SARS-CoV-2 infection in the Syrian hamster model causes inflammation as well as type I interferon dysregulation in both respiratory and non-respiratory tissues including the heart and kidney.

COVID-19 (coronavirus disease 2019) caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection is a disease affecting several organ systems. A model that captures all clinical symptoms of COVID-19 as well as long-haulers disease is needed. We investigated the host responses associated with infection in several major organ systems including the respiratory tract, the heart, and the kidneys after SARS-CoV-2 infection in Syrian hamsters. We found significant increases in inflammatory cytokines (IL-6, IL-1beta, and TNF) and type II interferons whereas type I interferons were inhibited. Examination of extrapulmonary tissue indicated inflammation in the kidney, liver, and heart which also lacked type I interferon upregulation. Histologically, the heart had evidence of myocarditis and microthrombi while the kidney had tubular inflammation. These results give insight into the multiorgan disease experienced by people with COVID-19 and possibly the prolonged disease in people with post-acute sequelae of SARS-CoV-2 (PASC).

Rapid Copper-free Click Conjugation to Lipid-Shelled Microbubbles for Ultrasound Molecular Imaging of Murine Bowel Inflammation.

Microbubbles are ultrasound contrast agents that can adhere to disease-related vascular biomarkers when functionalized with binding ligands such as antibodies or peptides. The biotin-streptavidin approach has predominantly been used as the microbubble labeling approach in preclinical imaging. However, due to the immunogenicity of avidin in humans, it is not suitable for clinical translation. What would aid clinical translation is a simple and effective microbubble functionalization approach that could be directly translated from animals to humans. We developed a targeted microbubble to P-selectin, a vascular inflammatory marker, labeled using a strain-promoted [3 + 2] azide-alkyne (azide-DBCO) reaction, comparing its ability to detect bowel inflammation to that of P-selectin targeted microbubbles labeled with a traditional biotin-streptavidin approach. Bowel inflammation was chemically induced using 2,4,6-trinitrobenzenesulfonic acid (TNBS) in Balb/C mice. Each mouse received both non-targeted and P-selectin targeted microbubbles (either biotin-streptavidin or azide-DBCO). Using the biotin-streptavidin reaction, there was a significant increase in the ultrasound molecular imaging signal in inflamed mice using P-selectin targeted (2.30 ± 0.91 a.u.) compared to isotype control microbubbles (1.14 ± 0.7 a.u.) (p = 0.009). Using the azide-DBCO reaction, there was a similar increase in the ultrasound molecular imaging signal in inflamed mice (2.54 ± 0.56 a.u) compared to the isotype control (0.44 ± 0.25 a.u) (p = 0.009). There were no significant differences between the two labeling approaches between non-targeted and P-selectin targeted microbubbles. Mouse inflammatory phenotypes and expression of P-selectin were validated using histology and immunostaining. We constructed P-selectin targeted microbubbles using an azide-DBCO click reaction, which could detect bowel inflammation in vivo. This reaction generated a similar ultrasound molecular imaging signal to biotin-strepavidin-labeled microbubbles. These data show the potential of click chemistry conjugation (azide-DBCO) as a quick, cost-efficient, and clinically translatable approach for developing targeted microbubbles.

Vascular endothelial growth factor receptor type 2-targeted contrast-enhanced US of pancreatic cancer neovasculature in a genetically engineered mouse model: potential for earlier detection.

