Reduced expression of DNA repair and redox signaling protein APE1/Ref-1 impairs human pancreatic cancer cell survival, proliferation, and cell cycle progression

Pancreatic cancer is a deadly disease that is virtually never cured. Understanding the chemoresistance intrinsic to this cancer will aid in developing new regimens. High expression of APE1/Ref-1, a DNA repair and redox signaling protein, is associated with resistance, poor outcome, and angiogenesis; little is known in pancreatic cancer. Immunostaining of adenocarcinoma shows greater APE1/Ref-1 expression than in normal pancreas tissue. A decrease in APE1/Ref-1 protein levels results in pancreatic cancer cell growth inhibition, increased apoptosis, and altered cell cycle progression. Endogenous cell cycle inhibitors increase when APE1/ Ref-1 is reduced, demonstrating its importance to proliferation and growth of pancreatic cancer.     

HDAC5, negatively regulated by miR‐148a‐3p,promotes colon cancer cell migration

Histone deacetylases (HDACs) are involved in many processes including tumor cell growth and proliferation and regulation of gene expression. To clarify the role of class IIa HDACs in the metastasis of colon adenocarcinoma, we used the class IIa HDAC inhibitor TMP269 and found that it effectively inhibited the migration ability of colon adenocarcinoma cells. Next, we silenced the member of class IIa HDACs and confirmed that the migratory ability of colon adenocarcinoma cells was significantly inhibited by silencing HDAC5 or HDAC7. HDAC5 plays a variety of roles in human cancers. Here, we examined the role of HDAC5 in colon adenocarcinoma. The results indicated that HDAC5 was highly expressed in tumor tissues and negatively correlated with the expression of miR‐148a‐3p. Moreover, the expression of HDAC5 was correlated with tumor progression. HDAC5 markedly increased the invasion and migration of cancer cells in vitro, an effect that could be inhibited by overexpression of miR‐148a‐3p. Following an intraperitoneal injection of colon adenocarcinoma cells in athymic nude mice, HDAC5 promoted tumor implant. Together, these findings showed that HDAC5 overexpression in colon adenocarcinoma is consistent with tumor progression and tumor cell migration and the impact of HDAC5 overexpression is reduced by miR‐148a‐3p.     

FR901228, a novel histone deacetylase inhibitor, induces cell cycle arrest and subsequent apoptosis in refractory human pancreatic cancer cells

Histone deacetylase (HDAC) inhibitors have antiproliferative activity against human cancer cells via cell cycle arrest, differentiation, and apoptosis. However, no report has focused on the apoptotic potential of HDAC inhibitors in refractory human pancreatic cancer. This study was designed to examine the apoptotic potential of FR901228, a novel HDAC inhibitor, in five human pancreatic cancer cell lines: Capan-1, BxPC-3, HPAF, Panc-1, and MIAPaCa-2. FR901228 markedly inhibited the proliferation of all five cell lines (IC50: 1-500 nM), with the greatest effect in MIAPaCa-2 cells. Treatment of each cell line with FR901228 (10-100 nM) caused cell cycle arrest at the G1 or G2/M phase and subsequent apoptosis. FR901228 induced expression of hyperacetylated histone H3 after 3 h of treatment and overexpression of p21Waf-1 after 6 h. In addition, FR901228 induced apoptosis by activating caspase-3, which led to cleavage of p21Waf-1 into a 15-kDa breakdown product and drove cancer cells from cell cycle arrest into apoptosis. FR901228 also decreased the protein level of survivin dramatically. Our results show that FR901228 markedly inhibits the growth of pancreatic cancer cells, not only through cell cycle arrest, but also through subsequent apoptosis; this was accompanied by caspase-3 activation, survivin degradation, and p21Waf-1 cleavage. FR901228 may prove clinically useful as an agent for refractory pancreatic cancers.     

