18F-FSPG PET/CT Imaging of System xC- Transporter Activity in Patients with Primary and Metastatic Brain Tumors.

Background The PET tracer (4S)-4-(3-[18F]fluoropropyl)-l-glutamate (18F-FSPG) targets the system xC- cotransporter, which is overexpressed in various tumors. Purpose To assess the role of 18F-FSPG PET/CT in intracranial malignancies. Materials and Methods Twenty-six patients (mean age, 54 years ± 12; 17 men; 48 total lesions) with primary brain tumors (n = 17) or brain metastases (n = 9) were enrolled in this prospective, single-center study (ClinicalTrials.gov identifier: NCT02370563) between November 2014 and March 2016. A 30-minute dynamic brain 18F-FSPG PET/CT scan and a static whole-body (WB) 18F-FSPG PET/CT scan at 60-75 minutes were acquired. Moreover, all participants underwent MRI, and four participants underwent fluorine 18 (18F) fluorodeoxyglucose (FDG) PET imaging. PET parameters and their relative changes were obtained for all lesions. Kinetic modeling was used to estimate the 18F-FSPG tumor rate constants using the dynamic and dynamic plus WB PET data. Imaging parameters were correlated to lesion outcomes, as determined with follow-up MRI and/or pathologic examination. The Mann-Whitney U test or Student t test was used for group mean comparisons. Receiver operating characteristic curve analysis was used for performance comparison of different decision measures. Results 18F-FSPG PET/CT helped identify all 48 brain lesions. The mean tumor-to-background ratio (TBR) on the whole-brain PET images at the WB time point was 26.6 ± 24.9 (range: 2.6-150.3). When 18F-FDG PET was performed, 18F-FSPG permitted visualization of non-18F-FDG-avid lesions or allowed better lesion differentiation from surrounding tissues. In participants with primary brain tumors, the predictive accuracy of the relative changes in influx rate constant Ki and maximum standardized uptake value to discriminate between poor and good lesion outcomes were 89% and 81%, respectively. There were significant differences in the 18F-FSPG uptake curves of lesions with good versus poor outcomes in the primary brain tumor group (P < .05) but not in the brain metastases group. Conclusion PET/CT imaging with (4S)-4-(3-[18F]fluoropropyl)-l-glutamate (18F-FSPG) helped detect primary brain tumors and brain metastases with a high tumor-to-background ratio. Relative changes in 18F-FSPG uptake with multi-time-point PET appear to be helpful in predicting lesion outcomes. Clinical trial registration no. NCT02370563 © RSNA, 2022 Online supplemental material is available for this article.

Pilot-phase PET/CT study targeting integrin αvß6 in pancreatic cancer patients using the cystine-knot peptide-based 18F-FP-R01-MG-F2.

PURPOSE: A novel cystine-knot peptide-based PET radiopharmaceutical, 18F-FP-R01-MG-F2 (knottin), was developed to selectively bind to human integrin αvß6 which is overexpressed in pancreatic cancer. The purpose of this study is to evaluate the safety, biodistribution, dosimetry, and lesion uptake of 18F-FP-R01-MG-F2 in patients with pancreatic cancer. METHODS: Fifteen patients (6 men, 9 women) with histologically confirmed pancreatic cancer were prospectively enrolled and underwent knottin PET/CT between March 2017 and February 2021 (ClinicalTrials.gov Identifier NCT02683824). Vital signs and laboratory results were collected before and after the imaging scans. Maximum standardized uptake values (SUVmax) and mean SUV (SUVmean) were measured in 24 normal tissues and pancreatic cancer lesions for each patient. From the biodistribution data, the organ doses and whole-body effective dose were calculated using OLINDA/EXM software. RESULTS: There were no significant changes in vital signs or laboratory values that qualified as adverse events or serious adverse events. At 1 h post-injection, areas of high 18F-FP-R01-MG-F2 uptake included the pituitary gland, stomach, duodenum, kidneys, and bladder (average SUVmean: 9.7-14.5). Intermediate uptake was found in the normal pancreas (average SUVmean: 4.5). Mild uptake was found in the lungs and liver (average SUVmean < 1.0). The effective dose was calculated to be 2.538 × 10-2 mSv/MBq. Knottin PET/CT detected all known pancreatic tumors in the 15 patients, although it did not detect small peri-pancreatic lymph nodes of less than 1 cm in short diameter in two of three patients who had lymph node metastases at surgery. Knottin PET/CT detected distant metastases in the lungs (n = 5), liver (n = 4), and peritoneum (n = 2), confirmed by biopsy and/or contrast-enhanced CT. CONCLUSION: 18F-FP-R01-MG-F2 is a safe PET radiopharmaceutical with an effective dose comparable to other diagnostic agents. Evaluation of the primary pancreatic cancer and distant metastases with 18F-FP-R01-MG-F2 PET is feasible, but larger studies are required to define the role of this approach. TRIAL REGISTRATION: NCT02683824.

