Biomedical subjects

Ralph Weissleder

Publications and source records attributed to Ralph Weissleder.

At least 19 recordsLinked to original sources

PubMed2007

Use of molecular imaging to quantify response to IKK-2 inhibitor treatment in murine arthritis.

OBJECTIVE: The NF-kappaB signaling pathway promotes the immune response in rheumatoid arthritis (RA) and in rodent models of RA. NF-kappaB activity is regulated by the IKK-2 kinase during inflammatory responses. To elucidate how IKK-2 inhibition suppresses disease development, we used a combination of in vivo imaging, transcription profiling, and histopathology technologies to study mice with antibody-induced arthritis. METHODS: ML120B, a potent, small molecule inhibitor of IKK-2, was administered to arthritic animals, and disease activity was monitored. NF-kappaB activity in diseased joints was quantified by in vivo imaging. Quantitative reverse transcriptase-polymerase chain reaction was used to evaluate gene expression in joints. Protease-activated near-infrared fluorescence (NIRF) in vivo imaging was applied to assess the amounts of active proteases in the joints. RESULTS: Oral administration of ML120B suppressed both clinical and histopathologic manifestations of disease. In vivo imaging demonstrated that NF-kappaB activity in inflamed arthritic paws was inhibited by ML120B, resulting in significant suppression of multiple genes in the NF-kappaB pathway, i.e., KC, epithelial neutrophil-activating peptide 78, JE, intercellular adhesion molecule 1, CD3, CD68, tumor necrosis factor alpha, interleukin-1beta, interleukin-6, inducible nitric oxide synthase, cyclooxygenase 2, matrix metalloproteinase 3, cathepsin B, and cathepsin K. NIRF in vivo imaging demonstrated that ML120B treatment dramatically reduced the amount of active proteases in the joints. CONCLUSION: Our data demonstrate that IKK-2 inhibition in the murine model of antibody-induced arthritis suppresses both inflammation and joint destruction. In addition, this study highlights how gene expression profiling can facilitate the identification of surrogate biomarkers of disease activity and treatment response in an experimental model of arthritis.

Administration, Oral↗

PubMed2007

Ly-6Chi monocytes dominate hypercholesterolemia-associated monocytosis and give rise to macrophages in atheromata.

Macrophage accumulation participates decisively in the development and exacerbation of atherosclerosis. Circulating monocytes, the precursors of macrophages, display heterogeneity in mice and humans, but their relative contribution to atherogenesis remains unknown. We report here that the Ly-6C(hi) monocyte subset increased dramatically in hypercholesterolemic apoE-deficient mice consuming a high-fat diet, with the number of Ly-6C(hi) cells doubling in the blood every month. Ly-6C(hi) monocytes adhered to activated endothelium, infiltrated lesions, and became lesional macrophages. Hypercholesterolemia-associated monocytosis (HAM) developed from increased survival, continued cell proliferation, and impaired Ly-6C(hi) to Ly-6C(lo) conversion and subsided upon statin-induced cholesterol reduction. Conversely, the number of Ly-6C(lo) cells remained unaffected. Thus, we believe that Ly-6C(hi) monocytes represent a newly recognized component of the inflammatory response in experimental atherosclerosis.

Animals↗

PubMed2006

Does FXIII deficiency impair wound healing after myocardial infarction?

Inadequate healing of myocardial infarction may contribute to local expansion of the infarct, frequently leading to chamber dilation, heart failure, or myocardial rupture. Experimental evidence in mouse models suggests that Factor XIII might play a key role in wound healing, and low persistent values lead to increased incidence of cardiac rupture following myocardial infarction. Here we would like to share our initial clinical experiences with strikingly similar observations in patients with this grave disease, and compare these observations to experimental findings.

Animals↗

PubMed2006

SPARC is a VCAM-1 counter-ligand that mediates leukocyte transmigration.

VCAM-1 is a cell surface molecule, which has been shown to mediate leukocyte adhesion to the endothelium and subsequent transmigration. Although VCAM-1 regulates adhesion through its interaction with VLA-4, VLA-4 does not play a role in VCAM-1-dependent diapedesis, an observation suggesting the presence of a second ligand for VCAM-1. We now report a novel interaction between VCAM-1 and secreted protein acidic and rich in cysteine (SPARC), which induces actin cytoskeletal rearrangement and intercellular gaps, physiological processes known to be important for leukocyte transmigration. The binding of leukocyte-derived SPARC to VCAM-1 was demonstrated to be necessary for leukocyte transmigration through endothelial monolayers (diapedesis) in vitro, and furthermore, SPARC null mice have abnormalities in leukocyte recruitment to the inflamed peritoneum in vivo. These findings provide new insight into the mechanisms of transendothelial leukocyte migration and suggest a potential, targetable interaction for therapeutic intervention.

