microPET/CT imaging of local and systemic inflammatory response using 64Cu-labeled anti-CD11b Antibody

495 Objectives This study was to develop PET tracer for targeting inflammatory cells and to noninvasively assess local and systemic inflammatory response by infiltration of CD11b+ myeloid cells. Methods BALB/c mice with acute or chronic inflammation in the ears were induced by 12-o-tetradecanoylphorbol-13-acetate (TPA). Anti-mouse CD11b antibody was conjugated with p-SCN-Bn-DOTA and then labeled with 64Cu. The specific binding affinity of 64Cu-DOTA-anti-CD11b to CD11b+ myeloid cells was confirmed by cell binding assays. microPET-CT imaging and biodistribution were evaluated at different times after intravenous injection of 64Cu-DOTA-anti-CD11b. Blocking experiments were also performed. Ear tissues from TPA challenged mice were assessed by H&E and immunohistochemistry staining. To verify the systemic response for TPA challenges, the cell sub-population from bone marrow and spleen were analyzed by flow cytometry. Results 64Cu-DOTA-anti-CD11b bound specifically to CD11b+ myeloid cells. microPET-CT images showed significantly higher uptake of 64Cu-DOTA-anti-CD11b Abs in the ears of mice with acute inflammation than in the ears of mice with chronic inflammation or ears of un-challenged mice. In addition, immunohistochemistry staining confirmed that the ear with acute inflammation had greater number of infiltrating CD11b+Ly6G+ granulocytes than ear from other groups. Interestingly, whole body PET-CT imaging of mice received 64Cu-DOTA-anti-CD11b showed different systemic response to TPA challenges. The uptake in bone marrow decreased in acute inflammation, but dramatically increased in chronic inflammation compared to normal mice. Flow cytometry studies revealed that observed PET imaging results of systemic inflammatory response were correlated with ratio of CD11b+Gr-1+ sub-population of myeloid cells in the bone marrow. The uptake of 64Cu-DOTA-anti-CD11b in bone marrow and spleen could be specifically blocked by cold anti-CD11b antibody. Conclusions 64Cu-DOTA-anti-CD11b antibody is a promising radiotracer for monitoring different stage of local and systemic inflammatory response.