title: Synergistic cytotoxicity of N-methyl-N'-nitro-N-nitrosoguanidine and absence of poly(ADP-ribose) glycohydrolase involves chromatin decondensation.
abstract: DNA-alkylating agents in combination with poly (ADP-ribose) (PAR) synthesis inhibitors are a promising treatment for cancer. In search of other efficacious alternatives, we hypothesized that the absence of poly(ADP-ribose) glycohydrolase (PARG), which leads to the inhibition of PAR hydrolysis, would lead to increased DNA alkylation after treatment with low doses of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). At a sublethal dose, MNNG shows synergistic cytotoxicity in PARG-null embryonic trophoblast stem (TS) cells. The PAR modifications of histone H1 and histone H2B are much more pronounced in PARG null-TS cells exposed to MNNG, suggesting their relevance in the efficacy of this combination therapy. Because the PAR modification of these chromatin binding proteins leads to chromatin remodeling, a possible mechanism for the observed synergistic effects involves the subsequent decondensation of chromatin, which may cause the genomic DNA to be more accessible to MNNG alkylation. Further analysis demonstrated chromatin decondensation in PARG null-TS cells as visualized by electron microscopy. In addition, treatment with MNNG led to an increase in O6- methylguanine levels in PARG null-TS cells compared to wild-type, which demonstrates increased DNA alkylation in the absence of PARG. Taken together, we provide compelling evidence that the absence of PARG leads to chromatin decondensation, which in turn leads to increased amounts of DNA alkylation and cell death induced by low doses of MNNG. Therefore, combination therapy of PARG inhibition and a DNA- alkylating agent is a potential treatment to induce the death of cancer cells.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, Washington State University, Pullman, WA 99164, USA.
authors.forename: Yiran
authors.initials: Y
authors.lastname: Zhou
authors.forename: Xiaoxing
authors.initials: X
authors.lastname: Feng
authors.forename: David W
authors.initials: DW
authors.lastname: Koh
mesh_terms: D000477:Alkylating Agents / Q000494:pharmacology*; D000478:Alkylation / Q000187:drug effects; D000818:Animals; D016923:Cell Death / Q000187:drug effects; D002478:Cells, Cultured; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism*; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004357:Drug Synergism; D053595:Embryonic Stem Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D006026:Glycoside Hydrolases / Q000037:antagonists & inhibitors*; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D009604:Nitrosoguanidines / Q000494:pharmacology*
chemical_list: D000477:Alkylating Agents; D002843:Chromatin; D006657:Histones; D009604:Nitrosoguanidines; D004247:DNA; D006026:Glycoside Hydrolases; C022407:poly ADP-ribose glycohydrolase