CYTOTOXIC EFFECTS OF VASCULAR SMOOTH-MUSCLE CELLS OF THE CHIMERIC TOXIN, HEPARIN-BINDING TGF-ALPHA-PSEUDOMONAS EXOTOXIN

Objective: Smooth muscle cell proliferation appears to be very important in restenosis after angioplasty. A chimeric toxin created by genetically fusing the gene encoding TGFalpha (targets the EGF receptor) to the gene encoding Pseudomonas exotoxin (PE) preferentially kills rapidly proliferating smooth muscle cells. Recently, a heparin binding EGF-like growth factor (HB-EGF) has been identified. The HB domain enhances the mitogenic activity for smooth muscle cells. The purpose of this study was to design a new chimeric toxin, having both heparin binding and EGF receptor binding function, and to determine whether it is more cytotoxic to smooth muscle cells. Methods: By recombinant DNA techniques, a new chimeric toxin, HB-TGFalpha-PE(4E)KDEL, was synthesised. Cytotoxic assays were performed by assessing the capacity to inhibit protein synthesis of rat vascular smooth muscle cells. Results: The toxin preferentially killed rapidly proliferating smooth muscle cells (p<0.025). The HB domain increased the cytotoxicity of the molecule when compared to the other chimeric toxins tested against smooth muscle cells. The cytotoxic effect of the new molecule was significantly decreased by exogenously added heparin (p<0.05). Conclusions: The presence of a heparin binding domain increases the smooth muscle cell cytotoxicity of the TGFalpha fusion toxin, perhaps because HB-TGFalpha-PE(4E)KDEL functions as a molecule with two ligands. It will be important to determine whether the greater smooth muscle cell cytotoxicity that exists in vitro will facilitate the specific targeting and killing of rapidly proliferating cells in vivo.