BACKGROUND: The antibiotic-peptide ^99mTc-alafosfalin was assessed as an infection imaging agent in Staphylococcus aureas infected mice by comparison with ^99mGa-citrate, and also examined for influence of septic status on tracer biodistribution by comparison with normal mice.
MATERIAL AND METHODS: Intramuscular doses of S. aureus were administered into the right thigh muscle of mice and the infection was allowed to develop for 20 hours. In separate experiments, ^99mTc-alafosfalin and ⁶⁷Ga-citrate were subsequently administered and allowed to localise. Quantitative organ distribution studies were performed in conjunction with scintigraphic images at 1 and 4 hours post injection. An additional biodistribution with ^99mTc-alafosfalin in normal mice was also performed.
RESULTS: ^99mTc-alafosfalin was predominantly renal excreted, with low liver, intestine and bone uptake. There was no difference in the uptake of these organs when infected mice were compared with normal mice. ^99mTc-alafosfalin activity in the intestine at 1 and 4 hours was substantially less than ⁶⁷Ga-citrate. For ^99mTc-alafosfalin, infected/non-infected thigh ratios of 2.8/1.0 and 3.6/1.0 were determined at 1 and 4 hours post injection respectively. ⁶⁷Ga-citrate gave ratios of 1.6/1.0 and 3.7/1.0 at the corresponding time points.
CONCLUSIONS: ^99mTc-alafosfalin uptake was more rapid than ⁶⁷Ga-citrate, yet diffuse at the infectious sites in mice. The small and juvenile mouse model resulted in uptake of the phosphonic acid tracer by active bone growth areas which may be a disadvantage. This ^99mTc-antibiotic peptide has potential as an infection imaging agent, and will be investigated further in another rodent infection model in the future.