Malignant pleural mesothelioma is incurable cancer with limited treatment options. MicroRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. In MPM, there is a global trend toward microRNA downregulation, some of which have tumour suppressor function. In our previous study, we demonstrated the downregulation of the miR-16 family in MPM. Additionally, the replacement of miR-16 based microRNAs was employed as a treatment strategy for mesothelioma patients in the Phase 1 clinical trial mesomiR-1. One microRNA has many targets and therefore the combination of multiple microRNAs may lead to a synergistic tumour suppressing outcomes for patients with MPM.
We analysed the growth inhibitory effects of a total of 75 microRNA mimics in MPM cell lines individually. A final panel of 11 microRNAs (miR-15a-5p, miR-15b-5p, miR-16-5p, miR-25-5p, miR-137-5p, miR-185-5p, miR-193a-3p, miR-340-5p, miR-375c-3p, miR-942-5p, let-7f-1-3p) were tested for synergistic growth-inhibitory response in MPM cells using SYBR cell-growth assays and CompuSyn software. Functional effects were also investigated using cell cycle and apoptosis assays. Pathway analysis was carried out to study the different pathways regulated by the microRNA combinations.
Amongst the 75 microRNAs studied, 11 showed significant cell inhibitory response in MPM when compared to MeT-5A (an immortalised normal mesothelial cell). Results generated from CompuSyn analysis indicated that among all microRNA combinations, only miR-193a-3p and miR-16-5p demonstrated a consistent synergistic cell inhibitory response amongst all concentrations (Combination index <1), whereas others were either additive or antagonistic. Cell cycle and apoptosis analysis supported CompuSyn results and showed that combination treatment with miR-193a-3p and miR-16-5p mimics provided the most profound anti-tumour response.
This study indicated that the restoration of tumour suppressor microRNAs miR-16-5p and mir-193a-3p in combination produced a synergistic anti-tumour effect in MPM cell lines compared to the normal mesothelial control MeT-5a, indicating their potential application as a therapy in MPM.