Molecular targeting with recombinant cytotoxins of interleukin-13 receptor α2-expressing glioma

A restricted receptor for interleukin 13 (IL-13Rα2) is over-expressed in high-grade astrocytoma (HGA), but not in normal organs. In order to design and examine new anti-HGA therapies, which are molecularly directed against IL-13Rα2, we established an IL-13Rα2-expressing syngeneic immunocompetent murine model of HGA. The model was obtained by transfecting G-26 murine glioma cells with IL-13Rα2. G-26-IL-13Rα2(+) cells, but not mock-transfected cells, became susceptible to IL-13 mutant-based cytotoxic proteins that kill human HGA cells. G-26-IL-13Rα2(+) cells maintained their tumorigenicity in immunocompetent C57BL/J6 mice and preserved their expression of IL-13Rα2 in vivo. These characteristics of the G-26-IL-13Rα2(+) tumors allowed us to test molecularly defined anti-glioma passive immunotherapy. A targeted recombinant chimera cytotoxin composed of multiply mutated IL-13 (IL-13.E13Y/R66D/S69D) and a derivative of Pseudomonas exotoxin (PE), PE1E, IL-13.E13Y/R66D/S69D-PE1E, was used in anti-tumor experiments. G-26-IL-13Rα2(+) cells were killed by IL-13.E13Y/R66D/S69D-PE1E in an IL-4-independent fashion. To test the cytotoxin in vivo, G-26-IL-13Rα2(+) tumors were established in C57BL/J6 mice and when the tumors reached a size of at least 50 mm³, the mice were treated with IL-13.E13Y/R66D/S69D-PE1E. In the mice treated with the targeted fusion sytotoxin, the tumors regressed and 80% of the animals were cured. This study documents the establishment of an IL-13Rα2-positive model of HGA in immunocompetent rodents. Furthermore, the effectiveness and safety of the targeted IL-13-based cytotoxin against IL-13Rα2-expressing tumors in a more clinically relevant in vivo HGA model is promising with regard to the future clinical utility of the cytotoxin.