Phosphoinositide 3-kinase/Akt involvement in arsenic trioxide resistance of human leukemia cells

The purpose of this study was to evaluate the possible involvement of the phosphoinositide 3-kinase (PI3K)/Akt survival pathway in determining resistance to arsenic trioxide (As2O3)-induced apoptosis. We employed a HL60 cell clone (HL60AR) with a constitutively active PI3K/Akt survival pathway, as well as U937 and K562 cells. In addition, we used parental (PT) HL60 cells overexpressing a constitutively active Akt. Selective pharmacological inhibitors of the PI3K/Akt axis (LY294002, wortmannin) were employed to influence the sensitivity to As2O3. While HL60PT cells were sensitive to 2.5 mMAs2O3 and died of apoptosis, HL60AR cells were resistant up to 5 mM As2 O3. Treatment with either LY294002 or wortmannin lowered resistance of HL60AR cells to As2O3. Also in U937 and K562 cells, inhibitors of the PI3K/Akt axis caused a decrease in As2O3 resistance. Overexpression of constitutively active Akt in HL60PT cells caused the induction of resistance to 2.5 mMAs2O3. Conversely, forced expression of a dominant negative Akt in HL60AR cells resulted in a decrease in As2O3 resistance. Moreover, HL60 cell resistance to 2.5 mMAs2O3 could be significantly reduced by incubation with SN50, a peptide inhibitor selective for the NF-kB transcription factor. Taken together our findings suggest that a constitutive activation of the PI3K/Akt pathway, which is increasingly detected in some types of acute myeloid leukemia, may contribute to As2O3 resistance, most likely through NF-kB activation. Selective pharmacological inhibitors of this survival pathway, as well as of NF-kB, might be usefully employed in the future to reverse resistance to this treatment.