Immune PET with ⁸⁹Zr anti-CD133 antibody can monitor colon cancer CD133 expression and its modulation by chemotherapy

Objectives: The goal of this study was to develop an ⁸⁹Zr-labeled anti-CD133 immune PET technique that can image tumor CD133 and monitor chemotherapy-mediated modulation of expression in vivo.

Methods: Anti-CD133 antibodies underwent sulfohydryl moiety-specific conjugation with maleimide-deferoxamine followed by ⁸⁹Zr labeling. Radiochemical purity, specific activity and radiolabel stability was assessed. Cell binding assays and Western blotting was performed. In vivo pharmacokinetics and biodistribution were assessed and PET studies were performed in mice.

Results: ⁸⁹Zr-CD133 IgG was efficiently synthesized by site-specific conjugation. High CD133 expressing HT29 colon cancer cells showed substantially greater ⁸⁹Zr-CD133 IgG binding compared to weak expressing CT26 colon cancer cells, and complete reduction of binding by excess cold antibody confirmed excellent target specificity. Among chemotherapeutic agents, src inhibition with PP2 or dasatinib stimulated HT29 cell CD133 expression >4-fold, whereas COX-2 inhibition with celecoxib dose-dependently suppressed CD133 expression to 19.9 ± 2.1% of basal level. These effects were accompanied by significant increases (170.2 ± 2.7% and 160.9 ± 16.2%) and reduction (50.3 ± 10.9% of basal level) of ⁸⁹Zr-CD133 IgG binding, respectively. When ⁸⁹Zr-CD133 IgG was injected into HT29 tumor-bearing mice, PET/CT displayed high-contrast tumor uptake at 6 days post-injection that was suppressed by excess cold antibody. Biodistribution studies showed high tumor uptake of 11.4 ± 1.3 %ID/gm, compared to a lower blood activity of 4.9 ± 1.6 %ID/gm. In the animals, celecoxib treatment substantially decreased tumor uptake in a manner that reflected reductions in tumor CD133 expression

Conclusions: ⁸⁹Zr-CD133 IgG PET can noninvasively image tumor CD133 expression and may be useful for monitoring chemotherapy-mediated tumor CD133 modulation in living subjects.