Cell-Active Small Molecule Inhibitors of the DNA-Damage Repair Enzyme Poly(ADP-ribose) Glycohydrolase (PARG): Discovery and Optimization of Orally Bioavailable Quinazolinedione Sulfonamides.

DNA damage repair enzymes are promising targets in the development of new therapeutic agents for a wide range of cancers and potentially other diseases. The enzyme poly(ADP-ribose) glycohydrolase (PARG) plays a pivotal role in the regulation of DNA repair mechanisms; however, the lack of potent drug-like inhibitors for use in cellular and in vivo models has limited the investigation of its potential as a novel therapeutic target. Using the crystal structure of human PARG in complex with the weakly active and cytotoxic anthraquinone 8a, novel quinazolinedione sulfonamides PARG inhibitors have been identified by means of structure-based virtual screening and library design. 1-Oxetan-3-ylmethyl derivatives 33d and 35d were selected for preliminary investigations in vivo. X-ray crystal structures help rationalize the observed structure-activity relationships of these novel inhibitors.

An assay to measure poly(ADP ribose) glycohydrolase (PARG) activity in cells.

After a DNA damage signal multiple polymers of ADP ribose attached to poly(ADP) ribose (PAR) polymerases (PARPs) are broken down by the enzyme poly(ADP) ribose glycohydrolase (PARG). Inhibition of PARG leads to a failure of DNA repair and small molecule inhibition of PARG has been a goal for many years. To determine whether biochemical inhibitors of PARG are active in cells we have designed an immunofluorescence assay to detect nuclear PAR after DNA damage. This 384-well assay is suitable for medium throughput high-content screening and can detect cell-permeable inhibitors of PARG from nM to µM potency. In addition, the assay has been shown to work in murine cells and in a variety of human cancer cells. Furthermore, the assay is suitable for detecting the DNA damage response induced by treatment with temozolomide and methylmethane sulfonate (MMS). Lastly, the assay has been shown to be robust over a period of several years.

First-in-Class Chemical Probes against Poly(ADP-ribose) Glycohydrolase (PARG) Inhibit DNA Repair with Differential Pharmacology to Olaparib.

The enzyme poly(ADP-ribose) glycohydrolase (PARG) performs a critical role in the repair of DNA single strand breaks (SSBs). However, a detailed understanding of its mechanism of action has been hampered by a lack of credible, cell-active chemical probes. Herein, we demonstrate inhibition of PARG with a small molecule, leading to poly(ADP-ribose) (PAR) chain persistence in intact cells. Moreover, we describe two advanced, and chemically distinct, cell-active tool compounds with convincing on-target pharmacology and selectivity. Using one of these tool compounds, we demonstrate pharmacology consistent with PARG inhibition. Further, while the roles of PARG and poly(ADP-ribose) polymerase (PARP) are closely intertwined, we demonstrate that the pharmacology of a PARG inhibitor differs from that observed with the more thoroughly studied PARP inhibitor olaparib. We believe that these tools will facilitate a wider understanding of this important component of DNA repair and may enable the development of novel therapeutic agents exploiting the critical dependence of tumors on the DNA damage response (DDR).