title: Plasma inhibitory activity (PIA): a pharmacodynamic assay reveals insights into the basis for cytotoxic response to FLT3 inhibitors.
abstract: We have developed a useful surrogate assay for monitoring the efficacy of FLT3 inhibition in patients treated with oral FLT3 inhibitors. The plasma inhibitory activity (PIA) for FLT3 correlates with clinical activity in patients treated with CEP-701 and PKC412. Using the PIA assay, along with in vitro phosphorylation and cytotoxicity assays in leukemia cells, we compared PKC412 and its metabolite, CGP52421, with CEP-701. While both drugs could effectively inhibit FLT3 in vitro, CEP-701 was more cytotoxic to primary samples at comparable levels of FLT3 inhibition. PKC412 appears to be more selective than CEP-701 and therefore less effective at inducing cytotoxicity in primary acute myeloid leukemia (AML) samples in vitro. However, the PKC412 metabolite CGP52421 is less selective than its parent compound, PKC412, and is more cytotoxic against primary blast samples at comparable levels of FLT3 inhibition. The plasma inhibitory activity assay represents a useful correlative tool in the development of small-molecule inhibitors. Our application of this assay has revealed that the metabolite CGP52421 may contribute a significant portion of the antileukemia activity observed in patients receiving oral PKC412. Additionally, our results suggest that nonselectivity may constitute an important component of the cytotoxic effect of FLT3 inhibitors in FLT3-mutant AML.
authors.affiliation: Kimmel Cancer Center at Johns Hopkins University, Baltimore, MD 21231, USA. levisma@jhmi.edu
authors.forename: Mark
authors.initials: M
authors.lastname: Levis
authors.forename: Patrick
authors.initials: P
authors.lastname: Brown
authors.forename: B Douglas
authors.initials: BD
authors.lastname: Smith
authors.forename: Adam
authors.initials: A
authors.lastname: Stine
authors.forename: Rosalyn
authors.initials: R
authors.lastname: Pham
authors.forename: Richard
authors.initials: R
authors.lastname: Stone
authors.forename: Daniel
authors.initials: D
authors.lastname: Deangelo
authors.forename: Ilene
authors.initials: I
authors.lastname: Galinsky
authors.forename: Frank
authors.initials: F
authors.lastname: Giles
authors.forename: Elihu
authors.initials: E
authors.lastname: Estey
authors.forename: Hagop
authors.initials: H
authors.lastname: Kantarjian
authors.forename: Pamela
authors.initials: P
authors.lastname: Cohen
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Wang
authors.forename: Johannes
authors.initials: J
authors.lastname: Roesel
authors.forename: Judith E
authors.initials: JE
authors.lastname: Karp
authors.forename: Donald
authors.initials: D
authors.lastname: Small
mesh_terms: D000970:Antineoplastic Agents / Q000097:blood / Q000493:pharmacokinetics; D002227:Carbazoles / Q000097:blood / Q000493:pharmacokinetics; D016022:Case-Control Studies; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004354:Drug Screening Assays, Antitumor; D004791:Enzyme Inhibitors / Q000097:blood / Q000493:pharmacokinetics; D005663:Furans; D006801:Humans; D007211:Indoles / Q000097:blood / Q000493:pharmacokinetics; D020128:Inhibitory Concentration 50; D007938:Leukemia / Q000097:blood / Q000188:drug therapy* / Q000473:pathology*; D010599:Pharmacokinetics; D010949:Plasma / Q000737:chemistry*; D019311:Staurosporine / Q000031:analogs & derivatives / Q000097:blood / Q000493:pharmacokinetics; D051941:fms-Like Tyrosine Kinase 3 / Q000037:antagonists & inhibitors*
chemical_list: D000970:Antineoplastic Agents; D002227:Carbazoles; D004791:Enzyme Inhibitors; D005663:Furans; D007211:Indoles; C119379:lestaurtinib; C497970:FLT3 protein, human; D051941:fms-Like Tyrosine Kinase 3; D019311:Staurosporine; C059539:midostaurin