Abstract A04: Dasatinib shows different cytotoxicity in triple-negative breast cancer cell lines (2018)

Abstract Background: Triple-negative breast cancer (TNBC) is defined by the lack of significant expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (HER2). Thus, TNBC is resistant to existing molecular targeted drugs such as trastuzumab or tamoxifen, and has a worse prognosis than non-TNBC. In addition, recent studies suggest that TNBC may represent a heterogeneous group of tumors with regards to gene expression, prognosis, and chemotherapy response. Although various molecular targeted drugs for TNBC have been attempted in clinical trials, almost all were negative outcomes because TNBC patients have a heterogeneous behavior. Therefore, in order to establish an efficient therapy, it is important to investigate the difference in response to molecular targeted drugs. From this viewpoint, we focused on dasatinib (Bcl-Abl/Src kinase inhibitor, approved in chronic myeloid leukemia) for the reason that it has been shown to be effective in some patients, even though it failed in clinical trials of unselected TNBC patients in the past. Here, to elucidate the mechanism of different response in dasatinib treatment on TNBC, we attempted to analyze the effects of dasatinib on cytotoxicity in some kinds of TNBC cell lines and to analyze the expression of targeted protein (Src) expression as a first step for elucidating the molecular mechanism of some kinds of TNBC cell lines. Methods: In this study, we used four TNBC cell lines such as HCC1806, HCC1395, MDA-MB-453, and MDA-MB-436, and one non-TNBC cell line, MCF-7. These cells were treated with a range of concentrations of dasatinib (0.001, 0.01, 0.1, 1, 10, or 100 μM) for 72 h. After treatment, cytotoxicity was evaluated by WST-8 assay and molecular expression was examined by Western blotting. Results and Discussion: WST-8 assay revealed that dasatinib showed high cytotoxicity in MCF7, HCC1395, and HCC1806 (IC50 were 0.162, 0.490, and 0.110 μM, respectively). Compared to these three cell lines, dasatinib showed low cytotoxicity in MDA-MB-453 and MDA-MB-436 (IC50 were 6.93 and 7.59 μM, respectively). Then, to investigate the mechanism that the dasatinib showed the different cytotoxicity among these cell lines, the expression of Src, target of dasatinib was examined. The higher expression of Src was observed in three cell lines, indicating relatively high cytotoxicity for dasatinib than the others. Although expression of Src was not observed in MDA-MB-453, that in MDA-MB-436 was the same extent as MCF7 despite low cytotoxicity for dasatinib. Thus, we evaluated the protein activity downstream of the Src pathway. Regarding the three cell lines in which dasatinib showed relatively high cytotoxicity, the phosphorylation of Akt after dasatinib treatment was degraded. However, there was no significant change of Akt activity in the two cell lines that showed relatively low cytotoxicity on dasatinib treatment. Now, in order to elucidate the molecular mechanism of dasatinib resistance observed in MDA-MB-436, we focus on autophagy that has reported to be suppressed by Src. In this regard, we indicated that the expression of LC3-II, known as a marker for autophagy, was higher in MDA-MB-436 than that of other cells in this study. Therefore, we are trying to clarify the relationship between Src and LC3-II. Conclusions: Each TNBC cell line shows the different response to dasatinib and the different Src expression, suggesting that the efficacy of dasatinib could not be dependent on the expression of Src. Thus, to clarify the mechanism of differences of cytotoxicity caused from a variety of TNBC cell lines, it is necessary to analyze more protein expressions upstream or downstream of the Src pathway. Citation Format: Yuya Haga, Kazuma Higashisaka, Lili Yang, Naoki Sekine, Kazuya Nagano, Yasuo Tsutsumi. Dasatinib shows different cytotoxicity in triple-negative breast cancer cell lines [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A04.