In vitro activity: Calcitriol is a potent inhibitor of PHA-induced lymphocyte proliferation, achieving 70% inhibition of tritiated thymidine incorporation after 72 h in culture. Calcitriol suppresses interleukin-2 (IL-2) production by PHA-stimulated peripheral blood mononuclear cells in a concentration-dependent fashion. Calcitriol increases the concentration of intracellular calcium ([Ca2+]i) within 5 s by mobilizing calcium from the endoplasmic reticulum and the formation of inositol 1,4, 5-trisphosphate and diacylglycerol. Calcitriol can inhibit the proliferation and promote the differentiation of human prostate adenocarcinoma cells. Calcitriol causes a selective decrease in the secreted levels of type IV collagenases (MMP-2 and MMP-9). Calcitriol has antiproliferative activity in squamous cell carcinoma and prostatic adenocarcinoma and enhances the antitumor activity of platinum-based agents. Calcitriol prior to paclitaxel significantly reduces clonogenic survival compared with either agent alone in the murine squamous cell carcinoma and PC-3 cells. Calcitriol is a potent anti-proliferative agent in a wide variety of malignant cell types. Calcitriol effects are associated with an increase in G0/G1 arrest, induction of apoptosis and differentiation, modulation of expression of growth factor receptors. Calcitriol potentiates the antitumor effects of many cytotoxic agents and inhibits motility and invasiveness of tumor cells and formation of new blood vessels.

Cell Assay: HeLa S3 cells are plated at a density of 1,000 cells/well in 96-well plates of Dulbecco’s modified Eagle’s medium (DMEM) with 10% fetal bovine serum (FBS), treated with 1% ethanol (control) or various concentrations of Calcitriol (100, 200, and 500 nM) for 72 h. A Cell Counting Kit8 (CCK-8) is used to determine cell proliferation. At 24, 48, 72, 96, 120, and 144 h after culturing with 200 nM Calcitriol, cells are harvested for analysis. Three independent experiments are performed in quadruplicate