Shenling Baizhu Decoction (SLBZD) may play a synergistic role of tirelizumab in the treatment of colorectal cancer by influencing the imbalance of colon flora and Tumor microenvironment

Objective: To explore whether SLBZD can play a synergistic role in promoting the efficacy of PD-1 inhibitors in the treatment of colorectal cancer by influencing the intestinal microenvironment and Tumor microenvironment. Method: Shenling Baizhu Decoction (SLBZD) and tirelizumab (TLzmab) treated the colorectal mouse model. The tumor growth rate, tumor weight, and tumor growth inhibition rate were evaluated. Fecal microbiota was detected by 16S rDNA sequencing and immune cell was detected by the flow cytometry analysis. Result: Compared to tumor weight, there exist significant differences between each group among the three groups. Compared to tumor volume, there was no statistically significant difference in tumor size between the control group and the TLzmab group at 7 days. However, there was a statistical difference in tumor size among the three groups at 18 days. By analyzing the diversity of the Gut microbiota, the diversity decreased after TLzmab treatment with a statistically significant difference. Compared with the control group, the diversity of the TLzmab+SLBZD group increased. The proportion of lymphocytes in the blood was analyzed by flow cytometry. Compared with the control group, Myeloid-derived suppressor cells (MDSCs) decreased and T regulatory cells (Treg) increased significantly in the TLzmab group. Compared with the control group and TLzmab group, the TLzmab+SLBZD group showed a significant increase in M1 type macrophages, while the M2 type macrophages, MDSCs, and Treg showed a significant decrease. Conclusion: An imbalance of Gut microbiota and imbalance of tumor immune microenvironment will occur during TLzmab treatment, which will lead to poor therapeutic effect of TLzmab or drug resistance. SLBZD will increase the abundance of Gut microbiota, which will lead to the increase of M1 macrophages in the tumor immune microenvironment and the decrease of M2 macrophages and Treg cells, thus exerting the synergistic effect of TLzmab. This study provides a new way to explore the improvement of ICIs through traditional Chinese medicine.