Melamed, L. | Search bioRxiv

bioRxiv2026

Augmenting Radiation Sensitivity by Targeting PAR-Dependent Replication Fork Vulnerability in IDH-Mutant Glioma

Mutations in isocitrate dehydrogenase 1 (IDH1) drive the early stages of gliomagenesis while simultaneously imposing replication stress that creates targetable vulnerabilities. Using both in vitro and in vivo models, we show that inhibition of poly(ADP-ribose) glycohydrolase (PARG) induces a poly(ADP-ribose) (PAR)-dependent augmentation of radiosensitivity in IDH1-mutant glioma cells. Metabolic repletion of NAD+ fails to rescue this effect, indicating that the vulnerability cannot be explained solely by NAD+ depletion. Instead, PARG inhibition profoundly alters replication fork progression and S-phase kinetics in IDH1-mutant cells. Mechanistically, ionizing radiation preferentially activates replication fork-associated damage response proteins DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and X-ray repair cross-complementing protein 1 (XRCC1) in IDH1-mutant cells, a response partially reversed by pharmacologic inhibition of mutant IDH1. Importantly, pharmacologic inhibition of DNA-PKcs with AZD7648 during irradiation disrupts fork-associated repair signaling and markedly enhances cytotoxicity in IDH1-mutant glioma models. Together, these findings identify a PAR-dependent replication fork vulnerability that can be therapeutically exploited to selectively enhance radiosensitivity in IDH1-mutant gliomas. Statement of significanceIDH-mutant gliomas harbor intrinsic replication stress yet lack targeted radiosensitization strategies. We identify a PAR-dependent replication fork vulnerability in which disruption amplifies radiation cytotoxicity by deregulating S-phase fork signaling. Pharmacologic DNA-PKcs inhibition exploits this dependency, providing a genotype-selective approach to enhance radiotherapy in IDH-mutant glioma.

cancer biology↗

bioRxiv2019

Regulation of CHD2 expression by the Chaserr long noncoding RNA is essential for viability

Genomic loci adjacent to genes encoding for transcription factors and chromatin remodelers are enriched for long non-coding RNAs (lncRNAs), but the functional importance of this enrichment is largely unclear. Chromodomain helicase DNA binding protein 2 (Chd2) is a chromatin remodeller with various reported functions in cell differentiation and DNA damage response. Heterozygous mutations in human CHD2 have been implicated in epilepsy, neurodevelopmental delay, and intellectual disability. Here we show that Chaserr, a highly conserved lncRNA transcribed from a region near the transcription start site of Chd2 and on the same strand, acts in concert with the CHD2 protein to maintain proper Chd2 expression levels. Loss of Chaserr in mice leads to early postnatal lethality in homozygous mice, and severe growth retardation in heterozygotes. Mechanistically, loss of Chaserr leads to substantially increased Chd2 mRNA and protein levels, which in turn lead to increased transcriptional interference by inhibiting promoters found downstream of highly expressed genes. We further show that Chaserr production represses Chd2 expression solely in cis, and that the phenotypic consequences of Chaserr loss are rescued when Chd2 is perturbed as well. Targeting Chaserr is thus a potentially viable strategy for increasing CHD2 levels in haploinsufficient individuals.

molecular biology↗