Molecular imaging in oncology: Current impact and future directions.

The authors define molecular imaging, according to the Society of Nuclear Medicine and Molecular Imaging, as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Although practiced for many years clinically in nuclear medicine, expansion to other imaging modalities began roughly 25 years ago and has accelerated since. That acceleration derives from the continual appearance of new and highly relevant animal models of human disease, increasingly sensitive imaging devices, high-throughput methods to discover and optimize affinity agents to key cellular targets, new ways to manipulate genetic material, and expanded use of cloud computing. Greater interest by scientists in allied fields, such as chemistry, biomedical engineering, and immunology, as well as increased attention by the pharmaceutical industry, have likewise contributed to the boom in activity in recent years. Whereas researchers and clinicians have applied molecular imaging to a variety of physiologic processes and disease states, here, the authors focus on oncology, arguably where it has made its greatest impact. The main purpose of imaging in oncology is early detection to enable interception if not prevention of full-blown disease, such as the appearance of metastases. Because biochemical changes occur before changes in anatomy, molecular imaging-particularly when combined with liquid biopsy for screening purposes-promises especially early localization of disease for optimum management. Here, the authors introduce the ways and indications in which molecular imaging can be undertaken, the tools used and under development, and near-term challenges and opportunities in oncology.

Reduced P-glycoprotein recognition of a radioiodine-labeled phosphonium cation by stilbenylation for mitochondrial membrane potential based-imaging.

The accumulation of radiolabeled phosphonium cations in cells is dependent on the mitochondrial membrane potential (MMP). However, the efflux of these cations from tumor cells via P-glycoprotein (P-gp) limits their clinical application as MMP-based imaging tracers. In the present study, we designed (E)-diethyl-4-[125I]iodobenzyl-4-stilbenylphosphonium ([125I]IDESP), which contains a stilbenyl substituent, as a P-gp inhibitor to reduce P-gp recognition, and evaluated its biological properties in comparison with 4-[125I]iodobenzyl dipropylphenylphosphonium ([125I]IDPP). The in vitro cellular uptake ratio of [125I]IDESP in P-gp expressing K562/Vin cells to the parent (P-gp negative) K562 cells was significantly higher than that of [125I]IDPP. The efflux rate of [125I]IDESP was not significantly different between K562 and K562/Vin, while [125I]IDPP was rapidly effluxed from K562/Vin compared with K562, and the efflux of [125I]IDPP from K562/Vin was inhibited by the P-gp inhibitor, cyclosporine A. The cellular uptake of [125I]IDESP was well correlated with the MMP levels. These results suggested that [125I]IDESP was accumulated in cells depending on the MMP levels, without being effluxed via P-gp, while [125I]IDPP was rapidly effluxed from the cells via P-gp. Despite having suitable in vitro properties for MMP-based imaging, [125I]IDESP showed rapid blood clearance and lower tumor accumulation than [125I]IDPP. Improvement in the normal tissue distribution of [125I]IDESP is required to develop an agent for use in in vivo MMP-based tumor imaging.

Synthesis and evaluation of 111 In-labeled tetrapeptide-based compounds as single-photon emission computed tomography imaging probes targeting granzyme B.

Granzyme B is an attractive target as a biomarker for contributing to improve the treatment with immune checkpoint inhibitor (ICI). In this study, we designed novel 111 In-labeled granzyme B-targeting single-photon emission computed tomography (SPECT) imaging probes, [111 In]IDT and [111 In]IDAT. Nonradioactive In-labeled granzyme B-targeting compounds ([nat In]IDT, [nat In]IDAT) showed the affinity for recombinant mouse granzyme B. [111 In]IDT and [111 In]IDAT were obtained with moderate radiochemical yield and high stability in mouse plasma (>95%). In a biodistribution experiment using tumor-bearing mice, [111 In]IDT and [111 In]IDAT showed moderate accumulation in tumor. Ex vivo autoradiography (ARG) indicated that the accumulation of radioactivity in tumor was correlated to expression of granzyme B confirmed by the immunohistochemical staining. These results indicated that [111 In]IDT and [111 In]IDAT showed the basic properties as granzyme B-targeting SPECT probes.

