Effect of auranofin combined with antineoplastic vorinostat on bactericidal activities against gram-negative bacteria and study on the target of auranofin

Abstract

Objective To find the target of auranofin with the antibacterial activity against gram-negative bacteria and to investigate the effect of the combination of auranofin and vorinostat on the antibacterial activity against gram-negative bacteria. Methods The strains of E. coli lacking thioredoxin reductase (TrxR) was used to find the target gene. The potential synergies of the combination of auranofin and vorinostat for E. coli strain, A. baumannii strain, P .aeruginosa strain, K. pneumonia strain and multidrug-resistant (MDR) A. baumannii strain were evaluated using susceptibility tests, micro-dilution checkerboard tests and time-kill studies. The genes related to Trx (trxA, trxB, trxC) and the gene expressed glutathione (gor) of E. coli BW25113 strains (WT) were separately knocked out to observe the effect of auranofin on minimum inhibitory concentration (MIC) and the time-kill kinetics of ΔtrxC and Δgor. Furthermore, the complemented strains (C-trxA, C-trxB, C-trxC, C-gor) were used to verify and define the genetic targets. Results According to the results of susceptibility tests, MICs of auranofin were 64 mg/L for E. coli strain BW25113 and K. pneumonia strain ATCC 43816, 128 mg/L for P. aeruginosa strain PA14 and 32 mg/L for both A. baumannii strain ATCC 17978 and A. baumannii strain AB5075. However, MICs of vorinostat are 512 mg/L for all isolates. The fractional inhibitory concentration indexes (FICIs) of the combination of auranofin and vorinostat for E. coli strain BW25113, A. baumannii strain ATCC 17978, MDR A. baumannii strain AB5075, K. pneumonia starin ATCC 43816 and P. aeruginosa strain PA14 were 0.313, 0.375, 0.375, 0.375, and 0.375, respectively, with all values <0.5, which showed synergy. In susceptibility tests of knockout strains, MICs of auranofin for ΔtrxC increased from 64 mg/L to 256 mg/L, decreased to 16 mg/L for Δgor, and no changes for ΔtrxA and ΔtrxB. Auranofin showed the same antibacterial activities against the complemented strains (C-trxC, C-gor) and E. col BW25113, which decreased by about 1.8 lg colong formins units (CFU)/mL of bacterial counts. However, the antibacterial activity of auranofin was significantly reduced for ΔtrxC, and decreased by<1 lg CFU/mL of bacterial counts. For Δgor, bacterial counts decreased 4.6 lg CFU/mL, and the antibacterial activity markedly increased. Conclusions The potential target gene of auranofin against gram-negative bacteria could be trxC, which provides new ideas and methods for the clinical treatment of multidrug-resistant gram-negative bacteria. Key words: Auranofin; Gram-negative bacteria; Thioredoxin reductase; Vorinostat; Synergy