SAHA and EGCG Promote Apoptosis in Triple-negative Breast Cancer Cells, Possibly Through the Modulation of cIAP2

Abstract

Background/Aim: Inhibition of apoptosis is one of the hallmarks of cancer, and anti-apoptotic genes are often targets of genetic and epigenetic alterations. Cellular inhibitor of apoptosis 2 (cIAP2) has a role in degrading caspases by linking them to ubiquitin molecules, and is upregulated in triple-negative breast cancer (TNBC). Previous studies have demonstrated that cIAP2 may play a role in the epithelial-to-mesenchymal transition (EMT). Materials and Methods: Suberoylanilide hydroxamic acid (SAHA), a histone deacetylase (HDAC) inhibitor, was administered to triple-negative breast cancer (TNBC) cells alone or in combination with epigallocatechin-3-gallate (EGCG), a DNA methyltransferase (DNMT) inhibitor isolated from green tea. Results: The compounds were able to decrease the expression of cIAP2 while increasing the expression of pro-apoptotic caspase 7. There were also changes in histone modifications, suggesting a role of epigenetic mechanisms in these changes in expression of cIAP2. These changes resulted in an increase in apoptosis. SAHA and EGCG were also capable of limiting TNBC cell migration across a fibronectin (FN) matrix. Conclusion: SAHA and EGCG reduce the metastatic potential of TNBC by inducing the apoptotic pathway. Hanahan and Weinberg first described the hallmarks of cancer in 2000, which included the inhibition of apoptosis as one of the key factors that drive cancer progression (1). This list was updated in 2011 and included two additional enabling characteristics, one of which was genome instability and mutation that encompasses epigenetic aberrations (2). This enabling characteristic can easily influence the hallmarks of cancer. The apoptotic pathway is a system of checks and balances, utilizing a suite of caspases to promote the process and baculovirus IAP repeat (BIR) proteins to inhibit the process. They are able to do so through linking pro-apoptotic proteins to ubiquitin molecules (3). Dysregulation of these proteins can allow cancer cells to evade apoptosis (4). Cellular inhibitor of apoptosis 2 (cIAP2), which is also known as BIRC3, has been shown to be upregulated in cancers, including triple-negative breast cancer (TNBC). TNBCs are typically more refractory to treatment due to the three silenced targets of hormonal cancer therapy: estrogen receptor alpha (ERα), progesterone receptor, and human epidermal growth factor receptor 2 (HER2). In our previous study, we began to elucidate the anti-cancer effects of suberoylanilide hydroxamic acid (SAHA) and epigallocatechin-3-gallate (EGCG) on TNBC cells through the lens of growth potentiation (5). That study has investigated downstream targets of oncogenic miR-221/222 after treatment with SAHA and EGCG in order to determine their abilities to directly restore expression of p27, PTEN, and ERα. After noting the ability of SAHA and EGCG to decrease the expression of miR-221/222, we aimed to investigate other oncogenes that are upregulated in TNBCs. cIAP2 was one of these genes. Jo et al. have linked cIAP2 to an increase in migration in TNBC...

Vorinostat (SAHA) and Breast Cancer: An Overview

“…cIAP2 degradates caspases by linking them to ubiquitin molecules. The expression of cIAP2 is upregulated in TNBC and plays a role in the EMT ( Table 3 ) [ 125 ].…”

Impact of Stilbenes as Epigenetic Modulators of Breast Cancer Risk and Associated Biomarkers

“…EGCG increases the formation of S-adenosyl-L-homocysteine, which acts as a DNMT1 inhibitor and hence appears to be important for managing the methylated biomarkers discussed in the previous section. EGCG, when paired with an HDAC inhibitor like suberoylanilide hydroxamic acid (SAHA) or vorinostat, and administered to triple-negative breast cancer (TNBC) cell lines, has been shown to induce apoptosis and prevent metastatic tendencies by down-regulating the apoptosis inhibitor gene cIAP2 [ 13 , 18 , 19 ]. This combination has also been found to repress the expression of microRNAs such as miR-221/222, which is attributed to the cell-renewal capabilities in TNBC cell lines, thus maintaining the PTEN/AKT/mTOR/NF-κB expression necessary for normal stem-cell maintenance [ 19 , 20 ].…”

Epigenetic Regulation and Dietary Control of Triple Negative Breast Cancer

“…In a recent study, Steed et al ( 100 ) used suberoylanilide hydroxamic acid (SAHA), a HDAC inhibitor, alone or in combination with EGCG in the TNBC cell line MDA-MB-231. The two compounds (SAHA and EGCG) decreased the expression of cellular inhibitor of apoptosis 2 ( cIAP2 ) while increasing the expression of pro-apoptotic caspase 7.…”