CYTOTOXICITY AND ANTITUMOR EFFECTS OF GROWTH FACTOR-TOXIN FUSION PROTEINS ON HUMAN GLIOBLASTOMA-MULTIFORME CELLS

The prognosis of glioblastoma multiforme remains poor despite advances in treatment by surgery, irradiation, and chemotherapy. Many malignan t gliomas overexpress growth factor receptors. The possibility of targ eting these receptors with selective cytotoxic molecules constructed b y fusing deoxyribonucleic acid (DNA)-encoding mutant forms of Pseudomo nas exotoxin A (PE) with complementary DNA-encoding growth factors was investigated. Several recombinant toxins have been produced, includin g those in which transforming growth factor (TGF)-alpha, 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. Th ese recombinant proteins are cytotoxic to cells that express specific cell-surface receptors. The cytotoxic activity of TGF-alpha, IGF-I, an d acidic FGF chimeric toxins was tested in vitro against human gliobla stoma cell lines. Each recombinant toxin exhibited potent and specific killing of cells. The TGF-alpha-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 x 10(-11) M). The acidic FGF-PE40 toxin was also active o n seven of the eight cell lines but was 50-fold less active than the T GF-alpha-PE40. The IGF-I-PE40 construct was active on only two cell li nes. To determine the possible therapeutic effect in animal TGF-alpha- PE40 was administered to nude mice bearing subcutaneous human glioblas toma xenografts. The animals were treated for 7 days via a continuous infusion pump placed in the peritoneal cavity. A constant serum level of TGF-alpha-PE40 was achieved that was nontoxic to the mice yet cause d a reduction in tumor volume and retarded growth beyond the treatment period. The overexpression of the epidemal growth factor receptor in glioblastomas multiforme and the potency and specificity of the TGF-al pha-PE40 construct designed to target this receptor suggests that TGF- alpha-PE40 has the potential to be an effective antitumor agent for th e adjuvant therapy of these carcinomas.