Noninvasive brain cancer imaging with a bispecific antibody fragment, generated via click chemistry

Discovery of a highly specific radiolabeled antibody targeting B-cell maturation antigen: Applications in PET imaging of multiple myeloma

PURPOSE

Multiple myeloma (MM) is characterized by the uncontrolled proliferation of monoclonal plasma cells (PC) in the bone marrow (BM). B-cell maturation antigen (BCMA) is predominantly expressed in malignant plasma cells, and associated with the proliferation, survival, and progression of various myeloma cells. Given these important roles, BCMA emerges as an ideal target antigen for MM therapy. However, effective stratification of patients who may benefit from targeted BCMA therapy and real-time monitoring the therapeutic efficacy poses significant clinical challenge. This study aims to develop a BCMA targeted diagnostic modality, and preliminarily explore its potential value in the radio-immunotherapy of MM.

EXPERIMENTAL DESIGN

Using zirconium-89 (89Zr, t1/2 = 78.4 h) for labeling the BCMA-specific antibody, the BCMA-targeting PET tracer [89Zr]Zr-DFO-BCMAh230430 was prepared. The EC50 values of BCMAh230430 and DFO-BCMAh230430 were determined by ELISA assay. BCMA expression was assessed in four different tumor cell lines (MM.1S, RPMI 8226, BxPC-3, and KYSE520) through Western blot and flow cytometry. In vitro binding affinity was determined by cell uptake studies of [89Zr]Zr-DFO-BCMAh230430 in these tumor cell lines. For in vivo evaluation, PET imaging and ex vivo biodistribution studies were conducted in tumor-bearing mice to evaluate imaging performance and systemic distribution of [89Zr]Zr-DFO-BCMAh230430. Immunochemistry analysis was performed to detect BCMA expression in tumor tissues, confirming the specificity of our probe. Furthermore, we explored the anti-tumor efficacy of Lutetium-177 labeled BCMA antibody, [177Lu]Lu-DTPA-BCMAh230430, in tumor bearing-mice to validate its radioimmunotherapy potential.

RESULTS

The radiolabeling of [89Zr]Zr-DFO-BCMAh230430 and [177Lu]Lu-DTPA-BCMAh230430 showed satisfactory radiocharacteristics, with a radiochemical purity exceeding 99%. ELISA assay results revealed closely aligned EC50 values for BCMAh230430 and DFO-BCMAh230430, which are 57 pM and 67 pM, respectively. Western blot and flow cytometry analyses confirmed the highest BCMA expression level. Cell uptake data indicated that MM.1S cells had a total cellular uptake (the sum of internalization and surface binding) of 38.3% ± 1.53% for [89Zr]Zr-DFO-BCMAh230430 at 12 h. PET imaging of [89Zr]Zr-DFO-BCMAh230430 displayed radioactive uptake of 7.71 ± 0.67%ID/g in MM.1S tumors and 4.13 ± 1.21%ID/g in KYSE520 tumors at 168 h post-injection (n = 4) (P < 0.05), consistent with ex vivo biodistribution studies. Immunohistochemical analysis of tumor tissues confirmed higher BCMA expression in MM.1S tumors xenograft compared to KYSE520 tumors. Notably, [177Lu]Lu-DTPA-BCMAh230430 showed some anti-tumor efficacy, evidenced by slowed tumor growth. Furthermore, no significant difference in body weight was observed in MM.1S tumor-bearing mice over 14 days of administration with or without [177Lu]Lu-DTPA-BCMAh230430.

CONCLUSIONS

Our study has successfully validated the essential role of [89Zr]Zr-DFO-BCMAh230430 in non-invasively monitoring BCMA status in MM tumors, showing favorable tumor uptake and specific binding affinity to MM tumors. Furthermore, our research revealed, as a proof-of-concept, the effectiveness of [177Lu]Lu-DTPA-BCMAh230430 in radioimmunotherapy for MM tumors. In conclusion, we present a novel BCMA antibody-based radiotheranostic modality that holds promise for achieving efficient and precise MM diagnostic and therapy.

Glioma stem cells remodel immunotolerant microenvironment in GBM and are associated with therapeutic advancements

Glioma is the most common primary tumor of the central nervous system (CNS). Glioblastoma (GBM) is incurable with current treatment strategies. Additionally, the treatment of recurrent GBM (rGBM) is often referred to as terminal treatment, necessitating hospice-level care and management. The presence of the blood-brain barrier (BBB) gives GBM a more challenging or "cold" tumor microenvironment (TME) than that of other cancers and gloma stem cells (GSCs) play an important role in the TME remodeling, occurrence, development and recurrence of giloma. In this review, our primary focus will be on discussing the following topics: niche-associated GSCs and macrophages, new theories regarding GSC and TME involving pyroptosis and ferroptosis in GBM, metabolic adaptations of GSCs, the influence of the cold environment in GBM on immunotherapy, potential strategies to transform the cold GBM TME into a hot one, and the advancement of GBM immunotherapy and GBM models.

Engineered Antibodies as Cancer Radiotheranostics

Radiotheranostics is a rapidly growing approach in personalized medicine, merging diagnostic imaging and targeted radiotherapy to allow for the precise detection and treatment of diseases, notably cancer. Radiolabeled antibodies have become indispensable tools in the field of cancer theranostics due to their high specificity and affinity for cancer-associated antigens, which allows for accurate targeting with minimal impact on surrounding healthy tissues, enhancing therapeutic efficacy while reducing side effects, immune-modulating ability, and versatility and flexibility in engineering and conjugation. However, there are inherent limitations in using antibodies as a platform for radiopharmaceuticals due to their natural activities within the immune system, large size preventing effective tumor penetration, and relatively long half-life with concerns for prolonged radioactivity exposure. Antibody engineering can solve these challenges while preserving the many advantages of the immunoglobulin framework. In this review, the goal is to give a general overview of antibody engineering and design for tumor radiotheranostics. Particularly, the four ways that antibody engineering is applied to enhance radioimmunoconjugates: pharmacokinetics optimization, site-specific bioconjugation, modulation of Fc interactions, and bispecific construct creation are discussed. The radionuclide choices for designed antibody radionuclide conjugates and conjugation techniques and future directions for antibody radionuclide conjugate innovation and advancement are also discussed.

Targeted Radionuclide Therapy in Glioblastoma

Despite the development of various novel therapies, glioblastoma (GBM) remains a devastating disease, with a median survival of less than 15 months. Recently, targeted radionuclide therapy has shown significant progress in treating solid tumors, with the approval of Lutathera for neuroendocrine tumors and Pluvicto for prostate cancer by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). This achievement has shed light on the potential of targeted radionuclide therapy for other solid tumors, including GBM. This review presents the current status of targeted radionuclide therapy in GBM, highlighting the commonly used therapeutic radionuclides emitting alpha, beta particles, and Auger electrons that could induce potent molecular and cellular damage to treat GBM. We then explore a range of targeting vectors, including small molecules, peptides, and antibodies, which selectively target antigen-expressing tumor cells with minimal or no binding to healthy tissues. Considering that radiopharmaceuticals for GBM are often administered locoregionally to bypass the blood-brain barrier (BBB), we review prominent delivery methods such as convection-enhanced delivery, local implantation, and stereotactic injections. Finally, we address the challenges of this therapeutic approach for GBM and propose potential solutions.

A bibliometric and knowledge-map analysis of bispecific antibodies in cancer immunotherapy from 2000 to 2023

Background

Bispecific antibody (BsAb)-based cancer immunotherapy has provided new avenues for the treatment of various malignancies. The approval of Blinatumomab has encouraged further investigation into these treatments, and a series of preclinical and clinical trials have been conducted, together with the publication of numerous articles. Here, the knowledge structure of BsAb-based cancer immunotherapy is summarized using bibliometric analysis to provide in-depth insight into current research trends and foci.

Methods

The studies included in the bibliometric analysis of BsAbs in cancer immunotherapy were retrieved from the online Web of Science Core Collection (WOSCC) database on April 16th, 2023. Visualization analysis was performed with the help of CtieSpace (version 6.2.2.msi [64-bit]), VOSviewer (version 1.6.19), R (version 4.2.1), and the Bibliometric analysis platform (R-based online data processing tool).

