Gadd45a, a growth arrest and DNA-damage gene, plays important roles in the control of cell cycle checkpoints, DNA repair and apoptosis. We show here that Gadd45a is involved in the control of cell contact inhibition and cellcell adhesion. Gadd45a can serve as an adapter to enhance the interaction between b-catenin and Caveolin-1, and in turn induces b-catenin translocation to cell membrane for maintaining cell-cell adhesion/contact inhibition. This is coupled with reduction of b-catenin in cytoplasm and nucleus following Gadd45a induction, which is reflected by the downregulation of cyclin D1, one of the b-catenin targeted genes. Additionally, Gadd45a facilitates ultraviolet radiation-induced degradation of cytoplasmic and nuclear b-catenin in a p53-dependent manner via activation of p38 kinase. These findings define a novel link that connects Gadd45a to cell-cell adhesion and cell contact inhibition, which might contribute to the role of Gadd45a in inhibiting tumorigenesis.

The black garlic is produced from the raw garlic by Milliard reaction at high temperature (~60–90°C) and humidity (~70–90%). In this process, the pungent odor and gastrointestinal irritation effects of the raw garlic are reduced. At the same time, unstable compounds such as allicin are converted into stable organosulfur compounds with antioxidant activity. Previous studies have confirmed that black garlic extract has anti-tumor effects and could inhibit the proliferation of various tumor cells, including breast cancer cells MCF-7. However, the mechanisms of the anti-tumor effects remain unclear. In this study, we found that the black garlic extract could inhibit the proliferation, invasion, and metastasis of estrogen receptor-positive breast cancer cells, promote their apoptosis, and inhibit their epithelial-mesenchymal transition. Mechanistically, the black garlic extract reduced the expression of the anti-apoptotic protein MCL-1, which was achieved by modulating the ROS-JNK signaling pathway. In addition, the black garlic extract also decreased the expression of BCL-2 and increased the expression of BAX and BIM. We also found that the black garlic extract, in combination with venetoclax, a BCL-2 inhibitor, synergistically kills the estrogen receptor-positive breast cancer cells. These results suggested that black garlic extract has great therapeutic value and prospects for estrogen receptor-positive breast cancer treatment.

Introduction: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with limited effective treatment options. New therapeutic approaches are urgently needed to improve the prognosis of TNBC. Reactive oxygen species (ROS) are inherent byproducts of oxidative metabolism, and forced stimulation of glucose oxidation in cancer cells raises oxidative stress and sensitizes cells to different stresses. Therefore, targeting the antioxidant capacity of cancer cells has become a promising anticancer strategy. As a redox modulator, selenocystine (SeC) has received a great deal of attention and has been shown effective against human melanoma, hormone receptor-positive breast cancer, and cancers of liver, lung and cervical in vitro. However, whether SeC exerts an anticancer effect on TNBC cells has never been explored. Methods: The dose-response effects and time course of effects of SeC on three different TNBC cell lines, MDA-MB-231, MDA-MB-436 and MDA-MB-468, were investigated in this study. Cellular viability was determined by the CCK-8 assay and cell morphology were recorded under a light microscope. Cellular apoptosis was detected using Annexin V/PI staining assay and cell cycle distribution was analyzed by flow cytometry. Results: SeC induced cell growth inhibition in all three TNBC cell lines. For 24, 48 and 72 hours of SeC treatments, the IC50 values were 40.8, 12.8 and 9.2 μM for MDA-MB-231 cells; 14.6, 5.4 and 3.0 μM for MDA-MB-436 cells; and 69.6, 29.3 and 19.9 μM for MDA-MB-468 cells. The changes of cellular morphology of TNBC cells in response to SeC treatment were similar to those cells undergoing apoptotic pathway. This result was confirmed by Annexin V/PI staining assays (Table 1). Cell cycle analysis further revealed that SeC also induced S-phase arrest in a dose-dependent manner (Table 2). Conclusion: In summary, SeC inhibited TNBC cell viability in a dose- and time-dependent manner which was attributed to the induction of apoptosis and S-phase arrest. Our finding indicates that SeC is a potential therapeutic agent for TNBC. Table 1. Apoptotic rate of TNBC cells after SeC treatment.Conc.(μM)MDA-MB-231MDA-MB-436MDA-MB-46805.8 %18.1 %26.7 %1025.5 %45.8 %60.7 %2040.1 %67.1 %70.9 %4054.7 %70.7 %74.5 % Table 2. SeC induces S-phase arrest in TNBC cells in a dose-dependent manner. Conc.(μM)G0/G1 (%)S (%)G2/M (%)MDA-MB-231016.655.927.5 1050.139.310.6 2045.548.16.4 4041.753.05.3MDA-MB-436042.127.630.3 1036.335.028.7 2034.340.725.0 4032.445.422.2MDA-MB-468059.123.717.2 1054.929.315.8 2050.135.714.2 4043.843.113.1 Citation Format: Long M, Qiu W, Wu J, Liu R, Su H. Selenocystine inhibits triple-negative breast cancer cell proliferation by inducing cell apoptosis and S-phase arrest. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-03-12.