Production of [211At]NaAt solution under GMP compliance for investigator-initiated clinical trial.

BACKGROUND: The alpha emitter astatine-211 (211At) is garnering attention as a novel targeted alpha therapy for patients with refractory thyroid cancer resistant to conventional therapy using beta emitter radioiodine (131I). Herein, we aimed to establish a robust method for the manufacturing and quality control of [211At]NaAt solution for intravenous administration under the good manufacturing practice guidelines for investigational products to conduct an investigator-initiated clinical trial. RESULTS: 211At was separated and purified via dry distillation using irradiated Bi plates containing 211At obtained by the nuclear reaction of 209Bi(4He, 2n)211At. After purification, the 211At trapped in the cold trap was collected in a reaction vessel using 15 mL recovery solution (1% ascorbic acid and 2.3% sodium hydrogen carbonate). After stirring the 211At solution for 1 h inside a closed system, the reaction solution was passed through a sterile 0.22 µm filter placed in a Grade A controlled area and collected in a product vial to prepare the [211At]NaAt solution. According to the 3-lot tests, decay collected radioactivity and radiochemical yield of [211At]NaAt were 78.8 ± 6.0 MBq and 40 ± 3%, respectively. The radiochemical purity of [211At]At- obtained via ion-pair chromatography at the end of synthesis (EOS) was 97 ± 1%, and remained > 96% 6 h after EOS; it was detected at a retention time (RT) 3.2-3.3 min + RT of I-. LC-MS analysis indicated that this principal peak corresponded with an astatide ion (m/z = 210.988046). In gamma-ray spectrometry, the 211At-related peaks were identified (X-ray: 76.9, 79.3, 89.3, 89.8, and 92.3 keV; γ-ray: 569.7 and 687.0 keV), whereas the peak at 245.31 keV derived from 210At was not detected during the 22 h continuous measurement. The target material, Bi, was below the 9 ng/mL detection limit in all lots of the finished product. The pH of the [211At]NaAt solution was 7.9-8.6; the concentration of ascorbic acid was 9-10 mg/mL. Other quality control tests, including endotoxin and sterility tests, confirmed that the [211At]NaAt solution met all quality standards. CONCLUSIONS: We successfully established a stable method of [211At]NaAt solution that can be administered to humans intravenously as an investigational product.

Immuno-PET and Targeted α-Therapy Using Anti-Glypican-1 Antibody Labeled with 89Zr or 211At: A Theranostic Approach for Pancreatic Ductal Adenocarcinoma.

Glypican-1 (GPC1) is overexpressed in several solid cancers and is associated with tumor progression, whereas its expression is low in normal tissues. This study aimed to evaluate the potential of an anti-GPC1 monoclonal antibody (GPC1 mAb) labeled with 89Zr or 211At as a theranostic target in pancreatic ductal adenocarcinoma. Methods: GPC1 mAb clone 01a033 was labeled with 89Zr or 211At with a deferoxamine or decaborane linker, respectively. The internalization ability of GPC1 mAb was evaluated by fluorescence conjugation using a confocal microscope. PANC-1 xenograft mice (n = 6) were intravenously administered [89Zr]GPC1 mAb (0.91 ± 0.10 MBq), and PET/CT scanning was performed for 7 d. Uptake specificity was confirmed through a comparative study using GPC1-positive (BxPC-3) and GPC1-negative (BxPC-3 GPC1-knockout) xenografts (each n = 3) and a blocking study. DNA double-strand breaks were evaluated using the γH2AX antibody. The antitumor effect was evaluated by administering [211At]GPC1 mAb (∼100 kBq) to PANC-1 xenograft mice (n = 10). Results: GPC1 mAb clone 01a033 showed increased internalization ratios over time. One day after administration, a high accumulation of [89Zr]GPC1 mAb was observed in the PANC-1 xenograft (SUVmax, 3.85 ± 0.10), which gradually decreased until day 7 (SUVmax, 2.16 ± 0.30). The uptake in the BxPC-3 xenograft was significantly higher than in the BxPC-3 GPC1-knockout xenograft (SUVmax, 4.66 ± 0.40 and 2.36 ± 0.36, respectively; P = 0.05). The uptake was significantly inhibited in the blocking group compared with the nonblocking group (percentage injected dose per gram, 7.3 ± 1.3 and 12.4 ± 3.0, respectively; P = 0.05). DNA double-strand breaks were observed by adding 150 kBq of [211At]GPC1 and were significantly suppressed by the internalization inhibitor (dynasore), suggesting a substantial contribution of the internalization ability to the antitumor effect. Tumor growth suppression was observed in PANC-1 mice after the administration of [211At]GPC1 mAb. Internalization inhibitors (prochlorperazine) significantly inhibited the therapeutic effect of [211At]GPC1 mAb, suggesting an essential role in targeted α-therapy. Conclusion: [89Zr]GPC1 mAb PET showed high tumoral uptake in the early phase after administration, and targeted α-therapy using [211At]GPC1 mAb showed tumor growth suppression. GPC1 is a promising target for future applications for the precise diagnosis of pancreatic ductal adenocarcinoma and GPC1-targeted theranostics.

