PF-3758309 dihydrochloride is a potent, reversible, orally active, ATP-competitive PAK4 inhibitor with a Kd value of 2.7 nM and a Ki value of 18.7 nM. PF-3758309 dihydrochloride exhibits the expected cellular functions of a PAK4 inhibitor, with the ability to inhibit anchorage independent growth, induction of apoptosis, cytoskeletal remodelling and inhibition of proliferation.