The Theranostic PSMA Ligand PSMA-617 in the Diagnosis of Prostate Cancer by PET/CT: Biodistribution in Humans, Radiation Dosimetry, and First Evaluation of Tumor Lesions

Synthesis and preclinical evaluation of novel 18F-labeled Glu-urea-Glu-based PSMA inhibitors for prostate cancer imaging: a comparison with 18F-DCFPyl and 18F-PSMA-1007

Background

Due to its high and consistent expression in prostate cancer (PCa), the prostate-specific membrane antigen (PSMA) represents an ideal target for molecular imaging and targeted therapy using highly specific radiolabeled PSMA ligands. To address the continuously growing clinical demand for ¹⁸F-labeled PSMA-probes, we developed two novel Glu-urea-Glu-(EuE)-based inhibitors, EuE-k-¹⁸F-FBOA (1) and EuE-k-β-a-¹⁸F-FPyl (2), both with optimized linker structure and different ¹⁸F-labeled aromatic moieties. The inhibitors were evaluated in a comparative preclinical study with ¹⁸F-DCFPyl and ¹⁸F-PSMA-1007.

Results

Radiolabeling procedures allowed preparation of (1) and (2) with high radiochemical yields (67 ± 7 and 53 ± 7%, d.c.) and purity (> 98%). When compared with ¹⁸F-DCFPyl (IC₅₀ = 12.3 ± 1.2 nM) and ¹⁸F-PSMA-1007 (IC₅₀ = 4.2 ± 0.5 nM), both metabolically stable EuE-based ligands showed commensurable or higher PSMA affinity (IC₅₀ = 4.2 ± 0.4 nM (1), IC₅₀ = 1.1 ± 0.2 nM (2)). Moreover, 1.4- and 2.7-fold higher internalization rates were observed for (1) and (2), respectively, resulting in markedly enhanced tumor accumulation in LNCaP-tumor-bearing mice ((1) 12.7 ± 2.0% IA/g, (2) 13.0° ± 1.0% IA/g vs. 7.3 ± 1.0% IA/g (¹⁸F-DCFPyl), 7.1 ± 1.5% IA/g (¹⁸F-PSMA-1007), 1 h p.i.). In contrast to (1), (2) showed higher kidney accumulation and delayed clearance kinetics. Due to the high hydrophilicity of both compounds, almost no unspecific uptake in non-target tissue was observed. In contrast, due to the less hydrophilic character (logP = − 1.6) and high plasma protein binding (98%), ¹⁸F-PSMA-1007 showed uptake in non-target tissue and predominantly hepatobiliary excretion, whereas, ¹⁸F-DCFPyl exhibited pharmacokinetics quite similar to those obtained with (1) and (2).

Conclusion

Both ¹⁸F-labeled EuE-based PSMA ligands showed excellent in vitro and in vivo PSMA-targeting characteristics. The substantially higher tumor accumulation in mice compared to recently introduced ¹⁸F-PSMA-1007 and ¹⁸F-DCFPyl suggests their high value for preclinical studies investigating the effects on PSMA-expression. In contrast to (2), (1) seems to be more promising for further investigation, due to the more reliable ¹⁸F-labeling procedure, the faster clearance kinetics with comparable high tumor uptake, resulting therefore in better high-contrast microPET imaging as early as 1 h p.i.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0382-8) contains supplementary material, which is available to authorized users.

Bone lesion absorbed dose profiles in patients with metastatic prostate cancer treated with molecular radiotherapy

OBJECTIVE

The aim of this study was to calculate the range of absorbed doses that could potentially be delivered by a variety of radiopharmaceuticals and typical fixed administered activities used for bone pain palliation in a cohort of patients with metastatic castration-resistant prostate cancer (mCRPC). The methodology for the extrapolation of the biodistribution, pharmacokinetics and absorbed doses from a given to an alternative radiopharmaceutical is presented.

METHODS

Sequential single photon emission CT images from 22 patients treated with 5 GBq of 186Re-HEDP were used to extrapolate the time-activity curves for various radiopharmaceuticals. Cumulated activity distributions for the delivered and extrapolated treatment plans were converted into absorbed dose distributions using the convolution dosimetry method. The lesion absorbed doses obtained for the different treatments were compared using the patient population distributions and cumulative dose-volume histograms.

RESULTS

The median lesion absorbed doses across the patient cohort ranged from 2.7 Gy (range: 0.6-11.8 Gy) for 1100 MBq of 166Ho-DOTMP to 21.8 Gy (range: 4.5-117.6 Gy) for 150 MBq of 89Sr-dichloride. 32P-Na3PO4, 153Sm-EDTMP, 166Ho-DOTMP, 177Lu-EDTMP and 188Re-HEDP would have delivered 41, 32, 85, 20 and 64% lower absorbed doses, for the typical administered activities as compared to 186Re-HEDP, respectively, whilst 89Sr-dichloride would have delivered 25% higher absorbed doses.

CONCLUSION

For the patient cohort studied, a wide range of absorbed doses would have been delivered for typical administration protocols in mCRPC. The methodology presented has potential use for emerging theragnostic agents. Advances in knowledge: The same patient cohort can receive a range of lesion absorbed doses from typical molecular radiotherapy treatments for patients with metastatic prostate cancer, highlighting the need to establish absorbed dose response relationships and to treat patients according to absorbed dose instead of using fixed administered activities.

18F-PSMA-1007 PET/CT at 60 and 120 minutes in patients with prostate cancer: biodistribution, tumour detection and activity kinetics

PURPOSE

PSMA-targeted PET in patients with prostate cancer (PCa) has a significant impact on treatment decisions. By far the most frequently used PSMA ligand is ⁶⁸Ga-labelled PSMA-11. However, due to the availability of larger amounts of activity, ¹⁸F-labelled PSMA ligands are of major interest. The aim of the present study was to evaluate the biodistribution and performance of the novel ¹⁸F-labelled ligand PSMA-1007 at two different time points.

METHODS

This retrospective analysis included 40 consecutive patients (mean age 68.7 ± 8.1 years) referred for PSMA PET/CT. ¹⁸F-PSMA-1007 PET/CT was performed for localization of biochemical relapse, primary staging or therapy follow-up. Circular regions of interest were placed on representative slices of the liver, spleen, kidney, abdominal aortic blood pool, bone marrow (fourth lumbar vertebral body), urinary bladder and gluteus muscle at 60 and 120 min after injection. In malignant lesions the maximum standardized uptake (SUV_max) was measured within volumes of interest at both time points. All SUVs at 60 min were compared with those at 120 min after injection.

RESULTS

The activity in the blood pool, urinary bladder and gluteus muscle was very low and decreased significantly over time (P < 0.001). Uptake in the liver, spleen and kidney showed a significant increase over time and uptake in the bone marrow remained stable. Overall, 135 PCa lesions were detected at 60 min and 136 lesions at 120 min after injection. The median SUV_max increased significantly (P < 0.001) from 10.98 to 15.51 between 60 and 120 min.

CONCLUSION

PCa lesions show a significant increase in ¹⁸F-PSMA-1007 uptake at 120 min compared with 60 min after injection. In addition, accumulation of the tracer in the urinary bladder was very low leading to improved contrast of adjacent PCa lesions. Increasing accumulation in the liver may limit the sensitivity of the tracer in detecting liver metastases.

Synthesis of Realistic Simultaneous Positron Emission Tomography and Magnetic Resonance Imaging Data

The investigation of the performance of different positron emission tomography (PET) reconstruction and motion compensation methods requires accurate and realistic representation of the anatomy and motion trajectories as observed in real subjects during acquisitions. The generation of well-controlled clinical datasets is difficult due to the many different clinical protocols, scanner specifications, patient sizes, and physiological variations. Alternatively, computational phantoms can be used to generate large data sets for different disease states, providing a ground truth. Several studies use registration of dynamic images to derive voxel deformations to create moving computational phantoms. These phantoms together with simulation software generate raw data. This paper proposes a method for the synthesis of dynamic PET data using a fast analytic method. This is achieved by incorporating realistic models of respiratory motion into a numerical phantom to generate datasets with continuous and variable motion with magnetic resonance imaging (MRI)-derived motion modeling and high resolution MRI images. In this paper, data sets for two different clinical traces are presented, ¹⁸F-FDG and ⁶⁸Ga-PSMA. This approach incorporates realistic models of respiratory motion to generate temporally and spatially correlated MRI and PET data sets, as those expected to be obtained from simultaneous PET-MRI acquisitions.

