In Vivo Evaluation of Indium-111–Labeled 800CW as a Necrosis-Avid Contrast Agent

Purpose

Current clinical measurements for tumor treatment efficiency rely often on changes in tumor volume measured as shrinkage by CT or MRI, which become apparent after multiple lines of treatment and pose a physical and psychological burden on the patient. Detection of therapy-induced cell death in the tumor can be a fast measure for treatment efficiency. However, there are no reliable clinical tools for detection of tumor necrosis. Previously, we studied the necrosis avidity of cyanine-based fluorescent dyes, which suffered long circulation times before tumor necrosis could be imaged due to low hydrophilicity. We now present the application of radiolabeled 800CW, a commercially available cyanine with high hydrophilicity, to image tumor necrosis in a mouse model.

Procedures

We conjugated 800CW to DOTA via a PEG linker, for labeling with single-photon emission-computed tomography isotope indium-111, yielding [¹¹¹In]In-DOTA-PEG₄-800CW. We then investigated specific [¹¹¹In]In-DOTA-PEG₄-800CW uptake by dead cells in vitro, using both fluorescence and radioactivity as detection modalities. Finally, we investigated [¹¹¹In]In-DOTA-PEG₄-800CW uptake into necrotic tumor regions of a 4T1 breast tumor model in mice.

Results

We successfully prepared a precursor and developed a reliable procedure for labeling 800CW with indium-111. We detected specific [¹¹¹In]In-DOTA-PEG₄-800CW uptake by dead cells, using both fluorescence and radioactivity. Albeit with a tumor uptake of only 0.37%ID/g at 6 h post injection, we were able to image tumor necrosis with a tumor to background ratio of 7:4. Fluorescence and radioactivity in cryosections from the dissected tumors were colocalized with tumor necrosis, confirmed by TUNEL staining.

Conclusions

[¹¹¹In]In-DOTA-PEG₄-800CW can be used to image tumor necrosis in vitro and in vivo. Further research will elucidate the application of [¹¹¹In]In-DOTA-PEG₄-800CW or other radiolabeled hydrophilic cyanines for the detection of necrosis caused by chemotherapy or other anti-cancer therapies. This can provide valuable prognostic information in treatment of solid tumors.

     

Evaluation of Necrosis Avidity and Potential for Rapid Imaging of Necrotic Myocardium of Radioiodinated Hypocrellins

Purpose

Rapid noninvasive delineation of necrotic myocardium in ischemic regions is very critical for risk stratification and clinical decision-making but still challenging. This study aimed to evaluate the necrosis avidity of radioiodinated hypocrellins and its potential for rapidly imaging necrotic myocardium.

Procedures

The aggregation constants of four natural hypocrellins were analyzed by UV/vis spectroscopy. Then, they were radiolabeled with iodine-131 by iodogen oxidation method. Necrosis avidity of iodine-131-labeled hypocrellins was evaluated in rat models with reperfused liver infarction and muscular necrosis by gamma counting, autoradiography, and histopathology. Their pharmacokinetic properties were examined in normal rats. The potential of iodine-131-labeled hypomycin A ([¹³¹I]HD) for early imaging of necrotic myocardium was explored in rat models with reperfused myocardial infarction. Finally, the possible mechanism of necrosis avidity was investigated by in vitro DNA binding and in vivo blocking experiments.

Results

The aggregation constants of four hypocrellins were all much smaller than that of hypericin, a most studied necrosis avid agent. The radiochemical purities of the four radiotracers after purification were all greater than 95 %, and more than 90 % of tracers remained intact after incubation in rat serum for 24 h. Among the four tracers, [¹³¹I]HD exhibited the highest necrotic to viable tissue uptake ratio and the fastest blood clearance. The necrotic myocardium could be clearly visualized 4 h after injection of [¹³¹I]HD by single-photon emission computed tomography/X-ray computed tomography (SPECT/CT). DNA binding studies suggested that HD could bind to DNA through intercalation. Blocking studies demonstrated that uptake of [¹³¹I]HD in necrotic muscle could be significantly blocked by excess unlabeled HD and ethidium bromide with 67 and 60 % decline at 6 h after coinjection, respectively.

Conclusions

[¹³¹I]HD can be used to rapidly visualize necrotic myocardium. The necrosis avidity mechanism of [¹³¹I]HD may be attributed to its binding to the exposed DNA in necrotic tissues.

