(B) The degree of polymerisation of Z α1-antitrypsin after 72 hours at 37°C, as determined by an end-point immunoassay using the 2C1 monoclonal antibody, in varying concentrations of compound (shown in panel A). Modification of the phenyl and indole heterocycle of GSK425 (pIC50 6.5) resulted in an ~100 fold increase in potency and the discovery of the 2-oxindole GSK716 (pIC50 8.3). Data presented as mean ± SD, n = 2 (GSK425) and n = 25 (GSK716). 