1α,25(OH)2D3 Analog, MART-10, Inhibits Neuroendocrine Tumor Cell Growth Through Induction of G0/G1 Cell-cycle Arrest and Apoptosis

Background: Neuroendocrine tumors (NETs) are the second most common digestive malignancy. For advanced NETs, survival is not satisfactory. Vitamin D has emerged as a promising anticancer drug. Materials and Methods: Cell proliferation assay, western blot, flow cytometry, and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assays were applied. Results: We demonstrated that RIN-m cells, neuroendocrine tumor cells, expressed Vitamin D receptor (VDR) and VDR expression increased with increasing exposure to 1,25-dihydroxyVitamin D3 [1,25(OH)2D3] or MART-10, a 1,25(OH)2D3 analog. MART-10 had anti-growth effect on RIN-m cells comparable to those of 1,25(OH)2D3. The growth inhibition of both drugs was mediated by induction of cell-cycle arrest at G0/G1 phase and apoptosis. Western blot assay further revealed that this G0/G1 arrest was due to the up-regulation of p27 and down-regulation of cyclin dependent kinase 4 (CDK4), with MART-10 also reducing CDK6. Apoptosis induction was further supported by increased cleaved caspase-3 expression after treatment. Conclusion: MART-10 appears to be a promising regimen for NET treatment.