Imaging demyelinated axons after spinal cord injuries with PET tracer [ 18 F]3F4AP.

Spinal cord injuries (SCI) often lead to lifelong disability. Among the various types of injuries, incomplete and discomplete injuries, where some axons remain intact, offer potential for recovery. However, demyelination of these spared axons can worsen disability. Demyelination is a reversible phenomenon, and drugs like 4-aminopyridine (4AP), which target K+ channels in demyelinated axons, show that conduction can be restored. Yet, accurately assessing and monitoring demyelination post-SCI remains challenging due to the lack of suitable imaging methods. In this study, we introduce a novel approach utilizing the positron emission tomography (PET) tracer, [ 18 F]3F4AP, specifically targeting K+ channels in demyelinated axons for SCI imaging. Rats with incomplete contusion injuries were imaged up to one month post-injury, revealing [ 18 F]3F4AP's exceptional sensitivity to injury and its ability to detect temporal changes. Further validation through autoradiography and immunohistochemistry confirmed [ 18 F]3F4AP's targeting of demyelinated axons. In a proof-of-concept study involving human subjects, [ 18 F]3F4AP differentiated between a severe and a largely recovered incomplete injury, indicating axonal loss and demyelination, respectively. Moreover, alterations in tracer delivery were evident on dynamic PET images, suggestive of differences in spinal cord blood flow between the injuries. In conclusion, [ 18 F]3F4AP demonstrates efficacy in detecting incomplete SCI in both animal models and humans. The potential for monitoring post-SCI demyelination changes and response to therapy underscores the utility of [ 18 F]3F4AP in advancing our understanding and management of spinal cord injuries.

Radiosynthesis automation, non-human primate biodistribution and dosimetry of K+ channel tracer [11C]3MeO4AP.

BACKGROUND: 4-Aminopyridine (4AP) is a medication for the symptomatic treatment of multiple sclerosis. Several 4AP-based PET tracers have been developed for imaging demyelination. In preclinical studies, [11C]3MeO4AP has shown promise due to its high brain permeability, high metabolic stability, high plasma availability, and high in vivo binding affinity. To prepare for the translation to human studies, we developed a cGMP-compatible automated radiosynthesis protocol and evaluated the whole-body biodistribution and radiation dosimetry of [11C]3MeO4AP in non-human primates (NHPs). METHODS: Automated radiosynthesis was carried out using a GE TRACERlab FX-C Pro synthesis module. One male and one female adult rhesus macaques were used in the study. A high-resolution CT from cranial vertex to knee was acquired. PET data were collected using a dynamic acquisition protocol with four bed positions and 13 passes over a total scan time of ~ 150 min. Based on the CT and PET images, volumes of interest (VOIs) were manually drawn for selected organs. Non-decay corrected time-activity curves (TACs) were extracted for each VOI. Radiation dosimetry and effective dose were calculated from the integrated TACs using OLINDA software. RESULTS: Fully automated radiosynthesis of [11C]3MeO4AP was achieved with 7.3 ± 1.2% (n = 4) of non-decay corrected radiochemical yield within 38 min of synthesis and purification time. [11C]3MeO4AP distributed quickly throughout the body and into the brain. The organs with highest dose were the kidneys. The average effective dose of [11C]3MeO4AP was 4.0 ± 0.6 µSv/MBq. No significant changes in vital signs were observed during the scan. CONCLUSION: A cGMP-compatible automated radiosynthesis of [11C]3MeO4AP was developed. The whole-body biodistribution and radiation dosimetry of [11C]3MeO4AP was successfully evaluated in NHPs. [11C]3MeO4AP shows lower average effective dose than [18F]3F4AP and similar average effective dose as other carbon-11 tracers.

Development and Pharmacochemical Characterization Discover a Novel Brain-Permeable HDAC11-Selective Inhibitor with Therapeutic Potential by Regulating Neuroinflammation in Mice.

