PET imaging of abdominal aortic aneurysm with ⁶⁴Cu-labeled anti-CD105 antibody fab fragment

The critical challenge in abdominal aortic aneurysm (AAA) research is the accurate diagnosis and assessment of AAA progression. Angiogenesis is a pathologic hallmark of AAA, and CD105 is highly expressed on newly formed vessels. Our goal was to use ⁶⁴Cu-labeled anti-CD105 antibody Fab fragment for noninvasive assessment of angiogenesis in the aortic wall in a murine model of AAA. Methods: Fab fragment of TRC105, a mAb that specifically binds to CD105, was generated by enzymatic papain digestion and conjugated to NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) for ⁶⁴Cu labeling. The binding affinity/specificity of NOTA-TRC105-Fab was evaluated by flow cytometry and various ex vivo studies. BALB/c mice were anesthetized and treated with calcium phosphate to induce AAA and underwent weekly PET scans using ⁶⁴Cu-NOTA-TRC105-Fab. Biodistribution and autoradiography studies were also performed to confirm the accuracy of PET results. Results: NOTA-TRC105-Fab exhibited high purity and specifically bound to CD105 in vitro. Uptake of ⁶⁴Cu-NOTA-TRC105-Fab increased from a control level of 3.4 ± 0.1 to 9.5 ± 0.4 percentage injected dose per gram (%ID/g) at 6 h after injection on day 5 and decreased to 7.2 ± 1.4 %ID/g on day 12, which correlated well with biodistribution and autoradiography studies (i.e., much higher tracer uptake in AAA than normal aorta). Of note, enhanced AAA contrast was achieved, due to the minimal background in the abdominal area of mice. Degradation of elastic fibers and highly expressed CD105 were observed in ex vivo studies. Conclusion: ⁶⁴Cu-NOTA-TRC105-Fab cleared rapidly through the kidneys, which enabled noninvasive PET imaging of the aorta with enhanced contrast and showed increased angiogenesis (CD105 expression) during AAA. ⁶⁴Cu-NOTA-TRC105-Fab PET may potentially be used for future diagnosis and prognosis of AAA.