PEGylated and Non-PEGylated TCP-1 Probes for Imaging of Colorectal Cancer.

PURPOSE: Previous studies indicate that 99mTc- and fluorescent-labeled c[Cys-Thr-Pro-Ser-Pro-Phe-Ser-His-Cys]OH (TCP-1) peptides were able to detect colorectal cancer (CRC) and tumor-associated vasculature. This study was designed to characterize the targeting properties of PEGylated and non-PEGylated TCP-1 peptides for CRC imaging. PROCEDURES: Cell uptake of cyanine 7 (Cy7)-labeled TCP-1 probes (Cy7-PEG4-TCP-1 and Cy7-TCP-1) was investigated in three CRC cell lines (human, HCT116 and HT29; mouse, CT26). Xenograft and orthotopic CRC tumor models with HCT116 and CT26 cells were used to characterize biodistribution and CRC tumor-targeting properties of TCP-1 fluorescence and radioligand with and without PEGylation, [99mTc]Tc-HYNIC-PEG4-TCP-1 vs. [99mTc]Tc-HYNIC-TCP-1. RESULTS: Fluorescence images showed that TCP-1 probes were distributed in the cytoplasm and nucleus of CRC cells. When CT26 cells were treated with unlabeled TCP-1 peptide prior to the cell incubation with Cy7-PEG4-TCP-1, cell fluorescent signals were significantly reduced relative to the cells without blockade. Relative to Cy7-TCP-1, superior brilliance and visibility of fluorescence was observed in the tumor with Cy7-PEG4-TCP-1 and maintained up to 18 h post-injection. [99mTc]Tc-HYNIC-PEG4-TCP-1 images in xenograft and orthotopic CRC models demonstrated that TCP-1 PEGylation preserved tumor-targeting capability of TCP-1, but its distribution (%ID/g) in the liver and intestine was higher than that of [99mTc]Tc-HYNIC-TCP-1 (1.51 ± 0.29 vs 0.53 ± 0.12, P < 0.01). Better tumor visualization by [99mTc]Tc-HYNIC-TCP-1 was observed in the orthotopic CRC model due to lower intestinal radioactivity. CONCLUSIONS: TCP-1-based probes undergo endocytosis and localize in the cytoplasm and nucleus of human and mouse CRC cells. Tumor detectability of fluorescent TCP-1 peptide with a PEG4 spacer is promising due to its enhanced tumor binding affinity and rapid clearance kinetics from nontumor tissues. Non-PEGylated [99mTc]Tc-HYNIC-TCP-1 exhibits lower nonspecific accumulation in the liver and gastrointestinal tract and might have better capability for detecting CRC lesions in clinical sites. TCP-1 may represent an innovative targeting molecule for detecting CRC noninvasively.

Use of radiolabeled hyaluronic acid for preclinical assessment of inflammatory injury and acute respiratory distress syndrome.

Acute respiratory distress syndrome (ARDS) is accompanied by a dramatic increase in lung hyaluronic acid (HA), leading to a dose-dependent reduction of pulmonary oxygenation. This pattern is associated with severe infections, such as COVID-19, and other important lung injury etiologies. HA actively participates in molecular pathways involved in the cytokine storm of COVID-19-induced ARDS. The objective of this study was to evaluate an imaging approach of radiolabeled HA for assessment of dysregulated HA deposition in mouse models with skin inflammation and lipopolysaccharide (LPS)-induced ARDS using a novel portable intensified Quantum Imaging Detector (iQID) gamma camera system. METHODS: HA of 10 kDa molecular weight (HA10) was radiolabeled with 125I and 99mTc respectively to produce [125I]I-HA10 and [99mTc]Tc-HA10, followed by comparative studies on stability, in vivo biodistribution, and uptake at inflammatory skin sites in mice with 12-O-tetradecanoylphorbol-13-acetate (TPA)-inflamed ears. [99mTc]Tc-HA10 was used for iQID in vivo dynamic imaging of mice with ARDS induced by intratracheal instillation of LPS. RESULTS: [99mTc]Tc-HA10 and [125I]I-HA10 had similar biodistribution and localization at inflammatory sites. [99mTc]Tc-HA10 was shown to be feasible in measuring skin injury and monitoring skin wound healing. [99mTc]Tc-HA10 dynamic pulmonary images yielded good visualization of radioactive uptake in the lungs. There was significantly increased lung uptake and slower lung washout in mice with LPS-induced ARDS than in control mice. Postmortem biodistribution measurement of [99mTc]TcHA10 (%ID/g) was 11.0 ± 3.9 vs. 1.3 ± 0.3 in the ARDS mice (n = 6) and controls (n = 6) (P < 0.001), consistent with upregulated HA expression as determined by enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry (IHC) staining. CONCLUSIONS: [99mTc]Tc-HA10 is promising as a biomarker for evaluating HA dysregulation that contributes to pulmonary injury in ARDS. Rapid iQID imaging of [99mTc]Tc-HA10 clearance from injured lungs may provide a functional template for timely assessment and quantitative monitoring of pulmonary pathophysiology and intervention in ARDS.

