A systematic review on the current status of PSMA-targeted imaging and radioligand therapy

Development and Evaluation of Novel 68Ga/177Lu-Labeled PSMA Inhibitors with Enhanced Pharmacokinetics and Tumor Imaging for Prostate Cancer

Prostate-specific membrane antigen (PSMA) has been a key target for diagnosing and treating prostate cancer, particularly in high-grade, metastatic, and therapy-resistant tumors. This study presents a series of novel 68Ga- and 177Lu-labeled PSMA inhibitors, derived from the previously developed [68Ga]Ga-Flu-1. We explored the impact of PEG chains, lipophilic macrocycles, and dimerization on their in vivo properties. The 68Ga- and 177Lu-labeled inhibitors were assessed for biodistribution and tumor targeting in PC3-PIP tumor xenografts, leading to the identification of several promising candidates based on imaging and tumor-specific uptake. Positron emission tomography (PET) imaging revealed that the poly(ethylene glycol)-modified [68Ga]Ga-BisPSMA-P4 demonstrated rapid tumor penetration and excellent tumor-to-background contrast. In comparative biodistribution studies, the naphthalene ring-modified [68Ga]Ga-BisPSMA-Nph-P4 showed higher tumor uptake (∼60% ID/g at 1 h postinjection) and rapid renal clearance (∼25% ID/g at 2 h postinjection). Additionally, [177Lu]Lu-BisPSMA-Nph-P4 displayed superior retention, with significant uptake on day 7, highlighting its potential as a novel PSMA inhibitor for prostate cancer diagnosis and treatment.

Real-time diagnosis of sampled lesions in targeted biopsy of prostate Cancer using a novel tracer [64Cu] Cu-DOTA-PSMA-3Q: a pilot preclinical study

PURPOSE

Prostate-specific membrane antigen positron emission tomography (PSMA-PET) guided targeted biopsy has shown potential for detecting more prostate cancer (PCa) cases. However, relying exclusively on imaging may risk missing lesions, an issue that could be addressed by incorporating radiation-guided technology. Accordingly, we aimed to develop a novel PSMA radiotracer with a long half-life, [64Cu]Cu-DOTA-PSMA-3Q, and evaluate its targeting accuracy. Additionally, this research explored the practicability of real-time lesion verification during surgical interventions.

METHODS

In this study, we synthesized the radiotracer [64Cu]Cu-DOTA-PSMA-3Q and verified its PSMA specificity and safety. We prospectively enrolled 18 patients with suspected PCa for PET/CT imaging to assess the efficacy of PCa detection; 10 patients underwent targeted biopsy combined with standard template biopsy at an interval of 24 h after injection. The radioactivity of the biopsy tissue was quantified in counts per minute (CPM) using a gamma spectrometer intraoperatively.

RESULTS

The efficacy and specificity of [64Cu]Cu-DOTA-PSMA-3Q were confirmed through preclinical cell and animal studies. In clinical settings, PET/CT imaging performed 2 h after injection visualized all of the PSMA-positive lesions both within and outside the prostate. The assessment of human organ radiation exposure indicated that the kidneys received the highest absorbed dose, followed by the bladder wall, salivary glands, and liver. In 10 patients, a total of 132 biopsy cores were extracted, with 53 cores histologically confirmed as PCa. The median CPM for PCa tissues was significantly greater at 134,148 CPM compared to 18,39 CPM for normal prostate tissues (P < 0.001). Receiver operating characteristic (ROC) curve analysis yielded an AUC of 0.8837, suggesting high diagnostic accuracy. The optimal diagnostic cut-off was established at 66 CPM, achieving a sensitivity of 77.36%.

CONCLUSIONS

Radiation-guided technology using [64Cu]Cu-DOTA-PSMA-3Q improves the reliability of PSMA-PET image-guided biopsy, enables instant confirmation of sample lesions during surgical procedures, and holds potential for achieving optimized puncture outcomes.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300072655, Registered 20 June 2023.

Investigating the significance of SPECT/CT-SUV for monitoring 177Lu-PSMA-targeted radionuclide therapy: a systematic review

BACKGROUND

Quantitative molecular imaging via single-photon emission computed tomography-derived standardised uptake value (SPECT/CT-SUV) is used to assess the response of metastatic castration-resistant prostate cancer (mCRPC) patients to targeted radionuclide therapy (TRT) with [177Lu]Lu-PSMA. This imaging technique determines the radiopharmaceutical distribution and internal dosimetry in patients who receive TRT. However, there is limited evidence regarding the role of image quantification in monitoring changes induced by [177Lu]Lu-PSMA. This systematic examines the role of quantitative SPECT/CT-SUV during [177Lu]Lu-PSMA TRT and assesses whether SUV changes correlate with quantitative imaging and biomarkers.

