Molecular Imaging and Biology最新文献

Purpose: Despite advancements in colorectal cancer (CRC) therapy, surgery remains the only curative option. Incomplete resection resulting in tumor cell positive surgical margins occurs in ~ 7% of CRC surgeries and is associated with recurrence and poor prognosis. Fluorescence-guided surgery (FGS) enhances tumor detection and enables real-time identification of tumor margins. Claudins, a large family of tight junction proteins, are being explored as cancer biomarkers and therapeutic targets due to their presence on the cell surface, tissue-specific expression, and selective upregulation in carcinomas. Claudin-1 (CLDN1) is overexpressed in CRC and associated with therapy resistance and metastasis, making it a promising target for fluorescence-based tumor detection.

Procedures: CLDN1 expression in CRC was analyzed using the Cancer Genome Atlas Colorectal Adenocarcinoma (TCGA-COAD) dataset. To enable in vivo tumor detection, a CLDN1 monoclonal antibody was conjugated to a near-infrared fluorescent dye (CLDN1-IR800). Sensitivity, specificity, and tumor-to-background ratio were tested in vitro and in vivo using CRC cell lines, patient-derived organoids, and an orthotopic, syngeneic model of CRC metastasis.

Results: This study demonstrates that CLDN1 is upregulated in 100% of CRC tumors compared to patient-matched normal adjacent colon in the TCGA-COAD dataset, with an average 40-fold increase in expression. CLDN1-IR800 showed specific binding and strong fluorescence in CLDN1-expressing CRC cells, with minimal signal in non-expressing cells or IgG-IR800 controls. In vivo, CLDN1-IR800 produced a significantly higher tumor-to-background ratio in CLDN1-expressing CRC cell line and patient-derived organoid xenografts compared to CLDN1-negative tumors or IgG-IR800-injected mice. Necropsy revealed significantly higher fluorescence in tumors than in other organs. In an orthotopic syngeneic mouse model, both primary and metastatic lesions were detectable. Ex vivo imaging confirmed signal in a panel of patient-derived organoids.

Conclusions: These findings demonstrate CLDN1's potential as a target for tumor detection and FGS in CRC.

Trimethoprim (TMP) is a reversible inhibitor of the prokaryotic enzyme dihydrofolate reductase (DHFR) used for the treatment or prophylaxis of bacterial infections. [¹¹C]trimethoprim ([¹¹C]TMP) is a positron emission tomography (PET) imaging isotopologue of TMP. TMP binds with 30,000-fold greater affinity to bacterial DHFR over the homologous mammalian enzyme in vitro, suggesting [¹¹C]TMP may selectively accumulate in tissues with cells expressing bacterial DHFR. This study characterizes the biodistribution and dosimetry of [¹¹C]TMP, informing its use in imaging bacterial infections and tracking mammalian cells expressing eDHFR as a reporter gene.

Methods: Four males with suspected infection, aged 59 ± 10 years old (mean ± SD) received 3 serial PET/CT scans after injection of 346 ± 305 MBq (range 129-797 MBq) of [¹¹C]TMP. Organ activities were measured in MIM v6.7, including brain, kidneys, spleen, liver, heart, lungs, bladder, intestines, gallbladder, pancreas, thyroid, and red marrow. Dosimetry calculations were performed in Olinda | EXM v1.1. Additionally, a dynamic whole-body PET/CT scan was performed on a separate participant. The associated trial was registered as NCT03424525.

Results: [¹¹C]TMP injections were well tolerated with no adverse events. The average injected activity of 346 MBq of [¹¹C]TMP yielded an estimated average dose of 4.9 mSv in the highest uptake organ (liver), 4.1 mSv in the spleen, and an effective dose of 1.6 mSv. Suspected sites of infection displayed uptake above background.

Conclusion: [¹¹C]TMP PET was safe and demonstrated low background uptake in most tissues. The data suggests feasibility for evaluation of varied bacterial infections, including musculoskeletal infections. Absorbed doses allow multiple [¹¹C]TMP PET scans each year within Radioactive Drug Research Committee (RDRC) limits, potentially enabling monitoring of infections and treatment response.

