SAHA‐sensitized prostate cancer cells to TNFα‐related apoptosis‐inducing ligand (TRAIL): Mechanisms leading to synergistic apoptosis

Abstract

Treatment of cancer cells with histone deacetylase inhibitors (HDACi) such as suberolylanilide hydroxamic acid (SAHA) activates genes that promote apoptosis. To enhance proapoptotic efficiency, SAHA has been used in combination with radiation, kinase inhibitors and cytotoxic drugs. Although several prostate cells respond to TNFα‐Related Apoptosis‐Inducing Ligand (TRAIL), LNCaP are resistant. This model system was utilized to examine the advantages of combined treatment with SAHA and TRAIL. In LNCaP cells, TRAIL induced synergistic apoptosis when combined with even with the lowest dose SAHA. Treatment with caspase inhibitor confirmed that SAHA‐induced apoptosis was mediated through caspases. In addition to induction of apoptosis, SAHA and TRAIL decreased the levels of proapoptotic proteins IKKα, IKKβ and IKKγ, suggesting that SAHA treatment may reduce the activity of NFκB. However, assay for NFκB luciferase reporter activity showed highly significant increase in SAHA‐treated cells, supporting earlier suggestions that HDACi promotes NFκB transcriptional activity. Further analyses to determine the mechanisms by which the combination of SAHA and TRAIL led to synergistic apoptosis indicated that the apoptotic response of LNCaP is due to a complex regulation of death receptor pathway and alterations of NFκB activity at several regulatory steps. © 2006 Wiley‐Liss, Inc.

Green tea polyphenol EGCG sensitizes human prostate carcinoma LNCaP cells to TRAIL-mediated apoptosis and synergistically inhibits biomarkers associated with angiogenesis and metastasis

“…LNCaP cells are known to be refractory to apoptosis induction by TRAIL (Deeb et al, 2004;Yamaguchi et al, 2005;Hu et al, 2006;Lakshmikanthan et al, 2006). We confirmed this in a dose-escalation experiment ( Figure 1a) and observed that LNCaP cells were refractory to TRAIL-induced cell death to a dose as high as 150 ng ml À1 while in PC3 cells 10 ng ml À1 TRAIL treatment resulted in about 70% inhibition of cell growth.…”

Therapeutic advantage of combining calcium channel blockers and TRAIL in prostate cancer

“…TRAIL is an effective apoptotic agent by itself or in combination with other apoptotic drugs. We have shown synergistic increase in apoptotic response when TRAIL was combined with antiprogestin mifepristone (43) or by inhibiting the function of heat shock protein 90 (27,34), inhibiting the proteasomal activity (34), or treatment with histone deacetylase inhibitor, SAHA (25). Our present results show that treatment with both TRAIL and CGP Figure 3.…”

“…In some cells, caspase-8 propagates death signal directly through the activation of procaspase-3, whereas in others, the apoptotic signal is amplified via the mitochondria. In the latter, caspase-8 cleaves Bid, which translocates into the mitochondria and initiates changes in the mitochondria leading to the release of cytochrome c. Bid, a member of the BH3 domain only subgroup of Bcl 2 family proteins, is a 22-kDa cytosolic protein that is cleaved by activated caspase-8 in cells treated with variety of apoptotic agents, such as TRAIL (24), histone deacetylase inhibitor (25), and UV radiation (26). The truncated 15-kDa Bid (tBid) is translocated into the mitochondria, where it participates in changes leading to the release of cytochrome c to the cytoplasm.…”

“…This assay is highly sensitive and is specific to cell death due to apoptosis but does not measure necrotic cells. Apoptosense kit has been used successfully in measuring apoptosis in prostate cancer cells (25,27,34). On completion of the experiments, cells were harvested and total protein was extracted as described below.…”

Combination therapy of established cancer using a histone deacetylase inhibitor and a TRAIL receptor agonist

“…However, a recent study provides compelling evidence that although HDACi can indeed induce expression of TRAIL and/or its cognate receptors, this event is not necessary to mediate synergistic apoptosis of target cells by using a combination of HDACi and recombinant TRAIL or anti-DR4/DR5 mAbs (33). Other studies have correlated synergistic tumor cell apoptosis by HDACi and activators of the TRAIL pathway with decreased expression of c-FLIP (8,25), decreased expression of apoptosis inhibitors and Bcl-2 (25), inhibition of Cdc2 protein and subsequent down-regulation of survivin and XIAP (26), and modulation of NF-B activity (28,34,35). It is not yet clear whether a common molecular event will be identified as being requisite to mediate synergistic apoptosis by HDACi and TRAIL activators, or whether the responses will depend on the cell type and/or HDACi under investigation.…”