Positron emission tomography reporter gene strategy for use in the central nervous system.

There is a growing need for monitoring or imaging gene therapy in the central nervous system (CNS). This can be achieved with a positron emission tomography (PET) reporter gene strategy. Here we report the development of a PET reporter gene system using the PKM2 gene with its associated radiotracer [18F]DASA-23. The PKM2 reporter gene was delivered to the brains of mice by adeno-associated virus (AAV9) via stereotactic injection. Serial PET imaging was carried out over 8 wk to assess PKM2 expression. After 8 wk, the brains were excised for further mRNA and protein analysis. PET imaging at 8 wk post-AAV delivery showed an increase in [18F]DASA-23 brain uptake in the transduced site of mice injected with the AAV mice over all controls. We believe PKM2 shows great promise as a PET reporter gene and to date is the only example that can be used in all areas of the CNS without breaking the blood-brain barrier, to monitor gene and cell therapy.

Detection of Carotid Artery Stenosis with Intraplaque Hemorrhage and Neovascularization Using a Scanning Interferometer.

Carotid artery stenosis (CAS) is a major cause of stroke or transient ischemic attack (TIA, mini-stroke) in the United States. Carotid endarterectomy (CEA), a surgical procedure, is used to treat CAS. According to the American Heart Association, 1 out of 5 patients underwent CEA inappropriately, which was most commonly due to apparent overestimation of stenosis severity, and half had uncertain indicators. The current imaging modalities are limited in providing critical information on carotid arterial plaque content, extent, and biology. To circumvent these limitations, we developed a sensing interferometer (SI) imaging system to assess vulnerable carotid plaques noninvasively to detect stenosis, neovascularization, and intraplaque hemorrhage (IPH). We have custom-built a SI prototype and its peripheral systems with back-mode-projection capability. We detected stenosis, neo-vessels, and IPH through SI imaging system in in vivo mice carotid atherosclerotic plaques and further verified the same plaques ex vivo through a histology scope, CRi Maestro, and histological analysis.

Ultra-selective carbon nanotubes for photoacoustic imaging of inflamed atherosclerotic plaques.

Disruption of vulnerable atherosclerotic plaques often leads to myocardial infarction and stroke, the leading causes of morbidity and mortality in the United States. A diagnostic method that detects high-risk atherosclerotic plaques at early stages could prevent these sequelae. The abundance of immune cells in the arterial wall, especially inflammatory Ly-6Chi monocytes and foamy macrophages, is indicative of plaque inflammation, and may be associated with plaque vulnerability. Hence, we sought to develop a new method that specifically targets these immune cells to offer clinically-relevant diagnostic information about cardiovascular disease. We combine ultra-selective nanoparticle targeting of Ly-6Chi monocytes and foamy macrophages with clinically-viable photoacoustic imaging (PAI) in order to precisely and specifically image inflamed plaques ex vivo in a mouse model that mimics human vulnerable plaques histopathologically. Within the plaques, high-dimensional single-cell flow cytometry (13-parameter) showed that our nanoparticles were almost-exclusively taken up by the Ly-6Chi monocytes and foamy macrophages that heavily infiltrate plaques. PAI identified inflamed atherosclerotic plaques that display ~6-fold greater signal compared to controls (P<0.001) six hours after intravenous injection of ultra-selective carbon nanotubes, with in vivo corroboration via optical imaging. Our highly selective strategy may provide a targeted, non-invasive imaging strategy to accurately identify and diagnose inflamed atherosclerotic lesions.

Human biodistribution and radiation dosimetry of [18F]DASA-23, a PET probe targeting pyruvate kinase M2.

