PET/CT-derived whole-body and bone marrow dosimetry of 89Zr-cetuximab

Investigating the fate of Zirconium-89 labelled antibody in cynomolgus macaques

BACKGROUND

Preclinical pharmacokinetic studies of therapeutic antibodies in non-human primates are desired because of the difficulty in extrapolating ADME data from animal models to humans. We evaluated the pharmacokinetics of 89Zr (Zirconium-89) -labelled anti-KLH human IgG and its metabolites to confirm their non-specific/physiological accumulation in healthy cynomolgus macaques. The anti-KLH antibody was used as a negative control, ensuring that the observed distribution reflected general IgG behavior rather than antigen-specific accumulation. This provides a valuable reference for comparing the biodistribution of targeted antibodies.

METHODS

Selected IgG was conjugated to desferrioxamine (DFO), labelled with 89Zr, and injected into healthy cynomolgus macaques. PET/CT images at the whole-body level were acquired at different time points, and standard uptake values (SUV) in regions of interest, such as the heart, liver, spleen, kidneys, bone, and muscles, were calculated. The distribution of a shortened antibody variant, 89Zr-labelled Fab, as well as that of [89Zr]Zr-DFO and [89Zr]Zr-oxalate, the expected metabolites of 89Zr- labelled IgG, was also assessed.

RESULTS

After 89Zr-labelled IgG injection, the SUV in the heart, vertebral body, and muscle decreased, in line with the 89Zr concentration decrease in the circulation, whereas radioactivity increased over time in the kidneys and liver. Autoradiography of the renal sections indicated that most of the 89Zr- labelled IgG radioactivity accumulated in the renal cortex. Relatively high accumulation in the kidneys was also observed in 89Zr- labelled Fab-injected macaques, and renal autoradiographs of these animals showed that the renal cortex was the preferred accumulation site. However, [89Zr]Zr-DFO was rapidly excreted into the urine, whereas [89Zr]Zr-oxalate was highly accumulated in the epiphysis of the long bones and vertebral body.

CONCLUSION

In the non-human primate cynomolgus macaque, 89Zr- labelled IgG accumulated in the kidneys and the liver. However, [89Zr]Zr-DFO and 89Zr did not accumulate in these organs. This preclinical pharmacokinetic study performed with human IgG in a non-human primate model using PET is of great significance as it sheds light on the basic fate and distribution of 89Zr- labelled IgG.

Preclinical studies and absorbed dose estimation of [89Zr]Zr-DFO-Bevacizumab for PET imaging of VEGF-expressing tumors

This study aimed to carry out the preclinical studies of [89Zr]Zr-DFO-Bevacizumab. The radiolabeled compound was prepared with radiochemical purity >99% (ITLC), and a specific activity of 74 GBq/g. Cellular studies indicated the great capability of [89Zr]Zr-DFO-Bevacizumab for binding to SKOV3 cell lines. High accumulation was observed in the tumor. The liver and spleen received the highest absorbed dose with 1.12 and 0.72 mGy/MBq, respectively. This radiopharmaceutical can be considered as a suitable PET agent for VEGF-expressing ovarian cancer imaging.

How to obtain the image-derived blood concentration from 89Zr-immuno-PET scans

BACKGROUND

PET scans using zirconium-89 labelled monoclonal antibodies (89Zr-mAbs), known as 89Zr-immuno-PET, are made to measure uptake in tumour and organ tissue. Uptake is related to the supply of 89Zr-mAbs in the blood. Measuring activity concentrations in blood, however, requires invasive blood sampling. This study aims to identify the best delineation strategy to obtain the image-derived blood concentration (IDBC) from 89Zr-immuno-PET scans.

METHODS

PET imaging and blood sampling of two 89Zr-mAbs were included, 89Zr-cetuximab and 89Zr-durvalumab. For seven patients receiving 89Zr-cetuximab, PET scans on 1-2 h, 2 and 6 days post-injection (p.i.) were analysed. Five patients received three injections of 89Zr-durvalumab. The scanning protocol for the first two injections consisted of PET scanning on 2, 5 and 7 days p.i. and for the third injection only on 7 days p.i. Blood samples were drawn with every PET scan and the sample-derived blood concentration (SDBC) was used as gold standard for the IDBC. According to an in-house developed standard operating procedure, the aortic arch, ascending aorta, descending aorta and left ventricle were delineated. Bland-Altman analyses were performed to assess the bias (mean difference) and variability (1.96 times the standard deviation of the differences) between IDBC and SDBC.

RESULTS

Overall, the activity concentration obtained from the IDBC was lower than from the SDBC. When comparing IDBC with SDBC, variability was smallest for the ascending aorta (20.3% and 17.0% for 89Zr-cetuximab and 89Zr-durvalumab, respectively). Variability for the other regions ranged between 17.9 and 30.8%. Bias for the ascending aorta was - 10.9% and - 11.4% for 89Zr-cetuximab and 89Zr-durvalumab, respectively.

CONCLUSIONS

Image-derived blood concentrations should be obtained from delineating the ascending aorta in 89Zr-immuno-PET scans, as this results in the lowest variability with respect to sample-derived blood concentrations.

From Bench to Bedside: Patient-Oriented Radiopharmaceutical Development in Nuclear Medicine Based on the Example of [89Zr]Zr-PSMA-DFO

The interdisciplinary possibilities inherent in nuclear medicine offer an opportunity for the patient-centered development of radioactive pharmaceuticals based on specific research questions. This approach provides radiopharmaceutical manufacturers with a robust scientific foundation on which to navigate the regulatory requirements for drug approval laid down by the law. A vivid illustration of this interdisciplinary cooperation has been the development of a Zr-89-labeled PSMA ligand where reliable results have been obtained across various domains, including chemistry, radiochemistry, biochemistry, and preclinical research. This comprehensive process extended to feasibility studies conducted with carefully selected patients from a single nuclear medicine clinic. The approach demonstrates how far close collaboration between different disciplines within nuclear medicine can further the move towards patient-oriented radiopharmaceutical treatments while simultaneously meeting regulatory demands. With such a strategy, innovative radiopharmaceutical solutions can be brought to the market more swiftly and efficiently, in line with the needs of patients.

