Examination of effectiveness of chemical scavengers as therapeutics in organophosphate poisoning

Cholinergic crisis triggered by inhibition of cholinesterases via organophosphorus nerve agents (OP) and pesticides is treated with atropine and a reactivator of inhibited cholinesterase, called oxime. Multiple in vitro and in vivo studies demonstrated that this standard therapy may secure survival, but is insufficient in preventing incapacitation and lacks efficacy against several nerve agents and pesticides. Over the years, novel therapy approaches have been closely investigated with promising candidates being non-oxime reactivators and scavengers based on enzymes (bioscavengers) or small molecules. The low efficacy and immunological compatibility are main disadvantages of bioscavengers, thus the focus of the presented thesis is on a small molecule scavenger and a non-oxime reactivator. Detoxification of OP by cyclodextrins (CD), a macrocycle, was recognized early and optimized by inserting a nucleophilic group at the rim of the CD cavity. But the development of a more potent scavenger with a broad spectrum activity is closely linked to gathering information about inclusion complexes in cyclodextrins and their influencing factors. For that reason a structure-activity study with a 6-pyridinium oximate substituted β-cyclodextrin and alkyl methylphosphonofluoridates (sarin derivatives) was performed. Therefore, it can be concluded that the oxime substituted β-cyclodextrin better detoxifies sarin derivatives than native β-cyclodextrin, conforming involvement of the nucleophilic group in OP degradation. Good inclusion of OP in the CD cavity is correlated with a higher stability constant and improved degradation. Data imply efficient detoxification of alkyl methylphosphonofluoridates, thus the oxime substituent β-cyclodextrin is a promising small molecule scavenger for poisoning with G-type nerve agents. Another novel approach for the treatment of OP poisoning could be the use of small molecules as non-oxime reactivators. The antimalarial drug amodiaquine was identified as a promising candidate without further investigating its potential against a broad range of OP. Therefore amodiaquine’s interaction with human acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in presence or absence of OP was investigated and revealed a reversible inhibition of cholinesterases by amodiaquine and a mixed competitive-non-competitive inhibition type with AChE. Amodiaquine inhibited AChE more potently than BChE, wherefore a dose escalation was not possible. Reactivation of cyclosarin-, sarin-, and VX-inhibited cholinesterases by amodiaquine occurred, whereas reactivation of tabun-inhibited cholinesterase was insufficient. In a dynamic model, amodiaquine was administered prior to soman poisoning, but no significant beneficial effect on cholinesterases or reactivation of inhibited cholinesterases was observed. However, amodiaquine’s mode of action in reactivating OP-inhibited cholinesterases is not fully understood, but research efforts should continue in order to generate a more potent non-oxime reactivator. In summary, small molecules as scavengers and non-oxime reactivators have a promising potential as novel therapeutics for the treatment of OP poisoning. Still, further investigations are necessary and should progress on existing experiences.