title: Centrally acting oximes in reactivation of tabun-phosphoramidated AChE.
abstract: Organophosphates (OP) inhibit acetylcholinesterase (AChE, EC 3.1.1.7), both in peripheral tissues and central nervous system (CNS), causing adverse and sometimes fatal effects due to the accumulation of neurotransmitter acetylcholine (ACh). The currently used therapy, focusing on the reactivation of inhibited AChE, is limited to peripheral tissues because commonly used quaternary pyridinium oxime reactivators do not cross the blood brain barrier (BBB) at therapeutically relevant levels. A directed library of thirty uncharged oximes that contain tertiary amine or imidazole protonable functional groups that should cross the BBB as unionized species was tested as tabun-hAChE conjugate reactivators along with three reference oximes: DAM (diacetylmonoxime), MINA (monoisonitrosoacetone), and 2-PAM. The oxime RS150D [N-((1-(3-(2-((hydroxyimino)methyl)-1H-imidazol-1-yl)propyl)-1H-1,2,3-triazol-4-yl)methyl)benzamide] was highlighted as the most promising reactivator of the tabun-hAChE conjugate. We also observed that oximes RS194B [N-(2-(azepan-1-yl)ethyl)-2-(hydroxyimino)acetamide] and RS41A [2-(hydroxyimino)-N-(2-(pyrrolidin-1-yl)ethyl)acetamide], which emerged as lead uncharged reactivators of phosphylated hAChE with other OPs (sarin, cyclosarin and VX), exhibited only moderate reactivation potency for tabun inhibited hAChE. This implies that geometry of oxime access to the phosphorus atom conjugated to the active serine is an important criterion for efficient reactivation, along with the chemical nature of the conjugated moiety: phosphorate, phosphonate, or phosphoramidate. Moreover, modification of the active center through mutagenesis enhances the rates of reactivation. The phosphoramidated-hAChE choline-binding site mutant Y337A showed three-times enhanced reactivation capacity with non-triazole imidazole containing aldoximes (RS113B, RS113A and RS115A) and acetamide derivative (RS194B) than with 2PAM.
authors.affiliation: Institute for Medical Research and Occupational Health, HR-10001 Zagreb, Croatia. zkovarik@imi.hr
authors.forename: Zrinka
authors.initials: Z
authors.lastname: Kovarik
authors.forename: Nikolina
authors.initials: N
authors.lastname: Maček
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Sit
authors.forename: Zoran
authors.initials: Z
authors.lastname: Radić
authors.forename: Valery V
authors.initials: VV
authors.lastname: Fokin
authors.forename: K
authors.initials: K
authors.lastname: Barry Sharpless
authors.forename: Palmer
authors.initials: P
authors.lastname: Taylor
mesh_terms: D000110:Acetylcholinesterase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001812:Blood-Brain Barrier / Q000187:drug effects; D020134:Catalytic Domain / Q000235:genetics; D002800:Cholinesterase Inhibitors / Q000633:toxicity*; D002801:Cholinesterase Reactivators / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D004353:Drug Evaluation, Preclinical; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010755:Organophosphates / Q000633:toxicity*; D010091:Oximes / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D058851:GPI-Linked Proteins; D010755:Organophosphates; D010091:Oximes; D011994:Recombinant Proteins; C548244:ACHE protein, human; D000110:Acetylcholinesterase; C009374:tabun