Fibrin matrix for local delivery of a mitotoxin to inhibit vascular smooth muscle cell proliferation

Successful use of mitotoxins to inhibit neointimal hyperplasia after vascular graft implantation will require local delivery of high concentrations of the toxin. As a first step to determine the feasibility of using a fibrin matrix delivery system for prosthetic grafts, we studied the effect of fibrin incorporation on the toxicity of a mitotoxin directed against the epidermal growth factor receptor on porcine vascular cells. Inhibition of protein synthesis as determined by ³H-leucine uptake was greater in smooth muscle cells (ICso 50 pM) compared with endothelial cells (ICso 5.0 nM). Fibrin clot incorporation of the 48 kd mitotoxin, accomplished by the addition of 0.32 U/ml thrombin and 32 mg/ml fibrinogen, prevented all inhibitory activity. Toxicity could be partially restored (ICso 70 nM) by coincubation of the mitotoxm-fibrin matrix with 250 U/ml urokinase. Using this fibrin matrix delivery system, therapeutic levels of this mitotoxin cannot be attained by diffusion alone, but will require local fibrinolvsis.