Combined antitumor effects of 1,25-dihydroxy vitamin D3 and Notch inhibitor in liver cancer

The combined antitumor effects of 1,25-dihydroxy vitamin D3 [1,25(OH)(2)D-3] and the Notch inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT, a synthetic secretase inhibitor) in liver cancer cells remain to be fully elucidated. In the present study, HepG2 cells were divided into six groups and different treatments were applied: Control, 10(-10) M 1,25(OH)(2)D-3, 10(-8) M 1,25(OH)(2)D-3, 10(-6) M 1,25(OH)(2)D-3, 1 mu M DAPT, 5 mu M DAPT, 10 mu M DAPT, and 10(-6) M 1,25(OH)(2)D-3 + 10 mu M DAPT. The proliferation, cell cycle, apoptosis, migration and invasion of the cells were then examined. The expression levels of Notch and its ligand Jagged were detected by reverse transcription-quantitative polymerase chain reaction and western blot analyses. The results revealed that 1,25(OH)(2)D-3 inhibited cell proliferation, migration and invasion; arrested cell cycle at the G1 phase, and promoted apoptosis in a concentration-dependent manner between 10(-10) and 10(-6) M. DAPT inhibited cell proliferation, migration and invasion, arrested cell cycle at the G1 phase, and promoted apoptosis in a concentration-dependent manner between 1 and 10 mu M. Additionally, 1,25(OH)(2)D-3 and/or DAPT reduced the expression of Notch1, Notch2, Jagged1 and Jagged2. The co-application of 10 mu M DAPT further increased the anticancer effect of 10(-6) M 1,25(OH)(2)D-3. Collectively, these results indicated that the treatment of HepG2 cells with 1,25(OH)(2)D-3 inactivated Notch signaling, prevented proliferation, migration and invasion, and promoted apoptosis. The combined application of 1,25(OH)(2)D-3 with DAPT may be a useful treatment for preventing the onset or progression of liver cancer.