Development of a CD163-Targeted PET Radiotracer That Images Resident Macrophages in Atherosclerosis

Tissue-resident macrophages are complementary to proinflammatory macrophages to promote the progression of atherosclerosis. The noninvasive detection of their presence and dynamic variation will be important to the understanding of their role in the pathogenesis of atherosclerosis. The goal of this study was to develop a targeted PET radiotracer for imaging CD163-positive (CD163+) macrophages in multiple mouse atherosclerosis models and assess the potential of CD163 as a biomarker for atherosclerosis in humans. Methods: CD163-binding peptide was identified using phage display and conjugated with a NODAGA chelator for 64Cu radiolabeling ([64Cu]Cu-ICT-01). CD163-overexpressing U87 cells were used to measure the binding affinity of [64Cu]Cu-ICT-01. Biodistribution studies were performed on wild-type C57BL/6 mice at multiple time points after tail vein injection. The sensitivity and specificity of [64Cu]Cu-ICT-01 in imaging CD163+ macrophages upregulated on the surface of atherosclerotic plaques were assessed in multiple mouse atherosclerosis models. Immunostaining, flow cytometry, and single-cell RNA sequencing were performed to characterize the expression of CD163 on tissue-resident macrophages. Human carotid atherosclerotic plaques were used to measure the expression of CD163+ resident macrophages and test the binding specificity of [64Cu]Cu-ICT-01. Results: [64Cu]Cu-ICT-01 showed high binding affinity to U87 cells. The biodistribution study showed rapid blood and renal clearance with low retention in all major organs at 1, 2, and 4 h after injection. In an ApoE-/- mouse model, [64Cu]Cu-ICT-01 demonstrated sensitive and specific detection of CD163+ macrophages and capability for tracking the progression of atherosclerotic lesions; these findings were further confirmed in Ldlr-/- and PCSK9 mouse models. Immunostaining showed elevated expression of CD163+ macrophages across the plaques. Flow cytometry and single-cell RNA sequencing confirmed the specific expression of CD163 on tissue-resident macrophages. Human tissue characterization demonstrated high expression of CD163+ macrophages on atherosclerotic lesions, and ex vivo autoradiography revealed specific binding of [64Cu]Cu-ICT-01 to human CD163. Conclusion: This work reported the development of a PET radiotracer binding CD163+ macrophages. The elevated expression of CD163+ resident macrophages on human plaques indicated the potential of CD163 as a biomarker for vulnerable plaques. The sensitivity and specificity of [64Cu]Cu-ICT-01 in imaging CD163+ macrophages warrant further investigation in translational settings.

Antibody-mediated targeting of human microglial leukocyte Ig-like receptor B4 attenuates amyloid pathology in a mouse model

Microglia help limit the progression of Alzheimer's disease (AD) by constraining amyloid-β (Aβ) pathology, effected through a balance of activating and inhibitory intracellular signals delivered by distinct cell surface receptors. Human leukocyte Ig-like receptor B4 (LILRB4) is an inhibitory receptor of the immunoglobulin (Ig) superfamily that is expressed on myeloid cells and recognizes apolipoprotein E (ApoE) among other ligands. Here, we find that LILRB4 is highly expressed in the microglia of patients with AD. Using mice that accumulate Aβ and carry a transgene encompassing a portion of the LILR region that includes LILRB4, we corroborated abundant LILRB4 expression in microglia wrapping around Aβ plaques. Systemic treatment of these mice with an anti-human LILRB4 monoclonal antibody (mAb) reduced Aβ load, mitigated some Aβ-related behavioral abnormalities, enhanced microglia activity, and attenuated expression of interferon-induced genes. In vitro binding experiments established that human LILRB4 binds both human and mouse ApoE and that anti-human LILRB4 mAb blocks such interaction. In silico modeling, biochemical, and mutagenesis analyses identified a loop between the two extracellular Ig domains of LILRB4 required for interaction with mouse ApoE and further indicated that anti-LILRB4 mAb may block LILRB4-mApoE by directly binding this loop. Thus, targeting LILRB4 may be a potential therapeutic avenue for AD.

Development of a CCR2 targeted 18F-labeled radiotracer for atherosclerosis imaging with PET

Atherosclerosis is a chronic inflammatory disease and the leading cause of morbidity and mortality worldwide. CC motif chemokine ligand 2 and its corresponding cognate receptor 2 (CCL2/CCR2) signaling has been implicated in regulating monocyte recruitment and macrophage polarization during inflammatory responses that plays a pivotal role in atherosclerosis initiation and progression. In this study, we report the design and synthesis of a novel 18F radiolabeled small molecule radiotracer for CCR2-targeted positron emission tomography (PET) imaging in atherosclerosis. The binding affinity of this radiotracer to CCR2 was evaluated via in vitro binding assay using CCR2+ membrane and cells. Ex vivo biodistribution was carried out in wild type mice to assess radiotracer pharmacokinetics. CCR2 targeted PET imaging of plaques was performed in two murine atherosclerotic models. The sensitive detection of atherosclerotic lesions highlighted the potential of this radiotracer for CCR2 targeted PET and warranted further optimization.

Toward Quantitative Multisite Preclinical Imaging Studies in Acute Myocardial Infarction: Evaluation of the Immune-Fibrosis Axis

The immune-fibrosis axis plays a critical role in cardiac remodeling after acute myocardial infarction. Imaging approaches to monitor temporal inflammation and fibroblast activation in mice have seen wide application in recent years. However, the repeatability of quantitative measurements remains challenging, particularly across multiple imaging centers. We aimed to determine reproducibility of quantitative inflammation and fibroblast activation images acquired at 2 facilities after myocardial infarction in mice. Methods: Mice underwent coronary artery ligation and sequential imaging with 68Ga-DOTA-ECL1i to assess chemokine receptor type 2 expression at 3 d after myocardial infarction and 68Ga-FAPI-46 to assess fibroblast activation protein expression at 7 d after myocardial infarction. Images were acquired at 1 center using either a local or a consensus protocol developed with the second center; the protocols differed in the duration of isoflurane anesthesia and the injected tracer dose. A second group of animals were scanned at the second site using the consensus protocol. Image analyses performed by each site and just by 1 site were also compared. Results: The uptake of 68Ga-DOTA-ECL1i in the infarct territory tended to be higher when the consensus protocol was used (P = 0.03). No difference was observed between protocol acquisitions for 68Ga-FAPI-46. Compared with the local protocol, the consensus protocol decreased variability between individual animals. When a matched consensus protocol was used, the 68Ga-DOTA-ECL1i infarct territory percentage injected dose per gram of tissue was higher on images acquired at site B than on those acquired at site A (P = 0.006). When normalized to body weight as SUV, this difference was mitigated. Both the percentage injected dose per gram of tissue and the SUV were comparable between sites for 68Ga-FAPI-46. Image analyses at the sites differed significantly, but this difference was mitigated when all images were analyzed at site A. Conclusion: The application of a standardized acquisition protocol may lower variability within datasets and facilitate comparison of molecular radiotracer distribution between preclinical imaging centers. Like clinical studies, multicenter preclinical studies should use centralized core-based image analysis to maximize reproducibility across sites.

Chemokine Receptor 2 Targeted PET/CT Imaging Distant Metastases in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and treatment-refractory malignancies. The lack of an effective screening tool results in the majority of patients being diagnosed at late stages, which underscores the urgent need to develop more sensitive and specific imaging modalities, particularly in detecting occult metastases, to aid clinical decision-making. The tumor microenvironment of PDAC is heavily infiltrated with myeloid-derived suppressor cells (MDSCs) that express C-C chemokine receptor type 2 (CCR2). These CCR2-expressing MDSCs accumulate at a very early stage of metastasis and greatly outnumber PDAC cells, making CCR2 a promising target for detecting early, small metastatic lesions that have scant PDAC cells. Herein, we evaluated a CCR2 targeting PET tracer (68Ga-DOTA-ECL1i) for PET imaging on PDAC metastasis in two mouse models. Positron emission tomography/computed tomography (PET/CT) imaging of 68Ga-DOTA-ECL1i was performed in a hemisplenic injection metastasis model (KI) and a genetically engineered orthotopic PDAC model (KPC), which were compared with 18F-FDG PET concurrently. Autoradiography, hematoxylin and eosin (H&E), and CCR2 immunohistochemical staining were performed to characterize the metastatic lesions. PET/CT images visualized the PDAC metastases in the liver/lung of KI mice and in the liver of KPC mice. Quantitative uptake analysis revealed increased metastasis uptake during disease progression in both models. In comparison, 18F-FDG PET failed to detect any metastases during the time course studies. H&E staining showed metastases in the liver and lung of KI mice, within which immunostaining clearly demonstrated the overexpression of CCR2 as well as CCR2+ cell infiltration into the normal liver. H&E staining, CCR2 staining, and autoradiography also confirmed the expression of CCR2 and the uptake of 68Ga-DOTA-ECL1i in the metastatic foci in KPC mice. Using our novel CCR2 targeted radiotracer 68Ga-DOTA-ECL1i and PET/CT, we demonstrated the sensitive and specific detection of CCR2 in the early PDAC metastases in two mouse models, indicating its potential in future clinical translation.