Actins↗

PubMed2006

Emerging concepts in molecular MRI.

Molecular magnetic resonance imaging (MRI) offers the potential to image some events at the cellular and subcellular level and many significant advances have recently been witnessed in this field. The introduction of targeted MR contrast agents has enabled the imaging of sparsely expressed biological targets in vivo. Furthermore, high-throughput screens of nanoparticle libraries have identified nanoparticles that act as novel contrast agents and which can be targeted with enhanced diagnostic specificity and range. Another class of magnetic nanoparticles have also been designed to image dynamic events; these act as 'switches' and could be used in vitro, and potentially in vivo, as biosensors. Other specialized MR probes have been developed to image enzyme activity in vivo. Lastly, the use of chemical exchange and off-resonance techniques have been developed, adding another dimension to the broad capabilities of molecular MRI and offering the potential of multispectral imaging. These and other advances in molecular MRI offer great promise for the future and have significant potential for clinical translation.

Animals↗

PubMed2006

Oligomerization of CXCL10 is necessary for endothelial cell presentation and in vivo activity.

The chemokine IFN-gamma-inducible protein of 10 kDa (IP-10; CXCL10) plays an important role in the recruitment of activated T lymphocytes into sites of inflammation by interacting with the G protein-coupled receptor CXCR3. IP-10, like other chemokines, forms oligomers, the role of which has not yet been explored. In this study, we used a monomeric IP-10 mutant to elucidate the functional significance of oligomerization. Although monomeric IP-10 had reduced binding affinity for CXCR3 and heparin, it was able to induce in vitro chemotaxis of activated T cells with the same efficacy as wild-type IP-10. However, monomeric IP-10 was unable to induce recruitment of activated CD8+ T cells into the airways of mice after intratracheal instillation. Use of a different IP-10 mutant demonstrated that this inability was due to lack of oligomerization rather than reduced CXCR3 or heparin binding. Molecular imaging demonstrated that both wild-type and monomeric IP-10 were retained in the lung after intratracheal instillation. However, in vitro binding assays indicated that wild-type, but not monomeric, IP-10 was retained on endothelial cells and could induce transendothelial chemotaxis of activated T cells. We therefore propose that oligomerization of IP-10 is required for presentation on endothelial cells and subsequent transendothelial migration, an essential step for lymphocyte recruitment in vivo.

Animals↗

PubMed2006

Molecular imaging of myocardial infarction.

Molecular tools are rapidly elucidating the molecular and cellular processes underlying myocardial infarction. To further understand these biological processes in vivo, investigators are embracing the burgeoning field of molecular imaging. Here we review important aspects of molecular imaging technology and then devote the majority of the text to studies that shed light on the in vivo pathogenesis of myocardial infarction. In particular, we focus on post-infarction healing and remodeling and discuss molecular imaging of proteolytic activity, angiogenesis, transglutaminase activity, and apoptosis. In the future, novel reporter agents and high-resolution cardiac imaging systems should enable imaging of emerging targets such as activated macrophages and myeloperoxidase activity, as well as stem cell-based and gene therapy-based myocardial regenerative strategies, in both experimental and clinical subjects.

Animals↗

PubMed2006

Multivalent effects of RGD peptides obtained by nanoparticle display.

The binding of RGD peptides to integrins offers an excellent system to study the multivalent mediated changes in affinity that arise when peptides, displayed on the surface of a nanoparticle carrier, bind to integrins displayed on the cell membrane. The IC50 of an RGD nanoparticle for endothelial adhesion was 1.0 nM nanoparticle or 20 nM peptide (20 peptide/nanoparticle) and was associated with strong multivalent effects, defined as a multivalent enhancement factor (MVE) of 38 (MVE=IC50 (peptide)/IC50 (peptide when displayed by nanoparticle)). The attachment of RGD peptides to nanoparticles resulted in an extension of the peptide blood half-life from 13 to 180 min. Based on the multivalent enhancement of affinity and extension of blood half-life, multivalent RGD nanoparticle-sized materials should be potent inhibitors of the alpha(V)beta(3) function on endothelial cells in vivo.

Animals↗

PubMed2006

Noninvasive vascular cell adhesion molecule-1 imaging identifies inflammatory activation of cells in atherosclerosis.