PURPOSE: To test ultrasonographic (US) imaging with vascular endothelial growth factor receptor type 2 (VEGFR2)-targeted microbubble contrast material for the detection of pancreatic ductal adenocarcinoma (PDAC) in a transgenic mouse model of pancreatic cancer development. MATERIALS AND METHODS: Experiments involving animals were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. Transgenic mice (n = 44; Pdx1-Cre, KRas(G12D), Ink4a(-/-)) that spontaneously develop PDAC starting at 4 weeks of age were imaged by using a dedicated small-animal US system after intravenous injection of 5 × 10(7) clinical-grade VEGFR2-targeted microbubble contrast material. The pancreata in wild-type (WT) mice (n = 64) were scanned as controls. Pancreatic tissue was analyzed ex vivo by means of histologic examination (with hematoxylin-eosin staining) and immunostaining of vascular endothelial cell marker CD31 and VEGFR2. The Wilcoxon rank sum test and linear mixed-effects model were used for statistical analysis. RESULTS: VEGFR2-targeted US of PDAC showed significantly higher signal intensities (26.8-fold higher; mean intensity ± standard deviation, 6.7 linear arbitrary units [lau] ± 8.5; P < .001) in transgenic mice compared with normal, control pancreata of WT mice (mean intensity, 0.25 lau ± 0.25). The highest VEGFR2-targeted US signal intensities were observed in smaller tumors, less than 3 mm in diameter (30.8-fold higher than control tissue with mean intensity of 7.7 lau ± 9.3 [P < .001]; and 1.7-fold higher than lesions larger than 3 mm in diameter with mean intensity of 4.6 lau ± 5.8 [P < .024]). Ex vivo quantitative VEGFR2 immunofluorescence demonstrated that VEGFR2 expression was significantly higher in pancreatic tumors (P < .001; mean fluorescent intensity, 499.4 arbitrary units [au] ± 179.1) compared with normal pancreas (mean fluorescent intensity, 232.9 au ± 83.7). CONCLUSION: US with clinical-grade VEGFR2-targeted microbubbles allows detection of small foci of PDAC in transgenic mice.

Quantitative Assessment of Inflammation in a Porcine Acute Terminal Ileitis Model: US with a Molecularly Targeted Contrast Agent.

PURPOSE: To evaluate the feasibility and reproducibility of ultrasonography (US) performed with dual-selectin-targeted contrast agent microbubbles (MBs) for assessment of inflammation in a porcine acute terminal ileitis model, with histologic findings as a reference standard. MATERIALS AND METHODS: The study had institutional Animal Care and Use Committee approval. Acute terminal ileitis was established in 19 pigs; four pigs served as control pigs. The ileum was imaged with clinical-grade dual P- and E-selectin-targeted MBs (MBSelectin) at increasing doses (0.5, 1.0, 2.5, 5.0, 10, and 20 × 10(8) MB per kilogram of body weight) and with control nontargeted MBs (MBControl). For reproducibility testing, examinations were repeated twice after the MBSelectin and MBControl injections. After imaging, scanned ileal segments were analyzed ex vivo both for inflammation grade (by using hematoxylin-eosin staining) and for expression of selectins (by using quantitative immunofluorescence analysis). Statistical analysis was performed by using the t test, intraclass correlation coefficients (ICCs), and Spearman correlation analysis. RESULTS: Imaging signal increased linearly (P < .001) between a dose of 0.5 and a dose of 5.0 × 10(8) MB/kg and plateaued between a dose of 10 and a dose of 20 × 10(8) MB/kg. Imaging signals were reproducible (ICC = 0.70), and administration of MBSelectin in acute ileitis resulted in a significantly higher (P < .001) imaging signal compared with that in control ileum and MBControl. Ex vivo histologic grades of inflammation correlated well with in vivo US signal (ρ = 0.79), and expression levels of both P-selectin (37.4% ± 14.7 [standard deviation] of vessels positive; P < .001) and E-selectin (31.2% ± 25.7) in vessels in the bowel wall of segments with ileitis were higher than in control ileum (5.1% ± 3.7 for P-selectin and 4.8% ± 2.3 for E-selectin). CONCLUSION: Quantitative measurements of inflammation obtained by using dual-selectin-targeted US are reproducible and correlate well with the extent of inflammation at histologic examination in a porcine acute ileitis model as a next step toward clinical translation.

Detection of pancreatic ductal adenocarcinoma in mice by ultrasound imaging of thymocyte differentiation antigen 1.