Results

A total of 1750 papers were identified. Analysis of annual publications and total citations indicated that publications have increased steadily over the past few decades. The USA, followed by Germany, had largest number of publications, making significant contributions to the field. The Memorial Sloan Kettering Cancer Center received the highest number of citations (n = 3769). However, its collaboration and cooperation with different institutions require further strengthening. MAbs and Clinical Cancer Research published the most papers, while Blood and Cancer Research were the most commonly co-cited journals. DM Goldenberg from the USA published the most articles with the highest H-index (34), and the most co-cited author (2137 citations) was PA Baeuerle; both these authors have distinguished achievements in this field. Analysis of co-cited references and keywords showed that the hotspots and research focus on the use of BsAbs for solid tumors have increased rapidly while the application of BsAb immunotherapy in hematologic malignancies has expanded significantly. The hot topics in the field included cytokine release syndrome, the efficacy and safety of BsAbs, resistance mechanisms, and the exploration and optimization of combination therapies.

Conclusion

Cancer immunotherapies based on BsAbs are a hot topic in research. Current studies focus on the construction and optimization of BsAb structure, as well as their combination with other treatment modalities to improve their efficacy and overcome resistance. Furthermore, it is expected that the ongoing investigation of BsAb-based immunotherapy for solid tumors will bear fruit with significant clinical application prospects in the near future.

Crosstalk with lung fibroblasts shapes the growth and therapeutic response of mesothelioma cells

Mesothelioma is an aggressive cancer of the mesothelial layer associated with an extensive fibrotic response. The latter is in large part mediated by cancer-associated fibroblasts which mediate tumour progression and poor prognosis. However, understanding of the crosstalk between cancer cells and fibroblasts in this disease is mostly lacking. Here, using co-cultures of patient-derived mesothelioma cell lines and lung fibroblasts, we demonstrate that fibroblast activation is a self-propagated process producing a fibrotic extracellular matrix (ECM) and triggering drug resistance in mesothelioma cells. Following characterisation of mesothelioma cells/fibroblasts signalling crosstalk, we identify several FDA-approved targeted therapies as far more potent than standard-of-care Cisplatin/Pemetrexed in ECM-embedded co-culture spheroid models. In particular, the SRC family kinase inhibitor, Saracatinib, extends overall survival well beyond standard-of-care in a mesothelioma genetically-engineered mouse model. In short, we lay the foundation for the rational design of novel therapeutic strategies targeting mesothelioma/fibroblast communication for the treatment of mesothelioma patients.

Fluorescence, ultrasonic and photoacoustic imaging for analysis and diagnosis of diseases

Biomedical imaging technology, which allows us to peer deeply within living subjects and visually explore the delivery and distribution of agents in living things, is producing tremendous opportunities for the early diagnosis and precise therapy of diseases. In this feature article, based on reviewing the latest representative examples of progress together with our recent efforts in the bioimaging field, we intend to introduce three typical kinds of non-invasive imaging technologies, i.e., fluorescence, ultrasonic and photoacoustic imaging, in which optical and/or acoustic signals are employed for analyzing various diseases. In particular, fluorescence imaging possesses a series of outstanding advantages, such as high temporal resolution, as well as rapid and sensitive feedback. Hence, in the first section, we will introduce the latest studies on developing novel fluorescence imaging methods for imaging bacterial infections, cancer and lymph node metastasis in a long-term and real-time manner. However, the issues of imaging penetration depth induced by photon scattering and light attenuation of biological tissue limit their widespread in vivo imaging applications. Taking advantage of the excellect penetration depth of acoustic signals, ultrasonic imaging has been widely applied for determining the location, size and shape of organs, identifying normal and abnormal tissues, as well as confirming the edges of lesions in hospitals. Thus, in the second section, we will briefly summarize recent advances in ultrasonic imaging techniques for diagnosing diseases in deep tissues. Nevertheless, the absence of lesion targeting and dependency on a professional technician may lead to the possibility of false-positive diagnosis. By combining the merits of both optical and acoustic signals, newly-developed photoacoustic imaging, simultaneously featuring higher temporal and spatial resolution with good sensitivity, as well as deeper penetration depth, is discussed in the third secretion. In the final part, we further discuss the major challenges and prospects for developing imaging technology for accurate disease diagnosis. We believe that these non-invasive imaging technologies will introduce a new perspective for the precise diagnosis of various diseases in the future.

ImmunoPET Directed to the Brain: A New Tool for Preclinical and Clinical Neuroscience

Immuno-positron emission tomography (immunoPET) is a non-invasive in vivo imaging method based on tracking and quantifying radiolabeled monoclonal antibodies (mAbs) and other related molecules, such as antibody fragments, nanobodies, or affibodies. However, the success of immunoPET in neuroimaging is limited because intact antibodies cannot penetrate the blood-brain barrier (BBB). In neuro-oncology, immunoPET has been successfully applied to brain tumors because of the compromised BBB. Different strategies, such as changes in antibody properties, use of physiological mechanisms in the BBB, or induced changes to BBB permeability, have been developed to deliver antibodies to the brain. These approaches have recently started to be applied in preclinical central nervous system PET studies. Therefore, immunoPET could be a new approach for developing more specific PET probes directed to different brain targets.

Hetero-bivalent agents targeting FAP and PSMA

PURPOSE

We developed a theranostic radiopharmaceutical that engages two key cell surface proteases, fibroblast activation protein alpha (FAP) and prostate-specific membrane antigen (PSMA), each frequently overexpressed within the tumor microenvironment (TME). The latter is also expressed in most prostate tumor epithelium. To engage a broader spectrum of cancers for imaging and therapy, we conjugated small-molecule FAP and PSMA-targeting moieties using an optimized linker to provide ⁶⁴Cu-labeled compounds.

METHODS

We synthesized FP-L1 and FP-L2 using two linker constructs attaching the FAP and PSMA-binding pharmacophores. We determined in vitro inhibition constants (K_i) for FAP and PSMA. Cell uptake assays and flow cytometry were conducted in human glioma (U87), melanoma (SK-MEL-24), prostate cancer (PSMA + PC3 PIP and PSMA - PC3 flu), and clear cell renal cell carcinoma lines (PSMA + /PSMA - 786-O). Quantitative positron emission tomography/computed tomography (PET/CT) and tissue biodistribution studies were performed using U87, SK-MEL-24, PSMA + PC3 PIP, and PSMA + 786-O experimental xenograft models and the KPC genetically engineered mouse model of pancreatic cancer.

RESULTS

⁶⁴Cu-FP-L1 and ⁶⁴Cu-FP-L2 were produced in high radiochemical yields (> 98%) and molar activities (> 19 MBq/nmol). K_i values were in the nanomolar range for both FAP and PSMA. PET imaging and biodistribution studies revealed high and specific targeting of ⁶⁴Cu-FP-L1 and ⁶⁴Cu-FP-L2 for FAP and PSMA. ⁶⁴Cu-FP-L1 displayed more favorable pharmacokinetics than ⁶⁴Cu-FP-L2. In the U87 tumor model at 2 h post-injection, tumor uptake of ⁶⁴Cu-FP-L1 (10.83 ± 1.02%ID/g) was comparable to ⁶⁴Cu-FAPI-04 (9.53 ± 2.55%ID/g). ⁶⁴Cu-FP-L1 demonstrated high retention 5.34 ± 0.29%ID/g at 48 h in U87 tumor. Additionally, ⁶⁴Cu-FP-L1 showed high retention in PSMA + PC3 PIP tumor (12.06 ± 0.78%ID/g at 2 h and 10.51 ± 1.82%ID/g at 24 h).

