Imaging Characteristics and First Experience of [<Superscript>68</Superscript>Ga]THP-PSMA,a Novel Probe for Rapid Kit-Based Ga-68 Labeling and PET Imaging: Comparative Analysis with [<Superscript>68</Superscript>Ga]PSMA I&amp;T

Purpose

[⁶⁸Ga]Trishydroxypyridinone (THP)–prostate-specific membrane antigen (PSMA) is a novel tracer that can be labeled in one step by cold reconstitution of a kit with unprocessed generator eluate, targeting PSMA via the lysine-urea-glutamate (KuE) motif. The aim of this study was to evaluate the human imaging characteristics of [⁶⁸Ga]THP-PSMA.

Procedures

[⁶⁸Ga]THP-PSMA positron emission tomography (PET)/x-ray computed tomography (CT) was performed in 25 patients with biochemical recurrence after radical prostatectomy for prostate cancer. Urinary and biliary excretion and tumor lesion uptake were quantified using standardized uptake values (SUVs). Imaging characteristics were assessed in terms of non-target organ uptake, background activity, target-to-background ratios (TBRs) of tumor lesions, and frequency of bladder halo artifacts. Findings were compared to a matched cohort of 25 patients undergoing PET/CT with the established agent [⁶⁸Ga]PSMA I&T.

Results

Physiologic uptake of [⁶⁸Ga]THP-PSMA was significantly lower in salivary glands (P?<?0.0001), liver (P?<?0.0001), spleen (P?<?0.0001), and kidneys (P?<?0.0001) than with [⁶⁸Ga]PSMA I&T. While biliary tracer excretion of [⁶⁸Ga]THP-PSMA was negligible, urinary tracer excretion of [⁶⁸Ga]THP-PSMA was fast, and significantly higher than for [⁶⁸Ga]PSMA I&T, contributing to a higher frequency of bladder artifacts. Malignant lesion uptake of [⁶⁸Ga]THP-PSMA assessed as either SUV or TBR was significantly lower than with [⁶⁸Ga]PSMA I&T.

Conclusion

[⁶⁸Ga]THP-PSMA yields suitable in vivo uptake characteristics. The simplified synthesis method for [⁶⁸Ga]THP-PSMA may facilitate wider application and higher patient throughput with PSMA imaging. However, direct intraindividual comparison studies are needed to assess the relative performance of [⁶⁸Ga]THP-PSMA vs other PSMA ligands in terms of clinical detection rate and image quality.

     

Preliminary PET/CT Imaging with Somatostatin Analogs [<Superscript>68</Superscript>Ga]DOTAGA-TATE and [<Superscript>68</Superscript>Ga]DOTAGA-TOC

Purpose

Somatostatin receptor positron emission tomography/X-ray computed tomography (SSTR-PET/CT) is a well-established technique for staging and detection of neuroendocrine tumors (NETs). Ga-68-labeled DOTA-conjugated octreotide analogs are the privileged radiotracers for diagnosis and therapeutic monitoring of NETs. Hence, we were interested in assessing the influence of promising, newer variant DOTAGA on the hydrophilicity, pharmacokinetics, and lesion pick-up of somatostatin analogs. Herein, the potential of ([⁶⁸Ga]DOTAGA, Tyr³, Thr⁸) octreotide ([⁶⁸Ga]DOTAGA-TATE) and ([⁶⁸Ga]DOTAGA, Tyr³) octreotide ([⁶⁸Ga]DOTAGA-TOC) as NET imaging agents has been investigated.

Procedures

Amenability of [⁶⁸Ga]DOTAGA-(TATE/TOC) to kit-type formulation has been demonstrated. Biodistribution studies were carried out in normal rats at 1 h post-injection (p.i.). [⁶⁸Ga]DOTAGA-(TATE/TOC) PET/CT scans were carried out in patients (70–170 MBq, 1 h p.i.) with histologically confirmed well-differentiated NETs.

Results

[⁶⁸Ga]DOTAGA-TATE exhibited hydrophilicity similar to [⁶⁸Ga]DOTA-TATE (log P = ?3.51 vs ?3.69) whereas [⁶⁸Ga]DOTAGA-TOC was more hydrophilic than [⁶⁸Ga]DOTA-TOC (log P = ?3.27 vs ?2.93). [⁶⁸Ga]DOTAGA-TATE and [⁶⁸Ga]DOTA-TATE showed almost identical blood and kidney uptake in normal rats whereas significantly fast clearance (p < 0.05) of [⁶⁸Ga]DOTAGA-TATE was observed from other non-specific organs (liver, lungs, spleen, intestine). [⁶⁸Ga]DOTAGA-TOC also demonstrated rapid clearance from blood and kidneys (p < 0.05) in comparison to [⁶⁸Ga]DOTA-TOC. The metastatic lesions in NET patients were well identified by [⁶⁸Ga]DOTAGA-TATE and [⁶⁸Ga]DOTAGA-TOC.

Conclusion

The phenomenal analogy was observed between [⁶⁸Ga]DOTAGA-TATE and [⁶⁸Ga]DOTA-TATE as well as between [⁶⁸Ga]DOTAGA-TOC and [⁶⁸Ga]DOTA-TOC in biodistribution studies in rats. The good lesion detection ability of the two radiotracers indicates their potential as NET imaging radiotracers.

     

Repeatability of [<Superscript>68</Superscript>Ga]DKFZ11-PSMA PET Scans for Detecting Prostate-specific Membrane Antigen-positive Prostate Cancer

Purpose

We studied the effect of varying specific activity of [⁶⁸Ga]DKFZ-PSMA11 ([⁶⁸Ga]DP11) on repeated imaging of prostate-specific membrane antigen-positive (PSMA+) xenograft tumors.

