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- Rubins, Daniel J., et al.
(author)
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In Vivo Evaluation and Dosimetry Estimate for a High Affinity Affibody PET Tracer Targeting PD-L1
- 2021
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In: Molecular Imaging and Biology. - : Springer. - 1536-1632 .- 1860-2002. ; 23, s. 241-249
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Journal article (peer-reviewed)abstract
- Purpose: In vivo imaging of programmed death ligand 1 (PD-L1) during immunotherapy could potentially monitor changing PD-L1 expression and PD-L1 expression heterogeneity within and across tumors. Some protein constructs can be used for same-day positron emission tomography (PET) imaging. Previously, we evaluated the PD-L1-targeting Affibody molecule [F-18]AlF-NOTA-Z(PD-L1_1) as a PET tracer in a mouse tumor model of human PD-L1 expression. In this study, we evaluated the affinity-matured Affibody molecule Z(PD-L1_4), to determine if improved affinity for PD-L1 resulted in increased in vivo targeting of PD-L1.Procedures: Z(PD-L1_4) was conjugated with NOTA and radiolabeled with either [F-18]AlF or Ga-68. [F-18]AlF-NOTA-Z(PD-L1_4) and [Ga-68]NOTA-Z(PD-L1_4) were evaluated in immunocompromised mice with LOX (PD-L1+) and SUDHL6 (PD-L1-) tumors with PET and ex vivo biodistribution measurements. In addition, whole-body PET studies were performed in rhesus monkeys to predict human biodistribution in a model with tracer binding to endogenous PD-L1, and to calculate absorbed radiation doses.Results: Ex vivo biodistribution measurements showed that both tracers had > 25 fold higher accumulation in LOX tumors than SUDHL6 ([F-18]AlF-NOTA-Z(PD-L1_4): LOX: 8.7 +/- 0.7 %ID/g (N = 4) SUDHL6: 0.2 +/- 0.01 %ID/g (N = 6), [Ga-68]NOTA-Z(PD-L1_4): LOX: 15.8 +/- 1.0 %ID/g (N = 6) SUDHL6: 0.6 +/- 0.1 %ID/g (N = 6)), considerably higher than Z(PD-L1_1). In rhesus monkeys, both PET tracers showed fast clearance through kidneys and low background signal in the liver ([F-18]AlF-NOTA-Z(PD-L1_4): 1.26 +/- 0.13 SUV, [Ga-68]NOTA-Z(PD-L1_4): 1.11 +/- 0.06 SUV). PD-L1-expressing lymph nodes were visible in PET images, indicating in vivo PD-L1 targeting. Dosimetry estimates suggest that both PET tracers can be used for repeated clinical studies, although high kidney accumulation may limit allowable radioactive doses.Conclusions: [F-18]AlF-NOTA-Z(PD-L1_4) and [Ga-68]NOTA-Z(PD-L1_4) are promising candidates for same-day clinical PD-L1 PET imaging, warranting clinical evaluation. The ability to use either [F-18] or [Ga-68] may expand access to clinical sites.
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| 2. |
- Trotter, Dinko E. Gonzalez, et al.
(author)
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In Vivo Imaging of the Programmed Death Ligand 1 by F-18 PET
- 2017
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In: Journal of Nuclear Medicine. - : Society of Nuclear Medicine. - 0161-5505 .- 1535-5667 .- 2159-662X. ; 58:11, s. 1852-1857
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Journal article (peer-reviewed)abstract
- Programmed death ligand 1 (PD-L1) is an immune regulatory ligand that binds to the T-cell immune check point programmed death 1. Tumor expression of PD-L1 is correlated with immune suppression and poor prognosis. It is also correlated with therapeutic efficacy of programmed death 1 and PD-L1 inhibitors. In vivo imaging may enable real-time follow-up of changing PD-L1 expression and heterogeneity evaluation of PD-L1 expression across tumors in the same subject. We have radiolabeled the PD-L1-binding Affibody molecule NOTA-Z(PD-L1_1) with F-18 and evaluated its in vitro and in vivo binding affinity, targeting, and specificity. Methods: The affinity of the PD-L1-binding Affibody ligand Z(PD-L1_1) was evaluated by surface plasmon resonance. Labeling was accomplished by maleimide coupling of NOTA to a unique cysteine residue and chelation of F-18-AlF. In vivo studies were performed in PD-L1-positive, PD-L1-negative, and mixed tumor-bearing severe combined immunodeficiency mice. Tracer was injected via the tail vein, and dynamic PET scans were acquired for 90 min, followed by gamma-counting biodistribution. Immunohistochemical staining with an antibody specific for anti-PD-L1 (22C3) was used to evaluate the tumor distribution of PD-L1. Immunohistochemistry results were then compared with ex vivo autoradiographic images obtained from adjacent tissue sections. Results: NOTA-Z(PD-L1_1) was labeled, with a radiochemical yield of 15.1% +/- 5.6%, radiochemical purity of 96.7% +/- 2.0%, and specific activity of 14.6 +/- 6.5 GBq/mu mol. Surface plasmon resonance showed a NOTA-conjugated ligand binding affinity of 1 nM. PET imaging demonstrated rapid uptake of tracer in the PD-L1-positive tumor, whereas the PD-L1-negative control tumor showed little tracer retention. Tracer clearance from most organs and blood was quick, with biodistribution showing prominent kidney retention, low liver uptake, and a significant difference between PD-L1-positive (percentage injected dose per gram [%ID/g] = 2.56 +/- 0.33) and -negative (% ID/g = 0.32 +/- 0.05) tumors (P = 0.0006). Ex vivo autoradiography showed excellent spatial correlation with immunohistochemistry in mixed tumors. Conclusion: Our results show that Affibody ligands can be effective at targeting tumor PD-L1 in vivo, with good specificity and rapid clearance. Future studies will explore methods to reduce kidney activity retention and further increase tumor uptake.
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