Recent studies have shown that the epigenetic protein histone deacetylase 11 (HDAC11) is highly expressed in the brain and critically modulates neuroimmune functions, making it a potential therapeutic target for neurological disorders. Herein, we report the development of PB94, which is a novel HDAC11 inhibitor. PB94 exhibited potency and selectivity against HDAC11 with IC50 = 108 nM and >40-fold selectivity over other HDAC isoforms. Pharmacokinetic/pharmacodynamic evaluation indicated that PB94 possesses promising drug-like properties. Additionally, PB94 was radiolabeled with carbon-11 as [11C]PB94 for positron emission tomography (PET), which revealed significant brain uptake and metabolic properties suitable for drug development in live animals. Furthermore, we demonstrated that neuropathic pain was associated with brain upregulation of HDAC11 and that pharmacological inhibition of HDAC11 by PB94 ameliorated neuropathic pain in a mouse model. Collectively, our findings support further development of PB94 as a selective HDAC11 inhibitor for neurological indications, including pain.

Radiosynthesis automation, non-human primate biodistribution and dosimetry of K + channel tracer [ 11 C]3MeO4AP.

Purpose: 4-Aminopyridine (4AP) is a medication for the symptomatic treatment of multiple sclerosis. Several 4AP-based PET tracers have been developed for imaging demyelination. In preclinical studies, [ 11 C]3MeO4AP has shown promise due to its high brain permeability, high metabolic stability, high plasma availability, and high in vivo binding affinity. To prepare for the translation to human studies, we developed a cGMP-compliant automated radiosynthesis protocol and evaluated the whole-body biodistribution and radiation dosimetry of [ 11 C]3MeO4AP in non-human primates (NHPs). Methods: Automated radiosynthesis was carried out using a GE TRACERlab FX-C Pro synthesis module. One male and one female adult rhesus macaques were used in the study. A high-resolution CT from cranial vertex to knee was acquired. PET data were collected using a dynamic acquisition protocol with 4 bed positions and 13 passes over a total scan time of ∼150 minutes. Based on the CT and PET images, volumes of interest (VOIs) were manually drawn for selected organs. Non-decay corrected time-activity curves (TACs) were extracted for each VOI. Radiation dosimetry and effective dose were calculated from the integrated TACs using OLINDA software. Results: Fully automated radiosynthesis of [ 11 C]3MeO4AP was achieved with 7.3 ± 1.2 % (n = 4) of non-decay corrected radiochemical yield within 38 min of synthesis and purification time. [ 11 C]3MeO4AP distributed quickly throughout the body and into the brain. The organs with highest dose were the kidneys. The average effective dose of [ 11 C]3MeO4AP was 4.27 ± 0.57 µSv/MBq. No significant changes in vital signs were observed during the scan. Conclusion: The cGMP compliant automated radiosynthesis of [ 11 C]3MeO4AP was developed. The whole-body biodistribution and radiation dosimetry of [ 11 C]3MeO4AP was successfully evaluated in NHPs. [ 11 C]3MeO4AP shows lower average effective dose than [ 18 F]3F4AP and similar average effective dose as other carbon-11 tracers.

Human biodistribution and radiation dosimetry of the demyelination tracer [18F]3F4AP.

PURPOSE: [18F]3F4AP is a novel PET radiotracer that targets voltage-gated potassium (K+) channels and has shown promise for imaging demyelinated lesions in animal models of neurological diseases. This study aimed to evaluate the biodistribution, safety, and radiation dosimetry of [18F]3F4AP in healthy human volunteers. METHODS: Four healthy volunteers (2 females) underwent a 4-h dynamic PET scan from the cranial vertex to mid-thigh using multiple bed positions after administration of 368 ± 17.9 MBq (9.94 ± 0.48 mCi) of [18F]3F4AP. Volumes of interest for relevant organs were manually drawn guided by the CT, and PET images and time-activity curves (TACs) were extracted. Radiation dosimetry was estimated from the integrated TACs using OLINDA software. Safety assessments included measuring vital signs immediately before and after the scan, monitoring for adverse events, and obtaining a comprehensive metabolic panel and electrocardiogram within 30 days before and after the scan. RESULTS: [18F]3F4AP distributed throughout the body with the highest levels of activity in the kidneys, urinary bladder, stomach, liver, spleen, and brain and with low accumulation in muscle and fat. The tracer cleared quickly from circulation and from most organs. The clearance of the tracer was noticeably faster than previously reported in nonhuman primates (NHPs). The average effective dose (ED) across all subjects was 12.1 ± 2.2 µSv/MBq, which is lower than the estimated ED from the NHP studies (21.6 ± 0.6 µSv/MBq) as well as the ED of other fluorine-18 radiotracers such as [18F]FDG (~ 20 µSv/MBq). No differences in ED between males and females were observed. No substantial changes in safety assessments or adverse events were recorded. CONCLUSION: The biodistribution and radiation dosimetry of [18F]3F4AP in humans are reported for the first time. The average total ED across four subjects was lower than most 18F-labeled PET tracers. The tracer and study procedures were well tolerated, and no adverse events occurred.

