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Fayn S, King AP, Gutsche NT, Duan Z, Buffington J, Olkowski CP, Fu Y, Hong J, Sail D, Baidoo KE, Swenson RE, Cheloha RW, Ho M, Choyke P, Escorcia FE. Nanobody-Based ImmunoPET for Hepatocellular Carcinoma. Int J Radiat Oncol Biol Phys 2023; 117:S44. [PMID: 37784500 DOI: 10.1016/j.ijrobp.2023.06.320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
PURPOSE/OBJECTIVE(S) HCC accounts for 75-90% of all primary liver cancers, the majority of which are treated with liver-directed therapy. Treatment response and recurrence are difficult to discern using conventional imaging with MR/CT. Tumor-selective PET imaging could help with clinical management in this setting. Here, we engineer HN3, a single-domain antibody (nanobody) specific to GPC3, a histopathologically-defining HCC marker, as an immunoPET agent. We compared both conventional and sortase-based site-specific modification methods for synthesizing HN3 immunoPET tracers. MATERIALS/METHODS Stochastic lysine conjugation with deferoxamine (DFO-NCS) was done to synthesize nHN3-DFO. ssHN3-DFO was engineered utilizing sortase-mediated conjugation of HN3 containing an LPETG C-terminal tag and a triglycine-DFO chelator. Biolayer interferometry (BLI) and radioligand saturation assays were done to determine binding affinity pre- and post-Zirconium-89 labeling. Following, PET/CT with a terminal 3-hour biodistribution was done in mice inoculated with isogenic A431 and A431-GPC3+ xenografts to determine conjugate specificity for GPC3. Finally, conjugates were evaluated in a HepG2 liver cancer model via ex vivo biodistribution studies and a comparative PET/CT study in mice bearing HepG2 tumors that were imaged with both [18F]FDG and 89Zr-ssHN3. RESULTS Both conjugates exhibited nanomolar binding affinity for GPC3 in vitro (11-30 nM for nHN3 and 10-15 nM for ssHN3). A431 and A431-GPC3+ PET/CT and biodistribution studies showed specificity to GPC3 by both probes, with more favorable tumor uptake by 89Zr-ssHN3 at 3 hours post-injection (14% IA/g vs. 7% IA/g for nHN3). Both tracers also displayed uptake in HepG2 (GPC3+) liver tumors, again with the site specifically conjugated probe having higher tumor accumulation and lower liver signal than the conventionally modified HN3 (7% IA/g vs. 5 % IA/g for tumor and 2% IA/g vs. 4% IA/g for liver at 1-hour post-injection). PET/CT studies in mice imaged with [18F]FDG and 89Zr-ssHN3 demonstrated more consistent tumor accumulation for the nanobody conjugate (4/4 mice had uptake by the tumor vs. 1/4 for FDG). CONCLUSION We successfully designed, synthesized, and characterized novel GPC3-selective nanobody PET probes that can image liver tumors in vivo. The site-specifically conjugated tracer showed more favorable biodistribution and pharmacokinetic properties, resulting in a much higher tumor: liver signal compared to 89Zr-nHN3. We also show the superiority of the 89Zr-ssHN3 imaging over conventional [18F]FDG, highlighting a clear advantage in using targeted tumor imaging for this cancer type. Successful translation of the site-specifically conjugated nanobody may ultimately aid in characterizing lesions following liver-directed therapy and allow for more comprehensive screening, early diagnosis, and post-treatment surveillance of HCC.
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Affiliation(s)
- S Fayn
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - A P King
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - N T Gutsche
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - Z Duan
- Antibody Engineering Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - J Buffington
- Antibody Engineering Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - C P Olkowski
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - Y Fu
- Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - J Hong
- Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - D Sail
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, MD
| | - K E Baidoo
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - R E Swenson
- Chemistry and Synthesis Center, National Heart, Lung, and Blood Institute, National Institutes of Health, Rockville, MD
| | - R W Cheloha
- Chemical Biology in Signaling Section, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD
| | - M Ho
- Antibody Engineering Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD; Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - P Choyke
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
| | - F E Escorcia
- Molecular Imaging Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD; Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD
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