Characterization of the status of hypoxia induced factors (HIF 1&2) during radiotherapy of Head and Neck cancer using in vivo imaging in mice

The Hypoxia Inducible Factors HIF-1 and HIF-2 are master transcriptional regulators which become stabilized in response to hypoxia and which activate a cellular program enabling cells to survive under hypoxic conditions - a common feature of most solid tumors. Interestingly, HIF 1 is not only stabilized by hypoxia but also accumulates in response to radiotherapy. The here proposed project is based on recently published studies of Chuan Li, in which a novel mechanism of HIF- 1 stabilization was discovered. These data indicated that HIF-1 stabilization was induced by radiotherapy via a mechanism independent from hypoxia, i.e. nitrosylation. Li and co-workers found that this mechanism had an important impact on tumor survival after irradiation thus making it a promising target for adjuvant drugs in combination with radiotherapy. The main objective of this research proposal is to characterize the protein levels of HIF-1 & 2 during radiotherapy using a mouse model system for Head and Neck (H&N) cancer and to test novel nitric oxide (NO) based strategies to inhibit HIF activity in order to enhance the tumor-suppressive effects of radiotherapy of H&N cancer. A luciferase-based reporter system allows us to monitor HIF-1&2 protein levels in living mice using an in vivo imaging system (IVIS200, Xenogen). Using this technology, HIF levels in xenograft tumors as well as in stromal cells of host mice can be quantified in the same organism before, during and after irradiation. Simultaneously, tumor growth can be followed up in real time. By performing tumor growth delay experiments upon administration of pan-NO-synthase inhibitors we hope to find evidence for the tumor-suppressive effect of these drugs and to demonstrate the feasibility to combine them with radiotherapy of H&N tumors.