Methionine restriction promotes cisplatin sensitivity of gastric cancer resistant cells by down-regulating circ-CDK13 level

Background: Methionine restriction (MR) is a research direction in the treatment of gastric cancer (GC). The aim of this study was to investigate the molecular mechanism of MR on enhancing cisplatin (DDP) sensitivity of drug-resistant GC cells.

Methods: Twenty pairs of GC tissues and adjacent normal gastric mucosa tissues were collected. DDP-resistant cell lines (KATO/DDP and MKN45/DDP), mouse model of GC and GC patient-derived organoid (PDO) models were established. Lentivirus-mediated METase overexpression was used for MR. Cell viability and apoptosis were detected by MTT assay and flow cytometry. Western blotting was used to detect multi-drug resistance-1 (MDR1), MDR-associated protein 1 (MRP1) eukaryotic initiation factor 4A-Ⅲ (EIF4A3), and METase protein expressions. The levels of circRNAs were detected by qRT-PCR. Tumor volume and weight were measured. The proliferation of tumor cells was detected by immunohistochemical staining.

Results: The differentially expressed circRNAs of GC were screened in Gene Expression Omnibus database. MR in KATO/DDP and MKN45/DDP cells significantly down-regulated circ-CDK13 level. Overexpression of circ-CDK13 significantly inhibited apoptosis of sensitive cells (KATO III and MKN45). Interference with circ-CDK13 significantly promoted apoptosis of drug-resistant cells (KATO/DDP and MKN45/DDP). MR enhanced the DDP sensitivity of GC resistant cells, GC PDO and GC mice by down-regulating circ-CDK13. EIF4A3 binds to the downstream flanking sequence of circ-CDK13, and interference with EIF4A3 reduces circ-CDK13 levels, but does not affect CDK13. The expressions of circ-CDK13 and EIF4A3 in GC clinical samples were increased and positively correlated. Simultaneously overexpression of METase and EIF4A3 in resistant cells inhibited apoptosis, and further interference with circ-CDK13 reversed this effect.

Conclusion: MR inhibits circ-CDK13 level by down-regulating EIF4A3, thereby increasing the sensitivity of GC drug-resistant cells to DDP.