BackgroundIn 2016 the first-in-human phase I study of a miRNA-based cancer therapy with a liposomal mimic of microRNA-34a-5p (miR-34a-5p) was closed due to five immune related serious adverse events (SAEs) resulting in four patient deaths. For future applications of miRNA mimics in cancer therapy it is mandatory to unravel the miRNA effects both on the tumor tissue and on immune cells. Here, we set out to analyze the impact of miR-34a-5p over-expression on the CXCL10/CXCL11/CXCR3 axis, which is central for the development of an effective cancer control.MethodsWe performed a whole genome expression analysis of miR-34a-5p transfected M1 macrophages followed by an over-representation and a protein–protein network analysis. In-silico miRNA target prediction and dual luciferase assays were used for target identification and verification. Target genes involved in chemokine signaling were functionally analyzed in M1 macrophages, CD4+ and CD8+ T cells.ResultsA whole genome expression analysis of M1 macrophages with induced miR-34a-5p over-expression revealed an interaction network of downregulated target mRNAs including CXCL10 and CXCL11. In-silico target prediction in combination with dual luciferase assays identified direct binding of miR-34a-5p to the 3′UTRs of CXCL10 and CXCL11. Decreased CXCL10 and CXCL11 secretion was shown on the endogenous protein level and in the supernatant of miR-34a-5p transfected and activated M1 macrophages. To complete the analysis of the CXCL10/CXCL11/CXCR3 axis, we activated miR-34a-5p transfected CD4+ and CD8+ T cells by PMA/Ionomycin and found reduced levels of endogenous CXCR3 and CXCR3 on the cell surface.ConclusionsMiR-34a-5p mimic administered by intravenous administration will likely not only be up-taken by the tumor cells but also by the immune cells. Our results indicate that miR-34a-5p over-expression leads in M1 macrophages to a reduced secretion of CXCL10 and CXCL11 chemokines and in CD4+ and CD8+ T cells to a reduced expression of CXCR3. As a result, less immune cells will be attracted to the tumor site. Furthermore, high levels of miR-34a-5p in naive CD4+ T cells can in turn hinder Th1 cell polarization through the downregulation of CXCR3 leading to a less pronounced activation of cytotoxic T lymphocytes, natural killer, and natural killer T cells and possibly contributing to lymphocytopenia.

During cervical carcinogenesis, T-helper (Th)-17 cells accumulate in the peripheral blood and tumor tissues of cancer patients. We previously demonstrated that Th17 cells are associated with therapy resistance as well as cervical cancer metastases and relapse, however, the underlying Th17-driven mechanisms supporting cervical cancer progression are not fully understood as yet. In this study, we found that Th17 cells promote migration and invasion of cervical cancer cells in 2D cultures and 3D spheroids. We demonstrated that Th17 cells induced the expression of miR-142-5p in cervical cancer cells supporting their migration and invasiveness. As the responsible mechanism, we identified the subunits C and D of the succinate dehydrogenase (SDH) complex as new targets of miR-142-5p and provided evidence that Th17 cells reduced the expression of SDHC and SDHD that was dependent on miR-142-5p. Functional downstream analysis with inhibitors of miR-142-5p and siRNA knock down of SDHC and SDHD revealed that Th17-induced miR-142-5p-mediated reduced expression of SDHC and SDHD was responsible for enhanced migration and invasion of cervical cancer cells. Consistently, cervical cancer patients exhibited high levels of succinate in their serum associated with lymph node metastases and diminished expression of SDHD in patients` biopsies significantly correlated with increased numbers of Th17 cells, advanced tumor stage and lymph node metastases. Correspondingly, a combination of weak or negative SDHD expression and a ratio of Th17/CD4+ T cells > 43.90 % in situ was associated with reduced recurrence free survival. In summary, we unraveled a novel molecular mechanism by which Th17 cells promote cervical cancer progression and suggest evaluation of Th17 cells as a potential target for immunotherapy in cervical cancer.