Fluorescently labelled vedolizumab to visualise drug distribution and mucosal target cells in inflammatory bowel disease

OBJECTIVE

Improving patient selection and development of biological therapies such as vedolizumab in IBD requires a thorough understanding of the mechanism of action and target binding, thereby providing individualised treatment strategies. We aimed to visualise the macroscopic and microscopic distribution of intravenous injected fluorescently labelled vedolizumab, vedo-800CW, and identify its target cells using fluorescence molecular imaging (FMI).

DESIGN

Forty three FMI procedures were performed, which consisted of macroscopic in vivo assessment during endoscopy, followed by macroscopic and microscopic ex vivo imaging. In phase A, patients received an intravenous dose of 4.5 mg, 15 mg vedo-800CW or no tracer prior to endoscopy. In phase B, patients received 15 mg vedo-800CW preceded by an unlabelled (sub)therapeutic dose of vedolizumab.

RESULTS

FMI quantification showed a dose-dependent increase in vedo-800CW fluorescence intensity in inflamed tissues, with 15 mg (153.7 au (132.3-163.7)) as the most suitable tracer dose compared with 4.5 mg (55.3 au (33.6-78.2)) (p=0.0002). Moreover, the fluorescence signal decreased by 61% when vedo-800CW was administered after a therapeutic dose of unlabelled vedolizumab, suggesting target saturation in the inflamed tissue. Fluorescence microscopy and immunostaining showed that vedolizumab penetrated the inflamed mucosa and was associated with several immune cell types, most prominently with plasma cells.

CONCLUSION

These results indicate the potential of FMI to determine the local distribution of drugs in the inflamed target tissue and identify drug target cells, providing new insights into targeted agents for their use in IBD.

TRIAL REGISTRATION NUMBER

NCT04112212.

Long Versus Short Axial Field of View Immuno-PET/CT: Semiquantitative Evaluation for 89Zr-Trastuzumab

The purpose of this study was to quantify any differences between the SUVs of 89Zr immuno-PET scans obtained using a PET/CT system with a long axial field of view (LAFOV; Biograph Vision Quadra) compared to a PET/CT system with a short axial field of view (SAFOV; Biograph Vision) and to evaluate how LAFOV PET scan duration affects image noise and SUV metrics. Methods: Five metastatic breast cancer patients were scanned consecutively on SAFOV and LAFOV PET/CT scanners. Four additional patients were scanned using only LAFOV PET/CT. Scans on both systems lasted approximately 30 min and were acquired 4 d after injection of 37 MBq of 89Zr-trastuzumab. LAFOV list-mode data were reprocessed to obtain images acquired using shorter scan durations (15, 10, 7.5, 5, and 3 min). Volumes of interest were placed in healthy tissues, and tumors were segmented semiautomatically to compare coefficients of variation and to perform Bland-Altman analysis on SUV metrics (SUVmax, SUVpeak, and SUVmean). Results: Using 30-min images, 2 commonly used lesion SUV metrics were higher for SAFOV than for LAFOV PET (SUVmax, 16.2% ± 13.4%, and SUVpeak, 10.1% ± 7.2%), whereas the SUVmean of healthy tissues showed minimal differences (0.7% ± 5.8%). Coefficients of variation in the liver derived from 30-min SAFOV PET were between those of 3- and 5-min LAFOV PET. The smallest SUVmax and SUVpeak differences between SAFOV and LAFOV were found for 3-min LAFOV PET. Conclusion: LAFOV 89Zr immuno-PET showed a lower SUVmax and SUVpeak than SAFOV because of lower image noise. LAFOV PET scan duration may be reduced at the expense of increasing image noise and bias in SUV metrics. Nevertheless, SUVpeak showed only minimal bias when reducing scan duration from 30 to 10 min.

Validation of an LC-MS/MS assay for rapid and simultaneous quantification of 21 kinase inhibitors in human plasma and serum for therapeutic drug monitoring

Kinase inhibitors have revolutionized cancer treatment in the past 25 years and currently form the cornerstone of many treatments. Due to the increasing evidence for therapeutic drug monitoring (TDM) of kinase inhibitors, the need is growing for new assays to rapidly evaluate kinase inhibitor plasma concentrations. In this study, we developed an LC-MS/MS assay for the rapid and simultaneous quantification of 21 kinase inhibitors. First, a literature search was conducted to ensure that the linear ranges of the analytes were in line with the reported therapeutic windows and/or TDM reference values. Subsequently, the assay was validated according to FDA and EMA guidelines for linearity, selectivity, carry-over, accuracy, precision, dilution integrity, matrix effect, recovery, and stability. The assay was fast, with a short run-time of 2 min per sample. Sample pre-treatment consisted of protein precipitation with methanol enriched with stable isotope-labeled internal standards (SIL-IS), and the mixture was vortexed and centrifuged before sample injection. Separation was achieved using a C18 column (3 μm,50 × 2.1 mm) with a gradient of two mobile phases (ammonium formate buffer pH 3.5 and acetonitrile). Analyte detection was conducted in positive ionization mode using selected reaction monitoring. The assay was accurate and precise in plasma as well as in serum. Extraction recovery ranged between 95.0% and 106.0%, and the matrix effect was 95.7%-105.2%. The stability of the analytes varied at room temperature and in refrigerated conditions. However, all drugs were found to be stable for 7 days in the autosampler. The clinical applicability of the analytical method (486 analyzed samples between 1 July 2022-1 July 2023) as well as external quality control testing results were evaluated. Taken together, the results demonstrate that the analytical method was validated and applicable for routine analyses in clinical practice.

Molecular imaging to support cancer immunotherapy

The advent of immune checkpoint inhibitors has reinvigorated the field of immuno-oncology. These monoclonal antibody-based therapies allow the immune system to recognize and eliminate malignant cells. This has resulted in improved survival of patients across several tumor types. However, not all patients respond to immunotherapy therefore predictive biomarkers are important. There are only a few Food and Drug Administration-approved biomarkers to select patients for immunotherapy. These biomarkers do not consider the heterogeneity of tumor characteristics across lesions within a patient. New molecular imaging tracers allow for whole-body visualization with positron emission tomography (PET) of tumor and immune cell characteristics, and drug distribution, which might guide treatment decision making. Here, we summarize recent developments in molecular imaging of immune checkpoint molecules, such as PD-L1, PD-1, CTLA-4, and LAG-3. We discuss several molecular imaging approaches of immune cell subsets and briefly summarize the role of FDG-PET for evaluating cancer immunotherapy. The main focus is on developments in clinical molecular imaging studies, next to preclinical studies of interest given their potential translation to the clinic.

Radiolabeled Monoclonal Antibody Against Colony-Stimulating Factor 1 Receptor Specifically Distributes to the Spleen and Liver in Immunocompetent Mice

Macrophages can promote tumor development. Preclinically, targeting macrophages by colony-stimulating factor 1 (CSF1)/CSF1 receptor (CSF1R) monoclonal antibodies (mAbs) enhances conventional therapeutics in combination treatments. The physiological distribution and tumor uptake of CSF1R mAbs are unknown. Therefore, we radiolabeled a murine CSF1R mAb and preclinically visualized its biodistribution by PET. CSF1R mAb was conjugated to N-succinyl-desferrioxamine (N-suc-DFO) and subsequently radiolabeled with zirconium-89 (89Zr). Optimal protein antibody dose was first determined in non-tumor-bearing mice to assess physiological distribution. Next, biodistribution of optimal protein dose and 89Zr-labeled isotype control was compared with PET and ex vivo biodistribution after 24 and 72 h in mammary tumor-bearing mice. Tissue autoradiography and immunohistochemistry determined radioactivity distribution and tissue macrophage presence, respectively. [89Zr]Zr-DFO-N-suc-CSF1R-mAb optimal protein dose was 10 mg/kg, with blood pool levels of 10 ± 2% injected dose per gram tissue (ID/g) and spleen and liver uptake of 17 ± 4 and 11 ± 4%ID/g at 72 h. In contrast, 0.4 mg/kg of [89Zr]Zr-DFO-N-suc-CSF1R mAb was eliminated from circulation within 24 h; spleen and liver uptake was 126 ± 44% and 34 ± 7%ID/g, respectively. Tumor-bearing mice showed higher uptake of [89Zr]Zr-DFO-N-suc-CSF1R-mAb in the liver, lymphoid tissues, duodenum, and ileum, but not in the tumor than did 89Zr-labeled control at 72 h. Immunohistochemistry and autoradiography showed that 89Zr was localized to macrophages within lymphoid tissues. Following [89Zr]Zr-DFO-N-suc-CSF1R-mAb administration, tumor macrophages were almost absent, whereas isotype-group tumors contained over 500 cells/mm2. We hypothesize that intratumoral macrophage depletion by [89Zr]Zr-DFO-N-suc-CSF1R-mAb precluded tumor uptake higher than 89Zr-labeled control. Translation of molecular imaging of macrophage-targeting therapeutics to humans may support macrophage-directed therapeutic development.

First-in-Human Study of the Biodistribution and Pharmacokinetics of 89Zr-CX-072, a Novel Immunopet Tracer Based on an Anti-PD-L1 Probody

PURPOSE

CX-072, a PD-L1-targeting Probody therapeutic, is engineered to be activated by tumor proteases that remove a masking peptide. To study effects on biodistribution and pharmacokinetics, we performed ⁸⁹Zr-CX-072 positron emission tomography (PET) imaging.

EXPERIMENTAL DESIGN

Patients received ∼1 mg, 37 MBq ⁸⁹Zr-CX-072 plus 0, 4, or 9 mg unlabeled CX-072 and PET scans at days 2, 4, and 7. After that, treatment comprised 10 mg/kg CX-072 q2 weeks (n = 7) + 3 mg/kg ipilimumab q3w 4× (n = 1). Normal organ tracer uptake was expressed as standardized uptake value (SUV)_mean and tumor uptake as SUV_max. PD-L1 expression was measured immunohistochemically in archival tumor tissue.

RESULTS

Three of the eight patients included received 10-mg protein dose resulting in a blood pool mean SUV_mean ± SD of 4.27 ± 0.45 on day 4, indicating sufficient available tracer. Tumor uptake was highest at day 7, with a geometric mean SUV_max 5.89 (n = 113) and present in all patients. The median follow-up was 12 weeks (4-76+). One patient experienced stable disease and two patients a partial response. PD-L1 tumor expression was 90% in one patient and ≤1% in the other patients. Mean SUV_mean ± SD day 4 at 10 mg in the spleen was 8.56 ± 1.04, bone marrow 2.21 ± 0.46, and liver 4.97 ± 0.97. Four patients out of seven showed uptake in normal lymph nodes and Waldeyer's ring. The tracer was intact in the serum or plasma.

CONCLUSIONS

⁸⁹Zr-CX-072 showed tumor uptake, even in lesions with ≤1% PD-L1 expression, and modest uptake in normal lymphoid organs, with no unexpected uptake in other healthy tissues.

