A model of spontaneous lung metastases visualised in fresh host tissue by green fluorescent protein expression

The authors describe a model of spontaneous lung metastases in nude mice us ing green fluorescent protein (GFP) expression as a marker. The human lung cell line H460M was transfected with the humanised GFP-S65T cDNA and a stab le fluorescent cell line termed H460M(GFP) was obtained. The latter kept in vitro biological features when compared to the parental H460M cell line, w hich suggests that GFP-expression does not influence H460M(GFP) cell line b ehaviour. In order to evaluate their metastatic potential and to determine the number of spontaneous metastases, H460M(GFP) cells were subcutaneously inoculated into nude mice. Animals were sacrificed at time intervals and ti ssues (lung, liver, spleen, node, and kidney) were analysed under fluoresce nce microscopy. These experiments demonstrated that 2 weeks after subcutane ous inoculation, 75% of animals exhibited fluorescent spontaneous lung micr ometastases. From the third week, 100% of animals exhibited an increasing n umber of metastases (10-16) which were only localised in the lungs. At the end of the study, the number of lung metastases had dramatically increased (42-400 at 7 weeks). Although these metastases were mainly localised in lun g, a few mice had an invasion of neighbouring lymph nodes. The H460M(GFP) c ell line allowed to follow the seeding and development of spontaneous lung metastases and may be considered a simple and powerful tool to study each s tep of the metastasis to screen new anticancer drugs.