Preliminary efficacy of [90Y]DOTA-biotin-avidin radiotherapy against non-muscle invasive bladder cancer.

PURPOSE: Bladder cancer represents 3% of all new cancer diagnoses per year. We propose intravesical radionuclide therapy using the ß-emitter 90Y linked to DOTA-biotin-avidin ([90Y]DBA) to deliver short-range radiation against non-muscle invasive bladder cancer (NMIBC). MATERIAL AND METHODS: Image-guided biodistribution of intravesical DBA was investigated in an animal model by radiolabeling DBA with the 68Ga and dynamic microPET imaging following intravesical infusion of [68Ga]DBA for up to 4 h and post-necropsy γ-counting of organs. The antitumor activity of [90Y]DBA was investigated using an orthotopic MB49 murine bladder cancer model. Mice were injected with luciferase-expressing MB49 cells and treated via intravesical administration with 9.2 MBq of [90Y]DBA or unlabeled DBA 3 days after the tumor implantation. Bioluminescence imaging was conducted after tumor implantation to monitor the bladder tumor growth. In addition, we investigated the effects of [90Y]DBA radiation on urothelial histology with immunohistochemistry analysis of bladder morphology. RESULTS: Our results demonstrated that DBA is contained in the bladder for up to 4 h after intravesical infusion. A single dose of [90Y]DBA radiation treatment significantly reduced growth of MB49 bladder carcinoma. Attaching 90Y-DOTA-biotin to avidin prevents its re-absorption into the blood and distribution throughout the rest of the body. Furthermore, immunohistochemistry demonstrated that [90Y]DBA radiation treatment did not cause short-term damage to urothelium at day 10, which appeared similar to the normal urothelium of healthy mice. CONCLUSION: Our data demonstrates the potential of intravesical [90Y]DBA as a treatment for non-muscle invasive bladder cancer.

Polyazamacrocycle Ligands Facilitate 89Zr Radiochemistry and Yield 89Zr Complexes with Remarkable Stability.

Over the last three decades, the chemistry of zirconium has facilitated antibody development and the clinical management of disease in the precision medicine era. Scientists have harnessed its reactivity, coordination chemistry, and nuclear chemistry to develop antibody-based radiopharmaceuticals incorporating zirconium-89 (89Zr: t1/2 = 78.4 h, ß+: 22.8%, Eß+max = 901 keV; EC: 77%, Eγ = 909 keV) to improve disease detection, identify patients for individualized therapeutic interventions. and monitor their response to those interventions. However, release of the 89Zr4+ ion from the radiopharmaceutical remains a concern, since it may confound the interpretation of clinical imaging data, negatively affect dosimetric calculations, and hinder treatment planning. In this report, we relate our novel observations involving the use of polyazamacrocycles as zirconium-89 chelators. We describe the synthesis and complete characterization of zirconium 2,2',2″,2‴-(1,4,7,10-tetraazacyclotridecane-1,4,7,10-tetrayl)tetraacetic acid (Zr-TRITA), zirconium 3,6,9,15-Tetraazabicyclo[9.3.1] pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (Zr-PCTA), and zirconium 2,2',2″-(1,4,7-triazacyclononane-1,4,7-triyl)triacetic acid (Zr-NOTA). In addition, we elucidate the solid-state structure of each complex using single-crystal X-ray diffraction analysis. Finally, we found that [89Zr]Zr-PCTA and [89Zr]Zr-NOTA demonstrate excellent stability in vitro and in vivo and provide a rationale for these observations. These innovative findings have the potential to guide the development of safer and more robust immuno-PET agents to improve precision medicine applications.

Granzyme B PET Imaging of the Innate Immune Response.

