Radioimmunotherapy against IL13Rα2 expressing tumors utilizing a novel retargeted-ligand delivery system

Objectives Our objective is to utilize a novel ligand-based delivery system that targets therapeutic radioactivity to cells expressing IL13Rα2, a tumor-restricted plasma membrane receptor that we discovered to be overexpressed in majority of Glioblastoma Multiforme (GBM) as well as other tumors. Based on our prior work that identified functionally relevant amino acid mutations, we designed a novel IL13Rα2-Targeted Quadruple Mutant of IL-13 (TQM13) that we hypothesized will bind with a high affinity towards the tumor-restricted IL13α2, but not the physiologically abundant IL13Rα1/IL4Rα heterodimer.

Methods We evaluated affinity towards the IL13 receptors using autoradiography, Biacore and functional assays. We labeled TQM13 with 131I using the IODEGEN method and confirmed its binding to IL13Rα2-expressing tumor sections. To test in vivo efficacy, we treated groups of mice bearing subcutaneous IL13Rα2-expressing G48a GBMs intratumorally with 131I-TQM13 (200μCi x2 doses) or controls (unlabeled TQM13, 131I labeled control or saline mock injections).

Results TQM13 specifically bound IL13Rα2-expressing GBM cells and specimens, but not normal brain or IL13Rα2-negative tissue. In Biacore experiments, TQM13 bound strongly to recombinant IL13Rα2 (KD~2nM) but did not significantly bind the reconstituted physiologically abundant IL13Rα1/IL4Rα receptor nor functionally activate it in TF-1 cells. Importantly, only 131I-TQM13 demonstrated in vivo anti-tumor activity against IL13Rα2 expressing tumors, with 100% survival at 27 days post treatment, compared to 0% of controls.

Conclusions We have successfully generated and radioiodinated an optimized, biomarker-targeted scaffolding that demonstrated specific binding activity towards the tumor-associated IL13Rα2 in vitro and potential to deliver therapeutic radioactivity in vivo. Thus, we utilized a novel ligand retargeting strategy to demonstrate the first reported in vivo immunotherapy success against a promising tumor-associated biomarker.

Research Support NINDS R21NS067471-0110 (Mintz), Dana-Foundation (Mintz