ATI-2307 Exhibits Equivalent Antifungal Activity in Cryptococcus neoformans Clinical Isolates With High and Low Fluconazole IC50

Abstract

Half maximal inhibitory concentrations (IC50) to the experimental drug ATI-2307 and complete inhibition (IC90) of the common clinically used antifungal drug amphotericin B were determined by microbroth dilution assay for a collection of 69 clinical isolates of Cryptococcus neoformans from Uganda that had high fluconazole IC50 values. The majority of the clinical isolates tested had fluconazole IC50 at or above 8 µg/mL, but were susceptible to both amphotericin B (IC90 ≤1 μg/mL) and ATI-2307 (IC50 ≤0.0312 µg/mL). No correlation between increased fluconazole minimum inhibitory concentration (MIC) and ATI-2307 or amphotericin B MIC was observed, suggesting that the cellular changes impacting fluconazole susceptibility did not impact the effectiveness of ATI-2307. Our results suggest that ATI-2307 is a promising new antifungal drug for use in the context of high fluconazole or other antifungal drug MICs and/or in combination drug therapy regimens.

Lack of Association between Fluconazole Susceptibility and ERG11 Nucleotide Polymorphisms in Cryptococcus neoformans Clinical Isolates from Uganda

“…The geometric mean for the isolates was 5.1 μg/mL. Recommended fluconazole breakpoints for C. neoformans are not defined yet and as such, we considered IC 50 < 8 μg/mL low, and IC 50 ≥ 8 μg/mL high [ 11 ].…”

“…The goal of the present study was to determine the fluconazole susceptibility of C. neoformans clinical isolates from a Ugandan patient cohort and investigate the presence of SNPs in a highly conserved coding region of the ERG11 gene. The C. neoformans isolates in this study were classified as having either low IC 50 values (56.1%) or high IC 50 values (43.9%) based on the classification recommended by Gerlach et al [ 11 ]. The high incidence of fluconazole IC 50 values ≥ 8 µg/mL in this group of C. neoformans clinical isolates is consistent with surveillance data in sub-Saharan Africa and elsewhere over the past two decades, with an increase in MICs across many geographical regions [ 9 , 32 , 33 , 34 ].…”

“…This increased resistance poses a public health challenge, especially in Africa where fluconazole is widely prescribed and frequently used as a monotherapy for both consolidation and maintenance CM therapy [ 9 ]. In addition, the increasing trend of high fluconazole IC 50 values observed among C. neoformans clinical isolates in Uganda [ 8 , 11 ] underscores the need to review the current recommended fluconazole dosages for optimal therapeutic outcomes [ 33 ]. Studies have recommended 800 mg/day for consolidation therapy of patients infected with isolates that have high MICs as a mechanism to improve clinical outcomes [ 33 ].…”

“…A KN99α reference strain [ 26 ], with a known fluconazole IC 50 of 2 μg/mL was included as an inter-assay calibration reference in every MIC plate to verify accuracy across all of tthe MIC plates. IC 50 was defined as the first fluconazole drug concentration at which ≥50% of the growth was inhibited [ 11 ].…”

“…Currently, there are no interpretive breakpoints for in vitro antifungal susceptibility testing of C. neoformans and thus it is difficult to define phenotypes associated with fluconazole susceptibility and resistance [ 10 ]. Instead, clinical isolates are typically described as having low or high IC 50 values [ 11 ].…”