RAD51 Predicts Poor Prognosis and Serves as a Therapeutic Target in Intrahepatic Cholangiocarcinoma.

Intrahepatic cholangiocarcinoma (ICC) is a highly aggressive malignancy with limited responsiveness to chemotherapy. RAD51, a key component of homologous recombination repair, has been implicated in tumor progression and therapeutic resistance in several cancers; however, its clinical and biological role in ICC is unclear. RAD51 expression was evaluated by immunohistochemistry in 96 patients having upfront surgery for ICC. Clinicopathological correlations and survival outcomes were analyzed. Functional studies were conducted in the ICC cell lines, HuCCT1 and TKKK, using small interfering RNA-mediated RAD51 knockdown and RAD51 inhibitor IBR2. High nuclear RAD51 expression was detected in 60 cases (62.5%). Patients with high RAD51 expression exhibited larger tumor sizes and more frequent lymph node metastases than those with low RAD51 expression. Kaplan-Meier analysis revealed that high RAD51 expression was significantly associated with worse disease-free survival and overall survival. Multivariate analysis confirmed RAD51 as an independent prognostic factor of poor survival. In vitro, RAD51 knockdown reduced ICC cell proliferation without affecting migration or invasion. IBR2-mediated pharmacological inhibition of RAD51 reduced cell proliferation with induced G2-phase arrest. Cisplatin treatment increased RAD51 messenger RNA expression and enhanced nuclear RAD51 foci colocalizing with γH2AX, indicating compensatory homologous recombination repair activation in response to DNA damage. Even low doses of IBR2 promoted cisplatin-induced cytotoxicity, increased lactate dehydrogenase release, and augmented apoptosis. RAD51 expression predicts poor prognosis after surgery for patients with ICC and functionally promotes ICC cell survival. Therapeutic targeting of RAD51 may enhance the antitumor efficacy of cisplatin and represents a promising strategy to improve prognosis.