Synergistic proapoptotic activity of recombinant TRAIL plus the Akt inhibitor Perifosine in acute myelogenous leukemia cells.

To potentiate the response of acute myelogenous leukemia
(AML) cells to tumor necrosis factor–related apoptosisinducing
ligand (TRAIL) cytotoxicity, we have examined the
efficacy of a combination with perifosine, a novel phosphatidylinositol-
3-kinase (PI3K)/Akt signaling inhibitor. The rationale
for using such a combination is that perifosine was
recently described to increase TRAIL-R2 receptor expression
and decrease the cellular FLICE-inhibitory protein (cFLIP) in
human lung cancer cell lines. Perifosine and TRAIL both
induced cell death by apoptosis in the THP-1 AML cell line,
which is characterized by constitutive PI3K/Akt activation,
but lacks functional p53. Perifosine, at concentrations below
IC50, dephosphorylated Akt and increased TRAIL-R2 levels,
as shown by Western blot, reverse transcription-PCR, and flow
cytometric analysis. Perifosine also decreased the long isoform
of cFLIP (cFLIP-L) and the X-linked inhibitor of
apoptosis protein (XIAP) expression. Perifosine and TRAIL
synergized to activate caspase-8 and induce apoptosis, which
was blocked by a caspase-8–selective inhibitor. Up-regulation
of TRAIL-R2 expression was dependent on a protein kinase
CA/c-Jun-NH2-kinase 2/c-Jun signaling pathway activated by
perifosine through reactive oxygen species production. Perifosine
also synergized with TRAIL in primary AML cells
displaying constitutive activation of the Akt pathway by
inducing apoptosis, Akt dephosphorylation, TRAIL-R2 upregulation,
cFLIP-L and XIAP down-regulation, and c-Jun
phosphorylation. The combined treatment negatively affected
the clonogenic activity of CD34+ cells from patients with AML.
In contrast, CD34+ cells from healthy donors were resistant to
perifosine and TRAIL treatment. Our findings suggest that the
combination of perifosine and TRAIL might offer a novel
therapeutic strategy for AML.