PET Imaging of VCAM-1 Expression and Monitoring Therapy Response in Tumor with a 68Ga-Labeled Single Chain Variable Fragment

In Vivo PET Detection of Lung Micrometastasis in Mice by Targeting Endothelial VCAM-1 Using a Dual-Contrast PET/MRI Probe

Current clinical diagnostic imaging methods for lung metastases are sensitive only to large tumours (1-2 mm cross-sectional diameter), and early detection can dramatically improve treatment. We have previously demonstrated that an antibody-targeted MRI contrast agent based on microparticles of iron oxide (MPIO; 1 μm diameter) enables the imaging of endothelial vascular cell adhesion molecule-1 (VCAM-1). Using a mouse model of lung metastasis, upregulation of endothelial VCAM-1 expression was demonstrated in micrometastasis-associated vessels but not in normal lung tissue, and binding of VCAM-MPIO to these vessels was evident histologically. Owing to the lack of proton MRI signals in the lungs, we modified the VCAM-MPIO to include zirconium-89 (89Zr, t1/2 = 78.4 h) in order to allow the in vivo detection of lung metastases by positron emission tomography (PET). Using this new agent (89Zr-DFO-VCAM-MPIO), it was possible to detect the presence of micrometastases within the lung in vivo from ca. 140 μm in diameter. Histological analysis combined with autoradiography confirmed the specific binding of the agent to the VCAM-1 expressing vasculature at the sites of pulmonary micrometastases. By retaining the original VCAM-MPIO as the basis for this new molecular contrast agent, we have created a dual-modality (PET/MRI) agent for the concurrent detection of lung and brain micrometastases.

PLGA Nanoparticles Containing VCAM-1 Inhibitor Succinobucol and Chemotherapeutic Doxorubicin as Therapy against Primary Tumors and Their Lung Metastases

The treatment of malignant tumors is usually accompanied by poor prognosis due to metastasis of tumor cells. Hence, it is crucial to enhance anti-metastasis efficacy when anti-tumor treatments are conducted. It has been reported that the vascular cell adhesion molecule-1 (VCAM-1) is highly expressed on the surface of tumor cells and plays an essential role in the metastasis of tumor cells. Thus, reducing VCAM-1 expression offers hope for inhibiting the metastasis of tumor cells. Evidence has shown that succinobucol (Suc) can selectively and efficiently inhibit VCAM-1 expression. Inspired by these, we designed dual drug-loaded PLGA nanoparticles (Co-NPs) to co-deliver VCAM-1 inhibitor Suc and the chemotherapeutic doxorubicin (Dox) which could both effectively suppress primary melanoma and its lung metastases. Co-NPs were composed of PLGA encapsulated Suc and Dox as hydrophobic cores and DSPE-mPEG₂₀₀₀ as surface modification materials. With an appropriate particle size (122.4 nm) and a negatively charged surface (-6.77 mV) we could achieve prolonged blood circulation. The in vitro experiments showed that Co-NPs had potent cytotoxicity against B16F10 cells and could significantly inhibit VCAM-1 expression and migration of B16F10 cells. Additionally, the in vivo experiments showed that Co-NPs could efficiently suppress not only primary melanoma but also its lung metastases. In conclusion, PLGA nanoparticles containing VCAM-1 inhibitor Suc and chemotherapeutic Dox as therapy against primary tumors and their lung metastases provides a promising drug delivery strategy for the treatment of metastatic malignant tumors.

Single-Chain Fragment Variable: Recent Progress in Cancer Diagnosis and Therapy

Simple Summary

Recombinant antibody fragments have shown remarkable potential as diagnostic and therapeutic tools in the fight against cancer. The single-chain fragment variable (scFv) that contains the complete antigen-binding domains of a whole antibody, has several advantages such as a high specificity and affinity for antigens, a low immunogenicity, and the proven ability to penetrate tumor tissues and diffuse. This review provides an overview of the current studies on the principle, generation, and applications of scFvs, particularly in the diagnosis and therapy of cancer, and underscores their potential use in clinical trials.

