Regulation of gene expression and cell growth in vivo by tetracycline using the hollow fiber assay

The hollow fiber assay presents a potentially unique tool to study the effe cts of regulated gene expression in cell lines that do not form tumors in v ivo. The hollow fibers allow small molecules to pass freely through while k eeping the cells within the fibers and segregated from host cells. OSp16.1 cells, derived from the U24 clone of the U2-OS osteogenic sarcoma tumor lin e, express the p16(INK4a) tumor suppressor under the regulation of tetracyc line (tet) (Mitra J et al. Mol Cell Bio 19:3916, 1999). The in vitro induct ion of p16 in the OSp16.1 cell line is regulated by tet. The hollow fiber a ssay was used to determine whether the regulation of the p16 gene could be achieved in vivo, since these cells did not grow in the xenograft model. Th ere were no differences in the in vivo growth pattern of U24 cells loaded i nto the hollow fibers with and without tet: 807% and 839% net growth, respe ctively. OSp16.1 cells in fibers in mice receiving 3.33 mg/kg/day tet had a 644% net growth after 21 days. There was a 194% net growth without tet. Im munoblotting of extracts prepared from the hollow fibers confirmed that p16 was induced in the absence of tet. These data demonstrate this assay is a useful tool for studying the effects of regulated gene expression in vivo.