Procedures

Athymic nude mice bearing PC3-PIP (PSMA+) and PC3 (PSMA?) bilateral flank tumors were assessed to study intra- and inter-day repeatability of [⁶⁸Ga]DP11 imaging in mice administered [⁶⁸Ga]DP11 or [⁶⁷Ga]DP11 (as a dilution tracer) using imaging and biodistribution studies.

Results

Region of interest (ROI) analysis of the [⁶⁸Ga]DP11 imaging study indicated that the uptake was constant on the same day or consecutive days. Prior imaging with [⁶⁸Ga]DP11 did not significantly influence the subsequent uptake of [⁶⁸Ga]DP11. Uptake of [⁶⁸Ga]DP11 (60 min) and [⁶⁷Ga]DP11 (24 h) in PC3-PIP tumors was 12.37 ± 4.19 %ID/g and 12.49 ± 6.88 %ID/g, respectively; [⁶⁸Ga]DP11 was 13.83 ± 3.77 and 17.76 ± 1.84 on same-day and 15.98 ± 5.82 %ID/g on second-day imaging.

Conclusions

This study demonstrates that [⁶⁸Ga]DP11, in a given PSMA+ lesion, is constant under several same-day or serial-day imaging conditions.

     

[<Superscript>68</Superscript>Ga]PSMA-HBED-CC Uptake in Osteolytic,Osteoblastic, and Bone Marrow Metastases of Prostate Cancer Patients

Purpose

The aim of this study was to evaluate potential differences in “Glu-NH-CO-NH-Lys” radio-labeled with [⁶⁸Ga]gallium N,N-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N-diacetic acid ([⁶⁸Ga]PSMA-HBED-CC) uptake in osteolytic, osteoblastic, mixed, and bone marrow metastases in prostate cancer (PC) patients.

Procedures

This retrospective study was approved by the local ethics committee. Patients who received [⁶⁸Ga]PSMA-HBED-CC positron emission tomography/computed tomography ([⁶⁸Ga]PSMA-PET/CT) with at least one positive bone metastasis were included in this study. Only patients who have not received systemic therapy for their PC were included. Bone metastases had to be confirmed by at least one other imaging modality or follow-up investigation. The maximum standardized uptake value (SUV_max) and mean Hounsfield units (HU_mean) of each metastasis were measured. Based on CT, each metastasis was classified as osteolytic (OL), osteoblastic (OB), bone marrow (BM), or mixed (M).

Results

One hundred fifty-four bone metastases in 30 patients were evaluated. Eighty out of 154 (51.9%) metastases were classified as OB, 21/154 (13.6%) as OL, 23/154 (14.9%) as M, and 30/154 (19.5%) as BM. The SUV_max for the different types of metastases were 10.6 ± 7.07 (OB), 24.0 ± 19.3 (OL), 16.0 ± 21.0 (M), and 14.7 ± 9.9 (BM). The SUV_max of OB vs. OL and OB vs. BM metastases differed significantly (p ≤ 0.025). A significant negative correlation between HU_mean and SUV_max (r = ?0.23, p < 0.05) was measured.

Conclusions

[⁶⁸Ga]PSMA-HBED-CC uptake is higher in osteolytic and bone marrow metastases compared to osteoblastic metastases. Information derived from [⁶⁸Ga]PSMA-PET and CT complement each other for the reliable diagnosis of the different types of bone metastases in PC patients.

     

Application of Cu-64 NODAGA-PSMA PET in Prostate Cancer

Introduction

The high diagnostic potential of ⁶⁴Cu-PSMA PET–CT imaging was clinically investigated in prostate cancer patients with recurrent disease and in the primary staging of selected patients with advanced local disease. The aim of our study is to assess the uptake behavior in the clinical setting of 64Copper Prostate-Specific Membrane Antigen (⁶⁴Cu PSMA) Positron Emission Tomography/Computed Tomography (PET/CT) in prostate cancer.

Methods

A retrospective study was performed in 23 patients with intermediate, high risk and progressive disease at primary staging of prostate cancer. All patients underwent ⁶⁴Cu-PSMA PET. Overall, 250 MBq (4 MBq per kg bodyweight, range 230–290 MBq) of ⁶⁴Cu-NODAGA PSMA was intravenously applied. PET images were performed 30 min (pelvis and abdomen) and 1–2 h post-injection (skull base to mid-thigh). Maximum standardized uptake values (SUVmax) were measured in the organs with high physiological uptake such as liver and kidney, and, additionally, background activity was measured in the gluteal area and in suspected tumor lesions using a HERMES workstation.

Results

PSMA uptake was detected in prostate bed in nine patients, in six patients in distant metastases (bone, lung and liver) and in nine patients in lymph nodes. Of 23 patients, 5 (20.8%) did not show any focal pathological uptake in the whole body. The number of sites (prostate bed, lymph nodes, distant metastases) with positive PSMA uptake was significantly associated with PSA values before imaging (P = 0.0032). The ⁶⁴Cu PSMA uptake increased significantly from 30 min to 1–3 h post-injection (Wilcoxon signed rank test, P?=?0.002).

Conclusions

⁶⁴Cu NODAGA-PSMA PET is a promising imaging tool in the detection of residual disease in patients with recurrent or primary progressive prostate cancer. Furthermore, the increased tracer uptake over time indicates in vivo stability of the diagnostic radiopharmaceutical.

