In-vivo inhibition of neutral endopeptidase 1 results in higher absorbed tumor doses of [177Lu]Lu-PP-F11N in humans: the lumed phase 0b study

BACKGROUND

A new generation of radiolabeled minigastrin analogs delivers low radiation doses to kidneys and are considered relatively stable due to less enzymatic degradation. Nevertheless, relatively low tumor radiation doses in patients indicate limited stability in humans. We aimed at evaluating the effect of sacubitril, an inhibitor of the neutral endopeptidase 1, on the stability and absorbed doses to tumors and organs by the cholecystokinin-2 receptor agonist [177Lu]Lu-PP-F11N in patients. In this prospective phase 0 study eight consecutive patients with advanced medullary thyroid carcinoma and a current somatostatin receptor subtype 2 PET/CT scan were included. Patients received two short infusions of ~ 1 GBq [177Lu]Lu-PP-F11N in an interval of ~ 4 weeks with and without Entresto® pretreatment in an open-label, randomized cross-over order. Entresto® was given at a single oral dose, containing 48.6 mg sacubitril. Adverse events were graded and quantitative SPECT/CT and blood sampling were performed. Absorbed doses to tumors and relevant organs were calculated.

RESULTS

Pretreatment with Entresto® showed no additional toxicity and increased the stability of [177Lu]Lu-PP-FF11N in blood significantly (p < 0.001). Median tumor-absorbed doses were 2.6-fold higher after Entresto® pretreatment (0.74 vs. 0.28 Gy/GBq, P = 0.03). At the same time, an increase of absorbed doses to stomach, kidneys and bone marrow was observed, resulting in a tumor-to-organ absorbed dose ratio not significantly different with and without Entresto®.

CONCLUSIONS

Premedication with Entresto® results in a relevant stabilization of [177Lu]Lu-PP-FF11N and consecutively increases radiation doses in tumors and organs. Trial registration clinicaltrails.gov, NCT03647657. Registered 20 August 2018.

Towards the Magic Radioactive Bullet: Improving Targeted Radionuclide Therapy by Reducing the Renal Retention of Radioligands

Targeted radionuclide therapy (TRT) is an emerging field and has the potential to become a major pillar in effective cancer treatment. Several pharmaceuticals are already in routine use for treating cancer, and there is still a high potential for new compounds for this application. But, a major issue for many radiolabeled low-to-moderate-molecular-weight molecules is their clearance via the kidneys and their subsequent reuptake. High renal accumulation of radioactive compounds may lead to nephrotoxicity, and therefore, the kidneys are often the dose-limiting organs in TRT with these radioligands. Over the years, different strategies have been developed aiming for reduced kidney retention and enhanced therapeutic efficacy of radioligands. In this review, we will give an overview of the efforts and achievements of the used strategies, with focus on the therapeutic potential of low-to-moderate-molecular-weight molecules. Among the strategies discussed here is coadministration of compounds that compete for binding to the endocytic receptors in the proximal tubuli. In addition, the influence of altering the molecular design of radiolabeled ligands on pharmacokinetics is discussed, which includes changes in their physicochemical properties and implementation of cleavable linkers or albumin-binding moieties. Furthermore, we discuss the influence of chelator and radionuclide choice on reabsorption of radioligands by the kidneys.

Matrix Metalloproteinase-Responsive Delivery of PEGylated Fibroblast Growth Factor 2

Attachment of polyethylene glycol (PEG) chains is a common, well-studied, and Food and Drug Administration-approved method to address the pharmacokinetic challenges of therapeutic proteins. Occasionally, PEGylation impairs the activity of pharmacodynamics (PD). To overcome this problem, disease-relevant cleavable linkers between the polymer and the therapeutic protein can unleash full PD by de-PEGylating the protein at its target site. In this study, we engineered a matrix metalloproteinase (MMP)-responsive fibroblast growth factor 2 (FGF-2) mutant that was site-specifically extended with a PEG polymer chain. Using bioinspired strategies, the bioconjugate was designed to release the native protein at the desired structure/environment with preservation of the proliferative capacity in vitro on NIH3T3 cells. In vivo, hepatic exposure was diminished but not its renal distribution over time compared to unconjugated FGF-2. By releasing the growth factor from the PEG polymer in response to MMP cleavage, restored FGF-2 may enter hard-to-reach tissues and activate cell surface receptors or nuclear targets.

Abstract 5037: DARPins as powerful targeting agents for radioligand therapeutics

The development of effective radioligand therapeutics (RLTs) is frequently hampered by the lack of high-quality targeting agents that selectively deliver radioactive payloads to the site of disease while sparing healthy tissues. Antibodies can have high affinity and specificity to tumor targets, but their large size results in limited tumor penetration and long systemic half-life is frequently causing haematological toxicities. Alternatively, targeting agents with low molecular weight such as small molecules and peptides often suffer from limited affinity and specificity to the tumor target, resulting in off-target effects and limited tumor retention. DARPins (Designed Ankyrin Repeat Proteins) developed by Molecular Partners combine small size (15 kDa) and ideal binding properties. Due to their rigid-body target binding mode DARPins combine very high affinity and specificity and unless engineered accordingly, DARPins have very short systemic half-lives. Thanks to a simple and robust architecture, DARPins can be efficiently coupled with radioactive payloads, even at elevated temperatures; and they can tolerate sequence-engineering approaches, which are not compatible with other protein scaffolds. To establish the DARPin platform for RLT, we have used DARPin candidates against different tumor targets. We have previously shown that increasing affinity to the tumor target correlates with elevated tumor uptake and long tumor residence in preclinical mouse models. We now also show that DARPins exhibit a homogeneous and deep tumor penetration in vivo that is highly superior to antibody benchmarks. Globular proteins below 60 kDa in size are typically cleared from the bloodstream via the renal pathway. This generally results in a strong kidney accumulation of small sized, protein-based targeting agents and their coupled residualizing radionuclides, leading to dose-limiting kidney toxicities. To overcome this limitation, we have undertaken an extensive engineering approach of the DARPin scaffold. Our results show that sequence engineering strongly reduces kidney uptake of DARPins without affecting their tumor uptake. This effect was confirmed with independent DARPin candidates suggesting a general applicability of the approach. Combined with other orthogonal strategies, we are able obtain favourable tumor to kidney ratios in preclinical mouse models. These results show that our proprietary optimized DARPin platform offers an attractive solution to the limitations of protein-based targeting agents for RLT applications. Together with the fact that high-affinity DARPins can be generated against a large variety of tumor targets, we conclude that our platform provides a powerful basis for the development of next-generation RLTs. Several DARPin-RLT programs in indications with high unmet medical need are currently in development.

Citation Format: Andreas Bosshart, Stephan Wullschleger, Martin Behe, Alain Blanc, Stefan Imobersteg, Alexandra Neculcea, Jacqueline Blunschi, Liridon Abduli, Sarah Schütz, Julia Wolter, Christian Reichen, Amelie Croset, Alessandra Villa, Christian Lizak, Anne Goubier, Roger Schibli, Daniel Steiner. DARPins as powerful targeting agents for radioligand therapeutics. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5037.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biannual highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

MAIN BODY

This selection of highlights provides commentary on 21 different topics selected by each coauthoring Editorial Board member addressing a variety of aspects ranging from novel radiochemistry to first-in-human application of novel radiopharmaceuticals.

CONCLUSION

Trends in radiochemistry and radiopharmacy are highlighted. Hot topics cover the entire scope of EJNMMI Radiopharmacy and Chemistry, demonstrating the progress in the research field, and include new PET-labelling methods for ¹¹C and ¹⁸F, the importance of choosing the proper chelator for a given radioactive metal ion, implications of total body PET on use of radiopharmaceuticals, legislation issues and radionuclide therapy including the emerging role of ¹⁶¹Tb.

Targeting mTORC1 Activity to Improve Efficacy of Radioligand Therapy in Cancer

Radioligand therapy (RLT) represents an effective strategy to treat malignancy by cancer-selective delivery of radioactivity following systemic application. Despite recent therapeutic successes, cancer radioresistance and insufficient delivery of the radioactive ligands, as well as cytotoxicity to healthy organs, significantly impairs clinical efficacy. To improve disease management while minimizing toxicity, in recent years, the combination of RLT with molecular targeted therapies against cancer signaling networks showed encouraging outcomes. Characterization of the key deregulated oncogenic signaling pathways revealed their convergence to activate the mammalian target of rapamycin (mTOR), in which signaling plays an essential role in the regulation of cancer growth and survival. Therapeutic interference with hyperactivated mTOR pathways was extensively studied and led to the development of mTOR inhibitors for clinical applications. In this review, we outline the regulation and oncogenic role of mTOR signaling, as well as recapitulate and discuss mTOR complex 1 (mTORC1) inhibition to improve the efficacy of RLT in cancer.

