Abstract 6111: Design of a small molecule screening assay to detect DNA trapping of PARP1/2

Abstract

Abstract Poly(ADP-ribose) polymerase (PARP) inhibitors are currently used in the clinic for the treatment of tumors with a defective DNA damage response (DDR). When PARP1 or PARP2 binds damaged DNA, it adds poly(ADP-ribose) chains to its own backbone and to other DDR proteins, which recruits and activates them. PARylated PARP1/2 next detaches from the DNA so that the other PARylated proteins can initiate the repair process. It has been observed that some PARP inhibitors prevent PARP1/2 from dissociating the DNA. The continuous presence of PARP at the site of damage prevents repair and blocks replication, leading to cell death. Therefore, drugs that trap PARP1/2 to the DNA tend to be significantly more cytotoxic than other PARP inhibitors, which is highly desirable. This study describes the design and optimization of novel PARPtrap assays to specifically assess the ability of a drug to trap PARP onto DNA. The assay is based on principles of fluorescence polarization and uses fluorescently labeled DNA probes that are excited by polarized light and emit light with a degree of polarization that is proportional to the rate of molecular rotation. The free DNA probes that rotate fast have low fluorescence polarization (FP), but high FP when are bound to PARP1 or PARP2. When NAD+ is added, the PARylated enzymes detach from the probe, reducing FP levels. If a PARP inhibitor is added, the inhibitor’s trapping ability increases FP in a dose-dependent manner. Proof-of-principle titration of known PARP-trapping inhibitors (Talazoparib, AZD305, Olaparib and Veliparib) was performed to validate the assay. We observed that: i)The known relative trapping efficacies of Talazoparib, Olaparib and Veliparib were similar to known relative efficacies. ii)Talazoparib, Olaparib and Veliparib had similar trapping efficacy against PARP1 and PARP2, as measured by their EC50, whereas AZD305 was 1,000 times more efficient at trapping PARP1 than it was PARP2, demonstrating selectivity between PARP1 and PARP2. iii)AZD305 displayed as efficient DNA trapping activity toward PARP1 as best-in-class Talazoparib. In summary, we have designed an innovative PARPtrap assay designed for the high throughput screening of small molecule libraries to specifically identify or compare inhibitors that are capable of trapping PARP1 and/or PARP2 onto DNA. Citation Format: Kasia Zientara-Rytter, Veronique T. Baron, Junguk Park, Pavel Shashkin, Henry Zhu. Design of a small molecule screening assay to detect DNA trapping of PARP1/2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6111.