In Vivo Labeling of Serum Albumin for PET

Abstract

The purpose of this study was to develop a novel in vivo albumin-labeling method to allow PET of cardiac function after myocardial infarction and vascular leakage and increased permeability in inflammatory diseases and malignant tumors. Methods To label albumin in vivo, we synthesized a NOTA (1,4,7-triazacyclononane-N,N′, N″-triacetic acid)-conjugated truncated form of Evans blue (NEB). 18F labeling was achieved by the formation of an 18F-aluminum fluoride (18F-AlF) complex, and 64Cu labeling was obtained by a standard chelation method. Sixty-minute dynamic PET imaging was performed on normal mice to evaluate the distribution of 18F-AlF-NEB, which was compared with in vitro–labeled mouse serum albumin (18F-fluorobenzyl-MSA). Electrocardiography-gated PET imaging was performed in a mouse model of myocardial infarction. Both dynamic and static PET scans were obtained in a mouse inflammation model induced by local injection of turpentine to evaluate vascular leakage. Tumor permeability was studied by dynamic and late-point static PET using 64Cu-NEB in a UM-22B xenograft model. Results NEB was successfully synthesized, and 18F labeling including work-up took about 20–30 min, with a radiochemical purity greater than 95% without the need for high-performance liquid chromatography purification. Most of the radioactivity was retained in the circulation system at 60 min after injection (26.35 ± 1.52 percentage injected dose per gram [%ID/g]). With electrocardiography-gated PET, ventricles of the heart and major arteries were clearly visualized. The myocardial infarction mice showed much lower left ventricular ejection fraction than the control mice. Inflammatory muscles showed significantly higher tracer accumulation than the contralateral healthy ones. UM-22B tumor uptake of 64Cu-NEB gradually increased with time (5.73 ± 1.11 %ID/g at 1 h and 8.03 ± 0.77 %ID/g at 2 h after injection). Conclusion The distribution and local accumulation of serum albumin can be noninvasively visualized and quantified by 18F-AlF-NEB and 64Cu-NEB PET. The simple labeling and broad applications make these imaging probes attractive for clinical translation.

Novel “Add-On” Molecule Based on Evans Blue Confers Superior Pharmacokinetics and Transforms Drugs to Theranostic Agents

“…System 1 was a gradient starting from 80% solvent A (50 mM NH 4 OAc) and 20% solvent B (CH 3 CN) for 2 min and increasing to 90% solvent B over 15 min at a flow rate of 1 mL/min. System 2 was a gradient starting from 95% solvent A and 5% solvent B and changing to 65% solvent B over 35 min at a flow rate of 1 mL/min.…”

“…EB-NH 2 was synthesized as described previously (4). To a solution of Boc-Lys-Fmoc (80-100 mM; 3.6 equivalents [Eq]) in anhydrous N,N-dimethylformamide (DMF) was added (1-[bis (dimethylamino)methylene]-1H-1,2,3-triazolo [4,5-b]pyridinium 3-oxide hexafluorophosphate) (HATU; 4.2 Eq) as a solid under argon.…”

“…In vivo studies were conducted under an animal protocol approved by the National Institutes of Health Clinical Center Animal Care and Use Committee. PET scans and their analysis were performed as previously described (4).…”

“…1; Supplemental Fig. 1) (supplemental materials are available at http://jnm.snmjournals.org): 64 Cu-NMEB-RGD, which has a high affinity for integrin a v b 3 and contains an albuminbinding moiety; 64 Cu-NMEB-RAD, a control peptide with no affinity for the integrin a v b 3 receptor (11) but retaining the albuminbinding moiety; 64 Cu-NOTA-RGD, which has a high affinity for the integrin a v b 3 receptor but lacks the albumin-binding moiety; and 64 Cu-NEB, which is the albumin-binding moiety (4,12).…”

“…We previously developed a radiolabeled truncated derivative of Evans blue (EB) that allowed imaging of the blood volume because of the affinity of EB for albumin (4). This result encouraged us to explore drug conjugates of EB derivatives that would use albumin as a reversible carrier for drug delivery.…”