# MicroRNA-625-3p Increases Chemosensitivity in Ovarian Cancer Cells Through Decreasing SSX2IP-Mediated Cisplatin Export in Extracellular Vesicles

## TL;DR

This study shows that miR-625-3p can make ovarian cancer cells more sensitive to chemotherapy by reducing the export of cisplatin through extracellular vesicles.

## Contribution

The novel contribution is identifying miR-625-3p as a regulator of cisplatin resistance via SSX2IP-mediated extracellular vesicle export in ovarian cancer.

## Key findings

- miR-625-3p is downregulated in chemoresistant ovarian cancer and associated with poor survival.
- Overexpression of miR-625-3p decreases cisplatin resistance in ovarian cancer cells.
- SSX2IP is a direct target of miR-625-3p and mediates cisplatin export via extracellular vesicles.

## Abstract

Around thirty percent of high-grade serous ovarian cancer patients are not responsive to first-line platinum-based chemotherapy. Their diseases typically do not respond or progress during treatment or recur within 6 months of completing treatment, suggesting the intrinsic characteristics of the tumor. There are currently no biomarkers that can predict intrinsic resistance. MicroRNAs are known to provide a master layer of regulation of gene expression, however, the molecular mechanisms by which microRNAs confer a chemoresistant phenotype in ovarian cancer have not been elucidated. We found that miR-625-3p is significantly downregulated in chemoresistant cases and is associated with poorer overall and progression-free survivals. Further functional studies showed that the overexpression of miR-625-3p significantly decreased cisplatin resistance in ovarian cancer cells. Moreover, we identified SSX2IP as a direct target of miR-625-3p. SSX2IP plays a critical role in controlling microtubule length and orientation. We demonstrated that SSX2IP confers cisplatin resistance through the facilitation of the export of cisplatin in extracellular vesicles by promoting microtubule-dependent vesical trafficking. This study is crucial for developing new predictive biomarkers for intrinsic chemoresistance, and new treatment strategies for high-grade serous ovarian cancer based on upregulating miR-625-3p or downregulating SSX2IP expression in ovarian cancer cells, which will enhance cisplatin sensitivity and improve patient survival rates.

Introduction: Advanced-stage high-grade serous ovarian cancer (HGSC) is a disease that is difficult to manage due to its heterogeneous clinical behavior. No reliable prediction of response to chemotherapy is currently available and the overall survival rate remains poor. Herein, we sought to determine the molecular mechanisms by which microRNAs (miRNAs) confer chemoresistance in ovarian cancer and demonstrate the efficacy of targeting miRNAs to sensitize HGSC to cisplatin treatment. Methods: Next-generation miRNA sequencing was performed using microdissected HGSC specimens to identify an miRNA signature for intrinsic chemoresistance, and miR-625-3p was selected for further study. The effects of miR-625-3p on cisplatin sensitivity were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays and cell death enzyme-linked immunosorbent assay. Transcriptome profiling analysis, online prediction algorithms, and reporter assays were used to demonstrate SSX2IP as the direct gene target of miR-625-3p. Cell death enzyme-linked immunosorbent assays, mass spectrometry, and high-speed confocal microscopy were used to determine the roles of SSX2IP in mediating the effects of miR-625-3p in cisplatin sensitivity via the extracellular vesicle (EV) secretion of cisplatin. Results: An miRNA signature for intrinsic chemoresistance was identified. Amongst all the downregulated miRNAs in the chemo-refractory samples, only miR-625-3p was associated with poorer overall survival and progression-free survival rates. Further functional studies showed that the overexpression of miR-625-3p significantly decreased cisplatin resistance in ovarian cancer cells both in vitro and in vivo. SSX2IP (Synovial Sarcoma, X Breakpoint 2 Interacting Protein) was confirmed to be the direct gene target of miR-625-3p and its upregulation abrogated miR-625-3p-mediated cisplatin resistance by enhancing the EV export of cisplatin in ovarian cancer cells. Conclusions: These findings provide a new paradigm for intrinsic cisplatin resistance acquisition by HGSC cells, which will be crucial for developing new treatment strategies for ovarian cancer based on the upregulation of miR-625-3p or downregulation of SSX2IP to enhance cisplatin sensitivity and improve patient survival rates.