Pharmacokinetic-pharmacodynamic and response sensitization modeling of the intraocular pressure-lowering effect of the EP4 Agonist 5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl}thiophene-2-carboxylate (PF-04475270).

Developing a population-based pharmacokinetic-pharmacodynamic (PKPD) model is a challenge in ophthalmology due to the difficulty of obtaining adequate pharmacokinetic (PK) samples from ocular tissues to inform the pharmacodynamic (PD) model. Using limited PK data, we developed a preclinical population-based PD model suitable for capturing the time course of dog intraocular pressure (IOP) that exhibited time-dependent sensitization after topical administration of PF-04475270 [5-{3-[(2S)-2-{(3R)-3-hydroxy-4-[3-(trifluoromethyl)phenyl]butyl}-5-oxopyrrolidin-1-yl]propyl}thiophene-2-carboxylate]. A physiologically relevant PK model was chosen to simultaneously capture the concentration profiles of CP-734432, a potent EP4 agonist and the active metabolite of PF-04475270, sampled from three ocular tissues of the anterior chamber: cornea, aqueous humor, and iris-ciliary body. Two population-based PD models were developed to characterize the IOP lowering profiles: model I, a standard indirect-response model (IRM); and model II, an extension of a standard IRM that empirically incorporated a response-driven positive feedback loop to account for the observed PD sensitization. The PK model reasonably described the PK profiles in all three ocular tissues. As for the PD, model I failed to capture the overall trend in the population IOP data, and model II more adequately characterized the overall data set. This integrated PKPD model may have general utility when PD sensitization is observed and is not a result of time-dependent PK. In addition, the model is applicable in the ophthalmology drug development setting in which PK information is limited but a population-based PD model could reasonably be established.