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A key role of HIF-1α in the radioresistance of Cancer Stem Cells in their hypoxic microenvironment
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International audience. The resistance of Head and Neck Squamous Cell Carcinoma (HNSCC) to chemo- and radio-therapies is partly explained by the presence of Cancer Stem Cells (CSCs) located in a hypoxic microenvironment. In these niches, poor in oxygen, the HIF-1α protein is expressed and Reactive Oxygen Species (ROS), produced in response to hypoxia and/or irradiation, play a key role in HIF-1α stabilization. However, mechanisms leading to HIF-1 expression and their consequences on the CSCs survival need to be clarified in response to carbon or photon radiations under hypoxia. For two HNSCC cell lines and their CSCs subpopulation, we observed a radioresistance in response to photons under hypoxia (OER>1.2). This result is associated with a stabilization of HIF-1α. Additionally, under hypoxia, HIF-1 appears earlier in CSCs than in non-CSCs, and its expression is correlated with ROS levels, confirming CSCs adaptive properties to hypoxia. To go further in the understanding of HIF-1α activation’s mechanism, we used DMSO as a ROS scavenger and observed the consequences on HIF-1α, whose expression was significantly decreased. Finally, inhibition of HIF-1α with a siRNA leads to the radiosensitization of the CSCs in their hypoxic microenvironment and even more after exposure to photons. Compared with photons, the oxygen effect is canceled after carbon ion exposure (OER=1) and interestingly, HIF-1 expression is fully inhibited following carbon ion irradiation. These results taken together demonstrate that HIF-1 plays a key role in the radioresistance of HNSCC CSCs and suggest that a therapeutic which silence HIF-1α could be a relevant alternative to kill or sensitize CSCs as observed with carbon ion irradiation.This work was supported by CPER ETOILE/UCBL, Labex Primes (ANR-11-LABX-0063), France Hadron (ANR-11-INBS-0007) and Lyric ( INCa-DGOS-4664 )
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