Current status of theranostics in prostate cancer

The aim of this review is to report on the current status of prostate-specific membrane antigen (PSMA)-directed theranostics in prostate cancer (PC) patients. The value of 68Ga-PSMA-directed PET imaging as a diagnostic procedure for primary and recurrent PC as well as the role of evolving PSMA radioligand therapy (PRLT) in castration-resistant (CR)PC is assessed. The most eminent data from mostly retrospective studies currently available on theranostics of prostate cancer are discussed. The current knowledge on 68Ga-PSMA PET/CT implicates that primary staging with PET/CT is meaningful in patients with high-risk PC and that the combination with pelvic multi parametric (mp)MR (or PET/mpMR) reaches the highest impact on patient management. There may be a place for 68Ga-PSMA PET/CT in intermediate-risk PC patients as well, however, only a few data are available at the moment. In secondary staging for local recurrence, 68Ga-PSMA PET/mpMR is superior to PET/CT, whereas for distant recurrence, PET/CT has equivalent results and is faster and cheaper compared to PET/mpMR. 68Ga-PSMA PET/CT is superior to 18F / 11Choline PET/CT in primary staging as well as in secondary staging. In patients with biochemical relapse, PET/CT positivity is directly associated with prostate-specific antigen (PSA) increase and amounts to roughly 50% when PSA is raised to ≤0.5 ng/ml and to ≥90% above 1 ng/ml. Significant clinical results have so far been achieved with the subsequent use of radiolabeled PSMA ligands in the treatment of CRPC. Accumulated activities of 30 to 50 GBq of 177Lu-PSMA ligands seem to be clinically safe with biochemical response and PERCIST/RECIST response in around 75% of patients along with xerostomia in 5-10% of patients as the only notable side effect. On the basis of the current literature, we conclude that PSMA-directed theranostics do have a major clinical impact in diagnosis and therapy of PC patients. We recommend that 68Ga-PSMA PET/CT should be performed in primary staging together with pelvic mpMR in high-risk patients and in all patients for secondary staging, and that PSMA-directed therapy is a potent strategy in CRPC patients when other treatment options have failed. The combination of PSMA-directed therapy with existing therapy modalities (such as 223Ra-chloride or androgen deprivation therapy) has to be explored, and prospective clinical multicenter trials with theranostics are warranted.

Hyperkalemia in patients treated with endoradiotherapy combined with amino acid infusion is associated with severe metabolic acidosis

Background

Amino acid co-infusion for renal protection in endoradiotherapy (ERT) applied as prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) or peptide receptor radionuclide therapy (PRRT) has been shown to cause severe hyperkalemia. The pathophysiology behind the rapid development of hyperkalemia is not well understood. We hypothesized that the hyperkalemia should be associated with metabolic acidosis.

Results

Twenty-two patients underwent ERT. Prior to the first cycle, excretory kidney function was assessed by mercapto-acetyltriglycine (MAG-3) renal scintigraphy, serum biochemistry, and calculated glomerular filtration rate (eGFR). All patients received co-infusion of the cationic amino acids L-arginine and L-lysine for nephroprotection. Clinical symptoms, electrolytes, and acid-base status were evaluated at baseline and after 4 h.

No patient developed any clinically relevant side effects. At baseline, acid base status and electrolytes were normal in all patients. Excretory kidney function was normal or only mildly impaired in all except two patients with stage 3 renal insufficiency. All patients developed hyperkalemia. Base excess and HCO₃⁻ were significantly lower after 4 h. In parallel, mean pH dropped from 7.36 to 7.29. There was a weak association between calculated (r = − 0.21) as well as MAG-3-derived GFR (r = − 0.32) and the rise in potassium after 4 h.

Conclusion

Amino acid co-infusion during ERT leads to severe metabolic acidosis which induces hyperkalemia by potassium hydrogen exchange. This novel finding implies that commercially available bicarbonate solutions might be an easy therapeutic option to correct metabolic acidosis rapidly.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0370-z) contains supplementary material, which is available to authorized users.

Expression of PSMA in tumor neovasculature of high grade sarcomas including synovial sarcoma, rhabdomyosarcoma, undifferentiated sarcoma and MPNST

AIMS

PSMA (prostate specific membrane antigen) is physiologically expressed in normal prostate tissue. It is overexpressed in prostate cancer cells and has been suggested as a target for antibody-based radioligand therapy. As PSMA expression so far has not been systematically analyzed in soft tissue tumors, the current study aims at investigating a large cohort of different subtypes.

METHODS AND RESULTS

Immunohistochemistry was used to detect PSMA expression in 779 samples of soft tissue tumors and Ewing sarcoma as a primary bone malignancy. CD34 coexpression was employed to study PSMA expression in the neovasculature. PSMA expression was found in the tumor-associated neovasculature of 151/779 soft tissue/bone tumors (19.38%) and was more frequent in malignant tumors compared to tumors with intermediate or benign biological potential (p=0.078). Strong neovascular PSMA expression was predominantly observed in subsets of different sarcomas including 3/20 rhabdomyosarcomas (15%), 4/21 malignant peripheral nerve sheath tumors (19.05%), 6/16 synovial sarcomas (35.29%) and 6/33 undifferentiated pleomorphic sarcomas (18.18%).

CONCLUSION

We conclude that PSMA is expressed in the neovasculature of a subset of soft tissue tumors to a variable extent. Our observation of strong PSMA expression predominantly occurring in sarcomas might provide a rationale to evaluate PSMA-targeted radioligand therapy in these entities.

Combined model-based and patient-specific dosimetry for 18F-DCFPyL, a PSMA-targeted PET agent

PURPOSE

Prostate-specific membrane antigen (PSMA), a type-II integral membrane protein highly expressed in prostate cancer, has been extensively used as a target for imaging and therapy. Among the available PET radiotracers, the low molecular weight agents that bind to PSMA are proving particularly effective. We present the dosimetry results for ¹⁸F-DCFPyL in nine patients with metastatic prostate cancer.

METHODS

Nine patients were imaged using sequential PET/CT scans at approximately 1, 12, 35 and 70 min, and a final PET/CT scan at approximately 120 min after intravenous administration of 321 ± 8 MBq (8.7 ± 0.2 mCi) of¹⁸F-DCFPyL. Time-integrated-activity coefficients were calculated and used as input in OLINDA/EXM software to obtain dose estimates for the majority of the major organs. The absorbed doses (AD) to the eye lens and lacrimal glands were calculated using Monte-Carlo models based on idealized anatomy combined with patient-specific volumes and activity from the PET/CT scans. Monte-Carlo based models were also developed for calculation of the dose to two major salivary glands (parotid and submandibular) using CT-based patient-specific gland volumes.

RESULTS

The highest calculated mean AD per unit administered activity of ¹⁸F was found in the lacrimal glands, followed by the submandibular glands, kidneys, urinary bladder wall, and parotid glands. The S-values for the lacrimal glands to the eye lens (0.42 mGy/MBq h), the tear film to the eye lens (1.78 mGy/MBq h) and the lacrimal gland self-dose (574.10 mGy/MBq h) were calculated. Average S-values for the salivary glands were 3.58 mGy/MBq h for the parotid self-dose and 6.78 mGy/MBq h for the submandibular self-dose. The resultant mean effective dose of ¹⁸F-DCFPyL was 0.017 ± 0.002 mSv/MBq.

CONCLUSIONS

¹⁸F-DCFPyL dosimetry in nine patients was obtained using novel models for the lacrimal and salivary glands, two organs with potentially dose-limiting uptake for therapy and diagnosis which lacked pre-existing models.

Global comparison of targeted alpha vs targeted beta therapy for cancer: In vitro, in vivo and clinical trials

Targeted therapy for cancer is a rapidly expanding and successful approach to the management of many intractable cancers. However, many immunotherapies fail in the longer term and there continues to be a need for improved targeted cancer cell toxicity, which can be achieved by radiolabelling the targeting vector with a radioisotope. Such constructs are successful in using a gamma ray emitter for imaging. However, traditionally, a beta emitter is used for therapeutic applications. The new approach is to use the short range and highly cytotoxic alpha radiation from alpha emitters to achieve improved efficacy and therapeutic gain. This paper sets out to review all experimental and theoretical comparisons of efficacy and therapeutic gain for alpha and beta emitters labelling the same targeting vector. The overall conclusion is that targeted alpha therapy is superior to targeted beta therapy, such that the use of alpha therapy in clinical settings should be expanded.

Synthesis and evaluation of a novel urea-based 68Ga-complex for imaging PSMA binding in tumor

INTRODUCTION

Prostate specific membrane antigen (PSMA) is a well-established target for diagnostic and therapeutic applications for prostate cancer. It is know that [⁶⁸Ga]PSMA 11 ([⁶⁸Ga]Glu-NH-CO-NH-Lys(Ahx)-HBED-CC) is the most well studied PET imaging agent for detecting over expressed PSMA binding sites of tumors in humans. In an effort to provide new agents with improved characteristics for PET imaging, we report a novel [⁶⁸Ga]-Glu-NH-CO-NH-Lys(Ahx)-linker-HBED-CC conjugate with a novel O-(carboxymethyl)-L-tyrosine, as the linker group.

METHODS

Radiosynthesis was performed by a direct method. In vitro binding and cell internalization of [⁶⁸Ga]10 was investigated in PSMA positive LNCaP cell lines. Biodistribution and MicroPET imaging studies were performed in LNCaP tumor bearing mice.