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces apoptosis via induction of 15-lipoxygenase-1 in colorectal cancer cells

Histone deacetylases (HDACs) mediate changes in nucleosome conformation and are important in the regulation of gene expression. HDACs are involved in cell cycle progression and differentiation, and their deregulation is associated with several cancers. HDAC inhibitors have emerged recently as promising chemotherapeutic agents. One such agent, suberoylanilide hydroxamic acid, is a potent inhibitor of HDACs that causes growth arrest, differentiation, and/or apoptosis of many tumor types in vitro and in vivo. Because of its low toxicity, suberoylanilide hydroxamic acid is currently in clinical trials for the treatment of cancer. HDAC inhibitors induce the expression of <2% of genes in cultured cells. In this study, we show that low micromolar concentrations of suberoylanilide hydroxamic acid induce the expression of 15-lipoxygenase-1 in human colorectal cancer cells. The expression of 15-lipoxygenase-1 correlates with suberoylanilide hydroxamic acid-induced increase in 13-S-hydroxyoctadecadienoic acid levels, growth inhibition, differentiation, and apoptosis observed with these cells. Furthermore, specific inhibition of 15-lipoxygenase-1 significantly reduced the suberoylanilide hydroxamic acid-induced effects. These novel findings are the first demonstration of a mechanistic link between the induction of 15-lipoxygenase-1 by a HDAC inhibitor and apoptosis in cancer cells. This result has important implications for the study of suberoylanilide hydroxamic acid and other HDAC inhibitors in the prevention and therapy of colorectal cancer and supports future investigations of the mechanisms by which HDAC inhibitors up-regulate 15-lipoxygenase-1.     

Pharmacologic inhibition of RAF-->MEK-->ERK signaling elicits pancreatic cancer cell cycle arrest through induced expression of p27Kip1

Expression of mutationally activated RAS is a feature common to the vast majority of human pancreatic adenocarcinomas. RAS elicits its effects through numerous signaling pathways including the RAF-->mitogen-activated protein (MAP)/extracellular signal-regulated kinase (ERK) kinase [MEK]-->ERK MAP kinase pathway. To assess the role of this pathway in regulating cell proliferation, we tested the effects of pharmacologic inhibition of MEK on human pancreatic cancer cell lines. In eight cell lines tested, MEK inhibition led to a cessation of cell proliferation accompanied by G0-G1 cell cycle arrest. Concomitant with cell cycle arrest, we observed induced expression of p27Kip1, inhibition of cyclin/cyclin-dependent kinase 2 (cdk2) activity, accumulation of hypophosphorylated pRb, and inhibition of E2F activity. Using both antisense and RNA interference techniques, we assessed the role of p27Kip1 in the observed effects of MEK inhibition on pancreatic cancer cell proliferation. Inhibition of p27Kip1 expression in Mia PaCa-2 cells restored the activity of cyclin/cdk2, phosphorylation of pRb, and E2F activity and partially relieved the effects of U0126 on pancreatic cancer cell cycle arrest. Consistent with the effects of p27Kip1 on cyclin/cdk2 activity, inhibition of CDK2 expression by RNA interference also led to G0-G1 cell cycle arrest. These data suggest that the expression of p27Kip1 is downstream of the RAF-->MEK-->ERK pathway and that the regulated expression of this protein plays an important role in promoting the proliferation of pancreatic cancer cells. Moreover, these data suggest that pharmacologic inhibition of the RAF-->MEK-->ERK signaling pathway alone might tend to have a cytostatic, as opposed to a cytotoxic, effect on pancreatic cancer cells.     

Ectopic Overexpression of Sonic Hedgehog (Shh) Induces Stromal Expansion and Metaplasia in the Adult Murine Pancreas

Ligand-dependent activation of the Hedgehog (Hh) signaling pathway has been implicated in both tumor initiation and metastasis of pancreatic ductal adenocarcinoma (PDAC). Prior studies in genetically engineered mouse models (GEMMs) have assessed the role of Hh signaling by cell autonomous expression of a constitutively active Gli2 within epithelial cells. On the contrary, aberrant pathway reactivation in the human exocrine pancreas occurs principally as a consequence of Sonic Hh ligand (Shh) overexpression from epithelial cells. To recapitulate the cognate pathophysiology of Hh signaling observed in the human pancreas, we examined GEMM where Hh ligand is conditionally overexpressed within the mature exocrine pancreas using a tamoxifen-inducible Elastase-Cre promoter (Ela-CreERT2;LSL-mShh). We also facilitated potential cell autonomous epithelial responsiveness to secreted Hh ligand by generating compound transgenic mice with concomitant expression of the Hh receptor Smoothened (Ela-CreERT2;LSL-mShh;LSL-mSmo). Of interest, none of these mice developed intraductal precursor lesions or PDAC during the follow-up period of up to 12 months after tamoxifen induction. Instead, all animals demonstrated marked expansion of stromal cells, consistent with the previously described epithelial-to-stromal paracrine Hh signaling. Hh responsiveness was mirrored by the expression of primary cilia within the expanded mesenchymal compartment and the absence within mature acinar cells. In the absence of cooperating mutations, Hh ligand overexpression in the mature exocrine pancreas is insufficient to induce neoplasia, even when epithelial cells coexpress the Smo receptor. This autochthonous model serves as a platform for studying epithelial stromal interactions in pancreatic carcinogenesis.     

