Abstract 1083: Nuclear receptors as novel targets in ER negative breast cancer
Authors: Guowei Gu, Yassine Rechoum, Kyle Covington, Bert O'Malley, David Mangelsdorf, John Minna, Suzanne Fuqua
Journal: Cancer Research (2012)

Abstract Background: Estrogen negative (ER-) breast cancer is the major clinical problem in breast cancer treatment due to the limited useful targets in ER- breast cancer. Nuclear receptors are good targets in ER- breast cancer because of the availibility of agonists and antagonists. Material and methods: We used microarray analysis of 227 ER-negative tumors to identify nuclear receptor (NR) targets, and performed hierarchical clustering using 41 NR's. Contributing receptors were scored using prediction analysis of microarrays (PAM) across clustered groups. The candidates gene expression levels were confirmed by qRT-PCR using TaqMan probes. pGIPZ lentiviral vectors carrying shRNA were used to knockdown the selected receptors. Cells were treated with Docetaxel, Doxorubicin and Cisplatin for three days and MTT growth assay was used to evaluate the knockdown effect on cells proliferation and chemosensitivity. Statistical analysis was performed using Red-R software. Results: The 41 NRs clustered the tumors into 5 distinct groups. Groups III and V were chosen according to the higher representative percentage of patients (61%). For each group we selected 4 genes that were the highest ranked discriminators of the group and three cell lines which match each groups’ signature. Thus, testicular receptor 2 (TR2), testicular receptor 4 (TR4), GCNF and RevErbb receptors were selected from group III and androgen receptor, thyroid hormone receptor beta (THRB), COUP-TF1 and ESRRg receptors were selected from group V. The expression levels of the selected receptors were confirmed by q-RT-PCR. The knockdown of TR2 in HCC38 cell line (group III) rendered cells more sensitive to Docetaxel or Doxorubicin. However, the knockdown of TR4 rendered cells more resistant to all the 3 chemotherapy drugs. TR2 knockdown dramatically downregulated TR4 gene expression, whereas TR4 knockdown upregulated TR2 expression suggesting that TR2 maybe the dominant factor in chemotherapeutic response. Knockdown of THRB in HCC 2185 cells (group V), rendered cells more resistant to chemotherapy drugs while THRB agonist could be able to reverse the resistance. Interestingly, COUP-TFI was upregulated in THRB knock down cells. Statistic analysis using clinical data from Sabatier R., BCRT 2011 showed that patients with low THRB or higher COUP-TFI have worse outcome. Conclusion: Clinical targeting of NRs in selected ER-negative breast cancers may be an interesting alternative therapy since more and more agonists and antagonists are being available. The clinical data showed that THRB and COUP-TF1 could be used as predictive factors for the outcome. The use of agonists (for THRB for example) or antagonists (for TR2 for example) combined with chemotherapy could be conceivable in the future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1083. doi:1538-7445.AM2012-1083