Human kallikrein 14: a new potential biomarker for ovarian and breast cancer

Human kallikrein gene 14 (KLK14) is a recently discovered member of the tissue kallikrein family of secreted serine proteases, which includes hK3/prostate-specific antigen, the best cancer biomarker to date. Given that KLK14 is hormonally regulated, differentially expressed in endocrine-related cancers, and a prognostic marker for breast and ovarian cancer at the mRNA level, we hypothesize that its encoded protein, hK14, like hK3/prostate-specific antigen, may constitute a new biomarker for endocrine-related malignancies. The objective of this study was to generate immunological reagents for hK14, to develop an ELISA and immunohistochemical techniques to study its expression in normal and cancerous tissues and biological fluids. Recombinant hK14 was produced in Pichia pastoris, purified by affinity chromatography, and injected into mice and rabbits for polyclonal antibody generation. Using the mouse and rabbit antisera, a sandwich-type immunofluorometric ELISA and immunohistochemical methodologies were developed for hK14. The ELISA was sensitive (detection limit of 0.1 micro g/liter), specific for hK14, linear from 0 to 20 micro g/liter with between-run and within-run coefficients of variation of <10%. hK14 was quantified in human tissue extracts and biological fluids. Highest levels were observed in the breast, skin, prostate, seminal plasma, and amniotic fluid, with almost undetectable levels in normal serum. hK14 concentration was higher in 40% of ovarian cancer tissues compared with normal ovarian tissues. Serum hK14 levels were elevated in a proportion of patients with ovarian (65%) and breast (40%) cancers. Immunohistochemical analyses indicated strong cytoplasmic staining of hK14 by the epithelial cells of normal and malignant skin, ovary, breast, and testis. In conclusion, we report the first ELISA and immunohistochemical assays for hK14 and describe its distribution in tissues and biological fluids. Our preliminary data indicate that hK14 is a potential biomarker for breast and ovarian cancers.