Vitamin B2 Controls a Key Cancer Cell Survival Switch — Scientists Find

Every morning, millions of people swallow a multivitamin containing riboflavin — vitamin B2 — and think nothing of it. Researchers at the University of Würzburg have now found reason to pay considerably more attention to that unremarkable yellow tablet. In a study published March 13 in Nature Cell Biology, José Pedro Friedmann Angeli and colleagues report that riboflavin directly controls the stability of FSP1, a protein that cancer cells depend on to avoid a lethal form of self-destruction called ferroptosis. Strip the vitamin away, and the protection collapses.

The Cancer Protein That Was Flying Under the Radar

Ferroptosis was only named in 2012, and the field around it has moved fast. The basic idea is that cells can be pushed to die by overwhelming their membranes with oxidised fats — a process called lipid peroxidation. Most cancer research in this space focused on GPX4, an enzyme that mops up these toxic fats using the antioxidant glutathione. Then, in 2019, two independent teams discovered FSP1: a completely separate backstop that recycles fat-soluble antioxidants like CoQ10 and vitamin K, keeping lipid peroxidation in check through a different route entirely. Cancer cells that express high levels of FSP1 can, in effect, shrug off attempts to trigger ferroptosis. What no one had worked out, until now, was what controls FSP1 itself.

What a CRISPR Screen Found When Nobody Expected Vitamin B2

The Würzburg team's approach was direct: engineer cancer cells that could only survive if FSP1 was working, then systematically knock out roughly 3,000 genes and see which knockouts caused those cells to die. The top hit was SCD1, a fat-metabolism gene whose link to ferroptosis was already known. But the second hit — RFK, or riboflavin kinase — was a genuine surprise. RFK is the enzyme that takes riboflavin and converts it into FMN, the first step in making FAD, a cofactor that FSP1 needs to function. Without RFK, FAD levels fall. Without FAD, FSP1 becomes unstable and gets degraded by the cell's own waste-disposal system. The chain is short, and the implication is stark: riboflavin availability is upstream of the entire FSP1 pathway.

Why Does Riboflavin Keep Cancer Cells Alive?

Here is where it gets genuinely odd. Standard lab cell culture media — the liquid scientists grow cancer cells in — contains riboflavin at concentrations 25 to 50 times higher than what circulates in human blood. That means most ferroptosis experiments in labs around the world have been running under conditions that artificially prop up FSP1. When the Würzburg team dropped riboflavin to physiological levels (around 20 nM), FSP1 expression fell sharply, and the cells became dramatically more sensitive to ferroptosis-inducing drugs. The effect was not subtle, and it was consistent across four different cancer cell lines: melanoma, breast cancer, lung adenocarcinoma, and large-cell lung carcinoma. FAD is not just a catalyst here — molecular dynamics simulations showed it physically stabilises FSP1's structure. Without it, specific residues in the protein (around positions 282–300) become disordered, and the whole thing unravels.

What This Means for Future Cancer Treatment

The paper goes beyond mechanism. The team tested roseoflavin — an antimicrobial compound produced by the soil bacterium Streptomyces davaonensis — as a potential drug lead. Roseoflavin looks enough like riboflavin that cells absorb and process it through the same pathway. The result is a corrupted version of FAD that slots into FSP1 and stabilises it structurally, but cannot carry out the electron-transfer chemistry the protein needs. FSP1 is frozen in place but switched off. At physiologically relevant riboflavin concentrations, roseoflavin triggered ferroptosis in the single-digit nanomolar range — far more potently than existing FSP1 inhibitors. Crucially, cells that lacked FSP1 entirely showed no extra sensitivity to roseoflavin, confirming the target is genuine and not a side effect.

The Questions Still Unanswered

The study was done entirely in cell lines, and roseoflavin's safety profile in humans is not well-established for oncology doses. Its antibiotic history shows it can reach tissues, which is promising, but nobody has run the kind of pharmacokinetic studies needed to know how it behaves in a tumour microenvironment with genuinely low riboflavin. There is also a harder conceptual question: if riboflavin-poor conditions in vivo naturally suppress FSP1, does that mean some tumours are already more ferroptosis-sensitive than lab models suggest? The answer matters enormously for patient stratification. Getting from a nanomolar hit in a dish to a clinical candidate is the hard part — but the mechanism is clean, the target is validated, and the direction is clear.

• Vitamin B2 is not just a nutrient — it directly determines how well cancer cells can defend themselves against a specific form of programmed cell death.
• Lab conditions may have misled researchers — standard cell culture contains up to 50× more riboflavin than human blood, potentially masking ferroptosis sensitivity in countless past experiments.
• Roseoflavin is an early drug lead — this bacterial compound exploits the same metabolic pathway as riboflavin, making it difficult for cancer cells to evolve resistance without crippling themselves.

"Our work unveils riboflavin's role in the FSP1-driven recycling of lipophilic antioxidants, offering fundamental insights into the complex interactions of nutrients, with important implications for understanding inconsistent outcomes in preclinical and clinical studies of antioxidant therapies." — Skafar, Friedmann Angeli et al., Nature Cell Biology, 2026.