Evaluation of protein drug stability with vitreous humor in a novel ex-vivo intraocular model

The stability of protein therapeutics during the residence time in the vitreous humor (VH) is an important consideration for intra ocular treatment and can possibly impact therapeutic efficacy and/or treatment intervals. Unavailability of the reliable Ex-vivo intravitreal (ExVit) model to estimate protein stability following IVT has driven the research focus to develop such model which can facilitate protein stability estimation before in-vivo experiments. In this manuscript, we have developed and evaluated three ExVit models, namely, ExVit static, semi-dynamic and dynamic. These models were utilized and compared when studying the in-vitro stability of model protein formulations under simulated intraocular conditions using porcine vitreous humor (VH). The ExVit static model exhibited significant precipitation and aggregation of proteins, most likely due to pH change occurred in the VH after isolation. The semi-dynamic model assessed was composed of two compartments i.e., VH- and buffer-compartment which has effectively stabilized the pH of the VH and facilitated the migration of VH degradation products. However, some limitations related to investigation of long-term protein stability were also observed with semi-dynamic model. The dynamic model developed, was comprised of three diffusion controlling barriers (two diffusion controlling membranes and a gel-matrix), which allowed modulation of the diffusion rate of macromolecules. The ability of dynamic model to modulate protein retention time in the VH will overcome the challenges faced by the semi-dynamic model such as long-term stability evaluation.