22-Oxa-1,25-Dihydroxyvitamin D3 Efficiently Inhibits Tumor Growth in Inoculated Mice and Primary Histoculutre of Cholangiocarcinoma

BACKGROUND: It is well known that 1 alpha,25-Dihydroxyvitamin D-3(1,25[OH](2)D-3) restrains cell proliferation and induces differentiation and apoptosis in normal and tumor cells. The authors of this report recently demonstrated that 1,25(OH)(2)D-3 effectively inhibits the proliferation of cholangiocarcinoma (CCA) cell lines. The antitumor activity and the underlying mechanism of 22-oxa-D-3, an analog of vitamin D, in mice and in tissue cultures from patients with CCA were further explored in the current study. METHODS: Cell growth and cell cycle distribution were examined in CCA cells by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. Mice were injected subcutaneously with 4 x 10(6) CA cells at both flank sides and intraperitoneal injections with phosphate-buffered saline or 22-oxa-D-3(15 mu g/kg/day) for 17 days thereafter. Tumors were removed the next day. The expression levels of cyclin D1 and the cyclin-dependent kinase inhibitor p21 were determined by Western blot analysis and immunohistochemistry. Growth inhibition of 22-oxa-D-3 in fresh tissue samples from patients with CCA was analyzed by using a histodrug response assay. RESULTS: 22-Oxa-D-3 effectively suppressed the growth of CCA cell lines in a time-dependent and dose-dependent manner. 22-Oxa-D-3 arrested CCA cells at G1 phase to S phase by the suppression of cyclin D1 expression and the up-regulation of p21. Supplementation of 22-oxa-D-3 to CCA-inoculated mice significantly inhibited tumor growth without hypercalcemia or serious side effects. The treatment also induced cellular apoptosis in tissue samples from patients with CCA. CONCLUSIONS: 22-Oxa-D-3 effectively suppressed tumor growth in CCA-inoculated mice and induced cellular apoptosis in tissue samples from patients with CCA. The current data encourage further investigation of 1,25(OH)(2)D-3 or its analogues as therapeutic agents in the treatment of patients with CCA. Cancer 2010;116:5535-43. (C) 2070 American Cancer Society