title: Modulation of the ribonucleotide reductase M1-gemcitabine interaction in vivo by N-ethylmaleimide.
abstract: Ribonucleotide reductase M1 (RRM1) is the regulatory subunit of the holoenzyme that catalyzes the conversion of ribonucleotides to 2'-deoxyribonucleotides. Its function is indispensible in cell proliferation and DNA repair. It also serves as a biomarker of therapeutic efficacy of the antimetabolite drug gemcitabine (2',2'-difluoro-2'-deoxycytidine) in various malignancies. However, a mechanistic explanation remains to be determined. This study investigated how the alkylating agent N-ethylmaleimide (NEM) interacts with the inhibitory activity of gemcitabine on its target protein RRM1 in vivo. We found, when cells were treated with gemcitabine in the presence of NEM, a novel 110 kDa band, along with the 90 kDa native RRM1 band, appeared in immunoblots. This 110 kDa band was identified as RRM1 by mass spectrometry (LC-MS/MS) and represented a conformational change resulting from covalent labeling by gemcitabine. It is specific to gemcitabine/NEM, among 11 other chemotherapy drugs tested. It was also detectable in human tumor xenografts in mice treated with gemcitabine. Among mutations of seven residues essential for RRM1 function, C218A, C429A, and E431A abolished the conformational change, while N427A, C787A, and C790A diminished it. C444A was unique since it was able to alter the conformation even in absence of gemcitabine treatment. We conclude that the thiol alkylator NEM can stabilize the gemcitabine-induced conformational change of RRM1, and this stabilized RRM1 conformation has the potential to serve as a specific biomarker of gemcitabine's therapeutic efficacy.
authors: Developmental Therapeutics Program, Karmanos Cancer Institute, Detroit, MI 48201, USA.
authors: Zhengming
authors: Z
authors: Chen
authors: Jun
authors: J
authors: Zhou
authors: Yingtao
authors: Y
authors: Zhang
authors: Gerold
authors: G
authors: Bepler
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D054316:Biomarkers, Pharmacological / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain / Q000187:drug effects; D045744:Cell Line, Tumor; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D015195:Drug Design; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008815:Mice, Inbred Strains; D011487:Protein Conformation / Q000187:drug effects; D012262:Ribonucleoside Diphosphate Reductase; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D023041:Xenograft Model Antitumor Assays; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D054316:Biomarkers, Pharmacological; D004791:Enzyme Inhibitors; D025521:Tumor Suppressor Proteins; D003841:Deoxycytidine; C475286:RRM1 protein, human; D012262:Ribonucleoside Diphosphate Reductase; D005033:Ethylmaleimide; D000093542:Gemcitabine