Clinical and economic outcomes of adding [18F]FES PET/CT in estrogen receptor status identification in metastatic and recurrent breast cancer in the US.

BACKGROUND AND OBJECTIVES: Correct identification of estrogen receptor (ER) status in breast cancer (BC) is crucial to optimize treatment; however, standard of care, involving biopsy and immunohistochemistry (IHC), and other diagnostic tools such as 2-deoxy-2-[18F]fluoro-D-glucose or 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG), can yield inconclusive results. 16α-[18F]fluoro-17ß-fluoroestradiol ([18F]FES) can be a powerful tool, providing high diagnostic accuracy of ER-positive disease. The aim of this study was to estimate the budget impact and cost-effectiveness of adding [18F]FES PET/CT to biopsy/IHC in the determination of ER-positive status in metastatic (mBC) and recurrent breast cancer (rBC) in the United States (US). METHODS: An Excel-based decision tree, combined with a Markov model, was developed to estimate the economic consequences of adding [18F]FES PET/CT to biopsy/IHC for determining ER-positive status in mBC and rBC over 5 years. Scenario A, where the determination of ER-positive status is carried out solely through biopsy/IHC, was compared to scenario B, where [18F]FES PET/CT is used in addition to biopsy/IHC. RESULTS: The proportion of true positive and true negative test results increased by 0.2 to 8.0 percent points in scenario B compared to scenario A, while re-biopsies were reduced by 94% to 100%. Scenario B resulted in cost savings up to 142 million dollars. CONCLUSIONS: Adding [18F]FES PET/CT to biopsy/IHC may increase the diagnostic accuracy of the ER status, especially when a tumor sample cannot be obtained, or the risk of a biopsy-related complication is high. Therefore, adding [18F]FES PET/CT to biopsy/IHC would have a positive impact on US clinical and economic outcomes.

KRAS Mutation Detection with (2S,4R)-4-[18F]FGln for Noninvasive PDAC Diagnosis.

Pancreatic ductal adenocarcinoma (PDAC), which has a poor prognosis and nonspecific symptoms and progresses rapidly, is the most common pancreatic cancer type. Inhibitors targeting KRAS G12D and G12C mutations have been pivotal in PDAC treatment. Cancer cells with different KRAS mutations exhibit various degrees of glutamine dependency; in particular, cells with KRAS G12D mutations exhibit increased glutamine uptake. (2S,4R)-4-[18F]FGln has recently been developed for clinical cancer diagnosis and tumor cell metabolism analysis. Thus, we verified the heterogeneity of glutamine dependency in PDAC models with different KRAS mutations by a visual and noninvasive method with (2S,4R)-4-[18F]FGln. Two tumor-bearing mouse models (bearing the KRAS G12D or G12C mutation) were injected with (2S,4R)-4-[18F]FGln, and positron emission tomography (PET) imaging features and biodistribution were observed and analyzed. The SUVmax in the regions of interest (ROI) was significantly higher in PANC-1 (G12D) tumors than in MIA PaCa-2 (G12C) tumors. Biodistribution analysis revealed higher tumor accumulation of (2S,4R)-4-[18F]FGln and other metrics, such as T/M and T/B, in the PANC-1 mouse models compared to those in the MIAPaCa-2 mouse models. In conclusion, PDAC cells with the KRAS G12D and G12C mutations exhibit various degrees of (2S,4R)-4-[18F]FGln uptake, indicating that (2S,4R)-4-[18F]FGln might be applied to detect KRAS G12C and G12D mutations and provide treatment guidance.

Immunohistochemical and histopathological validation of 18 F-PSMA-1007 PET/CT for intraprostatic cancerous lesions.