Purpose: CD4⁺ T cells (T helper and T reg) play an important role in the immune system and are influential in autoimmune diseases (e.g., rheumatoid arthritis, inflammatory bowel disease) and cancer (antitumor immunity). Non-invasive, whole-body anti-CD4 immunoPET can provide dynamic and spatial information (localization, proliferation, and migration) on CD4⁺ T cells. The cys-diabody format enables site-specific radiolabeling and rapid renal clearance, which results in high-contrast images at early time points.

Procedures: In this work, an anti-CD4 cys-diabody based on the hybridoma GK1.5 was reengineered by CDR-grafting (GK1.5 FR cDb) for higher expression in mammalian cell lines. An N-glycosylation motif in the variable light chain domain framework was removed by site-directed mutagenesis, resulting in GK1.5 N80D cDb. To investigate the impact of the variable domain glycan on the in vivo biodistribution and pharmacokinetics, both cys-diabodies were site-specifically conjugated with deferoxamine-maleimide and radiolabeled by chelation of zirconium-89. Serial immunoPET/CT imaging was used for non-invasive, whole-body assessment of specific targeting, biodistribution, and differential clearance of the two novel anti-CD4 cys-diabodies.

Results: The anti-CD4 cys diabody was successfully re-engineered by CDR-grafting (GK1.5 FR cDb) and aglycosylation (GK1.5 N80D cDb), resulting in a higher expression yield (~ tenfold increase) without impacting antigen specificity or affinity. Both cys-diabody variants were successfully ⁸⁹Zr-radiolabeled with similar specific activity and radiochemical purity. ImmunoPET imaging of ⁸⁹Zr-GK1.5 FR cDb and ⁸⁹Zr-GK1.5 N80D cDb in immunocompetent mice showed CD4 antigen-specific lymphoid tissue uptake in vivo. ⁸⁹Zr-GK1.5 FR cDb exhibited rapid hepatic clearance, resulting in significantly reduced uptake in lymph nodes and the spleen. Removal of the N-glycosylation motif in ⁸⁹Zr-GK1.5 N80D cDb restored diabody-typical biodistribution (renal clearance), resulting in higher target tissue uptake.

Conclusion: The novel reengineered anti-CD4 GK1.5 N80D cDb overcomes the previous production yield bottleneck and provides same-day ⁸⁹Zr-immunoPET imaging for non-invasive, whole-body visualization of murine CD4⁺ T cells.

Introduction: Obesity and type 2 diabetes (T2D) influence the tumor microenvironment by altering glucose metabolism, which has been shown to decrease immune cell infiltration and activation. Positron emission tomography (PET) imaging provides a non-invasive method to detect molecular markers of immune populations in the tumor microenvironment and systemic organs. The goal of this study is to utilize advanced molecular imaging to quantify differences in innate and adaptive immune responses in diabetic obese mice systemically and within the tumor microenvironment.

Methods: 5-6-week-old female C57BL6/J mice were placed on a high-fat diet (HFD) composed of 60% kcal fat or control low-fat diet with 10% kcal fat. Animals were treated with subsequent low doses of streptozotocin to induce T2D and blood glucose was monitored. Following induction of diabetes, E0771-luc + cells were implanted into the 4th mammary fat pad and allowed to grow to a tumor volume of 100mm³. PET imaging was acquired over the course of 5 days with the following tracers: [¹⁸F]-FDG PET for glucose metabolism, [⁶⁸Ga]Ga-RP832c (CD206) PET for M2 macrophages, and [⁶⁸Ga]Ga-GZP PET for granzyme B, an indicator of effector cell activation, and [¹⁸F]-DPA-714 PET for neuroinflammation. Regions of interest were identified for the tumor, brain, kidneys, heart, muscle, brown adipose tissue (BAT), to characterize differences in important organs and tumor tissue. Metrics of standardized uptake value (SUV) were extracted from imaging data including mean, max, peak, and tumor-to-background ratios. Following the final imaging timepoint, tumors were extracted for biological characterization via flow cytometry.

Results: Diabetic obese mice have no difference in tumor glucose metabolism, but have decreased FDG uptake in the brain and BAT compared to controls. Obesity and T2D systemically affect innate and adaptive immune infiltration and activation including significantly increased RP832c and GZP in muscle, heart, brain, and BAT. Hyperglycemic tumors had trending decreases in GZP SUV_mean and increased RP832c SUV_mean. Flow cytometry shows diabetic obese tumors have a significant increase in CD206 + macrophages and no significant difference in GZB + CD8 + T cells compared to controls.

