Synthesis, preclinical evaluation, and first-in-human study of Al18F-PSMA-Q for prostate cancer imaging

Preclinical and clinical evaluation of [64Cu]Cu-PSMA-Q PET/CT for prostate cancer detection and its comparison with [18F]FDG imaging

This study aimed to develop and evaluate [64Cu]Cu-PSMA-Q as a novel positron emission tomography (PET) imaging agent for prostate cancer detection, assessing its diagnostic accuracy and clinical applicability in comparison to [18F]FDG PET imaging. [64Cu]Cu-PSMA-Q was synthesized, purified, and subjected to comprehensive quality control. Its binding affinity, cellular uptake, and internalization were assessed in vitro using prostate-specific membrane antigen (PSMA)-positive LNCaP C4-2B cells. In vivo toxicity studies were conducted in 12 mouse models (6 per group). Small-animal PET/CT (positron emission tomography/computed tomography) imaging and biodistribution studies were performed on tumor-bearing mice. Clinical evaluation involved PET/CT imaging with [64Cu]Cu-PSMA-Q in 29 prostate cancer patients, with comparative analysis against [18F]FDG PET/CT imaging. Radiation dosimetry was calculated using OLINDA/EXM software, and diagnostic performance metrics, including maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), and tumor-to-background ratio, were analyzed using SPSS v24.0, with P < 0.05 considered statistically significant. Comparative analyses utilized t-tests or Mann-Whitney U tests as appropriate. [64Cu]Cu-PSMA-Q achieved over 99% radiochemical purity and a specific activity of 20.5 ± 1 GBq/μmol. In vitro studies demonstrated a dissociation constant (Kd) of 4.083 nM, along with high cellular uptake and internalization in LNCaP C4-2B cells. No significant toxicity was observed in mouse models. Small -animal PET/CT imaging revealed peak tumor uptake at 4 h post-injection in LNCaP C4-2B tumor xenografts. In clinical evaluations, [64Cu]Cu-PSMA-Q PET/CT detected more lesions than [18F]FDG, with significantly higher SUVmax, SUVmean, and tumor-to-background ratios. The mean effective radiation dose was calculated as 4.48 ± 0.99 mSv. [64Cu]Cu-PSMA-Q PET/CT demonstrated superior lesion detection and higher tumor-to-background ratios compared to [18F]FDG PET/CT for prostate cancer visualization. Its advantageous properties, including a favorable half-life, excellent safety profile, and enhanced diagnostic accuracy, support its potential for broad clinical adoption. This study establishes a foundation for further validation of [64Cu]Cu-PSMA-Q in prostate cancer management.

Preclinical Evaluation and First-in-Human PET Study of Al18F-Labeled Biphenyl-Based Dimeric PSMA Tracers

Prostate-specific membrane antigen (PSMA) is a crucial target for prostate cancer (PCa) imaging and therapy. This study developed a novel [18F]AlF-labeled dimeric PSMA tracer, [18F]AlF-PSMA-N5, using a biphenyl scaffold to improve imaging efficacy. Seven biphenyl-based ligands were synthesized and evaluated for PSMA binding affinity and in vivo performance in 22Rv1 tumor-bearing mice. [18F]AlF-PSMA-N5 exhibited high PSMA affinity (Ki = 0.31 ± 0.06 nM), acceptable radiochemical yield (25.6% ± 6.6%), and high purity (>95%). In xenograft models, it demonstrated high tumor uptake (SUVmax = 3.15) and a tumor-to-muscle ratio (T/M) of 22.57. Preliminary first-in-human studies in PCa patients showed that [18F]AlF-PSMA-N5 successfully identified primary tumors and metastatic lesions, offering superior image contrast and higher T/M ratios compared to [68Ga]Ga-PSMA-11. Additionally, it provided comparable tumor uptake and T/M ratios to [18F]DCFPyL. These findings highlight [18F]AlF-PSMA-N5 as a promising PET radiotracer for PCa imaging, with improved imaging quality and reduced nonspecific uptake.

Comparison of 64Cu-DOTA-PSMA-3Q and 64Cu-NOTA-PSMA-3Q utilizing NOTA and DOTA as bifunctional chelators in prostate cancer: preclinical assessment and preliminary clinical PET/CT imaging

OBJECTIVE

This study aims to investigate the efficacy and safety of prostate-specific membrane antigen (PSMA) radiolabeled with copper-64 (64Cu) using the bifunctional chelating agents (BFCAs) NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). As widely utilized BFCAs in the development of radiopharmaceuticals, NOTA and DOTA play a critical role in ensuring stable chelation with 64Cu. This study evaluates the stability, bioavailability, and therapeutic potential of these radiolabeled compounds in preclinical models and initial clinical trials.

METHODS

64Cu-DOTA-PSMA-3Q and 64Cu-NOTA-PSMA-3Q were synthesized by manual labeling. The radiochemical purity, stability, specificity and biological distribution of the product were evaluated by preclinical studies. In 23 patients with suspected prostate cancer, PET/CT imaging was used to evaluate the potential and differences in biological distribution of 64Cu-DOTA-PSMA-3Q and 64Cu-NOTA-PSMA-3Q in clinical diagnosis.

