Claudin-1 (CLDN-1), an integral transmembrane protein, is an attractive target for drug absorption, prevention of infection, and cancer therapy. Previously, we generated mouse anti-CLDN-1 monoclonal antibodies (mAbs) and found that they enhanced epidermal absorption of a drug and prevented hepatitis C virus infection in human hepatocytes. Here, we investigated anti-tumor activity of a human mouse chimeric IgG1, xi-3A2, from one of the anti-CLDN-1 mAbs, clone 3A2. Xi-3A2 accumulated in the tumor tissues in mice bearing with human CLDN-1 expressing tumor cells. Xi-3A2 activated Fc gamma receptor Ilia expressing reporter cells in the presence of human CLDN-1 expressing cells, suggesting xi-3A2 has a potential to exhibit antibody-dependent cellular cytotoxicity against CLDN-1 expressing tumor cells. We also constructed a mutant xi-3A2 antibody with Gly, Ser, and Ile substituted with Ala, Asp, and Arg at positions 236, 239, and 332 of the Fc domain. This mutant antibody showed greater activation of Fc gamma receptor Ilia and in vivo anti-tumor activity in mice bearing human CLDN-1-expressing tumors than xi 3A2 did. These findings indicate that the G236A/S239D/I332E mutant of xi-3A2 might be a promising lead for tumor therapy. (C) 2016 Elsevier Inc. All rights reserved.