Suppressive effect of 19-nor-1α-25-dihydroxyvitamin D2 on gastric cancer cells and peritoneal metastasis model

Abstract

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D(3) (calcitriol), inhibits the growth of several types of human cancer cells in vitro, but its therapeutic use is limited because it causes hypercalcemia. Among its analogs, 19-nor-1,25-dihydroxyvitamin D(2) (paricalcitol), has fewer calcemic effects and exhibits an activity equipotent to that of calcitriol. We assessed the antitumor and anti-inflammatory effects of paricalcitol in gastric cancer cells, and evaluated the potential role of vitamin D in the treatment of peritoneal metastatic gastric cancer. In this study, treatment with paricalcitol inhibited gastric cancer cell growth and induced cell cycle arrest. Paricalcitol also induced apoptosis and showed anti-inflammatory activity. Moreover, the growth of intraperitoneal metastases in vivo was reduced in mice treated with paricalcitol. (18)F-FDG uptake was significantly lower in the paricalcitol group compared to control group (SUV; control group 13.2 ± 5.3 vs paricalcitol group 4.5 ± 3.0). Intraperitoneal tumor volume was significantly lower in paricalcitol treated mice (control group 353.2 ± 22.9 mm(3) vs paricalcitol group 252.0 ± 8.4 mm(3)). These results suggest that the vitamin D analog, paricalcitol, has anticancer activity on gastric cancer cells by regulation of the cell cycle, apoptosis, and inflammation.

Keywords: Apoptosis; Neoplasms; Paricalcitol (19-nor-1α-25-dihydroxyvitamin D2); Stomach.

Fig. 1

Paricalcitol affects cell viability in gastric cancer cells. MKN45 cell was seeded in 24-well plates at a density of 5 × 10⁴ cells/well and treated with paricalcitol for 48 or 72 hr. Data are the mean ± SD of three independent experiments.

Fig. 2

Paricalcitol shows antiproliferative effects in gastric cancer cells. (A) Gastric cancer cells were treated with 10 nM paricalcitol, 100 nM paricalcitol, or vehicle for 48 hr, and the distribution of cells in the cell cycle was determined by propidium iodide (PI) staining. (B) The mean percent distribution of cells in the sub-G₁, G₀/G₁, S, and G₂/M phases of the cell cycle are shown. Values are means ± SD. ^*P = 0.005 (sub-G₁), P = 0.02 (G₀/G₁), and P = 0.002 (S).

Fig. 3

Paricalcitol regulates expression of cell cycle regulators in gastric cancer cells. Cells were treated with vehicle (control) or paricalcitol at 10 nM or 100 nM for 48 hr. Protein expression was determined using anti-p21, anti-p27, anti-CDK2, anti-CDK4, anti-CDK6, anti-Cyclin D1, and anti-Cyclin E antibodies.

Fig. 4

Paricalcitol regulates expression of apoptotic-related proteins in gastric cancer cells. The cells were treated with vehicle (control) or paricalcitol at 10 nM or 100 nM for 48 hr. (A) Protein expression was determined using anti-Bax, anti-Bcl-X_L, anti-Caspase 3, and anti-cleaved caspase-3 antibodies. (B) Apoptotic changes were observed by fluorescence microscopy. DAPI staining was used to visualize cell nuclei.

Fig. 5

Paricalcitol regulates expression of inflammation-related proteins in gastric cancer cells. The cells were treated with vehicle (control) or paricalcitol at 10 or 100 nM for 48 hr. Protein expression was determined using anti-STAT3, anti-COX-2, and anti-NF-κB antibodies. Relative protein levels were determined by densitometry and normalized to that oflamin-A. Values are means ± SD. ^*P = 0.005 (pSTAT3), P = 0.003 (COX-2), and P = 0.005 (NF-κB).

Fig. 6

In vivo imaging using ¹⁸F-FDG-PET in mice bearing peritoneal metastases. (A) Comparison of intra-abdomen ¹⁸F-FDG uptake (arrow) in mice from microPET images. (B) Comparison of ¹⁸F-FDG SUV uptake in control and paricalcitol group. ^*P = 0.005.

Fig. 7

In vivo antitumor effect of paricalcitol. (A) Bloody ascites was recognized in the peritoneal cavity of the peritoneal metastases model. (B) Multiple tumor nodules were recognized in the peritoneal cavity.