Technetium-99m-labeled stealth liposomes: A new Strategy to Identify metastasis in tumour model.

Objective: Stealth liposomes are useful carriers for delivering drugs to cancer sites. In this paper we describe the preparation and evaluation of Tc labelled stealth liposomes (PEG-Liposomes) as potential radiopharmaceuticals for SPECT imaging of cancer. This study is first to describe targeted localisation of radiolabeled stealth liposomes in tumourous cells, sparing normal cells of various organs in metastatic L1210 mouse tumour model in BDF1 mice.

Methods: Glutathione encapsulated stealth liposomes were made using lipid film hydration technique followed by probe sonication. Liposomes were radiolabeled using a lipophilic technetium complex, Tc-d,l-HMPAO. Labelled liposomes were purified by gel chromatography over sephadex G25 column. The tumour model was developed in immuno-competent BDF1 mice (F1DBA/2/C57-BL6 crosses) by injecting L1210 cells intraperitoneally. Biodistribution studies of the Tc- stealth liposomes were done in both tumour induced and normal mice. Histopathologic studies were done by excising the organs and the radioactivity in various sections was detected by autoradiography.

Results: The stealth liposomes could be synthesized as per a reported procedure and it showed similar retention factor in thin layer chromatography. Liposomes could be radiolabelled by using Tc-d,lHMPAO. Purification over sephadex G 25 column yielded radioachemical purity greater than 95%. Biodistribution studies and autoradiography studies showed significantly higher accumulation of Tc labelled stealth liposomes in liver, pancreas and ascitic fluid of the tumour induced mice as compared to normal mice.

Conclusions: Tc labelled stealth liposomes having radiochemical purity greater than 95% could be prepared which showed higher uptake in tumour.