Circular RNA hsa_circ_0004650 Enhances 5-Fluorouracil Resistance in Gastric Cancer Sponging miR-145-5p.

[BACKGROUND/AIM] Chemotherapy based on 5-fluorouracil (5-Fu) is the first-line treatment for advanced gastric cancer (GC) patients. Importantly, 5-Fu resistance is recognized as a major obstacle for the successful treatment of GC. Circular RNAs (circRNAs) are non-coding RNAs involved in the pathogenesis of GC. However, their role in the mechanism of 5-Fu resistance in GC remains largely unknown. The purpose of this study was to explore and elucidate the biological function and molecular mechanism of circRNAs underlying 5-Fu resistance in GC.

[MATERIALS AND METHODS] High-throughput sequencing results for intersection analysis were used to select a novel differentially expressed circRNA hsa_circ_0004650. The expression levels of the new circRNA between 5-Fu-sensitive and 5-Fu-resistant GC cells were evaluated using quantitative real-time polymerase chain reaction (qRT-PCR), and biological behaviors, such as proliferation and apoptosis of GC cells, were observed after silencing the hsa_circ_0004650. The mechanism of hsa_circ_0004650 sponges miR-145-5p to regulate 5-Fu resistance in GC cells was investigated by luciferase reporter assay, qRT-PCR, CCK-8 assay, Calcein AM/PI double fluorescence staining and flow cytometry.

[RESULTS] hsa_circ_0004650 was identified as a differentially expressed circRNA between 5-Fu-sensitive GC and 5-Fu-resistant GC cells. Hsa_circ_0004650 was up-regulated in 5-Fu-resistant GC cells. Silencing of hsa_circ_0004650 in 5-Fu-resistant GC cells, the survival rates of cells treated with increasing doses of 5-Fu for 24 h and 48 h were decreased (p<0.01); the mortality rates of SGC-7901-5-Fu cells were increased (17.86%±0.6 vs. 44.86%±1.52; p<0.001), and those of BGC-823-5-Fu cells were increased (8.17%±7.80 vs. 26.61%±1.12; p<0.001); and the apoptosis rates of cells treated with the same concentration of 5-Fu were increased (p<0.001). Mechanistically, miR-145-5p was confirmed as a downstream target of hsa_circ_0004650. By the down-regulation of the expression of miR-145-5p in 5-Fu-resistant GC cells, the survival rates of cells treated with increasing doses of 5-Fu for 24 h and 48 h were increased (p<0.05); the mortality rates of SGC-7901-5-Fu cells were decreased (12.86%±1.10 vs. 7.83%±0.53; p<0.01), those of BGC-823-5-Fu cells were decreased as well (16.99%±1.31 vs. 11.40%±0.72; p<0.01); and the apoptosis rates of cells treated with the same concentration of 5-Fu were decreased (p<0.001).

[CONCLUSION] The circRNA hsa_circ_0004650 promotes chemotherapy resistance to 5-Fu in GC cells through sponge adsorption of miR-145-5p, which offers a potential approach to overcome 5-Fu resistance in GC.