NEBULIZED INTERLEUKIN-2 LIPOSOMES - AEROSOL CHARACTERISTICS AND BIODISTRIBUTION

Although interleukin 2 (IL-2) has been associated with modest anti-tum our responses in man, treatment-related toxicity has Limited its wides pread use. The local delivery of liposomal formulations of interleukin 2 to the lung as aerosols has been demonstrated to be non-toxic, biol ogically active, and associated with regression of spontaneous pulmona ry metastases in dogs. This study was undertaken to evaluate the physi cal and biological characteristics of nebulized interleukin 2 liposome s. The aerosol droplet size distribution and the physical stability of interleukin 2 liposomes were examined in-vitro using an Andersen casc ade impactor and studies of liposome entrapment of interleukin 2 befor e and after nebulization. The biological stability of interleukin 2 li posomes after nebulization was demonstrated using the CTLL-2 bioassay for interleukin 2. In-vivo studies of pulmonary biodistribution and cl earance of inhaled technetium (Tc-99m)-labelled interleukin 2 liposome s were undertaken in a normal dog. Aerosols of free interleukin 2 and of interleukin 2 liposomes were compared in both in-vitro and in-vivo experiments. The mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD) of interleukin 2 liposomes were 1.98 mu m an d 2.02, respectively. Independent analysis of aerosol particle-size di stribution using the constitutive components of the interleukin 2 lipo somes (interleukin 2:lipid:HSA) demonstrated a close correlation of si ze distributions (r=0.9445; P <0.001). The entrapment of interleukin 2 in liposomes was 93+/-4.3% before nebulization and 90+/-8.9% after. A fter delivery to an anaesthetized dog, interleukin 2 liposome aerosols were deposited evenly throughout the lung (mean +/- s.d. central lung -to-peripheral lung deposition was 1.12+/-0.03). After approximately 2 4 h inhalation, interleukin 2 liposomes were retained within the lung and were taken up in part by the spleen. The results of this study are indicative of the stability of this interleukin 2 liposome formulatio n to nebulization. Such nebulization might be an attractive immunother apeutic strategy for treatment of pulmonary metastases and primary lun g cancers.