     

Targeted RGD nanoparticles for highly sensitive in vivo integrin receptor imaging

A new magnetic resonance imaging (MRI) contrast bearing RGD peptide is reported. In this study, ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles with various sizes were prepared. Particles sizes between 6 and 13 nm were tuned by varying the stirring rate. Remarkable negative contrast was observed because USPIO nanoparticles (13.1 ± 2.1 nm) generated high transversal relaxivity r₂ (188 ± 3 m m ^?1 s^?1) and saturation magnetization (94 emu g^?1 Fe). The USPIO nanoparticles were coated with PDA [2‐(pyridyldithio)‐ethylamine; PDA nanoparticles] containing functional polymer, which can be readily synthesized by Michael addition. The PDA nanoparticles were conjugated with RGD peptide (RGD nanoparticles) for targeting the specific site. The target specificity and high relaxivity allowed RGD nanoparticles to differentiate the expression level of integrin receptor on several cell lines and tumors (MCF‐7, A‐549, HT‐29 and HT‐1080) by in vitro and in vivo MR imaging. Importantly, a remarkable negative contrast (?51.3 ± 6.7%) was observed for in vivo MR imaging of MCF‐7 tumor. This result implies that the RGD nanoparticles that greatly enhance the MR imaging are highly sensitive for early stage tumor detection. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of Radioiodinated 1,4-Naphthoquinones as Necrosis Avid Agents for Rapid Myocardium Necrosis Imaging

Purpose

Identifying necrotic myocardium in ischemic regions is of great importance for risk stratification and clinical decision-making. However, rapid noninvasive imaging of necrotic myocardium is still challenging. This study sought to evaluate the potential of 1,4-naphthoquinones to rapidly visualize necrotic myocardium and the possible mechanisms of necrosis avidity.

Procedures

Six 1,4-naphthoquinones were radiolabeled with iodine-131 and the necrosis avidity was estimated in mouse models with muscular necrosis by gamma counting and autoradiography. The necrotic myocardium imaging property and biodistribution of [¹³¹I]naphthazarin (6) were determined in rat models with re-perfused myocardial infarction. A possible mechanism of necrosis avidity was explored by in vitro DNA-binding and in vivo blocking experiments.

Results

The radiochemical purities of the six radiotracers were greater than 95 %. The uptakes in necrotic muscles of all six radiotracers were higher than those in viable muscles, and [¹³¹I]naphthazarin (6) showed the highest necrotic-to-viable ratio and necrosis-to-blood ratio at all tested time points. The necrotic myocardium could be clearly visualized by single-photon emission computed tomography/x-ray computed tomography (SPECT/CT) using [¹³¹I]naphthazarin (6) as early as 3 h post-injection. Post-mortem biodistribution showed the uptake of [¹³¹I]naphthazarin (6) in necrotic myocardium was 11.67-fold higher than that in viable myocardium. Absorption spectra and emission spectra suggested naphthazarin (6) could bind to DNA through intercalation. The uptake of [¹³¹I]naphthazarin (6) in necrotic muscle could be significantly blocked by excessive ethidium bromide (a typical DNA intercalator) and cold naphthazarin (6) with 63.49 and 71.96 % decline at 3 h post-injection in vivo, respectively.

Conclusions

1,4-Naphthoquinones retained necrosis avidity and [¹³¹I]naphthazarin (6) rapidly visualized necrotic myocardium. The necrosis avidity mechanism of [¹³¹I]naphthazarin (6) may be attributed to its binding with exposed DNA in necrotic tissues.

     

[18F]AZD2461, an Insight on Difference in PARP Binding Profiles for DNA Damage Response PET Imaging

Background

Poly (ADP-ribose) polymerase (PARP) inhibitors are extensively studied and used as anti-cancer drugs, as single agents or in combination with other therapies. Most radiotracers developed to date have been chosen on the basis of strong PARP1–3 affinity. Herein, we propose to study AZD2461, a PARP inhibitor with lower affinity towards PARP3, and to investigate its potential for PARP targeting in vivo.

Methods

Using the Cu-mediated ¹⁸F-fluorodeboronation of a carefully designed radiolabelling precursor, we accessed the ¹⁸F-labelled isotopologue of the PARP inhibitor AZD2461. Cell uptake of [¹⁸F]AZD2461 in vitro was assessed in a range of pancreatic cell lines (PSN-1, PANC-1, CFPAC-1 and AsPC-1) to assess PARP expression and in vivo in xenograft-bearing mice. Blocking experiments were performed with both olaparib and AZD2461.

Results

[¹⁸F]AZD2461 was efficiently radiolabelled via both manual and automated procedures (9 %?±?3 % and 3 %?±?1 % activity yields non-decay corrected). [¹⁸F]AZD2461 was taken up in vivo in PARP1-expressing tumours, and the highest uptake was observed for PSN-1 cells (7.34?±?1.16 %ID/g). In vitro blocking experiments showed a lesser ability of olaparib to reduce [¹⁸F]AZD2461 binding, indicating a difference in selectivity between olaparib and AZD2461.

