DNAR-01 - PAR-Mediated DNA Damage Signaling in IDH Mutant Gliomas: Combining PARG Inhibition and Radiation for Selective Cytotoxicity.

Isocitrate dehydrogenase (IDH) 1 or 2 mutant gliomas have unique metabolic characteristics and DNA damage response. Radiotherapy and chemotherapy have been proven to be effective treatments for IDH mutant gliomas. Poly (ADP-ribose) (PAR) mediates DNA damage response and is regulated by opposing enzymes: poly (ADP-ribose) polymerases (PARPs) synthesize PAR, while poly (ADP-ribose) glycohydrolase (PARG) breaks it down. Combining PARG inhibitor (PARGi) and Temozolomide (TMZ) in IDH mutant cells leads to imbalanced NAD sequestration into PAR, causing metabolic lethality. This study characterizes the combination of PARGi and radiation. PARGi monotherapy showed no difference between IDH mutant and wild-type cells. However, we found that combining PARGi with radiation significantly increased cytotoxicity in IDH mutant glioma models, similar to PARPi and radiation. (Wang et al, ACi.Adv. 2020) Our findings showed that unlike TMZ+PARGi, PARGi and radiation did not consume and deplete NAD. Cytotoxicity was partially reversed by IDH inhibitor, highlighting the contribution of PAR-mediated DNA damage signaling in IDH mutant contexts. This convergence of vulnerabilities in IDH mutant cells identifies PAR-mediated DNA repair mechanisms that operate independently of NAD metabolism. IDH mutant enzyme generates 2 hydroxyglutarate (2HG), which is critical early in tumor development. However, the effect of 2HG on radiation sensitivity varies across cellular contexts. In this study, we found that IDH1 mutation and 2HG production enhance radiosensitivity in glioma cells both in vivo and in in vitro models, facilitated by PAR-dependent mechanisms. This augmentation of radiosensitivity is associated with S-phase blockage of the cell cycle, unveiling a vulnerability in the replication process of these cancer cells. In summary, this study demonstrates that the combination of PARGi and radiation regulates DNA repair pathways, augmenting cytotoxicity specifically in IDH mutant gliomas. Targeting PAR during radiation holds promise for treating IDH mutant gliomas, tailoring therapy to maximize durability while minimizing impact on normal cells.