Evaluation of LAT1 Expression in Patients With Lung Cancer and Mediastinal Tumors: 18F-FBPA PET Study With Immunohistological Comparison.

PURPOSE OF THE REPORT: L-type amino acid transporter-1 (LAT1) is a tumor-specific transporter expressed in various tumor types, with minimal expression in normal organs. We previously demonstrated 18F-fluoro-borono-phenylalanine (18F-FBPA) as a selective PET probe for LAT1 in a preclinical study. Herein, we evaluated LAT1 expression in preoperative patients with lung or mediastinal tumors using 18F-FBPA PET and immunofluorescence staining. PATIENTS AND METHODS: The study population included patients with histopathological diagnosis (n = 55): primary lung cancers (n = 21), lung metastases (n = 6), mediastinal tumors (n = 15), and benign lesion (n = 13). PET scanning was performed 1 hour after the injection of 18F-FBPA (232 ± 32 MBq). Immunofluorescence staining was performed on the resected tumor sections using LAT1 antibody. LAT1 staining was graded on a 4-grade scale and compared with the SUVmax on 18F-FBPA PET. RESULTS: A positive correlation was observed between the SUVmax of 18F-FBPA PET and LAT1 expression by immunofluorescence staining (r = 0.611, P < 0.001). The SUVmax of 18F-FBPA was 3.92 ± 1.46 in grade 3, 3.21 ± 1.82 in grade 2, 2.33 ± 0.93 in grade 1, and 1.50 ± 0.39 in grade 0 of LAT1 expression. Although 18F-FBPA PET showed variable uptake in lung cancers and mediastinal tumors, benign lesions showed significantly lower SUVmax than those in malignant lesions (P < 0.01). CONCLUSIONS: Uptake on 18F-FBPA PET reflected the expression level of LAT1 in lung and mediastinal tumors. It was suggested that 18F-FBPA PET can be used for the precise characterization of the tumor in pretreatment evaluation.

Initial Evaluation of [18F]FAPI-74 PET for Various Histopathologically Confirmed Cancers and Benign Lesions.

The 18F-labeled fibroblast activation protein inhibitor (FAPI) [18F]FAPI-74 has the benefit of a higher synthetic yield and better image resolution than 68Ga-labeled FAPI. We preliminarily evaluated the diagnostic performance of [18F]FAPI-74 PET in patients with various histopathologically confirmed cancers or suspected malignancies. Methods: We enrolled 31 patients (17 men and 14 women) with lung cancer (n = 7), breast cancer (n = 5), gastric cancer (n = 5), pancreatic cancer (n = 3), other cancers (n = 5), and benign tumors (n = 6). Twenty-seven of the 31 patients were treatment-naïve or preoperative, whereas recurrence was suspected in the remaining 4 patients. Histopathologic confirmation was obtained for the primary lesions of 29 of the 31 patients. In the remaining 2 patients, the final diagnosis was based on the clinical course. [18F]FAPI-74 PET scanning was performed 60 min after the intravenous injection of [18F]FAPI-74 (240 ± 31 MBq). The [18F]FAPI-74 PET images were compared between the primary or local recurrent lesions of malignant tumors (n = 21) and nonmalignant lesions (n = 8: type-B1 thymomas, granuloma, solitary fibrous tumor, and postoperative or posttherapeutic changes). The uptake and number of detected lesions on [18F]FAPI-74 PET were also compared with those on [18F]FDG PET for available patients (n = 19). Results: [18F]FAPI-74 PET showed higher uptake in primary lesions of various cancers than in nonmalignant lesions (median SUVmax, 9.39 [range, 1.83-25.28] vs. 3.49 [range, 2.21-15.58]; P = 0.053), but some of the nonmalignant lesions showed high uptake. [18F]FAPI-74 PET also showed significantly higher uptake than [18F]FDG PET (median SUVmax, 9.44 [range, 2.50-25.28] vs. 5.45 [range, 1.22-15.06] in primary lesions [P = 0.010], 8.86 [range, 3.51-23.33] vs. 3.84 [range, 1.01-9.75] in lymph node metastases [P = 0.002], and 6.39 [range, 0.55-12.78] vs. 1.88 [range, 0.73-8.35] in other metastases [P = 0.046], respectively). In 6 patients, [18F]FAPI-74 PET detected more metastatic lesions than [18F]FDG PET. Conclusion: [18F]FAPI-74 PET showed higher uptake and detection rates in primary and metastatic lesions than did [18F]FDG PET. [18F]FAPI-74 PET is a promising novel diagnostic modality for various tumors, especially for precise staging before treatment, including characterization of tumor lesions before surgery. Moreover, 18F-labeled FAPI ligand might serve a higher demand in clinical care in the future.

