Synthesis of Mannosylated Lipopeptides with Receptor Targeting Properties.

Present on the surface of antigen presenting cells (APCs), the mannose receptor (MR) has long been recognized as a front-line receptor in pathogen recognition. During the past decade many attempts have been made to target this receptor for applications including vaccine and drug development. In the present study, a library of vaccine constructs comprising fluorescently labeled mannosylated lipid-dendrimers that contained the ovalbumin CD4(+) epitope, OVA(323-339), as the model peptide antigen were synthesized using fluorenylmethyloxycarbonyl (Fmoc) solid phase peptide synthesis (SPPS). The vaccine constructs were designed with an alanine spacer between the O-linked mannose moieties to investigate the impact of distance between the mannose units on receptor-mediated uptake and/or binding in APCs. Uptake studies performed on F4/80(+) and CD11c(+) cells showed significant uptake and/or binding for lipopeptides containing mannose, and also the lipopeptide without mannose when compared to the control peptides (peptide with no lipid and peptide with no mannose and no lipid). Furthermore, mannan inhibition assays demonstrated that uptake of the mannosylated and lipidated peptides was receptor mediated. To address the specificity of receptor uptake, surface plasmon resonance studies were performed using biacore technology and confirmed high affinity of the mannosylated and lipidated vaccine constructs toward the MR. These studies confirm that both mannose and lipid moieties play significant roles in receptor-mediated uptake on APCs, potentially facilitating vaccine development.

Self-adjuvanting vaccine against group A streptococcus: application of fibrillized peptide and immunostimulatory lipid as adjuvant.

Peptides are of great interest to be used as vaccine antigens due to their safety, ease of manufacturing and specificity in generating immune response. There have been massive discoveries of peptide antigens over the past decade. However, peptides alone are poorly immunogenic, which demand co-administration with strong adjuvant to enhance their immunogenicity. Recently, fibril-forming peptides such as Q11 and lipoamino acid-based carrier have been identified to induce substantial immune responses when covalently linked to peptide epitope. In this study, we have incorporated either Q11 or lipoamino acids to a peptide epitope (J14) derived from M protein of group A streptococcus to develop self-adjuvanting vaccines. J14, Q11 and lipoamino acids were also conjugated together in a single vaccine construct in an attempt to evaluate the synergy effect of combining multiple adjuvants. Physicochemical characterization demonstrated that the vaccine constructs folded differently and self-assembled into nanoparticles. Significantly, only vaccine constructs containing double copies of lipoamino acids (regardless in conjugation with Q11 or not) were capable to induce significant dendritic cells uptake and subsequent J14-specific antibody responses in non-sizes dependent manners. Q11 had minimal impact in enhancing the immunogenicity of J14 even when it was used in combination with lipoamino acids. These findings highlight the impact of lipoamino acids moiety as a promising immunostimulant carrier and its number of attachment to peptide epitope was found to have a profound effect on the vaccine immunogenicity.

Pre-clinical evaluation of a whole-parasite vaccine to control human babesiosis.

Babesia spp. are tick-transmitted intra-erythrocytic protozoan parasites that infect humans and animals, causing a flu-like illness and hemolytic anemia. There is currently no human vaccine available. People most at risk of severe disease are the elderly, immunosuppressed, and asplenic individuals. B. microti and B. divergens are the predominant species affecting humans. Here, we present a whole-parasite Babesia vaccine. To establish proof-of-principle, we employed chemically attenuated B. microti parasitized red blood cells from infected mice. To aid clinical translation, we produced liposomes containing killed parasite material. Vaccination significantly reduces peak parasitemia following challenge. B cells and anti-parasite antibodies do not significantly contribute to vaccine efficacy. Protection is abrogated by the removal of CD4+ T cells or macrophages prior to challenge. Importantly, splenectomized mice are protected by vaccination. To further facilitate translation, we prepared a culture-based liposomal vaccine and demonstrate that this performs as a universal vaccine inducing immunity against different human Babesia species.

Mannosylated liposomes formulated with whole parasite P. falciparum blood-stage antigens are highly immunogenic in mice.