PURPOSE: To assess the safety, biodistribution, and radiation dosimetry of the novel positron emission tomography (PET) radiopharmaceutical 1-((2-fluoro-6-[[18F]]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([18F]DASA-23) in healthy volunteers. METHODS: We recruited 5 healthy volunteers who provided a written informed consent. Volunteers were injected with 295.0 ± 8.2 MBq of [18F]DASA-23 intravenously. Immediately following injection, a dynamic scan of the brain was acquired for 15 min. This was followed by serial whole-body PET/MRI scans acquired up to 3 h post-injection. Blood samples were collected at regular intervals, and vital signs monitored pre- and post-radiotracer administration. Regions of interest were drawn around multiple organs, time-activity curves were calculated, and organ uptake and dosimetry were estimated with OLINDA/EXM (version 1.1) software. RESULTS: All subjects tolerated the PET/MRI examination, without adverse reactions to [18F]DASA-23. [18F]DASA-23 passively crossed the blood-brain barrier, followed by rapid clearance from the brain. High accumulation of [18F]DASA-23 was noted in organs such as the gallbladder, liver, small intestine, and urinary bladder, suggesting hepatobiliary and urinary clearance. The effective dose of [18F]DASA-23 was 23.5 ± 5.8 µSv/MBq. CONCLUSION: We successfully completed a pilot first-in-human study of [18F]DASA-23. Our results indicate that [18F]DASA-23 can be used safely in humans to evaluate pyruvate kinase M2 levels. Ongoing studies are evaluating the ability of [18F]DASA-23 to visualize intracranial malignancies, NCT03539731. TRIAL REGISTRATION: ClinicalTrials.gov , NCT03539731 (registered 28 May 2018).

Nanomaterials for In Vivo Imaging.

In vivo imaging, which enables us to peer deeply within living subjects, is producing tremendous opportunities both for clinical diagnostics and as a research tool. Contrast material is often required to clearly visualize the functional architecture of physiological structures. Recent advances in nanomaterials are becoming pivotal to generate the high-resolution, high-contrast images needed for accurate, precision diagnostics. Nanomaterials are playing major roles in imaging by delivering large imaging payloads, yielding improved sensitivity, multiplexing capacity, and modularity of design. Indeed, for several imaging modalities, nanomaterials are now not simply ancillary contrast entities, but are instead the original and sole source of image signal that make possible the modality's existence. We address the physicochemical makeup/design of nanomaterials through the lens of the physical properties that produce contrast signal for the cognate imaging modality-we stratify nanomaterials on the basis of their (i) magnetic, (ii) optical, (iii) acoustic, and/or (iv) nuclear properties. We evaluate them for their ability to provide relevant information under preclinical and clinical circumstances, their in vivo safety profiles (which are being incorporated into their chemical design), their modularity in being fused to create multimodal nanomaterials (spanning multiple different physical imaging modalities and therapeutic/theranostic capabilities), their key properties, and critically their likelihood to be clinically translated.

Quantification of Cerenkov Luminescence Imaging (CLI) Comparable With 3-D PET Standard Measurements.

Cerenkov luminescence imaging (CLI) is commonly performed using two-dimensional (2-D) conventional optical imaging systems for its cost-effective solution. However, quantification of CLI comparable to conventional three-dimensional positron emission tomography (PET) is challenging using these systems due to both the high attenuation of Cerenkov radiation (CR) on mouse tissue and nonexisting depth resolution of CLI using 2-D imaging systems (2-D CLI). In this study, we developed a model that estimates effective tissue attenuation coefficient and corrects the tissue attenuation of CLI signal intensity independent of tissue depth and size. To evaluate this model, we used several thin slices of ham as a phantom and placed a radionuclide (89Zr and 64Cu) inside the phantom at different tissue depths and sizes (2, 7, and 12 mm). We performed 2-D CLI and MicroPET/CT (Combined small animal PET and Computed Tomography (CT)) imaging of the phantom and in vivo mouse model after administration of 89Zr tracer. Estimates of the effective tissue attenuation coefficient (µeff) for 89Zr and 64Cu were ∼2.4 and ∼2.6 cm-1, respectively. The computed unit conversion factor to %ID/g from 2-D CLI signal was 2.74 × 10-3 µCi/radiance estimated from phantom study. After applying tissue attenuation correction and unit conversion to the in vivo animal study, an average quantification difference of 10% for spleen and 35% for liver was obtained compared to PET measurements. The proposed model provides comparable quantification accuracy to standard PET system independent of deep tissue CLI signal attenuation.

Detection of Stem Cell Transplant Rejection with Ferumoxytol MR Imaging: Correlation of MR Imaging Findings with Those at Intravital Microscopy.

