An antibody-tumor necrosis factor fusion protein that synergizes with oxaliplatin for treatment of colorectal cancer

We have cloned and characterized a novel fusion protein (Sm3E-TNF), consisting of the monoclonal antibody Sm3E in single-chain Fv fragment format, fused to murine tumor necrosis factor. The protein, which was expressed in mammalian cells and purified as a non-covalent stable homotrimer, bound to the cognate carcinoembryonic antigen (CEA) and retained tumor necrosis factor activity. A quantitative biodistribution experiment, performed in immunocompetent mice with CT26 colon carcinomas transfected with human CEA, revealed that Sm3E-TNF was able to preferentially accumulate in the tumors with excellent selectivity (tumor:blood ratio = 56:1, twenty-four hours after intravenous administration). The fusion protein mediated a rapid hemorrhagic necrosis of a large portion of the tumor mass, but a rim survived and eventually regrew. Surprisingly, the combination of Sm3E-TNF with 5-fluorouracil led to a reduction of therapeutic activity, while a combination with oxaliplatin led to a prolonged stabilization, with complete tumor eradication in 40% of treated mice. These therapy results were confirmed in a second immunocompetent mouse model of colorectal cancer (CEA-transfected C51 tumors) and provide a rationale for the possible clinical use of oxaliplatin in combination with fully-human antibody-TNF fusions.