Comparative analysis of cancer cell responses to targeted radionuclide therapy (TRT) and external beam radiotherapy (EBRT)

The vast majority of our knowledge regarding cancer radiobiology and the activation of radioresistance mechanisms emerged from studies using external beam radiation therapy (EBRT). Yet, less is known about the cancer response to internal targeted radionuclide therapy (TRT). Our comparative phosphoproteomics analyzed cellular responses to TRT with lutetium-177-labeled minigastrin analogue [¹⁷⁷Lu]Lu-PP-F11N (β-emitter) and EBRT (ɣ-rays) in CCKBR-positive cancer cells. Activation of DNA damage response by p53 was induced by both types of radiotherapy, whereas TRT robustly increased activation of signaling pathways including epidermal growth factor receptor (EGFR), mitogen-activated protein kinases (MAPKs) or integrin receptor. Inhibition of EGFR or integrin signaling sensitized cancer cells to radiolabeled minigastrin. In vivo, EGFR inhibitor erlotinib increased therapeutic response to [¹⁷⁷Lu]Lu-PP-F11N and median survival of A431/CCKBR-tumor bearing nude mice. In summary, our study explores a complex scenario of cancer responses to different types of irradiation and pinpoints the radiosensitizing strategy, based on the targeting survival pathways, which are activated by TRT.

A multispecific anti-CD40 DARPin® construct induces tumor-selective CD40 activation and tumor regression

The CD40 receptor is an attractive target for cancer immunotherapy. Although a modest pharmacodynamic effect is seen in patients following administration of CD40-targeting monoclonal antibodies (mAb), the doses that could be safely administered do not result in a meaningful clinical response, most likely due to the limited therapeutic window associated with systemic CD40 activation. To overcome this issue, we developed a multispecific DARPin® construct, α-FAPxCD40, which has conditional activity at the site of disease. α-FAPxCD40 activation of CD40 depends on binding to fibroblast activation protein (FAP), a cell surface protease overexpressed in the stroma of solid tumors. In vitro studies demonstrated that α-FAPxCD40 potently activates human antigen-presenting cells in the presence, but not in the absence, of FAP-positive cells. After intravenous injection, a murine surrogate construct (α-mFAPxCD40) accumulated in FAP-positive tumors, elicited rejection of 88% of these tumors and induced memory anti-tumor immunity. Importantly, in contrast to the mouse anti-CD40 tested in parallel, the in vivo anti-tumor activity of α-mFAPxCD40 was neither associated with elevated blood cytokines nor with hepatotoxicity, both of which contribute to the clinical dose-limiting toxicities of several CD40 mAb. This study demonstrates that α-(m)FAPxCD40 engages CD40 in an FAP-restricted manner leading to tumor eradication without signs of peripheral toxicity. This distinct preclinical profile indicates that a favorable therapeutic index may be achieved in humans. It further supports the development of α-FAPxCD40, currently tested in a first-in-human clinical study in patients with solid tumors (NCT05098405).

Highlight selection of radiochemistry and radiopharmacy developments by editorial board

Background

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to update the readership on trends in the field of radiopharmaceutical development.

Results

This commentary of highlights has resulted in 23 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals.

Conclusion

Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Guideline on current good radiopharmacy practice (cGRPP) for the small-scale preparation of radiopharmaceuticals

This guideline on current good radiopharmacy practice (cGRPP) for small-scale preparation of radiopharmaceuticals represents the view of the Radiopharmacy Committee of the European Association of Nuclear Medicine (EANM). The guideline is laid out in the format of the EU Good Manufacturing Practice (GMP) guidelines as defined in EudraLex volume 4. It is intended for non-commercial sites such as hospital radiopharmacies, nuclear medicine departments, research PET centres and in general any healthcare establishments. In the first section, general aspects which are applicable to all levels of operations are discussed. The second section discusses the preparation of small-scale radiopharmaceuticals (SSRP) using licensed generators and kits. Finally, the third section goes into the more complex preparation of SSRP from non-licensed starting materials, often requiring a purification step and sterile filtration. The intention is that the guideline will assist radiopharmacies in the preparation of diagnostic and therapeutic SSRP’s safe for human administration.

Highlight selection of radiochemistry and radiopharmacy developments by editorial board (January-June 2020)

BACKGROUND

The Editorial Board of EJNMMI Radiopharmacy and Chemistry releases a biyearly highlight commentary to describe trends in the field.

RESULTS

This commentary of highlights has resulted in 19 different topics selected by each member of the Editorial Board addressing a variety of aspects ranging from novel radiochemistry to first in man application of novel radiopharmaceuticals.

CONCLUSION

Trends in radiochemistry and radiopharmacy are highlighted demonstrating the progress in the research field being the scope of EJNMMI Radiopharmacy and Chemistry.

Pharmacological inhibition of mTORC1 increases CCKBR-specific tumor uptake of radiolabeled minigastrin analogue [177Lu]Lu-PP-F11N

Rationale: A high tumor-to-healthy-tissue uptake ratio of radiolabeled ligands is an essential prerequisite for safe and effective peptide receptor radionuclide therapy (PRRT). In the present study, we searched for novel opportunities to increase tumor-specific uptake of the radiolabeled minigastrin analogue [¹⁷⁷Lu]Lu-DOTA-(DGlu)₆-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH₂ ([¹⁷⁷Lu]Lu-PP-F11N), that targets the cholecystokinin B receptor (CCKBR) in human cancers.

Methods: A kinase inhibitor library screen followed by proliferation and internalization assays were employed to identify compounds which can increase uptake of [¹⁷⁷Lu]Lu-PP-F11N in CCKBR-transfected human epidermoid carcinoma A431 cells and natural CCKBR-expressing rat pancreatic acinar AR42J cells. Western blot (WB) analysis verified the inhibition of the signaling pathways and the CCKBR level, whereas the cell-based assay analyzed arrestin recruitment. Biodistribution and SPECT imaging of the A431/CCKBR xenograft mouse model as well as histological analysis of the dissected tumors were used for in vivo validation.

Results: Our screen identified the inhibitors of mammalian target of rapamycin complex 1 (mTORC1), which increased cell uptake of [¹⁷⁷Lu]Lu-PP-F11N. Pharmacological mTORC1 inhibition by RAD001 and metformin increased internalization of [¹⁷⁷Lu]Lu-PP-F11N in A431/CCKBR and in AR42J cells. Analysis of protein lysates from RAD001-treated cells revealed increased levels of CCKBR (2.2-fold) and inhibition of S6 phosphorylation. PP-F11N induced recruitment of β-arrestin1/2 and ERK1/2 phosphorylation. In A431/CCKBR-tumor bearing nude mice, 3 or 5 days of RAD001 pretreatment significantly enhanced tumor-specific uptake of [¹⁷⁷Lu]Lu-PP-F11N (ratio [RAD001/Control] of 1.56 or 1.79, respectively), whereas metformin treatment did not show a significant difference. Quantification of SPECT/CT images confirmed higher uptake of [¹⁷⁷Lu]Lu-PP-F11N in RAD001-treated tumors with ratios [RAD001/Control] of average and maximum concentration reaching 3.11 and 3.17, respectively. HE staining and IHC of RAD001-treated tumors showed a significant increase in necrosis (1.4% control vs.10.6% of necrotic area) and the reduction of proliferative (80% control vs. 61% of Ki67 positive cells) and mitotically active cells (1.08% control vs. 0.75% of mitotic figures). No significant difference in the tumor vascularization was observed after five-day RAD001 or metformin treatment.

Conclusions: Our data demonstrates, that increased CCKBR protein level by RAD001 pretreatment has the potential to improve tumor uptake of [¹⁷⁷Lu]Lu-PP-F11N and provides proof-of-concept for the development of molecular strategies aimed at enhancing the level of the targeted receptor, to increase the efficacy of PRRT and nuclear imaging.

