The substance, artemisinin, is derived from the wormwood plant and has been used in China since ancient times to treat malaria. Work by Henry Lai and Narendra Singh, both UW bioengineers, indicated that artemisinin alone could selectively kill cancer cells while leaving normal cells unharmed. The trick to the compound’s effectiveness, according to Lai, appears to be in taking advantage of how cancer cells function. Because they multiply so rapidly, most cancer cells need more iron than normal cells to replicate DNA. To facilitate that, cancer cells have inlets on their surface, known as transferrin receptors, in greater numbers than other cells. Those receptors allow quick transport into the cell of transferrin, an iron-carrying protein found in blood. Once inside the cell, the artemisinin reacts with the iron, spawning highly reactive chemicals called “free radicals.” The free radicals attack other molecules and the cell membrane, breaking it apart and killing the cell.