X-linked inhibitor of apoptosis protein as a therapeutic target

VALD-3, a Schiff base ligand synthesized from o-vanillin derivatives, induces cell cycle arrest and apoptosis in breast cancer cells by inhibiting the Wnt/β-catenin pathway

Schiff base compounds and their metal complexes have become important synthetic organic drugs due to their extensive biological activities, which include anticancer, antibacterial and antiviral effects. In this study, we investigated the cytotoxic and apoptotic effects of VALD-3, a Schiff base ligand synthesized from o-vanillin derivatives, on human breast cancer cells and the possible underlying mechanisms. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-test was used to observe the proliferation of human breast cancer MCF-7 and MDA-MB-231 cells induced by VALD-3. Flow cytometry analysis showed that VALD-3 triggered cell cycle arrest and induced apoptosis of breast cancer cells. Western blot analysis revealed that VALD-3 upregulated pro-apoptotic proteins (Bad and Bax), downregulated anti-apoptotic proteins (Bcl-2, Bcl-xl, survivin and XIAP) and increased the expression of cleaved caspase-3, cleaved caspase-8, Cyto-c and cleaved PARP. VALD-3 also regulated the Wnt/β-catenin signaling pathway in breast cancer cells, inhibiting the activation of downstream molecules. By xenografting human breast cancer cells into nude mice, we found that VALD-3 significantly suppressed tumor cell growth while showing low toxicity against major organs. In addition, survival analysis showed that VALD-3 can significantly prolong the survival time of mice (P = 0.036). This study is the first to show that VALD-3 induces apoptosis and cell cycle arrest in human breast cancer cells by suppressing Wnt/β-catenin signaling, indicating that it could be a potential drug for the treatment of breast cancer.

Position of lipidation influences anticancer activity of Smac analogs

A small group of lipid-conjugated Smac mimetics was synthesized to probe the influence of the position of lipidation on overall anti-cancer activity. Specifically, new compounds were modified with lipid(s) in position 3 and C-terminus. Previously described position 2 lipidated analog M11 was also synthesized. The resulting mini library of Smacs lipidated in positions 2, 3 and C-terminus was screened extensively in vitro against a total number of 50 diverse cancer cell lines revealing that both the position of lipidation as well as the type of lipid, influence their anti-cancer activity and cancer type specificity. Moreover, when used in combination therapy with inhibitor of menin-MLL1 protein interactions, position 2 modified analog SM2 showed strong synergistic anti-cancer properties. The most promising lipid-conjugated analogs SM2 and SM6, showed favorable pharmacokinetics and in vivo activity while administered subcutaneously in the preclinical mouse model. Collectively, our findings suggest that lipid modification of Smacs may be a viable approach in the development of anti-cancer therapeutic leads.

HMGA2 regulates acute myeloid leukemia progression and sensitivity to daunorubicin via Wnt/β-catenin signaling

Acute myeloid leukemia (AML) is a malignant disease with an increasing prevalence in adults and children. However, valuable molecular diagnostic research is rare. In the present study, plasmids silencing and overexpressing high‑mobility group AT‑hook 2 (HMGA2) were respectively transfected in HL60 and NB4 cells. The effects of HMGA2 on AML cell viability, apoptosis, migration and invasion were determined by preforming MTT, flow cytometry, wound scratch and Transwell assays, respectively. Genes associated with apoptosis and Wnt signaling were evaluated by reverse transcription‑quantitative (RT‑q)‑PCR and western blotting. AML cell sensitivity to daunorubicin (DNR) and the regulatory effects of the Wnt signaling pathway via HMGA2 following treatment with the agonist LiCl or antagonist XAV939 were detected by MTT, RT‑qPCR and western blot analysis. The results revealed that the expression of HMGA2 was elevated more so in HL60, KG1, U937, Kasumi‑1, THP‑1 and K562 cells than in NB4 cells. Silencing HMGA2 suppressed cell viability, migration and invasion, enhanced cell apoptosis and sensitivity to DNR, and almost restored the DNR inhibitory function that was promoted by LiCl treatment. In addition, low expression of HMGA2 attenuated X‑linked inhibitor of apoptosis and Bcl‑2 mRNA and protein levels, and upregulated the expression of Bax and cleaved‑caspase‑3. Furthermore, silencing HMGA2 not only decreased Wnt and non‑phospho‑β‑catenin expressions, but also partially reversed the increased expressions of these proteins induced by LiCl treatment. On the other hand, overexpression of HMGA2 exhibited the opposite results after transfection in NB4 cells. The results of the present study demonstrated that HMGA2 played important roles in driving AML progression and chemosensitivity in HL60 and NB4 cells, potentially by activating the Wnt/β‑catenin signaling pathway. Therefore, it was suggested that HMGA2 may be a promising molecular marker for AML diagnosis.