Abstract LB037: 89ZED88082A PET imaging to visualize CD8+ T cells in patients with cancer treated with immune checkpoint inhibitor

T cell enhancing immune checkpoint inhibitors (ICI) are effective across several tumor types in a subset of patients. Insights into systemic localization of cytotoxic CD8+ T cells might support early treatment decisions. To address this, we performed a PET imaging study with a zirconium-89 (89Zr) labeled one-armed CD8-specific antibody 89ZED88082A to assess tracer performance, safety, and pharmacokinetics (PK) before and during treatment. Here we report preliminary data on uptake in tumor lesions before ICI. Methods: Patients with locally advanced or metastatic solid tumors that may benefit from ICI are eligible. In part A (imaging before treatment) and part B (imaging before and during treatment), 37 MBq (1 mCi) 89ZED88082A is administered with unlabeled one-armed antibody CED88004S to vary total protein dose. PET images are acquired at up to 4 time points: 1 h, and days (d) 2, 4, 7 post-injection followed by a tumor biopsy for CD8 immunohistochemistry and autoradiography (NCT04029181). Subsequently, patients receive atezolizumab (NCT02478099) or standard of care nivolumab ± ipilimumab. Tumor and lymph node 89ZED88082A uptake are assessed as (geometric mean) maximum standard uptake value (SUVmax), in other organs as SUVmean. Serum 89ZED88082A/CED88004S levels are measured for PK. Tumor response is according to (i)RECIST1.1. Results: For pretreatment imaging results, 32 patients (9 part A, 23 part B) were evaluable; 3 received 4 mg total tracer protein dose, 29 received 10 mg. No tracer infusion-related reactions occurred. Here we show results on d2 PET imaging with 10 mg protein dose, which was considered optimal based on superior 89Zr blood pool activity, clinical feasibility and serum antibody PK with a half-life of 28.6 h. 89ZED88082A uptake was observed within 1 h in spleen, and strong d2 imaging signal was seen across lymphoid organs including spleen (\bar{x}$ SUVmean 47.2), lymph nodes (SUVmax 4.2), bone marrow (\bar{x}$ SUVmean 5.0), small bowel and Waldeyer's ring. 89ZED88082A tumor uptake was seen at all main metastatic organ sites (overall lesion SUVmax 5.5, range 0.6-30.9) and varied across patients (\bar{x}$ per patient SUVmax 5.4, IQR 3.8-7.4). Higher tumor uptake showed a trend with better response (p=0.059) and longer PFS (p=0.033). Tumor uptake was higher in patients with mismatch-repair deficient (dMMR) than MMR proficient tumors (SUVmax 9.3 vs 4.9, p<0.001). Tumors with immune desert vs CD8+ cell stromal/inflamed profile had a \bar{x}$ SUVmax of 4.7 vs 8.3 (p=0.042). In tumor biopsies, autoradiography signal and CD8 staining were linearly associated (p<0.001). Conclusion: 89ZED88082A PET imaging is safe and shows high uptake in normal lymphoid organs. Uptake in tumor lesions is heterogeneous within and between patients. Tumor uptake is higher pretreatment in dMMR tumors and correlated with patient outcome. 89ZED88082A uptake on PET and by autoradiography reflects CD8 expression in tumor biopsies.

Citation Format: Laura Kist de Ruijter, Pim P. van de Donk, Jahlisa S. Hooiveld-Noeken, Danique Giesen, Alexander Ungewickell, Bernard M. Fine, Simon P. Williams, Sandra M. Sanabria Bohorquez, Mahesh Yadav, Hartmut Koeppen, Jing Jing, Sebastian Guelman, Mark T. Lin, Michael J. Mamounas, Jeffrey Eastham, Patrick K. Kimes, Andor W. Glaudemans, Adrienne H. Brouwers, Marjolijn N. Lub-de Hooge, Jourik A. Gietema, Carolina P. Schröder, Wim Timens, Mathilde Jalving, Sjoerd Elias, Sjoukje F. Oosting, Derk J. de Groot, Elisabeth G. de Vries. 89ZED88082A PET imaging to visualize CD8+ T cells in patients with cancer treated with immune checkpoint inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB037.

Preclinical PET imaging of bispecific antibody ERY974 targeting CD3 and glypican 3 reveals that tumor uptake correlates to T cell infiltrate

BACKGROUND

Bispecific antibodies redirecting T cells to the tumor obtain increasing interest as potential cancer immunotherapy. ERY974, a full-length bispecific antibody targeting CD3ε on T cells and glypican 3 (GPC3) on tumors, has been in clinical development However, information on the influence of T cells on biodistribution of bispecific antibodies, like ERY974, is scarce. Here, we report the biodistribution and tumor targeting of zirconium-89 (⁸⁹Zr) labeled ERY974 in mouse models using immuno-positron emission tomography (PET) imaging.

METHODS

To study both the role of GPC3 and CD3 on the biodistribution of [⁸⁹Zr]Zr-N-suc-Df-ERY974, ⁸⁹Zr-labeled control antibodies targeting CD3 and non-mammalian protein keyhole limpet hemocyanin (KLH) or KLH only were used. GPC3 dependent tumor targeting of [⁸⁹Zr]Zr-N-suc-Df-ERY974 was tested in xenograft models with different levels of GPC3 expression. In addition, CD3 influence on biodistribution of [⁸⁹Zr]Zr-N-suc-Df-ERY974 was evaluated by comparing biodistribution between tumor-bearing immunodeficient mice and mice reconstituted with human immune cells using microPET imaging and ex vivo biodistribution. Ex vivo autoradiography was used to study deep tissue distribution.

RESULTS

In tumor-bearing immunodeficient mice, [⁸⁹Zr]Zr-N-suc-Df-ERY974 tumor uptake was GPC3 dependent and specific over [⁸⁹Zr]Zr-N-suc-Df-KLH/CD3 and [⁸⁹Zr]Zr-N-suc-Df-KLH/KLH. In mice engrafted with human immune cells, [⁸⁹Zr]Zr-N-suc-Df-ERY974 specific tumor uptake was higher than in immunodeficient mice. Ex vivo autoradiography demonstrated a preferential distribution of [⁸⁹Zr]Zr-N-suc-Df-ERY974 to T cell rich tumor tissue. Next to tumor, highest specific [⁸⁹Zr]Zr-N-suc-Df-ERY974 uptake was observed in spleen and lymph nodes.

CONCLUSION

^[89Zr]Zr-N-suc-Df-ERY974 can potentially be used to study ERY974 biodistribution in patients to support drug development.

Mesothelin/CD3 half-life extended bispecific T-cell engager molecule shows specific tumor uptake and distributes to mesothelin and CD3 expressing tissues

BiTE ® (bispecific T-cell engager) molecules exert antitumor activity by binding one arm to CD3 on cytotoxic T-cells and the other arm to a tumor-associated antigen. We generated a fully mouse cross-reactive mesothelin (MSLN)-targeted BiTE molecule that is genetically fused to a Fc-domain for half-life extension, and evaluated biodistribution and tumor targeting of a zirconium-89 (89Zr)-labeled MSLN HLE BiTE molecule in 4T1 breast cancer bearing syngeneic mice with positron emission tomography (PET). Biodistribution of 50 µg 89Zr-MLSN HLE BiTE was studied over time by PET imaging in BALB/c mice and revealed uptake in tumor and lymphoid tissues with an elimination half-life of 63.4 hours. Compared to a non-targeting 89Zr-control HLE BiTE, the 89Zr-MLSN HLE BiTE showed a 2-fold higher tumor uptake and higher uptake in lymphoid tissues. Uptake in the tumor colocalized with mesothelin expression, while uptake in the spleen colocalized with CD3 expression. Evaluation of the effect of protein doses on the biodistribution and tumor targeting of 89Zr-MSLN HLE BiTE revealed for all dose groups that uptake in the spleen was faster than in the tumor (day 1 vs day 5). The lowest dose of 10 µg 89Zr-MSLN HLE BiTE had higher spleen uptake and faster blood clearance compared to higher doses of 50 µg and 200 µg. 89Zr-MSLN HLE BiTE tumor uptake was similar at all doses. Conclusion: The MSLN HLE BiTE showed specific tumor uptake and both arms contributed to the biodistribution profile. These findings support the potential for clinical translation of HLE BiTE molecules.

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 (SUV_mean) 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

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-020-01558-w.

89Zr-pembrolizumab biodistribution is influenced by PD-1-mediated uptake in lymphoid organs

Background

To better predict response to immune checkpoint therapy and toxicity in healthy tissues, insight in the in vivo behavior of immune checkpoint targeting monoclonal antibodies is essential. Therefore, we aimed to study in vivo pharmacokinetics and whole-body distribution of zirconium-89 (⁸⁹Zr) labeled programmed cell death protein-1 (PD-1) targeting pembrolizumab with positron-emission tomography (PET) in humanized mice.

Methods

Humanized (huNOG) and non-humanized NOG mice were xenografted with human A375M melanoma cells. PET imaging was performed on day 7 post ⁸⁹Zr-pembrolizumab (10 µg, 2.5 MBq) administration, followed by ex vivo biodistribution studies. Other huNOG mice bearing A375M tumors received a co-injection of excess (90 µg) unlabeled pembrolizumab or ⁸⁹Zr-IgG₄ control (10 µg, 2.5 MBq). Tumor and spleen tissue were studied with autoradiography and immunohistochemically including PD-1.

Results

PET imaging and biodistribution studies showed high ⁸⁹Zr-pembrolizumab uptake in tissues containing human immune cells, including spleen, lymph nodes and bone marrow. Tumor uptake of ⁸⁹Zr-pembrolizumab was lower than uptake in lymphoid tissues, but higher than uptake in other organs. High uptake in lymphoid tissues could be reduced by excess unlabeled pembrolizumab. Tracer activity in blood pool was increased by addition of unlabeled pembrolizumab, but tumor uptake was not affected. Autoradiography supported PET findings and immunohistochemical staining on spleen and lymph node tissue showed PD-1 positive cells, whereas tumor tissue was PD-1 negative.

Conclusion

⁸⁹Zr-pembrolizumab whole-body biodistribution showed high PD-1-mediated uptake in lymphoid tissues, such as spleen, lymph nodes and bone marrow, and modest tumor uptake. Our data may enable evaluation of ⁸⁹Zr-pembrolizumab whole-body distribution in patients.

Abstract 2769: PET imaging shows dose-dependent pharmacokinetics of a 89Zr-labeled mesothelin/CD3 half-life extended bispecific T-cell engager molecule in a syngeneic mouse model

BiTE® (bispecific T cell engager) immune therapy consists of two connected single-chain variable fragments, one targeting T-cells via CD3, and one targeting the tumor via a tumor-associated antigen. Given their short half-life, these molecules are administered by continuous intravenous (iv) infusion to ensure tumor accumulation. To extend plasma half-life, they are conjugated to an Fc domain, resulting in a molecule with an extended pharmacokinetic profile. To evaluate their biodistribution in a syngeneic mouse model, a molecule targeting murine mesothelin and murine CD3 (muMSLN HLE BiTE®), and a non-targeting control HLE BiTE® molecule were radiolabeled with the positron emission tomography (PET) isotope zirconium-89 (89Zr).

METHODS: The control and muMSLN HLE BiTE® were labeled with 89Zr. Immunocompetent BALB/c mice were engrafted in the lower mammary fat pad with mesothelin-positive murine mammary carcinoma cell line 4T1. PET imaging was performed at 1, 3, 5, 7 and 9 days after 50 µg 89Zr-muMSLN HLE BiTE® was administered by iv infusion (n = 8). Next, biodistribution of 10 µg (n = 6), 50 µg (n = 6) and 200 µg 89Zr-muMSLN HLE BiTE® (n = 5) and 50 µg 89Zr-control HLE BiTE® (n = 6) was compared via PET imaging on day 1, 3 and 5. PET-scans were quantified by mean standardized uptake value (SUVmean). Tracer injections were 4 MBq. To compare uptake in multiple groups, an analysis of variance followed by a post-hoc Tukey's multiple comparison test was performed. Values are expressed as mean ± standard deviation.

