HIF1α Expression under Normoxia in Prostate Cancer— Which Pathways to Target?

PurposeHIF1α over expression correlates with poor prognosis in a number of cancers. Although it is widely accepted that hypoxia induces HIF1α expression up-regulation by a reduction in oxygen dependent degradation, HIF1α up-regulation under normoxic conditions is noted with increasing frequency in many cancers. We reviewed the current knowledge of mechanisms of normoxic and hypoxic HIF1α up-regulation, and its therapeutic implications with a particular focus on its role as a potential biomarker in prostate cancer.Materials and MethodsAlthough the literature on the role of HIFs in cancer development and progression has been reviewed extensively, few publications have specifically considered the role of HIFs in prostate cancer. Therefore, we searched PubMed® and Google® with the key words prostate cancer, castration resistance, metastasis, hypoxia, HIF1α, HIF2α and regulation. Relevant articles, including original research studies and reviews, were selected based on contents and a synopsis was generated.ResultsNormoxic expression of HIF1α has an important role in the development of prostate cancer chemoresistance, radioresistance and castrate resistance. Thus, HIF1α could serve as a potential biomarker. Furthermore, agents that target HIF1α could be used as adjuvant therapy to decrease resistance to conventional treatment modalities. HIF1α over expression in prostate cancer can be regulated at 3 levels, including transcription, translation and protein stability, by a number of mechanisms such as gene amplification, single nucleotide polymorphism, increased transcription of HIF1α mRNA, expression of truncated isoforms of HIF1α and stabilization of HIF1α. However, there is no definitive consensus and the intriguing question of how HIF1α is up-regulated in prostate cancer is still unanswered.ConclusionsHIF1α over expression under normoxia could serve as a biomarker for chemoresistance, radioresistance and castrate resistance in prostate cancer. There is an urgent need to identify the cause of HIF1α over expression in castrate resistant prostate cancer cells and tumors to guide the choice of HIF inhibitors (transcription or translation based) that are best suited for treating castrate resistant prostate cancer.