Tumor-imaging potential of liposomes loaded with 111In-NTA: biodistribution in mice

EMT6 tumors in BALB/c mice have been successfully imaged with small (less than 0.1 mu), unilamellar lipid vesicles (SUVs) loaded with 111In nitrilotriacetic acid (111In NTA). Neutral SUVs prepared from distearoyl phosphatidylcholine (DSPC) and cholesterol (CH) (ratio 2:1) delivered sufficient radioactivity to allow tumor visualization 24 hr after i.v. injection; so did positively and negatively charged SUVs with the ratio 4:1:1 for DSPC:CH:X, were X was stearylamine or dicetyl phosphate. Other SUVs containing a 6-aminomannose or 6-aminomannitol derivative of cholesterol did not cause significant tumor accumulation of 111In NTA, and tumor images were not readily discernible. The maximum tumor-associated radioactivity, 18.5% of injected dose per gram of tissue, was achieved with neutral SUVs. This level of tumor-associated 111In was over 4 times that observed when unencapsulated 111In NTA was injected. Neutral SUVs also gave the lowest specific activities in the liver and spleen (14.6% and 18.8% of dose respectively)