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.

PET/CT Imaging of Chemokine Receptors in Inflammatory Atherosclerosis Using Targeted Nanoparticles.

UNLABELLED: Atherosclerosis is inherently an inflammatory process that is strongly affected by the chemokine-chemokine receptor axes regulating the trafficking of inflammatory cells at all stages of the disease. Of the chemokine receptor family, some specifically upregulated on macrophages play a critical role in plaque development and may have the potential to track plaque progression. However, the diagnostic potential of these chemokine receptors has not been fully realized. On the basis of our previous work using a broad-spectrum peptide antagonist imaging 8 chemokine receptors together, the purpose of this study was to develop a targeted nanoparticle for sensitive and specific detection of these chemokine receptors in both a mouse vascular injury model and a spontaneously developed mouse atherosclerosis model. METHODS: The viral macrophage inflammatory protein-II (vMIP-II) was conjugated to a biocompatible poly(methyl methacrylate)-core/polyethylene glycol-shell amphiphilic comblike nanoparticle through controlled conjugation and polymerization before radiolabeling with (64)Cu for PET imaging in an apolipoprotein E-deficient (ApoE(-/-)) mouse vascular injury model and a spontaneous ApoE(-/-) mouse atherosclerosis model. Histology, immunohistochemistry, and real-time reverse transcription polymerase chain reaction were performed to assess the plaque progression and upregulation of chemokine receptors. RESULTS: The chemokine receptor-targeted (64)Cu-vMIP-II-comb showed extended blood retention and improved biodistribution. PET imaging showed specific tracer accumulation at plaques in ApoE(-/-) mice, confirmed by competitive receptor blocking studies and assessment in wild-type mice. Histopathologic characterization showed the progression of plaque including size and macrophage population, corresponding to the elevated concentration of chemokine receptors and more importantly increased PET signals. CONCLUSION: This work provides a useful nanoplatform for sensitive and specific detection of chemokine receptors to assess plaque progression in mouse atherosclerosis models.

PET imaging of chemokine receptors in vascular injury-accelerated atherosclerosis.

UNLABELLED: Atherosclerosis is the pathophysiologic process behind lethal cardiovascular diseases. It is a chronic inflammatory progression. Chemokines can strongly affect the initiation and progression of atherosclerosis by controlling the trafficking of inflammatory cells in vivo through interaction with their receptors. Some chemokine receptors have been reported to play an important role in plaque development and stability. However, the diagnostic potential of chemokine receptors has not yet been explored. The purpose of this study was to develop a positron emitter-radiolabeled probe to image the upregulation of chemokine receptor in a wire-injury-accelerated apolipoprotein E knockout (ApoE(-/-)) mouse model of atherosclerosis. METHODS: A viral macrophage inflammatory protein II (vMIP-II) was used to image the upregulation of multiple chemokine receptors through conjugation with DOTA for (64)Cu radiolabeling and PET. Imaging studies were performed at 2 and 4 wk after injury in both wire-injured ApoE(-/-) and wild-type C57BL/6 mice. Competitive PET blocking studies with nonradiolabeled vMIP-II were performed to confirm the imaging specificity. Specific PET blocking with individual chemokine receptor antagonists was also performed to verify the upregulation of a particular chemokine receptor. In contrast, (18)F-FDG PET imaging was performed in both models to evaluate tracer uptake. Immunohistochemistry on the injury and sham tissues was performed to assess the upregulation of chemokine receptors. RESULTS: (15)O-CO PET showed decreased blood volume in the femoral artery after the injury. (64)Cu-DOTA-vMIP-II exhibited fast in vivo pharmacokinetics with major renal clearance. PET images showed specific accumulation around the injury site, with consistent expression during the study period. Quantitative analysis of tracer uptake at the injury lesion in the ApoE(-/-) model showed a 3-fold increase over the sham-operated site and the sites in the injured wild-type mouse. (18)F-FDG PET showed significantly less tracer accumulation than (64)Cu-DOTA-vMIP-II, with no difference observed between injury and sham sites. PET blocking studies identified chemokine receptor-mediated (64)Cu-DOTA-vMIP-II uptake and verified the presence of 8 chemokine receptors, and this finding was confirmed by immunohistochemistry. CONCLUSION: (64)Cu-DOTA-vMIP-II was proven a sensitive and useful PET imaging probe for the detection of 8 up-regulated chemokine receptors in a model of injury-accelerated atherosclerosis.

