PF-04859989 HCl is a brain-penetrable and irreversible inhibitor of kynurenine amino transferase II (KAT II), which is the enzyme responsible for most of the brain synthesis of kynurenic acid.

KAT II:23 nM(human), KAT II:263 nM(rat), KAT I:22 μM, KAT IV:>50 μM, KAT III:11 μM

The IC50s values are 23 and 263 nM for hKAT II and rKAT II. PF-04859989 HCl is selective for KAT II over human KAT I, KAT III, and KAT IV (IC50s of 22, 11, and >50 μM, respectively)[3].

Acute administration of the KAT II inhibitor PF-04859989 (5 or 10 mg/kg) was associated with a short-onset, time-dependent decrease in firing rate and burst activity of DA neurons, both parameters reaching a 50% reduction within 45 min. Furthermore, PF-04859989 reduced the number of spontaneously active DA cells as measured 4-6 after administration. Pretreatment with d-cycloserine (30 mg/kg) or CGP-52432 (10 mg/kg) prevented the inhibitory action of PF-04859989 (5 mg/kg) on firing rate and burst firing activity. In contrast, pretreatment with methyllycaconitine (MLA, 4 mg/kg) did not change the response, whereas picrotoxin (4.5 mg/kg) partially prevented the inhibitory effects of PF-04859989 (5 mg/kg, i.v.)[2].