The human immune system is a complex system which protects against invaders and maintains tissue homeostasis. It is broadly divided into the innate and adaptive branches. Granzyme B is serine protease that plays an important role in both and can serve as a biomarker for cellular activation. Because of this, a granzyme B PET agent (GZP) has recently been developed and has been shown to be able to monitor response to immunotherapy. Here, we evaluated the utility of granzyme B PET imaging to assess the innate immune response. We subcutaneously administered LPS to mice to induce inflammation and performed granzyme B PET imaging after 24 and 120 h. We dissected out tissue in the region of injection and performed granzyme B immunofluorescence (IF) to confirm specificity of the GZP radiotracer. Granzyme B PET imaging demonstrated increased uptake in the region of LPS injection after 24 h, which normalized at 120 h. Granzyme B immunofluorescence showed specific staining in tissue from the 24 h time point compared to the PBS-injected control. These findings support the use of granzyme B PET for imaging innate immunity. In certain clinical contexts, the use of GZP PET imaging may be superior to currently available agents, and we therefore suggest further preclinical studies with the ultimate goal of translation to clinical use.

A case of a critically injured diver with multiorgan failure and severe pulmonary overinflation syndrome in a resource-limited setting.

A diver practicing controlled emergency ascent training on the island of Guam suffered bilateral pneumothorax, pneumomediastinum, coronary arterial gas embolism, and developed multiple organ dysfunction syndrome. Due to limitations of available resources he was medically managed in the intensive care unit until he could be transferred to University of California San Diego for definitive management. We provide an account of our management of the patient, the pathophysiology of injury as well as a review of the safety of recreational diving skills training, current standards of practice and potential pitfalls when considering proper management of a critically injured diver.

Recent Advances in Zirconium-89 Chelator Development.

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

Immobilization of the Gas Signaling Molecule H2 S by Radioisotopes: Detection, Quantification, and In Vivo Imaging.

Hydrogen sulfide (H2 S) has multifunctional roles as a gas signaling molecule in living systems. However, the efficient detection and imaging of H2 S in live animals is very challenging. Herein, we report the first radioisotope-based immobilization technique for the detection, quantification, and in vivo imaging of endogenous H2 S. Macrocyclic (64) Cu complexes that instantly reacted with gaseous H2 S to form insoluble (64) CuS in a highly sensitive and selective manner were prepared. The H2 S concentration in biological samples was measured by a thin-layer radiochromatography method. When (64) Cu-cyclen was injected into mice, an elevated H2 S concentration in the inflamed paw was clearly visualized and quantified by Cerenkov luminescence and positron emission tomography (PET) imaging. PET imaging was also able to pinpoint increased H2 S levels in a millimeter-sized infarcted lesion of the rat heart.

Synthesis and Evaluation of New Generation Cross-Bridged Bifunctional Chelator for (64)Cu Radiotracers.

Bifunctional chelators have been successfully used to construct (64)Cu-labeled radiopharmaceuticals. Previously reported chelators with cross-bridged cyclam backbones have various essential features such as high stability of the copper(II) complex, high efficiency of radiolabeling at room temperature, and good biological inertness of the radiolabeled complex, along with rapid body clearance. Here, we report a new generation propylene-cross-bridged chelator with hybrid acetate/phosphonate pendant groups (PCB-TE1A1P) developed with the aim of combining these key properties in a single chelator. The PCB-TE1A1P was synthesized from cyclam with good overall yield. The Cu(II) complex of our chelator showed good robustness in kinetic stability evaluation experiments, such as acidic decomplexation and cyclic voltammetry studies. The Cu(II) complex of PCB-TE1A1P remained intact under highly acidic conditions (12 M HCl, 90 °C) for 8 d and showed quasi-reversible reduction/oxidation peaks at -0.77 V in electrochemical studies. PCB-TE1A1P was successfully radiolabeled with (64)Cu ions in an acetate buffer at 60 °C within 60 min. The electrophoresis study revealed that the (64)Cu-PCB-TE1A1P complex has net negative charge in aqueous solution. The biodistribution and in vivo stability study profiles of (64)Cu-PCB-TE1A1P indicated that the radioactive complex was stable under physiological conditions and cleared rapidly from the body. A whole body positron emission tomography (PET) imaging study further confirmed high in vivo stability and fast clearance of the complex in mouse models. In conclusion, PCB-TE1A1P has good potential as a bifunctional chelator for (64)Cu-based radiopharmaceuticals, especially those involving peptides.

New bifunctional chelator for 64Cu-immuno-positron emission tomography.