Preclinical development of ZED8, an 89Zr immuno-PET reagent for monitoring tumor CD8 status in patients undergoing cancer immunotherapy

BACKGROUND

ZED8 is a novel monovalent antibody labeled with zirconium-89 for the molecular imaging of CD8. This work describes nonclinical studies performed in part to provide rationale for and to inform expectations in the early clinical development of ZED8, such as in the studies outlined in clinical trial registry NCT04029181 [1].

METHODS

Surface plasmon resonance, X-ray crystallography, and flow cytometry were used to characterize the ZED8-CD8 binding interaction, its specificity, and its impact on T cell function. Immuno-PET with ZED8 was assessed in huCD8⁺ tumor-bearing mice and in non-human primates. Plasma antibody levels were measured by ELISA to determine pharmacokinetic parameters, and OLINDA 1.0 was used to estimate radiation dosimetry from image-derived biodistribution data.

RESULTS

ZED8 selectively binds to human CD8α at a binding site approximately 9 Å from that of MHCI making mutual interference unlikely. The equilibrium dissociation constant (K_D) is 5 nM. ZED8 binds to cynomolgus CD8 with reduced affinity (66 nM) but it has no measurable affinity for rat or mouse CD8. In a series of lymphoma xenografts, ZED8 imaging was able to identify different CD8 levels concordant with flow cytometry. In cynomolgus monkeys with tool compound ⁸⁹Zr-aCD8v17, lymph nodes were conspicuous by imaging 24 h post-injection, and the pharmacokinetics suggested a flat-fixed first-in-human dose of 4 mg per subject. The whole-body effective dose for an adult human was estimated to be 0.48 mSv/MBq, comparable to existing ⁸⁹Zr immuno-PET reagents.

CONCLUSION

⁸⁹Zr immuno-PET with ZED8 appears to be a promising biomarker of tissue CD8 levels suitable for clinical evaluation in cancer patients eligible for immunotherapy.

Radiopharmaceuticals for PET and SPECT Imaging: A Literature Review over the Last Decade

Positron emission tomography (PET) uses radioactive tracers and enables the functional imaging of several metabolic processes, blood flow measurements, regional chemical composition, and/or chemical absorption. Depending on the targeted processes within the living organism, different tracers are used for various medical conditions, such as cancer, particular brain pathologies, cardiac events, and bone lesions, where the most commonly used tracers are radiolabeled with 18F (e.g., [18F]-FDG and NA [18F]). Oxygen-15 isotope is mostly involved in blood flow measurements, whereas a wide array of 11C-based compounds have also been developed for neuronal disorders according to the affected neuroreceptors, prostate cancer, and lung carcinomas. In contrast, the single-photon emission computed tomography (SPECT) technique uses gamma-emitting radioisotopes and can be used to diagnose strokes, seizures, bone illnesses, and infections by gauging the blood flow and radio distribution within tissues and organs. The radioisotopes typically used in SPECT imaging are iodine-123, technetium-99m, xenon-133, thallium-201, and indium-111. This systematic review article aims to clarify and disseminate the available scientific literature focused on PET/SPECT radiotracers and to provide an overview of the conducted research within the past decade, with an additional focus on the novel radiopharmaceuticals developed for medical imaging.

Radioimmunotherapy for solid tumors: spotlight on Glypican-1 as a radioimmunotherapy target

Radioimmunotherapy (i.e., the use of radiolabeled tumor targeting antibodies) is an emerging approach for the diagnosis, therapy, and monitoring of solid tumors. Often using paired agents, each targeting the same tumor molecule, but labelled with an imaging or therapeutic isotope, radioimmunotherapy has achieved promising clinical results in relatively radio-resistant solid tumors such as prostate. Several approaches to optimize therapeutic efficacy, such as dose fractionation and personalized dosimetry, have seen clinical success. The clinical use and optimization of a radioimmunotherapy approach is, in part, influenced by the targeted tumor antigen, several of which have been proposed for different solid tumors. Glypican-1 (GPC-1) is a heparan sulfate proteoglycan that is expressed in a variety of solid tumors, but whose expression is restricted in normal adult tissue. Here, we discuss the preclinical and clinical evidence for the potential of GPC-1 as a radioimmunotherapy target. We describe the current treatment paradigm for several solid tumors expressing GPC-1 and suggest the potential clinical utility of a GPC-1 directed radioimmunotherapy for these tumors.

PET/CT Imaging of 89Zr-N-sucDf-Pembrolizumab in Healthy Cynomolgus Monkeys

PURPOSE

Programmed cell death-1 receptor (PD-1) and its ligand (PD-L1) are the targets for immunotherapy in many cancer types. Although PD-1 blockade has therapeutic effects, the efficacy differs between patients. Factors contributing to this variability are PD-L1 expression levels and immune cells present in tumors. However, it is not well understood how PD-1 expression in the tumor microenvironment impacts immunotherapy response. Thus, imaging of PD-1-expressing immune cells is of interest. This study aims to evaluate the biodistribution of Zirconium-89 (89Zr)-labeled pembrolizumab, a humanized IgG4 kappa monoclonal antibody targeting PD-1, in healthy cynomolgus monkeys as a translational model of tracking PD-1-positive immune cells.

PROCEDURES

Pembrolizumab was conjugated with the tetrafluorophenol-N-succinyl desferal-Fe(III) ester (TFP-N-sucDf) and subsequently radiolabeled with 89Zr. Four cynomolgus monkeys with no previous exposure to humanized monoclonal antibodies received tracer only or tracer co-injected with pembrolizumab intravenously over 5 min. Thereafter, a static whole-body positron emission tomography (PET) scan was acquired with 10 min per bed position on days 0, 2, 5, and 7. Image-derived standardized uptake values (SUVmean) were quantified by region of interest (ROI) analysis.

