Abstract BS02-1: Hypoxia metabolism in breast cancer – How to overcome resistance to anti-angiogenic therapy

Abstract

Background. Hypoxia is recognised to induce a multigene programme mainly via HIF1a and also HIF2a transcription factors. Bioinformatics analysis of multiple gene array data sets in breast cancer showed a core hypoxia response programme of approximately 90 genes associated with poor outcome independently of other factors. This core response was significantly over-expressed in triple receptor negative cancers. Additionally, microRNAs associated with hypoxia were shown to give additional worse prognosis associations (mir-210). mir-210 targeted the mitochondrial iron chaperone responsible for regulation of key enzymes in the Krebs cycle and showed an adaptive response to hypoxia involving switching off the mitochondrial metabolism. Aims and methods. To assess in human breast cancer the hypoxia transcriptome we conducted gene microarray studies before and after 2 weeks of bevacizumab 15mg/kg single dose before neoadjuvant chemotherapy. This was correlated with imaging by DCE-MRI Ktrans analysis. Results. The study showed that high Ktrans was an excellent predictor for the biological affect of VEGF inhibition and extensive gene induction occurred, including many components of the HIF pathway, but also glycogen metabolism and lipid metabolism. We investigated these further in xenograft models to see which of the adaption pathways may be most important for survival under hypoxic conditions. We showed that induction of CA9, a key enzyme regulating extracellular pH, was critical for survival under anti-angiogenic therapy and blocking CA9 could synergise and also produce radiosensitivity. Reactivating mitochondria under hypoxic conditions induced by angiogenesis also showed additional anti-cancer benefits and is the basis now for a new phase I study in our department. Additionally, surprisingly, induction of glycogen and lipid storage occurred and this was essential for survival on reoxygenation and for protection against free radical damage, which greatly increased when either pathway was inhibited. We investigated, by bioinformatic approaches, the expression of 133 key enzymes in metabolism, showed that they were strongly associated with different subtypes of breast cancer, which may help in selection of patients for future intervention studies. To additionally define the hypoxia transcription, we conducted RNA sequencing of MCF7 cells in normoxia and mild hypoxia. This revealed marked induction of many long non-coding RNAs, suppression of all transfer RNAs and induction of novel antisense RNAs. Conclusions. Overall, therefore, although anti-angiogenic therapy alone is now withdrawn from clinical utility in breast cancer, the massive induction of hypoxic microenvironment and synergy with many other therapeutics, suggests that as new approach using induced essentiality should be reassessed in breast cancer. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr BS02-1.