INTRODUCTION: Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer (PCa). In this study, we aim to immunohistochemically and histopathological validate the fluorine-18 (18 F)-PSMA-1007 positron emission tomography/computed tomography (PET/CT) for intraprostatic PCa lesions. METHODS: Between February 2019 and October 2020, patients with biopsy-proven, treatment-naïve intermediate-to-high-risk PCa undergoing an 18 F-PSMA-1007 PET/CT before robot-assisted radical prostatectomy (RARP) were prospectively enrolled. For all PCa lesions found on whole-mount histopathology, location, size, International Society of Urological Pathology (ISUP) grade group (GG), and immune reactive score (IRS) were assessed after PSMA staining. ISUP GG ≥ 3 PCa was defined as clinically significant (cs) PCa. All lesions were matched on PSMA PET/CT and the maximum standardized uptake value (SUVmax) was measured. RESULTS: A total of 125 lesions were analyzed in the 80 RARP specimens, of which 49 (40%) were csPCa and 76 (60%) non-csPCa. Linear multivariable regressions showed that an increase in SUVmax significantly correlated with a higher ISUP GG (p values between 0.021 and 0.001) and a higher IRS (p = 0.017). Logistic multivariable regression showed that csPCa significantly correlated with a higher SUVmax (odds ratio, OR: 1.17 [95% confidence interval, CI: 1.04-1.21, p = 0.005]), an increase in tumor length (OR: 1.05 [95% CI 1.01-1.10, p = 0.020]) and a higher IRS (OR; 1.24 [95% CI 1.07-1.47, p = 0.006]). A SUVmax threshold of 4 would have resulted in one (2%) missed lesion with csPCa. CONCLUSION: This prospective study revealed that 18 F-PSMA-1007 PET/CT SUVmax is correlated with the ISUP GG and IRS, and thereby could be a tool to characterize intraprostatic PCa lesions.

Preclinical Investigation of Radiopharmaceuticals: An Accurate and Multidisciplinary Approach.

BACKGROUND: The development of less expensive and pivotal methodologies capable of supporting the researchers in the radiopharmaceutical pre-clinical investigations could provide a crucial incentive for conducting biomedical research involved in the realization of tailored target therapies. OBJECTIVE: The aim of this pilot study was to evaluate the capability of a digital autoradiography system equipped with a laser scanning device to perform [18F] choline biodistribution evaluation in a xenograft mouse model of prostate cancer. METHODS: PC3 prostate cancer cells were used to develop NOD/SCID mice xenografts. The biodistribution of the radiopharmaceuticals was evaluated at 30, 60, and 120 min after injecting in excised organs by using a digital autoradiography system equipped with a super-resolution laser screen. Histological and immunohistochemical analyses were performed to correlate the [18F] choline uptake with morphological and molecular tumours characteristics. RESULTS: The reported data clearly indicate the possibility of performing accurate biodistribution studies using the digital autoradiographic system equipped with a super-resolution screen. Specifically, a significant increase in the [18F] choline inhibitor uptake in PC3 tumours compared to heart, bowel, liver, and kidney at both 30 and 60 min was observed. More importantly, the digital autoradiographic system showed signal uptake almost exclusively in the PC3 tumors at 60 min post-injection. Noteworthy, immunohistochemical analysis demonstrated a strong overlapping between the [18F] choline uptake and the proliferation index (Ki67 expression). CONCLUSION: The use of an autoradiography system in pre-clinical investigations could shed new light on the molecular mechanisms that orchestrate the tissues damage induced by therapeutical radiopharmaceuticals.

18F-sodium fluoride positron emission tomography (NaF-18-PET/CT) radiomic signatures to evaluate responses to alpha-particle Radium-223 dichloride therapy in osteosarcoma metastases.

Patients with osteoblastic metastases from high risk osteosarcoma continue to have a poor prognosis after progression from standard-of-care multi-agent chemotherapy. In a first-in-human dose escalation trial of bone targeted Radium 223 dichloride alpha-particle therapy in 18 patients with advanced osteosarcoma only 1 patient responded based on conventional Response Evaluation Criteria in Solid Tumors (RECIST). Na18F PET response Criteria in Solid Tumors(NAFCIST), based on Sodium fluoride-18 (Na18F) positron emission tomography (PET)-CT was developed to better evaluate bone specific response. To further appreciate the spatial and temporal heterogeneity of the partial or mixed responses, a radiomics method was developed. Analyses were performed with 18F-sodium fluoride positron emission tomography imaging studies before and after alpha-particle therapy. Radioactive 18F- -atom concentrations were measured in soft-tissues, in approximately 1000 concentration data points for 18F- per 1 cm3 metastatic tumor. Data was analyzed from the SUV intensity values, the histogram of intensities and entropy values. Radiomics may inform intra-tumoral and inter-tumoral heterogeneity in response of bone forming osteosarcoma to alpha particle therapy. Each patient (and each tumor) represents an "N of 1" case and warrants in depth analysis individually.

Economical droplet-based microfluidic production of [18F]FET and [18F]Florbetaben suitable for human use.