     

Tumor Targeting <Emphasis Type="Italic">via</Emphasis> Sialic Acid: [<Superscript>68</Superscript>Ga]DOTA-en-pba as a New Tool for Molecular Imaging of Cancer with PET

Purpose

The aim of this study was to demonstrate the potential of Ga-68-labeled macrocycle (DOTA-en-pba) conjugated with phenylboronic vector for tumor recognition by positron emission tomography (PET), based on targeting of the overexpressed sialic acid (Sia).

Procedures

The imaging reporter DOTA-en-pba was synthesized and labeled with Ga-68 at high efficiency. Cell binding assay on Mel-C and B16-F10 melanoma cells was used to evaluate melanin production and Sia overexpression to determine the best model for demonstrating the capability of [⁶⁸Ga]DOTA-en-pba to recognize tumors. The in vivo PET imaging was done with B16-F10 tumor-bearing SCID mice injected with [⁶⁸Ga]DOTA-en-pba intravenously. Tumor, blood, and urine metabolites were assessed to evaluate the presence of a targeting agent.

Results

The affinity of [⁶⁸Ga]DOTA-en-pba to Sia was demonstrated on B16-F10 melanoma cells, after the production of melanin as well as Sia overexpression was proved to be up to four times higher in this cell line compared to that in Mel-C cells. Biodistribution studies in B16-F10 tumor-bearing SCID mice showed blood clearance at the time points studied, while uptake in the tumor peaked at 60 min post-injection (6.36?±?2.41 % ID/g). The acquired PET images were in accordance with the ex vivo biodistribution results. Metabolite assessment on tumor, blood, and urine samples showed that [⁶⁸Ga]DOTA-en-pba remains unmetabolized up to at least 60 min post-injection.

Conclusions

Our work is the first attempt for in vivo imaging of cancer by targeting overexpression of sialic acid on cancer cells with a radiotracer in PET.

     

To Explore a Representative Hypoxic Parameter to Predict the Treatment Response and Prognosis Obtained by [<Superscript>18</Superscript>F]FMISO-PET in Patients with Non-small Cell Lung Cancer

Purpose

To explore a representative hypoxic parameter to predict the treatment response and prognosis for [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) positron emission tomography (PET)/X-ray computed tomography (CT) in patients with non-small cell lung cancer (NSCLC).

Procedures

Twenty-nine patients with NSCLC underwent FMISO-PET scans before chemoradiotherapy (CRT). The maximum standard uptake values (SUVmax) in the tumor, normal lung, aortic arch, and vertical ridge muscle were measured, and the tumor-to-lung (T/L) ratios, tumor-to-blood (T/B) ratios, ands tumor-to-muscle (T/M) ratios were calculated and analyzed. Fractional hypoxic volume (FHV) was expressed as percentage of hypoxic volume.

Results

SUVmax, T/L ratio, T/B ratio, and FHV were all significantly different between the responders and the non-responders (SUVmax, 2.07?±?0.53 vs. 2.61?±?0.69, P?=?0.026; T/L ratio, 3.16?±?0.85 vs. 4.09?±?1.46, P?=?0.047; T/B ratio, 1.27?±?0.20 vs. 1.48?±?0.32, P?=?0.042; 38.92?±?18.47 vs. 52.91?±?11.29 %, P?=?0.020). However, the T/M ratio was not significantly different between the two populations (1.46?±?0.31 vs. 1.67?±?0.33, P?=?0.098). The correlation ratio between hypoxic parameters and treatment responses ranged from high to low as FHV (r?=?0.412); SUVmax (r?=?0.400); T/L ratio (r?=?0.379), P?<?0.05; and T/B ratio (r?=?0.355), P?=?0.059. According to the area under curve (AUC) to predict response, the hypoxic parameters were arranged as FHV (AUC?=?0.748), SUVmax (AUC?=?0.731), T/L ratio (AUC?=?0.719), and T/B ratio (AUC?=?0.705). Binary logistic regression analyses showed that FHV was the only independent predictor for treatment response with the P value of 0.038. In the progression-free survival (PFS) prediction, both FHV and SUVmax reached statistical significance by Kaplan–Meier plots (FHV, 46.99 %, P?=?0.010; SUVmax, 1.99, P?=?0.046) while only FHV was the independent prognostic factor in multivariate analysis by Cox proportional hazard model (P?=?0.037).

Conclusion

FHV may be a representative hypoxic parameter to predict the CRT response and PFS in patients with NSCLC.

     

Assessing Glomerular Filtration in Small Animals Using [<Superscript>68</Superscript>Ga]DTPA and [<Superscript>68</Superscript>Ga]EDTA with PET Imaging

Purpose

Determining the glomerular filtration rate (GFR) is essential for clinical medicine but also for pre-clinical animal studies. Functional imaging using positron emission tomography (PET) allows repetitive almost non-invasive measurements. The aim of the study was the development and evaluation of easily synthesizable PET tracers for GFR measurements in small animals.

Procedures

Diethylenetriaminepentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) were labeled with Ga-68. The binding to blood cells and plasma proteins was tested in vitro. The distribution of the tracers in rats was analyzed by PET imaging and ex vivo measurements. From the time-activity-curve of the blood compartment (heart) and the total tracer mass excreted by the kidney, the GFR was calculated. These values were compared directly with the inulin clearance in the same animals.

Results

Both tracers did not bind to blood cells. [⁶⁸Ga]DPTA but not [⁶⁸Ga]EDTA showed strong binding to plasma proteins. For this reason, [⁶⁸Ga]DPTA stayed much longer in the blood and only 30 % of the injected dose was eliminated by the kidney within 60 min whereas the excretion of [⁶⁸Ga]EDTA was 89 ± 1 %. The calculated GFR using [⁶⁸Ga]EDTA was comparable to the measured inulin clearance in the same animal. Using [⁶⁸Ga]-DPTA, the measurements led to values which were 80 % below the normal GFR. The results also revealed that definition of the volume of interest for the blood compartment affects the calculation and may lead to a slight overestimation of the GFR.

