PET imaging of acute and chronic inflammation in living mice

Purpose In this study, we evaluated the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced acute and chronic inflammation in living mice by PET imaging of TNF-alpha and integrin alpha(v)beta(3) expression. Methods TPA was topically applied to the right ear of BALB/c mice every other day to create the inflammation model. Cu-64-DOTA-etanercept and Cu-64-DOTA-E{E[ c (RGDyK)](2)}(2) were used for PET imaging of TNF-a and integrin alpha(v)beta(3) expression in both acute and chronic inflammation. Hematoxylin and eosin staining, ex vivo autoradiography, direct tissue sampling, and immunofluorescence staining were also performed to confirm the non-invasive PET imaging results. Results The ear thickness increased significantly and the TNF-alpha level more than tripled after a single TPA challenge. MicroPET imaging using 64Cu-DOTA-etanercept revealed high activity accumulation in the inflamed ear, reaching 11.1 +/- 1.3, 13.0 +/- 2.0, 10.9 +/- 1.4, 10.2 +/- 2.2% ID/g at 1, 4, 16, and 24 h post injection, respectively (n= 3). Repeated TPA challenges caused TPA-specific chronic inflammation and reduced Cu-64-DOTA-etanercept uptake due to lowered TNF-alpha expression. Cu-64-DOTA- E{E[c(RGDyK)](2)}(2) uptake in the chronically inflamed ears ( after four and eight TPA challenges) was significantly higher than in the control ears and those after one TPA challenge. Immunofluorescence staining revealed increased integrin beta(3) expression, consistent with the non-invasive PET imaging results using Cu-64-DOTA- E{E[c(RGDyK)](2)}(2) as an integrin alpha(v)beta(3)-specific radiotracer. Biodistribution and autoradiography studies further confirmed the quantification capability of microPET imaging. Conclusion Successful PET imaging of TNF-alpha expression in acute inflammation and integrin alpha(v)beta(3) expression in chronic inflammation provides the rationale for multiple target evaluation over time to fully understand the inflammation.