Thermal stability of freeze-dried mammalian interferons: Analysis of freeze-drying conditions and accelerated storage tests for murine interferon

Abstract

Conditions of Interferon processing were analyzed to select those that promote stability after freeze-drying. The effects of various preparative methods and treatment conditions were assessed by measuring the retention of biological activity by lyophilized interferon samples in two kinds of accelerated storage tests: the linear nonisothermal stability (LNS) test, a rapid method used for direct comparison of two or more preparations of interferon, and the multiple isothermal storage (MIS) test, a slow method requiring weeks to months to obtain data for the prediction of stability of a given preparation stored under various conditions. The most stable preparations of Newcastle-disease-virus-induced mouse L cell interferon were obtained using the following conditions: 1) perchlorate treatment to inactivate residual inducing virus, 2) nonspecific adsorption using zeolite for partial purification, 3) suspending medium of 0.5% bovine serum albumin in 0.1 m sodium phosphate buffer at pH 7, and 4) sublimation of ice in vacuo with a starting temperature of −30 °C to a final residual moisture of about 3%. The final product, reference reagent G002-904-511, was stable throughout the course of the LNS test. From an extensive MIS test, this reference interferon was predicted to lose 1000 units of activity in 110 years at 4 °C and 1000 units in 100 days at 37 °C. After 6 years of storage at 37 °C when the predicted residual activity would be about 20% of the original potency, 35% of initial interferon activity remained, confirming the usefulness of the short-term predictive test.