The long noncoding RNA XIAP-AS1 promotes XIAP transcription by XIAP-AS1 interacting with Sp1 in gastric cancer cells

Long noncoding RNAs (lncRNAs) play roles in the tumorigenesis, proliferation and metastasis of tumor cells. Previous studies indicate that the transcription factor Sp1 is responsible for transcription of the XIAP gene, but it is unknown whether lncRNAs are involved in XIAP transcription. Herein, we identified a novel lncRNA, denoted as XIAP-AS1, transcribed from the first intron of the complementary strand of the XIAP gene. Using RNA FISH, cell fractionation and qRT-PCR, XIAP-AS1 was determined to be located primarily in the nucleus. After various XIAP-AS1 deletion mutants were expressed, RIP assays showed that only the full-length XIAP-AS1 RNA interacted with Sp1 and thereby participated in XIAP transcription. ChIP assays showed that XIAP-AS1 knockdown decreased the binding of Sp1 to the promoter region of XIAP. XIAP-AS1 knockdown promoted tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in gastric tumor cells, as cleaved caspase-3 and caspase-9 was detected. Moreover, in an in vivo mouse xenograft model, tumor cell proliferation was inhibited by XIAP-AS1 knockdown in response to TRAIL administration. In conclusion, our results indicate that XIAP-AS1 is involved in XIAP transcription by interacting with Sp1. Additionally, XIAP-AS1 is a potential target for TRAIL-induced apoptosis in gastric cancer cells.

Targeting of X-linked inhibitor of apoptosis protein and PI3-kinase/AKT signaling by embelin suppresses growth of leukemic cells

The X-linked inhibitor of apoptosis (XIAP) is a viable molecular target for anticancer drugs that overcome apoptosis-resistance of malignant cells. XIAP is an inhibitor of apoptosis, mediating through its association with BIR3 domain of caspase 9. Embelin, a quinone derivative isolated from the Embelia ribes plant, has been shown to exhibit chemopreventive, anti-inflammatory, and apoptotic activities via inhibiting XIAP activity. In this study, we found that embelin causes a dose-dependent suppression of proliferation in leukemic cell lines K562 and U937. Embelin mediated inhibition of proliferation correlates with induction of apoptosis. Furthermore, embelin treatment causes loss of mitochondrial membrane potential and release of cytochrome c, resulting in subsequent activation of caspase-3 followed by polyadenosin-5’-diphosphate-ribose polymerase (PARP) cleavage. In addition, embelin treatment of leukemic cells results in a decrease of constitutive phosphorylations/activation level of AKT and downregulation of XIAP. Gene silencing of XIAP and AKT expression showed a link between XIAP expression and activated AKT in leukemic cells. Interestingly, targeting of XIAP and PI3-kinase/AKT signaling augmented inhibition of proliferation and induction of apoptosis in leukemic cells. Altogether these findings raise the possibility that embelin alone or in combination with inhibitors of PI3-kinase/AKT pathway may have therapeutic usage in leukemia and possibly other malignancies with up-regulated XIAP pathway.

Downregulation of X-linked inhibitor of apoptosis protein by '7-Benzylidenenaltrexone maleate' sensitizes pancreatic cancer cells to TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potential biological anticancer agent. However, a wide range of human primary cancers, including pancreatic cancer, display resistance to apoptosis induction by TRAIL. Therefore, this resistance needs to be overcome to allow TRAIL to be successfully used in cancer therapy. In this study, we performed a compound screen to isolate TRAIL sensitizers and found that one of the identified compounds, 7-benzylidenenaltrexone maleate (BNTX), sensitized pancreatic cancer cells to TRAIL-induced apoptotic cell death. The combination of BNTX with TRAIL promoted the release of cytochrome c from mitochondria into cytosol with caspase activation and a resulting increase in annexin V-stained cells. From a mechanistic perspective, we found that BNTX downregulated X-linked inhibitor of apoptosis protein (XIAP) expression when used in combination with TRAIL, and found that TRAIL-induced apoptosis was augmented by siRNA-mediated knockdown of XIAP. We further demonstrated that BNTX promoted the ubiquitin/proteasome-dependent degradation of XIAP protein via protein kinase C (PKC) alpha/AKT pathway inhibition. Moreover, combined treatment by BNTX with TRAIL suppressed growth of pancreatic tumor xenograft of animal model. Therefore, we suggest that inhibitor of apoptosis protein-mediated resistance of pancreatic cancer cells to anticancer therapeutics can be overcome by inhibiting the PKCα/AKT pathway.

