Characterization of a Phage Display-Derived Human Monoclonal Antibody (NHS76) Counterpart to Chimeric TNT-1 Directed Against Necrotic Regions of Solid Tumors

To eliminate the human anti-mouse antibody (HAMA) response seen in patients treated with murine and chimeric antibodies, fully human monoclonal antibodies (MAbs) are now being developed. Tumor Necrosis Therapy (TNT) is an approach to tumor targeting that utilizes MAbs directed against common intracellular antigens such as nucleic acids, accessible only in necrotic areas of solid tumors. By binding to the necrotic core of tumors, these TNT MAbs can circumvent many of the limitations of MAbs directed against tumor cell surface antigens. Chimeric TNT-1 (chTNT-1) was first developed from the parent murine antibody by genetically engineering the murine variable regions to the human IgG₁ and kappa constant regions. Although the chimeric antibody's behavior was similar to that of the murine version, the 35% murine homology it shares allows for the potential of a HAMA response. A human antibody derived from a phage display library, designated NHS76, has been developed with similar binding characteristics to the TNT-1. To demonstrate that this genetically engineered human counterpart to chTNT-1 has similar pharmacokinetic characteristics, in vivo behavior, and targeting abilities, both antibodies were rigorously tested in parallel. For these studies, biodistribution analysis in LS174T human colon tumor-bearing nude mice was performed to compare the uptake levels in tumor and normal organs. In addition, mouse imaging and autoradiographic studies were conducted to demonstrate positive uptake in necrotic regions of tumor and negative uptake in viable tissues and organs. The results of these studies confirm the comparable nature of both antibodies and provide the necessary preclinical data to show the suitability of NHS76 as an improved product for the therapy of solid tumors in man.