BACKGROUND & AIMS: Early detection of pancreatic ductal adenocarcinoma (PDAC) allows for surgical resection and increases patient survival times. Imaging agents that bind and amplify the signal of neovascular proteins in neoplasms can be detected by ultrasound, enabling accurate detection of small lesions. We searched for new markers of neovasculature in PDAC and assessed their potential for tumor detection by ultrasound molecular imaging. METHODS: Thymocyte differentiation antigen 1 (Thy1) was identified as a specific biomarker of PDAC neovasculature by proteomic analysis. Up-regulation in PDAC was validated by immunohistochemical analysis of pancreatic tissue samples from 28 healthy individuals, 15 with primary chronic pancreatitis tissues, and 196 with PDAC. Binding of Thy1-targeted contrast microbubbles was assessed in cultured cells, in mice with orthotopic PDAC xenograft tumors expressing human Thy1 on the neovasculature, and on the neovasculature of a genetic mouse model of PDAC. RESULTS: Based on immunohistochemical analyses, levels of Thy1 were significantly higher in the vascular of human PDAC than chronic pancreatitis (P = .007) or normal tissue samples (P < .0001). In mice, ultrasound imaging accurately detected human Thy1-positive PDAC xenografts, as well as PDACs that express endogenous Thy1 in genetic mouse models of PDAC. CONCLUSIONS: We have identified and validated Thy1 as a marker of PDAC that can be detected by ultrasound molecular imaging in mice. The development of a specific imaging agent and identification of Thy1 as a new biomarker could aid in the diagnosis of this cancer and management of patients.

The gap junction protein Cx43 regulates B-lymphocyte spreading and adhesion.

The gap junction protein connexin43 (Cx43) is widely expressed in mammalian cells and forms intercellular channels for the transfer of small molecules between adjacent cells, as well as hemichannels that mediate bidirectional transport of molecules between the cell and the surrounding environment. Cx43 regulates cell adhesion and migration in neurons and glioma cells, and we now show that Cx43 influences BCR-, LFA-1- and CXCL12-mediated activation of the Rap1 GTPase. Using shRNA knockdown of Cx43 in WEHI 231 cells, we show that Cx43 is required for sustained Rap1 activation and BCR-mediated spreading. To determine the domains of Cx43 that are important for this effect, Cx43-null J558 µm3 B cells (which express a wild-type IgM BCR) were transfected with wild-type Cx43-GFP or a C-terminal-truncated Cx43 (Cx43ΔT-GFP). Expression of wild-type Cx43-GFP, but not Cx43ΔT-GFP, was sufficient to restore sustained, BCR-mediated Rap1 activation and cell spreading. Cx43, and specifically the C-terminal domain, was also important for LFA-1- and CXCL12-mediated Rap1 activation, spreading and adhesion to an endothelial cell monolayer. These data show that Cx43 has an important and previously unreported role in B-cell processes that are essential to normal B-cell development and immune responses.

Molecular imaging of inflammation in inflammatory bowel disease with a clinically translatable dual-selectin-targeted US contrast agent: comparison with FDG PET/CT in a mouse model.

PURPOSE: To develop and test a molecular imaging approach that uses ultrasonography (US) and a clinically translatable dual-targeted (P- and E-selectin) contrast agent (MBSelectin) in the quantification of inflammation at the molecular level and to quantitatively correlate selectin-targeted US with fluorodeoxyglucose (FDG) combined positron emission tomography (PET) and computed tomography (CT) in terms of visualization and quantification of different levels of inflammation in a murine acute colitis model. MATERIALS AND METHODS: Animal studies were approved by the Institutional Administrative Panel on Laboratory Animal Care at Stanford University. MBSelectin was developed by covalently binding an analog of the naturally occurring binding ligand P-selectin glycoprotein ligand 1 fused to a human fragment crystallizable(or Fc) domain onto the lipid shell of perfluorobutane and nitrogen-containing MBs. Binding specificity of MBSelectin was assessed in vitro with a flow chamber assay and in vivo with a chemically induced acute colitis murine model. US signal was quantitatively correlated with FDG uptake at PET/CT and histologic grade. Statistical analysis was performed with the Student t test, analysis of variance, and Pearson correlation analysis. RESULTS: MBSelectin showed strong attachment to both human and mouse P- and E-selectin compared with MBControl in vitro (P ≤ .002). In vivo, US signal was significantly increased (P < .001) in mice with acute colitis (173.8 arbitrary units [au] ± 134.8 [standard deviation]) compared with control mice (5.0 au ± 4.5). US imaging signal strongly correlated with FDG uptake on PET/CT images (ρ = 0.89, P < .001). Ex vivo analysis enabled confirmation of inflammation in mice with acute colitis and high expression levels of P- and E-selectin in mucosal capillaries (P = .014). CONCLUSION: US with MBSelectin specifically enables detection and quantification of inflammation in a murine acute colitis model, leveraging the natural pathway of leukocyte recruitment in inflammatory tissue. US imaging with MBSelectin correlates well with FDG uptake at PET/CT imaging.

