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-isoformselective inhibitors of PI3K such as LY294002 may produce unwanted toxicity to normal tissues, we have investigated the role of the leukocyte-restricted p110d 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 p110d-selective compound IC87114 inhibited constitutive phosphorylation of the PI3K target Akt/PKB and reduced cell number to a mean of 6675% (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-jB 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.

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This study shows that fibrillar collagen I is the physiological inducer of a novel class of invadosomes, which we named “linear invadosomes.” They are dependent on the scaffold protein Tks5 and are able to degrade extracellular matrix elements. Moreover, we demonstrate that they are β1- and β3-integrin independent, unlike classical invadosomes.