Natural prostaglandins (PGs) such as PGD2, PGE2, PGF2(2alpha), and PGI2 exhibited the highest affinity for their respective cognate receptors, but were the least selective agents when tested in receptor binding assays. Travoprost acid ([+]-fluprostenol) was the most FP-receptor-selective compound, exhibiting a high affinity (Ki = 35 +/- 5 nM) for the FP receptor, and minimal affinity for DP (Ki = 52,000 nM), EP1 (Ki = 9540 nM), EP3 (Ki = 3501 nM), EP4 (Ki = 41,000 nM), IP (Ki > 90,000 nM), and TP (Ki = 121,000 nM) receptors. Travoprost acid was the most potent PG analog tested in FP receptor functional phosphoinositide turnover assays in the following cell types: human ciliary muscle (EC50 = 1.4 nM), human trabecular meshwork (EC50 = 3.6 nM), and mouse fibroblasts and rat aortic smooth muscle cells (EC50 = 2.6 nM). Although latanoprost acid exhibited a relatively high affinity for the FP receptor (Ki = 98 nM), it had significant functional activity at FP (EC50 = 32-124 nM) and EP1 (EC50 = 119 nM) receptors. Bimatoprost acid was less selective, exhibiting a relatively high affinity for the FP (Ki = 83 nM), EP1 (Ki = 95 nM), and EP3 (Ki = 387 nM) receptors. Bimatoprost acid exhibited functional activity at the EP1 (EC50 = 2.7 nM) and FP (EC50 = 2.8-3.8 nM in most cells) receptors. Bimatoprost (nonhydrolyzed amide) also behaved as an FP agonist at the cloned human FP receptor (EC50 = 681 nM), in h-TM (EC50 = 3245 nM) and other cell types. Unoprostone and S-1033 bound with low affinity (Ki = 5.9 microM to > 22 microM) to the FP receptor, were not selective, but activated the FP receptor. In conclusion, travoprost acid has the highest affinity, the highest FP-receptor-selectivity, and the highest potency at the FP receptor as compared to the other ocular hypotensive PG analogs known so far, including free acids of latanoprost, bimatoprost, and unoprostone isopropyl ester.

Purpose. To determine the functional agonist potencies of the intraocular pressure (IOP)-lowering prostaglandin F (FP)-class prostaglandin (PG) analogues (e.g., travoprost, latanoprost, bimatoprost, and unoprostone isopropyl ester) in human trabecular meshwork (h-TM) cells, by using phosphoinositide (PI) turnover and intracellular Ca²⁺ ([Ca²⁺]_i) mobilization, and to confirm the FP nature of these receptors by using an FP receptor antagonist, 11β-fluoro-15-epi-15-indanyl-PGF_2α (AL-8810). methods. FP-receptor-mediated PI turnover and [Ca²⁺]_i mobilization were measured in h-TM cells by determining the accumulation of [³H]-inositol phosphates ([³H]-IPs) by anion-exchange chromatography and real-time fluorescence imaging, respectively. results. Various PG analogues concentration-dependently stimulated production of [³H]-IPs in h-TM cells with the following agonist potencies (median effective concentration; EC₅₀): travoprost acid (EC₅₀ = 2.4 nM) > cloprostenol (EC₅₀ = 4.5 nM) > (±)-fluprostenol (EC₅₀ = 10.8 nM) > latanoprost acid (EC₅₀ = 34.7 nM) > bimatoprost acid (EC₅₀ = 112 nM) > PGF_2α (EC₅₀ = 120 nM) ≫ unoprostone (UF-021; EC₅₀ = 3280 nM) > S-1033 (EC₅₀ = 4570 nM; all n = 3–9). Prodrug derivatives of these compounds exhibited the following potencies: travoprost (isopropyl ester; EC₅₀ = 89.1 nM) > latanoprost (isopropyl ester; EC₅₀ = 778 nM) > bimatoprost (amide; EC₅₀ = 1410–6940 nM). Travoprost acid, PGF_2α, unoprostone, and S-1033 were tested in addition for [Ca²⁺]_i mobilization and found to have rapid and dose-dependent effects. The FP receptor-selective antagonist AL-8810 antagonized the (±)-fluprostenol-induced PI turnover in these cells (K _i = 2.56 ± 0.62 μM) as well as that induced by bimatoprost and acids of latanoprost and travoprost. The agonist and antagonist potencies of the PG analogues from the PI turnover assays in h-TM cells correlated well with PI turnover data obtained from the cloned human ciliary body FP receptor (r = 0.92; P < 0.0001). conclusions. The pharmacology of the h-TM cell FP-receptor-mediated PI turnover and [Ca²⁺]_i mobilization was defined using numerous synthetic (FP-selective) PG agonist analogues and an FP receptor antagonist, AL-8810. Bimatoprost, travoprost, latanoprost, unoprostone isopropyl ester, and their respective free acids were shown to be FP agonists in the h-TM cells.

