New stable butyrate derivatives alter proliferation and differentiation in human mammary cells

Two new butyric esters which were devised to extend the half-life of n-butyric acid in vivo, were used to study their effects on a number of phenotypic characteristics including cell morphology, cell proliferation, colony formation, cell-surface antigen and estrogen receptor expression in 3 normal immortalized cell lines and 2 carcinoma cell lines derived from the human mammary gland. When treated with butyric esters, human mammary cells acquired numerous cytoplasmic granules and vacuoles, reminiscent of secretory functions, and increased in volume. Modulation of the expression of membrane-associated antigens recognized by the monoclonal antibodies (MAbs) 115D8, 140C1 and 125B5 was also observed. Furthermore, butyrate derivatives inhibited the proliferation of all the cell lines tested and the colony-forming capacity of those that grew in soft agar. The inhibitory effects were, however, reversible upon removal of butyric esters from the culture medium. In the human breast carcinoma cell line, MCF-7, in which the cytostatic effects of butyric esters were the most pronounced, cells accumulated in the G0/G1 phase of the cell cycle. This cell line was the only one to contain estrogen receptors which decreased in number when treated with butyric esters without any modification in their binding affinity. Moreover, the stimulatory effects of estrogen on MCF-7 cell proliferation were antagonized by butyric esters. Our results demonstrate that many of the proliferative and differentiation changes previously reported for n-butyrates in tumor cells are similarly produced by the new stable butyrate derivatives in normal and malignant human mammary cell lines.