Current equipment and methods for preparation of radiopharmaceuticals for positron emission tomography (PET) are expensive and best suited for large-scale multi-doses batches. Microfluidic radiosynthesizers have been shown to provide an economic approach to synthesize these compounds in smaller quantities, but can also be scaled to clinically-relevant levels. Batch microfluidic approaches, in particular, offer significant reduction in system size and reagent consumption. Here we show a simple and rapid technique to concentrate the radioisotope, prior to synthesis in a droplet-based radiosynthesizer, enabling production of clinically-relevant batches of [18F]FET and [18F]FBB. The synthesis was carried out with an automated synthesizer platform based on a disposable Teflon-silicon surface-tension trap chip. Up to 0.1 mL (4 GBq) of radioactivity was used per synthesis by drying cyclotron-produced aqueous [18F]fluoride in small increments directly inside the reaction site. Precursor solution (10 µL) was added to the dried [18F]fluoride, the reaction chip was heated for 5 min to perform radiofluorination, and then a deprotection step was performed with addition of acid solution and heating. The product was recovered in 80 µL volume and transferred to analytical HPLC for purification. Purified product was formulated via evaporation and resuspension or a micro-SPE formulation system. Quality control testing was performed on 3 sequential batches of each tracer. The method afforded production of up to 0.8 GBq of [18F]FET and [18F]FBB. Each production was completed within an hour. All batches passed quality control testing, confirming suitability for human use. In summary, we present a simple and efficient synthesis of clinically-relevant batches of [18F]FET and [18F]FBB using a microfluidic radiosynthesizer. This work demonstrates that the droplet-based micro-radiosynthesizer has a potential for batch-on-demand synthesis of 18F-labeled radiopharmaceuticals for human use.

Prognostic significance of volume-based 18F-FDG PET/CT parameters and correlation with PD-L1 expression in patients with surgically resected lung adenocarcinoma.

ABSTRACT: The aim of this study was to retrospectively analyze 18F-FDG positron emission tomography/computed tomography (18F-FDG PET/CT) metabolic variables, programmed death-ligand 1 (PD-L1) and phosphorylated signal transducer and activator of transcription 3 (p-STAT3) tumor expression, and other factors as predictors of disease-free survival (DFS) in patients with lung adenocarcinoma (LUAD) (stage IA-IIIA) who underwent surgical resection. We still lack predictor of immune checkpoint (programmed cell death-1 [PD-1]/PD-L1) inhibitors. Herein, we investigated the correlation between metabolic parameters from 18F-FDG PET/CT and PD-L1 expression in patients with surgically resected LUAD.Seventy-four patients who underwent 18F-FDG PET/CT prior to treatment were consecutively enrolled. The main 18F-FDG PET/CT-derived variables were primary tumor maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Surgical tumor specimens were analyzed for PD-L1 and p-STAT3 expression using immunohistochemistry. Correlations between immunohistochemistry results and 18F-FDG PET/CT-derived variables were compared. Associations of PD-L1 and p-STAT3 tumor expression, 18F-FDG PET/CT-derived variables, and other factors with DFS in resected LUAD were evaluated.All tumors were FDG-avid. The cutoff values of low and high SUVmax, MTV, and TLG were 12.60, 14.87, and 90.85, respectively. The results indicated that TNM stage, PD-L1 positivity, and high 18F-FDG PET/CT metabolic volume parameters (TLG ≥90.85 or MTV ≥14.87) were independent predictors of worse DFS in resected LUAD. No 18F-FDG metabolic parameters associated with PD-L1 expression were observed (chi-square test), but we found that patients with positive PD-L1 expression have significantly higher SUVmax (P = .01), MTV (P = .00), and TLG (P = .00) than patients with negative PD-L1 expression.18F-FDG PET/CT metabolic volume parameters (TLG ≥90.85 or MTV ≥14.87) were more helpful in prognostication than the conventional parameter (SUVmax), PD-L1 expression was an independent predictor of DFS in patients with resected LUAD. Metabolic parameters on 18F-FDG PET/CT have a potential role for 18F-FDG PET/CT in selecting candidate LUAD for treatment with checkpoint inhibitors.

Comparison between 18 F-DCFPyL PET and MRI for the detection of transition zone prostate cancer.