Improved Stability and Practicality for Synthesis of 4-Borono-2-[18F]fluoro-l-phenylalanine by Combination of [18O]O2 Single-Use and [18F]CH3COOF Labeling Agents.

Purpose: 4-Borono-2-[18F]fluoro-l-phenylalanine ([18F]FBPA) synthesized with [18F]F2, produced using the 18O(p, n)18F reaction, has been reported for increasing radioactivity. However, a dedicated system and complex procedure is required to reuse the costly [18O]O2 gas; also, the use of [18F]F2 as a labeling agent reduces the labeling rate and radiochemical purity. We developed a stable and practical method for [18F]FBPA synthesis by combining [18F]F2, produced using a [18O]O2 single-use system, and a [18F]CH3COOF labeling agent. Methods: The produced [18F]F2 was optimized, and then [18F]FBPA was synthesized. For passivation of the target box, 0.5% F2 was pre-irradiated in argon. Gaseous products were discarded; the target box was filled with [18O]O2 gas, and then irradiated (first irradiation). Then, the [18O]O2 gas was discarded, 0.05-0.08% F2 in argon was fed into the target box, and it was again irradiated (second irradiation). The [18F]F2 obtained after this was passed through a CH3COONa column, converting it into the [18F]CH3COOF labeling agent, which was then used for [18F]FBPA synthesis. Results: The mean amount of as-obtained [18F]F2 was 55.0 ± 3.3 GBq and that of as-obtained [18F]CH3COOF was 21.6 ± 1.4 GBq after the bombardment. The radioactivity and the radiochemical yield based on [18F]F2 of [18F]FBPA were 4.72 ± 0.34 GBq and 12.2 ± 0.1%, respectively. The radiochemical purity and molar activity were 99.3 ± 0.1% and 231 ± 22 GBq/mmol, respectively. Conclusion: We developed a method for [18F]FBPA production, which is more stable and practical compared with the method using [18O]O2 gas-recycling and [18F]F2 labeling agent.

Fibroblast activation protein targeted therapy using [177Lu]FAPI-46 compared with [225Ac]FAPI-46 in a pancreatic cancer model.

PURPOSE: Fibroblast activation protein (FAP), which has high expression in cancer-associated fibroblasts of epithelial cancers, can be used as a theranostic target. Our previous study used 64Cu and 225Ac-labelled FAP inhibitors (FAPI-04) for a FAP-expressing pancreatic cancer xenograft imaging and therapy. However, the optimal therapeutic radionuclide for FAPI needs to be investigated further. In this study, we evaluated the therapeutic effects of beta-emitter (177Lu)-labelled FAPI-46 and alpha-emitter (225Ac)-labelled FAPI-46 in pancreatic cancer models. METHODS: PET scans (1 h post injection) were acquired in PANC-1 xenograft mice (n = 9) after the administration of [18F]FAPI-74 (12.4 ± 1.7 MBq) for the companion imaging. The biodistribution of [177Lu]FAPI-46 and [225Ac]FAPI-46 were evaluated in the xenograft model (total n = 12). For the determination of treatment effects, [177Lu]FAPI-46 and [225Ac]FAPI-46 were injected into PANC-1 xenograft mice at different doses: 3 MBq (n = 6), 10 MBq (n = 6), 30 MBq (n = 6), control (n = 4) for [177Lu]FAPI-46, and 3 kBq (n = 3), 10 kBq (n = 2), 30 kBq (n = 6), control (n = 7) for [225Ac]FAPI-46. Tumour sizes and body weights were followed. RESULTS: [18F]FAPI-74 showed rapid clearance by the kidneys and high accumulation in the tumour and intestine 1 h after administration. [177Lu]FAPI-46 and [225Ac]FAPI-46 also showed rapid clearance by the kidneys and relatively high accumulation in the tumour at 3 h. Both [177Lu]FAPI-46 and [225Ac]FAPI-46 showed tumour-suppressive effects, with a mild decrease in body weight. The treatment effects of [177Lu]FAPI-46 were relatively slow but lasted longer than those of [225Ac]FAPI-46. CONCLUSION: This study suggested the possible application of FAPI radioligand therapy in FAP-expressing pancreatic cancer. Further evaluation is necessary to find the best radionuclide with shorter half-life, as well as the combination with therapies targeting tumour cells directly.

Advantages of FBPA PET in evaluating early response of anti-PD-1 immunotherapy in B16F10 melanoma-bearing mice: Comparison to FDG PET.