A new tetraazamacrocyclic bifunctional chelator, TE2A-Bn-NCS, was synthesized in high overall yield from cyclam. An extra functional group (NCS) was introduced to the N-atom of TE2A for specific conjugation with antibody. The Cu complex of TE2A-Bn-NCS showed high kinetic stability in acidic decomplexation and cyclic voltammetry studies. X-ray structure determination of the Cu-TE2A-Bn-NH2 complex confirmed octahedral geometry, in which copper atom is strongly coordinated by four macrocyclic nitrogens in equatorial positions and two carboxylate oxygen atoms occupy the elongated axial positions. Trastuzumab was conjugated with TE2A-Bn-NCS and then radiolabeled with 64Cu quantitatively at room temperature within 10 min. Biodistribution studies showed that the 64Cu-labeled TE2A-Bn-NCS-trastuzumab conjugates maintain high stability in physiological conditions, and NIH3T6.7 tumors were clearly visualized up to 3 days by 64Cu-immuno-positron emission tomography imaging in animal models.

Evaluating the Combined Anticancer Response of Checkpoint Inhibitor Immunotherapy and FAP-Targeted Molecular Radiotherapy in Murine Models of Melanoma and Lung Cancer.

Immunotherapy has dramatically improved outcomes for some cancer patients; however, novel treatments are needed for more patients to achieve a long-lasting response. FAP-targeted molecular radiotherapy has shown efficacy in both preclinical and clinical models and has immunomodulatory effects. Here, we studied if combined immunotherapy and radiotherapy could increase antitumor efficacy in murine models of lung cancer and melanoma and interrogated the mechanisms by which these treatments attenuate tumor growth. Using LLC1 and B16F10 murine models of lung cancer and melanoma, respectively, we tested the efficacy of 177Lu-FAPI-04 alone and in combination with immunotherapy. Alone, 177Lu-FAPI-04 significantly reduced tumor growth in both models. In animals with melanoma, combined therapy resulted in tumor regression while lung tumor growth was attenuated, but tumors did not regress. Combined therapy significantly increased caspase-3 and decreased Ki67 compared with immunotherapy alone. Flow cytometry demonstrated that tumor-associated macrophages responded in a tumor-dependent manner which was distinct in animals treated with both therapies compared with either therapy alone. These data demonstrate that 177Lu-FAPI-04 is an effective anticancer therapy for melanoma and lung cancer which mediates effects at least partially through induction of apoptosis and modulation of the immune response. Translational studies with immunotherapy and 177Lu-FAPI-04 are needed to demonstrate the clinical efficacy of this combined regimen.

Immuno-PET Monitoring of Lymphocytes Using the CD8-Specific Antibody REGN5054.

Assessment of immune-cell subsets within the tumor immune microenvironment is a powerful approach to better understand cancer immunotherapy responses. However, the use of biopsies to assess the tumor immune microenvironment poses challenges, including the potential for sampling error, restricted sampling over time, and inaccessibility of some tissues/organs, as well as the fact that single biopsy analyses do not reflect discordance across multiple intrapatient tumor lesions. Immuno-positron emission tomography (PET) presents a promising translational imaging approach to address the limitations and assess changes in the tumor microenvironment. We have developed 89Zr-DFO-REGN5054, a fully human CD8A-specific antibody conjugate, to assess CD8+ tumor-infiltrating lymphocytes (TIL) pre- and posttherapy. We used multiple assays, including in vitro T-cell activation, proliferation, and cytokine production, and in vivo viral clearance and CD8 receptor occupancy, to demonstrate that REGN5054 has minimal impact on T-cell activity. Preclinical immuno-PET studies demonstrated that 89Zr-DFO-REGN5054 specifically detected CD8+ T cells in lymphoid tissues of CD8-genetically humanized immunocompetent mice (VelociT mice) and discerned therapy-induced changes in CD8+ TILs in two models of response to a CD20xCD3 T-cell activating bispecific antibody (REGN1979, odronextamab). Toxicology studies in cynomolgus monkeys showed no overt toxicity, and immuno-PET imaging in cynomolgus monkeys demonstrated dose-dependent clearance and specific targeting to lymphoid tissues. This work supports the clinical investigation of 89Zr-DFO-REGN5054 to monitor T-cell responses in patients undergoing cancer immunotherapy.

