Weei-Chin Lin

DNA2 Nuclease Inhibition Confers Synthetic Lethality in Cancers with Mutant p53 and Synergizes with PARP Inhibitors

Abstract The tumor suppressor p53 promotes tumor-suppressive activities including cell-cycle inhibition, apoptosis, senescence, autophagy, and DNA repair. However, somatic mutations in the TP53 gene are one of the most common alterations in human cancers. We previously showed that mutant p53 (mutp53) can bind TopBP1, an ATR activator, to attenuate its ATR-activating function. A partially defective ATR function caused by mutp53 makes cancer cells more vulnerable to inhibitors of other TopBP1-independent ATR activators, such as DNA2. DNA2 plays a role in homologous recombination (HR) repair by resecting DNA ends in double-strand breaks and preparing them for invasion of homologous duplex. Here we identify a new DNA2 inhibitor, namely d16, and show that d16 exhibits anticancer activities and overcomes chemotherapy resistance in mutp53-bearing cancers. Similar to DNA2 depletion, d16 treatment results in cell-cycle arrest mainly at S-phase. Moreover, reexpression of mutp53 in a p53-null cancer cell line makes cells more vulnerable to d16-mediated inhibition of ATR activity. As d16 also inhibits HR, a combination of d16 and PARP inhibitors displays synergistic induction of cell death. DNA2 is often overexpressed in cancer, particularly in cancer cells harboring mutp53. Overexpression of DNA2 is associated with poor outcome in ovarian cancer. Overall, our results provide a rationale to target DNA2 as a new synthetic lethality approach in mutp53-bearing cancers, and further extend the benefit of PARP inhibitors beyond BRCA-mutated cancers. Significance: This study identifies a new DNA2 inhibitor as a synthetic lethal targeted therapy for mutp53-harboring cancers, and provides a new therapeutic strategy by combining DNA2 inhibitors with PARP inhibitors for these cancers.

ACTL6A promotes repair of cisplatin-induced DNA damage, a new mechanism of platinum resistance in cancer

Significance Platinum resistance remains as a major issue in the therapy for many types of cancer. However, the mechanisms of resistance have not been fully elucidated. ACTL6A gene is frequently amplified in several types of cancer such as lung squamous cell carcinoma, ovarian cancer, and esophageal cancer. ACTL6A is a subunit shared by multiple complexes, including SWI/SNF, INO80, and NuA4/TIP60. We unveil a new role for ACTL6A in repairing cisplatin-induced DNA damage, providing a novel mechanism for cisplatin resistance. We also show that the action of ACTL6A in the repair of cisplatin-induced DNA lesions is through the SWI/SNF remodeling complex. Furthermore, we demonstrate that an HDAC inhibitor can abolish cisplatin resistance caused by ACTL6A overexpression.