RESULTS

In vitro binding to LNCaP cells showed that ^natGa labeled O-(carboxymethyl)-L-tyrosine conjugate, [^natGa]10, displayed excellent affinity and specificity (IC₅₀ = 16.5 nM) a value comparable to that of PSMA 11. In vitro cell binding and internalization showed excellent uptake and retention; [⁶⁸Ga]10 displayed significantly higher cellular internalization than [⁶⁸Ga]PSMA 11 (12.5 vs 7.4% ID/10⁶ cells at 1 h). Biodistribution studies in LNCaP tumor-bearing mice exhibited a high specific uptake in PSMA expressing tumors and fast clearance in normal organs (19.7 tumor/blood; 20.7 tumor/muscle at 1 h after iv injection). MicroPET imaging studies in mice confirmed that [⁶⁸Ga]10 displayed excellent uptake and distinctive tumor localization, which was blocked by iv injection of a competing drug, 2-PMPA.

CONCLUSIONS

The preliminary results strongly suggest that [⁶⁸Ga]10 may be promising candidates as a PET imaging radiotracer for detecting PSMA expression in prostate cancer.

Integration of CT urography improves diagnostic confidence of 68Ga-PSMA-11 PET/CT in prostate cancer patients

Background

To prove the feasibility of integrating CT urography (CTU) into ⁶⁸Ga-PSMA-11 PET/CT and to analyze the impact of CTU on assigning focal tracer accumulation in the ureteric space to either ureteric excretion or metastatic disease concerning topographic attribution and diagnostic confidence.

Methods

Ten prostate cancer patients who underwent ⁶⁸Ga-PSMA-11 PET/CT including CTU because of biochemical relapse or known metastatic disease were retrospectively analyzed. CTU consisted of an excretory phase 10 min after injection of 80 mL iodinated contrast material. Ureter opacification at CTU was evaluated using the following score: 0, 0% opacification; 1, < 50%; 2, 50–99%; 3, 100%. Topographic attribution and confidence of topographic attribution of focal tracer accumulation in the ureteric space were separately assessed for ⁶⁸Ga-PSMA-11 PET/CT without and with CTU. Diagnostic confidence was evaluated using the following score: 0, < 25% confidence; 1, 26–50%; 2, 51–75%; 3, 76–100%.

Results

At CTU, mean ureter opacification score was 2.6 ± 0.7. At ⁶⁸Ga-PSMA-11 PET/CT without CTU, mean confidence of topographic attribution of focal tracer accumulation was 2.5 ± 0.7 in total and 2.6 ± 0.7 for metastatic disease. At ⁶⁸Ga-PSMA-11 PET/CT with CTU, mean confidence of topographic attribution of focal areas of tracer accumulation was significantly higher with 2.9 ± 0.2 in total and 2.7 ± 0.9 for metastatic disease (p < 0.001). In 4 of 34 findings (12%) attribution to either ureteric excretion or metastatic disease was discrepant between ⁶⁸Ga-PSMA-11 PET/CT without and with CTU (n.s).

Conclusions

Integration of CTU into ⁶⁸Ga-PSMA-11 PET/CT is feasible and increases diagnostic confidence of assigning focal areas of tracer accumulation in the ureteric space to either metastatic disease or ureteric excretion.

Type I collagen-targeted PET probe for pulmonary fibrosis detection and staging in preclinical models

Pulmonary fibrosis is scarring of the lungs that can arise from radiation injury, drug toxicity, environmental or genetic causes, and for unknown reasons [idiopathic pulmonary fibrosis (IPF)]. Overexpression of collagen is a hallmark of organ fibrosis. We describe a peptide-based positron emission tomography (PET) probe (⁶⁸Ga-CBP8) that targets collagen type I. We evaluated ⁶⁸Ga-CBP8 in vivo in the bleomycin-induced mouse model of pulmonary fibrosis. ⁶⁸Ga-CBP8 showed high specificity for pulmonary fibrosis and high target/background ratios in diseased animals. The lung PET signal and lung ⁶⁸Ga-CBP8 uptake (quantified ex vivo) correlated linearly (r² = 0.80) with the amount of lung collagen in mice with fibrosis. We further demonstrated that the ⁶⁸Ga-CBP8 probe could be used to monitor response to treatment in a second mouse model of pulmonary fibrosis associated with vascular leak. Ex vivo analysis of lung tissue from patients with IPF supported the animal findings. These studies indicate that ⁶⁸Ga-CBP8 is a promising candidate for noninvasive imaging of human pulmonary fibrosis.

The use of PET/CT in prostate cancer

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) has recently emerged as a promising diagnostic imaging platform for prostate cancer. Several radiolabelled tracers have demonstrated efficacy for cancer detection in various clinical settings. In this review, we aim to illustrate the diverse use of PET/CT with different tracers for the detection of prostate cancer.

METHODS

We searched MEDLINE using the terms 'prostate cancer', 'PET', 'PET/CT' and 'PET/MR'). The current review was limited to ¹⁸F-NaF PET/CT, choline-based PET/CT, fluciclovine PET/CT and PSMA-targeted PET/CT, as these modalities have been the most widely adopted.

RESULTS

NaF PET/CT has shown efficacy in detecting bone metastases with high sensitivity, but relatively low specificity. Currently, choline PET/CT has been the most extensively studied modality. Although having superior specificity, choline PET/CT suffers from low sensitivity, especially at low PSA levels. Nevertheless, choline PET/CT was found to significantly improve upon conventional imaging modalities (CIM) in the detection of metastatic lesions at biochemical recurrence (BCR). Newer methods using fluciclovine and PSMA-targeted radiotracers have preliminarily demonstrated great promise in primary and recurrent staging of prostate cancer. However, their superior efficacy awaits confirmation in larger series.

CONCLUSIONS

PET/CT has emerged as a promising staging modality for both primary and recurrent prostate cancer. Newer tracers have increased detection accuracies for small, incipient metastatic foci. The clinical implications of these occult PET/CT detected disease foci require organized evaluation. Efforts should be aimed at defining their natural history as well as responsiveness and impact of metastasis-directed therapy.

68Ga-PSMA PET/CT: Joint EANM and SNMMI procedure guideline for prostate cancer imaging: version 1.0

The aim of this guideline is to provide standards for the recommendation, performance, interpretation and reporting of ⁶⁸Ga-PSMA PET/CT for prostate cancer imaging. These recommendations will help to improve accuracy, precision, and repeatability of ⁶⁸Ga-PSMA PET/CT for prostate cancer essentially needed for implementation of this modality in science and routine clinical practice.

68 Ga-PSMA PET/CT for the detection of bone metastases in prostate cancer: a systematic review of the published literature

BACKGROUND

68 Ga-labelled prostate-specific membrane antigen (PSMA) is a promising PET ligand for the detection of prostate cancer. Little attention has been given to the ability of 68 Ga-PSMA PET/CT to detect malignant bone lesions and whether this approach is superior to existing bone imaging modalities.

AIM

To review the existing data of 68 Ga-PSMA PET/CT for the diagnosis of bone metastases in prostate cancer.

METHODS

Systematic review of the peer-reviewed literature.

RESULTS

Among 1858 papers in the original search, 37 papers were included in the analysis (six case reports and 31 case series). The vast majority of the studies were low-level evidence studies. Most studies presented data on detection rates without a reference standard. All but two studies were of a retrospective nature. Several cohort studies showed bone metastasis in 5-60% of patients with prostate cancer, including in patients with very low-PSA values. For primary staging, 68 Ga-PSMA PET/CT outperformed bone scans, while the superiority of 68 Ga-PSMA PET/CT compared with bone scans with respect to biochemical recurrence and metastatic castration-resistant prostate cancer (mCRPC) remains to be demonstrated.

CONCLUSION

68 Ga-PSMA PET/CT has shown to be a promising technique for use in prostate cancer. 68 Ga-PSMA PET/CT shows more lesions than bone scans, but data on diagnostic performance are very limited and indicate improved diagnostic performance in primary staging but not in mCRPC. Properly designed studies are needed to clarify the diagnostic performance of 68 Ga-PSMA PET/CT as well as its superiority over existing methods before 68 Ga-PSMA PET/CT can be routinely used for bone imaging.

Predictors of overall survival in metastatic castration-resistant prostate cancer patients receiving [177Lu]Lu-PSMA-617 radioligand therapy

Prostate-specific membrane antigen (PSMA) is a promising target for the diagnosis of and therapy for metastatic castration-resistant prostate cancer (mCRPC). The aim of this study was to measure overall-survival (OS) in mCRPC patients who received either abiraterone or enzalutamide prior to PSMA therapy. The second aim of this study was to analyse the predictors of OS according to different pre-therapeutic parameters and also the responses to the first cycle of radioligand therapy (RLT) base on PSA level. Patients with mCRPC and a history of therapy with either abiraterone or enzalutamide or both, were included in this study. Different laboratory tests and pre-therapeutic parameters have been included into the analysis. One-hundred patients received a total of 347 cycles of Lu-PSMA (median: three cycles). 69 patients showed a decline in PSA two months after the first cycle, and 38 of those patients showed a PSA decline of = > 50%. The median OS was 60 weeks. In the multivariate analysis, the level of albumin, AST and haemoglobin, existence of liver metastases and a decline of > 14% in PSA level had a significant impact on overall-survival. The median OS is significantly longer in patients without hepatic involvement, with high levels of albumin and Hb and low levels of AST. A decline in PSA levels of more than 14% was the most important response parameter with regard to overall survival.

