Survivin, a novel inhibitor of apoptosis, is expressed in cancer cells and not in normal adult tissues, and is recognised as a potential target in anticancer therapy. The induction of a natural antisense of survivin, effector cell protease receptor-1 (EPR-1), in a human colon cancer cell line resulted in a downregulation of survivin expression, with a similar decrease in cell proliferation, an increase in apoptosis and an increase in the sensitivity to anticancer agents. In addition, subcutaneous (s.c.) tumours from EPR-1 transfectants showed a significant reduction in size compared with parental cells, and this antitumour efficacy was further enhanced in combination with anticancer agents. These findings suggest that regulation of survivin by the induction of EPR-1 cDNA may have significant potential as a therapy for human colon cancer.