The PDK1 master kinase is overexpressed in acute myeloid leukemia and promotes PKC-mediated survival of leukemic blasts

PDK1 is a master kinase that activates at least six protein kinase groups including AKT, PKC and S6K and is a potential target in the treatment of a range of malignancies. Here we show overexpression of PDK1 in over 40% of myelomonocytic acute leukaemia patients. Overexpression of PDK1 occurred uniformly throughout the leukaemic population, including putative leukaemia initiating cells. Clinical outcome analysis revealed PDK1 overexpression was associated with poorer treatment outcome. Primary acute myeloid leukaemia blasts overexpressing PDK1 showed improved in vitro survival and ectopic expression of PDK1 promoted the survival of myeloid cell lines. Analysis of PDK1 target kinases revealed that PDK1 overexpression was most closely associated with increased phosphorylation of PKC isoenzymes and inhibition of PKC strongly inhibited the survival advantage of PDK1 overexpressing cells. Membrane localization studies implicated PKCα as a major target for PDK1 in this disease. PDK1 overexpressing blasts showed differential sensitivity to PDK1 inhibition (in the low micromolar range) suggesting oncogene addiction, whilst normal bone marrow progenitors were refractory to PDK1 inhibition at effective inhibitor concentrations. PDK1 inhibition also targeted subpopulations of leukaemic blasts with a putative leukaemia initiating cell phenotype. Together these data show that overexpression of PDK1 is common in acute myelomonocytic leukaemia and is associated with poorer treatment outcome, probably arising from the cytoprotective function of PDK1. We also show that therapeutic targeting of PDK1 has the potential to be both an effective and selective treatment for these patients and is also compatible with current treatment regimes.