Why Targeting PSMA Is a Game Changer in the Management of Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is highly expressed on prostate adenocarcinomas, exhibits only limited expression in benign and extraprostatic tissues, and thus represents an ideal target for the diagnosis and management of prostate cancer. Since its discovery over 30 y ago, significant effort has been made to develop clinical technology targeting PSMA. The last 5 y have seen an explosion of development of new agents targeting PSMA for diagnostic and therapeutic use. Imaging agents targeting PSMA have been developed for SPECT and PET platforms. PSMA PET imaging appears to outperform traditional imaging in the high-risk localized-disease state, in patients with biochemical recurrence after treatment, and in advanced disease. To date, most of the reported clinical studies of therapeutic agents have used PSMA-targeted radiometals to deliver β-radiation to metastatic disease sites, with ¹⁷⁷Lu being the most widely investigated therapeutic radioisotope. Studies of both antibodies and small-molecule agents have been published and have demonstrated encouraging results. Safety appears generally limited to mild transient bone marrow toxicity and xerostomia because of uptake of the small-molecule agents in the salivary glands. Radiologic responses can be dramatic, and decreases in pain have been observed. The effect on overall survival, however, has yet to be demonstrated.

Theranostics in nuclear medicine practice

The importance of personalized medicine has been growing, mainly due to a more urgent need to avoid unnecessary and expensive treatments. In nuclear medicine, the theranostic approach is an established tool for specific molecular targeting, both for diagnostics and therapy. The visualization of potential targets can help predict if a patient will benefit from a particular treatment. Thanks to the quick development of radiopharmaceuticals and diagnostic techniques, the use of theranostic agents has been continually increasing. In this article, important milestones of nuclear therapies and diagnostics in the context of theranostics are highlighted. It begins with a well-known radioiodine therapy in patients with thyroid cancer and then progresses through various approaches for the treatment of advanced cancer with targeted therapies. The aim of this review was to provide a summary of background knowledge and current applications, and to identify the advantages of targeted therapies and imaging in nuclear medicine practices.

Assessment of PSMA targeting ligands bearing novel chelates with application to theranostics: Stability and complexation kinetics of 68Ga3+, 111In3+, 177Lu3+ and 225Ac3

INTRODUCTION

Recent successes in the treatment of metastatic castration-resistant prostate cancer (mCRPCa) by systemic endoradiotherapy has sparked renewed interest in developing small molecule ligands targeting prostate-specific membrane antigen (PSMA) and chelators capable of stable complexation of metal radionuclides for imaging and therapy. As the size and coordination number of metals for imaging, such as ⁶⁸Ga³⁺, and for targeted therapy, such as ¹⁷⁷Lu³⁺ and ²²⁵Ac³⁺, are substantially different, they may show a preference for macrocycles of different denticity. We have prepared three simple conjugates that target PSMA and form radiometal complexes through coordination by either octa-, deca-, or dodecadentate tetraazacyclododecane chelators. The complex formation and metal ion selectivity of these constructs were determined at two relevant temperatures, complex stability was examined in vitro, and tumor targeting was demonstrated in preclinical PCa models with a view towards identifying a candidate with potential value as a theranostic agent for the imaging and therapy of mCRPCa.

METHODS

Three bifunctional chelates with high denticity, including the octadentate chelate DOTA, the decadentate 3p-C-DEPA and a novel dodecadentate analogue of DEPA, were synthesized and conjugated to a glutamate-urea-lysine (EuK) pharmacophore (EuK-DOTA, EuK-107 and EuK-106, respectively) to enable targeting of PSMA. The metal ion selectivity for each construct was determined by incubation at 25 °C and 95 °C with the trivalent radiometals ⁶⁸Ga³⁺, ¹¹¹In³⁺, ¹⁷⁷Lu³⁺ and ²²⁵Ac³⁺. PSMA binding affinity was determined by competitive binding using LNCaP cells, while in vivo tumor targeting of the ⁶⁸Ga-labeled constructs was examined by positron emission tomography (PET) in LNCaP xenograft tumor-bearing mice.

RESULTS

PMSA affinities (IC₅₀ values) were 13.3 ± 0.9 nM for EuK-DOTA, 18.0 ± 3.7 nM for EuK-107 and 42.6 ± 6.6 nM for EuK-106. EuK-107 and EuK-DOTA proved to rapidly and near quantitatively complex ⁶⁸Ga³⁺, ¹¹¹In³⁺, ¹⁷⁷Lu³⁺ and ²²⁵Ac³⁺ at 95 °C, with EuK-107 also rapidly complexing ¹¹¹In³⁺ and ¹⁷⁷Lu³⁺ at 25 °C. The inability of EuK-106 to chelate ¹⁷⁷Lu³⁺ and ²²⁵Ac³⁺ suggests that size of the cavity of the macrocylic ring may be more critical than the number of donor groups for the chelation of larger radiometals. In vivo, ⁶⁸Ga-EuK-107 proved to have similar uptake to ⁶⁸Ga-DKFZ-PSMA-617, a theranostic ligand currently in clinical evaluation, in a PSMA positive xenograft tumor model.

CONCLUSIONS

The broad metal ion selectivity, good in vitro affinity for PSMA and good in vivo tumor targeting suggest that EuK-107, with the 3p-C-DEPA chelator, merits further evaluation as a theranostics construct in prostate cancer.

Procedures for the GMP-Compliant Production and Quality Control of [18F]PSMA-1007: A Next Generation Radiofluorinated Tracer for the Detection of Prostate Cancer

Radiolabeled tracers targeting the prostate-specific membrane antigen (PSMA) have become important radiopharmaceuticals for the PET-imaging of prostate cancer. In this connection, we recently developed the fluorine-18-labelled PSMA-ligand [18F]PSMA-1007 as the next generation radiofluorinated Glu-ureido PSMA inhibitor after [18F]DCFPyL and [18F]DCFBC. Since radiosynthesis so far has been suffering from rather poor yields, novel procedures for the automated radiosyntheses of [18F]PSMA-1007 have been developed. We herein report on both the two-step and the novel one-step procedures, which have been performed on different commonly-used radiosynthesisers. Using the novel one-step procedure, the [18F]PSMA-1007 was produced in good radiochemical yields ranging from 25 to 80% and synthesis times of less than 55 min. Furthermore, upscaling to product activities up to 50 GBq per batch was successfully conducted. All batches passed quality control according to European Pharmacopoeia standards. Therefore, we were able to disclose a new, simple and, at the same time, high yielding production pathway for the next generation PSMA radioligand [18F]PSMA-1007. Actually, it turned out that the radiosynthesis is as easily realised as the well-known [18F]FDG synthesis and, thus, transferable to all currently-available radiosynthesisers. Using the new procedures, the clinical daily routine can be sustainably supported in-house even in larger hospitals by a single production batch.

PSMA-Based [(18)F]DCFPyL PET/CT Is Superior to Conventional Imaging for Lesion Detection in Patients with Metastatic Prostate Cancer

PURPOSE

Current standard of care conventional imaging modalities (CIM) such as X-ray computed tomography (CT) and bone scan can be limited for detection of metastatic prostate cancer and therefore improved imaging methods are an unmet clinical need. We evaluated the utility of a novel second-generation low molecular weight radiofluorinated prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) radiotracer, [(18)F]DCFPyL, in patients with metastatic prostate cancer.

PROCEDURES

Nine patients with suspected prostate cancer recurrence, eight with CIM evidence of metastatic prostate cancer and one with biochemical recurrence, were imaged with [(18)F]DCFPyL PET/CT. Eight of the patients had contemporaneous CIM for comparison. A lesion-by-lesion comparison of the detection of suspected sites of metastatic prostate cancer was carried out between PET and CIM. Statistical analysis for estimated proportions of inter-modality agreement for detection of metastatic disease was calculated accounting for intra-patient correlation using general estimating equation (GEE) intercept-only regression models.

RESULTS

One hundred thirty-nine sites of PET positive [(18)F]DCFPyL uptake (138 definite, 1 equivocal) for metastatic disease were detected in the eight patients with available comparison CIM. By contrast, only 45 lesions were identified on CIM (30 definite, 15 equivocal). When lesions were negative or equivocal on CIM, it was estimated that a large portion of these lesions or 0.72 (95 % confidence interval (CI) 0.55-0.84) would be positive on [(18)F]DCFPyL PET. Conversely, of those lesions negative or equivocal on [(18)F]DCFPyL PET, it was estimated that only a very small proportion or 0.03 (95 % CI 0.01-0.07) would be positive on CIM. Delayed 2-h-post-injection time point PET yielded higher tumor radiotracer uptake and higher tumor-to-background ratios than an earlier 1-h-post-injection time point.

