percentage of tumor cell inhibition, while 1a/1b completely inhibited tumor cell growth. Additionally, apoptotic effects of 1a/1b were studied on HL-60 cell line. 1a/1b-treated cells showed apoptosis morphology, loss of mitochondrial potential, and DNA fragmentation.

Dendrimers for vaccine and immunostimulatory uses. A review

Dendrimers are well-defined (monodisperse) synthetic globular polymers with a range of interesting chemical and biological properties. Chemical properties include the presence of multiple accessible surface functional groups that can be used for coupling biologically relevant molecules and methods that allow for precise heterofunctionalization of surface groups. Biologically, dendrimers are highly biocompatible and have predictable biodistribution and cell membrane interacting characteristics determined by their size and surface charge. Dendrimers have optimal characteristics to fill the need for efficient immunostimulating compounds (adjuvants) that can increase the efficiency of vaccines, as dendrimers can provide molecularly defined multivalent scaffolds to produce highly defined conjugates with small molecule immunostimulators and/or antigens. The review gives an overview on the use of dendrimers as molecularly defined carriers/presenters of small antigens, including constructs that have built-in immunostimulatory (adjuvant) properties, and as stand-alone adjuvants that can be mixed with antigens to provide efficient vaccine formulations. These approaches allow the preparation of molecularly defined vaccines with highly predictable and specific properties and enable knowledge-based vaccine design substituting the traditional empirically based approaches for vaccine development and production.

Increasing the antigenicity of synthetic tumor-associated carbohydrate antigens by targeting Toll-like receptors

SYNTHETIC CANCER VACCINES: A number of fully synthetic vaccine candidates have been designed, chemically synthesized, and immunologically evaluated to establish a strategy to overcome the poor immunogenicity of tumor-associated carbohydrates and glycopeptides and to determine the importance of Toll-like receptor (TLR) engagement for antigenic responses against these compounds.Epithelial cancer cells often overexpress mucins that are aberrantly glycosylated. Although it has been realized that these compounds offer exciting opportunities for the development of immunotherapy for cancer, their use is hampered by the low antigenicity of classical immunogens composed of a glycopeptide derived from a mucin conjugated to a foreign carrier protein. We have designed, chemically synthesized, and immunologically evaluated a number of fully synthetic vaccine candidates to establish a strategy to overcome the poor immunogenicity of tumor-associated carbohydrates and glycopeptides. The compounds were also designed to allow study of the importance of Toll-like receptor (TLR) engagement for these antigenic responses in detail. We have found that covalent attachment of a TLR2 agonist, a promiscuous peptide T-helper epitope, and a tumor-associated glycopeptide gives a compound (1) that elicits in mice exceptionally high titers of IgG antibodies that recognize MCF7 cancer cells expressing the tumor-associated carbohydrate. Immunizations with glycolipopeptide 2, which contains lipidated amino acids instead of a TLR2 ligand, gave significantly lower titers of IgG antibodies; this demonstrates that TLR engagement is critical for optimum antigenic responses. Although mixtures of compound 2 with Pam(3)CysSK(4) (3) or monophosphoryl lipid A (4) elicited titers of IgG antibodies similar to those seen with 1, the resulting antisera had impaired ability to recognize cancer cells. It was also found that covalent linkage of the helper T-epitope to the B-epitope is essential, probably because internalization of the helper T-epitope by B-cells requires assistance of the B-epitope. The results presented here show that synthetic vaccine development is amenable to structure-activity relationship studies for successful optimization of carbohydrate-based cancer vaccines.

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.

Toward the development of prophylactic and therapeutic human papillomavirus type-16 lipopeptide vaccines

Four lipid-core peptide systems were synthesized using stepwise solid-phase peptide synthesis, incorporating a sequence from the human papillomavirus type-16 (HPV-16) E7 protein (E744-62), for the purpose of developing vaccines against HPV-16 associated cervical cancer. d-Mannose was conjugated to the vaccine in order to investigate whether the targeting of dendritic cell mannose receptors would improve vaccine efficacy. The ability of the vaccines to clear or reduce the size of HPV-16 associated tumors was assessed in C57BL/6 (H-2b) mice using the TC-1 HPV-16 tumor model. Overall, significant reductions in the size of TC-1 tumors were observed in the mouse model, with the conjugation of mannose to these vaccines demonstrated to clear or reduce the size of TC-1 tumors to a greater extent than non-mannose-containing vaccines (37 out of 40 versus 21 out of 30 tumors cleared, respectively).