CONCLUSIONS

⁶⁴Cu-FP-L1 demonstrated high and specific tumor targeting of FAP and PSMA. This compound should enable imaging of lesions expressing FAP, PSMA, or both on the tumor cell surface or within the TME. FP-L1 can readily be converted into a theranostic for the management of heterogeneous tumors.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Laser capture microdissection-capillary zone electrophoresis-tandem mass spectrometry (LCM-CZE-MS/MS) for spatially resolved top-down proteomics: a pilot study of zebrafish brain

Mass spectrometry (MS)-based spatially resolved top-down proteomics (TDP) of tissues is crucial for understanding the roles played by microenvironmental heterogeneity in the biological functions of organs and for discovering new proteoform biomarkers of diseases. There are few published spatially resolved TDP studies. One of the challenges relates to the limited performance of TDP for the analysis of spatially isolated samples using, for example, laser capture microdissection (LCM) because those samples are usually mass-limited. We present the first pilot study of LCM-capillary zone electrophoresis (CZE)-MS/MS for spatially resolved TDP and used zebrafish brain as the sample. The LCM-CZE-MS/MS platform employed a non-ionic detergent and a freeze-thaw method for efficient proteoform extraction from LCM isolated brain sections followed by CZE-MS/MS without any sample cleanup step, ensuring high sensitivity. Over 400 proteoforms were identified in a CZE-MS/MS analysis of one LCM brain section via consuming the protein content of roughly 250 cells. We observed drastic differences in proteoform profiles between two LCM brain sections isolated from the optic tectum (Teo) and telencephalon (Tel) regions. Proteoforms of three proteins (npy, penkb, and pyya) having neuropeptide hormone activity were exclusively identified in the isolated Tel section. Proteoforms of reticulon, myosin, and troponin were almost exclusively identified in the isolated Teo section, and those proteins play essential roles in visual and motor activities. The proteoform profiles accurately reflected the main biological functions of the Teo and Tel regions of the brain. Additionally, hundreds of post-translationally modified proteoforms were identified.

Immunotherapy for glioblastoma: the promise of combination strategies

Glioblastoma (GBM) treatment has remained almost unchanged for more than 20 years. The current standard of care involves surgical resection (if possible) followed by concomitant radiotherapy and chemotherapy. In recent years, immunotherapy strategies have revolutionized the treatment of many cancers, increasing the hope for GBM therapy. However, mostly due to the high, multifactorial immunosuppression occurring in the microenvironment, the poor knowledge of the neuroimmune system and the presence of the blood-brain barrier, the efficacy of immunotherapy in GBM is still low. Recently, new strategies for GBM treatments have employed immunotherapy combinations and have provided encouraging results in both preclinical and clinical studies. The lessons learned from clinical trials highlight the importance of tackling different arms of immunity. In this review, we aim to summarize the preclinical evidence regarding combination immunotherapy in terms of immune and survival benefits for GBM management. The outcomes of recent studies assessing the combination of different classes of immunotherapeutic agents (e.g., immune checkpoint blockade and vaccines) will be discussed. Finally, future strategies to ameliorate the efficacy of immunotherapy and facilitate clinical translation will be provided to address the unmet medical needs of GBM.

Diagnosis of Glioblastoma by Immuno-Positron Emission Tomography

Simple Summary

Neuroimaging has transformed the way brain tumors are diagnosed and treated. Although different non-invasive modalities provide very helpful information, in some situations, they present a limited value. By merging the specificity of antibodies with the resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry”, like a “virtual biopsy”. This review provides and focuses on immuno-PET applications and future perspectives of this promising imaging approach for glioblastoma.

Abstract

Neuroimaging has transformed neuro-oncology and the way that glioblastoma is diagnosed and treated. Magnetic Resonance Imaging (MRI) is the most widely used non-invasive technique in the primary diagnosis of glioblastoma. Although MRI provides very powerful anatomical information, it has proven to be of limited value for diagnosing glioblastomas in some situations. The final diagnosis requires a brain biopsy that may not depict the high intratumoral heterogeneity present in this tumor type. The revolution in “cancer-omics” is transforming the molecular classification of gliomas. However, many of the clinically relevant alterations revealed by these studies have not yet been integrated into the clinical management of patients, in part due to the lack of non-invasive biomarker-based imaging tools. An innovative option for biomarker identification in vivo is termed “immunotargeted imaging”. By merging the high target specificity of antibodies with the high spatial resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry” in patients. This review provides the state of the art of immuno-PET applications and future perspectives on this imaging approach for glioblastoma.

64Cu-labeled daratumumab F(ab')2 fragment enables early visualization of CD38-positive lymphoma

PURPOSE

Abnormal CD38 expression in some hematologic malignancies, including lymphoma, has made it a biomarker for targeted therapies. Daratumumab (Dara) is the first FDA-approved CD38-specific monoclonal antibody, enabling successfully immunoPET imaging over the past years. Radiolabeled Dara however has a long blood circulation and delayed tumor uptake which can limit its applications. The focus of this study is to develop ⁶⁴Cu-labeled Dara-F(ab')₂ for the visualization of CD38 in lymphoma models.

METHODS

F(ab')₂ fragment was prepared from Dara using an IdeS enzyme and purified with Protein A beads. Western blotting, flow cytometry, and surface plasmon resonance (SPR) were performed for in vitro assay. Probes were labeled with ⁶⁴Cu after the chelation of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Small animal PET imaging and quantitative analysis were performed after injection of ⁶⁴Cu-labeled Dara-F(ab')₂, IgG-F(ab')₂, and Dara for evaluation in lymphoma models.

RESULTS

Flow cytometry and SPR assay proved the specific binding ability of Dara-F(ab')₂ and NOTA-Dara-F(ab')₂ in vitro. Radiolabeling yield of [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ was over 90% and with a specific activity of 4.0 ± 0.6 × 10³ MBq/μmol (n = 5). PET imaging showed [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ had a rapid and high tumor uptake as early as 2 h (6.9 ± 1.2%ID/g) and peaked (9.5 ± 0.7%ID/g) at 12 h, whereas [⁶⁴Cu]Cu-NOTA-Dara reached its tumor uptake peaked at 48 h (8.3 ± 1.4%ID/g, n = 4). In comparison, IgG-F(ab')₂ and HBL-1 control groups found no noticeable tumor uptake. [⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ had significantly lower uptake in blood pool, bone, and muscle than [⁶⁴Cu]Cu-NOTA-Dara and its tumor-to-blood and tumor-to-muscle ratios were significantly higher than controls.

CONCLUSIONS

[⁶⁴Cu]Cu-NOTA-Dara-F(ab')₂ showed a rapid and high tumor uptake in CD38-positive lymphoma models with favorable imaging contrast, showing its promise as a potential PET imaging agent for future clinical applications.

High-performance renal imaging with a radiolabeled, non-excretable chimeric fusion protein

Ideal nuclear imaging tracers should exhibit high target uptake and low background signal. Traditional renal scintigraphy and SPECT scans examine kidney function via static or dynamic tracing of radioactive probes in the kidneys. The lack of tracer affinity to specific biological processes and high background uptake from urinary excretion have added many difficulties to precision renal diagnosis. In this issue of Theranostics, Jin and colleagues innovatively devised a recombinant probe for preferential kidney imaging through targeting of tubular neonatal Fc receptor and proximal tubular basement membrane for sustained tubular reabsorption and accumulation. This work has broad implications regarding how an in depth understanding of physiology and pathology may be of service for tracer development, renal diagnosis, and disease theranostics.

Glioblastoma multiforme (GBM): An overview of current therapies and mechanisms of resistance

Glioblastoma multiforme (GBM) is a WHO grade IV glioma and the most common malignant, primary brain tumor with a 5-year survival of 7.2%. Its highly infiltrative nature, genetic heterogeneity, and protection by the blood brain barrier (BBB) have posed great treatment challenges. The standard treatment for GBMs is surgical resection followed by chemoradiotherapy. The robust DNA repair and self-renewing capabilities of glioblastoma cells and glioma initiating cells (GICs), respectively, promote resistance against all current treatment modalities. Thus, durable GBM management will require the invention of innovative treatment strategies. In this review, we will describe biological and molecular targets for GBM therapy, the current status of pharmacologic therapy, prominent mechanisms of resistance, and new treatment approaches. To date, medical imaging is primarily used to determine the location, size and macroscopic morphology of GBM before, during, and after therapy. In the future, molecular and cellular imaging approaches will more dynamically monitor the expression of molecular targets and/or immune responses in the tumor, thereby enabling more immediate adaptation of tumor-tailored, targeted therapies.