Expansion of Pathogenic Cardiac Macrophages in Immune Checkpoint Inhibitor Myocarditis

BACKGROUND

Immune checkpoint inhibitors (ICIs), antibodies targeting PD-1 (programmed cell death protein 1)/PD-L1 (programmed death-ligand 1) or CTLA4 (cytotoxic T-lymphocyte-associated protein 4), have revolutionized cancer management but are associated with devastating immune-related adverse events including myocarditis. The main risk factor for ICI myocarditis is the use of combination PD-1 and CTLA4 inhibition. ICI myocarditis is often fulminant and is pathologically characterized by myocardial infiltration of T lymphocytes and macrophages. Although much has been learned about the role of T-cells in ICI myocarditis, little is understood about the identity, transcriptional diversity, and functions of infiltrating macrophages.

METHODS

We used an established murine ICI myocarditis model (Ctla4+/-Pdcd1-/- mice) to explore the cardiac immune landscape using single-cell RNA-sequencing, immunostaining, flow cytometry, in situ RNA hybridization, molecular imaging, and antibody neutralization studies.

RESULTS

We observed marked increases in CCR2 (C-C chemokine receptor type 2)+ monocyte-derived macrophages and CD8+ T-cells in this model. The macrophage compartment was heterogeneous and displayed marked enrichment in an inflammatory CCR2+ subpopulation highly expressing Cxcl9 (chemokine [C-X-C motif] ligand 9), Cxcl10 (chemokine [C-X-C motif] ligand 10), Gbp2b (interferon-induced guanylate-binding protein 2b), and Fcgr4 (Fc receptor, IgG, low affinity IV) that originated from CCR2+ monocytes. It is important that a similar macrophage population expressing CXCL9, CXCL10, and CD16α (human homologue of mouse FcgR4) was expanded in patients with ICI myocarditis. In silico prediction of cell-cell communication suggested interactions between T-cells and Cxcl9+Cxcl10+ macrophages via IFN-γ (interferon gamma) and CXCR3 (CXC chemokine receptor 3) signaling pathways. Depleting CD8+ T-cells or macrophages and blockade of IFN-γ signaling blunted the expansion of Cxcl9+Cxcl10+ macrophages in the heart and attenuated myocarditis, suggesting that this interaction was necessary for disease pathogenesis.

CONCLUSIONS

These data demonstrate that ICI myocarditis is associated with the expansion of a specific population of IFN-γ-induced inflammatory macrophages and suggest the possibility that IFN-γ blockade may be considered as a treatment option for this devastating condition.

Chemokine Receptor 2 Is A Theranostic Biomarker for Abdominal Aortic Aneurysms

Abdominal aortic aneurysm (AAA) is a degenerative vascular disease impacting aging populations with a high mortality upon rupture. There are no effective medical therapies to prevent AAA expansion and rupture. We previously demonstrated the role of the monocyte chemoattractant protein-1 (MCP-1) / C-C chemokine receptor type 2 (CCR2) axis in rodent AAA pathogenesis via positron emission tomography/computed tomography (PET/CT) using CCR2 targeted radiotracer 64 Cu-DOTA-ECL1i. We have since translated this radiotracer into patients with AAA. CCR2 PET showed intense radiotracer uptake along the AAA wall in patients while little signal was observed in healthy volunteers. AAA tissues collected from individuals scanned with 64 Cu-DOTA-ECL1i and underwent open-repair later demonstrated more abundant CCR2+ cells compared to non-diseased aortas. We then used a CCR2 inhibitor (CCR2i) as targeted therapy in our established male and female rat AAA rupture models. We observed that CCR2i completely prevented AAA rupture in male rats and significantly decreased rupture rate in female AAA rats. PET/CT revealed substantial reduction of 64 Cu-DOTA-ECL1i uptake following CCR2i treatment in both rat models. Characterization of AAA tissues demonstrated decreased expression of CCR2+ cells and improved histopathological features. Taken together, our results indicate the potential of CCR2 as a theranostic biomarker for AAA management.

Multiparametric Immunoimaging Maps Inflammatory Signatures in Murine Myocardial Infarction Models

In the past 2 decades, research on atherosclerotic cardiovascular disease has uncovered inflammation to be a key driver of the pathophysiological process. A pressing need therefore exists to quantitatively and longitudinally probe inflammation, in preclinical models and in cardiovascular disease patients, ideally using non-invasive methods and at multiple levels. Here, we developed and employed in vivo multiparametric imaging approaches to investigate the immune response following myocardial infarction. The myocardial infarction models encompassed either transient or permanent left anterior descending coronary artery occlusion in C57BL/6 and Apoe-/-mice. We performed nanotracer-based fluorine magnetic resonance imaging and positron emission tomography (PET) imaging using a CD11b-specific nanobody and a C-C motif chemokine receptor 2-binding probe. We found that immune cell influx in the infarct was more pronounced in the permanent occlusion model. Further, using 18F-fluorothymidine and 18F-fluorodeoxyglucose PET, we detected increased hematopoietic activity after myocardial infarction, with no difference between the models. Finally, we observed persistent systemic inflammation and exacerbated atherosclerosis in Apoe-/- mice, regardless of which infarction model was used. Taken together, we showed the strengths and capabilities of multiparametric imaging in detecting inflammatory activity in cardiovascular disease, which augments the development of clinical readouts.

Expansion of Disease Specific Cardiac Macrophages in Immune Checkpoint Inhibitor Myocarditis

Background

Immune checkpoint inhibitors (ICIs), antibodies targeting PD-1/PD-L1 or CTLA4 have revolutionized cancer management but are associated with devastating immune-related adverse events (irAEs) including myocarditis. The main risk factor for ICI myocarditis is the use of combination PD-1 and CTLA4 inhibition. ICI-myocarditis is often fulminant and is pathologically characterized by myocardial infiltration of T lymphocytes and macrophages. While much has been learned regarding the role of T-cells in ICI-myocarditis, little is understood regarding the identity, transcriptional diversity, and functions of infiltrating macrophages.

Methods

We employed an established murine ICI myocarditis model ( Ctla4 +/- Pdcd1 -/- mice) to explore the cardiac immune landscape using single-cell RNA-sequencing, immunostaining, flow cytometry, in situ RNA hybridization and molecular imaging and antibody neutralization studies.

Results

We observed marked increases in CCR2 + monocyte-derived macrophages and CD8 + T-cells in this model. The macrophage compartment was heterogeneous and displayed marked enrichment in an inflammatory CCR2 + subpopulation highly expressing Cxcl9 , Cxcl10 , Gbp2b , and Fcgr4 that originated from CCR2 + monocytes. Importantly, a similar macrophage population expressing CXCL9 , CXCL10 , and CD16α (human homologue of mouse FcgR4) was found selectively expanded in patients with ICI myocarditis compared to other forms of heart failure and myocarditis. In silico prediction of cell-cell communication suggested interactions between T-cells and Cxcl9 + Cxcl10 + macrophages via IFN-γ and CXCR3 signaling pathways. Depleting CD8 + T-cells, macrophages, and blockade of IFN-γ signaling blunted the expansion of Cxcl9 + Cxcl10 + macrophages in the heart and attenuated myocarditis suggesting that this interaction was necessary for disease pathogenesis.

Conclusion

These data demonstrate that ICI-myocarditis is associated with the expansion of a specific population of IFN-γ induced inflammatory macrophages and suggest the possibility that IFN-γ blockade may be considered as a treatment option for this devastating condition.

Positron Emission Tomography Imaging of Vessel Wall Matrix Metalloproteinase Activity in Abdominal Aortic Aneurysm

BACKGROUND

Matrix metalloproteinases (MMPs) play a key role in the pathogenesis of abdominal aortic aneurysm (AAA). Imaging aortic MMP activity, especially using positron emission tomography to access high sensitivity, quantitative data, could potentially improve AAA risk stratification. Here, we describe the design, synthesis, characterization, and evaluation in murine AAA and human aortic tissue of a first-in-class MMP-targeted positron emission tomography radioligand, 64Cu-RYM2.

