Micro-SPECT/CT–Based Pharmacokinetic Analysis of 99mTc-Diethylenetriaminepentaacetic Acid in Rats with Blood–Brain Barrier Disruption Induced by Focused Ultrasound

This study evaluated the pharmacokinetics of 99mTc-diethylenetriamine pentaacetate acid (99mTc-DTPA) after intravenous administration in healthy and F98 glioma–bearing F344 rats in the presence of blood–brain barrier disruption (BBB-D) induced by focused ultrasound (FUS). The pharmacokinetics of the healthy and tumor-containing brains after BBB-D were compared to identify the optimal time period for combined treatment. Methods: Healthy and F98 glioma–bearing rats were injected intravenously with Evans blue (EB) and 99mTc-DTPA; these treatments took place with or without BBB-D induced by transcranial FUS of 1 hemisphere of the brain. The permeability of the BBB was quantified by EB extravasation. Twelve rats were scanned for 2 h to estimate uptake of 99mTc radioactivity with respect to time for the pharmacokinetic analysis. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining was performed to examine tissue damage. Results: The accumulations of EB and 99mTc-DTPA in normal brains or brains with a tumor were significantly elevated after the intravenous injection when BBB-D was induced. The disruption-to-nondisruption ratio of the brains and the tumor–to–ipsilateral brain ratio of the tumors in terms of radioactivity reached a peak at 45 and 60 min, respectively. EB injection followed by sonication showed that there was an increase of about 2-fold in the tumor–to–ipsilateral brain EB ratio of the target tumors (7.36), compared with the control tumors (3.73). TUNEL staining showed no significant differences between the sonicated tumors and control tumors. Conclusion: This study demonstrates that 99mTc-DTPA micro-SPECT/CT can be used for the pharmacokinetic analysis of BBB-D induced by FUS. This method should be able to provide important information that will help with establishing an optimal treatment protocol for drug administration after FUS-induced BBB-D in clinical brain disease therapy.

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