Conclusion

Taken together, we show the importance of screening the PARP selectivity profile of radiolabelled PARP inhibitors for use as PET imaging agents.

     

Improving T1 and T2 magnetic resonance imaging contrast agents through the conjugation of an esteramide dendrimer to high‐water‐coordination Gd(III) hydroxypyridinone complexes

Commercial gadolinium magnetic resonance imaging (MRI) contrast agents are limited by low relaxivity (r₁) and coordination to only a single water molecule (q = 1). Consequently, gram quantities of these agents must be injected to obtain sufficient diagnostic contrast. In this study, MRI contrast agents for T₁ and T₂ relaxivity were synthesized using hydroxypyridinone and terephthalamide chelators with mesityl and 1,4,7‐triazacyclononane capping moieties. When covalently conjugated to a highly biocompatible esteramide dendrimer, T₂ relaxation rates up to 52 m m ^?1 s^?1 and T₁ relaxation rates up to 31 m m ^?1 s^?1 per gadolinium were observed under clinically relevant conditions. These values are believed to be brought about by using a dendritic macromolecule to decrease the molecular tumbling time of the small molecule complexes. These agents also show high aqueous solubility and low toxicity in vitro. In this study we report six new compounds: three discrete complexes and three dendrimer conjugates. Copyright © 2012 John Wiley & Sons, Ltd.     

An Efficient Automated Radiosynthesis and Bioactivity Confirmation of VMAT2 Tracer [18F]FP-(+)-DTBZ

Purpose

The aim of this study was to optimize the radiolabeling method of [¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]FP-(+)-DTBZ) to fulfill the demand of preclinical and clinical application.

Procedures

Optimized labeling conditions were performed by altering the molar ratio of precursor to base (P/B), base species, solvents, reaction temperature, reaction time, and precursor concentration through manual radiosynthesis of [¹⁸F]FP-(+)-DTBZ. The conditions with the highest radiochemical yield (RCY) were applied to automated radiosynthesis, and the crude product was purified with a Sep-Pak Plus C18 cartridge. Quality control and stability of [¹⁸F]FP-(+)-DTBZ were carried out by HPLC. In vitro cellular uptake and blocking assays were conducted in human neuroblastoma cell line SH-SY5Y. In vivo imaging with small animal positron emission tomography (microPET) was performed with Sprague–Dawley rats.

Results

Under the optimized conditions (P/K₂CO₃?=?1:8, heating at 120 °C for 3 min in dimethyl sulfoxide), an RCY of 88.7 % was obtained with 1.0 mg precursor. The optimized reaction conditions were successfully applied to an automated module and gave a high activity yield (AY) of 30–55 % in about 40 min with a >?99.0 % radiochemical purity (RCP) and a >?44.4 GBq/μmol molar activity (A_m). Stability test displayed that the RCP retained >?98.0 % in 8 h in saline and in phosphate buffer saline (PBS, pH 7.4). In vitro cellular uptake assay showed accumulation of [¹⁸F]FP-(+)-DTBZ in SH-SY5Y cells, which could be significantly inhibited by vesicular monoamine transporter 2 (VMAT2) inhibitor DTBZ. MicroPET images of rat brain displayed that the striatum showed the highest uptake with a standardized uptake value (SUV) of 3.91?±?0.30 at ~?70 min. Co-injection with DTBZ (1.0 mg/kg) resulted in a 75 % decrease of the striatal SUV, confirming the specificity of [¹⁸F]FP-(+)-DTBZ to VMAT2.

Conclusions

We obtained an optimized radiolabeling method of [¹⁸F]FP-(+)-DTBZ and successfully applied it to a commercial available module. The automated synthesis gave a high AY and RCP of [¹⁸F]FP-(+)-DTBZ with high and specific binding to VMAT2, facilitating its routine application for VMAT2 tracing.

     

Ferumoxytol Does Not Impact Standardized Uptake Values on PET/MR Scans

Purpose

Tumor response assessments on positron emission tomography (PET)/magnetic resonance imaging (MRI) scans require correct quantification of radiotracer uptake in tumors and normal organs. Historically, MRI scans have been enhanced with gadolinium (Gd)-based contrast agents, which are now controversial due to brain deposition. Recently, ferumoxytol nanoparticles have been identified as an alternative to Gd-based contrast agents because they provide strong tissue enhancement on MR images but are not deposited in the brain. However, it is not known if the strong T1- and T2-contrast obtained with iron oxide nanoparticles such as ferumoxytol could affect MR-based attenuation correction of PET data. The purpose of our study was to investigate if ferumoxytol administration prior to a 2-deoxy-2-[¹⁸F]fluoro-d-glucose [¹⁸F]FDG PET/MR scan would change standardized uptake values (SUV) of normal organs.