BACKGROUND: Noninvasive imaging of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1) may identify early stages of inflammation in atherosclerosis. We hypothesized that a novel, second-generation VCAM-1-targeted agent with enhanced affinity had sufficient sensitivity to enable real-time detection of VCAM-1 expression in experimental atherosclerosis in vivo, to quantify pharmacotherapy-induced reductions in VCAM-1 expression, and to identify activated cells in human plaques. METHODS AND RESULTS: In vivo phage display in apolipoprotein E-deficient mice identified a linear peptide affinity ligand, VHPKQHR, homologous to very late antigen-4, a known ligand for VCAM-1. This peptide was developed into a multivalent agent detectable by MRI and optical imaging (denoted VINP-28 for VCAM-1 internalizing nanoparticle 28, with 20 times higher affinity than previously reported for VNP). In vitro, VINP-28 targeted all cell types expressing VCAM-1. In vivo, MRI and optical imaging in apolipoprotein E-deficient mice (n=28) after injection with VINP-28 or saline revealed signal enhancement in the aortic root of mice receiving VINP-28 (P<0.05). VINP-28 colocalized with endothelial cells and other VCAM-1-expressing cells, eg, macrophages, and was spatially distinct compared with untargeted control nanoparticles. Atheromata of atorvastatin-treated mice showed reduced VINP-28 deposition and VCAM-1 expression. VINP-28 enhanced early lesions in juvenile mice and resected human carotid artery plaques. CONCLUSIONS: VINP-28 allows noninvasive imaging of VCAM-1-expressing endothelial cells and macrophages in atherosclerosis and spatial monitoring of anti-VCAM-1 pharmacotherapy in vivo and identifies inflammatory cells in human atheromata. This clinically translatable agent could noninvasively detect inflammation in early, subclinical atherosclerosis.

Amino Acid Sequence↗

PubMed2006

Cyclophosphamide increases transgene expression mediated by an oncolytic adenovirus in glioma-bearing mice monitored by bioluminescence imaging.

Approaches to improve the oncolytic potency of replication-competent adenoviruses include the insertion of therapeutic transgenes into the viral genome. Little is known about the levels and duration of in vivo transgene expression by cells infected with such "armed" viruses. Using a tumor-selective adenovirus encoding firefly luciferase (AdDelta24CMV-Luc) we investigated these questions in an intracranial mouse model for malignant glioma. Luciferase expression was detected by bioluminescence imaging, and the effect of the immunosuppressive agent cyclophosphamide (CPA) on transgene expression was assessed. Intratumoral AdDelta24CMV-Luc injection led to a localized dose-dependent expression of luciferase. Surprisingly, this expression decreased rapidly during the course of 14 days. In contrast, mice injected with nonreplicating Ad.CMV-Luc demonstrated stable transgene expression. Treatment of mice with CPA in combination with AdDelta24CMV-Luc retarded the loss of transgene expression. Staining of mouse brains for inflammatory cells demonstrated decreased tumor infiltration by immune cells in CPA-treated mice. Moreover, in immunodeficient NOD/SCID mice loss of transgene expression was less rapid and not prevented by CPA treatment. Together, our data demonstrate that transgene expression and viral replication decrease rapidly after intratumoral injection of oncolytic adenovirus in mouse brains and that treatment with the immunomodulator CPA prolongs viral-mediated gene expression.

Adenoviridae↗

PubMed2006

Cyclophosphamide enhances glioma virotherapy by inhibiting innate immune responses.

Clinical trials are testing oncolytic viruses (OVs) as therapies for cancer. We have shown that animals that have brain tumors and are treated with a herpes simplex virus (HSV)-derived OV live significantly longer when cyclophosphamide (CPA) is preadministered. Here, we explore the mechanisms behind this finding. In a syngeneic rat glioma model, intratumoral HSV administration is associated with rapid increase of natural killer cells, microglia/macrophages (CD68+ and CD163+), and IFN-gamma. Pretreatment with CPA enhances HSV replication and oncolysis and reduces an HSV-mediated increase in CD68+ and CD163+ cells and intratumoral IFN-gamma. Molecular imaging shows CPA pretreatment to inhibit HSV-induced infiltration of tumor-associated phagocytic cells. Our results reveal molecular and cellular mechanisms that inhibit intratumoral spread of HSV and suggest a therapeutic path for improving the efficacy of virotherapy as a treatment for cancer.

Animals↗

PubMed2006

Enzyme-targeted fluorescent imaging probes on a multiple antigenic peptide core.

