Synthesis and Evaluation of Protein Conjugates of GM3 Derivatives Carrying Modified Sialic Acids as Highly Immunogenic Cancer Vaccine Candidates

GM3, a sialylated trisaccharide antigen expressed by a number of tumors, is an attractive target in the design of therapeutic cancer vaccines. However, a serious problem associated with GM3 is that it is poorly immunogenic. To overcome this problem for the development of GM3-based cancer vaccines, four GM3 derivatives, including 5'-N-p-methylphenylacetyl, 5'-N-p-methoxyphenylacetyl, 5'-N-p-acetophenylacetyl and 5'-N-p-chlorophenylacetyl GM3, were synthesized and then coupled to a carrier protein, keyhole limpet haemocyanin (KLH). The resultant glycoconjugates were evaluated as vaccines in mouse and compared to the KLH conjugate of 5'-N-phenylacetyl GM3 (GM3NPhAc), a highly immunogenic GM3 derivative that was previously investigated as a vaccine candidate. All of the four new GM3 derivatives were proved to be more immunogenic than GM3NPhAc and elicit very strong T cell-dependent immune responses desirable for cancer immunotherapy. It was concluded that the new GM3 derivatives can form promising vaccine candidates that may be used to combine with cell glycoengineering for cancer immunotherapy.