Silencing of circRACGAP1 Sensitizes Gastric Cancer Cells to Apatinib via Modulating Autophagy by Targeting miR-3657 and ATG7

Background: The positive results of the apatinib phase III trial have cast new light on treatment for patients with advanced gastric cancer (GC). However, in terms of safety, apatinib toxicities may lead to a dose modification or treatment interruption. Therefore, properly intervene is urgently needed to reduce toxicities and help patients benefit from apatinib treatment. Methods: The in vitro and in vivo assays were conducted to investigate the mechanisms of apatinib in GC. Autophagy functional assays were performed. MicroRNA sequencing and circular RNA sequencing of the GC tumor xenografts from the control and apatinib groups were performed to further study the mechanism. Results: In this study, we found that apatinib inhibited the growth of GC cells and xenograft tumors. Apatinib promoted autophagy activation via upregulation of ATG7 expression, and autophagy inhibition enhanced apatinib-induced apoptosis. With microRNA and circular RNA sequencing analyses of GC xenograft models, we demonstrated that circRACGAP1 functioned as an endogenous sponge for miR-3657 to inhibit its activity and further upregulate ATG7 expression. Silencing of circRACGAP1 inhibited apatinib-induced autophagy, which was rescued by miR-3657. Moreover, knockdown of circRACGAP1 sensitized GC cells to apatinib via autophagy inhibition in vitro and in vivo. Conclusions: These findings provided the first evidence that the circRACGAP1-miR-3657-ATG7 axis mediates a novel regulatory pathway critical for the regulation of autophagy and apatinib sensitivity in GC cells and xenografts. Thus, specific blockage of circRACGAP1 may be a potential therapeutic strategy to reduce the toxicities of apatinib and enhance its therapeutic effect in human GC. Funding Statement: This study was supported by grants from the National Natural Science Foundation of China (No. 81672896 and No. 81520108027), the National Key Research and Development Program: the key technology of palliative care and nursing for cancer patients (ZDZX2017ZL-01), the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) (JX10231802), and Jiangsu Provincial Key Research and Development Special Fund (BE2015666). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: All experiments were carried out according to the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals (NIH Publication No. 80-23) revised in 1996. The animal studies were reviewed and approved by the Ethics Committee for Animal Studies at Nanjing Medical University.