Design, synthesis, and evaluation of anti-LHRH vaccine candidates based on a lipopeptide delivery system

Chang, Cheng-Hung (2015). Design, synthesis, and evaluation of anti-LHRH vaccine candidates based on a lipopeptide delivery system PhD Thesis, School of Chemistry and Molecular Biosciences, The University of Queensland. doi:10.14264/uql.2015.795

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Author Chang, Cheng-Hung
Thesis Title Design, synthesis, and evaluation of anti-LHRH vaccine candidates based on a lipopeptide delivery system
School, Centre or Institute School of Chemistry and Molecular Biosciences
Institution The University of Queensland
DOI 10.14264/uql.2015.795
Publication date 2015-08-14
Thesis type PhD Thesis
Supervisor Istvan Toth
Pegah Varamini
Total pages 116
Language eng
Subjects 1107 Immunology
0304 Medicinal and Biomolecular Chemistry
Formatted abstract
Luteinising hormone-releasing hormone (LHRH), also known as gonadotropin-releasing hormone (GnRH) and luliberin, is a key hormone associated with controlling functions of reproductive organs in both males and females. Anti-LHRH vaccines can produce immunity against LHRH resulting in castration effects, which can be applied for contraception in animals or the treatment of hormone-dependent diseases. A self- adjuvanting delivery system for peptide-based vaccines is a safe and effective approach to address the problem of toxic adjuvants used in animals and humans. Lipid core peptide (LCP) provides self-adjuvanting properties and is recognised to interact with specific Toll- like receptors on antigen presenting cells. Lipidic adjuvant, in conjugation with polylysine or a carbohydrate core in a multiple antigen peptide (MAP) system, has shown significant contribution to enhance the immunogenicity of small antigens like peptides and these approaches of modification have been adapted to reder immunogenicity studies.

One of the approaches is use carbohydrates to induce immunity is an effective and new strategy if the obstacles associated with poor quality of antibody response are overcome. Modified monosaccharaides such as glucose or galactose scaffold offer MAP system-like properties that provide attachment sites for conjugation of multiple identical epitopes. Moreover, different carbohydrate groups provide different orientations for the side chains. This structural conformation-related effect may augment immunity in vaccination. A carbohydrate-based anti-LHRH vaccine candidate was synthesised with a galactose scaffold. D-galactose was modified as a scaffold to provide conjugation sites for the attachment of four LHRH epitopes. However, due to low efficiency of the method, the synthesis resulted in a low yield of galactose scaffold, therefore sufficient final vaccine candidate was not achieved to be used in immunological studies.

Another approach of modification uses three components to form four branched vaccine candidates –(1 [Th(K-LP)LHRH], 2 [LHRH(K-LP)Th], 3 [LHRH(K-Th)LP], 4 [Th(K- LHRH)LP])– were designed and synthesised by assembling a promiscuous CD4+ T cell epitope (influenza HA2 light chain), a self-peptide LHRH, and an adjuvanting lipid moiety (2 × C16LAAs with 2 × Ser spacer) in different spatial arrangements. In vivo studies revealed effective anti-LHRH immunity was produced by all vaccine candidates with no need for coadministrstration of supplemental adjuvants. Furthermore, in vitro experiments revealed that the four compounds induced a significant direct antiproliferative effect (up to 55%) on a LHRH receptor-positive prostatic cancer cell line, LNCaP, (p < 0.05). This effect iiwas shown to be weaker in the LHRH receptor-negative cell line, SKOV-3, (p > 0.05). Marked degenerative changes were observed in morphology and follicular development in the ovaries of immunised mice. There was a decrease in the number of healthy antral follicles and an increase in the number of degenerative antral and atretic follicles, approximately 30% higher in treated ovaries than in control ovaries. In light of these results, compounds 2, 3 and 4 are promising candidates for immunisation against the LHRH peptide.

Last but not the least, a library of anti-LHRH vaccine candidates were designed using a MAP system, incorporating a lipopeptide system, and a combination of different lengths of LHRH epitope with a universal T helper epitope. Compounds synthesised using the MAP system demonstrated promising immunogenicity possibly through increasing contact with antigen presenting cells by multiple epitopes. Compounds were synthesised via solid phase peptide synthesis and azide-alkyne cycloaddition. This technique was used to overcome the problem of purification due to the high hydrophobicity of lipopeptide. Among all candidates, truncated LHRH-T helper epitope immunised mice demonstrated potential in vaccine development when the C-terminus of truncated LHRH was free in space.

Overall, this project unravelled the ability of different applied synthetic strategies and delivery systems to stimulate anti-LHRH immune response, and contributes to the development of future immunocontraceptives or vaccines against hormone-dependent cancers.
Keyword Anti-LHRH vaccine
Vaccine delivery system
Lipid core peptide

Document type: Thesis
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Created: Sat, 01 Aug 2015, 13:52:49 EST by Mr Cheng-hung Chang on behalf of School of Chemistry & Molecular Biosciences