Breast cancer--new aspects of tumor biology: are calcitriol and cyclooxygenase-2 possible targets for breast cancer?

Up until now there have been many advances in treatment options for breast cancers such as targeted therapies like monoclonal antibodies, tyrosine kinase inhibitors, mTOR antagonists, and vaccines. Despite these advances, there are still many more that warrant further exploration. Two of these targets might be the cyclooxygenase-2 (COX-2), the key enzyme required to convert arachidonic acid to prostaglandins, and calcitriol [1,25(OH)2D3] which is the biologically active form of vitamin D. Both calcitriol and the inhibition of COX-2 have shown antiproliferative and prodifferentiation, as well as pro-apoptotic effects in different malignancies in vitro and in vivo, and the key prostaglandin catabolic enzyme 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is known to have tumor suppressor activity. Furthermore, the combination ofcalcitriol and nonsteroidal anti-inflammatory drugs (NSAIDs), such as non-selective and selective COX-2 inhibitors, acting synergistically to achieve significant cell growth inhibition in prostate cancer. Some epidemiological studies suggest that vitamin D confers a moderate benefit against breast cancer while most epidemiological studies presume that NSAIDs confer the same. Nevertheless there is growing body of evidence that COX-2 expression is a fundamental step in breast cancer carcinogenesis. To date, clinical trials have been conducted in patients with different malignancies using treatment strategies including COX-2 inhibitors and calcitriol and are showing partially encouraging results. The goal of this review is to shed light on the association between the prostaglandin as well as vitamin D metabolism relating to the incidence and therapy of breast cancers. Moreover, this review will also highlight potential treatment options, as well as extract any existing interactions between the two metabolisms.