Abstract P4-05-15: Examining the role of Nm23-H1 in the metastatic profile of triple negative breast cancer (TNBC)

Background: Triple negative breast cancer makes up 10-20% of all mammary tumors. It is so named because it exhibits low or no expression of both the estrogen receptor (ER) and progesterone receptor (PR), and has low or no expression of the human epidermal growth factor (HER2) receptor. With no current molecular targets identified, treatment options for TNBCs are limited to conventional chemotherapy, which has been shown to be only moderately effective. Furthermore, diagnosis is correlated with high rates of relapse and metastatic disease, low survival rate five years past diagnosis, and overall poor prognosis. Nm23-H1 is the most well characterized in a class of metastasis suppressor genes that have received increased attention as a potential therapeutic target in breast cancers. Nm23-H1 mRNA is expressed at relatively low levels in highly metastatic tumor cells compared to normal and non-neoplastic tissues. Low expression levels correlate with increased metastasis and poor clinical prognosis in several type cancers, including breast cancer. Nm23-H1 inhibits a class of Rho small GTPases, including Rac1, Rho and cdc42, which mediate cell-to-cell adhesion and cytoskeletal reorganization, which ultimately modulates the metastatic profile, i.e. metastasis, cellular motility, and invasion. Methods: Western blotting was used to examine the basal level of expression in a panel of mesenchymal and epithelial TNBC cell lines. Transient siRNA was used to silence Nm23-H1 in MDA MB 231 cells to determine the effects on downstream Nm23-H1 targets IQGAP2, Rac1, Rho and Cdc42. The effects of Nm23-H1 inhibition on the invasive potential of TNBC cells were assessed using Matrigel chamber assays. Spheroid migration assays were employed to assess the effects of Nm23-H1 inhibition on the migratory potential of TNBC cells. Results: Our studies indicate that Nm23-H1 protein is expressed in all TNBC cell lines tested but to varying degrees, with mesenchymal cells expressing higher levels compared to epithelial cells. Immunoblotting showed that silencing Nm23-H1 resulted in an increase in phosphorylated Rac and Rac and the cytoskeletal intermediate filament vimentin. Silencing also decreased the invasion and migration of TNBC cells compared to control cells. Conclusion: These results suggest a paradoxical role of the metastasis suppressor protein Nm23-H1 as an oncogene in TNBC cells. Nm23-H1 plays a vital role in the promotion of TNBC cellular migration, invasion, and the expression of proteins associated with motility and invasion. These data strongly suggest an oncogenic potential of Nm23-H1 in a subset of TNBCs and warrants further investigation of this protein a potential molecular marker for metastatic TNBCs. Citation Format: Tanisha Z McGlothen, Rachel Tobin, Tiffanie Alcaide, LaTonia Taliaferro-Smith, Liu Tongrui, O9Regan Ruth. Examining the role of Nm23-H1 in the metastatic profile of 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 P4-05-15.