A positron emission tomography imaging probe selectively targeting the BD1 bromodomain and extra-terminal domain.

The two tandem bromodomains of BET (bromodomain and extra-terminal domain) proteins (BD1 and BD2) may play distinct and critical roles in neurological diseases. To better understand the underlying mechanisms of the BD1 bromodomain and facilitate brain permeable domain-selective inhibitor development, we describe here the development of the first BET BD1 positron emission tomography (PET) radioligand [11C]1a. Compound 1a was tested to possess potent binding affinities and good selectivity (>20-fold over BD2) for BD1 bromodomains of BRD2 (Kd = 25 nM), BRD3 (Kd = 24 nM), and BRD4 (Kd = 19 nM). Physicochemical characterization of 1a indicated the brain permeability and specific binding. [11C]1a was radiosynthesized in a good radiochemical yield (RCY: 25-30%) and molar activity (258 GBq µmol-1). The PET imaging studies of [11C]1a in mice showed moderate brain uptake (with peak SUV = 0.7) and binding specificity. Furthermore, [11C]1a demonstrated translational potential in the non-human primate (NHP) PET imaging study, which sets the stage for clinical translation.

Increased Macrophage-Specific Arterial Infiltration Relates to Noncalcified Plaque and Systemic Immune Activation in People With Human Immunodeficiency Virus.

BACKGROUND: Persistent immune activation is thought to contribute to heightened atherosclerotic cardiovascular disease (ASCVD) risk among people with human immunodeficiency virus (PWH). METHODS: Participants (≥18 years) with or without human immunodeficiency virus (HIV) and without history of clinical ASCVD were enrolled. We hypothesized that increased macrophage-specific arterial infiltration would relate to plaque composition and systemic immune activation among PWH. We applied a novel targeted molecular imaging approach (technetium-99m [99mTc]-tilmanocept single photon emission computed tomography [SPECT]/CT) and comprehensive immune phenotyping. RESULTS: Aortic 99mTc-tilmanocept uptake was significantly higher among PWH (n = 20) than participants without HIV (n = 10) with similar 10-year ASCVD risk (P = .02). Among PWH, but not among participants without HIV, noncalcified aortic plaque volume related directly to aortic 99mTc-tilmanocept uptake at different uptake thresholds. An interaction (P = .001) was seen between HIV status and noncalcified plaque volume, but not calcified plaque (P = .83). Systemic levels of caspase-1 (P = .004), CD14-CD16+ (nonclassical/patrolling/homing) monocytes (P = .0004) and CD8+ T cells (P = .005) related positively and CD4+/CD8+ T-cell ratio (P = .02) inversely to aortic 99mTc-tilmanocept uptake volume. CONCLUSIONS: Macrophage-specific arterial infiltration was higher among PWH and related to noncalcified aortic plaque volume only among PWH. Key systemic markers of immune activation relating to macrophage-specific arterial infiltration may contribute to heightened ASCVD risk among PWH. CLINICAL TRIALS REGISTRATION: NCT02542371.

Near-Infrared Fluorescence Imaging of Carotid Plaques in an Atherosclerotic Murine Model.