Aptamer-Functionalized Microbubbles Targeted to P-selectin for Ultrasound Molecular Imaging of Murine Bowel Inflammation.

PURPOSE: Our objectives were to develop a targeted microbubble with an anti-P-selectin aptamer and assess its ability to detect bowel inflammation in two murine models of acute colitis. PROCEDURES: Lipid-shelled microbubbles were prepared using mechanical agitation. A rapid copper-free click chemistry approach (azide-DBCO) was used to conjugate the fluorescent anti-P-selectin aptamer (Fluor-P-Ap) to the microbubble surface. Bowel inflammation was chemically induced using 2,4,6-trinitrobenzenesulfonic acid (TNBS) in both Balb/C and interleukin-10-deficient (IL-10 KO) mice. Mouse bowels were imaged using non-linear contrast mode following an i.v. bolus of 1 × 108 microbubbles. Each mouse received a bolus of aptamer-functionalized and non-targeted microbubbles. Mouse phenotypes and the presence of P-selectin were validated using histology and immunostaining, respectively. RESULTS: Microbubble labelling of Fluor-P-Ap was complete after 20 min at 37 ̊C. We estimate approximately 300,000 Fluor-P-Ap per microbubble and confirmed fluorescence using confocal microscopy. There was a significant increase in ultrasound molecular imaging signal from both Balb/C (p = 0.003) and IL-10 KO (p = 0.02) mice with inflamed bowels using aptamer-functionalized microbubbles in comparison to non-targeted microbubbles. There was no signal in healthy mice (p = 0.4051) using either microbubble. CONCLUSIONS: We constructed an aptamer-functionalized microbubble specific for P-selectin using a clinically relevant azide-DBCO click reaction, which could detect bowel inflammation in vivo. Aptamers have potential as a next generation targeting agent for developing cost-efficient and clinically translatable targeted microbubbles.

Chemically-induced trout model of acute intestinal inflammation using TNBS.

Chemically-induced models of intestinal inflammation are a useful tool for the study of immune responses and inflammation. Although well established in mammals, application of these models is currently limited in teleosts. Based on a variety of factors, including genetic diversity, known toxicological sensitivity, and economic importance, we propose salmonids as a model family of fishes for studying intestinal inflammation. We present a rainbow trout model of chemically-induced intestinal inflammation using 2,4,6-trinitrobenzene sulfonic acid (TNBS), assessed through histological analysis of primary and secondary intestinal folding, enterocyte morphology, goblet cell size and frequency, tissue layer thickness, and immune cell infiltration. Twenty-four hours after treatment with one of three concentrations of TNBS, trout developed classic signs of intestinal inflammation, including notably increased thickness of primary and secondary folds, and increased immune cell infiltration as compared to controls. This study provides a simple, reproducible model of rapid TNBS-induction of moderate intestinal inflammation.

Contrast-enhanced ultrasound imaging for assessment of intestinal inflammation in rainbow trout.

The intestine is essential for nutritional uptake and as a barrier to pathogens. Inflammation of the intestine can result from chemical contaminants, dietary irritants, or disease and may lead to serious health consequences, including reduced growth rates or increased pathogen susceptibility. Traditionally, intestinal inflammation in fish has been detected through histology completed post-mortem through excision and processing of the affected tissue. However, in human clinical settings, tools have been developed to assess intestinal inflammation non-invasively. Contrast-enhanced ultrasound (CEUS) imaging is an important tool for measuring inflammation in patients because it is cost-effective and minimally invasive. Specifically, CEUS allows real-time visualization and quantification of vascular perfusion. Changes in blood flow are typical in areas of inflamed or diseased tissue, and by measuring these changes, it is possible to assess the degree of inflammation. We demonstrate that standard CEUS protocols used for small mammals can be used to quantify vascular perfusion in the intestines of rainbow trout. Our resolution was sufficient to measure a significant difference in perfusion between control and TNBS-inflamed trout intestines, with inflamed intestines showing decreased perfusion. The presence of inflammation in the TNBS-treated intestines was verified ex vivo histologically and was characterized by the thickening of intestinal folds. The minimally invasive nature of CEUS imaging presents the opportunity to evaluate intestinal health in novel ways by allowing for longitudinal observations and avoiding mortality in valuable or at-risk specimens. Recent developments of highly portable, cost-effective CEUS systems will allow broad application of this tool, from industry to research.

