FdUMP[10] is active against leukemia stem cells (LSCs) from cell lines and primary patient samples. (A) Colony formation assays. Primary patient samples or cell lines were incubated with the indicated drug for 24 hours and placed in methylcellulose media. Plates were read on or after day 7. All experiments were done in triplicate. Primary AML is the combined results of 3 independent primary patient samples. Colony numbers are normalized to controls, and error bars represent the SE. (B) Colony formation assays. As in panel A, the result shown is the combination of 4 separate normal HSC donors.