Purpose To determine whether endogenous labeling of macrophages with clinically applicable nanoparticles enables noninvasive detection of innate immune responses to stem cell transplants with magnetic resonance (MR) imaging. Materials and Methods Work with human stem cells was approved by the institutional review board and the stem cell research oversight committee, and animal experiments were approved by the administrative panel on laboratory animal care. Nine immunocompetent Sprague-Dawley rats received intravenous injection of ferumoxytol, and 18 Jax C57BL/6-Tg (Csf1r-EGFP-NGFR/FKBP1A/TNFRSF6) 2Bck/J mice received rhodamine-conjugated ferumoxytol. Then, 48 hours later, immune-matched or mismatched stem cells were implanted into osteochondral defects of the knee joints of experimental rats and calvarial defects of Jax mice. All animals underwent serial MR imaging and intravital microscopy (IVM) up to 4 weeks after surgery. Macrophages of Jax C57BL/6-Tg (Csf1r-EGFP-NGFR/FKBP1A/TNFRSF6) 2Bck/J mice express enhanced green fluorescent protein (GFP), which enables in vivo correlation of ferumoxytol enhancement at MR imaging with macrophage quantities at IVM. All quantitative data were compared between experimental groups by using a mixed linear model and t tests. Results Immune-mismatched stem cell implants demonstrated stronger ferumoxytol enhancement than did matched stem cell implants. At 4 weeks, T2 values of mismatched implants were significantly lower than those of matched implants in osteochondral defects of female rats (mean, 10.72 msec for human stem cells and 11.55 msec for male rat stem cells vs 15.45 msec for sex-matched rat stem cells; P = .02 and P = .04, respectively) and calvarial defects of recipient mice (mean, 21.7 msec vs 27.1 msec, respectively; P = .0444). This corresponded to increased recruitment of enhanced GFP- and rhodamine-ferumoxytol-positive macrophages into stem cell transplants, as visualized with IVM and histopathologic examination. Conclusion Endogenous labeling of macrophages with ferumoxytol enables noninvasive detection of innate immune responses to stem cell transplants with MR imaging. © RSNA, 2017 Online supplemental material is available for this article.

A Pixel Pitch-Matched Ultrasound Receiver for 3-D Photoacoustic Imaging With Integrated Delta-Sigma Beamformer in 28-nm UTBB FD-SOI.

This paper presents a pixel pitch-matched readout chip for 3-D photoacoustic (PA) imaging, featuring a dedicated signal conditioning and delta-sigma modulation integrated within a pixel area of 250 µm by 250 µm. The proof-of-concept receiver was implemented in an STMicroelectronics's 28-nm Fully Depleted Silicon On Insulator technology, and interfaces to a 4 × 4 subarray of capacitive micromachined ultrasound transducers (CMUTs). The front-end signal conditioning in each pixel employs a coarse/fine gain tuning architecture to fulfill the 90-dB dynamic range requirement of the application. The employed delta-sigma beamforming architecture obviates the need for area-consuming Nyquist ADCs and thereby enables an efficient in-pixel A/D conversion. The per-pixel switched-capacitor ΔΣ modulator leverages slewing-dominated and area-optimized inverter-based amplifiers. It occupies only 1/4th of the pixel, and its area compares favorably with state-of-the-art designs that offer the same SNR and bandwidth. The modulator's measured peak signal-to-noise-and-distortion ratio is 59.9 dB for a 10-MHz input bandwidth, and it consumes 6.65 mW from a 1-V supply. The overall subarray beamforming approach improves the area per channel by 7.4 times and the single-channel SNR by 8 dB compared to prior art with similar delay resolution and power dissipation. The functionality of the designed chip was evaluated within a PA imaging experiment, employing a flip-chip bonded 2-D CMUT array.

Pilot prospective evaluation of (18)F-FPPRGD2 PET/CT in patients with cervical and ovarian cancer.