Synthesis and Evaluation of 99mTc-Labeled PSMA-Targeted Tracers Based on the Lys-Urea-Aad Pharmacophore for Detecting Prostate Cancer with Single Photon Emission Computed Tomography.

Prostate-specific membrane antigen (PSMA) is a well-validated prostate cancer marker but reported PSMA-targeted tracers derived from the Lys-urea-Glu pharmacophore including the clinically validated [99mTc]Tc-EDDA/HYNIC-iPSMA have high off-target uptake in kidneys, spleen, and salivary glands. In this study, we synthesized and evaluated three novel 99mTc-labeled PSMA-targeted tracers and investigated if the tracers derived from the Lys-urea-Aad pharmacophore could have minimized uptake in off-target organs/tissues. In vitro competition binding assays showed that compared with HYNIC-iPSMA, the three novel ligands had slightly weaker PSMA binding affinity (average Ki = 3.11 vs. 8.96-11.6 nM). Imaging and ex vivo biodistribution studies in LNCaP tumor-bearing mice showed that [99mTc]Tc-EDDA/HYNIC-iPSMA and the three novel tracers successfully visualized LNCaP tumor xenografts in SPECT images and were excreted mainly via the renal pathway. The average tumor uptake at 1 h post-injection varied from 5.40 to 18.8%ID/g, and the tracers derived from the Lys-urea-Aad pharmacophore had much lower uptake in the spleen and salivary glands. Compared with the clinical tracer [99mTc]Tc-EDDA/HYNIC-iPSMA, the Lys-urea-Aad-derived [99mTc]Tc-EDDA-KL01127 had lower background uptake and superior tumor-to-background contrast ratios and is therefore promising for clinical translation to detect prostate cancer lesions with SPECT.

In vivo molecular imaging stratifies rats with different susceptibilities to hyperoxic acute lung injury.

99mTc-hexamethylpropyleneamine oxime (HMPAO) and 99mTc-duramycin in vivo imaging detects pulmonary oxidative stress and cell death, respectively, in rats exposed to >95% O2 (hyperoxia) as a model of acute respiratory distress syndrome (ARDS). Preexposure to hyperoxia for 48 h followed by 24 h in room air (H-T) is protective against hyperoxia-induced lung injury. This study's objective was to determine the ability of 99mTc-HMPAO and 99mTc-duramycin to track this protection and to elucidate underlying mechanisms. Rats were exposed to normoxia, hyperoxia for 60 h, H-T, or H-T followed by 60 h of hyperoxia (H-T + 60). Imaging was performed 20 min after intravenous injection of either 99mTc-HMPAO or 99mTc-duramycin. 99mTc-HMPAO and 99mTc-duramycin lung uptake was 200% and 167% greater (P < 0.01) in hyperoxia compared with normoxia rats, respectively. On the other hand, uptake of 99mTc-HMPAO in H-T + 60 was 24% greater (P < 0.01) than in H-T rats, but 99mTc-duramycin uptake was not significantly different (P = 0.09). Lung wet-to-dry weight ratio, pleural effusion, endothelial filtration coefficient, and histological indices all showed evidence of protection and paralleled imaging results. Additional results indicate higher mitochondrial complex IV activity in H-T versus normoxia rats, suggesting that mitochondria of H-T lungs may be more tolerant of oxidative stress. A pattern of increasing lung uptake of 99mTc-HMPAO and 99mTc-duramycin correlates with advancing oxidative stress and cell death and worsening injury, whereas stable or decreasing 99mTc-HMPAO and stable 99mTc-duramycin reflects hyperoxia tolerance, suggesting the potential utility of molecular imaging for identifying at-risk hosts that are more or less susceptible to progressing to ARDS.

Radionuclide imaging of apoptosis for clinical application.