Purpose: PET with L-4-borono-2-[18F] fluoro-phenylalanine (FBPA) was reported to be useful to differentiate malignant tumors and inflammation. Although immunotherapy with immune checkpoint inhibitors (ICIs) has been applied to cancer treatment recently, FDG PET may not be suitable to determine the effect of ICIs because of false-positive findings caused by treatment-related inflammation. In this study, we aimed to demonstrate that FBPA PET allowed detection of the early response of anti-PD-1 immunotherapy in tumor-bearing mice, comparing the results with those of FDG PET. Materials and methods: Mice with B16F10 melanoma tumor xenografts were prepared. Anti-mouse PD-1 antibody or PBS was administered twice intraperitoneally to the tumor-bearing mice on Day 0 (3 days after inoculation) and Day 5 (treatment or control group ). PET/CT imaging was performed twice for each mouse on Day 0 before the anti-PD-1 antibody/PBS administration and on Day 7 using a micro-PET/CT scanner. FBPA and FDG PET/CT studies were conducted separately. SUVmax and the tumor to liver ratio (T/L ratio) were used as parameters exhibiting tumor activity. Tumor uptake volume (TUV) and metabolic tumor volume (MTV) were also calculated for FBPA and FDG, respectively. Changes between pre- and posttreatment SUVmax or T/L ratio were observed using the formula as follows: [(posttreatment parameter values/pretreatment values - 1) × 100] (%). Results: Tumors in TrG were smaller than those in CoG on Day 7. SUVmax and T/L ratio represented no differences between TrG and CoG in FBPA and FDG PET before treatment. FBPA PET on Day 7 demonstrated that SUVmax, T/L ratio, and TUV in TrG were statistically smaller than those in CoG. %T/L ratio and %SUVmax exhibited the same trend in FBPA PET. However, FDG PET on Day 7 revealed no differences in all parameters between TrG and CoG. T/L ratio and %SUVmax in TrG represented larger values than those in CoG without statistical significances. Conclusion: This study demonstrated that FBPA PET allowed detection of the early response of anti-PD-1 immunotherapy in B16F10 melanoma-bearing mice. FDG PET did not detect the response. Further studies are required to determine whether FBPA PET is useful in evaluating the treatment effect of ICIs in humans.

Evaluation of Integrin αvß3 Expression in Murine Xenograft Models: [68Ga]Ga-DOTA-C(RGDfK) PET Study with Immunohistochemical Confirmation.

Tumor blood flow (TBF) is related to drug delivery and hypoxia, both of which can impact the efficacy of anti-cancer therapies. Although integrin αvß3 expression is related to tumor angiogenesis, it remains unclear whether the degree of angiogenesis affects TBF. This study aimed to evaluate the expression of integrin αvß3 in mouse tumor models using [68Ga]Ga-DOTA-c(RGDfK) peptide positron emission tomography (PET) and immunohistochemical staining. PET studies were conducted using mouse C6 glioma models and MIA PaCa-2 (n = 6 each). The [68Ga]Ga-DOTA-c(RGDfK) peptide was injected via the tail vein (2.17 ± 0.28 MBq), and 10 min static PET scans were performed. Immunohistochemical analysis was conducted using an integrin αVß3 antibody. [68Ga]Ga-DOTA-c(RGDfK) peptide PET revealed higher uptake of the radiotracer in C6 gliomas than in MIA PaCa-2 tumors. The mean standardized uptake value was significantly higher in C6 gliomas (0.35 ± 0.058) than in MIA PaCa-2 tumors (0.17 ± 0.045). Histological analysis revealed intense integrin αVß3 expression in the C6 gliomas, whereas the MIA PaCa-2 tumors had low expression levels. This study showed that the expression of integrin αvß3 can be differentiated by the [68Ga]Ga-DOTA-c(RGDfK) peptide, suggesting the potential applicability of this peptide in the evaluation of the relationship between angiogenesis and TBF.

One-pot and one-step automated radio-synthesis of [18F]AlF-FAPI-74 using a multi purpose synthesizer: a proof-of-concept experiment.

BACKGROUND: Fibroblast activation protein (FAP) is overexpressed in the stroma of many types of cancer. [18F]AlF-FAPI-74 is a positron emission tomography tracer with high selectivity for FAP, which has already shown high accumulation within human tumors in clinical studies. However, [18F]AlF-FAPI-74 radiosynthesis has not been optimized using an automated synthesizer. Herein, we report a one-pot and one-step automated radiosynthesis method using a multi purpose synthesizer. RESULTS: Radiosynthesis of [18F]AlF-FAPI-74 was performed using a cassette-type multi purpose synthesizer CFN-MPS200. After the recovery rate of trapped [18F]fluoride onto the anion-exchange cartridge using a small amount of eluent was investigated manually, a dedicated [18F]AlF-FAPI-74 synthesis cassette and synthesis program for one-pot and one-step fluorination was developed. The solutions for the formulation of [18F]AlF-FAPI-74 synthesized using this were evaluated to obtain stable radiochemical purity. The recovery rate of [18F]fluoride with only 300 µL of eluent ranged 90 ± 9% by introduction from the male side and elution from the female side of the cartridge. In automated synthesis, the eluted [18F]fluoride and precursor solution containing aluminum chloride were mixed; then, fluorination was performed in a one-pot and one-step process at room temperature for 5 min, followed by 15 min at 95 °C. As a result, the radioactivity of [18F]AlF-FAPI-74 was 11.3 ± 1.1 GBq at the end of synthesis from 32 to 40 GBq of [18F]fluoride, and its radiochemical yield was 37 ± 4% (n = 10). The radiochemical purity at the end of the synthesis was ≥ 97% for all formulation solutions. When the diluent was saline, the radiochemical purity markedly decreased after 4 h of synthesis. In contrast, with phosphate-buffered saline (pH 7.4) or 10 mM phosphate-buffered saline (pH 6.7) containing 100 mg of sodium ascorbate, the radiochemical purity was stable at 97%. Non-radioactive AlF-FAPI-74 and total impurities, including non-radioactive AlF-FAPI-74, were 0.3 ± 0.1 µg/mL and 2.8 ± 0.6 µg/mL. Ethanol concentration and residual DMSO were 5.5 ± 0.2% and 21 ± 6 ppm, respectively. CONCLUSIONS: We established a one-pot one-step automated synthesis method using a CFN-MPS200 synthesizer that provided high radioactivity and stable radiochemical purity for possible clinical applications.

