Differential effects of vitamin D treatment on inflammatory and non-inflammatory breast cancer cell lines.

Vitamin D is a known regulator of breast cancer cell proliferation, apoptosis, migration, invasion and differentiation in vitro. Recent studies have suggested a preventative role for vitamin D in breast cancer development and suggested a possible therapeutic application of vitamin D for patients with various forms of breast cancer. Inflammatory breast cancer (IBC) is a highly aggressive and phenotypically unique form of breast cancer that has a very poor prognosis. IBC invades the dermal lymphatics of the breast as tumor emboli early in the course of the disease. Because of the invasive nature of IBC, novel therapeutics are needed desperately. In the current study we examined the effect of the active form of vitamin D, calcitriol, treatment on the aggressive IBC phenotype. Herein we demonstrate that although the vitamin D receptor (VDR) is present in both IBC and non-IBC cell lines, the effect of vitamin D treatment is significant only on the IBC cells. SUM149 IBC cells showed increased protein concentration in response to 24 h of calcitriol exposure; likely mediated by an increase in protein synthesis as opposed to increased cellular proliferation. In addition, treatment with 100 nM calcitriol showed a significant decrease in SUM149 migration (67.8 % decrease, P = 0.030), invasion (43.9 % decrease, P = 0.015), and tumor spheroid size (69.4 % decrease, P = 0.018) compared to nontreated control groups. Finally, calcitriol treatment of SUM149 cells led to significantly fewer IBC experimental metastases as compared to control. Our study demonstrates that calcitriol treatment of SUM149 affected several of the processes important for IBC metastasis but had little effect on MDA-MB-231 cells. Therefore, calcitriol treatment may have the potential to decrease the rate and incidence of metastasis in IBC patients.