We investigated the effect of protein extract of Asterina pectinifera on the activity of 4 enzymes that may play a role in adenocarcinoma of the colon: quinone reductase (QR), glutathione S-transferase (GST), ornithine decarboxylase (ODC), and cyclooxygenase (COX)-2. QR and GST activity increased in HT-29 human colon adenocarcinoma cells increased that had been exposed to 4 concentrations of the protein extract (80, 160, 200, and 240 microg/mL). Additionally, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ODC activity decreased significantly in cells exposed to the extract in concentrations of 160 microg/mL (p<0.05), 200 microg/mL (p<0.005), and 240 microg/mL (p<0.005). TPA-induced COX-2 activity also decreased in cells exposed to extract concentrations of 10, 20, 40, and 60 microg/mL. COX-2 expression was also inhibited in cells exposed to this extract. These results suggest that this protein extract of A pectinifera has chemopreventive activity in HT-29 human colon adenocarcinoma cells, and therefore, may have the potential to function as a chemopreventive agent in human colorectal cancer.