Citrus compound quercetin slows lung cancer cells in lab tests

In the lab at Universitätsklinikum Erlangen, lung cancer cells that normally keep dividing and spreading slowed down when they were exposed to quercetin. Nearly all of their migration stopped at the highest dose tested. The compound comes from a familiar source: it is found in citrus fruits, onions and buckwheat, and is already known for its anti-inflammatory properties.

Lung cancer is the most common cancer worldwide and causes more deaths than any other, yet current treatments do not work for every patient. Dr. Susetta Finotto, of the Department of Molecular Pneumology, pointed to a key difference: “Many drugs against lung cancer target a single molecule. Quercetin, by contrast, attacked at several points simultaneously in our experiments.” The team examined its effect on lung cancer cells in the lab, on mouse lung sections and in living mice.

The mechanism is what makes the results interesting. Quercetin slowed cell division and, in one of the two cell types studied, reduced oxidative stress, the damage caused by reactive oxygen compounds that can contribute to cancer. It also lowered the amounts of EGFR, a protein that receives growth signals and passes them into the cell, and of PD-L1, which helps cancer cells hide from the immune system. In mouse lung sections, quercetin increased interferon-alpha-2, a messenger that helps the immune system defend against tumors. The mice’s gut microbiome also shifted, with more bacteria producing certain short-chain fatty acids, which travel through the bloodstream to the lungs and can inhibit cancer cell growth there. Carvalho, the lead author, reported that “the higher the quercetin dose, the fewer cancer cells migrated.”

What this changes, and for whom, is for now limited. No patient is treated with quercetin on the basis of this work, and the study does not show that eating more citrus or onions protects anyone. The mouse data are thin: only a few animals developed a tumor, so the authors call for further studies to confirm the reduction in tumor foci. Whether any of this transfers to humans is, in their words, unclear. The most realistic near-term benefit is a better understanding of how several cancer pathways interact, which could guide future drug research. Finotto’s team plans to examine the possible preventive effect next, but the article gives no timetable for that work or for any clinical trial.