TK216-d4 is the deuterium labeled TK216. TK216 is an orally active and potent E26 transformation specific (ETS) inhibitor[1]. TK216 directly binds EWS-FLI1 and inhibits EWS-FLI1 protein interactions. TK216 blocks the binding between EWS-FLI1 and RNA helicase A. TK216 has anticancer activity[2].