METHODS

A systematic review was conducted in accordance with the PRISMA guidelines. The MEDLINE/PubMed databases were searched from January 2016 to July 2024 to identify relevant articles. The inclusion criterion was the use of quantitative SPECT/CT-SUV during [177Lu]Lu-PSMA TRT for patients with mCRPC. The records were screened to determine their eligibility. The abstracts of 62 records were screened, and 28 were excluded because they were not relevant; the full texts of 34 original papers were retrieved and assessed for eligibility.

RESULTS

A total of five studies were included in this systematic review (two prospective studies and three retrospective studies). The sample sizes of the studies ranged from 6 to 73 patients. The highest number of lesions analysed was 144. Three studies reported the SPECT/CT-SUV following cycle 1, and only one study reported the correlation with pretherapy PET/CT (r = 0.9, p = 0.005). SPECT/CT-SUV changes between the first two to three cycles were reported in one study. None of the studies reported the SPECT/CT-SUV for normal organs. One study reported correlations between SPECT/CT-derived SUV and PET/CT-derived SUV in target and nontarget tissues.

CONCLUSION

Quantitative SPECT/CT-SUV can be used to predict responses to subsequent PSMA-TRT cycles. Disease burden and tumour heterogeneity are the leading causes of TRT individualisation.

Fully Automated Production of (((S)-1-Carboxy-5-(6-([18F]fluoro)-2-methoxynicotinamido)pentyl)carbamoyl)-l-glutamic Acid ([18F]JK-PSMA-7)

Background: The radiotracer [18F]JK-PSMA-7, a prostate cancer imaging agent for positron emission tomography (PET), was previously synthesized by indirect radiofluorination using an 18F-labeled active ester as a prosthetic group, which had to be isolated and purified before it could be linked to the pharmacologically active Lys-urea-Glu motif. Although this procedure could be automated on two-reactor modules like the GE TRACERLab FX2N (FXN) to afford the tracer in modest radiochemical yields (RCY) of 18-25%, it is unsuitable for cassette-based systems with a single reactor. Methods: To simplify implementation on an automated synthesis module, the radiosynthesis of [18F]JK-PSMA-7 was devised as a one-pot, two-step reaction. The new method is based on direct ("late-stage") radiofluorination of an appropriate onium triflate precursor and subsequent deprotection with ortho-phosphoric acid. It was successfully established on the cassette-based Trasis AllInOne (AIO) module. Results: Overall, the new protocol enabled the production of [18F]JK-PSMA-7 in activity yields of 39 ± 4% (RCY = 58%) with an overall synthesis time of about 1 h. In a single production run with an initial activity of 36-43 GBq, 13-19 GBq of [18F]JK-PSMA-7 with a radiochemical purity of >99% was obtained. Conclusions: We have established a highly reliable, GMP-compliant process for the automated radiosynthesis of [18F]JK-PSMA-7 on the Trasis AllinOne (AIO) synthesizer, ensuring consistent and efficient production of this radioligand.

Future Prospect of Low-Molecular-Weight Prostate-Specific Membrane Antigen Radioisotopes Labeled as Theranostic Agents for Metastatic Castration-Resistant Prostate Cancer

Prostate cancer ranks as the fourth most common cancer among men, with approximately 1.47 million new cases reported annually. The emergence of prostate-specific membrane antigen (PSMA) as a critical biomarker has revolutionized the diagnosis and treatment of prostate cancer. Recent advancements in low-molecular-weight PSMA inhibitors, with their diverse chemical structures and binding properties, have opened new avenues for research and therapeutic applications in prostate cancer management. These novel agents exhibit enhanced tumor targeting and specificity due to their small size, facilitating rapid uptake and localization at the target site while minimizing the retention in non-target tissues. The primary aim of this study is to evaluate the potential of low-molecular-weight PSMA inhibitors labeled with radioisotopes as theranostic agents for prostate cancer. This includes assessing their efficacy in targeted imaging and therapy and understanding their pharmacokinetic properties and mechanisms of action. This study is a literature review focusing on in vitro and clinical research data. The in vitro studies utilize PSMA-targeted radioligands labeled with radioisotopes to assess their binding affinity, specificity, and internalization in prostate cancer cell lines. Additionally, the clinical studies evaluate the safety, effectiveness, and biodistribution of radiolabeled PSMA ligands in patients with advanced prostate cancer. The findings indicate promising outcomes regarding the safety and efficacy of PSMA-targeted radiopharmaceuticals in clinical settings. The specific accumulation of these agents in prostate tumor lesions suggests their potential for various applications, including imaging and therapy. This research underscores the promise of radiopharmaceuticals targeting PSMA in advancing the diagnosis and treatment of prostate cancer. These agents improve diagnostic accuracy and patients' outcomes by enhancing imaging capabilities and enabling personalized treatment strategies.