Imaging Strategy that Achieves Ultrahigh Contrast by Utilizing Differential Esterase Activity in Organs: Application in Early Detection of Pancreatic Cancer.

Most nanoparticles show much higher uptake in mononuclear phagocyte system (MPS) organs than in tumors, which has been a long-lasting dilemma in nanomedicine. Here, we report an imaging strategy that selectively decreases MPS organ uptakes by utilizing the differential esterase activity in tumors and other organs. When an esterase-labile radiotracer loaded liposome was injected into the body, radioactivity was rapidly excreted from the liver and spleen after breakage of the ester bond by esterase. However, the lipophilic radiotracer delivered to the tumor remained in the tumor with minimal bond cleavage. The underlying mechanism was fully characterized in vitro and in vivo in colon tumor models. As a proof of concept, the liposomal radiotracer was further optimized for the early detection of pancreatic cancer. The folate-coated liposomal radiotracer showed highly selective tumor uptake. At 4 h postinjection, a pancreatic tumor a few millimeters in size was unambiguously visualized in orthotopic tumor models by PET imaging. At 24 h, an exceptionally high tumor-to-background ratio was achieved, enabling the visualization of tumors alone with minimal background noise. More than 9% of the total radioactivity was found in the tumor. Utilizing our imaging strategy, various tumor imaging agents can be developed for sensitive detection with ultrahigh contrast.

3D optical/CT as a preclinical companion imaging platform for glioblastoma drug development.

Multimodality 3D Optical Imaging (OI)/CT has the potential to play a major role in drug development for glioblastomas (GBM), as it is an accessible preclinical method. To demonstrate the potential of 3D OI/CT to visualize orthotopic GBM implantation, we labeled GBM cells with Cy7 and imaged their location using 3D OI/CT. To confirm the accuracy of the spatial localization and demonstrate the ability to image locoregionally delivered therapies, we labeled mouse albumin with Cy7 (Cy7ALB) and delivered it via locoregional infusion 1 mm or 3 mm into the brain and demonstrated correlation of signal between the 3D OI/CT and post necropsy brain slices. In addition, we demonstrated the potential of systemically delivered Cy7ALB contrast to detect blood-brain barrier (BBB) permeability caused by orthotopic GBMs using 3D OI/CT. We also tested the potential of 3D OI/CT to assess focal BBB permeability induced by high intensity focused ultrasound (HIFU), a methodology being used in clinical trials to noninvasively permeabilize the BBB for systemic therapeutic delivery to GBM. We demonstrated the ability of systemic Cy7ALB contrast together with 3D OI/CT to accurately assess real-time HIFU-induced BBB permeability, which correlated to post necropsy imaging of brains. Furthermore, we demonstrated that 3D OI/CT can also image the therapeutic distribution of a Cy7-labeled anti-PD-1 antibody, a prototype translational antibody therapy. We successfully imaged real-time antibody distribution after HIFU-induced BBB permeability, which correlated with post necropsy Cy7 signal and translational PET imaging after injection of [89Zr] anti-PD-1 antibody. Thus, we demonstrated the broad potential of using 3D OI/CT as an accessible preclinical tool to develop anti-GBM therapies.

Multimodality molecular imaging of the alveolar-capillary barrier in lung disease using albumin based optical and PET tracers.

Inflammatory changes caused by viruses, bacteria, exposure to toxins, commonly used drugs and even surgical intervention have the potential of causing abnormal epithelial permeability, which is manifest as infiltrative processes on computed tomography (CT), including the widespread infiltrates seen in COVID-19 pneumonia and acute respiratory distress syndrome (ARDS). We utilized a previously published mouse model of ARDS, intranasal delivery of LPS, to induce the alveolar-capillary barrier permeability seen in lung disease. We intravenously injected mice with Cy7 or 68-Gallium (68Ga) labeled mouse albumin and imaged using optical imaging (OI)/CT and PET. We observed significantly increased lung levels of Cy7-albumin on 3D OI/CT, which matched the abnormal appearance on microCT. This uptake correlated with fluorescence seen on sectioned lungs. To examine the translational potential of these findings, we radiolabeled albumin with 68Ga. We found that in mice with LPS-induced lung injury, 68Ga-albumin PET correlated with our optical imaging findings and demonstrated abnormal activity in the lung fields, indicative of abnormal epithelial permeability. These findings indicate 68Ga-albumin can be utilized as a sensitive translational radiotracer for quantifying the abnormal epithelial permeability that is seen in various lung pathologies, including COVID-19 induced pneumonia and ARDS. The ability to use Cy7-albumin 3D OI/CT imaging as a preclinical translational surrogate for 68Ga-albumin offers an accessible high throughput means to rapidly screen potential therapeutics against lung diseases that clinically manifest with endothelial permeability.