Inducing death in tumor cells: roles of the inhibitor of apoptosis proteins

The heterogeneous group of diseases collectively termed cancer results not just from aberrant cellular proliferation but also from a lack of accompanying homeostatic cell death. Indeed, cancer cells regularly acquire resistance to programmed cell death, or apoptosis, which not only supports cancer progression but also leads to resistance to therapeutic agents. Thus, various approaches have been undertaken in order to induce apoptosis in tumor cells for therapeutic purposes. Here, we will focus our discussion on agents that directly affect the apoptotic machinery itself rather than on drugs that induce apoptosis in tumor cells indirectly, such as by DNA damage or kinase dependency inhibition. As the roles of the Bcl-2 family have been extensively studied and reviewed recently, we will focus in this review specifically on the inhibitor of apoptosis protein (IAP) family. IAPs are a disparate group of proteins that all contain a baculovirus IAP repeat domain, which is important for the inhibition of apoptosis in some, but not all, family members. We describe each of the family members with respect to their structural and functional similarities and differences and their respective roles in cancer. Finally, we also review the current state of IAPs as targets for anti-cancer therapeutics and discuss the current clinical state of IAP antagonists.

Cancer's Achilles' Heel: Apoptosis and Necroptosis to the Rescue

Apoptosis, and the more recently discovered necroptosis, are two avenues of programmed cell death. Cancer cells survive by evading these two programs, driven by oncogenes and tumor suppressor genes. While traditional therapy using small molecular inhibitors and chemotherapy are continuously being utilized, a new and exciting approach is actively underway by identifying and using synergistic relationship between driver and rescue genes in a cancer cell. Through these synthetic lethal relationships, we are gaining tremendous insights into tumor vulnerabilities and specific molecular avenues for induction of programmed cell death. In this review, we briefly discuss the two cell death processes and cite examples of such synergistic manipulations for therapeutic purposes.

Lipid-conjugated Smac analogues

A small library of monovalent and bivalent Smac mimics was synthesized based on 2 types of monomers, with general structure NMeAla-Xaa-Pro-BHA (Xaa=Cys or Lys). Position 2 of the compounds was utilized to dimerize both types of monomers employing various bis-reactive linkers, as well as to modify selected compounds with lipids. The resulting library was screened in vitro against metastatic human breast cancer cell line MDA-MB-231, and the two most active compounds selected for in vivo studies. The most active lipid-conjugated analogue M11, showed in vivo activity while administered both subcutaneously and orally. Collectively, our findings suggest that lipidation may be a viable approach in the development of new Smac-based therapeutic leads.

Enhancement of cellular radiation sensitivity through degradation of Chk1 by the XIAP-XAF1 complex

X-linked inhibitor of apoptosis (XIAP) and Chk1 are potential molecular targets in radiotherapy. However, their molecular association in the regulation of radiation sensitivity has been rarely studied. Here, we show that XIAP modulates radiation sensitivity by regulating stability of Chk1 in lung cancer cells. Both Chk1 and XIAP are highly expressed in various lung cancer cells. Overexpression of XIAP increased cell survival following genotoxic treatments by preventing downregulation of Chk1. However, XIAP reversed Chk1-protective activity in the presence of XIAP-associated factor 1 (XAF1) by degrading Chk1 via ubiquitination-dependent proteasomal proteolysis. The XIAP-XAF1 complex-mediated Chk1 degradation also required CUL4A and DDB1. Chk1 or XIAP was associated with DDB1 and CUL4A. Depletion of CUL4A or DDB1 prevented the XIAP-XAF1-mediated Chk1 degradation suggesting involvement of a CUL4A/DDB1-based E3 ubiquitin ligase in the process or its collaboration with XIAP E3 ligase activity. Taken together, our findings show that XIAP plays a dual role in modulation of Chk1 stability and cell viability following IR. In the absence of XAF1, XIAP stabilizes Chk1 under IR with corresponding increase of cell viability. By contrast, when XAF1 is overexpressed, XIAP facilitates Chk1 degradation, which leads to enhancement of radiation sensitivity. This selective regulation of Chk1 stability by XIAP and XAF1 could be harnessed to devise a strategy to modulate radiation sensitivity in lung cancer cells.

