Enhanced Epithelial-to-Mesenchymal Transition and Chemoresistance in Advanced Retinoblastoma Tumors Is Driven by miR-181a

SIMPLE SUMMARY: Our study identified the differential expression and potential effects of microRNAs in retinoblastoma vs. pediatric retina and advanced vs. non-advanced tumors. We provide evidence of the epithelial–mesenchymal transition (EMT) and chemoresistance programs in advanced tumors, which were potentially attributed to miR-181a-5p. We analyzed the differential expression of relevant EMT- and chemoresistance-related proteins in advanced vs. non-advanced tumors and chemotherapy-adapted Y79 cells to assess whether EMT and chemoresistance mechanisms were linked. We further examined the possible role of TGFβ as a potential regulator of such differences and highlighted the role of miR-181a-5p in EMT- and chemoresistance-related gene expression and drug sensitivity. ABSTRACT: Advanced retinoblastoma (Rb) tumors display high metastatic spread to distant tissues, causing a potent threat to vision and life. Through transcriptomic profiling, we discovered key upregulated genes that belonged to the epithelial–mesenchymal transition (EMT) and chemotherapy resistance pathways in advanced Rb tumors. Through in vitro models, we further showed that Rb null tumor cells under prolonged chemo drug exposure, acquires a metastasis-like phenotype through the EMT program mediated by ZEB1 and SNAI2 and these cells further acquires chemotherapeutic resistance through cathepsin-L- and MDR1-mediated drug efflux mechanisms. Using a miRNA microarray, we identified miR-181a-5p as being significantly reduced in advanced Rb tumors, which was associated with an altered EMT and drug-resistance genes. We showed that enhancing miR-181a-5p levels in Rb null chemo-resistant sublines reduced the ZEB1 and SNAI2 levels and halted the mesenchymal transition switch, further reducing the drug resistance. We thus identified miR-181a-5p as a therapeutically exploitable target for EMT-triggered drug-resistant cancers that halted their invasion and migration and sensitized them to low-dose chemotherapy drugs.