METHODS

The broad spectrum MMP inhibitor, RYM2 was synthetized, and its potency as an MMP inhibitor was evaluated by a competitive inhibition assay. Toxicology studies were performed. Tracer biodistribution was evaluated in a murine model of AAA induced by angiotensin II infusion in Apolipoprotein E-deficient mice. 64Cu-RYM2 binding to normal and aneurysmal human aortic tissues was assessed by autoradiography.

RESULTS

RYM2 functioned as an MMP inhibitor with nanomolar affinities. Toxicology studies showed no adverse reaction in mice. Upon radiolabeling with Cu-64, the resulting tracer was stable in murine and human blood in vitro. Biodistribution and metabolite analysis in mice showed rapid renal clearance and acceptable in vivo stability. In vivo positron emission tomography/computed tomography in a murine model of AAA showed a specific aortic signal, which correlated with ex vivo measured MMP activity and Cd68 gene expression. 64Cu-RYM2 specifically bound to normal and aneurysmal human aortic tissues in correlation with MMP activity.

CONCLUSIONS

64Cu-RYM2 is a first-in-class MMP-targeted positron emission tomography tracer with favorable stability, biodistribution, performance in preclinical AAA, and importantly, specific binding to human tissues. These data set the stage for 64Cu-RYM2-based translational imaging studies of vessel wall MMP activity, and indirectly, inflammation, in AAA.

Nuclear Methods for Immune Cell Imaging: Bridging Molecular Imaging and Individualized Medicine

Inflammation is a key mechanistic contributor to the progression of cardiovascular disease, from atherosclerosis through ischemic injury and overt heart failure. Recent evidence has identified specific roles of immune cell subpopulations in cardiac pathogenesis that diverges between individual patients. Nuclear imaging approaches facilitate noninvasive and serial quantification of inflammation severity, offering the opportunity to predict eventual outcome, stratify patient risk, and guide novel targeted molecular therapies against specific leukocyte subpopulations. Here, we will discuss the established and emerging nuclear imaging methods to label and track exogenous and endogenous immune cells, with a particular focus on clinical situations in which targeted molecular inflammation imaging would be advantageous. The expanding options for imaging inflammation provide the foundation to bridge between molecular imaging and individual therapy.

A Long-Circulating Vector for Aptamers Based upon Polyphosphodiester-Backboned Molecular Brushes

Aptamers face challenges for use outside the ideal conditions in which they are developed. These difficulties are most palpable in vivo due to nuclease activities, rapid clearance, and off-target binding. Herein, we demonstrate that a polyphosphodiester-backboned molecular brush can suppress enzymatic digestion, reduce non-specific cell uptake, enable long blood circulation, and rescue the bioactivity of a conjugated aptamer in vivo. The backbone along with the aptamer is assembled via solid-phase synthesis, followed by installation of poly(ethylene glycol) (PEG) side chains using a two-step process with near-quantitative efficiency. The synthesis allows for precise control over polymer size and architecture. Consisting entirely of building blocks that are generally recognized as safe for therapeutics, this novel molecular brush is expected to provide a highly translatable route for aptamer-based therapeutics.

Reprogramming alveolar macrophage responses to TGF-β reveals CCR2+ monocyte activity that promotes bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is a major impediment to lung transplant survival and is generally resistant to medical therapy. Extracorporeal photophoresis (ECP) is an immunomodulatory therapy that shows promise in stabilizing BOS patients, but its mechanisms of action are unclear. In a mouse lung transplant model, we show that ECP blunts alloimmune responses and inhibits BOS through lowering airway TGF-β bioavailability without altering its expression. Surprisingly, ECP-treated leukocytes were primarily engulfed by alveolar macrophages (AMs), which were reprogrammed to become less responsive to TGF-β and reduce TGF-β bioavailability through secretion of the TGF-β antagonist decorin. In untreated recipients, high airway TGF-β activity stimulated AMs to express CCL2, leading to CCR2+ monocyte-driven BOS development. Moreover, we found TGF-β receptor 2-dependent differentiation of CCR2+ monocytes was required for the generation of monocyte-derived AMs, which in turn promoted BOS by expanding tissue-resident memory CD8+ T cells that inflicted airway injury through Blimp-1-mediated granzyme B expression. Thus, through studying the effects of ECP, we have identified an AM functional plasticity that controls a TGF-β-dependent network that couples CCR2+ monocyte recruitment and differentiation to alloimmunity and BOS.

Cardiac immune cell infiltration associates with abnormal lipid metabolism

CD36 mediates the uptake of long-chain fatty acids (FAs), a major energy substrate for the myocardium. Under excessive FA supply, CD36 can cause cardiac lipid accumulation and inflammation while its deletion reduces heart FA uptake and lipid content and increases glucose utilization. As a result, CD36 was proposed as a therapeutic target for obesity-associated heart disease. However, more recent reports have shown that CD36 deficiency suppresses myocardial flexibility in fuel preference between glucose and FAs, impairing tissue energy balance, while CD36 absence in tissue macrophages reduces efferocytosis and myocardial repair after injury. In line with the latter homeostatic functions, we had previously reported that CD36^-/- mice have chronic subclinical inflammation. Lipids are important for the maintenance of tissue homeostasis and there is limited information on heart lipid metabolism in CD36 deficiency. Here, we document in the hearts of unchallenged CD36^-/- mice abnormalities in the metabolism of triglycerides, plasmalogens, cardiolipins, acylcarnitines, and arachidonic acid, and the altered remodeling of these lipids in response to an overnight fast. The hearts were examined for evidence of inflammation by monitoring the presence of neutrophils and pro-inflammatory monocytes/macrophages using the respective positron emission tomography (PET) tracers, ⁶⁴Cu-AMD3100 and ⁶⁸Ga-DOTA-ECL1i. We detected significant immune cell infiltration in unchallenged CD36^-/- hearts as compared with controls and immune infiltration was also observed in hearts of mice with cardiomyocyte-specific CD36 deficiency. Together, the data show that the CD36^-/- heart is in a non-homeostatic state that could compromise its stress response. Non-invasive immune cell monitoring in humans with partial or total CD36 deficiency could help evaluate the risk of impaired heart remodeling and disease.

Reverse translation approach generates a signature of penetrating fibrosis in Crohn's disease that is associated with anti-TNF response

OBJECTIVE

Fibrosis is a common feature of Crohn's disease (CD) which can involve the mesenteric fat. However, the molecular signature of this process remains unclear. Our goal was to define the transcriptional signature of mesenteric fibrosis in CD subjects and to model mesenteric fibrosis in mice to improve our understanding of CD pathogenesis.

DESIGN

We performed histological and transcriptional analysis of fibrosis in CD samples. We modelled a CD-like fibrosis phenotype by performing repeated colonic biopsies in mice and analysed the model by histology, type I collagen-targeted positron emission tomography (PET) and global gene expression. We generated a gene set list of essential features of mesenteric fibrosis and compared it to mucosal biopsy datasets from inflammatory bowel disease patients to identify a refined gene set that correlated with clinical outcomes.

RESULTS

Mesenteric fibrosis in CD was interconnected to areas of fibrosis in all layers of the intestine, defined as penetrating fibrosis. We found a transcriptional signature of differentially expressed genes enriched in areas of the mesenteric fat of CD subjects with high levels of fibrosis. Mice subjected to repeated colonic biopsies showed penetrating fibrosis as shown by histology, PET imaging and transcriptional analysis. Finally, we composed a composite 24-gene set list that was linked to inflammatory fibroblasts and correlated with treatment response.

CONCLUSION

We linked histopathological and molecular features of CD penetrating fibrosis to a mouse model of repeated biopsy injuries. This experimental system provides an innovative approach for functional investigations of underlying profibrotic mechanisms and therapeutic concepts in CD.

