AT 56

PGD24 is a lipid mediator involved in sleep and inflammatory responses. PGD2 activates two different types of receptors. PGD2 regulates sleep and pain via DP1 receptors in the central nervous system. This prostanoid also causes contraction of airway smooth muscle via DP1 receptors and mediates chemotaxis of eosinophils and basophils into the lung via DP2 receptors in the periphery. Therefore, PGD2 coordinately regulates allergic reactions, especially airway inflammation, via these two receptors. AT-56 is an orally active and selective inhibitor of lipocalin-type prostaglandin D synthase.

In vitro: AT-56 inhibited human and mouse L-PGDSs in a concentration (3-250 μM)-dependently but did not affect the activities of hematopoietic PGD synthase (H-PGDS), cyclooxygenase-1 and -2, and microsomal PGE synthase-1. AT-56 inhibited L-PGDS activity in a competitive manner against the substrate PGH2 (Km=14 μM) with a Ki value of 75 μM but did not inhibit the binding of 13-cis-retinoic acid, a nonsubstrate lipophilic ligand, to L-PGDS. [2].

In vivo: Orally administered AT-56 (<30 mg>

Clinical trial: Up to now, AT-56 is still in the preclinical development stage.

Reference:
[1] Daisuke Irikura, Kosuke Aritake, Nanae Nagata, Toshihiko Maruyama, Shigeru Shimamoto, and Yoshihiro Urade.  Biochemical, Functional, and Pharmacological Characterization of AT-56, an Orally Active and Selective Inhibitor of Lipocalin-type Prostaglandin D Synthase. J Biol Chem. 2009 Mar 20;284(12):7623-30.

The G-protein coupled receptor 56, expressed in colonic stem and cancer cells, binds progastrin to promote proliferation and carcinogenesis.[Pubmed:28380450]

Oncotarget. 2017 Jun 20;8(25):40606-40619.

Overexpression of human progastrin increases colonic mucosal proliferation and colorectal cancer progression in mice. The G-protein coupled receptor 56 (GPR56) is known to regulate cell adhesion, migration, proliferation and stem cell biology, but its expression in the gut has not been studied. We hypothesized that the promotion of colorectal cancer by progastrin may be mediated in part through GPR56. Here, we found that GPR56 expresses in rare colonic crypt cells that lineage trace colonic glands consistent with GPR56 marking long-lived colonic stem-progenitor cells. GPR56 was upregulated in transgenic mice overexpressing human progastrin. While recombinant human progastrin promoted the growth and survival of wild-type colonic organoids in vitro, colonic organoids cultured from GPR56-/- mice were resistant to progastrin. We found that progastrin directly bound to, and increased the proliferation of, GPR56-expressing colon cancer cells in vitro, and proliferation was increased in cells that expressed both GPR56 and the cholecystokinin-2 receptor (CCK2R). In vivo, deletion of GPR56 in the mouse germline abrogated progastrin-dependent colonic mucosal proliferation and increased apoptosis. Loss of GPR56 also inhibited progastrin-dependent colonic crypt fission and colorectal carcinogenesis in the azoxymethane (AOM) mouse model of colorectal cancer. Overall, we found that progastrin binds to GPR56 expressing colonic stem cells, which in turn promotes their expansion, and that this GPR56-dependent pathway is an important driver and potential new target in colorectal carcinogenesis.

Biochemical, functional, and pharmacological characterization of AT-56, an orally active and selective inhibitor of lipocalin-type prostaglandin D synthase.[Pubmed:19131342]

J Biol Chem. 2009 Mar 20;284(12):7623-30.

We report here that 4-dibenzo[a,d]cyclohepten-5-ylidene-1-[4-(2H-tetrazol-5-yl)-butyl]-piperidine (AT-56) is an orally active and selective inhibitor of lipocalin-type prostaglandin (PG) D synthase (L-PGDS). AT-56 inhibited human and mouse L-PGDSs in a concentration (3-250 microm)-dependent manner but did not affect the activities of hematopoietic PGD synthase (H-PGDS), cyclooxygenase-1 and -2, and microsomal PGE synthase-1. AT-56 inhibited the L-PGDS activity in a competitive manner against the substrate PGH(2) (K(m) = 14 microm) with a K(i) value of 75 microm but did not inhibit the binding of 13-cis-retinoic acid, a nonsubstrate lipophilic ligand, to L-PGDS. NMR titration analysis revealed that AT-56 occupied the catalytic pocket, but not the retinoid-binding pocket, of L-PGDS. AT-56 inhibited the production of PGD(2) by L-PGDS-expressing human TE-671 cells after stimulation with Ca(2+) ionophore (5 microm A23187) with an IC(50) value of about 3 microm without affecting their production of PGE(2) and PGF(2alpha) but had no effect on the PGD(2) production by H-PGDS-expressing human megakaryocytes. Orally administered AT-56 (<30 mg/kg body weight) decreased the PGD(2) production to 40% in the brain of H-PGDS-deficient mice after a stab wound injury in a dose-dependent manner without affecting the production of PGE(2) and PGF(2alpha) and also suppressed the accumulation of eosinophils and monocytes in the bronco-alveolar lavage fluid from the antigen-induced lung inflammation model of human L-PGDS-transgenic mice.