Method for the synthesis of highly pure vaccines using the lipid core peptide system

Traditional vaccines consisting of whole attenuated microorganisms, killed microorganisms, or microbial components, administered with an adjuvant (e.g. alum), have been proved to be extremely successful. However, to develop new vaccines, or to improve upon current vaccines, new vaccine development techniques are required. Peptide vaccines offer the capacity to administer only the minimal microbial components necessary to elicit appropriate immune responses, minimizing the risk of vaccination associated adverse effects, and focusing the immune response toward important antigens. Peptide vaccines, however, are generally poorly immunogenic, necessitating administration with powerful, and potentially toxic adjuvants. The attachment of lipids to peptide antigens has been demonstrated as a potentially safe method for adjuvanting peptide epitopes. The lipid core peptide (LCP) system, which incorporates a lipidic adjuvant, carrier, and peptide epitopes into a single molecular entity, has been demonstrated to boost immunogenicity of attached peptide epitopes without the need for additional adjuvants. The synthesis of LCP systems normally yields a product that cannot be purified to homogeneity. The current study describes the development of methods for the synthesis of highly pure LCP analogs using native chemical ligation. Because of the highly lipophilic nature of the LCP lipid adjuvant, difficulties (e.g. poor solubility) were experienced with the ligation reactions. The addition of organic solvents to the ligation buffer solubilized lipidic species, but did not result in successful ligation reactions. In comparison, the addition of approximately 1% (w/v) sodium dodecyl sulfate (SDS) proved successful, enabling the synthesis of two highly pure, tri-epitopic Streptococcus pyogenes LCP analogs. Subcutaneous immunization of B10.BR (H-2(k)) mice with one of these vaccines, without the addition of any adjuvant, elicited high levels of systemic IgG antibodies against each of the incorporated peptides.

Synthesis of a highly pure lipid core peptide based self-adjuvanting triepitopic group A streptococcal vaccine, and subsequent immunological evaluation

We have developed a highly pure, self-adjuvanting, triepitopic Group A Streptococcal vaccine based on the lipid core peptide system, a vaccine delivery system incorporating lipidic adjuvant, carrier, and peptide epitopes into a single molecular entity. Vaccine synthesis was performed using native chemical ligation. Due to the attachment of a highly lipophilic adjuvant, addition of 1% (w/v) sodium dodecyl sulfate was necessary to enhance peptide solubility in order to enable ligation. The vaccine was synthesized in three steps to yield a highly pure product (97.7% purity) with an excellent overall yield. Subcutaneous immunization of B10.BR (H-2(k)) mice with the synthesized vaccine, with or without the addition of complete Freund's adjuvant, elicited high serum IgG antibody titers against each of the incorporated peptide epitopes.

Enhanced protection against Streptococcus pyogenes infection by intranasal vaccination with a dual antigen component M protein/SfbI lipid core peptide vaccine formulation

We investigated the efficacy of a synthetic Streptococcus pyogenes vaccine targeting two virulence factors using the Lipid Core Peptide (LCP) delivery system. BALB/c mice were immunised intranasally with LCPs containing peptides encompassing T-cell and B-cell epitopes of the conserved C-repeat region of the M protein (J8) or the fibronectin-binding repeats region (FNBR) of SfbI, or a combination formulation containing peptides representing both antigens. LCPs were co-administered with the TLR2/6 agonist MALP-2 as mucosal adjuvant. Humoral and cellular immune responses stimulated at systemic and mucosal levels were strongest in mice immunised with the dual antigen formulation. Mice were completely protected following a respiratory challenge with a lethal dose of a heterologous S. pyogenes strain, whereas there was 70% and 90% survival in mice immunised with LCP-J8 and LCP-FNBR, respectively. This is the first report demonstrating the elicitation of better protective immunity by a dual antigen component S. pyogenes vaccine.

