Scientists at Scripps Research have identified how cancer cells lacking the senataxin (SETX) protein become reliant on a less accurate DNA repair pathway. The study, published in Cell Reports on October 28, 2025, explores the mechanisms behind this vulnerability and its potential for targeted cancer therapy.
SETX is a helicase protein that unwinds genetic material and resolves RNA-DNA tangles known as R-loops. Mutations in SETX are associated with rare neurological disorders such as ataxia and amyotrophic lateral sclerosis (ALS), as well as certain cancers including uterine, skin, and breast cancers. Researchers sought to understand how tumor cells survive despite the stress caused by high levels of R-loops.
The research team led by Wu used cells deficient in SETX to observe their response to double-strand breaks occurring at R-loop sites. They found that these cells experience increased DNA damage but activate an emergency repair mechanism called break-induced replication (BIR).
"We were surprised but excited to find that the cell turns on an emergency DNA repair mechanism called break-induced replication (BIR)," says Wu.
BIR is typically responsible for rescuing damaged DNA during replication but can also serve as a backup for double-strand breaks. This process rapidly copies large sections of DNA to repair broken strands but tends to introduce more errors than standard repair pathways.
"It's like an emergency repair team that works intensively but makes more mistakes," says Wu.
Further investigation revealed that in the absence of SETX, R-loops accumulate at break sites, disrupting normal repair signals. The resulting over-processing of broken DNA exposes long stretches of single-stranded DNA, which attracts BIR machinery—particularly PIF1, a key helicase involved in BIR. This sequence of events triggers BIR-mediated damage repair.
While BIR helps keep SETX-deficient cells alive, it creates a dependency: blocking BIR leads to cell death due to unrepaired breaks. This concept of synthetic lethality forms the basis for several targeted cancer therapies.
Wu's group discovered that three proteins related to BIR—PIF1, RAD52, and XPF—are crucial for survival in SETX-deficient cells.
"What's important is that these aren't essential in normal cells, which means we could selectively kill SETX-deficient tumors," says Wu.
Wu cautioned that translating these findings into clinical treatments will require further work.
"We're now exploring ways to inhibit these BIR factors, trying to find ones with the right activity and low toxicity," she adds.
The team is also investigating which tumors have high R-loop accumulation and under what conditions. Identifying suitable candidates for BIR-targeted therapy remains a priority for future research.
Although SETX mutations are not common across all cancers, many tumors accumulate R-loops through other processes such as oncogene activation or hormone signaling—for example, estrogen-driven breast cancers—which suggests broader therapeutic possibilities beyond just those with SETX mutations.
Authors of the study include Tong Wu, Youhang Li, Yuqin Zhao and Sameer Bikram Shah from Scripps Research; and Linda Z. Shi from the University of California San Diego.