Curcumin loaded sub-30 nm targeting therapeutic lipid nanoparticles for synergistically blocking nasopharyngeal cancer growth and metastasis

Systemic chemotherapy is still the primary treatment for advanced-stage nasopharyngeal carcinoma (NPC), but only limited therapeutic success has been achieved in the past decade because of drug resistance and systemic toxicity. Curcumin (Cur) is an effective alternative to chemotherapeutics because it showed remarkable therapeutic potential in the treatment of NPC. However, lack of tissue specificity and poor penetration in solid tumors are the major obstacles to effective therapy. Therefore, in this work, a self-assembled sub-30 nm therapeutic lipid nanoparticle loaded with Cur, named as Cur@α-NTP-LN, was constructed, specifically targeting scavenger receptor class B member 1 (SR-B1) and enhancing its therapeutic effects on NPC in vivo. Our results showed that Cur@α-NTP-LNs were effective and superior to free Cur on NPC cell-specific targeting, suppressing cell proliferation and inducing cell apoptosis. In vivo and ex vivo optical imaging revealed that Cur@α-NTP-LNs exerted high targeting efficiency, specifically accumulating in NPC xenograft tumors and delivering Cur into the tumor center after systemic administration. Furthermore, Cur@α-NTP-LNs exhibited a remarkable inhibitory effect on the growth of NPC subcutaneous tumors, with over 71 and 47% inhibition compared to Cur- and α-NTP-LNs-treated groups, respectively. In addition, Cur@α-NTP-LNs almost blocked NPC metastasis in a lung metastasis model of NPC and significantly improved the survival rate. Thus, the sub-30 nm Cur@α-NTP-LNs enhanced the solubility of Cur and demonstrated the ability of targeted Cur delivery into the center of the solid NPC tumor, performing synergistic inhibitory effects on the growth of NPC tumor and its metastasis with high efficiency.

Current State of Targeted Radiometal-Based Constructs for the Detection and Treatment of Disease in the Brain

The continual development of radiopharmaceutical agents for the field of nuclear medicine is integral to promoting the necessity of personalized medicine. One way to greatly expand the selection of radiopharmaceuticals available is to broaden the range of radionuclides employed in such agents. Widening the scope of development to include radiometals with their variety of physical decay characteristics and chemical properties opens up a myriad of possibilities for new actively targeted molecules and bioconjugates. This is especially true to further advance the imaging and treatment of disease in the brain. Over the past few decades, imaging of disease in the brain has heavily relied on agents which exploit metabolic uptake. However, through utilizing the broad range of physical characteristics that radiometals offer, the ability to target other processes has become more available. The varied chemistries of radiometals also allows for them to incorporated into specifically designed diverse constructs. A major limitation to efficient treatment of disease in the brain is the ability for relevant agents to penetrate the blood-brain barrier. Thus, along with efficient disease targeting, there must be intentional thought put into overcoming this challenge. Here, we review the current field of radiometal-based agents aimed at either imaging or therapy of brain disease that have been evaluated through at least in vivo studies.

Endoglin/CD105-Based Imaging of Cancer and Cardiovascular Diseases: A Systematic Review

Molecular imaging of pathologic lesions can improve efficient detection of cancer and cardiovascular diseases. A shared pathophysiological feature is angiogenesis, the formation of new blood vessels. Endoglin (CD105) is a coreceptor for ligands of the Transforming Growth Factor-β (TGF-β) family and is highly expressed on angiogenic endothelial cells. Therefore, endoglin-based imaging has been explored to visualize lesions of the aforementioned diseases. This systematic review highlights the progress in endoglin-based imaging of cancer, atherosclerosis, myocardial infarction, and aortic aneurysm, focusing on positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), near-infrared fluorescence (NIRF) imaging, and ultrasound imaging. PubMed was searched combining the following subjects and their respective synonyms or relevant subterms: "Endoglin", "Imaging/Image-guided surgery". In total, 59 papers were found eligible to be included: 58 reporting about preclinical animal or in vitro models and one ex vivo study in human organs. In addition to exact data extraction of imaging modality type, tumor or cardiovascular disease model, and tracer (class), outcomes were described via a narrative synthesis. Collectively, the data identify endoglin as a suitable target for intraoperative and diagnostic imaging of the neovasculature in tumors, whereas for cardiovascular diseases, the evidence remains scarce but promising.

Pinpointing Brain TREM2 Levels in Two Mouse Models of Alzheimer's Disease

PURPOSE

The triggering receptor expressed on myeloid cells 2 (TREM2) is expressed by brain microglia. Microglial activation, as observed in Alzheimer's disease (AD) as well as in transgenic mice expressing human amyloid-beta, appears to increase soluble TREM2 (sTREM2) levels in CSF and brain. In this study, we used two different transgenic mouse models of AD pathology and investigated the potential of TREM2 to serve as an in vivo biomarker for microglial activation in AD.

PROCEDURES

We designed and generated a bispecific antibody based on the TREM2-specific monoclonal antibody mAb1729, fused to a single-chain variable fragment of the transferrin receptor binding antibody 8D3. The 8D3-moiety enabled transcytosis of the whole bispecific antibody across the blood-brain barrier. The bispecific antibody was radiolabeled with I-125 (ex vivo) or I-124 (PET) and administered to transgenic AD and wild-type (WT) control mice. Radioligand retention in the brain of transgenic animals was compared to WT mice by isolation of brain tissue at 24 h or 72 h, or with in vivo PET at 24 h, 48 h, and 72 h. Intrabrain distribution of radiolabeled mAb1729-scFv8D3_CL was further studied by autoradiography, while ELISA was used to determine TREM2 brain concentrations.

RESULTS

Transgenic animals displayed higher total exposure, calculated as the AUC based on SUV determined at 24h, 48h, and 72h post injection, of PET radioligand [¹²⁴I]mAb1729-scFv8D3_CL than WT mice. However, differences were not evident in single time point PET images or SUVs. Ex vivo autoradiography confirmed higher radioligand concentrations in cortex and thalamus in transgenic mice compared to WT, and TREM2 levels in brain homogenates were considerably higher in transgenic mice compared to WT.

CONCLUSION

Antibody-based radioligands, engineered to enter the brain, may serve as PET radioligands to follow changes of TREM2 in vivo, but antibody formats with faster systemic clearance to increase the specific signal in relation to that from blood in combination with antibodies showing higher affinity for TREM2 must be developed to further progress this technique for in vivo use.

Noninvasive Evaluation of CD20 Expression Using 64Cu-Labeled F(ab')2 Fragments of Obinutuzumab in Lymphoma

CD20-overexpressed non-Hodgkin lymphoma typically indicates progressive malignancy. Obinutuzumab is a next-generation Food and Drug Administration-approved humanized monoclonal antibody that targets CD20. Previous studies with ⁸⁹Zr-labeled obinutuzumab have successfully imaged CD20 in vivo. However, delayed tumor uptake and increased radioactive exposure caused by long blood circulation limit its clinical translation. This study aimed to develop ⁶⁴Cu-labeled F(ab')₂ fragments of obinutuzumab for imaging CD20 in lymphoma xenograft tumor models. Methods: F(ab')₂ fragments were produced from obinutuzumab using an IgG-degrading enzyme of Streptococcus pyogenes (IdeS) enzyme and purified with protein A beads. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and high-performance liquid chromatography were performed to evaluate the products and their stability. F(ab')₂ products were conjugated with p-SCN-Bn-NOTA (NOTA) for ⁶⁴Cu radiolabeling. Western blotting was performed to screen the CD20 expression levels of lymphoma cells. Enzyme-linked immunosorbent assay, flow cytometry, and confocal imaging were used to test the binding affinity in vitro. Serial PET imaging and biodistribution studies in subcutaneous lymphoma-bearing mice were performed using ⁶⁴Cu-NOTA-F(ab')₂-obinutuzumab or ⁶⁴Cu-NOTA-F(ab')₂-IgG. Results: F(ab')₂-obinutuzumab and F(ab')₂-IgG produced by the IdeS digestion system were confirmed with sodium dodecyl sulfate polyacrylamide gel electrophoresis and high-performance liquid chromatography. The radiochemical purity of ⁶⁴Cu-labeled F(ab')₂ fragments was no less than 98%, and the specific activity was 56.3 ± 7.9 MBq/mg (n = 6). Among the 5 lymphoma cell lines, Ramos showed the strongest expression of CD20, and CLL-155 showed the lowest, as confirmed by enzyme-linked immunosorbent assay, flow cytometry, and confocal imaging. PET imaging revealed rapid and sustained tumor uptake of ⁶⁴Cu-NOTA-F(ab')₂-obinutuzumab in Ramos tumor-bearing mice. The peak tumor uptake (9.08 ± 1.67 percentage injected dose per gram of tissue [%ID/g]) in the Ramos model was significantly higher than that in the CCL-155 model (2.78 ± 0.62 %ID/g) or the ⁶⁴Cu-NOTA-F(ab')₂-IgG control (1.93 ± 0.26 %ID/g, n = 4, P < 0.001). The tumor-to-blood and tumor-to-muscle ratios were 7.3 ± 1.6 and 21.9 ± 9.0, respectively, at 48 h after injection in the ⁶⁴Cu-NOTA-F(ab')₂-obinutuzumab group. Of the measured off-target organs, the kidneys showed the highest uptake. Ex vivo immunofluorescent staining verified the differential CD20 expression in the Ramos and CCL-155 tumor models. Conclusion: This study demonstrated that ⁶⁴Cu-NOTA-F(ab')₂-obinutuzumab had a rapid and sustained tumor uptake in CD20-positive lymphoma with high contrast, which could enable noninvasive evaluation of CD20 levels in the clinic.

