Diagnostic and Therapeutic Radiopharmaceuticals: A "Hot" Topic

Preclinical evaluation of [13xLa]La-FAP-2286 as a novel theranostic agent for tumors expressing fibroblast activation protein

In this study, a novel theranostic radiopharmaceutical, [13xLa]La-FAP-2286, for targeting Fibroblast Activation Protein (FAP)-positive tumors. The theranostic pair of 132La (half-life: 4.59 h, 42.1% β⁺) and 135La (half-life: 18.91 h, 100% EC) was produced via proton bombardment of natural barium in a 30 MeV cyclotron, achieving high radionuclidic purity (99.9%) and radiochemical purity (RCP > 99%). Stability tests revealed the RCP greater than 91% over 24 h in human serum and PBS buffer. Cellular studies confirmed high binding affinity (KD = 0.51 ± 0.12 nM) and effective internalization of [13xLa]La-FAP-2286 in FAP + tumor cells. Distribution coefficient (log D) measurements demonstrated high hydrophilicity of the complex with a value of - 3.21 ± 0.14. Imaging and biodistribution studies in tumor-bearing mice further confirmed tumor targeting, with significant uptake observed up to 48 h post-injection. These results suggest [13xLa]La-FAP-2286 can be considered a candidate for theranostic applications, offering both practical PET imaging and targeted Auger-electron therapy for cancer treatment.

Radiotracers for Molecular Imaging of Angiotensin-Converting Enzyme 2

Angiotensin-converting enzymes (ACE) are well-known for their roles in both blood pressure regulation via the renin-angiotensin system as well as functions in fertility, immunity, hematopoiesis, and many others. The two main isoforms of ACE include ACE and ACE-2 (ACE2). Both isoforms have similar structures and mediate numerous effects on the cardiovascular system. Most remarkably, ACE2 serves as an entry receptor for SARS-CoV-2. Understanding the interaction between the virus and ACE2 is vital to combating the disease and preventing a similar pandemic in the future. Noninvasive imaging techniques such as positron emission tomography and single photon emission computed tomography could noninvasively and quantitatively assess in vivo ACE2 expression levels. ACE2-targeted imaging can be used as a valuable tool to better understand the mechanism of the infection process and the potential roles of ACE2 in homeostasis and related diseases. Together, this information can aid in the identification of potential therapeutic drugs for infectious diseases, cancer, and many ACE2-related diseases. The present review summarized the state-of-the-art radiotracers for ACE2 imaging, including their chemical design, pharmacological properties, radiochemistry, as well as preclinical and human molecular imaging findings. We also discussed the advantages and limitations of the currently developed ACE2-specific radiotracers.

Development of a Novel, Easy-to-Prepare, and Potentially Valuable Peptide Coupling Technology Utilizing Amide Acid as a Linker

The process of synthesizing radionuclide-coupled drugs, especially shutdown technology that links bipotent chelators with biomolecules, utilizes traditional coupling reactions, including emerging click chemistry; these reactions involve different drawbacks, such as complex and cumbersome reaction steps, long reaction times, and the use of catalysts at various pH values, which can negatively impact the effects of the chelating agent. To address the above problems in this study, This research designed a novel bipotent chelator coupled with peptides. In the present study, dichloromethane was used as a solvent, and the reaction was conducted at room temperature for 12 h. A one-step ring-opening method was employed to introduce the coupling functional group of tridentate amide acid. The coupling materials consisted of the amino active site of the peptide and diethylene glycol anhydride. In this paper, this study explored the reactions between different equivalents of acid anhydride coupled to the peptide (peptide sequence: HLRKLRKR) and determined that the maximum conversion of the peptide feedstock was 87%. To determine the selectivity of the reaction sites in this polypeptide, This study identified the peptide sequence at the reaction site using nuclear magnetic resonance (NMR) and liquid chromatography-mass spectrometry (LC-MS). For the selected peptide, the first reactive site was on the terminal amino group, followed by the amino group on the tetra- and hepta-lysine side chains. The tridentate amic acid framework functions as a chelating agent, capable of binding a range of lanthanide ions. This significantly reduces and optimizes the time and cost associated with synthesizing radionuclide-coupled drugs.

Editorial for the Special Issue "Molecular Biology in Targeted Radionuclide Therapy Radiopharmaceutical Design"

Targeted radionuclide therapy (TRT) is gaining wide and rapid acceptance in clinical practice as it can deliver alpha or beta irradiation to a tumor-associated target which may be present in the tumor cell itself or in the microenvironment [...].