P092

The use of in vivo imaging technology to determine compound efficacy in a mouse lung infection model

Colin Osborne1, Alex Moffat2, Charles Dean1, Angela Woods1, Ruth Caughlan1, Ellie Growcott3, Kathy Banner3. 1Novartis Institutes for BioMedical Research Inc, Cambridge, MA, United States, 2University of Bristol, Bristol, United Kingdom, 3Novartis Institutes for BioMedical Research Inc, Horsham, United Kingdom.

Pseudomonas aeruginosa lung infections are a major cause of morbidity and mortality in cystic fibrosis (CF) patients (Lyczak et al, 2002). Rodent lung infection models are an important tool for testing novel therapeutics against the infectious component of CF. The objective of this study was to investigate the use of a bacterial luminescence based imaging technology as a means of evaluating compound efficacy in a mouse lung infection model. The application of this technology would allow the same animal to be imaged over time, acting as its own control, and serve to reduce animal numbers required for efficacy experiments.

Female balb/c mice (18-20g, n = 5 per group) were made neutropenic by pre-treatment with cyclophosamide (4 days, 150 mg/kg intraperitoneally (i.p.) and 1 day, 100 mg/kg i.p., prior to infection), then infected intranasally (50 μl of approx. 1 x 105 cfu/mouse) with strains of P. aeruginosa that had been tagged with constitutively expressed luxCDABE (luciferase) (Pa-lux). Two different strains of Pa-lux were investigated. Two hours post infection, animals were treated subcutaneously with ciprofloxacin (10 and 20 mg/kg) with control animals receiving vehicle (saline) alone. Imaging and microbial analysis of harvested infected lungs was carried out 24 hours post treatment. Mice were imaged under isoflurane anaesthesia using the Xenogen IVIS-100 system. For bacterial quantification, mice were euthanized by carbon dioxide asphyxiation, the lungs aseptically removed and homogenized, and then plated on blood agar plates for bacterial colony forming unit (cfu) determination. Bacterial levels in vehicle treated mice were over log10 9.3 for both strains and a clear reduction in cfu/lung was found after ciprofloxacin treatment (>log10 4 at doses of 20 mg/kg). Imaging also showed a significant difference in bioluminescent signal intensity between vehicle and compound treated animals. Vehicle treated animals gave a signal of approximately log10 8 photons/sec/cm2 with ciprofloxacin treatment at 20 mg/kg giving a log10 2.5 to 3 reduction, depending on the strain of Pa-lux used. A dose response in both cfu/lung and photons/sec/cm2 was observed when lower doses of ciprofloxacin were investigated.

These results show that in vivo imaging can be an effective method of evaluating compound efficacy in a mouse infection model. This technology could also be utilised to evaluate the kinetics of the infection and treatment.

Lyczak, J.B. et al. (2002) Clin Microbiol Rev 15, 194-222