Pharmacokinetic Characterization of Single-Stranded DNA in Murine Models Using High-Specific-Activity ⁶⁸ Ga Radiolabeling Coupled with Dynamic Positron Emission Tomography

This study aimed to develop an efficient concentration methodology to enhance the specific activity of ⁶⁸Ga. By systematically optimizing chelation parameters, we established the relationships between the molar amounts of single-stranded DNA (A20) and varying ⁶⁸Ga specific activities, thereby maximizing the radiochemical yield in DNA radiolabeling systems. <b>Method</b>: The ⁶⁸Ga eluate was subjected to ionic enrichment and initially purified using cation-exchange chromatography, followed by concentration through an organic/aqueous phase protocol employing acetone/NaCl eluents. Systematic chelation experiments were performed by reacting gradient concentrations of A20 (1 or 3 nmol) with radiometal solutions at defined specific activities (1, 5, and 10 mCi/mL). The resulting reaction mixtures were subsequently purified using PD-10 columns. Dynamic PET/CT imaging of the purified ⁶⁸Ga-labeled A20 (⁶⁸Ga-A20) was performed over a 60 min interval to assess its biodistribution and metabolic kinetics in murine models. <b>Results</b>: Extraction of ⁶⁸Ga using water resulted in the introduction of sodium ions, which could interfere with subsequent labeling reactions. In contrast, acetone-based extraction effectively prevented contamination from exogenous ions. Optimization of the extraction protocol led to a 5-fold increase in the radioactivity concentration of ⁶⁸Ga. Labeling studies demonstrated an efficiency of 75.03% when 3 nmol (100 μM) of A20 was used, and the ⁶⁸Ga radioactivity concentration was maintained at 1 mCi/mL. Dynamic PET/CT imaging revealed that ⁶⁸Ga-A20 was predominantly eliminated via the renal pathway in healthy mice. Following curve-fitting analysis, the calculated half-lives were 6.61 ± 0.26 min in blood, 13.53 ± 1.04 min in kidney, and 7.61 ± 0.27 min in liver. <b>Conclusion</b>: This study demonstrated that the radioactivity concentration of ⁶⁸Ga can be effectively enhanced by processing the ⁶⁸Ga solution through cation-exchange chromatography followed by acetone extraction, representing a critical advancement in improving radiolabeling efficiency. Additionally, the results indicated that ⁶⁸Ga-A20 was primarily eliminated via the renal pathway in healthy mice.