When Dr. Thomas Catley watches proteins cling to DNA with nanometer precision, he sees more than molecular mechanics—he sees the possibility of sparing patients from some of chemotherapy's cruelest side effects. In a study published in Molecular Cell, researchers at the University of Sheffield and UT Southwestern Medical Center have uncovered a subtle biological difference between cancer cells and healthy cells that could one day protect the heart, brain, and other vital organs from the collateral damage of cancer treatment.
The discovery centers on a protein called HSF1, which acts as a highly specific regulator for the enzymes topoisomerase II (TOP2). These enzymes are critical targets of a major class of chemotherapy drugs known as TOP2 poisons. To divide rapidly, cancer cells rely on two variants of these enzymes—TOP2A and TOP2B—to cut, untangle, and repair DNA. TOP2 poisons exploit this process by trapping the enzymes mid-cut, leaving catastrophic DNA damage that forces cancer cells to self-destruct.
The problem is that these drugs cannot tell a tumor from healthy tissue. Nondividing cells in the heart, brain, and nervous system also depend on TOP2 enzymes to function. Because these cells cannot be replaced, the collateral damage they suffer causes the devastating, lasting side effects that make chemotherapy so grueling.
But here is the key difference the Sheffield and UT Southwestern team identified: while cancer cells use both TOP2A and TOP2B, healthy nondividing cells rely almost exclusively on TOP2B. Using atomic force microscopy, the researchers watched these enzymes bind directly to DNA and found that HSF1 enhances TOP2B's attachment to genetic material—but leaves TOP2A untouched.
This discovery opened a new therapeutic strategy. When the UT Southwestern team introduced an HSF1 inhibitor alongside TOP2 chemotherapy, they dramatically reduced the drug's toxic impact on healthy, nondividing cells. Crucially, because cancer cells still depend on TOP2A to multiply, the chemotherapy retained its full power against tumors.
The combination has already shown promise in mice. "We are currently testing whether combination therapy with HSF1 inhibitors can protect mice from the secondary toxicity of chemotherapy with TOP2 poisons," said Ram Madabhushi, associate professor at UT Southwestern who led the research.
For the roughly 20 million people worldwide diagnosed with cancer each year, this research represents a carefully grounded reason for hope—not a cure, but something perhaps equally valuable: the chance that future treatments might destroy tumors without destroying the lives that survive them.