Successful imaging of atherosclerosis, one of the leading global causes of death, is crucial for diagnosis and intervention. Near-infrared fluorescence (NIRF) imaging has been widely adopted along with multimodal/hybrid imaging systems for plaque detection. We evaluate two macrophage-targeting fluorescent tracers for NIRF imaging (TLR4-ZW800-1C and Feraheme-Alexa Fluor 750) in an atherosclerotic murine cohort, where the left carotid artery (LCA) is ligated to cause stenosis, and the right carotid artery (RCA) is used as a control. Imaging performed on dissected tissues revealed that both tracers had high uptake in the diseased vessel compared to the control, which was readily visible even at short exposure times. In addition, ZW800-1C's renal clearance ability and Feraheme's FDA approval puts these two tracers in line with other NIRF tracers such as ICG. Continued investigation with these tracers using intravascular NIRF imaging and larger animal models is warranted for clinical translation.

Evaluation of the potassium channel tracer [18F]3F4AP in rhesus macaques.

Demyelination causes slowed or failed neuronal conduction and is a driver of disability in multiple sclerosis and other neurological diseases. Currently, the gold standard for imaging demyelination is MRI, but despite its high spatial resolution and sensitivity to demyelinated lesions, it remains challenging to obtain specific and quantitative measures of molecular changes involved in demyelination. To understand the contribution of demyelination in different diseases and to assess the efficacy of myelin-repair therapies, it is critical to develop new in vivo imaging tools sensitive to changes induced by demyelination. Upon demyelination, axonal K+ channels, normally located underneath the myelin sheath, become exposed and increase in expression, causing impaired conduction. Here, we investigate the properties of the K+ channel PET tracer [18F]3F4AP in primates and its sensitivity to a focal brain injury that occurred three years prior to imaging. [18F]3F4AP exhibited favorable properties for brain imaging including high brain penetration, high metabolic stability, high plasma availability, high reproducibility, high specificity, and fast kinetics. [18F]3F4AP showed preferential binding in areas of low myelin content as well as in the previously injured area. Sensitivity of [18F]3F4AP for the focal brain injury was higher than [18F]FDG, [11C]PiB, and [11C]PBR28, and compared favorably to currently used MRI methods.

Positron annihilation localization by nanoscale magnetization.

In positron emission tomography (PET), the finite range over which positrons travel before annihilating with an electron places a fundamental physical limit on the spatial resolution of PET images. After annihilation, the photon pair detected by the PET instrumentation is emitted from a location that is different from the positron-emitting source, resulting in image blurring. Here, we report on the localization of positron range, and hence annihilation quanta, by strong nanoscale magnetization of superparamagnetic iron oxide nanoparticles (SPIONs) in PET-MRI. We found that positron annihilations localize within a region of interest by up to 60% more when SPIONs are present (with [Fe] = 3 mM) compared to when they are not. The resulting full width at half maximum of the PET scans showed the spatial resolution improved by up to [Formula: see text] 30%. We also found evidence suggesting that the radiolabeled SPIONs produced up to a six-fold increase in ortho-positronium. These results may also have implications for emerging cancer theranostic strategies, where charged particles are used as therapeutic as well as diagnostic agents and improved dose localization within a tumor is a determinant of better treatment outcomes.

A Radio-Nano-Platform for T1/T2 Dual-Mode PET-MR Imaging.

PURPOSE: This study aimed to develop a chelate-free radiolabeled nanoparticle platform for simultaneous positron emission tomography (PET) and magnetic resonance (MR) imaging that provides contrast-enhanced diagnostic imaging and significant image quality gain by integrating the high spatial resolution of MR with the high sensitivity of PET. METHODS: A commercially available super-paramagnetic iron oxide nanoparticle (SPION) (Feraheme®, FH) was labeled with the [89Zr]Zr using a novel chelate-free radiolabeling technique, heat-induced radiolabeling (HIR). Radiochemical yield (RCY) and purity (RCP) were measured using size exclusion chromatography (SEC) and radio-thin layer chromatography (radio-TLC). Characterization of the non-radioactive isotope 90Zr-labeled FH was performed by transmission electron microscopy (TEM). Simultaneous PET-MR phantom imaging was performed with different 89Zr-FH concentrations. The MR quantitative image analysis determined the contrast-enhancing properties of FH. The signal-to-noise ratio (SNR) and full-width half-maximum (FWHM) of the line spread function (LSF) were calculated before and after co-registering the PET and MR image data. RESULTS: High RCY (92%) and RCP (98%) of the [89Zr]Zr-FH product was achieved. TEM analysis confirmed the 90Zr atoms adsorption onto the SPION surface (≈ 10% average radial increase). Simultaneous PET-MR scans confirmed the capability of the [89Zr]Zr-FH nano-platform for this multi-modal imaging technique. Relative contrast image analysis showed that [89Zr]Zr-FH can act as a dual-mode T1/T2 contrast agent. For co-registered PET-MR images, higher spatial resolution (FWHM enhancement ≈ 3) and SNR (enhancement ≈ 8) was achieved at a clinical dose of radio-isotope and Fe. CONCLUSION: Our results demonstrate FH is a highly suitable SPION-based platform for chelate-free labeling of PET tracers for hybrid PET-MR. The high RCY and RCP confirmed the robustness of the chelate-free HIR technique. An overall image quality gain was achieved compared to PET- or MR-alone imaging with a relatively low dosage of [89Zr]Zr-FH. Additionally, FH is suitable as a dual-mode T1/T2 MR image contrast agent.

