Selection, Analysis and Improvement of Anti-Angiogenesis Compounds Identified by an Anti-HIF-1α Screening and Validation System.

Cancer cells resort to activating hypoxia-inducible factor-1 (HIF-1) as one of several responses to hypoxic conditions. Overexpression of HIF-1, the transcriptional regulator for a group of malignant-pathway related genes including vascular endothelial growth factor (VEGF), is associated with increased tumor growth, vascularization, and metastasis. HIF-1 is composed of an inducible subunit, HIF-1α and a constitutively expressed subunit, HIF-1ß. HIF-1 activity is mainly dependent on the level of HIF-1α protein, the inducible and regulatory subunit of the HIF-1 heterodimer complex; thus, identification of novel anti-HIF-1α agents will lead to effective blockage of the HIF-1 (HIF-1α)-mediated "switch-on" function for those malignant-pathway related genes and suppression of the HIF-1α/VEGF-mediated signaling pathway that promotes cancer progression and metastasis. While there is an extremely large number of small molecule compounds in the database (compound libraries), the currently existing screening system is inefficient and time-consuming; or, at best, the application of the existing screening system is very limited as it is usually not coupled with biological validation processes. The further development of potential drugs is partly hindered due to the cumbersome steps in between the primary screen and consequent validation: the slow, exhausted and sometimes lack of a linked biological validation process contributes to the dismal fate of scant compounds uncovered in the primary screen. To improve upon the status quo, we developed a prototype screening system that is coupled anti-HIF-1α primary screen with secondary anti-VEGF/anti-angiogenesis validation screens. We used breast cancer cells as the model to select potent anti-HIF-1α small-molecule compounds by their abilities to inhibit transactivation of a VEGF promoter fused to a luciferase reporter gene under hypoxia. Positive compounds were then validated by a series of assays that confirm compounds' anti-HIF-1α activities including measurement of their effects on HIF-1α downstream VEGF gene expression and angiogenic ability of breast cancer cells. Moreover, we demonstrated that we could further improve the compound's potency of anti-HIF-1α and anti-angiogenesis by modifying the identified lead to synthesize a superior (novel) drug.