| Assay Method Information | |
| | In Vitro Scintillation Proximity Assay (SPA) |
| Description: | In principle, the assay relies upon the well established SPA technology for the detection of poly(ADP-ribosyl)ation of biotinylated target proteins, i.e histones. This ribosylation is induced using nicked DNA activated PARP-1 enzyme and [3H]-nicotinamide adenine dinucleotide ([3H]-NAD+) as ADP-ribosyl donor.Histones (type II-A, supplier: Sigma) were biotinylated using the biotinylation kit of Amersham and stored aliquoted at −20° C. A stock solution of 100 mg/ml SPA poly(vinyl toluene) (PVT) beads (supplier: Amersham) was made in PBS. A stock solution of 61.6 nM [3H]-NAD− was made by adding [3H]-NAD+ (0.1 mCi/ml, supplier: Perkin Elmer) to incubation buffer (50 mM Tris/HCl, pH 8; 0.2 mM DTT; 4 mM MgCl2). A solution of 4 mM NAD+ (supplier: Sigma) was made. Human PARP-1 enzyme was obtained from Trevigen. Biotinylated histones and PVT-SPA beads were mixed and pre-incubated for 30 minutes at room temperature. PARP-1 enzyme (concentration was lot dependent) was mixed with the nicked DNA and the mixture was pre-incubated for 30 minutes at 4° C. Equal parts of this histones/PVT-SPA beads solution and PARP-1 enzyme/DNA solution were mixed and 75 μl of this mixture together with 1 μl of compound in DMSO and 25 μl of [3H]-NAD+was added per well into a 96-well microtiterplate. The final concentrations in the incubation mixture were 2 μg/ml for the biotinylated histones, 2 mg/ml for the PVT-SPA beads, 0.25 μg/ml for the nicked DNA and between 0.1-0.2 μg/ml for the PARP-1 enzyme. After incubation of the mixture for 20 minutes at room temperature, the reaction was terminated by adding 100 μl of 4 mM NAD+ in water (final concentration 2 mM) and plates were mixed. The beads were sedimented by centrifugation (10 min, 800 rpm) and plates transferred to a TopCountNXT (Packard) for scintillation counting, values were expressed as counts per minute (cpm). For each experiment, controls (containing PARP-1 enzyme and DMSO without compound), a blank incubation (containing DMSO but no PARP-1 enzyme, no DNA or compound) and samples (containing PARP-1 enzyme, DNA and compound dissolved in DMSO) were run in parallel. All compounds tested were dissolved and eventually further diluted in DMSO. A dose-response curve was made wherein the compounds were tested at concentrations between 10−5M and 3×10−9M. In each test, the blank value was subtracted from both the control and the sample values. The control sample represented maximal PARP-1 enzyme activity. For each sample, the amount of cpm was expressed as a percentage of the mean cpm value of the controls. When appropriate, IC50-values (concentration of the drug needed to reduce the PARP-1 enzyme activity to 50% of the control) were computed using linear interpolation between the experimental points just above and below the 50% level. Herein the effects of test compounds are expressed as pIC50 (the negative log value of the IC50-value). |
| Affinity data for this assay | |
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