RAD18 May Function As A Predictor Of Response To Preoperative Concurrent Chemoradiotherapy In Patients With Locally Advanced Rectal Cancer Through Caspase-9-caspase-3-dependent Apoptotic Pathway

Objective : The study discussed whether RAD18 can be a predictive indicator of preoperative chemoradiotherapy sensitivity in rectal cancer and further explored the effects of RAD18 on chemoradiotherapy sensitivity of rectal cancer and the potential molecular mechanism,providing clinical instructions for individualized treatment of rectal cancer.Methods:The expression level of RAD18 in rectal cancer tissues was detected by immunohistochemistry.The correlation between RAD18 expression and the curative effect of preoperative concurrent chemoradiotherapy was analyzed.The interference vector shRNA-RAD18 and negative control vector shRNA-NC were constructed and transfected into rectal cancer cell lines HCT-116 and DLD-1.The effects of RAD18 on the cell proliferation of HCT-116 and DLD-1 were observed by CCK-8 assay and cell colony formation assay.Immunofluorescence assay and apoptosis assay were used to observe the effect of RAD18 on the γH2AX expression and the cell apoptosis rate after chemoradiotherapy.The expression levels of caspase-9 and caspase-3 were detected by western blot.Finally,the xenograft nude mouse model confirmed that RAD18 could affect the sensitivity of chemoradiotherapy through caspase-9-caspase-3 dependent apoptosis pathway in vivo.Results : The expression level of RAD18 was negatively correlated with clinicalresponse in patients with locally advanced rectal cancer(r=-0.3,p=0.03).Inhibition of RAD18 expression not only decreased the cell proliferation of HCT-116 and DLD-1 and increased the double-strand DNA damages,but also promoted the activation of apoptotic proteins caspase-9 and caspase-3 and improved the cell apoptotic rate,thus increasing the sensitivity of rectal cancer cells to 5-Fu and irradiation.In vivo,it also confirmed that inhibited RAD18 promoted the sensitivity of chemoradiation in rectal cancer.Conclusion: The study has shown that RAD18 could be a potential marker to predict preoperative chemoradiotherapy sensitivity in patients with locally advanced rectal cancer.It may guide clinicians to provide individualized treatments for each LARC patient,thus improving the prognosis of LARC patients.