The development of a blood-stage malaria vaccine has largely focused on the subunit approach. However, the limited success of this strategy, mainly due to antigenic polymorphism and the failure to maintain potent parasite-specific immune responses, indicates that other approaches must be considered. Whole parasite (WP) vaccines offer many advantages over sub-units; they represent every antigen on the organism, thus limiting the effects of antigenic polymorphism, and similarly they compensate for individual Immune-Response (Ir) gene-regulated non-responsiveness to any particular antigen. From a development perspective, they negate the need to identify and compare the relative efficacies of individual candidate antigens. WP vaccines induce protective immunity that is largely cell-mediated. However, WP blood-stage vaccines present a number of challenges for the development pathway. Key issues are cryopreservation and storage and the possible induction of antibodies against red blood cell surface antigens, even if the parasites are grown in blood group O, Rh negative blood. Here, we used a novel adaptation of an immunomagnetic method from STEMCELL™ Technologies to remove the red cell membranes from human red blood cells parasitized with P. falciparum. We then used these antigens to construct liposomes which were modified to present mannose on their membrane to target the liposome to antigen presenting cells. We then compared the immunogenicity of freshly prepared and lyophilized liposome vaccines. Following vaccination of mice, liposomes induced significantly lower antibody responses to human red cells but potent strain- and species-transcending cell-mediated immune responses to parasite antigens. These data support transitioning the P. falciparum liposomal vaccine into clinical studies.

Poly(amino acids) as a potent self-adjuvanting delivery system for peptide-based nanovaccines.

To be optimally effective, peptide-based vaccines need to be administered with adjuvants. Many currently available adjuvants are toxic, not biodegradable; they invariably invoke adverse reactions, including allergic responses and excessive inflammation. A nontoxic, biodegradable, biocompatible, self-adjuvanting vaccine delivery system is urgently needed. Herein, we report a potent vaccine delivery system fulfilling the above requirements. A peptide antigen was coupled with poly-hydrophobic amino acid sequences serving as self-adjuvanting moieties using solid-phase synthesis, to produce fully defined single molecular entities. Under aqueous conditions, these molecules self-assembled into distinct nanoparticles and chain-like aggregates. Following subcutaneous immunization in mice, these particles successfully induced opsonic epitope-specific antibodies without the need of external adjuvant. Mice immunized with entities bearing 15 leucine residues were able to clear bacterial load from target organs without triggering the release of soluble inflammatory mediators. Thus, we have developed a well-defined and effective self-adjuvanting delivery system for peptide antigens.

Induction of Plasmodium-Specific Immune Responses Using Liposome-Based Vaccines.

In the development of vaccines, the ability to initiate both innate and subsequent adaptive immune responses need to be considered. Live attenuated vaccines achieve this naturally, while inactivated and sub-unit vaccines generally require additional help provided through delivery systems and/or adjuvants. Liposomes present an attractive adjuvant/delivery system for antigens. Here, we review the key aspects of immunity against Plasmodium parasites, liposome design considerations and their current application in the development of a malaria vaccine.

Highly Immunogenic Trimethyl Chitosan-based Delivery System for Intranasal Lipopeptide Vaccines against Group A Streptococcus.

BACKGROUND: Group A streptococcus (GAS) primarily colonizes the mucosal region of the upper respiratory tract, slowly leading to systemic infections. Thus, GAS-specific antibody responses are desirable at mucosal sites for early prevention against GAS colonization. METHODS: Herein, we developed a potent nanoliposomes-based delivery system for mucosally active lipid core peptide (LCP)-based vaccines. RESULTS: Trimethyl chitosan (TMC)-coated liposomes that bore a B-cell epitope derived from GAS Mprotein, stimulated potent epitope-specific mucosal and systemic antibody titres after only one boost following intranasal immunization in Swiss outbred mice. The immune responses were durable even at day 139 post-primary immunization. CONCLUSION: The enhanced vaccine efficacy, lowered dose, and simple and cost-effective process of producing the coated nanoliposomes should be particularly useful in developing potent peptide-based vaccines to prevent infections at the mucosal sites.

Development of New Gonadotropin-Releasing Hormone-Modified Dendrimer Platforms with Direct Antiproliferative and Gonadotropin Releasing Activity.

