Application of oligosaccharidic gold nanoparticles to the vaccines for the therapy of breast cancer: synthesis of neu5GcLactose antigen starting from a complex ganglioside mixture

Gangliosides, sphingolipids containing sialic acid residue(s), are components of the external layer of cell plasma membranes where they are inserted with the hydrophilic head group turned towards the extra cellular environment. In this strategic position, gangliosides contribute to very special cell processes as development, differentiation and oncogenic transformation. Analysis of the tumour associated ganglioside component profile may aid in the characterization of tumour cells and to establish the degree of malignant transformation. Furthermore, gangliosides that become prominently exposed on tumour cell during oncogenic dedifferentiation may be used as targets for specific immunohistological identification and possible therapeutic approaches. In humans the main sialic acid is N-acetyl-neuraminic acid (Neu5Ac), whereas N-glycolyl neuraminic acid (Neu5Gc) is not expressed in normal human tissues because a species-specific genetic mutation abrogate its biosynthesis. However breast cancer cells contain ganglioside GM3 carryng not only Neu5Ac but also Neu5Gc which resulted highly immunogenic and can be considered a good target for immunotherapy development. Some laboratories produced murine or human monoclonal antibodies (MAbs) against GM3(NeuGc) ganglioside antigen but the low specificity of these monoclonal antibodies made them only partially useful for the cancer diagnosis and therapy. The aim of this thesis was to synthesize the oligosaccaridic chain of GM3(NeuGc) and obtain an idiotopic antigen that mimic the oligosaccharide of GM3(NeuGc). The first part of the research involved the synthesis of the oligosaccharide α-Neu5Gc-(2-3)-β-Gal-(1-4)-β-Glc: starting from the natural GM3, which contains the Neu5Ac, we removed the acetyl group from the sialic acid and then synthesized the GM3(NeuGc). Later we removed the ceramide portion in order to obtain the free oligo-saccharide chain of GM3(NeuGc). Because the it is known that the oligosaccharidic molecules alone are not capable to induce an antibody response enough specific and efficient, we decided to synthesized a complex between the prepared oligosaccharide and gold nanoparticles. For this purpose we performed a two-phase synthesis: a thiol ligand (thio-acetyl-nonanole) is first tied with the free oligo-saccharide chain of GM3(NeuGc) and then strongly bound to colloidal gold thus obtaining the gold-glyconanoparticles.