RESULTS

89Zr-N-sucDf-pembrolizumab was synthesized with high radiochemical purity (> 99 %) and acceptable molar activity (> 7 MBq/nmol). In animals dosed with tracer only, 89Zr-N-sucDf-pembrolizumab distribution in lymphoid tissues such as mesenteric lymph nodes, spleen, and tonsils increased over time. Except for the liver, low radiotracer distribution was observed in all non-lymphoid tissue including the lung, muscle, brain, heart, and kidney. When a large excess of pembrolizumab was co-administered with a radiotracer, accumulation in the lymph nodes, spleen, and tonsils was reduced, suggestive of target-mediated accumulation.

CONCLUSIONS

89Zr-N-sucDf-pembrolizumab shows preferential uptake in the lymphoid tissues including the lymph nodes, spleen, and tonsils. 89Zr-N-sucDf-pembrolizumab may be useful in tracking the distribution of a subset of immune cells in non-human primates and humans.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02760225.

Advances in Imaging Modalities and Contrast Agents for the Early Diagnosis of Colorectal Cancer

Colorectal cancer is one of the most common gastrointestinal cancers worldwide. The mortality rate of colorectal cancer has declined by more than 20% due to the rapid development of early diagnostic techniques and effective treatment. At present, there are many diagnostic modalities available for the evaluation of colorectal cancer, such as the carcinoembryonic antigen test, the fecal occult blood test, endoscopy, X-ray barium meal, computed tomography, magnetic resonance imaging, and radionuclide examination. Sensitive and specific imaging modalities have played an increasingly important role in the diagnosis of colorectal cancer following the rapid development of novel contrast agents. This review discusses the applications and challenges of different imaging techniques and contrast agents applied to detect colorectal cancer, for the purpose of the early diagnosis and treatment of patients with colorectal cancer.

PET/CT Imaging of Human TNFα Using [89Zr]Certolizumab Pegol in a Transgenic Preclinical Model of Rheumatoid Arthritis

PURPOSE

Tumor necrosis factor alpha (TNFα) drives inflammation and bone degradation in patients with rheumatoid arthritis (RA). Some RA patients experience a rapid clinical response to TNFα inhibitors such as certolizumab pegol (CZP) while other patients show limited to no response. Current methods for imaging RA have limited sensitivity and do not assist in the selection of patients most likely to respond to immune-mediated therapy. Herein, we developed a novel positron emission tomography (PET) radiotracer for immuno-PET imaging of TNFα in transgenic human TNFα-expressing mice.

PROCEDURES

CZP was modified with p-isothiocyanatobenzyl-deferoxamine (DFO) and radiolabeled with Zr-89. The biological activity of [⁸⁹Zr]DFO-CZP was evaluated by HPLC and binding assay using human recombinant TNFα (hTNFα). The feasibility of specific immuno-PET imaging of human TNFα was assessed in a transgenic mouse model of RA that expresses human TNFα. This model resembles the progression of RA in humans by maintaining lower levels of circulating hTNFα and exhibits chronic arthritis in the forepaw and hind paw joints. The dosimetry of [⁸⁹Zr]DFO-CZP in humans was estimated using microPET/CT imaging in Sprague Dawley rats.

RESULTS

[⁸⁹Zr]DFO-CZP was isolated with radiolabeling yields of 85 ± 6 % (n = 5) and specific activities ranging from 74 to 185 MBq/mg (n = 5). Following size exclusion purification, the radiochemical purity of [⁸⁹Zr]DFO-CZP was greater than 97 %. [⁸⁹Zr]DFO-CZP retained high immunoreactivity with more than 95 % of the radioactivity shifted into higher molecular weight complexes. Images showed increasing uptake of the tracer in forepaw and hind paw joints with disease progression. No uptake was observed in the model previously administered with an excess amount of unmodified CZP and in normal control mice, demonstrating in vivo specific uptake of [⁸⁹Zr]DFO-CZP.

CONCLUSION

The feasibility of immuno-PET imaging of human TNFα with [⁸⁹Zr]DFO-CZP has been demonstrated in a preclinical model of RA.

Safety and tolerability of Miltuximab® - a first in human study in patients with advanced solid cancers

OBJECTIVES

Miltuximab® is a chimeric antibody targeting Glypican-1 (GPC-1), a cell surface antigen which is overexpressed in solid cancers. Miltuximab® has shown promising safety and efficacy in radioimmunotherapy models of prostate cancer. This first in human study used Miltuximab® radiolabelled with Gallium-67 ([67Ga]Ga-DOTA-Miltuximab®). The primary study endpoint was to establish safety and tolerability of Miltuximab®. Secondary endpoints were biodistribution, tumour targeting and pharmacokinetic analysis.

METHODS

Four cohorts of three patients (9 with advanced prostate cancer, 2 with pancreatic and 1 with bladder cancer) were dosed with 1 mg, ~250 MBq of [67Ga]Ga-DOTA-Miltuximab®. Cohort 1 received [67Ga]Ga-DOTA-Miltuximab® alone, while cohorts 2-4 were pre-infused with increasing doses (3.5, 11.5 and 24 mg, respectively) of unlabelled Miltuximab®-DOTA 1 hour prior to [67Ga]Ga-DOTA-Miltuximab®. Safety and tolerability were assessed by clinical and standard laboratory assessments. Patients underwent whole body gamma-camera scans and SPECT/CT scans up to 144 h post-infusion. Total organ radiation exposure was determined by dosimetry of whole-body gamma scans.

RESULTS

The dosing regimen was well tolerated, with no drug-related adverse events observed. Liver and spleen uptake of [67Ga]Ga-DOTA-Miltuximab® was observed. Liver uptake was reduced by pre-infusion of unlabelled Miltuximab®-DOTA. Dosimetry analysis showed a favorable exposure profile. [67Ga]Ga-DOTA-Miltuximab® targeting to tumour sites was observed in two prostate cancer patients who had failed enzalutamide treatment. Higher doses of unlabelled antibody achieved lower liver uptake and increased antibody serum half life.

CONCLUSIONS

This study is the first in human for Miltuximab® a first in class antibody targeting GPC-1. The trial met its primary endpoint of safety, demonstrating its potential as a safe and tolerable monoclonal antibody. This safety data, together with targeting to tumour lesions and biodistribution information supports the further clinical development of Miltuximab® as a theranostic agent in a planned Phase I human trial.

