title: Comparison of luminescence ADP production assay and radiometric scintillation proximity assay for Cdc7 kinase.
abstract: Several assay technologies have been successfully adapted and used in HTS to screen for protein kinase inhibitors; however, emerging comparative analysis studies report very low hit overlap between the different technologies, which challenges the working assumption that hit identification is not dependent on the assay method of choice. To help address this issue, we performed two screens on the cancer target, Cdc7-Dbf4 heterodimeric protein kinase, using a direct assay detection method measuring [(33)P]-phosphate incorporation into the substrate and an indirect method measuring residual ADP production using luminescence. We conducted the two screens under similar conditions, where in one, we measured [(33)P]-phosphate incorporation using scintillation proximity assay (SPA), and in the other, we detected luminescence signal of the ATP-dependent luciferase after regenerating ATP from residual ADP (LUM). Surprisingly, little or no correlation were observed between the positives identified by the two methods; at a threshold of 30% inhibition, 25 positives were identified in the LUM screen whereas the SPA screen only identified two positives, Tannic acid and Gentian violet, with Tannic acid being common to both. We tested 20 out of the 25 positive compounds in secondary confirmatory study and confirmed 12 compounds including Tannic acid as Cdc7-Dbf4 kinase inhibitors. Gentian violet, which was only positive in the SPA screen, inhibited luminescence detection and categorized as a false positive. This report demonstrates the strong impact in detection format on the success of a screening campaign and the importance of carefully designed confirmatory assays to eliminate those compounds that target the detection part of the assay.
authors.affiliation: HTS Core Facility, Molecular Pharmacology and Chemistry Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
authors.forename: Toshimitsu
authors.initials: T
authors.lastname: Takagi
authors.forename: David
authors.initials: D
authors.lastname: Shum
authors.forename: Monika
authors.initials: M
authors.lastname: Parisi
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Santos
authors.forename: Constantin
authors.initials: C
authors.lastname: Radu
authors.forename: Paul
authors.initials: P
authors.lastname: Calder
authors.forename: Zahra
authors.initials: Z
authors.lastname: Rizvi
authors.forename: Mark G
authors.initials: MG
authors.lastname: Frattini
authors.forename: Hakim
authors.initials: H
authors.lastname: Djaballah
mesh_terms: D000244:Adenosine Diphosphate / Q000096:biosynthesis*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D049449:Luminescence; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012588:Scintillation Counting
chemical_list: D018797:Cell Cycle Proteins; D000244:Adenosine Diphosphate; C068619:CDC7 protein, human; D017346:Protein Serine-Threonine Kinases