BACKGROUND: We aimed to compare the diagnostic performance of 18 F-DCFPyL positron emission tomography (PET) and multiparameter magnetic resonance imaging (mp-MRI) in detecting transition zone (TZ) prostate cancer (PCa). METHODS: This retrospective study included 20 patients who underwent 18 F-DCFPyL PET/MRI and 32 patients who underwent 18 F-DCFPyL PET/CT and MRI from January 2019 to June 2020. All patients had TZ lesions and underwent prostate biopsies. One senior (reader 1) and one junior (reader 2) nuclear medicine physician evaluated each TZ lesion independently, according to the molecular imaging prostate-specific membrane antigen scoring system and the Prostate Imaging Reporting and Data System version 2.1 (PI-RADS v2.1). The histologic diagnosis of prostate biopsy was used as the reference standard. The diagnostic performance of the two methods was compared in terms of inter-reader agreement and area under the receiver operating characteristic (AUC-ROC) curve. RESULTS: Of the 52 patients, 43 had TZ PCa. For inter-reader agreement, the kappa value was 0.883 for 18 F-DCFPyL PET and 0.393 for mp-MRI. For PET, both readers had the same diagnostic sensitivity, specificity, and accuracy of 93.0%, 77.8%, and 90.4%, respectively. For mp-MRI, the diagnostic sensitivity, specificity, and accuracy was 67.4%, 33.3%, and 61.5% for reader 1, and 51.2%, 44.4%, and 51.9% for reader 2, respectively. PET outperformed mp-MRI for both readers with an AUC of 0.872 for PET versus 0.584 for mp-MRI, p = .0209 for reader 1, and an AUC of 0.860 for PET versus 0.505 for mp-MRI, p = .0213 for reader 2. Among the 43 patients with TZ PCa, 18 F-DCFPyL PET detected a distant bone metastasis missed by the CT in one case and two small lymph node metastases missed by the CT and MRI in another case. CONCLUSIONS: These results suggest that 18 F-DCFPyL PET, which was almost independent of the experience of the readers, was more objective in the evaluation of TZ lesions, and had higher diagnostic value than mp-MRI.

Predictive value of 3'-deoxy-3'-18F-fluorothymidine PET in the early response to anti-programmed death-1 therapy in patients with advanced non-small cell lung cancer.

BACKGROUND: Anti-programmed death-1 (anti-PD-1) therapy has shown clinical success in patients with advanced non-small cell lung cancer (NSCLC). However, it is difficult to evaluate the early response to anti-PD-1 therapy. We determined whether changes in 3'-deoxy-3'-[18F]-fluorothymidine (18F-FLT) PET parameters before and soon after treatment initiation predicted the therapeutic effect of anti-PD-1 antibody. METHODS: Twenty-six patients with advanced NSCLC treated with anti-PD-1 antibody were enrolled prospectively and underwent 18F-FLT PET before and at 2 and 6 weeks after treatment initiation. Changes in maximal standardized uptake value (ΔSUVmax), proliferative tumor volume (ΔPTV) and total lesion proliferation (ΔTLP) of the lesions were calculated and evaluated for their associations with the clinical response to therapy. RESULTS: The disease control rate was 64%. Patients with non-progressive disease (non-PD) had significantly decreased TLP at 2 weeks, and decreased SUVmax, PTV, and TLP at 6 weeks, compared with those with PD, while three of eight (37.5%) patients who responded had increased TLP from baseline at 2 weeks (ie, pseudoprogression). Among the parameters that changed between baseline and 2 weeks, ΔPTV0-2 and ΔTLP0-2 had the highest accuracy (76.0%) to predict PD. Among the parameters that changed between baseline and 6 weeks, ΔSUVmax0-6, ΔPTV0-6 and ΔTLP0-6 had the highest accuracy (90.9%) to predict PD. ΔTLP0-2 (≥60%, HR 3.41, 95% CI 1.34-8.65, p=0.010) and ΔTLP0-6 (≥50%, HR 31.4, 95% CI 3.55 to 276.7, p=0.0019) were indicators of shorter progression-free survival. CONCLUSIONS: Changes in 18F-FLT PET parameters may have value as an early predictive biomarker for the response to anti-PD-1 therapy in patients with NSCLC. However, it should be noted that pseudoprogression was observed in 18F-FLT PET imaging at 2 weeks after treatment initiation. TRIAL REGISTRATION NUMBER: jRCTs051180147.

Automatic radiosynthesis and preclinical evaluation of 18F-AlF-PSMA-NF as a potential PET probe for prostate cancer imaging.

