Erratum

Administration of pharmaceuticals containing radioactive isotopes and capable of specific binding to certain proteins is one of the approaches used in the treatment or diagnosis of malignant tumors. High renal accumulation of radioactive compounds after administration of radioconjugates with molecular mass less than 70 KDa is of the challenges that need to be solved. The purpose of the study was to identify the most effective approaches to reduce the accumulation of radioactivity in the kidneys after administration of radioconjugates used for diagnostic imaging and targeted therapy for cancer. Material and Methods. We conducted a literature search on the topic of the review in the electronic databases PubMed, Scopus and Web of Science from 1987 to 2023, 82 articles were used for writing the review. Results. The review presents a description of approaches used to improve the biodistribution of radioconjugates, mainly in preclinical studies. The advantages and disadvantages of such techniques have been described. Conclusion. Reducing renal radioactivity using radioconjugates of molecules with molecular masses less than 70 KDa is a challenging but achievable task. It is concluded that the use of cleavable linkers in such radioconjugates is highly promising, since this approach does not change the pharmacokinetics of such drugs. It is noted that the advantage of introducing concomitant substances compared to changing the structure of radioconjugates is a lesser dependence on the characteristics of a particular radiopharmaceutical. This approach also does not require prior work to modify the radioconjugate, but has limited efficiency.

The aim of this study was to create and evaluate a cell model designed for in vitro and in vivo testing of anti-human PD-L1 therapeutic and diagnostic agents' specificity. Materials and Methods. Genetically modified cells expressing human PD-L1 (strain CT26-PD-L1) were obtained by retroviral transduction of murine CT26 carcinoma cells. PD-L1 gene activity was assessed by real-time PCR, and PD-L1 expression on cells was identified by flow cytometry. Cells were tested using recombinant single-domain human anti-PD-L1 antibodies (nanoantibodies) conjugated with radioisotopes 68 Ga or 177 Lu. Immunoreactive fraction and cell internalization of the radioconjugates were evaluated in vitro. For in vivo experiments CT26-PD-L1 cells were transplanted into mice, radioimmunoconjugates were injected 9-14 days later, in 1-48 h the tumors were retrieved and subjected to direct radiometry. Intact CT26 cells not expressing the antigen served as a control. Results. CT26-PD-L1 strain of murine tumor cells expressing human membrane PD-L1 was created. When transplanted into intact BALB/c mice or sublethally irradiated F1(DBAxBALB/c) mice, these cells formed tumors. Thus, a significant advantage of the model was the possibility of in vivo testing of human PD-L1-affinity agents using animals under conventional vivarium conditions. When radioimmunoconjugates were administered to tumor bearing mice, radionuclides accumulated in tumors generated from the transplanted CT26-PD-L1 cells, but not CT26 cells. CT26-PD-L1 cells internalized anti-PD-L1 nanobodies in vitro. Due to a high density of target molecules, CT26-PD-L1 cells allowed both to confirm pharmaceuticals' specificity and to quantify the target-binding fraction of conjugates in a single test. Conclusion. The created cells are the first genetically engineered cells designed to evaluate affinity of anti-human PD-L1 therapeutic and diagnostic agents in Russia. Test results confirmed the model suitability for in vitro and in vivo testing of the specificity of pharmaceuticals targeting human PD-L1.

INTRODUCTION: According to the literature, 68 Ga-FAPI-04 has receptor specificity for malignant neoplasms with overexpression of the fibroblast activation protein and is used to visualize various types of neoplasms, in particular head and neck cancer, gastrointestinal tract, lung, breast cancer with a high contrast ratio of the tumor to the background, and may possibly become an alternative to 18 F-FDG. OBJECTIVE: The results of the first experience of using PET/CT with 68 Ga-FAPI-04 in Russia. MATERIALS AND METHODS: A comparative analysis of the results of 68 Ga-FAPI-04 and 18 F-FDG PET/CTs with an interval of 1–3 days was carried out in 13 patients (four women and nine men) with various oncological diseases, examined from February to December 2021 in Granov Russian Research Center of Radiology and Surgical Technologies. RESULTS: In all 13 patients, it was possible to identify both primary tumors and their metastases with different tracer uptake. 68 Ga-FAPI PET/CT compared with 18 F-FDG PET/CT revealed more metastatic foci (135 vs 127) predominantly in the liver, peritoneum, mesentery, omentum, and brain due to low background uptake in these organs. In our observation, foci of increased 68 Ga-FAPI-04 uptake localized in non-enlarged retroperitoneal lymph nodes in two patients. Also, in two patients with bone metastases from bladder cancer and stomach cancer, one false positive and one false negative result was obtained with 68 Ga-FAPI-04. DISCUSSION: The high uptake of 68 Ga-FAPI-04 in the tumor makes it a promising tracer for many types of cancer, especially in cases, where conventional 18 F-FDG PET/CT faces limitations due to its pharmacokinetics. At the same time, PET/CT with 68 Ga-FAPI-04, aimed at visualizing the tumor microenvironment, may have a higher sensitivity in detecting small lesions due to the predominance of stroma in them. 68 Ga-FAPI showed better results in detecting both lytic and osteoblastic bone metastases compared to 18 F-FDG. CONCLUSION: 68 Ga-FAPI is a promising tracer for molecular imaging of most malignant neoplasms and requires further study. 68 Ga-FAPI-04 can become an addition or a full-fledged solution when other tracers have limitations.

