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: Cerenkov luminescence imaging (CLI) can provide high-resolution images of 18 F-FDG–avid tumors but requires prolonged acquisition times because of low photon sensitivity. In this study, we proposed a new modality, termed β-radioluminescence imaging (β-RLI), which incorporates a scintillator with a -rejection strategy for imaging β particles. We performed a comparative evaluation of β-RLI with CLI in both in vitro and in vivo systems. Methods: Using in vitro phantoms, we characterized the photon sensitivity and resolution of CLI and β-RLI. We also conducted a series of in vivo experiments with xenograft mouse models using both amelanotic (A375, UMSCC1-Luc) and melanotic (B16F10-Luc) cell lines. The B16F10 and UMSCC1 cell lines were transfected with the luciferase gene (Luc). CLI was acquired over 300 s, and β-RLI was acquired using two 10-s acquisitions. We correlated 18 F - FDG activities, as assessed by PET, with tumor radiances for both β-RLI and CLI. We also compared tumor signal-to-background ratios (SBRs) between these modalities for amelanotic and melanotic tumors. Results: For in vitro experiments, the photon sensitivity for β-RLI was 560-fold greater than that for CLI. However, the spatial resolution for β-RLI (4.4 mm) was inferior to that of CLI (1.0 mm). For in vivo experiments, correlations between 18 F-FDG activity and tumor radiance were 0.52 ( P 〈 0.01) for β-RLI, 0.81 ( P = 0.01) for amelanotic lesions with CLI, and –0.08 (negative contrast; P = 0.80) for melanotic lesions with CLI. Nine of 13 melanotic lesions had an SBR less than 1 for CLI, despite an SBR greater than 1 among all lesions for β-RLI. Conclusion: β-RLI can produce functional images of both amelanotic and melanotic tumors in a shorter time frame than CLI. Further engineering developments are needed to realize the full clinical potential of this modality.

Description: The advancement of breast cancer therapy is limited by the biologic behaviors of cancer cells, such as metastasis and recurrence. β-adrenoceptors (ADRB) are reported to be associated with the biologic behaviors of breast cancer and may influence glucose metabolism. Here, we sought to investigate the relationship between the activation of ADRB and the expression of glucose transporter (GLUT)-1 and hexokinase (HK)-2 and to clarify the impact of ADRB on 18 F-FDG PET imaging in breast cancer. Methods: ADRB1/2 expression in 4T1, MDA-MB-231, and MCF-7 breast cancer cell lines was detected by Western blotting and immunofluorescence. ADRB-dependent regulation of GLUT-1 and HK-2 was determined by in vitro pharmacologic intervention. 4T1 breast cancer cells were treated with phosphate-buffered saline, isoproterenol, or propranolol, and the transcription and expression of GLUT-1 and HK-2 were measured by quantitative real-time polymerase chain reaction (RT-PCR) and Western blotting, respectively. ADRB1/2 was, respectively, blocked by small-interfering RNA to investigate the direct relationship between ADRB1/2 and HK-2. To evaluate the impact of ADRB on 18 F-FDG PET imaging, BALB/c mice bearing 4T1 tumors were injected with phosphate-buffered saline, isoproterenol, or propranolol, and 18 F-FDG PET imaging was performed. The tumor-to-nontumor (T/NT) values of tumors and brown adipose tissue were calculated by defining the liver as a reference. The in vivo expression of GLUT-1 and HK-2 was observed by immunohistochemical analysis and Western blotting. Results: MDA-MB-231, MCF-7, and 4T1 breast cancer cells were positive for ADRB1/2 expression. The protein expression and posttranscriptional level of HK-2 were significantly decreased by treatment with propranolol in vitro, whereas GLUT-1 expression was not significantly altered by pharmacologic intervention. The expression of HK-2 could be reduced in ADRB2-blocked 4T1 cells. Mice in the propranolol-treated group exhibited lower T/NT values for the tumors and brown adipose tissue than the control group. Immunohistochemical analysis and Western blotting revealed reduced HK-2 expression in the tumors of propranolol-treated mice. Conclusion: The expression of HK-2 was regulated by the activation of ADRB2 in 4T1 breast cancer cells primarily at the posttranscriptional level. Additionally, propranolol prevented glucose metabolism and 18 F-FDG PET imaging of 4T1 breast cancer tumors.