CONCLUSIONS

A novel PSMA-targeted PET radiotracer, [(18)F]DCFPyL, was able to a large number of suspected sites of prostate cancer, many of which were occult or equivocal by CIM. This study provides strong preliminary evidence for the use of this second-generation PSMA-targeted PET radiotracer for detection of metastatic prostate cancer and lends further support for the importance of PSMA-targeted PET imaging in prostate cancer.

Clinical Translation and First In-Human Use of [44Sc]Sc-PSMA-617 for PET Imaging of Metastasized Castrate-Resistant Prostate Cancer

Background: Various trivalent radiometals are well suited for labeling of DOTA-conjugated variants of Glu-ureido-based prostate-specific membrane antigen (PSMA) inhibitors. The DOTA-conjugate PSMA-617 has proven high potential in PSMA radioligand therapy (PSMA-RLT) of prostate cancer as well as PET imaging when labeled with lutetium-177 and gallium-68 respectively. Considering the relatively short physical half-life of gallium-68 this positron emitter precludes prolonged acquisition periods, as required for pre-therapeutic dosimetry or intraoperative applications. In this context, the positron emitter scandium-44 is an attractive alternative for PET imaging. We report the synthesis of [⁴⁴Sc]Sc-PSMA-617 as radiopharmaceutical with generator produced scandium-44, its in vitro characterization and clinical translation as part of a first in-human study.

Methods: Scandium-44 was obtained from a ⁴⁴Ti/⁴⁴Sc radionuclide generator. PSMA-617 was labeled with 142.4±12.7 MBq of scandium-44 in analogy to [⁶⁸Ga]Ga-PSMA-617 and evaluated in vitro and in cell studies using PSMA+ LNCaP cells. A first-in-human investigation was subsequently carried out in a cohort of 4 patients (mean age 70±1.8 a) registered for [¹⁷⁷Lu]Lu-PSMA-617 therapy. 50.5±9.3 MBq (40 µg, 38.4 nmol) [⁴⁴Sc]Sc-PSMA-617 were applied via intravenous injection (i.v.), respectively. A Siemens Biograph 2 PET/CT system was used to acquire initial dynamic PET data (30 min) of abdomen in list mode followed by static PET/CT data (skull to mid-thigh) at 45 min, 2 and 18 h post-injection (p.i.). For quantitative analysis, dynamic images were reconstructed as 6 data sets of 300 s each. The noise ratio was measured in liver, lung and an additional region outside the body. SUV values in different organs and lesions were measured and compared to [⁶⁸Ga]Ga-PSMA-11 data of the same patients. Residence times and organ absorbed doses were calculated using OLINDA/EXM software.

Results: Quantitative radiochemical yields of ≥98 % were achieved using 18 nmol of PSMA-617 after 20 min at 95 °C with apparent molar activity of 6.69±0.78 MBq/nmol. Following purification, >99 % radiochemical purity was obtained. [⁴⁴Sc]Sc-PSMA-617 showed high stability (>95 %) in serum for 24 h. The binding affinity and internalization fraction were determined in PSMA+ LNCaP cells (IC₅₀ = 4.72±0.7 nM and internalization fraction: 15.78±2.14 % IA/10⁶ LNCaP cells) and compared to [⁶⁸Ga]Ga-PSMA-11 (12.0±2.8 nM and 9.47±2.56 % IA/10⁶ LNCaP cells). Physiological tracer uptake was observed in kidneys, liver, spleen, small intestine, urinary bladder, and salivary glands and pathological uptake in both soft and skeletal metastases. SUV values were significantly lower in the kidneys (14.0) compared to [⁶⁸Ga]Ga-PSMA-11 OET (30.5). All other measured SUV values did not show a statistically significant difference. Tumor to liver ratios were found to lie between 1.9 and 8.3 for [⁶⁸Ga]Ga-PSMA-11 and between 2.5 and 8.8 for [⁴⁴Sc]Sc-PSMA-617 after 120 min. For [⁴⁴Sc]Sc-PSMA-617 the ratios were higher and no statistically significant differences were observed. Total and % activity were highest in liver followed by kidneys, spleen, small intestine and salivary glands. Rapid wash out was seen in liver and spleen and gradually over time in kidneys. Kidneys received the highest radiation absorbed dose of 0.354 (0.180-0.488) mSv/MBq. No adverse pharmacological effects were observed.

Conclusion: In conclusion [⁴⁴Sc]Sc-PSMA-617 PET is suitable for PET imaging of prostate cancer tissue. [⁴⁴Sc]Sc-PSMA-617 shows promise to enable pre-therapeutic dosimetry in clinical settings. However, the clinical advantages for individual dosimetry or other applications like intraoperative applications have to be investigated in further studies.

Glu-Ureido-Based Inhibitors of Prostate-Specific Membrane Antigen: Lessons Learned During the Development of a Novel Class of Low-Molecular-Weight Theranostic Radiotracers

In recent years, several radioligands targeting prostate-specific membrane antigen (PSMA) have been clinically introduced as a new class of theranostic radiopharmaceuticals for the treatment of prostate cancer (PC). In the second decade of the 21^st century, a new era in nuclear medicine was initiated by the clinical introduction of small-molecule PSMA inhibitor radioligands, 40 y after the clinical introduction of ¹⁸F-FDG. Because of the high incidence and mortality of PC, the new PSMA radioligands have already had a remarkable impact on the clinical management of PC. For the continuing clinical development and long-term success of theranostic agents, designing modern prospective clinical trials in theranostic nuclear medicine is essential. First-in-human studies with PSMA radioligands derived from small-molecule PSMA inhibitors showed highly sensitive imaging of PSMA-positive PC by means of PET and SPECT as well as a dramatic response of metastatic castration-resistant PC after PSMA radioligand therapy. This tremendous success logically led to the initiation of prospective clinical trials with several PSMA radioligands. Meanwhile, MIP-1404, PSMA-11, 2-(3-{1-carboxy-5-[(6-fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (DCFPyL), PSMA-617, PSMA-1007, and others have entered or will enter prospective clinical trials soon in several countries. The significance becomes apparent by, for example, the considerable increase in the number of publications about PSMA-targeted PET imaging from 2013 to 2016 (e.g., a search of the Web of Science for "PSMA" AND "PET" found only 19 publications in 2013 but 218 in 2016). Closer examination of the initial success of PC treatment with PSMA inhibitor radiotracers leads to several questions from the basic research perspective as well as from the perspective of clinical demands: What lessons have been learned regarding the design of PSMA radioligands that have already been developed? Has an acceptable compromise between optimal PSMA radioligand design and a broad range of clinical demands been reached? Can the lessons learned from multiple successes within the PSMA experience be transferred to further theranostic approaches?

68Ga-PSMA PET/CT in prostate cancer

Positron emission tomography/computed tomography (PET/CT) with ⁶⁸Ga-PSMA is a non-invasive diagnostic technique to image prostate cancer with increased prostate-specific membrane antigen (PSMA) expression. PSMA is a transmembrane protein present in all prostatic tissues. Increased PSMA expression is seen in several malignancies, although prostate cancer is the tumour where it presents higher concentrations. Almost all prostate adenocarcinomas show PSMA expression in most of lesions, primary and metastatic. Immunohistochemistry has demonstrated that the expression of PSMA increases in patients with de-differentiated, metastatic or hormone-refractory tumours. Moreover, the expression level of PSMA has a prognostic value for disease outcome. PET measures the three-dimensional distribution of ⁶⁸Ga-PSMA, producing semi-quantitative images that allow for non-invasive assessment of PSMA expression.

Preclinical evaluation of heat-denatured [18F]FDG-labeled red blood cells for detecting splenic tissues with PET in rats

INTRODUCTION

Heat-denatured ^99mTc-labeled red blood cells (RBCs) are used for detecting splenic tissues with scintigraphy. The present study aimed to evaluate the feasibility of using heat-denatured [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG)-labeled RBCs in detecting splenic tissues using positron emission tomography (PET) in rats.

METHODS

RBCs were washed with phosphate buffered saline, labeled with [¹⁸F]FDG at 38°C, and heat-denatured at 50°C for 15 min. In vitro stability was assessed by measuring extracellular radioactivity during the 0-180 min incubation at 37°C. Thin layer chromatography (TLC) of the extracellular fluid was performed. The autologous RBCs were intravenously injected in four rats and PET scanning was simultaneously performed for 30 min. Time-activity curves of several organs, including the spleen, were analyzed on the PET images.

RESULTS

Labeling efficiency was 92%. Low levels of radioactivity were released from the labeled RBCs for 180 min. TLC revealed that 80% of the released radioactivity was due to [¹⁸F]FDG-6-phosphate. Whole body images showed strong uptake of heat-denatured [¹⁸F]FDG-labeled RBCs in the spleen soon after injection in all four rats. Time-activity curves revealed that the splenic uptake continued to increase for 30 min and the amount of radioactivity in the other organs, except the urinary bladder, decreased after the initial surge.

CONCLUSIONS

Heat-denatured [¹⁸F]FDG-labeled RBCs are suitable spleen-specific agents for PET. This method is clinically relevant as an alternative for heat-denatured ^99mTc-labeled RBC scintigraphy.