Developing a Microbubble-Based Contrast Agent for Synchrotron Multiple-Image Radiography.

PURPOSE: Multiple-image radiography (MIR) is an analyzer-based synchrotron X-ray imaging approach capable of dissociating absorption, refraction, and scattering components of X-ray interaction with the material. It generates additional image contrast mechanisms (besides absorption), especially in the case of soft tissues, while minimizing absorbed radiation dose. Our goal is to develop a contrast agent for MIR using ultrasound microbubbles by carrying out a systematic assessment of size, shell material, and concentration. PROCEDURES: Microbubbles were synthesized with two different shell materials: phospholipid and polyvinyl-alcohol. Polydisperse perfluorobutane-filled lipid microbubbles were divided into five size groups using centrifugation. Two distributions of air-filled polymer microbubbles were generated: 2-3 µm and 3-4 µm. A subset of polymer microbubbles 3-4 µm had iron oxide nanoparticles incorporated into their shell or coated on their surface. Microbubbles were immobilized in agar with different concentrations: 5 × 107, 5 × 106, and 5 × 105 MBs/ml. MIR was conducted on the BioMedical Imaging and Therapy beamline at the Canadian Light Source. Three images were generated: Gaussian amplitude, refraction, and ultra-small-angle X-ray scattering (USAXS). The contrast signal was quantified by measuring mean pixel values and comparing them with agar. RESULTS: No difference was detected in absorption or refraction images of all tested microbubbles. Using USAXS, a significant signal increase was observed with lipid microbubbles 6-10 µm at the highest concentration (p = 0.02), but no signal was observed at lower concentrations. CONCLUSIONS: These data indicate that lipid microbubbles 6-10 µm are candidates as contrast agents for MIR, specifically for USAXS. A minimum concentration of 5 × 107 microbubbles (lipid-shell 6-10 µm) per milliliter was needed to generate a detectable signal.

SARS-CoV-2 Variant-Specific Infectivity and Immune Profiles Are Detectable in a Humanized Lung Mouse Model.

Small animal models that accurately model pathogenesis of SARS-CoV-2 variants are required for ongoing research efforts. We modified our human immune system mouse model to support replication of SARS-CoV-2 by implantation of human lung tissue into the mice to create TKO-BLT-Lung (L) mice and compared infection with two different variants in a humanized lung model. Infection of TKO-BLT-L mice with SARS-CoV-2 recapitulated the higher infectivity of the B.1.1.7 variant with more animals becoming infected and higher sustained viral loads compared to mice challenged with an early B lineage (614D) virus. Viral lesions were observed in lung organoids but no differences were detected between the viral variants as expected. Partially overlapping but distinct immune profiles were also observed between the variants with a greater Th1 profile in VIDO-01 and greater Th2 profile in B.1.1.7 infection. Overall, the TKO-BLT-L mouse supported SARS-CoV-2 infection, recapitulated key known similarities and differences in infectivity and pathogenesis as well as revealing previously unreported differences in immune responses between the two viral variants. Thus, the TKO-BLT-L model may serve as a useful animal model to study the immunopathobiology of newly emerging variants in the context of genuine human lung tissue and immune cells.

Developing a Microbubble-Based Contrast Agent for Synchrotron In-Line Phase Contrast Imaging.

