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

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.