Fibronectin fibers are highly tensed in healthy organs in contrast to tumors and virus-infected lymph nodes

The extracellular matrix (ECM) acts as reservoir for a plethora of growth factors and cytokines some of which are hypothesized to be regulated by ECM fiber tension. Yet, ECM fiber tension has never been mapped in healthy versus diseased organs. Using our recently developed tension nanoprobe derived from the bacterial adhesin FnBPA5, which preferentially binds to structurally relaxed fibronectin fibers, we discovered here that fibronectin fibers are kept under high tension in selected healthy mouse organs. In contrast, tumor tissues and virus-infected lymph nodes exhibited a significantly higher content of relaxed or proteolytically cleaved fibronectin fibers. This demonstrates for the first time that the tension of ECM fibers is significantly reduced upon pathological tissue transformations. This has wide implications, as the active stretching of fibronectin fibers adjusts critical cellular niche parameters and thereby tunes the reciprocal cell-ECM crosstalk. Mapping the tensional state of fibronectin fibers opens novel and unexpected diagnostic opportunities.

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Mechanobiology of extracellular matrix changes upon pathological transformations.

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Fibronectin is significantly more relaxed in tumors than in healthy organs.

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Relaxed fibronectin is found close to myofibroblasts and dense collagen fibers.

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Viral infection reduces fibronectin fiber tension in lymph nodes.

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Use of a tension-sensitive adhesin to probe fibronectin fiber tension in tissues

New Insights into Arrestin Recruitment to GPCRs

G protein-coupled receptors (GPCRs) are cellular master regulators that translate extracellular stimuli such as light, small molecules or peptides into a cellular response. Upon ligand binding, they bind intracellular proteins such as G proteins or arrestins, modulating intracellular signaling cascades. Here, we use a protein-fragment complementation approach based on nanoluciferase (split luciferase assay) to assess interaction of all four known human arrestins with four different GPCRs (two class A and two class B receptors) in live cells. Besides directly tagging the 11S split-luciferase subunit to the receptor, we also could demonstrate that membrane localization of the 11S subunit with a CAAX-tag allowed us to probe arrestin recruitment by endogenously expressed GPCRs. Varying the expression levels of our reporter constructs changed the dynamic behavior of our assay, which we addressed with an advanced baculovirus-based multigene expression system. Our detection assay allowed us to probe the relevance of each of the two arrestin binding sites in the different GPCRs for arrestin binding. We observed remarkable differences between the roles of each arresting binding site in the tested GPCRs and propose that the distinct advantages of our system for probing receptor interaction with effector proteins will help elucidate the molecular basis of GPCR signaling efficacy and specificity in different cell types.

Design of Radiolabeled Analogs of Minigastrin by Multiple Amide-to-Triazole Substitutions

The insertion of single 1,4-disubstituted 1,2,3-triazoles as metabolically stable bioisosteres of trans-amide bonds (triazole scan) was recently applied to the ¹⁷⁷Lu-labeled tumor-targeting analog of minigastrin, [Nle¹⁵]MG11. The reported novel mono-triazolo-peptidomimetics of [Nle¹⁵]MG11 showed either improved resistance against enzymatic degradation or a significantly increased affinity toward the target receptor but never both. To enhance further the tumor-targeting properties of the minigastrin analogs, we studied conjugates with multiple amide-to-triazole substitutions for additive or synergistic effects. Promising candidates were identified by modification of two or three amide bonds, which yielded both improved stability and increased receptor affinity of the peptidomimetics in vitro. Biodistribution studies of radiolabeled multi-triazolo-peptidomimetics in mice bearing receptor-positive tumor xenografts revealed up to 4-fold increased tumor uptake in comparison to the all-amide reference compound [Nle¹⁵]MG11. In addition, we report here for the first time a linear peptidomimetic with three triazole insertions in its backbone and maintained biological activity.

Triazolo-Peptidomimetics: Novel Radiolabeled Minigastrin Analogs for Improved Tumor Targeting

MG11 is a truncated analog of minigastrin, a peptide with high affinity and specificity toward the cholecystokinin-2 receptor (CCK2R), which is overexpressed by different tumors. Thus, radiolabeled MG11 derivatives have great potential for use in cancer diagnosis and therapy. A drawback of MG11 is its fast degradation by proteases, leading to moderate tumor uptake in vivo. We introduced 1,4-disubstituted 1,2,3-triazoles as metabolically stable bioisosteres to replace labile amide bonds of the peptide. The "triazole scan" yielded peptidomimetics with improved resistance to enzymatic degradation and/or enhanced affinity toward the CCK2R. Remarkably, our lead compound achieved a 10-fold increase in receptor affinity, resulting in a 2.6-fold improved tumor uptake in vivo. Modeling of the ligand-CCK2R complex suggests that an additional cation-π interaction of the aromatic triazole moiety with the Arg³⁵⁶ residue of the receptor is accountable for these observations. We show for the first time that the amide-to-triazole substitution strategy offers new opportunities in drug development that go beyond the metabolic stabilization of bioactive peptides.

Cholecystokinin 2 Receptor Agonist 177Lu-PP-F11N for Radionuclide Therapy of Medullary Thyroid Carcinoma: Results of the Lumed Phase 0a Study

Treatment of patients with advanced medullary thyroid carcinoma (MTC) is still a challenge. For more than 2 decades, it has been known that the cholecystokinin 2 receptor is a promising target for the treatment of MTC with radiolabeled minigastrin analogs. Unfortunately, kidney toxicity has precluded their therapeutic application so far. In 6 consecutive patients, we evaluated with advanced 3-dimensional dosimetry whether improved minigastrin analog ¹⁷⁷Lu-DOTA-(d-Glu)₆-Ala-Tyr-Gly-Trp-Nle-Asp-PheNH₂ (¹⁷⁷Lu-PP-F11N) is a suitable agent for the treatment of MTC. Methods: Patients received 2 injections of about 1 GBq (∼80 μg) of ¹⁷⁷Lu-PP-F11N with and without a solution of succinylated gelatin (SG, a plasma expander used for nephroprotection) in a random crossover sequence to evaluate biodistribution, pharmacokinetics, and tumor and organ dosimetry. An electrocardiogram was obtained and blood count and blood chemistry were measured up to 12 wk after the administration of ¹⁷⁷Lu-PP-F11N to assess safety. Results: In all patients, ¹⁷⁷Lu-PP-F11N accumulation was visible in tumor tissue, stomach, and kidneys. Altogether, 13 tumors were eligible for dosimetry. The median absorbed doses for tumors, stomach, kidneys, and bone marrow were 0.88 (interquartile range [IQR]: 0.85-1.04), 0.42 (IQR: 0.25-1.01), 0.11 (IQR: 0.07-0.13), and 0.028 (IQR: 0.026-0.034) Gy/GBq, respectively. These doses resulted in median tumor-to-kidney dose ratios of 11.6 (IQR: 8.11-14.4) without SG and 13.0 (IQR: 10.2-18.6) with SG; these values were not significantly different (P = 1.0). The median tumor-to-stomach dose ratio was 3.34 (IQR: 1.14-4.70). Adverse reactions (mainly hypotension, flushing, and hypokalemia) were self-limiting and not higher than grade 1. Conclusion: ¹⁷⁷Lu-PP-F11N accumulates specifically in MTC at a dose that is sufficient for a therapeutic approach. With a low kidney and bone marrow radiation dose, ¹⁷⁷Lu-PP-F11N shows a promising biodistribution. The dose-limiting organ is most likely the stomach. Further clinical studies are necessary to evaluate the maximum tolerated dose and the efficacy of ¹⁷⁷Lu-PP-F11N.

High-Resolution SPECT Imaging of Stimuli-Responsive Soft Microrobots

Untethered small-scale robots have great potential for biomedical applications. However, critical barriers to effective translation of these miniaturized machines into clinical practice exist. High resolution tracking and imaging in vivo is one of the barriers that limit the use of micro- and nanorobots in clinical applications. Here, the inclusion of radioactive compounds in soft thermoresponsive magnetic microrobots is investigated to enable their single-photon emission computed tomography imaging. Four microrobotic platforms differing in hydrogel structure and four ^99m Tc[Tc]-based radioactive compounds are investigated in order to achieve optimal contrast agent retention and optimal imaging. Single microrobot imaging of structures as low as 100 µm in diameter, as well as tracking of shape switching from tubular to planar configurations by inclusion of ^99m Tc[Tc] colloid in the hydrogel structure, is reported.

