Background: Epigenetic dysregulation is an integral step in the progression of pancreatic neuroendocrine tumors. We hypothesized that tumor suppressor repression by DNA methyltransferase 1 in pancreatic neuroendocrine tumors could be targeted with epigenetic treatment.
Methods: Resected pancreatic neuroendocrine tumors from 32 patients were stained for DNA methyltransferase 1 and scored. Human (BON1) and murine (STC) pancreatic neuroendocrine tumor cells were treated with DNA methyltransferase 1 inhibitor 5-azacytidine and chemotherapeutic agents 5-fluorouracil and temozolomide. Cell proliferation assay and tumor suppressor gene analysis were performed with qRT-PCR and Clarion S microarray. Tumor measurements were compared in a murine treatment model.
Results: High DNA methyltransferase scores were associated with high Ki-67 (6.7% vs 70.6% P < .01), mitotic rate (0.0% vs 31.3%), and grade (20.0% vs 80.4%, P < .01). Treatment with 5-azacytidine and chemotherapy resulted in a reduction of cell proliferation compared to chemotherapy alone in BON1 (77.3% vs 53.1%, P < .001) and STC (73.4% vs 34.2%, P < .001). Treatment with 5-azacytidine and chemotherapy resulted in upregulation of tumor suppressors CDKN1A (7.6 rel. fold, P < .001), BRCA2 (4.3 rel. fold, P < .001), and CDH1 (6.0 rel. fold, P = .026) in BON1 and CDKN1a (14.5 rel. fold, P < .001) and CDH (17.5 rel. fold, P < .001) in STC. In microarray, 5-azacytidine drove global genetic changes in combination treatment. In vivo tumors treated with chemotherapy measured 88.6 ± 19.54 mm3 vs 52.89 ± 10.51 mm3 in those treated with combination therapy (P = .009).
Conclusion: Epigenetic dysregulation with DNA methyltransferase 1 is associated with pancreatic neuroendocrine tumors and is a potential targetable strategy. 5-azacytidine and chemotherapy in combination can reduce cell proliferation, upregulate silenced tumor suppressor genes, and decrease in vivo tumors in pancreatic neuroendocrine tumors.
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