Peptide dendrimers have a variety of applications in biology such as the vehicles for drug and gene delivery, molecular inhibitors, protein mimics, and synthetic vaccines. The multiple antigenic peptide (MAP) system is a well-known example of a discrete, dendrimeric scaffold. We explored a novel application of the MAP-based scaffold by designing molecular probes that fluoresce only after enzymatic treatment. The probes, which were synthesized on solid support, incorporate a cathepsin S dipeptide substrate (Leu-Arg), and a poly(ethylene glycol) (PEG) chain in their dendritic arms. The fluorescence emission of the near-infrared fluorochromes attached to the N-termini of the dendritic arms was quenched. Mechanistic studies revealed formation of H-type dye aggregates within the tetravalent MAP system. By varying the length of the PEG chain, three probes were synthesized, CyPEG-1, CyPEG-2, and CyPEG-3 with 4, 8, and 12 ethylene oxide units, respectively. CyPEG-2 showed optimum aqueous solubility and quenching efficiency for imaging applications. Upon proteolytic activation with cathepsin S (EC 3.4.22.27), CyPEG-2 showed greater than 70-fold increase and more than 95% recovery in fluorescence emission.

Cathepsins↗

PubMed2006

Selective antitumor effect of novel protease-mediated photodynamic agent.

A new approach to selective photodynamic therapy (PDT) was developed by designing chlorin e6 (Ce6)-containing macromolecules, which are sensitive to tumor-associated proteases. The agents are nontoxic in their native state but become fluorescent and produce singlet oxygen on protease conversion. Coupled with optimized delivery systems, we show that (a) the agents efficiently accumulate in tumors due to the enhanced permeability and retention effect, (b) the agents are locally activated by proteases, (c) local drug concentrations can be measured by quantitative fluorescence tomography, and (d) light-treated tumors show reduced growth. A single low dose of PDT (0.125 mg Ce6 equivalent/kg) was sufficient to suppress tumor growth by >50%. Activatable singlet oxygen generation agents provide increased efficacy with reduced toxicity, and it could become a powerful PDT.

Animals↗

PubMed2006

Monocyte accumulation in mouse atherogenesis is progressive and proportional to extent of disease.

Monocytes participate importantly in the pathogenesis of atherosclerosis, but their spatial and temporal recruitment from circulation remains uncertain. This study tests the hypothesis that monocyte accumulation in atheroma correlates with the extent of disease by using a sensitive and simple quantitative assay that allows tracking of highly enriched populations of blood monocytes. A two-step isolation method yielded viable and functionally intact highly enriched peripheral blood monocyte populations (>90%). Recipient mice received syngeneic monocytes labeled in two ways: by transgenically expressing EGFP or with a radioactive tracer [(111)In]oxine. After 5 days, more labeled cells accumulated in the aorta, principally the aortic root and ascending aorta, of 10-wk-old ApoE(-/-) compared with 10-wk-old C57BL/6 mice (223 +/- 3 vs. 87 +/- 22 cells per aorta). Considerably more monocytes accumulated in 20-wk-old ApoE(-/-) mice on either chow (314 +/- 41 cells) or high-cholesterol diet (395 +/- 53 cells). Fifty-week-old ApoE(-/-) mice accumulated even more monocytes in the aortic root, ascending aorta, and thoracic aorta after both chow (503 +/- 67 cells) or high-cholesterol diet (648 +/- 81 cells). Labeled monocyte content in the aorta consistently correlated with lesion surface area. These data indicate that monocytes accumulate continuously during atheroma formation, accumulation increases in proportion to lesion size, and recruitment is augmented with hypercholesterolemia. These results provide insights into mechanisms of atherogenesis and have implications for the duration of therapies directed at leukocyte recruitment.

Animals↗

PubMed2006

Inflammation in atherosclerosis: visualizing matrix metalloproteinase action in macrophages in vivo.