Targeting survivin in cancer: novel drug development approaches

Survivin is a well-established target in experimental cancer therapy. The molecule is over-expressed in most human tumors, but hardly detectable in normal tissues. Multiple functions in different subcellular compartments have been assigned. It participates in the control of cell division, apoptosis, the cellular stress response, and also in the regulation of cell migration and metastasis. Survivin expression has been recognized as a biomarker: high expression indicates an unfavorable prognosis and resistance to chemotherapeutic agents and radiation treatment. Survivin is an unconventional drug target and several indirect approaches have been exploited to affect its function and the phenotype of survivin-expressing cells. Interference with the expression of the survivin gene, the utilization of its messenger RNA, the intracellular localization, the interaction with binding partners, the stability of the survivin protein, and the induction of survivin-specific immune responses have been taken into consideration. A direct strategy to inhibit survivin has been based on the identification of a specifically interacting peptide. This peptide can recognize survivin intracellularly and cause the degradation of the ligand–survivin complex. Technology is being developed that might allow the derivation of small molecular-weight, drug-like compounds that are functionally equivalent to the peptide ligand.

Expression of vimentin and survivin in clear cell renal cell carcinoma and correlation with p53

PURPOSE

This study focuses on investigating the expression correlation of vimentin, survivin and p53 in clear cell renal cell carcinoma (ccRCC) and the clinical significance.

METHODS

The mRNA and protein expression levels of the vimentin, survivin and p53 were determined in ccRCC and adjacent normal renal tissues, using quantitative real-time-polymerase chain reaction (qRT-PCR) and Western blot. We detected the expression and localization of vimentin, survivin and p53 protein in ccRCC by immunohistochemistrical SP method and analyzed the relationships among clinical pathologic parameters and patient prognosis.

RESULTS

The expression of vimentin and survivin was significantly increased in ccRCC compared with adjacent normal renal tissues, which were positively correlated with the pathological grade and clinical stage (P < 0.05). p53 was highly expressed in ccRCC compared with normal tissues (P < 0.05), which was not positively correlated with the pathological grade and clinical stage (P > 0.05). Furthermore, univariate and multivariate analysis showed that high expression levels of vimentin and survivin were independent prognostic indicators for ccRCC. The levels of vimentin and survivin were positively correlated in ccRCC (r = 0.428, P < 0.01).

CONCLUSIONS

Reliable basis about biological behavior and prognosis judgments of ccRCC can be provided by combining detection of vimentin and survivin. Foundation and new ideas for gene therapy of ccRCC may be provided by further studying the relationship among vimentin, survivin and p53 in ccRCC.

Radioprotective effect of a pan-caspase inhibitor in a novel model of radiation injury to the nucleus of the abducens nerve

There is increasing evidence that neuronal cell death occurs via extrinsic (death receptors) and intrinsic (mitochondria) pathways. Radiation induces caspase activation fundamentally via the mitochondrial pathway. Caspases are the key regulators of apoptosis. Healthy male Sprague‑Dawley rats were used in the present study to examine the radioprotective effect of a type of pan-caspase inhibitor, z-VAD-fmk, following radiation, to investigate the effects of caspase blockade in a model of the nucleus of the abducens nerve. z-VAD-fmk was injected intracerebroventricularly as a bolus injection (0.2 µg/h for 1 h) into rats prior to exposure to radiation. Irradiation was conducted at room temperature at a dose of radiation of 4 Gy. The present study performed immunohistochemistry, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and western blot analysis and identified no significant changes in the expression of the X-linked inhibitor of apoptosis protein (XIAP) following radiation (P>0.05). As compared with the radiation alone group, the quantification of TUNEL-positive neurons was reduced in z-VAD‑fmk-treated animals following radiation (P<0.01). Inhibition of caspase induced by z-VAD‑fmk reduced the expression and activation of caspase-3, -8 and -9 (P<0.01). z-VAD-fmk effectively prevented radiation-induced apoptosis and this caspase inhibitor may be a potential therapeutic target in the treatment of brain radiation injury. The nucleus of the abducens nerve may be used as a radiation injury model, providing visual information and data on the apoptotic morphology of the abducens nucleus.

Novel dimeric Smac analogs as prospective anticancer agents

A small library of monovalent Smac mimics with general structure NMeAla-Tle-(4R)-4-Benzyl-Pro-Xaa-cysteamide, was synthesized (Xaa=hydrophobic residue). The library was screened in vitro against human breast cancer cell lines MCF-7 and MDA-MB-231, and two most active compounds oligomerized via S-alkylation giving bivalent and trivalent derivatives. The most active bivalent analogue SMAC17-2X was tested in vivo and in physiological conditions (mouse model) it exerted a potent anticancer effect resulting in ∼23.4days of tumor growth delay at 7.5mg/kg dose. Collectively, our findings suggest that bivalent Smac analogs obtained via S-alkylation protocol may be a suitable platform for the development of new anticancer therapeutics.

