Repurposing auranofin for the treatment of cutaneous staphylococcal infections

Abstract

The scourge of multidrug-resistant bacterial infections necessitates the urgent development of novel antimicrobials to address this public health challenge. Drug repurposing is a proven strategy to discover new antimicrobial agents; given that these agents have undergone extensive toxicological and pharmacological analysis, repurposing is an effective method to reduce the time, cost and risk associated with traditional antibiotic innovation. In this study, the in vitro and in vivo antibacterial activities of an antirheumatic drug, auranofin, was investigated against multidrug-resistant Staphylococcus aureus. The results indicated that auranofin possesses potent antibacterial activity against all tested strains of S. aureus, including meticillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA), with minimum inhibitory concentrations (MICs) ranging from 0.0625μg/mL to 0.125μg/mL. In vivo, topical auranofin proved superior to conventional antimicrobials, including fusidic acid and mupirocin, in reducing the mean bacterial load in infected wounds in a murine model of MRSA skin infection. In addition to reducing the bacterial load, topical treatment of auranofin greatly reduced the production of inflammatory cytokines, including tumour necrosis factor-α (TNFα), interleukin-6 (IL-6), interleukin-1 beta (IL-1β) and monocyte chemoattractant protein-1 (MCP-1), in infected skin lesions. Moreover, auranofin significantly disrupted established in vitro biofilms of S. aureus and Staphylococcus epidermidis, more so than the traditional antimicrobials linezolid and vancomycin. Taken together, these results support that auranofin has potential to be repurposed as a topical antimicrobial agent for the treatment of staphylococcal skin and wound infections.

Keywords: Auranofin; Inflammatory cytokines; Multidrug resistance; Repurposing; Topical antimicrobials.

Fig. 1

Efficacy of treatment of meticillin-resistant Staphylococcus aureus (MRSA) murine skin lesions with auranofin 0.5%, 1% and 2%, linezolid and clindamycin (25 mg/kg), mupirocin (2%), fusidic acid (2%) and petroleum jelly (control). Statistical analysis was performed by the two-tailed Student's t-test. *^,# P-values of ≤0.05 were considered significant; auranofin was compared both with controls (*) and with antibiotics (^#).

Fig. 2

Effect of auranofin on inflammatory cytokines in meticillin-resistant Staphylococcus aureus (MRSA) skin lesions with auranofin 0.5%, 1% and 2%, linezolid and clindamycin (25 mg/kg), mupirocin (2%), fusidic acid (2%) and petroleum jelly (control). Statistical analysis was performed by the two-tailed Student's t-test. * P-values of ≤0.05 were considered significant. IL-6, interleukin-6; TNFα, tumour necrosis factor-α; IL-1β; interleukin-1 beta; MCP-1, monocyte chemoattractant protein-1.

Fig. 3

Synergistic activity of auranofin in combination with three topical antimicrobials (mupirocin, retapamulin and fusidic acid).

Fig. 4

Activity of auranofin against planktonic persister cells and established biofilms of Staphylococcus aureus and Staphylococcus epidermidis. (A) Effect of auranofin on planktonic S. aureus persister cells. (B) Effect of auranofin and control antibiotics (vancomycin and linezolid) on established biofilms of S. aureus and S. epidermidis. Statistical analysis was performed using the two-tailed Student's t-test. *^,# P-values of ≤0.05 were considered significant; auranofin was compared both with controls (*) and with antibiotics (^#). MIC, minimum inhibitory concentration.

Fig. 5

Cytotoxicity assay in human keratinocyte (HaCaT) cells. IC₅₀, concentration of auranofin required to inhibit 50% of HaCaT cell growth.