When Chesta Jain and her colleagues in Ann Arbor peered into the iron-rich cores of colorectal cancer cells, they uncovered a hidden lifeline: a fragile metabolic thread that keeps these aggressive tumors alive. At the University of Michigan Health Rogel Cancer Center, the team discovered that colorectal cancer cells—unlike normal cells—survive their own iron overload by relying on mitochondrial complex II, a little-known component of cellular respiration. This finding, published in Cell Metabolism, could reshape how scientists approach one of the deadliest and most iron-hungry forms of cancer.
Iron is essential for life, but in excess, it triggers a violent form of cell death called ferroptosis. Normal cells self-destruct when iron builds up. Yet colorectal cancer cells accumulate iron at alarming levels without dying—sometimes carrying up to 10 times more iron than healthy tissue. For years, researchers assumed defects in ferroptosis pathways explained this resilience. But when the Rogel team knocked out key ferroptotic enzymes, tumor growth continued unchecked. That’s when they turned their attention deeper into the cell’s power plants—the mitochondria.
Using a metabolism-focused CRISPR screen, the researchers identified a surprising protector: cellular heme, an iron-containing molecule. Tracing its influence, they found that mitochondrial complex II acts as a critical buffer against iron toxicity by regulating coenzyme Q. "Complex II in colon cancer was absolutely critical for buffering iron toxicity. When we knock out complex II in cell lines or mouse models, the requirement for iron turns very toxic because they have no way to buffer it, and so those cancer cells start to die," said senior author Yatrik Shah, Ph.D., Horace W. Davenport Collegiate Professor of Physiology at Michigan Medicine. In mouse models, eliminating complex II slashed iron levels in tumor cells and triggered widespread cancer cell death—while leaving healthy cells largely unharmed.
Even more intriguing, the relationship appears to be bidirectional: iron itself regulates complex II activity, suggesting a dangerous feedback loop that fuels tumor growth. This dual dependency—where complex II protects against iron toxicity, and iron boosts complex II function—could represent a metabolic Achilles’ heel. Because normal cells don’t stockpile iron the way cancer cells do, targeting complex II may offer a rare opportunity for precision: killing tumors without widespread side effects. The team observed minimal toxicity in mice when complex II was disrupted, a promising sign for future therapies.
The discovery opens new doors for drug development. Inhibitors targeting mitochondrial complexes already exist for other diseases, and the Rogel team plans to test whether they can be repurposed for colorectal cancer. Given that many cancers—from pancreatic to liver—also hoard iron, this mechanism might extend beyond the colon. For the nearly 1.7 million people diagnosed with colorectal cancer worldwide each year, this research offers more than just insight—it offers a beacon of hope, forged in the quiet labs of Ann Arbor, where science is quietly rewriting the rules of cancer survival.