Characterization of TCP-1 probes for molecular imaging of colon cancer.

Molecular probes capable of detecting colorectal cancer (CRC) are needed for early CRC diagnosis. The objective of this study was to characterize c[CTPSPFSHC]OH (TCP-1), a small peptide derived from phage display selection, for targeting human CRC xenografts using technetium-99m ((99m)Tc)-labeled TCP-1 and fluorescent cyanine-7 (Cy7)-labeled form of the peptide (Cy7-TCP-1). (99m)Tc-TCP-1 was generated by modifying TCP-1 with succinimidyl-6-hydrazino-nicotinamide (S-HYNIC) followed by radiolabeling. In vitro saturation binding experiments were performed for (99m)Tc-TCP-1 in human HCT116 colon cancer cells. SCID mice with human HCT116 cancer xenografts were imaged with (99m)Tc-TCP-1 or control peptide using a small-animal SPECT imager: Group I (n=5) received no blockade; Group II (n=5) received a blocking dose of non-radiolabeled TCP-1. Group III (n=5) were imaged with (99m)Tc-labeled control peptide (inactive peptide). SCID mice with human PC3 prostate cancer xenografts (Group IV, n=5) were also imaged with (99m)Tc-TCP-1. Eight additional SCID mice bearing HCT116 xenografts in dorsal skinfold window chambers (DSWC) were imaged by direct positron imaging of (18)F-fluorodeoxyglucose ((18)F-FDG) and fluorescence microscopy of Cy7-TCP-1. In vitro(99m)Tc-HYNIC-TCP-1 binding assays on HCT 116 cells indicated a mean Kd of 3.04±0.52nM. In cancer xenografts, (99m)Tc-TCP-1 radioactivity (%ID/g) was 1.01±0.15 in the absence of blockade and was reduced to 0.26±0.04 (P<0.01) with blockade. No radioactive uptake was observed in the PC3 tumors with (99m)Tc-TCP-1 or HCT116 tumors with inactive peptide. Cy7-TCP-1 activity localized not only in metabolically active tumors, as defined by (18)F-FDG imaging, but also in peritumoral microvasculature. In conclusion, TCP-1 probes may have a distinct targeting mechanism with high selectivity for CRC and tumor-associated vasculature. Molecular imaging with TCP-1 probes appears promising to detect malignant colorectal lesions.

Therapy operating characteristic curves: tools for precision chemotherapy.

The therapy operating characteristic (TOC) curve, developed in the context of radiation therapy, is a plot of the probability of tumor control versus the probability of normal-tissue complications as the overall radiation dose level is varied, e.g., by varying the beam current in external-beam radiotherapy or the total injected activity in radionuclide therapy. This paper shows how TOC can be applied to chemotherapy with the administered drug dosage as the variable. The area under a TOC curve (AUTOC) can be used as a figure of merit for therapeutic efficacy, analogous to the area under an ROC curve (AUROC), which is a figure of merit for diagnostic efficacy. In radiation therapy, AUTOC can be computed for a single patient by using image data along with radiobiological models for tumor response and adverse side effects. The mathematical analogy between response of observers to images and the response of tumors to distributions of a chemotherapy drug is exploited to obtain linear discriminant functions from which AUTOC can be calculated. Methods for using mathematical models of drug delivery and tumor response with imaging data to estimate patient-specific parameters that are needed for calculation of AUTOC are outlined. The implications of this viewpoint for clinical trials are discussed.

