Abstract 4506: UPR biomarker expression correlates with inhibition of migration of TNBC cells treated with low doses of chemotherapy
Authors: Raiter Annat , Lipovetsky Julia , Hardy Britta , Yerushalmi Rinat 
Published: July 2017

Abstract
Much attention has been directed to the study of triple-negative breast cancer (TNBC) because of its short disease-free interval from diagnosis and more aggressive course in the metastatic setting. TNBC also lacks specific target receptors for treatment. Third-generation metronomic chemotherapy using available agents that target DNA repair complexes (i.e., taxanes), and cell proliferation (i.e., anthracycline) have shown promise results. However, specific regimens for TNBC at the different disease stages have not been clearly defined. Therefore, researchers are seeking molecular biomarkers to predict response to current chemotherapeutic agents. In a previous study of TNBC, we demonstrated that low doses of anthracyclines and taxanes, which are known to increase endoplasmic reticulum stress, increased tumor cell expression of glucose-regulated protein 78 (GRP78), a key regulator of the unfolding protein response (UPR), resulting in tumor cell apoptosis. GRP78 gene expression is upregulated via CREB2L1, an endoplasmic reticulum transmembrane transcription factor and member of the CREB/ATF family of transcription factors. CREB3L1 is a metastatic suppressor and functions as a transducer of UPR. The aim of the present study was to investigate the effect of low doses of doxorubicin and paclitaxel on UPR activation in metastatic TNBC cells by determining CREB3L1 protein expression in correlation to cell-surface GRP78 expression. Furthermore, we related CREB3L1 and cell-surface GRP78 expression with the migration potential of the cells in response to treatment. We found that metronomic doses of doxorubicin significantly induced CREB3L1 and cell surface GRP78 expression in TNBC cells. CREB3L1 increased by 2.5-fold in MDAMB231 and by 3-fold in MDAMB468 (p&lt;0.04); GRP78 increased by 3.7-fold and 6.1-fold, respectively (p&lt;0.01). Similar results were obtained with low doses of paclitaxel. A strong correlation was observed between CREB3L1 and cell-surface GRP78 protein expression. The increased expression of both proteins in MDAMB231 (highly metastatic) and MDAMB468 (moderated metastatic) was associated with significant inhibition of the migration capacity of the treated TNBC cells. In contrast, the migration capacity of treated estrogen-positive MCF7 cells (non-metastatic) and Her2- positive BT474 cells (highly metastatic) was poorly inhibited, coinciding with a non-significant increase in CREB3L1 and GRP78 expression. The results demonstrated that the drug effect via the UPR was specific for TNBC and unrelated to the metastatic profile of the cells. This study is the first stage in the identification of UPR-related biomarkers of beneficial outcome of metronomic chemotherapy for TNBC. Future mechanistic studies should focus on the possible use of cell surface GRP78 and CREB3L1 as targets for combination therapies.
Citation Format: Annat Raiter, Julia Lipovetsky, Britta Hardy, Rinat Yerushalmi. UPR biomarker expression correlates with inhibition of migration of TNBC cells treated with low doses of chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4506. doi:10.1158/1538-7445.AM2017-4506