At Ulm University in Germany, researchers have uncovered a natural molecular safeguard hidden inside human cells—a tiny peptide that could prevent one of cancer treatment's cruelest long-term consequences: secondary leukemia.
The discovery matters because survival rates for cancer patients have improved dramatically over recent decades, meaning more people must navigate the difficult terrain of life after treatment. Yet that victory comes shadowed by a serious threat: chemotherapy and radiotherapy can damage DNA in ways that, years later, spark the development of new blood cancers. These secondary leukemias arise when treatment-induced cellular stress causes breaks in a particularly vulnerable stretch of the genome—a region of just about 400 base pairs in the MLL or KMT2A gene that Professor Lisa Wiesmüller, head of the Gynecological Oncology Section at Ulm University Hospital, has studied for years.
The new study, published in Nature Communications, identifies how these harmful DNA breaks occur and, more importantly, how to stop them. The culprit is an enzyme called endonuclease G (EndoG), which cuts DNA like molecular scissors. Wiesmüller's group had pinpointed EndoG as the trigger for these dangerous breaks back in 2015. But stopping the enzyme entirely posed a problem: EndoG also helps chemotherapy do its job by killing cancer cells. Researchers needed a scalpel, not a sledgehammer.
The breakthrough came from an unexpected source. A member of Wiesmüller's team stumbled upon a clue buried in a specialist article: a region of the DNA repair protein Ku80 bears striking similarities to a natural EndoG inhibitor found in fruit flies. That observation, almost hidden in academic literature, sparked a new line of inquiry. The researchers discovered that Ku80 does indeed interact directly with EndoG, and they used this knowledge to synthesize peptides—small protein building blocks—that mimic the protective effect of this natural interaction.
In cell models, one of these peptides significantly reduced the DNA alterations associated with leukemia. Crucially, the peptide worked with surgical precision. Rather than shutting down EndoG altogether, it inhibited only those specific DNA damages that arise when EndoG and Ku80 interact—leaving the enzyme free to assist chemotherapy in killing cancer cells. This targeted approach emerged from rare collaboration among cancer researchers, structural biologists, and biophysicists. Using high-resolution single-molecule microscopy, Professor J. Christof M. Gebhardt from Ulm's Institute of Experimental Physics could actually watch these molecular interactions happen in real time, visualizing the peptide's protective effect directly in living cells.
Wiesmüller is careful to temper expectations: these peptides are not yet finished drugs but "lead compounds"—molecular blueprints that show researchers where therapeutic intervention might be possible. Smaller, more cell-permeable molecules could be developed using this protective mechanism as a foundation, potentially offering cancer survivors a new kind of protection.
For patients who have already fought one cancer and won, the prospect of preventing a treatment-induced second one represents something precious: the chance to keep living without that shadow hanging overhead.