Long-acting aldicarb hydrolase as a medical countermeasure for aldicarb poisoning

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As one of the Chemicals of Concern (CoC) identified by the US Department of Homeland Security, aldicarb belongs to the Cholinergic Warfare and Pesticides category. As the most toxic carbamate pesticide – a potent, fast-acting inhibitor of acetylcholinesterase (AChE), aldicarb is readily absorbed from all routes of exposure, including oral and dermal exposure. In all species tested, the acute oral toxicities of aldicarb are similar. Due to its physical properties documented in literature, aldicarb could be used by terrorists to cause mass casualty. Organophosphorus (OP) warfare/pesticides and carbamate pesticides have a common mode of action for their neurotoxicity as AChE inhibitors. Currently available options for treating this type of poisoning, such as administration of atropine or co-administration of atropine and pralidoxime (2-PAM), have limited efficacy. There have been extensive efforts in development of improved options for treatment of OP poisoning. Relatively less studies have been carried out in development of aldicarb poisoning treatment. Reported studies indicated that 2-PAM had neither positive nor negative effects on survival in animal studies on aldicarb intoxication. This outcome is understandable, as 2-PAM was developed to reactivate phosphorylated AChE (an intermediate formed from the inhibition reaction of AChE with an OP), but not carbamylated AChE (an intermediate formed from the reaction of AChE with a carbamate like aldicarb). It is highly desired to develop a new, effective post- exposure treatment option for aldicarb poisoning. This investigation will focus on rational design and discovery of an engineered enzyme capable of rapidly and efficiently detoxifying aldicarb as a catalytic aldicarb bioscavenger for aldicarb poisoning. As an effective bioscavenger, it must be able to react with aldicarb more rapidly than AChE so as to protect AChE from reaction (carbamylation) with aldicarb. In preliminary studies, we have demonstrated that an Fc-fused cocaine hydrolase (Fc-CocH), developed previously in our lab for treatment of cocaine use disorders (CUDs), can more potently bind with aldicarb than with AChE and wild-type butyrylcholinesterase (BChE) and can also catalyze aldicarb hydrolysis. In further in vivo rescue experiment, this Fc-CocH protein powerfully rescued all mice that had been injected intraperitoneally (IP) with a lethal dose (~2 × LD50) of aldicarb. With the encouraging preliminary data, taking advantage of our positive experience in preclinical and clinical development of Fc-CocHs, we propose to first evaluate an in-house library of Fc-CocHs for their activities with aldicarb in order to select the one with the highest catalytic activity for aldicarb hydrolysis and the best overall in vivo profiles, followed by lead optimization to optimize its catalytic activity against aldicarb, substrate selectivity, post-exposure in vivo efficacy, and toxicity/immunogenicity profiles. Accomplishment of this investigation will deliver a couple of safe, highly efficient aldicarb hydrolases that are promising for treatment of aldicarb poisoning. The one with the best overall in vivo profiles will serve as a clinical candidate, and the second best will serve as a backup, for further preclinical and clinical development in the future.