RESULTS: PET imaging following 50 µg 89Zr-muMSLN HLE BiTE® dosed iv revealed a blood elimination half-life of 63.4 hours. Uptake in tumor, spleen, thymus and liver were visible from 3 days post injection (pi). On day 5, tumor uptake was highest (SUVmean = 1.50 ± 0.2) with a tumor to blood ratio of 1.9 ± 0.3 and a spleen to blood of 1.7 ± 0.2. Heart SUVmean 5 days pi revealed that 10 μg 89Zr-muMSLN HLE cleared faster from the blood (0.5 ± 0.1) than the 50 μg (0.8 ± 0.1, P < 0.01) and the 200 μg dose group (0.8 ± 0.1, P < 0.01). Tumor SUVmean was higher in 50 µg (1.5 ± 0.2) than the 10 µg dose group (1.2 ± 0.1, P < 0.01), but similar to the 200 μg dose group (1.3 ± 0.1, P = 0.28). Spleen uptake 5 days pi was dose-dependent (SUVmean: 10 µg = 1.6 ± 0.2; 50 µg = 1.3 ± 0.1; 200 µg = 0.8 ± 0.1, P < 0.01). Spleen and tumor SUVmean 5 days pi of 50 µg 89Zr-muMSLN HLE BiTE® were higher than 50 µg 89Zr-control HLE BiTE® (spleen = 0.5 ± 0.1, P < 0.01; tumor = 0.8 ± 0.1, P < 0.01), while blood SUVmean of 50 µg 89Zr-control HLE BiTE® was similar (0.6 ± 0.1, P = 0.12).

CONCLUSION: PET imaging with a 89Zr-labeled muMSLN HLE BiTE® in a tumor-bearing syngeneic mouse model revealed a long blood half-life, specific uptake in tumor and spleen, and dose-dependent pharmacokinetics. Taken together, the HLE BiTE® molecule demonstrates an extended pharmacokinetic profile over previously evaluated small, canonical, BiTE® molecules.

Citation Format: Frans V. Suurs, Grit Lorenczewski, Julie M. Bailis, Sabine Stienen, Matthias Friedrich, Elisabeth G.E. de Vries, Derk Jan A. de Groot, Marjolijn N. Lub-de Hooge. PET imaging shows dose-dependent pharmacokinetics of a 89Zr-labeled mesothelin/CD3 half-life extended bispecific T-cell engager molecule in a syngeneic mouse model [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2769.

Molecular imaging in lymphoma beyond 18F-FDG-PET: understanding the biology and its implications for diagnostics and therapy

Mature lymphoproliferative diseases are a heterogeneous group of neoplasms arising from different stages of B-cell and T-cell development. With improved understanding of the molecular processes in lymphoma and novel treatment options, arises a growing need for the molecular characterisation of tumours. Molecular imaging with single-photon-emission CT and PET using specific radionuclide tracers can provide whole-body information to investigate cancer biology, to evaluate phenotypic heterogeneity, to identify resistance to targeted therapy, and to assess the biodistribution of drugs in patients. In this Review, we evaluate the existing literature on molecular imaging in lymphoma, other than ¹⁸F-fluordeoxyglucose molecular imaging. The aim is to examine the contribution of molecular imaging to the understanding of the biology of lymphoma and to discuss potential implications for the diagnostics and therapy of this disease. Finally, we discuss possible applications for molecular imaging of patients with lymphoma in the clinical context.

Molecular Imaging of PD-L1 Expression and Dynamics with the Adnectin-Based PET Tracer 18F-BMS-986192

¹⁸F-BMS-986192, an adnectin-based human programmed cell death ligand 1 (PD-L1) tracer, was developed to noninvasively determine whole-body PD-L1 expression by PET. We evaluated the usability of ¹⁸F-BMS-986192 PET to detect different PD-L1 expression levels and therapy-induced changes in PD-L1 expression in tumors. Methods: In vitro binding assays with ¹⁸F-BMS-986192 were performed on human tumor cell lines with different total cellular and membrane PD-L1 protein expression levels. Subsequently, PET imaging was performed on immunodeficient mice xenografted with these cell lines. The mice were treated with interferon γ (IFNγ) intraperitoneally for 3 d or with the mitogen-activated protein kinase kinase inhibitor selumetinib by oral gavage for 24 h. Afterward, ¹⁸F-BMS-986192 was administered intravenously, followed by a 60-min dynamic PET scan. Tracer uptake was expressed as percentage injected dose per gram of tissue. Tissues were collected to evaluate ex vivo tracer biodistribution and to perform flow cytometric, Western blot, and immunohistochemical tumor analyses. Results: ¹⁸F-BMS-986192 uptake reflected PD-L1 membrane levels in tumor cell lines, and tumor tracer uptake in mice was associated with PD-L1 expression measured immunohistochemically. In vitro IFNγ treatment increased PD-L1 expression in the tumor cell lines and caused up to a 12-fold increase in tracer binding. In vivo, IFNγ affected neither PD-L1 tumor expression measured immunohistochemically nor ¹⁸F-BMS-986192 tumor uptake. In vitro, selumetinib downregulated cellular and membrane levels of PD-L1 in tumor cells by 50% as measured by Western blotting and flow cytometry. In mice, selumetinib lowered cellular, but not membrane, PD-L1 levels of tumors, and consequently, no treatment-induced change in ¹⁸F-BMS-986192 tumor uptake was observed. Conclusion: ¹⁸F-BMS-986192 PET imaging allows detection of membrane-expressed PD-L1 as soon as 60 min after tracer injection. The tracer can discriminate a range of tumor cell PD-L1 membrane expression levels.

The Biodistribution of a CD3 and EpCAM Bispecific T-Cell Engager Is Driven by the CD3 Arm

Bispecific T-cell engager (BiTE) molecules are designed to engage and activate cytotoxic T cells to kill tumor cells. Little is known about their biodistribution in immunocompetent settings. Methods: To explore their pharmacokinetics and the role of the immune cells, BiTE molecules were radiolabeled with the PET isotope ⁸⁹Zr and studied in immunocompetent and immunodeficient mouse models. Results: PET images and ex vivo biodistribution in immunocompetent mice with [⁸⁹Zr]Zr-DFO-N-suc-muS110, targeting mouse CD3 (dissociation constant [K_D], 2.9 nM) and mouse epithelial cell adhesion molecule (EpCAM; K_D, 21 nM), and with [⁸⁹Zr]Zr-DFO-N-suc-hyS110, targeting only mouse CD3 (K_D, 2.9 nM), showed uptake in the tumor, spleen, and other lymphoid organs, whereas the human-specific control BiTE [⁸⁹Zr]Zr-DFO-N-suc-AMG 110 showed similar tumor uptake but lacked spleen uptake. [⁸⁹Zr]Zr-DFO-N-suc-muS110 spleen uptake was lower in immunodeficient than in immunocompetent mice. After repeated administration of nonradiolabeled muS110 to immunocompetent mice, ⁸⁹Zr-muS110 uptake in the spleen and other lymphoid tissues decreased and was comparable to uptake in immunodeficient mice, indicating saturation of CD3 binding sites. Autoradiography and immunohistochemistry demonstrated colocalization of [⁸⁹Zr]Zr-DFO-N-suc-muS110 and [⁸⁹Zr]Zr-DFO-N-suc-hyS110 with CD3-positive T cells in the tumor and spleen but not with EpCAM expression. Also, uptake in the duodenum correlated with a high incidence of T cells. Conclusion: [⁸⁹Zr]Zr-DFO-N-suc-muS110 biodistribution is dependent mainly on the T-cell-targeting arm, with a limited contribution from its second arm, targeting EpCAM. These findings highlight the need for extensive biodistribution studies of novel bispecific constructs, as the results might have implications for their respective drug development and clinical translation.

Development and Evaluation of Interleukin-2-Derived Radiotracers for PET Imaging of T Cells in Mice

Recently, N-(4-¹⁸F-fluorobenzoyl)-interleukin-2 (¹⁸F-FB-IL2) was introduced as a PET tracer for T cell imaging. However, production is complex and time-consuming. Therefore, we developed 2 radiolabeled IL2 variants, namely aluminum ¹⁸F-fluoride-(restrained complexing agent)-IL2 (¹⁸F-AlF-RESCA-IL2) and ⁶⁸Ga-gallium-(1,4,7-triazacyclononane-4,7-diacetic acid-1-glutaric acid)-IL2 (⁶⁸Ga-Ga-NODAGA-IL2), and compared their in vitro and in vivo characteristics with ¹⁸F-FB-IL2. Methods: Radiolabeling of ¹⁸F-AlF-RESCA-IL2 and ⁶⁸Ga-Ga-NODAGA-IL2 was optimized, and stability was evaluated in human serum. Receptor binding was studied with activated human peripheral blood mononuclear cells (hPBMCs). Ex vivo tracer biodistribution in immunocompetent BALB/cOlaHsd (BALB/c) mice was performed at 15, 60, and 90 min after tracer injection. In vivo binding characteristics were studied in severe combined immunodeficient (SCID) mice inoculated with activated hPBMCs in Matrigel. Tracer was injected 15 min after hPBMC inoculation, and a 60-min dynamic PET scan was acquired, followed by ex vivo biodistribution studies. Specific uptake was determined by coinjection of tracer with unlabeled IL2 and by evaluating uptake in a control group inoculated with Matrigel only. Results: ⁶⁸Ga-Ga-NODAGA-IL2 and ¹⁸F-AlF-RESCA-IL2 were produced with radiochemical purity of more than 95% and radiochemical yield of 13.1% ± 4.7% and 2.4% ± 1.6% within 60 and 90 min, respectively. Both tracers were stable in serum, with more than 90% being intact tracer after 1 h. In vitro, both tracers displayed preferential binding to activated hPBMCs. Ex vivo biodistribution studies on BALB/c mice showed higher uptake of ¹⁸F-AlF-RESCA-IL2 than of ¹⁸F-FB-IL2 in liver, kidney, spleen, bone, and bone marrow. ⁶⁸Ga-Ga-NODAGA-IL2 uptake in liver and kidney was higher than ¹⁸F-FB-IL2 uptake. In vivo, all tracers revealed uptake in activated hPBMCs in SCID mice. Low uptake was seen after a blocking dose of IL2 and in the Matrigel control group. In addition, ¹⁸F-AlF-RESCA-IL2 yielded the highest-contrast PET images of target lymph nodes. Conclusion: Production of ¹⁸F-AlF-RESCA-IL2 and ⁶⁸Ga-Ga-NODAGA-IL2 is simpler and faster than that of ¹⁸F-FB-IL2. Both tracers showed good in vitro and in vivo characteristics, with high uptake in lymphoid tissue and hPBMC xenografts.

Probody Therapeutic Design of 89Zr-CX-072 Promotes Accumulation in PD-L1-Expressing Tumors Compared to Normal Murine Lymphoid Tissue

PURPOSE

Probody therapeutic CX-072 is a protease-activatable antibody that is cross-reactive with murine and human programmed death-ligand 1 (PD-L1). CX-072 can be activated in vivo by proteases present in the tumor microenvironment, thereby potentially reducing peripheral, anti-PD-L1-mediated toxicities. To study its targeting of PD-L1-expressing tissues, we radiolabeled CX-072 with the PET isotope zirconium-89 (⁸⁹Zr).

