The Effects And Mechanism Of Oxaliplatin On Myeloid-derived Sppressor Cells' Differentiation In The Tumor Microenvironment Of Colorectal Cancer

BACKGROUND&OBJECTIVE:Colorectal cancer(CRC)is the third most common malignancy in the world.The pathogenesis of colorectal cancer is complex.Systemic chemotherapy,based on oxaliplatin(OXP),combined with surgical resection is the main program of CRC therapy.Chemotherapy in the treatment of cancers such as colorectal cancer can not only affect the tumor cells,but also affect the tumor microenvironment,which plays a crucial role in anti-tumor effect and tumor prognosis.MDSCs,a kind of important immunomodulatory cells in the tumor microenvironment,can differentiate into M1/M2 macrophages,which can be tumor suppressive or promoted.Such differentiation might mediate the resistance of chemotherapeutic drugs in tumor treatment.Howerver,the mechanism is not clear.NLRP3/Caspasel signaling pathway is an important pathway for the function of inflammasome.The expression of IRF5 was significantly increased in MDSCs after the inhibition of NLRP3 activity.IRF5,which is closely related to macrophage differentiation,is the specific marker of M1 macrophages.Through the bioinformatics analysis,our investigation group found that IRF5 promoter region has a caspase-1 digestion recognition sequence.,which may be one of the targets of MDSCs differentiation.The aim of this study was to investigate the effect and mechanism of oxaliplatin on myeloid-derived sppressor cells' differentiation in the tumor microenvironment of colorectal cancerthe,and to find new ideas in oxaliplatin-resistant colorectal cancer treatment.METHOD1.The DSS-induced chronic enteritis model and CT26 subcutaneous transplanted tumor model were established in Balb/c mice.The mice were divided into control group(PBS),low dose OXP group(OXP 1mg/kg)and high dose OXP group(OXP 10mg/kg).HE staining of intestinal tissue was used to confirm enteritis.HE staining and Ki67 staining of subcutaneous tumor tissue were used to confirm subcutaneous tumor.The proportion of MDSCs(CD11b+Gr-1+)and CD11b+Gr-1+MCH-II+ in peripheral blood,spleen,bone marrow and subcutaneous tumor were detected by flow cytometry.2.Bone marrow(BM)cells from Balb/c mice were cultured in vitro to produce MDSCs.After treated with OXP in different doses,the proportion of MDSCs(CD11b+Gr-1+)and CD11b+Gr-1+MCH-II+ cells were detected by flow cytometry.3.Construction of mouse IRF5 and IRF5 mutation plasmid.The expression of IRF5 and Caspasel protein were detected by Western blot.4.The experimental data were analyzed by SPSS 13.0 software.The comparison between the two groups was carried out by two independent samples.The comparison between the two groups was based on one-way ANOVA.If the variance of the data is homogeneous,LSD method is used.If not,use Dunnett T3 method instead.P<0.05 is defined as a significant statistical difference..Result1.In the DSS-induced chronic enteritis mouse model,the proportion of MDSCs in the bone marrow,peripheral blood and spleen decreased significantly with the increase of OXP dose.In the spleen,the expression of CD11b+Gr-1high subgroup was significantly decreased.The CD11b+Gr-1high MHC-II+ subgroup was significantly increased(P<0.05).2.In tumor-bearing mice,the proportion of MDSCs in bone marrow,peripheral blood,spleen and tumor were significantly increased with the increase of OXP dose(P<0.05).In subcutaneous tumors,the proportion of CD11b+Gr-1+MHC-II+ cells in MDSCs population significantly decreased.3.Compared with the non-tumor microenvironment,in the tumor microenvironment,Group1 decreased while Group2 increased in vitro.The proportion of CD 11b+Gr-1hhigh cells in Group1 and CD11b+Gr-1low cells in Group2 were mainly affected by the tumor microenvironment.The proportion of CD11b+Gr-1low cells decreased in Group 1 and the expression of MHC-II-increased in CD11b+Gr-1low population.Meanwhile,the proportion of CD11b+Gr-1high cells increased in Group2 and the expression of MHC-II+ decreased in CD11b+Gr-1high population.Low concentration of OXP had no significant effect on the differentiation of MDSCs in tumor microenvironment or non-tumor microenvironment in vitro.4.Caspasel binds to IRF5 and acts on DY cleavage site to decompose IRF5,which downregulates the expression of IRF5.Conclusion1.The effects of OXP in the tumor microenvironment for the differentiation and regulation of MDSCs have two sides.On the one hand,OXP itself can play an anti-MDSCs role,and promote MDSCs to differentiate into M1 macrophages.On the other hand,in the tumor microenvironment,during the process of OXP killing tumor cells,tumor cells,for the purpose of self-protection,can release the relevant factors,so that a large number of MDSCs generated and the differentiation of MDSCs into M1 macrophage was inhibited in the local tumor,which forms a tumor microenvironment that is potent to tumor survival.2.In the absence of the effect of OXP in vitro,the tumor cells themselves can secret the relevant factors that can inhibit MDSCs from differentiating into Ml macrophages,resulting in the formation of a tumor growth favorable tumor microenvironment.Low concentration of OXP had no significant effect on the differentiation of MDSCs in tumor microenvironment or non-tumor microenvironment.3.Caspasel binds to IRF5 and acts on DY cleavage site to decompose IRF5,which downregulates the expression of IRF5.