OBJECTIVE: X-ray phase contrast imaging generates contrast from refraction of X-rays, enhancing soft tissue contrast compared to conventional absorption-based imaging. Our goal is to develop a contrast agent for X-ray in-line phase contrast imaging (PCI) based on ultrasound microbubbles (MBs), by assessing size, shell material, and concentration. METHODS: Polydisperse perfluorobutane-core lipid-shelled MBs were synthesized and size separated into five groups between 1 and 10 µm. We generated two size populations of polyvinyl-alcohol (PVA)-MBs, 2-3 µm and 3-4 µm, whose shells were either coated or integrated with iron oxide nanoparticles (SPIONs). Microbubbles were then embedded in agar at three concentrations: 5 × 107, 5 × 106 and 5 × 105 MBs/ml. In-line phase contrast imaging was performed at the Canadian Light Source with filtered white beam micro-computed tomography. Phase contrast intensity was measured by both counting detectable MBs, and comparing mean pixel values (MPV) in minimum and maximum intensity projections of the overall samples. RESULTS: Individual lipid-MBs 6-10 µm, lipid-MBs 4-6 µm and PVA-MBs coated with SPIONs were detectable at each concentration. At the highest concentration, lipid-MBs 6-10 µm and 4-6 µm showed an overall increase in positive contrast, whereas at a moderate concentration, only lipid-MBs 6-10 µm displayed an increase. Negative contrast was also observed from two largest lipid-MBs at high concentration. CONCLUSION: These data indicate that lipid-MBs larger than 4 µm are candidates for PCI, and 5 × 106 MBs/ml may be the lowest concentration suitable for generating visible phase contrast in vivo. SIGNIFICANCE: Identifying a suitable MB for PCI may facilitate future clinical translation.

Contrast-enhanced ultrasound imaging for assessing organ perfusion in rainbow trout (Oncorhynchus mykiss).

Contrast-enhanced ultrasound (CEUS) imaging has great potential as a non-lethal, inexpensive monitoring tool in aquatic toxicology. It is a well-established clinical imaging approach that combines real-time, quantitative assessment of organ blood flow, with morphological data. In humans, it has been extensively used to measure changes in blood flow that can be attributed to cancer, inflammation, and other biological abnormalities. However, it has yet to be explored as a tool for fish physiology or environmental toxicology. In this study, our goal was to determine if CEUS could be used to visualize and measure blood flow in the liver of a rainbow trout. All rainbow trout received two injections of an ultrasound contrast agent, microbubbles. A subset received a third injection after administration of propranolol, a non-specific beta1 & 2-blocker, to determine if changes in blood flow could be detected. Ultrasound contrast time-intensity curves (TIC) were obtained, fit to a lognormal model, and different perfusion parameters were calculated. Contrast enhancement was observed in all rainbow trout livers, with high percentage between repeated measurements, including blood flow (80.6 ± 27.3%), area under the curve (73.2 ± 14%), blood volume (84 ± 14.2%) and peak enhancement (86.7 ± 7.5%). After administration of propranolol, we detected a non-significant (p > 0.05) increase in area under the curve (102.6 ± 44.2%), peak enhancement (77.3 ± 106.4), blood volume (48.2 ± 74.5%), and decrease in hepatic blood flow (-17.3 ± 37.1%). These data suggest that CEUS imaging is suitable to measure organ blood flow in fish, and demonstrates tremendous potential for exploring different organs, fish species, and effects of chemical contaminants in future studies.

Sex and age bias viral burden and interferon responses during SARS-CoV-2 infection in ferrets.

SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) hospitalizations and deaths disportionally affect males and older ages. Here we investigated the impact of male sex and age comparing sex-matched or age-matched ferrets infected with SARS-CoV-2. Differences in temperature regulation was identified for male ferrets which was accompanied by prolonged viral replication in the upper respiratory tract after infection. Gene expression analysis of the nasal turbinates indicated that 1-year-old female ferrets had significant increases in interferon response genes post infection which were delayed in males. These results provide insight into COVID-19 and suggests that older males may play a role in viral transmission due to decreased antiviral responses.

Characterization of Magneto-Endosymbionts as MRI Cell Labeling and Tracking Agents.

