Highlights of the 32th Annual Congress of the EANM, Barcelona 2019: the nucleolympic games of nuclear medicine—a global competition for excellence

Update on Preclinical Development and Clinical Translation of Cholecystokinin-2 Receptor Targeting Radiopharmaceuticals

Simple Summary

Peptide analogs, derived from the natural peptide hormone gastrin, are promising candidates for improving the visualization and treatment of tumors. Gastrin specifically binds to the cholecystokinin-2 receptor, a G-protein-coupled receptor expressed on the cell surface of different tumors. This enables specific targeting of tumor cells using gastrin analogs, labeled with radioisotopes. The receptor is expressed at high incidence in medullary thyroid carcinoma, a rare form of thyroid cancer lacking effective treatments at an advanced stage. Different radiolabeled gastrin analogs as well as nonpeptidic compounds targeting CCK2R have been developed. Specific modifications have been introduced in order to safely deliver the radiation to the tumor site. In this review, recent strategies applied to improve the targeting properties are described. These developments enabled the introduction of new radiolabeled peptide analogs for imaging and therapy in cancer patients. In addition to highlighting the current clinical trials, the perspectives for future applications are given.

Abstract

The cholecystokinin-2 receptor (CCK2R) has been a target of interest for molecular imaging and targeted radionuclide therapy for two decades. However, so far CCK2R targeted imaging and therapy has not been introduced in clinical practice. Within this review the recent radiopharmaceutical development of CCK2R targeting compounds and the ongoing clinical trials are presented. Currently, new gastrin derivatives as well as nonpeptidic substances are being developed to improve the properties for clinical use. A team of specialists from the field of radiopharmacy and nuclear medicine reviewed the available literature and summarized their own experiences in the development and clinical testing of CCK2R targeting radiopharmaceuticals. The recent clinical trials with novel radiolabeled minigastrin analogs demonstrate the potential for both applications, imaging as well as targeted radiotherapy, and reinforce the clinical applicability within a theranostic concept. The intense efforts in optimizing CCK2R targeting radiopharmaceuticals has led to new substances for clinical use, as shown in first imaging studies in patients with advanced medullary thyroid cancer. The first clinical results suggest that the wider clinical implication of CCK2R-targeted radiopharmaceuticals is reasonable.

Emerging Radionuclides in a Regulatory Framework for Medicinal Products - How Do They Fit?

Recent years have seen the establishment of several radionuclides as medicinal products in particular in the setting of theranostics and PET. [¹⁷⁷Lu]Lutetium Chloride or [⁶⁴Cu]Copper Chloride have received marketing authorization as radionuclide precursor, [⁶⁸Ga]Gallium Chloride has received regulatory approval in the form of different ⁶⁸Ge/⁶⁸Ga generators. This is a formal requirement by the EU directive 2001/83, even though for some of these radionuclide precursors no licensed kit is available that can be combined to obtain a final radiopharmaceuticals, as it is the case for Technetium-99m. In view of several highly promising, especially metallic radionuclides for theranostic applications in a wider sense, the strict regulatory environment poses the risk of slowing down development, in particular for radionuclide producers that want to provide innovative radionuclides for clinical research purposes, which is the basis for their further establishment. In this paper we address the regulatory framework for novel radionuclides within the EU, the current challenges in particular related to clinical translation and potential options to support translational development within Europe and worldwide.

Recent Advances in Radiometals for Combined Imaging and Therapy in Cancer

Nuclear medicine is defined as the use of radionuclides for diagnostic and therapeutic applications. The imaging modalities positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are based on γ-emissions of specific energies. The therapeutic technologies are based on β^- -particle-, α-particle-, and Auger electron emitters. In oncology, PET and SPECT are used to detect cancer lesions, to determine dosimetry, and to monitor therapy effectiveness. In contrast, radiotherapy is designed to irreparably damage tumor cells in order to eradicate or control the disease's progression. Radiometals are being explored for the development of diagnostic and therapeutic radiopharmaceuticals. Strategies that combine both modalities (diagnostic and therapeutic), referred to as theranostics, are promising candidates for clinical applications. This review provides an overview of the basic concepts behind therapeutic and diagnostic radiopharmaceuticals and their significance in contemporary oncology. Select radiometals that significantly impact current and upcoming cancer treatment strategies are grouped as clinically suitable theranostics pairs. The most important physical and chemical properties are discussed. Standard production methods and current radionuclide availability are provided to indicate whether a cost-efficient use in a clinical routine is feasible. Recent preclinical and clinical developments and outline perspectives for the radiometals are highlighted in each section.