Negative contrast Cerenkov luminescence imaging of blood vessels in a tumor mouse model using [68Ga]gallium chloride

Synthesis, radiolabeling, and preclinical in vivo evaluation of 68Ga-radiolabelled nanodiamonds

PURPOSE

Nanodiamonds (NDs) represent a new class of nanoparticles and have gained increasing interest in medical applications. Modifying the surface coating by attaching binding ligands or imaging probes can transform NDs into multi-modal targeting probes. This study evaluated the biokinetics and biodistribution of ⁶⁸Ga-radiolabelled NDs in a xenograft model.

PROCEDURES

NDs were coated with an albumin-derived copolymer modified with desferrioxamine to provide a chelator for radiolabeling. In vivo studies were conducted in AR42J tumor-bearing CD1 mice to evaluate biodistribution and tumor accumulation of the NDs.

RESULTS

Coated NDs were successfully radiolabeled using ⁶⁸Ga at room temperature with radiolabeling efficiencies up to 91.8 ± 3.2 % as assessed by radio-TLC. In vivo studies revealed the highest accumulation in the liver and spleen, whereas tumor radioactivity concentration was low.

CONCLUSIONS

Radiolabeling of coated NDs could be achieved. However, the obtained results indicate these coated NDs' limitations in their biodistribution within the conducted studies.

Preclinical PET and MR Evaluation of 89Zr- and 68Ga-Labeled Nanodiamonds in Mice over Different Time Scales

Nanodiamonds (NDs) have high potential as a drug carrier and in combination with nitrogen vacancies (NV centers) for highly sensitive MR-imaging after hyperpolarization. However, little remains known about their physiological properties in vivo. PET imaging allows further evaluation due to its quantitative properties and high sensitivity. Thus, we aimed to create a preclinical platform for PET and MR evaluation of surface-modified NDs by radiolabeling with both short- and long-lived radiotracers. Serum albumin coated NDs, functionalized with PEG groups and the chelator deferoxamine, were labeled either with zirconium-89 or gallium-68. Their biodistribution was assessed in two different mouse strains. PET scans were performed at various time points up to 7 d after i.v. injection. Anatomical correlation was provided by additional MRI in a subset of animals. PET results were validated by ex vivo quantification of the excised organs using a gamma counter. Radiolabeled NDs accumulated rapidly in the liver and spleen with a slight increase over time, while rapid washout from the blood pool was observed. Significant differences between the investigated radionuclides were only observed for the spleen (1 h). In summary, we successfully created a preclinical PET and MR imaging platform for the evaluation of the biodistribution of NDs over different time scales.

, a Chelator for 68Ga Positron Emission Tomography: Hydroxide Coordination Increases Biological Stability of [68Ga][Ga(Bn2DT3A)(OH)]. Inorg Chem 2022;61:17059-17067. [PMID: 36251390 DOI: 10.1021/acs.inorgchem.2c01992] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The chelator Bn₂DT3A was used to produce a novel ⁶⁸Ga complex for positron emission tomography (PET). Unusually, this system is stabilized by a coordinated hydroxide in aqueous solutions above pH 5, which confers sufficient stability for it to be used for PET. Bn₂DT3A complexes Ga³⁺ in a hexadentate manner, forming a mer-mer complex with log K([Ga(Bn₂DT3A)]) = 18.25. Above pH 5, the hydroxide ion coordinates the Ga³⁺ ion following dissociation of a coordinated amine. Bn₂DT3A radiolabeling displayed a pH-dependent speciation, with [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- being formed above pH 5 and efficiently radiolabeled at pH 7.4. Surprisingly, [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- was found to show an increased stability in vitro (for over 2 h in fetal bovine serum) compared to [⁶⁸Ga][Ga(Bn₂DT3A)]. The biodistribution of [⁶⁸Ga][Ga(Bn₂DT3A)(OH)]^- in healthy rats showed rapid clearance and excretion via the kidneys, with no uptake seen in the lungs or bones.

DestVI identifies continuums of cell types in spatial transcriptomics data

Most spatial transcriptomics technologies are limited by their resolution, with spot sizes larger than that of a single cell. Although joint analysis with single-cell RNA sequencing can alleviate this problem, current methods are limited to assessing discrete cell types, revealing the proportion of cell types inside each spot. To identify continuous variation of the transcriptome within cells of the same type, we developed Deconvolution of Spatial Transcriptomics profiles using Variational Inference (DestVI). Using simulations, we demonstrate that DestVI outperforms existing methods for estimating gene expression for every cell type inside every spot. Applied to a study of infected lymph nodes and of a mouse tumor model, DestVI provides high-resolution, accurate spatial characterization of the cellular organization of these tissues and identifies cell-type-specific changes in gene expression between different tissue regions or between conditions. DestVI is available as part of the open-source software package scvi-tools ( https://scvi-tools.org ).

Targeting and imaging of HER2 overexpression tumor with a new peptide-based 68Ga-PET radiotracer

Human epidermal growth factor receptor 2 (HER2) overexpression, as a predictive biomarker, is associated with more tumor aggressiveness and worse clinical outcomes in cancer, whereas it's accurate identification has led to the choice of effective treatments in many patients. In this study, a peptide-based PET probe (⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY) was developed for imaging HER2 expression in tumors. The DOTA-(Ser)₃-LTVSPWY was labeled with ⁶⁸Ga and then was evaluated in vitro with HER2-positive SKOV-3 cell line; moreover, the in vivo biodistribution and PET/CT imaging were performed in xenografted tumor-bearing nude mice. The ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY displayed the high radiochemical purity greater than 95% and good stability in normal saline and human serum. The cellular binding experiments showed that the cell uptake in HER2-positive ovarian cancer cells could be effectively blocked by non-labeled peptide. The K_d and B_max values for radiolabeled peptide were obtained at 2.5 ± 0.6 nM and (3.4 ± 0.2) × 10⁵ sites per cell, respectively. Biodistribution study demonstrated that tumor-to-blood and tumor-to-muscle ratios were about 1.73 ± 0.36 and 3.78 ± 0.17 at 120 min after the injection of the radiolabeled peptide, respectively. Tumor imaging by PET/CT exhibited high contrast tumor image at 60 min after injection in animal models. Consequently, the results were indicative of the specific accumulation of ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY peptide in HER2-positive tumors and the suitability of its application as a PET probe for the diagnosis of HER2-overexpression tumor.

