The Effects of PI3K/Akt/mTOR Signaling Pathway Inhibitors on the Expression of Immune Checkpoint Ligands in Acute Myeloid Leukemia Cell Line

Up-regulation of immune checkpoint ligands is considered as one of the most important immune escape mechanisms in acute myeloid leukemia (AML). Herein, we investigate a relationship between the inhibition of PI3K/Akt/mTOR signaling pathways and the regulation of immune checkpoint ligands in AML cells. The HL-60 cell line was treated with idelalisib as PI3K inhibitor, MK-2206 as Akt inhibitor, and everolimus as mTOR inhibitor either in a single or combined format. Cell viability and apoptosis were evaluated using MTT and flow cytometry assays, respectively. The relative expression of PD-L1, galectin-9, and CD155 was determined by real-time PCR. Our findings demonstrated decreased proliferation and increased apoptosis of HL-60 cells after treatment with idelalisib, MK-2206, and everolimus. As expected, the combined treatment showed a more inhibiting effect than the single treatment. Interestingly, our results elucidated that the expression of PD-L1 and Gal-9 but not MK-2206 decreased after treatment with idelalisib and everolimus. Regarding CD155, the expression of this molecule was downregulated after treatment with everolimus, but not idelalisib and MK-2206. However, combined treatment of HL-60 cells with two or three inhibitors decreased the expression levels of PD-L1, Gal-9, and CD155 checkpoint ligands. We showed that PI3K/Akt/mTOR pathway inhibitors not only serve as cytotoxic drugs but also regulate the expression of immune checkpoint ligands and interfere with the immune evasion mechanisms of AML leukemic cells. Combinational treatment approaches to block these pathways might be a promising and novel therapeutic strategy for AML patients via interfering in immune escape mechanisms.

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