Gonadotropin-releasing hormone (GnRH) agonists (e.g., triptorelin) are used for androgen suppression therapy. They possess improved stability as compared to the natural GnRH, yet they suffer from a poor pharmacokinetic profile. To address this, we used a GnRH peptide-modified dendrimer platform with and without lipidation strategy. Dendrimers were synthesized on a polylysine core and bore either native GnRH (1, 2, and 5) or lipid-modified GnRH (3 and 4). Compound 3, which bore a lipidic moiety in a branched tetramer structure, showed approximately 10-fold higher permeability and metabolic stability and 39 times higher antitumor activity against hormone-resistant prostate cancer cells (DU145) relative to triptorelin. In gonadotropin-release experiments, dendrimer 3 was shown to be the most potent construct. Dendrimer 3 showed similar luteinizing hormone (LH)-release activity to triptorelin in mice. Our findings indicate that dendrimer 3 is a promising analog with higher potency for the treatment of hormone-resistant prostate cancer than the currently available GnRH agonists.

A semi-synthetic whole parasite vaccine designed to protect against blood stage malaria.

UNLABELLED: Although attenuated malaria parasitized red blood cells (pRBCs) are promising vaccine candidates, their application in humans may be restricted for ethical and regulatory reasons. Therefore, we developed an organic microparticle-based delivery platform as a whole parasite malaria-antigen carrier to mimic pRBCs. Killed blood stage parasites were encapsulated within liposomes that are targeted to antigen presenting cells (APCs). Mannosylated lipid core peptides (MLCPs) were used as targeting ligands for the liposome-encapsulated parasite antigens. MLCP-liposomes, but not unmannosylated liposomes, were taken-up efficiently by APCs which then significantly upregulated expression of MHC-ll and costimulatory molecules, CD80 and CD86. Two such vaccines using rodent model systems were constructed - one with Plasmodium chabaudi and the other with P. yoelii. MLCP-liposome vaccines were able to control the parasite burden and extended the survival of mice. Thus, we have demonstrated an alternative delivery system to attenuated pRBCs with similar vaccine efficacy and added clinical advantages. Such liposomes are promising candidates for a human malaria vaccine. STATEMENT OF SIGNIFICANCE: Attenuated whole parasite-based vaccines, by incorporating all parasite antigens, are very promising candidates, but issues relating to production, storage and safety concerns are significantly slowing their development. We therefore developed a semi-synthetic whole parasite malaria vaccine that is easily manufactured and stored. Two such prototype vaccines (a P. chabaudi and a P. yoelii vaccine) have been constructed. They are non-infectious, highly immunogenic and give good protection profiles. This semi-synthetic delivery platform is an exciting strategy to accelerate the development of a licensed malaria vaccine. Moreover, this strategy can be potentially applied to a wide range of pathogens.

Lipid core peptide/poly(lactic-co-glycolic acid) as a highly potent intranasal vaccine delivery system against Group A streptococcus.

Rheumatic heart disease represents a leading cause of mortality caused by Group A Streptococcus (GAS) infections transmitted through the respiratory route. Although GAS infections can be treated with antibiotics these are often inadequate. An efficacious GAS vaccine holds more promise, with intranasal vaccination especially attractive, as it mimics the natural route of infections and should be able to induce mucosal IgA and systemic IgG immunity. Nanoparticles were prepared by either encapsulating or coating lipopeptide-based vaccine candidate (LCP-1) on the surface of poly(lactic-co-glycolic acid) (PLGA). In vitro study showed that encapsulation of LCP-1 vaccine into nanoparticles improved uptake and maturations of antigen-presenting cells. The immunogenicity of lipopeptide incorporated PLGA-based nanoparticles was compared with peptides co-administered with mucosal adjuvant cholera toxin B in mice upon intranasal administration. Higher levels of J14-specific salivary mucosal IgA and systemic antibody IgG titres were observed for groups immunized with encapsulated LCP-1 compared to LCP-1 coated nanoparticles or free LCP-1. Systemic antibodies obtained from LCP-1 encapsulated PLGA NPs inhibited the growth of bacteria in six different GAS strains. Our results show that PLGA-based lipopeptide delivery is a promising approach for rational design of a simple, effective and patient friendly intranasal GAS vaccine resulting in mucosal IgA response.

