Selection and Use of Antioxidants-radioprotectors in the Composition of Therapeutic Radiopharmaceuticals (Review)

Abstract

Introduction. The use of radiopharmaceuticals for targeted radionuclide therapy (TRT), the efficacy of which was established during clinical trials, is safe and effective for various pathological conditions, including cancer. The main feature of therapeutic radiopharmaceuticals (RPs) is the use of β–- and α-emitting radionuclides (RNs) in the finished dosage form (FD). Among the radionuclides used for radionuclide therapy, lutetium-177 is currently one of the most popular in clinical practice because of its chemical and nuclear characteristics. The list of RPs based on lutetium-177 is constantly expanding, and Lutathera® ([177Lu]Lu-DOTA-TATE) and Pluvicto™ ([177Lu]Lu-PSMA-617) have been approved for clinical use in several countries.Text. Because of the high activity of RNs in a single dose of therapeutic RPs (up to 8 GBq in a monodose for 177Lu), ionizing radiation of the used RNs leads to a decrease in RPs quality owing to radiolytic degradation of the vector molecule. This leads to a decreased specific accumulation of radioactivity in the foci of pathology, reduced therapeutic effect, and potentially increases the risk of radiotoxicity to non-target organs and tissues. The degree and intensity of radiolytic degradation of the vector molecule and, consequently, the shelf life of RPs depend on many factors, among which the activity concentration of the radionuclide in the preparation, its half-life, and the energy of the emitted particles are the most important. To suppress the effects of radiolysis, various excipients with antioxidant (radioprotective) properties were introduced into the compositions of the finished dosage forms. Among the substances studied, the most popular were gentisic acid, ascorbic acid, and ethanol. In this work, the advantages and disadvantages of various antioxidants and their combinations used in therapeutic RPs were considered in lutetium-177 preparations.Conclusion. Selection of the optimal composition of the dosage form is an urgent task, as it will ensure high-quality RPs both at the time of preparation and during the shelf life and delivery to the end user, which will greatly facilitate the use and centralized supply of therapeutic RPs. The necessity of creating a unified approach for the selection of antioxidants at the pharmaceutical development stage of radiopharmaceuticals is shown. For this purpose, an approach combining studies of radical reaction kinetics with studies of radiation-chemical yields of radiolysis products under identical or maximally similar conditions with subsequent verification of the stability of RPs dosage form seems to be very promising and has proven to be effective. In contrast, the empirical approach, which implies the selection of radioprotectors based on a direct study of their influence on the preservation of the level of radiochemical purity, is suboptimal because of the high market value of both radionuclides and non-radioactive precursors.