Imaging using radiolabelled targeted proteins: radioimmunodetection and beyond

The use of radiolabelled antibodies was proposed in 1970s for staging of malignant tumours. Intensive research established chemistry for radiolabelling of proteins and understanding of factors determining biodistribution and targeting properties. The use of radioimmunodetection for staging of cancer was not established as common practice due to approval and widespread use of [¹⁸F]-FDG, which provided a more general diagnostic use than antibodies or their fragments. Expanded application of antibody-based therapeutics renewed the interest in radiolabelled antibodies. RadioimmunoPET emerged as a powerful tool for evaluation of pharmacokinetics of and target engagement by biotherapeutics. In addition to monoclonal antibodies, new radiolabelled engineered proteins have recently appeared, offering high-contrast imaging of expression of therapeutic molecular targets in tumours shortly after injection. This creates preconditions for noninvasive determination of a target expression level and stratification of patients for targeted therapies. Radiolabelled proteins hold great promise to play an important role in development and implementation of personalised targeted treatment of malignant tumours. This article provides an overview of biodistribution and tumour-seeking features of major classes of targeting proteins currently utilized for molecular imaging. Such information might be useful for researchers entering the field of the protein-based radionuclide molecular imaging.

Current Perspectives on 89Zr-PET Imaging

⁸⁹Zr is an emerging radionuclide that plays an essential role in immuno-positron emission tomography (PET) imaging. The long half-life of ⁸⁹Zr (t_1/2 = 3.3 days) is favorable for evaluating the in vivo distribution of monoclonal antibodies. Thus, the use of ⁸⁹Zr is promising for monitoring antibody-based cancer therapies. Immuno-PET combines the sensitivity of PET with the specificity of antibodies. A number of studies have been conducted to investigate the feasibility of ⁸⁹Zr immuno-PET imaging for predicting the efficacy of radioimmunotherapy and antibody therapies, imaging target expression, detecting target-expressing tumors, and the monitoring of anti-cancer chemotherapies. In this review, we summarize the current status of PET imaging using ⁸⁹Zr in both preclinical and clinical studies by highlighting the use of immuno-PET for the targets of high clinical relevance. We also present ⁸⁹Zr-PET applications other than immuno-PET, such as nanoparticle imaging and cell tracking. Finally, we discuss the limitations and the ongoing research being performed to overcome the remaining hurdles.

Interactions Between Tumor Biology and Targeted Nanoplatforms for Imaging Applications

Although considerable efforts have been conducted to diagnose, improve, and treat cancer in the past few decades, existing therapeutic options are insufficient, as mortality and morbidity rates remain high. Perhaps the best hope for substantial improvement lies in early detection. Recent advances in nanotechnology are expected to increase the current understanding of tumor biology, and will allow nanomaterials to be used for targeting and imaging both in vitro and in vivo experimental models. Owing to their intrinsic physicochemical characteristics, nanostructures (NSs) are valuable tools that have received much attention in nanoimaging. Consequently, rationally designed NSs have been successfully employed in cancer imaging for targeting cancer-specific or cancer-associated molecules and pathways. This review categorizes imaging and targeting approaches according to cancer type, and also highlights some new safe approaches involving membrane-coated nanoparticles, tumor cell-derived extracellular vesicles, circulating tumor cells, cell-free DNAs, and cancer stem cells in the hope of developing more precise targeting and multifunctional nanotechnology-based imaging probes in the future.

Analysis of Progress and Challenges of EGFR-Targeted Molecular Imaging in Cancer With a Focus on Affibody Molecules

Epidermal growth factor receptor (EGFR)-targeted cancer therapy requires an accurate estimation of EGFR expression in tumors to identify responsive patients, monitor therapeutic effect, and estimate prognosis. The EGFR molecular imaging is an optimal method for evaluating EGFR expression in vivo accurately and noninvasively. In this review, we discuss the recent advances in EGFR-targeted molecular imaging in cancer, with a special focus on the development of imaging agents, including epidermal growth factor (EGF) ligand, monoclonal antibodies, antibody fragments, Affibody, and small molecules. Each substrate or probe, whether it is an endogenous ligand, antibody, peptide, or small molecule labeled with fluorochrome or radionuclide, has unique advantages and limitations. Antibody-based probes have high affinity but a long metabolic cycle and therefore offer poor imaging quality. Affibody molecules promise to surpass antibody-based probes due to their small size, stable chemical properties, and high affinity to the target. Small-molecule probes are safe, have favorable pharmacokinetics, and show high affinity and specificity, in addition to having an ideal size, but are inadequate for delayed imaging after injection due to their fast clearance.

Biodistribution, pharmacokinetics and radioimmunotherapy of 188Re-cetuximab in NCI-H292 human lung tumor-bearing nude mice

Background Cetuximab is a fully humanized IgG1 subclass monoclonal that binds specifically to the human epidermal growth factor receptor (EGFR). Although EGFR is expressed in normal cells, the overexpression of EGFR is detected in many human cancers, such as colon, rectum and lung tumors. In this study, cetuximab with a combination of radiotherapy nuclear ¹⁸⁸Re achieved better therapeutic effect on lung cancer. Methods¹⁸⁸Re-cetuximab administered by the i.v. route in human NCI-H292 lung tumor-bearing mice was investigated. NanoSPECT/CT images were taken to evaluate the distribution and tumor targeting of ¹⁸⁸Re-cetuximab in mice. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by the tumor growth inhibition, survival ratio. Results For nanoSPECT/CT imaging, a significant uptake in tumor was observed at 24 and 48 h following the injection of ¹⁸⁸Re-cetuximab. The anti-tumor effect of ¹⁸⁸Re-cetuximab was assessed by tumor growth inhibition and the survival ratio. The tumor-bearing mice treated with ¹⁸⁸Re-cetuximab showed a better mean tumor growth inhibition rate (MGI = 0.049) and longer median survival time and lifespan (62.50 d; 70.07%) than those treated with ¹⁸⁸Re-perrhenate and cetuximab only by single injection. A synergistic effect of tumor growth inhibition was observed with the combination index exceeding one for ¹⁸⁸Re-cetuximab (CI = 6.135 and 9.276). Conclusion The tumor targeting and localization of 188Re-cetuximab were confirmed in this study. Synergistic therapeutic efficacy was demonstrated for the radioimmunotherapy of ¹⁸⁸Re-cetuximab. The results of this study reveal the potential advantage and benefit obtained from ¹⁸⁸Re-cetuximab for diagnosis and therapy of oncology applications in the future.

