A synthetic tissue kallikrein inhibitor suppresses cancer cell invasiveness

Serine proteinases modulate the interaction of tumor cells with extracellul ar matrix components during extravasation and metastasis. The serine protei nase tissue kallikrein has been previously demonstrated in several human ad enocarcinomas, and we presently report the localization of immunoreactive k allikrein and its mRNA in pancreatic adenocarcinoma. In addition, a synthet ic peptide-based inhibitor specific for tissue kallikrein (FE999024) was us ed in our studies to explore a possible role for kallikrein in cancer cell invasiveness. Matrigel invasion assays were performed with a human breast-c ancer cell line, MDA-MB-231, which expresses tissue kallikrein in culture. In the presence of FE999024 invasion through Matrigel was inhibited in a do se-dependent manner to a maximum of 39%. We also developed a novel ex vivo assay in which breast cancer cells are infused into the pulmonary circulati on of artificially ventilated explanted rat lungs. At intervals up to 6 hou rs after infusion pulmonary invasion was quantified by bronchial alveolar l avage to recover human cancer cells from the airspace. invading cells in th e lung interstitium were also quantified after immunohistochemistry with a monoclonal antibody specific for human cytokeratin 18. The synthetic kallik rein inhibitor attenuates breast cancer cell invasion into the airspace by 33% when quantified by lavage recovery and up to 34% as quantified in the l ung interstitium by cytokeratin 18 immunostaining. Our results indicate tis sue kallikrein may participate in the invasion and metastasis of human aden ocarcinomas. The newly developed explanted rodent lung assay should be usef ul for the study of cancer cells, neutrophils, or other extravasating-cells .