Description: Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease. Late detection of then nonresectable or metastasized tumors emphasizes the need for novel imaging approaches. Here, we report on so far nonexploited potentials of α v β 3 integrin–targeted molecular imaging technologies for detection of PDAC using genetically engineered mouse models. Methods: Immunohistochemistry and Western blot were used for characterization of α v β 3 expression in murine and human PDAC. We applied IntegriSense 680 fluorescence molecular tomography, intraoperative fluorescence imaging, and 68 Ga-NODAGA-RGD PET for α v β 3 integrin molecular in vivo imaging of spontaneous PDAC occurring in Ptf1a +/Cre ;Kras +/LSL-G12D ;p53 LoxP/LoxP mice. (NODAGA is 1,4,7-triazacyclononane-1,4-bis[acetic acid]-7-[2-glutaric acid] and RGD is arginine-glycine-aspartic acid.) Results: α v β 3 integrin is expressed in tumor cells of human and murine PDAC. IntegriSense fluorescence molecular tomography and 68 Ga-NODAGA-RGD PET enabled faithful visualization of PDAC. Furthermore, intraoperative optical imaging with IntegriSense 680 allowed good delineation of tumor borders. Conclusion: Imaging approaches targeting α v β 3 integrin expand the potential of molecular imaging for identification of α v β 3 -positive PDAC with potential implications in early detection, fluorescence-guided surgery, and therapy monitoring.

Description: Radiolabeled bombesin (BBN) analogs that bind to the gastrin-releasing peptide receptor (GRPR) represent a topic of active investigation for the development of molecular probes for PET or SPECT of prostate cancer (PCa). RM1 and AMBA have been identified as the 2 most promising BBN peptides for GRPR-targeted cancer imaging and therapy. In this study, to develop a clinically translatable BBN-based PET probe, we synthesized and evaluated 18 F-AlF- (aluminum-fluoride) and 64 Cu-radiolabeled RM1 and AMBA analogs for their potential application in PET imaging of PCa. Methods: 1,4,7-triazacyclononane, 1-glutaric acid-4,7 acetic acid (NODAGA)–conjugated RM1 and AMBA were synthesized and tested for their GRPR-binding affinities. The NODAGA-RM1 and NODAGA-AMBA probes were further radiolabeled with 64 Cu or 18 F-AlF and then evaluated in a subcutaneous PCa xenograft model (PC3) by small-animal PET imaging and biodistribution studies. Results: NODAGA-RM1 and NODAGA-AMBA can be successfully synthesized and radiolabeled with 64 Cu and 18 F-AlF. 64 Cu- and 18 F-AlF-labeled NODAGA-RM1 demonstrated excellent serum stability and tumor-imaging properties in the in vitro stability assays and in vivo imaging studies. 64 Cu-NODAGA-RM1 exhibited tumor uptake values of 3.3 ± 0.38, 3.0 ± 0.76, and 3.5 ± 1.0 percentage injected dose per gram of tissue (%ID/g) at 0.5, 1.5, and 4 h after injection, respectively. 18 F-AlF-NODAGA-RM1 exhibited tumor uptake values of 4.6 ± 1.5, 4.0 ± 0.87, and 3.9 ± 0.48 %ID/g at 0.5, 1, and 2 h, respectively. Conclusion: The high-stability, efficient tumor uptake and optimal pharmacokinetic properties highlight 18 F-AlF-NODAGA-RM1 as a probe with great potential and clinical application for the PET imaging of prostate cancer.