Conclusion: PET imaging reveals that obesity and T2D alter glucose metabolism and immune activation while suppressing tumor-immune activation in diabetic obese mice both within the tumor microenvironment and systemically.

Purpose: Acute myocardial infarction (MI) is a leading cause of morbidity and mortality worldwide. Sphingosine-1-phosphate (S1P) is a bioactive lipid mediator influencing numerous physiological processes. S1PR1 is the predominant isoform of the S1P receptor in cardiomyocytes and vascular endothelial cells. S1PR1 plays a critical role in preventing adverse cardiac remodeling. The importance of S1PR1 in cardiac physiology has led to the development of novel treatments for MI, including S1PR1 gene delivery strategies aimed at preventing heart failure. Monitoring the dynamic changes of S1PR1 post-MI is clinically significant for assessing cardiac remodeling. This study validated the ability of specific S1PR1 PET radiotracer [¹⁸F]FS1P1 to track changes in this signaling pathway, thereby providing a non-invasive diagnostic tool to quantify S1PR1 expression for investigating MI in vivo.

Procedures: We characterized the S1PR1 radiotracer [¹⁸F]FS1P1 in an echo-guided mouse model of MI. [¹⁸F]FDG PET was used to delineate the infarct area. Masson trichrome staining was used to identify cardiac fibrosis. Immunofluorescence (IF) experiment was conducted to demonstrate changes in S1PR1 expression after MI. Autoradiography was performed to evaluate the distribution of [¹⁸F]FS1P1 in MI heart tissues. MI (n = 4) and sham (n = 4) mice were scanned with [¹⁸F]FS1P1 PET at 2 days and 2 weeks post-MI, radioactivity uptake in the myocardium was calculated as the percentage of the injected dose per gram (%ID/g).

Results: The uptake of [¹⁸F]FS1P1 was significantly decreased by 31.8% in the infarct region at 2 days post-MI compared to the sham group (1.3 ± 0.3 vs. 1.9 ± 0.3), and decreased by 37.6% at 2 weeks post-MI (1.2 ± 0.5). Additionally, [¹⁸F]FS1P1 signal decreased by 20.8% in the non-infarct remote area at 2 weeks post-MI compared with the sham control (1.6 ± 0.4 vs. 2.0 ± 0.2). Autoradiography study confirmed the trend of decreased [¹⁸F]FS1P1 uptake in the MI tissues. IF studies confirmed that the change in the [¹⁸F]FS1P1 PET signal corresponded with the change in S1PR1 expression.

Conclusions: This study demonstrated the downregulation of S1PR1 expression following MI and validated the use of [¹⁸F]FS1P1 PET imaging as an effective tool for detecting changes in S1PR1 expression post-MI.

Purpose: In target-specific cancer imaging, antibodies and their fragments are conjugated with fluorescent dyes to work as targeting molecules. We have recently developed indocyanine green (ICG) derivatives with anionic functional groups at the benzoindolenine moiety. When the ICG derivatives are used for antibody-based imaging, the chemical characteristics of the conjugated dyes may influence the pharmacokinetics of the targeting molecules. Therefore, in this study, we evaluated the in vivo pharmacokinetics of IgG and Fab conjugated with the ICG derivatives bearing anionic functional groups.

Procedures: A linker for conjugation was introduced into the methine chain of ICG and ICG derivatives possessing sulfonic acid (SC-Cy) or carboxylic acid (CC-Cy) groups at the benzoindolenine moiety. ICG, SC-Cy, or CC-Cy was conjugated with IgG, innate trastuzumab, and its Fab fragment. To evaluate the pharmacokinetics of these IgG-dyes and Fab-dyes, in vivo fluorescence imaging was performed in tumor-bearing mice at 0.25-96 h after intravenous administration of the imaging agents.

