An iron-covered nanoparticle could soon be used to treat a recalcitrant form of leukemia. Ferumoxytol, a drug already approved for treating anemia, seems to kill not only acute myeloid leukemia (AML) cells, but also the stem cells that give rise to them, according to a research team led by Jan Grimm of Memorial Sloan Kettering Cancer Center and Monica Guzman of Weill Cornell Medical College (Nat. Nanotechnol. 2019, DOI: 10.1038/s41565-019-0406-1). The team discovered the anticancer properties of the iron-coated nanoparticles while studying their possible use for drug delivery. They saw that in both a mouse model of leukemia and mice given transplants of human leukemic cells, treatment with ferumoxytol reduced the number of circulating leukemic cells. The team proposes that some leukemic cells express low levels of an iron transporter called ferroportin, so they cannot regulate iron metabolism as well as healthy cells. Treatment with ferumoxytol floods the cancer cells with iron, leading to production of hydroxide and hydroperoxide radicals—products of the Fenton reaction. The radicals contribute to oxidative stress and eventual cell death. Guzman and Grimm say AML is hard to cure and a drug that seems to kill leukemic stem cells could be a welcome addition to current therapies. The team is now planning a clinical trial.