22-oxa-1,25-dihydroxyvitamin D3 efficiently inhibits tumor growth in inoculated mice and primary histoculture of cholangiocarcinoma.

Abstract

It is well known that 1α,25-Dihydroxyvitamin D3 (1,25[OH]2 D3) 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 D3 effectively inhibits the proliferation of cholangiocarcinoma (CCA) cell lines. The antitumor activity and the underlying mechanism of 22-oxa-D3, an analog of vitamin D, in mice and in tissue cultures from patients with CCA were further explored in the current study. 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 4×10(6) CCA cells at both flank sides and intraperitoneal injections with phosphate-buffered saline or 22-oxa-D3 (15 μg/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-D3 in fresh tissue samples from patients with CCA was analyzed by using a histodrug response assay. 22-oxa-D3 effectively suppressed the growth of CCA cell lines in a time-dependent and dose-dependent manner. 22-oxa-D3 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-D3 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. 22-oxa-D3 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 D3 or its analogues as therapeutic agents in the treatment of patients with CCA.