A selective inhibitor of the p110δ isoform of PI 3-kinase inhibits AML cell proliferation and survival and increases the cytotoxic effects of VP16

Current therapy for acute myeloid leukaemia (AML) is suboptimal with a high incidence of relapse. There is strong evidence that constitutive phosphoinositide 3-kinase (PI3K) activity plays a significant role in the pathophysiology of AML. PI3K products are derived from the activity of a number of PI3K catalytic isoforms (class I, II and III) but the relative contribution of these enzymes in AML remains unknown. As non-isoform-selective inhibitors of PI3K such as LY294002 may produce unwanted toxicity to normal tissues, we have investigated the role of the leukocyte-restricted p110 delta PI3K isoform in 14 cases of AML. p110d was detected in all cases whereas the expression levels of the other class I PI3Ks varied more widely, and were often undetectable. The p110 delta-selective compound IC87114 inhibited constitutive phosphorylation of the PI3K target Akt/PKB and reduced cell number to a mean of 66 +/- 5% (range 14-88%). In eight cases, the combination of IC87114 and VP16 (a topoisomerase II inhibitor) was synergistic in reducing viable cell number, and was associated with a reduction in constitutive NF-kappa B activity. IC87114 did not have direct adverse effects or enhance the activity of VP16 on the proliferation and survival of normal haemopoietic progenitors. Overall, our results identify the p110d isoform as a potential therapeutic target in AML and support a clinical approach to use isoform-selective over broad-spectrum PI3K inhibitors.