In the United States, breast cancer is the most common non-skin malignancy and the second leading cause of cancer-related death in women. However, earlier detection and new, more effective treatments may be responsible for the decrease in overall death rates. Approximately 60% of breast tumors are estrogen receptor (ER) positive and thus their cellular growth is hormone-dependent. Elevated levels of estrogens, even in post-menopausal women, have been implicated in the development and progression of hormone-dependent breast cancer. Hormone therapies seek to inhibit local estrogen action and biosynthesis, which can be produced by pathways utilizing the enzymes aromatase or steroid sulfatase (STS). Cyclooxygenase-2 (COX-2), typically involved in inflammation processes, is a major regulator of aromatase expression in breast cancer cells.
STS, COX-2, and aromatase are critical for estrogen biosynthesis and have been shown to be over-expressed in breast cancer. While there continues to be extensive study and successful design of potent aromatase inhibitors, much remains unclear about the regulation of STS and the clinical applications for its selective inhibition. Further studies exploring the relationships of STS with COX-2 and aromatase enzymes will aid in the understanding of its role in cancer cell growth and in the development of future hormone-dependent breast cancer therapies.
After confirming the high potency of two STS enzyme inhibitors DU-14 and DU-15 in MCF-7 and MDA-MB-231 breast cancer cells, our initial studies investigated the effects of these compounds on STS, aromatase and COX-2 gene expression by Real-Time RT-PCR, on cancerous cellular growth using the Promega(R) MTS assay, and on STS enzyme activity using a tritium conversion radioassay. We then examined the individual effects, if any, of several COX isozyme inhibitors (celecoxib, NS-398, SC-560 and six non-steroidal anti-inflammatory drugs), aromatase inhibitors (letrozole and exemestane), and anti-estrogen 4-hydroxy tamoxifen. We found that these alternate target therapies can affect STS in vitro. To examine combinational effects, DU-14 and DU-15 were also combined with these same drugs. Furthermore, breast cancer cells were treated with potential regulatory factors, such as cytokines, steroids, and PKA and NK-kB pathway inhibitors, to better understand the regulation of STS and its interrelationships with aromatase and cyclooxygenase enzymes.