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[64Cu]Cu(DDC)2 NPs: A Novel PET Probe for Noninvasive Visualization of NPL4 Expression in Tumors In Vivo
Shun Huang1,2, Xiang Liang1,3, Dazhi Shi1
1GDMPA Key Laboratory for Quality Control and Evaluation of Radiopharmaceuticals, Department of Nuclear Medicine, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China.
Abstract:
Nuclear protein localization 4 (NPL4) plays a key role in the ubiquitination pathway and has emerged as a promising target for cancer therapy. The ditiocarb-copper complex, Cu(DDC)2, an anticancer metabolite derived from the antialcoholism drug disulfiram (DSF), exhibits a high affinity for NPL4. Thus, quantifying NPL4 expression in tumors is crucial for ubiquitination research and for developing NPL4-targeted diagnostic and therapeutic strategies. In this study, we replaced the cold copper ion in Cu(DDC)2 with the positron-emitting isotope copper-64 and developed three methods for visualizing NPL4 in tumors in vivo using positron emission tomography/computed tomography (PET/CT): (1) an in vivo "synthesis-free" method for preparing [64Cu]Cu(DDC)2, (2) an in vitro synthesis method, and (3) a stabilization method using PEG5000-PLA5000 (PP) to enhance [64Cu]Cu(DDC)2's hydrophilicity by preparing [64Cu]Cu(DDC)2 NPs. Micro-PET/CT imaging showed minimal uptake of [64Cu]Cu(DDC)2 in NPL4-positive tumors with the in vivo "synthesis-free" method, resulting in poor lesion visualization. However, in vitro synthesized [64Cu]Cu(DDC)2 and [64Cu]Cu(DDC)2 NPs successfully visualized NPL4-positive U87MG tumors. Compared to [64Cu]Cu(DDC)2, [64Cu]Cu(DDC)2NPs demonstrated significantly higher tumor uptake (7.2 ± 0.7% ID/g vs 3.8 ± 0.6% ID/g at 12 h postinjection, P = 0.001) and tumor-to-muscle (T/M) ratio (7.8 ± 1.2 vs. 3.2 ± 0.7, P = 0.001). Tumor uptake of [64Cu] Cu (DDC)2NPs was consistent with NPL4 expression levels and was inhibited by an excess of Cu(DDC)2. The optimal PP stabilizer concentration was determined to be 0.0005%. This study successfully developed a PET probe, [64Cu]Cu(DDC)2NPs, and established a novel imaging modality for in vivo visualization of NPL4 expression, potentially guiding future NPL4-targeted therapies.
Insights
This study developed a novel PET imaging probe, [64Cu]Cu(DDC)2 nanoparticles, for visualizing Nuclear protein localization 4 (NPL4) expression in tumors. This advancement offers a new tool for guiding NPL4-targeted cancer therapies.
Area of Science:
- Biomedical Imaging
- Radiochemistry
- Cancer Biology
Background:
- Nuclear protein localization 4 (NPL4) is crucial in ubiquitination and a promising cancer therapy target.
- Quantifying NPL4 expression is vital for NPL4-targeted diagnostics and therapeutics.
- Cu(DDC)2, derived from disulfiram, binds NPL4 and is a potential imaging agent.
Purpose of the Study:
- To develop and evaluate novel positron emission tomography (PET) imaging probes for in vivo visualization of NPL4 expression in tumors.
- To compare different methods for preparing and stabilizing 64Cu-labeled Cu(DDC)2 for PET imaging.
- To establish a new imaging modality for guiding NPL4-targeted cancer therapies.
Main Methods:
- Developed three methods for preparing 64Cu-labeled Cu(DDC)2: in vivo "synthesis-free", in vitro synthesis, and nanoparticle (NP) formulation with PEG5000-PLA5000 (PP) stabilization.
- Utilized micro-PET/CT imaging to assess tumor uptake and lesion visualization of the developed probes in NPL4-positive tumors.
- Investigated the effect of PP concentration and competition with unlabeled Cu(DDC)2 on probe performance.
Main Results:
- The in vivo "synthesis-free" method showed poor tumor uptake and lesion visualization.
- In vitro synthesized [64Cu]Cu(DDC)2 and [64Cu]Cu(DDC)2 NPs successfully visualized NPL4-positive tumors.
- [64Cu]Cu(DDC)2 NPs exhibited significantly higher tumor uptake (7.2 ± 0.7% ID/g) and tumor-to-muscle ratio (7.8 ± 1.2) compared to [64Cu]Cu(DDC)2.
- Tumor uptake of [64Cu]Cu(DDC)2 NPs correlated with NPL4 expression and was inhibited by excess Cu(DDC)2.
Conclusions:
- [64Cu]Cu(DDC)2 NPs represent a promising PET probe for in vivo NPL4 visualization.
- The developed nanoparticle-based imaging modality can effectively guide NPL4-targeted cancer therapies.
- This study establishes a novel approach for non-invasively assessing NPL4 expression in tumors.