Liposome-based intranasal delivery of lipopeptide vaccine candidates against group A streptococcus.

UNLABELLED: Group A streptococcus (GAS), an exclusively human pathogen, causes a wide range of diseases ranging from trivial to life threatening. Treatment of infection is often ineffective following entry of bacteria into the bloodstream. To date, there is no vaccine available against GAS. In this study, cationic liposomes encapsulating lipopeptide-based vaccine candidates against GAS have been employed for intranasal vaccine delivery. Cationic liposomes were prepared with dimethyldioctadecylammonium bromide (DDAB) using the film hydration method. Female Swiss mice were immunized intranasally with the liposomes. In contrast to unmodified peptides, lipopeptides entrapped by liposomes induced both mucosal and systemic immunity, IgA and IgG (IgG1 and IgG2a) production in mice, respectively. High levels of antibody (IgA and IgG) titres were detected even five months post immunization. Thus, the combination of lipopeptides and liposomes generates a very promising delivery system for intranasal vaccines. STATEMENT OF SIGNIFICANCE: Group A streptococcus, causing rheumatic heart diseases, kills approximately half a million people annually. There is no vaccine available against the infection. Mucosal immunity is vital in ensuring an individual is protected as this gram positive bacteria initially colonizes at the throat. Herein, we demonstrated that lipopeptides entrapped by liposomes induced both mucosal and systemic immunity. High levels of antibody (IgA and IgG) titres were detected even five months post immunization and lead vaccine candidate was able to induce humoral immune responses even after single immunization. Thus, the combination of lipopeptides and liposomes generates a very promising delivery system for intranasal vaccines.

Investigation of structure-activity relationships of synthetic anti-gonadotropin releasing hormone vaccine candidates.

The immunoneutralization of gonadotropin-releasing hormone (GnRH) can be used for the treatment of human hormone-dependent male and female cancers or as immunocontraceptives in animals. Vaccine candidates 1 [Th(K-LP)GnRH], 2 [GnRH(K-LP)Th], 3 [GnRH(K-Th)LP], and 4 [Th(K-GnRH)LP] (for which K=lysine, LP=lipopeptide Ser-Ser-C16 -C16 , and Th=T helper cell epitope influenza HA2), were synthesized by assembling a CD4(+) T helper cell epitope (Th), GnRH, and an adjuvanting lipid moiety (LP) in various spatial arrangements. All compounds were efficiently taken up by antigen-presenting cells with significant immunogenicity without an external adjuvant. Compounds 2, 3, and 4, in which GnRH is conjugated through its C terminus, produced higher GnRH-specific antibody responses than construct 1, in which the GnRH moiety is conjugated through its N terminus. All four constructs induced a significant antiproliferative effect (up to 55 %) on GnRH-receptor-positive LNCaP cells, but showed weaker activity in the GnRH-receptor-negative SKOV-3 cell line. Marked degenerative changes were observed in morphology and follicular development in the ovaries of immunized mice, with approximately 30 % higher degenerative antral and atretic follicles.

Self-adjuvanting therapeutic peptide-based vaccine induce CD8+ cytotoxic T lymphocyte responses in a murine human papillomavirus tumor model.

Vaccine candidates for the treatment of human papillomavirus (HPV)-associated cancers are aimed to activate T-cells and induce development of cytotoxic anti-tumor specific responses. Peptide epitopes derived from HPV-16 E7 oncogenic protein have been identified as promising antigens for vaccine development. However, peptide-based antigens alone elicit poor cytotoxic T lymphocyte (CTL) responses and need to be formulated with an adjuvant (immunostimulant) to achieve the desired immune responses. We have reported the ability of polyacrylate 4-arm star-polymer (S4) conjugated with HPV-16 E744-57 (8Qmin) epitope to reduce and eradicate TC-1 tumor in the mouse model. Herein, we have studied the mechanism of induction of immune responses by this polymer-peptide conjugate and found prompt uptake of conjugate by antigen presenting cells, stimulating stronger CD8(+) rather than CD4(+) or NK cell responses.

Polyacrylate-based delivery system for self-adjuvanting anticancer peptide vaccine.

