ANGIOSTATIN-MEDIATED SUPPRESSION OF CANCER METASTASES BY PRIMARY NEOPLASMS ENGINEERED TO PRODUCE GRANULOCYTE MACROPHAGE COLONY-STIMULATING FACTOR/

We determined whether tumor cells consistently generating granulocyte/ macrophage colony-stimulating factor (GM-CSF) can recruit and activate macrophages to generate angiostatin and, hence, inhibit the growth of distant metastasis. Two murine melanoma lines, B16-F10 (syngeneic to C57BL/6 mice) and K-1735 (syngeneic to C3H/HeN mice), were engineered to produce GM-CSF. High GM-CSF (>1 ng/10(6) cells)- and low GM-CSF (<1 0 pg/10(6) cells)-producing clones were identified. Parental, low, and high GM-CSF-producing cells were injected subcutaneously into syngene ic and into nude mice. Parental and low-producing cells produced rapid ly growing tumors, whereas the high-producing cells produced slow-grow ing tumors. Macrophage density inversely correlated with tumorigenicit y and directly correlated with steady state levels of macrophage metal loelastase (MME) mRNA. B16 and K-1735 subcutaneous (s.c.) tumors produ cing high levels of GM-CSF significantly suppressed lung metastasis of 3LL, UV-2237 fibrosarcoma, K-1735 M2, and B16-F10 cells, but parental or low-producing tumors did not. The level of angiostatin in the seru m directly correlated with the production of GM-CSF by the s.c. tumors . Macrophages incubated with medium conditioned by GM-CSF-producing B1 6 or K-1735 cells had higher MME activity and generated fourfold more angiostatin than control counterparts. These data provide direct evide nce that GM-CSF released from a primary tumor can upregulate angiostat in production and suppress growth of metastases.