Procedures

Thirty pediatric patients (6–18 years) with malignant tumors underwent [¹⁸F]FDG-PET/MR scans (dose 3 MBq/kg). Fifteen patients received an intravenous ferumoxytol injection (5 mg Fe/kg) prior to the [¹⁸F]FDG-PET/MR scans (group 1). Fifteen additional age- and sex-matched patients received unenhanced [¹⁸F]FDG-PET/MR scans (group 2). For attenuation correction of PET data, we used a Dixon-based gradient echo sequence (TR 4.2 ms, TE 1.1, 2.3 ms, FA 5), which accounted for soft tissue, lung, fat, and background air. We used a mixed linear effects model to compare the tissue MRI enhancement, quantified as the signal-to-noise ratio (SNR), as well as tissue radiotracer signal, quantified as SUVmean and SUVmax, between group 1 and group 2. Alpha was assumed at 0.05.

Results

The MRI enhancement of the blood and solid extra-cerebral organs, quantified as SNR, was significantly higher on ferumoxytol-enhanced MRI scans compared to unenhanced scans (p?<?0.001). However, SUVmean and SUVmax values, corrected based on the patients’ body weight or body surface area, were not significantly different between the two groups (p?>?0.05).

Conclusion

Ferumoxytol administration prior to a [¹⁸F]FDG PET/MR scan did not change standardized uptake values (SUV) of solid extra-cerebral organs. This is important, because it allows injection of ferumoxytol contrast prior to a PET/MRI procedure and, thereby, significantly accelerates image acquisition times.

     

Enhanced MRI relaxivity of Gd3+‐based contrast agents geometrically confined within porous nanoconstructs

Gadolinium chelates, which are currently approved for clinical MRI use, provide relaxivities well below their theoretical limit, and they also lack tissue specificity. Recently, the geometrical confinement of Gd³⁺‐based contrast agents (CAs) within porous structures has been proposed as a novel, alternative strategy to improve relaxivity without chemical modification of the CA. Here, we have characterized and optimized the performance of MRI nanoconstructs obtained by loading [Gd(DTPA)(H₂O)]^2? (Magnevist®) into the pores of injectable mesoporous silicon particles. Nanoconstructs with three different pore sizes were studied, and at 60 MHz, they exhibited longitudinal relaxivities of ~24 m m ^?1 s^?1 for 5–10 nm pores and ~10 m m ^?1 s^?1 for 30 – 40 nm pores. No enhancement in relaxivity was observed for larger pores sizes. Using an outer‐sphere compound, [GdTTHA]^3?, and mathematical modeling, it was demonstrated that the relaxivity enhancement is due to the increase in rotational correlation times (CA adsorbed on the pore walls) and diffusion correlation times (reduced mobility of the water molecules), as the pore sizes decreases. It was also observed that extensive CA adsorption on the outer surface of the silicon particles negates the advantages offered by nanoscale confinement. Upon incubation with HeLa cells, the nanoconstructs did not demonstrate significant cytotoxicity for up to 3 days post incubation, at different particle/cell ratios. In addition, the nanoconstructs showed complete degradation after 24 h of continuous agitation in phosphate‐buffered saline. These data support and confirm the hypothesis that the geometrical confinement of Gd³⁺‐chelate compounds into porous structures offers MRI nanoconstructs with enhanced relaxivity (up to 6 times for [Gd(DTPA)(H₂O)]^2?, and 4 times for [GdTTHA]^3?) and, potentially, improved stability, reduced toxicity and tissue specificity. Copyright © 2012 John Wiley & Sons, Ltd.     

Imaging evaluation of ablative margin and index tumor immediately after radiofrequency ablation for hepatocellular carcinoma: comparison between multidetector-row CT and MR imaging

Purpose

To prospectively compare multidetector-row CT (MDCT) and MR imaging (MRI) in the assessment of the ablative margin (AM) and index tumor immediately after radiofrequency (RF) ablation for hepatocellular carcinoma (HCC) and assess whether non-contrast MRI with limited sequences (T1- and T2-weighted imaging only) was superior to a conventional MDCT protocol.

Methods

A total of 33 consecutive patients with 42 HCCs were included in this study. Both MDCT and MR images were independently reviewed by two radiologists regarding the ability to visually discriminate between the AM and index tumor, and the AM status within ablation zones. The AM status was classified as AM-plus (AM completely surrounding the tumor), AM-zero (AM was partly discontinuous, without protrusion of the tumor), and AM-minus (AM was partly discontinuous, with protrusion of the tumor). During the follow-up period, the cumulative local tumor progression rates were analyzed using the Kaplan–Meier method and Cox proportional hazards model. To determine the added value of contrast-enhanced MR images, both reviewers separately evaluated the two sets (unenhanced and enhanced) of MR images.