The 82Sr/82Rb generator is used to produce a medical radiopharmaceutical rubidium-82 chloride in saline solution for PET investigation. In this work, we studied the effect of the amount of stable strontium and calcium delivered to the sorbent (hydrated tin dioxide), on the maximum volume of radiopharmaceutical solution that can be obtained from the generator. Sr and Ca may be delivered to the sorbent from the initial solution of strontium-82 or from the eluent (0.9% NaCl) during medical application of the generator. It is shown that this volume depends on the value CSr + 0.11CCa, where CSr and CCa - molar concentrations of the elements in 1 g of the sorbent. The obtained results make it possible to increase significantly the productivity and reliability of the used generators.

Erratum

INTRODUCTION: According to the literature, 68Ga-FAPI-04 has receptor specificity for malignant neoplasms with overexpression of the fibroblast activation protein and is used to visualize various types of neoplasms, in particular head and neck cancer, gastrointestinal tract, lung, breast cancer with a high contrast ratio of the tumor to the background, and may possibly become an alternative to 18F-FDG.OBJECTIVE: The results of the first experience of using PET/CT with 68Ga-FAPI-04 in Russia.MATERIALS AND METHODS: A comparative analysis of the results of 68Ga-FAPI-04 and 18F-FDG PET/CTs with an interval of 1–3 days was carried out in 13 patients (four women and nine men) with various oncological diseases, examined from February to December 2021 in Granov Russian Research Center of Radiology and Surgical Technologies.RESULTS: In all 13 patients, it was possible to identify both primary tumors and their metastases with different tracer uptake. 68Ga-FAPI PET/CT compared with 18F-FDG PET/CT revealed more metastatic foci (135 vs 127) predominantly in the liver, peritoneum, mesentery, omentum, and brain due to low background uptake in these organs. In our observation, foci of increased 68Ga-FAPI-04 uptake localized in non-enlarged retroperitoneal lymph nodes in two patients. Also, in two patients with bone metastases from bladder cancer and stomach cancer, one false positive and one false negative result was obtained with 68Ga-FAPI-04.DISCUSSION: The high uptake of 68Ga-FAPI-04 in the tumor makes it a promising tracer for many types of cancer, especially in cases, where conventional 18F-FDG PET/CT faces limitations due to its pharmacokinetics. At the same time, PET/CT with 68Ga-FAPI-04, aimed at visualizing the tumor microenvironment, may have a higher sensitivity in detecting small lesions due to the predominance of stroma in them. 68Ga-FAPI showed better results in detecting both lytic and osteoblastic bone metastases compared to 18F-FDG.CONCLUSION: 68Ga-FAPI is a promising tracer for molecular imaging of most malignant neoplasms and requires further study. 68Ga-FAPI-04 can become an addition or a full-fledged solution when other tracers have limitations.

Quantification of the immunoreactive fraction (IRF) of radioactive isotope-labeled antibodies or their fragments is necessary to assess the specific activity of radiopharmaceuticals. Traditionally, cells expressing the target molecules on their surface are used to determine IRF, but such analysis is time-consuming and has difficulties with standardization.The aim of the study was to develop a fast and reliable method for quantitative determination of IRF by 68 Ga-labeled VHH antibodies to PD-L1 based on the use of magnetic particles coated with antigen molecules.Materials and Methods.Commercially available magnetic particles coated with protein A have been used in our study.The antigen conjugated with the Fc fragment (PD-L1-Fc) was immobilized on the particles.The IRF value of 68 Ga radionuclide-labeled nanobodies (VHH) against PD-L1 ( 68 Ga-VHH-PD-L1) was determined using magnetic particles coated with antigen molecules and cells expressing the antigen on their surface.When VHH antibodies were conjugated to 68 Ga radionuclide, protein molecules were modified using bifunctional chelating agents: tetraazacyclododecanetetraacetic acid (DOTA) or deferoxamine (DFO).The magnitude of IRF was defined as the ratio of radioactivity specifically bound to particles or cells to the total radioactivity added to the sample.Results.The specificity of the 68 Ga-VHH-PD-L1 radioimmunoconjugate binding to the antigen-coated magnetic particles has been proved.Some special aspects, which should be taken into consideration when using this method, have been established.The comparison of the IRF estimates using the antigen-expressing cells and magnetic particles has not revealed any significant differences in the results obtained in our study.Nevertheless, the presented method based on magnetic particles with immobilized antigen molecules requires only 15 min to determine the radioimmunoconjugate IRF, which is of fundamental importance for the routine assessment of the specificity of radiopharmaceuticals containing short-lived isotopes.

