Unexpected properties of endostatin-producing mouse BCR-ABL-transformed cells.

We investigated whether a genetic modification of BCR-ABL-transformed mouse cells that resulted in endostatin (ES) production altered their oncogenic potential. Mouse B210 cells, which express p210bcr-abl fusion protein and induce leukemia-like disease and extremely rarely solid tumors after intravenous (i.v.) administration, were used. The cells were transfected with a plasmid carrying genes for mouse ES and resistance to blasticidine. Transduced cells were isolated in media supplemented with blasticidine. Production of ES was determined by Western blotting. For further tests, two clones were selected, and their pathogenicity after i.v. inoculation was tested. Compared with the parental B210 cells, the capability of both gene-modified cell clones to induce lethal leukemia was reduced. However, mice that did not succumb to leukemia subsequently developed solid tumors. They were composed of poorly differentiated cells with irregular nuclei and roughly granular chromatin and were well vascularized. FISH revealed the presence of the BCR-ABL fusion gene both in tumors and spleens. Immunohistological investigation of the tumors demonstrated the production of ES in vivo and the cell lines derived from the tumors produced detectable amounts of ES, this demonstrating that the formation of solid tumors was not associated with the loss or silencing of the ES gene.