Development of ebsulfur analogues as potent antibacterials against methicillin-resistant Staphylococcus aureus

Abstract

Antibiotic resistance is a worldwide problem that needs to be addressed. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the dangerous “ESKAPE” pathogens that rapidly evolve and evade many current FDA-approved antibiotics. Thus, there is an urgent need for new anti-MRSA compounds. Ebselen (also known as 2-phenyl-1,2-benzisoselenazol-3(2H)-one) has shown promising activity in clinical trials for cerebral ischemia, bipolar disorder, and noise-induced hearing loss. Recently, there has been a renewed interest in exploring the antibacterial properties of ebselen. In this study, we synthesized an ebselen-inspired library of 33 compounds where the selenium atom has been replaced by sulfur (ebsulfur derivatives) and evaluated them against a panel of drug sensitive and drug resistant S. aureus and non-S. aureus strains. Within our library, we identified three outstanding analogues with potent activity against all S. aureus strains tested (MIC values mostly ≤2 μg/mL), and numerous additional ones with overall very good to good antibacterial activity (1–7.8 μg/mL). We also characterized the time-kill analysis, anti-biofilm ability, hemolytic activity, mammalian cytotoxicity, membrane-disruption ability, and reactive oxygen species (ROS) production of some of these analogues.

Identification of Ebsulfur Analogues with Broad‐Spectrum Antifungal Activity

“…In our previousw ork, we have verified that all the compounds tested were at least 95 % pure by NMR and HRMS. [26] We used the commerciallyavailable AmB, FLC, ITC, POS, and VOR as positivec ontrols. The MIC values listed for the controls were either tested herein or acquired from some of our previously published manuscripts on unrelated antifungal agents.…”

“…Compounds 2b-d were systematically prepared to contain p-substituted halogen atoms that increasedi nb ulkiness with F < Cl < Br.T he SAR comparison for these compounds, however,w as flat with all three compounds generally displaying MIC values from 1.56-6.25 mgmL À1 .W e then tested the p-substituted isopropyl analogue (2e), which was previously found to be among the best ebsulfur antibacterial analogues. [26] Compound 2e displayed good MIC values (3.13-6.25 mgmL À1 )s imilarly to those of 2b-d.L astly,w e tested the p-ethinyl analogue( 2f)a nd found that 2f displayed mostly poor activity against Candida strains( ! 12.5 mgmL À1 ).…”

“…Lastly,w et ested the oxidized analogues 4e, 4f,a nd 4n.O xidizing the sulfur atom to sulfoxide completely abolish antifungal activity.T his finding was in accord with our previous report of these compounds as antibacterials and with other reportsi n the literature that the biological activity of ebselen( 1)a nd ebsulfur (2a)w as highly dependent on the SeÀNo rS ÀN bonds. [26,35] Ebselen has been reported to use the electrophilic SeÀNb ond to covalently bind to cysteine residues of multiple enzyme targets. [23] Invasive aspergillosis is highly correlated with fulminant development and poor prognosis.…”

“…We selected ebsulfur because we previouslyo bserved that this compound was bacteriostatic and we pondered whetherasimilarf ungistatic effect would be observed. [26] We commencedo ur study by dosing all of our tested compounds( 1, 2a, 3a,a nd AmB) at 1 their respective MIC values (Figure 2A). For ebsulfur (2a), although the MIC value for ebsulfur against strain Bw as greater than 12.5 mgmL À1 ,w ed ecided to test this compound at 12.5 mgmL À1 because we were concerned that higher concentration may lead to precipitation of the compounds.…”

“…[25] The ebsulfur or 1,2-benzisothiazol-3(2H)-one scaffold has been demonstrated to have av ery narrow spectrum of antibacterial activity [only really being active against methicillin-resistant Staphylococcusa ureus (MRSA)],i no ur previousw ork. [26] This scaffold is interesting because it is structurally very similar to ebselen( 1, Figure 1). Therefore, we hypothesized that ebsulfur (2a, Figure 1) and its analogues would have as afety profile similar to that of ebselen.…”