Detection of peritoneal micrometastases of gastric carcinoma with green fluorescent protein and carcinoembryonic antigen promoter.

The aim of this study was to specifically visualize micrometastases in the peritoneal cavity, which cannot be detected by conventional methods, by using enhanced Green Fluorescent Protein (EGFP) containing carcinoembryonic antigen (CEA) promoter in an upstream position. In in vitro experiments, two cell lines from human gastric cancer, MKN45 and MKN1, and a cell line from human fibrosarcoma, HT1080, were transduced with pCEA-EGFP, which contains the CEA promoter region. MKN45 and MKN1, which expressed CEA mRNA, showed positive fluorescence after transduction of pCEA-EGFP, whereas HT1080 did not. In in vivo experiments, 7 days after 10(7) MKN45 had been injected into the peritoneal cavity of BALB/c nude mice, pCEA-EGFP was transduced in the peritoneal cavity using a fusogenic liposome with the envelope protein of Hemagglutinating Virus of Japan on the surface. On the peritoneum of the abdominal wall, fluorescent nodules were detected by fluorescence stereomicroscopy. These nodules had a minimal size of approximately 0.15 mm and could not be detected by conventional stereomicroscopy or macroscopy. They were histologically confirmed to be cancer cells by H&E staining. The results suggest that visualization of peritoneal micrometastasis of gastric cancer using CEA promoter and EGFP can offer a new strategy for diagnosis of micrometastasis.