Plant flavone apigenin inhibits HDAC and remodels chromatin to induce growth arrest and apoptosis in human prostate cancer cells: In vitro and in vivo study

Apigenin (4′,5,7,‐trihydroxyflavone), an anticancer agent, selectively toxic to cancer cells induces cell cycle arrest and apoptosis through mechanisms that have not been fully elucidated. Our studies indicate that apigenin‐mediated growth inhibitory responses are due to inhibition of class I histone deacetylases (HDACs) in prostate cancer cells. Treatment of PC‐3 and 22Rv1 cells with apigenin (20–40 µM) resulted in the inhibition of HDAC enzyme activity, specifically HDAC1 and HDAC3 at the protein and message level. Apigenin‐mediated HDAC inhibition resulted in global histone H3 and H4 acetylation, as well as localized hyperacetylation of histone H3 on the p21/waf1 promoter. A corresponding increase was observed in p21/waf1 and bax protein and mRNA expression after apigenin exposure, consistent with the use of HDAC inhibitor, trichostatin A. The downstream events demonstrated cell cycle arrest and induction of apoptosis in both cancer cells. Studies of PC‐3 xenografts in athymic nude mice further demonstrated that oral intake of apigenin at doses of 20 and 50 µg/mouse/d over an 8‐wk period resulted in a marked reduction in tumor growth, HDAC activity, and HDAC1 and HDAC3 protein expression at both doses of apigenin. An increase in p21/waf1 expression was observed in apigenin‐fed mice, compared to the control group. Furthermore, apigenin intake caused a significant decrease in bcl2 expression with concomitant increase in bax, shifting the bax/bcl2 ratio in favor of apoptosis. Our f indings confirm for the first time that apigenin inhibits class I HDACs, particularly HDAC1 and HDAC3 and its exposure results in reversal of aberrant epigenetic events that promote malignancy. © 2011 Wiley Periodicals, Inc.     

Histone deacetylases 1, 2 and 3 are highly expressed in prostate cancer and HDAC2 expression is associated with shorter PSA relapse time after radical prostatectomy

High activity of histone deacetylases (HDACs) causes epigenetic alterations associated with malignant cell behaviour. Consequently, HDAC inhibitors have entered late-phase clinical trials as new antineoplastic drugs. However, little is known about expression and function of specific HDAC isoforms in human tumours including prostate cancer. We investigated the expression of class I HDACs in 192 prostate carcinomas by immunohistochemistry and correlated our findings to clinicopathological parameters including follow-up data. Class I HDAC isoforms were strongly expressed in the majority of the cases (HDAC1: 69.8%, HDAC2: 74%, HDAC3: 94.8%). High rates of HDAC1 and HDAC2 expression were significantly associated with tumour dedifferentiation. Strong expression of all HDACs was accompanied by enhanced tumour cell proliferation. In addition, HDAC2 was an independent prognostic marker in our prostate cancer cohort. In conclusion, we showed that the known effects of HDACs on differentiation and proliferation of cancer cells observed in vitro can also be confirmed in vivo. The class I HDAC isoforms 1, 2 and 3 are differentially expressed in prostate cancer, which might be important for upcoming studies on HDAC inhibitors in this tumour entity. Also, the highly significant prognostic value of HDAC2 clearly deserves further study.     