Non-[18F]FDG PET-Radiopharmaceuticals in Oncology

Molecular imaging is a growing field, driven by technological advances, such as the improvement of PET-CT scanners through the introduction of digital detectors and scanners with an extended field of view, resulting in much higher sensitivity and a variety of new specific radiopharmaceuticals that allow the visualization of specific molecular pathways and even theragnostic approaches. In oncology, the development of dedicated tracers is crucial for personalized therapeutic approaches. Novel peptides allow the visualization of many different targets, such as PD-1 and PD-L1 expression, chemokine expression, HER expression, T-cell imaging, microenvironmental imaging, such as FAP imaging, and many more. In this article, we review recent advances in the development of non-[18F]FDG PET radiopharmaceuticals and their current clinical applications in oncology, as well as some future aspects.

The Value of PSMA-RADS Version 2.0 in the Assessment of Pulmonary Metastases in Patients With Prostate Cancer and the Improvement of Differential Diagnosis Efficiency by PSMA PET/CT Parameters

PURPOSE

The aim of this study was to investigate the application of PSMA-RADS version 2.0 in assessment of pulmonary metastases in patients with prostate cancer and whether PSMA PET/CT parameters provide incremental value.

PATIENTS AND METHODS

From October 2016 to July 2023, PC patients with pulmonary opacities (including pulmonary metastases, lung cancer, and pulmonary benign opacities) who underwent Al 18 F-PSMA-BCH PET/CT scans were retrospectively analyzed. CT imaging characteristics, including the longest diameter, density, smoothness, lobulation, pleural retraction, and vacuole sign, as well as PET parameters including SUV max and tumor-to-background ratio, were measured and analyzed. Additionally, the pulmonary PSMA-RADS score for each patient was determined. Independent predictors of pulmonary metastases were identified through univariate analysis and multivariate logistic regression analysis, which were utilized to construct a parallel diagnostic test. The differential diagnostic performances were evaluated using receiver operating characteristic analysis.

RESULTS

A total of 148 pulmonary opacities from 96 patients were retrospectively included. The number of pulmonary benign opacities, lung cancer, and pulmonary metastases were 48 (32.4%), 20 (13.5%), and 80 (54.1%), respectively. The number of opacities across different PSMA-RADS scores from 2 to 5 was 8 (5.4%), 88 (59.5%), 7 (4.7%), and 45 (30.4%). SUV max and smooth edges were independent predictors of pulmonary metastases (both P < 0.05), and the AUC of the parallel test for these 2 parameters was 0.86 (95% confidence interval: 0.79, 0.94; P < 0.001). Furthermore, the diagnostic accuracy of the parallel test across PSMA-RADS score from 2 to 5 was 85.7%, 79.6%, 100%, and 92.9%, respectively.

CONCLUSIONS

Al 18 F-PSMA-BCH PET/CT parameters were helpful in differentiating pulmonary metastases in PC patients and provided incremental value when integrated with PSMA-RADS version 2.0.

Rational design of NT-PSMA heterobivalent probes for prostate cancer theranostics

Targeting the prostate-specific membrane antigen (PSMA) with radiopharmaceuticals for imaging and/or therapy has demonstrated significant advancement in the management of prostate cancer patients. However, PSMA targeting remains unsuccessful in prostate cancers with low expression of PSMA, which account for 15% of cases. The neurotensin receptor-1 (NTS1) has been highlighted as a suitable oncotarget for imaging and therapy of PSMA-negative prostate cancer lesions. Therefore, heterobivalent probes targeting both PSMA and NTS1 could improve the prostate cancer management. Herein, we report the development of a branched hybrid probe (JMV 7489) designed to target PSMA and/or NTS1 bearing relevant pharmacophores and DOTA as the chelating agent. The new ligand was synthesized with a hybrid approach, which includes both syntheses in batch and in the solid phase. Saturation binding experiments were next performed on HT-29 and PC3-PIP cells to derive K d and B max values. On the PC3-PIP cells, [68Ga]Ga-JMV 7489 displayed good affinity towards PSMA (K d = 53 ± 17 nM; B max = 1393 ± 29 fmol/106 cells) in the same range as the corresponding reference monomer. A lower affinity value towards NTS1 was depicted (K d = 157 ± 71 nM; B max = 241 ± 42 fmol/106 cells on PC3-PIP cells; K d = 246 ± 1 nM; B max = 151 ± 44 fmol/106 cells on HT-29 cells) and, surprisingly, it was also the case for the corresponding monomer [68Ga]Ga-JMV 7089. These results indicate that the DOTA macrocycle and the linker are critical elements to design heterobivalent probes targeting PSMA and NTS1 with high affinity towards NTS1.