89Zr-trastuzumab PET supports clinical decision making in breast cancer patients, when HER2 status cannot be determined by standard work up

Background

Up-to-date information on human epidermal growth factor receptor 2 (HER2) status in breast cancer (BC) is important, as expression can vary during the course of the disease, necessitating anti-HER2 therapy adjustments. Repeat biopsies, however, are not always possible. In this feasibility trial we assessed whether ⁸⁹Zr-trastuzumab PET could support diagnostic understanding and aid clinical decision making, when HER2 status could not be determined by standard work up. Additionally, HER2 status on circulating tumour cells (CTCs) was assessed.

Patients and methods

⁸⁹Zr-trastuzumab PET was performed in patients if disease HER2 status remained unclear after standard work up (bone scan, ¹⁸F-FDG PET, CT and if feasible a biopsy). PET result and central pathologic revision of available tumour biopsies were reported to the referring physician. CTC HER2 status prior to PET was evaluated afterwards and therefore not reported. Diagnostic understanding and treatment decision questionnaires were completed by the referring physicians before, directly after and ≥ 3 months after ⁸⁹Zr-trastuzumab PET.

Results

Twenty patients were enrolled: 8 with two primary cancers (HER2-positive and HER2-negative BC or BC and non-BC), 7 with metastases inaccessible for biopsy, 4 with prior HER2-positive and -negative metastases and 1 with primary BC with equivocal HER2 status. ⁸⁹Zr-trastuzumab PET was positive in 12 patients, negative in 7 and equivocal in 1 patient. In 15/20 patients, ⁸⁹Zr-trastuzumab PET supported treatment decision. The scan altered treatment of 8 patients, increased physicians’ confidence without affecting treatment in 10, and improved physicians’ disease understanding in 18 patients. In 10/20 patients CTCs were detected; 6/10 showed HER2 expression. CTC HER2 status was not correlated to ⁸⁹Zr-trastuzumab PET result or treatment decision.

Conclusion

⁸⁹Zr-trastuzumab PET supports clinical decision making when HER2 status cannot be determined by standard work up. The impact of CTC HER2 status needs to be further explored.

Electronic supplementary material

The online version of this article (10.1007/s00259-018-4099-8) contains supplementary material, which is available to authorized users.

Understanding the in vivo fate of radioimmunoconjugates for nuclear imaging

Over the past 25 years, antibodies have emerged as extraordinarily promising vectors for the delivery of radionuclides to tumors for nuclear imaging. While radioimmunoconjugates often produce very high activity concentrations in target tissues, they also are frequently characterized by elevated activity concentrations in healthy organs as well. The root of this background uptake lies in the complex network of biological interactions between the radioimmunoconjugate and the subject. In this review, we seek to provide an overview of these interactions and thus paint a general picture of the in vivo fate of radioimmunoconjugates. To cover the entire story, we have divided our discussion into 2 parts. First, we will address the path of the entire radioimmunoconjugate as it travels through the body. And second, we will cover the fate of the radionuclide itself, as its course can diverge from the antibody under certain circumstances. Ultimately, our goal is to provide the nuclear imaging field with a resource covering these important-yet often underestimated-pathways.

Noninvasive Biomarkers of Colorectal Cancer: Role in Diagnosis and Personalised Treatment Perspectives

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide. It has been estimated that more than one-third of patients are diagnosed when CRC has already spread to the lymph nodes. One out of five patients is diagnosed with metastatic CRC. The stage of diagnosis influences treatment outcome and survival. Notwithstanding the recent advances in multidisciplinary management and treatment of CRC, patients are still reluctant to undergo screening tests because of the associated invasiveness and discomfort (e.g., colonoscopy with biopsies). Moreover, the serological markers currently used for diagnosis are not reliable and, even if they were useful to detect disease recurrence after treatment, they are not always detected in patients with CRC (e.g., CEA). Recently, translational research in CRC has produced a wide spectrum of potential biomarkers that could be useful for diagnosis, treatment, and follow-up of these patients. The aim of this review is to provide an overview of the newer noninvasive or minimally invasive biomarkers of CRC. Here, we discuss imaging and biomolecular diagnostics ranging from their potential usefulness to obtain early and less-invasive diagnosis to their potential implementation in the development of a bespoke treatment of CRC.

Influence of composition of cysteine-containing peptide-based chelators on biodistribution of 99mTc-labeled anti-EGFR affibody molecules

Epidermal growth factor receptor (EGFR) is overexpressed in a number of cancers and is the molecular target for several anti-cancer therapeutics. Radionuclide molecular imaging of EGFR expression should enable personalization of anti-cancer treatment. Affibody molecule is a promising type of high-affinity imaging probes based on a non-immunoglobulin scaffold. A series of derivatives of the anti-EGFR affibody molecule ZEGFR:2377, having peptide-based cysteine-containing chelators for conjugation of ^99mTc, was designed and evaluated. It was found that glutamate-containing chelators Gly-Gly-Glu-Cys (GGEC), Gly-Glu-Glu-Cys (GEEC) and Glu-Glu-Glu-Cys (EEEC) provide the best labeling stability. The glutamate containing conjugates bound to EGFR-expressing cells specifically and with high affinity. Specific targeting of EGFR-expressing xenografts in mice was demonstrated. The number of glutamate residues in the chelator had strong influence on biodistribution of radiolabeled affibody molecules. Increase of glutamate content was associated with lower uptake in normal tissues. The ^99mTc-labeled variant containing the EEEC chelator provided the highest tumor-to-organ ratios. In conclusion, optimizing the composition of peptide-based chelators enhances contrast of imaging of EGFR-expression using affibody molecules.

