BRCA1 and cancer: For example, this approach proved to be efficient in BRCA1 or BRCA2 deficient cancer cells and patient-derived xenografts (HR and NHEJ deficient cancers): a study by Xu et al.27 demonstrated that G4-stabilizing fluoroquinolones CX-5461 and related compound CX-3543 induce replication dependent damage and cell death in these cells.