Tumor uptake of 67Ga-carrying liposomes.

The in vivo distribution, excretion, and tumor localization of liposome-encapsulated 67Ga in normal and Ehrlich tumor (solid form)-bearing mice were studied. In normal mice, multilamellar vesicles (MLVs) were taken up mainly by the liver and spleen, whereas small unilamellar vesicles (SUVs) exhibited a broader tissue distribution. When 67Ga was encapsulated in MLVs or SUVs, the excretion of the radiotracer in the urine and feces was less than that observed for free tracer at 72 h after i.v. administration. In tumor-bearing mice, SUVs were found to accumulate preferentially in tumors. The tumor uptake of neutral, positive, and negative SUVs was 10%-13% of the administered dose per gram of tumor tissue at 24 h after their injection. These values were about three times higher than those found for free 67Ga-nitrilotriacetic acid (67Ga-NTA) or 67Ga-citrate. Significant differences in tumor uptake due to different surface charges of liposomes were not observed. Enhanced tumor-to-blood and tumor-to-muscle ratios were also observed at 24 h after injection. These results suggest that 67Ga-carrying liposomes may be a useful for tumor imaging.