Veterinary trypanocidal benzoxaboroles are peptidase-activated prodrugs.

Federica Giordani,Mark C Field,Andrew W Pountain,Isabel M Vincent,Fernando Fernández-Cortés,Daniel Paape,Michael J Witty,Clément Regnault,Ning Zhang,Rosemary Peter,Eva Rico,Kevin D Read,Jonathan M Wilkes,Michael P Barrett,David Horn,Yvonne Freund,Justin J J Van Der Hooft,Liam J Morrison,Darren Y Edwards

doi:10.1371/journal.ppat.1008932

Abstract

Livestock diseases caused by Trypanosoma congolense, T. vivax and T. brucei, collectively known as nagana, are responsible for billions of dollars in lost food production annually. There is an urgent need for novel therapeutics. Encouragingly, promising antitrypanosomal benzoxaboroles are under veterinary development. Here, we show that the most efficacious subclass of these compounds are prodrugs activated by trypanosome serine carboxypeptidases (CBPs). Drug-resistance to a development candidate, AN11736, emerged readily in T. brucei, due to partial deletion within the locus containing three tandem copies of the CBP genes. T. congolense parasites, which possess a larger array of related CBPs, also developed resistance to AN11736 through deletion within the locus. A genome-scale screen in T. brucei confirmed CBP loss-of-function as the primary mechanism of resistance and CRISPR-Cas9 editing proved that partial deletion within the locus was sufficient to confer resistance. CBP re-expression in either T. brucei or T. congolense AN11736-resistant lines restored drug-susceptibility. CBPs act by cleaving the benzoxaborole AN11736 to a carboxylic acid derivative, revealing a prodrug activation mechanism. Loss of CBP activity results in massive reduction in net uptake of AN11736, indicating that entry is facilitated by the concentration gradient created by prodrug metabolism.

Highlights

Development of new drugs for infectious diseases has taken new urgency in recent years given the emergence and spread of antimicrobial resistance [1] that threatens global health
AN11736 is a member of the benzoxaborole class identified as a development candidate for animal African trypanosomiasis, a deadly livestock disease with huge economic
Our results indicate that AN11736 acts as a prodrug that, once inside trypanosomes, is cleaved by specific serine carboxypeptidases, creating a concentration gradient resulting in more parent drug entering the trypanosome cell

Summary

Introduction

Development of new drugs for infectious diseases has taken new urgency in recent years given the emergence and spread of antimicrobial resistance [1] that threatens global health. Drug resistant veterinary pathogens seriously compromise global food security. Animal African trypanosomiasis (AAT or nagana) affects millions of domestic animals each year [2] causing billions of dollars’ worth of lost productivity in a part of the world where food scarcity impacts the population heavily. Given the rise of resistance to existing trypanocides [3], the Global Alliance for Livestock Veterinary Medicines has developed a programme to seek new drugs for AAT (https://www.galvmed.org/livestock-and-diseases/livestock-diseases/animal-africantrypanosomosis/). Acoziborole is undergoing Phase II/III clinical trials for human African trypanosomiasis (HAT) [9, 10], a neglected tropical disease with unmet medical needs [11]. Acoziborole may play a key role in the HAT elimination programme [12], being active against both bloodstream and CNS involved stages of the disease after a single, oral dose [9]

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Results

Conclusion