Abstract: A factor has been purified from rat liver homogenate which displays preferential growth inhibitory effects on non-liver metastasizing tumor cells. The purification steps include heat treatment, ammonium sulfate precipitation, anion exchange chromatography, hydrophobic interaction chromatography, cation exchange chromatography, gel filtration chromatography, and preparative isoelectric focusing. The growth inhibitor obtained has an apparent M.sub.r of 38 kD to 40 kD and a pI of 9.1, it is not affected by reducing agents, and displays no biological TGF-b activity. This inhibitor exhibits less antiproliferative effect on liver metastasizing cells than on their non-liver metastasizing counterparts in two tumor systems: the murine RAW117 large cell lymphoma, and the human A375 melanoma.

Abstract: The invention relates to the purification and characterization of growth stimulatory and inhibitory protein factors produced by various organs which appear to play a role in the successful formation of metastatic colonies of tumor cells. In particular, it has been found that syngeneic organs secrete protein growth stimulatory and inhibitory factors which can, at low concentrations, affect metastatic tumor cells. The ability of a malignant cell to respond to these factors is believed to be related to tumor cell metastasis to specific body organs. In particular a lung growth stimulatory glycoprotein having a molecular weight of approximately 66,000 daltons has been found to stimulate growth of lung-metastatic rat and human mammary tumor cells in serum deprived medium.