Using Imaging to Predict Treatment Response in Genitourinary Malignancies

CONTEXT

Over the previous2 decades, there have been numerous advancements in the diagnostic evaluation, therapeutic management, and postoperative assessment of genitourinary malignancies.

OBJECTIVE

To present a review of current and novel imaging modalities and their utility in the assessment of therapeutic response in the systemic management of renal, testicular, and prostate cancers.

EVIDENCE ACQUISITION

A PubMed/Medline search of the current published literature inclusive of prospective and retrospective original research, systematic reviews, and meta-analyses was conducted evaluating imaging modalities for renal cell carcinoma, prostate cancer, and testicular cancer. All relevant literature was individually reviewed and summarized to provide a concise description of the currently available imaging modalities and their efficacy in assessing treatment response of the genitourinary malignancies targeted in this review.

EVIDENCE SYNTHESIS

Conventional imaging techniques play a pivotal role in predicting the treatment response of genitourinary malignancies and have, therefore, been incorporated into clinical guidelines. Advancements in imaging technology have led to increased utilization for prognostication of a genitourinary cancer's response to therapy.

CONCLUSIONS

A good understanding of current recommended imaging techniques to evaluate treatment response in genitourinary malignancies is of paramount importance for today's clinician, who faces increasing treatment modalities.

PATIENT SUMMARY

In this review, we summarize available imaging modalities in the evaluation of treatment response in kidney, prostate, or testicular tumors. We believe that a good understanding of current imaging modalities is of paramount importance for healthcare providers treating these cancers.

Targeted alpha therapy of mCRPC: Dosimetry estimate of 213Bismuth-PSMA-617

Purpose

PSMA-617 is a small molecule targeting the prostate-specific membrane antigen (PSMA). In this work, we estimate the radiation dosimetry for this ligand labeled with the alpha-emitter ²¹³Bi.

Methods

Three patients with metastatic prostate cancer underwent PET scans 0.1 h, 1 h, 2 h, 3 h, 4 h and 5 h after injection of ⁶⁸Ga-PSMA-617. Source organs were kidneys, liver, spleen, salivary glands, bladder, red marrow and representative tumor lesions. The imaging nuclide ⁶⁸Ga was extrapolated to the half-life of ²¹³Bi. The residence times of ²¹³Bi were forwarded to the instable daughter nuclides. OLINDA was used for dosimetry calculation. Results are discussed in comparison to literature data for ²²⁵Ac-PSMA-617.

Results

Assuming a relative biological effectiveness of 5 for alpha radiation, the dosimetry estimate revealed equivalent doses of mean 8.1 Sv _RBE5/GBq for salivary glands, 8.1 Sv _RBE5/GBq for kidneys and 0.52 Sv _RBE5/GBq for red marrow. Liver (1.2 Sv _RBE5/GBq), spleen (1.4 Sv _RBE5/GBq), bladder (0.28 Sv _RBE5/GBq) and other organs (0.26 Sv_RBE5/GBq) were not dose-limiting. The effective dose is 0.56 Sv _RBE5/GBq. Tumor lesions were in the range 3.2–9.0 Sv_RBE5/GBq (median 7.6 Sv_RBE5/GBq). Kidneys would limit the cumulative treatment activity to 3.7 GBq; red marrow might limit the maximum single fraction to 2 GBq. Despite promising results, the therapeutic index was inferior compared to ²²⁵Ac-PSMA-617.

Conclusions

Dosimetry of ²¹³Bi-PSMA-617 is in a range traditionally considered reasonable for clinical application. Nevertheless, compared to ²²⁵Ac-PSMA-617, it suffers from higher perfusion-dependent off-target radiation and a longer biological half-life of PSMA-617 in dose-limiting organs than the physical half-life of ²¹³Bi, rendering this nuclide as a second choice radiolabel for targeted alpha therapy of prostate cancer.

Electronic supplementary material

The online version of this article (10.1007/s00259-017-3817-y) contains supplementary material, which is available to authorized users.

Prostate-specific membrane antigen PET imaging and immunohistochemistry in adenoid cystic carcinoma-a preliminary analysis

BACKGROUND

Adenoid cystic carcinoma (AdCC) of the head and neck is an uncommon malignant epithelial tumour of the secretory glands. Many patients develop slowly growing local recurrence and/or distant metastasis, for which treatment options are limited. A retrospective analysis of 9 AdCC patients was conducted to analyse the visualization of AdCC on PSMA PET/CT and to investigate the expression of PSMA on primary, recurrent and metastatic AdCC tumour tissue using immunohistochemistry.

RESULTS

Local recurrence occurred in six patients and eight developed distant metastasis. All PET/CTs depicted PSMA-ligand uptake. Four PSMA PET/CTs showed suspected residual disease, eight scans depicted uptake in areas suspected of distant metastasis. Median Maximum Standardized Uptake Value (SUVmax) in local recurrent and distant metastatic AdCC was 2.52 (IQR 2.41-5.95) and 4.01 (IQR 2.66-8.71), respectively. All primary tumours showed PSMA expression on immunohistochemistry (5-90% expression), as well as all available specimens of local recurrence and distant metastases.

CONCLUSION

PSMA PET/CT is able to detect and visualize local recurrent and distant metastatic AdCC. PSMA-specific targeting is supported by PSMA expression on immunohistochemistry.

Investigation of the halo-artifact in 68Ga-PSMA-11-PET/MRI

OBJECTIVES

Combined positron emission tomography (PET) and magnetic resonance imaging (MRI) targeting the prostate-specific membrane antigen (PSMA) with a 68Ga-labelled PSMA-analog (68Ga-PSMA-11) is discussed as a promising diagnostic method for patients with suspicion or history of prostate cancer. One potential drawback of this method are severe photopenic (halo-) artifacts surrounding the bladder and the kidneys in the scatter-corrected PET images, which have been reported to occur frequently in clinical practice. The goal of this work was to investigate the occurrence and impact of these artifacts and, secondly, to evaluate variants of the standard scatter correction method with regard to halo-artifact suppression.

METHODS

Experiments using a dedicated pelvis phantom were conducted to investigate whether the halo-artifact is modality-, tracer-, and/or concentration-dependent. Furthermore, 31 patients with history of prostate cancer were selected from an ongoing 68Ga-PSMA-11-PET/MRI study. For each patient, PET raw data were reconstructed employing six different variants of PET scatter correction: absolute scatter scaling, relative scatter scaling, and relative scatter scaling combined with prompt gamma correction, each of which was combined with a maximum scatter fraction (MaxSF) of MaxSF = 75% or MaxSF = 40%. Evaluation of the reconstructed images with regard to halo-artifact suppression was performed both quantitatively using statistical analysis and qualitatively by two independent readers.

RESULTS

The phantom experiments did not reveal any modality-dependency (PET/MRI vs. PET/CT) or tracer-dependency (68Ga vs. 18F-FDG). Patient- and phantom-based data indicated that halo-artifacts derive from high organ-to-background activity ratios (OBR) between bladder/kidneys and surrounding soft tissue, with a positive correlation between OBR and halo size. Comparing different variants of scatter correction, reducing the maximum scatter fraction from the default value MaxSF = 75% to MaxSF = 40% was found to efficiently suppress halo-artifacts in both phantom and patient data. In 1 of 31 patients, reducing the maximum scatter fraction provided new PET-based information changing the patient's diagnosis.

CONCLUSION

Halo-artifacts are particularly observed for 68Ga-PSMA-11-PET/MRI due to 1) the biodistribution of the PSMA-11-tracer resulting in large OBRs for bladder and kidneys and 2) inaccurate scatter correction methods currently used in clinical routine, which tend to overestimate the scatter contribution. If not compensated for, 68Ga-PSMA-11 uptake pathologies may be masked by halo-artifacts leading to false-negative diagnoses. Reducing the maximum scatter fraction was found to efficiently suppress halo-artifacts.

Quantitative accuracy of 177Lu SPECT imaging for molecular radiotherapy

The purpose of this study is to investigate the optimal reference geometry for gamma camera calibration. Yet another question of interest was to assess the influence of the number of 3D Ordered Subsets Expectation Maximization (3D-OSEM) updates on activity quantification for SPECT imaging with 177Lu. The accuracy of 177Lu activity quantification was assessed both in small and in large objects. Two different reference geometries, namely a cylindrical homogeneous phantom and a Jaszczak 16 ml sphere surrounded by cold water, were used to determine the gamma camera calibration factor of a commercial SPECT/CT system. Moreover, the noise level and the concentration recovery coefficient were evaluated as a function of the number of 3D-OSEM updates by using the SPECT/CT images of the reference geometry phantoms and those of a cold Jaszczak phantom with three hot spheres (16ml, 8ml and 4ml), respectively. The optimal choice of the number of 3D-OSEM updates was based on a compromise between the noise level achievable in the reconstructed SPECT images and the concentration recovery coefficients. The quantitative accuracy achievable was finally validated on a test phantom, where a spherical insert composed of two concentric spheres was used to simulate a lesion in a warm background. Our data confirm and extend previous observations. Using the calibration factor obtained with the cylindrical homogeneous phantom and the Jaszczak 16 ml sphere, the recovered activity in the test phantom was underestimated by -16.4% and -24.8%, respectively. Our work has led us to conclude that gamma camera calibration performed with large homogeneous phantom outperforms calibration executed with the Jaszczak 16ml sphere. Furthermore, the results obtained support the assumption that approximately 50 OSEM updates represent a good trade-off to reach convergence in small volumes, meanwhile minimizing the noise level.