Data are presented on ligands based on bombesin derivatives, which are peptides that specifically bind to gastrin-releasing factor receptors, that are promising for use in nuclear medicine. An analysis of developments related to the creation of radiopharmaceuticals (RPs) based on gastrin-releasing peptide-receptor agonists for radionuclide diagnostics and systemic radiation therapy is carried out. The stages of pharmaceutical development of the first Russian RPs 68 Ga-NOTA-AMBA and 177 Lu-DOTA-AMBA are described, including the synthesis technology using automated modules, as well as drug specifications.

One of the most important characteristics of radiolabeled antibodies and their derivatives is the size of the immunoreactive fraction. Measuring this parameter requires a high density of target molecules, which is rarely achievable with tumor cells. The solution to the problem of radioimmunoconjugate testing was the creation of recombinant cells carrying human endoglin (CD105). The recipients of the endoglin gene ( ENG ) were rat C6 glioma cells, which are characterized by ease of cultivation and high transfection efficiency. The obtained C6-ENG cells carried 1.3 × 10 6 CD105 molecules on the membrane and were used to determine the immunoreactive fraction of 68 Ga and 89 Zr radiolabeled anti-CD105 monoclonal antibodies and their Fab-fragments. The creation of stable recombinant cell lines for in vitro testing the specific activity of radiolabeled antibodies and their derivatives seems promising for the development of new radiopharmaceuticals.

The Sr-82/Rb-82 generator is used to produce a radiopharmaceutical rubidium-82 chloride in saline solution for PET imaging. In this work, we studied the effect of the amount of stable strontium and calcium delivered to the sorbent (on the basis of hydrated tin dioxide) on the maximum volume of radiopharmaceutical solution that can be obtained from the generator. Sr and Ca may be delivered to the sorbent from the initial solution of strontium-82 chloride or from the eluent (0.9% NaCl) during medical application of the generator. It is shown that this volume depends on the value C-Sr + 0.11C(Ca), where C-Sr and C-Ca are molar concentrations of the elements in 1 g of the sorbent. The obtained results make it possible to increase significantly the productivity and reliability of the used generators.

The 82Sr/82Rb generator is used to produce a medical radiopharmaceutical rubidium-82 chloride in saline solution for PET investigation. In this work, we studied the effect of the amount of stable strontium and calcium delivered to the sorbent (hydrated tin dioxide), on the maximum volume of radiopharmaceutical solution that can be obtained from the generator. Sr and Ca may be delivered to the sorbent from the initial solution of strontium-82 or from the eluent (0.9% NaCl) during medical application of the generator. It is shown that this volume depends on the value CSr + 0.11CCa, where CSr and CCa - molar concentrations of the elements in 1 g of the sorbent. The obtained results make it possible to increase significantly the productivity and reliability of the used generators.

The 82 Sr/ 82 Rb generator is used to produce a radiopharmaceutical rubidium-82 chloride in saline solution for PET imaging. In this work, we studied the effect of the amount of stable strontium and calcium delivered to the sorbent (on the basis of hydrated tin dioxide) on the maximum volume of radiopharmaceutical solution that can be obtained from the generator. Sr and Ca may be delivered to the sorbent from the initial solution of strontium-82 chloride or from the eluent (0.9% NaCl) during medical application of the generator. It is shown that this volume depends on the value C Sr + 0.11 C Ca , where C Sr and C Ca are molar concentrations of the elements in 1 g of the sorbent. The obtained results make it possible to increase significantly the productivity and reliability of the used generators.

The pharmaceutical development of innovative radiopharmaceuticals (RPs) based on bispecific high-affinity hypervariable fragments of single-domain monoclonal antibodies (nanoantibodies) to the surface receptors of T-regulatory cells (GITR and CTLA-4) is described: 68 Ga-DFO-anti-CTLA4-GITR and 177 Lu-DOTA-anti-CTLA4-GITR. The specified RPs are intended for diagnostics using the immuno-PET method ( 68 Ga-DFO-anti-CTLA4-GITR) and systemic radiation therapy ( 177 Lu-DOTA-anti-CTLA4-GITR) of the generalized forms of socially significant cancer. As part of pharmaceutical development, technologies are created for introducing chelating groups into the bispecific nanoantibody molecule, as well as methods for obtaining the main active substance and the finished dosage form of the radioactive drug with selection of the optimal composition of excipients to ensure the stability of the radionuclide complex and the precursor molecule.

