Abstract 2150: Therapeutic efficacy of an optimized quadruply mutated IL13-based bacterial cytotoxin in an orthotopic murine glioma model.
Authors: Nguyen Van , Zhu Dongqin , Conyers Jesse M. , Debinski Waldemar , Mintz Akiva 
Published: August 2014

Abstract
Interleukin 13 receptor alpha 2 (IL13Rα2) is a tumor-restricted plasma membrane receptor that is overexpressed on greater than 70% of Glioblastoma Multiformes (GBMs) as well as in other malignancies, including melanoma, adenocarcinoma, ovarian cancer and renal cell carcinoma. We and others have therapeutically exploited this attractive target using IL13-based targeting strategies to deliver bacterial toxins, chemotherapeutics, nanoparticles, viruses and immunotherapy directly to the IL13Rα2 tumor-restricted biomarker. In past work, we found multiple mutational hotspots on IL13 that (a) abrogated its binding to the physiologically abundant IL13Rα1/IL4Rα receptor heterodimer, and (b) increased its binding to the tumor-restricted IL13Rα2. Based on these findings, we created a delivery platform established as an optimized IL13Rα2-Targeted Quadruple Mutant of IL13 (TQM13; IL13.E13K/R66D/S69D/K105R) that we demonstrated binds with high affinity towards IL13Rα2, but not the IL13Rα1/IL4Rα receptor heterodimer. Of importance, we demonstrated the ability of radiolabeled TQM13 to target IL13Rα2-expressing tumors in vivo using positron emission tomography (PET). The objective of this current work was to demonstrate for the first time the in vivo IL13Rα2-targeted killing effect of our optimized TQM13 ligand genetically fused to a potent derivative of Pseudomonas exotoxin (PE).
We successfully expressed TQM13 and TQM13-PE proteins in an E. coli expression system, denatured, refolded and purified them via Nickel-based affinity and ion exchange chromatography. We demonstrated IL13Rα2-specific affinity of TQM13 using a novel IL13Rα2-inducible system in which B16 melanoma cells expressed varying amounts of IL13Rα2 in proportion to the concentration of doxycycline. Of importance, the number of induced TQM13 binding sites (in vitro and in vivo) was comparable to the range seen in GBM and other malignancies (50,000-4,500,000 receptors/cell). In addition, we demonstrated that TQM13-PE killed cells in direct proportion to IL13Rα2 expression. Therefore, we tested the efficacy of TQM13-PE in an orthotopic murine GBM model by injecting mice with 1 μg of TQM13-PE intracranially on day 7 and 14 post stereotactic tumor cell implantation. We found a significant increase in survival only in mice bearing IL13Rα2-expressing orthotopic tumors, in contrast to mice bearing IL13Rα2-negative tumors.
Thus, we have successfully generated an optimized, biomarker-targeted anti-GBM agent that demonstrated specific therapeutic potential against the tumor-associated IL13Rα2 biomarker in vivo.
Citation Format: Van Nguyen, Dongqin Zhu, Jesse M. Conyers, Waldemar Debinski, Akiva Mintz. Therapeutic efficacy of an optimized quadruply mutated IL13-based bacterial cytotoxin in an orthotopic murine glioma model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2150. doi:10.1158/1538-7445.AM2013-2150