Uracil processing by SMUG1 in the absence of UNG triggers homologous recombination and selectively kills BRCA1/2-deficient tumors.

Summary: Cancer cells with BRCA mutations have a broken repair system, making them vulnerable to drugs called PARP inhibitors. However, these cancers often learn to resist the treatment. Scientists have discovered a new "backdoor" to destroy these resistant tumors.

Our DNA occasionally accumulates "uracil," a chemical error. Normally, an enzyme called UNG fixes this quietly. But researchers found that if they block UNG, a backup enzyme called SMUG1 steps in. SMUG1 is a messy repairman; its work creates severe DNA breaks that require a specific tool (Homologous Recombination) to fix. Normal cells have this tool and survive, but BRCA-deficient cancer cells don't. Consequently, blocking UNG forces the cancer cells to fatally damage their own DNA, offering a promising new strategy for treating drug-resistant cancers.