Use of technetium-99m-liposomes in tumor imaging.

UNLABELLED

In this study, liposomes labeled with 99mTc have been evaluated as tumor imaging agents.

METHODS

Liposomes containing reduced glutathione and carrying either a negative surface charge or no surface charge were labeled with 99mTc using the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO). The 99mTc-liposomes were intravenously injected into the tail vein of nuce mice which had been implanted intramuscularly in the thigh with nontransfected Chinese hamster ovary cells. Gamma camera images were acquired at 1, 4 and 22 hr and compared with tissue biodistribution studies at 24 hr postinjection.

RESULTS

Tumors could be distinguished from normal thigh muscle at 4 hr postinjection for both formulations. Tumor-to-muscle ratios were not significantly different for the two formulations due to the increased normal muscle activity at 24 hr for the neutral liposomes. Liver-to-tumor, liver-to-blood, spleen-to-tumor and spleen-to-blood ratios were significantly lower for the neutral 99mTc-liposomes than for the negative 99mTc-liposomes. Neutral 99mTc-liposomes were cleared slower by the reticuloendothelial system, and therefore remained in the circulation for a longer period of time.

CONCLUSION

The results of this study indicate that both formulations could be used as tumor imaging agents, but that neutral 99mTc-liposomes would be more suitable as a drug delivery agent due to their increased total uptake by the tumor and decreased nonspecific uptake by the reticuloendothelial system.