Mouse endostatin inhibits the formation of lung and liver metastases

Angiogenesis is required fur tumor formation, Several studies have demonstr ated that tumor angiogenesis is regulated by a balance between proangiogene sis and antiangiogenesis factors and that this balance varies in different organ environments, To investigate whether expression of an angiogenesis in hibitor by cancer cells could alter this balance and prevent tumor formatio n in different organ environments, we engineered stable transfectants from RenCa mouse renal carcinoma cells and SW620 human colon carcinoma cells to constitutively secrete a mouse endostatin protein with c-myc and polyhistid ine (His) tags, Production and secretion of the endostatin-c-myc-His fusion protein by endostatin-transfected cells were confirmed by immunofluorescen ce staining and Western blot analysis. The endostatin transfectants and con trol transfectants, stably transfected with a control plasmid, had similar in vitro growth rates compared with their parental cell lines. Conditioned medium from endostatin-transfected cells inhibited human umbilical vein end othelial cell proliferation by 36-51% compared with conditioned medium from control cells. After inoculation into mice, flank tumors from endostatin-t ransfected cells were 73-91% smaller than flank tumors from control cells a fter 3 weeks. Inoculation of a cell mixture containing 25% endostatin-trans fected cells and 75% control cells resulted in inhibition of flank tumor fo rmation as effective as after inoculation of 100% endostatin-transfected ce lls. Formation of lung metastases by RenCa endostatin-transfected cells and formation of liver metastases by SW620 endostatin-transfected cells were d ramatically inhibited compared with formation of metastases by control cell s. These findings demonstrate that endostatin can inhibit tumor formation i n different organ environments and that gene delivery of endostatin into ev en a minority of tumor cells may be an effective strategy to prevent progre ssion of micrometastases to macroscopic disease.