Purpose: The intraocular pharmacodynamics of PF-04523655, a small-interfering RNA (siRNA) directed against RTP801, was characterized using rat models of retinopathy.
Methods: Rat models of streptozotocin-induced diabetes and wet AMD were used to determine the onset, extent, and duration of siRNA inhibition of retinal RTP801 expression by PF-04523655, and this inhibition was characterized by pharmacokinetic/pharmacodynamic (PK/PD) modeling. A rat model of wet AMD was also used to examine PF-04523655 dose-dependent effects on the incidence of clinical grade 3 or 4 choroidal neovascularization lesions. Whole homogenate versus laser-capture microdissected (LCM) retinal samples were analyzed by quantitative PCR for RTP801 expression.
Results: RTP801 expression in RPE/choroid (RPE/C) increased in diabetic rats by up to 70% above nondiabetic rat levels. Inhibition of retinal RTP801 expression by PF-04523655 began 1 day after intravitreous injection and was observed through day 7 in the neurosensory retina and through day 14 or longer in RPE/C. PF-04523655 inhibition of RTP801 expression was maintained well after clearance of PF-04523655 from the eye and was best characterized by an effect compartment PK/PD model. Moreover, PF-04523655 administration decreased the incidence of clinical grade 3 or 4 lesions by approximately 60% (P = 0.053), and dose-dependently inhibited retinal RTP801 expression (P < 0.01). RTP801 expression was enriched in the outer nuclear layer in LCM samples.
Conclusions: In rodent retinopathy models, administration of the siRNA, PF-04523655, reduced RTP801 expression in the retina, consistent with the RNA-induced silencing complex (RISC) mechanism of action. The pharmacodynamic profile from the animal models could be useful to elucidate dose and exposure dependency of RTP801 expression inhibition by siRNA.
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