Homoharringtonine targets XPC to inhibit DNA damage repair and sensitize tumors to platinum-based chemotherapy

DNA damage repair (DDR) is essential for preserving genomic stability and also represents a key targetable axis in cancer drug development. Here, we identify and validate homoharringtonine (HHT), a clinically approved antileukemic drug, as a novel DDR inhibitor using a phenotype-driven, high-content screen based on 53BP1 Tudor-domain foci formation. Mechanistically, HHT directly binds XPC, a critical nucleotide excision repair (NER) factor, with high affinity (Kd = 158.4 nM) in a manner dependent on Thr795 of XPC. HHT disrupts XPC-damaged DNA binding, impairs NER, and reduces non-homologous end joining (NHEJ) efficiency. Consequently, HHT sensitizes tumor cells to platinum-based chemotherapy in vitro and in vivo. These findings establish a phenotype-based platform for DDR inhibitor discovery, identify HHT as a first-in-class XPC inhibitor and uncover a previously unrecognized mechanism of HHT that may be exploited to enhance platinum-based therapy in solid tumors.