Conclusions

[⁶⁸Ga]EDTA is a suitable tracer for GFR calculation from PET imaging in small animals. It is easy to be labeled, and the results are in good accordance with the inulin clearance. [⁶⁸Ga]DTPA led to a marked underestimation of GFR due to its strong binding to plasma proteins and is therefore not an appropriate tracer for GFR measurements.

     

Comparison of <Superscript>11</Superscript>C-4DST and <Superscript>18</Superscript>F-FDG PET/CT imaging for advanced renal cell carcinoma: preliminary study

Purpose

4′-[Methyl-¹¹C]-thiothymidine (4DST) has been developed as an in vivo cell proliferation marker based on its DNA incorporation mechanism. This study evaluated the potential of 4DST PET/CT for imaging cellular proliferation in advanced clear cell renal cell carcinoma (RCC), compared with FDG PET/CT. Both 4DST and FDG uptake were compared with biological findings based on surgical pathology.

Methods

Five patients (3 men and 2 women; mean (±SD) age 64.8 ± 11.0 years) with a single RCC (mean diameter: 9.3 ± 3.2 cm) were examined by PET/CT using 4DST and FDG. The dynamic emission scan of 4DST for RCC over 35 min followed by a static emission scan of the body for 4DST and FDG. Then we compared the maximum standardized uptake value (SUVmax) of 20 areas of RCC on both 4DST and FDG images with (1) the Ki-67 index of cellular proliferation (2) Fuhrman grade system for nuclear grade (G) in RCC and (3) pathological phosphorylated grade of mammalian target of rapamycin (pmTOR).

Results

All patient cases showed clear uptake of FDG and 4DST in RCC tumors, with mean 4DST SUVmax of 7.3 ± 2.2 (range 4.3–9.4) and mean FDG SUVmax of 6.0 ± 2.8 (range 3.4–10.4). The correlation coefficient between SUVmax and Ki-67 index was higher with 4DST (r = 0.61) than with FDG (r = 0.43). Tumor 4DST uptake (G0: 1.4, G2: 2.6, G2 5.6, G4: 5.7) and tumor FDG uptake (G0: 1.8, G2: 2.9, G2 3.7, G4: 4.1) were both related to Fuhrman grade system. The 4DST uptake increased as the pmTOR grade increases (G0: 3.1, G1: 4.8, G2: 4.7, G3: 6.2); in contrast FDG uptake was unrelated to pmTOR grade (G0: 2.8, G2: 4.0, G2 3.3, G4: 3.6).

Conclusion

A higher correlation with the proliferation of RCC was observed for 4DST than for FDG. The 4DST uptake exhibits the possibility to predict pmTOR grade, indicating that 4DST has potential for the evaluation of therapeutic effect with mTOR inhibitor in patients with RCC.

     

Targeting PSMA with a Cu-64 Labeled Phosphoramidate Inhibitor for PET/CT Imaging of Variant PSMA-Expressing Xenografts in Mouse Models of Prostate Cancer

Purpose

Prostate-specific membrane antigen (PSMA) is highly up-regulated in prostate tumor cells, providing an ideal target for imaging applications of prostate cancer. CTT-1297 (IC₅₀?=?27 nM) is an irreversible phosphoramidate inhibitor of PSMA that has been conjugated to the CB-TE1K1P chelator for incorporation of Cu-64. The resulting positron emission tomography (PET) agent, [⁶⁴Cu]ABN-1, was evaluated for selective uptake both in vitro and in vivo in PSMA-positive cells of varying expression levels. The focus of this study was to assess the ability of [⁶⁴Cu]ABN-1 to detect and distinguish varying levels of PSMA in a panel of prostate tumor-bearing mouse models.

Procedures

CTT-1297 was conjugated to the CB-TE1K1P chelator using click chemistry and radiolabeled with Cu-64. Internalization and binding affinity of [⁶⁴Cu]ABN-1 was evaluated in the following cell lines having varying levels of PSMA expression: LNCaP late-passage?>?LNCaP early passage?≈?C4-2B?>?CWR22rv1 and PSMA-negative PC-3 cells. PET/X-ray computed tomography imaging was performed in NCr nude mice with subcutaneous tumors of the variant PSMA-expressing cell lines.

Results

[⁶⁴Cu]ABN-1 demonstrated excellent uptake in PSMA-positive cells in vitro, with ～80 % internalization at 4 h for each PSMA-positive cell line with uptake (fmol/mg) correlating to PSMA expression levels. The imaging data indicated significant tumor uptake in all models. The biodistribution for late-passage LNCaP (highest PSMA expression) demonstrated the highest specific uptake of [⁶⁴Cu]ABN-1 with tumor-to-muscle and tumor-to-blood ratios of 30?±?11 and 21?±?7, respectively, at 24 h post-injection. [⁶⁴Cu]ABN-1 cleared through all tissues except for PSMA-positive kidneys.

Conclusion

[⁶⁴Cu]ABN-1 demonstrated selective uptake in PSMA-positive cells and tumors, which correlated to the level of PSMA expression. The data reported herein suggest that [⁶⁴Cu]ABN-1 will selectively target and image variant PSMA expression and in the future will serve as a non-invasive method to follow the progression of prostate cancer in men.