Abstract LB-106: Overcoming limitations of current Antibody-Drug Conjugates (ADCs) by a novel linker technology

We introduce a novel and versatile ADC-linker technology that is based on site-specific enzymatic payload conjugation to ‘off-the-shelf’ antibodies, i.e., without the need to reduce or engineer the antibody. The functionalization takes place site-specifically and stoichiometrically (drug-to-antibody ratio, DAR = 2.0) at the Fc-part of antibodies. The resulting ADCs show favorable biophysical properties such as high solubility and stability using different payloads. Additionally, initial ELISA findings show that our modification does not interfere with Fc-gamma receptor and FcRn binding. Importantly, our ADCs showed superior efficacy in different tumor animal models as compared to control Thiomab™ ADCs. Using native trastuzumab (non-engineered) as the targeting antibody and amanitin as payload, we generated within 36 hours highly homogeneous and pure ADCs with a well-defined DAR of 2.0 as confirmed by LC-MS. In in-vitro assays our ADCs demonstrated potent cytotoxicity in all tested cell-lines (SKBR-3, BT-474, JIMT-1, and NCI-N87) as compared to the control Thiomab™ ADCs, most strikingly for the JIMT-1 cell-line: EC50 of 0.15nM vs 2.5nM. In the mouse JIMT-1 tumor model, our anti-HER2 ADC was highly potent and resulted in complete tumor remission in all mice (10/10 mice) at a single dose of 2mg/kg. In contrast, the control Thiomab™-functionalized ADC showed tumor regrowth in 4 out of 10 animals, starting on day 50. The same high potency was observed for the NCI-N87 xenograft model at a dose of 3mg/kg in which tumor growth inhibition was significantly delayed versus the reference ADC (8/10 vs 4/10 animals alive on day 110). These encouraging results obtained so far indicate that our linker technology a) allows for fast (&lt; 36 hours) and straightforward manufacturing of ADCs using different payloads without protein engineering efforts, b) results in ADCs with favorable biophysical properties and a clear defined drug-to-antibody ratio, and c) enables the generation of highly potent and stable, thus safer, next-generation ADCs.

Citation Format: Philipp Rene Spycher, Julia Carina Frei, Jöri Elias Wehrmüller, Isabella Attinger-toller, Dragan Grabulovski, Torsten Hechler, Michael Kulke, Andreas Pahl, Martin Behe, Roger Schibli. Overcoming limitations of current Antibody-Drug Conjugates (ADCs) by a novel linker technology [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 LB-106.

Comparison of desferrioxamine and NODAGA for the gallium-68 labeling of exendin-4

INTRODUCTION

Radiolabeled exendin-4 (Ex4) derivatives are used to target the glucagon-like peptide-1 receptor (GLP-1R) for the clinical diagnosis of insulinomas, a rare type of neuroendocrine tumor. Gallium-68 is an ideal diagnostic nuclide for this application and a study evaluating an exendin-4-NODAGA conjugate is currently underway. However, in complexion with the chelator DFO, its in vivo stability has been a matter of dispute. The aim of this work was to directly compare [⁶⁸Ga]Ga-Ex4NOD with [⁶⁸Ga]Ga-Ex4DFO in vitro and in vivo.

METHODS

In our approach, we directly compared N'-[5-(acetyl-hydroxy-amino)pentyl]-N-[5-[3-(5-aminopentyl-hydroxy-carbamoyl)propanoylamino]pentyl]-N-hydroxy-butane diamide (desferriox-amine B, DFO) and 2-(4,7-bis (carboxymethyl)-1,4,7-triazonan-1-yl) pentanedioic acid (NODAGA) conjugated to exendin-4 in vitro and in vivo. We radiolabeled the peptides with gallium-68, followed by HPLC quality control. In vitro characterization was performed in CHL cells overexpressing the GLP-1R and in vivo studies were conducted with CD1 nu/nu mice carrying tumors derived from these cells.

RESULTS

We found that both peptides could be radiolabeled with a molar activity of about 9.33 MBq/nmol without further purification. They internalized equally well into GLP-1R-expressing cells and their IC₅₀ was similar with 15.6 ± 7.8 nM and 18.4 ± 3.0 nM for [^natGa]Ga-Ex4NOD and [^natGa]Ga-Ex4DFO, respectively. In vivo, [⁶⁸Ga]Ga-Ex4NOD accumulated more in all tissue, while [⁶⁸Ga]Ga-Ex4DFO exhibited a more favorable target-to-kidney ratio.

CONCLUSION AND RELEVANCE

DFO is a suitable chelator for the radiolabeling of exendin-4 derivatives with gallium-68 for in vitro and preclinical in vivo studies. DFO performed better in vivo due to its significantly lower kidney accumulation (p < 0.0001). It was also found to be stable in vivo in mice, contrary to earlier reports. Based on our results, the DFO chelating system in combination with exendin-4 would be an interesting option for clinical imaging of insulinomas.

SUN-334 Evaluation of the CCK-2 Receptor Agonist 177Lu-PP-F11N for PRRT of Medullary Thyroid Carcinoma: Results of a Phase 0 "Lumed" Study

Introduction: Despite the introduction of new molecular targeted therapies, there is still an unmet need for an effective systemic therapy for advanced medullary thyroid carcinoma (MTC). As MTC expresses cholecystokinine-2 (CCK-2) receptors at a high incidence and density, targeting the CCK-2 receptor with radiolabelled gastrin analogues is a potential approach for radionuclide therapy. Unfortunately, kidney and bone marrow toxicity precluded therapeutic applications of CCK-2 receptor specific radiotracers until now. The aim of this prospective study is the feasibility testing of targeting CCK-2 receptors with the novel gastrin analogue [¹⁷⁷Lu-DOTA-(DGlu)6-Ala-Tyr-Gly-Trp-Nleu-Asp-PheNH2] (¹⁷⁷Lu-PP-F11N) in six patients with advanced MTC (ClinicalTrials.gov: NCT02088645). Subjects and Methods: Six patients received two injections of 1 GBq ¹⁷⁷Lu-PP-F11N, one injection with and the other without Physiogel (Gelofusin = plasma expander for nephroprotection) infusion. Planar scintigraphy and SPECT/CT scans were performed at several time points for up to 72 h post injection in order to calculate tumour- and organ doses using 3D voxel- and MIRD based dosimetry (Dosimetry Research Tool v5.2, Siemens Medical Solutions, USA). Blood samples were taken for bone marrow dose calculations. ECG, blood count and blood chemistry were measured up to 12 weeks after the second administration of ¹⁷⁷Lu-PP-F11N in order to evaluate adverse events. Results: Adverse reactions (mainly hypotension, flushing and hypokalemia) were self-limiting and not higher than grade 1, according to CTCAE version 4.03. In all patients, ¹⁷⁷Lu-PP-F11N accumulation was visible in tumor tissue, in the kidneys, stomach and the colon. Altogether, 14 tumours were eligible for dosimetry. The median (range) radiation dose for tumours, kidneys and bone marrow was 0.88 Gy/GBq (0.69-2.85), 0.090 (0.045-0.115) and 0.010 (0.008-0.016). These resulted in median tumour-to-kidney dose ratios of 12.8 (6.0-52.4) (without Physiogel) and 12.4 (6.4-29.8) (with Physiogel), which was not significantly different. The median tumour-to-bone marrow dose ratio was 87.9 (52.8-316.4). Discussion/Conclusion: The administration of the novel CCK-2 receptor ligand ¹⁷⁷Lu-PP-F11N was safe in all six examined patients. Visualization of metastasized/recurrent disease in all patients provides evidence that CCK-2 receptor targeting with ¹⁷⁷Lu-PP-F11N is feasible in patients with MTC. The dosimetry results indicate tumour doses that could enable radionuclide therapy. Dosimetry results for kidneys and bone marrow revealed low organ doses, as well as excellent tumour-to-kidney and tumour-to-bone marrow ratios. Further studies will be necessary to evaluate the theranostic potential of ¹⁷⁷Lu-PP-F11N in patients with CCK-2 receptor expressing tumours.