A Chelate-Free Nano-Platform for Incorporation of Diagnostic and Therapeutic Isotopes.

PURPOSE: Using our chelate-free, heat-induced radiolabeling (HIR) method, we show that a wide range of metals, including those with radioactive isotopologues used for diagnostic imaging and radionuclide therapy, bind to the Feraheme (FH) nanoparticle (NP), a drug approved for the treatment of iron anemia. MATERIAL AND METHODS: FH NPs were heated (120°C) with nonradioactive metals, the resulting metal-FH NPs were characterized by inductively coupled plasma mass spectrometry (ICP-MS), dynamic light scattering (DLS), and r1 and r2 relaxivities obtained by nuclear magnetic relaxation spectrometry (NMRS). In addition, the HIR method was performed with [90Y]Y3+, [177Lu]Lu3+, and [64Cu]Cu2+, the latter with an HIR technique optimized for this isotope. Optimization included modifying reaction time, temperature, and vortex technique. Radiochemical yield (RCY) and purity (RCP) were measured using size exclusion chromatography (SEC) and thin-layer chromatography (TLC). RESULTS: With ICP-MS, metals incorporated into FH at high efficiency were bismuth, indium, yttrium, lutetium, samarium, terbium and europium (>75% @ 120 oC). Incorporation occurred with a small (less than 20%) but statistically significant increases in size and the r2 relaxivity. An improved HIR technique (faster heating rate and improved vortexing) was developed specifically for copper and used with the HIR technique and [64Cu]Cu2+. Using SEC and TLC analyses with [90Y]Y3+, [177Lu]Lu3+ and [64Cu]Cu2+, RCYs were greater than 85% and RCPs were greater than 95% in all cases. CONCLUSION: The chelate-free HIR technique for binding metals to FH NPs has been extended to a range of metals with radioisotopes used in therapeutic and diagnostic applications. Cations with f-orbital electrons, more empty d-orbitals, larger radii, and higher positive charges achieved higher values of RCY and RCP in the HIR reaction. The ability to use a simple heating step to bind a wide range of metals to the FH NP, a widely available approved drug, may allow this NP to become a platform for obtaining radiolabeled nanoparticles in many settings.

Assessing the interactions between radiotherapy and antitumour immunity.

Immunotherapy, specifically the introduction of immune checkpoint inhibitors, has transformed the treatment of cancer, enabling long-term tumour control even in individuals with advanced-stage disease. Unfortunately, only a small subset of patients show a response to currently available immunotherapies. Despite a growing consensus that combining immune checkpoint inhibitors with radiotherapy can increase response rates, this approach might be limited by the development of persistent radiation-induced immunosuppression. The ultimate goal of combining immunotherapy with radiotherapy is to induce a shift from an ineffective, pre-existing immune response to a long-lasting, therapy-induced immune response at all sites of disease. To achieve this goal and enable the adaptation and monitoring of individualized treatment approaches, assessment of the dynamic changes in the immune system at the patient level is essential. In this Review, we summarize the available clinical data, including forthcoming methods to assess the immune response to radiotherapy at the patient level, ranging from serum biomarkers to imaging techniques that enable investigation of immune cell dynamics in patients. Furthermore, we discuss modelling approaches that have been developed to predict the interaction of immunotherapy with radiotherapy, and highlight how they could be combined with biomarkers of antitumour immunity to optimize radiotherapy regimens and maximize their synergy with immunotherapy.

