The role of hypoxia-inducible factor-1 in hyperthermia-induced tumor reoxygenation and therapy resistance
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Imbalance between oxygen consumption and supply often makes tumors hypoxic (Bristow and Hill 2008). Tumor hypoxia is significantly correlated with aggressive tumor growth, ineffective response to radiation and chemotherapy, and as a result, poor patient prognosis. Hyperthermia (HT) is a strong adjuvant treatment to overcome these challenges of tumor hypoxia because it causes tumor reoxygenation at temperatures lower than 43ºC (Song, Park, and Griffin 2001). However, the detailed molecular mechanisms of how HT enhances tumor oxygenation have not been elucidated. Here we determine that 1 hour HT activates hypoxia-inducible factor-1 (HIF-1) and its downstream targets, vascular endothelial growth factor (VEGF), lactate dehydrogenase A (LDHA), and pyruvate dehydrogenase kinase 1 (PDK1) in tumors. Consistent with HIF-1 activation and upregulation of its downstream genes, HT also enhances tumor perfusion/vascularization and decreases oxygen consumption rates. As a result, tumor hypoxia is reduced after HT suggesting that these physiological changes contribute to HT-induced tumor reoxygenation. Since HIF-1 is a potent regulator of tumor vascularization and metabolism, our findings suggest that HIF-1 plays a role in HT-induced tumor reoxygenation by transactivating its downstream targets. Mechanistically, we demonstrate that NADPH oxidase-mediated reactive oxygen species (ROS) production upregulates HIF-1 after HT. Further, we determine that this pathway is initiated by increased transcription of NADPH oxidase-1 (NOX1) through the ERK pathway.
A major research effort at Duke focuses on combinations of HT and doxorubicin in the treatment of locally advanced breast and other cancers. Thus, we investigated whether there are HIF-1 responses to doxorubicin treatment. We reveal that doxorubicin also activates HIF-1. Unlike HT, doxorubicin-induced HIF-1 promotes persistent tumor angiogenesis. We also reveal that the signal transducer and activator of transcription 1 (STAT1)/inducible nitric oxide synthase (iNOS) pathway causes HIF-1α accumulation in an oxygen-independent manner. We show that activated STAT1 upregulates iNOS expression and promotes nitric oxide (NO) production in tumor cells resulting in HIF-1α stabilization. We further determine that both iNOS inhibitor, 1400W and STAT1 inhibitor, epigallocatechin-3-gallate (EGCG) significantly decrease intracellular NO production and suppress doxorubicin-induced normoxic HIF-1α accumulation.
HIF-1 is often considered a promising therapeutic target because of its role in tumor progression (Semenza 2003) and therapy resistance (Moeller et al. 2004). However, our findings suggest that HIF-1 plays a pleiotropic role in response to HT and chemotherapy. Therefore, to preferentially take advantage of HT-induced HIF-1 activation and also to suppress its deleterious effects induced by chemotherapy or as we have previously reported, by radiation (Moeller et al. 2004), HIF-1 inhibition needs to be carefully regulated in a time-sensitive manner to achieve optimal therapeutic effects.
Reactive oxygen species
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