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 potentcatalytic toxins show promise for intracranial therapy of braincancer and an advantage over systemic therapy. Glioblastomamultiforme (GBM) is the most common form of brain cancer andoverexpresses IL-13R. Thus, we developed an interleukin-13 receptortargeting fusion protein, DT₃₉₀IL13, composed of human interleukin-13and the first 389 amino acids of diphtheria toxin. To measureits ability to inhibit GBM, DT₃₉₀IL13 was tested in vitro andfound to inhibit selectively the U373 MG GBM cell line withan IC₅₀ around 12 pmol/l. Cytotoxicity was neutralized by anti-human-interleukin-13antibody, but not by control antibodies. In vivo, small U373MG glioblastoma xenografts in nude mice completely regressedin most animals after five intratumoral injections of 1 µgof DT₃₉₀IL13 q.o.d., but not by the control fusion protein DT₃₉₀IL-2.DT₃₉₀IL13 was also tested against primary explant GBM cellsof a patient's excised tumor and the IC₅₀ was similar to thatmeasured for U373 MG. Further studies showed a therapeutic windowfor DT₃₉₀IL13 of 1–30 µg/injection and histologystudies and enzyme measurements showed that the maximum tolerateddose 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.