Development and Application of FASA, a Model for Quantifying Fatty Acid Metabolism Using Stable Isotope Labeling.

It is well understood that fatty acids can be synthesized, imported, and modified to meet requisite demands in cells. However, following the movement of fatty acids through the multiplicity of these metabolic steps has remained difficult. To better address this problem, we developed Fatty Acid Source Analysis (FASA), a model that defines the contribution of synthesis, import, and elongation pathways to fatty acid homeostasis in saturated, monounsaturated, and polyunsaturated fatty acid pools. Application of FASA demonstrated that elongation can be a major contributor to cellular fatty acid content and showed that distinct pro-inflammatory stimuli (e.g., Toll-like receptors 2, 3, or 4) specifically reprogram homeostasis of fatty acids by differential utilization of synthetic and elongation pathways in macrophages. In sum, this modeling approach significantly advances our ability to interrogate cellular fatty acid metabolism and provides insight into how cells dynamically reshape their lipidomes in response to metabolic or inflammatory signals.

Heat-induced radiolabeling and fluorescence labeling of Feraheme nanoparticles for PET/SPECT imaging and flow cytometry.

Feraheme (FH) nanoparticles (NPs) have been used extensively for treatment of iron anemia (due to their slow release of ionic iron in acidic environments). In addition, injected FH NPs are internalized by monocytes and function as MRI biomarkers for the pathological accumulation of monocytes in disease. We have recently expanded these applications by radiolabeling FH NPs for positron emission tomography (PET) or single-photon emission computed tomography (SPECT) imaging using a heat-induced radiolabeling (HIR) strategy. Imaging FH NPs using PET/SPECT has important advantages over MRI due to lower iron doses and improved quantitation of tissue NP concentrations. HIR of FH NPs leaves the physical and biological properties of the NPs unchanged and allows researchers to build on the extensive knowledge obtained about the pharmacokinetic and safety aspects of FH NPs. In this protocol, we present the step-by-step procedures for heat (120 °C)-induced bonding of three widely employed radiocations (89Zr4+ or 64Cu2+ for PET, and 111In3+ for SPECT) to FH NPs using a chelateless radiocation surface adsorption (RSA) approach. In addition, we describe the conversion of FH carboxyl groups into amines and their reaction with an N-hydroxysuccinimide (NHS) of a Cy5.5 fluorophore. This yields Cy5.5-FH, a fluorescent FH that enables the cells internalizing Cy5.5-FH to be examined using flow cytometry. Finally, we describe procedures for in vivo and ex vivo uptake of Cy5.5-FH by monocytes and for in vivo microPET/CT imaging of HIR-FH NPs. Synthesis of HIR-FH requires experience with working with radioactive cations and can be completed within <4 h. Synthesis of Cy5.5-FH NPs takes ∼17 h.

Mature B cells accelerate wound healing after acute and chronic diabetic skin lesions.

Chronic wounds affect 12-15% of patients with diabetes and are associated with a drastic decrease in their quality of life. Here, we demonstrate that purified mature naive B220+ /CD19+ /IgM+ /IgD+ B cells improve healing of acute and diabetic murine wounds after a single topical application. B cell treatment significantly accelerated acute wound closure by 2-3 days in wild-type mice and 5-6 days in obese diabetic mice. The treatment led to full closure in 43% of chronic diabetic wounds, as compared to only 5% in saline-treated controls. Applying equivalent numbers of T cells or disrupted B cells failed to reproduce these effects, indicating that live B cells mediated pro-healing responses. Topically applied B cell treatment was associated with significantly reduced scar size, increased collagen deposition and maturation, enhanced angiogenesis, and increased nerve growth into and under the healing wound. ß-III tubulin+ nerve endings in scars of wounds treated acutely with B cells showed increased relative expression of growth-associated protein 43. The improved healing associated with B cell treatment was supported by significantly increased fibroblast proliferation and decreased apoptosis in the wound bed and edges, altered kinetics of neutrophil infiltration, as well as an increase in TGF-ß and a significant reduction in MMP2 expression in wound granulation tissue. Our findings indicate that the timeline and efficacy of wound healing can be experimentally manipulated through the direct application of mature, naive B cells, which effectively modify the balance of mature immune cell populations within the wound microenvironment and accelerate the healing process.

