Acriflavine, a Potent Inhibitor of HIF-1α, Disturbs Glucose Metabolism and Suppresses ATF4-Protective Pathways in Melanoma under Non-hypoxic Conditions

Simple Summary Hypoxia is a common feature in solid tumors such as melanoma, contributing locally and systemically to tumor progression. Although the hypoxia response in tumor cells is well understood, the role of constitutively activated hypoxia-inducible factor (HIF)-1 alpha in normoxic conditions is less known. Here, we used acriflavine, a chemical inhibitor of HIF-1 alpha, to investigate the role of this transcription factor on the progression of melanoma under normoxic conditions. The data indicated that acriflavine disturbs glucose metabolism and induces melanoma cell death under normoxia. As a result, we describe a possible clinical option that may target melanoma cells irrespective of the hypoxic microenvironment of the tumors. However, the translational importance of these findings should be confirmed in pre-clinical models. Hypoxia-inducible factor (HIF)-1 alpha is constitutively expressed in melanoma cells under normoxic conditions and its elevated expression correlates with the aggressiveness of melanoma tumors. Here, we used acriflavine, a potent inhibitor of HIF-1 alpha dimerization, as a tool to investigate whether HIF-1 alpha-regulated pathways contribute to the growth of melanoma cells under normoxia. We observed that acriflavine differentially modulated HIF-1 alpha-regulated targets in melanoma under normoxic conditions, although acriflavine treatment resulted in over-expression of vascular endothelial growth factor (VEGF), its action clearly downregulated the expression of pyruvate dehydrogenase kinase 1 (PDK1), a well-known target of HIF-1 alpha. Consequently, downregulation of PDK1 by acrifavine resulted in reduced glucose availability and suppression of the Warburg effect in melanoma cells. In addition, by inhibiting the AKT and RSK2 phosphorylation, acriflavine also avoided protective pathways necessary for survival under conditions of oxidative stress. Interestingly, we show that acriflavine targets activating transcription factor 4 (ATF4) for proteasomal degradation while suppressing the expression of microphthalmia-associated transcription factor (MITF), a master regulator of melanocyte development and a melanoma oncogene. Since acriflavine treatment results in the consistent death of melanoma cells, our results suggest that inhibition of HIF-1 alpha function in melanoma could open new avenues for the treatment of this deadly disease regardless of the hypoxic condition of the tumor.

Automated summary

The study found that HIF-1α is constitutively expressed in melanoma cells under normoxic conditions and its elevated expression is associated with the aggressiveness of melanoma tumors. Using acriflavine as an inhibitor of HIF-1α dimerization, the researchers investigated whether HIF-1α-regulated pathways contribute to the growth of melanoma cells under normoxia. Results showed that acriflavine can differentially modulate HIF-1α-regulated targets, inhibiting glucose metabolism and the Warburg effect, ultimately leading to cell death.