Abstract 3029: FAP-mediated tumor accumulation of a T-cell agonistic FAP/4-1BB DARPin drug candidate analyzed by SPECT/CT and quantitative biodistribution

Immunomodulating agents have revolutionized anti-cancer therapy. However, monotherapy is often not sufficient, and development of combination treatments is hampered by cumulative toxicity. In an attempt to overcome this challenge, a tumor-restricted agonistic 4-1BB/FAP DARPin drug candidate, which induces T-cell co-stimulation only when clustered by binding to fibroblast activation protein alpha (FAP) expressing cells, has been developed. FAP is a type II membrane-bound glycoprotein abundantly expressed in the stroma of many solid tumors by cancer-associated fibroblasts. As shown previously using in vitro and in vivo models (HT-29), co-stimulation induced by a FAP-targeted 4-1BB agonistic DARPin molecule leads to enhanced activation and expansion of CD8+ T-cells. To support clinical development of the drug candidate, tumor localization and accumulation were studied by whole-body SPECT/CT imaging and quantitative biodistribution using Indium-111 labeled DARPin molecules in a human colorectal adenocarcinoma (HT-29) xenograft model in CD1 nude mice. Immunohistochemical staining of tumor stroma confirmed local expression of FAP. Labeled 4-1BB/FAP DARPin molecules specifically accumulated in FAP-expressing tumor in vivo. SPECT/CT imaging and biodistribution revealed a maximum tumor accumulation of around 15% of the injected dose per gram of tissue around 72 h post injection. High tumor/blood ratios were observed one week post injection because the activity in the blood decreased according to the expected serum half-life of 26 h, determined in separate pharmacokinetic studies in BALB/c mice following single dose intravenous bolus injections. Based on the decrease of radioactivity in the tumor, a tumor residence half-life of approximately 4 days was calculated, indicating an extended tumor retention potentially due to FAP binding. No accumulation was observed in the muscle tissue that was choosen as a rather weakly-perfused control tissue. Taken together, FAP-targeting of a 4-1BB agonist DARPin molecule resulted in expected high tumor accumulation and retention compared to an untargeted version of the molecule, both relevant observations for further preclinical and clinical studies. These findings suggest that tumor-targeting via FAP has the potential to induce T-cell activation restricted to the tumor site, and thereby reducing toxicities caused by systemic 4-1BB activation. In conclusion, immunostimulatory drugs with tumor-targeted activity may have the potential to circumvent current limitations of immunotherapy and allow safe and effective use, in particular in combination therapy.

Citation Format: Christian Reichen, Ralph Bessey, Christine DePasquale, Stefan Imobersteg, Martin Behe, Alain Blanc, Roger Schibli, Alexander Link, Laurent Juglair, Joanna Taylor, Patricia Schildknecht, Julia Hepp, Elmar vom Baur, Hong Ji, Christof Zitt, Victor Levitsky, Keith M. Dawson, Michael T. Stumpp, Dan Snell. FAP-mediated tumor accumulation of a T-cell agonistic FAP/4-1BB DARPin drug candidate analyzed by SPECT/CT and quantitative biodistribution [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 3029.

Production and separation of 43Sc for radiopharmaceutical purposes

Background

The favorable decay properties of ⁴³Sc and ⁴⁴Sc for PET make them promising candidates for future applications in nuclear medicine. An advantage ⁴³Sc (T_1/2 = 3.89 h, Eβ⁺_av = 476 keV [88%]) exhibits over ⁴⁴Sc, however, is the absence of co-emitted high energy γ-rays. While the production and application of ⁴⁴Sc has been comprehensively discussed, research concerning ⁴³Sc is still in its infancy. This study aimed at developing two different production routes for ⁴³Sc, based on proton irradiation of enriched ⁴⁶Ti and ⁴³Ca target material.

Results

⁴³Sc was produced via the ⁴⁶Ti(p,α)⁴³Sc and ⁴³Ca(p,n)⁴³Sc nuclear reactions, yielding activities of up to 225 MBq and 480 MBq, respectively. ⁴³Sc was chemically separated from enriched metallic ⁴⁶Ti (97.0%) and ⁴³CaCO₃ (57.9%) targets, using extraction chromatography. In both cases, ~90% of the final activity was eluted in a small volume of 700 μL, thereby, making it suitable for direct radiolabeling. The prepared products were of high radionuclidic purity, i.e. 98.2% ⁴³Sc were achieved from the irradiation of ⁴⁶Ti, whereas the product isolated from irradiated ⁴³Ca consisted of 66.2% ⁴³Sc and 33.3% ⁴⁴Sc. A PET phantom study performed with ⁴³Sc, via both nuclear reactions, revealed slightly improved resolution over ⁴⁴Sc. In order to assess the chemical purity of the separated ⁴³Sc, radiolabeling experiments were performed with DOTANOC, attaining specific activities of 5–8 MBq/nmol, respectively, with a radiochemical yield of >96%.

Conclusions

It was determined that higher ⁴³Sc activities were accessible via the ⁴³Ca production route, with a comparatively less complex target preparation and separation procedure. The product isolated from irradiated ⁴⁶Ti, however, revealed purer ⁴³Sc with minor radionuclidic impurities. Based on the results obtained herein, the ⁴³Ca route features some advantages (such as higher yields and direct usage of the purchased target material) over the ⁴⁶Ti path when aiming at ⁴³Sc production on a routine basis.

Electronic supplementary material

The online version of this article (10.1186/s41181-017-0033-9) contains supplementary material, which is available to authorized users.

Guidance on validation and qualification of processes and operations involving radiopharmaceuticals

BACKGROUND

Validation and qualification activities are nowadays an integral part of the day by day routine work in a radiopharmacy. This document is meant as an Appendix of Part B of the EANM "Guidelines on Good Radiopharmacy Practice (GRPP)" issued by the Radiopharmacy Committee of the EANM, covering the qualification and validation aspects related to the small-scale "in house" preparation of radiopharmaceuticals. The aim is to provide more detailed and practice-oriented guidance to those who are involved in the small-scale preparation of radiopharmaceuticals which are not intended for commercial purposes or distribution.

RESULTS

The present guideline covers the validation and qualification activities following the well-known "validation chain", that begins with editing the general Validation Master Plan document, includes all the required documentation (e.g. User Requirement Specification, Qualification protocols, etc.), and leads to the qualification of the equipment used in the preparation and quality control of radiopharmaceuticals, until the final step of Process Validation.

CONCLUSIONS

A specific guidance to the qualification and validation activities specifically addressed to small-scale hospital/academia radiopharmacies is here provided. Additional information, including practical examples, are also available.

Methoxinine - an alternative stable amino acid substitute for oxidation-sensitive methionine in radiolabelled peptide conjugates

Radiolabelled peptides with high specificity and affinity towards receptors that are overexpressed by tumour cells are used in nuclear medicine for the diagnosis (imaging) and therapy of cancer. In some cases, the sequences of peptides under investigations contain methionine (Met), an amino acid prone to oxidation during radiolabelling procedures. The formation of oxidative side products can affect the purity of the final radiopharmaceutical product and/or impair its specificity and affinity towards the corresponding receptor. The replacement of Met with oxidation resistant amino acid analogues, for example, norleucine (Nle), can provide a solution. While this approach has been applied successfully to different radiolabelled peptides, a Met → Nle switch only preserves the length of the amino acid side chain important for hydrophobic interactions but not its hydrogen-bonding properties. We report here the use of methoxinine (Mox), a non-canonical amino acid that resembles more closely the electronic properties of Met in comparison to Nle. Specifically, we replaced Met¹⁵ by Mox¹⁵ and Nle¹⁵ in the binding sequence of a radiometal-labelled human gastrin derivative [d-Glu¹⁰ ]HG(10-17), named MG11 (d-Glu-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH₂ ). A comparison of the physicochemical properties of ¹⁷⁷ Lu-DOTA[X¹⁵ ]MG11 (X = Met, Nle, Mox) in vitro (cell internalization/externalization properties, receptor affinity (IC₅₀ ), blood plasma stability and logD) showed that Mox indeed represents a suitable, oxidation-stable amino acid substitute of Met in radiolabelled peptide conjugates. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Position paper on requirements for toxicological studies in the specific case of radiopharmaceuticals

This is a position paper of the Radiopharmacy Committee of the EANM (European Association of Nuclear Medicine) addressing toxicology studies for application of new diagnostic and therapeutic radiopharmaceuticals (RP) that are not approved (i.e., not having a marketing authorization or a monograph in the European Pharmacopoeia), excluding endogenous and ubiquitous substances in humans. This paper discusses the requirements for clinical trials with radiopharmaceuticals for clinical research applications, not necessarily intended to aim at a marketing authorization. If marketing authorization is intended, scientific advice of the competent authorities is mandatory and cannot be replaced by this position paper. The position paper reflects the view of the Radiopharmacy Committee of the EANM and can be used as a basis for discussions with the responsible authorities.

EANM guideline for the preparation of an Investigational Medicinal Product Dossier (IMPD)

The preparation of an Investigational Medicinal Product Dossier (IMPD) for a radiopharmaceutical to be used in a clinical trial is a challenging proposition for radiopharmaceutical scientists working in small-scale radiopharmacies. In addition to the vast quantity of information to be assembled, the structure of a standard IMPD is not well suited to the special characteristics of radiopharmaceuticals. This guideline aims to take radiopharmaceutical scientists through the practicalities of preparing an IMPD, in particular giving advice where the standard format is not suitable. Examples of generic IMPDs for three classes of radiopharmaceuticals are given: a small molecule, a kit-based diagnostic test and a therapeutic radiopharmaceutical.