Abstract

Cancer remains a public health problem worldwide. Although conventional therapies have led to some excellent outcomes, some patients fail to respond to treatment, they have few therapeutic alternatives and a poor survival prognosis. Several strategies have been proposed to overcome this issue. The most recent approach is immunotherapy, particularly the use of recombinant antibodies and their derivatives, such as the single-chain fragment variable (scFv) containing the complete antigen-binding domains of a whole antibody that successfully targets tumor cells. This review describes the recent progress made with scFvs as a cancer diagnostic and therapeutic tool, with an emphasis on preclinical approaches and their potential use in clinical trials.

Novel PET Imaging of Inflammatory Targets and Cells for the Diagnosis and Monitoring of Giant Cell Arteritis and Polymyalgia Rheumatica

Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are two interrelated inflammatory diseases affecting patients above 50 years of age. Patients with GCA suffer from granulomatous inflammation of medium- to large-sized arteries. This inflammation can lead to severe ischemic complications (e.g., irreversible vision loss and stroke) and aneurysm-related complications (such as aortic dissection). On the other hand, patients suffering from PMR present with proximal stiffness and pain due to inflammation of the shoulder and pelvic girdles. PMR is observed in 40-60% of patients with GCA, while up to 21% of patients suffering from PMR are also affected by GCA. Due to the risk of ischemic complications, GCA has to be promptly treated upon clinical suspicion. The treatment of both GCA and PMR still heavily relies on glucocorticoids (GCs), although novel targeted therapies are emerging. Imaging has a central position in the diagnosis of GCA and PMR. While [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) has proven to be a valuable tool for diagnosis of GCA and PMR, it possesses major drawbacks such as unspecific uptake in cells with high glucose metabolism, high background activity in several non-target organs and a decrease of diagnostic accuracy already after a short course of GC treatment. In recent years, our understanding of the immunopathogenesis of GCA and, to some extent, PMR has advanced. In this review, we summarize the current knowledge on the cellular heterogeneity in the immunopathology of GCA/PMR and discuss how recent advances in specific tissue infiltrating leukocyte and stromal cell profiles may be exploited as a source of novel targets for imaging. Finally, we discuss prospective novel PET radiotracers that may be useful for the diagnosis and treatment monitoring in GCA and PMR.

Engineering nanobodies for next-generation molecular imaging

In recent years, nanobodies have emerged as ideal imaging agents for molecular imaging. Molecular nanobody imaging combines the specificity of nanobodies with the sensitivity of state-of-the-art molecular imaging modalities, such as positron emission tomography (PET). Given that modifications of nanobodies alter their pharmacokinetics (PK), the engineering strategies that combine nanobodies with radionuclides determine the effectiveness, reliability, and safety of the molecular imaging probes. In this review, we introduce conjugation strategies that have been applied to nanobodies, including random conjugation, ^99mTc tricarbonyl chemistry, sortase A-mediated site-specific conjugation, maleimide-cysteine chemistry, and click chemistries. We also summarize the latest advances in nanobody tracers, emphasizing their preclinical and clinical use. In addition, we elaborate on nanobody-based near-infrared fluorescence (NIRF) imaging and image-guided surgery.

State of the Art in Radiolabeling of Antibodies with Common and Uncommon Radiometals for Preclinical and Clinical Immuno-PET

Inert and stable radiolabeling of monoclonal antibodies (mAb), antibody fragments, or antibody mimetics with radiometals is a prerequisite for immuno-PET. While radiolabeling is preferably fast, mild, efficient, and reproducible, especially when applied for human use in a current Good Manufacturing Practice compliant way, it is crucial that the obtained radioimmunoconjugate is stable and shows preserved immunoreactivity and in vivo behavior. Radiometals and chelators have extensively been evaluated to come to the most ideal radiometal–chelator pair for each type of antibody derivative. Although PET imaging of antibodies is a relatively recent tool, applications with ⁸⁹Zr, ⁶⁴Cu, and ⁶⁸Ga have greatly increased in recent years, especially in the clinical setting, while other less common radionuclides such as ⁵²Mn, ⁸⁶Y, ⁶⁶Ga, and ⁴⁴Sc, but also ¹⁸F as in [¹⁸F]AlF are emerging promising candidates for the radiolabeling of antibodies. This review presents a state of the art overview of the practical aspects of radiolabeling of antibodies, ranging from fast kinetic affibodies and nanobodies to slow kinetic intact mAbs. Herein, we focus on the most common approach which consists of first modification of the antibody with a chelator, and after eventual storage of the premodified molecule, radiolabeling as a second step. Other approaches are possible but have been excluded from this review. The review includes recent and representative examples from the literature highlighting which radiometal–chelator–antibody combinations are the most successful for in vivo application.

