Expansion of tumors beyond a critical volume is dependent on the ability of the tumor to develop a vascular network. New therapeutics aimed at interfering with the tumor vasculature have been successful in treating small slowly-progressing tumors. However, these same agents appear to be less effective in treating large established tumors. Therefore, there is a need for alternative interventions for patients with larger primary tumors. We have been developing a series of agents that specifically target the established vasculature of solid tumors. Coaguligands, one class of these vascular targeting agents (VTAs), target a truncated form of the procoagulant tissue factor to tumor blood vessels. Truncated tissue factor (tTF) has very weak ability to induce blood coagulation by itself, but becomes a powerful thrombogen for tumor blood vessels when targeted by monoclonal antibodies to tumor vasculature. The coaguligand specifically induces coagulation of tumor vasculature, leading to tumor infarction. We have developed three coaguligands (PGN-502, PGN-503, and PGN-504) that link truncated tissue factor to vascular targeting monoclonal antibodies. These fusion proteins have been expressed in stably transfected CHO cells and purified by Protein A and ion exchange chromatography. The purified proteins are stable and active in vitro. Each binds its respective ligand in vitro, can bind to purified coagulation factor VIIa, and in turn activate factor X. Purified tTF:His6, a non-targeted recombinant tissue factor, does not bind to any of the targets but has the ability to activate factor X . In addition, these three drugs can initiate coagulation in isolated human plasma in a dose-dependent manner. An additional three drug candidates that are tTF fused to single chain Fv (scFv) versions of the targeting antibodies also have been produced, purified, and evaluated for in vitro activity. Early results suggest that targeted tissue factor can be safely administered to animals at levels below one milligram per kilogram. Safety can be assessed by monitoring platelet numbers 24 hours following administration of drug. Untargeted tTF administration and naked antibody show no signs of toxicity after a single administration. Efficacy and safety of a single dose of targeted tissue factor in a syngeneic rat tumor model will be discussed.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA