Interaction of ocular hypotensive agents (PGF2 alpha analogs-bimatoprost, latanoprost, and travoprost) with MDR efflux pumps on the rabbit cornea

Abstract

Purpose: The objectives of this work were (i) to screen ocular hypotensive prostaglandin (PGF2 alpha) analogs--bimatoprost, latanoprost, and travoprost as well as their free acid forms--for interaction with efflux pumps on the cornea and (ii) to assess the modulation of efflux upon co-administration of these prostaglandin analogs.

Methods: Cultured rabbit primary corneal epithelial cells (rPCEC) were employed as an in vitro model for rabbit cornea. Transporter-specific interaction studies were carried out using Madin-Darby canine kidney (MDCK) cells overexpressing MDR1, MRP1, MRP2, MRP5, and BCRP. Freshly excised rabbit cornea was used as an ex vivo model to determine transcorneal permeability.

Results: Cellular accumulation studies clearly showed that all prostaglandin analogs and their free acid forms are substrates of MRP1, MRP2, and MRP5. Bimatoprost was the only prostaglandin analog in this study to interact with P-gp. In addition, none of these molecules showed any affinity for BCRP. K (i) values of these prostaglandin analogs obtained from dose-dependent inhibition of erythromycin efflux in rPCEC showed bimatoprost (82.54 microM) and travoprost (94.77 microM) to have similar but higher affinity to efflux pumps than latanoprost (163.20 microM). Ex vivo studies showed that the permeation of these molecules across cornea was significantly elevated in the presence of specific efflux modulators. Finally, both in vitro and ex vivo experiments demonstrated that the efflux of these prostaglandin analogs could be modulated by co-administering them together.

Conclusion: Bimatoprost, latanoprost, travoprost, and their free acid forms are substrates of multiple drug efflux pumps on the cornea. Co-administration of these molecules together is a viable strategy to overcome efflux, which could simultaneously elicit a synergistic pharmacological effect, since these molecules have been shown to activate different receptor population for the reduction of intraocular pressure (IOP).

FIG. 1.

Chemical structures of prostaglandin analogs—bimatoprost, latanoprost, travoprost, and their respective free acid forms.

FIG. 2.

(A) Cellular accumulation of [¹⁴C] erythromycin (0.2 μCi/mL) by primary corneal epithelial cells (rPCEC) in the presence of a P-gp inhibitor (GF120918, 2 μM), MRP inhibitor (MK571, 50 μM), bimatoprost (B, 50 μM), latanoprost (L, 50 μM), and travoprost (T, 50 μM). Each data point represents mean ± SD (n = 4). ** Significant difference from control (P < 0.01). (B) Cellular accumulation of [¹⁴C] erythromycin (0.2 μCi/mL) by rPCEC in the presence of free acid forms of bimatoprost (BA, 100 μM), latanoprost (LA, 100 μM), and travoprost (TA, 100 μM). Each data point represents mean ± SD (n = 4). *Significant difference from control (P < 0.05).

FIG. 3.

Dose-dependent inhibition of [¹⁴C] erythromycin (0.2 μCi/mL) efflux by (A) bimatoprost, (B) latanoprost, and (C) travoprost in primary corneal epithelial cells (rPCEC). Each data point represents mean ± SD (n = 4).

FIG. 4.

Cellular accumulation of bimatoprost (B, 10 μM) in the presence of latanoprost (B+L, 50 μM), travoprost (B+T, 50 μM), 6α-methyl prednisolone (B+MPL, 500 μM), and prednisolone (B+PL, 500 μM). Each data point represents mean ± SD (n = 4). Significant differences from control: **P < 0.01; *P < 0.05.

FIG. 5.

Transcorneal permeability of bimatoprost (B, 50 μM) in the presence of latanoprost (B+L, 50 μM) and travoprost (B+T, 50 μM) across freshly excised rabbit cornea. Each data point represents mean ± SD (n = 3). Significant differences from control: **P < 0.01; *P < 0.05.