RESULTS

The radiochemical purities of 64Cu-DOTA-PSMA-3Q and 64Cu-NOTA-PSMA-3Q are more than 98% and have good stability in vitro. Biodistribution studies in healthy mice revealed that both tracers primarily underwent renal excretion post-injection. Liver uptake of 64Cu-DOTA-PSMA-3Q was significantly higher than that of 64Cu-NOTA-PSMA-3Q at 1 h after injection (P<0.05). Micro-PET/CT imaging in 22Rv1 tumor-bearing mice demonstrated similar tumor uptake for both tracers at 1 h after injection (P>0.05). However, after 24 h, 64Cu-DOTA-PSMA-3Q exhibited significantly better tumor retention compared to 64Cu-NOTA-PSMA-3Q (P<0.05). In clinical PET/CT imaging involving 23 patients with suspected prostate cancer, no adverse reactions or significant changes in vital signs were observed, underscoring the safety of both tracers. Notably, 64Cu-NOTA-PSMA-3Q demonstrated higher uptake in the lacrimal glands (17.73 vs. 10.84), parotid glands (20.98 vs. 16.30), and submandibular glands (20.26 vs. 17.28) compared to 64Cu-DOTA-PSMA-3Q. Conversely, uptake in the sublingual glands was lower for 64Cu-NOTA-PSMA-3Q (7.10 vs. 7.49). Of particular clinical relevance, liver uptake of 64Cu-NOTA-PSMA-3Q was significantly lower than that of 64Cu-DOTA-PSMA-3Q (4.04 vs. 8.18), highlighting a key difference in their biodistribution profiles.

CONCLUSIONS

Both NOTA and DOTA are suitable chelators for the development of 64Cu-labeled PSMA-3Q tracers for PET/CT imaging. DOTA showed better tumor retention 24 h after injection, while NOTA showed lower uptake in the liver, in addition, NOTA was higher uptake in the salivary glands, while DOTA was lower uptake in these tissues. Overall, these findings highlight the importance of selecting the right chelating agent to optimize clinical imaging outcomes.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300072655, Registered 20 June 2023.

A novel androgen-independent radiotracer with dual targeting of NTSR1 and PSMA for PET/CT imaging of prostate cancer

A substantial proportion of patients with prostate cancer (PCa) develop treatment resistance or mortality after androgen deprivation therapy (ADT). Current methods for identifying and locating recurrent lesions using prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging, which relies on androgen levels, often result in diagnostic delays. Therefore, the development of an androgen-independent radiotracer is critical for the early identification of recurrent lesions. The neurotensin receptor 1 (NTSR1) is highly expressed in androgen-independent PCa lesions. Here, we synthesized a bispecific ligand targeting PSMA and NTSR1 by solid-phase peptide synthesis and formulated a68Ga-labeled bispecific radiotracer, ([68Ga]Ga-NT-PSMA). This radiotracer exhibited a high radiochemical yield (71.27 % ± 1.58 %) and demonstrated an affinity for NTSR1 (39.32 ± 2.98 nM) and PSMA (63.47 ± 5.14 nM) in vitro. Small animal PET imaging showed comparable uptake of [68Ga]Ga-NT-PSMA and the monomeric radiotracer [68Ga]Ga-DOTA-NT20.3 in mice bearing androgen-independent PC3 (3.64 ± 0.49 %ID/g vs. 5.60 ± 1.42 %ID/g, nonsignificant [ns]) and DU145 tumors (2.49 ± 0.20 %ID/g vs. 2.34 ± 0.18 %ID/g, ns) at 90 min post-injection. In androgen-dependent 22Rv1 xenografts, [68Ga]Ga-NT-PSMA uptake was lower (1.94 ± 0.29 %ID/g) than [68Ga]Ga-PSMA-11 (3.94 ± 0.26 %ID/g, P < 0.001). Nevertheless, [68Ga]Ga-NT-PSMA effectively imaged all three xenograft types with high contrast, an achievement not possible with monomeric radiotracers alone. These results indicate that imaging with [68Ga]Ga-NT-PSMA is independent of the androgen dependence of the model, highlighting its potential as a promising nuclear medicine diagnostic tool for the early identification and localization of castration-resistant PCa lesions.

Recent advancements in new tracers from first-in-human studies

Recent advancements in the development of positron emission tomography (PET) tracers have significantly enhanced our ability to image neuroinflammatory processes and neurotransmitter systems, which are vital for understanding and treating neurodegenerative and psychiatric disorders. Similarly, innovative tracers in oncology provide detailed images of the metabolic and molecular characteristics of tumors, which are crucial for tailoring targeted therapies and monitoring responses, including radiotherapy. Notable advancements include programmed death ligand 1 (PD-L1)-targeting agents for lung cancer, prostate-specific membrane antigen-based tracers for prostate cancer, chemokine receptor-targeting agents for hematological malignancies, human epidermal growth factor receptor 2 (HER2)-targeting tracers for various cancers, Claudin 18 based tracers for epithelial tumors, glutamine tracers for colorectal cancer, and ascorbic acid analogs for assessing cancer metabolism and therapy efficacy. Additionally, novel tracers have been developed for non-neurological and non-oncological applications, including adrenal imaging, amyloidosis, and human immunodeficiency virus (HIV) infection. This overview focuses on the newly developed tracers, particularly those used in neurology and oncology.

