Annexin A5-functionalized nanoparticles for in vivo dual modality imaging of apoptosis

Objectives Noninvasive detection of apoptosis may play an important role in the evaluation of therapy efficiency and disease progression. In this study, we aim to develop Annexin A5-functionalized nanoparticles for dual optical/nuclear imaging of apoptosis.

Methods Poly (ethylene glycol) (PEG)-coated, core-crosslinked polymeric micelles (CCPM) were dual-labeled with a near-infrared fluorescence fluorophores (Cy7) and a radioisotope (111In). CCPM nanoparticles were conjugated with Annexin A5. To evaluate the specificity of Annexin A5-CCPM to apoptotic cells, three different preclinical models of apoptosis, including a tumor model, a liver apoptosis model, and an inflammation model were carried out.

Results In mice bearing EL4 lymphoma treated with cyclophosphamide and etoposide, the tumor apoptosis was clearly visualized by both SPECT and fluorescence molecular tomography after i.v. administration of 111In-labeled Annexin A5-CCPM. In contrast, there was little accumulation of this nanoradiotracer in the tumors of untreated mice. The biodistribution data was consistent with the imaging data. In liver apoptosis model, the apoptotic liver induced by anti-Fas antibody was clearly visualized by both nuclear and optical images. In contrast, significantly lower signals were detected in healthy livers of untreated mice after injection of 111In-labeled Annexin A5-CCPM and in apoptotic livers after injection of 111In-labeled CCPM. Similarly, 111In-labeled Annexin A5-CCPM showed a significantly higher uptake in the site of inflammation induced by intramuscular injection of turpentine (4.9 %ID/g) than that in the healthy site (0.6 %ID/g). Moreover, in all three models, histological analysis revealed colocalization between radioactivity and fluorescence signals from the nanoparticles, and drug-induced apoptosis.

Conclusions Annexin A5-CCPM allowed visualization of apoptosis by both nuclear and optical techniques. The complementary information acquired with multiple imaging techniques should be advantageous in assessing and validating early response to therapy