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Scientists Discover Fen1 Pathway Shielding Cells from Alovudine Toxicity

Life Sciences and Bio Pharma

Business Honor - Fen1 Pathway Protects Cells from Alovudine

Business Honor
12 August, 2025

Scientists discovered a Fen1-related pathway protecting cells from alovudine toxicity, advancing targeted cancer treatment strategies.

Researchers at the Tokyo Metropolitan University have uncovered a new cellular pathway which protects healthy cells from the toxic effects of the chain-terminating nucleoside analog alovudine, a compound used in antiviral and anticancer treatment. The finding paves the way for improved cancer therapy as well as more precise drug efficacy assessment tools. CTNAs such as alovudine mimic the components of DNA and interfere with DNA replication, especially in rapidly dividing cancer or infected cells. Their toxic action on normal cells has limited their therapeutic applications. Alovudine, which was once being developed as a potential drug for HIV treatment, was discontinued at Phase II clinical trials because of such toxicities.

The group, under Professor Kouji Hirota, emphasized how normal cells are able to withstand CTNA stress. They found the flap endonuclease-1 (Fen1), an important enzyme involved in DNA repair, to play a crucial role in avoiding alovudine toxicity. Fen1 cuts short single-stranded DNA overhangs as replication occurs. With its absence, replication is profoundly impaired, especially when alovudine is incorporated. Remarkably, the scientists discovered that deletion of 53BP1, a protein that accumulates in DNA nicks, restored partial resistance to alovudine, indicating a pathway where 53BP1 contributes to replication failure in Fen1-deficient cells.

This research is consistent with previous studies on BRCA1 and homologous recombination (HR), another DNA repair process. Inhibition of both Fen1 and BRCA1 significantly reduced cell resistance, indicating their independent but essential functions. The implications for biopharma, healthcare, and life sciences are substantial: cancers frequently exhibit Fen1 deficiencies, which could make this a drug sensitivity biomarker. In addition, knowing how to overcome CTNA resistance can optimize treatments and minimize off-target effects, improving medical security by reducing harmful drug side effects. Next, the researchers intend to explore their findings in human cells and various forms of cancer, bringing them one step closer to personalized and more effective cancer treatments.