Facile automatic production is important for the application of prostate-specific membrane antigen (PSMA) tracers in clinical practice. We developed a new 18F-AlF-labelled PSMA probe-18F-AlF-PSMA-NF-and explore its automated production method and potential value in clinical settings. 18F-AlF-PSMA-NF was prepared using an automated method with dimethylformamide (DMF) as the solvent in a positron emission tomography (PET)-MF-2 V-IT-I synthesizer. Tracer characteristics were examined both in vitro and in vivo. Micro-PET/computed tomography (CT) was performed to investigate the utility of 18F-AlF-PSMA-NF for imaging PSMA-positive tumours in vivo. 18F-AlF-PSMA-NF was prepared automatically within 35 min with a non-attenuation correction yield of 37.9 ± 11.2%. The tracer was hydrophilic, had a high affinity for PSMA (Kd = 2.58 ± 0.81 nM), and showed stability in both in vitro and in vivo conditions. In the cellular experiments, 18F-AlF-PSMA-NF uptake in PSMA-positive LNCaP cells was significantly higher than that in PSMA-negative PC-3 cells (P < 0.001), and could be blocked by excess ZJ-43-a PSMA inhibitor (P < 0.001). LNCaP tumours were clearly visualized by 18F-AlF-PSMA-NF on micro-PET/CT, with a high level of uptake (13.72 ± 2.01 percent injected dose per gram of tissue [%ID/g]) and high tumour/muscle ratio (close to 50:1). The PSMA-positive LNCaP tumours had a significantly higher uptake than PSMA-negative PC-3 tumours (13.72 ± 2.01%ID/g vs. 1.07 ± 0.48%ID/g, t = 10.382, P < 0.001), and could be blocked by ZJ-43 (13.72 ± 2.01%ID/g vs. 2.77 ± 1.44%ID/g, t = 8.14, P < 0.001). A new 18F-AlF-labelled PSMA probe-18F-AlF-PSMA-NF-was successfully developed and can be prepared automatically. It has the biological characteristics resembling that of a PSMA-based probe and can potentially be used in clinical settings.

PET Imaging of Melanoma Using Melanin-Targeted Probe.

Melanin exists in the most of melanoma lesions. Melanin plays an important role in melanoma progression, metastasis, therapy response, and the overall survival of patients. Therefore, melanin is a critical target for melanoma diagnosis and therapy. Many melanin targeting probes, such as radioisotope-labeled benzamide analogs, have been developed for melanoma diagnosis using positron emission tomography (PET). The N-(2-(diethylamino)-ethyl)-18F-5-fluoropicolinamide (18F-P3BZA) probe is one of the benzamide analogs and has been preliminarily tested for clinical diagnosis of melanoma in our recent studies. It has shown high specificity and favorable in vivo performance for PET of melanoma. Herein, we describe the detailed synthesis protocol of 18F-P3BZA and PET/CT imaging procedure for animal models and patients.

Comparison of visual criteria for amyloid-PET reading: could criteria merging reduce inter-rater variability?

BACKGROUND: Three different amyloid tracers labeled with 18-flourine have been introduced into clinical use. The leaflets of tracers indicate different visual criteria for PET reporting. In clinical practice, it is not yet ascertained whether these criteria are equivalent in terms of diagnostic accuracy or if anyone is better than another. We aimed to evaluate the inter and intra-rater variability of visual assessment of 18F-Florbetapir PET/CT images among six independent readers with different clinical experience. METHODS: We analyzed 252 PET/CT scans, visually assessed by each reader three times, applying independently the three different reading criteria proposed. Each reader evaluated the regional uptake specifying for each cortical region a numeric value of grading of positivity in order to assign a final score. At the end of each reading a level of confidence was determined by assigning a score from 0 (negative) to 4 (positive). After first reading, those cases in which the evaluations by two experienced readers did not match (discordant cases) were independently reevaluated merging all the three different visual interpretation criteria. RESULTS: Good agreement was observed for visual interpretation among the six readers' confidence-level using independently the three visual reading criteria: ICC=0.83 (0.80-0.86) for 18F-florbetapir, ICC=0.84 (0.81-0.87) for 18F-florbetaben, and ICC=0.86 (0.83-0.88) for 18F-flutemetamol reading. A good inter-rater agreement was observed for final-score too: ICC=0.74 (0.70-0.78) for 18F-florbetapir; ICC=0.82 (0.79-0.85) for 18F-florbetaben; ICC=0.84 (0.81-0.87) for 18F-flutemetamol. Intra-rater agreement was good for final-score (from 0.76 to 0.90; P<0.001) and confidence-level (Spearman's rho from 0.89 to 1.00; P<0.001). Disagreement between the two experienced readers was observed in 22 of 252 cases (9%). The agreement converged over a second round of independent reading in 12 of 22 cases (54%), by merging all the criteria. CONCLUSIONS: All the criteria proposed are useful to determine the grading of positivity or negativity of amyloid deposition and their merging improves the diagnostic confidence and provides a better agreement.

18F-AzaFol for Detection of Folate Receptor-ß Positive Macrophages in Experimental Interstitial Lung Disease-A Proof-of-Concept Study.