Detection of atherosclerotic plaques in ApoE-deficient mice using (99m)Tc-duramycin.

UNLABELLED: Apoptosis of macrophages and smooth muscle cells is linked to atherosclerotic plaque destabilization. The apoptotic cascade leads to exposure of phosphatidylethanolamine (PE) on the outer leaflet of the cell membrane, thereby making apoptosis detectable using probes targeting PE. The objective of this study was to exploit capabilities of a PE-specific imaging probe, (99m)Tc-duramycin, in localizing atherosclerotic plaque and assessing plaque evolution in apolipoprotein-E knockout (ApoE(-/-)) mice. METHODS: Atherosclerosis was induced in ApoE(-/-) mice by feeding an atherogenic diet. (99m)Tc-duramycin images were acquired using a small-animal SPECT imager. Six ApoE(-/-) mice at 20weeks of age (Group I) were imaged and then sacrificed for ex vivo analyses. Six additional ApoE(-/-) mice (Group II) were imaged at 20 and 40weeks of age before sacrifice. Six ApoE wild-type (ApoE(+/+)) mice (Group III) were imaged at 40weeks as controls. Five additional ApoE(-/-) mice (40weeks of age) (Group IV) were imaged with a (99m)Tc-labeled inactive peptide, (99m)Tc-LinDUR, to assess (99m)Tc-duramycin targeting specificity. RESULTS: Focal (99m)Tc-duramycin uptake in the ascending aorta and aortic arch was detected at 20 and 40weeks in the ApoE(-/-) mice but not in ApoE(+/+) mice. (99m)Tc-duramycin uptake in the aortic lesions increased 2.2-fold on quantitative imaging in the ApoE(-/-) mice between 20 and 40weeks. Autoradiographic and histological data indicated significantly increased (99m)Tc-duramycin uptake in the ascending aorta and aortic arch associated with advanced plaques. Quantitative autoradiography showed that the ratio of activity in the aortic arch to descending thoracic aorta, which had no plaques or radioactive uptake, was 2.1 times higher at 40weeks than at 20weeks (6.62±0.89 vs. 3.18±0.29, P<0.01). There was barely detectable focal uptake of (99m)Tc-duramycin in the aortic arch of ApoE(+/+) mice. No detectable (99m)Tc-LinDUR uptake was observed in the aortas of ApoE(-/-) mice. CONCLUSIONS: PE-targeting properties of (99m)Tc-duramycin in the atherosclerotic mouse aortas were noninvasively characterized. (99m)Tc-duramycin is promising in localizing advanced atherosclerotic plaques.

Quantifying and Reducing Uncertainties in Cancer Therapy.

There are two basic sources of uncertainty in cancer chemotherapy: how much of the therapeutic agent reaches the cancer cells, and how effective it is in reducing or controlling the tumor when it gets there. There is also a concern about adverse effects of the therapy drug. Similarly in external-beam radiation therapy or radionuclide therapy, there are two sources of uncertainty: delivery and efficacy of the radiation absorbed dose, and again there is a concern about radiation damage to normal tissues. The therapy operating characteristic (TOC) curve, developed in the context of radiation therapy, is a plot of the probability of tumor control vs. the probability of normal-tissue complications as the overall radiation dose level is varied, e.g. by varying the beam current in external-beam radiotherapy or the total injected activity in radionuclide therapy. The TOC can be applied to chemotherapy with the administered drug dosage as the variable. The area under a TOC curve (AUTOC) can be used as a figure of merit for therapeutic efficacy, analogous to the area under an ROC curve (AUROC), which is a figure of merit for diagnostic efficacy. In radiation therapy AUTOC can be computed for a single patient by using image data along with radiobiological models for tumor response and adverse side effects. In this paper we discuss the potential of using mathematical models of drug delivery and tumor response with imaging data to estimate AUTOC for chemotherapy, again for a single patient. This approach provides a basis for truly personalized therapy and for rigorously assessing and optimizing the therapy regimen for the particular patient. A key role is played by Emission Computed Tomography (PET or SPECT) of radiolabeled chemotherapy drugs.

