AID	Name	Type	Comment
485311	Probe Development Summary for Inhibitors of DNA Polymerase Beta	summary

The base excision repair system in human cells is a target for therapeutic modulation of the response to irradiation treatment and DNA-damaging drugs. A key enzyme in this system is the bi-functional DNA polymerase known as DNA polymerase Beta (Pol Beta).

The following is a homogeneous kinetic assay to study the primer extension and strand-displacement reaction catalyzed by pol beta.

A stepwise description of the 1536-well assay is shown in next Table. Three microliters of reagents (buffer in column 3 and 4 as negative control and 10 nM Pol beta in columns 1, 2, and 5-48) was dispensed into 1,536-well black solid-bottomed plate. Compounds (23 nL) were transferred via Kalypsys pin tool equipped with 1536-pin array (10 nL slotted pins, V&P Scientific, San Diego, CA). The plates were incubated for 15 min at room temperature, and 1 uL substrate (50 nM final concentration) were added to start the reaction and immediately read at 0 min read on Viewlux reader. The plate were further incubated for 10 min at room temperature, and then read on Viewlux again. Throughout the screen, reagent bottle and all liquid lines were chilled and made light-tight to minimize reagent degradation. All screening operations were performed on a fully integrated robotic system (Kalypsys, San Diego, CA) containing one RX-130 and two RX-90 anthropomorphic robotic arms (Staubli, Duncan, SC). Library plates were screened starting from the lowest and proceeding to the highest concentration, and a double-dipping step of the highest concentration was required to access higher concentrations of compounds. Vehicle-only plates, with DMSO being pin-transferred to the entire column 5-48 compound area, were inserted uniformly at the beginning and the end of each library in order to monitor for and record any shifts in the background, which can be affected by reagent dispensers or loss in enzyme activity overtime. Screening data were corrected, normalized, and concentration-effect relationships were derived by using publicly-available curve fitting algorithms developed in-house (http://ncgc.nih.gov/pub/openhts). A four parameter Hill equation was fitted to the concentration-response data by minimizing the residual error between the modeled and observed responses.

Compound Ranking:

1. Compounds are first classified as having full titration curves, partial modulation, partial curve (weaker actives), single point activity (at highest concentration only), or inactive. See data field "Curve Description". For this assay, apparent inhibitors are ranked higher than compounds that showed apparent activation.
2. For all inactive compounds, PUBCHEM_ACTIVITY_SCORE is 0. For all active compounds, a score range was given for each curve class type given above. Active compounds have PUBCHEM_ACTIVITY_SCORE between 40 and 100. Inconclusive compounds have PUBCHEM_ACTIVITY_SCORE between 1 and 39. Fit_LogAC50 was used for determining relative score and was scaled to each curve class' score range.

Grant Number: MH090863-01