Background: Interstitial lung disease (ILD) is a common and severe complication in rheumatic diseases. Folate receptor-ß is expressed on activated, but not resting macrophages which play a key role in dysregulated tissue repair including ILD. We therefore aimed to pre-clinically evaluate the potential of 18F-AzaFol-based PET/CT (positron emission computed tomography/computed tomography) for the specific detection of macrophage-driven pathophysiologic processes in experimental ILD. Methods: The pulmonary expression of folate receptor-ß was analyzed in patients with different subtypes of ILD as well as in bleomycin (BLM)-treated mice and respective controls using immunohistochemistry. PET/CT was performed at days 3, 7, and 14 after BLM instillation using the 18F-based folate radiotracer 18F-AzaFol. The specific pulmonary accumulation of the radiotracer was assessed by ex vivo PET/CT scans and quantified by ex vivo biodistribution studies. Results: Folate receptor-ß expression was 3- to 4-fold increased in patients with fibrotic ILD, including idiopathic pulmonary fibrosis and connective tissue disease-related ILD, and significantly correlated with the degree of lung remodeling. A similar increase in the expression of folate receptor-ß was observed in experimental lung fibrosis, where it also correlated with disease extent. In the mouse model of BLM-induced ILD, pulmonary accumulation of 18F-AzaFol reflected macrophage-related disease development with good correlation of folate receptor-ß positivity with radiotracer uptake. In the ex vivo imaging and biodistribution studies, the maximum lung accumulation was observed at day 7 with a mean accumulation of 1.01 ± 0.30% injected activity/lung in BLM-treated vs. control animals (0.31 ± 0.06% % injected activity/lung; p < 0.01). Conclusion: Our preclinical proof-of-concept study demonstrated the potential of 18F-AzaFol as a novel imaging tool for the visualization of macrophage-driven fibrotic lung diseases.

One-Pot Radiosynthesis and Biological Evaluation of a Caspase-3 Selective 5-[123,125I]iodo-1,2,3-triazole derived Isatin SPECT Tracer.

Induction of apoptosis is often necessary for successful cancer therapy, and the non-invasive monitoring of apoptosis post-therapy could assist in clinical decision making. Isatins are a class of compounds that target activated caspase-3 during apoptosis. Here we report the synthesis of the 5-iodo-1,2,3-triazole (FITI) analog of the PET tracer [18F]ICMT11 as a candidate tracer for imaging of apoptosis with SPECT, as well as PET. Labelling with radioiodine (123,125I) was achieved in 55 ± 12% radiochemical yield through a chelator-accelerated one-pot cycloaddition reaction mediated by copper(I) catalysis. The caspase-3 binding affinity and selectivity of FITI compares favourably to that of [18F]ICMT11 (Ki = 6.1 ± 0.9 nM and 12.4 ± 4.7 nM, respectively). In biodistribution studies, etoposide-induced cell death in a SW1222 xenograft model resulted in a 2-fold increase in tumour uptake of the tracer. However, the tumour uptake was too low to allow in vivo imaging of apoptosis with SPECT.

Synthesis and Preclinical Evaluation of the Fibrin-Binding Cyclic Peptide 18F-iCREKA: Comparison with Its Contrasted Linear Peptide.

Purpose: Cys-Arg-Glu-Lys-Ala (CREKA) is a pentapeptide which can target fibrin-fibronectin complexes. Our previous study has built a probe called iCREKA which was based on CREKA and has proved the feasibility and specificity of iCREKA by the fluorescence experiment. The purpose of this study is to achieve the 18F-labeled iCREKA and make preclinical evaluation of the 18F-iCREKA with comparison of its contrasted linear peptide (LP). Methods: CREKA, LP, and iCREKA were labeled by the Al18F labeling method, respectively. These 18F-labeled peptides were evaluated by the radiochemistry, binding affinity, in vitro stability, in vivo stability, micro-PET imaging, and biodistribution tests. Results: 18F-NOTA-iCREKA was stable both in vitro and in vivo. However, 18F-NOTA-CREKA and 18F-NOTA-LP were both unstable. The FITC or 18F-labeled iCREKA could be abundantly discovered only in matrix metalloproteinases- (MMPs-) 2/9 highly expressed U87MG cells, while the FITC or 18F-labeled LP could also be abundantly discovered in MMP-2/9 lowly expressed Caov3 cells. Biodistribution and micropositron emission tomography (PET) imaging revealed that the U87MG xenografts showed a higher uptake of 18F-NOTA-iCREKA than 18F-NOTA-LP while the Caov3 xenografts showed very low uptake of both 18F-NOTA-iCREKA and 18F-NOTA-LP. The tumor-to-muscle (T/M) ratio of 18F-NOTA-iCREKA (9.93 ± 0.42) was obviously higher than 18F-NOTA-LP (2.69 ± 0.35) in U87MG xenografts. Conclusions: The novel CREKA-based probe 18F-NOTA-iCREKA could get a high uptake in U87MG cells and high T/M ratio in U87MG mice. It was more stable and specific than the 18F-NOTA-LP.

