Stromal cell-associated expression of kallikrein-related peptidase 6 (KLK6) indicates poor prognosis of ovarian cancer patients.

Several members of the human kallikrein-related peptidase family, including KLK6, are up-regulated in ovarian cancer. High KLK6 mRNA or protein expression, measured by quantitative polymerase chain reaction and enzyme-linked immunoassay, respectively, was previously found to be associated with a shortened overall and progression-free survival (OS and PFS, respectively). In the present study, we aimed at analyzing KLK6 protein expression in ovarian cancer tissue by immunohistochemistry. Using a newly developed monospecific polyclonal antibody, KLK6 immunoexpression was initially evaluated in normal tissues. We observed strong staining in the brain and moderate staining in the kidney, liver, and ovary, whereas the pancreas and the skeletal muscle were unreactive, which is in line with previously published results. Next, both tumor cell- and stromal cell-associated KLK6 immunoexpression were analyzed in tumor tissue specimens of 118 ovarian cancer patients. In multivariate Cox regression analysis, only stromal cell-associated expression, besides the established clinical parameters FIGO stage and residual tumor mass, was found to be statistically significant for OS and PFS [high vs. low KLK6 expression; hazard ratio (HR), 1.92; p=0.017; HR, 1.80; p=0.042, respectively]. These results indicate that KLK6 expressed by stromal cells may considerably contribute to the aggressiveness of ovarian cancer.

Polyclonal antibodies against kallikrein-related peptidase 4 (KLK4): immunohistochemical assessment of KLK4 expression in healthy tissues and prostate cancer.

KLK4 is a member of the human kallikrein-related peptidase family of (chymo)trypsin-like serine proteases. The aim of the present study was to generate polyclonal antibodies (pAb) directed against KLK4 for the analysis of KLK4 by immunohistochemistry in human tissues. Recombinantly expressed human mature KLK4 was used for immunization of chickens. pAb 617A is an affinity-purified monospecific pAb fraction reacting with a linear epitope within a flexible surface-exposed loop of KLK4. pAb 617C is the KLK-directed pAb fraction completely depleted from pAb 617A. In healthy adult tissues, KLK4 was immunodetected by both antibody fractions in kidney, liver, and prostate, but not in other organs such as colon and lung. To evaluate protein expression of KLK4 in prostate cancer, samples of tumor tissue plus corresponding tumor-free areas of 44 prostate cancer patients, represented on a tissue microarray, were investigated. Distinct KLK4 immunostaining was observed with both antibodies in cancerous glandular epithelial cells, but not in surrounding stromal cells. KLK4 expression was lower in stage pT3+4 than in pT1+2 tumors, which was highly significant when employing pAb 617A. Thus, our results indicate that KLK4, which is expressed in the healthy prostate, is upregulated in early-stage but not late-stage prostate cancer.