Construction of a novel bispecific fusion protein to enhance targeting for pancreatic cancer imaging

Early detection and diagnosis are the most important endeavors for reducing associated morbidity and mortality of pancreatic ductal adenocarcinoma (PDAC). Developing molecular imaging probes that can specifically and effectively target cancer-associated biological pathways is one of the key points for sensitive and accurate diagnosis for PDAC. Herein, a small-sized, bispecific fusion protein constructed by genetic fusion of different binding domains of antibodies, termed Bi50, with enhanced targeting effect for PDAC is reported. Bi50 has excellent bispecific targeting for vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) simultaneously in vitro and in vivo. Additionally, Bi50 shows increased intratumoral permeability and enrichment characteristics in the tumor than the control protein, which is constructed directly connecting two individual Fabs. Moreover, Bi50 can not only target areas rich in vasculature but also bind with affinity to tumor parenchymal cells, achieving "multilevel" targeting effect. Our work demonstrates that the bispecific fusion protein Bi50 has great potential as an efficient, targeted molecular imaging probe.

Interactions Between Tumor Biology and Targeted Nanoplatforms for Imaging Applications

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

A promising cancer diagnosis and treatment strategy: targeted cancer therapy and imaging based on antibody fragment

With the arrival of the precision medicine and personalized treatment era, targeted therapy that improves efficacy and reduces side effects has become the mainstream approach of cancer treatment. Antibody fragments that further enhance penetration and retain the most critical antigen-specific binding functions are considered the focus of research targeting cancer imaging and therapy. Thanks to the superior penetration and rapid blood clearance of antibody fragments, antibody fragment-based imaging agents enable efficient and sensitive imaging of tumour sites. In tumour-targeted therapy, antibody fragments can directly inhibit tumour proliferation and growth, serve as an ideal carrier for delivery of anti-tumour drugs, or manipulate the immune system to eliminate tumour cells. In this review, the excellent physicochemical properties and the basic structure of antibody fragments are expressly depicted depicted, the progress of antibody fragments in cancer therapy and imaging are thoroughly summarized, and the future development of antibody fragments is predicted.

PET Imaging of Receptor Tyrosine Kinases in Cancer

Overexpression and/or mutations of the receptor tyrosine kinase (RTK) subfamilies, such as epidermal growth factor receptors (EGFR) and vascular endothelial growth factor receptors (VEGFR), are closely associated with tumor cell growth, differentiation, proliferation, apoptosis, and cellular invasiveness. Monoclonal antibodies (mAb) and tyrosine kinase inhibitors (TKI) specifically inhibiting these RTKs have shown remarkable success in improving patient survival in many cancer types. However, poor response and even drug resistance inevitably occur. In this setting, the ability to detect and visualize RTKs with noninvasive diagnostic tools will greatly refine clinical treatment strategies for cancer patients, facilitate precise response prediction, and improve drug development. Positron emission tomography (PET) agents using targeted radioactively labeled antibodies have been developed to visualize tumor RTKs and are changing clinical decisions for certain cancer types. In the present review, we primarily focus on PET imaging of RTKs using radiolabeled antibodies with an emphasis on the clinical applications of these immunoPET probes. Mol Cancer Ther; 17(8); 1625-36. ©2018 AACR.

ImmunoPET imaging of CD38 expression in hepatocellular carcinoma using 64Cu-labeled daratumumab

CD38 is expressed on the surface of many immune cells, which are closely associated with antitumor immunity and immune tolerance of tumor cells. Therefore, monitoring CD38 expression has gained great attention for tracking the progression of tumors and cancer treatment. Herein, we aim to develop a PET tracer using an anti-CD38 monoclonal antibody (daratumumab) to monitor CD38 expression in hepatocellular carcinoma (HCC). In this study, daratumumab was radiolabeled with ⁶⁴Cu (t_1/2=12.7 h) to obtain ⁶⁴Cu-NOTA-daratumumab. Relative CD38 expression in HepG2 and Huh7 HCC cell lines was assessed using western blot. The specificity of ⁶⁴Cu-NOTA-daratumumab to both cell lines was examined using an in vitro cell-binding assay. PET imaging in subcutaneous models of HCC was performed to evaluate the capability and specificity of ⁶⁴Cu-NOTA-daratumumab to target CD38 in vivo. Region-of-interest analysis and ex vivo biodistribution were performed to verify the tracer targeting capability of CD38. Through cellular studies of two HCC cell lines, CD38 expression was found to be higher in HepG2 and minimal in Huh7 cells. ⁶⁴Cu-NOTA-daratumumab showed relatively high affinity to CD38 (K_a=18.21 ± 1.74 nM), while the affinity of Huh7 was in the micromolar range for daratumumab binding to the cells (K_a=3.98 ± 0.87 μM). At 48 h post-injection, PET imaging of subcutaneous models with ⁶⁴Cu-NOTA-daratumumab revealed tumor uptakes of 12.23 ± 2.4 and 2.7 ± 1.2 %ID/g for HepG2 and Huh7, respectively (n=4), which correlated well with relative CD38 expression of the cells. Moreover, the ⁶⁴Cu-NOTA-IgG nonspecific analogue showed a significantly lower uptake in HepG2 subcutaneous model in mice, suggesting a specific binding of daratumumab with CD38 in vivo. Our cellular studies and PET imaging confirmed the capability and specificity of ⁶⁴Cu-NOTA-daratumumab for the imaging of CD38 in murine models of HCC. This study supports our claim that ⁶⁴Cu-NOTA-daratumumab is an effective PET tracer for the non-invasive evaluation of CD38 expression and sensitive detection of CD38-positive tumor lesions in HCC.

Current outlook on radionuclide delivery systems: from design consideration to translation into clinics

Radiopharmaceuticals have proven to be effective agents, since they can be successfully applied for both diagnostics and therapy. Effective application of relevant radionuclides in pre-clinical and clinical studies depends on the choice of a sufficient delivery platform. Herein, we provide a comprehensive review on the most relevant aspects in radionuclide delivery using the most employed carrier systems, including, (i) monoclonal antibodies and their fragments, (ii) organic and (iii) inorganic nanoparticles, and (iv) microspheres. This review offers an extensive analysis of radionuclide delivery systems, the approaches of their modification and radiolabeling strategies with the further prospects of their implementation in multimodal imaging and disease curing. Finally, the comparative outlook on the carriers and radionuclide choice, as well as on the targeting efficiency of the developed systems is discussed.

Recent Advances in Targeting Nuclear Molecular Imaging Driven by Tetrazine Bioorthogonal Chemistry

Molecular imaging techniques apply sophisticated technologies to monitor, directly or indirectly, the spatiotemporal distribution of molecular or cellular processes for biomedical, diagnostic, or therapeutic purposes. For example, Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) imaging, the most representative modalities of molecular imaging, enable earlier and more accurate diagnosis of cancer and cardiovascular diseases. New possibilities for noninvasive molecular imaging in vivo have emerged with advances in bioorthogonal chemistry. For example, tetrazine-related Inverse Electron Demand Diels-Alder (IEDDA) reactions can rapidly generate short-lived radioisotope probes in vivo that provide strong contrast for SPECT and PET. Here, we review pretargeting strategies for molecular imaging and novel radiotracers synthesized via tetrazine bioorthogonal chemistry. We systematically describe advances in direct radiolabeling and pretargeting approaches in SPECT and PET using metal and nonmetal radioisotopes based on tetrazine bioorthogonal reactions, and we discuss prospects for the future of such contrast agents.

