Antibody affinity maturation and scFv-fusion proteins
Metastatic solid tumors are generally lethal diseases in children. Antibody based targeted therapy is now an established treatment modality. Because of immunogenicity, murine or chimeric antibodies may be less effective compared to fully human versions. Antibody affinity is another critical variable affecting therapeutic efficacy. Based on modeling, higher affinity antibody will have improved therapeutic index. Since late effects such as second cancer are clearly the result of bystander damage, improving therapeutic index is particularly important in treating children with cancer. In our laboratory, fully human antibodies targeting pediatric solid tumors are selected using phage display techniques. In order to improve the antibodies’ targeting efficiency, affinity maturation is performed by single chain Fv (scFv) platform based on phage and ribosome displays. These improved scFv constructs are used to build scFv-streptavidin fusion proteins for multistep targeting in radioimmunotherapy. I plan to combine antibody targeting with small molecules and standard chemotherapy to design a more effective treatment strategy for pediatric solid tumors, including those that spread to the central nervous system.
Antibody directed enzyme pro-drug therapy (ADEPT)
By exploiting drugs that can synergize with chemotherapeutic drugs, tumor resistance can be overcome, toxic drug doses can be decreased and their toxic side effects can be reduced. In ADEPT, selectivity for the target is achieved by an antibody in an antibody-enzyme conjugate. A non-toxic prodrug is converted into a cytotoxic drug by the enzyme at the tumor site. Recombinant methioninase can effectively deplete tissue methionine to effect human tumor shrinkage in animal models. We have constructed scFv-methioninase for ADEPT. We previously reported synergistic action of methionine depletion and chemotherapy for neuroblastoma. Even for highly resistant cell lines, the synergy with microtubule depolymerizing agents was consistently seen. With scFv-methioninase, the enzyme is targeted to the tumor site where a nontoxic prodrug called selenomethionine can be activated.
Hu J, Cheung NK. Methionine depletion with recombinant methioninase: In vitro and in vivo efficacy against neuroblastoma and its synergism with chemotherapeutic drugs. International J. of Cancer 124:1700-1706, 2009. [PubMed Abstract]
Hu J, Huang XD, Ling CC, Bundle DR, Cheung NKV. Reducing epitope spread during affinity maturation of an anti-ganglioside GD2 antibody. Journal of Immunology, 2009 (in press).