CR4056 is a selective inhibitor of human recombinant MAO-A with an IC50 of 202.7 nM. CR4056 is also a ligand of imidazoline-2 receptor (I2R) with an IC50 of 596 nM. IC50 & Target: IC50: 202.7 nM (MAO-A), 596 nM (I2R)In Vitro: CR4056 is an imidazoline-2 receptor (I2R) ligand with an IC50 of 596±76 nM. CR4056 is also an inhibitor of both human recombinant MAO-A and MAO-B with IC50s of 202.7±10.3 and >10000, respectively. The co-treatment of bortezomib (BTZ) with CR4056 at all the concentrations used (range 3 to 30 μM) does not induce any significant difference in cell survival compare with BTZ-treated cells, either in H929 or in RPMI 8226 myeloma cells. In Vivo: Two hours after a single oral dose of 20 mg/kg CR4056, endogenous norepinephrine (NE) levels increase by 68.2%±14.1% (P<0.05 versus vehicle) in the parieto-occipital cortex. Sub-chronic (four days) oral treatment with 20 mg/kg CR4056 once daily, significantly increases NE levels both in the cerebral cortex (63.1%±4.2%; P<0.05 versus vehicle) and in the lumbar spinal cord (51.3%±6.7%; P<0.05 versus vehicle). CR4056 dose-dependently reduces mechanical hyperalgesia (effective dose [ED50]=5.8 mg/kg) (P<0.001). CR4056 (10 mg/kg) and piroxicam (10 mg/kg) significantly reverse the decrease in withdrawal threshold caused by capsaicin (P<0.001 versus vehicle). The highest tested dose of CR4056 (30 mg/kg) completely reverses the effect of capsaicin, increasing paw withdrawal threshold (PWT) to 239±12 g (P<0.001 versus vehicle) after 1 hour. CR4056 dose-dependently decreases streptozotocin (STZ)-induced diabetic pain in rats (F[4, 35]=31.27, P<0.001). CR4056 significantly increases the mechanical withdrawal thresholds of both ipsilateral (F[4, 30]=19.97, P<0.001) and contralateral (F[4, 30]=31.58, P<0.001) hind paws compare with vehicle control.