Effects of 1,25(OH)2D3 on Cancer Cells and Potential Applications in Combination with Established and Putative Anti-Cancer Agents

The diverse effects of 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3), the bio-active form of vitamin D, on cancer cell metabolism and proliferation has made it an interesting candidate as a supporting therapeutic option in cancer treatment. An important strategy in cancer therapy is the use of combination chemotherapy to overcome drug resistance associated with numerous anti-cancer agents and to provide better means of avoiding undesirable side effects. This complex strategy is widely adopted by oncologists and several established cocktails of chemotherapeutics are routinely administered to cancer patients. Among the principles followed in designing such treatment regimens is the use of drugs with different mechanisms of action to overcome the issue of tumor heterogeneity and to evade resistance. In light of the profound and diverse effects of 1,25(OH)(2)D-3 reported by in vitro and in vivo studies, we discuss how these effects could support the use of this molecule in combination with classical cytotoxic drugs, such as platins and anti-metabolites, for the treatment of solid and hematological tumors. We also examine recent evidence supporting synergistic activities with other promising anti-cancer drug candidates, and postulate mechanisms through which 1,25(OH)(2)D-3 may help evade chemoresistance.