     

A Feasibility Study Showing [<Superscript>68</Superscript>Ga]Citrate PET Detects Prostate Cancer

Purpose

The management of advanced or recurrent prostate cancer is limited in part by the lack of effective imaging agents. Metabolic changes in prostate cancer have previously been exploited for imaging, culminating in the recent US FDA approval of [¹¹C]choline for the detection of subclinical recurrent disease after definitive local therapy. Despite this milestone, production of [¹¹C]choline requires an on-site cyclotron, limiting the scope of medical centers at which this scan can be offered. In this pilot study, we tested whether prostate cancer could be imaged with positron emission tomography (PET) using [⁶⁸Ga]citrate, a radiotracer that targets iron metabolism but is produced without a cyclotron.

Procedures

Eight patients with castrate-resistant prostate cancer were enrolled in this single-center feasibility study. All patients had evidence of metastatic disease by standard of care imaging [X-ray computed tomography (CT), bone scan, or magnetic resonance imaging (MRI)] prior to PET with [⁶⁸Ga]citrate. Patients were intravenously injected with increasing doses of [⁶⁸Ga]citrate (136.9 to a maximum of 259 MBq). Uptake time was steadily increased from 1 h to approximately 3.5 h for the final 4 patients, and all patients were imaged with a PET/MRI. Qualitative and semi-quantitative (maximum standardized uptake value (SUV_max)) assessment of the metastatic lesions was performed and compared to the standard of care imaging.

Results

At 1- and 2-h imaging times post injection, there were no detectable lesions with [⁶⁸Ga]citrate PET. At 3- to 4-h uptake time, there were a total of 71 [⁶⁸Ga]citrate-positive lesions (67 osseous, 1 liver, and 3 lymph node). Of these, 65 lesions were visible on the standard of care imaging (CT and/or bone scan). One PET-avid osseous vertebral body metastasis was not apparent on either CT or bone scan. Twenty-five lesions were not PET-avid but seen on CT and bone scan (17 bone, 6 lymph node, 1 pleural, and 1 liver). The average of the maximum SUVs for bone or soft tissue metastases for patients treated at higher doses and uptake time was statistically higher than the corresponding parameter in normal liver, muscle, and bone. Visually obvious blood pool activity was observed even 3–4 h post injection, suggesting that further optimization of the [⁶⁸Ga]citrate imaging protocol is required to maximize signal-to-background ratios.

Conclusions

Our preliminary results support that PET with [⁶⁸Ga]citrate may be a novel tool for imaging prostate cancer. Future studies are needed to determine the optimal imaging protocol, the clinical significance of [⁶⁸Ga]citrate uptake, and its role in therapeutic decisions.

     

Convenient Preparation of [<Superscript>68</Superscript>Ga]DKFZ-PSMA-11 Using a Robust Single-Vial Kit and Demonstration of Its Clinical Efficacy

Purpose

[⁶⁸Ga]DKFZ-PSMA-11 has proved to be an important diagnostic radiotracer for targeting prostate-specific membrane antigen (PSMA) overexpression in both recurrent prostate cancer (PC) and relevant metastatic sites. However, the widespread, routine clinical use of such a potential radiopharmaceutical demands availability of a ready-to-use kit formulation to enable convenient radiopharmaceutical preparation. Herein, we report the development of a freeze-dried kit vial for the formulation of [⁶⁸Ga]DKFZ-PSMA-11 and its clinical use in patients using a “shake-bake-inject” methodology.

Procedures

The freeze-dried kit vial was developed after optimization of ligand content (PSMA-11) and pH conditions. The kit was formulated using ⁶⁸Ga from two different commercially available generators. Positron emission tomography/X-ray computed tomography (PET/CT) images of PC patients were obtained using the kit-formulated radiotracer.

Results

[⁶⁸Ga]DKFZ-PSMA-11 was prepared in >98 % radiochemical yield and purity using the freeze-dried kit vials. Kits were optimized for the preparation of four patient doses. The clinical utility was evaluated in patients with histologically confirmed prostate cancer, and the images were of good quality as well as conforming to tumor marker and clinical expectations.

Conclusion

The development of a simple and ready-to-use freeze-dried DKFZ-PSMA-11 kit for the preparation of Ga-68-based radiotracers constitutes a major step towards the expedition of the widespread and economical screening of PC patients.

     

[<Superscript>18</Superscript>F]Fluorocholine Uptake of Parathyroid Adenoma Is Correlated with Parathyroid Hormone Level

Purpose

The aim of the study was to investigate the relationship between [¹⁸F]fluoromethyl-dimethyl-2-hydroxyethylammonium ([¹⁸F]FCh) positron emission tomography (PET) parameters, laboratory parameters, and postoperative histopathological results in patients with primary hyperparathyroidism (pHPT) due to parathyroid adenomas.

Procedures

This retrospective study was conducted in 52 patients with biochemically proven pHPT. [¹⁸F]FCh-PET parameters (maximum standardized uptake value: SUV_max) in early phase (after 2 min) and late phase (after 50 min), metabolic volume, and adenoma-to-background ratio (ABR), preoperative laboratory results (PTH and serum calcium concentration), and postoperative histopathology (location, size, volume, and weight of adenoma) were assessed. Relationship of PET parameters, laboratory parameters, and histopathological parameters was assessed using the Mann-Whitney U test and Spearman correlation coefficient. MRI characteristics of parathyroid adenomas were also analyzed.