Method for the Synthesis of Multi-Epitopic Streptococcus pyogenes Lipopeptide Vaccines Using Native Chemical Ligation

The aim of this study was to investigate methods for the synthesis of highly pure, well-characterized analogues of the lipid core peptide (LCP) system. Difficulties synthesizing and purifying conventional LCP systems have led to the requirement for a technique to produce highly pure, LCP-based vaccines for potential use in human clinical trials. The current study describes methods for the attachment of lipophilic adjuvants onto multi-epitopic peptide vaccines. Described is the synthesis, using native chemical ligation, of a highly pure, tri-epitopic, group A streptococcal (GAS) lipopeptide vaccine candidate. Intranasal immunization of the described tri-epitopic GAS lipopeptide with the mucosal adjuvant cholera toxin B subunit induced high serum IgG antibody titers specific for each of the incorporated peptide epitopes.

Dendrisomes: Vesicular Structures Derived from a Cationic Lipidic Dendron

The behavior of a novel synthetic lipidic cationic lysine-based dendron (partial dendrimer) in aqueous media and its ability, with and without cholesterol, to self-assemble into higher order structures was studied to gain an understanding of these structures as potential drug carriers. The dendron was prepared by solid-phase peptide synthesis. A reverse-phase evaporation (REV) technique was used to prepare cationic vesicular aggregates of the dendron with different molar ratios of cholesterol. The size and zeta potential of these supramolecular aggregates or "dendrisomes" was determined by photon correlation spectroscopy (PCS). Dendrisome morphology and thermotropic properties were studied by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Radiolabeled penicillin G was used as a model of a negatively charged water-soluble compound to investigate the encapsulation efficiency of the dendrisomes. In vitro release of the drug was determined using as a comparator a REV liposome formulation. Dendrisomes of all compositions have higher encapsulation efficiencies and slower release rates compared to the comparator. Cholesterol was found both to increase the size of the aggregates from around 310 to 560 nm and to increase shape irregularities, but did not change the positive zeta potential, in the order of +50 mV, of the dendrisomes. Cholesterol decreases penicillin G entrapment efficiency but increases solute leakage at 25 degrees C.

Increased adjuvant activity of minimal CD8 T cell peptides incorporated into lipid‐core‐peptides

A problem facing the use of subunit peptide and protein vaccines is their inability to stimulate protective immune responses. Many different approaches have been utilized to overcome this inefficient immune activation. The approach we have taken is to modify the vaccine antigen so that it now has adjuvant properties. To do this, multiple copies of minimal CD8 T cell epitopes were attached to a poly lysine lipid core. These constructs are known as lipid-core-peptides (LCP). The research presented here examines the adjuvant activity of LCP. Using mouse models, we were able to show that LCP were indeed able to activate antigen-presenting cells in vitro and to activate cytotoxic T-cell responses in vivo. More importantly, LCP were able to stimulate the development of a protective antitumour immune response.

Potential of lipid core peptide technology as a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens

This study demonstrates the effectiveness of a novel self-adjuvanting vaccine delivery system for multiple different synthetic peptide immunogens by use of lipid core peptide (LCP) technology. An LCP formulation incorporating two different protective epitopes of the surface antiphagocytic M protein of group A streptococci (GAS)--the causative agents of rheumatic fever and subsequent rheumatic heart disease--was tested in a murine parenteral immunization and GAS challenge model. Mice were immunized with the LCP-GAS formulation, which contains an M protein amino-terminal type-specific peptide sequence (8830) in combination with a conserved non-host-cross-reactive carboxy-terminal C-region peptide sequence (J8) of the M protein. Our data demonstrated immunogenicity of the LCP-8830-J8 formulation in B10.BR mice when coadministered in complete Freund's adjuvant and in the absence of a conventional adjuvant. In both cases, immunization led to induction of high-titer GAS peptide-specific serum immunoglobulin G antibody responses and induction of highly opsonic antibodies that did not cross-react with human heart tissue proteins. Moreover, mice were completely protected from GAS infection when immunized with LCP-8830-J8 in the presence or absence of a conventional adjuvant. Mice were not protected, however, following immunization with an LCP formulation containing a control peptide from a Schistosoma sp. These data support the potential of LCP technology in the development of novel self-adjuvanting multi-antigen component vaccines and point to the potential application of this system in the development of human vaccines against infectious diseases.

