Design of an in situ forming methylcellulose hydrogel as universal vehicle for preclinical intravitreal injection of particulate formulations.

Abstract

Preclinical development of novel intravitreal pharmaceuticals is reliant on the use of animal pharmacokinetic (PK) and pharmacodynamic (PD) models, incipiently performed in small rodents. As most novel molecular entities exhibit fast intravitreal clearance, tailored preclinical extended-release (XR) formulations like microparticle suspensions are required to ensure sufficient exposure in the eye for 1 - 4 weeks which are required for PD experiments. Still, their use is very limited due to three major drawbacks: (i) Limited injectability of high particle concentrations, (ii) high intravitreal mobility, and (iii) attachment to vitreoretinal tissues and the lens. (ii) and (iii) complicate or prohibit PK and PD readouts. We developed a universal hydrogel vehicle to specifically enable microparticulate XR formulations for preclinical intravitreal injection. By optimizing the interplay of methylcellulose and kosmotropic additives, namely Na-citrate and Na-tartrate, rapid thermal gelation at vitreous temperature of 34°C was ensured. The hydrogel vehicle enabled injection of microparticulate XR formulations (Poly-lactide-co-glycolide and silica matrix particles) even when using non-siliconized syringes with small 34 gauge needles. Reduced intravitreal mobility and facilitated separation of formulation from retinal tissues was demonstrated ex vivo in porcine eyes. Rheological examination validated almost complete obstruction of embedded particulate XR formulations. In vitro XR of drugs (small molecules up to full length antibodies) was not altered. Experiments on ARPE-19 cells in vitro showed good tolerability and low toxicity. Furthermore, the hydrogel vehicle masked the cytotoxicity of embedded silica microparticles in high concentration. Our results suggest the hydrogel vehicle as a highly promising universal vehicle for preclinical intravitreal injection.