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 alpha,25-dihydroxyvitamin D-3 [1 alpha,25(OH)(2)D-3] or MART-10, a 1 alpha,25(OH)(2)D-3 analog. MART-10 had anti-growth effect on RIN-m cells comparable to those of 1 alpha,25(OH)(2)D-3. The growth inhibition of both drugs was mediated by induction of cell-cycle arrest at G(0)/G(1) phase and apoptosis. Western blot assay further revealed that this G(0)/G(1) 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.