Background: To enhance monoclonal antibody uptake in tumors, seven novel vasoactive immunoconjugates were developed that selectively alter the vascular permeability and/or blood volume of tumors in vivo. These immunoconjugates, composed of IL-1 beta, IL-2, TNF-alpha, physalaemin, leukotriene B4, histamine, and bradykinin chemically linked to TNT-1, a murine monoclonal antibody that binds necrotic regions in tumors, have been tested for their effects on antibody uptake in vivo.
Methods: Groups of four mice, each bearing the ME-180 human cervical carcinoma, were pretreated either 3 or 24 hours before the administration of I-125 labeled TNT-1 F(ab')2 fragment. Three-day biodistribution studies then were performed to determine the amount of radiolabeled antibody in the tumors and normal organs of the mice. In addition, mechanism of action studies were performed to determine if the vasoactive immunoconjugate affected the vascular permeability or blood volume of the tumor vessels.
Results: TNT-1/IL-2 gave the highest percent injected dose/g in tumor (4.80), compared with TNT-1/TNF (4.00), TNT-1/IL-1 (3.83), TNT-1/leukotriene-B4 (2.84), TNT-1/histamine (2.80), TNT-1/physalaemin (2.19), TNT-1/bradykinin (1.57), or TNT-1 alone (1.28). All of these immunoconjugates showed specific enhancement of monoclonal antibody uptake in tumor with no changes seen in normal tissues. Quantitative studies that demonstrated the mechanism of action of these immunoconjugates showed that TNT-1/IL-2 and TNT-1/histamine produced a marked change in the vasopermeability of tumor vessels but had no effect on tumor blood volume. In contrast, TNT-1/IL-1 and TNT-1/TNF produced a combination of effects, and TNT-1/leukotriene B4, TNT-1/bradykinin, and TNT-1/physalaemin affected only tumor blood volume.
Conclusions: These studies indicate that pretreatment with vasoactive immunoconjugates may improve monoclonal antibody uptake in tumors significantly and thereby increase the therapeutic index of monoclonal antibody-directed immunotherapy.