Vaccination can provide a safe alternative to chemotherapy by using the body's natural defense mechanisms to create a potent immune response against tumor cells. Peptide-based therapeutic vaccines against human papillomavirus (HPV)-related cancers are usually designed to elicit cytotoxic T cell responses by targeting the HPV-16 E7 oncoprotein. However, peptides alone lack immunogenicity, and an additional adjuvant or external delivery system is required. In this study, we developed new polymer-peptide conjugates to create an efficient self-adjuvanting system for peptide-based therapeutic vaccines. These conjugates reduced tumor growth and eradicated E7-positive TC-1 tumors in mice after a "single shot" immunization, without the help from an external adjuvant. The new conjugates had a significantly higher anticancer efficacy than the antigen formulated with a commercial adjuvant. Furthermore, the polymer-peptide conjugates were promptly taken up by antigen presenting cells, including dendritic cells and macrophages, and efficiently activated CD4(+) T-helper cells and CD8(+) cytotoxic T lymphocyte cells.

Liposomes as nanovaccine delivery systems.

Since the discovery of liposomes by Alec Bangham in mid-1960s, these phospholipid vesicles have been widely used as pharmaceutical carriers. Liposomes have been extensively studied in the vaccine delivery field as a carrier and an immune stimulating agent. Liposomes are usually formulated as nanoparticles, mimicking the properties of pathogens, and have the ability to induce humoral and cell-mediated immune responses. In this review, we focused on modern nanotechnology-based approaches for the improvement of liposomal vaccine delivery systems. Topics such as size-dependent uptake, processing and activation of antigen presenting cells, targeting liposomes and route of administration are discussed.

Apoptogenic activity of ethyl acetate extract of leaves of Memecylon edule on human gastric carcinoma cells via mitochondrial dependent pathway.

OBJECTIVE: To evaluate the anti-proliferative and apoptogenic activity of ethyl acetate extract from the leaves of Memecylon edule (EtAc-LME) in MKN-74, NUGC gastric cancer cells and non cancerous gastric mucous cells (GES-1), and to explore the mechanism of EtAc-LME induced apoptosis. METHODS: The mechanism of EtAc-LME induced apoptosis was explored by analysing the activation of pro-caspases, PARP cleavage, expression of cytochrome-c (Cyt-c) was determined by western blotting, mRNA expression of Bcl-2, Bax by RT-PCR, loss of mitochondrial potential using DiOC6 dye, annexin binding assay and its influence on cell cycle arrest by flow cytometry. RESULTS: The results indicated that EtAc-LME inhibited the gastric cancer cell growth in dose-dependent manner and cytotoxicity was more towards the gastric cancer cells (NUGC and MKN-74) compared to normal gastric cells (GES-1), suggesting more specific cytotoxicity to the malignant cells. Over expression of Cyt-c and subsequent activation of caspases-3 and down regulation of Bcl-2 and loss in mitochondrial potential in EtAc-LME treated MKN-74 and NUGC cells suggested that EtAc-LME induced apoptosis by mitochondrial dependent pathway. CONCLUSIONS: The present findings suggest that ethyl acetate extract of Memecylon edule induces apoptosis selectively in gastric cancer cells emphasizing the importance of this traditional medicine for its potential in the treatment of gastric cancer.

Liposome-based delivery system for vaccine candidates: constructing an effective formulation.

The discovery of liposomes in 1965 by Bangham and coworkers changed the prospects of drug delivery systems. Since then, the application of liposomes as vaccine delivery systems has been studied extensively. Liposomal vaccine delivery systems are made up of nano- or micro-sized vesicles consisting of phospholipid bilayers, in which the bioactive molecule is encapsulated/entrapped, adsorbed or surface coupled. In general, liposomes are not immunogenic on their own; thus, liposomes combined with immunostimulating ligands (adjuvants) or various other formulations have been used as vaccine delivery systems. A thorough understanding of formulation parameters allows the design of effective liposomal vaccine delivery systems. This article provides an overview of various factors that influence liposomal immunogenicity. In particular, the effects of vesicle size, surface charge, bilayer composition, lamellarity, pegylation and targeting of liposomes are described.