New Developments in Dual-Labeled Molecular Imaging Agents

Intraoperative detection of tumors has had a profound impact on how cancer surgery is performed and addresses critical unmet needs in surgical oncology. Tumor deposits, margins, and residual cancer can be imaged through the use of fluorescent contrast agents during surgical procedures to complement visual and tactile guidance. The combination of fluorescent and nuclear contrast into a multimodality agent builds on these capabilities by adding quantitative, noninvasive nuclear imaging capabilities to intraoperative imaging. This review focuses on new strategies for the development and evaluation of targeted dual-labeled molecular imaging agents while highlighting the successful first-in-human application of this technique.

Antibody Fragment and Affibody ImmunoPET Imaging Agents: Radiolabelling Strategies and Applications

Antibodies have long been recognised as potent vectors for carrying diagnostic medical radionuclides, contrast agents and optical probes to diseased tissue for imaging. The area of ImmunoPET combines the use of positron emission tomography (PET) imaging with antibodies to improve the diagnosis, staging and monitoring of diseases. Recent developments in antibody engineering and PET radiochemistry have led to a new wave of experimental ImmunoPET imaging agents that are based on a range of antibody fragments and affibodies. In contrast to full antibodies, engineered affibody proteins and antibody fragments such as minibodies, diabodies, single-chain variable region fragments (scFvs), and nanobodies are much smaller but retain the essential specificities and affinities of full antibodies in addition to more desirable pharmacokinetics for imaging. Herein, recent key developments in the PET radiolabelling strategies of antibody fragments and related affibody molecules are highlighted, along with the main PET imaging applications of overexpressed antigen-associated tumours and immune cells.

A novel plectin/integrin-targeted bispecific molecular probe for magnetic resonance/near-infrared imaging of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest human malignancies with poor patient outcomes often resulting from delayed diagnosis. Therefore, early diagnosis can lead to a better prognosis and improved outcomes. In this study, we have developed a novel conjugate complex of plectin/integrin-targeted bispecific molecular probe, termed Gd-Cy7-PTP/RGD, to be used for magnetic resonance/near-infrared imaging (MRI/NIRF) of pancreatic cancer in vivo. This bispecific molecular probe comprises four parts: Gd(III) for MRI, cyanine 7 (Cy7) for NIRF, the peptide PTP for binding to plectin-1 specifically overexpressed on the surface of PDAC cells, and the peptide RGD for targeting integrin widely expressed on pancreatic duct epithelial cells and angiogenesis. Remarkably, the combination of PTP and RGD greatly increased the targeting efficiency in vitro and in vivo compared to that of either single peptide. Moreover, such bispecific molecular probes target pancreatic neoplasms and angiogenesis simultaneously, producing a "multi-level" targeting effect confirmed by immunofluorescence testing in vitro and in vivo. Under the guidance of MRI/NIRF dual-modality imaging, NIRF-guided delineation of surgical margins during operations was successfully achieved in orthotopic pancreatic cancer. This study promotes further exploration of bispecific molecular probes for clinical application.

Aligning physics and physiology: Engineering antibodies for radionuclide delivery

The exquisite specificity of antibodies and antibody fragments renders them excellent agents for targeted delivery of radionuclides. Radiolabeled antibodies and fragments have been successfully used for molecular imaging and radioimmunotherapy (RIT) of cell surface targets in oncology and immunology. Protein engineering has been used for antibody humanization essential for clinical applications, as well as optimization of important characteristics including pharmacokinetics, biodistribution, and clearance. Although intact antibodies have high potential as imaging and therapeutic agents, challenges include long circulation time in blood, which leads to later imaging time points post-injection and higher blood absorbed dose that may be disadvantageous for RIT. Using engineered fragments may address these challenges, as size reduction and removal of Fc function decreases serum half-life. Radiolabeled fragments and pretargeting strategies can result in high contrast images within hours to days, and a reduction of RIT toxicity in normal tissues. Additionally, fragments can be engineered to direct hepatic or renal clearance, which may be chosen based on the application and disease setting. This review discusses aligning the physical properties of radionuclides (positron, gamma, beta, alpha, and Auger emitters) with antibodies and fragments and highlights recent advances of engineered antibodies and fragments in preclinical and clinical development for imaging and therapy.

Antibody-based PET of uPA/uPAR signaling with broad applicability for cancer imaging

Mounting evidence suggests that the urokinase plasminogen activator (uPA) and its receptor (uPAR) play a central role in tumor progression. The goal of this study was to develop an 89Zr-labeled, antibody-based positron emission tomography (PET) tracer for quantitative imaging of the uPA/uPAR system. An anti-uPA monoclonal antibody (ATN-291) was conjugated with a deferoxamine (Df) derivative and subsequently labeled with 89Zr. Flow cytometry, microscopy studies, and competitive binding assays were conducted to validate the binding specificity of Df-ATN-291 against uPA. PET imaging with 89Zr-Df-ATN-291 was carried out in different tumors with distinct expression levels of uPA. Biodistribution, histology examination, and Western blotting were performed to correlate tumor uptake with uPA or uPAR expression. ATN-291 retained uPA binding affinity and specificity after Df conjugation. 89Zr-labeling of ATN-291 was achieved in good radiochemical yield and high specific activity. Serial PET imaging demonstrated that, in most tumors studied (except uPA- LNCaP), the uptake of 89Zr-Df-ATN-291 was higher compared to major organs at 120 h post-injection, providing excellent tumor contrast. The tumor-to-muscle ratio of 89Zr-Df-ATN-291 in U87MG was as high as 45.2 ± 9.0 at 120 h p.i. In vivo uPA specificity of 89Zr-Df-ATN-291 was confirmed by successful pharmacological blocking of tumor uptake with ATN-291 in U87MG tumors. Although the detailed mechanisms behind in vivo 89Zr-Df-ATN-291 tumor uptake remained to be further elucidated, quantitative PET imaging with 89Zr-Df-ATN-291 in tumors can facilitate oncologists to adopt more relevant cancer treatment planning.

Reassembly of 89 Zr-Labeled Cancer Cell Membranes into Multicompartment Membrane-Derived Liposomes for PET-Trackable Tumor-Targeted Theranostics

Nanoengineering of cell membranes holds great potential to revolutionize tumor-targeted theranostics, owing to their innate biocompatibility and ability to escape from the immune and reticuloendothelial systems. However, tailoring and integrating cell membranes with drug and imaging agents into one versatile nanoparticle are still challenging. Here, multicompartment membrane-derived liposomes (MCLs) are developed by reassembling cancer cell membranes with Tween-80, and are used to conjugate 89 Zr via deferoxamine chelator and load tetrakis(4-carboxyphenyl) porphyrin for in vivo noninvasive quantitative tracing by positron emission tomography imaging and photodynamic therapy (PDT), respectively. Radiolabeled constructs, 89 Zr-Df-MCLs, demonstrate excellent radiochemical stability in vivo, target 4T1 tumors by the enhanced permeability and retention effect, and are retained long-term for efficient and effective PDT while clearing gradually from the reticuloendothelial system via hepatobiliary excretion. Toxicity evaluation confirms that the MCLs do not impose acute or chronic toxicity in intravenously injected mice. Additionally, 89 Zr-labeled MCLs can execute rapid and highly sensitive lymph node mapping, even for deep-seated sentinel lymph nodes. The as-developed cell membrane reassembling route to MCLs could be extended to other cell types, providing a versatile platform for disease theranostics by facilely and efficiently integrating various multifunctional agents.

ImmunoPET imaging of CD38 in murine lymphoma models using 89Zr-labeled daratumumab

PURPOSE

CD38 is considered a potential biomarker for multiple myeloma (MM) and has shown a strong link with chronic lymphocytic leukemia due to high and uniform expression on plasma cells. In vivo evaluation of CD38 expression may provide useful information about lesion detection and prognosis of treatment in MM. In this study, immunoPET imaging with ⁸⁹Zr-labeled daratumumab was used for differentiation of CD38 expression in murine lymphoma models to provide a potential non-invasive method for monitoring CD38 in the clinic.