High detection rate in [18F]PSMA-1007 PET: interim results focusing on biochemical recurrence in prostate cancer patients.

OBJECTIVE: 18F-labeled prostate-specific membrane antigen (PSMA) ligand, [18F]PSMA-1007, has the benefit of a higher synthetic yield and minimal excretion in the urine. High detection efficacy was reported in biochemical recurrence (BCR) of prostate cancer after radical prostatectomy. Thus, we evaluated the preliminary diagnostic utility of [18F]PSMA-1007 PET in patients with prostate cancer, focusing on the BCR which is not detected on conventional imaging. METHODS: We enrolled a total of 28 patients (age 51-79 years) with BCR of prostate cancer. BCR was defined as a continuous increase in PSA after radical prostatectomy or radiation therapy without any apparent recurrent lesions on conventional diagnostic imaging (CT and bone scintigraphy). PSMA-PET scanning was performed approximately 60 min after intravenous injection of [18F]PSMA-1007 (259 ± 37 MBq). PSMA-PET images were evaluated for lesion detection as well as its relation to PSA values and location. RESULTS: Abnormal uptake, which was suspected to be recurrence or metastasis, was detected in 92.9% (26/28) of patients with BCR. The SUVmax was 8.4 ± 6.4 in local recurrence, 11.5 ± 11.8 in pelvic lymph nodes (LN), and 4.1 ± 1.6 in bone metastasis. The detection rates were 66.7% in the PSA group-1 (0.1-0.5 ng/mL), 85.7% in the PSA group-2 (0.5-1.0 ng/mL), and 100% in the PSA group-3 (above 1.0 ng/mL). Among the PET-positive BCR patients (n = 26), local recurrence was detected in 57.7% (15/26), pelvic LN in 42.3% (11/26), and bone metastasis in 15.4% (4/26). In 53% (8/15) of BCR patients who were suspected of local recurrence, focal uptake was detected adjacent to the bladder on [18F]PSMA-1007 PET. This suggested the significant advantage of having minimal physiological urine excretion. CONCLUSIONS: [18F]PSMA-1007 PET showed a high detection rate in recurrent and metastatic lesions. In patients with BCR, its high detection led to suitable treatment strategies, such as salvage radiation therapy or surgical removal of recurrent lymph nodes. TRIAL REGISTRATION: (UMIN Clinical Trials Registry) UMIN000037697.

Individual dosimetry system for targeted alpha therapy based on PHITS coupled with microdosimetric kinetic model.

BACKGROUND: An individual dosimetry system is essential for the evaluation of precise doses in nuclear medicine. The purpose of this study was to develop a system for calculating not only absorbed doses but also EQDX(α/ß) from the PET-CT images of patients for targeted alpha therapy (TAT), considering the dose dependence of the relative biological effectiveness, the dose-rate effect, and the dose heterogeneity. METHODS: A general-purpose Monte Carlo particle transport code PHITS was employed as the dose calculation engine in the system, while the microdosimetric kinetic model was used for converting the absorbed dose to EQDX(α/ß). PHITS input files for describing the geometry and source distribution of a patient are automatically created from PET-CT images, using newly developed modules of the radiotherapy package based on PHITS (RT-PHITS). We examined the performance of the system by calculating several organ doses using the PET-CT images of four healthy volunteers after injecting 18F-NKO-035. RESULTS: The deposition energy map obtained from our system seems to be a blurred image of the corresponding PET data because annihilation γ-rays deposit their energies rather far from the source location. The calculated organ doses agree with the corresponding data obtained from OLINDA 2.0 within 20%, indicating the reliability of our developed system. Test calculations by replacing the labeled radionuclide from 18F to 211At suggest that large dose heterogeneity in a target volume is expected in TAT, resulting in a significant decrease of EQDX(α/ß) for higher-activity injection. CONCLUSIONS: As an extension of RT-PHITS, an individual dosimetry system for nuclear medicine was developed based on PHITS coupled with the microdosimetric kinetic model. It enables us to predict the therapeutic and side effects of TAT based on the clinical data largely available from conventional external radiotherapy.