Results

Visual discrimination between the AM and index tumor was possible in four (9.5%) and 34 (81%) of the 42 ablation zones using MDCT and MRI, respectively (p < 0.001). Thirty-eight and four cases were classified as AM-plus and AM-zero on MDCT images, respectively, whereas the ablation zones were categorized as AM-plus (n = 32), AM-zero (n = 9), and AM-minus (n = 1) when examining the MR images. The cumulative incidence of local tumor progression was significantly lower in cases with AM-plus on MRI (p = 0.007). Contrast-enhanced MRI had no added value for the assessment of the AM and index tumor.

Conclusion

MRI was superior to MDCT for the differential assessment of the AM and index tumor immediately after RF ablation for HCC. Non-contrast MRI was also superior to the conventional MDCT protocol.

     

Design of ProCAs (Protein‐Based Gd3+ MRI Contrast Agents) with High Dose Efficiency and Capability for Molecular Imaging of Cancer Biomarkers

Magnetic resonance imaging (MRI) is the leading imaging technique for disease diagnostics, providing high resolution, three‐dimensional images noninvasively. MRI contrast agents are designed to improve the contrast and sensitivity of MRI. However, current clinically used MRI contrast agents have relaxivities far below the theoretical upper limit, which largely prevent advancing molecular imaging of biomarkers with desired sensitivity and specificity. This review describes current progress in the development of a new class of protein‐based MRI contrast agents (ProCAs) with high relaxivity using protein design to optimize the parameters that govern relaxivity. Further, engineering with targeting moiety allows these contrast agents to be applicable for molecular imaging of prostate cancer biomarkers by MRI. The developed protein‐based contrast agents also exhibit additional in vitro and in vivo advantages for molecular imaging of disease biomarkers, such as high metal‐binding stability and selectivity, reduced toxicity, proper blood circulation time, and higher permeability in tumor tissue in addition to improved relaxivities.     

Evaluation of Clostridium difficile Infection with PET/CT Imaging in a Mouse Model

Purpose

Existing clinical or microbiological scores are not sensitive enough to obtain prompt identification of patients at risk of complicated Clostridium difficile infection (CDI). Our aim was to use a CDI animal model to evaluate 2-deoxy-2-[¹⁸F]fluoro-D-glucose positron emission tomography ([¹⁸F]FDG-PET) as a marker of severe course of infection.

Procedures

CDI was induced with cefoperazone for 10 days followed by clindamycin 1 day before C. difficile inoculation. Mice were divided into wild type (n?=?6), antibiotic without infection (AC n?=?4), h001-infected (n?=?5, ribotype 001), and h027-infected (n?=?5, ribotype 027). Two days after inoculation, [¹⁸F]FDG-PET was acquired. Weight, general animal condition, and survival were monitored daily for 9 days.

Results

h001 group showed symptoms for 4 days with 0 % mortality and a similar colon uptake than control animals (h001 0.52?±?0.20, WT 0.42?±?0.07, and AC 0.36?±?0.06). The h027 group showed symptoms up to 7 days, with 66.7 % of mortality 4 days after infection, and significantly higher colon uptake (0.93?±?0.38, p?<?0.05). Clinical score was associated to colon and cecum uptake (rho?=?0.78, p?=?0.0001) (rho?=?0.73, p?=?0.0003).

Conclusion

High toxin producer ribotype 027 induced more severe CDI infections, correlating with higher colon and cecum [¹⁸F]FDG uptake. Colon uptake may purportedly serve as early predictor of CDI severity.

     

Fluorine-19 Cellular MRI Detection of In Vivo Dendritic Cell Migration and Subsequent Induction of Tumor Antigen-Specific Immunotherapeutic Response

Purpose

A major hurdle in the advancement of cell-based cancer immunotherapies is the inability to track in vivo therapeutic cell migration. With respect to dendritic cell (DC)-based cancer immunotherapies, this lack of knowledge represents an even greater hurdle as the quantity of tumor-antigen specific DC reaching a secondary lymphoid organ post injection is predictive of the magnitude of the ensuing tumor-specific immune response. We propose fluorine-19 (F-19) cellular magnetic resonance imaging (MRI) as a suitable and non-invasive imaging modality capable of detecting and quantifying DC migration in vivo and thus, serving as a surrogate marker of DC-based immunotherapeutic effectiveness.

Procedures

Murine DC were generated from bone marrow precursors and labeled with a [¹⁹F]perfluorocarbon ([¹⁹F]PFC)-based cell labeling agent. DC were characterized by viability and phenotyping assessments as well as characterized by ability to induce in vivo tumor-specific immune responses following immunization in a B16-F10 mouse model of melanoma. The in vivo migration of [¹⁹F]PFC (PFC)-labeled DC was first compared to control unlabeled DC by microscopy and then measured using F-19 cellular MRI.

