Interleukin-13 receptor alpha2 chain: a potential biomarker and molecular target for ovarian cancer therapy. Kioi M et al. BACKGROUND: Epithelial ovarian cancer demonstrates high mortality due to diagnosis at an advanced stage. In the search for a biomarker for early diagnosis and a target for therapy, the issue of whether interleukin-13 receptor (IL-13R), shown to be expressed on a variety of human cancers, is expressed in ovarian tumor samples was explored. In addition, whether this receptor serves as a biomarker and can be targeted by IL-13 cytotoxin was examined. METHODS: IL-13R expression in 15 normal and 68 ovarian tumor tissue samples was determined by immunohistochemistry. Correlation between clinicopathologic features and IL-13R expression was analyzed. The efficacy of IL-13R-directed cytotoxin was determined in mice with subcutaneous, orthotopic, and peritoneal metastatic ovarian cancer. RESULTS: Immunohistochemical analyses revealed that 83% of ovarian cancer specimens express IL-13Ralpha2, a high-affinity IL-13R subunit chain, whereas normal ovary samples expressed none or very low levels. The majority of clear cell ovarian carcinomas with the worst prognosis showed strong staining for IL-13Ralpha2. IL-13 cytotoxin was highly cytotoxic to the IGROV-1 ovarian cancer cell line in vitro, and it mediated significant antitumor activity against a xenografted tumor model. The antitumor effects were confirmed by treating orthotopically implanted or peritoneal metastatic ovarian tumors, which showed significant extension of survival in immunodeficient mice. IL-13 cytotoxin also prevented cachexia in treated mice. The soluble form of IL-13Ralpha2 was detected in the serum of mice with peritoneal metastasis, and the level decreased to baseline in the treated group. CONCLUSIONS: IL-13Ralpha2 is a promising target for ovarian cancer therapy, and the soluble form of IL-13R may be a possible surrogate marker for disease monitoring. Cancer. Published 2006 by the American Cancer Society.