Abstract P6-03-11: Erk5 as a therapeutic target in triple negative breast cancer (TNBC)
Authors: Miranda Mariska Sauzine , Ejeh Fares Al , Shi Wei , Simpson Peter , Lakhani Sunil , Khanna Kum Kum 
Published: May 2015

TNBC is a subtype of breast cancer known for its aggressive behavior and poor prognosis. TNBC accounts for 17-24% of all invasive breast cancers and is a subtype that lacks the expression of hormone receptors; oestrogen [ER], progesterone [PR]) and epidermal growth factor receptor 2 (HER2) receptors. Currently there has been a shift from using empirically derived agents that inhibit tumor cell growth and/or survival, to molecular therapies that target specific molecules that regulate these and other important biological processes. Despite the success of some new-targeted therapies to treat breast cancer, the outlook for the majority of patients with TNBC remains poor. Therefore we have utilized the KinexTM antibody array to resolve potential new targetable "nodes". We have screened 43 primary breast cancer biopsies (16 TNBC, 16 ER/PR positive and 11 HER2-positive) and 16 breast cancer cell lines for protein/phosphoprotein levels. Extracellular-signal-regulated kinase 5 (Erk5) is a member of the MAPK family. Erk5 has a large, unique C-terminal-half not found in other MAPK family members and because of this unique 400-amino acid extension, ERK5 is also called big MAP kinase 1 (BMK1). By extensive in silico analyses, we identified that the Erk5 metagene is prognostic and identifies TNBC/BLBC with poor prognosis. Our kinome study of primary breast cancer has further confirmed that the MEK5-Erk5 pathway is upregulated in the TNBC subgroup compared to the other TNBC subgroups and that pharmacological inhibition of Erk5 is therapeutic against primary MDA-MB-231 TNBC xenografts (1).

Our preliminary data has shown that Erk5 is overexpressed in the TNBC subtype at the protein level. We have also shown that silencing Erk5 by siRNA or shRNA inhibits migration of TNBC cell lines in vitro. Expression of Erk5 (total and phosphoproteins) will be investigated in primary breast tumours and metastases samples from patient by immunohistochemistry. We will also overexpress Erk5 in non-metastatic breast cancer cell lines to study the effect of Erk5 overexpression on metastases. In an elegant study, site directed mutagenesis was used to modify Erk5 and show that phosphorylations of the C-terminal domain of kinase activated Erk5 is required for the transcriptional activity of Erk5. Using in vitro and in vivo models we will determine if the transcriptional activity of activated Erk5 is a major player to drive metastatic phenotype. Moreover, whether kinase-dependent or transcription-dependent activity of Erk5 on several pathways is sufficient to drive metastasis will also be determined.

Our results strongly suggest the MEK5-Erk5 pathway as a prognostic and therapeutic pathway in a poor-prognosis subset of TNBC/BCLC. Characterization of this pathway in clinical cohorts particularly in TNBC tumors, mechanistic understanding of its contribution to metastasis and therapeutic targeting in vivo would help develop a personalised approach to identify and treat TNBC tumors and metastases with activated Erk5 pathway.

1. Al-Ejeh F, Miranda M et al. Kinome profiling reveals breast cancer heterogeneity and identifies targeted therapeutic opportunities for triple negative breast cancer. Oncotarget. March 19, 2014.

Citation Format: Mariska Sauzine Miranda, Fares Al Ejeh, Wei Shi, Peter Simpson, Sunil Lakhani, Kum Kum Khanna. Erk5 as a therapeutic target in triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P6-03-11.