Imagine DNA as a zipper being copied strand by strand. Now, picture a sneaky molecule that looks like a zipper tooth but snaps the whole thing shut. That’s what Chain-Terminating Nucleoside Analogs (CTNAs) do. They mimic DNA building blocks and sneak into replicating strands, halting growth, especially in fast-dividing cells like viruses or cancer.
Since the 1980s, CTNAs have been used to fight HIV and cancer. One such drug, alovudine, showed promise against HIV. But there was a catch: healthy cells didn’t always tolerate it, and clinical trials were stopped due to toxicity.
Researchers from Tokyo Metropolitan University have uncovered a clever defense system inside healthy cells that helps them dodge the toxic effects of a powerful drug called alovudine, used to fight viruses and cancer. At the heart of this system is Fen1, a DNA repair enzyme with a knack for trimming messy bits of DNA called “flaps” that appear during replication.
Think of Fen1 as a molecular tailor, snipping off loose threads to keep the genetic fabric smooth. Without Fen1, another protein called 53BP1 accumulates at the damage sites, exacerbating the damage. But when Fen1 is active, it keeps 53BP1 in check, allowing cells to tolerate the drug.
Human cells can write RNA sequences into DNA
This discovery not only highlights Fen1’s unsung role in DNA repair but also opens doors to smarter cancer treatments and better ways to predict how well current therapies will work.
In a clever twist of molecular detective work, Tokyo scientists used genetically modified chicken cells to uncover how healthy cells resist the toxic effects of alovudine, a drug designed to halt DNA replication in viruses and cancer. When they disabled Fen1, a DNA repair enzyme that trims loose “flaps” during replication, the cells became highly vulnerable, like a printer jammed with dangling paper strips.
But surprisingly, when they also removed 53BP1, a protein that typically rushes to damaged DNA sites, the cells bounced back. It turns out that without Fen1, flaps pile up, and 53BP1 crowds around them, blocking other repair tools from doing their job. This molecular traffic jam shuts down replication entirely.
By removing 53BP1, the road clears, and backup repair crews can step in. This discovery not only reveals a hidden rescue pathway but also hints at smarter ways to design cancer treatments that spare healthy cells.
In a molecular tug-of-war, Tokyo researchers have uncovered how two DNA repair systems, Fen1 and BRCA1, work independently to help cells survive the toxic punch of alovudine, a drug used to stop viruses and cancer cells from replicating. Using genetically modified chicken cells, they found that knocking out either Fen1 or BRCA1’s repair pathway (called homologous recombination) made cells more vulnerable.
But knocking out both? That was a knockout blow to DNA replication. This shows Fen1 isn’t just a sidekick; it’s a standalone hero in the fight against drug-induced damage.
Even more exciting, many cancer cells lack Fen1, making it a potential biomarker to predict how well treatments like alovudine might work. The team now plans to test these findings in human cells and explore how they could be used to treat tough cancers like solid tumors.
Journal Reference:
- Md Bayejid Hosen, Ryotaro Kawasumi, Kouji Hirota. The flap endonuclease-1 promotes cellular tolerance to a chain-terminating nucleoside analog, alovudine, by counteracting the toxic effect of 53BP1. Nucleic Acids Research. DOI: 10.1093/nar/gkaf617