Inflammation imaging of atherosclerosis in Apo-E-deficient mice using a (99m)Tc-labeled dual-domain cytokine ligand.

UNLABELLED: Interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) play a critical role in initiating and accelerating atherosclerosis. This study evaluated the imaging properties of (99m)Tc-TNFR2-Fc-IL-1RA ((99m)Tc-TFI), a dual-domain cytokine radioligand that targets TNF-α and IL-1ß pathways, in assessing atherosclerosis development in apolipoprotein-E-deficient (ApoE(-)(/)(-)) mice. METHODS: The feasibility and specificity of detecting atherosclerosis with (99m)Tc-TFI SPECT imaging were investigated in ApoE(-)(/)(-) and ApoE(+)(/)(+) mice. Fifty-four ApoE(-)(/)(-) mice were fed either an atherogenic diet (AGD) or a normal diet (ND) beginning at 5 weeks of age. Eighteen Apo-E wild-type (ApoE(+)(/)(+)) mice were fed an ND. Two groups of ApoE(-)(/)(-) mice (n=12 each group) on AGD and ND were imaged three times with (99m)Tc-TFI and a high-resolution SPECT system at 20-25, 30-40, and 48-52 weeks to study the evolution of atherosclerotic plaque. RESULTS: Focal radioactive accumulations in the aortic arch region were observed in the ApoE(-)(/)(-) mice (n=12) on AGD but not in the ApoE(+)(/)(+) mice on ND (n=10). Apo-E(-)(/)(-) mice on ND (n=11) exhibited lower radioactive uptake than ApoE(-)(/)(-) mice on AGD (P<0.05). Co-injection of an excess of cold ligand with (99m)Tc-TFI resulted in significant reduction of (99m)Tc-TFI uptake in the ApoE(-)(/)(-) mice on AGD. Longitudinal studies showed that (99m)Tc-TFI uptake in the aortas of ApoE(-)(/)(-) mice progressively increased from 20 to 48 weeks. Real-time PCR assays demonstrated that atherosclerotic aortas expressed significantly higher IL-1ß and TNF-α than the aortas from wild-type controls. CONCLUSIONS: Atherosclerotic plaques were detected by (99m)Tc-TFI imaging in ApoE(-)(/)(-) mice. (99m)Tc-TFI is promising for specific detection of inflammatory response in atherosclerotic plaques.

Molecular Imaging in the College of Optical Sciences - An Overview of Two Decades of Instrumentation Development.

During the past two decades, researchers at the University of Arizona's Center for Gamma-Ray Imaging (CGRI) have explored a variety of approaches to gamma-ray detection, including scintillation cameras, solid-state detectors, and hybrids such as the intensified Quantum Imaging Device (iQID) configuration where a scintillator is followed by optical gain and a fast CCD or CMOS camera. We have combined these detectors with a variety of collimation schemes, including single and multiple pinholes, parallel-hole collimators, synthetic apertures, and anamorphic crossed slits, to build a large number of preclinical molecular-imaging systems that perform Single-Photon Emission Computed Tomography (SPECT), Positron Emission Tomography (PET), and X-Ray Computed Tomography (CT). In this paper, we discuss the themes and methods we have developed over the years to record and fully use the information content carried by every detected gamma-ray photon.

SPECT imaging of inflammatory response in ischemic-reperfused rat hearts using a 99mTc-labeled dual-domain cytokine ligand.

