Dissemination in athymic nude mice of lacZ transfected small cell lung cancer cells identified by X-gal staining.

The small cell lung cancer cell lines GLC-2 and DMS 456 were genetically labeled with the lacZ gene and examined for invasive and metastatic potential in META/Bom nude mice. The lacZ gene encodes the enzyme beta-D- galactosidase, and cells expressing this enzyme were identified by staining with the chromogenic substrate X-gal. lacZ expressing cells were investigated after subcutaneous (s.c.) inoculation and intravenous (i.v.) injection. The X-gal detection of beta-D-galactosidase activity proved to be a rapid and easy means for specific and highly sensitive identification of metastases. All primary s.c. tumors stained by X-gal. The primary tumors of GLC-2 regularly demonstrated local invasive growth and produced multiple metastases in several organs. In contrast, primary DMS 456 tumors only occasionally demonstrated local invasion and very rarely generated secondary foci. No experimental metastases were found after i.v. injection of the examined tumor lines. The results indicate an intratumoral heterogeneity among individual SCLC tumors in the capacity for invasion and metastatic spread. The different metastatic pattern of GLC-2 after s.c. and i.v. inoculation supports the hypothesis that initial steps of the metastatic cascade occurring in the primary tumor are necessary for the subsequent production of growing metastases.