The phytological future of prostate cancer staging: PSMA-PET and the dandelion theory

PSMA-PET is changing how we stage prostate cancer, both in the primary setting and with relapse after treatment. It allows us to identify lesions in the bones and lymph nodes that were not previously visible on conventional imaging with bone scan and CT/MRI. In this Special Report we review the ‘state of the art’ for PSMA imaging and discuss the implications for treatment decisions in prostate cancer. We liken early high risk or metastatic prostate to a common phytological problem: the dandelion. In this analogous situation, we consider the additional evidence needed for us to start plucking out the original dandelion and for us to focus attention on killing the seeded weeds that are identifiable elsewhere in the lawn.

Recent advances in nuclear medicine in endocrine oncology

PURPOSE OF REVIEW

The purpose is to review recent advances concerning the role of nuclear medicine in endocrine oncology.

RECENT FINDINGS

For I therapy of thyroid cancer a thyrotropin (TSH) more than 30 mU/l has for many years been deemed a condition sine qua non. However, new data show that patients with lower TSH levels at the time of ablation have the same rate of successful ablation as those with TSH more than 30 mU/l.I-124 combined integrated positron emission tomography and computed X-ray tomography was shown to be highly accurate in predicting findings on posttherapy radioiodine scanning and was shown to have a high prognostic power.In neuroendocrine tumors, long-term complication rates of peptide receptor radionuclide therapy were reported. Furthermore first preclinical and clinical results of peptide receptor radionuclide therapy with somatostatin receptor antagonists were published.In nuclear medicine, prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and therapy is of interest. PSMA was shown to also be expressed in neoplasms of the thyroid, the adrenal glands and neuroendocrine tumors.

SUMMARY

Further individualization of thyroid cancer patient care by means of I-124-positron emission tomography and computed X-ray tomography-based selection of the therapeutic strategy is possible. I therapy might not require as intensive TSH stimulation as thought previously. For endocrine-related malignancies PSMA targeting deserves further investigation.

Multiparametric [11C]Acetate positron emission tomography-magnetic resonance imaging in the assessment and staging of prostate cancer

Background

The aim of this study was to evaluate whether MP [¹¹C]Acetate PET-MRI enables an accurate differentiation of benign and malignant prostate tumors as well as local and distant staging.

Materials and methods

Fifty-six consecutive patients fulfilling the following criteria were included in this IRB-approved prospective study: elevated PSA levels or suspicious findings at digital rectal examination or TRUS; and histopathological verification. All patients underwent MP [¹¹C]Acetate PET-MRI of the prostate performed on separate scanners with PET/CT using [¹¹C]Acetate and 3T MP MR imaging. Appropriate statistical tests were used to determine diagnostic accuracy, local and distant staging.

Results

MP imaging with two MRI parameters (T2w and DWI) achieved the highest sensitivity, specificity, and diagnostic accuracy of 95%, 68.8%, and 88%, with an AUC of 0.82 for primary PCa detection. Neither assessments with a single parameter (AUC, 0.54–0.79), nor different combinations with up to five parameters (AUC, 0.67–0.79) achieved equally good results. MP [¹¹C]Acetate PET-MRI improved local staging with a sensitivity, specificity, and diagnostic accuracy of 100%, 96%, and 97% compared to MRI alone with 72.2%, 100%, and 95.5%. MP [¹¹C]Acetate PET-MRI correctly detected osseous and liver metastases in five patients.

Conclusions

MP [¹¹C]Acetate PET-MRI merges morphologic with functional information, and allows insights into tumor biology. MP [¹¹C]Acetate PET-MRI with two MRI-derived parameters (T2 and DWI) yields the highest diagnostic accuracy. The addition of more parameters does not improve diagnostic accuracy of primary PCa detection. MP [¹¹C]Acetate PET-MRI facilitates improved local and distant staging, providing “one-stop” staging in patients with primary PCa, and therefore has the potential to improve therapy.

Patient summary

In this report we investigated MP [¹¹C]Acetate PET-MRI for detection, local and distant staging of prostate cancer. We demonstrate that MP [¹¹C]Acetate PET-MRI with two MRI-derived parameters (T2 and DWI) achieves the best diagnostic accuracy for primary prostate cancer detection and that MP [¹¹C]Acetate PET-MRI enables an improved local and distant staging.

PSMA Ligands for PET Imaging of Prostate Cancer

Targeting the prostate-specific membrane antigen (PSMA) with ⁶⁸Ga-labeled and ¹⁸F-labeled PET agents has become increasingly important in recent years. Imaging of biochemically recurrent prostate cancer has been established as a widely accepted clinical indication for PSMA ligand PET/CT in many parts of the world because of the results of multiple, primarily retrospective, studies that indicate superior detection efficacy compared with standard-of-care imaging. For high-risk primary prostate cancer, evidence is growing that this modality significantly aids in the detection of otherwise occult nodal and bone metastases. For both clinical indications in recurrent as well as in primary prostate cancer, preliminary data demonstrate a substantial impact on clinical management. Emerging data imply that intraprostatic tumor localization, therapy stratification, and treatment monitoring of advanced disease in specific clinical situations might become future indications. Current criteria for image reporting of PSMA ligand PET are evolving given the expanding body of literature on physiologic and pathologic uptake patterns and pitfalls. This article intends to give an educational overview on the current status of PSMA ligand PET imaging, including imaging procedure and interpretation, clinical indications, diagnostic potential, and impact on treatment planning.

PSMA ligands in prostate cancer - Probe optimization and theranostic applications

Due to its selective overexpression in prostate cancer (PCa), the prostate-specific membrane antigen (PSMA) has been recognized as a highly promising target for diagnostic and therapeutic applications. So far, various PSMA ligands have been developed for radiolabeling with radioisotopes such as ⁶⁸Ga or ¹⁸F which can be used for specific visualization and diagnosis of PSMA-expressing PCa. In addition, PSMA ligands suitable for radiolabeling with ¹³¹I or ¹⁷⁷Lu have become available to the clinics, allowing PSMA-based radioligand therapies. Here, we provide a comprehensive review of the most frequently used PSMA ligands, their structural modifications, and the impact of those on clinical applications.

[177Lu]pentixather: Comprehensive Preclinical Characterization of a First CXCR4-directed Endoradiotherapeutic Agent

Purpose: Based on the clinical relevance of the chemokine receptor 4 (CXCR4) as a molecular target in cancer and on the success of [68Ga]pentixafor as an imaging probe for high-contrast visualization of CXCR4-expression, the spectrum of clinical CXCR4-targeting was expanded towards peptide receptor radionuclide therapy (PRRT) by the development of [177Lu]pentixather. Experimental design: CXCR4 affinity, binding specificity, hCXCR4 selectivity and internalization efficiency of [177Lu]pentixather were evaluated using different human and murine cancer cell lines. Biodistribution studies (1, 6, 48, 96h and 7d p.i.) and in vivo metabolite analyses were performed using Daudi-lymphoma bearing SCID mice. Extrapolated organ doses were cross-validated with human dosimetry (pre-therapeutic and during [177Lu]pentixather PRRT) in a patient with multiple myeloma (MM). Results: [177Lu]pentixather binds with high affinity, specificity and selectivity to hCXCR4 and shows excellent in vivo stability. Consequently, and supported by >96% plasma protein binding and a logP=-1.76, delaying whole-body clearance of [177Lu]pentixather, tumor accumulation was high and persistent, both in the Daudi model and the MM patient. Tumor/background ratios (7d p.i.) in mice were 499±202, 33±7, 4.0±0.8 and 116±22 for blood, intestine, kidney and muscle, respectively. In the patient, high tumor/kidney and tumor/liver dose ratios of 3.1 and 6.4 were observed during [177Lu]pentixather PRRT (7.8 GBq), with the kidneys being the dose-limiting organs. Conclusions: [177Lu]pentixather shows excellent in vivo CXCR4-targeting characteristics and a suitable pharmacokinetic profile, leading to high tumor uptake and retention and thus high radiation doses to tumor tissue during PRRT, suggesting high clinical potential of this [68Ga]pentixafor/[177Lu]pentixather based CXCR4-targeted theranostic concept.