Results

The majority of patients underwent a PET/MR scan, 42 patients (80.7 %); 10 patients (19.3 %) underwent PET/CT. We found a strong positive correlation between late-phase SUV_max and preoperative PTH level (r?=?0.768, p?<?0.001) and between late-phase ABR and preoperative PTH level (r?=?0.680, p?<?0.001). The surgical specimen volume was positively correlated with the PET/MR lesion volume (r?=?0.659, p?<?0.001). No significant association was observed between other [¹⁸F]FCh-PET parameters, laboratory parameters, and histopathological findings. Cystic adenomas were larger than non-cystic adenomas (p?=?0.048).

Conclusions

[¹⁸F]FCh uptake of parathyroid adenomas is strongly correlated with preoperative PTH serum concentration. Therefore, the preoperative PTH level might potentially be able to predict success of [¹⁸F]FCh-PET imaging in hyperparathyroidism, with higher lesion-to-background ratios being expected in patients with high PTH. PET/MR is accurate in estimating the volume of parathyroid adenomas.

     

<Emphasis Type="Italic">In Vitro</Emphasis> and <Emphasis Type="Italic">In Vivo</Emphasis> Comparison of Selected Ga-68 and Zr-89 Labelled Siderophores

Purpose

Some [⁶⁸Ga]siderophores show promise in specific and sensitive imaging of infection. Here, we compare the in vitro and in vivo behaviour of selected Ga-68 and Zr-89 labelled siderophores.

Procedures

Radiolabelling was performed in HEPES or sodium acetate buffer systems. Radiochemical purity of labelled siderophores was determined using chromatography. Partition coefficients, in vitro stability and protein binding affinities were determined. Ex vivo biodistribution and animal imaging was studied in mice.

Results

Certain differences among studied siderophores were observed in labelling efficiency. Protein binding and stability tests showed highest stabilities and lowest protein binding affinities for Ga-68 and [⁸⁹Zr]triacetylfusarinine C (TAFC). All studied Ga-68 and [⁸⁹Zr]siderophores exhibited a similar biodistribution and pharmacokinetics in mice with the exception of [⁸⁹Zr]ferrioxamine E (FOXE).

Conclusions

Zr-89 and [⁶⁸Ga]siderophores showed analogous in vitro and in vivo behaviour. Tested [⁸⁹Zr]siderophores could be applied for longitudinal positron emission tomography (PET) studies of fungal infections and especially TAFC for the development of novel bioconjugates.

     

Quantitative Analysis of [<Superscript>18</Superscript>F]FMISO PET for Tumor Hypoxia: Correlation of Modeling Results with Immunohistochemistry

Purpose

Quantitative evaluation of tumor hypoxia based on H-1-(3-[¹⁸F]fluoro-2-hydroxypropyl)-2-nitroimidazole ([¹⁸F]FMISO) positron emission tomography (PET) can deliver important information for treatment planning in radiotherapy. However, the merits and limitations of different analysis methods in revealing the underlying physiological feature are not clear. This study aimed to assess these quantitative analysis methods with the support of immunohistological data.

Procedures

Sixteen nude mice bearing xenografted human squamous cell carcinomas (FaDu or CAL-33) were scanned using 2-h dynamic [¹⁸F]FMISO PET. Tumors were resected and sliced, and the hypoxia marker pimonidazole was immunostained followed by H&E staining. The pimonidazole signal was segmented using a k-means clustering algorithm, and the hypoxic fraction (HF) was calculated as the hypoxic area/viable tumor-tissue-area ratio pooled over three tissue slices from the apical, center, and basal layers. PET images were analyzed using various methods including static analysis [standard uptake value (SUV), tumor-to-blood ratio (T/B), tumor-to-muscle ratio (T/M)] and kinetic modeling (Casciari αk _A , irreversible and reversible two-tissue compartment k ₃, Thorwarth w _A k ₃, Patlak K _i , Logan V _d , Cho K), and correlated with HF.

Results

No significant correlation was found for static analysis. A significant correlation between k ₃ of the irreversible two-tissue compartment model and HF was observed (r?=?0.61, p?=?0.01). The correlation between HF and αk _A of the Casciari model could be improved through reducing local minima by testing more sets of initial values (r?=?0.59, p?=?0.02) or by reducing the model complexity by fixing three parameters (r?=?0.63, p?=?0.0008).

Conclusions

With support of immunohistochemistry data, this study shows that various analysis methods for [¹⁸F]FMISO PET perform differently for assessment of tumor hypoxia. A better fitting quality does not necessarily mean a higher physiological correlation. Hypoxia PET analysis needs to consider both the mathematical stability and physiological fidelity. Based on the results of this study, preference should be given to the irreversible two-tissue compartment model as well as the Casciari model with reduced parameters.

     

Radiochemical Synthesis,Rodent Biodistribution and Tumor Uptake,and Dosimetry Calculations of [<Superscript>11</Superscript>C] Methylated LY2181308

Purpose

The aim of the study was to develop a rapid and reproducible method to label LY2181308, an antisense oligonucleotide to Survivin, with carbon-11 in order to study its in vivo biodistribution and tumor uptake in rodents and its human dosimetry based on baboon data.

Methods

Randomly [¹¹C] methylated LY2181308 was produced with [¹¹C] methyl iodide. The biodistribution was performed in female Sprague–Dawley (SD) rats and EMT-6 tumor-bearing mice in the presence of nonradioactive LY2181308. Human dosimetry calculations were based on baboon PET studies.

Results

In SD rats, the kidney and liver were the organs with the most accumulation of radioactivity. Tumor uptake in mice was also relatively high after 5 min and remained constant for up to 1 h. Baboon dosimetry suggested that up to 42 mCi of radioactivity could be administered to human with a dose-limiting organ being the kidneys with a radiation dose of 32 µGy/MBq (0.118 rad/mCi).