UNLABELLED: Soluble tumor necrosis factor (TNF) receptor-2 (TNFR2) and interleukin-1 receptor antagonist (IL-1ra) were fused to the Fc portion of IgG1 using recombinant DNA technology. The resulting dual-domain cytokine ligand, TNFR2-Fc-IL-1ra, specifically binds to TNF and to the type I IL-1 receptor (IL-1RI). This study was designed to characterize the kinetic profile of (99m)Tc-labeled TNFR2-Fc-IL-1ra (TFI) for imaging inflammatory response in an ischemic-reperfused (IR) rat heart model. METHODS: The IR model was created by ligating the left coronary artery for 45 min, followed by 2-h reperfusion. Cardiac SPECT images of TFI in the IR model (n = 6) were dynamically acquired for 3 h. Correlative data of myocardial TFI distribution versus microsphere-determined tissue blood flow were acquired in 3 extra IR hearts. Inflammation targeting affinity of TFI was compared with 2 individual cytokine radioligands, (99m)Tc-IL-1ra-Fc (IF) and (99m)Tc-TNFR2-Fc (TF) (n = 6 each group). Myocardial cytokine expression was evaluated by immunochemical assay. RESULTS: Increased TFI uptake was found in the ischemic area and correlated with the severity of ischemia. At 3 h after injection, the ratio of hot-spot accumulation in the ischemic area to a remote viable zone was 5.39 ± 1.11 for TFI, which was greater than that for IF (3.28 ± 0.81) and TF (3.29 ± 0.75) (P < 0.05). The in vivo uptake profiles of TFI, TF, and IF were consistent with ex vivo radioactive measurements and correlated with upregulated IL-1 and TNF expression. CONCLUSION: The dual-domain TFI is promising for noninvasive detection of inflammatory reactions in IR myocardium because of its more potent affinity to the inflammatory sites compared with TF and IF.

Imaging of rat cerebral ischemia-reperfusion injury using(99m)Tc-labeled duramycin.

OBJECTIVES: Prompt identification of necrosis and apoptosis in the infarct core and penumbra region is critical in acute stroke for delineating the underlying ischemic/reperfusion molecular pathologic events and defining therapeutic alternatives. The objective of this study was to investigate the capability of (99m)Tc-labeled duramycin in detecting ischemia-reperfusion injury in rat brain after middle cerebral artery (MCA) occlusion. METHODS: Ischemic cerebral injury was induced in ten rats by vascular insertion of a nylon suture in the left MCA for 3 hr followed by 21-24hr reperfusion. After i.v. injection of (99m)Tc-duramycin (1.0-3.5 mCi), dynamic cerebral images were acquired for 1 hr in six rats using a small-animal SPECT imager. Four other rats were imaged at 2 hr post-injection. Ex vivo images were obtained by autoradiography after sacrifice. Histologic analyses were performed to assess cerebral infarction and apoptosis. RESULTS: SPECT images showed that (99m)Tc-duramycin uptake in the left cerebral hemisphere was significantly higher than that in the right at 1 and 2 hr post-injection. The level of radioactive uptake in the ischemic brain varied based on ischemic severity. The average ratio of left cerebral hot-spot uptake to right hemisphere radioactivity, as determined by computerized ROI analysis, was 4.92±0.79. Fractional washout at 1 hr was 38.2±4.5% of peak activity for left cerebral hot-spot areas and 80.9±2.0% for remote control areas (P<0.001). Based on triphenyltetrazolium chloride staining and autoradiograph image data, the hotspot uptake may be associated primarily with the ischemic penumbra, in which high apoptotic activity was observed by cleaved caspase-3 immunocytochemical staining. CONCLUSIONS: (99m)Tc-duramycin SPECT imaging may be useful for detecting and quantifying ongoing apoptotic neuronal cell loss induced by ischemia-reperfusion injury.

Characterization of 99mTc-labeled cytokine ligands for inflammation imaging via TNF and IL-1 pathways.