A lipid core peptide construct containing a conserved region determinant of the group A streptococcal M protein elicits heterologous opsonic antibodies

The study reported here investigated the immunogenicity and protective potential of a lipid core peptide (LCP) construct containing a conserved region determinant of M protein, defined as peptide J8. Parenteral immunization of mice with LCP-J8 led to the induction of high-titer serum immunoglobulin G J8-specific antibodies when the construct was coadministered with complete Freund's adjuvant (CFA) or administered alone. LCP-J8 in CFA had significantly enhanced immunogenicity compared with the monomeric peptide J8 given in CFA. Moreover, LCP-J8/CFA and LCP-J8 antisera opsonized four different group A streptococcal (GAS) strains, and the antisera did not cross-react with human heart tissue proteins. These data indicate the potential of an LCP-based M protein conserved region GAS vaccine in the induction of broadly protective immune responses in the absence of a conventional adjuvant.

Enhancing the immunogenicity and modulating the fine epitope recognition of antisera to a helical group A streptococcal peptide vaccine candidate from the M protein using lipid-core peptide technology

A conserved helical peptide vaccine candidate from the M protein of group A streptococci, p145, has been described. Minimal epitopes within p145 have been defined and an epitope recognized by protective antibodies, but not by autoreactive T cells, has been identified. When administered to mice, p145 has low immunogenicity. Many boosts of peptide are required to achieve a high antibody titre (> 12 800). To attempt to overcome this low immunogenicity, lipid-core peptide technology was employed. Lipid-core peptides (LCP) consist of an oligomeric polylysine core, with multiple copies of the peptide of choice, conjugated to a series of lipoamino acids, which acts as an anchor for the antigen. Seven different LCP constructs based on the p145 peptide sequence were synthesized (LCP1-->LCP7) and the immunogenicity of the compounds examined. The most immunogenic constructs contained the longest alkyl side-chains. The number of lipoamino acids in the constructs affected the immunogenicity and spacing between the alkyl side-chains increased immunogenicity. An increase in immunogenicity (enzyme-linked immunosorbent assay (ELISA) titres) of up to 100-fold was demonstrated using this technology and some constructs without adjuvant were more immunogenic than p145 administered with complete Freund's adjuvant (CFA). The fine specificity of the induced antibody response differed for the different constructs but one construct, LCP4, induced antibodies of identical fine specificity to those found in endemic human serum. Opsonic activity of LCP4 antisera was more than double that of p145 antisera. These data show the potential for LCP technology to both enhance immunogenicity of complex peptides and to focus the immune response towards or away from critical epitopes.

Lipoamino acid-based adjuvant carrier system: enhanced immunogenicity of group a streptococcal peptide epitopes

Lipoamino acid-based synthetic peptides (lipid core peptides, LCP) derived from the type-specific and conserved region determinants of group A streptococci (GAS) were evaluated as potential candidate sequences in a vaccine to prevent GAS-associated diseases, including rheumatic heart disease and poststreptococcal acute glomerulonephritis. The LCP peptides had significantly enhanced immunogenicity as compared with the monomeric peptide epitopes. Furthermore, the peptides incorporated into the LCP system generated epitope-specific antibodies without the use of any conventional adjuvant.

Synthesis of (S)-alpha-amino oleic acid

An efficient synthesis of (S)-alpha-amino oleic acid was developed. The fully protected FA derivative was obtained in four steps starting from methyl (2S)-2-[bis(tert-butoxycarbonyl)amino]-5-oxopentanoate. These steps are (i) olefination of the starting aldehyde with the appropriate phosphonate anion, (ii) hydrogenation of the double bonds, (iii) controlled reduction of omega-ethyl ester to an aldehyde in the presence of alpha-methyl ester, and (iv) a Wittig reaction of the latter aldehyde with the suitable ylide. Free alpha-amino oleic acid was prepared after deprotection of the amino group followed by saponification in a total yield of 24%. N-tert-Butoxycarbonyl-protected amino oleic acid and the corresponding amino alcohol were prepared in high yield. The structures of the products have been established by various spectroscopic techniques.