C-X-C Chemokine Receptor Type 4-Targeted Imaging in Glioblastoma Multiforme Using 64Cu-Radiolabeled Ultrasmall Gold Nanoclusters

Glioblastoma multiforme (GBM) is the most prevalent and aggressive primary malignant brain cancer in adults, and it carries a poor prognosis. Despite the current multimodality treatment, including surgery, radiation, and chemotherapy, the overall survival is still poor. Neurooncological imaging plays an important role in the initial diagnosis and prediction of the treatment response of GBM. Positron emission tomography (PET) imaging using radiotracers that target disease-specific hallmarks, which are both noninvasive and specific, has drawn much attention. C-X-C chemokine receptor 4 (CXCR4) plays an important role in neoangiogenesis and vasculogenesis, and, moreover, it is reported to be overexpressed in GBM, which is associated with poor patient survival; thus, CXCR4 can be an ideal candidate for PET imaging of GBM. Nanomaterials, which possess multifunctional capabilities, effective drug delivery, and favorable pharmacokinetics, are now being applied to improve the diagnosis and therapy of the most difficult-to-treat cancers. Herein, we engineered an ultrasmall, renal-clearable gold nanoclusters intrinsically radiolabeled with ⁶⁴Cu (⁶⁴Cu-AuNCs-FC131) for targeted PET imaging of CXCR4 in a U87 intracranial GBM mouse model. These targeted nanoclusters demonstrated specific binding to U87 cells with minimal cytotoxicity. The in vivo biodistribution showed favorable pharmacokinetics and efficient renal clearance. PET/computed tomography imaging of the U87 model revealed the effective delivery of ⁶⁴Cu-AuNCs-FC131 into the tumors. In vivo toxicity studies demonstrated insignificant safety concerns at various dosages, indicating its potential as a useful platform for GBM imaging and drug delivery.

Assessment of ultrasmall nanocluster for early and accurate detection of atherosclerosis using positron emission tomography/computed tomography

The development of atherosclerosis therapy is hampered by the lack of molecular imaging tools to identify the relevant biomarkers and determine the dynamic variation in vivo. Here, we show that a chemokine receptor 2 (CCR2) targeted gold nanocluster conjugated with extracellular loop 1 inverso peptide (AuNC-ECL1i) determines the initiation, progression and regression of atherosclerosis in apolipoprotein E knock-out (ApoE^-/-) mouse models. The CCR2 targeted ⁶⁴Cu-AuNC-ECL1i reveals sensitive detection of early atherosclerotic lesions and progression of plaques in ApoE^-/- mice. CCR2 targeting specificity was confirmed by the competitive receptor blocking studies. In a mouse model of aortic arch transplantation, ⁶⁴Cu-AuNC-ECL1i accurately detects the regression of plaques. Human atherosclerotic tissues show high expression of CCR2 related to the status of the disease. This study confirms CCR2 as a useful marker for atherosclerosis and points to the potential of ⁶⁴Cu-AuNC-ECL1i as a targeted molecular imaging probe for future clinical translation.

The Latest Advances in Imaging Crosstalk Between the Immune System and Fibrosis in Cardiovascular Disease

Inflammation and fibrosis are hallmarks of tissue repair process and organ failure progression in cardiovascular diseases. Paradigm-shifting research on diverse immune cell populations within the cardiovascular system have enabled discovery of new biomarkers fostering development of diagnostic and therapeutic agents at the molecular level to better manage cardiovascular diseases. To date, a variety of molecular imaging agents have been developed to visualize the biomarkers expressed on immune cells and fibroblasts within their crosstalk network, which drives the pathogenesis of fibrosis triggered by both innate and adaptive immunity. Herein, key biomarkers up-regulated in the immune-fibrosis axis are discussed. The promising molecular imaging agents to reveal this critical pathological process are summarized.

Ultrasmall Nanoclusters: Synthesis and Applications as an Emerging Platform for Imaging and Therapy

Background:

Ultrasmall nanoclusters (USNCs) have attracted tremendous attention owing to their unique properties that make them desirable for the development of personalized medicine, such as tunable emission, straightforward modification, and renal clearance. Hence, USNCs have emerged as potential materials for nanotheranostics.

Objective:

For decades, great efforts have been devoted to the bio-applications of USNCs, promising platforms to satisfy the increasing demand for precise diagnostic and targeted therapeutics. Herein, we summarize the most recent advances of USNCs in biomedical applications and provide our perspective on the future development of USNCs.

Results:

This review briefly summarized the synthetic methods of metallic USNCs and discussed their recent applications for cancer imaging and therapy.

Conclusion:

USNCs have shown their potential for accurate diagnosis and specific delivery of therapeutics in preclinical research.

CC Chemokine Receptor 5 Targeted Nanoparticles Imaging the Progression and Regression of Atherosclerosis Using Positron Emission Tomography/Computed Tomography

Chemokines and chemokine receptors play an important role in the initiation and progression of atherosclerosis by mediating the trafficking of inflammatory cells. Chemokine receptor 5 (CCR5) has major implications in promoting the development of plaques to advanced stage and related vulnerability. CCR5 antagonist has demonstrated the effective inhibition of atherosclerotic progression in mice, making it a potential biomarker for atherosclerosis management. To accurately determine CCR5 in vivo, we synthesized CCR5 targeted Comb nanoparticles through a modular design and construction strategy with control over the physiochemical properties and functionalization of CCR5 targeting peptide d-Ala-peptide T-amide (DAPTA-Comb). In vivo pharmacokinetic evaluation through 64Cu radiolabeling showed extended blood circulation of 64Cu-DAPTA-Combs conjugated with 10%, 25%, and 40% DAPTA. The different organ distribution profiles of the three nanoparticles demonstrated the effect of DAPTA on not only physicochemical properties but also targeting efficiency. In vivo positron emission tomography/computed tomography (PET/CT) imaging in an apolipoprotein E knockout mouse atherosclerosis model (ApoE-/-) showed that the three 64Cu-DAPTA-Combs could sensitively and specifically detect CCR5 along the progression of atherosclerotic lesions. In an ApoE-encoding adenoviral vector (AAV) induced plaque regression ApoE-/- mouse model, decreased monocyte recruitment, CD68+ macrophages, CCR5 expression, and plaque size were all associated with reduced PET signals, which not only further confirmed the targeting efficiency of 64Cu-DAPTA-Combs but also highlighted the potential of these targeted nanoparticles for atherosclerosis imaging. Moreover, the up-regulation of CCR5 and colocalization with CD68+ macrophages in the necrotic core of ex vivo human plaque specimens warrant further investigation for atherosclerosis prognosis.

CXCR4-Binding Positron Emission Tomography Tracers Link Monocyte Recruitment and Endothelial Injury in Murine Atherosclerosis

OBJECTIVE

vMIP-II (viral macrophage inflammatory protein 2)/vCCL2 (viral chemotactic cytokine ligand 2) binds to multiple chemokine receptors, and vMIP-II-based positron emission tomography tracer (64Cu-DOTA-vMIP-II: vMIP-II tracer) accumulates at atherosclerotic lesions in mice. Given that it would be expected to react with multiple chemokine receptors on monocytes and macrophages, we wondered if its accumulation in atherosclerosis lesion-bearing mice might correlate with overall macrophage burden or, alternatively, the pace of monocyte recruitment. Approach and Results: We employed a mouse model of atherosclerosis regression involving adenoassociated virus 8 vector encoding murine Apoe (AAV-mApoE) treatment of Apoe-/- mice where the pace of monocyte recruitment slows before macrophage burden subsequently declines. Accumulation of 64Cu-DOTA-vMIP-II at Apoe-/- plaque sites was strong but declined with AAV-mApoE-induced decline in monocyte recruitment, before macrophage burden reduced. Monocyte depletion indicated that monocytes and macrophages themselves were not the only target of the 64Cu-DOTA-vMIP-II tracer. Using fluorescence-tagged vMIP-II tracer, competitive receptor blocking with CXCR4 antagonists, endothelial-specific Cre-mediated deletion of CXCR4, CXCR4-specific tracer 64Cu-DOTA-FC131, and CXCR4 staining during disease progression and regression, we show endothelial cell expression of CXCR4 is a key target of 64Cu-DOTA-vMIP-II imaging. Expression of CXCR4 was low in nonplaque areas but strongly detected on endothelium of progressing plaques, especially on proliferating endothelium, where vascular permeability was increased and monocyte recruitment was the strongest.

CONCLUSIONS

Endothelial injury status of plaques is marked by CXCR4 expression and this injury correlates with the tendency of such plaques to recruit monocytes. Furthermore, our findings suggest positron emission tomography tracers that mark CXCR4 can be used translationally to monitor the state of plaque injury and monocyte recruitment.

