GC-04. Individual and cell-based carriers for delivery of therapeutic compounds: from design consideration to in vivo studies

Summary

Introduction

The main task of radionuclide therapy is to deliver the required therapeutic dose of radiation to the tumor site, while minimizing damage to health. For effective treatment of malignant neoplasms, appropriate therapeutic radionuclides should be selected that provide the required amount of radiation energy to destroy the tumor. The aim of this work is to study the encapsulation processes of the ²²⁵Ac radionuclide into the CaCO₃ particles of various sizes (micrometric and submicrometric), and the opportunity of retaining the daughter isotopes of encapsulated ²²⁵Ac under the in vitro and in vivo conditions.

Materials and methods

CaCO₃ cores were obtained by mixing of CaCl₂ and Na₂CO₃ salts at equivalent molar ratio. Human serum albumin (HSA) and tannic acid (DC) were used to create a polymer shell of the carriers. The pSCN-Bn-DOTA chelating agent (Sigma-Aldrich) was chosen for the radioactive labeling procedure. In the presence of acetic acid and pentaacetic acid diethylenetriamine, the chelator was covalently linked to HSA and subsequently modified with ²²⁵Ac. For in vitro experiments, we used a human cervical carcinoma cell line grown in a medium based on Alpha Minimum Essential Medium (Alpha-MEM), Dulbecco’s Modified Eagle’s Medium (DMEM), supplemented by fetal bovine serum (FBS, HyClone, USA), ultraglutamine I (Lonza, Switzerland) and penicillin/streptomycin (Biolot, Russia). The structures were visualized using acetoxymethyl calcein (calcein AM), propidium iodide (IP), and 4’,6-diamidino-2’-phenylindole dihydrochloride (DAPI). For in vivo experiments, we used 9-10 week old Wistar rats.

Results

Using the developed technology for radionuclide encapsulation, it was possible to achieve a high efficiency of daughter isotopes retention: retention of ²²¹Fr reached 54.5±3.6% after 28 days (the leakage for ²²¹Fr was 45.5±3.6%, and <22% for ²¹³Bi). The in vivo experiments have confirmed the ability of these particles to retain ²²⁵Ac and its daughter isotopes. The activity of “free” ²¹³Bi from ²²⁵Ac-HSA in the kidneys and urine was significantly higher as compared to the developed ²²⁵Ac-carriers. In particular, the radioactivity level of ²²⁵Ac-HSA during 240 hours was in the range of 19÷20% for kidneys and from 26±3.1% to 16.5±4.1% in urine. However, when injecting the developing labeled carriers, the level of radioactivity in the kidneys and urine was approximately the same throughout the observation period (from 4 to 240 hours), i.e., less than 5%. This indicates that there is no significant leakage of daughter isotopes from the carriers. The obtained indicators are acceptable for the normal functioning of organ systems.

Conclusion

In this work, we studied CaCO₃ particles with a polymer shell of various sizes used as carriers of a radioisotope for encapsulating ²²⁵Ac (a therapeutically relevant alpha emitter) and retaining its daughter isotopes upon their in vitro and in vivo testing. The complete physicochemical characterization of the carriers confirmed their biocompatibility and stability in biological media. Moreover, no morphological changes in the kidneys were found, which indicates a good retention capacity of the developing carriers and, as a consequence, their increased potential for sequestering toxic daughter radionuclides during therapy with alpha-radionuclides.

Acknowledgments

This work was financially supported by the Russian Science Foundation (project No. 19-75-10010). The work on the interaction of the developed particles with biological systems was partially supported by the Russian Science Foundation (project No. 19-75-00039).

Keywords

Polyelectrolyte capsules, in vivo, biodistribution, radionuclides, daughter isotopes, retention.