Results

Culture conditions were optimized such that >?90 % of DC labeled with PFC without affecting viability, phenotype, and function. This optimization permitted consistent detection of PFC-labeled DC migration using F-19 cellular MRI and resulted in the first successful comparison of in vivo migration between PFC-labeled and control unlabeled therapeutic cells of the same origin. PFC-labeled DC are migration-competent in vivo in a B16-F10 tumor-bearing mouse model.

Conclusions

We report a non-invasive and longitudinal imaging modality capable of detecting and quantifying therapeutic cell migration at both 9.4 and 3 Tesla (T) and suitable for therapeutic cell tracking in a tumor-bearing mouse model. F-19 MRI cell tracking is broadly applicable across disease states and is conducive to clinical translation.

     

Assessment of Chemotherapy-Induced Organ Damage with Ga-68 Labeled Duramycin

Purpose

Evaluation of [⁶⁸Ga]NODAGA-duramycin as a positron emission tomography (PET) tracer of cell death for whole-body detection of chemotherapy-induced organ toxicity.

Procedures

Tracer specificity of Ga-68 labeled NODAGA-duramycin was determined in vitro using competitive binding experiments. Organ uptake was analyzed in untreated and doxorubicin, busulfan, and cisplatin-treated mice 2 h after intravenous injection of [⁶⁸Ga]NODAGA-duramycin. In vivo data were validated by immunohistology and blood parameters.

Results

In vitro experiments confirmed specific binding of [⁶⁸Ga]NODAGA-duramycin. Organ toxicities were detected successfully using [⁶⁸Ga]NODAGA-duramycin PET/X-ray computed tomography (CT) and confirmed by immunohistochemistry and blood parameter analysis. Organ toxicities in livers and kidneys showed similar trends in PET/CT and immunohistology. Busulfan and cisplatin-related organ toxicities in heart, liver, and lungs were detected earlier by PET/CT than by blood parameters and immunohistology.

Conclusion

[⁶⁸Ga]NODAGA-duramycin PET/CT was successfully applied to non-invasively detect chemotherapy-induced organ toxicity with high sensitivity in mice. It, therefore, represents a promising alternative to standard toxicological analyses with a high translational potential.

     

Can diffusion-weighted magnetic resonance imaging of clear cell renal carcinoma predict low from high nuclear grade tumors

Objective

To assess the diagnostic performance of the apparent diffusion coefficient (ADC) in predicting the Fuhrman nuclear grading of clear cell renal cell carcinomas (ccRCC).

Materials and methods

A total of 129 patients who underwent partial and radical nephrectomies with pathology-proven ccRCC were retrospectively evaluated. Histopathological characteristics and nuclear grades were analyzed. In addition, conventional magnetic resonance imaging (MRI) features were assessed in consensus by two radiologists to discriminate nuclear grading. ADC values were obtained from a region of interest (ROI) measurement in the ADC maps calculated from diffusion-weighted imaging (DWI) using b values of 50, 500, and 800 s/mm². The threshold values for predicting and differentiating low-grade cancers (Fuhrman I–II) from high grade (Fuhrman III–IV) was obtained using binary logistic regression. The ADC cut-off value for differentiating low- and high-grade tumors was determined using classification analysis.

Results

Significant associations (P < 0.001) were found between nuclear grading, conventional MR features, and DWI. Hemorrhage, necrosis, perirenal fat invasion, enhancement homogeneity, and cystic component were identified as independent predictors of tumor grade. High-grade ccRCC had significantly lower mean ADC values compared to low-grade tumors. An ADC cut-off value of 1.6 × 10⁻³ mm²/s had an optimal predictive percentage of 65.5% for low-grade tumors above this threshold and 81% for high-grade ccRCC below this threshold. Overall predictive accuracy was 70.5%.

Conclusion

The addition of ADC values to a model based on MRI conventional features demonstrates increased sensitivity and high specificity improving the distinguishing accuracy between both high-grade and low-grade ccRCC.

     

Exploring with [18F]UCB-H the in vivo Variations in SV2A Expression through the Kainic Acid Rat Model of Temporal Lobe Epilepsy

Purpose

The main purpose of this study was to understand how the positron emission tomography (PET) measure of the synaptic vesicle 2A (SV2A) protein varies in vivo during the development of temporal lobe epilepsy (TLE) in the kainic acid rat model.

