Potential use of 68Ga-apo-transferrin as a PET imaging agent for detecting Staphylococcus aureus infection

(67)Ga citrate has been extensively used to detect infection and inflammation since 1971. However, its clinical utility is compromised due to several limitations. The present project explored whether (68)Ga-apo-transferrin ((68)Ga-TF), when prepared in vitro, is a useful agent for positron emission tomography (PET) imaging of bacterial infection.

An infection was induced in male Wistar rats by injecting 5 × 10(5) CFU units of Staphyococcus aureus in the right thigh muscle. (68)Ga-TF was synthesized by mixing (68)GaCl(3) with apo-transferrin (TF, 2 mg) in sodium carbonate (0.1 M, pH 7.0) and incubating at 40 °C for 1 h. Animals were injected with 10-15 MBq of (68)Ga-TF containing approximately 0.2 mg TF and imaged at different time intervals using Siemens Biograph PET-CT.

When (68)Ga-TF were injected in the infected rats, the infection lesion was detectable within 20 min post injection. The biodistribution showed the uptake at the lesion increased with time as shown by significantly increased standard uptake values for up to 4 h post injection. There was a considerable decrease in the background activity during the same period of study, giving higher target-to-muscle ratios. Blood pool activity at 3 h post injection was insignificant. (68)GaCl(3) (when not conjugated to TF) did not localize at the infection lesion up to 120 min post injection.

The preliminary results suggest that (68)Ga-TF is capable of detecting S. aureus infection in the rat model, within an hour after intravenous injection.