Cell-surface molecules containing
growth factor receptors, adhesion molecules and transporter
proteins are often over-expressed in various
cancer cells, and could be regarded as suitable targets for therapeutic
monoclonal antibodies (mAb). Anti-
cancer therapeutic mAb are claimed to bind these cell-surface molecules on viable
cancer cells: therefore, it is necessary to produce mAb recognizing
epitopes on the extracellular domains of native but not denatured
proteins. We have experienced difficulty in obtaining mAb bound to viable
cancer cells using synthetic
peptides or
recombinant proteins produced in bacteria as immunogens, although these immunogens are relatively easy to prepare. In this context, we have concluded that viable
cancer cells or cells transfected with
cDNA encoding target
proteins are suitable immunogens for the production of anti-
cancer therapeutic mAb. Furthermore, we selected rats as the immunized animals, because of their excellent capacity to generate diverse
antibodies. Because many target candidates are multi-pass (type IV)
membrane proteins, such as 7-pass
G protein-coupled receptors and 12-pass transporter
proteins belonging to the solute carrier family, and their possible immunogenic extracellular regions are very small, production of specific mAb was extremely difficult. In this review, we summarize the successful preparation and characterization of rat mAb immunized against the extracellular domain of type I, type II and type IV membrane
oncoproteins fused to
green fluorescent protein as an approach using reverse genetics, and also introduce the discovery of cell-death-inducing
antibodies as an approach using forward genetics and a strategy to produce reshaped
antibodies using mimotope
peptides as the immunogen.