Procedures

Twenty Sprague Dawley male rats were administered with multiple systemic doses of saline (control group, n?=?5) or kainic acid (5 mg/kg/injection, epileptic group, n?=?15). Both groups were scanned at the four phases of TLE (early, latent, transition, and chronic phase) with the [¹⁸F]UCB-H PET radiotracer and T2-structural magnetic resonance imaging. At the end of the scans (3 months post-status epilepticus), rats were monitored for 7 days with electroencephalography for the detection of spontaneous electrographic seizures. Finally, the immunofluorescence staining for SV2A expression was performed.

Results

Control rats presented a significant increase in [¹⁸F]UCB-H binding at the last two scans, compared with the first ones (p?<?0.001). This increase existed but was lower in epileptic animals, producing significant group differences in all the phases of the disease (p?<?0.028). Furthermore, the quantification of the SV2A expression in vivo with the [¹⁸F]UCB-H radiotracer or ex vivo with immunofluorescence led to equivalent results, with a positive correlation between both.

Conclusions

Even if further studies in humans are required, the ability to detect a progressive decrease in SV2A expression during the development of temporal lobe epilepsy supports the use of [¹⁸F]UCB-H as a useful tool to differentiate, in vivo, between healthy and epileptic animals along with the development of the epileptic disease.

     

Preclinical Evaluation and Dosimetry of [111In]CHX-DTPA-scFv78-Fc Targeting Endosialin/Tumor Endothelial Marker 1 (TEM1)

Purpose

Endosialin/tumor endothelial marker-1 (TEM1) is an attractive theranostic target expressed by the microenvironment of a wide range of tumors, as well as by sarcoma and neuroblastoma cells. We report on the radiolabeling and preclinical evaluation of the scFv78-Fc, a fully human TEM1-targeting antibody fragment cross-reactive with mouse TEM1.

Procedures

The scFv78-Fc was conjugated with the chelator p-SCN-Bn-CHX-A”-DTPA, followed by labeling with indium-111. The number of chelators per molecule was estimated by mass spectrometry. A conventional saturation assay, extrapolated to infinite antigen concentration, was used to determine the immunoreactive fraction of the radioimmunoconjugate. The radiopharmaceutical biodistribution was assessed in immunodeficient mice grafted with Ewing’s sarcoma RD-ES and neuroblastoma SK-N-AS human TEM1-positive tumors. The full biodistribution studies were preceded by a dose-escalation experiment based on the simultaneous administration of the radiopharmaceutical with increasing amounts of unlabeled scFv78-Fc. Radiation dosimetry extrapolations to human adults were obtained from mouse biodistribution data according to established methodologies and additional assumptions concerning the impact of the tumor antigenic sink in the cross-species translation.

Results

[¹¹¹In]CHX-DTPA-scFv78-Fc was obtained with a radiochemical purity >?98 % after 1 h incubation at 42 °C and ultrafiltration. It showed good stability in human serum and >?70 % immunoreactive fraction. Biodistribution data acquired in tumor-bearing mice confirmed fast blood clearance and specific tumor targeting in both xenograft models. The radiopharmaceutical off-target uptake was predominantly abdominal. After a theoretical injection of [¹¹¹In]CHX-DTPA-scFv78-Fc to the reference person, the organs receiving the highest absorbed dose would be the spleen (0.876 mGy/MBq), the liver (0.570 mGy/MBq) and the kidneys (0.298 mGy/MBq). The total body dose and the effective dose would be 0.058 mGy/MBq and 0.116 mSv/MBq, respectively.

Conclusions

[¹¹¹In]CHX-DTPA-scFv78-Fc binds specifically to endosialin/TEM1 in vitro and in vivo. Dosimetry estimates are in the range of other monoclonal antibodies radiolabeled with indium-111. [¹¹¹In]CHX-DTPA-scFv78-Fc could be potentially translated into clinic.

     

Preserved Extrastriatal 123I-FP-CIT Binding in Scans Without Evidence of Dopaminergic Deficit (SWEDD)

Purpose

Scans without evidence of dopaminergic deficit (SWEDD) have been initially described in a minority of subjects with suspected Parkinson’s disease (PD). Although a highly controversial entity, longitudinal studies showed that SWEDD cases mostly involve non-degenerative conditions mimicking PD or misattribution of scan images to normal status. Using the Parkinson’s Progression Markers Initiative (PPMI) cohort, we undertook a case-controlled analysis of [123I]N-ω-fluoropropyl-2β-carbomethoxy-iodophenyl nortropane ([123I]FP-CIT) single photon emission computed tomography (SPECT) images to measure extrastriatal serotonergic transporter (SERT) density in SWEDD and PD.

Procedures

We included 37 SWEDD cases (mean age 60 years, 33 % female) with available [123I]FP-CIT SPECT imaging and high-resolution T1-weighted magnetic resonance imaging (MRI) for coregistration. Sixty-one controls and 62 similarly aged PD subjects were included for group comparisons. Regional [123I]FP-CIT was extracted with PETPVE12 using geometric transfer matrix and partial volume effect correction.

