Photons for Therapy: Targeted Photodynamic Therapy for Infected and Contaminated Wounds

Introduction: Battlefield wounds are frequently contaminated with pathogenic microorganisms present on uniforms and skin. Although the development of serious infections can often be prevented by antibiotics, the rise in worldwide incidence of multiply antibiotic-resistant bacteria necessitates the discovery of alternative methods. In addition, traumatic wounds and burns may contain non-perfused tissue where antibiotics cannot penetrate efficiently. The possibility also exists of the use of biological weapons with unknown antibiotic susceptibility. Rationale: Previously workers have used photodynamic therapy to kill bacteria in vitro, but the use of this approach has seldom been reported in vivo in animal models of infection. We report on the use of a targeted polycationic photosensitizer conjugate between poly-L-lysine and chlorin(e6) that can penetrate the Gram (-) outer membrane together with harmless red laser light to kill Escherichia coli and Pseudomonas aeruginosa infecting excisional wounds in mice. Methods and Results: We used genetically engineered luminescent bacteria that allowed the infection to be imaged in mouse wounds using a sensitive CCD camera. Wounds were infected with 5x10 bacteria, followed by application of the conjugate in solution and illumination with red light. There was a light-dose dependent loss of luminescence as measured by image analysis in the wound treated with conjugate and light, not seen in control wounds. This strain of E. coli is non-invasive and the infection in untreated wounds spontaneously resolved in a few days and all wounds healed equally well showing the photodynamic treatment did not damage the host tissue. P. aeruginosa is highly invasive and mice with photosensitizer alone, light alone or untreated infected wounds all died while 90% of PDT treated mice survived. Wounds treated with PDT healed significantly better than those treated with an alternative antimicrobial (silver nitrate). We then treated mice with an infection caused by Staphylococcus aureus that had been allowed to grow in abscesses below the skin. Conjugate injected into the infected area together with surface illumination successfully killed the bacteria. Conclusions: In view of the development of cheap portable light sources PDT may have a role to play in preventing and treating infection in combat wounds. 1.0 INTRODUCTION Photodynamic therapy (PDT) is a therapy for cancer and other diseases that has received regulatory approvals for several indications in many countries [1]. Its use as a cancer treatment is based on the observation that Paper presented at the RTO HFM Symposium on “Combat Casualty Care in Ground Based Tactical Situations: Trauma Technology and Emergency Medical Procedures”, held in St. Pete Beach, USA, 16-18 August 2004, and published in RTO-MP-HFM-109. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 01 SEP 2004 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Photons for Therapy: Targeted Photodynamic Therapy for Infected and Contaminated Wounds 5a. CONTRACT NUMBER