Pharmacokinetics, dosimetry and comparative efficacy of 188Re-liposome and 5-FU in a CT26-luc lung-metastatic mice model

The biodistribution, pharmacokinetics, dosimetry and comparative therapeutic efficacy of intravenously administrated 188Re-N,N-bis(2-mercaptoethyl)-N′,N′-diethylethylenediamine (BMEDA)-labeled pegylated liposome (188Re-liposome) and 5-FU were investigated in a CT26-luc lung-metastatic model. After intravenous administration of 188Re-liposome, tumor accumulation from the radioactivity was observed. Levels of radioactivity in tumors were maintained at steady levels (from 5.40 to 5.67 %ID/g) after 4 to 24 h. In pharmacokinetics, the AUC(0→∞), MRT(0→∞) and Cl of 188Re-liposome in blood via intravenous route were 998 h %ID/ml, 28.7 h and 0.1 ml/h, respectively. The total excreted fractions of feces and urine were 0.61 and 0.26, respectively. Absorbed doses for 188Re-liposome in the liver and red marrow were 0.31 and 0.08 mSv/MBq, respectively. Tumor-absorbed doses for 188Re-liposome ranged from 48.4 to 1.73 mGy/MBq at 10 to 300 g tumor spheres. In therapeutic efficacy, the survival times of mice after 188Re-liposome [80% maximum tolerated dose (MTD); 29.6 MBq], 5-FU (80% MTD; 144 mg/kg), liposome or normal saline treatments were evaluated. Consequently, radiotherapeutics of 188Re-liposome attained a longer lifespan (increase of 34.9%; P=.005) in mice than in the normal saline group. The increase in lifespan of the 188Re-liposome group was 2.5-fold greater than that of the 5-FU group. Therefore, intravenous administration of 188Re-liposome could provide a benefit and it is a promising strategy for delivery of passive nanotargeted radiotherapeutics in oncology applications.