Therapeutic Strategies to Block the Hypoxic Response

Patients with the low levels of O2 (hypoxia) in their primary tumors have a higher risk for metastasis and death, indicating a need to therapeutically inhibit the effectors of hypoxia. Many strategies have been developed and investigated to block the hypoxic response. For example, inhibitors of HIF-1 and HIF-2 function by altering the transcription, translation, dimerization, nuclear translocation, DNA-binding, or ubiquitination of the HIF proteins. Hypoxia-activated prodrugs inhibit the hypoxic response through hypoxia-mediated reduction of an inactive, or minimally active, chemical to a cytotoxic agent. Most hypoxia-activated prodrugs function by inducing DNA damage, but others with more novel functions, including prodrugs that release EGFR/HER2 inhibitors also exist. Despite the existence of many therapeutics to combat the hypoxic response, there has been very little success in late phase clinical trials, potentially due to a lack of biomarkers that can be used to stratify patients who would benefit from a hypoxia-targeted therapy.