The use of monoclonal antibodies in the search for anti-cancer therapeutics has been a research field of great potential since the hybridoma technology was introduced by Köhler and Milstein in the mid 70s. The use of recombinant technologies in the production of monoclonal antibodies has improved their efficiency and the selection by providing the ability to make chimeric and humanized antibodies. One of the major outcomes of using monoclonal antibodies in cancer treatment is the ability to specifically target cancer tissue and spare the surrounding cells. This is an advantage over classic cancer treatments such as chemo- and radiotherapy which are not as selective.
The ganglioside N-glycolyl-GM3 has been shown to be expressed only in cancer tissues, e.g. of melanoma and breast tumors, whereas the very closely related form N-acetyl-GM3 is found to be overexpressed in cancer tissue, but is also found in healthy tissue. This suggests that an antibody that can distinguish between N-glycolyl-GM3 and N-acetyl-GM3, might be a good starting point for the production of antibodies against these types of cancers. Monoclonal antibodies against N-glycolyl-GM3 have been raised in vivo in mice at the Center for Molecular Immunology, Havana (CIM). Two of these antibodies, called 14F7 and P3, have been shown to display a high specificity for N-glycolyl-GM3 that have not been found for other candidate molecules. These antibodies could act as a direct therapeutic against these cancers. In addition, an anti-idiotypic antibody called 1E10 has been raised that mimicks the antigen binding properties of N-glycolyl-GM3 and may act as a vaccine. Extensive clinical trials for the 1E10 vaccine have been made (they are now in phase II clinical trials). However, structural knowledge of the antibodies is of interest to bring more insight to the binding properties of the antibodies and the three-dimensional structure of the antibodies may serve as a foundation for improvement of the vaccine
In this study, the Fab fragment of P3, in its chimeric form P3Q, has been prepared, purified, crystallized and the structure has been solved to a resolution of 1.75Å. In addition, trials to solve the structure of P3Q in complex with parts of the ganglisoside and in complex with 1E10 have been made.