Model-Informed Radiopharmaceutical Therapy Optimization: A Study on the Impact of PBPK Model Parameters on Physical, Biological, and Statistical Measures in 177Lu-PSMA Therapy

Purpose: To investigate the impact of physiologically based pharmacokinetic (PBPK) parameters on physical, biological, and statistical measures in lutetium-177-labeled radiopharmaceutical therapies (RPTs) targeting the prostate-specific membrane antigen (PSMA). Methods: Using a clinically validated PBPK model, realistic time-activity curves (TACs) for tumors, salivary glands, and kidneys were generated based on various model parameters. These TACs were used to calculate the area-under-the-TAC (AUC), dose, biologically effective dose (BED), and figure-of-merit BED (fBED). The effects of these parameters on radiobiological, pharmacokinetic, time, and statistical features were assessed. Results: Manipulating PBPK parameters significantly influenced AUC, dose, BED, and fBED outcomes across four different BED models. Higher association rates increased AUC, dose, and BED values for tumors, with minimal impact on non-target organs. Increased internalization rates reduced AUC and dose for tumors and kidneys. Higher serum protein-binding rates decreased AUC and dose for all tissues. Elevated tumor receptor density and ligand amounts enhanced uptake and effectiveness in tumors. Larger tumor volumes required dosimetry adjustments to maintain efficacy. Setting the tumor release rate to zero intensified the impact of association and internalization rates, enhancing tumor targeting while minimizing the effects on salivary glands and kidneys. Conclusions: Optimizing PBPK parameters can enhance the efficacy of lutetium-177-labeled RPTs targeting PSMA, providing insights for personalized and effective treatment regimens to minimize toxicity and improve therapeutic outcomes.

Permutational Encoding Strategy Accelerates HIT Validation from Single-Stranded DNA-Encoded Libraries

DNA-Encoded Libraries (DELs) allow the parallel screening of millions of compounds for various applications, including de novo discovery or affinity maturation campaigns. However, library construction and HIT resynthesis can be cumbersome, especially when library members present an unknown stereochemistry. We introduce a permutational encoding strategy suitable for the construction of highly pure single-stranded single-pharmacophore DELs, designed to distinguish isomers at the sequencing level (e.g., stereoisomers, regio-isomers, and peptide sequences). This approach was validated by synthesizing a mock 921,600-member 4-amino-proline single-stranded DEL ("DEL1"). While screening DEL1 against different targets, high-throughput sequencing results showed selective enrichment of the most potent stereoisomers, with enrichment factors that outperform conventional encoding strategies. The versatility of our methodology was additionally validated by encoding 24 scaffolds derived from different permutations of the amino acid sequence of a previously described cyclic peptide targeting Fibroblast Activation Protein (FAP-2286). The resulting library ("DEL2") was interrogated against human FAP, showing selective enrichment of five cyclic peptides. We observed a direct correlation between enrichment factors and on-DNA binding affinities. The presented encoding methodology accelerates drug discovery by facilitating library synthesis and streamlining HIT resynthesis while enhancing enrichment factors at the DEL sequencing level. This facilitates the identification of HIT candidates prior to medicinal chemistry and affinity maturation campaigns.

PSMA-based therapeutics for prostate cancer

INTRODUCTION

The prostate cancer (PCa) consists the most frequently diagnosed malignancy of urogenital system in males. Traditionally, treatment of localized PCa was based on surgery or radiotherapy while hormonotherapy was used in more advanced stages. However, the implementation of radiolabels has revolutionized the landscape of prostate cancer. Specifically, prostate-specific membrane antigen (PSMA) has been investigated in different aspects of PCa therapeutic era.

AREAS COVERED

A literature review is presented about the implications of PSMA radiolabels on prostate cancer treatment. PSMA tracers were initially used as an imaging technique. Afterwards, PSMA labeled with isotopes presenting cytotoxic abilities, such as lutetium-117 and actinium-225, while reports exist about the use of radioligand immunotherapy. Meanwhile, ongoing trials examine the development of novel radionuclides as well as the evolution of the PSMA-targeted ligands.

