Targeting glioblastoma multiforme with an IL-13/diphtheria toxin fusion protein in vitro and in vivo in nude mice

Fusion proteins composed of tumor binding agents and potent catalytic toxins show promise for intracranial therapy of brain cancer and an advantage over systemic therapy. Glioblastoma multiforme (GBM) is the most common form of brain cancer and overexpresses IL-13R. Thus, we developed an interleukin-13 receptor targeting fusion protein, DT₃₉₀IL13, composed of human interleukin-13 and the first 389 amino acids of diphtheria toxin. To measure its ability to inhibit GBM, DT₃₉₀IL13 was tested in vitro and found to inhibit selectively the U373 MG GBM cell line with an IC₅₀ around 12 pmol/l. Cytotoxicity was neutralized by anti-human-interleukin-13 antibody, but not by control antibodies. In vivo, small U373 MG glioblastoma xenografts in nude mice completely regressed in most animals after five intratumoral injections of I μg of DT₃₉₀IL13 q.o.d., but not by the control fusion protein DT₃₉₀IL-2. DT₃₉₀IL13 was also tested against primary explant GBM cells of a patient's excised tumor and the IC₅₀ was similar to that measured for U373 MG. Further studies showed a therapeutic window for DT₃₉₀IL13 of 1-30 μg/injection and histology studies and enzyme measurements showed that the maximum tolerated dose of DT₃₉₀IL13 had little effect on kidney, liver, spleen, lung and heart in non-tumor-bearing immunocompetent mice. Together, these data suggest that DT₃₉₀IL13 may provide an important, alternative therapy for brain cancer.