ATM Regulates 3-Methylpurine-DNA Glycosylase and Promotes Therapeutic Resistance to Alkylating Agents

Abstract

Alkylating agents are a frontline therapy for the treatment of several aggressive cancers including pediatric glioblastoma, a lethal tumor in children. Unfortunately, many tumors are resistant to this therapy. We sought to identify ways of sensitizing tumor cells to alkylating agents while leaving normal cells unharmed; increasing therapeutic response while minimizing toxicity. Using a siRNA screen targeting over 240 DNA damage response genes, we identified novel sensitizers to alkylating agents. In particular the base excision repair (BER) pathway, including 3-methylpurine-DNA glycosylase (MPG), as well as ataxia telangiectasia mutated (ATM) were identified in our screen. Interestingly, we identified MPG as a direct novel substrate of ATM. ATM-mediated phosphorylation of MPG was required for enhanced MPG function. Importantly, combined inhibition or loss of MPG and ATM resulted in increased alkylating agent-induced cytotoxicity in vitro and prolonged survival in vivo. The discovery of the ATM-MPG axis will lead to improved treatment of alkylating agent-resistant tumors.

Poly-ADP-Ribose Polymerase as a Therapeutic Target in Pediatric Diffuse Intrinsic Pontine Glioma and Pediatric High-Grade Astrocytoma

“…For our pilot studies, niraparib was administered (1 dose/day  3 days) 25 days after cell implantation. As in our previous work, mice developed tumors by this time (18). Mice were sacrificed 6 hours after the last dose of niraparib.…”

“…To test the in vivo efficacy of niraparib, we used a SJG2 orthotopic xenograft NSG mouse model, previously established by our group (18). We conducted a small pilot experiment (n ¼ 3) to ensure that SJG2 cells retain PARP1 expression in vivo and to test whether Niraparib was capable of penetrating into the tumor and inhibiting PARP activity ( Fig.…”

“…Both temozolomide and radiotherapy also damage the developing cortex, deep brain structures, and posterior fossa, leading to adverse sequelae in patients, with higher risk when applied at a younger age (11)(12)(13)(14)(15)(16). Chemo-and radiosensitizers may offer the opportunity to improve the therapeutic index by increasing efficacy of radiotherapy or chemotherapeutic drugs while reducing toxicity and damage to developing brain (17,18).…”

Base Excision Repair, a Pathway Regulated by Posttranslational Modifications

“…It remains to be seen whether MPG is a direct substrate for p300-dependent acetylation in vivo. The DNA glycosylase activity of MPG was, however, shown to be directly enhanced by phosphorylation at serine 172 (S172) by the ataxia telangiectasia mutated (ATM) kinase (46). Phosphorylation of MPG in vivo was furthermore required for efficient DNA repair following treatment with the alkylating agent temozolomide.…”

Understanding and Targeting Alkylator Resistance in Glioblastoma

“…Elderly patients commonly present with glioblastoma lacking all (epigenetic) positive prognostic markers (except the predictive MGMT ; ref. In this issue of Cancer Discovery , Agnihotri and colleagues ( 9 ) hypothesized that alternate MGMT-independent mechanisms of DNA repair and treatment resistance could explain why pediatric glioblastoma fails to respond to alkylating agents. Using siRNA screening, multiple members of the BER pathway mediating alkylating agent resistance in pediatric glioblastoma were identifi ed, including 3-methylpurine-DNA glycosylase (MPG).…”