Macrophage cell tracking PET imaging using mesoporous silica nanoparticles via in vivo bioorthogonal F-18 labeling

We introduce an efficient cell tracking imaging protocol using positron emission tomography (PET). Since macrophages are known to home and accumulate in tumor tissues and atherosclerotic plaque, we design a PET imaging protocol for macrophage cell tracking using aza-dibenzocyclooctyne-tethered PEGylated mesoporous silica nanoparticles (DBCO-MSNs) with the short half-life F-18-labeled azide-radiotracer via an in vivo strain-promoted alkyne azide cycloaddition (SPAAC) covalent labeling reaction inside macrophage cells in vivo. This PET imaging protocol for in vivo cell tracking successfully visualizes the migration of macrophage cells into the tumor site by the bioorthogonal SPAAC reaction of DBCO-MSNs with [¹⁸F]fluoropentaethylene glycolic azide ([¹⁸F]2) to form ¹⁸F-labeled aza-dibenzocycloocta-triazolic MSNs (¹⁸F-DBCOT-MSNs) inside RAW 264.7 cells. The tissue radioactivity distribution results were consistent with PET imaging findings. In addition, PET images of atherosclerosis in ApoE^-/- mice fed a western diet for 30 weeks were obtained using the devised macrophage cell-tracking protocol.