Lestaurtinib (CEP-701, KT-5555) is a derivative of the indolocarbazole K252 and a staurosporine analog. It is an orally active inhibitor of receptor protein tyrosine kinases (RPTKs), which inhibits FLT3 and Trk, with an IC50 of 3 nM and < 25 nM, respectively. It also inhibits JAK2 with an IC50 of 0.9 nM.