PURPOSE: We report the effect of antiangiogenic therapy on the biodistribution of (18)F-FPPRGD2 (a surrogate biomarker of integrin αvß3 expression), and the potential of (18)F-FPPRGD2 to predict the prognosis in patients with cervical cancer and ovarian cancer in this clinical scenario. METHODS: Data from six women, age range 30 - 59 years (mean ± SD 44.0 ± 12.5 years), who had undergone a (18)F-FPPRGD2 PET/CT scan and bevacizumab-containing therapy were prospectively collected and analyzed. We compared baseline (18)F-FPPRGD2 and (18)F-FDG uptake in the lesions and tumor-to-background (T/B) ratios. The maximum and mean (18)F-FPPRGD2 standardized uptake values (SUVmax and SUVmean) were recorded for 13 normal organs, as well as in all the identified malignant lesions on the pretreatment scan and the 1-week post-treatment scan. We also measured changes in (18)F-FPPRGD2 uptake from before to 1 week after treatment, and compared them to the changes in (18)F-FDG uptake from before to 6 weeks after treatment. Treatment outcomes were correlated with these changes. RESULTS: The uptake in lesions and T/B ratio of (18)F-FPPRGD2 were lower than those of (18)F-FDG (SUVmax 3.7 ± 1.3 vs. 6.0 ± 1.8, P < 0.001; SUVmean 2.6 ± 0.7 vs. 4.2 ± 1.3, P < 0.001; T/B ratio based on SUVmax 2.4 ± 1.0 vs. 2.6 ± 1.0, P < 0.04; T/B ratio based on SUVmean 1.9 ± 0.6 vs. 2.4 ± 1.0, P < 0.003). One patient did not return for the follow-up scan and in another patient no lesions were identified on the pretreatment scan. (18)F-FPPRGD2 uptake in lesions in the remaining four patients had significantly changed 1 week after treatment (SUVmean 3.3 ± 1.0 vs. 2.7 ± 1.0, P < 0.001), while uptake in all normal tissues analyzed was not affected by treatment. One patient with clinical disease progression had a decrease in lesional (18)F-FPPRGD2 SUVmean of 1.6 % and in (18)F-FDG SUVmean of 9.4 %. Two patients with a clinical complete response to treatment had decreases in lesional (18)F-FPPRGD2 SUVmean of 25.2 % and 25.0 % and in (18)F-FDG SUVmean of 6.1 % and 71.8 %. One patient with a clinical partial response had a decrease in lesional (18)F-FPPRGD2 SUVmean of 7.9 % and in (18)F-FDG SUVmean of 76.4 %. CONCLUSION: This pilot study showed that (18)F-FPPRGD2 and (18)F-FDG provide independent information about the biology of ovarian and cervical cancers. Bevacizumab-containing therapy does not affect (18)F-FPPRGD2 uptake in normal organs, but does result in statistically significant changes in lesions. In addition, (18)F-FPPRGD2 may have potential for early prediction of response to such treatments. These preliminary findings have to be confirmed in larger studies.

Validation of 64Cu-DOTA-rituximab injection preparation under good manufacturing practices: a PET tracer for imaging of B-cell non-Hodgkin lymphoma.

Manufacturing of 64Cu-1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-rituximab injection under good manufacturing practices (GMP) was validated for imaging of patients with CD20+ B-cell non-Hodgkin lymphoma. Rituximab was purified by size exclusion high performance liquid chromatography (HPLC) and conjugated to DOTA-mono-(N-hydroxysuccinimidyl) ester. 64CuCl2, buffers, reagents, and other raw materials were obtained as high-grade quality. Following a semi-automated synthesis of 64Cu-DOTA-rituximab, a series of quality control tests was performed. The product was further tested in vivo using micro-positron emission tomography/computed tomography (PET/CT) to assess targeting ability towards human CD20 in transgenic mice. Three batches of 64Cu-DOTA-rituximab final product were prepared as per GMP specifications. The radiolabeling yield from these batches was 93.1 ± 5.8%; these provided final product with radiopharmaceutical yield, purity, and specific activity of 59.2 ± 5.1% (0.9 ± 0.1 GBq of 64Cu), > 95% (by HPLC and radio-thin layer chromatography), and 229.4 ± 43.3 GBq/µmol (or 1.5 ± 0.3 MBq/µg), respectively. The doses passed apyrogenicity and human serum stability specifications, were sterile up to 14 days, and retained > 60% immunoreactivity. In vivo micro-PET/CT mouse images at 24 hours postinjection showed that the tracer targeted the intended sites of human CD20 expression. Thus, we have validated the manufacturing of GMP grade 64Cu-DOTA-rituximab for injection in the clinical setting.

Glioblastoma Multiforme Recurrence: An Exploratory Study of (18)F FPPRGD2 PET/CT.

