Description: Purpose: To test whether plasmid-binding cationic microbubbles (MBs) enhance ultrasound-mediated gene delivery efficiency relative to control neutral MBs in cell culture and in vivo tumors in mice. Materials and Methods: Animal studies were approved by the institutional animal care committee. Cationic and neutral MBs were characterized in terms of size, charge, circulation time, and DNA binding. Click beetle luciferase (CBLuc) reporter plasmids were mixed with cationic or neutral MBs. The ability of cationic MBs to protect bound plasmids from nuclease degradation was tested by means of a deoxyribonuclease (DNase) protection assay. Relative efficiencies of ultrasound-mediated transfection (ultrasound parameters: 1 MHz, 1 W/cm 2 , 20% duty cycle, 1 minute) of CBLuc to endothelial cells by using cationic, neutral, or no MBs were compared in cell culture. Ultrasound-mediated gene delivery to mouse hind limb tumors was performed in vivo ( n = 24) with insonation (1 MHz, 2 W/cm 2 , 50% duty cycle, 5 minutes) after intravenous administration of CBLuc with cationic, neutral, or no MBs. Tumor luciferase activity was assessed by means of serial in vivo bioluminescence imaging and ex vivo analysis. Results were compared by using analysis of variance. Results: Cationic MBs (+15.8 mV; DNA binding capacity, 0.03 pg per MB) partially protected bound DNA from DNase degradation. Mean CBLuc expression of treated endothelial cells in culture was 20-fold higher with cationic than with neutral MBs (219.0 relative light units [RLUs]/µg protein ± 92.5 [standard deviation] vs 10.9 RLUs/µg protein ± 2.7, P = .001) and was significantly higher ( P 〈 .001) than that in the no MB and no ultrasound control groups. Serial in vivo bioluminescence of mouse tumors was significantly higher with cationic than with neutral MBs ([5.9 ± 2.2] to [9.3 ± 5.2] vs [2.4 ± 0.8] to [2.9 ± 1.1] x 10 4 photons/sec/cm 2 /steradian, P 〈 .0001) and versus no MB and no ultrasound controls ( P 〈 .0001). Results of ex vivo analysis confirmed these results ( = 0.88, P 〈 .0001). Conclusion: Plasmid-binding cationic MBs enhance ultrasound-mediated gene delivery efficiency relative to neutral MBs in both cell culture and mouse hind limb tumors. © RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112368/-/DC1

Description: Purpose: (4 S )-4-(3-[ 18 F]fluoropropyl)- l -glutamate (BAY 94-9392, alias [ 18 F]FSPG) is a new tracer to image x C – transporter activity with positron emission tomography (PET). We aimed to explore the tumor detection rate of [ 18 F]FSPG in patients relative to 2-[ 18 F]fluoro-2-deoxyglucose ([ 18 F]FDG). The correlation of [ 18 F]FSPG uptake with immunohistochemical expression of x C – transporter and CD44, which stabilizes the xCT subunit of system x C – , was also analyzed. Experimental Design: Patients with non–small cell lung cancer (NSCLC, n = 10) or breast cancer ( n = 5) who had a positive [ 18 F]FDG uptake were included in this exploratory study. PET images were acquired following injection of approximately 300 MBq [ 18 F]FSPG. Immunohistochemistry was done using xCT- and CD44-specific antibody. Results: [ 18 F]FSPG PET showed high uptake in the kidney and pancreas with rapid blood clearance. [ 18 F]FSPG identified all 10 NSCLC and three of the five breast cancer lesions that were confirmed by pathology. [ 18 F]FSPG detected 59 of 67 (88%) [ 18 F]FDG lesions in NSCLC, and 30 of 73 (41%) in breast cancer. Seven lesions were additionally detected only on [ 18 F]FSPG in NSCLC. The tumor-to-blood pool standardized uptake value (SUV) ratio was not significantly different from that of [ 18 F]FDG in NSCLC; however, in breast cancer, it was significantly lower ( P 〈 0.05). The maximum SUV of [ 18 F]FSPG correlated significantly with the intensity of immunohistochemical staining of x C – transporter and CD44 ( P 〈 0.01). Conclusions: [ 18 F]FSPG seems to be a promising tracer with a relatively high cancer detection rate in patients with NSCLC. [ 18 F]FSPG PET may assess x C – transporter activity in patients with cancer. Clin Cancer Res; 18(19); 5427–37. ©2012 AACR .