EXPERIMENTAL DESIGN

⁸⁹Zr-labeled CX-072, nonspecific Probody control molecule (PbCtrl) and CX-072 parental antibody (CX-075) were injected in BALB/c nude mice bearing human MDA-MB-231 tumors or C57BL/6J mice bearing syngeneic MC38 tumors. Mice underwent serial PET imaging 1, 3, and 6 days after intravenous injection (pi), followed by ex vivo biodistribution. Intratumoral ⁸⁹Zr-CX-072 distribution was studied by autoradiography on tumor tissue sections, which were subsequently stained for PD-L1 by IHC. Activated CX-072 species in tissue lysates were detected by Western capillary electrophoresis.

RESULTS

PET imaging revealed ⁸⁹Zr-CX-072 accumulation in MDA-MB-231 tumors with 2.1-fold higher tumor-to-blood ratios at 6 days pi compared with ⁸⁹Zr-PbCtrl. Tumor tissue autoradiography showed high ⁸⁹Zr-CX-072 uptake in high PD-L1-expressing regions. Activated CX-072 species were detected in these tumors, with 5.3-fold lower levels found in the spleen. Furthermore, ⁸⁹Zr-CX-072 uptake by lymphoid tissues of immune-competent mice bearing MC38 tumors was low compared with ⁸⁹Zr-CX-075, which lacks the Probody design.

CONCLUSIONS

⁸⁹Zr-CX-072 accumulates specifically in PD-L1-expressing tumors with limited uptake in murine peripheral lymphoid tissues. Our data may enable clinical evaluation of ⁸⁹Zr-CX-072 whole-body distribution as a tool to support CX-072 drug development (NCT03013491).

Molecular imaging biomarkers for immune checkpoint inhibitor therapy

Immune checkpoint inhibitors (ICIs) have substantially changed the field of oncology over the past few years. ICIs offer an alternative treatment strategy by exploiting the patients' immune system, resulting in a T cell mediated anti-tumor response. These therapies are effective in multiple different tumor types. Unfortunately, a substantial group of patients do not respond to ICIs. Molecular imaging, using single-photon emission computed tomography (SPECT) and positron emission tomography (PET), can provide non-invasive whole-body visualization of tumor and immune cell characteristics and might support patient selection or response evaluations for ICI therapies. In this review, recent studies with 18F-fluorodeoxyglucose-PET imaging, imaging of immune checkpoints and imaging of immune cells will be discussed. These studies are until now mainly exploratory, but the first results suggest that molecular imaging biomarkers could have a role in the evaluation of ICI therapy.

Clinical-grade N-(4-[18F]fluorobenzoyl)-interleukin-2 for PET imaging of activated T-cells in humans

Background

Molecular imaging of immune cells might be a potential tool for response prediction, treatment evaluation and patient selection in inflammatory diseases as well as oncology. Targeting interleukin-2 (IL2) receptors on activated T-cells using positron emission tomography (PET) with N-(4-[¹⁸F]fluorobenzoyl)-interleukin-2 ([¹⁸F]FB-IL2) could be such a strategy. This paper describes the challenging translation of the partly manual labeling of [¹⁸F]FB-IL2 for preclinical studies into an automated procedure following Good Manufacturing Practices (GMP), resulting in a radiopharmaceutical suitable for clinical use.

Methods

The preclinical synthesis of [¹⁸F]FB-IL2 was the starting point for translation to a clinical production method. To overcome several challenges, major adaptations in the production process were executed. The final analytical methods and production method were validated and documented. All data with regards to the quality and safety of the final drug product were documented in an investigational medicinal product dossier.

Results

Restrictions in the [¹⁸F]FB-IL2 production were imposed by hardware configuration of the automated synthesis equipment and by use of disposable cassettes. Critical steps in the [¹⁸F]FB-IL2 production comprised the purification method, stability of recombinant human IL2 and the final formulation. With the GMP compliant production method, [¹⁸F]FB-IL2 could reliably be produced with consistent quality complying to all specifications.

Conclusions

To enable the use of [¹⁸F]FB-IL2 in clinical studies, a fully automated GMP compliant production process was developed. [¹⁸F]FB-IL2 is now produced consistently for use in clinical studies.

Electronic supplementary material

The online version of this article (10.1186/s41181-019-0062-7) contains supplementary material, which is available to authorized users.

Abstract 1134: PET-imaging of 89Zr-labeled bispecific T-cell engagers in syngeneic tumor bearing mice

BACKGROUND Bispecific T-cell engagers (BiTE®) harness the immune system against cancer. BiTE® antibody constructs are small proteins of ~53 kDa existing of two connected single-chain variable fragments. MuS110, a BiTE® with affinity for murine CD3 (KD= 2.9 nM) and murine EpCAM (KD= 21 nM), was radiolabeled with positron emission tomography (PET) isotope zirconium-89 (89Zr) to study its pharmacokinetics and involvement of the immune system in an immunocompetent mouse model bearing a syngeneic tumor.

METHODS MuS110 and two control BiTE® antibody constructs (hyS110 and AMG110) were radiolabeled with 89Zr. HyS110 has affinity for murine CD3 and human EpCAM, AMG110 for human CD3 and human EpCAM. The human and murine variants of EpCAM and CD3 are not cross-reactive. Either immunocompetent BALB/c or immunodeficient nude BALB/c mice were all orthotopically engrafted in the lower mammary fat pad with EpCAM-positive murine breast cancer cell line 4T1. PET-imaging was performed at 0.5, 3, 6, 24, 48 and 72 h after intravenous (iv) administration of 10 µg 89Zr-muS110. Distribution of 10 µg 89Zr-muS110, 89Zr-hyS110 and 89Zr-AMG110 was assessed 24 h after administration in BALB/c and nude BALB/c mice with PET-imaging and ex-vivo biodistribution. In addition, a group of BALB/c mice received 10 µg muS110 iv daily for 5 days followed by 10 µg 89Zr-muS110 or 10 µg 89Zr-AMG110 and PET-imaging 24 h after tracer administration. Values are expressed as median (interquartile range).

RESULTS PET-imaging revealed fast renal clearance of 89Zr-muS110 in the BALB/c mice resulting in a blood half-life of 0.93 h (one-phase decay). Tumor- and spleen-to-blood ratios increased to 3.7 (3.0 to 4.5) and 9.3 (7.5 to 11.1) after 72 h. Ex-vivo biodistribution 24 h after tracer administration showed 89Zr-muS110 and 89Zr-hyS110 accumulation in the spleen with 8.2 % injected dose per gram (ID/g) and 8.7 %ID/g, in comparison to 89Zr-AMG110 (2.3 %ID/g; vs 89Zr-muS110 P<0.05, vs 89Zr-hyS110 P<0.05). In mesenteric lymph nodes (mesLNs), 89Zr-muS110 and 89Zr-hyS110 resulted in a higher uptake (3.5 and 6.4 %ID/g) than 89Zr-AMG110 (2.0 %ID/g; vs 89Zr-muS110 P<0.05, vs 89Zr-hyS110 P<0.05). Tumor uptake did not differ for 89Zr-muS110 and 89Zr-AMG110 (2.6 vs 2.2 %ID/g, P>0.05). In nude BALB/c mice spleen and mesLN uptake of 89Zr-muS110 was lower than in BALB/c mice (spleen: 3.4 vs 8.2 %ID/g, P<0.05; mesLNs: 1.7 vs 3.5, P<0.05). In addition, in nude BALB/c mice, tumor uptake was the same for 89Zr-muS110 and 89Zr-AMG110 (1.5 vs 1.7 %ID/g, P>0.05). 89Zr-muS110 uptake was lower in spleen and mesLNs following 5 days of 10 µg muS110 iv compared to control mice

(spleen: 4.2 vs 8.2 %ID/g, P<0.01; mesLNs: 1.9 vs 3.5, P<0.01), likely representing target saturation.

CONCLUSION Distribution of BiTE® 89Zr-muS110 is predominantly mediated by the affinity for CD3, resulting in uptake in lymphoid tissues.

Citation Format: Frans V. Suurs, Derk J. de Groot, Urszula M. Domanska, Grit Lorenczewski, Sabine Stienen, Matthias Friedrich, Elisabeth G. de Vries, Marjolijn N. Lub-de Hooge. PET-imaging of 89Zr-labeled bispecific T-cell engagers in syngeneic tumor bearing mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1134.

A review of bispecific antibodies and antibody constructs in oncology and clinical challenges

Bispecific antibodies (bsAbs) are antibodies that bind two distinct epitopes to cancer.. For use in oncology, one bsAb has been approved and 57 bsAbs are in clinical trials, none of which has reached phase 3. These bsAbs show great variability in design and mechanism of action. The various designs are often linked to the mechanisms of actions. The majority of bsAbs engage immune cells to destroy tumor cells. However, some bsAbs are also used to deliver payloads to tumors or to block tumor signaling pathways. This review provides insight into the choice of construct for bsAbs, summarizes the clinical development of bsAbs in oncology and identifies subsequent challenges.

89Zr-labeled Bispecific T-cell Engager AMG 211 PET Shows AMG 211 Accumulation in CD3-rich Tissues and Clear, Heterogeneous Tumor Uptake

PURPOSE

Biodistribution of bispecific antibodies in patients is largely unknown. We therefore performed a feasibility study in 9 patients with advanced gastrointestinal adenocarcinomas to explore AMG 211 biodistribution (also known as MEDI-565), an approximately 55 kDa bispecific T-cell engager (BiTE®) directed against carcinoembryonic antigen (CEA) on tumor cells and cluster of differentiation 3 (CD3) on T-cells.

EXPERIMENTAL DESIGN

⁸⁹Zr-labeled AMG 211 as tracer was administered alone or with cold AMG 211, for PET imaging before and/or during AMG 211 treatment.

RESULTS

Before AMG 211 treatment, the optimal imaging dose was 200-μg ⁸⁹Zr-AMG 211 + 1,800-μg cold AMG 211. At 3 hours, the highest blood pool standardized uptake value (SUV)_mean was 4.0, and tracer serum half-life was 3.3 hours. CD3-mediated uptake was clearly observed in CD3-rich lymphoid tissues including spleen and bone marrow (SUV_mean 3.2 and 1.8, respectively), and the SUV_mean decreased more slowly than in other healthy tissues. ⁸⁹Zr-AMG 211 remained intact in plasma and was excreted predominantly via the kidneys in degraded forms. Of 43 visible tumor lesions, 37 were PET quantifiable, with a SUV_max of 4.0 [interquartile range (IQR) 2.7-4.4] at 3 hours using the optimal imaging dose. The tracer uptake differed between tumor lesions 5-fold within and 9-fold between patients. During AMG 211 treatment, tracer was present in the blood pool, whereas tumor lesions were not visualized, possibly reflecting target saturation.

CONCLUSIONS

This first-in-human study shows high, specific ⁸⁹Zr-AMG 211 accumulation in CD3-rich lymphoid tissues, as well as a clear, inter- and intraindividual heterogeneous tumor uptake.

89Zr-atezolizumab imaging as a non-invasive approach to assess clinical response to PD-L1 blockade in cancer

Programmed cell death protein-1/ligand-1 (PD-1/PD-L1) blockade is effective in a subset of patients with several tumor types, but predicting patient benefit using approved diagnostics is inexact, as some patients with PD-L1-negative tumors also show clinical benefit^1,2. Moreover, all biopsy-based tests are subject to the errors and limitations of invasive tissue collection^3-11. Preclinical studies of positron-emission tomography (PET) imaging with antibodies to PD-L1 suggested that this imaging method might be an approach to selecting patients^12,13. Such a technique, however, requires substantial clinical development and validation. Here we present the initial results from a first-in-human study to assess the feasibility of imaging with zirconium-89-labeled atezolizumab (anti-PD-L1), including biodistribution, and secondly test its potential to predict response to PD-L1 blockade (ClinicalTrials.gov identifiers NCT02453984 and NCT02478099). We imaged 22 patients across three tumor types before the start of atezolizumab therapy. The PET signal, a function of tracer exposure and target expression, was high in lymphoid tissues and at sites of inflammation. In tumors, uptake was generally high but heterogeneous, varying within and among lesions, patients, and tumor types. Intriguingly, clinical responses in our patients were better correlated with pretreatment PET signal than with immunohistochemistry- or RNA-sequencing-based predictive biomarkers, encouraging further development of molecular PET imaging for assessment of PD-L1 status and clinical response prediction.