Results: The three IgG-dyes exhibited similar pharmacokinetics and tumor accumulation profiles post injection. Thus, the differences in the dye's chemical properties had minimal influence when the ICG derivatives were conjugated with IgG. In contrast, the pharmacokinetics and tumor accumulation profiles of the Fab-dyes were remarkably different. While Fab-SC-Cy exhibited high accumulation in the kidney but no accumulation in the tumors, Fab-CC-Cy showed higher tumor accumulation. This could be attributed to the excessively high negative charge density in the benzoindolenine moiety of SC-Cy, which influenced the excretion route of the Fab fragment.

Conclusions: The IgG conjugated with SC-Cy or CC-Cy dyes exhibited favorable pharmacokinetics profiles. In contrast, Fab-CC-Cy demonstrated superior performance in tumor imaging compared to Fab-SC-Cy. Our findings suggest that introducing anionic functional groups into the benzoindolenine moiety of ICG could lead to the development of near-infrared dyes that could be useful in antibody-based tumor imaging.

Purpose: Ischemic stroke is a significant threat to human life and health, and timely diagnosis is essential for improving patient outcomes. Magnetic Particle Imaging (MPI), as an emerging high-sensitivity imaging technology, holds significant potential for the diagnosis of ischemic stroke. It is necessary to conduct multimodal MPI research based on the characteristics of the animal model and the detection needs of ischemic stroke.

Procedures: We used tree shrews, which have a close phylogenetic relationship with primates, as experimental subjects and established a photothrombotic (PT) stroke model. Considering the body size of tree shrews and the high-sensitivity detection requirements for ischemic stroke, a dedicated MPI receiving system for tree shrews was developed based on the primate brain MPI equipment. After validating the MPI system's performance, multimodal MPI fusion imaging of the tree shrew brain was performed by combining magnetic resonance imaging (MRI) and computed tomography (CT).

Results: The sensitivity of the receiving system for tree shrews is 0.017 mg Fe/mL, which is 8 times higher than that of the original system. Within one hour after the establishment of the PT stroke model, the MPI signal intensity in ischemic stroke tree shrews was approximately 25% lower than in the control group, while MRI showed no significant differences. On the 6th and 12th days after ischemic stroke onset, MRI images revealed clear lesion locations. Anatomical results of the tree shrew brain revealed significant lesions, confirming the successful establishment of the PT stroke model.

Conclusions: The dedicated MPI receiving system developed in this study significantly enhanced MPI sensitivity. The multimodal MPI imaging platform integrates the advantages of MRI and CT structural imaging based on high-sensitivity detection, enabling early detection of ischemic stroke in tree shrews.

Purpose: Sentinel lymph node (SLN) mapping is a critical procedure in the staging and treatment of cancers, such as breast cancer and melanoma. Current radiocolloids used in SLN localization, like [^99mTc]Tc-Sulfur Colloid, face limitations in imaging resolution and specificity. This study aims to evaluate the biodistribution of [⁶⁸Ga]Ga-DOTA-nanoHSA, a novel nanoparticle-based radiotracer, for SLN mapping using PET/CT imaging in both healthy and tumor-bearing murine models and compare results with [^99mTc]Tc-Sulfur Colloid as the current gold standard for lymph node staging in breast cancer. Additionally, the maximum tolerated dose and potential systemic toxicity of the carrier were assessed in humanized mice.

Methods: Nanoalbumin radiotracers were prepared by thermal denaturation of human serum albumin (HSA), followed by conjugation with 2,2',2″,2″'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) and labeling with gallium-68. The stability of [⁶⁸Ga]Ga-DOTA-nanoHSA was evaluated in the tracer formulations and in mouse serum. The novel radiotracers were administered subcutaneously and intratumorally in healthy and tumor-bearing mice, respectively, to evaluate SLN uptake via PET/CT imaging. Biodistribution was assessed in major organs, and the tracers' ability to accurately localize SLNs was compared to an existing standard. Toxicity was evaluated in humanized mice, where body weight, clinical scoring, and blood chemistry were monitored over a 14-days period. Mice received escalating doses of DOTA-nanoHSA to determine the maximum tolerated dose.

