ATM, ATR and DNA-PKcs expressions correlate to adverse clinical outcomes in epithelial ovarian cancers

AZD6738, A Novel Oral Inhibitor of ATR, Induces Synthetic Lethality with ATM Deficiency in Gastric Cancer Cells

Ataxia telangiectasia and Rad3-related (ATR) can be considered an attractive target for cancer treatment due to its deleterious effect on cancer cells harboring a homologous recombination defect. The aim of this study was to investigate the potential use of the ATR inhibitor, AZD6738, to treat gastric cancer.In SNU-601 cells with dysfunctional ATM, AZD6738 treatment led to an accumulation of DNA damage due to dysfunctional RAD51 foci formation, S phase arrest, and caspase 3-dependent apoptosis. In contrast, SNU-484 cells with functional ATM were not sensitive to AZD6738. Inhibition of ATM in SNU-484 cells enhanced AZD6738 sensitivity to a level comparable with that observed in SNU-601 cells, showing that activation of the ATM-Chk2 signaling pathway attenuates AZD6738 sensitivity. In addition, decreased HDAC1 expression was found to be associated with ATM inactivation in SNU-601 cells, demonstrating the interaction between HDAC1 and ATM can affect sensitivity to AZD6738. Furthermore, in an in vivo tumor xenograft mouse model, AZD6738 significantly suppressed tumor growth and increased apoptosis.These findings suggest synthetic lethality between ATR inhibition and ATM deficiency in gastric cancer cells. Further clinical studies on the interaction between AZD 6738 and ATM deficiency are warranted to develop novel treatment strategies for gastric cancer. Mol Cancer Ther; 16(4); 566-77. ©2017 AACR.

Gynecologic Cancers: Emerging Novel Strategies for Targeting DNA Repair Deficiency

The presence of a BRCA mutation, somatic or germline, is now established as a standard of care for selecting patients with ovarian cancer for treatment with a PARP inhibitor. During the clinical development of the PARP inhibitor class of agents, a subset of women without BRCA mutations were shown to respond to these drugs (termed "BRCAness"). It was hypothesized that other genetic abnormalities causing a homologous recombinant deficiency (HRD) were sensitizing the BRCA wild-type cancers to PARP inhibition. The molecular basis for these other causes of HRD are being defined. They include individual gene defects (e.g., RAD51 mutation, CHEK2 mutation), homozygous somatic loss, and whole genome properties such as genomic scarring. Testing this knowledge is possible when selecting patients to receive molecular therapy targeting DNA repair, not only for patients with ovarian cancer but also endometrial and cervical cancers. The validity of HRD assays and multiple gene sequencing panels to select a broader population of patients for treatment with PARP inhibitor therapy is under evaluation. Other non-HRD targets for exploiting DNA repair defects in gynecologic cancers include mismatch repair (MMR), checkpoint signaling, and nonhomologous end-joining (NHEJ) DNA repair. This article describes recent evidence supporting strategies in addition to BRCA mutation for selecting patients for treatment with PARP inhibitor therapy. Additionally, the challenges and opportunities of exploiting DNA repair pathways other than homologous recombination for molecular therapy in gynecologic cancers is discussed.

Cancer therapy and replication stress: forks on the road to perdition

Deregulated DNA replication occurs in cancer where it contributes to genomic instability. This process is a target of cytotoxic therapies. Chemotherapies exploit high DNA replication in cancer cells by modifying the DNA template or by inhibiting vital enzymatic activities that lead to slowing or stalling replication fork progression. Stalled replication forks can be converted into toxic DNA double-strand breaks resulting in cell death, i.e., replication stress. While likely crucial for many cancer treatments, replication stress is poorly understood due to its complexity. While we still know relatively little about the role of replication stress in cancer therapy, technical advances in recent years have shed new light on the effect that cancer therapeutics have on replication forks and the molecular mechanisms that lead from obstructed fork progression to cell death. This chapter will give an overview of our current understanding of replication stress in the context of cancer therapy.