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BACKGROUND: IL-13 receptor (IL-13R) targeted cytotoxin, IL13-PE38QQR, has been shown to have very potent anti-tumor activity to IL-13R-expressing head and neck tumor cells in vitro and in vivo. However, its effect is limited in aggressive tumors. To further improve the anti-tumor activity and safety of IL-13 cytotoxin, we employed continuous infusion technique in animal model of head and neck cancer. MATERIALS AND METHODS: We surgically implanted continuous infusion (CI) pump intraperitoneally that released drug for 7 days, and its anti-tumor effect was evaluated. A comparison was made for antitumor activity and safety with intravenously (IV) administered IL-13 cytotoxin in a head and neck (KCCT873 and HN12) subcutaneous (SC) xenograft tumor models in nude mice. Vital organ toxicities were assessed by histologic examinations and blood serum chemistry analyses. RESULTS: The 50 or 75 micro g/kg/day for 7 days of IL-13 cytotoxin either by IV or CI administration did not show any difference in safety or anti-tumor activity. IV administration of 150 or 200 micro g/kg/day of IL-13 cytotoxin for 7 days was lethal to nude mice, whereas 200 micro g/kg/day X 7 days of CI administration was highly effective in the regression of established tumors without any toxicities. Additionally, CI administration of IL-13 cytotoxin (200 micro g/kg/day) showed growth inhibition of larger HN12 tumors in nude mice. CONCLUSION: With a CI schedule, IL-13 cytotoxin can be systemically administrated at approximately twice the dose otherwise given by daily IV bolus administration.