Comparative biodistribution analysis across four different 89Zr-monoclonal antibody tracers-The first step towards an imaging warehouse

Rationale: Knowledge on monoclonal antibody biodistribution in healthy tissues in humans can support clinical drug development. Molecular imaging with positron emission tomography (PET) can yield information in this setting. However, recent imaging studies have analyzed the behavior of single antibodies only, neglecting comparison across different antibodies. Methods: We compared the distribution of four ⁸⁹Zr-labeled antibodies in healthy tissue in a retrospective analysis based on the recently published harmonization protocol for ⁸⁹Zr-tracers and our delineation protocol. Results: The biodistribution patterns of ⁸⁹Zr-lumretuzumab, ⁸⁹Zr-MMOT0530A, ⁸⁹Zr-bevacizumab and ⁸⁹Zr-trastuzumab on day 4 after tracer injection were largely similar. The highest tracer concentration was seen in healthy liver, spleen, kidney and intestines. About one-third of the injected tracer dose was found in the circulation, up to 15% in the liver and only 4% in the spleen and kidney. Lower tracer concentration was seen in bone marrow, lung, compact bone, muscle, fat and the brain. Despite low tracer accumulation per gram of tissue, large-volume tissues, especially fat, can influence overall distribution: On average, 5-7% of the injected tracer dose accumulated in fat, with a peak of 19% in a patient with morbid obesity. Conclusion: The similar biodistribution of the four antibodies is probably based on their similar molecular structure, binding characteristics and similar metabolic pathways. These data provide a basis for a prospectively growing, online accessible warehouse of molecular imaging data, which enables researchers to increase and exchange knowledge on whole body drug distribution and potentially supports drug development decisions.

Molecular Imaging of Radiolabeled Bispecific T-Cell Engager 89Zr-AMG211 Targeting CEA-Positive Tumors

Purpose: AMG 211, a bispecific T-cell engager (BiTE) antibody construct, targets carcinoembryonic antigen (CEA) and the CD3 epsilon subunit of the human T-cell receptor. AMG 211 was labeled with zirconium-89 (⁸⁹Zr) or fluorescent dye to evaluate the tumor-targeting properties.Experimental Design: ⁸⁹Zr-AMG211 was administered to mice bearing CEA-positive xenograft tumors of LS174T colorectal adenocarcinoma or BT474 breast cancer cells, as well as CEA-negative HL-60 promyelocytic leukemia xenografts. Biodistribution studies with 2- to 10-μg ⁸⁹Zr-AMG211 supplemented with unlabeled AMG 211 up to 500-μg protein dose were performed. A BiTE that does not bind CEA, ⁸⁹Zr-Mec14, served as a negative control. ⁸⁹Zr-AMG211 integrity was determined in tumor lysates ex vivo Intratumoral distribution was studied with IRDye800CW-AMG211. Moreover, ⁸⁹Zr-AMG211 was manufactured according to Good Manufacturing Practice (GMP) guidelines for clinical trial NCT02760199Results: ⁸⁹Zr-AMG211 demonstrated dose-dependent tumor uptake at 6 hours. The highest tumor uptake was observed with a 2-μg dose, and the lowest tumor uptake was observed with a 500-μg dose. After 24 hours, higher uptake of 10-μg ⁸⁹Zr-AMG211 occurred in CEA-positive xenografts, compared with CEA-negative xenografts. Although the blood half-life of ⁸⁹Zr-AMG211 was approximately 1 hour, tumor retention persisted for at least 24 hours. ⁸⁹Zr-Mec14 showed no tumor accumulation beyond background level. Ex vivo autoradiography revealed time-dependent disintegration of ⁸⁹Zr-AMG211. 800CW-AMG211 was specifically localized in CEA-expressing viable tumor tissue. GMP-manufactured ⁸⁹Zr-AMG211 fulfilled release specifications.Conclusions: ⁸⁹Zr-AMG211 showed dose-dependent CEA-specific tumor targeting and localization in viable tumor tissue. Our data enabled its use to clinically evaluate AMG 211 in vivo behavior. Clin Cancer Res; 24(20); 4988-96. ©2018 AACR.

Abstract 3035: 89Zr-labeled anti-PD-L1 Probody therapeutic CX-072 biodistribution in mice bearing human xenograft or murine syngeneic tumors

BACKGROUND Immune checkpoint inhibiting antibodies have antitumor activity across several tumor types, but are not effective in all patients and can elicit side effects. CX-072, a fully human Probody™ therapeutic currently in a phase 1/2 clinical trial, is reactive to the murine and human programmed cell death-ligand 1 (PD-L1) immune checkpoint. Probody therapeutics are engineered antibodies with target-binding region blocking masking peptides, which can be preferentially cleaved by tumor-associated proteases, yielding fully active antibodies. CX-072 may thus preserve anti-tumor efficacy, while limiting side effects. We radiolabeled CX-072 with the positron emission tomography (PET) isotope zirconium-89 (89Zr) to reveal its tumor targeting properties and whole body distribution using non-invasive PET imaging.

METHODS CX-072 and a non-specific Probody therapeutic control (PbCtrl) were radiolabeled with 89Zr. For in vivo studies, PD-L1 expressing MDA-MB-231 human breast cancer cells were subcutaneously (sc) engrafted in Balb/c nude mice. To assess tracer protein dose dependency of the tumor uptake, mice received 10 μg 89Zr-CX-072 or 89Zr-PbCtrl (~5 MBq) supplemented with 0, 40 or 240 µg of unlabeled CX-072 or PbCtrl. To evaluate 89Zr-CX-072 biodistribution in an immune-competent setting, C57BL6 mice were implanted sc with low PD-L1 expressing MC38 syngeneic murine colon adenocarcinoma cells. All mice underwent serial in vivo PET imaging 1, 3 and 6 days post injection (pi), quantified by mean standardized uptake value (SUVmean) and followed by ex vivo biodistribution. Activated Probody species in tissues were detected by Western capillary electrophoresis.

RESULTS PET imaging revealed increasing 89Zr-CX-072 tumor accumulation between 1-6 days pi, with the highest SUVmean of 1.5 (± 0.2) observed for 10 µg at 6 days pi. Ex vivo biodistribution analysis showed 8.7 % injected dose per gram (%ID/g) tumor uptake for 10 µg 89Zr-CX-072 versus 3.8 %ID/g for 10 µg 89Zr-PbCtrl (P<0.01) in MDA-MB-231 xenografted mice. In the syngeneic MC38 model biodistribution analysis showed modest tumor uptake for 10 μg 89Zr-CX-072 and 89Zr-PbCtrl (6.5 vs 5.5 %ID/g, P=0.24; tumor-to-blood ratio of 0.61 vs 0.45, P<0.05). 89Zr-CX-072 uptake in lymphoid tissues (spleen, lymph nodes) was similar to 89Zr-PbCtrl. Activated Probody species were predominantly detected in tumor with lesser amounts present in lymphoid tissues.

CONCLUSION 89Zr-CX-072 accumulates more in PD-L1-expressing tumor tissues than in lymphoid tissues. A sub-study of an ongoing clinical study (PROCLAIM-CX-072) is designed to validate study drug distribution in patients using a good manufacturing practice (GMP) quality 89Zr-CX-072 tracer.

Citation Format: Danique Giesen, Linda N. Broer, Marjolijn N. Lub-de Hooge, Irina Popova, Bruce Howng, Olga Vasiljeva, Elisabeth G. de Vries, Martin Pool. 89Zr-labeled anti-PD-L1 Probody therapeutic CX-072 biodistribution in mice bearing human xenograft or murine syngeneic tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3035.

Abstract 3028: PET imaging with the bispecific 89Zr-antibody ERY974 targeting CD3 and glypican 3 in tumor-bearing mouse models

BACKGROUND: ERY974, a modified monoclonal IgG4 bispecific antibody directed against human CD3 on T cells and glypican 3 (GPC3) on tumor cell, is currently in phase I clinical trial. The oncofetal protein GPC3 is overexpressed in several tumor types. Radiolabeling ERY974 with positron emission tomography (PET) isotope zirconium-89 (89Zr) enables non-invasive molecular imaging of tumor targeting and whole-body distribution. We aimed to evaluate 89Zr-ERY974 tumor targeting and effect of T cells on tumor uptake in mouse models, including a humanized mouse model.

METHODS: ERY974 and two control molecules namely bispecific CD3xkeyhole limpet hemocyanin (KLH) and KLHxKLH antibodies were radiolabeled with 89Zr. Studies were performed in immunodeficient NOD/Shi-SCID/IL-2Rgnull (NOG) as well as human CD34+ hematopoietic stem cell engrafted NOG mice (huNOG), all subcutaneously inoculated with GPC3 overexpressing human hepatocellular carcinoma HepG2 cells. Mice received 10 µg 89Zr-ERY974, 89Zr-CD3xKLH or 89Zr-KLHxKLH intravenously, with subsequent µPET scanning at 24, 72, 120 and 168 h followed by ex vivo biodistribution. Organs of interest were quantified on µPET scans as mean standardized uptake value (SUVmean) and with ex vivo biodistribution as % injected dose/gram of tissue (%ID/g). Tumor, spleen and lymph nodes were analyzed with autoradiography and immunohistochemical CD3 staining.

RESULTS: µPET imaging revealed increased tumor-to-blood ratio (TBR) of 89Zr-ERY974 in NOG over time with maximal TBR of 2.2±0.3 at 168 h post tracer injection (pi). At 168 h, tumor uptake was specific as 89Zr-CD3xKLH and 89Zr-KLHxKLH showed a TBR of only 0.6±0.2 and 0.8±0.3, respectively. In huNOG mice human CD3+ T cells were present in tumor, spleen and lymph nodes. In huNOG mice tumor uptake of 89Zr-ERY974 was higher than in NOG mice as measured on µPET scans (SUVmean at 168 h pi 6.9±2.6 vs 2.9±0.2; P<0.01) and with ex vivo biodistribution (60.9±26.2 %ID/g vs 16.7±2.3 %ID/g; P<0.001), whereas 89Zr-CD3xKLH tumor uptake in both mouse models was lower (P<0.05) but were similar in these mouse models. Autoradiography 168 h following 89Zr-ERY974 administration to huNOG mice showed 89Zr in extensive T cell infiltrate areas in the tumors of huNOG mice, whereas T cell infiltrate was lower in tumors of 89Zr-CD3xKLH and 89Zr-KLHxKLH injected huNOG mice. Spleens of huNOG mice showed CD3+ specific uptake as 89Zr-ERY974 and 89Zr-CD3xKLH uptake were higher than 89Zr-KLHxKLH uptake(P<0.05), whereas spleen uptake in NOG mice of the 3 tracers was similar. Moreover, in huNOG CD3+ mesenteric lymph nodes 89Zr-ERY974 uptake was higher than 89Zr-KLHxKLH uptake (P<0.05)

CONCLUSION: 89Zr-ERY974 demonstrates specific tumor uptake in NOG and huNOG mice, while in huNOG mice tumor uptake colocalized with T cell rich infiltrate and also uptake in in spleen and lymph nodes was observed.