Conclusions

[¹¹C] Methylated LY2181308 to rodents and baboons showed its biodistribution, tumor uptake, and human dosimetry evaluation. These results should facilitate the understanding of the pharmacokinetics of LY2181308 prior to use as a potential new therapeutic agent in oncology as well as to warrant more in vivo validations as a potentially useful tumor-imaging agent.

     

Study of Vesicular Monoamine Transporter 2 in Myopic Retina Using [<Superscript>18</Superscript>F]FP-(+)-DTBZ

Purpose

To investigate the relationship between expression level of vesicular monoamine transporter 2 (VMAT2) and myopia, as well as the feasibility of noninvasive myopia diagnosis through imaging VMAT2 in retina by using [¹⁸F]fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]FP-(+)-DTBZ).

Procedures

The right eyes of ten guinea pigs were deprived of vision to establish form-deprived (FD) myopia and the left eyes were untreated as the self-control eyes. The location and expression level of VMAT2 in the eyes were detected by micro-positron emission tomography (PET)/X-ray computed tomography (CT) imaging through using [¹⁸F]FP-(+)-DTBZ. Immunofluorescence staining and Western blot were used to confirm the location and expression level of VMAT2 in the eyes. The concentrations of dopamine (DA) and its metabolites including 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were also investigated by high-performance liquid chromatography.

Results

The right eyes deprived of vision were obviously myopic (??3.17?±?1.33 D) after procedure, while the left eyes were hyperopic (4.60?±?0.83 D, P?<?0.0001). The main expressions of VMAT2 in the eyes were located in retina. VMAT2 was significantly reduced in the myopic retina compared to the normal one from PET/CT results (P?=?0.0008), which could also be verified by Western blots (P?=?0.029). The concentrations of DA, DOPAC, and HVA in the FD eyes were all significantly less than those in the control eyes (P?=?0.024, P?=?0.018, P?=?0.008). As a role of storing and releasing DA in vesicles, VMAT2 was demonstrated positively correlating with the amounts of DA (P?=?0.030), DOPAC (P?=?0.038), and HVA (P?=?0.025) through Pearson’s correlation coefficient test.

Conclusions

We demonstrate that [¹⁸F]FP-(+)-DTBZ can be used to noninvasively image VMAT2 in retina. The expression level of VMAT2 in retina may act as a new biomarker for myopia diagnosis. The decreasing of VMAT2 expression level may play an important role in the development of myopia through correspondingly reducing the amount of DA in retina.

     

Uptake of Radium-223 Dichloride and Early [<Superscript>18</Superscript>F]NaF PET Response Are Driven by Baseline [<Superscript>18</Superscript>F]NaF Parameters: a Pilot Study in Castration-Resistant Prostate Cancer Patients

Purpose

The purpose of this study is to identify predictive factors on baseline [¹⁸F]NaF positron emission tomography (PET)/computed tomography (CT) of early response to radium-223 dichloride after 3 cycles of treatment in metastatic castration-resistant prostate cancer patients.

Procedures

Analysis of 152 metastases was performed in six consecutive patients who underwent [¹⁸F]NaF PET/CT at baseline and for early monitoring after 3 cycles of radium-223 dichloride. All metastases depicted on whole-body [¹⁸F]NaF PET/CT were contoured and CT (density in Hounsfield units, sclerotic, mixed, or lytic appearance) as well as [¹⁸F]NaF [maximum standardized uptake value (SUV_max), SUV_mean, and lesion volume (V_18F-NaF)] patterns were recorded. Tumor response was defined as percentage change in SUV_max and SUV_mean between baseline and post-treatment PET. Bone lesions were defined as stable, responsive, or progressive, according to thresholds derived from a recent multicentre test-retest study in [¹⁸F]NaF PET/CT. Total [¹⁸F]NaF uptake in metastases, defined as MATV × SUV_mean, was correlated to uptake of radium-223 on biodistribution scintigraphy performed 7 days after the first cycle of treatment.

Results

Among metastases, 116 involved the axial skeleton and 36 the appendicular skeleton. Lesions were sclerotic in 126 cases and mixed in 26 cases. No lytic lesion was depicted. ROC analysis showed that SUV_max and SUV_mean were better predictors of lesion response than V_18F-NaF and density on CT (P < 0.0001 and P = 0.001, respectively). SUV_max and SUV_mean were predictors of individual tumor response in separate multivariate models (P = 0.01 and P = 0.02, respectively). CT pattern (mixed versus sclerotic) and lesion density were independent predictors only when assessing response with delta SUV_max (P = 0.002 and 0.007, respectively). A good correlation between total [¹⁸F]NaF uptake within metastases and their relative radium-223 uptake assessed by two observers 7 days after treatment (r = 0.72 and 0.77, P < 0.0001) was found.

Conclusions

SUV_max and SUV_mean on baseline [¹⁸F]NaF PET/CT are independent predictors of bone lesions’ response to 3 cycles of radium-223 dichloride, supporting the use of NaF to select patients more likely to respond to treatment.

     

Comparison of [<Superscript>11</Superscript>C]Choline ([<Superscript>11</Superscript>C]CHO) and [<Superscript>18</Superscript>F]Bombesin (BAY 86-4367) as Imaging Probes for Prostate Cancer in a PC-3 Prostate Cancer Xenograft Model

Purpose

Carbon-11- and fluorine-18-labeled choline derivatives are commonly used in prostate cancer imaging in the clinical setting for staging and re-staging of prostate cancer. Due to a limited detection rate of established positron emission tomography (PET) tracers, there is a clinical need for innovative tumor-specific PET compounds addressing new imaging targets. The aim of this study was to compare the properties of [¹⁸F]Bombesin (BAY 86-4367) as an innovative biomarker for prostate cancer imaging targeting the gastrin-releasing peptide receptor and [¹¹C]Choline ([¹¹C]CHO) in a human prostate tumor mouse xenograft model by small animal PET/X-ray computed tomography (CT).