PURPOSE: Magneto-endosymbionts (MEs) show promise as living magnetic resonance imaging (MRI) contrast agents for in vivo cell tracking. Here we characterize the biomedical imaging properties of ME contrast agents, in vitro and in vivo. PROCEDURES: By adapting and engineering magnetotactic bacteria to the intracellular niche, we are creating magneto-endosymbionts (MEs) that offer advantages relative to passive iron-based contrast agents (superparamagnetic iron oxides, SPIOs) for cell tracking. This work presents a biomedical imaging characterization of MEs including: MRI transverse relaxivity (r 2) for MEs and ME-labeled cells (compared to a commercially available iron oxide nanoparticle); microscopic validation of labeling efficiency and subcellular locations; and in vivo imaging of a MDA-MB-231BR (231BR) human breast cancer cells in a mouse brain. RESULTS: At 7T, r 2 relaxivity of bare MEs was higher (250 s-1 mM-1) than that of conventional SPIO (178 s-1 mM-1). Optimized in vitro loading of MEs into 231BR cells yielded 1-4 pg iron/cell (compared to 5-10 pg iron/cell for conventional SPIO). r 2 relaxivity dropped by a factor of ~3 upon loading into cells, and was on the same order of magnitude for ME-loaded cells compared to SPIO-loaded cells. In vivo, ME-labeled cells exhibited strong MR contrast, allowing as few as 100 cells to be detected in mice using an optimized 3D SPGR gradient-echo sequence. CONCLUSIONS: Our results demonstrate the potential of magneto-endosymbionts as living MR contrast agents. They have r 2 relaxivity values comparable to traditional iron oxide nanoparticle contrast agents, and provide strong MR contrast when loaded into cells and implanted in tissue.

Spectroscopic Photoacoustic Molecular Imaging of Breast Cancer using a B7-H3-targeted ICG Contrast Agent.

Purpose: Breast cancer imaging methods lack diagnostic accuracy, in particular for patients with dense breast tissue, and improved techniques are critically needed. The purpose of this study was to evaluate antibody-indocyanine green (ICG) conjugates, which undergo dynamic absorption spectrum shifts after cellular endocytosis and degradation, and spectroscopic photoacoustic (sPA) imaging to differentiate normal breast tissue from breast cancer by imaging B7-H3, a novel breast cancer associated molecular target. Methods: Quantitative immunohistochemical staining of endothelial and epithelial B7-H3 expression was assessed in 279 human breast tissue samples, including normal (n=53), benign lesions (11 subtypes, n=129), and breast cancers (4 subtypes, n=97). After absorption spectra of intracellular and degraded B7-H3-ICG and Isotype control-ICG (Iso-ICG) were characterized, sPA imaging in a transgenic murine breast cancer model (FVB/N-Tg(MMTVPyMT)634Mul) was performed and compared to imaging of control conditions [B7-H3-ICG in tumor negative animals (n=60), Iso-ICG (n=30), blocking B7-H3+B7-H3-ICG (n=20), and free ICG (n=20)] and validated with ex vivo histological analysis. Results: Immunostaining showed differential B7-H3 expression on both the endothelium and tumor epithelium in human breast cancer with an area under the ROC curve of 0.93 to differentiate breast cancer vs non-cancer. Combined in vitro/in vivo imaging showed that sPA allowed specific B7-H3-ICG detection down to the 13 nM concentration and differentiation from Iso-ICG. sPA molecular imaging of B7-H3-ICG showed a 3.01-fold (P<0.01) increase in molecular B7-H3-ICG signal in tumors compared to control conditions. Conclusions: B7-H3 is a promising target for both vascular and epithelial sPA imaging of breast cancer. Leveraging antibody-ICG contrast agents and their dynamic optical absorption spectra allows for highly specific sPA imaging of breast cancer.

Molecular Contrast-Enhanced Ultrasound Imaging of Radiation-Induced P-Selectin Expression in Healthy Mice Colon.

PURPOSE: To evaluate the feasibility of using molecular contrast-enhanced ultrasound (mCEUS) to image radiation (XRT)-induced expression of cell adhesion molecules that mediate inflammatory response to XRT in healthy mouse colon tissue. METHODS AND MATERIALS: The colons of male BALB/c mice (aged 6-8 weeks, n=9) were irradiated with 14 Gy using a Kimtron IC-225 x-ray irradiator operating at 225 kV/13.0 mA at a dose rate of 0.985 Gy/min. The head and thorax regions were shielded during irradiation. A second control cohort of mice was left untreated (n=6). Molecular CEUS was carried out before and 24 hours after irradiation using a VEVO2100 system and MS250 21-MHz center frequency transducer. Each imaging session comprised mCEUS imaging with P-selectin targeted microbubbles and control microbubbles targeted with an isotype control IgG. Quantification of mCEUS was carried out by measuring the differential targeted enhancement (dTE) parameter. The perfusion parameters peak enhancement and area under the curve were also extracted from the initial injection bolus. Animals were sacrificed at 24 hours and the colon was resected for immunohistochemistry analysis (P-selectin/CD31-stained vessel). RESULTS: For P-selectin targeted microbubble, a significant increase (40 a.u.; P=.013) in dTE (P-dTE) was observed in irradiated mice over 24 hours. In contrast, a nonsignificant change in P-selectin dTE was observed in control mice. For control microbubbles, no significant difference in the IgG dTE parameter was noted in treated and control animals over 24 hours. A nonsignificant increase in the peak enhancement and area under the curve perfusion parameters associated with blood volume was noted in animals treated with radiation. Quantitative histology indicated significantly elevated P-selectin expression per blood vessel (36% in treated; 14% in control). CONCLUSION: Our results confirm the feasibility of using mCEUS for imaging of XRT-induced expression of P-selectin as a potential approach to monitoring healthy tissue inflammatory damage during radiation therapy.