Description: Cerenkov luminescence imaging (CLI) is an emerging new molecular imaging modality that is relatively inexpensive, easy to use, and has high throughput. CLI can image clinically available PET and SPECT probes using optical instrumentation. Cerenkov luminescence endoscopy (CLE) is one of the most intriguing applications that promise potential clinical translation. We developed a prototype customized fiberscopic Cerenkov imaging system to investigate the potential in guiding minimally invasive surgical resection. Methods: All experiments were performed in a dark chamber. Cerenkov luminescence from 18 F-FDG samples containing decaying radioactivity was transmitted through an optical fiber bundle and imaged by an intensified charge-coupled device camera. Phantoms filled with 18 F-FDG were used to assess the imaging spatial resolution. Finally, mice bearing subcutaneous C6 glioma cells were injected intravenously with 18 F-FDG to determine the feasibility of in vivo imaging. The tumor tissues were exposed, and CLI was performed on the mouse before and after surgical removal of the tumor using the fiber-based imaging system and compared with a commercial optical imaging system. Results: The sensitivity of this particular setup was approximately 45 kBq (1.21 μCi)/300 μL. The 3 smallest sets of cylindric holes in a commercial SPECT phantom were identifiable via this system, demonstrating that the system has a resolution better than 1.2 mm. Finally, the in vivo tumor imaging study demonstrated the feasibility of using CLI to guide the resection of tumor tissues. Conclusion: This proof-of-concept study explored the feasibility of using fiber-based CLE for the detection of tumor tissue in vivo for guided surgery. With further improvements of the imaging sensitivity and spatial resolution of the current system, CLE may have a significant application in the clinical setting in the near future.

Description: Integrin α v β 6 is a cell surface receptor minimally expressed by healthy tissue but elevated in lung, colon, skin, ovarian, cervical, and pancreatic cancers. A molecular PET agent for integrin α v β 6 could provide significant clinical utility by facilitating both cancer staging and treatment monitoring to more rapidly identify an effective therapeutic approach. Methods: Here, we evaluated 2 cystine knot peptides, R 0 1 and S 0 2, previously engineered with a 3–6 nM affinity for integrin α v β 6 , for 18 F radiolabeling and PET imaging of BxPC3 pancreatic adenocarcinoma xenografts in mice. Cystine knot peptides were labeled with N -succinimidyl-4- 18 F-fluorobenzoate and evaluated for binding affinity and serum stability. Peptides conjugated with 18 F-fluorobenzoate (2–3 MBq) were injected via the tail vein into nude mice xenografted with BxPC3 (integrin α v β 6 –positive) or 293 (integrin α v β 6 –negative) tumors. Small-animal PET scans were acquired at 0.5, 1, and 2 h after injection. Ex vivo -counting of dissected tissues was performed at 0.5 and 2 h. Results: 18 F-fluorobenzoate peptides were produced in 93% ( 18 F-fluorobenzoate-R 0 1) and 99% ( 18 F-fluorobenzoate-S 0 2) purity. 18 F-fluorobenzoate-R 0 1 and 18 F-fluorobenzoate-S 0 2 had affinities of 1.1 ± 0.2 and 0.7 ± 0.4 nM, respectively, and were 87% and 94%, respectively, stable in human serum at 37°C for 2 h. 18 F-fluorobenzoate-R 0 1 and 18 F-fluorobenzoate-S 0 2 exhibited 2.3 ± 0.6 and 1.3 ± 0.4 percentage injected dose per gram (%ID/g), respectively, in BxPC3 xenografted tumors at 0.5 h ( n = 4–5). Target specificity was confirmed by low tumor uptake in integrin α v β 6 –negative 293 tumors (1.4 ± 0.6 and 0.5 ± 0.2 %ID/g, respectively, for 18 F-fluorobenzoate-R 0 1 and 18 F-fluorobenzoate-S 0 2; both P 〈 0.05; n = 3–4) and low muscle uptake (3.1 ± 1.0 and 2.7 ± 0.4 tumor to muscle for 18 F-fluorobenzoate-R 0 1 and 18 F-fluorobenzoate-S 0 2, respectively). Small-animal PET data were corroborated by ex vivo -counting of dissected tissues, which demonstrated low uptake in nontarget tissues with only modest kidney uptake (9.2 ± 3.3 and 1.9 ± 1.2 %ID/g, respectively, at 2 h for 18 F-fluorobenzoate-R 0 1 and 18 F-fluorobenzoate-S 0 2; n = 8). Uptake in healthy pancreas was low (0.3% ± 0.1% for 18 F-fluorobenzoate-R 0 1 and 0.03% ± 0.01% for 18 F-fluorobenzoate-S 0 2; n = 8). Conclusion: These cystine knot peptide tracers, in particular 18 F-fluorobenzoate-R 0 1, show translational promise for molecular imaging of integrin α v β 6 overexpression in pancreatic and other cancers.

