A Subset Screen of the Compounds Australia Scaffold Library Identifies 7-Acylaminodibenzoxazepinones as Potent and Selective Hits for Anti-Giardia Drug Discovery

Abstract

On an annual basis the flagellate protozoan, Giardia duodenalis, is responsible for an estimated one billion human infections of which approximately two hundred million cause disease. However, the treatment of Giardia infections is reliant on a small group of chemotherapeutic classes that have a broad spectrum of antimicrobial activity and increasing treatment failure rates. To improve this situation, we need new drugs. In this study we screened the Compounds Australia Scaffolds Library for compounds with potent and selective activity against these parasites. Unlike previous drug discovery efforts that have focused on drug repurposing, this library is comprised of commercially available synthetic compounds arranged into lead-like scaffolds to facilitate structure activity relationship assessments and de novo drug discovery. A screen of 2451 compounds in this library identified 40 hits (>50% inhibitory activity at 10 µM, over 48 h). Secondary testing identified three compounds with IC50 values <1 μM and >50-fold selectivity for parasites over mammalian cells and a hit series, CL9406, comprising compounds with potent (lowest IC50 180 nM) and selective activity for Giardia parasites. The most promising compound in this series, SN00797640, displayed selective activity against assemblage A, B, and metronidazole resistant parasites which was parasiticidal (minimum lethal concentration 625 nM) and synergistic with albendazole. SN00797640 was well-tolerated when administered to mice at doses of 50 mg/kg daily for three days paving the way for pre-clinical in vivo activity assessment.

Thieno[3,2-b]pyrrole 5-carboxamides as potent and selective inhibitors of Giardia duodenalis

“…Given the activity of 1 in previously published anti- Giardia activity assays ( Hart et al, 2022 ), the anti- Giardia activity of all CL9569 scaffold compounds was assessed against assemblage B BRIS/91/HEPU/1279 trophozoites. These experiments identified three additional compounds within series ( 2 , 3 and 12 ; Table 1 ) with activity (IC 50 values ≤ 10 μM) against G. duodenalis trophozoites.…”

“…Growth inhibition was calculated as a percentage relative to vehicle controls minus media background and IC 50 values were determined using non-linear regression curve analysis (variable slope, 4 parameters; GraphPad Prism). Minimum lethal concentration (MLC) assessments were performed as previously described ( Hart et al, 2022 ) with all experiments conducted at least three times in duplicate.…”

“…The in vivo tolerability of 2c was assessed in female outbred Swiss mice (Animal Research Centre, Perth Australia, ethics approval ESK/01/17/AEC and GRIDD/03/21/AEC (Griffith University approved April 10, 2017 and March 21, 2021 respectively) using the dose escalation protocol previously described ( Hart et al, 2022 ). Groups of three mice were used to assess increasing doses of each compound and all mice were assessed for adverse effects for seven days post compound administration.…”

“…To identify new treatment options for giardiasis, our group recently assessed the Compounds Australia Scaffold Library for new chemotypes with selective anti- Giardia activity ( Hart et al, 2022 ). In this work we extended these studies by examining the anti- Giardia activity of series CL9569 compounds.…”

“…In this work we extended these studies by examining the anti- Giardia activity of series CL9569 compounds. This compound series was not examined in the original study, but representative compound SN00798525 ( 1 ) demonstrated promising potency (IC 50 1.2 μM) and selectivity for Giardia parasites over human cells (IC 50 > 10 μM) and bacteria (IC 50 > 50 μM) ( Hart et al, 2022 ). To build on this work, we assessed the remaining Compounds Australia CL9569 scaffold compounds for anti- Giardia activity.…”