EXPERT OPINION

Currently, PSMA radioligand treatment of prostate cancer is approved in the metastatic stage of the disease. Meanwhile, a variety of trials exist about its possible role in less advanced stages. However, plenty of parameters should be addressed before these implementations, such as PSMA dosage, dosimetry issues, and its safety profile. A future well-designed study with proper patient selection is mandatory to further explore PSMA radioligand theranostics perspectives.

[68Ga]PSMA-11 for positron emission tomography (PET) imaging of prostate-specific membrane antigen (PSMA)-positive lesions in men with prostate cancer

INTRODUCTION

Theranostics targeting prostate-specific membrane antigen (PSMA) represent a new targeted approach for prostate cancer care that combines diagnostic and therapeutic radiopharmaceuticals to diagnose and treat the disease. Positron emission tomography (PET) is the imaging method of choice and several diagnostic radiopharmaceuticals for quantifying PSMA have received FDA approval and are in clinical use. [68Ga]Ga-PSMA-11 is one such imaging agent and the focus of this article. One beta-emitting radioligand therapy ([177Lu]Lu-PSMA-617) has also received FDA approval for prostate cancer treatment, and several other alpha- and beta-emitting radioligand therapies are in clinical trials.

AREAS COVERED

Theranostics targeting PSMA in men with prostate cancer are discussed with a focus on use of [68Ga]Ga-PSMA-11 for imaging PSMA-positive lesions in men with prostate cancer. The review covers [68Ga]Ga-PSMA-11 manufacture, current regulatory status, comparison of [68Ga]Ga-PSMA-11 to other imaging techniques, clinical updates, and emerging applications of artificial intelligence for [68Ga]Ga-PSMA-11 PET.

EXPERT OPINION

[68Ga]Ga-PSMA-11 is used in conjunction with a PET/CT scan to image PSMA positive lesions in men with prostate cancer. It is manufactured by chelating precursor with68Ga, either from a generator or cyclotron, and has regulatory approval around the world. It is widely used clinically in conjunction with radioligand therapies like [177Lu]Lu-PSMA-617.

Research progress on asialoglycoprotein receptor-targeted radiotracers designed for hepatic nuclear medicine imaging

Asialoglycoprotein receptor (ASGPR) specifically recognizes glycans terminated with β-d-galactose or N-acetylgalactosamine. Its exclusive expression in mammalian hepatocytes renders it an ideal hepatic-targeted biomarker. To date, ASGPR-targeted ligands have been actively developed for drug delivery and hepatic imaging. This review provides a comprehensive summary of the progress achieved to-date in the field of developing ASGPR-targeted nuclear medicine imaging (NMI) radiotracers, highlighting the recent advancements over the last decade in terms of structure, radionuclides and labeling strategies. The biodistribution patterns, imaging characteristics, challenges and future prospective are discussed.

Palladium-Mediated S-Arylation of Cysteine Residues with 4-[18F]Fluoroiodobenzene ([18F]FIB)

Transition-metal-mediated bioconjugation chemistry has been used extensively to design and synthesize molecular probes to visualize, characterize, and quantify biological processes within intact living organisms at the cellular and subcellular levels. We demonstrate the development and validation of chemoselective [18F]fluoro-arylation chemistry of cysteine residues using Pd-mediated S-arylation chemistry with 4-[18F]fluoroiodobenzene ([18F]FIB) as an aryl electrophile. The novel bioconjugation technique proceeded in excellent radiochemical yields of 73-96% within 15 min under ambient and aqueous reaction mixture conditions, representing a versatile novel tool for decorating peptides and peptidomimetics with short-lived positron emitter 18F. The chemoselective S-arylation of several peptides and peptidomimetics containing multiple reactive functional groups confirmed the versatility and functional group compatibility. The synthesis and radiolabeling of a novel prostate-specific membrane antigen (PSMA) binding radioligand [18F]6 was accomplished using the novel labeling protocol. The validation of radioligand [18F]6 in a preclinical prostate cancer model with PET resulted in favorable accumulation and retention in PSMA-expressing LNCaP tumors. At the same time, a significantly lower salivary gland uptake was observed compared to clinical PSMA radioligand [18F]PSMA-1007. This finding coincides with ongoing discussions about the molecular basis of the off-target accumulation of PSMA radioligands currently used for clinical imaging and therapy of prostate cancer.