INTRODUCTION: TNFR2-Fc and IL-1ra-Fc are recombinant cytokine ligands that target TNF and IL-1. TNFR2-Fc-IL-1ra, a dual-domain agent that incorporates both ligands, allows bifunctional binding of IL-1 receptors and TNF. This study was designed to characterize (99m)Tc-labeled forms of these ligands, (99m)Tc-IL-1ra-Fc (IF), (99m)Tc-TNFR2-Fc (TF), and (99m)Tc-TNFR2-Fc-IL-1ra (TFI), for inflammation imaging. METHODS: The cytokine ligands were labeled with (99m)Tc by a direct approach via 2-iminothiolane (2-IT) reduction at various 2-IT/protein molar ratios. In vivo inflammation targeting studies were carried out in a mouse ear edema model created by topical application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the right ear of ICR mice. RESULTS: Radiolabeling yields increased with increasing amounts of 2-IT. When the 2-IT/protein ratio reached 1000, the radiolabeling yield was greater than 90% without significant colloid production. TPA-treated ears showed high radioligand uptake, which was clearly detected by SPECT and autoradiographic imaging. The activities (%ID/g) in the inflamed and control ears at 3h after injection were 2.76 ± 0.20 vs. 0.69 ± 0.12 for IF, 5.86 ± 0.40 vs. 2.86 ± 0.61 for TF, and 7.61 ± 0.86 vs. 1.99 ± 0.31 for TFI (P<0.05 vs. controls). TFI showed significantly higher uptake in the inflamed ears compared to TF and IF (P<0.05). Blocking study results indicated specificity of radioligand binding with decreased radioactive uptake in the inflamed ears. Western blotting and ELISA analysis further confirmed a high expression of IL-1ß and TNF-α in the inflamed ears. CONCLUSIONS: (99m)Tc-labeled cytokine ligands are a promising approach for detecting and understanding the inflammatory process. TFI may be more useful than the single-domain ligands for noninvasive detection of inflammatory sites.

Detection of myocardial ischemia-reperfusion injury using a fluorescent near-infrared zinc(II)-dipicolylamine probe and 99mTc glucarate.

A fluorescent zinc 2,2'-dipicolylamine coordination complex PSVue®794 (probe 1) is known to selectively bind to phosphatidylserine exposed on the surface of apoptotic and necrotic cells. In this study, we investigated the cell death targeting properties of probe 1 in myocardial ischemia-reperfusion injury. A rat heart model of ischemia-reperfusion was used. Probe 1, control dye, or 99mTc glucarate was intravenously injected in rats subjected to 30-minute and 5-minute myocardial ischemia followed by 2-hour reperfusion. At 90 minutes or 20 hours postinjection, myocardial uptake was evaluated ex vivo by fluorescence imaging and autoradiography. Hematoxylin-eosin and cleaved caspase-3 staining was performed on myocardial sections to demonstrate the presence of ischemia-reperfusion injury and apoptosis. Selective accumulation of probe 1 could be detected in the area at risk up to 20 hours postinjection. Similar topography and extent of uptake of probe 1 and 99mTc glucarate were observed at 90 minutes postinjection. Histologic analysis demonstrated the presence of necrosis, but only a few apoptotic cells could be detected. Probe 1 selectively accumulates in myocardial ischemia-reperfusion injury and is a promising cell death imaging tool.

A (99m)Tc-labeled dual-domain cytokine ligand for imaging of inflammation.

INTRODUCTION: Interleukin (IL)-1 and IL-18 are potent proinflammatory cytokines in inflammation-related diseases. Their actions are regulated by IL-1 receptor antagonist (IL-1ra) and IL-18 binding protein (IL-18bp). This study was designed to (99m)Tc-radiolabel an IL-1ra and IL-18bp dual-domain cytokine ligand, IL-18bp-Fc-IL-1ra, for specific inflammation targeting. METHODS: The (99m)Tc-IL-18bp-Fc-IL-1ra was obtained by direct labeling via 2-iminothiolane reduction. Competitive binding of (99m)Tc-labeled and unlabeled IL-18bp-Fc-IL-1ra to rat polymorphonuclear leukocytes was assessed in vitro. A mouse ear edema model was used to evaluate specific targeting properties of (99m)Tc-IL-18bp-Fc-IL1ra in vivo. The correlation between (99m)Tc-IL-18bp-Fc-IL-1ra uptake and (111)In-labeled polymorphonuclear neutrophil infiltration was studied using ischemic-reperfused rat hearts. RESULTS: Direct (99m)Tc-labeling yielded a stable dual-domain cytokine radioligand with radiochemical purity greater than 95% after gel filtration. Competitive binding studies showed specific targeting of (99m)Tc-IL-18bp-Fc-IL-1ra to inflammatory cells. The (99m)Tc-IL-18bp-Fc-IL-1ra uptake was 1.80±0.17 % injected dose per gram (%ID/g) in the inflamed ear without blocking, whereas uptake in the presence of IL-18bp-Fc-IL-1ra was 1.09±0.08 %ID/g (P<.05). The amounts of IL-1ß and IL-18 were significantly increased in the inflamed ears compared to the vehicle controls. A significant correlation of (99m)Tc-IL-18bp-Fc-IL-1ra with (111)In-labeled neutrophil distribution was observed in the ischemic-reperfused hearts (P<.001). CONCLUSION: Targeting proinflammatory cytokines with (99m)Tc-IL-18bp-Fc-IL-1ra may provide a suitable approach for specific detection of inflammatory sites.