Increased Prostate-Specific Membrane Antigen Uptake in a Gallbladder Stone

ABSTRACT

An Al 18F-prostate-specific membrane antigen (PSMA) Q PET/CT scan was performed in a 67-year-old man to identify any potential recurrent prostate cancer lesions, which revealed no recurrent or metastatic lesions. However, a large gallbladder stone with increased PSMA uptake was incidentally detected, which could be a potential pitfall in the interpretation of PSMA PET imaging.

Optimized Therapeutic 177Lu-Labeled PSMA-Targeted Ligands with Improved Pharmacokinetic Characteristics for Prostate Cancer

Clinical trials have shown the significant efficacy of [¹⁷⁷Lu]Lu-PSMA-617 for treating prostate cancer. However, the pharmacokinetic characteristics and therapeutic performance of [¹⁷⁷Lu]Lu-PSMA-617 still need further improvement to meet clinical expectations. The aim of this study was to evaluate the feasibility and therapeutic potential of three novel ¹⁷⁷Lu-labeled ligands for the treatment of prostate cancer. The novel ligands were efficiently synthesized and radiolabeled with non-carrier added ¹⁷⁷Lu; the radiochemical purity of the final products was determined by Radio-HPLC. The specific cell-binding affinity to PSMA was evaluated in vitro using prostate cancer cell lines 22Rv1and PC-3. Blood pharmacokinetic analysis, biodistribution experiments, small animal SPCET imaging and treatment experiments were performed on normal and tumor-bearing mice. Among all the novel ligands developed in this study, [¹⁷⁷Lu]Lu-PSMA-Q showed the highest uptake in 22Rv1 cells, while there was almost no uptake in PC-3 cells. As the SPECT imaging tracer, [¹⁷⁷Lu]Lu-PSMA-Q is highly specific in delineating PSMA-positive tumors, with a shorter clearance half-life and higher tumor-to-background ratio than [¹⁷⁷Lu]Lu-PSMA-617. Biodistribution studies verified the SPECT imaging results. Furthermore, [¹⁷⁷Lu]Lu-PSMA-Q serves well as an effective therapeutic ligand to suppress tumor growth and improve the survival rate of tumor-bearing mice. All the results strongly demonstrate that [¹⁷⁷Lu]Lu-PSMA-Q is a PSMA-specific ligand with significant anti-tumor effect in preclinical models, and further clinical evaluation is worth conducting.

Blocking Studies to Evaluate Receptor-Specific Radioligand Binding in the CAM Model by PET and MR Imaging

Simple Summary

In the development of new targeted radiopharmaceuticals, it is mandatory to demonstrate their target-specific binding. Rodents are still primarily used for these experiments. With respect to the 3Rs principles, the demand for alternative methods to reduce the number of animal experiments is continuously increasing. In the present study, we investigated whether radiotracer uptake specificity can be evaluated by blocking studies in the CAM model. PET and MR imaging were used to visualize and quantify ligand accumulation. It was demonstrated that the CAM model could be used to evaluate the target-specific binding of a radiopharmaceutical. Due to intrinsic limitations of the CAM model, animal testing will still be required at more advanced stages of compound development. Still, the CAM model could significantly reduce the number of experiments through early compound pre-selection.

Abstract

Inhibition studies in small animals are the standard for evaluating the specificity of newly developed drugs, including radiopharmaceuticals. Recently, it has been reported that the tumor accumulation of radiotracers can be assessed in the chorioallantoic membrane (CAM) model with similar results to experiments in mice, such contributing to the 3Rs principles (reduction, replacement, and refinement). However, inhibition studies to prove receptor-specific binding have not yet been performed in the CAM model. Thus, in the present work, we analyzed the feasibility of inhibition studies in ovo by PET and MRI using the PSMA-specific ligand [¹⁸F]siPSMA-14 and the corresponding inhibitor 2-PMPA. A dose-dependent blockade of [¹⁸F]siPSMA-14 uptake was successfully demonstrated by pre-dosing with different inhibitor concentrations. Based on these data, we conclude that the CAM model is suitable for performing inhibition studies to detect receptor-specific binding. While in the later stages of development of novel radiopharmaceuticals, testing in rodents will still be necessary for biodistribution analysis, the CAM model is a promising alternative to mouse experiments in the early phases of compound evaluation. Thus, using the CAM model and PET and MR imaging for early pre-selection of promising radiolabeled compounds could significantly reduce the number of animal experiments.