EXPRESSION AND ACTIVITIES OF A RECOMBINANT BASIC FIBROBLAST GROWTH FACTOR-SAPORIN FUSION PROTEIN

A fusion protein containing the full-length sequences of the mitogen, basic fibroblast growth factor (FGF-2), and the ribosome inactivating protein, saporin (SAP), has been expressed in E. coli. As expected, it binds with high affinity to heparin-Sepharose like FGF-2 and can disp lace the binding of radiolabeled FGF-2 to its high affinity receptor. In contrast, the fusion protein only has much lower ribosome-inactivat ing activity than free saporin, although full ribosome-inactivating pr otein activity can be generated by proteolytic removal of the FGF-2 mo iety. Cytotoxicity experiments with B16-F10 mouse melanoma cells estab lish that the fusion protein is active as a chemical conjugate against these intact cells. Presumably these cells have the ability to activa te the SAP component of the fusion protein through an intracellular me tabolism of the fusion protein. Because we also show the fusion protei n has tumor growth inhibition properties and antimetastatic activity i n in vivo models of melanoma, the findings support the hypothesis that FGF-based ligand-mediated cytotoxicity can serve to target cytotoxic agents in vivo.