METHODS

Daratumumab was radiolabeled with ⁸⁹Zr (t_1/2 = 78.4 h) via conjugation with desferrioxamine (Df). After Western blot (WB) was used to screen CD38 expression in five lymphoma cell lines, flow cytometry and cellular binding assays were performed to test the binding ability of labeled or conjugated daratumumab with CD38 in vitro. PET imaging and biodistribution studies were performed to evaluate CD38 expression after injection of ⁸⁹Zr-Df-daratumumab. ⁸⁹Zr-Df-IgG was also evaluated as a non-specific control group in the Ramos model. Finally, CD38 expression in tumor tissues was verified by histological analysis.

RESULTS

Using WB screening, the Ramos cell line was found to express the highest level of CD38 while the HBL-1 cell line had the lowest expression. Df-conjugated and ⁸⁹Zr-labeled daratumumab displayed similar high binding affinities with Ramos cells. PET imaging of ⁸⁹Zr-Df-daratumumab showed a high tumor uptake of up to 26.6 ± 8.0 %ID/g for Ramos at 120 h post-injection, and only up to 6.6 ± 2.9 %ID/g for HBL-1 (n = 4). Additionally, ⁸⁹Zr-Df-IgG demonstrated a low tumor uptake in the Ramos model (only 4.3 ± 0.8 %ID/g at 120 h post-injection). Ex vivo biodistribution studies showed similar trends with imaging results. Immunofluorescence staining of tumor tissues verified higher CD38 expression of Ramos than that of HBL-1.

CONCLUSIONS

The role of ⁸⁹Zr-Df-daratumumab was investigated for evaluating CD38 expression in lymphoma models non-invasively and was found to be to a promising imaging agent of CD38-positive hematological diseases such as MM in future clinical applications.

Dual-Targeted Molecular Imaging of Cancer

Molecular imaging is critical to personalized and precision medicine. Although singly targeted imaging probes are making an impact both clinically and preclinically, molecular imaging strategies using bispecific probes have enabled improved visualization of cancer in recent years through synergistic targeting of two ligands. In this Focus on Molecular Imaging review, we outline how peptide-, antibody-, and nanoparticle-based platforms have affected this emerging strategy, providing examples and pointing out areas in which the greatest clinical impact may be realized.

Chelator-Free Labeling of Metal Oxide Nanostructures with Zirconium-89 for Positron Emission Tomography Imaging

Radiolabeling of molecules or nanoparticles to form imaging probes is critical for positron emission tomography (PET) imaging, which, with high sensitivity and the ability for quantitative imaging, has been widely used in the clinic. While conventional radiolabeling often employs chelator molecules, a general method for chelator-free radiolabeling of a wide range of materials remains to be developed. Herein, we determined that 10 different types of metal oxide (M_xO_y, M = Gd, Ti, Te, Eu, Ta, Er, Y, Yb, Ce, or Mo, x = 1-2, y = 2-5) nanomaterials with polyethylene glycol (PEG) modification could be labeled with ⁸⁹Zr, a PET tracer, via a simple yet general chelator-free radiolabeling method upon simple mixing. High-labeling yields and good serum stabilities are achieved with this method, owing to the strong bonding between oxyphilic ⁸⁹Zr⁴⁺ with oxygen atoms on the M_xO_y surface. Selecting ⁸⁹Zr-Gd₂O₃-PEG as a multimodal imaging probe, we have successfully demonstrated in vivo PET imaging of draining lymph nodes, which are also visualized under magnetic resonance imaging, showing advantages over free ⁸⁹Zr in the mapping of draining lymph node networks. Our work describes a general and simple method for chelator-free radiolabeling of metal oxide nanostructures, which is promising for the development of multifunctional nanoprobes in biomedical imaging.

ImmunoPET Imaging of CD146 in Murine Models of Intrapulmonary Metastasis of Non-Small Cell Lung Cancer

CD146 has been identified as an excellent biomarker for lung cancer as its overexpression in solid tumors has been linked to disease progression, invasion, and metastasis. Previously, our group described a positive correlation between ⁶⁴Cu-labeled YY146 uptake and increased expression of CD146 in six human lung cancer cell lines using subcutaneous tumor models. In this study, we investigate a monoclonal antibody called YY146 for immunoPET imaging of CD146 in two intrapulmonary metastasis models of non-small cell lung cancer (NSCLC). The binding and immunoreactivity of the tracer were assessed by in vitro assays. Radiolabeling of YY146 with positron emitting Cu-64 (⁶⁴Cu-NOTA-YY146) enabled PET imaging of intrapulmonary metastasis. Mice were intravenously injected with two million tumor cells, and CT imaging was used to verify the presence of lung metastases. ⁶⁴Cu-NOTA-YY146 was injected into tumor-bearing mice, and animals were subjected to PET/CT imaging at 4, 24, and 48 h postinjection. Both the average and maximum lung PET signal intensities were quantified and compared between high and low CD146-expressing metastases. Further validation was accomplished through immunofluorescence imaging of resected tissues with CD31 and CD146. In flow cytometry, YY146 revealed strong binding to CD146 in H460 cells due to its high expression with minimal binding to CD146-low expressing H358 cells. Both YY146 and NOTA-YY146 showed similar binding, suggesting that NOTA conjugation did not elicit any negative effects on its binding affinity. Imaging of ⁶⁴Cu-NOTA-YY146 in H460 tumor-bearing mice revealed rapid, persistent, and highly specific tracer accumulation. Uptake of ⁶⁴Cu-NOTA-YY146 in the whole lung was calculated for H460 and H358 as 7.43 ± 0.38 and 3.95 ± 0.47% ID/g at 48 h postinjection (n = 4, p < 0.05), and the maximum lung signals were determined to be 13.85 ± 1.07 (H460) and 6.08 ± 0.73% ID/g (H358) at equivalent time points (n = 4, p < 0.05). To ensure the specificity of the tracer, a nonspecific antibody was injected into H460 tumor-bearing mice. Ex vivo biodistribution and immunofluorescence imaging validated the PET findings. In summary, ⁶⁴Cu-NOTA-YY146 allowed for successful imaging of CD146-expressing intrapulmonary metastases of NSCLC in mice. This preliminary study provides evidence supporting the future clinical utilization of ⁶⁴Cu-NOTA-YY146 for possible treatment monitoring of CD146-targeted therapy or improving patient stratification.

Radiolabeled pertuzumab for imaging of human epidermal growth factor receptor 2 expression in ovarian cancer

PURPOSE

Human epidermal growth factor receptor 2 (HER2) is over-expressed in over 30% of ovarian cancer cases, playing an essential role in tumorigenesis and metastasis. Non-invasive imaging of HER2 is of great interest for physicians as a mean to better detect and monitor the progression of ovarian cancer. In this study, HER2 was assessed as a biomarker for ovarian cancer imaging using 64Cu-labeled pertuzumab for immunoPET imaging.

METHODS

HER2 expression and binding were examined in three ovarian cancer cell lines (SKOV3, OVCAR3, Caov3) using in vitro techniques, including western blot and saturation binding assays. PET imaging and biodistribution studies in subcutaneous models of ovarian cancer were performed for non-invasive in vivo evaluation of HER2 expression. Additionally, orthotopic models were employed to further validate the imaging capability of 64Cu-NOTA-pertuzumab.

RESULTS

HER2 expression was highest in SKOV3 cells, while OVCAR3 and Caov3 displayed lower HER2 expression. 64Cu-NOTA-pertuzumab showed high specificity for HER2 (Ka = 3.1 ± 0.6 nM) in SKOV3. In subcutaneous tumors, PET imaging revealed tumor uptake of 41.8 ± 3.8, 10.5 ± 3.9, and 12.1 ± 2.3%ID/g at 48 h post-injection for SKOV3, OVCAR3, and Caov3, respectively (n = 3). In orthotopic models, PET imaging with 64Cu-NOTA-pertuzumab allowed for rapid and clear delineation of both primary and small peritoneal metastases in HER2-expressing ovarian cancer.

CONCLUSIONS

64Cu-NOTA-pertuzumab is an effective PET tracer for the non-invasive imaging of HER2 expression in vivo, rendering it a potential tracer for treatment monitoring and improved patient stratification.

Alternative reagents to antibodies in imaging applications

Antibodies have been indispensable tools in molecular biology, biochemistry and medical research. However, a number of issues surrounding validation, specificity and batch variation of commercially available antibodies have prompted research groups to develop novel non-antibody binding reagents. The ability to select highly specific monoclonal non-antibody binding proteins without the need for animals, the ease of production and the ability to site-directly label has enabled a wide variety of applications to be tested, including imaging. In this review, we discuss the success of a number of non-antibody reagents in imaging applications, including the recently reported Affimer.

