Background: The natural history of colorectal neoplasia may be influenced by steroid hormones and nutritional compounds. We evaluated the effect of the anti-estrogenic tamoxifen (Tx), and the synthetic retinoid fenretinimide (4-HPR) on the growth of human colorectal cancer cells.
Methods: DLD-1, CACO-2, SW-620, and COLO-205 colon cancer cells, and SW-1463 and SW-837 rectal cancer cells were cultured under serum-free conditions. Quadruplicates wells (4 x 10(4) cells/well) were created for each treated, and untreated groups in each cell line. Cells were treated with 1 microM Tx, 5 microM Tx, 1 microM 4-HPR, 1 microM Tx with 1 microM 4-HPR, and 5 microM Tx with microM 4-HPR. Cell growth was measured colorimetrically with the hexosaminidase assay (405 nm), and was compared among the different groups. Cells were analyzed for estrogen receptors using an enzyme immunoassay.
Results: Tamoxifen, 4-HPR, or both, inhibited the growth in DLD-1 (P = .001), COLO-205 (P = .02), SW-620 (P = .001), and CACO-2 (P = .02) cell lines. Tamoxifen with 4-HPR inhibited cell growth more (P = .03) than did either Tx or 4-HPR in DLD-1, COLO-205, and SW620 cancer cells. Tamoxifen, 4-HPR, or both, had no effect on the growth of SW-837 (P = .14) cancer cells. Tamoxifen with 4-HPR promoted (P = .02) growth in SW-1463 cells, but not when added separately. Estrogen receptors were not found in any of the cells.
Conclusions: Under serum-free conditions, Tx, 4-HPR, or both, inhibit the growth of human colon cancer cells but not of rectal cancer cells. Combined treatment with Tx and 4-HPR is more effective than treatment with either of the agents alone in inhibiting of cell growth. The mechanism of inhibition is not clear yet, and further studies are warranted.