Inhibition of tumor growth correlates with the expression level of a humanangiostatin transgene in transfected B16F10 melanoma cells

Although the therapeutic value of angiostatin, a proteolytic fragment of pl asminogen, has been recognized for the treatment of cancer, the production of bioactive angiostatin remains a difficult task. Here we report that expr ession of a cDNA encoding a secreted, four-kr ingle human angiostatin inhib ited tumor growth of B16F10 melanoma cells in mice but did not suppress tum or cell growth in culture. After transfection and selection, stable express ion of the angiostatin cDNA was demonstrated in several B16F10 clones by qu antitative mRNA analysis using the Taqman method. Cells that expressed angi ostatin at either a low, medium, or high level were injected into C57BL/6 m ice. s.c, Growth of B16F10 tumors was diminished by the angiostatin transge ne, and the inhibition was directly proportional to the expression level of angiostatin in the transfected cells. However, suppression of s.c. tumor g rowth was transient, and eventually, tumors emerged with a strongly decreas ed expression of the transgene. Angiostatin expression also reduced long me tastasis from i.v.-injected B16F10 cells. Our data indicate that a cDNA enc oding bioactive human angiostatin is potentially useful for gene therapy of human cancers, but the delivery of the transgene may require repeated dosi ng to achieve sustained dormancy of primary tumors and cancer metastases.