Flavonoid from citrus fruits slowed the growth of cancer cells

The interest in quercetin is not accidental, as lung cancer is one of the most common and deadly forms of cancer in the world. Existing treatment methods are not suitable for all patients, so scientists are constantly looking for new approaches. As Dr. Susetta Finotto emphasizes, many drugs against lung cancer target a single molecule, whereas quercetin acted at several points in their experiments. The team tested its effect in three systems: on cancer cells in a test tube, on mouse lung slices, and on living animals.

First and foremost, quercetin slowed the division of tumor cells, and in one of the two cell types studied, it also reduced oxidative stress — the damage caused by reactive oxygen species, which can contribute to the development of cancer. The effect on cell migration was particularly pronounced: the higher the quercetin dose, the fewer cancer cells moved, and at the highest dose, migration was almost completely stopped. This is fundamentally important, as the ability to spread is a prerequisite for the formation of metastases.

Researchers have also figured out the molecular targets. Quercetin reduced the levels of two proteins in cancer cells: EGFR, which transmits growth signals into the cell, and PD‑L1, which allows the tumor to mask itself from the immune system. In lung tissue sections from mice, the substance also increased the amount of interferon‑alpha‑2 — a signaling molecule that helps the immune system fight the tumor. Moreover, in mice that received quercetin, the gut microbiome changed: there were more bacteria producing certain short‑chain fatty acids. These acids travel from the intestines to the lungs via the bloodstream and inhibit the growth of cancer cells there.

In experiments on mice, experts observed signs that animals that received quercetin had fewer tumor foci. However, tumors developed in only a few animals, so the conclusion requires confirmation in further studies. And it’s still too early to extrapolate the results from mice to humans.

Nevertheless, the team is optimistic. “Our results suggest that a diet rich in quercetin may support the treatment of lung cancer,” says Finotto. “We also believe it may have a preventive effect. We want to explore this further.”

It’s important to remember that we’re talking about laboratory data and animal models, not proven therapies for patients. Under no circumstances should quercetin be considered a substitute for treatment — this area is only just beginning to be studied.