Self-assembled gold coating enhances X-ray imaging of alginate microcapsules

Therapeutic biomolecules produced from cells encapsulated within alginate microcapsules (MCs) offer a potential treatment for a number of diseases. However the fate of such MCs once implanted into the body is difficult to establish. Labelling the MCs with medical imaging contrast agents may aid their detection and give researchers the ability to track them over time thus aiding the development of such cellular therapies. Here we report the preparation of MCs with a self-assembled gold nanoparticle (AuNPs) coating which results in distinctive contrast and enables them to be readily identified using a conventional small animal X-ray micro-CT scanner. Cationic Reversible Addition-Fragmentation chain Transfer (RAFT) homopolymer modified AuNPs (PAuNPs) were coated onto the surface of negatively charged alginate MCs resulting in hybrids which possessed low cytotoxicity and high mechanical stability in vitro. As a result of their high localized Au concentration, the hybrid MCs exhibited a distinctive bright circular ring even with a low X-ray dose and rapid scanning in post-mortem imaging experiments facilitating their positive identification and potentially enabling them to be used for in vivo tracking experiments over multiple time-points.

Future prospects for SPECT imaging using the radiolanthanide terbium-155 - production and preclinical evaluation in tumor-bearing mice

INTRODUCTION

We assessed the suitability of the radiolanthanide (155)Tb (t1/2=5.32 days, Eγ=87 keV (32%), 105keV (25%)) in combination with variable tumor targeted biomolecules using preclinical SPECT imaging.

METHODS

(155)Tb was produced at ISOLDE (CERN, Geneva, Switzerland) by high-energy (~1.4 GeV) proton irradiation of a tantalum target followed by ionization and on-line mass separation. (155)Tb was separated from isobar and pseudo-isobar impurities by cation exchange chromatography. Four tumor targeting molecules - a somatostatin analog (DOTATATE), a minigastrin analog (MD), a folate derivative (cm09) and an anti-L1-CAM antibody (chCE7) - were radiolabeled with (155)Tb. Imaging studies were performed in nude mice bearing AR42J, cholecystokinin-2 receptor expressing A431, KB, IGROV-1 and SKOV-3ip tumor xenografts using a dedicated small-animal SPECT/CT scanner.

RESULTS

The total yield of the two-step separation process of (155)Tb was 86%. (155)Tb was obtained in a physiological l-lactate solution suitable for direct labeling processes. The (155)Tb-labeled tumor targeted biomolecules were obtained at a reasonable specific activity and high purity (>95%). (155)Tb gave high quality, high resolution tomographic images. SPECT/CT experiments allowed excellent visualization of AR42J and CCK-2 receptor-expressing A431 tumors xenografts in mice after injection of (155)Tb-DOTATATE and (155)Tb-MD, respectively. The relatively long physical half-life of (155)Tb matched in particular the biological half-lives of (155)Tb-cm09 and (155)Tb-DTPA-chCE7 allowing SPECT imaging of KB tumors, IGROV-1 and SKOV-3ip tumors even several days after administration.

CONCLUSIONS

The radiolanthanide (155)Tb may be of particular interest for low-dose SPECT prior to therapy with a therapeutic match such as the β(-)-emitting radiolanthanides (177)Lu, (161)Tb, (166)Ho, and the pseudo-radiolanthanide (90)Y.

Distribution, elimination, and renal handling of (99m)technetium-Demogastrin 1

Radiolabeled cholecystokinin/gastrin (CCK) receptor-targeting peptides are promising compounds for radiodiagnosis and radiotherapy of certain malignancies. This study evaluated the pharmacokinetic profile of a CCK-2 receptor-specific peptide, Demogastrin 1, labeled with technetium-99m ((99m)Tc-Demogastrin 1), in rats. To investigate the fate of (99m)Tc-Demogastrin 1 in the rat, biodistribution and elimination studies in vivo were performed, and elimination parameters in perfused rat liver and kidney were determined. Biodistribution studies showed that (99m)Tc-Demogastrin 1 was rapidly cleared from the blood and most organs. A significant amount of radioactivity was detected in the CCK-2 receptor-rich organs, such as the stomach. Low radioactivity was found in the CCK-1 receptor-rich organs. Radioactivity in bowels and stomach declined relatively slowly. High and long-term retention of radioactivity in the kidneys was observed. Elimination of (99m)Tc-Demogastrin 1 via the bile was negligible. A high and rapid renal excretion was observed in elimination experiments in vivo. In the perfused kidney, glomerular filtration was found to be the main renal excretion mechanism of (99m)Tc-Demogastrin 1. Demogastrin 1 was distributed preferentially to the organs expressing CCK-2 receptors. The decisive elimination route of (99m)Tc-Demogastrin 1 in rats was urinary excretion. A high and prolonged renal retention may limit potential clinical use of the compound.

The influence of the combined treatment with Vadimezan (ASA404) and taxol on the growth of U251 glioblastoma xenografts

Background

One of the most important biological characteristics of Glioblastoma multiforme (GBM) is high vascular density. Vadimezan (ASA404, DMXAA) belongs to the class of small molecule vascular disrupting agents (VDA) that cause disruption of established tumor vessels and subsequent tumor hemorrhagic necrosis. Its selective antivascular effect is mediated by intratumoral induction of several cytokines including tumor necrosis factor-α (TNF-α), granulocyte-colony-stimulating factor (G-CSF), interleukin 6 (IL-6) and macrophage inflammatory protein 1α (MIP-1α). Preclinical studies have demonstrated that ASA404 acts synergistically with taxanes. In this study, we investigated if treatment of mice bearing U251 human glioblastoma xenografts with ASA404 and taxol may be synergistic. Therapy response was evaluated by measuring changes in tumor size and metabolic activity using ¹⁸F-FDG PET (Fluorodeoxyglucose - positron emision tomography) imaging.

Methods

U251 cells were inoculated s.c. in the right hind limb of NMRI-Foxn1^nu athymic female nude mice. Animals were randomly assigned into 4 groups (7–9 animals/group) for treatment: control, taxol, ASA404, and ASA404 plus taxol. The animals received either a single dose of taxol (10 mg/kg), ASA404 (27.5 mg/kg), or taxol (10 mg/kg) plus ASA404 (27.5 mg/kg) administered i.p.; ASA404 was administred 24 h after the treatment with taxol. 4 and 24 h after treatment with ASA404 (28 and 48 h hours after treatment with taxol) ¹⁸ F-FDG PET scans were performed.

Results

The treatment with taxol did not affect the tumor growth in comparison to untreated controls. The treatment of animals with single dose ASA404 alone or in combination with taxol caused a significant delay in tumor growth. The combined treatment did not decrease the growth of the xenografts significantly more than ASA404 alone, but early changes in tumor ¹⁸ F-FDG uptake preceded subsequent growth inhibition. The tumor weights, which were determined at the end of treatment, were lower in case of combined treatment.

Conclusions

The treatment with ASA404 alone or in combination with taxol showed antitumoral effects in our glioblastoma model probably through destruction of blood vessels. The implications for the anticancer effect of this compound warrant further preclinical studies. ¹⁸F-FDG PET appears to be a promising tool to monitor treatment with ASA404 early in the course of therapy.

Activated platelets in carotid artery thrombosis in mice can be selectively targeted with a radiolabeled single-chain antibody

Background

Activated platelets can be found on the surface of inflamed, rupture-prone and ruptured plaques as well as in intravascular thrombosis. They are key players in thrombosis and atherosclerosis. In this study we describe the construction of a radiolabeled single-chain antibody targeting the LIBS-epitope of activated platelets to selectively depict platelet activation and wall-adherent non-occlusive thrombosis in a mouse model with nuclear imaging using in vitro and ex vivo autoradiography as well as small animal SPECT-CT for in vivo analysis.

Methodology/Principal Findings

LIBS as well as an unspecific control single-chain antibody were labeled with ¹¹¹Indium (¹¹¹In) via bifunctional DTPA ( = ¹¹¹In-LIBS/¹¹¹In-control). Autoradiography after incubation with ¹¹¹In-LIBS on activated platelets in vitro (mean 3866±28 DLU/mm², 4010±630 DLU/mm² and 4520±293 DLU/mm²) produced a significantly higher ligand uptake compared to ¹¹¹In-control (2101±76 DLU/mm², 1181±96 DLU/mm² and 1866±246 DLU/mm²) indicating a specific binding to activated platelets; P<0.05. Applying these findings to an ex vivo mouse model of carotid artery thrombosis revealed a significant increase in ligand uptake after injection of ¹¹¹In-LIBS in the presence of small thrombi compared to the non-injured side, as confirmed by histology (49630±10650 DLU/mm² vs. 17390±7470 DLU/mm²; P<0.05). These findings could also be reproduced in vivo. SPECT-CT analysis of the injured carotid artery with ¹¹¹In-LIBS resulted in a significant increase of the target-to-background ratio compared to ¹¹¹In-control (1.99±0.36 vs. 1.1±0.24; P<0.01).

