Studies on Receptor Binding and Signal Transduction Pathways of Unoprostone Isopropyl

Abstract

We examined the binding characteristics of unoprostone isopropyl and its metabolite, M1 (M1), in bovine corpus luteum membranes, mobilization of intracellular calcium in human ciliary muscle cells and cyclic AMP generation in rabbit iris-ciliary body. The ligand binding assay of 3H-unoprostone isopropyl and M1 did not demonstrate any specific binding of these compounds in the bovine corpus luteum membranes. However, there was a high specific binding of prostaglandin F2alpha. Competitive ligand binding studies showed that neither the docosanoid, unoprostone isopropyl, nor M1 binds to prostaglandin receptor sites. In human ciliary muscle cells that express EP1, EP2 and FP receptors, unoprostone isopropyl did not increase the mobilization of intracellular calcium nor was it able to generate cyclic AMP at low concentrations in rabbit iris-ciliary body. Similar observations were made with M1 on the above signal transduction pathways. From these results, it is concluded that unoprostone isopropyl and M1 do not bind to prostaglandin (PG) receptor sites in the bovine corpus luteum membranes and do not have affinity for PG receptors linked to intracellular calcium and cyclic AMP second messenger systems.

Real-Time Intracellular Ca2+ Mobilization by Travoprost Acid, Bimatoprost, Unoprostone, and Other Analogs via Endogenous Mouse, Rat, and Cloned Human FP Prostaglandin Receptors

“…However, given our findings that unoprostone isopropyl and unoprostone free acid have micromolar binding affinities, we feel it would be difficult to detect appreciable specific binding using nanomolar concentrations of this weak radioligand. Bhattacherjee et al (2001) also reported that unoprostone failed to mobilize [Ca 2ϩ ] i in primary human ciliary muscle cells. We have found that [Ca 2ϩ ] i mobilization in response to FP prostaglandins in human ciliary muscle can be quite weak and donor dependent, perhaps suggesting that low receptor expression and/or poor signal coupling in these primary cultures may contribute to the lack of response observed with weak FP agonists.…”

“…In our hands, bimatoprost readily bound to the FP receptor and displaced [ 3 H]travoprost acid and [ 3 H]PGF 2␣ (this study). Bhattacherjee et al (2001) found no specific binding of unoprostone isopropyl ester or unoprostone using […”

“…The ocular antihypertensive drugs travoprost (TRAVATAN) and latanoprost (Xalatan) are well characterized prodrugs of FP receptor agonists (Hellberg et al, 2001;Stjernschantz et al, 1995). However, two additional IOPlowering prostaglandin analogs, bimatoprost (Lumigan ) and unoprostone isopropyl ester (Rescula ), have recently been reported to have no observed activity at FP or other known prostaglandin receptors (Bhattacherjee et al, 2001;Woodward et al, 2001) despite being PGF 2␣ analogs.…”

“…(Taniguchi et al, 1996). Unoprostone (and its isopropyl ester) has recently been reported as a docosanoid and also claimed to exert its biological activities independent of any known prostaglandin receptors (Bhattacherjee et al, 2001).…”

Human Ciliary Muscle Cell Responses to FP-Class Prostaglandin Analogs: Phosphoinositide Hydrolysis, Intracellular Ca2+ Mobilization and MAP Kinase Activation

“…Akin to the claims for bimatoprost (8,51), unoprostone has been suggested to mediate its actions via non-prostaglandin receptors (53,54). However, our studies have clearly demonstrated unopros- 137 6 10%** (160 6 11 at 1 nM)** (6)-Fluprostenol 131 6 6%** (162% at 1 mM)** PGE 2 118 6 6%*** S-1033 115 6 6% (200% at 10 mM) Unoprostone (UF-021) 105 6 4%*** (125% at 10 nM)** PGI 2 87 6 4%*** Comparative data for the PG analogs were obtained for MAP kinase stimulation in normal h-CM cells using a 5 min incubation paradigm.…”