Repurposing the Nonsteroidal Anti-inflammatory Drug Diflunisal as an Osteoprotective, Antivirulence Therapy for Staphylococcus aureus Osteomyelitis

Abstract

dStaphylococcus aureus osteomyelitis is a common and debilitating invasive infection of bone. Treatment of osteomyelitis is confounded by widespread antimicrobial resistance and the propensity of bacteria to trigger pathological changes in bone remodeling that limit antimicrobial penetration to the infectious focus. Adjunctive therapies that limit pathogen-induced bone destruction could therefore limit morbidity and enhance traditional antimicrobial therapies. In this study, we evaluate the efficacy of the U.S. Food and Drug Administration-approved, nonsteroidal anti-inflammatory (NSAID) compound diflunisal in limiting S. aureus cytotoxicity toward skeletal cells and in preventing bone destruction during staphylococcal osteomyelitis. Diflunisal is known to inhibit S. aureus virulence factor production by the accessory gene regulator (agr) locus, and we have previously demonstrated that the Agr system plays a substantial role in pathological bone remodeling during staphylococcal osteomyelitis. Consistent with these observations, we find that diflunisal potently inhibits osteoblast cytotoxicity caused by S. aureus secreted toxins independently of effects on bacterial growth. Compared to commonly used NSAIDs, diflunisal is uniquely potent in the inhibition of skeletal cell death in vitro. Moreover, local delivery of diflunisal by means of a drug-eluting, bioresorbable foam significantly limits bone destruction during S. aureus osteomyelitis in vivo. Collectively, these data demonstrate that diflunisal potently inhibits skeletal cell death and bone destruction associated with S. aureus infection and may therefore be a useful adjunctive therapy for osteomyelitis. Osteomyelitis is an invasive infection of bone, most frequently caused by the Gram-positive pathogen Staphylococcus aureus (1). Treatment of osteomyelitis is confounded by an increasing prevalence of antimicrobial resistance, as well as the propensity for patients to develop pathological changes in bone remodeling that limit antimicrobial penetration to the infectious focus. For this reason, patients suffering from osteomyelitis often undergo multiple surgical debridements to remove infected and necrotic bone, while also receiving prolonged antimicrobial therapy (1, 2). Despite these aggressive measures, a subset of patients with acute osteomyelitis will progress to chronic infection, which is highly refractory to further intervention and may require months to years of antimicrobial treatment. Moreover, although adult osteomyelitis is often secondary to comorbidities such as trauma, surgery, diabetes, or vascular insufficiency, hematogenous osteomyelitis in previously healthy children is more prevalent in the current era of community-acquired staphylococcal infections (3). Children are inherently vulnerable to adverse outcomes during osteomyelitis given the presence of active epiphyseal plates and thus have the potential to develop limb-length discrepancy (4). Taken together, these facts illustrate the need for adjunctive therapies that lessen the morbidity ...

Therapeutics and delivery vehicles for local treatment of osteomyelitis

“…82 Some identified quorum sensing inhibitors include savirin, 83 Hamamelitannin, 82,84 farnesol, [85][86][87] and the nonsteroidal anti-inflammatory drug (NSAID) diflunisal. 88 In one study, the antimicrobials cefazolin, cefalonium, cephalexin, cefoxitin, daptomycin, linezolid, tobramycin, and fusidic acid were tested alone or with Hamamelitannin against in vitro S. aureus biofilms. In all cases except fusidic acid, treatment with the quorum sensing inhibitor was superior to antimicrobial monotherapy.…”

Pharmacological Targeting of the Host–Pathogen Interaction: Alternatives to Classical Antibiotics to Combat Drug-Resistant Superbugs

“…Treatment with naringenin, a flavonoid present in grapefruits and tomatoes, reduced transcription of S. aureus genes encoding AgrA and alpha-toxin, attenuating alpha-toxin mediated injury to alveolar epithelial cells, and reduced pulmonary inflammation and injury in a mouse pneumonia model [44]. Very recently, the nonsteroidal anti-inflammatory drug diflunisal was shown to block S. aureus AgrA transcriptional regulation of small peptide toxin virulence factors known as phenol soluble modulins (PSMs); diflunisal treatment reduced PSM production and diminished bone destruction in a murine osteomyelitis model of infection [45]. …”

Advances in the local and targeted delivery of anti-infective agents for management of osteomyelitis

“…A recent study found that the FDA-approved nonsteroidal anti-inflammatory drug diflunisal inhibits the agr quorum-sensing system and downstream toxin production through inhibition of AgrA’s binding to the promoter P3 (possibly interrupting the phosphorylation of AgrC) to induce the transcription of various virulence factors [66]. Local delivery of diflunisal during experimental osteomyelitis was highly efficacious in limiting bone destruction in an experimental model of osteomyelitis, despite having no significant effect on bacterial burdens at the site of infection [69]. In vitro , diflunisal decreased the production of osteolytic toxins known as phenol-soluble modulins, providing a mechanistic basis for the decrease in cortical bone destruction in vivo [69].…”

“…Local delivery of diflunisal during experimental osteomyelitis was highly efficacious in limiting bone destruction in an experimental model of osteomyelitis, despite having no significant effect on bacterial burdens at the site of infection [69]. In vitro , diflunisal decreased the production of osteolytic toxins known as phenol-soluble modulins, providing a mechanistic basis for the decrease in cortical bone destruction in vivo [69]. Future studies will determine whether such an approach improves traditional antimicrobial therapy by limiting bone destruction and potentially improving antimicrobial penetration into infected tissues.…”