HCK and hematopoietic and lymphoid system neoplasm: Previous reportshave indicated that inhibitors may bind with lower affinity when kinasedomains do not adopt a preferred conformation.19 Thus, the unique conformation of the Hck active site inducedby A-419259 in the crystal structure may more closely resemble theactive conformation present in blood cancer cells, thereby explainingits remarkable potency against AML cells.14 In vitro kinase assays showed that A-419259 potency was less influencedby Hck autophosphorylation than that of PP1, providing support forthis possibility.