CC Chemokine Receptor 2-Targeting Copper Nanoparticles for Positron Emission Tomography-Guided Delivery of Gemcitabine for Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy with dire prognosis due to aggressive biology, lack of effective tools for diagnosis at an early stage, and limited treatment options. Detection of PDAC using conventional radiographic imaging is limited by the dense, hypovascular stromal component and relatively scarce neoplastic cells within the tumor microenvironment (TME). The CC motif chemokine 2 (CCL2) and its cognate receptor CCR2 (CCL2/CCR2) axis are critical in fostering and maintaining this kind of TME by recruiting immunosuppressive myeloid cells such as the tumor-associated macrophages, thereby presenting an opportunity to exploit this axis for both diagnostic and therapeutic purposes. We engineered CCR2-targeting ultrasmall copper nanoparticles (Cu@CuOx) as nanovehicles not only for targeted positron emission tomography imaging by intrinsic radiolabeling with 64Cu but also for loading and delivery of the chemotherapy drug gemcitabine to PDAC. This 64Cu-radiolabeled nanovehicle allowed sensitive and accurate detection of PDAC malignancy in autochthonous genetically engineered mouse models. The ultrasmall Cu@CuOx showed efficient renal clearance, favorable pharmacokinetics, and minimal in vivo toxicity. Systemic administration of gemcitabine-loaded Cu@CuOx effectively suppressed the progression of PDAC tumors in a syngeneic xenograft mouse model and prolonged survival. These CCR2-targeted ultrasmall nanoparticles offer a promising image-guided therapeutic agent and show great potential for translation.

Chemokine Receptor 2-targeted Molecular Imaging in Pulmonary Fibrosis. A Clinical Trial

Rationale: Idiopathic pulmonary fibrosis (IPF) is a progressive inflammatory lung disease without effective molecular markers of disease activity or treatment responses. Monocyte and interstitial macrophages that express the C-C motif CCR2 (chemokine receptor 2) are active in IPF and central to fibrosis.Objectives: To phenotype patients with IPF for potential targeted therapy, we developed ⁶⁴Cu-DOTA-ECL1i, a radiotracer to noninvasively track CCR2⁺ monocytes and macrophages using positron emission tomography (PET).Methods: CCR2⁺ cells were investigated in mice with bleomycin- or radiation-induced fibrosis and in human subjects with IPF. The CCR2⁺ cell populations were localized relative to fibrotic regions in lung tissue and characterized using immunolocalization, single-cell mass cytometry, and Ccr2 RNA in situ hybridization and then correlated with parallel quantitation of lung uptake by ⁶⁴Cu-DOTA-ECL1i PET.Measurements and Main Results: Mouse models established that increased ⁶⁴Cu-DOTA-ECL1i PET uptake in the lung correlates with CCR2⁺ cell infiltration associated with fibrosis (n = 72). As therapeutic models, the inhibition of fibrosis by IL-1β blockade (n = 19) or antifibrotic pirfenidone (n = 18) reduced CCR2⁺ macrophage accumulation and uptake of the radiotracer in mouse lungs. In lung tissues from patients with IPF, CCR2⁺ cells concentrated in perifibrotic regions and correlated with radiotracer localization (n = 21). Human imaging revealed little lung uptake in healthy volunteers (n = 7), whereas subjects with IPF (n = 4) exhibited intensive signals in fibrotic zones.Conclusions: These findings support a role for imaging CCR2⁺ cells within the fibrogenic niche in IPF to provide a molecular target for personalized therapy and monitoring.Clinical trial registered with www.clinicaltrials.gov (NCT03492762).

Magnetic Resonance Imaging-Guided Focused Ultrasound-Based Delivery of Radiolabeled Copper Nanoclusters to Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine glioma (DIPG) is an invasive pediatric brainstem malignancy exclusively in children without effective treatment due to the often-intact blood-brain tumor barrier (BBTB), an impediment to the delivery of therapeutics. Herein, we used focused ultrasound (FUS) to transiently open BBTB and delivered radiolabeled nanoclusters (⁶⁴Cu-CuNCs) to tumors for positron emission tomography (PET) imaging and quantification in a mouse DIPG model. First, we optimized FUS acoustic pressure to open the blood-brain barrier (BBB) for effective delivery of ⁶⁴Cu-CuNCs to pons in wildtype mice. Then the optimized FUS pressure was used to deliver radiolabeled agents in DIPG mouse. Magnetic resonance imaging (MRI)-guided FUS-induced BBTB opening was demonstrated using a low molecular weight, short-lived ⁶⁸Ga-DOTA-ECL1i radiotracer and PET/CT before and after treatment. We then compared the delivery efficiency of ⁶⁴Cu-CuNCs to DIPG tumor with and without FUS treatment and demonstrated the FUS-enhanced delivery and time-dependent diffusion of ⁶⁴Cu-CuNCs within the tumor.

Targeted PET Imaging of Chemokine Receptor 2-Positive Monocytes and Macrophages in the Injured Heart

Proinflammatory macrophages are important mediators of inflammation after myocardial infarction and of allograft injury after heart transplantation. The aim of this study was to image the recruitment of proinflammatory chemokine receptor 2-positive (CCR2+) cells in multiple heart injury models. Methods: ⁶⁴Cu-DOTA-extracellular loop 1 inverso (ECL1i) PET was used to image CCR2+ monocytes and macrophages in a heart transplantation mouse model. Flow cytometry was performed to characterize CCR2+ cells. Autoradiography on a human heart specimen was conducted to confirm binding specificity. ⁶⁴Cu- and ⁶⁸Ga-DOTA-ECL1i were compared in an ischemia-reperfusion injury mouse model. Results: ⁶⁴Cu-DOTA-ECL1i showed sensitive and specific detection of CCR2+ cells in all tested mouse models, with efficacy comparable to that of ⁶⁸Ga-DOTA-ECL1i. Flow cytometry demonstrated specific expression of CCR2 on monocytes and macrophages. The tracer binds to human CCR2. Conclusion: This work establishes the utility of ⁶⁴Cu-DOTA-ECL1i to image CCR2+ monocytes and macrophages in mouse models and provides the requisite preclinical information to translate the targeted clinical-grade CCR2 imaging probe for clinical investigation of heart diseases.

CCR2 Positron Emission Tomography for the Assessment of Abdominal Aortic Aneurysm Inflammation and Rupture Prediction

BACKGROUND

The monocyte chemoattractant protein-1/CCR2 (chemokine receptor 2) axis plays an important role in abdominal aortic aneurysm (AAA) pathogenesis, with effects on disease progression and anatomic stability. We assessed the expression of CCR2 in a rodent model and human tissues, using a targeted positron emission tomography radiotracer (⁶⁴Cu-DOTA-ECL1i).

METHODS

AAAs were generated in Sprague-Dawley rats by exposing the infrarenal, intraluminal aorta to PPE (porcine pancreatic elastase) under pressure to induce aneurysmal degeneration. Heat-inactivated PPE was used to generate a sham operative control. Rat AAA rupture was stimulated by the administration of β-aminopropionitrile, a lysyl oxidase inhibitor. Biodistribution was performed in wild-type rats at 1 hour post tail vein injection of ⁶⁴Cu-DOTA-ECL1i. Dynamic positron emission tomography/computed tomography imaging was performed in rats to determine the in vivo distribution of radiotracer.

RESULTS

Biodistribution showed fast renal clearance. The localization of radiotracer uptake in AAA was verified with high-resolution computed tomography. At day 7 post-AAA induction, the radiotracer uptake (standardized uptake value [SUV]=0.91±0.25) was approximately twice that of sham-controls (SUV=0.47±0.10; P<0.01). At 14 days post-AAA induction, radiotracer uptake by either group did not significantly change (AAA SUV=0.86±0.17 and sham-control SUV=0.46±0.10), independent of variations in aortic diameter. Competitive CCR2 receptor blocking significantly decreased AAA uptake (SUV=0.42±0.09). Tracer uptake in AAAs that subsequently ruptured (SUV=1.31±0.14; P<0.005) demonstrated uptake nearly twice that of nonruptured AAAs (SUV=0.73±0.11). Histopathologic characterization of rat and human AAA tissues obtained from surgery revealed increased expression of CCR2 that was co-localized with CD68⁺ macrophages. Ex vivo autoradiography demonstrated specific binding of ⁶⁴Cu-DOTA-ECL1i to CCR2 in both rat and human aortic tissues.

CONCLUSIONS

CCR2 positron emission tomography is a promising new biomarker for the noninvasive assessment of AAA inflammation that may aid in associated rupture prediction.

