Prostaglandin FP receptor antagonists: discovery, pharmacological characterization and therapeutic utility

In contrast to the availability of potent and selective antagonists of several prostaglandin receptor types (including DP₁ , DP₂ , EP and TP receptors), there has been a paucity of well-characterized, selective FP receptor antagonists. The earliest ones included dimethyl amide and dimethyl amine derivatives of PGF_2α , but these have failed to gain prominence. The fluorinated PGF_2α analogues, AL-8810 and AL-3138, were subsequently discovered as competitive and non-competitive FP receptor antagonists respectively. Non-prostanoid structures, such as the thiazolidinone AS604872, the D-amino acid-based oligopeptide PDC31 and its peptidomimic analogue PDC113.824 came next, but the latter two are allosteric inhibitors of FP receptor signalling. AL-8810 has a sub-micromolar in vitro potency and ≥2 log unit selectivity against most other PG receptors when tested in several cell- and tissue-based functional assays. Additionally, AL-8810 has demonstrated therapeutic efficacy as an FP receptor antagonist in animal models of stroke, traumatic brain injury, multiple sclerosis, allodynia and endometriosis. Consequently, it appears that AL-8810 has become the FP receptor antagonist of choice. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Revisiting the usefulness of thromboxane-A2 modulation in the treatment of bronchoconstriction in asthma

Airway smooth muscle (ASM) is the effector cell in the bronchoconstrictory pathway. It is believed that the bronchoconstriction present in asthma is associated with changes in the airway milieu that affect ASM excitation-contraction coupling and Ca(2+)-handling. Asthmatics also react differently to ventilatory mechanical strain. Deep inspiration (DI), which produces bronchodilation in healthy individuals, is less effective in asthmatics, and even enhances bronchoconstriction in moderate to severely affected patients. Our laboratory has previously studied the mechanotransductory pathway of airway stretch-activated contractions (Rstretch) leading to DI-induced bronchoconstriction. We demonstrated the ability of agonists acting through thromboxane A2 (TxA2) receptors to amplify airway Rstretch responses. Despite the involvement of excitatory prostanoids in bronchoconstriction, clinical trials on treatments targeting TxA2-synthase inhibition and TP-receptor antagonism have produced mixed results. Studies in Western populations produced mostly negative results, whereas studies performed in Asian populations showed mostly positive outcomes. In this review, we discuss the role of TxA2-synthase inhibition and TP-receptor antagonism in the treatment of asthmatics. We present information regarding variations in study designs and the possible role of TP-receptor gene polymorphisms in previous study outcome discrepancies. Perhaps future studies should focus on asthmatic patients with DI-induced bronchoconstriction in particular, planting the seed for the individualized treatments for asthmatics.