Synthesis and preliminary evaluation of radiolabeled bis(zinc(II)-dipicolylamine) coordination complexes as cell death imaging agents.

The aim of this study was the development of (99m)Tc labeled bis(zinc(II)-dipicolylamine) (Zn²âº-DPA) coordination complexes, and the in vivo evaluation of their usefulness as radiotracers for the detection of cell death. DPA ligand 1 was labeled with (99m)Tc via the (99m)Tc-tricarbonyl core ([(99m)Tc(CO)3-1]³âº) or via HYNIC ((99m)Tc-HYNIC-1) in good radiochemical yields. Highest in vitro stabilities were demonstrated for [(99m)Tc(CO)3-1]³âº. A mouse model of hepatic apoptosis (anti-Fas mAb) was used to demonstrate binding to apoptotic cells. (99m)Tc-HYNIC-1 showed the best targeting of apoptotic hepatic tissue with a 2.2 times higher liver uptake in anti-Fas treated mice as compared to healthy animals. A rat model of ischemia-reperfusion injury was used to further explore the ability of the (99m)Tc-labeled Zn²âº-DPA coordination complexes to target cell death. Selective accumulation could be detected for both tracers in the area at risk, correlating with histological proof of cell death. Area at risk to normal tissue uptake ratios were 3.82 for [(99m)Tc(CO)3-1]³âº and 5.45 for (99m)Tc-HYNIC-1.

Kinetic characterization of a novel cationic (99m)Tc(I)-tricarbonyl complex, (99m)Tc-15C5-PNP, for myocardial perfusion imaging.

BACKGROUND: Intense liver uptake of (99m)Tc-sestamibi (MIBI) often interferes with visualization of myocardial perfusion in the inferior wall of the left ventricle. To develop improved myocardial perfusion agents, crown ether-containing dithiocarbamates and bisphosphines have been introduced in recent years. This study was designed to investigate the myocardial imaging properties and in vivo kinetics of a cationic (99m)Tc(I)-tricarbonyl complex, (99m)Tc-15C5-PNP, in comparison with MIBI. METHODS: Dynamic cardiac images were acquired for 60 minutes after intravenous tracer injection using a small-animal SPECT system in healthy control rats and rats with myocardial infarcts. Myocardial and liver time-activity curves were generated for radiopharmaceutical kinetic analysis. RESULTS: Good visualization of the left ventricular wall and perfusion defects could be achieved 20 minutes after (99m)Tc-15C5-PNP administration. (99m)Tc-15C5-PNP images in all hearts with infarcts showed perfusion defects, which were comparable to MIBI images. The kinetic curves plotted from 1 to 60 minutes demonstrated that (99m)Tc-15C5-PNP has a shorter washout half-life (6.4 ± 3.2 vs 124 ± 30.5 minutes, P < .01) in the liver, lower residual liver activity (14.5 ± 10.2% vs 36.5 ± 28.9%, P < .01), and higher heart/liver ratio than MIBI. CONCLUSIONS: (99m)Tc-15C5-PNP has potential for rapid myocardial perfusion imaging with low liver uptake.

Evaluating the protective role of ischaemic preconditioning in rat hearts using a stationary small-animal SPECT imager and 99mTc-glucarate.

