Photoimmuno-antimicrobial therapy for Staphylococcus aureus implant infection.

INTRODUCTION: Implant infections caused by Staphylococcus aureus are responsible for high mortality and morbidity worldwide. Treatment of these infections can be difficult especially when bacterial biofilms are involved. In this study we investigate the potential of infrared photoimmunotherapy to eradicate staphylococcal infection in a mouse model. METHODS: A monoclonal antibody that targets Wall Teichoic Acid surface components of both S. aureus and its biofilm (4497-IgG1) was conjugated to a photosensitizer (IRDye700DX) and used as photoimmunotherapy in vitro and in vivo in mice with a subcutaneous implant pre-colonized with biofilm of Staphylococcus aureus. A dose of 400 µg and 200 µg of antibody-photosensitizer conjugate 4497-IgG-IRDye700DXwas administered intravenously to two groups of 5 mice. In addition, multiple control groups (vancomycin treated, unconjugated IRDye700DX and IRDye700DX conjugated to a non-specific antibody) were used to verify anti-microbial effects. RESULTS: In vitro results of 4497-IgG-IRDye700DX on pre-colonized (biofilm) implants showed significant (p<0.01) colony-forming units (CFU) reduction at a concentration of 5 µg of the antibody-photosensitizer conjugate. In vivo, treatment with 4497-IgG-IRDye700DX showed no significant CFU reduction at the implant infection. However, tissue around the implant did show a significant CFU reduction with 400 µg 4497-IgG-IRDye700DX compared to control groups (p = 0.037). CONCLUSION: This study demonstrated the antimicrobial potential of photoimmunotherapy for selectively eliminating S. aureus in vivo. However, using a solid implant instead of a catheter could result in an increased bactericidal effect of 4497-IgG-IRDye700DX and administration locally around an implant (per operative) could become valuable applications in patients that are difficult to treat with conventional methods. We conclude that photoimmunotherapy could be a potential additional therapy in the treatment of implant related infections, but requires further improvement.

EGFR-Targeted Nanobody Functionalized Polymeric Micelles Loaded with mTHPC for Selective Photodynamic Therapy.

meta-Tetra(hydroxyphenyl)chlorin (mTHPC) is one of the most potent second-generation photosensitizers, clinically used for photodynamic therapy (PDT) of head and neck squamous cell carcinomas. However, improvements are still required concerning its present formulation (i.e., Foscan, a solution of mTHPC in ethanol/propylene glycol (40:60 w/w)), as mTHPC has the tendency to aggregate in aqueous media, e.g., biological fluids, and it has limited tumor specificity. In the present study, polymeric micelles with three different diameters (17, 24, and 45 nm) based on benzyl-poly(ε-caprolactone)-b-poly(ethylene glycol) (PCLn-PEG; n = 9, 15, or 23) were prepared with mTHPC loadings ranging from 0.5 to 10 wt % using a film-hydration method as advanced nanoformulations for this photosensitizer. To favor the uptake of the micelles by cancer cells that overexpress the epidermal growth factor receptor (EGFR), the micelles were decorated with an EGFR-targeted nanobody (named EGa1) through maleimide-thiol chemistry. The enhanced binding of the EGFR-targeted micelles at 4 °C to EGFR-overexpressing A431 cells, compared to low-EGFR-expressing HeLa cells, confirmed the specificity of the micelles. In addition, an enhanced uptake of mTHPC-loaded micelles by A431 cells was observed when these were decorated with the EGa1 nanobody, compared to nontargeted micelles. Both binding and uptake of targeted micelles were blocked by an excess of free EGa1 nanobody, demonstrating that these processes occur through EGFR. In line with this, mTHPC loaded in EGa1-conjugated PCL23-PEG (EGa1-P23) micelles demonstrated 4 times higher photocytotoxicity on A431 cells, compared to micelles lacking the nanobody. Importantly, EGa1-P23 micelles also showed selective PDT against A431 cells compared to the low-EGFR-expressing HeLa cells. Finally, an in vivo pharmacokinetic study shows that after intravenous injection, mTHPC incorporated in the P23 micelles displayed prolonged blood circulation kinetics, compared to free mTHPC, independently of the presence of EGa1. Thus, these results make these micelles a promising nanomedicine formulation for selective therapy.