Maintenance of genome integrity requires the functional interplay between Fanconi anemia (FA) and homologous recombination (HR) repair pathways. Endogenous acetaldehyde, a product of cellular metabolism, is a potent source of DNA damage, particularly toxic to cells and mice lacking the FA protein FANCD2. Here, we investigate whether HR‐compromised cells are sensitive to acetaldehyde, similarly to FANCD2‐deficient cells. We demonstrate that inactivation of HR factors BRCA1, BRCA2, or RAD51 hypersensitizes cells to acetaldehyde treatment, in spite of the FA pathway being functional. Aldehyde dehydrogenases (ALDHs) play key roles in endogenous acetaldehyde detoxification, and their chemical inhibition leads to cellular acetaldehyde accumulation. We find that disulfiram (Antabuse), an ALDH2 inhibitor in widespread clinical use for the treatment of alcoholism, selectively eliminates BRCA1/2‐deficient cells. Consistently, Aldh2 gene inactivation suppresses proliferation of HR‐deficient mouse embryonic fibroblasts (MEFs) and human fibroblasts. Hypersensitivity of cells lacking BRCA2 to acetaldehyde stems from accumulation of toxic replication‐associated DNA damage, leading to checkpoint activation, G2/M arrest, and cell death. Acetaldehyde‐arrested replication forks require BRCA2 and FANCD2 for protection against MRE11‐dependent degradation. Importantly, acetaldehyde specifically inhibits in vivo the growth of BRCA1/2‐deficient tumors and ex vivo in patient‐derived tumor xenograft cells (PDTCs), including those that are resistant to poly (ADP‐ribose) polymerase (PARP) inhibitors. The work presented here therefore identifies acetaldehyde metabolism as a potential therapeutic target for the selective elimination of BRCA1/2‐deficient cells and tumors.

Graphical Abstract Highlights d POLA1 inhibitors (PolAis) cause the uncoupling of leading and lagging strand synthesis d PolAi results in ssDNA formation at the lagging strand and a replication catastrophe d ssDNA caused by PolAis does not activate an ATRdependent stress response d RPA surplus allows cells to duplicate their genome with elevated strand uncoupling and ssDNA

No abstract

BRCA1 or BRCA2 germline mutations predispose to breast, ovarian and other cancers. High-throughput sequencing of tumour genomes revealed that oncogene amplification and BRCA1/2 mutations are mutually exclusive in cancer, however the molecular mechanism underlying this incompatibility remains unknown. Here, we report that activation of β-catenin, an oncogene of the WNT signalling pathway, inhibits proliferation of BRCA1/2-deficient cells. RNA-seq analyses revealed β-catenin-induced discrete transcriptome alterations in BRCA2-deficient cells, including suppression of CDKN1A gene encoding the CDK inhibitor p21. This accelerates G1/S transition, triggering illegitimate origin firing and DNA damage. In addition, β-catenin activation accelerates replication fork progression in BRCA2-deficient cells, which is critically dependent on p21 downregulation. Importantly, we find that upregulated p21 expression is essential for the survival of BRCA2-deficient cells and tumours. Thus, our work demonstrates that β-catenin toxicity in cancer cells with compromised BRCA1/2 function is driven by transcriptional alterations that cause aberrant replication and inflict DNA damage.