In a reporter-gene assay conducted with a human rhabdomyosarcoma (A204) cell line, ACE-083 inhibited signaling by activin A, activin B, myostatin and GDF11 in a dose-dependent manner, with IC50 values ranging from approximately 40–700 pM (Table 1) or, in alternative units, 5–80 ng/mL (see Supplementary Fig. S2). The gene discussed is MSTN; the disease is rhabdomyosarcoma.