RECOMBINANT ANTIBODY-BASED MOLECULAR THERAPEUTICS FOR BRAIN TUMOR IMMUNOTHERAPY

A28 The limited efficacy of surgery, radiotherapy, and chemotherapy in the treatment of malignant glioma calls for innovative approaches targeting specific biological features of these tumors. Monoclonal antibodies (MAbs), with high specificity and high affinity for their target antigens, can be utilized in targeted therapy for delivery of agents such as radionuclides, enzymes, drugs, or toxins in vivo. Success in MAb-based therapy for brain tumor requires the identification of glioma-associated antigens and the proper selection of target-specific MAbs for each patient. We have validated a panel of promising molecular malignant glioma targets, such as epidermal growth factor receptor type III variant (EGFRvIII) and human transmembrane glycoprotein nmb (GPNMB), and we have performed genetic and immunohistochemical (IHC) evaluation of gliomas to determine incidence, distribution, and pattern of localization of specific antigens in brain tumors, as well as the survival analysis. Univariate and multivariate analyses correlated expression of GPNMB with survival of 39 GBM patients using RNA expression and IHC data, establishing that these patients, whose tumors have relatively high mRNA GPNMB transcript levels, >3-fold over normal brain, as well as positive immunohistochemistry, have a significantly higher risk of death. We have developed both murine and human high-affinity single-chain fragment antibodies from phage and yeast display libraries and immunotoxins with Pseudomonas exotoxin PE38 that are reactive with either EGFRvIII or GPNMB in vitro and in vivo. Antibody engineering also provides a powerful approach for redesigning Abs for use in oncological applications: In preclinical tests for malignant glioma treatment, affinity-matured recombinant Ab fragments in the form of scFv-CH3 fusion and two immunotoxins, MR1-1(dsFv)PE38 for EGFRvIII and F6V(scFv)PE38 for GPNMB, all demonstrate efficient tumor targeting and offer the promise of improved tumor control without substantial toxicity. The IND of MR1-1 immunotoxin was issued in August 2007, and Phase I clinical trials are ongoing at Duke (Dr. D. Bigner, P.I.).