Citation Format: Stijn J. Waaijer, Danique Giesen, Takahiro Ishiguro, Yuji Sano, Norihisa Ohishi, Athos Gianella-Borradori, Carolien P. Schröder, Elisabeth G. de Vries, Marjolijn N. Lub-de Hooge. PET imaging with the bispecific 89Zr-antibody ERY974 targeting CD3 and glypican 3 in tumor-bearing mouse models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3028.

Influence of protein properties and protein modification on biodistribution and tumor uptake of anticancer antibodies, antibody derivatives, and non-Ig scaffolds

Newly developed protein drugs that target tumor-associated antigens are often modified in order to increase their therapeutic effect, tumor exposure, and safety profile. During the development of protein drugs, molecular imaging is increasingly used to provide additional information on their in vivo behavior. As a result, there are increasing numbers of studies that demonstrate the effect of protein modification on whole body distribution and tumor uptake of protein drugs. However, much still remains unclear about how to interpret obtained biodistribution data correctly. Consequently, there is a need for more insight in the correct way of interpreting preclinical and clinical imaging data. Summarizing the knowledge gained to date may facilitate this interpretation. This review therefore provides an overview of specific protein properties and modifications that can affect biodistribution and tumor uptake of anticancer antibodies, antibody fragments, and nonimmunoglobulin scaffolds. Protein properties that are discussed in this review are molecular size, target interaction, FcRn binding, and charge. Protein modifications that are discussed are radiolabeling, fluorescent labeling drug conjugation, glycosylation, humanization, albumin binding, and polyethylene glycolation.

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.

Theranostics Using Antibodies and Antibody-Related Therapeutics

In theranostics, radiolabeled compounds are used to determine a treatment strategy by combining therapeutics and diagnostics in the same agent. Monoclonal antibodies (mAbs) and antibody-related therapeutics represent a rapidly expanding group of cancer medicines. Theranostic approaches using these drugs in oncology are particularly interesting because antibodies are designed against specific targets on the tumor cell membrane and immune cells as well as targets in the tumor microenvironment. In addition, these drugs are relatively easy to radiolabel. Noninvasive molecular imaging techniques, such as SPECT and PET, provide information on the whole-body distribution of radiolabeled mAbs and antibody-related therapeutics. Molecular antibody imaging can potentially elucidate drug target expression, tracer uptake in the tumor, tumor saturation, and heterogeneity for these parameters within the tumor. These data can support drug development and may aid in patient stratification and monitoring of the treatment response. Selecting a radionuclide for theranostic purposes generally starts by matching the serum half-life of the mAb or antibody-related therapeutic and the physical half-life of the radionuclide. Furthermore, PET imaging allows better quantification than the SPECT technique. This information has increased interest in theranostics using PET radionuclides with a relatively long physical half-life, such as ⁸⁹Zr. In this review, we provide an overview of ongoing research on mAbs and antibody-related theranostics in preclinical and clinical oncologic settings. We identified 24 antibodies or antibody-related therapeutics labeled with PET radionuclides for theranostic purposes in patients. For this approach to become integrated in standard care, further standardization with respect to the procedures involved is required.

89Zr-mAb3481 PET for HER3 tumor status assessment during lapatinib treatment

Treatment of human epidermal growth factor receptor 2 (HER2)-driven breast cancer with tyrosine kinase inhibitor lapatinib can induce a compensatory HER3 increase, which may attenuate antitumor efficacy. Therefore, we explored in vivo HER3 tumor status assessment after lapatinib treatment with zirconium-89 (⁸⁹Zr)-labeled anti-HER3 antibody mAb3481 positron emission tomography (PET). Lapatinib effects on HER3 cell surface expression and mAb3481 internalization were evaluated in human breast (BT474, SKBR3) and gastric (N87) cancer cell lines using flow cytometry. Next, in vivo effects of daily lapatinib treatment on⁸⁹Zr-mAb3481 BT474 and N87 xenograft tumor uptake were studied. PET-scans (BT474 only) were made after daily lapatinib treatment for 9 days, starting 3 days prior to ⁸⁹Zr-mAb3481 administration. Subsequently, ex vivo ⁸⁹Zr-mAb3481 organ distribution analysis was performed and HER3 tumor levels were measured with Western blot and immunohistochemistry. In vitro, lapatinib increased membranous HER3 in BT474, SKBR3 and N87 cells, and consequently mAb3481 internalization 1.7-fold (BT474), 1.4-fold (SKBR3) and 1.4-fold (N87). ⁸⁹Zr-mAb3481 BT474 tumor uptake was remarkably high at SUV_mean 5.6±0.6 (51.8±7.7%ID/g) using a 10 μg ⁸⁹Zr-mAb3481 protein dose in vehicle-treated mice. However, compared to vehicle, lapatinib did not affect ⁸⁹Zr-mAb3481 ex vivo uptake in BT474 and N87 tumors, while HER3 tumor expression remained unchanged. In conclusion, lapatinib increased in vitro HER3 tumor cell expression, but not when these cells were xenografted. ⁸⁹Zr-mAb3481 PET accurately reflected HER3 tumor status. ⁸⁹Zr-mAb3481 PET showed high, HER3-specific tumor uptake, and such an approach might sensitively assess HER3 tumor heterogeneity and treatment response in patients.

89Zr-Onartuzumab PET imaging of c-MET receptor dynamics

PURPOSE

c-MET and its ligand hepatocyte growth factor are often dysregulated in human cancers. Dynamic changes in c-MET expression occur and might predict drug efficacy or emergence of resistance. Noninvasive visualization of c-MET dynamics could therefore potentially guide c-MET-directed therapies. We investigated the feasibility of 89Zr-labelled one-armed c-MET antibody onartuzumab PET for detecting relevant changes in c-MET levels induced by c-MET-mediated epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor erlotinib resistance or heat shock protein-90 (HSP90) inhibitor NVP-AUY-922 treatment in human non-small-cell lung cancer (NSCLC) xenografts.

METHODS

In vitro membrane c-MET levels were determined by flow cytometry. HCC827ErlRes, an erlotinib-resistant clone with c-MET upregulation, was generated from the exon-19 EGFR-mutant human NSCLC cell line HCC827. Mice bearing HCC827 and HCC827ErlRes tumours in opposite flanks underwent 89Zr-onartuzumab PET scans. The HCC827-xenografted mice underwent 89Zr-onartuzumab PET scans before treatment and while receiving biweekly intraperitoneal injections of 100 mg/kg NVP-AUY-922 or vehicle. Ex vivo, tumour c-MET immunohistochemistry was correlated with the imaging results.

RESULTS

In vitro, membrane c-MET was upregulated in HCC827ErlRes tumours by 213 ± 44% in relation to the level in HCC827 tumours, while c-MET was downregulated by 69 ± 9% in HCC827 tumours following treatment with NVP-AUY-922. In vivo, 89Zr-onartuzumab uptake was 26% higher (P < 0.05) in erlotinib-resistant HCC827ErlRes than in HCC827 xenografts, while HCC827 tumour uptake was 33% lower (P < 0.001) following NVP-AUY-922 treatment.

CONCLUSION

The results show that 89Zr-onartuzumab PET effectively discriminates relevant changes in c-MET levels and could potentially be used clinically to monitor c-MET status.

89Zr-Lumretuzumab PET Imaging before and during HER3 Antibody Lumretuzumab Treatment in Patients with Solid Tumors

Purpose: We evaluated biodistribution and tumor targeting of ⁸⁹Zr-lumretuzumab before and during treatment with lumretuzumab, a human epidermal growth factor receptor 3 (HER3)-targeting monoclonal antibody.Experimental Design: Twenty patients with histologically confirmed HER3-expressing tumors received ⁸⁹Zr-lumretuzumab and underwent positron emission tomography (PET). In part A, ⁸⁹Zr-lumretuzumab was given with additional, escalating doses of unlabeled lumretuzumab, and scans were performed 2, 4, and 7 days after injection to determine optimal imaging conditions. In part B, patients were scanned following tracer injection before (baseline) and after a pharmacodynamic (PD)-active lumretuzumab dose for saturation analysis. HER3 expression was determined immunohistochemically in skin biopsies. Tracer uptake was calculated as standardized uptake value (SUV).Results: Optimal PET conditions were found to be 4 and 7 days after administration of ⁸⁹Zr-lumretuzumab with 100-mg unlabeled lumretuzumab. At baseline using 100-mg unlabeled lumretuzumab, the tumor SUVmax was 3.4 (±1.9) at 4 days after injection. SUVmean values for normal blood, liver, lung, and brain tissues were 4.9, 6.4, 0.9 and 0.2, respectively. Saturation analysis (n = 7) showed that 4 days after lumretuzumab administration, tumor uptake decreased by 11.9% (±8.2), 10.0% (±16.5), and 24.6% (±20.9) at PD-active doses of 400, 800, and 1,600 mg, respectively, when compared with baseline. Membranous HER3 was completely downregulated in paired skin biopsies already at and above 400-mg lumretuzumab.Conclusions: PET imaging showed biodistribution and tumor-specific ⁸⁹Zr-lumretuzumab uptake. Although, PD-active lumretuzumab doses decreased ⁸⁹Zr-lumretuzumab uptake, there was no clear evidence of tumor saturation by PET imaging as the tumor SUV did not plateau with increasing doses. Clin Cancer Res; 23(20); 6128-37. ©2017 AACR.

Harnessing Integrative Omics to Facilitate Molecular Imaging of the Human Epidermal Growth Factor Receptor Family for Precision Medicine

Cancer is a growing problem worldwide. The cause of death in cancer patients is often due to treatment-resistant metastatic disease. Many molecularly targeted anticancer drugs have been developed against 'oncogenic driver' pathways. However, these treatments are usually only effective in properly selected patients. Resistance to molecularly targeted drugs through selective pressure on acquired mutations or molecular rewiring can hinder their effectiveness. This review summarizes how molecular imaging techniques can potentially facilitate the optimal implementation of targeted agents. Using the human epidermal growth factor receptor (HER) family as a model in (pre)clinical studies, we illustrate how molecular imaging may be employed to characterize whole body target expression as well as monitor drug effectiveness and the emergence of tumor resistance. We further discuss how an integrative omics discovery platform could guide the selection of 'effect sensors' - new molecular imaging targets - which are dynamic markers that indicate treatment effectiveness or resistance.

