Targeting RPRD1B Overcomes Chemoresistance in Gastric Cancer by Suppressing the TOPBP1-mediated DNA Damage Repair Pathway

Despite the widespread adoption of 5-fluorouracil (5-FU)-based regimens as first-line therapy for gastric cancer, a substantial number of patients develop innate or acquired resistance, highlighting the critical need to identify its underlying molecular drivers. RPRD1B (CREPT), a gene frequently overexpressed in GC, has been clinically associated with advanced tumor stage and poor prognosis. Functionally, RPRD1B promotes aggressive tumorigenic phenotypes by accelerating cell-cycle progression, potentiating proliferative signaling, and enhancing the migratory and invasive capacities of cancer cells. However, its functional role in mediating chemotherapy resistance has not been elucidated. We established 5-FU-resistant gastric cancer cell lines (from AGS/MGC803 parents via stepwise drug exposure) to study RPRD1B’s mechanism, and developed an AAV-based system to therapeutically target RPRD1B to overcome 5-FU resistance. In this study, we demonstrated that GC patients with high tumor expression of RPRD1B (CREPT) exhibited a poor response to 5-fluorouracil (5-FU)-based chemotherapy. Furthermore, RPRD1B expression was positively correlated with the expression of TOPBP1, a critical DNA damage response and repair effector. Mechanistically, RPRD1B transcriptionally upregulates TOPBP1 by recruiting RNA polymerase II to its promoter, thereby enhancing DNA damage repair. Using an AAV-delivered shRNA to knockdown RPRD1B in a nude mouse xenograft model, we effectively overcame 5-FU resistance in gastric tumors in vivo. Our findings identify RPRD1B as a promising therapeutic target for reversing chemoresistance in gastric cancer.