Recent Advances in Zirconium-89 Chelator Development

The interest in zirconium-89 (⁸⁹Zr) as a positron-emitting radionuclide has grown considerably over the last decade due to its standardized production, long half-life of 78.2 h, favorable decay characteristics for positron emission tomography (PET) imaging and its successful use in a variety of clinical and preclinical applications. However, to be utilized effectively in PET applications it must be stably bound to a targeting ligand, and the most successfully used ⁸⁹Zr chelator is desferrioxamine B (DFO), which is commercially available as the iron chelator Desferal^®. Despite the prevalence of DFO in ⁸⁹Zr-immuno-PET applications, the development of new ligands for this radiometal is an active area of research. This review focuses on recent advances in zirconium-89 chelation chemistry and will highlight the rapidly expanding ligand classes that are under investigation as DFO alternatives.

Extracellular domain shedding influences specific tumor uptake and organ distribution of the EGFR PET tracer 89Zr-imgatuzumab

Preclinical positron emission tomography (PET) imaging revealed a mismatch between in vivo epidermal growth factor receptor (EGFR) expression and EGFR antibody tracer tumor uptake. Shed EGFR ectodomain (sEGFR), which is present in cancer patient sera, can potentially bind tracer and therefore influence tracer kinetics. To optimize EGFR-PET, we examined the influence of sEGFR levels on tracer kinetics and tumor uptake of EGFR monoclonal antibody 89Zr-imgatuzumab in varying xenograft models. Human cancer cell lines A431 (EGFR overexpressing, epidermoid), A549 and H441 (both EGFR medium expressing, non-small cell lung cancer) were xenografted in mice. Xenografted mice received 10, 25 or 160 μg 89Zr-imgatuzumab, co-injected with equal doses 111In-IgG control. MicroPET scans were made 24, 72 and 144 h post injection, followed by biodistribution analysis. sEGFR levels in liver and plasma samples were determined by ELISA. 89Zr-imgatuzumab uptake in A431 tumors was highest (29.8 ± 5.4 %ID/g) in the 160 μg dose group. Contrary, highest uptake in A549 and H441 tumors was found at the lowest (10 μg) 89Zr-imgatuzumab dose. High 89Zr-imgatuzumab liver accumulation was found in A431 xenografted mice, which decreased with antibody dose increments. 89Zr-imgatuzumab liver uptake in A549 and H441 xenografted mice was low at all doses. sEGFR levels in liver and plasma of A431 bearing mice were up to 1000-fold higher than levels found in A549, H441 and non-tumor xenografted mice. 89Zr-imgatuzumab effectively visualizes EGFR-expressing tumors. High sEGFR levels can redirect 89Zr-imgatuzumab to the liver, in which case tumor visualization can be improved by increasing tracer antibody dose.

Quantitative assessment of Zirconium-89 labeled cetuximab using PET/CT imaging in patients with advanced head and neck cancer: a theragnostic approach

Biomarkers predicting treatment response to the monoclonal antibody cetuximab in locally advanced head and neck squamous cell carcinomas (LAHNSCC) are lacking. We hypothesize that tumor accessibility is an important factor in treatment success of the EGFR targeting drug. We quantified uptake of cetuximab labeled with Zirconium-89 (⁸⁹Zr) using PET/CT imaging.

Seventeen patients with stage III-IV LAHNSCC received a loading dose unlabeled cetuximab, followed by 10 mg 54.5±9.6 MBq ⁸⁹Zr-cetuximab. PET/CT images were acquired either 3 and 6 or 4 and 7 days post-injection. ⁸⁹Zr-cetuximab uptake was quantified using standardized uptake value (SUV) and tumor-to-background ratio (TBR), and correlated to EGFR immunohistochemistry. TBR was compared between scan days to determine optimal timing.

Uptake of ⁸⁹Zr-cetuximab varied between patients (day 6-7: SUV_peak range 2.5-6.2). TBR increased significantly (49±28%, p < 0.01) between first (1.1±0.3) and second scan (1.7±0.6). Between groups with a low and high EGFR expression a significant difference in SUV_mean (2.1 versus 3.0) and SUV_peak (3.2 versus 4.7) was found, however, not in TBR. Data is available at www.cancerdata.org (DOI: 10.17195/candat.2016.11.1).

In conclusion, ⁸⁹Zr-cetuximab PET imaging shows large inter-patient variety in LAHNSCC and provides additional information over FDG-PET and EGFR expression. Validation of the predictive value is recommended with scans acquired 6-7 days post-injection.

The use of radiocobalt as a label improves imaging of EGFR using DOTA-conjugated Affibody molecule

Several anti-cancer therapies target the epidermal growth factor receptor (EGFR). Radionuclide imaging of EGFR expression in tumours may aid in selection of optimal cancer therapy. The ¹¹¹In-labelled DOTA-conjugated Z_EGFR:2377 Affibody molecule was successfully used for imaging of EGFR-expressing xenografts in mice. An optimal combination of radionuclide, chelator and targeting protein may further improve the contrast of radionuclide imaging. The aim of this study was to evaluate the targeting properties of radiocobalt-labelled DOTA-Z_EGFR:2377. DOTA-Z_EGFR:2377 was labelled with ⁵⁷Co (T_1/2 = 271.8 d), ⁵⁵Co (T_1/2 = 17.5 h), and, for comparison, with the positron-emitting radionuclide ⁶⁸Ga (T_1/2 = 67.6 min) with preserved specificity of binding to EGFR-expressing A431 cells. The long-lived cobalt radioisotope ⁵⁷Co was used in animal studies. Both ⁵⁷Co-DOTA-Z_EGFR:2377 and ⁶⁸Ga-DOTA-Z_EGFR:2377 demonstrated EGFR-specific accumulation in A431 xenografts and EGFR-expressing tissues in mice. Tumour-to-organ ratios for the radiocobalt-labelled DOTA-Z_EGFR:2377 were significantly higher than for the gallium-labelled counterpart already at 3 h after injection. Importantly, ⁵⁷Co-DOTA-Z_EGFR:2377 demonstrated a tumour-to-liver ratio of 3, which is 7-fold higher than the tumour-to-liver ratio for ⁶⁸Ga-DOTA-Z_EGFR:2377. The results of this study suggest that the positron-emitting cobalt isotope ⁵⁵Co would be an optimal label for DOTA-Z_EGFR:2377 and further development should concentrate on this radionuclide as a label.

