To clarify the inhibitory effect of monomeric L-arabinose on gastric cancer and elucidate its molecular mechanism, this study aims to investigate whether L-arabinose regulates the cell cycle via the microtubule-associated protein 1 light chain 3/autophagy-related gene 5(LC3/Atg5)-mediated autophagy-ribosomal protein L19(RPL19) axis, thereby inducing G2/M phase (post-DNA synthesis/mitotic phase) arrest and suppressing tumor growth in gastric cancer.

① In vitro experiments: Human gastric cancer cells were cultured and divided into a blank control group and an L-arabinose treatment group. Cell proliferation was detected by CCK-8 assay and colony formation assay. Cell cycle distribution was analyzed by flow cytometry. The protein and mRNA expression levels of cell cycle-related proteins [Cyclin B1, cyclin-dependent kinase inhibitor 1A (P21, CDKN1A), cyclin-dependent kinase inhibitor 1B (P27, CDKN1B)] and RPL19 were measured by Western blotting and qPCR, respectively. Each group was set with 3 replicates. ② Mechanism validation experiments: Based on the above grouping, an RPL19 overexpression group, a 3-methyladenine (3-MA) intervention group, and a 3-MA combined with L-arabinose group were additionally established. Cell cycle and RPL19 protein expression were detected by flow cytometry and Western blotting, with 3 replicates per group. ③ In vivo experiments: A mouse model of gastric cancer xenograft was established and randomly divided into a control group (normal saline) and an L-arabinose treatment group, with 5 mice in each group. Tumor volume and weight were measured regularly to observe tumor growth.

① In vitro experiments: Compared with the control group, L-arabinose treatment significantly inhibited the proliferation and induced G2/M phase arrest in gastric cancer cells (P<0.05), and obviously downregulated the protein expression of Cyclin B1 and upregulated the expression of P21 and P27(P<0.05). ② Mechanism validation: L-arabinose treatment significantly downregulated the protein expression of RPL19(P<0.05), but had no notable effect on its mRNA level (P>0.05). Overexpression of RPL19 significantly reversed the G2/M phase arrest induced by L-arabinose (P<0.05). After treatment with the autophagy inhibitor 3-MA, the downregulation of RPL19 and the anti-tumor effects of L-arabinose were both significantly attenuated (P<0.05). ③ In vivo experiments: Compared with the control group, the growth of xenograft tumors was significantly slower, and both tumor volume and weight were markedly reduced in the L-arabinose treatment group (P<0.05). Overexpression of RPL19 reversed the inhibitory effect of L-arabinose on tumor growth in vivo.

L-arabinose can activate LC3/Atg5-mediated autophagic flux to downregulate RPL19 protein expression, regulate the expression of cell cycle-related proteins such as cyclin B1, p21, and p27, thereby inducing G2/M phase arrest in gastric cancer cells, and ultimately exert an inhibitory effect on gastric cancer growth both in vitro and in vivo. These findings provide experimental evidence for the application of L-arabinose in the prevention and treatment of gastric cancer.