Prostaglandin D synthase (PGDS) catalyzes the isomerization of PGH2 to produce PGD2. PGD2 induces sleep, regulates nociception, inhibits platelet aggregation, and acts as an allergic mediator. Two distinct types of PGDS have been identified, namely the lipocalin-type enzyme (β-trace, L-PGDS) and the hematopoietic-type enzyme (H-PGDS). L-PGDS is localized in the central nervous system, male genital organs of various mammals, and the human heart and is a major protein in human cerebrospinal fluid (CSF). AT-56 is a selective, competitive, and highly bioavailable inhibitor of lipocalin-type prostaglandin D synthase (L-PGDS) with a Ki value of 75 μM. It inhibits the production of PGD2 by L-PGDS-expressing cells purified from human CSF and recombinant mouse cells with an IC50 value of 95 μM. At concentrations as high as 100 μM in vitro or 30 mg/kg in vivo, AT-56 does not affect the production of PGE2, PGF2α, or H-PGDS-catalyzed PGD2. At 10 mg/kg AT-56, the numbers of total cells, infiltrating eosinophils, and monocytes in bronchoalveolar lavage fluid of L-PGDS transgenic mice were decreased to 23, 6, and 41% of controls, respectively.
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