64Cu-PSMA-617: A novel PSMA-targeted radio-tracer for PET imaging in gastric adenocarcinoma xenografted mice model

Here, we report that it's feasible for imaging gastric adenocarcinoma mice model with prostate-specific membrane antigen (PSMA) targeting imaging agents, which could potentially provide an alternate and readily translational tool for managing gastric adenocarcinoma. DKFZ-PSMA-617, a PSMA targeting ligand reported recently, was chosen to be radio-labeled with nuclide ⁶⁴Cu. ⁶⁴Cu-PSMA-617 was radio-synthesized in high radio-chemical yield and specific activity up to 19.3 GBq/µmol. It showed good stability in vitro. The specificity of ⁶⁴Cu-PSMA-617 was confirmed by cell uptake experiments in PSMA (+) LNCaP cell and PSMA (-) PC-3 and gastric adenocarcinoma BGC-823 cells. Micro-PET imaging in BGC-823 and PC-3 xenografts nude mice was evaluated (n = 4). And the tumors were visualized and better tumor-to-background achieved till 24 h. Co-administration of N- [[[(1S)-1-Carboxy-3-methylbutyl]amino]-carbonyl]-L-glutamic acid (ZJ-43) can substantially block the uptake in those tumors. Dissected tumor tissues were analyzed by auto-radiography and immunohistochemistry, and these results confirmed the PSMA expression in neo-vasculature which explained the target molecular imaging of ⁶⁴Cu-PSMA-617. All those results suggested ⁶⁴Cu-PSMA-617 may serve as a novel radio-tracer for tumor imaging more than prostate cancer.

Diagnostic performance of 68Ga-PSMA-11 (HBED-CC) PET/CT in patients with recurrent prostate cancer: evaluation in 1007 patients

Purpose

Since the clinical introduction of ⁶⁸Ga-PSMA-11 PET/CT, this imaging method has rapidly spread and is now regarded as a significant step forward in the diagnosis of recurrent prostate cancer (PCa). The aim of this study was to analyse the influence of several variables with possible influence on PSMA ligand uptake in a large cohort.

Methods

We performed a retrospective analysis of 1007 consecutive patients who were scanned with ⁶⁸Ga-PSMA-11 PET/CT (1 h after injection) from January 2014 to January 2017 to detect recurrent disease. Patients with untreated primary PCa or patients referred for PSMA radioligand therapy were excluded. The possible effects of different variables including PSA level and PSA doubling time (PSA_DT), PSA velocity (PSA_Vel), Gleason score (GSC, including separate analysis of GSC 7a and 7b), ongoing androgen deprivation therapy (ADT), patient age and amount of injected activity were evaluated.

Results

In 79.5% of patients at least one lesion with characteristics suggestive of recurrent PCa was detected. A pathological (positive) PET/CT scan was associated with PSA level and ADT. GSC, amount of injected activity, patient age, PSA_DT and PSA_Vel were not associated with a positive PET/CT scan in multivariate analysis.

Conclusion

⁶⁸Ga-PSMA-11 PET/CT detects tumour lesions in a high percentage of patients with recurrent PCa. Tumour detection is clearly associated with PSA level and ADT. Only a tendency for an association without statistical significance was found between higher GSC and a higher probability of a pathological PET/CT scan. No associations were found between a pathological ⁶⁸Ga-PSMA-11 PET/CT scan and patient age, amount of injected activity, PSA_DT or PSA_Vel.

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-017-3711-7) contains supplementary material, which is available to authorized users.

Overall survival and response pattern of castration-resistant metastatic prostate cancer to multiple cycles of radioligand therapy using [177Lu]Lu-PSMA-617

PURPOSE

Up to 30% of patients with castration-resistant prostate cancer (CRPC) do not show any response to the first cycle of radioligand therapy (RLT) with [¹⁷⁷Lu]Lu-PSMA-617 (Lu-PSMA). We evaluated patient response to the second and third cycles of RLT in patients that underwent at least three cycles. The second aim of this study was to calculate the median overall survival (OS) of responders and non-responders after the first cycle and after all three cycles of RLT.

METHODS

CRPC patients were treated with Lu-PSMA, with a median interval of 8 weeks between each cycle. The tumour marker prostate-specific antigen (PSA) was used as the marker for response evaluation.

RESULTS

Fifty-two patients underwent a total of 190 cycles of RLT (3-6 cycles per patient). Of these, 80.8% showed a decline in PSA 2 months after the first cycle, with 44.2% showing a PSA decline of ≥50%. When compared to baseline PSA, 73.1% showed a PSA decline after the third cycle. 50% of patients that did not show any response to the first cycle also did not respond to the second and third cycles. The median OS was 60 weeks in all patients. The median OS was significantly longer for patients that showed any PSA decline after the first cycle compared to patients without PSA decline (68 vs. 33 weeks). There was a significant difference in median OS between responders and non-responders for a change in PSA after the third cycle compared to baseline PSA.

CONCLUSION

Patients with a positive response to RLT, regardless of the rate of decline, had a significantly longer median OS. Of the patients that did not show any response to the first cycle, 50% responded to the second or third cycles.

Comparison of PSMA-HBED and PSMA-I&T as diagnostic agents in prostate carcinoma

PURPOSE

Gallium(68)-labelled prostate-specific membrane antigen (PSMA) radiopharmaceuticals can be used to detect prostate cancer (PCa) cells due the their over expression of PSMA. The ⁶⁸Ga HBED-PSMA (PSMA-HBED) ligand has been most widely used and can be considered the current gold standard agent. Further PSMA ligands based on the DOTAGA and DOTA conjugates have more recently been developed. These agents (PSMA-I&T and PSMA-617) have potential theranostic capabilities as they can be conjugated with therapeutic radioisotopes. In this study, we examine whether PSMA-I&T has comparative efficacy, such that it could replace PSMA-HBED as a diagnostic agent in prostate carcinoma.

METHODS

19 patients with PCa referred for ⁶⁸Ga-PSMA imaging were imaged with PSMA-HBED and PSMA-I&T PET-CT imaging within a 2-week period. The two pharmaceuticals were synthesised using click chemistry. Imaging was performed using the same standardised methodology on a Siemens Biograph mCT. All sites of PSMA binding thought to represent PCa (probable or definite) were included in a lesion analysis that examined lesion concordance and lesional binding efficiency (SUV_peak) between the two radiopharmaceuticals. For each patient, SUV_mean of the LV cavity blood pool, bone, muscle and liver were determined as image background measures.

RESULTS

Across all patients, PSMA uptake was observed in 47 lesions (10 bone lesions, 19 nodal lesions, 18 high-grade intraprostatic binding). Lesions were concordant between the agents in all except for two small (<4 mm) nodal lesions which were not visualised with PSMA-I&T. SUV_peak assessment showed significantly greater overall lesion binding with HBED (paired t test, p = 0.0001). LV blood pool and bone marrow SUV_mean were significantly higher for I&T than HBED (paired t test, blood pool p < 1 × 10-5, bone marrow p < 0.005).

CONCLUSION

Intra-patient comparative imaging demonstrates higher lesional PSMA-HBED binding than PSMA-I&T and that the HBED agent is likely to have better lesion contrast. While there was concordance in 96% of lesions, 2 small nodal lesions were appreciated with PSMA-HBED imaging while considered normal with PSMA-I&T. These findings suggest that HBED-PSMA has a slightly higher diagnostic accuracy in comparison to PSMA-I&T.

Targeted Radionuclide Therapy: An Evolution Toward Precision Cancer Treatment

OBJECTIVE

This article reviews recent developments in targeted radionuclide therapy (TRT) approaches directed to malignant liver lesions, bone metastases, neuroendocrine tumors, and castrate-resistant metastatic prostate cancer and discusses challenges and opportunities in this field.

CONCLUSION

TRT has been employed since the first radioiodine thyroid treatment almost 75 years ago. Progress in the understanding of the complex underlying biology of cancer and advances in radiochemistry science, multimodal imaging techniques including the concept of "see and treat" within the framework of theranostics, and universal traction with the notion of precision medicine have all contributed to a resurgence of TRT.

The Rise of PSMA Ligands for Diagnosis and Therapy of Prostate Cancer

The prostate-specific membrane antigen (PSMA) has received increased consideration during the past few years as an excellent target for both imaging and therapy of prostate cancer. After many years of outstanding preclinical research, the first significant step forward in clinical use was achieved in 2008 with the first human experience with the small-molecule PSMA inhibitors ¹²³I-MIP-1972 and ¹²³I-MIP-1095. A clinical breakthrough followed in 2011 with ⁶⁸Ga-PSMA-11 for PET imaging and ¹³¹I-MIP-1095 for endoradiotherapy of metastatic prostate cancer. Since then, PET/CT with ⁶⁸Ga-PSMA-11 has rapidly spread worldwide, and endoradiotherapy with PSMA ligands has been conducted at increasing numbers of centers. ⁶⁸Ga-PSMA-11 is currently the subject of multicenter studies in different countries. Since 2013, ¹³¹I-related PSMA therapy has been replaced by ¹⁷⁷Lu-labeled ligands, such as PSMA-617, which is also the subject of multicenter studies. Alternative PSMA ligands for both imaging and therapy are available. Among them is ^99mTc-MIP-1404, which has recently entered a phase 3 clinical trial. This article focuses on the highlights of the development and clinical application of PSMA ligands.