Preformulation Studies of a Liposomal Formulation Containing Sirolimus for the Treatment of Dry Eye Disease

Abstract

Purpose: The aim of this study was to develop and characterize a liposomal product containing sirolimus to be administered subconjunctivally for the treatment of nonresponsive keratoconjunctivitis sicca (KCS) or dry eye. Methods: Formulations were prepared using an ethanol injection method and an adaptation of the heating method in pursuance of the most suitable methodology for future industrial production. Liposomes were loaded with either a high dose of 1mg/mL of sirolimus or a less toxic dose of 0.4mg/mL. The effects of critical process and formulation parameters were investigated. Liposomes were characterized in terms of size, zeta potential, polydispersity, differential scanning calorimetry, morphology, entrapment efficiency, phospholipid content, thermal stability, and sterility. The formulation was evaluated clinically in dogs with spontaneous KCS. Results: Sterile liposomal dispersions with sizes ranging from 140 to 211nm, were successfully obtained. High entrapment efficiency of 93%-98% was achieved. The heating method allowed an easier production of liposomes with high entrapment efficiency, to significantly shorten production time and the elimination of the use of alcohol. The poor stability of the obtained liposomes in aqueous dispersion made the inclusion of a lyophilization step necessary to the manufacturing process. In vivo testing of the liposomal sirolimus formulations in the spontaneous KCS dog model have produced promising results, particularly with a sirolimus dose of 1mg/mL, indicating the need for further development and study of proposed formulations in the treatment of canine KCS. Clinical improvement in tear production in dogs with spontaneous KCS treated with the 1mg/mL dose product was observed. Conclusions: The heating method allowed easier production of high entrapment efficiency liposomes to significantly shorten production time and the elimination of the use of alcohol. Tear production was increased in dogs administered with the formulation.