Evaluation of 99mTc-Pheophorbide-a use in infection imaging: a rat model

This study aims to prepare (99m)Technetium Pheophorbide-a ((99m)Tc-PH-A) complex and evaluate its efficiency as an infection imaging agent. First, PH-A was obtained from Spirulina maxima algae, and the product compound was confirmed using (1)H NMR and MS (ESI) methods. The PH-A was then labeled with (99m)Tc using the tin chloride method and its biological efficacy as a potential radiotracer for Staphylococcus aureus (S. aureus) infection was evaluated in bacterially infected and sterile inflamed rats. The radiochemical stability of the (99m)Tc-PH-A in human serum was determined by thin-layer radiochromatography (TLRC). The radiochemical purity was 87±3.2% and remained constant at more than 80±0.1% even in serum for 120 min after radiolabeling. These experiments indicated that the ratio of (99m)Tc-PH-A uptake in bacterially infected muscle, as compared to normal muscle, [target/non-target (T/NT)=5.6 at 1h] was over four times higher than that in sterile inflamed muscle (T/NT=1.29 at 1h). Disappearance of activity from the kidney and liver indicated that the urinary and hepatobiliary systems were the normal routes of excretion of the complex. (99m)Technetium Pheophorbide prepared with high yield is able to localize well in the bacterially infected muscle of the rats and (99m)Tc-PH-A may be developed as a radiopharmaceutical agent to distinguish infection from inflammation by nuclear imaging.