Description: Endoscopic imaging is an invaluable diagnostic tool allowing minimally invasive access to tissues deep within the body. It has played a key role in screening colon cancer and is credited with preventing deaths through the detection and removal of precancerous polyps. However, conventional white-light endoscopy offers physicians structural information without...

Description: 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 (MB Selectin ) 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. MB Selectin 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 MB Selectin 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: MB Selectin showed strong attachment to both human and mouse P- and E-selectin compared with MB Control 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 ( = 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 MB Selectin 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 MB Selectin correlates well with FDG uptake at PET/CT imaging. © RSNA, 2013 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.13122509/-/DC1

Description: Cerenkov luminescence endoscopy (CLE) is an optical technique that captures the Cerenkov photons emitted from highly energetic moving charged particles (β + or β – ) and can be used to monitor the distribution of many clinically available radioactive probes. A main limitation of CLE is its limited sensitivity to small concentrations of radiotracer, especially when used with a light guide. We investigated the improvement in the sensitivity of CLE brought about by using a β – radiotracer that improved Cerenkov signal due to both higher β-particle energy and lower noise in the imaging optics because of the lack of positron annihilation. Methods: The signal-to-noise ratio (SNR) of 90 Y was compared with that of 18 F in both phantoms and small-animal tumor models. Sensitivity and noise characteristics were demonstrated using vials of activity both at the surface and beneath 1 cm of tissue. Rodent U87MG glioma xenograft models were imaged with radiotracers bound to arginine-glycine-aspartate (RGD) peptides to determine the SNR. Results: noise from 18 F was demonstrated by both an observed blurring across the field of view and a more pronounced fall-off with distance. A decreased background and increased energy of the β particles resulted in a 207-fold improvement in the sensitivity of 90 Y compared with 18 F in phantoms. 90 Y-bound RGD peptide produced a higher tumor-to-background SNR than 18 F in a mouse model. Conclusion: The use of 90 Y for Cerenkov endoscopic imaging enabled superior results compared with an 18 F radiotracer.

Description: Herein we aimed to evaluate the utility of N -(2,5-dimethoxybenzyl)-2- 18 F-fluoro- N -(2-phenoxyphenyl)acetamide ( 18 F-PBR06) for detecting alterations in translocator protein (TSPO) (18 kDa), a biomarker of microglial activation, in a mouse model of Alzheimer's disease (AD). Methods: Wild-type (wt) and AD mice (i.e., APP L/S ) underwent 18 F-PBR06 PET imaging at predetermined time points between the ages of 5–6 and 15–16 mo. MR images were fused with PET/CT data to quantify 18 F-PBR06 uptake in the hippocampus and cortex. Ex vivo autoradiography and TSPO/CD68 immunostaining were also performed using brain tissue from these mice. Results: PET images showed significantly higher accumulation of 18 F-PBR06 in the cortex and hippocampus of 15- to 16-mo-old APP L/S mice than age-matched wts (cortex/muscle: 2.43 ± 0.19 vs. 1.55 ± 0.15, P 〈 0.005; hippocampus/muscle: 2.41 ± 0.13 vs. 1.55 ± 0.12, P 〈 0.005). And although no significant difference was found between wt and APP L/S mice aged 9–10 mo or less using PET ( P = 0.64), we were able to visualize and quantify a significant difference in 18 F-PBR06 uptake in these mice using autoradiography (cortex/striatum: 1.13 ± 0.04 vs. 0.96 ± 0.01, P 〈 0.05; hippocampus/striatum: 1.266 ± 0.003 vs. 1.096 ± 0.017, P 〈 0.001). PET results for 15- to 16-mo-old mice correlated well with autoradiography and immunostaining (i.e., increased 18 F-PBR06 uptake in brain regions containing elevated CD68 and TSPO staining in APP L/S mice, compared with wts). Conclusion: 18 F-PBR06 shows great potential as a tool for visualizing TSPO/microglia in the progression and treatment of AD.