Apoptosis was a natural, non-inflammatory, energy-dependent form of programmed cell death (PCD) that can be discovered in a variety of physiological and pathological processes. Based on its characteristic biochemical changes, a great number of apoptosis probes for single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have been developed. Radionuclide imaging with these tracers were potential for the repetitive and selective detection of apoptotic cell death in vivo, without the need for invasive biopsy. In this review, we overviewed molecular mechanism and specific biochemical changes in apoptotic cells and summarized the existing tracers that have been used in clinical trials as well as their potentialities and limitations. Particularly, we highlighted the clinic applications of apoptosis imaging as diagnostic markers, early-response indicators, and prognostic predictors in multiple disease fields.

Association between T wave morphology parameters and abnormal cardiac SPECT imaging.

BACKGROUND: T-wave morphology dispersion (TMD) described the electrocardiographic T-wave heterogeneity during a single cardiac cycle. Total cosine R-to-T (TCRT) is the average of the cosines of the angles between the QRS and T vectors on the ECG. We examine the predictive value of TMD and TCRT calculation to assess abnormal myocardial perfusion. METHODS: Retrospective single center cohort study including all patients referred for evaluation of ischemia by myocardial SPECT scanning with no known history of ischemic heart disease, from 1 January 2019 to 31 December 2019. Study endpoint was the correlation between the calculated TMD and TCRT values and detection of myocardial injury or ischemia by myocardial SPECT. RESULTS: Among 606 patients, calculated TCRT was 0.401 ± 0.53 for the normal group and 0.283 ± 0.62 for the abnormal group (p = 0.007). Measured TMD was 22.9 ± 16.6 degrees (p < 0.001) in the normal group, compared to 31.5 ± 22.8 degrees (p < 0.001) for the abnormal group. CONCLUSIONS: The results demonstrate a correlation between the decreased TCRT values and increase TMD and myocardial ischemia seen in SPECT results. The TCRT and TMD can be used as simple and non-invasive markers to predict abnormal SPECT results and ischemic heart disease in patients with no known cardiac history.

Synthesis and Characterization of Hydroxyethylamino- and Pyridyl-Substituted 2-Vinyl Chromone Derivatives for Detection of Cerebral Abnormal Prion Protein Deposits.

Prion diseases are fatal neurodegenerative diseases characterized by the deposition of abnormal prion protein aggregates (PrPSc) in the brain. In this study, we developed hydroxyethylamino-substituted styrylchromone (SC) and 2-(2-(pyridin-3-yl)vinyl)-4H-chromen-4-one (VPC) derivatives for single-photon emission computed tomography (SPECT) imaging of PrPSc deposits in the brain. The binding affinity of these compounds was evaluated using recombinant mouse prion protein (rMoPrP) aggregates, which resulted in the inhibition constant (Ki) value of 61.5 and 88.0 nM for hydroxyethyl derivative, (E)-2-(4-((2-hydroxyethyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NHEtOH) and (E)-2-(4-((2-hydroxyethyl)(methyl)amino)styryl)-6-iodo-4H-chromen-4-one (SC-NMeEtOH), respectively. However, none of the VPC derivatives showed binding affinity for the rMoPrP aggregates. Fluorescent imaging demonstrated that the accumulation pattern of SC-NHEtOH matched with the presence of PrPSc in the brain slices from mouse-adapted bovine spongiform encephalopathy-infected mice. A biodistribution study of normal mice indicated low initial brain uptake of [125I]SC-NHEtOH (0.88% injected dose/g (% ID/g) at 2 min) despite favorable washout from the brain (0.26% ID/g, at 180 min) was displayed. [125I]SC-NHEtOH exhibited binding affinities to both artificial prion aggregates as well as prion deposits in the brain. However, significant improvement in the binding affinity for PrPSc and blood-brain barrier permeability is necessary for the development of successful in vivo imaging probes for the detection of cerebral PrPSc in the brain.

Use of radioiodine in nuclear medicine-A brief overview.