Pharmacokinetics, Biodistribution, and Radiation Dosimetry for 89Zr-Trastuzumab in Patients with Esophagogastric Cancer

Trastuzumab with chemotherapy improves clinical outcomes in patients with human epidermal growth factor receptor 2 (HER2)-positive esophagogastric adenocarcinoma (EGA). Despite the therapeutic benefit, responses are rarely complete, and most patients develop progression. To our knowledge, this is the first report evaluating ⁸⁹Zr-trastuzumab in HER2-positive EGA; here, we evaluate the safety, pharmacokinetics, biodistribution, and dosimetry ⁸⁹Zr-trastuzumab. Methods: Trastuzumab was conjugated with deferoxamine and radiolabeled with ⁸⁹Zr. A mean activity of 184 MBq was administered to 10 patients with metastatic HER2-positive EGA. PET imaging, whole-body probe counts, and blood draws were performed to assess pharmacokinetics, biodistribution, and dosimetry. Results: No clinically significant toxicities were observed. At the end of infusion, the estimated ⁸⁹Zr-trastuzumab in plasma volume was a median 102% (range, 78%-113%) of the injected dose. The median biologic half-life T_1/2β was 111 h (range, 78-193 h). The median biologic whole-body retention half-life was 370 h (range, 257-578 h). PET images showed optimal tumor visualization at 5-8 d after injection. The maximum tumor SUV ranged from no to minimal uptake in 3 patients to a median of 6.8 (range, 2.9-22.7) for 20 lesions in 7 patients. Dosimetry estimates from OLINDA showed that the organs receiving the highest absorbed doses were the liver and heart wall, with median values of 1.37 and 1.12 mGy/MBq, respectively. Conclusion:⁸⁹Zr-trastuzumab imaging tracer is safe and provides high-quality images in patients with HER2-positive EGA, with an optimal imaging time of 5-8 d after injection.

Recombinant Human Thyroid-Stimulating Hormone Versus Thyroid Hormone Withdrawal in 124I PET/CT-Based Dosimetry for 131I Therapy of Metastatic Differentiated Thyroid Cancer

Patients with metastatic differentiated thyroid cancer (DTC) may be prepared using either thyroid-stimulating hormone withdrawal (THW) or recombinant human thyroid-stimulating hormone (rhTSH) injections before ¹³¹I administration for treatment. The objective of this study was to compare the absorbed dose to the critical organs and tumors determined by ¹²⁴I PET/CT-based dosimetry for ¹³¹I therapy of metastatic DTC when the same patient was prepared with and imaged after both THW and rhTSH injections. Methods: Four DTC patients at MedStar Washington Hospital Center were first prepared using the rhTSH method and imaged by ¹²⁴I PET/CT at 2, 24, 48, 72, and 96 h after administration of approximately 30-63 MBq of ¹²⁴I. After 5-8 wk, the same patients were prepared using the THW method and imaged as before. The ¹²⁴I PET/CT images acquired as part of a prospective study were used to perform retrospective dosimetric calculations for ¹³¹I therapy for the normal organs with the dosimetry package 3D-RD. The absorbed doses from ¹³¹I for the lungs, liver, heart, kidneys, and bone marrow were obtained for each study (rhTSH and THW). Twenty-two lesions in 3 patients were identified. The contours were drawn on each PET image of each study. Time-integrated activity coefficients were calculated and used as input in OLINDA/EXM sphere dose calculator to obtain the absorbed dose to tumors. Results: The THW-to-rhTSH organ absorbed dose ratio averaged over 5 organs for the first 3 patients was 1.5, 2.5, and 0.64, respectively, and averaged over 3 organs for the fourth patient was 1.1. The absorbed dose per unit administered activity to the bone marrow was 0.13, 0.086, 0.33, and 0.068 mGy/MBq after rhTSH and 0.11, 0.14, 0.22, and 0.080 mGy/MBq after THW for each patient, respectively. With the exception of 3 lesions of 1 patient, the absorbed dose per unit administered activity of ¹³¹I was higher in the THW study than in the rhTSH study. The ratio of the average tumor absorbed dose after stimulation by THW compared with stimulation by rhTSH injections was 3.9, 27, and 1.4 for patient 1, patient 2, and patient 3, respectively. The ratio of mean tumor to bone marrow absorbed dose per unit administered activity of ¹³¹I, after THW and rhTSH, was 232 and 62 (patient 1), 12 and 0.78 (patient 2), and 22 and 11 (patient 3), respectively. Conclusion: The results suggest a high patient variability in the overall absorbed dose to the normal organs per MBq of ¹³¹I administered, between the 2 TSH stimulation methods. The tumor-to-dose-limiting-organ (bone marrow) absorbed dose ratio, that is, the therapeutic index, was higher in the THW-aided than rhTSH-aided administrations. Additional comparison for tumor and normal organ absorbed dose in patients prepared using both methods is needed before definitive conclusions may be drawn regarding rhTSH versus THW patient preparation methods for ¹³¹I therapy of metastatic DTC.

Noninvasive monitoring of cancer therapy induced activated T cells using [18F]FB-IL-2 PET imaging

Cancer immunotherapy urgently calls for methods to monitor immune responses at the site of the cancer. Since activated T lymphocytes may serve as a hallmark for anticancer responses, we targeted these cells using the radiotracer N-(4-[¹⁸F]fluorobenzoyl)-interleukin-2 ([¹⁸F]FB-IL-2) for positron emission tomography (PET) imaging. Thus, we noninvasively monitored the effects of local tumor irradiation and/or immunization on tumor-infiltrating and systemic activated lymphocytes in tumor-bearing mice. A 10- and 27-fold higher [¹⁸F]FB-IL-2 uptake was observed in tumors of mice receiving tumor irradiation alone or in combination with immunization, respectively. This increased uptake was extended to several non-target tissues. Administration of the CXCR4 antagonist AMD3100 reduced tracer uptake by 2.8-fold, indicating a CXCR4-dependent infiltration of activated T lymphocytes upon cancer treatment. In conclusion, [¹⁸F]FB-IL-2 PET can serve as a clinical biomarker to monitor treatment-induced infiltration of activated T lymphocytes and, on that basis, may guide cancer immunotherapies.

