Distribution and Metabolism of [3H]Tafluprost in Ocular Tissues Following Administration of a Single Ocular Dose to Cynomolgus Monkey

Abstract

Purpose: : Tafluprost is an ester prodrug of the biologically active metabolite, AFP–172, and currently under development as an ocular hypotensive agent. The purpose of this study was to evaluate the distribution and the metabolism of [³H]tafluprost in ocular tissues after a single ocular dose to cynomolgus monkeys. Furthermore, the ocular hypotensive effects of the major metabolites of tafluprost were investigated.

Methods: : Single topical ocular doses of [³H]tafluprost were administered to male/female cynomolgus monkeys at dose levels of 1 µg per eye for the tissue distribution and 10 µg per eye for the metabolite profiling. The concentrations of radioactivity were measured in ocular tissues and plasma with liquid scintillation counting. Metabolites in selected ocular tissues were profiled by HPLC with on–line radiodetection and structural analysis was done by electrospray ionization LC–MS/MS. The IOP lowering efficacies of major metabolites were examined by injection of chemically synthesized metabolites into the anterior chamber of male cynomolgus monkeys.

Results: : Following a single ocular administration of [³H]tafluprost, the highest concentrations of [³H]tafluprost–derived radioactivity were observed in bulbar conjunctiva and palpebral conjunctiva with 323 and 180 ng eq./g, respectively, at 0.083 hour postdose; and in cornea with 784 ng eq./g at 0.25 hour post dose. Levels of non–volatile radioactivity in plasma peaked with 0.907 ng eq./g at 0.083 hour postdose and declined steadily. Most of the radioactivity in aqueous humor and the other ocular tissues was associated with three major metabolites identified as AFP–172, 1,2–dinor–AFP–172 and 1,2,3,4–tetranor–AFP–172. AFP–172 was predominant in the ocular tissues at early phase and still remained at 8 hours postdose. Small amounts of unchanged tafluprost were detected in ciliary body, cornea and iris. AFP–172 injected intraoculary to normotensive monkeys significantly reduced IOP, while the other two metabolites did not show any obvious IOP lowering effect.

Conclusions: : Tafluprost was rapidly absorbed into ocular tissues and the systemic circulation following topical ocular administration. The most abundant and only pharmacologically active metabolite in ocular tissues was AFP–172. These results give further evidence that AFP–172 contributes to the ocular hypotensive effect of tafluprost.

Keywords: metabolism • intraocular pressure • ciliary body