GSK256066 is a slow and tight binding inhibitor of PDE4B with apparent IC50 of 3.2 pM. GSK256066 is an extremely potent inhibitor of LPS-stimulated TNFalpha production in PBMCs with pIC50 of 11.0 and IC50 of 10 pM and human whole-blood cultures with pIC50 of 9.90 and IC50 of 126 pM.