Specific and rapid scintigraphic detection of infection with Tc-99m-labeled interleukin-8

Interleukin-8 (IL-8) is a chemotactic cytokine involved in activation and r ecruitment of neutrophils to areas of infection. In our previous studies in rabbits we tested I-123-labeled IL-8 for its potential to image infections and showed that IL-8 rapidly and efficiently accumulated in infectious foc i. However, labeling of IL-8 with I-123 is costly and laborious and the spe cific activity of the preparation was low. In this study IL-8 was labeled w ith Tc-99m through the hydrazinonicotinamide (HYNIC) chelator. Methods: The leukocyte receptor-binding capacity of the preparation was determined in v itro. Rabbits with Escherichia coil abscesses were injected intravenously w ith 7 MBq Tc-99m-HYNIC-IL-8. Biodistribution of the radiolabel was determin ed by gamma camera imaging and tissue counting at 8 h after injection. Tc-9 9m-HYNIC-lysozyme was used as a size-matched control. Results: The leukocyt e receptor-binding capacity of the Tc-99m-HYNIC-IL-8 preparation was preser ved as determined in vitro, but labeling efficiency was modest with a speci fic activity of 3 MBq/mug. Tc-99m-HYNIC-IL-8 accumulated rapidly in the abs cess up to 0.33 +/- 0.06 percentage injected dose per gram (%ID/g) at 8 h a fter injection (vs. 0.025 +/- 0.003 %ID/g for 99mTc-HYNIC-lysozyme). Total uptake in the abscess was 4.9 +/- 0.7 %ID (vs. 0.44 +/- 0.05 %ID for 99mTc- HYNIC-lysozyme). Abscess-to-contralateral muscle ratios increased up to 127 +/- 23 (compared with 6.7 +/- 1.1 for Tc-99m-HYNIC-lysozyme) and abscess-t o-blood ratios increased to 11.9 +/- 2.2 (0.24 +/- 0.03 for 99mTc-HYNIC-lys ozyme). The radiolabel was excreted renally, with a retention in the kidney s of 28 %ID. Gamma camera imaging rapidly visualized the abscess from 1 h a fter injection onward, with abscess-to-background ratios improving with tim e up to 22 at 8 h after injection (vs. 2.7 for Tc-99m-HYNIC-lysozyme), as d etermined by quantitative analysis of the images. Most important, only a tr ansient (30 min) moderate drop of leukocyte counts and no leukocytosis were observed after injection of an imaging dose of 99mTc-HYNIC-IL-8. Conclusio n: IL-8 can be labeled with (TC)-T-99m using HYNIC as a chelator. By this m ethod the leukocyte receptor-binding capacity is preserved. The preparation allows rapid visualization of infection in a rabbit model with high target -to-background ratios. The mild transient drop of leukocyte counts and the absence of leukocytosis suggest that Tc-99m-HYNIC-IL-8 may be used as an im aging agent with only mild and transient side effects.