We have determined the agonist activity of a number of natural prostaglandins and prostaglandin analogs at the FP prostaglandin receptor cloned from a human ciliary body cDNA library using phosphoinositide (PI) turnover assays. Travoprost acid (EC₅₀ = 3.2 ± 0.6 nM) was the most potent agonist in these cells followed by bimatoprost free acid (17-phenyl-trinor PGF_2α; EC₅₀ = 5.8 ± 2.6 nM), fluprostenol (EC₅₀ = 6.1 ± 1.5 nM), and latanoprost 50 free acid (PHXA85; EC₅₀ = 54.6 ± 12.4 nM) which was 17-fold weaker (p < 0.001) than travoprost acid. Unoprostone and S-1033 were significantly (p < 0.001) weaker than travoprost acid. The amide prodrug, bimatoprost (EC₅₀= 694 ± 293 nM), activated this FP receptor with an intermediate potency. The isopropyl ester prodrugs, travoprost (EC₅₀ = 42.3 ± 6.7 nM), latanoprost (EC₅₀ = 126 ± 347 nM) and unoprostone isopropyl ester (EC₅₀ = 9100 ± 2870 nM), also exhibited FP agonist activity. However, other compounds such as PGI₂, bradykinin, histamine, and serotonin were inactive. The agonist activities of bimatoprost, unoprostone (UF-021), fluprostenol and acids of travoprost and latanoprost were antagonized by AL-8810 (11 β-fluoro-15-epi-15-indanyl-PGF_2α), an FP-receptor-selective antagonist (K_i = 1.0 – 2.1 μM; n = 3). These studies have demonstrated, for the first time, agonist activities of the currently known and marketed ocular hypotensive prostaglandin analogs at the cloned human ciliary body FP prostaglandin receptor.

Damage to the optic nerve and the death of associated retinal ganglion cells (RGCs) by elevated intraocular pressure (IOP), also known as glaucoma, is responsible for visual impairment and blindness in millions of people worldwide. The ocular hypertension (OHT) and the deleterious mechanical forces it exerts at the back of the eye, at the level of the optic nerve head/optic disc and lamina cribosa, is the only modifiable risk factor associated with glaucoma that can be treated. The elevated IOP occurs due to the inability of accumulated aqueous humor (AQH) to egress from the anterior chamber of the eye due to occlusion of the major outflow pathway, the trabecular meshwork (TM) and Schlemm’s canal (SC). Several different classes of pharmaceutical agents, surgical techniques and implantable devices have been developed to lower and control IOP. First-line drugs to promote AQH outflow via the uveoscleral outflow pathway include FP-receptor prostaglandin (PG) agonists (e.g., latanoprost, travoprost and tafluprost) and a novel non-PG EP2-receptor agonist (omidenepag isopropyl, Eybelis^®). TM/SC outflow enhancing drugs are also effective ocular hypotensive agents (e.g., rho kinase inhibitors like ripasudil and netarsudil; and latanoprostene bunod, a conjugate of a nitric oxide donor and latanoprost). One of the most effective anterior chamber AQH microshunt devices is the Preserflo^® microshunt which can lower IOP down to 10–13 mmHg. Other IOP-lowering drugs and devices on the horizon will be also discussed. Additionally, since elevated IOP is only one of many risk factors for development of glaucomatous optic neuropathy, a treatise of the role of inflammatory neurodegeneration of the optic nerve and retinal ganglion cells and appropriate neuroprotective strategies to mitigate this disease will also be reviewed and discussed.