Imaging in Colorectal Cancer: Progress and Challenges for the Clinicians

The use of imaging in colorectal cancer (CRC) has significantly evolved over the last twenty years, establishing important roles in surveillance, diagnosis, staging, treatment selection and follow up. The range of modalities has broadened with the development of novel tracer and contrast agents, and the fusion of technologies such as positron emission tomography (PET) and computed tomography (CT). Traditionally, the most widely used modality for assessing treatment response in metastasised colon and rectal tumours is CT, combined with use of the RECIST guidelines. However, a growing body of evidence suggests that tumour size does not always adequately correlate with clinical outcomes. Magnetic resonance imaging (MRI) is a more versatile technique and dynamic contrast-enhanced (DCE)-MRI and diffusion-weighted (DW)-MRI may be used to evaluate biological and functional effects of treatment. Integrated fluorodeoxyglucose (FDG)-PET/CT combines metabolic and anatomical imaging to improve sensitivity and specificity of tumour detection, and a number of studies have demonstrated improved diagnostic accuracy of this modality in a variety of tumour types, including CRC. These developments have enabled the progression of treatment strategies in rectal cancer and improved the detection of hepatic metastatic disease, yet are not without their limitations. These include technical, economical and logistical challenges, along with a lack of robust evidence for standardisation and formal guidance. In order to successfully apply these novel imaging techniques and utilise their benefit to provide truly personalised cancer care, advances need to be clinically realised in a routine and robust manner.

An automatic delineation method for bone marrow absorbed dose estimation in (89)Zr PET/CT studies

Background

The study aims to develop and validate an automatic delineation method for estimating red bone marrow (RM) activity concentration and absorbed dose in ⁸⁹Zr positron emission tomography/computed tomography (PET/CT) studies. Five patients with advanced colorectal cancer received 37.1 ± 0.9 MBq [⁸⁹Zr] cetuximab within 2 h after administration of a therapeutic dose of 500 mg m⁻² unlabelled cetuximab. Per patient, five PET/CT scans were acquired on a Gemini TF-64 PET/CT scanner at 1, 24, 48, 96 and 144 h post injection. Low dose CT data were used to manually generate volumes of interest (VOI) in the lumbar vertebrae (LV). In addition, LV VOI were generated automatically using an active contour method in a low dose CT. RM activity was then determined by mapping the low dose CT-derived RM VOI onto the corresponding PET scans. Finally, these activities were used to derive residence times and, subsequently, the self and total RM absorbed doses using OLINDA/EXM 1.1.

Results

High correlations (r² > 0.85) between manual and automated VOI methods were obtained for both RM activity concentrations and total absorbed doses. On average, the automatic method provided values that were lower than 5 % compared to the manual method.

Conclusions

An automated and efficient VOI method, based on an active contour approach, was developed, enabling accurate estimates of RM activity concentrations and total absorbed doses.

Electronic supplementary material

The online version of this article (doi:10.1186/s40658-016-0149-0) contains supplementary material, which is available to authorized users.

Magnetic Resonance Imaging and Other Imaging Modalities in Diagnostic and Tumor Response Evaluation

Functional imaging is emerging as a valuable contributor to the clinical management of patients with rectal cancer. Techniques such as diffusion-weighted magnetic resonance imaging, perfusion imaging, and positron emission tomography can offer meaningful insights into tissue architecture, vascularity, and metabolism. Moreover, new techniques targeting other aspects of tumor biology are now being developed and studied. This study reviews the potential role of functional imaging for the diagnosis, treatment monitoring, and assessment of prognosis in patients with rectal cancer.

ImmunoPET with Anti-Mesothelin Antibody in Patients with Pancreatic and Ovarian Cancer before Anti-Mesothelin Antibody-Drug Conjugate Treatment

PURPOSE

Mesothelin (MSLN) is frequently overexpressed in pancreatic and ovarian cancers, making it a potential drug target. We performed an (89)Zr-PET imaging study with MMOT0530A, a MSLN antibody, in conjunction with a phase I study with the antibody-drug conjugate DMOT4039A, containing MMOT0530A bound to MMAE. The aim was to study antibody tumor uptake, whole-body distribution, and relation between uptake, response to treatment, and MSLN expression.

EXPERIMENTAL DESIGN

Before DMOT4039A treatment, patients received 37 MBq (89)Zr-MMOT0530A followed by PET/CT imaging 2, 4, and 7 days postinjection. Tracer uptake was expressed as standardized uptake value (SUV). MSLN expression was determined with immunohistochemistry (IHC) on archival tumor tissue.

RESULTS

Eleven patients were included, 7 with pancreatic and 4 with ovarian cancer. IHC MSLN expression varied from absent to strong. Suitable tracer antibody dose was 10 mg MMOT0530A and optimal imaging time was 4 and 7 days postinjection. Tumor tracer uptake occurred in 37 lesions with mean SUVmax of 13.1 (±7.5) on PET 4 days postinjection, with 11.5 (±7.5) in (N= 17) pancreatic and 14.5 (±8.7) in (N= 20) ovarian cancer lesions. Within patients, a mean 2.4-fold (±1.10) difference in uptake between tumor lesions existed. Uptake in blood, liver, kidneys, spleen, and intestine reflected normal antibody distribution. Tracer tumor uptake was correlated to IHC. Best response to DMOT4039A was partial response in one patient.

CONCLUSIONS

With (89)Zr-MMOT0530A-PET, pancreatic and ovarian cancer lesions as well as antibody biodistribution could be visualized. This technique can potentially guide individualized antibody-based treatment.

Molecular imaging using PET for breast cancer

Molecular imaging can visualize the biological processes at the molecular and cellular levels in vivo using certain tracers for specific molecular targets. Molecular imaging of breast cancer can be performed with various imaging modalities, however, positron emission tomography (PET) is a sensitive and non-invasive molecular imaging technology and this review will focus on PET molecular imaging of breast cancer, such as FDG-PET, FLT-PET, hormone receptor PET, and anti-HER2 PET.