Radiopharmaceuticals, the medicinal products containing radioactive isotopes, hold a special place among the other medicines. The aim of the study was to analyse regulatory peculiarities of the production and subsequent life cycle of radiopharmaceuticals, associated with the unique physicochemical properties, production process, distribution, and clinical use. The article reviews regulatory decisions adopted in Russia and a number of other countries that, in certain circumstances, allow medical organisations not licensed as manufacturers to compound radiopharmaceuticals for in-house use without marketing authorisation. Unstable isotopes in radiopharmaceuticals reduce the risk of microbial contamination, so the quality control requirements may be relaxed. The described regulatory framework, which came into effect 12 years ago, provided an opportunity for a many-fold increase in the number of radiopharmaceuticals for radionuclide diagnosis and treatment of severe socially significant diseases. In recent years, a number of countries have adopted regulations making it possible to supply the radiopharmaceuticals manufactured by medical organisations outside the usual marketing authorisation track to other medical organisations. If adopted in Russia, a similar regulation will further expand the access to effective methods of diagnosis and treatment for patients.

N-vinylpyrrolidone-co-allylamine copolymers (VP-co-AA) containing iminodiacetic (IDA) chelation units were prepared in the range of molecular masses of the copolymers from 9000 to 30,000 Da depending on polymerization conditions. Non-radioactive organometallic species Re(CO)3+ were introduced into polymeric carriers under mild conditions; the prepared metal–polymeric complexes were characterized by IR, NMR, ESI-MS and HPLC. IR spectra data confirmed the coordination of M(CO)3+ moiety to the polymeric backbone via IDA chelation unit (appearance of characteristic fac-M(CO)3+ vibrations (2005, 1890 cm−1), as well as the appearance of group of signals in 1H NMR spectra, corresponding to those inequivalent to methylene protons CH2COO (dd, 4.2 ppm), coordinated to metal ions. The optimal conditions for labeling the PVP-co-AA-IDA copolymers with radioactive 99mTc(CO)3+ species were determined. The radiochemical yields reached 97%. The obtained radiolabeled polymers were stable in blood serum for 3 h. In vivo distribution experiments in intact animals showed the high primary accumulation of technetium-99m MPC (MM = 15,000 Da) in blood with subsequent excretion via the urinary tract.

Copolymer of N-vinylpyrrolidone (VP) with vinylformamide (VFA) and N-vinyliminodiacetic acid (VIDA) was synthesized; its metal-polymer complexes (MPCs) with gallium were obtained. The complexes were characterized by size exclusion chromatography, hydrodynamic and optical methods, scanning electron microscopy, and spectral methods (UV, IR, 1Н NMR spectroscopy). It was demonstrated that in going from polymer to complex, hydrodynamic parameters of macromolecules change only slightly, although the polymer contains intramolecular Ga(VIDA)2 fragments in its structure. A new method for preparation of MPCs with gallium and gallium-68 radionuclide was suggested. The obtained metal-polymer complex is stable over a wide range of pH values as well as in the histidine challenge reaction. In vivo distribution experiments in intact animals showed high primary accumulation of thegallium-68 MPC in blood with subsequent excretion via urinary tract.

The paper presents a 82 Sr/ 82 Rb-generator and shows the possibility and perspectives to use the radiopharmaceutical (RFP) «Rubidium chloride, from 82Rb generator» (hereinafter referred to as « 82 Rb-chloride») for the diagnosis of brain tumors (GM) based on the experience of the use of the radiopharmaceutical in the FGBI «RRCRST» of the Ministry of Healthcare of Russia. Results of observation of 23 patients are presented with malignant and benign tumors, and non-neoplastic lesions in the brain. The tendency was detected for the prevalence of increased accumulation of 82 Rb-chloride in malignant tumors as compared to benign tumors and in arteriovenous malformations (AVM) in which the 82Rb-chloride is accumulated within the vascular phase, but it is not retained. Ultra-short half-life of the radionuclide [ 82 Rb] (76 sec) and low radiation exposure arising when the 82Rb-chloride is intravenously injected, create completely new possibility for sequential use of two or more radiopharmaceuticals at examining a patient. For example, PET imaging with 18 F-FDG, 11 C-L-methionine or 11 C-choline can be performed in 7 minutes after the injection of the 82Rb-chloride to a patient. The efficiency of using 82 Rb-chloride as a diagnostic tool in the neurooncological patients is stated. The method was develop for dosing and injection of the radiopharmaceutical from a generator. Using a single generator of Rubidium-82 it is possible to run about 800 PET studies. Generator is reliable and easy in use.