Assessment of Inflammation in an Acute on Chronic Model of Inflammatory Bowel Disease with Ultrasound Molecular Imaging.

BACKGROUND: Ultrasound (US) molecular imaging has shown promise in assessing inflammation in preclinical, murine models of inflammatory bowel disease. These models, however, initiated acute inflammation on previously normal colons, in contrast to patients where acute exacerbations are often in chronically inflamed regions. In this study, we explored the potential of dual P- and E-selectin targeted US imaging for assessing acute inflammation on a murine quiescent chronic inflammatory background. METHODS: Chronic colitis was induced using three cycles of 4% DSS in male FVB mice. Acute inflammation was initiated 2 weeks after the final DSS cycle through rectal administration of 1% TNBS. Mice at different stages of inflammation were imaged using a small animal ultrasound system following i.v. injection of microbubbles targeted to P- and E-selectin. In vivo imaging results were correlated with ex vivo immunofluorescence and histology. RESULTS: Induction of acute inflammation resulted in an increase in the targeted US signal from 5.5 ± 5.1 arbitrary units (a.u.) at day 0 to 61.0 ± 45.2 a.u. (P < 0.0001) at day 1, 36.3 ± 33.1 a.u. at day 3, returning to levels similar to control at day 5. Immunofluorescence showed significant increase in the percentage of P- and E-selectin positive vessels at day 1 (P-selectin: 21.0 ± 7.1% of vessels; P < 0.05; E-selectin: 16.4 ±3.7%; P < 0.05) compared to day 0 (P-selectin: 10.3 ± 5.7%; E-selectin: 7.3 ± 7.0%). CONCLUSIONS: Acute inflammation can be accurately measured in a clinically relevant murine model of chronic IBD using ultrasound molecular imaging with a dual P- and E- selectin-targeted contrast agent.

Photoacoustic Tomography Detects Early Vessel Regression and Normalization During Ovarian Tumor Response to the Antiangiogenic Therapy Trebananib.

UNLABELLED: The primary aim of this study was to assess the potential of in vivo photoacoustic tomography for direct functional measurement of ovarian tumor response to antiangiogenic therapy. METHODS: In vivo studies were performed with institutional animal care and use committee approval. We used an orthotopic mouse model of ovarian cancer treated with trebananib (n = 9) or vehicle (n = 9). Tumor-bearing mice were randomized into trebananib or vehicle groups at day 10 and dosed on days 12, 15, and 18 after implantation. Photoacoustic tomography and blood draws were performed at day 10 and then 24 h after each drug dose. Tumors were excised for histopathology after the final studies on day 19. Data analysis to test for statistical significance was performed blinded. RESULTS: Blockade of angiopoietin signaling using trebananib resulted in reduced total hemoglobin-weighted photoacoustic signal (n = 9, P = 0.01) and increased oxyhemoglobin-weighted photoacoustic signal (n = 9, P < 0.01). The latter observation indicated normalization of the residual tumor vessels, which was also implied by low levels of angiopoietin 1 in serum biomarker profiling (0.76 ± 0.12 ng/mL). These noninvasive measures reflected a 30% reduction in microvessel density and increased vessel maturation in ex vivo sections. CONCLUSION: Photoacoustic tomography is able to evaluate both vessel regression and normalization in response to trebananib. Noninvasive imaging data were supported by modulation of serum markers in vitro and ex vivo histopathology.