Retinoids, a group of compounds consisting of vitamin A (retinol) and its natural metabolites, have been shown in numerous experimental systems to act as cancer chemopreventive agents and cancer chemotherapeutic agents. While previous research has shown that retinoic acid (RA) is a very potent vitamin A metabolite which causes cell differentiation and inhibition of the growth of tumor cells, we have recently identified two new potent, bioactive vitamin A metabolites, 4-OHretinol and 4-oxoretinol, in a number of cultured tumor cell lines. Although we first isolated these bioactive retinoids, 4- OHretinol and 4-oxoretinol, from a murine cell line (Achkar et al. (1996) PNAS 93:4879-4884), we have recently shown that estrogen receptor (ER) positive cultured human breast cancer cell lines such as MCF-7 can synthesize 4-OHretinol and 4-oxoretinol from retinol under certain culture conditions. In contrast, estrogen receptor negative breast cancer cells do not synthesize 4-OH-retinol and 4-oxoretinol from retinol. We have also recently shown that 4-oxoretinol is growth inhibitory for both ER positive and ER negative breast cancer lines, whereas RA is growth inhibitory in ER positive but not in ER negative breast tumor lines. In this proposal, we want to explore the activity of these new, bioactive retinol metabolites on normal human breast epithelial cells and on breast cancer cells: a) to determine more about the molecular mechanism by which 4-OHretinol and 4-oxoretinol can induce cell growth arrest, and b) to compare 4-oxoretinol with RA with respect to the regulation of gene expression. We will assess whether or not 4- oxoretinol synergizes with RXR specific ligands, N-(4-hydroxyphenyl) retinamide, interferon, TGFbeta, and/or tamoxifen with respect to the growth arrest of breast cancer cells and the regulation of gene expression. We also plan to characterize biochemically the enzyme(s) which converts retinol to 4-OHretinol and 4-oxoretinol, to clone the gene(s) for the enzyme(s), and to delineate its regulation in human breast cancer cells. Tetracycline inducible antisense RNA techniques will be employed to block the expression of this gene. Our proposed studies may lead to the use of 4-oxoretinol or related compounds in the prevention and/or treatment of human breast cancer.
