WP1066 is a Stat3 inhibitor and JAK2 inhibitor. WP1066 is also a novel analogue of the JAK2 inhibitor AG490, in JAK2 V617F-positive erythroleukemia HEL cells and in blood cells from patients with polycythemia vera. WP1066 significantly inhibited JAK2 and its downstream signal transducer and activator of transcription-3, signal transducer and activator of transcription-5, and extracellular signal-regulated kinase-1/2 pathways in a dose- and time-dependent manner. WP1066 is active both in vitro and ex vivo and should be further developed for the treatment of neoplasms expressing the JAK2 V617F mutation.