Conclusions/Significance

Nuclear imaging with ¹¹¹In-LIBS allows the detection of platelet activation in vitro and ex vivo with high sensitivity. Using SPECT-CT, wall-adherent activated platelets in carotid arteries could be depicted in vivo. These results encourage further studies elucidating the role of activated platelets in plaque pathology and atherosclerosis and might be of interest for further developments towards clinical application.

In vivo testing of 177Lu-labelled anti-PSMA antibody as a new radioimmunotherapeutic agent against prostate cancer

AIM

The goal of the present study was to test the (177)Lu-labelled anti-PSMA monoclonal antibody 3/F11 ((177)Lu-DOTA-3/F11) as a new radioimmunotherapeutic agent in a prostate cancer SCID mouse xenograft model.

MATERIALS AND METHODS

The mAb 3/F11 was (177)Lu labelled using 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as chelating agent. DOTA-3/F11 was tested for cell binding and serum immunoreactivity by flow cytometry. The biodistribution and the therapeutic efficacy of (177)Lu-DOTA-3/F11 in mice bearing PSMA-positive C4-2 prostate cancer xenografts were evaluated.

RESULTS

3/F11 and DOTA-3/F11 showed high and specific cell binding and similar serum half-lives of approximately seven days. Biodistribution studies revealed an increasing tumour uptake of (177)Lu DOTA-3/F11 over time with maximum tumour-to-muscle and tumour-to-blood ratios after 72 h. A single dose of 1 MBq (177)Lu-DOTA-3/F11 inhibited tumour growth and prolonged survival.

CONCLUSION

This study indicated that (177)Lu-DOTA-3/F11 may be a suitable radioimmunotherapeutic agent for the treatment of prostate cancer.

Non-invasive in vivo imaging of tumor-associated CD133/prominin

Background

Cancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance.

Methodology/Principal Findings

Here, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities. The CD133-specific monoclonal antibody AC133.1 was used for quantitative fluorescence-based optical imaging of mouse xenograft models based on isogenic pairs of CD133 positive and negative cell lines. A first set consisted of wild-type U251 glioblastoma cells, which do not express CD133, and lentivirally transduced CD133-overexpressing U251 cells. A second set made use of HCT116 colon carcinoma cells, which uniformly express CD133 at levels comparable to primary glioblastoma stem cells, and a CD133-negative HCT116 derivative. Not surprisingly, visualization and quantification of CD133 in overexpressing U251 xenografts was successful; more importantly, however, significant differences were also found in matched HCT116 xenograft pairs, despite the lower CD133 expression levels. The binding of i.v.-injected AC133.1 antibodies to CD133 positive, but not negative, tumor cells isolated from xenografts was confirmed by flow cytometry.

Conclusions/Significance

Taken together, our results show that non-invasive antibody-based in vivo imaging of tumor-associated CD133 is feasible and that CD133 antibody-based tumor targeting is efficient. This should facilitate developing clinically applicable cancer stem cell imaging methods and CD133 antibody-based therapeutics.

Scintigraphic assessment of salivary gland function in a rat model

BACKGROUND

Salivary gland dysfunction with xerostomia is a major clinical problem without a causal therapy in most cases. The development of an animal model for scintigraphic assessment of salivary gland function has great clinical relevance for the investigation of promising new diagnostic and therapeutic strategies for chronic salivary gland diseases. This study reports the first experiences with scintigraphic analyses of salivary gland function in a rat model.

MATERIALS AND METHODS

Anatomical and scintigraphic studies were performed for topographic differentiation of major salivary glands of Wistar rats. (⁹⁹m)technetium pertechnetate salivary gland scanning was performed, appropriate regions of interest were determined and the gland-to-background ratio was examined for the evaluation of salivary gland function.

RESULTS

The quantitative analysis of salivary gland scintigraphy revealed a reliable comparison of major salivary glands on both sides with the gland-to-background ratio ranging from 1.26 to 1.94 with an average of 1.51.

CONCLUSION

This model seems to be appropriate for functional studies in an experimental setting.

Peripheral and central biodistribution of (111)In-labeled anti-beta-amyloid autoantibodies in a transgenic mouse model of Alzheimer's disease

Active as well as passive immunization against beta-amlyoid (Abeta) has been proposed as a treatment to lower cerebral amyloid burden and stabilize cognitive decline in Alzheimer's disease (AD). To clarify the mechanism of action underlying passive immunization, the in vivo distribution (and sites of degradation) of peripherally administered radiolabeled human and mouse anti-Abeta antibodies were analyzed in a transgenic mouse model of AD. In APP23 mice, a model in which mutated human amyloid precursor protein is overexpressed, the biodistribution of intravenously applicated (111)indium-conjugated affinity-purified human polyclonal autoantibodies (NAbs-Abeta) was compared to that of monoclonal anti-Abeta(1-17) (6E10), anti-Abeta(17-24) antibodies (4G8) and anti-CD-20 (Rituximab), a non-Abeta targeting control. Blood clearance half-lives were 50+/-6h for Rituximab, 20-30h for NAbs-Abeta, 29+/-5h for 4G8 and 27+/-3h for 6E10. Blood activity was higher for 6E10 at 4h as compared to 4G8, Rituximab and NAbs-Abeta. At the 96h time point, Rituximab had the highest blood activity among the antibodies tested. As expected, all antibodies displayed hepatobiliary clearance. Additionally, NAbs-Abeta was excreted in the urinary tract. Liver and kidney uptake of NAbs-Abeta increased over time and was higher than in the monoclonal antibodies at 48h/96h. The brain-to-blood radioactivity ratio for NAbs-Abeta at later time points (>48h) was higher than that of 6E10, 4G8 and Rituximab. In addition, the distribution varied, with highest values found in the hippocampus. Our data indicate a cerebral accumulation of human NAbs-Abeta in the APP23 model. Further studies with human immunoglobulins and particularly with those that recognize different Abeta-epitopes are required in order to delineate in more detail the mode of action of NAbs-Abeta.

Bioreversibly crosslinked polyplexes of PEI and high molecular weight PEG show extended circulation times in vivo

Copolymers consisting of branched PEI 25 kDa grafted with high molecular weight PEG at a low degree of substitution were successfully synthesized using a simple two-step procedure. The resulting AB-type and ABA-type copolymers were tested for cytotoxicity and DNA condensation and complexation properties. Their polyplexes with plasmid DNA were characterized in terms of DNA size and surface charge, transfection efficiency and blood compatibility. Pharmacokinetic profiles of the complexes containing (32)P-labeled plasmid were assessed before and after surface crosslinking. A set of four copolymers containing one or two PEG 20 kDa or PEG 30 kDa chains was obtained. The cytotoxicity of PEI was strongly reduced after copolymerization. The copolymer polyplexes showed hydrodynamic diameters of less than 200 nm, comparable to PEI 25. Similarly, no reduction in DNA condensation and complexation properties was found. In fact, PEI-PEG(30 k) copolymers exhibited better condensation and complexation properties than PEI 25. The transfection efficiency of copolymer polyplexes was increased 10-fold compared to PEI 25 control and the hemolytic activity was markedly reduced. After intravenous injection into mice, plasmids complexed to PEI-PEG(30 k) copolymers resulted in significantly increased circulation times. After stabilizing the polyplexes with a redox sensitive, biodegradable crosslinker, blood levels of plasmid could be further increased up to 125% compared to PEI. These results demonstrate that polyplexes prepared using a combined strategy of surface crosslinking and PEGylation seem to provide promising properties as stable, long circulating vectors.