Molecular Imaging Visualizes Recruitment of Inflammatory Monocytes and Macrophages to the Injured Heart

RATIONALE

Paradigm shifting studies have revealed that the heart contains functionally diverse populations of macrophages derived from distinct embryonic and adult hematopoietic progenitors. Under steady-state conditions, the heart is largely populated by CCR2- (C-C chemokine receptor type 2) macrophages of embryonic descent. After tissue injury, a dramatic shift in macrophage composition occurs whereby CCR2+ monocytes are recruited to the heart and differentiate into inflammatory CCR2+ macrophages that contribute to heart failure progression. Currently, there are no techniques to noninvasively detect CCR2+ monocyte recruitment into the heart and thus identify patients who may be candidates for immunomodulatory therapy.

OBJECTIVE

To develop a noninvasive molecular imaging strategy with high sensitivity and specificity to visualize inflammatory monocyte and macrophage accumulation in the heart.

METHODS AND RESULTS

We synthesized and tested the performance of a positron emission tomography radiotracer (⁶⁸Ga-DOTA [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-ECL1i [extracellular loop 1 inverso]) that allosterically binds to CCR2. In naive mice, the radiotracer was quickly cleared from the blood and displayed minimal retention in major organs. In contrast, biodistribution and positron emission tomography demonstrated strong myocardial tracer uptake in 2 models of cardiac injury (diphtheria toxin induced cardiomyocyte ablation and reperfused myocardial infarction). ⁶⁸Ga-DOTA-ECL1i signal localized to sites of tissue injury and was independent of blood pool activity as assessed by quantitative positron emission tomography and ex vivo autoradiography. ⁶⁸Ga-DOTA-ECL1i uptake was associated with CCR2+ monocyte and CCR2+ macrophage infiltration into the heart and was abrogated in CCR2^-/- mice, demonstrating target specificity. Autoradiography demonstrated that ⁶⁸Ga-DOTA-ECL1i specifically binds human heart failure specimens and with signal intensity associated with CCR2+ macrophage abundance.

CONCLUSIONS

These findings demonstrate the sensitivity and specificity of ⁶⁸Ga-DOTA-ECL1i in the mouse heart and highlight the translational potential of this agent to noninvasively visualize CCR2+ monocyte recruitment and inflammatory macrophage accumulation in patients.

Folate Receptor α-Targeted 89Zr-M9346A Immuno-PET for Image-Guided Intervention with Mirvetuximab Soravtansine in Triple-Negative Breast Cancer

Folate receptor α (FRα) is a well-studied tumor biomarker highly expressed in many epithelial tumors such as breast, ovarian, and lung cancers. Mirvetuximab soravtansine (IMGN853) is the antibody-drug conjugate of FRα-binding humanized monoclonal antibody M9346A and cytotoxic maytansinoid drug DM4. IMGN853 is currently being evaluated in multiple clinical trials, in which the immunohistochemical evaluation of an archival tumor or biopsy specimen is used for patient screening. However, limited tissue collection may lead to inaccurate diagnosis due to tumor heterogeneity. Herein, we developed a zirconium-89 (⁸⁹Zr)-radiolabeled M9346A (⁸⁹Zr-M9346A) as an immuno-positron emission tomography (immuno-PET) radiotracer to evaluate FRα expression in triple-negative breast cancer (TNBC) patients, providing a novel means to guide intervention with therapeutic IMGN853. In this study, we verified the binding specificity and immunoreactivity of ⁸⁹Zr-M9346A by in vitro studies in FRα^high cells (HeLa) and FRα^low cells (OVCAR-3). In vivo PET/computed tomography (PET/CT) imaging in HeLa xenografts and TNBC patient-derived xenograft (PDX) mouse models with various levels of FRα expression demonstrated its targeting specificity and sensitivity. Following PET imaging, the treatment efficiencies of IMGN853, pemetrexed, IMGN853 + pemetrexed, paclitaxel, and saline were assessed in FRα^high and FRα^low TNBC PDX models. The correlation between ⁸⁹Zr-M9346A tumor uptake and treatment response using IMGN853 in FRα^high TNBC PDX model suggested the potential of ⁸⁹Zr-M9346A PET as a noninvasive tool to prescreen patients based on the in vivo PET imaging for IMGN853-targeted treatment.

Assessment of Copper Nanoclusters for Accurate in Vivo Tumor Imaging and Potential for Translation

Nanoparticles have been widely used for preclinical cancer imaging. However, their successful clinical translation is largely hampered by potential toxicity, unsatisfactory detection of malignancy at early stages, inaccurate diagnosis of tumor biomarkers, and histology for imaging-guided treatment. Herein, a targeted copper nanocluster (CuNC) is reported with high potential to address these challenges for future translation. Its ultrasmall structure enables efficient renal/bowel clearance, minimized off-target effects in nontargeted organs, and low nonspecific tumor retention. The pH-dependent in vivo dissolution of CuNCs affords minimal toxicity and potentially selective drug delivery to tumors. The intrinsic radiolabeling through the direct addition of ⁶⁴Cu to CuNC (⁶⁴Cu-CuNCs-FC131) synthesis offers high specific activity for sensitive and accurate detection of CXCR4 via FC131-directed targeting in novel triple negative breast cancer (TNBC) patient-derived xenograft mouse models and human TNBC tissues. In summary, this study not only reveals the potential of CXCR4-targeted ⁶⁴Cu-CuNCs for TNBC imaging in clinical settings, but also provides a useful strategy to design and assess the translational potential of nanoparticles for cancer theranostics.

Functional, Degradable Zwitterionic Polyphosphoesters as Biocompatible Coating Materials for Metal Nanostructures

A zwitterionic polyphosphoester (zPPE), specifically l-cysteine-functionalized poly(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane (zPBYP), has been developed as a poly(ethylene glycol) (PEG) alternative coating material for gold nanoparticles (AuNPs), the most extensively investigated metal nanoparticulate platform toward molecular imaging, photothermal therapy, and drug delivery applications. Thiol-yne conjugation of cysteine transformed an initial azido-terminated and alkynyl-functionalized PBYP homopolymer into zPBYP, offering hydrolytic degradability, biocompatibility, and versatile reactive moieties for installation of a range of functional groups. Despite minor degradation during purification, zPPEs were able to stabilize AuNPs presumably through multivalent interactions between combinations of the side chain zwitterions (thioether and phosphoester groups of the zPPEs with the AuNPs). ³¹P NMR studies in D₂O revealed ca. 20% hydrolysis of the phosphoester moieties of the repeat units had occurred during the workup and purification by aqueous dialysis at pH 3 over ca. 1 d, as observed by the ³¹P signal of the phosphotriesters resonating at ca. -0.5 to -1.7 shifting downfield to ca. 1.1 to -0.4 ppm, attributed to transformation to phosphates. Further hydrolysis of side chain and backbone units proceeded to an extent of ca. 75% over the next 2 d in nanopure water (pH 5-6). The NMR degradation results were consistent with the broadening and red-shift of the surface plasmon resonance (SPR) observed by UV-vis spectroscopy of the zPPE-coated AuNPs in water over time. All AuNP formulations in this study, including those with citrate, PEG, and zPPE coatings, exhibited negligible immunotoxicity, as determined by cytokine overexpression in the presence of the nanostructures relative to those in cell culture medium. Notably, the zPPE-coated AuNPs displayed superior antifouling properties, as assessed by the extent of cytokine adsorption relative to both the PEGylated and citrate-coated AuNPs. Taken together, the physicochemical and biological evaluations of zPPE-coated AuNPs in conjunction with PEGylated and citrate-coated analogues indicate the promise of zPPEs as favorable alternatives to PEG coatings, with negligible immunotoxicity, good antifouling performance, and versatile reactive groups that enable the preparation of highly tailored nanomaterials for diverse applications.

Focused Ultrasound Enabled Trans-Blood Brain Barrier Delivery of Gold Nanoclusters: Effect of Surface Charges and Quantification Using Positron Emission Tomography

Focused ultrasound (FUS) technology is reported to enhance the delivery of ⁶⁴ Cu-integrated ultrasmall gold nanoclusters (⁶⁴ Cu-AuNCs) across the blood-brain barrier (BBB) as measured by positron emission tomography (PET). To better define the optimal physical properties for brain delivery, ⁶⁴ Cu-AuNCs with different surface charges are synthesized and characterized. In vivo biodistribution studies are performed to compare the individual organ uptake of each type of ⁶⁴ Cu-AuNCs. Quantitative PET imaging post-FUS treatment shows site-targeted brain penetration, retention, and diffusion of the negative, neutral, and positive ⁶⁴ Cu-AuNCs. Autoradiography is performed to compare the intrabrain distribution of these nanoclusters. PET Imaging demonstrates the effective BBB opening and successful delivery of ⁶⁴ Cu-AuNCs into the brain. Of the three ⁶⁴ Cu-AuNCs investigated, the neutrally charged nanostructure performs the best and is the candidate platform for future theranostic applications in neuro-oncology.

