STK39 and acute myeloid leukemia: Western blot (WB) analysis in human AML cells showed that both Compound 12 and WNK463 produced a dose-dependent inhibition of WNK1 activity as measured by the reduction of phosphorylation of the WNK kinase substrates OXSR1 and STK39 (Fig. 4a), consistent with previously reported EC50 values for this phosphorylation20,21.