Pharmacokinetics of <sup>188</sup>Re-nanodiamonds complex in mice bearing experimental Ehrlich carcinoma
Targeted radionuclide therapy of tumors is one of the most active areas of research in precision cancer treatment. Nanodiamonds (NDs) have attracted enhanced attention as potential radionuclide carriers for targeting of cancer. The authors present results of the study of pharmacokinetic properties of NDs labeled with <sup>188</sup>Re (<sup>188</sup>Re-NDs) according to a route of the drug administration. Experimental research was carried out on mice with the solid form of Ehrlich tumor, the labeled NDs were administered intratumorally, intravenously and intragastrically. Pharmacokinetic properties of carrier-free sodium perrhenate (Na<sup>188</sup>ReO<sub>4</sub>) after intratumoral administration served as control. Obtained data demonstrated that maximum specific radioactivity, 98.5%/g in the tumor, was after intratumoral administration of <sup>188</sup>Re-NDs, and then it was cleared from the tumor very rapidly. The maximum of specific radioactivity in the tumor following intravenous and intragastrical administration of the <sup>188</sup>Re-NDs complex were 2.85%/g and 3.14%/g respectively. Concentration of carrier-free Na<sup>188</sup>ReO<sub>4</sub> in the tumor was considerably lower as compared with the concentration of <sup>188</sup>Re-ND complex. High level of the <sup>188</sup>Re-ND complex was detected in the thyroid and the stomach. Results of the study show that the highest level of radioactivity in the tumor was detected after intratumoral administration of the Na<sup>188</sup>ReO<sub>4</sub>-ND complex. A route of administration of the Na<sup>188</sup>ReO<sub>4</sub>-NDs complex did not effect considerably on the level of radioactivity in internal organs and tissues, however, the rate of accumulation of radioactivity in these organs and tissues depended on the route of administration.