PURPOSE: To prospectively evaluate fluorine 18 ((18)F) 2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid (RGD) peptide (PEG3-E[c{RGDyk}]2) (FPPRGD2) positron emission tomography (PET) in patients with glioblastoma multiforme (GBM). MATERIALS AND METHODS: The institutional review board approved this HIPAA-compliant protocol. Written informed consent was obtained from each patient. (18)F FPPRGD2 uptake was measured semiquantitatively in the form of maximum standardized uptake values (SUV(max)) and uptake volumes before and after treatment with bevacizumab. Vital signs and laboratory results were collected before, during, and after the examinations. A nonparametric version of multivariate analysis of variance was used to assess safety outcome measures simultaneously across time points. A paired two-sample t test was performed to compare SUV(max). RESULTS: A total of 17 participants (eight men, nine women; age range, 25-65 years) were enrolled prospectively. (18)F FPPRGD2 PET/computed tomography (CT), (18)F fluorodeoxyglucose (FDG) PET/CT, and brain magnetic resonance (MR) imaging were performed within 3 weeks, prior to the start of bevacizumab therapy. In eight of the 17 patients (47%), (18)F FPPRGD2 PET/CT was repeated 1 week after the start of bevacizumab therapy; six patients (35%) underwent (18)F FPPRGD2 PET/CT a third time 6 weeks after starting bevacizumab therapy. There were no changes in vital signs, electrocardiographic findings, or laboratory values that qualified as adverse events. One patient (6%) had recurrent GBM identified only on (18)F FPPRGD2 PET images, and subsequent MR images enabled confirmation of recurrence. Of the 17 patients, 14 (82%) had recurrent GBM identified on (18)F FPPRGD2 PET and brain MR images, while (18)F FDG PET enabled identification of recurrence in 13 (76%) patients. Two patients (12%) had no recurrent GBM. CONCLUSION: (18)F FPPRGD2 is a safe PET radiopharmaceutical that has increased uptake in GBM lesions. Larger cohorts are required to confirm these preliminary findings.

Biodistribution of the ¹8F-FPPRGD2 PET radiopharmaceutical in cancer patients: an atlas of SUV measurements.

PURPOSE: The aim of this study was to investigate the biodistribution of 2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid (RGD) peptide (PEG3-E[c{RGDyk}]2) ((18)F-FPPRGD2) in cancer patients and to compare its uptake in malignant lesions with (18)F-FDG uptake. METHODS: A total of 35 patients (11 men, 24 women, mean age 52.1 ± 10.8 years) were enrolled prospectively and had (18)F-FPPRGD2 PET/CT prior to treatment. Maximum standardized uptake values (SUVmax) and mean SUV (SUVmean) were measured in 23 normal tissues in each patient, as well as in known or suspected cancer lesions. Differences between (18)F-FPPRGD2 uptake and (18)F-FDG uptake were also evaluated in 28 of the 35 patients. RESULTS: Areas of high (18)F-FPPRGD2 accumulation (SUVmax range 8.9 - 94.4, SUVmean range 7.1 - 64.4) included the bladder and kidneys. Moderate uptake (SUVmax range 2.1 - 6.3, SUVmean range 1.1 - 4.5) was found in the choroid plexus, salivary glands, thyroid, liver, spleen, pancreas, small bowel and skeleton. Compared with (18)F-FDG, (18)F-FPPRGD2 showed higher tumor-to-background ratio in brain lesions (13.4 ± 8.5 vs. 1.1 ± 0.5, P < 0.001), but no significant difference in body lesions (3.2 ± 1.9 vs. 4.4 ± 4.2, P = 0.10). There was no significant correlation between the uptake values (SUVmax and SUVmean) for (18)F FPPRGD2 and those for (18)F-FDG. CONCLUSION: The biodistribution of (18)F-FPPRGD2 in cancer patients is similar to that of other RGD dimer peptides and it is suitable for clinical use. The lack of significant correlation between (18)F-FPPRGD2 and (18)F-FDG uptake confirms that the information provided by each PET tracer is different.

Parts per billion detection of uranium with a porphyrinoid-containing nanoparticle and in vivo photoacoustic imaging.

Chemical tools that can report radioactive isotopes would be of interest to the defense community. Here we report ∼250 nm polymeric nanoparticles containing porphyrinoid macrocycles with and without pre-complexed depleted uranium and demonstrate that the latter species may be detected easily and with high sensitivity via photoacoustic imaging. The porphyrinoid macrocycles used in the present study are non-aromatic in the absence of the uranyl cation, but aromatic after cation complexation. We solubilized both the freebase and metalated forms of the macrocycles in poly(lactic-co-glycolic acid) and found a peak in the photoacoustic spectrum at 910 nm excitation in the case of the uranyl complex. The signal was stable for at least 15 minutes and allowed detection of uranium concentrations down to 6.2 ppb (5.7 nM) in vitro and 0.57 ppm (19 fCi; 0.52 µM) in vivo. To the best of our knowledge, this is the first report of a nanoparticle that detects an actinide cation via photoacoustic imaging.

Transferring biomarker into molecular probe: melanin nanoparticle as a naturally active platform for multimodality imaging.

