Growth inhibition of carcinogen-transformed MCF-12F breast epithelial cells and hormone-sensitive BT-474 breast cancer cells by 1α-hydroxyvitamin D5

Several studies have established the active form of vitamin D-3 as an effective tumor-suppressing agent; however, its antitumor activity is achieved at doses that are hypercalcemic in vivo. Therefore, less calcemic vitamin D-3 analog, 1 alpha-hydroxy-24-ethyl-cholecalciferol (1 alpha[OH]D5), was evaluated for its potential use in breast cancer chemoprevention. Previously, 1 alpha(OH)D5 showed anticarcinogenic activity in several in vivo and in vitro models. However, its effects on growth of normal tissue were not known. The present study was conducted to determine the effects of 1 alpha(OH)D5 on the growth of normal mouse mammary gland and normal-like human breast epithelial MCF-12F cells and to compare these effects with carcinogen-transformed MCF-12F and breast cancer cells. No significant difference was observed in the growth or morphology of cultured mouse mammary gland and MCF-12F cells in the presence of 1 alpha(OH)D5. However, the transformed MCF-12F cells underwent growth inhibition (40-60%, P < 0.05) upon 1 alpha(OH)D5 treatment as determined by cell viability assays. Cell cycle analysis showed marked increase (50%) in G-1 phase for cells treated with 1 alpha(OH)D5 compared with the controls. Moreover, the percentage of cells in the synthesis (S) phase of cell cycle was decreased by 70% in transformed MCF-12F, BT-474 and MCF-7 cells. The growth arrest was preceded by an increase in expression of cell cycle regulatory proteins p21(Waf-1) and p27(Kip-1). In addition, differential expression studies of parent and transformed MCF-12F cell lines using microarrays showed that prohibitin mRNA was increased 4-fold in the transformed cells. These results indicate that the growth inhibitory effect of 1 alpha(OH)D5 was achieved in both carcinogen-transformed MCF-12F and breast cancer cells at a dose that was non-inhibitory in normal-like breast epithelial cells.