Application of a Novel CD206+ Macrophage-Specific Arterial Imaging Strategy in HIV-Infected Individuals.

Background: The ability to noninvasively assess arterial CD206+ macrophages may lead to improved understanding of human immunodeficiency virus (HIV)-associated cardiovascular disease. Methods: We trialed a novel macrophage-specific arterial imaging technique. Results: We demonstrated colocalization between technetium Tc 99m tilmanocept (99mTc-tilmanocept) and CD206+ macrophages ex vivo. In vivo application of 99mTc-tilmanocept single-photon emission computed tomography/computed tomography revealed high-level 99mTc-tilmanocept uptake across 20.4% of the aortic surface volume among HIV-infected subjects, compared with 4.3% among non-HIV-infected subjects (P = .009). Among all subjects, aortic high-level 99mTc-tilmanocept uptake was related to noncalcified aortic plaque volume (r = 0.87; P = .003) on computed tomographic angiography, and this relationship held when we controlled for HIV status. Conclusion: These first-in-human data introduce a novel macrophage-specific arterial imaging technique in HIV. Clinical Trials Registration: NCT02542371.

Heat-induced-radiolabeling and click chemistry: A powerful combination for generating multifunctional nanomaterials.

A key advantage of nanomaterials for biomedical applications is their ability to feature multiple small reporter groups (multimodality), or combinations of reporter groups and therapeutic agents (multifunctionality), while being targeted to cell surface receptors. Here a facile combination of techniques for the syntheses of multimodal, targeted nanoparticles (NPs) is presented, whereby heat-induced-radiolabeling (HIR) labels NPs with radiometals and so-called click chemistry is used to attach bioactive groups to the NP surface. Click-reactive alkyne or azide groups were first attached to the nonradioactive clinical Feraheme (FH) NPs. Resulting "Alkyne-FH" and "Azide-FH" intermediates, like the parent NP, tolerated 89Zr labeling by the HIR method previously described. Subsequently, biomolecules were quickly conjugated to the radioactive NPs by either copper-catalyzed or copper-free click reactions with high efficiency. Synthesis of the Alkyne-FH or Azide-FH intermediates, followed by HIR and then by click reactions for biomolecule attachment, provides a simple and potentially general path for the synthesis of multimodal, multifunctional, and targeted NPs for biomedical applications.

Limiting Cholesterol Biosynthetic Flux Spontaneously Engages Type I IFN Signaling.

Cellular lipid requirements are achieved through a combination of biosynthesis and import programs. Using isotope tracer analysis, we show that type I interferon (IFN) signaling shifts the balance of these programs by decreasing synthesis and increasing import of cholesterol and long chain fatty acids. Genetically enforcing this metabolic shift in macrophages is sufficient to render mice resistant to viral challenge, demonstrating the importance of reprogramming the balance of these two metabolic pathways in vivo. Unexpectedly, mechanistic studies reveal that limiting flux through the cholesterol biosynthetic pathway spontaneously engages a type I IFN response in a STING-dependent manner. The upregulation of type I IFNs was traced to a decrease in the pool size of synthesized cholesterol and could be inhibited by replenishing cells with free cholesterol. Taken together, these studies delineate a metabolic-inflammatory circuit that links perturbations in cholesterol biosynthesis with activation of innate immunity.

Heat-Induced Radiolabeling of Nanoparticles for Monocyte Tracking by PET.

Heat-induced radiolabeling (HIR) yielded (89) Zr-Feraheme (FH) nanoparticles (NPs) that were used to determine NP pharmacokinetics (PK) by positron emission tomography (PET). Standard uptake values indicated a fast hepatic uptake that corresponded to blood clearance, and a second, slow uptake process by lymph nodes and spleen. By cytometry, NPs were internalized by circulating monocytes and monocytes in vitro. Using an IV injection of HIR (89) Zr-FH (rather than in vitro cell labeling), PET/PK provided a view of monocyte trafficking, a key component of the immune response.