Cytotoxicity and antitumor effects of growth factor-toxin fusion proteins on human glioblastoma multiforme cells

Abstract

✓ The prognosis of glioblastoma multiforme remains poor despite advances in treatment by surgery, irradiation, and chemotherapy. Many malignant gliomas overexpress growth factor receptors. The possibility of targeting these receptors with selective cytotoxic molecules constructed by fusing deoxyribonucleic acid (DNA)-encoding mutant forms of Pseudomonas exotoxin A (PE) with complementary DNA-encoding growth factors was investigated. Several recombinant toxins have been produced, including those in which transforming growth factor (TGF)-α, insulin-like growth factor (IGF)-I and acidic fibroblast growth factor (FGF) were fused to mutant forms of PE lacking the native cell-binding domain. These recombinant proteins are cytotoxic to cells that express specific cell-surface receptors. The cytotoxic activity of TGF-α, IGF-I, and acidic FGF chimeric toxins was tested in vitro against human glioblastoma cell lines. Each recombinant toxin exhibited potent and specific killing of cells. The TGF-α-PE40 construct was cytotoxic to seven of the eight cell lines and was active at concentrations as low as 0.5 ng/ml (1.1 × 10−11 M). The acidic FGF-PE40 toxin was also active on seven of the eight cell lines but was 50-fold less active than the TGF-α-PE40. The IGF-I-PE40 construct was active on only two cell lines. To determine the possible therapeutic effect in animals, TGF-α-PE40 was administered to nude mice bearing subcutaneous human glioblastoma xenografts. The animals were treated for 7 days via a continuous infusion pump placed in the peritoneal cavity. A constant serum level of TGF-α-PE40 was achieved that was nontoxic to the mice yet caused a reduction in tumor volume and retarded growth beyond the treatment period. The overexpression of the epidermal growth factor receptor in glioblastomas multiforme and the potency and specificity of the TGF-α-PE40 construct designed to target this receptor suggests that TGF-α-PE40 has the potential to be an effective antitumor agent for the adjuvant therapy of these carcinomas.