IL‐13 cytotoxin has potent antitumor activity and synergizes with paclitaxel in a mouse model of oral squamous cell carcinoma

Interleukin-13 receptor-targeted cytotoxin (IL13-PE38) is highly cytotoxic to certain types of human cancers expressing abundant levels of IL-13Ralpha2 chain. Although IL13-PE38 is being tested in a Phase III clinical trial in brain tumors, the activity of IL13-PE38 alone or when combined with taxane, a chemotherapeutic drug for oral squamous cell carcinoma (OSCC), has not been investigated. Here, we show that approximately 40% of OSCCs (n = 50) in a tissue array are strongly positive for IL-13Ralpha2, whereas normal oral mucosa (n = 10) expresses very low or undetectable levels evaluated by immunohistochemistry. IL13-PE38 was highly cytotoxic to OSCC cell lines, but not cytotoxic to normal oral fibroblasts. IL13-PE38 mediated a synergistic antitumor effect with paclitaxel in OSC-19 in vitro and in vivo in the orthotopic OSCC tongue tumor model. Real-time tumor growth was monitored by optical imaging using a Xenogen-IVIS imaging system. Treated animals showed significant (p < 0.05) improvement in survival, which correlated with in vivo imaging of tumor response without evidence of visible toxicity. Gene transfer of IL-13Ralpha2 in oral cancer cells increased sensitivity of OSCC cell line to IL13-PE38 in vitro. Retrovirus-mediated gene-transfer of IL-13Ralpha2 in HSC-3 into tongue tumors in vivo dramatically enhanced the antitumor activity of IL13-PE38, providing complete elimination of established tumors and prolonging survival of these animals. These results indicate that IL13-PE38 in combination with paclitaxel acting via different mechanisms may be a potential treatment option for IL-13Ralpha2 expressing OSCC or for the treatment of non-IL-13Ralpha2 expressing OSCC combined with gene transfer of IL-13Ralpha2.