Enhanced Cerenkov luminescence tomography analysis based on Y2O3:Eu3+ rare earth oxide nanoparticles

Cerenkov luminescence imaging offers a new diagnostic alternative to radiation imaging, but lacks intensity and penetration. In this study, a Cerenkov luminescence signal and its image quality were enhanced using rare earth oxide nanoparticles as a basis for Cerenkov luminescence excited fluorescence imaging and Cerenkov luminescence excited fluorescence tomography. The results also provided 3D-imaging and quantitative information. The approach was evaluated using phantom and mice models and 3D reconstruction and quantitative studies were performed in vitro, showing improved optical signal intensity, similarity, accuracy, signal-to-noise ratio, and spatial distribution information. The method offers benefits for both optical imaging research and radiopharmaceutical development.

Cerenkov luminescence imaging: physics principles and potential applications in biomedical sciences

Cerenkov luminescence imaging (CLI) is a novel imaging modality to study charged particles with optical methods by detecting the Cerenkov luminescence produced in tissue. This paper first describes the physical processes that govern the production and transport in tissue of Cerenkov luminescence. The detectors used for CLI and their most relevant specifications to optimize the acquisition of the Cerenkov signal are then presented, and CLI is compared with the other optical imaging modalities sharing the same data acquisition and processing methods. Finally, the scientific work related to CLI and the applications for which CLI has been proposed are reviewed. The paper ends with some considerations about further perspectives for this novel imaging modality.

(68)Ga-labeled 3PRGD2 for dual PET and Cerenkov luminescence imaging of orthotopic human glioblastoma

β-Emitters can produce Cerenkov radiation that is detectable by Cerenkov luminescence imaging (CLI), allowing the combination of PET and CLI with one radiotracer for both tumor diagnosis and visual guidance during surgery. Recently, the clinical feasibility of CLI with the established therapeutic reagent Na(131)I and the PET tracer (18)F-FDG was demonstrated. (68)Ga possesses a higher Cerenkov light output than (18)F and (131)I, which would result in higher sensitivity for CLI and improve the outcome of CLI in clinical applications. However, the research on (68)Ga-based tumor-specific tracers for CLI is limited. In this study, we examined the use of (68)Ga-radiolabeled DOTA-3PRGD2 ((68)Ga-3PRGD2) for dual PET and CLI of orthotopic U87MG human glioblastoma. For this purpose, the Cerenkov efficiencies of (68)Ga and (18)F were measured with the IVIS Spectrum system (PerkinElmer, USA). The CLI signal intensity of (68)Ga was 15 times stronger than that of (18)F. PET and CLI of (68)Ga-3PRGD2 were performed in U87MG human glioblastoma xenografts. Both PET and CLI revealed a remarkable accumulation of (68)Ga-3PRGD2 in the U87MG human glioblastoma xenografts at 1 h p.i. with an extremely low background in the brain when compared with (18)F-FDG. Furthermore, (68)Ga-3PRGD2 was used for dual PET and CLI of orthotopic human glioblastoma. The orthotopic human glioblastoma was clearly visualized by both imaging modalities. In addition, the biodistribution of (68)Ga-3PRGD2 was assessed in normal mice to estimate the radiation dosimetry. The whole-body effective dose is 20.1 ± 3.3 μSv/MBq, which is equal to 3.7 mSv per whole-body PET scan with a 5 mCi injection dose. Thus, (68)Ga-3PRGD2 involves less radiation exposure in patients when compared with (18)F-FDG (7.0 mSv). The use of (68)Ga-3PRGD2 in dual PET and CLI shows great promise for tumor diagnosis and image-guided surgery.

Molecular imaging using nanoparticle quenchers of Cerenkov luminescence

Cerenkov luminescence (CL) imaging is an emerging technique that collects the visible photons produced by radioisotopes. Here, molecular imaging strategies are investigated that switch the CL signal off. The noninvasive molecularly specific detection of cancer is demonstrated utilizing a combination of clinically approved agents, and their analogues. CL is modulated in vitro in a dose dependent manner using approved small molecules (Lymphazurin), as well as the clinically approved Feraheme and other preclinical superparamagnetic iron oxide nanoparticles (SPIO). To evaluate the quenching of CL in vivo, two strategies are pursued. [(18) F]-FDG is imaged by PET and CL in tumors prior to and following accumulation of nanoparticles. Initially, non-targeted particles are administered to mice bearing tumors in order to attenuate CL. For targeted imaging, a dual tumor model (expressing the human somatostatin receptor subtype-2 (hSSTr2) and a control negative cell line) is used. Targeting hSSTr2 with octreotate-conjugated SPIO, quenched CL enabling non-invasive distinction between tumors' molecular expression profiles is demonstrated. In this work, the quenching of Cerenkov emissions is demonstrated in several proof of principle models using a combination of approved agents and nanoparticle platforms to provide disease relevant information including tumor vascularity and specific antigen expression.