Expression profile of class I histone deacetylases in human cancer tissues

Histone deacetylase (HDAC) activity is one of the widely used and well-established mechanisms for regulation of various genes in cancer. To identify which subtype of class I HDACs are overexpressed in cancers, we analyzed the expression of class I HDAC isotypes composed of HDAC1, 2, 3 and 8 in several cell lines and human cancer tissues, including cancer of the stomach, esophagus, colon, prostate, breast, ovary, lung, pancreas and thyroid. The results showed that >75% of human cancer tissues and their corresponding non-cancerous epithelium showed high expression of these class I HDACs. However, the immunoreactivity of HDAC8 in both prostatic cancer tissue and non-cancerous prostate glands was lower than that in other cancer tissues. Furthermore, 5-40% of cancer tissues overexpressed class I HDACs, when compared with normal epithelium. The results suggest the potential usefulness of HDAC inhibitors for the treatment of a wide variety of human cancers.     

Green tea polyphenols causes cell cycle arrest and apoptosis in prostate cancer cells by suppressing class I histone deacetylases

Green tea polyphenols (GTPs) reactivate epigenetically silenced genes in cancer cells and trigger cell cycle arrest and apoptosis; however, the mechanisms whereby these effects occur are not well understood. We investigated the molecular mechanisms underlying the antiproliferative effects of GTP, which may be similar to those of histone deacetylase (HDAC) inhibitors. Exposure of human prostate cancer LNCaP cells (harboring wild-type p53) and PC-3 cells (lacking p53) with 10-80 μg/ml of GTP for 24 h resulted in dose-dependent inhibition of class I HDAC enzyme activity and its protein expression. GTP treatment causes an accumulation of acetylated histone H3 in total cellular chromatin, resulting in increased accessibility to bind with the promoter sequences of p21/waf1 and Bax, consistent with the effects elicited by an HDAC inhibitor, trichostatin A. GTP treatment also resulted in increased expression of p21/waf1 and Bax at the protein and message levels in these cells. Furthermore, treatment of cells with proteasome inhibitor, MG132 together with GTP prevented degradation of class I HDACs, compared with cells treated with GTP alone, indicating increased proteasomal degradation of class I HDACs by GTP. These alterations were consistent with G(0)-G(1) phase cell cycle arrest and induction of apoptosis in both cell lines. Our findings provide new insight into the mechanisms of GTP action in human prostate cancer cells irrespective of their p53 status and suggest a novel approach to prevention and/or therapy of prostate cancer achieved via HDAC inhibition.     

Targeted inhibition of histone deacetylases and hedgehog signaling suppress tumor growth and homologous recombination in aerodigestive cancers

Standard combined modality therapies for aerodigestive tract malignancies have suboptimal outcomes, and targeting cancer-specific molecular pathways in combination with radiation could improve the therapeutic ratio. Dysregulation of epigenetic modulators such as histone deacetylases (HDACs), and developmental morphogens such as the hedgehog (HH) pathway have been implicated in aerodigestive tumor progression and metastasis. We hypothesized that simultaneous targeting of HDACs and the HH-pathway mediator Smoothened (Smo) represents an opportunity to overcome therapeutic resistance in these cancers. We evaluated the effects of the HDAC inhibitor SAHA and Smo inhibitor GDC-0449 with radiation in multiple aerodigestive cancer cell lines. Isobologram analyses showed that SAHA and GDC-0449 synergistically suppressed cancer cell proliferation in vitro. SAHA and GDC-0449 cooperatively enhanced G₀/G₁ cell cycle arrest which was associated with up-regulation of p21^waf. GDC-0449 prevented SAHA-induced up-regulation of Gli-1 and Gli-2. Both Smo and Ptc-1 expression was cooperatively suppressed by SAHA and GDC-0449. The combination of SAHA and GDC-0449 induced radiation sensitization with 2 Gy as determined by colony formation assays and cytogenetic analyses, which correlated with higher residual γ-H2AX and 53BP1 foci. In mouse tumor xenografts of the SqCC/Y1 cell line, SAHA and GDC-0449 delayed tumor growth longer and prolonged survival more than either agent alone. In summary, we have identified synergistic effect of HDAC and HH signaling for radiosensitization to improve therapeutic outcomes for aerodigestive malignancies.