Radiolabeled chemotactic cytokines: new agents for scintigraphic imaging of infection and inflammation.

Several radiopharmaceuticals are currently used for diagnosis of inflammatory and infectious diseases in patients. Most inflammatory and infectious processes can be visualized with radiolabeled autologous leukocytes, currently considered to be the most appropriate radiopharmaceutical for this purpose. This agent is very well capable to delineate most inflammatory and infectious foci in a relatively short time after injection. The time-consuming and intricate labeling procedure and the handling of potentially contaminated blood, however cause that there is a great interest in the development of new radiopharmaceuticals comprising the same imaging qualities but without these disadvantages. Besides radiolabeled leukocytes several other radiopharmaceuticals, such as (67)Ga-citrate, radiolabeled anti-granulocyte antibodies and FDG are used to image infection and inflammation. These agents accumulate in infectious and inflammatory lesions in a non-specific manner or have suboptimal diagnostic characteristics. Nowadays, there is a great interest in the development of radiolabeled chemotactic and chemokinetic cytokines that accumulate and are retained in infectious and inflammatory foci by specific interaction with infiltrated inflammatory cells. In this review we describe the specific characteristics of the chemotactic and chemokinetic compounds that are currently studied as potential radiopharmaceutical to visualize infectious and inflammatory foci. The characteristics of a series of cytokines (IL-1, IL-2), chemokines (IL-8, PF-4, MCP-1, NAP-2), complement factors (C5a, C5adR), chemotactic peptides (fMLF) and other chemotactic factors (LTB4) are described. The potentials of these compounds to serve as an imaging agent are discussed.

A role of the Duffy antigen for the maintenance of plasma chemokine concentrations.

We examined plasma chemokine concentrations and chemokine clearance rates in Duffy antigen knockout mice. The plasma concentrations of eotaxin and MCP-1 in Duffy antigen knockout mice were less than one-third of those in wild-type mice. When eotaxin or hMGSA was intravenously injected, the chemokine disappeared more rapidly from the plasma of Duffy antigen knockout mice than from the plasma of wild-type mice. The half-lives of hIP-10 and interferon-gamma, which do not have an affinity for the Duffy antigen, in plasma were indistinguishable between Duffy antigen knockout mice and wild-type mice. These results suggest that the Duffy antigen delays the disappearance of chemokines from the plasma, resulting in the maintenance of plasma chemokine concentrations.

Targeting cytokine/chemokine receptors: a challenge for molecular nuclear medicine.

Radiolabelled cytokines and chemokines are a group of radiopharmaceuticals that, by highlighting in vivo the binding to specific high-affinity receptors expressed on selected cell populations, allow the molecular and functional characterisation of immune-mediated processes Recently, several authors have described the use of radiolabelled cytokines and chemokines not only for imaging of inflammation and infection, but also as an approach to study in vivo the biology of primary and metastatic cancer cells. The latter avenue of research has been pursued particularly to help oncologists in therapeutic decision making and to follow up the efficacy of new immune therapies. In this paper we describe the characteristics of cytokines and chemokines, focussing on their role as radiopharmaceuticals for the imaging of cancer cells in vivo, a new challenge for molecular nuclear medicine.

Los factores genéticos determinantes de la resistencia a la infección por VIH y del control de la progresión al SIDA: Implicaciones sobre la patogénesis y las estrategias terapéuticas para la erradicación del VIH. Una revisión

Esta revisión describe y discute los factores genéticos que al menos en parte, determinan la resistencia a la infección y que controlan el curso progresivo de la enfermedad en las personas infectadas por el virus de la inmunodeficiencia humana. Los factores genéticos podrían explicar la no progresión o la progresión lenta de la enfermedad, de una proporción de individuos infectados por VIH denominados no progresores a largo plazo. En general, este grupo permanece sin síntomas durante más de 10 años, mantiene estable sus niveles circulantes de cT CD4+ y habitualmente tiene baja carga viral. No obstante que los fenómenos de la no progresión y de la progresión rápida son aún incomprendidos, es probable que ciertos alelos de clase I y clase II del complejo principal de histocompatibilidad se asocien con un riesgo menor o mayor para desarrollar el síndrome de inmunodeficiencia adquirida...