89Zr-Chloride Can Be Used for Immuno-PET Radiochemistry Without Loss of Antigen Reactivity In Vivo.

89Zr immuno-PET continues to be assessed in numerous clinical trials. This report evaluates the use of 89Zr-chloride in the radiolabeling of monoclonal antibodies conjugated with desferrioxamine B (DFO), describes its effects on radiopharmaceutical reactivity toward antigen, and offers guidance on how to ensure long-term stability and purity. Methods:89Zr-DFO-trastuzumab and 89Zr-DFO-cetuximab were prepared using 89ZrCl4 The stability of each was evaluated for 7 d in 20 mM histidine/240 mM sucrose buffer, 0.25 M sodium acetate (NaOAc) buffer containing 5 mg·mL-1n-acetyl-l-cysteine (NAC), or 0.25 M NaOAc containing 5 mg·mL-1 l-methionine (L-MET). To assess antigen reactivity, 89Zr-DFO-trastuzumab was evaluated using the Lindmo method and tested in PET/CT imaging of mouse models of human epidermal growth factor receptor 2-positive or -negative lung cancer. Results: Using 89ZrCl4, 89Zr-DFO-trastuzumab and 89Zr-DFO-cetuximab were prepared with increased specific activity and retained purities of 95% after 3 d when formulated in NaOAc buffer containing L-MET. Based on Lindmo analysis and small-animal PET/CT imaging, 89Zr-DFO-trastuzumab remained reactive toward antigen after being prepared with 89ZrCl4Conclusion:89ZrCl4 facilitated the radiosynthesis of 89Zr immuno-PET agents with increased specific activity. L-MET enhanced long-term solution stability better than all other formulations examined, and 89Zr-DFO-trastuzumab remained reactive toward antigen. Although further evaluation is necessary, these initial results suggest that 89ZrCl4 may be useful in immuno-PET radiochemistry as radiolabeled monoclonal antibodies are increasingly integrated into precision medicine strategies.

Melanocortin 1 Receptor-Targeted α-Particle Therapy for Metastatic Uveal Melanoma.

New effective therapies are greatly needed for metastatic uveal melanoma, which has a very poor prognosis with a median survival of less than 1 y. The melanocortin 1 receptor (MC1R) is expressed in 94% of uveal melanoma metastases, and a MC1R-specific ligand (MC1RL) with high affinity and selectivity for MC1R was previously developed. Methods: The 225Ac-DOTA-MC1RL conjugate was synthesized in high radiochemical yield and purity and was tested in vitro for biostability and for MC1R-specific cytotoxicity in uveal melanoma cells, and the lanthanum-DOTA-MC1RL analog was tested for binding affinity. Non-tumor-bearing BALB/c mice were tested for maximum tolerated dose and biodistribution. Severe combined immunodeficient mice bearing uveal melanoma tumors or engineered MC1R-positive and -negative tumors were studied for biodistribution and efficacy. Radiation dosimetry was calculated using mouse biodistribution data and blood clearance kinetics from Sprague-Dawley rat data. Results: High biostability, MC1R-specific cytotoxicity, and high binding affinity were observed. Limiting toxicities were not observed at even the highest administered activities. Pharmacokinetics and biodistribution studies revealed rapid blood clearance (<15 min), renal and hepatobillary excretion, MC1R-specific tumor uptake, and minimal retention in other normal tissues. Radiation dosimetry calculations determined pharmacokinetics parameters and absorbed α-emission dosages from 225Ac and its daughters. Efficacy studies demonstrated significantly prolonged survival and decreased metastasis burden after a single administration of 225Ac-DOTA-MC1RL in treated mice relative to controls. Conclusion: These results suggest significant potential for the clinical translation of 225Ac-DOTA-MC1RL as a novel therapy for metastatic uveal melanoma.