Radioiodines have a long history in nuclear medicine. Herein, we discuss the production, properties and applications of these versatile iodine-based imaging and theragnostic agents. There are 38 isotopes of iodine (I) including one stable form (127 I). The most common radionuclides used in medical imaging and treatment, including Iodine-123 (123 I), Iodine-124 (124 I), Iodine-125 (125 I) and Iodine-131 (131 I), are discussed in this review.

Quantitative Radionuclide Imaging Analysis of Enhanced Drug Delivery Induced by Photoimmunotherapy.

Photoimmunotherapy (PIT) is an upcoming potential cancer treatment modality, the effect of which is improved in combination with chemotherapy. PIT causes a super-enhanced permeability and retention (SUPR) effect. Here, we quantitatively evaluated the SUPR effect using radiolabeled drugs of varying molecular weights (18F-5FU, 111In-DTPA, 99mTc-HSA-D, and 111In-IgG) to determine the appropriate drug size. PIT was conducted with an indocyanine green-labeled anti-HER2 antibody and an 808 nm laser irradiation. Mice were subcutaneously inoculated with HER2-positive cells in both hindlimbs. The tumor on one side was treated with PIT, and the contralateral side was not treated. The differences between tumor accumulations were evaluated using positron emission tomography or single-photon emission computed tomography. Imaging studies found increased tumor accumulation of agents after PIT. PIT-treated tumors showed significantly increased uptake of 18F-5FU (p < 0.001) and 99mTc-HSA-D (p < 0.001). A tendency toward increased accumulation of 111In-DTPA and 111In-IgG was observed. These findings suggest that some low- and medium-molecular-weight agents are promising candidates for combined PIT, as are macromolecules; hence, administration after PIT could enhance their efficacy. Our findings encourage further preclinical and clinical studies to develop a combination therapy of PIT with conventional anticancer drugs.

Effect of different parietal hypoperfusion on neuropsychological characteristics in mild cognitive impairment.

BACKGROUND: In early-stage amnestic mild cognitive impairment (aMCI), differences in the neuropsychological characteristics of each individual are subtle. We investigated differences in neuropsychological performance between aMCI patients with and without hypoperfusion in the medial parietal regions (MP). We further compared patients with hypoperfusion in the left and right lateral parietal regions. METHODS: We examined 165 aMCI patients (mean age: 76.8 ± 5.5 years; 87 women) who had undergone neuropsychological measurement and single-photon emission computed tomography. We classified participants into two subgroups with and without hypoperfusion: MP hypoperfusion (+) and MP hypoperfusion (-); classification was based on Z-scores (calculated by three-dimensional stereotactic surface projection technique) of three regions of interest in the parietal lobes (i.e. MP regions including posterior cingulate cortex and precuneus and left and right inferior parietal lobules (lateral parietal regions)). The MP hypoperfusion (-) group was classified into left lateral parietal hypoperfusion (+) and right lateral parietal hypoperfusion (+) subgroups. We performed either univariate or multivariate ancova to compare neuropsychological scores for continuous variables between groups and examined dichotomous variables using χ2 tests. RESULTS: In the overall aMCI sample, scores on logical memory delayed recall in the MP hypoperfusion (+) group were significantly lower than those in the MP hypoperfusion (-) group. Total scores on Rey-Osterrieth Complex Figure Test delayed recall were also marginally lower in the MP hypoperfusion (+) group than in the MP hypoperfusion (-) group. Comparisons of neuropsychological test scores between the left and right lateral parietal hypoperfusion (+) groups revealed no significant differences. CONCLUSIONS: The present findings suggest that MP hypoperfusion (+) is associated with more robust memory deficits than MP hypoperfusion (-). Combining neuropsychological tests and single-photon emission computed tomography findings may be useful for early detection of cognitive decline in aMCI.

Radioligands targeting purinergic P2X7 receptor.

The purinergic P2X7 receptor (P2X7R) is an adenosine triphosphate (ATP) ligand-gated cationic channel receptor. P2X7R is closely associated with various inflammatory, immune, cancer, neurological, musculoskeletal and cardiovascular disorders. P2X7R is an interesting therapeutic target as well as molecular imaging target. This brief digest highlights the radioligands targeting P2X7R recently developed in drug discovery and molecular imaging agent development.