Diagnostic Accuracy of 18F-PSMA-1007 PET/CT Imaging for Lymph Node Staging of Prostate Carcinoma in Primary and Biochemical Recurrence.

Prostate-specific membrane antigen (PSMA)-ligand PET/CT is performed on patients with prostate cancer to stage the disease initially or to identify sites of recurrence after definitive therapy. On the basis of clinical results, 18F-PSMA-1007 is a promising PSMA PET tracer, but detailed histologic confirmation has been lacking. Methods: Ninety-six patients with prostate cancer underwent 18F-PSMA-1007 PET/CT followed by either radical prostatectomy with lymphadenectomy or salvage lymphadenectomy. The histologic findings of PSMA PET-positive nodes were analyzed retrospectively. A lesion-based and patient-based analysis was performed comparing all positive lesions and only lesions larger than 3 mm on histopathology. Results: Of the patients, 90.6% received 18F-PSMA-1007 PET/CT for staging before the primary treatment, whereas 9.4% underwent imaging for biochemical recurrence. In 34.4% of the cohort, positive lymph nodes were present on imaging. In total, 1,746 lymph nodes were dissected in 96 patients. 18F-PSMA-1007 PET had a lesion-based sensitivity of 81.7%, a specificity of 99.6%, a positive predictive value of 92.4%, and a negative predictive value of 98.9% for detecting positive lymph nodes larger than 3 mm. In the analysis of all malignant nodes regardless of size, the overall sensitivity, specificity, positive predictive value, and negative predictive value on lesion-based analysis were 71.2%, 99.5%, 91.3%, and 97.9%, respectively. The patient-based analysis showed a sensitivity of 85.9% and a specificity of 99.5% for lymph nodes larger than 3 mm. Conclusion:18F-PSMA-1007 PET/CT reliably detects malignant lymph nodes and has an exceptional specificity of more than 99% for nodal metastases.

18F-FBPA PET in Sarcoidosis: Comparison to Inflammation-Related Uptake on FDG PET.

A 68-year-old man with sarcoidosis showed high F-FDG uptake in the mediastinal and hilar lymph nodes on F-FDG PET, suggesting active inflammation. F-fluoro-boronophenylalanine (FBPA) PET showed no significant uptake in the mediastinal and hilar lymph nodes, suggesting its cancer specificity as a substrate of L-type amino acid transporter 1. F-fluoro-boronophenylalanine PET can be used for precise evaluation in oncology when the differentiation between inflammation and metastasis is inconclusive on F-FDG PET.

Automated [18F]PSMA-1007 production by a single use cassette-type synthesizer for clinical examination.

BACKGROUND: [18F]PSMA-1007, a positron emission tomography (PET) tracer, specifically targets prostate-specific membrane antigen (PSMA), which is highly expressed in prostate cancer. PSMA-PET is effective especially for regional detection of biochemical recurrence, which significantly affects patient management. Herein, we established and optimized a one-step radiolabeling protocol to separate and purify [18F]PSMA-1007 with a CFN-MPS200 synthesizer for clinical application. RESULTS: A dedicated single use cassette and synthesis program for [18F]PSMA-1007 was generated using a single-step method for direct precursor radiolabeling. In the cassette, three tube types (fluoro-elastomer, PharMed® BPT, silicone) and two different precursor salts (trifluoroacetic acid or acetic acid) were compared for optimization. Furthermore, three-lot tests were performed under optimized conditions for quality confirmation. Activity yields and mean radiochemical purity of [18F]PSMA-1007 were > 5000 MBq and 95%, respectively, at the end of synthesis, and the decay-corrected mean radiochemical yield from all three cassettes was approximately 40% using a trifluoroacetic acid salt precursor. Fluoro-elastomer tubings significantly increased the amount of non-radioactive PSMA-1007 (8.5 ± 3.1 µg/mL) compared to those with other tubings (0.3 µg/mL). This reduced the molar activity of [18F]PSMA-1007 synthesized in the cassette assembled by fluoro-elastomer tubings (46 GBq/µmol) compared to that with PharMed® BPT and silicone tubings (1184 and 1411 GBq/µmol, respectively). Residual tetrabutylammonium, acetonitrile, and dimethyl sulfoxide levels were <  2.6 µg/mL, < 8 ppm, and <  11 ppm, respectively, and ethanol content was 8.0-8.1% in all three cassettes and two different salts. Higher activity yields, radiochemical purities, and decay-corrected radiochemical yields were obtained using an acetic acid salt precursor rather than a trifluoroacetic acid salt precursor (7906 ± 1216 MBq, 97% ± 0%, and 56% ± 4%). In the three-lot tests under conditions optimized with silicone cassettes and acetic acid salt precursor, all quality items passed the specifications required for human use. CONCLUSIONS: We successfully automated the production of [18F]PSMA-1007 for clinical use and optimized synthesis procedures with a CFN-MPS200 synthesizer using a silicone cassette and acetic acid salt precursor. Cassette availability will facilitate a wide spread use of [18F]PSMA-1007-PET, leading to an effective prostate cancer management.