Developing multifunctional and easily prepared nanoplatforms with integrated different modalities is highly challenging for molecular imaging. Here, we report the successful transfer of an important molecular target, melanin, into a novel multimodality imaging nanoplatform. Melanin is abundantly expressed in melanotic melanomas and thus has been actively studied as a target for melanoma imaging. In our work, the multifunctional biopolymer nanoplatform based on ultrasmall (<10 nm) water-soluble melanin nanoparticle (MNP) was developed and showed unique photoacoustic property and natural binding ability with metal ions (for example, (64)Cu(2+), Fe(3+)). Therefore, MNP can serve not only as a photoacoustic contrast agent, but also as a nanoplatform for positron emission tomography (PET) and magnetic resonance imaging (MRI). Traditional passive nanoplatforms require complicated and time-consuming processes for prebuilding reporting moieties or chemical modifications using active groups to integrate different contrast properties into one entity. In comparison, utilizing functional biomarker melanin can greatly simplify the building process. We further conjugated αvß3 integrins, cyclic c(RGDfC) peptide, to MNPs to allow for U87MG tumor accumulation due to its targeting property combined with the enhanced permeability and retention (EPR) effect. The multimodal properties of MNPs demonstrate the high potential of endogenous materials with multifunctions as nanoplatforms for molecular theranostics and clinical translation.

(18)F-FPPRGD2 PET/CT: pilot phase evaluation of breast cancer patients.

PURPOSE: To present data from the first prospective pilot phase trial of breast cancer participants imaged with fluorine 18 ((18)F)-2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid ( RGD arginine-glycine-aspartic acid ) peptide (PEG3-E[c{ RGD arginine-glycine-aspartic acid yk}]2) ( FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) ), a radiopharmaceutical agent used in positron emission tomographic (PET) imaging. MATERIALS AND METHODS: The local institutional review board approved the HIPAA-compliant protocol. Written informed consent was obtained from each patient. Eight women (age range, 44-67 years; mean age, 54.3 years ± 8.8 [standard deviation]) with newly diagnosed or recurrent breast cancer were recruited between November 2010 and February 2011. (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) PET/computed tomographic (CT) and (18)F-fluorodeoxyglucose ( FDG fluorine 18 fluorodeoxyglucose ) PET/CT examinations were performed within 3 weeks of each other. Dynamic (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) PET and two whole-body static (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) PET/CT scans were obtained. During this time, vital signs and electrocardiograms were recorded at regular intervals. Blood samples were obtained before the injection of (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) and at 24 hours and 1 week after injection to evaluate for toxicity. A nonparametric version of multivariate analysis of variance was used to assess the safety outcome measures simultaneously across time points. A paired two-sample t test was performed to compare the maximum standardized uptake values ( SUVmax maximum standardized uptake value ). RESULTS: (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) was well tolerated, without noticeable changes in vital signs, on electrocardiograms, or in laboratory values. A total of 30 lesions were evaluated at (18)F- FDG fluorine 18 fluorodeoxyglucose PET/CT and (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) PET/CT. The primary breast lesions had (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) uptake with SUVmax maximum standardized uptake value of 2.4-9.4 (mean, 5.6 ± 2.8) 60 minutes after injection, compared with (18)F- FDG fluorine 18 fluorodeoxyglucose uptake with SUVmax maximum standardized uptake value of 2.8-18.6 (mean, 10.4 ± 7.2). Metastatic lesions also showed (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) uptake, with SUVmax maximum standardized uptake value of 2.4-9.7 (mean, 5.0 ± 2.3) at 60 minutes, compared with (18)F- FDG fluorine 18 fluorodeoxyglucose uptake with SUVmax maximum standardized uptake value of 2.2-14.6 (mean, 6.6 ± 4.2). CONCLUSION: Data from this pilot phase study suggest that (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) is a safe PET radiopharmaceutical agent. Evaluation of (18)F- FPPRGD2 2-fluoropropionyl labeled PEGylated dimeric RGD peptide (PEG3-E[c{RGDyk}]2) in participants with breast cancer demonstrated significant uptake in the primary lesion and in the metastases. Larger cohorts are required to confirm these preliminary findings.

A radiofluorinated divalent cystine knot peptide for tumor PET imaging.