Focused ultrasound-enabled delivery of radiolabeled nanoclusters to the pons

The goal of this study was to establish the feasibility of integrating focused ultrasound (FUS)-mediated delivery of ⁶⁴Cu-integrated gold nanoclusters (⁶⁴Cu-AuNCs) to the pons for in vivo quantification of the nanocluster brain uptake using positron emission tomography (PET) imaging. FUS was targeted at the pons for the blood-brain barrier (BBB) disruption in the presence of systemically injected microbubbles, followed by the intravenous injection of ⁶⁴Cu-AuNCs. The spatiotemporal distribution of the ⁶⁴Cu-AuNCs in the brain was quantified using in vivo microPET/CT imaging at different time points post injection. Following PET imaging, the accumulation of radioactivity in the pons was further confirmed using autoradiography and gamma counting, and the gold concentration was quantified using inductively coupled plasma-mass spectrometry (ICP-MS). We found that the noninvasive and localized BBB opening by the FUS successfully delivered the ⁶⁴Cu-AuNCs to the pons. We also demonstrated that in vivo real-time microPET/CT imaging was a reliable method for monitoring and quantifying the brain uptake of ⁶⁴Cu-AuNCs delivered by the FUS. This drug delivery platform that integrates FUS, radiolabeled nanoclusters, and PET imaging provides a new strategy for noninvasive and localized nanoparticle delivery to the pons with concurrent in vivo quantitative imaging to evaluate delivery efficiency. The long-term goal is to apply this drug delivery platform to the treatment of pontine gliomas.

A Vinyl Ether-Functional Polycarbonate as a Template for Multiple Postpolymerization Modifications

A highly-reactive vinyl ether-functionalized aliphatic polycarbonate and its block copolymer were developed as templates for multiple post-polymerization conjugation chemistries. The vinyl ether-functional six-membered cyclic carbonate monomer was synthesized by a well-established two-step procedure starting from 2,2-bis(hydroxymethyl)propionic acid. An organobase-catalyzed ring-opening polymerization of the synthesized monomer afforded polycarbonates with pendant vinyl ether functionalities (PMVEC). The vinyl ether moieties on the resulting polymers were readily conjugated with hydroxyl- or thiol-containing compounds via three different post-polymerization modification chemistries - acetalization, thio-acetalization, and thiol-ene reaction. Acetal-functionalized polycarbonates were studied in depth to exploit their acid-labile acetal functionalities. Acetalization of the amphiphilic diblock copolymer of poly(ethylene glycol) methyl ether (mPEG) and PMVEC, mPEG113-b-PMVEC13, with the model hydroxyl compound 4- methylbenzyl alcohol resulted in a maximum of 42% acetal and 58% hydroxyl side chain groups. Nonetheless, the amphiphilicity of the block polymer allowed for its self-assembly in water to afford nanostructures, as characterized via dynamic light scattering and transmission electron microscopy. The kinetics of acetal cleavage within the block polymer micelles were examined in acidic buffered solutions (pH 4 and 5). In addition, mPEG-b-PMVEC and its hydrolyzed polymer mPEG-b-PMHEC (i.e., after full cleavage of acetals) exhibited minimal cytotoxicity to RAW 264.7 mouse macrophages, indicating that this polymer system represents a biologically non-hazardous material with pH-responsive activity.

Investigating the pharmacokinetics and biological distribution of silver-loaded polyphosphoester-based nanoparticles using (111) Ag as a radiotracer

Purified (111) Ag was used as a radiotracer to investigate silver loading and release, pharmacokinetics, and biodistribution of polyphosphoester-based degradable shell crosslinked knedel-like (SCK) nanoparticles as a comparison to the previously reported small molecule, N-heterocyclic silver carbene complex analog (SCC1) for the delivery of therapeutic silver ions in mouse models. Biodistribution studies were conducted by aerosol administration of (111) Ag acetate, [(111) Ag]SCC1, and [(111) Ag]SCK doses directly into the lungs of C57BL/6 mice. Nebulization of the (111) Ag antimicrobials resulted in an average uptake of 1.07 ± 0.12% of the total aerosolized dose given per mouse. The average dose taken into the lungs of mice was estimated to be 2.6 ± 0.3% of the dose inhaled per mouse for [(111) Ag]SCC1 and twice as much dose was observed for the [(111) Ag]SCKs (5.0 ± 0.3% and 5.9 ± 0.8% for [(111) Ag]aSCK and [(111) Ag]zSCK, respectively) at 1 h post administration (p.a.). [(111) Ag]SCKs also exhibited higher dose retention in the lungs; 62-68% for [(111) Ag]SCKs and 43% for [(111) Ag]SCC1 of the initial 1 h dose were observed in the lungs at 24 h p.a.. This study demonstrates the utility of (111) Ag as a useful tool for monitoring the pharmacokinetics of silver-loaded antimicrobials in vivo.

Preparation and in vitro antimicrobial activity of silver-bearing degradable polymeric nanoparticles of polyphosphoester-block-poly(L-lactide)

The development of well-defined polymeric nanoparticles (NPs) as delivery carriers for antimicrobials targeting human infectious diseases requires rational design of the polymer template, an efficient synthetic approach, and fundamental understanding of the developed NPs, e.g., drug loading/release, particle stability, and other characteristics. Herein, we developed and evaluated the in vitro antimicrobial activity of silver-bearing, fully biodegradable and functional polymeric NPs. A series of degradable polymeric nanoparticles (dNPs), composed of phosphoester and L-lactide and designed specifically for silver loading into the hydrophilic shell and/or the hydrophobic core, were prepared as potential delivery carriers for three different types of silver-based antimicrobials-silver acetate or one of two silver carbene complexes (SCCs). Silver-loading capacities of the dNPs were not influenced by the hydrophilic block chain length, loading site (i.e., core or shell), or type of silver compound, but optimization of the silver feed ratio was crucial to maximize the silver loading capacity of dNPs, up to ca. 12% (w/w). The release kinetics of silver-bearing dNPs revealed 50% release at ca. 2.5-5.5 h depending on the type of silver compound. In addition, we undertook a comprehensive evaluation of the rates of hydrolytic or enzymatic degradability and performed structural characterization of the degradation products. Interestingly, packaging of the SCCs in the dNP-based delivery system improved minimum inhibitory concentrations up to 70%, compared with the SCCs alone, as measured in vitro against 10 contemporary epidemic strains of Staphylococcus aureus and eight uropathogenic strains of Escherichia coli. We conclude that these dNP-based delivery systems may be beneficial for direct epithelial treatment and/or prevention of ubiquitous bacterial infections, including those of the skin and urinary tract.

Development of a Vinyl Ether-Functionalized Polyphosphoester as a Template for Multiple Postpolymerization Conjugation Chemistries and Study of Core Degradable Polymeric Nanoparticles

A novel polyphosphoester (PPE) with vinyl ether side chain functionality was developed as a versatile template for postpolymerization modifications, and its degradability and biocompatibility were evaluated. An organo-catalyzed ring-opening polymerization of ethylene glycol vinyl ether-pendant cyclic phosphotriester monomer allowed for construction of poly(ethylene glycol vinyl ether phosphotriester) (PEVEP). This vinyl ether-functionalized PPE scaffold was coupled with hydroxyl- or thiol-containing model small molecules via three different types of conjugation chemistries-thiol-ene "click" reaction, acetalization, or thio-acetalization reaction-to afford modified polymers that accommodated either stable thio-ether or hydrolytically labile acetal or thio-acetal linkages. Amphiphilic diblock copolymers of poly(ethylene glycol) and PEVEP formed well-defined micelles with a narrow and monomodal size distribution in water, as confirmed by dynamic light scattering (DLS), transmission electron microscopy, and atomic force microscopy. The stability of the micelles and the hydrolytic degradability of the backbone and side chains of the PEVEP block segment were assessed by DLS and nuclear magnetic resonance spectroscopy (1H and 31P), respectively, in aqueous buffer solutions at pH values of 5.0 and 7.4 and at temperatures of 25 and 37 °C. The hydrolytic degradation products of the PEVEP segments of the block copolymers were then identified by electrospray ionization, gas chromatography, and matrix-assisted laser desorption/ionization mass spectrometry. The parent micelles and their degradation products were found to be non-cytotoxic at concentrations up to 3 mg/mL, when evaluated with RAW 264.7 mouse macrophages and OVCAR-3 human ovarian adenocarcinoma cells.

