Radiation-induced DNA Methylation And Its Immune Reaction On Pancreatic Carcinoma

Background: Iodine 125 (¹²⁵I) seed irradiation is an effective treatment for unresectable pancreatic cancers. However, the radiobiological mechanisms underlying brachytherapy remain unclear. Therefore, we investigated the influence of continuous and low-energy ¹²⁵I irradiation on apoptosis, expression of DNA methyltransferases (DNMTs) and cell growth in pancreatic cancers.Materials and Methods: For in vitro ¹²⁵I seed irradiation, SW-1990 cells were divided into three groups: control (0 Gy), 2 Gy, and 4 Gy. To create an animal model of pancreatic cancer, the SW 1990 cells were surgically implanted into the mouse pancreas. At 10 d post–implantation, the 30 mice with pancreatic cancer underwent ¹²⁵I seed implantation and were separated into three groups: 0 Gy, 2 Gy, and 4 Gy group. At 48 or 72 h after irradiation, apoptosis was detected by flow cytometry; changes in DNMTs mRNA and protein expression were assessed by real-time PCR and western blotting analysis, respectively. At 28 d after ¹²⁵I seed implantation, in vivo apoptosis was evaluated with TUNEL staining, while DNMTs protein expression was detected with immunohistochemical staining. The tumor volume was measured 0 and 28 d after ¹²⁵I seed implantation. Subcutaneous rat pancreatic tumor model, divided into an empty particle group, 200cGy, 400cGy group, tumor volume observed 28 days after irradiation, and detection rat blood, spleen CD4 +, CD8 + ratio, the tumor was detected by immunohistochemistry VEGF Expression, Elisa peripheral blood of TNFα, TGFβ, NFkB and other cytokines. We also further explore the tumor block farming successfully established a rat model of orthotopic pancreatic cancer.Results:¹²⁵I seed irradiation induced significant apoptosis, especially at 4 Gy. DNMT1 and DNMT3b mRNA and protein expression were substantially higher in the 2 Gy group than in the control group. Conversely, the 4 Gy cell group exhibited significantly decreased DNMT3b mRNA and protein expression relative to the control group. There were substantially more TUNEL positive in the ¹²⁵I seed implantation treatment group than in the control group, especially at 4 Gy. The 4 Gy seed implantation group showed weaker staining for DNMT1 and DNMT3b protein relative to the control group. Consequently, ¹²⁵I seed implantation inhibited cancer growth and reduced cancer volume. Immune to rats, the continuous low dose rate irradiation can inhibit tumor growth, and cause the body increased the proportion of peripheral blood CD4, increase the body immune function. Exposure to low doses of TNFαexpression in peripheral blood increased, synergistic antitumor effects.Conclusion:¹²⁵I seed implantation kills pancreatic cancer cells, especially at 4 Gy. ¹²⁵I-induced apoptosis and changes in DNMT1 and DNMT3b expression suggest potential mechanisms underlying effective brachytherapy. At the same time can significantly improve the immune function and cytokines in blood TNFαchange. 5 pancreatic tumors implanted under the capsule of the block modeling approach is the recommended to Lewis rats with normal immunity to pancreatic cancer in situ method of modeling, simple, fast, high rate of tumor formation.