A comprehensively revised strategy that improves the specific activity and long-term stability of clinically relevant 89Zr-immuno-PET agents.

Zirconium-89 is currently being used in numerous clinical trials involving monoclonal antibodies and positron emission tomography. This report describes a revised strategy that reduces preparation time while increasing the specific activity of clinically relevant immuno-PET agents. Additionally, it demonstrates that n-acetyl-l-cysteine acts as a superior radioprotective agent that improves long-term stability without compromising antigen affinity in vivo.

Practical Guidelines for Cerenkov Luminescence Imaging with Clinically Relevant Isotopes.

Cerenkov luminescence imaging (CLI) is a relatively new imaging modality that utilizes conventional optical imaging instrumentation to detect Cerenkov radiation derived from standard and often clinically approved radiotracers. Its research versatility, low cost, and ease of use have increased its popularity within the molecular imaging community and at institutions that are interested in conducting radiotracer-based molecular imaging research, but that lack the necessary resources and infrastructure. Here, we provide a description of the materials and procedures necessary to conduct a Cerenkov luminescence imaging experiment using a variety of imaging instrumentation, radionuclides, and animal models.

High in Vivo Stability of 64Cu-Labeled Cross-Bridged Chelators Is a Crucial Factor in Improved Tumor Imaging of RGD Peptide Conjugates.

Although the importance of bifunctional chelators (BFCs) is well recognized, the chemophysical parameters of chelators that govern the biological behavior of the corresponding bioconjugates have not been clearly elucidated. Here, five BFCs closely related in structure were conjugated with a cyclic RGD peptide and radiolabeled with Cu-64 ions. Various biophysical and chemical properties of the Cu(II) complexes were analyzed with the aim of identifying correlations between individual factors and the biological behavior of the conjugates. Tumor uptake and body clearance of the 64Cu-labeled bioconjugates were directly compared by animal PET imaging in animal models, which was further supported by biodistribution studies. Conjugates containing propylene cross-bridged chelators showed higher tumor uptake, while a closely related ethylene cross-bridged analogue exhibited rapid body clearance. High in vivo stability of the copper-chelator complex was strongly correlated with high tumor uptake, while the overall lipophilicity of the bioconjugate affected both tumor uptake and body clearance.

Evaluation of macrocyclic hydroxyisophthalamide ligands as chelators for zirconium-89.

The development of bifunctional chelators (BFCs) for zirconium-89 immuno-PET applications is an area of active research. Herein we report the synthesis and evaluation of octadentate hydroxyisophthalamide ligands (1 and 2) as zirconium-89 chelators. While both radiometal complexes could be prepared quantitatively and with excellent specific activity, preparation of 89Zr-1 required elevated temperature and an increased reaction time. 89Zr-1 was more stable than 89Zr-2 when challenged in vitro by excess DTPA or serum proteins and in vivo during acute biodistribution studies. Differences in radiometal complex stability arise from structural changes between the two ligand systems, and suggest further ligand optimization is necessary to enhance 89Zr chelation.

Zirconium tetraazamacrocycle complexes display extraordinary stability and provide a new strategy for zirconium-89-based radiopharmaceutical development.

We report our initial investigations into the use of tetraazamacrocycles as zirconium-89 chelators. We describe the synthesis and complete characterization of several Zr tetraazamacrocycle complexes, and definitively describe the first crystal structure of zirconium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Zr-DOTA) using single crystal X-ray diffraction analysis. After evaluating several radioactive analogs, we found that 89Zr-DOTA is superior to 89Zr-DFO, the only 89Zr-complex to be used clinically in 89Zr-radiopharmaceutical applications. Finally, we provide a rationale for the unanticipated and extraordinary stability of these complexes in vitro and in vivo. These results may inform the development of safer and more robust immuno-PET agents for precision medicine applications.