A divalent knottin containing two separate integrin binding epitopes (RGD) in the adjacent loops, 3-4A, was recently developed and reported in our previous publication. In the current study, 3-4A was radiofluorinated with a 4-nitrophenyl 2-(18)F-fluoropropinate ((18)F-NFP) group and the resulting divalent positron emission tomography (PET) probe, (18)F-FP-3-4A, was evaluated as a novel imaging probe to detect integrin αvß3 positive tumors in living animals. Knottin 3-4A was synthesized by solid phase peptide synthesis, folded, and site-specifically conjugated with (18/19)F-NFP to produce the fluorinated peptide (18/19)F-fluoropropinate-3-4A ((18/19)F-FP-3-4A). The stability of (18)F-FP-3-4A was tested in both phosphate buffered saline (PBS) buffer and mouse serum. Cell uptake assays of the radiolabeled peptides were performed using U87MG cells. In addition, small animal PET imaging and biodistribution studies of (18)F-FP-3-4A were performed in U87MG tumor-bearing mice. The receptor targeting specificity of the radiolabeled peptide was also verified by coinjecting the probe with a blocking peptide cyclo(RGDyK). Our study showed that (18)F-FP-3-4A exhibited excellent stability in PBS buffer (pH 7.4) and mouse serum. Small animal PET imaging and biodistribution data revealed that (18)F-FP-3-4A exhibited rapid and good tumor uptake (3.76 ± 0.59% ID/g and 2.22 ± 0.62% ID/g at 0.5 and 1 h, respectively). (18)F-FP-3-4A was rapidly cleared from the normal tissues, resulting in excellent tumor-to-normal tissue contrasts. For example, liver uptake was only 0.39 ± 0.07% ID/g and the tumor to liver ratio was 5.69 at 1 h p.i. Furthermore, coinjection of cyclo(RGDyK) with (18)F-FP-3-4A significantly inhibited tumor uptake (0.41 ± 0.12 vs 1.02 ± 0.19% ID/g at 2.5 h) in U87MG xenograft models, demonstrating specific accumulation of the probe in the tumor. In summary, the divalent probe (18)F-FP-3-4A is characterized by rapid and high tumor uptake and excellent tumor-to-normal tissue ratios. (18)F-FP-3-4A is a highly promising knottin based PET probe for translating into clinical imaging of tumor angiogenesis.

99mTc-labeled cystine knot peptide targeting integrin αvß6 for tumor SPECT imaging.

Integrin αvß6 is overexpressed in a variety of cancers, and its expression is often associated with poor prognosis. Therefore, there is a need to develop affinity reagents for noninvasive imaging of integrin αvß6 expression since it may provide early cancer diagnosis, more accurate prognosis, and better treatment planning. We recently engineered and validated highly stable cystine knot peptides that selectively bind integrin αvß6 with no cross-reactivity to integrins αvß5, α5ß1, or αvß3, also known to be overexpressed in many cancers. Here, we developed a single photon emission computed tomography (SPECT) probe for imaging integrin αvß6 positive tumors. Cystine knot peptide, S02, was first conjugated with a single amino acid chelate (SAAC) and labeled with [(99m)Tc(H2O)3(CO)3](+). The resulting probe, (99m)Tc-SAAC-S02, was then evaluated by in vitro cell uptake studies using two αvß6 positive cell lines (human lung adenocarcinoma cell line HCC4006 and pancreatic cancer cell line BxPC-3) and two αvß6 negative cell lines (human lung adenocarcinoma cell line H838 and human embryonic kidney cell line 293T). Next, SPECT/CT and biodistribution studies were performed in nude mice bearing HCC4006 and H838 tumor xenografts to evaluate the in vivo performance of (99m)Tc-SAAC-S02. Significant differences in the uptake of (99m)Tc-SAAC-S02 were observed in αvß6 positive vs negative cells (P < 0.05). Biodistribution and small animal SPECT/CT studies revealed that (99m)Tc-SAAC-S02 accumulated to moderate levels in antigen positive tumors (∼2% ID/g at 1 and 6 h postinjection, n = 3 or 4/group). Moreover, the probe demonstrated tumor-to-background tissue ratios of 6.81 ± 2.32 (tumor-to-muscle) and 1.63 ± 0.18 (tumor-to-blood) at 6 h postinjection in αvß6 positive tumor xenografts. Co-incubation of the probe with excess amount of unlabeled S02 as a blocking agent demonstrated significantly reduced tumor uptake, which is consistent with specific binding to the target. Renal filtration was the main route of clearance. In conclusion, knottin peptides are excellent scaffolds for which to develop highly stable imaging probes for a variety of oncological targets. (99m)Tc-SAAC-S02 demonstrates promise for use as a SPECT agent to image integrin αvß6 expression in living systems.