Plasma Escherichia coli beta-galactosidase as a marker of tumor burden and response to experimental anti-neoplastic therapy in nude mice xenografted with lacZ transduced human tumor cells.
Klíčová slova
Abstraktní
Genetic labeling of tumor cells with the Escherichia coli lacZ reporter gene, encoding the enzyme beta-galactosidase, is widely used for histochemical detection of micrometastases in mice. Recently, we have developed a novel, highly sensitive and specific immunocapture chemiluminescence assay for the quantitation of E. coli beta-galactosidase. This assay achieved a detection limit of 0.01 mU of E. coli beta-galactosidase per milliliter, and 97% signal recovery of purified enzyme added to mouse plasma. LacZ transduced MDA-MB-231 BAG human breast cancer cells grown in vitro released soluble beta-galactosidase into the culture medium, and the concentration found correlated with cell density. Growth of the same cells in nude mice produced readily measurable levels of E. coli beta-galactosidase enzyme activity in host plasma and a highly significant correlation could be demonstrated between the size of primary tumor xenografts and the host plasma level of E. coli beta-galactosidase activity. When mice bearing MDA-MB-231 BAG tumor xenografts were treated intravenously with a single injection of doxorubicin (5 mg/kg), the mean tumor volume after 16 days was reduced 4-fold in the group of doxorubicin-treated mice compared with saline-treated control mice, and the mean level of plasma E. coli beta-galactosidase was correspondingly reduced 3.8-fold in the doxorubicin-treated mice compared with control mice. Sensitive and specific measurement of soluble E. coli beta-galactosidase in blood, using an immunocapture chemiluminescence assay, thus provides objective assessment of tumor burden in mice xenografted with lacZ transduced human tumors. This assay may have important applications as a tool for determining the efficacy of new experimental anti-tumor agents.