Interaction of cationic partial dendrimers with charged and neutral liposomes

Amphipathic partial dendrimers having three lipidic (C(14)) chains coupled to dendritic lysine head groups with eight, 16 or 32 free terminal amino groups have been synthesised by solid-phase peptide synthesis. Liposomes were prepared with positive, negative and neutral charge using the dehydration-rehydration method and their interaction with the partial dendrimers studied. The interaction efficiency of the partial cationic dendrimers studied was greater than 88%. Interaction of the cationic partial dendrimer converted liposomes with very low or negative charge into positively charged species. Apparent vesicle size increased with the head size of the partial dendrimer but, in the case of negatively charged liposomes, large changes in properties were observed after ultracentrifugation due to the formation of myelin figures. To investigate the mode of interaction with the liposomes, adsorption studies were performed by adding the partial dendrimer after the preparation of dehydration-rehydration vesicles. The results indicated that adsorption is inversely proportional to the head size of the partial dendrimer molecules and the extent of adsorption was similar on both positively and negatively charged liposomes. Adsorption produced liposomes with greater or similar zeta potentials to liposomes that incorporated partial dendrimer through the dehydration-rehydration method. Taking account of the different interaction efficiencies, this suggests there is a degree of partial dendrimer entrappment inside the liposomes.

Oral uptake and translocation of a polylysine dendrimer with a lipid surface

A series of lipidic peptide dendrimers based on lysine with 16 surface alkyl (C(12)) chains has been synthesised in our laboratories. One of the series, a fourth generation dendrimer with a diameter of 2.5 nm was chosen to study its absorption after oral administration to female Sprague-Dawley rats (180 g, 9 weeks old). It was synthesised as the tritiated derivative (all acetyl portions) and had a molecular weight of 6300 and log P (octanol/water) of 1.24. First a single oral dose 14 mg/kg was administered by gavage. Maximum levels of dendrimer observed were 15% in the small intestine, 5% in the large intestine and 3% in the blood at 6 h after administration, while 1.5% reached the liver, 0.1% the spleen and 0. 5% the kidneys. In a parallel study with a higher dose of 28 mg/kg, approximately 1% was absorbed via Peyer's patches of the small intestine at 3 h. The maximum uptake by small intestine enterocytes was 4% of the dose after 3 h. After 12 h, 0.3 and 4% dendrimer was measured respectively in Peyer's patches and enterocytes of the large intestine. When calculated on the basis of target tissue weight, the total percentage of the dose absorbed through Peyer's patches was greater than through normal enterocytes in the small intestine after 3 and 24 h, but the opposite was true in the large intestine. These levels of uptake and translocation are lower than those exhibited by polystyrene particles in the range from 50 to 3000 nm. This might suggest that there is an optimum size for nanoparticulate uptake by the gut.

Synthesis and properties of novel lipopeptides and lipid mimetics

Lipid mimetics, synthetic molecules that resemble natural lipids either structurally or functionally, have been developed as potential medicinal substances. They have been successfully applied in the development of drug and peptide delivery systems and for the development of inhibitors or lipid metabolizing enzymes. Phospholipase A2 is considered to be involved as the rate-limiting step in the production of lipid mediators of inflammatory responses and, as such, it has been a target for drug design. A series of lipid mimetics including lipopeptides, amides and alcohols of lipidic alpha-amino acids, have been tested by bulk and monolayer assay techniques. The findings suggested the direct interaction of the tested compounds with porcine pancreatic phospholipase A2. The inactivation of the enzyme occurred in a competitive manner. The most active compound I (2-amino-N-hexadecyl-L-hexanamide) showed an apparent IC50 of 12 microM and inhibitory power Z = 13 in the monolayer assay.

Synthesis of lipidic amino acid and dipeptide inhibitors of human platelet phospholipase A2

Phospholipases A2 (PLA2s) catalyze the hydrolysis of glycerophospholipids at the sn-2 position, and their inhibition is considered a rational approach for the prevention and treatment of inflammation. A number of amides and esters of alpha-amino acids with saturated linear side chains, esters of alpha-amino alcohols and derivatives of lipidic peptides were prepared and tested against secreted humal platelet phospholipase A2. Among the compounds tested the amides of free amino acids with long-chain amines presented the highest in vitro inhibitory activity.