Evaluation of D-isomer of 18F-FBPA for oncology PET focusing on the differentiation of glioma and inflammation.

OBJECTIVES: L-4-borono-2-18F-fluoro-phenylalanine (L-[18F]FBPA), a substrate of L-type amino acid transporter 1 (LAT1), is a tumor-specific probe used in positron emission tomography (PET). On the other hand, it has not been examined whether another isomer D-[18F]FBPA accumulates specifically in the tumor. Here, we compared the accumulation of D-[18F]FBPA in C6 glioma and inflammation to evaluate the performance of D-[18F]FBPA as a tumor-specific probe. METHODS: HEK293-LAT1 and HEK293-LAT2 cells were tested for [14C]-leucine or [14C]-alanine transport, and IC50 values of L- and D-FBPA were evaluated in both cell types. PET was conducted in rat xenograft model of C6 glioma with LAT1 expression and model of turpentine oil-induced subcutaneous inflammation (n=10 for both models). The concentrations of D-[18F]FBPA were compared between glioma and inflammatory lesion using standardized uptake value (SUV). RESULTS: In contrast to L-FBPA, which inhibited substrate uptake in both HEK293-LAT1 and -LAT2 cells, D-FBPA showed no inhibitory effect on both cells, suggesting low transporter selectivity of D-[18F]FBPA against LAT1 and LAT2. Static PET analysis showed low accumulation of D-[18F]FBPA in C6 glioma and inflammatory lesion (SUVmax=0.80±0.16, 0.56±0.09, respectively). Although there was a statistical difference in SUVmax between these tissues, it was difficult to distinguish glioma from inflammation on the PET image due to its low uptake level. Therefore, it was suggested that D-[18F]FBPA is not a suitable tumor-specific probe for oncology PET in contrast to L-[18F]FBPA. CONCLUSION: This study demonstrated that D-[18F]FBPA is not a LAT1-specific PET probe and shows low uptake in C6 glioma, indicating its unsuitability as a tumor diagnosis PET probe.

Evaluation of the total distribution volume of 18F-FBPA in normal tissues of healthy volunteers by non-compartmental kinetic modeling.

OBJECTIVE: Boron neutron capture therapy (BNCT) is a noninvasive radiation therapy method for cancer treatment. In BNCT, 4-borono-2-[18F]-fluoro-L-phenylalanine (18F-FBPA) PET has been employed to estimate 10B accumulation in target tumors and normal tissues if 10B borono-L-phenylalanine (10B-BPA) is used as a boron carrier. The purpose of the current study was to evaluate the total distribution volume (Vt) of 18F-FBPA in normal organs of healthy volunteers by kinetic analysis and to estimate boron concentration in normal organs for the therapeutic dose of 10B-BPA using obtained Vt values. METHODS: Six healthy volunteers were injected with 18F-FBPA (3-5 MBq/kg), and 7 PET-CT scans were performed subsequently. 18F-FBPA radioactivity in whole blood and plasma was measured before, and eight times after the injection. PET images were analyzed by PMOD software. Twelve volumetric regions of interest including the brain, heart, right lung, spleen, liver, parotid salivary glands, esophagus, stomach, pancreas, intestines, and bone marrow were drawn manually for each subject and analyzed with the Logan plot and two Ichise multilinear analyses (MA1 and MA2). The better model was defined by several goodness-of-fit parameters and residual distribution. After Vt values had been derived, boron concentration was estimated in ppm for the 10B-BPA-fructose (10B-BPA-fr) dose 30 g 1 and 2 h post-injection using Vt and interpolated plasma activity data. RESULTS: The Ichise MA2 model showed the best fit among all models. Akaike Information Criterion (AIC) was the lowest for the Ichise's MA2 in all regions (mean AIC value - 14.0) comparing to the other models (Logan plot mean AIC 31.4; Ichise MA1 model mean AIC - 4.2). Mean Vt values of the Ichise MA2 model ranged from 0.94 ± 0.14 ml/ml in the pancreas to 0.16 ± 0.02 ml/ml in the right lung. Estimated boron concentration for 10B-BPA-fr had the highest value in the pancreas (14.0 ± 1.9 ppm 1 h after, and 5.7 ± 1.7 ppm 2 h after the 18F-FBPA administration) and the lowest value in the right lung (2.4 ± 0.3 ppm 1 h, and 1.0 ± 0.3 ppm 2 h post-injection). CONCLUSION: The 10B concentration in normal tissues was best estimated using Vt values of 18F-FBPA with the Ichise multilinear analysis 2 (MA2). TRAIL REGISTRY: The UMIN clinical trial number: UMIN000022850.

