CX-5461 is a DNA G-quadruplex stabilizer with selective lethality in BRCA1/2 deficient tumours

Hong Xu,Grant W Brown,Nigel J O’Neil,Jason Wong,Daniel Lai,Anni Zhang,Angela Hsin Chin Tsai,Damian Yap,Marco Di Antonio,Tak W Mak,David W Cescon ,Derek S Chiu,Shankar Balasubramanian,Steven Mckinney,Peter C Stirling,Teresa Ruiz De Algara ,Nancy Dos Santos,Vivien Wei,Shu-Chuan Lin,Jennifer Silvester,Jessica Garcia,Brandon Ho,Daniel Le ,Judit P Banáth ,John Soong,Frank B Ye ,Tomo Osako,Farhia Kabeer,Priscilla Soriano,Carlos Caldas,Kelsie L Thu ,Phil Hieter,Darren N Saunders,James D Brenton,Jian Xian,Sohrab P Shah,Veena Mathew,Marcel B Bally,Samuel Aparicio

doi:10.1038/ncomms14432

Abstract

G-quadruplex DNAs form four-stranded helical structures and are proposed to play key roles in different cellular processes. Targeting G-quadruplex DNAs for cancer treatment is a very promising prospect. Here, we show that CX-5461 is a G-quadruplex stabilizer, with specific toxicity against BRCA deficiencies in cancer cells and polyclonal patient-derived xenograft models, including tumours resistant to PARP inhibition. Exposure to CX-5461, and its related drug CX-3543, blocks replication forks and induces ssDNA gaps or breaks. The BRCA and NHEJ pathways are required for the repair of CX-5461 and CX-3543-induced DNA damage and failure to do so leads to lethality. These data strengthen the concept of G4 targeting as a therapeutic approach, specifically for targeting HR and NHEJ deficient cancers and other tumours deficient for DNA damage repair. CX-5461 is now in advanced phase I clinical trial for patients with BRCA1/2 deficient tumours (Canadian trial, NCT02719977, opened May 2016).

Highlights

G-quadruplex DNAs form four-stranded helical structures and are proposed to play key roles in different cellular processes
We have uncovered a new and unanticipated mechanism of CX-5461 activity in homologous recombination (HR) and non-homologous end joining (NHEJ) deficient cancer cells. We show that both CX-5461 and the related compound CX-3543 induce DNA damage and are dependent on BRCA1/2-mediated HR and DNA-PK-mediated NHEJ pathway for damage repair
Our data suggest that the CX drugs, and possibly other G4 stabilizers have the potential to treat cancers deficient for BRCA1, BRCA2, NHEJ pathway members and some other genes involved in DNA damage repair and DNA replication

Summary

Results

To identify potential novel drugs for cancers with BRCA2 mutations, we tested a total of 17 commercially available inhibitors (Supplementary Table 1) by clonogenic assays in isogenic BRCA2 knockout and wild type (WT) HCT116 cell line pairs published by us[21]. This clonogenic screen identified CX-5461, a previously described RNA pol I inhibitor[15,17] to be highly toxic to BRCA2 knockout HCT116 cells as compared with isogenic BRCA2 WT cells (Fig. 1a).

10–7 SYBRgreen

B18 CX5461 10 μM

Discussion

Methods