Bicyclic azetidines target acute and chronic stages of Toxoplasma gondii by inhibiting parasite phenylalanyl t-RNA synthetase

Arthur Gonse,Manmohan Sharma,Stuart L Schreiber,Yong Fu,Joshua B Radke,Payal Mittal,Taher Uddin,Eamon Comer,Bruno Melillo,L David Sibley,Amit Sharma,Arnab K Chatterjee,Anil K Gupta

doi:10.1038/s41467-022-28108-y

Abstract

Toxoplasma gondii commonly infects humans and while most infections are controlled by the immune response, currently approved drugs are not capable of clearing chronic infection in humans. Hence, approximately one third of the world’s human population is at risk of reactivation, potentially leading to severe sequelae. To identify new candidates for treating chronic infection, we investigated a series of compounds derived from diversity-oriented synthesis. Bicyclic azetidines are potent low nanomolar inhibitors of phenylalanine tRNA synthetase (PheRS) in T. gondii, with excellent selectivity. Biochemical and genetic studies validate PheRS as the primary target of bicyclic azetidines in T. gondii, providing a structural basis for rational design of improved analogs. Favorable pharmacokinetic properties of a lead compound provide excellent protection from acute infection and partial protection from chronic infection in an immunocompromised mouse model of toxoplasmosis. Collectively, PheRS inhibitors of the bicyclic azetidine series offer promise for treatment of chronic toxoplasmosis.

Highlights

Toxoplasma gondii commonly infects humans and while most infections are controlled by the immune response, currently approved drugs are not capable of clearing chronic infection in humans
We analyzed a series of bicyclic azetidines for their ability to inhibit T. gondii growth in vitro as tachyzoites, to target bradyzoites from tissue cysts produced in vivo, and to protect against acute and chronic toxoplasmosis in a relevant mouse model
In light of prior studies demonstrating the efficacy of phenylalanine tRNA synthetase (PheRS) inhibitors against apicomplexan parasites[15,16,18], we assessed the activity of 28 structurally unique compounds from the bicyclic azetidine series to determine their activities against the type II ME49 strain expressing firefly luciferase (FLuc)[19] tachyzoites of T. gondii using a luciferase-based growth screen to determine half-maximal effective concentration (EC50) (Fig. 1a, Table S1)

Summary

Introduction

Toxoplasma gondii commonly infects humans and while most infections are controlled by the immune response, currently approved drugs are not capable of clearing chronic infection in humans. We analyzed a series of bicyclic azetidines for their ability to inhibit T. gondii growth in vitro as tachyzoites, to target bradyzoites from tissue cysts produced in vivo, and to protect against acute and chronic toxoplasmosis in a relevant mouse model. Several compounds in this series exhibited high potency and selectivity for inhibition of T. gondii PheRS and provided effective inhibition of parasite growth in vitro and in vivo. These findings suggest that PheRS inhibitors based on the bicyclic azetidine scaffold deserve further attention as multistage inhibitors of T. gondii

Methods

Results

Conclusion