Human Epidermal Growth Factor Receptor 3-Specific Tumor Uptake and Biodistribution of 89Zr-MSB0010853 Visualized by Real-Time and Noninvasive PET Imaging

The human epidermal growth factor receptor 3 (HER3) is an interesting target for antitumor therapy. For optimal HER3 signaling inhibition, a biparatopic Nanobody construct (MSB0010853) was developed that binds 2 different HER3 epitopes. In addition, MSB0010853 contains a third HER3 epitope that binds albumin to extend its circulation time. MSB0010853 is cross-reactive with HER3 and albumin of mouse origin. We aimed to gain insight into MSB0010853 biodistribution and tumor uptake by radiolabeling the Nanobody construct with ⁸⁹Zr. Methods: MSB0010853 was radiolabeled with ⁸⁹Zr. Dose- and time-dependent tumor uptake was studied in nude BALB/c mice bearing a subcutaneous HER3 overexpressing H441 non-small cell lung cancer xenograft. Dose-dependent biodistribution of ⁸⁹Zr-MSB0010853 was assessed ex vivo at 24 h after intravenous injection. Protein doses of 5, 10, 25, 100, and 1,000 μg were used. Time-dependent biodistribution of MSB0010853 was analyzed ex vivo at 3, 6, 24, and 96 h after intravenous administration of 25 μg of ⁸⁹Zr-MSB0010853. PET imaging and biodistribution were performed 24 h after administration of 25 μg of ⁸⁹Zr-MSB0010853 to mice bearing human H441, FaDu (high HER3 expression), or Calu-1 (no HER3 expression) tumor xenografts. Results: Radiolabeling of MSB0010853 with ⁸⁹Zr was performed with a radiochemical purity of greater than 95%. Ex vivo biodistribution showed protein dose- and time-dependent distribution of ⁸⁹Zr-MSB0010853 in all organs. Uptake of ⁸⁹Zr-MSB0010853 in H441 tumors was only time-dependent. Tumor could be visualized up to at least 96 h after injection. The highest mean SUV of 0.6 ± 0.2 was observed at 24 h after injection of 25 μg of ⁸⁹Zr-MSB0010853. ⁸⁹Zr-MSB0010853 tumor uptake correlated with HER3 expression and was highest in H441 (6.2 ± 1.1 percentage injected dose per gram [%ID/g]) and lowest in Calu-1 (2.3 ± 0.3 %ID/g) xenografts. Conclusion:⁸⁹Zr-MSB0010853 organ distribution and tumor uptake in mice are time-dependent, and tumor uptake correlates with HER3 expression. In contrast to tumor uptake except for kidney uptake, organ distribution of ⁸⁹Zr-MSB0010853 is protein dose-dependent for the tested doses. ⁸⁹Zr-MSB0010853 PET imaging gives insight into the in vivo behavior of MSB0010853.

89Zr-Bevacizumab PET: Potential Early Indicator of Everolimus Efficacy in Patients with Metastatic Renal Cell Carcinoma

Currently, biomarkers that predict the efficacy of everolimus in metastatic renal cell carcinoma (mRCC) patients are lacking. Everolimus inhibits vascular endothelial growth factor A (VEGF-A) expression. We performed PET scans on mRCC patients with ⁸⁹Zr-bevacizumab, a VEGF-A-binding antibody tracer. The aims were to determine a change in tumor tracer uptake after the start of everolimus and to explore whether ⁸⁹Zr-bevacizumab PET can identify patients with early disease progression. Methods:⁸⁹Zr-bevacizumab PET was done before and 2 and 6 wk after the start of everolimus, 10 mg/d, in mRCC patients. Routine CT scans were performed at baseline and every 3 mo thereafter. Tumor tracer uptake was quantified using SUV_max The endpoints were a change in tumor tracer uptake and treatment response on CT after 3 mo. Results: Thirteen patients participated. The median SUV_max of 94 tumor lesions was 7.3 (range, 1.6-59.5). Between patients, median tumor SUV_max varied up to 8-fold. After 2 wk, median SUV_max was 6.3 (1.7-62.3), corresponding to a mean decrease of 9.1% (P < 0.0001). Three patients discontinued everolimus early. At 6 wk, a mean decrease in SUV_max of 23.4% compared with baseline was found in 70 evaluable lesions of 10 patients, with a median SUV_max of 5.4 (1.1-49.4, P < 0.0001). All 10 patients who continued treatment had stable disease at 3 mo. Conclusion: Everolimus decreases ⁸⁹Zr-bevacizumab tumor uptake. Further studies are warranted to evaluate the predictive value of ⁸⁹Zr-bevacizumab PET for everolimus antitumor efficacy.

Threshold Analysis and Biodistribution of Fluorescently Labeled Bevacizumab in Human Breast Cancer

In vivo tumor labeling with fluorescent agents may assist endoscopic and surgical guidance for cancer therapy as well as create opportunities to directly observe cancer biology in patients. However, malignant and nonmalignant tissues are usually distinguished on fluorescence images by applying empirically determined fluorescence intensity thresholds. Here, we report the development of fSTREAM, a set of analytic methods designed to streamline the analysis of surgically excised breast tissues by collecting and statistically processing hybrid multiscale fluorescence, color, and histology readouts toward precision fluorescence imaging. fSTREAM addresses core questions of how to relate fluorescence intensity to tumor tissue and how to quantitatively assign a normalized threshold that sufficiently differentiates tumor tissue from healthy tissue. Using fSTREAM we assessed human breast tumors stained in vivo with fluorescent bevacizumab at microdose levels. Showing that detection of such levels is achievable, we validated fSTREAM for high-resolution mapping of the spatial pattern of labeled antibody and its relation to the underlying cancer pathophysiology and tumor border on a per patient basis. We demonstrated a 98% sensitivity and 79% specificity when using labeled bevacizumab to outline the tumor mass. Overall, our results illustrate a quantitative approach to relate fluorescence signals to malignant tissues and improve the theranostic application of fluorescence molecular imaging. Cancer Res; 77(3); 623-31. ©2016 AACR.

Tumor-Specific Uptake of Fluorescent Bevacizumab-IRDye800CW Microdosing in Patients with Primary Breast Cancer: A Phase I Feasibility Study

Purpose: To provide proof of principle of safety, breast tumor-specific uptake, and positive tumor margin assessment of the systemically administered near-infrared fluorescent tracer bevacizumab-IRDye800CW targeting VEGF-A in patients with breast cancer.Experimental Design: Twenty patients with primary invasive breast cancer eligible for primary surgery received 4.5 mg bevacizumab-IRDye800CW as intravenous bolus injection. Safety aspects were assessed as well as tracer uptake and tumor delineation during surgery and ex vivo in surgical specimens using an optical imaging system. Ex vivo multiplexed histopathology analyses were performed for evaluation of biodistribution of tracer uptake and coregistration of tumor tissue and healthy tissue.Results: None of the patients experienced adverse events. Tracer levels in primary tumor tissue were higher compared with those in the tumor margin (P < 0.05) and healthy tissue (P < 0.0001). VEGF-A tumor levels also correlated with tracer levels (r = 0.63, P < 0.0002). All but one tumor showed specific tracer uptake. Two of 20 surgically excised lumps contained microscopic positive margins detected ex vivo by fluorescent macro- and microscopy and confirmed at the cellular level.Conclusions: Our study shows that systemic administration of the bevacizumab-IRDye800CW tracer is safe for breast cancer guidance and confirms tumor and tumor margin uptake as evaluated by a systematic validation methodology. The findings are a step toward a phase II dose-finding study aimed at in vivo margin assessment and point to a novel drug assessment tool that provides a detailed picture of drug distribution in the tumor tissue. Clin Cancer Res; 23(11); 2730-41. ©2016 AACR.

Imaging the distribution of an antibody-drug conjugate constituent targeting mesothelin with ⁸⁹Zr and IRDye 800CW in mice bearing human pancreatic tumor xenografts

Mesothelin is a tumor differentiation antigen expressed by epithelial tumors, including pancreatic cancer. Currently, mesothelin is being targeted with an antibody-drug conjugate (ADC) consisting of a mesothelin-specific antibody coupled to a highly potent chemotherapeutic drug. Considering the toxicity of the ADC and reduced accessibility of pancreatic tumors, non-invasive imaging could provide necessary information. We therefore developed a zirconium-89 (⁸⁹Zr) labeled anti-mesothelin antibody (⁸⁹Zr-AMA) to study its biodistribution in human pancreatic tumor bearing mice. Biodistribution and dose-finding of ⁸⁹Zr-AMA were studied 144 h after tracer injection in mice with subcutaneously xenografted HPAC. MicroPET imaging was performed 24, 72 and 144 h after tracer injection in mice bearing HPAC or Capan-2. Tumor uptake and organ distribution of ⁸⁹Zr-AMA were compared with nonspecific ¹¹¹In-IgG. Biodistribution analyses revealed a dose-dependent ⁸⁹Zr-AMA tumor uptake. Tumor uptake of ⁸⁹Zr-AMA was higher than ¹¹¹In-IgG using the lowest tracer dose. MicroPET showed increased tumor uptake over 6 days, whereas activity in blood pool and other tissues decreased. Immunohistochemistry showed that mesothelin was expressed by the HPAC and CAPAN-2 tumors and fluorescence microscopy revealed that AMA-800CW was present in tumor cell cytoplasm. ⁸⁹Zr-AMA tumor uptake is antigen-specific in mesothelin-expressing tumors. ⁸⁹Zr-AMA PET provides non-invasive, real-time information about AMA distribution and tumor targeting.

Abstract 4208: Development of 18F-IL2: a PET radiotracer for imaging activated T-cells

Introduction: Activation of T-cells is accompanied by a strong up-regulation of interleukin-2 (IL2) receptor (CD25). Therefore PET imaging of IL2 receptors might be a suitable imaging biomarker for T-cell activation. 18F-IL2 PET could detect CD25-positive T-cells and the migration of these T-cells to distant sites of inflammation in SCID mice subcutaneously injected with human peripheral blood mononuclear cells1 and NOD mice with insulitis. Also a strong correlation was found between the accumulation of 18F-IL2 and the number of injected activated T-cells in immune-competent rats.2 In tumor bearing mice, 18F-IL2 PET could detect treatment-induced accumulation of activated T-cells in the tumor following local radiotherapy and/or vaccination.

Cancer immunotherapy is increasingly obtaining a place in clinical practice. However not all patients benefit. A biomarker for upfront or early response prediction for these immunotherapies might support patient selection before and during therapy. Potentially 18F-IL2 PET might serve this purpose. Therefore we aimed to accommodate the production of 18F-IL2 for use in clinical imaging studies.

Material and methods: In order to produce a GMP-compliant tracer the production is being implemented on the Eckert & Ziegler PharmTracer synthesis module. In this synthesis module, disposable cassettes, reactors and vials are used to avoid cross-contamination between productions. First the prosthetic group N-succinimidyl 4-fluorobenzoate (18F-SFB) is produced in 3 steps from cyclotron-produced 18F-fluoride. Subsequently, 18F-SFB is conjugated to human recombinant IL2 (Proleukin®). Various methods for synthesis and purification of 18F-SFB have been evaluated. Also purification of 18F-IL2 has been optimized. Quality control has been performed using ultra performance liquid chromatography (UPLC) and Thin Layer Chromatography (TLC).

Results: 18F-SFB was successfully synthesized with the Eckert & Ziegler PharmTracer synthesis module with decay-corrected radiochemical yields comparable to literature (range 28-64%). Major challenges have been encountered, most importantly regarding the purification of the 18F-SFB and 18F-IL2, stability of the IL2 and specific activity. The activated ester 18F-SFB was purified by high performance liquid chromatography (HPLC) to remove any impurities that could interfere with the conjugation. 18F-IL2 has been purified using PD-10 columns with PBS containing 0.05% SDS as mobile phase.

Conclusions: Several challenges for the GMP-compliant production of 18F-IL2 have been overcome. In the near future this tracer will be used in preclinical and clinical studies to non-invasively image activated T-cells before and during cancer immunotherapy. This can provide insight in the effects of cancer immunotherapy on the immune response.

References:

1. Di Gialleonardo V, et al. J Nucl Med.2012;53(5):679-86.

2. Di Gialleonardo V, et al. Eur J Nucl Med Mol Imaging.2012;39(10):1551-60.

Citation Format: Elly L. van der Veen, Petra Maarsingh, Anton G.T. Terwisscha van Scheltinga, Marjolijn N. Lub-de Hooge, Geke A.P. Hospers, Erik F.J. de Vries, Elisabeth G.E. de Vries. Development of 18F-IL2: a PET radiotracer for imaging activated T-cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4208.