Fluorine-18 (18F)-labeled retinoid x receptor (RXR) partial agonist whose tissue transferability is affected by other RXR ligands.

Bexarotene (1), a retinoid X receptor (RXR) agonist approved for the treatment of cutaneous T cell lymphoma (CTCL), was reported to migrate into baboon brain based on findings obtained by positron emission tomography (PET) with a 11C-labeled tracer. However, co-administration of non-radioactive 1 had no effect on the distribution of [11C]1, probably due to non-specific binding of 1 as a result of its high lipophilicity. Here, we report a fluorine-18 (18F)-labeled PET tracer [18F]6 derived from RXR partial agonist CBt-PMN (2), which has lower lipophilicity and weaker RXR-binding ability than [11C]1. The concomitant administration of 1 or 2 with [18F]6 with resulted in decreased accumulation of [18F]6 in liver, together with increased brain uptake and increased accumulation in kidney and muscle, as visualized by PET. A plausible explanation of these findings is the inhibition of [18F]6 uptake into the liver by concomitantly administered 1 or 2, leading to an increase in blood concentration of [18F]6 followed by increased accumulation in other tissues.

Bridging the Imaging Gap: PSMA PET/CT Has a High Impact on Treatment Planning in Prostate Cancer Patients with Biochemical Recurrence-A Narrative Review of the Literature.

68Ga- and 18F-labeled prostate-specific membrane antigen (PSMA) molecules have created new opportunities for the unmet diagnostic needs in prostate cancer. The purpose of this article is to give an overview of studies that have examined the role of PSMA PET in treatment planning for prostate cancer patients with biochemical recurrence (BCR). Methods: Medline, Embase, Web of Science, Google Scholar, and Cochrane Central were searched for relevant articles. After excluding the articles that did not fulfill the required criteria, we included in this review 12 publications that reported the impact of PSMA PET on the treatment plan for prostate cancer patients with BCR. Results: All studies in our review emphasized the impact of PSMA PET images on therapy management in prostate cancer patients with BCR. Overall, the impact of PSMA PET/CT on therapy management varied between 30% and 76% among the 1,346 patients included in the review. Upstaging was reported in 32%-67% of the patients. Patients with low prostate-specific antigen values (<0.5 ng/mL) also demonstrated positive lesions, which could not have been detected by means of conventional imaging techniques. Important modifications to the original treatment plan included avoidance of systemic therapy (17%-40%) and PET-directed local therapy (in ≤60% of the patients). Conclusion: PSMA imaging demonstrated a high clinical impact in patients with BCR, with modifications to the original treatment plan occurring among half the patients. Detecting recurrence in BCR can prevent unnecessary toxicity and lead to individualized therapy.

Dynamic [18F]FET-PET/MRI using standard MRI-based attenuation correction methods.

AIM: To assess if tumour grading based on dynamic [18F]FET positron emission tomography/magnetic resonance imaging (PET/MRI) studies is affected by different MRI-based attenuation correction (AC) methods. METHODS: Twenty-four patients with suspected brain tumours underwent dynamic [18F]FET-PET/MRI examinations and subsequent low-dose computed tomography (CT) scans of the head. The dynamic PET data was reconstructed using the following AC methods: standard Dixon-based AC and ultra-short echo time MRI-based AC (MR-AC) and a model-based AC approach. All data were reconstructed also using CT-based AC (reference). For all lesions and reconstructions, time-activity curves (TACs) and time to peak (TTP) were extracted using different region-of-interest (ROI) and volume-of-interest (VOI) definitions. According to the most common evaluation approaches, TACs were categorised into two or three distinct curve patterns. Changes in TTP and TAC patterns compared to PET using CT-based AC were reported. RESULTS: In the majority of cases, TAC patterns did not change. However, TAC pattern changes as well as changes in TTP were observed in up to 8% and 17% of the cases when using different MR-AC methods and ROI/VOI definitions, respectively. However, these changes in TTP and TAC pattern were attributed to different delineations of the ROIs/VOIs in PET corrected with different AC methods. CONCLUSION: PET/MRI using different MR-AC methods can be used for the assessment of TAC patterns in dynamic [18F]FET studies, as long as a meaningful delineation of the area of interest within the tumour is ensured. KEY POINTS: • PET/MRI using different MR-AC methods can be used for dynamic [18F]FET studies. • A meaningful segmentation of the area of interest needs to be ensured, mandating a visual validation of the delineation by an experienced reader.

