title: Mechanism of interaction of novel uncharged, centrally active reactivators with OP-hAChE conjugates.
abstract: A library of more than 200 novel uncharged oxime reactivators was used to select and refine lead reactivators of human acetylcholinesterase (hAChE) covalently conjugated with sarin, cyclosarin, VX, paraoxon and tabun. N-substituted 2-hydroxyiminoacetamido alkylamines were identified as best reactivators and reactivation kinetics of the lead oximes, RS41A and RS194B, were analyzed in detail. Compared to reference pyridinium reactivators, 2PAM and MMB4, molecular recognition of RS41A reflected in its Kox constant was compromised by an order of magnitude on average for different OP-hAChE conjugates, without significant differences in the first order maximal phosphorylation rate constant k(2). Systematic structural modifications of the RS41A lead resulted in several-fold improvement with reactivator, RS194B. Kinetic analysis indicated K(ox) reduction for RS194B as the main kinetic constant leading to efficient reactivation. Subtle structural modifications of RS194B were used to identify essential determinants for efficient reactivation. Computational molecular modeling of RS41A and RS194B interactions with VX inhibited hAChE, bound reversibly in Michaelis type complex and covalently in the pentacoordinate reaction intermediate suggests that the faster reactivation reaction is a consequence of a tighter RS194B interactions with hAChE peripheral site (PAS) residues, in particular with D74, resulting in lower interaction energies for formation of both the binding and reactivation states. Desirable in vitro reactivation properties of RS194B, when coupled with its in vivo pharmacokinetics and disposition in the body, reveal the potential of this oxime design as promising centrally and peripherally active antidotes for OP toxicity.
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California at San Diego, La Jolla, CA 92093-0650, USA. zradic@ucsd.edu
authors.forename: Zoran
authors.initials: Z
authors.lastname: Radić
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Sit
authors.forename: Edzna
authors.initials: E
authors.lastname: Garcia
authors.forename: Limin
authors.initials: L
authors.lastname: Zhang
authors.forename: Suzana
authors.initials: S
authors.lastname: Berend
authors.forename: Zrinka
authors.initials: Z
authors.lastname: Kovarik
authors.forename: Gabriel
authors.initials: G
authors.lastname: Amitai
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: D000081:Acetamides / Q000737:chemistry / Q000494:pharmacology; D000110:Acetylcholinesterase / Q000737:chemistry / Q000378:metabolism*; D002800:Cholinesterase Inhibitors / Q000633:toxicity; D002801:Cholinesterase Reactivators / Q000737:chemistry / Q000494:pharmacology*; D004353:Drug Evaluation, Preclinical; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D010755:Organophosphates / Q000633:toxicity; D009943:Organophosphorus Compounds / Q000633:toxicity; D010091:Oximes / Q000737:chemistry / Q000494:pharmacology*; D010261:Paraoxon / Q000633:toxicity; D012524:Sarin / Q000633:toxicity
chemical_list: D000081:Acetamides; D002800:Cholinesterase Inhibitors; D002801:Cholinesterase Reactivators; D058851:GPI-Linked Proteins; D010755:Organophosphates; D009943:Organophosphorus Compounds; D010091:Oximes; C572498:RS194B; C572497:RS41A; D012524:Sarin; C548244:ACHE protein, human; D000110:Acetylcholinesterase; D010261:Paraoxon; C009374:tabun; C053914:cyclohexyl methylphosphonofluoridate