ImmunoPET and Near-Infrared Fluorescence Imaging of Pancreatic Cancer with a Dual-Labeled Bispecific Antibody Fragment

Dual-targeted imaging agents have shown improved targeting efficiencies in comparison to single-targeted entities. The purpose of this study was to quantitatively assess the tumor accumulation of a dual-labeled heterobifunctional imaging agent, targeting two overexpressed biomarkers in pancreatic cancer, using positron emission tomography (PET) and near-infrared fluorescence (NIRF) imaging modalities. A bispecific immunoconjugate (heterodimer) of CD105 and tissue factor (TF) Fab' antibody fragments was developed using click chemistry. The heterodimer was dual-labeled with a radionuclide (⁶⁴Cu) and fluorescent dye. PET/NIRF imaging and biodistribution studies were performed in four-to-five week old nude athymic mice bearing BxPC-3 (CD105/TF^+/+) or PANC-1 (CD105/TF^-/-) tumor xenografts. A blocking study was conducted to investigate the specificity of the tracer. Ex vivo tissue staining was performed to compare TF/CD105 expression in tissues with PET tracer uptake to validate in vivo results. PET imaging of ⁶⁴Cu-NOTA-heterodimer-ZW800 in BxPC-3 tumor xenografts revealed enhanced tumor uptake (21.0 ± 3.4%ID/g; n = 4) compared to the homodimer of TRC-105 (9.6 ± 2.0%ID/g; n = 4; p < 0.01) and ALT-836 (7.6 ± 3.7%ID/g; n = 4; p < 0.01) at 24 h postinjection. Blocking studies revealed that tracer uptake in BxPC-3 tumors could be decreased by 4-fold with TF blocking and 2-fold with CD105 blocking. In the negative model (PANC-1), heterodimer uptake was significantly lower than that found in the BxPC-3 model (3.5 ± 1.1%ID/g; n = 4; p < 0.01). The specificity was confirmed by the successful blocking of CD105 or TF, which demonstrated that the dual targeting with ⁶⁴Cu-NOTA-heterodimer-ZW800 provided an improvement in overall tumor accumulation. Also, fluorescence imaging validated the PET imaging, allowing for clear delineation of the xenograft tumors. Dual-labeled heterodimeric imaging agents, like ⁶⁴Cu-NOTA-heterodimer-ZW800, may increase the overall tumor accumulation in comparison to single-targeted homodimers, leading to improved imaging of cancer and other related diseases.

Chelator-Free Radiolabeling of Nanographene: Breaking the Stereotype of Chelation

Macrocyclic chelators have been widely employed in the realm of nanoparticle-based positron emission tomography (PET) imaging, whereas its accuracy remains questionable. Here, we found that ⁶⁴ Cu can be intrinsically labeled onto nanographene based on interactions between Cu and the π electrons of graphene without the need of chelator conjugation, providing a promising alternative radiolabeling approach that maintains the native in vivo pharmacokinetics of the nanoparticles. Due to abundant π bonds, reduced graphene oxide (RGO) exhibited significantly higher labeling efficiency in comparison with graphene oxide (GO) and exhibited excellent radiostability in vivo. More importantly, nonspecific attachment of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) on nanographene was observed, which revealed that chelator-mediated nanoparticle-based PET imaging has its inherent drawbacks and can possibly lead to erroneous imaging results in vivo.

bisFabs: Tools for rapidly screening hybridoma IgGs for their activities as bispecific antibodies

Bispecific antibodies are a growing class of therapeutic molecules. Many of the current bispecific formats require DNA engineering to convert the parental monoclonal antibodies into the final bispecific molecules. We describe here a method to generate bispecific molecules from hybridoma IgGs in 3-4 d using chemical conjugation of antigen-binding fragments (Fabs) (bisFabs). Proteolytic digestion conditions for each IgG isotype were analyzed to optimize the yield and quality of the final conjugates. The resulting bisFabs showed no significant amounts of homodimers or aggregates. The predictive value of murine bisFabs was tested by comparing the T-cell redirected cytotoxic activity of a panel of antibodies in either the bisFab or full-length IgG formats. A variety of antigens with different structures and expression levels was used to extend the comparison to a wide range of binding geometries and antigen densities. The activity observed for different murine bisFabs correlated with those observed for the full-length IgG format across multiple different antigen targets, supporting the use of bisFabs as a screening tool. Our method may also be used for the screening of bispecific antibodies with other mechanisms of action, allowing for a more rapid selection of lead therapeutic candidates.

64Cu-Labeled Trastuzumab Fab-PEG24-EGF Radioimmunoconjugates Bispecific for HER2 and EGFR: Pharmacokinetics, Biodistribution, and Tumor Imaging by PET in Comparison to Monospecific Agents

Heterodimerization of EGFR with HER2 coexpressed in breast cancer (BC) promotes tumor growth, and increased EGFR expression is associated with trastuzumab resistance. Our aim was to construct ⁶⁴Cu-labeled bispecific radioimmunoconjugates (bsRIC) composed of trastuzumab Fab, which binds HER2 linked through a polyethylene glycol (PEG₂₄) spacer to EGF, and to compare their pharmacokinetic, biodistribution, and tumor imaging characteristics by positron-emission tomography (PET). bsRICs were generated by linking maleimide modified trastuzumab Fab with thiolated EGF through a thioether bond. HER2 and EGFR binding were assessed in vitro in MDA-MB-231 (EGFR^mod/HER2^low), MDA-MB-468 (EGFR^high/HER2^neg), MDA-MB-231-H2N (EGFR^mod/HER2^mod), and SKOV3 (EGFR^low/HER2^high) cells by competition and saturation cell binding assays to estimate the dissociation constant (K_d). The elimination of the ⁶⁴Cu-NOTA-trastuzumab Fab-PEG₂₄-EGF bsRICs from the blood of Balb/c mice was compared to monospecific ⁶⁴Cu-NOTA-trastuzumab Fab and ⁶⁴Cu-NOTA-EGF. MicroPET/CT imaging was performed in NOD/SCID mice bearing subcutaneous MDA-MB-468, MDA-MB-231/H2N, or SKOV3 human BC xenografts at 24 and 48 h postinjection (p.i.) of bsRICs. Tumor and normal tissue uptake were quantified by biodistribution studies and compared to monospecific agents. The binding of bsRICs to MDA-MB-231 cells was decreased to 24.5 ± 5.2% by excess EGF, while the binding of bsRICs to SKOV3 cells was decreased to 38.6 ± 5.4% by excess trastuzumab Fab, demonstrating specific binding to both EGFR and HER2. ⁶⁴Cu-labeled bsRICs incorporating the PEG₂₄ spacer were eliminated more slowly from the blood than ⁶⁴Cu-bsRICs without the PEG spacer and were cleared much more slowly than ⁶⁴Cu-NOTA-Fab or ⁶⁴Cu-NOTA-EGF. All three tumor xenografts were visualized by microPET/CT at 24 and 48 h p.i. of bsRICs. Biodistribution studies at 48 h p.i. in NOD/SCID mice with MDA-MB-231/H2N tumors demonstrated significantly greater tumor uptake of ⁶⁴Cu-NOTA-Fab-PEG₂₄-EGF (4.9 ± 0.4%ID/g) than ⁶⁴Cu-NOTA-Fab (1.9 ± 0.3%ID/g; P < 0.0001) and ⁶⁴Cu-NOTA-EGF (0.7 ± 0.2%ID/g; P < 0.0001). Furthermore, preadministration of an excess of trastuzumab Fab or trastuzumab Fab-PEG₂₄-EGF significantly decreased the tumor uptake of ⁶⁴Cu-NOTA-Fab-PEG₂₄-EGF in SK-OV-3 and MDA-MB-468 xenografts by 4.4-fold (P = 0.0012) and 1.8-fold (P = 0.0031), respectively. ⁶⁴Cu-labeled bsRICs bound HER2 or EGFR and were taken up specifically in vivo in tumor xenografts expressing one or both receptors. The PEG₂₄ linker prolonged the blood residence time contributing to the higher tumor uptake of the bsRICs than monospecific agents.