Aldehyde-functional polycarbonates as reactive platforms

Ozonolysis of allyl-functional polycarbonates provides aldehyde-functional polycarbonates that have potential to be reactive platforms for transformation into diverse active materials.

Holistic assessment of covalently labeled core-shell polymeric nanoparticles with fluorescent contrast agents for theranostic applications

The successful development of degradable polymeric nanostructures as optical probes for use in nanotheranostic applications requires the intelligent design of materials such that their surface response, degradation, drug delivery, and imaging properties are all optimized. In the case of imaging, optimization must result in materials that allow differentiation between unbound optical contrast agents and labeled polymeric materials as they undergo degradation. In this study, we have shown that use of traditional electrophoretic gel-plate assays for the determination of the purity of dye-conjugated degradable nanoparticles is limited by polymer degradation characteristics. To overcome these limitations, we have outlined a holistic approach to evaluating dye and peptide-polymer nanoparticle conjugation by utilizing steady-state fluorescence, anisotropy, and emission and anisotropy lifetime decay profiles, through which nanoparticle-dye binding can be assessed independently of perturbations, such as those presented during the execution of electrolyte gel-based assays. This approach has been demonstrated to provide an overall understanding of the spectral signature-structure-function relationship, ascertaining key information on interactions between the fluorophore, polymer, and solvent components that have a direct and measurable impact on the emissive properties of the optical probe. The use of these powerful techniques provides feedback that can be utilized to improve nanotheranostics by evaluating dye emissivity in degradable nanotheranostic systems, which has become increasingly important as modern platforms transition to architectures intentionally reliant on degradation and built-in environmental responses.

Poly(D-glucose carbonate) block copolymers: a platform for natural product-based nanomaterials with Solvothermatic characteristics

A natural product-based polymer platform, having the characteristics of being derived from renewable materials and capable of breaking down, ultimately, into natural byproducts, has been prepared through the ring-opening polymerization (ROP) of a glucose-based bicyclic carbonate monomer. ROP was carried out via chain extension of a polyphosphoester (PPE) macroinitiator in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) organocatalyst to afford the PPE-b-poly(D-glucose carbonate) (PDGC) block copolymer. This new copolymer represents a functional architecture that can be rapidly transformed through thiol-yne reactions along the PPE segment into a diverse variety of amphiphilic polymers, which interestingly display stimuli-sensitive phase behavior in the form of a lower critical solution temperature (LCST). Below the LCST, they undergo self-assembly to form spherical core-shell nanostructures that display a poorly defined core-shell morphology. It is expected that hydrophobic patches are exposed within the micellar corona, reminiscent of the surface complexity of proteins, making these materials of interest for triggered and reversible assembly disassembly processes.

Construction of a Reactive Diblock Copolymer, Polyphosphoester-block-Poly(L-lactide), as a Versatile Framework for Functional Materials that are Capable of Full Degradation and Nanoscopic Assembly Formation

The development of a diblock copolymer, polyphosphoester-block-poly(L-lactide), which has potential for being fully-degradable and biocompatible, was achieved by one-pot sequential ring-opening polymerizations (ROPs) of two cyclic monomers: alkyne-functionalized phospholane and L-lactide (LLA). A kinetic study of the polymerization in each step was investigated in a detailed manner by nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC), revealing living/controlled characteristics with narrow molecular weight distributions and a linear increase of molecular weights vs. monomer conversion and time. Subsequently, photo-induced thiol-yne "click" reactions with small molecule thiols bearing either carboxylic acid or amino groups afforded amphiphilic diblock copolymers with carboxylate or amino side-chain functionalities along the polyphosphoester segment of the diblock copolymer backbone. Finally, direct dissolution of the two different types of amphiphilic diblock copolymers in aqueous solutions yielded well-defined spherical micelles with corresponding negative or positive surface charges, respectively, as confirmed by transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential analyses.

Synthesis, characterization, and in vivo efficacy of shell cross-linked nanoparticle formulations carrying silver antimicrobials as aerosolized therapeutics

The use of nebulizable, nanoparticle-based antimicrobial delivery systems can improve efficacy and reduce toxicity for treatment of multi-drug-resistant bacteria in the chronically infected lungs of cystic fibrosis patients. Nanoparticle vehicles are particularly useful for applying broad-spectrum silver-based antimicrobials, for instance, to improve the residence time of small-molecule silver carbene complexes (SCCs) within the lung. Therefore, we have synthesized multifunctional, shell cross-linked knedel-like polymeric nanoparticles (SCK NPs) and capitalized on the ability to independently load the shell and core with silver-based antimicrobial agents. We formulated three silver-loaded variants of SCK NPs: shell-loaded with silver cations, core-loaded with SCC10, and combined loading of shell silver cations and core SCC10. All three formulations provided a sustained delivery of silver over the course of at least 2-4 days. The two SCK NP formulations with SCC10 loaded in the core each exhibited excellent antimicrobial activity and efficacy in vivo in a mouse model of Pseudomonas aeruginosa pneumonia. SCK NPs with shell silver cation-load only, while efficacious in vitro, failed to demonstrate efficacy in vivo. However, a single dose of core SCC10-loaded SCK NPs (0.74 ± 0.16 mg Ag) provided a 28% survival advantage over sham treatment, and administration of two doses (0.88 mg Ag) improved survival to 60%. In contrast, a total of 14.5 mg of Ag(+) delivered over 5 doses at 12 h intervals was necessary to achieve a 60% survival advantage with a free-drug (SCC1) formulation. Thus, SCK NPs show promise for clinical impact by greatly reducing antimicrobial dosage and dosing frequency, which could minimize toxicity and improve patient adherence.

Detection of living anionic species in polymerization reactions using hyperpolarized NMR

Intermediates during the anionic polymerization of styrene were observed using hyperpolarized NMR. Dissolution dynamic nuclear polarization (DNP) of monomers provides a sufficient signal-to-noise ratio for detection of (13)C NMR signals in real time as the reaction progresses. Because of its large chemical shift dispersion, (13)C is well-suited to distinguish and characterize the chemical species that arise during the reaction. At the same time, incorporation of hyperpolarized small-molecule monomers is a unique way to generate polymers that exhibit a transient signal enhancement at the active site. This strategy is applicable despite the decay of the hyperpolarization of the polymer due to rapid spin-lattice relaxation. Real-time measurements on polymerization reactions provide both mechanistic and kinetic information without the need for stable isotope labeling of the molecules of interest. These capabilities are orthogonal to currently established methods that separate synthesis and analysis into two steps, making dissolution DNP an attractive method to study polymerization reactions.

Determination of organophosphorus pesticides in wheat flour by supercritical fluid extraction and gas chromatography with nitrogen-phosphorus detection

Application of supercritical fluid extraction (SFE) for selective isolation of organophosphorus pesticides from a real-world matrix (wheat flour) has been described. The method uses extraction with supercritical carbon dioxide at 206.8 bar and 60 degrees C, followed by quantitation by gas chromatography with nitrogen-phosphorous detection without clean-up of the extracts. Comparison of SFE with a method currently employed for sample preparation (i.e., organic solvent extraction followed by liquid-liquid extraction and gel permeation chromatography clean-up) shows that the SFE technique simplifies the sample preparation step and speeds up the determination of organophosphorus pesticides in flour. Extraction times were 60 min for a 7 g sample size. This technique was able to determine organophosphorus pesticides (ethoprophos, diazinon, chlorpyrifos methyl, fenitrothion, parathion, phenthoate, EPN) in samples at the 10 ng/g level.

Analysis of cholesterol and cholesteryl esters in human serum using capillary supercritical fluid chromatography

Capillary supercritical fluid chromatography (SFC) using carbon dioxide as a mobile phase was applied for the determination of free cholesterol and cholesteryl esters in human serum. Serum samples were extracted with methanol-chloroform (2:1, v/v), and the extracts were analyzed by pressure programmed capillary SFC-flame-ionization detection (FID) without thermal degradation and derivatization. The total cholesterol concentrations obtained from SFC analysis were compared with those from GC or enzymatic analysis. The capillary SFC-FID method having high resolution gave an acceptable average relative standard deviation of 2.6%, and a detection limit of 4-6 pg. The quantitative results were acceptable for the simultaneous analysis of cholesterol and its esters in biological fluids. The concentration profiles of each compound in various samples, normal Korean human serum, Western human serum, and from high-cholesterol patient plasma, have been compared with this method.