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Research Articles: Therapeutics, Targets, and Development

Targeting IL-13R2-positive cancer with a novel recombinant immunotoxin composed of a single-chain antibody and mutated Pseudomonas exotoxin

Tumor Vaccines and Biotechnology Branch, Division of Cellular and Gene Therapies, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland

Requests for reprints: Raj K. Puri, Tumor Vaccines and Biotechnology Branch, Division of Cellular and Gene Therapies, Center for Biologics Evaluation and Research, Food and Drug Administration, NIH Building 29B, Room 2NN20, 29 Lincoln Drive, Bethesda, MD 20892. Phone: 301-827-0471; Fax: 301-827-0449. E-Mail: raj.puri{at}fda.hhs.gov

Abstract

We have shown previously that high-affinity receptors for interleukin-13 (IL-13R2) are overexpressed on a variety of solid cancer cells, diseased fibroblasts, and other cells, and a chimeric fusion protein composed of human IL-13 and mutated Pseudomonas exotoxin (IL-13-PE38) is highly and specifically cytotoxic to these cells in vitro and in vivo. To improve the specificity for the target, we isolated specific antibodies against IL-13R2 from human single-chain Fv (scFv) antibody phage library and developed immunotoxin by selecting two high-affinity clones of scFv and fused to PE. The fusion chimeric gene was expressed in Escherichia coli, and highly purified IL-13R-specific immunotoxin, termed anti-IL-13R2(scFv)-PE38, was tested for its cytotoxicity. This molecule was highly cytotoxic to U251 glioma and PM-RCC renal cell carcinoma cell lines in vitro. The cytotoxic activity was neutralized by purified extracellular domain of IL-13R2 but not by IL-13, indicating that cytotoxic activity is specific. Anti-IL-13R2(scFv)-PE38 showed significant antitumor activity in immunodeficient mice with s.c. glioma tumors. Both i.p. and i.t. routes of administration showed antitumor activity in a dose-dependent manner. The maximum tolerated dose of anti-IL-13R2(scFv)-PE38 was 200 µg/kg i.p. twice daily for 5 days. These results indicate that anti-IL-13R2(scFv)-PE38 is a highly selective therapeutic agent for cancer therapy and should be further tested in animal models of human cancer. [Mol Cancer Ther 2008;7(6):1579–87]

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Received 9/24/07; revised 3/ 6/08; accepted 3/21/08.