Distribution of LAT1-targeting PET tracer was independent of the tumor blood flow in rat xenograft models of C6 glioma and MIA PaCa-2.

OBJECTIVE: L-type amino acid transporter 1 (LAT1) is strongly expressed on the cell membrane in various types of human cancer cells, while being minimally expressed in normal or inflammatory tissues. Therefore, LAT1-targeting PET tracers have been developed for cancer-specific imaging. The purpose of this study was to study the distribution of two LAT1-targeting PET tracers, L-4-borono-2-18F-fluoro-phenylalanine (18F-FBPA) and L-3-18F-alpha-methyl tyrosine (18F-FAMT), in relation to the tumor blood flow, using rat xenograft models. METHODS: Rat tumor xenograft models of C6 glioma (n = 4; tumors = 8) and MIA PaCa-2 (pancreatic cancer) (n = 4; tumors = 6) were used. The expressions of LAT1 and CD98hc were evaluated by both immunofluorescence staining and western blot analysis. Dynamic PET was performed after injection of 18F-FAMT or 18F-FBPA (scan duration = 70 min) following 15O-water PET (scan duration = 10 min). The PET data were subjected to kinetic analyses, and the K1, k2, and total distribution volume (Vt) were calculated using the one-tissue compartment model. The accumulation of the LAT1 tracers was expressed in terms of their Vt. Tumor blood flow (TBF) was represented by the K1 value in 15O-water PET. RESULTS: LAT1/CD98hc expression was confirmed in both xenografts by immunofluorescence staining. Western blot analysis showed higher functional expression of LAT1 in the C6 glioma cells as compared to the MIA PaCa-2 cells (C6 glioma/MIA PaCa-2 relative expression ratio = 1.70). The Vt values of both 18F-FBPA and 18F-FAMT were significantly higher in the C6 glioma xenografts than in the MIA PaCa-2 xenografts (C6 glioma: 2.27 ± 0.35 and 2.03 ± 0.23, respectively; MIA PaCa-2: 1.28 ± 0.26 and 1.35 ± 0.15, respectively). Meanwhile, there was no significant correlation of the Vt value of either 18F-FBPA or 18F-FAMT with the TBF, in either the C6 glioma or the MIA PaCa-2 xenografts. CONCLUSIONS: This study revealed that total distribution volumes of the LAT1-targeting PET tracers 18F-FBPA and 18F-FAMT were independent of the tumor blood flow and might reflect the functional expression levels of LAT1 in the C6 glioma and MIA PaCa-2 xenograft models.

Impact of 18F-PSMA-1007 Uptake in Prostate Cancer Using Different Peptide Concentrations: Preclinical PET/CT Study on Mice.

PET radioligands with low molar activity (MA) may underestimate the quantity of the target of interest because of competitive binding of the target with unlabeled ligand. The aim of this study was to evaluate the change in the whole-body distribution of 18F-PSMA-1007 targeting prostate-specific membrane antigen (PSMA) when solutions with different peptide concentrations are used. Methods: Mouse xenograft models of LNCaP (PSMA-positive prostate cancer) (n = 18) were prepared and divided into 3 groups according to the peptide concentration injected: a high-MA group (1,013 ± 146 GBq/µmol; n = 6), a medium-MA group (100.7 ± 23.1 GBq/µmol; n = 6), and a low-MA group (10.80 ± 2.84 GBq/µmol; n = 6). Static PET scans were performed 1 h after injection (scan duration, 10 min). SUVmean in tumor and normal organs was compared by the multiple-comparison test. Immunohistochemical staining and Western blot analysis were performed to confirm expression of PSMA in tumor, salivary gland, and kidney. Results: The low-MA group (SUVmean, 1.12 ± 0.30) showed significantly lower uptake of 18F-PSMA-1007 in tumor than did the high-MA group (1.97 ± 0.77) and the medium-MA group (1.81 ± 0.57). On the other hand, in salivary gland, both the low-MA group (SUVmean, 0.24 ± 0.04) and the medium-MA group (0.57 ± 0.08) showed significantly lower uptake than the high MA group (1.27 ± 0.28). The tumor-to-salivary gland SUVmean ratio was 1.73 ± 0.55 in the high-MA group, 3.16 ± 0.86 in the medium-MA group, and 4.78 ± 1.29 in the low-MA group. The immunohistochemical staining and Western blot analysis revealed significant overexpression of PSMA in tumor and low expression in salivary gland and kidney. Conclusion: A decrease in the MA level of the injected 18F-PSMA-1007 solution resulted in decreased uptake in tumor and, to a greater degree, in normal salivary gland. Thus, there is a possibility of minimizing the adverse effects in salivary gland by setting an appropriate MA level in PSMA-targeting therapy.