Combination fusion protein therapy of refractory brain tumors: demonstration of efficacy in cell culture.

Primary brain tumors including anaplastic astrocytomas and glioblastoma multiforme are difficult to treat because of their locally invasive nature and relative resistance to chemotherapy and radiation therapy. Novel agents that can kill multi-drug resistant tumor cells and reach tumor cells at distant sites in the brain are needed. One such class of agents is fusion proteins which consist of brain-tumor-selective peptide ligands fused to peptide toxins. The ligand directs the protein to the glioma cell surface; the peptide toxin is then internalized into the cell, translocates to the cytosol and catalytically inactivates protein synthesis leading to cell death. Fusion proteins are toxic to multi-drug resistant brain tumor cells. Because of the large molecular weight of these molecules, a unique delivery system has been developed--convection-enhanced delivery (CED). The method creates a bulk flow which supplements diffusion and achieves drug concentrations in the brain parenchyma orders of magnitude greater than by systemic administration. Patients with recurrent glioma treated with individual fusion protein CED have obtained clinical remissions lasting years. However, toxicities to normal brain have been observed and relapses ultimately occurred. To address the clinical need of these patients and improve upon the therapeutic index observed to date with single fusion protein CED, we generated a novel fusion protein DAB389EGF and tested it in combination with another active fusion protein, IL13PE38QQR. We observed potent glioma cytotoxicity with each fusion protein and synergistic toxicity with the combination. Further, brain tumor cells showed heterogeneous expression of individual receptors suggesting that the combination--DAB389EGF and IL13PE38QQR may show improved efficacy and should undergo further preclinical development for therapy of patients with relapsed high-grade gliomas.