Some proteins in the human body are easy to block with a drug; they have an obvious spot in their structure where a drug can fit, like a key in a lock. But other proteins are more difficult to target, with no clear drug-binding sites. To design a drug that blocks a cancer-related protein, scientists took a hint from the protein's paralog, or 'twin.' Using innovative chemical biology methods, the scientists pinpointed a druggable site on the paralog, and then used that knowledge to characterize drugs that bound to a similar -- but more difficult to detect -- spot on its twin. Ultimately, they found drugs that only bound to the protein of interest and not its highly similar sibling.