Results: [⁶⁸Ga]Ga-DOTA-nanoHSA tracers (30 nm and 70 nm) were reliably produced with high radiochemical purity (RCP > 90%). The stability of [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) in the final formulations at pH 3.5 and 7.0 and in mouse serum was confirmed up to 4-6 h. [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) demonstrated effective SLN localization in both healthy and tumor-bearing mice, with high uptake in SLNs and minimal off-target accumulation in non-lymphatic organs. DOTA-nanoHSA was well-tolerated in humanized mice, with no significant changes in body weight, clinical scores, or blood chemistry parameters, even at higher doses. No dose-dependent toxicity was observed.

Conclusion: [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) demonstrated significant potential as a novel imaging agent for SLN mapping. Its favorable toxicity profile, combined with its effectiveness in SLN localization, suggests it could be a valuable alternative for SLN biopsy in clinical practice. Further studies are warranted to confirm these findings in human trials.

Background: Fluorescence-guided molecular imaging may improve colorectal cancer (CRC) patient outcomes by enabling early detection and better surgical treatment, relying on developing targeted fluorescent tracers to highlight tumours. This study investigates visualising primary colon tumours by topically applying EMI-137, a targeted fluorescent tracer designed to bind to c-Met receptor. We introduce a novel viscous formulation to enhance the tracer's performance, aiming for a clear, robust fluorescent signal by improving contact with mucosal surface of ex vivo colon specimens.

Methods: We evaluated fluorescence properties of EMI-137 in phosphate-buffered saline (PBS) and in methylcellulose (m-cellulose) and determined emission spectrum of the tracer in both formulations. Flow cytometry was used to determine EMI-137's specificity for c-Met receptor and its optimal concentration. Live-cell imaging visually confirmed EMI-137's fluorescence signal for the c-Met receptor, highlighting its distinctive characteristics across various solvents. In a prospective cohort study, freshly excised colon cancer specimens were incubated with EMI-137 in PBS or m-cellulose. Specimens underwent a meticulous washing process. Near-infrared fluorescence imaging was performed and compared with histopathological analysis to validate detection accuracy.

Results: Fluorospectrometry showed that m-cellulose enhanced EMI-137's fluorescence intensity compared to PBS. Flow cytometry showed dose-dependent binding of EMI-137 in HT-29 cells, with an optimum at 500 nM. Microscopy confirmed targeting of c-Met receptors. Topical EMI-137 dissolved in m-cellulose visualised colon tumours effectively, resulting in a high tumour-to-background ratio. Histopathological analysis confirmed c-Met expression in these colon tumours.

Conclusion: EMI-137 in a novel viscous vehicle effectively imaged c-Met expressing colon tumors, potentially facilitating fluorescent-guided tumor imaging.

Purpose: Sarcomas, malignancies of mesenchymal origin, present significant diagnostic and therapeutic challenges due to their heterogeneity and low incidence. This review aims to examine the evolving role of fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in the management of soft tissue and musculoskeletal sarcomas. Specifically, it seeks to evaluate 18F-FDG PET/CT's utility in detecting metastatic lesions, differentiating benign from malignant tumors, and assessing treatment responses.

Procedures: A comprehensive review of the literature was conducted to analyze advancements in PET imaging for sarcomas. Emphasis was placed on 18F-FDG PET/CT's role in complementing conventional imaging techniques, such as computed tomography (CT) and magnetic resonance imaging (MRI). Key aspects of PET imaging in musculoskeletal and cardiac tumors were examined, including its sensitivity and specificity in identifying metastases and its metabolic characterization of various tumor types.

Results: 18F-FDG PET/CT has demonstrated high sensitivity and specificity in detecting metastatic sarcoma lesions and grading musculoskeletal tumors, such as osteosarcoma, chondrosarcoma, and Ewing sarcoma. Its ability to provide metabolic insights has enhanced differentiation between benign and malignant tumors, including myxomas, lipomas, angiosarcomas, and leiomyosarcomas. Furthermore, in primary and secondary cardiac tumors, 18F-FDG PET/CT has proven valuable for treatment planning by offering detailed metabolic characterization.

Conclusions: 18F-FDG PET/CT serves as a critical imaging modality in the diagnosis, staging, and treatment monitoring of sarcomas. By complementing conventional imaging techniques, it enhances the accuracy of tumor characterization and facilitates improved clinical decision-making. Its application in both musculoskeletal and cardiac sarcomas underscores its growing significance in oncologic imaging, making it a valuable tool in optimizing patient outcomes.