The design of a pharmaceutically acceptable liposomal formulation of recombinant interleukin-2 (rIL-2) for locoregional anticancer immunotherapy

Liposomes composed of egg-phosphatidylcholine and egg-phosphatidylglycerol containing recombinant interleukin-2 (rIL-2) were prepared and characterise d for use in locoregional anticancer immunotherapy. During the encapsulatio n studies it was observed that the protein precipitated. Therefore, the imp act of the precipitation phenomenon on the characteristics and in vivo perf ormance of rIL-2 liposomes was studied. Recombinant IL-2 was diluted in var ious aqueous media and the amount of precipitated protein determined. Also, the in vitro bioactivity, chemical stability, and in vivo antitumor effica cy of liposomes prepared with precipitated rIL-2 or non-precipitated rIL-2 were assessed. Massive protein precipitation (60 up to >95% of total protein) was observed upon dilution of rIL-2 in salt-containing media, but not upon dilution in 5% glucose or water. Liposomes prepared with precipitated rIL-2 were shown to release 50% of the entrapped rIL-2 over a three-day period at 37 degrees C in protein-containing media. Loss of rIL-2 bioactivity and chemical inte grity was observed during storage at 4 degrees C over a 4-week period. Loco regional administration of precipitated rIL-2 in the guinea pig Line 10 tum or model resulted in significantly more tumor growth inhibition than admini stration of non-precipitated rIL-2. Liposomes containing non-precipitated r IL-2 were found to elicit similar antitumor effects as precipitated rIL-2. The results point to the importance of proper characterisation of new rIL-2 formulations as the physical properties of formulated rIL-2 may strongly i nfluence its bioactivity.