Targeted elimination of myeloid-derived suppressor cells via regulation of the STAT pathway alleviates tumor immunosuppression in neuroblastoma

Neuroblastoma (NB) has high morality rates and is the most common malignant tumor found in children. High aggregation of myeloid-derived suppressor cells (MDSCs) in the tumor microenvironment results in immunosuppression and affects therapeutic effectiveness. At present, doxorubicin (DOX) and dopamine (DA) are the specific drugs used to selectively remove or mature MDSCs. The aim of the present study was to explore the feasibility and underlying mechanism of targeting elimination of MDSCs via DOX or DA administration to alleviate tumor immunosuppression in NB. In the present study, a BALB/c tumor-bearing mouse model was established, and mice were grouped into the control, DOX2.5, DOX5 and DA50 mg/kg groups. DOX or DA were injected intravenously on days 7 and 12 after inoculation, following which the parameters related to the signal transducer and activator of transcription (STAT) pathway in MDSCs, the proportion of MDSCs, T cell infiltration, programmed death-1 (PD-1) on the surface of T cells, the number of regulatory T cells (Tregs), polarization of tumor-related macrophages (TAMs) and tumor growth were compared between the groups on days 14, 17 and 23 after inoculation. The results demonstrated that following DOX or DA administration, STAT1/phosphorylated (p)-STAT1 decreased, whereas STAT3/p-STAT3, STAT5/p-STAT5 and STAT6/p-STAT6 increased, which was accompanied by a decrease in the MDSC proportion in each experimental group. Simultaneously, T cell infiltration in tumors was increased, whereas expression of PD-1, the number of Tregs, TAM polarization and tumor growth were inhibited. The most significant findings were observed in the DOX2.5 mg/kg group. To conclude, low dose DOX or DA administration could effectively regulate the STAT pathway to eliminate MDSCs, alleviate immunosuppression and improve the immune response against NB tumor cells.