PET imaging of HER2 expression with an 18F-fluoride labeled aptamer.

BACKGROUND/PURPOSE: Aptamers are oligonucleotide or peptide molecules that bind to a target molecule with high affinity and specificity. The present study aimed to evaluate the target specificity and applicability for in vivo molecular imaging of an aptamer labeled with a radioisotope. METHODS: The human epidermal growth factor receptor 2 (HER2/ErbB2) aptamer was radiolabeled with 18F-fluoride. HER2-positive tumor cell uptake of the aptamer was evaluated in comparison to negative controls by flow cytometry and confocal microscopy. Using 18F-labeled HER2-specific aptamer positron emission tomography (PET), in vivo molecular images of BT474 tumor-bearing mice were taken at 60, 90 and 120 minutes after injection. RESULTS: In flow cytometric analysis, HER2 aptamer showed strong binding to HER2-positive BT474 cells, while binding to HER2-negative MDA-MB231 cells was quite low. Likewise, in confocal microscopic images, the aptamer was bound to HER2-positive breast cancer cells, with minimal binding to HER2-negative cells. In vivo PET molecular imaging of BT474 tumor-bearing mice revealed significant higher uptake of the 18F-labeled HER2 specific aptamer into the tumor compared to the that of HER2-negative cell tumor(p = 0.033). HER2 aptamer was able to preferentially bind to HER2-positive breast cancer cells both in vitro and in vivo, by recognizing HER2 structure on the surface of these cells. CONCLUSION: The 18F-labeled aptamer enabled appropriate visualization of HER2 expression by human breast cancer cells. The results suggest that a radiolabeled HER2 aptamer could potentially be applied in the development of treatment strategies or in targeted therapy against HER2-positive breast cancer cells.

Use of the PET ligand florbetapir for in vivo imaging of pancreatic islet amyloid deposits in hIAPP transgenic mice.

AIMS/HYPOTHESIS: Islet amyloid deposits contribute to beta cell dysfunction and death in most individuals with type 2 diabetes but non-invasive methods to determine the presence of these pathological protein aggregates are currently not available. Therefore, we examined whether florbetapir, a radiopharmaceutical agent used for detection of amyloid-ß deposits in the brain, also allows identification of islet amyloid in the pancreas. METHODS: Saturation binding assays were used to determine the affinity of florbetapir for human islet amyloid polypeptide (hIAPP) aggregates in vitro. Islet amyloid-prone transgenic mice that express hIAPP in their beta cells and amyloid-free non-transgenic control mice were used to examine the ability of florbetapir to detect islet amyloid deposits in vitro, in vivo and ex vivo. Mice or mouse pancreases were subjected to autoradiographic, histochemical and/or positron emission tomography (PET) analyses to assess the utility of florbetapir in identifying islet amyloid. RESULTS: In vitro, florbetapir bound synthetic hIAPP fibrils with a dissociation constant of 7.9 nmol/l. Additionally, florbetapir bound preferentially to amyloid-containing hIAPP transgenic vs amyloid-free non-transgenic mouse pancreas sections in vitro, as determined by autoradiography (16,475 ± 5581 vs 5762 ± 575 density/unit area, p < 0.05). In hIAPP transgenic and non-transgenic mice fed a high-fat diet for 1 year, intravenous administration of florbetapir followed by PET scanning showed that the florbetapir signal was significantly higher in amyloid-laden hIAPP transgenic vs amyloid-free non-transgenic pancreases in vivo during the first 5 min of the scan (36.83 ± 2.22 vs 29.34 ± 2.03 standardised uptake value × min, p < 0.05). Following PET, pancreases were excised and florbetapir uptake was determined ex vivo by γ counting. Pancreatic uptake of florbetapir was significantly correlated with the degree of islet amyloid deposition, the latter assessed by histochemistry (r = 0.74, p < 0.001). CONCLUSIONS/INTERPRETATION: Florbetapir binds to islet amyloid deposits in a specific and quantitative manner. In the future, florbetapir may be useful as a non-invasive tool to identify islet amyloid deposits in humans.