Induction of pseudonormoxia as adjuvant therapeutic strategy for cancer

Hypoxia is a hallmark of several solid tumors and it is often associated with chemotherapy resistance. The O2 levels decrease induces the activation of Hypoxia-inducible factor 1 (HIF-1) which coordinates cellular adaptive changes and metabolic reprogramming. Under normoxic conditions, HIF-1α subunit has a high turnover strictly regulated by the activation of prolyl hydroxylases (PHDs). At low oxygen levels, PHDs activity is inhibited and HIF-1α is stabilized and migrates into the nucleus where it bounds the HIF-1β exerting its transcriptional activity. Our research group has demonstrated that the lack of respiratory complex I (CI) imbalances the α-ketoglutarate (αKG)/succinate (SA) ratio towards αKG, metabolites that regulate the PHDs activity. The chronic activation of PHDs leads to HIF-1α destabilization even when O2 is available, a condition that we termed pseudonormoxia, and hampered tumor growth in vitro and in vivo. We hypothesized that pseudonormoxia may be induced by unbalancing the αKG/SA ratio mimicking a normoxic condition and leading to the block of tumor progression. In this context, the aim of this PhD project was to prove that HIF-1α destabilization and pseudonormoxia can be pharmacologically induced by increasing αKG levels using CI inhibitors (indirect approach) or cell permeable αKG ester derivatives (direct approach) in order to identify novel and safe adjuvant therapeutic agents for aggressive cancers. We screened a panel of compounds, composed by molecules that potentially may act as CI inhibitors and seven αKGlogues, for their ability to specifically destabilize HIF-1α in cancer cells, while being not toxic for their non-cancer counterpart. From these experiments, we identified four promising compounds that fit these criteria and that will be used for further investigations. The link between HIF-1α stabilization and mitochondrial function opens to new metabolic-based therapeutic approaches for cancers for which adaptation to hypoxia is a step that must be overcome to progress toward malignancy.