The S phase of the cell cycle inhibits cell growth though inhibition of DNA synthesis when stress-induced DNA damage occurs (24). chrysin and 5-FU exhibited anticancer properties via different pathways. Furthermore, the present study found that chrysin enhanced the chemotherapeutic effect of 5-FU in AGS/FR cells. In the resistant cells, the combination of chrysin and 5-FU improved the anticancer effect via G2/M phase arrest. These findings indicated that chrysin potentiated the chemotherapeutic effect of 5-FU in gastric cancer AGS and AGS/FR cells via cell cycle arrest. Therefore, chrysin may be used to treat gastric cancers that have become resistant to 5-FU. level. Nevertheless, the anticancer effects of chrysin observed in this study were consistent with those in other studies. Therefore, the application of chrysin with 5-FU may be clinically implemented to treat patients with 5-FU-resistant gastric cancer. The combination of chrysin and 5-FU upregulated p21 expression in AGS cells and AGS/FR cells (Fig. 2C). The cyclin-dependent kinase inhibitor, p21 serves a key role in the cell cycle and is regulated by various stimuli, including p53 (21), and the PI3K/Akt pathway (22). Several studies have reported that chrysin also exerted anticancer effects through upregulating p21-induced G1 phase arrest in A375 melanoma cells (8) and G2 phase arrest in esophageal squamous carcinoma (23). In the present study, chrysin induced Ebastine G2/M phase arrest and 5-FU induced G0/G1 phase arrest in AGS cells. The combination of chrysin and 5-FU caused cell accumulation in the S phase, suggesting a complementary effect of cell arrest by chrysin and 5-FU (Fig. 3A). The S phase of the IL8 cell cycle inhibits cell growth though inhibition of DNA synthesis when stress-induced DNA damage occurs (24). These results correlated with S phase arrest through upregulated p53 and p21 expression (Fig. 2C). AGS/FR cells exhibited downregulated p-Akt expression (Fig. 3C). Akt regulates cyclin-dependent kinase inhibitor p21 and the cell cycle. Phosphorylated Akt promotes cell growth and angiogenesis. Kim (25) reported that Akt signaling was overactivated in chemo-resistant colon cancer cells, and that inhibition of Akt signaling may be a good pharmacological target (25). In the present study, the combination of chrysin and 5-FU decreased p-Akt expression and increased p21 expression in AGS/FR cells. Increased p21 inhibits the cyclin B1/cdc2 complex protein expression, with this complex regulating G2/M phase. Therefore, the results of the present study indicated that the combination of chrysin and 5-FU induced G2/M phase arrest via inhibition of cdc2 and cyclin B1 by p21 upregulation in AGS/FR cells. As shown in Fig. 1C, AGS/FR cells were resistant to high doses of 5-FU (100 M). The present study found that co-treatment of chrysin with 5-FU caused similar effects to chrysin treatment alone. Nevertheless, the CI value of chrysin and 5-FU was 1 at 48 h, suggesting synergy (Fig. 1E). It is possible that the combined effect of chrysin and 5-FU occurs though chrysin-induced cell arrest as previously described (8). In conclusion, the combination of chrysin and 5-FU in AGS cells enhanced inhibition of cell viability through S phase arrest. Furthermore, the results of the present study suggested that chrysin improved 5-FU resistance via G2/M phase arrest in AGS/FR cells. These results indicated that chrysin potentiates the anticancer effect of 5-FU and may be utilized for the treatment of 5-FU resistant gastric cancer. Supplementary Material Supporting Data:Click here to view.(633K, pdf) Acknowledgements Not applicable. Ebastine Funding The present study was supported by the Bio Ebastine & Medical Technology Development Program of the NRF funded by the Korean Government (grant no. 2015M3A9B6074045) and the NRF grant funded by the Korea government, MSIT (grant no. 2017R1A2B4008254). Availability of data and materials All data generated or analyzed during this study are included in this published article. Authors’ contributions SYL and JJ were responsible for study conception and drafting this article. SKL established the AGS/FR cells. JJ reviewed the article and provided necessary suggestions. All authors read and approved the final manuscript. Ethics approval and consent to participate Not Ebastine applicable. Patient consent for publication Not.