Transient adenoviral N-methylpurine DNA glycosylase overexpression imparts chemotherapeutic sensitivity to human breast cancer cells

Abstract

In an effort to improve the efficacy of cancer chemotherapy by intervening into the cellular responses to chemotherapeutic change, we have used adenoviral overexpression of N-methylpurine DNA glycosylase (MPG or ANPG/AAG) in breast cancer cells to study its ability to imbalance base excision repair (BER) and sensitize cancer cells to alkylating agents. Our results show that MPG-overexpressing cells are significantly more sensitive to the alkylating agents methyl methanesulfonate, N-methyl-N′-nitro-N-nitrosoguanidine, methylnitrosourea, dimethyl sulfate, and the clinical chemotherapeutic temozolomide. Sensitivity is further increased through coadministration of the BER inhibitor methoxyamine, which covalently binds abasic or apurinic/apyrimidinic (AP) sites and makes them refractory to subsequent repair. Methoxyamine reduction of cell survival is significantly greater in cells overexpressing MPG than in control cells, suggesting a heightened production of AP sites that, if made persistent, results in increased cellular toxicity. We further explored the mechanism of MPG-induced sensitivity and found that sensitivity was associated with a significant increase in the number of AP sites and/or single-strand breaks in overexpressing cells, confirming a MPG-driven accumulation of toxic BER intermediates. These data establish transient MPG overexpression as a potential therapeutic approach for increasing cellular sensitivity to alkylating agent chemotherapy.

Comparison of the Base Excision and Direct Reversal Repair Pathways for Correcting 1,N6-Ethenoadenine in Strongly Positioned Nucleosome Core Particles

“…Abnormal expression of both AAG and ALKBH2 has been observed in cancer pathologies. Overexpression of AAG has been associated with both decreased sensitivity to various chemotherapeutic agents in mouse embryonic stem cells and increased sensitivity in breast cancer cells. , ALKBH2 also has clinical significance, as its knockdown in bladder cancer tissues limited tumor development, while downregulation led to increased sensitivity to alkylating agents and chemotherapeutics . The potential for AlkB homologue inhibitors to serve as anticancer agents has also been investigated .…”

Kinetics of DNA Adducts and Abasic Site Formation in Tissues of Mice Treated with a Nitrogen Mustard

“…AP sites exist partially as the ring-opened aldehyde and react with nucleophiles such as methoxyamine (TRC102) to form a stable oxime adduct. The methoxyamine-AP site oxime inhibits the base excision repair (BER) pathway , and enhanced the cytotoxicity of Temozolomide , in cultured human breast, − ovarian, and colon cancer cells. , Indeed, methoxyamine is part of seven ongoing or recently completed clinical trials. − The reactivity of the ring-opened aldehyde form has also been exploited to quantitate AP sites in DNA (Scheme ) employing the aldehyde reactive probe or O -(pyridin-3-yl-methyl)­hydroxylamine (PMOA) …”

Focus on DNA Glycosylases—A Set of Tightly Regulated Enzymes with a High Potential as Anticancer Drug Targets

“…In contrast, in another study, decreased expression of MPG in MPG-deficient bone marrow mouse cells confers instead resistance to alkylating agents [66]. Moreover, overexpression of MPG in a human mammary gland adenocarcinoma cell line, sensitizes the cells to treatment with different alkylating agents (MMS, N-methyl-NV-nitro-N-nitroso-guanidine, methyl nitrosourea, dimethyl sulphate, and temozolomide) [176]. These apparently contradictory results have since been explained by the finding that the cytotoxic BER intermediates, including 5 dRP lesions, are efficiently repaired in certain cell lines, but not in others [177].…”