Abstract
High-grade gliomas (HGG) are aggressive brain cancers treated with surgical resection
and the Stupp Protocol, comprising concurrent chemoradiotherapy and adjuvant
chemotherapy. However, since the Stupp Protocol, no significant therapeutic advances
have translated clinically, halting improvements in patient survival. Therefore, identifying
novel drug targets that enhance the Stupp Protocol’s therapeutic benefit is paramount.
A promising avenue is targeting somatic gain-of-function mutations in isocitrate
dehydrogenase (IDH) 1/2 genes. IDH-mutant HGG accumulate the oncometabolite D-2-
Hydroxyglutarate, depleting the essential metabolites; nicotinamide adenine dinucleotide
(NAD+) and nucleotides. This impairs metabolic pathways and DNA damage responses,
sensitising HGG to chemoradiotherapy and targeted therapies.
We investigated if targeting metabolic vulnerabilities within NAD+ and nucleotide
biosynthetic pathways could enhance chemoradiotherapy by screening a HGG panel,
including an isogenic IDH1-mutant, for sensitivity to metabolic inhibitors combined with
chemo- and radiotherapy. Identifying NUDT5, a Nudix hydrolase that catabolises
ADP-Ribose to replenish NAD+ pools, and synthesises nuclear ATP for chromatin remodelling,
as crucial for HGG survival.
Cell viability assays determined NUDT5 inhibition (NUDT5i) sensitised IDH1-wildtype
HGG to X-rays and α-particle radiotherapy modalities, whereas IDH1-mutant HGG were
sensitive to NUDT5i monotherapy. Subsequent live-cell imaging analysis indicated
NUDT5i induced cytostasis then cytotoxicity in IDH1-mutant HGG, suggesting IDH1-
mutations confer exploitable dependencies on NUDT5 for proliferation and survival.
NUDT5i did not significantly deplete NAD+ levels and NAD+ precursor supplementation
failed to rescue cell survival and proliferation, indicating NUDT5i effects are NAD+
independent. However, preliminary investigations into nucleoside supplementation
partially rescued NUDT5i effects on viability and preliminary γ-H2AX measurements
suggest NUDT5i induces DNA damage and impairs post-irradiation DNA repair in IDH1-
wildtype HGG, while IDH1-mutant HGG exhibit impaired damage recognition. Implying
NUDT5i may deplete nucleotide pools, inducing different radiosensitisation or
cytostasis/toxicity mechanisms dependent on IDH1 status.
This study identified NUDT5i as a promising HGG therapy, potentially enhancing Stupp
Protocol effectiveness regardless of IDH status and radiotherapy modality.