Overcoming Temozolomide Resistance in Glioblastoma via Enhanced NAD+ Bioavailability and Inhibition of Poly-ADP-Ribose Glycohydrolase

Abstract

Glioblastoma multiforme (GBM) is an incurable brain cancer with an average survival of approximately 15 months. Temozolomide (TMZ) is a DNA alkylating agent for the treatment of GBM. However, at least 50% of the patients treated with TMZ show poor response, primarily due to elevated expression of the repair protein O6-methylguanine-DNA methyltransferase (MGMT) or due to defects in the mismatch repair (MMR) pathway. These resistance mechanisms are either somatic or arise in response to treatment, highlighting the need to uncover treatments to overcome resistance. We found that administration of the NAD+ precursor dihydronicotinamide riboside (NRH) to raise cellular NAD+ levels combined with PARG inhibition (PARGi) triggers hyperaccumulation of poly(ADP-ribose) (PAR), resulting from both DNA damage-induced and replication-stress-induced PARP1 activation. Here, we show that the NRH/PARGi combination enhances the cytotoxicity of TMZ. Specifically, NRH rapidly increases NAD+ levels in both TMZ-sensitive and TMZ-resistant GBM-derived cells and enhances the accumulation of PAR following TMZ treatment. Furthermore, NRH promotes hyperaccumulation of PAR in the presence of TMZ and PARGi. This combination strongly suppresses the cell growth of GBM cells depleted of MSH6 or cells expressing MGMT, suggesting that this regimen may improve the efficacy of TMZ to overcome treatment resistance in GBM.

CHK1 inhibitor induced PARylation by targeting PARG causes excessive replication and metabolic stress and overcomes chemoresistance in ovarian cancer

“…In agreement with previous studies, PARGi causes synergistic lethality when combined with DNA-damaging agents [ 12 , 15 , 31 ] and following NRH supplementation to increase in NAD + levels [ 23 ]. In our studies, PARGi augmented prexasertib-induced replication stress responses, accumulation of PARylation, increased DNA damage and synergistic OC cell death.…”

“…PARG deficiency impairs cells’ ability to repair both DNA single and double-strand breaks [ 23 ]. Thus, PARG inhibitors are shown to exhibit antitumor activity against several cancer cells including those from ovarian, breast, pancreatic, lung, and brain cancers [ 15 , 23 , 28 – 31 ]. Recent studies showed PARG inhibitor sensitizes OC cells to platinum drugs and PARP-targeted therapies [ 12 , 32 , 33 ].…”

“…Additionally, we and others showed that CHK1 regulates integrity of the Fanconi anemia-BRCA-RAD51 repair complex and HR-mediated repair of DSB and sensitizes tumor cells to PARP-targeted therapies [ 37 – 40 ]. Further, we have found that PARGi leads to elevated CHK1 activation in glioma stem cells and cell lines, along with enhanced apoptosis [ 23 , 31 ]. These studies suggest an important role for PARP and PARG in response to CHK1 inhibition and repair of DNA lesions and cell survival.…”

Overexpression of the WWE domain of RNF146 modulates poly-(ADP)-ribose dynamics at sites of DNA damage

“…U2OS and ES-2 cells were obtained from ATCC. LN428 cells were a kind gift from Dr. Ian Pollack (University of Pittsburgh) and have been described by us previously [40, 67]. 293-FT cells were obtained from Thermo Fisher Scientific.…”

“…Six human dePARylation proteins have been recognized so far, with poly-ADP-ribose glycohydrolase (PARG) shown to be highly correlated to the DDR [34, 35]. First identified in both bovine and human cells [36, 37], PARG has been an enzyme of significant interest, both for biological characterization of mono- and poly-ADP-ribose metabolism and cellular function [38, 39] and the role of the PARP/PAR/PARG axis in cancer [31, 40, 41]. PARG possesses both exo-glycohydrolase and endo-glycohydrolase activities to hydrolyze the ribose-ribose bonds within PAR [42], releasing free PAR chains or mono-ADP-ribose moieties [36, 43].…”