To the best of our knowledge, one ACPP has been tested in a phase 1 clinical study and used for imaging purposes.94 This ACPP was designed to visualize tumours during surgical procedures and resembled the ACPP designed by the Tsien group, containing an inhibitory domain and a protease-sensitive linker.19,95,96 In this construct, the CPP as well as the inhibitory domain each carried a fluorophore thereby inducing FRET. The gene discussed is ACP3; the disease is neoplasm.