HER2 targeted polyplexes: the effect of polyplex composition and conjugation chemistry on in vitro and in vivo characteristics

Knowledge of the influence of targeting ligands on pharmacokinetics and biodistribution of polymeric nonviral vectors is presently limited. We investigated the properties of three structurally different conjugates of polyethylenglycol-modified polyethylenimine coupled to the HER2 specific antibody Trastuzumab. Unlike polyethylenimine, conjugates formed small (100-230 nm) DNA polyplexes with zeta-potentials of +/- 2 mV at a broad range of N/P ratios. Stability as assessed by heparin displacement was slightly improved compared to unmodified copolymers. Erythrocyte aggregation and hemolysis were strongly reduced with conjugates. Conjugate polyplexes showed significant differences in specificity and transfection efficiency in vitro. These could be attributed to differences in cell binding and uptake assessed by flow cytometry. Pharmacokinetics of conjugates in mice revealed significant improvements over free plasmid DNA and polyethylenimine. Area under the plasma level-time curve of conjugates was increased up to 48% or 114% compared to that of polyethylenimine or free plasmid DNA, respectively. Deposition of conjugate polyplexes in lung and spleen was significantly reduced compared to that of polyethylenimine. Differences could be attributed to antibody conjugation since no significant differences in pharmacokinetics and biodistribution were found between conjugates. These findings demonstrate that conjugated antibodies not only confer active targeting but also significantly improve in vivo properties of polyplexes.

[Lys40(Ahx-DTPA-111In)NH2]-Exendin-4 is a highly efficient radiotherapeutic for glucagon-like peptide-1 receptor-targeted therapy for insulinoma

PURPOSE

Although metabolic changes make diagnosis of insulinoma relatively easy, surgical removal is hampered by difficulties in locating it, and there is no efficient treatment for malignant insulinoma. We have previously shown that the high density of glucagon-like peptide-1 receptors (GLP-1R) in human insulinoma cells provides an attractive target for molecular imaging and internal radiotherapy. In this study, we investigated the therapeutic potential of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4, an (111)In-labeled agonist of GLP-1, in a transgenic mouse model of human insulinoma.

EXPERIMENTAL DESIGN

[Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 was assessed in the Rip1Tag2 mouse model of pancreatic beta-cell carcinogenesis, which exhibits a GLP-1R expression comparable with human insulinoma. Mice were injected with 1.1, 5.6, or 28 MBq of the radiopeptide and sacrificed 7 days after injection. Tumor uptake and response, the mechanism of action of the radiopeptide, and therapy toxicity were investigated.

RESULTS

Tumor uptake was >200% injected activity per gram, with a dose deposition of 3 Gy/MBq at 40 pmol [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4. Other GLP-1R-positive organs showed > or =30 times lower dose deposition. A single injection of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 resulted in a reduction of the tumor volume by up to 94% in a dose-dependent manner without significant acute organ toxicity. The therapeutic effect was due to increased tumor cell apoptosis and necrosis and decreased proliferation.

CONCLUSIONS

The results suggest that [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 is a promising radiopeptide capable of selectively targeting insulinoma. Furthermore, Auger-emitting radiopharmaceuticals such as (111)In are able to produce a marked therapeutic effect if a high tumor uptake is achieved.

Molekulare Bildgebung der Apoptose bei kardiovaskulären Erkrankungen

Molecular imaging of functional parameters such as apoptosis (programmed cell death) in vivo opens new possibilities in clinical diagnostic and scientific research. Especially in the case of cardiovascular diseases that are mainly responsible for both morbidity and mortality in Western industrial nations, innovative non-invasive examination strategies are necessary for early diagnosis of these diseases. Since apoptosis unlike necrosis is present even after minor alterations of the microenvironment of cells and has been shown to be involved in a large number of cardiovascular diseases, there are currently several experimental studies underway with the goal of imaging apoptosis in vivo. The review discusses the basics of apoptosis in myocardial infarction, myocarditis, atherosclerosis, restenosis after angioplasty and stent implantation, currently used imaging techniques, achieved results, and future possibilities for molecular imaging of apoptosis.

[Combination of radiological and nuclear medical imaging in animals: an overview about today's possibilities]

Molecular imaging of small animals has made considerable progress in the last years. Various research fields are interested in imaging small animals due to the lower numbers of animals per experiment. This has advantages with respect to financial, ethical and research aspects. Non-invasive imaging allows examination of one animal several times during the same experiment. This makes it possible to follow a pathological process in the same animal over time. However, the radiological methods used such as magnetic resonance imaging or computed tomography as well as the nuclear medicine methods such as single photon emission computed tomography or positron emission tomography suffer from disadvantages. Molecular aspects are limited in the radiological methods while anatomical localization is difficult in nuclear medicine. The fusion of these methods leads to additional information. This review shows today's possibilities with their advantages as well as disadvantages.

Crosslinked nanocarriers based upon poly(ethylene imine) for systemic plasmid delivery: In vitro characterization and in vivo studies in mice

Crosslinked poly(ethylene imine) (PEI) polyplexes for intracellular DNA release were generated using a low molecular weight crosslinking reagent, Dithiobis(succinimidyl propionate) (DSP). Disulfide bonds of the crosslinked polyplexes were susceptible to intracellular redox conditions and DNA release was observed using an ethidium bromide exclusion assay and dynamic light scattering. Transfection experiments were performed to elucidate the effect of extra- and intracellular redox conditions. Pharmacokinetics and organ accumulation of uncrosslinked and crosslinked polyplexes were compared and gene expression patterns were measured in mice 24 h after intravenous injection. Crosslinked PEI and plasmid DNA formed stable polyplexes in a size range of 100-300 nm, with zeta potentials between +16.4 and +26.1 mV. DNA release occurred after cleavage of the disulfide bonds. Cell culture experiments under reducing conditions as well as with glutathione loaded cells confirmed the proposed intracellular activation. A significant influence of the intracellular glutathione status on the transfection efficiency was observed. Pharmacokinetic profiles of crosslinked PEI/DNA polyplexes in mice after intravenous administration showed higher blood levels for crosslinked polyplexes. These polyplexes accumulated mainly in the liver and the lungs. In vivo transfection data revealed significantly reduced (unwanted) lung transfection while liver transfection predominated. These studies suggest that crosslinked polyplexes are more stable in circulation and retain their transfection efficiency after intravenous administration.

Trastuzumab−Polyethylenimine−Polyethylene Glycol Conjugates for Targeting Her2-Expressing Tumors

In this study, we describe the synthesis and characterization of a conjugate consisting of poly(ethylene glycol 2,000 Da)(10)-graft-poly(ethylene imine 25 kDa) (PEG-PEI) covalently coupled to Trastuzumab (Herceptin) via N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP) for specific gene delivery to Her2-expressing cell lines. The efficiency of DNA condensation was studied using an ethidium bromide exclusion assay and demonstrated negligible differences compared to PEG-PEI. Conjugate complex sizes were determined by dynamic light scattering to be in the range 130-180 nm. zeta potentials at different N/P ratios were close to neutral. Flow cytometry and confocal microscopy revealed efficient binding and uptake of Trastuzumab-PEI-PEG complexes using Her2-positive SK-BR-3 cells. In contrast, binding and uptake into Her2-negative OVCAR-3 cells was negligible. In good correlation with these findings, reporter gene expression using targeted complexes in SK-BR-3 cells was up to sevenfold higher than that of unmodified PEG-PEI complexes. With the use OVCAR-3 cells, no significant difference in expression efficiencies could be observed between conjugate and PEG-PEI complexes. Inhibition experiments with free Trastuzumab showed a significant decrease in reporter gene expression using SK-BR-3 cells but no decrease using OVCAR-3 cells, strongly supporting a specific Her2-receptor-mediated uptake mechanism. Our results suggest that Trastuzumab-PEI-PEG might be a promising new bioconjugate for targeted gene transfer to Her2-positive tumor cells in vivo.

Two-photon absorption-controlled multidose drug release: a novel approach for secondary cataract treatment

Tens of millions of cataract surgeries are done every year and the number is increasing heavily. Posterior capsule opacification is the major postoperative complication with an incidence of 10 to 50% within 5 years, depending on the age of the patient. We present a novel approach for secondary cataract treatment in a noninvasive manner. Photochemically triggered drug release from a polymer enables repeated drug applications for cataract treatment years after implantation of the intraocular lens, just when needed. However, light in the visible spectral range must pass through the lens but must not induce drug release. We demonstrate that two-photon absorption photochemistry is a powerful tool to overcome this problem. With wavelengths in the visible regime, a photochemical reaction that requires energies in the UV is triggered. The high intensities needed for this process never occur in any lighting condition in daily lives, but may be easily obtained with focused laser beams routinely used in ophthalmology. The properties of the therapeutic system are specified and the function is demonstrated by in-vitro cell tests. Noninvasive multidose photochemically triggered drug release from implanted intraocular lenses carrying a drug depot may be a therapeutic as well as an economic choice to established treatments of secondary cataracts.