Development of Gold Nanorods Conjugated with Radiolabeled Anti-human Epidermal Growth Factor Receptor 2 (HER2) Monoclonal Antibody as Single-Photon Emission Computed Tomography/Photoacoustic Dual-Imaging Probes Targeting HER2-Positive Tumors.

Surgery remains one of the main treatments of cancer and both precise pre- and intraoperative diagnoses are crucial in order to guide the operation. We consider that using an identical probe for both pre- and intra-operative diagnoses would bridge the gap between surgical planning and image-guided resection. Therefore, in this study, we developed gold nanorods (AuNRs) conjugated with radiolabeled anti-human epidermal growth factor receptor 2 (HER2) monoclonal antibody, and investigated their feasibility as novel HER2-targeted dual-imaging probes for both single photon emission computed tomography (SPECT) (preoperative diagnosis) and photoacoustic (PA) imaging (intraoperative diagnosis). To achieve the purpose, AuNRs conjugated with different amount of trastuzumab (Tra) were prepared, and Tra-AuNRs were labeled with indium-111. After the evaluation of binding affinity to HER2, cell binding assay and biodistribution studies were carried out for optimization. AuNRs with moderate trastuzumab conjugation (Tra2-AuNRs) were proposed as the novel probe and demonstrated significantly higher accumulation in NCI-N87 (HER2 high-expression) tumors than in SUIT2 (low-expression) tumors 96 h post-injection along with good affinity towards HER2. Thereafter, in vitro PA imaging and in vivo SPECT imaging studies were performed. In in vitro PA imaging, Tra2-AuNRs-treated N87 cells exhibited significant PA signal increase than SUIT2 cells. In in vivo SPECT, signal increase in N87 tumors was more notable than that in SUIT2 tumors. Herein, we report that the Tra2-AuNRs enabled HER2-specific imaging, suggesting the potential as a robust HER2-targeted SPECT and PA dual-imaging probe.

[Evaluation of Post-reconstruction Filtering in Resolution Recovery Reconstruction for Bone SPECT Imaging].

PURPOSE: The aim of this study was to clarify the optimal post-reconstruction filtering type in the three- dimensional ordered subset expectation maximization (3D-OSEM) method for bone single photon emission computed tomography (SPECT) from image quality and quantitative values. METHOD: We scanned a National Electrical Manufactures Association's body phantom for bone SPECT filled with radioactive solution of 99mTc whose radioactivity concentration was accurately measured. The SPECT images were created using the 3D-OSEM method. Post-reconstruction filtering was performed using a Butterworth filter (BW), a Gaussian filter (GA), and a Hanning filter (HA) with various parameters. The image quality was evaluated by the normalized mean-squared error (NMSE) value and % of contrast-to-noise ratio (QNR17). The image quality was evaluated by the error values between the measured radioactivity concentration and the true radioactivity concentration in the BG region and insert sphere. RESULTS: The minimum NMSE values were 0.034 (BW), 0.036 (GA), and 0.035 (HA), and there was no difference depending on the filter type. The values of QNR17 were 2.5 (BW), 2.6 (GA), and 2.6 (HA), and there was no difference depending on the filter type. The BG region was greatly affected by parameter changes in GA but less by those in BW and HA. The error values of the 37 mm insert sphere were 18.0% (BW), 28.2% (GA), and 26.2% (HA), and BW showed the lowest value. CONCLUSION: Our results suggest that the post-reconstruction filtering type used in the 3D-OSEM method was BW from the image quality and quantitative values.

[Evaluation of the Number of Sampling Angles in Three Dimensional Ordered Subset Expectation Maximization: Comparison of Step and Shoot Acquisition and Continuous Acquisition].