OBJECTIVE: To examine the protective role of ischaemic preconditioning (IPC) in rat hearts using Tc-glucarate (GLA) and a stationary SPECT imager, FastSPECT. METHODS: Twenty-four rats with 30 min myocardial ischaemia and 150 min reperfusion (IR) were studied as follows. The IPC group (n=6) underwent IPC (five cycles of 4 min ligation of the left coronary artery and reflow) before IR. The control group (n=7) was treated by IR without IPC. The SPT group (n=6) was subjected to IPC and an adenosine antagonist, 8-(p-sulfophenyl)-theophylline (SPT). The vehicle group (n=5) received IPC and SPT carrier vehicle. GLA was delivered intravenously 30 min post-reperfusion, and 2-h dynamic cardiac images were acquired by FastSPECT. RESULTS: GLA showed 'hot-spot' accumulation in the ischaemic area-at-risk (IAR) and exhibited lower retention (% 5 min peak) in the IPC and vehicle groups (33.8+/-2.6 vs. 35.7+/-9.2, P>0.05) than in the control and SPT groups (63.1+/-5.3 vs. 54.8+/-4.8, P>0.05). The infarct size (% IAR) was larger in the control and SPT groups (48.2+/-6.3 vs. 41.7+/-6.3, P>0.05) than that in the IPC and vehicle groups (21.0+/-1.9 vs. 19.1+/-4.6, P>0.05). In terms of the ex-vivo IAR-to-normal radioactivity ratio, there was a statistical difference between the control and IPC groups (7.4+/-0.9 vs. 3.0+/-0.4), as well as the SPT and vehicle groups (7.4+/-1.0 vs. 3.4+/-0.5). CONCLUSION: IPC offers cardioprotection and relates to the activation of adenosine receptors in rat hearts. FastSPECT GLA imaging is not only useful in detecting early ischaemia-reperfusion injury, but also valuable in evaluating cardioprotection.

An implantable synthetic SPECT lesion: a bridge from phantom to reality.

UNLABELLED: Small-animal imaging systems are often characterized using phantoms, which may not predict performance in clinical applications. An implantable synthetic SPECT lesion would facilitate characterization of lesion detectability in a living animal. METHODS: Anion-exchange columns with bed volumes of 100-300 nL were constructed from medical-grade polyvinyl chloride tubing and resin. The columns were tested in an excised mouse femur and implanted in the femur of a living mouse. Imaging was performed using a prototype dual-modality SPECT/CT system. RESULTS: Activity of 7.4-22.2 MBq (0.2-0.6 mCi) localized within the synthetic lesion. The synthetic lesions were reused multiple times. Mice tolerated the implanted columns without complications for up to 8 wk. CONCLUSION: A reusable, synthetic SPECT lesion was constructed and implanted in the femur of a living mouse. The synthetic lesion is useful for the development of imaging schemes and for more realistically evaluating imaging-system performance in the context of a living animal.

SemiSPECT: a small-animal single-photon emission computed tomography (SPECT) imager based on eight cadmium zinc telluride (CZT) detector arrays.

The first full single-photon emission computed tomography (SPECT) imager to exploit eight compact high-intrinsic-resolution cadmium zinc telluride (CZT) detectors, called SemiSPECT, has been completed. Each detector consists of a CZT crystal and a customized application-specific integrated circuit (ASIC). The CZT crystal is a 2.7 cm x 2.7 cm x -0.2 cm slab with a continuous top electrode and a bottom electrode patterned into a 64 x 64 pixel array by photolithography. The ASIC is attached to the bottom of the CZT crystal by indium-bump bonding. A bias voltage of -180 V is applied to the continuous electrode. The eight detectors are arranged in an octagonal lead-shielded ring. Each pinhole in the eight-pinhole aperture placed at the center of the ring is matched to each individual detector array. An object is imaged onto each detector through a pinhole, and each detector is operated independently with list-mode acquisition. The imaging subject can be rotated about a vertical axis to obtain additional angular projections. The performance of SemiSPECT was characterized using 99mTc. When a 0.5 mm diameter pinhole is used, the spatial resolution on each axis is about 1.4 mm as estimated by the Fourier crosstalk matrix, which provides an algorithm-independent average resolution over the field of view. The energy resolution achieved by summing neighboring pixel signals in a 3 x 3 window is about 10% full-width-at-half-maximum of the photopeak. The overall system sensitivity is about 0.5 x 10(-4) with the energy window of +/-10% from the photopeak. Line-phantom images are presented to visualize the spatial resolution provided by SemiSPECT, and images of bone, myocardium, and human tumor xenografts in mice demonstrate the feasibility of preclinical small-animal studies with SemiSPECT.