The efficacy of gemcitabine on the immunocompetent murine Panc02 pancreatic cancer and its regulatory roles on the tumor immune environment

Objective To establish an immunocompetent pancreatic cancer subcutaneous bearing murine model and clarify the roles of gemcitabine on this tumor and its possible regulatory roles on the systemic and local tumor immune environment. Methods The C57BL/6J mice synergic pancreatic adenocarcinoma cell line Panc02 cell was subcutaneously implanted to establish the immunocompetent murine pancreatic cancer model. When the tumors grew to 75-100 mm3, the tumor bearing mice were subdivided into the control group and chemotherapy group. For the chemotherapy group, gemcitabine was admitted 50 mg/kg intraperitoneally twice a week, totally for 4 weeks.The tumor growth curve was depicted and after the mice were sacrificed, the body weight, tumor weight and spleen weight were measured and compared. Flow cytometry was adopted to detect 10 immune cell populations in tumor tissue and peripheral blood. Real time quantitative reverse transcriptionpolymerase chain reaction was used to measure the relative mRNA level of 7 cytokines in tumor tissue and spleen. The CD34 and lymphatic vessel endothelial hyaluronan receptor 1(LYVE-1) were labeled by immunohistochemistry and Western blotting, and then the microvessel density(MVD) and lymphatic vessel density(LVD) were analyzed. Results The tumor volume of chemotherapy group was significantly lower than that of the control group at each time point(P< 0.05). The body weight of chemotherapy group was significantly lower than that of the control group[(21.00±1.88) g vs.(28.36±1.06)g,P< 0.01]. The tumor weight of chemotherapy group was significantly lower than that of the control group[(641.67±289.92) mg vs.(1 492.00±462.73) mg, P< 0.01]. The weight of spleen of the two groups was not significantly different. Compared to the control group, the CD11c+ dendritic cell population[(22.93±2.26)% vs.(16.53±2.68)%, P< 0.05]in peripheral blood was significantly elevated, however, the CD11b+ Gr- 1+ MDSC population significantly declined[(3.00±0.10)% vs.(7.03±0.32)%, P< 0.01]. After chemotherapy, in tumor tissue, the CD3+ T lymphocyte population[(10.70±1.21)% vs.(21.10±3.54)%,P< 0.01]and myeloid derived suppressor cells(MDSC)[(5.10±2.11)% vs.(10.50±0.72)%, P< 0.05] declined, however, the dendritic cell population[(17.13±3.21)% vs.(10.43±1.60)%, P< 0.05], CD19+ B lymphocyte population[(17.13±2.68)% vs.(7.90±1.87)%, P< 0.01], Gr- 1+ granulocyte population[(79.50±5.86)% vs.(46.00±3.75)%, P< 0.01] and CD3+ NK1.1+ natural killer T cells(NKT)population[(9.77±1.56)% vs.(4.90±1.81)%,P<0.05]elevated.After chemotherapy, in spleen, the interleukin- 4(IL- 4)expression elevated(P< 0.05), however, the tumor necrosis factor -α(TNF-α)(P< 0.05)and IL-2 expression(P<0.01)declined.After chemotherapy, in tumor tissue, the IL- 4 and transforming growth factor-β(TGF-β) expression elevated(P< 0.05), however IL- 6, IFN-γ, TNF-αand IL-2 declined(P< 0.01).After chemotherapy, the product of MDSC,arginase- 1,significantly declined(P< 0.05).After chemotherapy, the MVD(18.47±2.61 vs.30.40±3.92,P< 0.05)and LVD(6.66±2.77 vs.16.27±2.02,P< 0.01)both declined. Conclusion Gemcitabine can effectively inhibit the Panc02 pancreatic cancer and attenuate the angiogenesis and lymphangiogensis, however it can also induce strong systemic and local immunosuppressive effects. The induced immunosuppressive effects and the decline of drug concentration induced by the attenuated-angiogenesis are likely to be important factors to affect chemotherapy efficacy, and they could be promising targets for improving the chemotherapeutic effects. Key words: Immunocompetent mice; Pancreatic cancer; Gemcitabine; Chemotherapy; Immune cell populations; Microvessel density; Lymphatic vessel density