Three dimensional ordered subset expectation maximization (3D-OSEM) improves spatial resolution and contrast. Continuous acquisition, and step and shoot acquisition are used in single photon emission computed tomography (SPECT). The purpose of this study was to evaluate the effect of 3D-OSEM when acquisition method was different. We evaluated spatial resolution using a line source phantom and uniformity using a pool phantom. The phantoms were acquired by step and shoot acquisition and continuous acquisition at changing step angles. These projection data were reconstructed using filtered back projection (FBP) and 3D-OSEM. We evaluated reconstruction images using the full width half maximum (FWHM) of line source and root mean square uncertainty (%RMSU) of pool phantom. 3D-OSEM improved spatial resolution and uniformity compared with FBP. Change of FWHM in radial direction and %RMSU by using 3D-OSEM was approximately equal to continuous acquisition in step and shoot acquisition. However, even if using 3D-OSEM, distance between center of rotation and the location of line source is long, a large sampling step angle produced an increase FWHM in tangential direction using continuous acquisition. Step angles need to be set based on the sampling theorem using continuous acquisition.

[Verification of Image Reconstruction Method and Collimator Suitable for Quantitative Analysis of Striatum in Dopamine Transporter Scintigraphy].

Specific binding ratio (SBR) is mainly used as a quantitative index of dopamine transporter scintigraphy, although it was reported that standardized uptake value (SUV) is useful for clinical diagnosis in recent years. The aim of this study is to evaluate whether xSPECT is useful for SUV in dopamine transporter scintigraphy. xSPECT is a recently developed, high-resolution image reconstruction technique that transforms single photon emission computed tomography (SPECT) to a computed tomography (CT) coordinate system. Furthermore, low-penetration high-resolution (LPHR), which there has been no previous physical evaluation report was also evaluated. The radioactive concentration of the image with xSPECT is automatically calculated by the periodic sensitivity calibration and one volume sensitivity calibration. In the case of images with conventional reconstruction methods as filtered back projection (FBP) and ordered subset expectation maximization (OSEM), the calibration factor related to the photon count and radioactive concentration was calculated from measuring a cylinder phantom filled with Iodine-123. Radioactive concentrations of the SUV factor were measured by SPECT data acquisition with the striatal phantom in various conditions. Radioactive concentrations with conventional reconstruction methods had a lower value (for example, with FBP it was 7.53 kBq/ml, with OSEM it was 7.22 kBq/ml) compared to the actual measurement value, although that with xSPECT (12.45 kBq/ml) got close to the actual measurement value (14.68 kBq/ml). LPHR showed an approximation to low-energy high-resolution (LEHR) in terms of spatial resolution and scatter fraction estimated from energy windows. The quantitative accuracy of radioactive concentration was the highest under xSPECT.

Targeting phosphatidylserine for radionuclide-based molecular imaging of apoptosis.

One major characteristic of programmed cell death (apoptosis) results in the increased expression of phosphatidylserine (PS) on the outer membrane of dying cells. Consequently, PS represents an excellent target for non-invasive imaging of apoptosis by single-photon emission computed tomography (SPECT) and positron emission tomography (PET). Annexin V is a 36 kDa protein which binds with high affinity to PS in the presence of Ca2+ ions. This makes radiolabeled annexins valuable apoptosis imaging agents for clinical and biomedical research applications for monitoring apoptosis in vivo. However, the use of radiolabeled annexin V for in vivo imaging of cell death has been met with a variety of challenges which have prevented its translation into the clinic. These difficulties include: complicated and time-consuming radiolabeling procedures, sub-optimal biodistribution, inadequate pharmacokinetics leading to poor tumour-to-blood contrast ratios, reliance upon Ca2+ concentrations in vivo, low tumor tissue penetration, and an incomplete understanding of what constitutes the best imaging protocol following induction of apoptosis. Therefore, new concepts and improved strategies for the development of PS-binding radiotracers are needed. Radiolabeled PS-binding peptides and various Zn(II) complexes as phosphate chemosensors offer an innovative strategy for radionuclide-based molecular imaging of apoptosis with PET and SPECT. Radiolabeled peptides and Zn(II) complexes provide several advantages over annexin V including better pharmacokinetics due to their smaller size, better availability, simpler synthesis and radiolabeling strategies as well as facilitated tissue penetration due to their smaller size and faster blood clearance profile allowing for optimized image contrast. In addition, peptides can be structurally modified to improve metabolic stability along with other pharmacokinetic and pharmacodynamic properties. The present review will summarize the current status of radiolabeled annexins, peptides and Zn(II) complexes developed as radiotracers for imaging apoptosis through targeting PS utilizing PET and SPECT imaging.