BACKGROUND: Matrix metalloproteinases (MMPs) in inflamed atherosclerotic plaques may contribute to extracellular matrix remodeling and the onset of acute thrombotic complications. METHODS AND RESULTS: To test the hypothesis that optical molecular imaging with the use of an activatable near-infrared fluorescence (NIRF) probe can detect enzymatic action of MMP in atherosclerotic plaques, we used a NIRF substrate for gelatinases (MMP-2/gelatinase-A and MMP-9/gelatinase-B) in apolipoprotein E-deficient (apoE-/-) mice that consumed a high-cholesterol diet for 12 weeks and age-matched apoE+/+ mice as control. The aortas of apoE-/- mice at 24 hours after probe yielded intense NIRF signals, as detected by NIRF reflectance ex vivo, compared with negligible signals in aortas of apoE+/+ mice with/without probe administration or atherosclerotic apoE-/- aortas without probe. Gelatinase inhibitor treatment abolished NIRF signals in apoE-/- mouse aortas ex vivo. Sites of gelatinase activity visualized by NIRF colocalized with macrophage accumulation, immunoreactive MMP-2 and MMP-9, and gelatinolytic activity detected by in situ zymography. Furthermore, fluorescence molecular tomography indicated in vivo that atherosclerotic aortas of apoE-/- mice produced NIRF signals for gelatinase action, whereas aortas of apoE+/+ mice injected with the probe or apoE-/- aortas with no probe exhibited negligible NIRF signals. CONCLUSIONS: These results suggest the feasibility of noninvasively imaging the enzymatic action of MMPs in vivo, an approach that may gauge inflammatory foci in atherosclerosis, assess cardiovascular risk, and evaluate the effects of therapeutic interventions.

Animals↗

PubMed2006

Near infrared thoracoscopy of tumoral protease activity for improved detection of peripheral lung cancer.

Improvement in tumor detection using "smart" probes in combination with microcatheter fluorescence thoracoscopy was evaluated in a mouse model. These imaging probes increase in fluorescence intensity after protease activation; cathepsin B is a major activator of the probes used in this study. Lewis lung carcinoma cells were orthotopically implanted in the subpleural lung parenchyma. Two activatable near infrared (NIR) probes with different excitation and emission wavelength were administered intravenously to determine whether wavelength would modulate target to background ratio (TBR). Mice were selectively intubated and thoracoscopy performed. A 0.8 mm outer diameter imaging catheter was used to record simultaneous white-light (anatomic) and NIR (protease expression) images. At both wavelength pairs evaluated (680/700 and 750/780 nm excitation/emission), the intrinsic luminosity differences between tumors and normal lung in uninjected animals was low (p > 0.3 and p = 0.4, respectively and TBR near 1). In mice receiving protease probes IV, tumors were significantly more fluorescent than adjacent lung (p < 0.0005 for 680/700 and p < 0.006 for 750/780) and TBR increased to approximately 9-fold. Confirmatory fluorescence microscopy and immunohistochemistry were similar and revealed that normal lung had very low levels when compared to tumors of cathepsin B and probe fluorescence. In conclusion, protease sensitive imaging probes selective for cathepsin B, imaged with NIR microcatheters, significantly increase the TBR, making small peripheral lung tumors more readily apparent. Such an approach may be a useful adjunct in staging or restaging patients with lung cancer to find minimal disease in the pleural and subpleural space.

Animals↗

PubMed2006

Molecular imaging in cancer.

Medical imaging technologies have undergone explosive growth over the past few decades and now play a central role in clinical oncology. But the truly transformative power of imaging in the clinical management of cancer patients lies ahead. Today, imaging is at a crossroads, with molecularly targeted imaging agents expected to broadly expand the capabilities of conventional anatomical imaging methods. Molecular imaging will allow clinicians to not only see where a tumor is located in the body, but also to visualize the expression and activity of specific molecules (e.g., proteases and protein kinases) and biological processes (e.g., apoptosis, angiogenesis, and metastasis) that influence tumor behavior and/or response to therapy. This information is expected to have a major impact on cancer detection, individualized treatment, and drug development, as well as our understanding of how cancer arises.

Animals↗

PubMed2006

The impact of human EGFR kinase domain mutations on lung tumorigenesis and in vivo sensitivity to EGFR-targeted therapies.

To understand the role of human epidermal growth factor receptor (hEGFR) kinase domain mutations in lung tumorigenesis and response to EGFR-targeted therapies, we generated bitransgenic mice with inducible expression in type II pneumocytes of two common hEGFR mutants seen in human lung cancer. Both bitransgenic lines developed lung adenocarcinoma after sustained hEGFR mutant expression, confirming their oncogenic potential. Maintenance of these lung tumors was dependent on continued expression of the EGFR mutants. Treatment with small molecule inhibitors (erlotinib or HKI-272) as well as prolonged treatment with a humanized anti-hEGFR antibody (cetuximab) led to dramatic tumor regression. These data suggest that persistent EGFR signaling is required for tumor maintenance in human lung adenocarcinomas expressing EGFR mutants.

Adenocarcinoma↗