Hypoxia-inducible Factor 1-α: A Key Regulator of Immune Checkpoint Receptors in Acute Myeloid Leukemia Cell Lines.

The Warburg effect is one of the most important metabolic alterations in tumor cells. Hypoxia-inducible factor 1-alpha (HIF-1α) targets a broad range of gene promoters in normoxic and hypoxic conditions in cancers. Herein, we investigate the effects of HIF-1α inhibition on cell viability and messenger RNA (mRNA) expression of immune checkpoint receptors (ICRs) in acute myeloid leukemia cell lines. K-562 and HL-60 cells were treated with silibinin as an HIF-1α inhibitor. Cell viability was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, followed by quantification of V-domain immunoglobulin suppressor of T-cell activation (VISTA), T-cell immunoglobulin and mucin domain 3 (TIM3), and Galectin-9 mRNA expression via quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The expression levels of VISTA, TIM3, and Galectin-9 decreased after silibinin treatment within both K-562 and HL-60 cells; however, there were some disparities in gene expression levels between the two cell lines. VISTA and TIM3 expression were reduced by approximately 70% in K-562 at the 40% inhibitory concentration (IC40), while no significant changes were observed in HL-60 cells. Conversely, Galectin-9 expression was decreased significantly at both the IC30 and IC40 in HL-60, whereas it was almost consistent in K-562 cells.  Collectively, we have shown that silibinin could serve as a cytotoxic small-molecule inhibitor and regulate the expression of ICRs, potentially counteracting T-cell exhaustion.