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 thiopyrylium salt for PET/NIR-II tumor imaging and image-guided surgery

All tumor imaging modalities have resolution limits below which deeply situated small metastatic foci may not be identified. Moreover, incomplete lesion excision will affect the outcomes of the patients. Scintigraphy is adept in locating lesions, and second near-infrared window (NIR-II) imaging may allow precise real-time tumor delineation. To achieve complete excision of all lesions, multimodality imaging is a promising method for tumor identification and management. Here, a NIR-II thiopyrylium salt, XB1034, was first synthesized and bound to cetuximab and trans-cyclooctene (TCO) to produce XB1034-cetuximab-TCO. This probe provides excellent sensitivity and high temporal resolution NIR-II imaging in mice bearing tumors developed from human breast cancer cells MDA-MB-231. To enable PET imaging, 68 Ga-NETA-tetrazine is subsequently injected into the mice to undergo a bio-orthogonal reaction with the preinjected XB1034-cetuximab-TCO. PET images achieved in the tumor models using the pretargeting strategy are of much higher quality than those obtained using the direct radiolabeling method. Moreover, real-time NIR-II imaging allows accurate tumor excision and sentinel lymph node mapping. In conclusion, XB1034 is a promising molecular imaging probe for tumor diagnosis and treatment.

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.

203/212Pb Theranostic Radiopharmaceuticals for Image-guided Radionuclide Therapy for Cancer

Receptor-targeted image-guided Radionuclide Therapy (TRT) is increasingly recognized as a promising approach to cancer treatment. In particular, the potential for clinical translation of receptor-targeted alpha-particle therapy is receiving considerable attention as an approach that can improve outcomes for cancer patients. Higher Linear-energy Transfer (LET) of alpha-particles (compared to beta particles) for this purpose results in an increased incidence of double-strand DNA breaks and improved-localized cancer-cell damage. Recent clinical studies provide compelling evidence that alpha-TRT has the potential to deliver a significantly more potent anti-cancer effect compared with beta-TRT. Generator-produced 212Pb (which decays to alpha emitters 212Bi and 212Po) is a particularly promising radionuclide for receptor-targeted alpha-particle therapy. A second attractive feature that distinguishes 212Pb alpha-TRT from other available radionuclides is the possibility to employ elementallymatched isotope 203Pb as an imaging surrogate in place of the therapeutic radionuclide. As direct non-invasive measurement of alpha-particle emissions cannot be conducted using current medical scanner technology, the imaging surrogate allows for a pharmacologically-inactive determination of the pharmacokinetics and biodistribution of TRT candidate ligands in advance of treatment. Thus, elementally-matched 203Pb labeled radiopharmaceuticals can be used to identify patients who may benefit from 212Pb alpha-TRT and apply appropriate dosimetry and treatment planning in advance of the therapy. In this review, we provide a brief history on the use of these isotopes for cancer therapy; describe the decay and chemical characteristics of 203/212Pb for their use in cancer theranostics and methodologies applied for production and purification of these isotopes for radiopharmaceutical production. In addition, a medical physics and dosimetry perspective is provided that highlights the potential of 212Pb for alpha-TRT and the expected safety for 203Pb surrogate imaging. Recent and current preclinical and clinical studies are presented. The sum of the findings herein and observations presented provide evidence that the 203Pb/212Pb theranostic pair has a promising future for use in radiopharmaceutical theranostic therapies for cancer.