Antibody-Based Tracers for PET/SPECT Imaging of Chronic Inflammatory Diseases.

Chronic inflammatory diseases are often progressive, resulting not only in physical damage to patients but also social and economic burdens, making early diagnosis of them critical. Nuclear medicine techniques can enhance the detection of inflammation by providing functional as well as anatomical information when combined with other modalities such as magnetic resonance imaging, computed tomography or ultrasonography. Although small molecules and peptides were mainly used for the treatment and imaging of chronic inflammatory diseases in the past, antibodies and their fragments have also been emerging for chronic inflammatory diseases as they show high specificity to their targets and can have various biological half-lives depending on how they are engineered. In addition, imaging with antibodies or their fragments can visualize the in vivo biodistribution of the probes or help monitor therapeutic responses, thereby providing physicians with a greater understanding of drug behavior in vivo and another means of monitoring their patients. In this review, we introduce various targets and radiolabeled antibody-based probes for the molecular imaging of chronic inflammatory diseases in preclinical and clinical studies. Targets can be classified into three different categories: 1) cell-adhesion molecules, 2) surface markers on immune cells, and 3) cytokines or enzymes. The limitations and future directions of using radiolabeled antibodies for imaging inflammatory diseases are also discussed.

MicroSPECT/CT Imaging of Cell-Line and Patient-Derived EGFR-Positive Tumor Xenografts in Mice with Panitumumab Fab Modified with Hexahistidine Peptides To Enable Labeling with 99mTc(I) Tricarbonyl Complex.

We aimed to investigate the feasibility of conjugating synthetic hexahistidine peptides (His6) peptides to panitumumab Fab (PmFab) to enable labeling with [99mTc(H2O)3(CO)3]+ complex and study these radioimmunoconjugates for imaging EGFR-overexpressing tumor xenografts in mice by microSPECT/CT. Fab were reacted with a 10-fold excess of sulfo-SMCC to introduce maleimide functional groups for reaction with the terminal thiol on peptides [CGYGGHHHHHH] that harbored the His6 motif. Modification of Fab with His6 peptides was assessed by SDS-PAGE/Western blot, and the number of His6 peptides introduced was quantified by a radiometric assay incorporating 123I-labeled peptides into the conjugation reaction. Radiolabeling was achieved by incubation of PmFab-His6 in PBS, pH 7.0, with [99mTc(H2O)3(CO)3]+ in a 1.4 MBq/µg ratio. The complex was prepared by adding [99mTcO4]- to an Isolink kit (Paul Scherrer Institute). Immunoreactivity was assessed in a direct (saturation) binding assay using MDA-MB-468 human triple-negative breast cancer (TNBC) cells. Tumor and normal tissue uptake and imaging properties of 99mTc-PmFab-His6 (70 µg; 35-40 MBq) injected i.v. (tail vein) were compared to irrelevant 99mTc-Fab 3913 in NOD/SCID mice engrafted subcutaneously (s.c.) with EGFR-overexpressing MDA-MB-468 or PANC-1 human pancreatic ductal carcinoma (PDCa) cell-line derived xenografts (CLX) at 4 and 24 h post injection (p.i.). In addition, tumor imaging studies were performed with 99mTc-PmFab-His6 in mice with patient-derived tumor xenografts (PDX) of TNBC, PDCa, and head and neck squamous cell carcinoma (HNSCC). Biodistribution studies in nontumor bearing Balb/c mice were performed to project the radiation absorbed doses for imaging studies in humans with 99mTc-PmFab-His6. PmFab was derivatized with 0.80 ± 0.03 His6 peptides. Western blot and SDS-PAGE confirmed the presence of His6 peptides. 99mTc-PmFab-His6 was labeled to high radiochemical purity (≥95%), and the Kd for binding to EGFR on MDA-MB-468 cells was 5.5 ± 0.4 × 10-8 mol/L. Tumor uptake of 99mTc-PmFab-His6 at 24 h p.i. was significantly (P < 0.05) higher than irrelevant 99mTc-Fab 3913 in mice with MDA-MB-468 tumors (14.9 ± 3.1%ID/g vs 3.0 ± 0.9%ID/g) and in mice with PANC-1 tumors (5.6 ± 0.6 vs 0.5 ± 0.1%ID/g). In mice implanted orthotopically in the pancreas with the same PDCa PDX, tumor uptake at 24 h p.i. was 4.2 ± 0.2%ID/g. Locoregional metastases of these PDCa tumors in the peritoneum exhibited slightly and significantly lower uptake than the primary tumors (3.1 ± 0.3 vs 4.2 ± 0.3%ID/g; P = 0.02). In mice implanted with different TNBC or HNSCC PDX, tumor uptake at 24 h p.i. was variable and ranged from 3.7 to 11.4%ID/g and 3.8-14.5%ID/g, respectively. MicroSPECT/CT visualized all CLX and PDX tumor xenografts at 4 and 24 h p.i. Dosimetry estimates revealed that in humans, the whole body dose from administration of 740-1110 MBq of 99mTc-PmFab-His6 would be 2-3 mSv, which is less than for a 99mTc-medronate bone scan (4 mSv).