Results

PD subjects showed significantly lower [123I]FP-CIT binding in both striatal (caudate nucleus and putamen) and extrastriatal regions (pallidum and insula) compared with controls and SWEDD (all between-group p?<?0.0001). PD group also showed lower binding in the thalamus relative to controls (p?=?0.007). Receiver operating characteristics (ROC) area under the curve (AUC) did not show a significant difference when using extrastriatal region in addition to striatal ROIs for the separation of SWEDD and PD (95 % ROC-AUC for both methods, p?=?0.52). In addition, striatal [123I]FP-CIT binding contralateral to the clinically more affected side was usually lower for PD (>?75 %) but not for SWEDD (<?49 %, p?<?0.002). No significant difference regarding [123I]FP-CIT binding was observed between SWEDD and controls.

Conclusion

These findings corroborate the view that SWEDD cases represent a heterogeneous group of conditions not involving dopaminergic and serotonergic terminals. Further studies are warranted to be assessed whether using extrastriatal [123I]FP-CIT evaluation can be of help in the assessment of degenerative parkinsonism.

     

Optimal Dosing Strategy for Fluorescence-Guided Surgery with Panitumumab-IRDye800CW in Head and Neck Cancer

Purpose

To identify the optimal dosing strategy for fluorescence-guided surgery in patients with head and neck squamous cell carcinoma, we conducted a dose-ranging study evaluating the anti-epidermal growth factor receptor (EGFR) therapeutic antibody, panitumumab, that was fluorescently labeled with the near-infrared dye IRDye800CW.

Procedures

Patients (n?=?24) received either 0.5 or 1.0 mg/kg panitumumab-IRDye800CW in the weight-based dosing group or 25 or 50 mg panitumumab-IRDye800CW in the fixed dosing group. Following surgery, whole primary specimens were imaged in a closed-field device and the mean fluorescence intensity (MFI) and tumor-to-background ratio (TBR) were assessed. Clinical variables, including dose, time of infusion-to-surgery, age, unlabeled dose, gender, primary tumor site, and tumor size, were analyzed to evaluate the factors affecting the fluorescence intensity in order to identify the optimal dose for intraoperative fluorescence imaging.

Results

A total of 24 primary tumor specimens were imaged and analyzed in this study. Although no correlations between TBR and dose of panitumumab-IRDye800CW were found, there were moderate–strong correlations between the primary tumor MFI and panitumumab-IRDye800CW dose for fixed dose (mg) (R²?=?0.42) and for dose/weight (mg/kg) (R²?=?0.54). Results indicated that the optimal MFI was at approximately 50 mg for fixed dose and 0.75 mg/kg for dose/weight. No significant differences were found for the primary tumor MFI and TBRs between the weight-based dosing and the fixed dosing groups. MFIs significantly increased when the infusion-to-surgery window was reduced to within 2 days (vs. 3 days or more, p?<?0.05).

Conclusions

Antibody-based imaging for surgical resection is under investigation in multiple clinical trials. Our data suggests that a fixed dose of 50 mg is an appropriate diagnostic dose for successful surgical fluorescence imaging.

     

Contrast-enhanced ultrasonography for blood flow detection in hepatocellular carcinoma during lenvatinib therapy

Purpose

Blood flow reduction after initiation of lenvatinib therapy may not always indicate tumor necrosis. This study aimed to compare the blood flow detectability of contrast-enhanced ultrasonography (CEUS), contrast-enhanced computed tomography (CT), and contrast-enhanced magnetic resonance imaging (MRI) in hepatocellular carcinoma (HCC) during lenvatinib therapy.

Methods

A total of 12 cases underwent CEUS and contrast-enhanced CT/MRI within 2 weeks during lenvatinib therapy. Vascularity on CEUS and CT/MRI was compared.

Results

At the time of CEUS examination, the median period from the start of lenvatinib was 227?±?210 (31–570) days. CEUS showed hyperenhancement in eight cases (66.7%), hypoenhancement in two cases (16.7%), and no enhancement in one case (8.3%), while CT/MRI showed hyperenhancement in one case (8.3%), ring enhancement in three cases (25.0%), and hypoenhancement in eight cases (66.7%) (p?=?0.007). Transarterial chemoembolization (n?=?3), radiofrequency ablation (n?=?2), and stereotactic body radiation therapy (n?=?2) were performed after blood flow detection by CEUS.

Conclusions

The viability of the HCC should be confirmed using CEUS when contrast-enhanced CT/MRI reveals lesion hypoenhancement during lenvatinib therapy.