In Vivo Assessment of VCAM-1 Expression by SPECT/CT Imaging in Mice Models of Human Triple Negative Breast Cancer

Recent progress in breast cancer research has led to the identification of Vascular Cell Adhesion Molecule-1 (VCAM-1) as a key actor of metastatic colonization. VCAM-1 promotes lung-metastases and is associated with clinical early recurrence and poor outcome in triple negative breast cancer (TNBC). Our objective was to perform the in vivo imaging of VCAM-1 in mice models of TNBC. The Cancer Genomic Atlas (TCGA) database was analyzed to evaluate the prognostic role of VCAM-1 in TNBC. MDA-MB-231 (VCAM-1+) and control HCC70 (VCAM-1-) TNBC cells were subcutaneously xenografted in mice and VCAM-1 expression was assessed in vivo by single-photon emission computed tomography (SPECT) imaging using ^99mTc-cAbVCAM1-5. Then, MDA-MB-231 cells were intravenously injected in mice and VCAM-1 expression in lung metastasis was assessed by SPECT imaging after 8 weeks. TCGA analysis showed that VCAM-1 is associated with a poor prognosis in TNBC patients. In subcutaneous tumor models, ^99mTc-cAbVCAM1-5 uptake was 2-fold higher in MDA-MB-231 than in HCC70 (p < 0.01), and 4-fold higher than that of the irrelevant control (p < 0.01). Moreover, ^99mTc-cAbVCAM1-5 uptake in MDA-MB-231 lung metastases was also higher than that of ^99mTc-Ctl (p < 0.05). ^99mTc-cAbVCAM1-5 is therefore a suitable tool to evaluate the role of VCAM-1 as a marker of tumor aggressiveness of TNBC.

Endothelial dysfunction: from the particular to the general. Return to the «Old Paradigm»?

The vascular endothelium is a heterogeneous structure with diverse functions, being an active metabolic system. Endothelial cells mediate inflammatory and immune processes, regulate leukocyte adhesion, permeability and vascular tone, participate in the hemostasis system, stimulate the processes of angiogenesis. Endothelial dysfunction can initiate individual disorders, but more often it is a universal link in the pathogenesis of many diseases. Currently, endothelial dysfunction is presented as an imbalance between the production of vasodilating, angioprotective, antiproliferative factors, on the one hand, and vasoconstrictive, prothrombotic, proliferative factors, on the other hand. The manifestations of endothelial dysfunction, the direction and severity of these changes may vary depending on the disease. The review provides examples of combined endothelial disorders in the most studied and common diseases (essential hypertension, type 2 diabetes, systemic diseases of the connective tissue, atherosclerosis, and malignant tumors). Despite the presence of rare cases of isolated endothelial dysfunction, it can be argued that in the absolute majority of diseases, endothelial dysfunction has combined type of violations. The allocation of individual endothelial disorder spectra, typical for a specific disease, is problematic, due to the universality and nonspecificity of the manifestations of endothelial dysfunction. These conclusions allow us to return to the origins of this problem, considering endothelial dysfunction as a holistic concept, not limited to a certain range of its disorders.

Single-Chain Variable Fragment Antibody of Vascular Cell Adhesion Molecule 1 as a Molecular Imaging Probe for Colitis Model Rabbit Investigation

Vascular cell adhesion molecule-1 (VCAM-1) can be a promising target for colitis study because of its critical role in inflammation development. Single-chain variable fragment (scFv) antibody presents fast blood clearance when served as an imaging probe. We applied the probe of ^99mTc-scFv-VCAM-1 to colitis rabbit to examine its imaging performance. The colitis model rabbit was prepared, and a typical inflammatory lesion was confirmed in the colon. The probe of ^99mTc-scFv-VCAM-1 was synthesized and injected into the model animal before imaging examination. Scintigraphy detected colitis lesions in both SPECT planar and SPECT/CT fused images, with higher target-to-nontarget ratios in the model group (2.71 ± 0.31) than those in the control group (1.12 ± 0.10). Biodistribution study determined tracer uptake in different organs, and autoradiography (ARG) confirmed probe accumulation in colon lesions. The uptake ratio of the model colon to the control colon was 4.71 ± 0.61 in quantitative analysis of the ARG regions of interest. Stronger VCAM-1 expression in the model colon than that in the control colon was confirmed by western blotting and immunohistochemistry. Our imaging study indicates molecular imaging with scFv-VCAM-1 as a promising way for inflammatory bowel disease diagnosis and evaluation.