Suppression of Ehrlich Ascites Tumor Cell Proliferation via G1 Arrest Induced by Dietary Nucleic Acid-Derived Nucleosides

Objectives: Dietary nucleic acids play roles in maintaining various physiological functions. However, the effects of nucleic acid-derived nucleosides on cancer have yet to be clearly elucidated. Methods: We examined the anti-cancer effect of nucleic acids and nucleosides in an in vivo mouse model and an in vitro cell model using Ehrlich ascites tumor (EAT) cells. ICR mice with EAT cells served as a suitable tumor model to elucidate their anti-proliferation activity. EAT cells are fast-growing tumors characterized by increased progressive ascites fluid formation. Results: An anti-proliferative impact was observed in an in vivo mouse and an in vitro cell model. However, DNA exhibited anti-proliferative effects in mouse model, while this phenomenon wasn't observed in the in vitro cell model. Conversely, DNA hydrolysate demonstrated distinct anti-proliferative effects in EAT cells, suggesting that nucleotides or nucleosides generated during nucleic acid digestion act as active constituents. Furthermore, we examined various nucleosides and two nucleoside transporter inhibitors, identifying guanosine and 2'-deoxyguanosine as pivotal in the anti-proliferative effect. The uptake of these compounds into cells is likely facilitated by the Na+-independent equilibrative nucleoside transporter 2 (ENT2). Notably, these nucleotides impeded the progression of cancer cells from the G1 phase to the S phase in the cell cycle. An even more intriguing finding has emerged the expression of CCAAT/enhancer-binding protein (C/EBPβ) is increased by guanosine and 2'-deoxyguanosine. Furthermore, immunostaining has revealed that C/EBPβ diffuses into the nucleus, indicating its presence. This suggests that guanosine or 2-deoxyguanosine induces G1 arrest in cancer cells via the activation of C/EBPβ. Conclusions: In conclusion, our study provides evidence that nucleoside transporters, particularly ENT2, may play a role in the anti-proliferative effects of guanosine and 2'-deoxyguanosine. These nucleosides suppress DNA synthesis and cell proliferation, possibly by interfering with the transition of cells from the G1 phase to the S phase via the activation of C/EBPβ. Funding Sources: This work was supported by JSPS KAKENHI. Fordays Co., Ltd. provided a part of the grant.