Triple negative breast cancer is associated with a bad prognosis caused by an aggressive phenotype and early metastasis. ER and HER-2 directed targeted therapy is impossible due to lack of expression of these receptors. Previous studies have indicated the VEGF pathway as an interesting target for this type of cancer and clinical data with bevacizumab are available. HSP90 is a chaperone molecule that plays a central role in posttranslational folding and stabilization of proteins, many of which are essential in oncogenesis. HSP90 inhibition leads to proteasome mediated degradation of mis-folded client proteins. In the VEGF-pathway this likely leads to a decrease in protein levels, activity of HIF1\#945; and VEGF receptor stability. HSP90 inhibitors are appealing antitumor agents as prior studies showed that breast cancer cells are sensitive to these drugs. The aim of this study is to analyze the effect of HSP90 inhibitors on VEGF excretion by breast cancer cell lines. Methods: The effect of the HSP90 inhibitor NVP-AUY922 on the triple negative breast cancer cell line MDA-MB-231 is studied by MTT assay for cytotoxicity, by ELISA for VEGF excretion in the medium and Western blot for cellular HIF1\#945; expression under normoxic as well as hypoxic conditions. These results are compared with the effect on an ER-positive cell line (MCF-7). Results: MDA-MB-231 cells (IC50 22 nM) cells are less sensitive to HSP90 inhibition than MCF-7 cells (IC50 11 nM). MDA-MB-231 excreted higher VEGF levels (1040 pg/mL) in the medium following 24 hours of normoxic exposure, compared to MCF-7 cells (549 pg/mL). Under hypoxic conditions the VEGF excretion also increased more in MDA-MB-231 to 277% than in MCF-7 to 215% both compared to (vs) normoxic control (NoC). Interestingly, treatment with NVP-AUY922 (50 nM) decreased VEGF excretion significantly and most pronounced in MDA-MB-231, under normoxic (MDA-MB-231 to 38±7%, p = 0.03 vs NoC, MCF-7 to 76±7% (ns) vs NoC) as well as hypoxic conditions (MDA-MB-231 to 75±20% p = 0.03 vs hypoxic control, HyC, and MCF-7 to 175±23% (ns) vs HyC). Both cell lines show HIF1\#945; expression in normoxic and induction in hypoxic condition. HSP90 inhibitor (50 nM) reduced HIF1\#945; in MDA-MB-231 cells 8,5-fold in hypoxia but did not affect the expression in MCF-7 cells. In conclusion: NVP-AUY922 interferes with the VEGF pathway in breast cancer cells. In the triple negative cell line it reduced the cell survival and exhibited the highest effect on VEGF excretion under NoC and HyC compared to MCF-7 cells. MDA-MB-231 cells also showed the strongest effect of NVP-AUY922 according to the HIF1\#945; expression. This implies that the VEGF pathway in MDA-MB-231 is more responsive to HSP90 inhibition. Since the VEGF pathway is mainly important in an environment in which angiogenesis is possible, these results warrant further testing of this drug in an in vivo model to analyze its potential role for the treatment of triple negative breast cancer.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4688.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009