Procedures

We carried out a dual-tracer small animal PET/CT study comparing [¹⁸F]Bombesin and [¹¹C]CHO. The androgen-independent human prostate tumor cell line PC-3 was implanted subcutaneously in the flanks of nu/nu NMRI mice (n?=?10) (PET/CT measurements of two [¹¹C]Choline mice could not be analyzed due to technical reasons). [¹⁸F]Bombesin and [¹¹C]CHO PET/CT imaging was performed about 3–4 weeks after the implantation of PC-3 cells on two separate days. After the intravenous tail vein injection of 14 MBq [¹⁸F]Bombesin and 37 MBq [¹¹C]CHO, respectively, a dynamic study over 60 min was acquired in list mode using an Inveon animal PET/CT scanner (Siemens Medical Solutions). The sequence of [¹⁸F]Bombesin and [¹¹C]CHO was randomized. Image analysis was performed using summed images as well as dynamic data. To calculate static and dynamic tumor-to-muscle (T/M), tumor-to-blood (T/B), liver-to-blood (L/B), and kidney-to-blood (K/B) ratios, 4?×?4?×?4 mm³ volumes of interest (VOIs) of tumor, muscle (thigh), liver, kidney, and blood derived from transversal slices were used.

Results

The mean T/M ratio of [¹⁸F]Bombesin and [¹¹C]CHO was 6.54?±?2.49 and 1.35?±?0.30, respectively. The mean T/B ratio was 1.83?±?0.79 for [¹⁸F]Bombesin and 0.55?±?0.10 for [¹¹C]CHO. The T/M ratio as well as the T/B ratio for [¹⁸F]Bombesin were significantly higher compared to those for [¹¹C]CHO (p?<?0.001, respectively). Kidney and liver uptake was statistically significantly lower for [¹⁸F]Bombesin (K/B 3.41?±?0.81, L/B 1.99?±?0.38) compared to [¹¹C]CHO [K/B 7.91?±?1.85 (p?<?0.001), L/B 6.27?±?1.99 (p?<?0.001)]. The magnitudes of the time course of T/M and T/B ratios (T/M and T/B_dyn ratios) were statistically significantly different (showing a higher uptake of [¹⁸F]Bombesin compared to [¹¹C]CHO); additionally, also the change of the T/M and T/B ratios over time was significantly different between both tracers in the dynamic analysis (p?<?0.001, respectively). Furthermore, there was a statistically significantly different change of the K/B and L/B ratios over time between the two tracers in the dynamic analysis (p?=?0.026 and p?<?0.001, respectively).

Conclusions

[¹⁸F]Bombesin (BAY 86-4367) visually and semi-quantitatively outperforms [¹¹C]CHO in the PC-3 prostate cancer xenograft model. [¹⁸F]Bombesin tumor uptake was significantly higher compared to [¹¹C]CHO. [¹⁸F]Bombesin showed better imaging properties compared to the clinically utilized [¹¹C]CHO due to a higher tumor uptake as well as a lower liver and kidney uptake.

     

Synthesis and <Emphasis Type="Italic">In Vitro</Emphasis> and <Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of [<Superscript>3</Superscript>H]LRRK2-IN-1 as a Novel Radioligand for LRRK2

Purpose

LRRK2 (leucine-rich repeat kinase 2) has recently been proven to be a promising drug target for Parkinson’s disease (PD) due to an apparent enhanced activity caused by mutations associated with familial PD. To date, there have been no reports in which a LRRK2 inhibitor has been radiolabeled and used for in in vitro or in vivo studies of LRRK2. In the present study, we radiolabeled the LRRK2 ligand, LRRK-IN-1, for the purposes of performing in vitro (IC₅₀, K _d , B _max, autoradiography) and in vivo (biodistribution, and blocking experiments) evaluations in rodents and human striatum tissues.

Procedures

[³H]LRRK2-IN-1 was prepared with high radiochemical purity (>99 %) and a specific activity of 41 Ci/mmol via tritium/hydrogen (T/H) exchange using Crabtree’s catalyst. For IC⁵⁰, K _d , and B _max determination, LRRK2-IN-1 was used as a competing drug for nonspecific binding assessment. The specific binding of the tracer was further evaluated via an in vivo blocking study in mice with a potent LRRK2 inhibitor, Pf-06447475.

Results

In vitro binding studies demonstrated a saturable binding site for [³H]LRRK2-IN-1 in rat kidney, rat brain striatum and human brain striatum with K _d of 26 ± 3 and 43 ± 8, 48 ± 2 nM, respectively. In rat, the density of LRRK2 binding sites (B _max) was higher in kidney (6.4 ± 0.04 pmol/mg) than in brain (2.5 ± 0.03 pmol/mg), however, in human brain striatum, the B _max was 0.73 ± 0.01 pmol/mg protein. Autoradiography imaging in striatum of rat and human brain tissues gave results consistent with binding studies. In in vivo biodistribution and blocking studies in mice, co-administration with Pf-06447475 (10 mg/kg) reduced the uptake of [³H]LRRK2-IN-1 (%ID/g) by 50–60% in the kidney or brain.

Conclusion

The high LRRK2 brain density observed in our study suggests the feasibility for positron emission tomography imaging of LRRK2 (a potential target) with radioligands of higher affinity and specificity.