Elastin-like polypeptide incorporated thermally sensitive liposome improve antibiotic therapy against musculoskeletal bacterial pathogens.

Musculoskeletal infections caused by bacteria such as Staphylococcus aureus and Pseudomonas aeruginosa in children and adults can lead to adverse outcomes including a need for extensive surgical debridement and limb amputation. To enable targeted antimicrobial release in infected tissues, the objective of this study was to design and investigate novel elastin-like polypeptide (ELP)-based thermally sensitive liposomes in vitro. ELP biopolymers can change their phase behaviour at higher temperatures. We hypothesised that ELP-TSL will improve therapeutic efficacy by releasing antimicrobial payloads locally at higher temperatures (≥39 °C). ELP-TSL library were formulated by varying cholesterol and phospholipid composition by the thin film and extrusion method. A broad-spectrum antimicrobial (Ciprofloxacin or Cipro) was encapsulated inside the liposomes by the ammonium sulphate gradient method. Cipro release from ELP-TSLs was assessed in physiological buffers containing ∼25% serum by fluorescence spectroscopy, and efficacy against Staphylococcus aureus and Pseudomonas aeruginosa was assessed by disc diffusion and planktonic assay. Active loading of Cipro achieved an encapsulation efficiency of 40-70% in the ELP-TSL depending upon composition. ELP-TSL Cipro release was near complete at ≥39 °C; however, the release rates could be delayed by cholesterol. Triggered release of Cipro from ELP-TSL at ∼42 °C induced significant killing of S. aureus and P. aeruginosa compared to 37 °C. Our in vitro data suggest that ELP-TSL may potentially improve bacterial wound therapy in patients.

Targeted antibiotic delivery using low temperature-sensitive liposomes and magnetic resonance-guided high-intensity focused ultrasound hyperthermia.

Chronic non-healing wound infections require long duration antibiotic therapy, and are associated with significant morbidity and health-care costs. Novel approaches for efficient, readily-translatable targeted and localised antimicrobial delivery are needed. The objectives of this study were to 1) develop low temperature-sensitive liposomes (LTSLs) containing an antimicrobial agent (ciprofloxacin) for induced release at mild hyperthermia (∼42 °C), 2) characterise in vitro ciprofloxacin release, and efficacy against Staphylococcus aureus plankton and biofilms, and 3) determine the feasibility of localised ciprofloxacin delivery in combination with MR-HIFU hyperthermia in a rat model. LTSLs were loaded actively with ciprofloxacin and their efficacy was determined using a disc diffusion method, MBEC biofilm device, and scanning electron microscopy (SEM). Ciprofloxacin release from LTSLs was assessed in a physiological buffer by fluorescence spectroscopy, and in vivo in a rat model using MR-HIFU. Results indicated that < 5% ciprofloxacin was released from the LTSL at body temperature (37 °C), while >95% was released at 42 °C. Precise hyperthermia exposures in the thigh of rats using MR-HIFU during intravenous (i.v.) administration of the LTSLs resulted in a four fold greater local concentration of ciprofloxacin compared to controls (free ciprofloxacin + MR-HIFU or LTSL alone). The biodistribution of ciprofloxacin in unheated tissues was fairly similar between treatment groups. Triggered release at 42 °C from LTSL achieved significantly greater S. aureus killing and induced membrane deformation and changes in biofilm matrix compared to free ciprofloxacin or LTSL at 37 °C. This technique has potential as a method to deliver high concentration antimicrobials to chronic wounds.

High Intensity Focused Ultrasound (HIFU) Heating Improves Perfusion and Antimicrobial Efficacy in Mouse Staphylococcus Abscess.

Chronic wounds typically require long-duration treatment with a combination of antibiotics administered systemically. This incurs adverse side effects and can require aversive surgical treatments and limb amputations. To improve non-invasive antimicrobial therapy, the objective of this study was to investigate antimicrobial chemotherapy combined with high-intensity focused ultrasound (HIFU) heating (HT). A Staphylococcus aureus abscess (80 ± 30 mm3) was generated in the mouse flank region. Once the average temperature (~42 °C-46 °C) in the abscess was reached with HIFU-HT, a broad-spectrum antimicrobial (ciprofloxacin, 10 mg/kg) and perfusion marker (Evans blue dye, 40 mg/kg wt) were administered intravenously via the tail vein. Four hours later, mean abscess perfusion and colony-forming units (CFUs) per gram of abscess were determined. HIFU-HT increased abscess perfusion by ~2.5-fold (4 ± 0.6 µg/mL Evans blue) compared with control (1.5 ± 0.7 µg/mL), and improved antimicrobial efficacy to decrease percentage average survival of S. aureus by ~20% (46 ± 7 CFUs/g of abscess) versus that seen with ciprofloxacin alone (61 ± 4 CFU/g). Our in vivo data suggest that HIFU-HT can improve antimicrobial treatment responses against deep-seated bacteria in abscess wounds via enhanced perfusion.