T6B-mediated inhibition of the miRISC decreases myeloid-derived suppressor cell abundance and enhances survival in a murine ovarian cancer model

Introduction/Rationale: MicroRNAs play a critical role in regulating post-transcriptional gene expression. Dysregulation of microRNA concentrations has been associated with tumor initiation, progression, and metastasis in various cancer models. Previous studies demonstrated that global inhibition of the microRNA-induced silencing complex (miRISC) assembly can be accomplished through peptide-mediated interreference. Here, we implement a similar mechanism by overexpressing the peptide (T6B) in ovarian cancer (OvCa) cells to evaluate the effect of T6B-mediated tumor miRISC inhibition on the immune tumor microenvironment (TME).

Methods: In vivo murine studies using mFTCβ +/- T6B OvCa cells were conducted to assess the impact of T6B-mediated tumor miRISC inhibition on the immune TME. Harvested tumors and ascites were used to evaluate immune cell phenotypes and cytokine distribution via flow cytometry, immunohistochemistry (IHC), and Western blotting. RNA sequencing of mFTCβ cells and NanoString analyses of harvested tumors were used to identify T6B-mediated gene expression levels compared to controls.

Results: We observed an increased probability of survival in T6B-overexpressing mFTCβ tumor-bearing mice compared to control tumors. Flow cytometric and IHC analyses of ascites and tumors, respectively, revealed an increase in dendritic cell and macrophage populations, as well as a decrease in Ly6G+ granulocytic cells in T6B-overexpressing tumors. Gene expression profiling of myeloid cells revealed that tumor T6B downregulated the expression levels of factors associated with immunosuppression, such as Cxcl2, Arg1, and Marco. Moreover, the TME of T6B-overexpressing tumors exhibited decreased inflammatory factors – such as IL-6, CXCL1, CCL5, CCL11, and G-CSF – compared to control.

Conclusion: The results of this study offer significant insight into the immune TME of T6B-overexpressing OvCa tumors, providing the groundwork for further exploration into utilizing tumor-specific T6B-mediated inhibition of miRISC formation.