Translation of New Molecular Imaging Approaches to the Clinical Setting: Bridging the Gap to Implementation

Molecular imaging with PET is a rapidly emerging technique. In breast cancer patients, more than 45 different PET tracers have been or are presently being tested. With a good rationale, after development of the tracer and proven feasibility, it is of interest to evaluate whether there is a potential meaningful role for the tracer in the clinical setting-such as in staging, in the (early) prediction of a treatment response, or in supporting drug choices. So far, only (18)F-FDG PET has been incorporated into breast cancer guidelines. For proof of the clinical relevance of tracers, especially for analysis in a multicenter setting, standardization of the technology and access to the novel PET tracer are required. However, resources for PET implementation research are limited. Therefore, next to randomized studies, novel approaches are required for proving the clinical value of PET tracers with the smallest possible number of patients. The aim of this review is to describe the process of the development of PET tracers and the level of evidence needed for the use of these tracers in breast cancer. Several breast cancer trials have been performed with the PET tracers (18)F-FDG, 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT), and (18)F-fluoroestradiol ((18)F-FES). We studied them to learn lessons for the implementation of novel tracers. After defining the gap between a good rationale for a tracer and implementation in the clinical setting, we propose solutions to fill the gap to try to bring more PET tracers to daily clinical practice.

Development, preclinical safety, formulation, and stability of clinical grade bevacizumab-800CW, a new near infrared fluorescent imaging agent for first in human use

There is a dire need for better visualization of cancer and analysis of specific targets in vivo. Molecular imaging with fluorescence is gaining more and more attention, as it allows detection of these targets and has advantages over radioactivity, such as no radiation dose, and lower costs. A key challenge in optical imaging however, is translation of the newly developed tracers from pre-clinical phase to clinical application. We describe the development and safety testing of clinical grade bevacizumab-800CW, an antibody-based targeted agent for non-invasive imaging of vascular endothelial growth factor A (VEGF-A). Development included implementing the manufacturing process and analytical methods according to current Good Manufacturing Practice (cGMP), formulation studies, extended characterization and stability testing. For safety pharmacology an extended single dose toxicity study in mice was performed. Bevacizumab-800CW was formulated in isotonic phosphate buffered sodium chloride solution at pH 7. The production was robust and showed a reproducible labeling efficiency, and no impurities. The binding affinity to VEGF-A remained intact. The optimized product meets all release specifications, is stable up to at least 3months and its characteristics did not significantly differ from the unlabeled bevacizumab. Toxicity testing in mice showed no remarkable findings. In conclusion, sterile bevacizumab-800CW (6mg=6ml) can be produced in stock according to current Good Manufacturing Practice. It is ready for first-in-human use.

Biodistribution and PET Imaging of Labeled Bispecific T Cell-Engaging Antibody Targeting EpCAM

AMG 110, a bispecific T cell engager (BiTE) antibody construct, induces T cell-mediated cancer cell death by cross-linking epithelial cell adhesion molecule (EpCAM) on tumor cells with a cluster of differentiation 3 ε (CD3ε) on T cells. We labeled AMG 110 with (89)Zr or near-infrared fluorescent dye (IRDye) 800CW to study its tumor targeting and tissue distribution.

METHODS

Biodistribution and tumor uptake of (89)Zr-AMG 110 was studied up to 6 d after intravenous administration to nude BALB/c mice bearing high EpCAM-expressing HT-29 colorectal cancer xenografts. Tumor uptake of (89)Zr-AMG 110 was compared with uptake in head and neck squamous cell cancer FaDu (intermediate EpCAM) and promyelocytic leukemia HL60 (EpCAM-negative) xenografts. Intratumoral distribution in HT-29 tumors was studied using 800CW-AMG 110.

RESULTS

Tumor uptake of (89)Zr-AMG 110 can be clearly visualized using small-animal PET imaging up to 72 h after injection. The highest tumor uptake of (89)Zr-AMG 110 at the 40-μg dose level was observed at 6 and 24 h (respectively, 5.35 ± 0.22 and 5.30 ± 0.20 percentage injected dose per gram; n = 3 and 4). Tumor uptake of (89)Zr-AMG 110 was EpCAM-specific and correlated with EpCAM expression. 800CW-AMG 110 accumulated at the tumor cell surface in viable EpCAM-expressing tumor tissue.

CONCLUSION

PET and fluorescent imaging provided real-time information about AMG 110 distribution and tumor uptake in vivo. Our data support using (89)Zr and IRDye 800CW to evaluate tumor and tissue uptake kinetics of bispecific T cell engager antibody constructs in preclinical and clinical settings.

Abstract LB-B11: Assessment of HER3 status during lapatinib treatment in HER3-positive breast cancer using 89Zr-anti-HER3 mAb

Treatment of human epidermal growth factor receptor 2 (HER2)-driven breast cancer with the HER-targeting tyrosine kinase inhibitor lapatinib can lead to a rapid compensatory increase in expression, signaling activity and relocalization of HER3 to the plasma membrane, which may attenuate the response to lapatinib. This might imply a potential role for a more dynamic assessment of HER3 tumor status using molecular imaging techniques, such as positron emission tomography (PET), instead of immunohistochemical HER3 staining on tumor biopsies. Here, we explored the feasibility of a dynamic assessment of HER3 status during lapatinib treatment in human breast cancer xenografts using zirconium-89 labeled anti-human HER3 monoclonal antibody (mAb) as a potential tracer for animal PET imaging.

The anti-human HER3 mouse mAb MAB3481 was used for all experiments. The effect of lapatinib treatment on HER3 expression and HER3 mAb internalization in human breast cancer cell lines SKBR3 and BT474 was determined using flow cytometry. Biodistribution was performed using 89Zr-anti-HER3 mAb in mice bearing BT474 or SKBR3 tumors. Mice received daily vehicle or a lapatinib dose of 25, 50 or 100 mg/kg orally. A tracer dose of 89Zr-anti-HER3 mAb combined with the aspecific tracer 111In-IgG was injected 3 days after treatment. Ex vivo organ distribution assessment of 89Zr-anti-HER3 mAb was performed 6 days after tracer injection. Ex vivo tumor analysis using western blotting, ELISA and immunohistochemistry were performed to measure HER3 levels.

In vitro, lapatinib treatment resulted in a ∼2-fold increase in membranous HER3 expression and HER3 internalization in SKBR3 and BT474 tumor cells. 89Zr-anti-HER3 mAb tumor uptake was significantly higher compared to 111In-IgG uptake in BT474 (P &lt; 0.01), demonstrating HER3 specific tumor uptake. SKBR3 xenografts did not show HER3 specific uptake, which was likely caused by the poor viability of the tumors. HER3 upregulation was observed in BT474 xenografts after lapatinib treatment for 9 days. The enhanced HER3 expression was related to a 76 ± 9% increase in 89Zr-anti-HER3 mAb tumor uptake at 25 mg/kg and 92 ± 27% at 50 mg/kg lapatinib. Lapatinib at the highest concentration (100 mg/kg) strongly inhibited tumor growth and did not increase tumor uptake of the tracer.

In conclusion, HER3-specific uptake of 89Zr-anti-HER3 mAb was shown in breast cancer xenografts. HER3 upregulation after lapatinib treatment was related to an enhanced 89Zr-anti-HER3 mAb uptake in these xenografts. These promising data warrant future dynamic assessment of HER3 status with 89Zr-anti-HER3 mAb PET imaging.

Citation Format: Arjan Kol, Martin Pool, Steven de Jong, Elisabeth GE de Vries, Marjolijn N. Lub-de Hooge, Anton GT Terwisscha van Scheltinga. Assessment of HER3 status during lapatinib treatment in HER3-positive breast cancer using 89Zr-anti-HER3 mAb. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr LB-B11.

Abstract A86: Extracellular domain shedding influences specific tumor uptake and kinetics of EGFR PET tracer 89Zr-imgatuzumab

Background

Overexpression and mutations of epidermal growth factor receptor (EGFR) are associated with tumor cell growth, differentiation, proliferation, apoptosis and cellular invasiveness. Imgatuzumab is a novel EGFR monoclonal antibody (mAb), glycoengineered for enhanced antibody-dependent cellular cytotoxicity. Molecular imaging using radiolabeled mAbs can potentially support decision making during (pre)clinical development and clinical practice. However, preclinical EGFR imaging studies revealed a mismatch between in vivo EGFR expression levels and tumor tracer uptake. Factors suggested causing the mismatch include differences in perfusion rates, vascularity, vascular permeability, interstitial pressure and mAb plasma half-life. Another factor that might influence tracer kinetics is shed EGFR (sEGFR) extracellular domain (ECD), which is found in sera of cancer patients with EGFR expressing tumors. We radiolabeled imgatuzumab with zirconium-89 (89Zr) and determined the influence of sEGFR on 89Zr-imgatuzumab tracer kinetics and tumor uptake in xenograft models.

Methods

Imgatuzumab was conjugated to N-Suc-desferal and radiolabeled with 89Zr. MicroPET imaging was performed 24, 72 and 144 hours post injection of 10, 25 and 160 μg 89Zr-imgatuzumab (5 MBq). As a non-specific control, 111In-DTPA-IgG (1 MBq) was used in equal doses in the same animals. Imaging studies were performed in A431 (human epidermoid carcinoma, EGFR overexpressing) and A549 and H441 (both human non-small cell lung cancer, medium EGFR expressing) subcutaneous xenograft bearing mice. Ex vivo biodistribution analysis was performed after the last scan. sEGFR levels in liver lysates and plasma were obtained using a human EGFR ECD ELISA assay.

Results

Increasing 89Zr-imgatuzumab dose from 10 to 160 μg enhanced tumor uptake in A431 bearing mice from 8.7 ± 3.1 to 31.4 ± 11.6% ID/g. On contrary, dose escalation between 10 and 160 μg 89Zr-imgatuzumab lowered tumor uptake from 13.8 ± 5.9 to 6.7 ± 0.8% ID/g in A549 and from 27.6 ± 3.6 to 15.5 ± 3.2% ID/g in H441 bearing mice. High liver uptake of 22.0 ± 5.4% ID/g was observed in A431 tumors at 10 μg 89Zr-imgatuzumab, this was higher than A549 (7.4 ± 1.5% ID/g, p&lt;0.0001) and H441 (8.4 ± 2.1% ID/g, p&lt;0.001) bearing mice. Liver uptake in A431 bearing mice could be blocked with 160 μg 89Zr-imgatuzumab to 7.1 ± 1.6% ID/g. Human EGFR ECD ELISA showed presence of 790 ± 267 ng/g protein sEGFR in liver lysates and 831 ± 173 ng/ml in plasma of A431 bearing mice, while sEGFR levels in liver and plasma of A549 and H441 tumor bearing mice were comparable to non tumor bearing control mice.

Conclusion

89Zr-imgatuzumab effectively accumulates in EGFR expressing tumors. A431 tumors extensively shedded EGFR, which highly influenced 89Zr-imgatuzumab kinetics in A431 bearing mice. These results support the use of shed antigen measurements and subsequent tracer dose adjustment in future EGFR imaging studies.

Citation Format: Martin Pool, Arjan Kol, Marjolijn N. Lub-de Hooge, Christian A. Gerdes, Steven de Jong, Elisabeth G.E. de Vries, Anton G.T. Terwisscha van Scheltinga. Extracellular domain shedding influences specific tumor uptake and kinetics of EGFR PET tracer 89Zr-imgatuzumab. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A86.

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.