Description: Human copper transporter 1 (CTR1) is overexpressed in a variety of cancers. This study aimed to evaluate the use of 64 CuCl 2 as a theranostic agent for PET and radionuclide therapy of malignant melanoma. Methods: CTR1 expression levels were detected by Western blot analysis of a group of tumor cell lines. Two melanoma cell lines (B16F10 and A375M) that highly expressed CTR1 were then selected to study the uptake and efflux of 64 CuCl 2 . Mice bearing B16F10 or A375M tumors ( n = 4 for each group) were subjected to 5 min of static whole-body PET scans at different time points after intravenous injection of 64 CuCl 2 . Dynamic scans were also obtained for B16F10 tumor–bearing mice. All mice were sacrificed at 72 h after injection of 64 CuCl 2 , and biodistribution studies were performed. Mice bearing B16F10 or A375M tumors were further subjected to 64 CuCl 2 radionuclide therapy. Specifically, when the tumor size reached 0.5–0.8 cm in diameter, tumor-bearing mice were systemically administered 64 CuCl 2 (74 MBq) or phosphate-buffered saline, and tumor sizes were monitored over the treatment period. Results: CTR1 was found to be overexpressed in the cancer cell lines tested at different levels, and high expression levels in melanoma cells and tissues were observed (melanotic B16F10 and amelanotic A375M). 64 CuCl 2 displayed high and specific uptake in B16F10 and A375M cells. In vivo 64 CuCl 2 PET imaging demonstrated that both B16F10 and A375M tumors were clearly visualized. Radionuclide treatment studies showed that the tumor growth in both the B16F10 and the A375M models under 64 CuCl 2 treatment were much slower than that of the control group. Conclusion: Both melanotic and amelanotic melanomas (B16F10 and A375M) tested were found to overexpress CTR1. The tumors can be successfully visualized by 64 CuCl 2 PET and further treated by 64 CuCl 2 , highlighting the high potential of using 64 CuCl 2 as a theranostic agent for the management of melanoma.

Description: Macrophages are cellular mediators of vascular inflammation and are involved in the formation of atherosclerotic plaques. These immune cells secrete proteases such as matrix metalloproteinases and cathepsins that contribute to disease formation and progression. Here, we demonstrate that activity-based probes (ABPs) targeting cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes can also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations. Methods: Macrophage-rich carotid lesions were induced in FVB mice fed on a high-fat diet by streptozotocin injection followed by ligation of the left common carotid artery. Mice with carotid atherosclerotic plaques were injected with the optical or dual-modality probes BMV109 and BMV101, respectively, via the tail vein and noninvasively imaged by optical and small-animal PET/CT at different time points. After noninvasive imaging, the murine carotid arteries were imaged in situ and ex vivo, followed by immunofluorescence staining to confirm target labeling. Additionally, human carotid plaques were topically labeled with the probe and analyzed by both sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunofluorescence staining to confirm the primary targets of the probe. Results: Quantitative analysis of the signal intensity from both optical and PET/CT imaging showed significantly higher levels of accumulation of BMV109 and BMV101 ( P 〈 0.005 and P 〈 0.05, respectively) in the ligated left carotid arteries than the right carotid or healthy arteries. Immunofluorescence staining for macrophages in cross-sectional slices of the murine artery demonstrated substantial infiltration of macrophages in the neointima and adventitia of the ligated left carotid arteries compared with the right. Analysis of the human plaque tissues by sodium dodecyl sulfate polyacrylamide gel electrophoresis confirmed that the primary targets of the probe were cathepsins X, B, S, and L. Immunofluorescence labeling of the human tissue with the probe demonstrated colocalization of the probe with CD68, elastin, and cathepsin S, similar to that observed in the experimental carotid inflammation murine model. Conclusion: We demonstrate that ABPs targeting the cysteine cathepsins can be used in murine models of atherosclerosis to noninvasively image activated macrophage populations using both optical and PET/CT methods. The probes could also be used to topically label human carotid plaques demonstrating similar specific labeling of activated macrophage populations. Therefore, ABPs targeting the cysteine cathepsins are potentially valuable new reagents for rapid and noninvasive imaging of atherosclerotic disease progression and plaque vulnerability.