Time-series hyperpolarized xenon-129 MRI of lobar lung ventilation of COPD in comparison to V/Q-SPECT/CT and CT.

PURPOSE: To derive lobar ventilation in patients with chronic obstructive pulmonary disease (COPD) using a rapid time-series hyperpolarized xenon-129 (HPX) magnetic resonance imaging (MRI) technique and compare this to ventilation/perfusion single-photon emission computed tomography (V/Q-SPECT), correlating the results with high-resolution computed tomography (CT) and pulmonary function tests (PFTs). MATERIALS AND METHODS: Twelve COPD subjects (GOLD stages I-IV) participated in this study and underwent HPX-MRI, V/Q-SPECT/CT, high-resolution CT, and PFTs. HPX-MRI was performed using a novel time-series spiral k-space sampling approach. Relative percentage ventilations were calculated for individual lobe for comparison to the relative SPECT lobar ventilation and perfusion. The absolute HPX-MRI percentage ventilation in each lobe was compared to the absolute CT percentage emphysema score calculated using a signal threshold method. Pearson's correlation and linear regression tests were performed to compare each imaging modality. RESULTS: Strong correlations were found between the relative lobar percentage ventilation with HPX-MRI and percentage ventilation SPECT (r = 0.644; p < 0.001) and percentage perfusion SPECT (r = 0.767; p < 0.001). The absolute CT percentage emphysema and HPX percentage ventilation correlation was also statistically significant (r = 0.695, p < 0.001). The whole lung HPX percentage ventilation correlated with the PFT measurements (FEV1 with r = - 0.886, p < 0.001*, and FEV1/FVC with r = - 0.861, p < 0.001*) better than the whole lung CT percentage emphysema score (FEV1 with r = - 0.635, p = 0.027; and FEV1/FVC with r = - 0.652, p = 0.021). CONCLUSION: Lobar ventilation with HPX-MRI showed a strong correlation with lobar ventilation and perfusion measurements derived from SPECT/CT, and is better than the emphysema score obtained with high-resolution CT. KEY POINTS: • The ventilation hyperpolarized xenon-129 MRI correlates well with ventilation and perfusion with SPECT/CT with the advantage of higher temporal and spatial resolution. • The hyperpolarized xenon-129 MRI correlates with the PFT measurements better than the high-resolution CT with the advantage of avoiding the use of ionizing radiation.