Vitamin D is known for its anticancer potential. Prostaglandin E2 (PGE2) is a proliferative and inflammation-activating agent. The production of PGE2 is dependent on the activity of cyclooxygenase-2 (COX2). A link between vitamin D and PGE2 metabolism was shown recently.

In MDA-MB-231 and MCF-7 breast cancer cell lines, we investigated the influence of calcitriol and the COX2 inhibitor celecoxib on cell growth via the MTT test, as well as on the protein and mRNA expression of COX2 using western blot and quantitative real-time polymerase chain reaction (qRT-PCR).

The proliferation of MCF-7 and MDA-MB-231 was inhibited by both calcitriol and the COX2 inhibitor celecoxib and even more strongly by their combination. Moreover, calcitriol inhibited COX2 protein expression in MDA-MB-231 cells, as well as COX2 mRNA expression in both cell lines.

The combination of calcitriol and celecoxib demonstrated a synergistic growth-inhibitory effect in breast cancer cell lines.