Original Comparison of 99mTc-alafosfalin

BACKGROUND: The antibiotic-peptide 99mTc-alafosfalin was assessed as an infection imaging agent in Staphylococcus au-reas 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 ex-periments, 99mTc-alafosfalin and 67Ga-citrate were subsequent-ly administered and allowed to localise. Quantitative organ dis-tribution studies were performed in conjunction with scintigraph-ic images at 1 and 4 hours post injection. An additional biodis-tribution with 99mTc-alafosfalin in normal mice was also per-formed. RESULTS: 99mTc-alafosfalin was predominantly renal excreted, with low liver, intestine and bone uptake. There was no differ-ence in the uptake of these organs when infected mice were compared with normal mice. 99mTc-alafosfalin activity in the in-testine 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 injec-tion 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 phosphon-ic acid tracer by active bone growth areas which may be a dis-advantage. This 99mTc-antibiotic peptide has potential as an in-fection imaging agent, and will be investigated further in anoth-er rodent infection model in the future