CI-1044 is an inhibitor of PDE4 (IC50s: 0.29, 0.08, 0.56, 0.09 μM for PDE4A5, PDE4B2, PDE4C2 and PDE4D3).

PDE4B2:0.08 μM, PDE4C2:0.56 μM, PDE4A5:0.29 μM, PDE4D3:0.09 μM

CI-1044 selectively inhibits PDE4 crude extract from U937 cells (IC50: 0.27 μM). It being threefold more potent than rolipram (IC50=0.91 μM) and tenfold less potent than cilomilast (IC50=0.026 μM) in the same assay. For CI-1044, cilomilast and rolipram, the production of TNF-α is dose-dependently decreased with mean IC50 values from three separate experiments of 0.31±0.05, 0.26±0.05 and 0.11±0.01 μM, respectively, in the presence of PDE4 inhibitors.

CI-1044 dose-dependently inhibits the accumulation of eosinophils in Bronchoalveolar lavages (BAL) fluids (ID50: 3.25 mg/kg). CI-1044 (p.o.) plasma levels increase proportionally with doses ranging between 0.1 and 40 mg/kg. Following repeated administration with CI-1044( p.o.), the ID50 value represents 0.5 mg/kg. TNF-α production is dose-dependently inhibited by CI-1044, rolipram, and cilomilast (ID50s: 0.4, 1.4, and 1.6 mg/kg) following single oral administration. A single dose treatment with CI-1044 (10 mg/kg, p.o.) 24, 8, 3, or 1 h before the antigen challenge induces 6, 56, 48, and 79% inhibition in the number of eosinophils in BAL.