Small-molecule IAP antagonists sensitize cancer cells to TRAIL-induced apoptosis: roles of XIAP and cIAPs

TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent because it shows apoptosis-inducing activity in transformed, but not in normal, cells. As with most anticancer agents, however, its clinical use is restricted by either inherent or acquired resistance by cancer cells. We demonstrate here that small-molecule SMAC mimetics that antagonize the inhibitor of apoptosis proteins (IAP) potently sensitize previously resistant human cancer cell lines, but not normal cells, to TRAIL-induced apoptosis, and that they do so in a caspase-8-dependent manner. We further show that the compounds have no cytotoxicity as single agents. Also, we demonstrate that several IAP family members likely participate in the modulation of cellular sensitivity to TRAIL. Finally, we note that the compounds that sensitize cancer cells to TRAIL are the most efficacious in binding to X-linked IAP, and in inducing cellular-IAP (cIAP)-1 and cIAP-2 degradation. Our studies thus describe valuable compounds that allow elucidation of the signaling events occurring in TRAIL resistance, and demonstrate that these agents act as potent TRAIL-sensitizing agents in a variety of cancer cell lines.

The radio-sensitizing effect of xanthohumol is mediated by STAT3 and EGFR suppression in doxorubicin-resistant MCF-7 human breast cancer cells

BACKGROUND

Chemotherapeutic drug resistance remains a clinical obstacle in cancer management. Drug-resistant cancer cells usually exhibit cross-resistance to ionizing radiation, which has devastating consequences for patients. With a better understanding of the molecular mechanisms, it will be possible to develop strategies to overcome this cross-resistance and to increase therapeutic sensitivity.

METHODS

Natural and synthetic flavonoid compounds including xanthohumol, the principal flavonoid in hops, were investigated for its radio-sensitizing activity on human breast cancer MCF-7 and adriamycin-resistant MCF-7 (MCF-7/ADR) cells. Chemo-sensitizing or radio-sensitizing effect was analyzed by tetrazolium-based colorimetric assay and flow cytometry. Western blot analysis, confocal microscopy, gene silencing with siRNA transfection and luciferase reporter gene assay were performed to examine signaling molecule activation.

RESULTS

Among the tested flavonoid compounds, pretreatment of the cells with xanthohumol significantly sensitized MCF-7/ADR cells to the radiation treatment by inducing apoptosis. In MCF-7/ADR cells, treatment with xanthohumol alone or with gamma-rays significantly decreased levels of anti-apoptotic proteins. Multi-drug resistance 1 (MDR1), epidermal growth factor receptor (EGFR) and signal transducer and activator of transcription 3 (STAT3) expression levels in MCF-7/ADR cells were suppressed by xanthohumol treatment. In addition, xanthohumol treatment increased death receptor (DR)-4 and DR5 expression. The xanthohumol-induced changes of these resistance-related molecules in MCF-7/ADR cells were synergistically increased by gamma-ray treatment.

CONCLUSIONS

Xanthohumol restored sensitivity of MCF-7/ADR cells to doxorubicin and radiation therapies.

GENERAL SIGNIFICANCE

Our results suggest that xanthohumol may be a potent chemo- and radio-sensitizer, and its actions are mediated through STAT3 and EGFR inhibition.

Withaferin A-induced apoptosis in human breast cancer cells is associated with suppression of inhibitor of apoptosis family protein expression

The present study provides novel insight into the mechanism of apoptosis induction by withaferin A (WA), which is a bioactive constituent of an Ayurvedic medicine plant (Withania somnifera). Exposure of MDA-MB-231 and MCF-7 human breast cancer cells to WA resulted in suppression of XIAP, cIAP-2, and Survivin protein levels. The WA-induced apoptosis was significantly attenuated by ectopic expression of XIAP, Survivin, and cIAP-2 in both cells. However, the WA-mediated inhibition of MDA-MB-231 xenograft growth in vivo was associated with suppression of Survivin protein level only. These results indicate important contribution of Survivin suppression in WA-induced apoptosis.

Gene therapy for cisplatin-induced ototoxicity: a systematic review of in vitro and experimental animal studies

OBJECTIVE

Ototoxicity is a frequent adverse event of cisplatin treatment. No therapy is currently available for cisplatin-induced ototoxicity. A systematic review of experimental animal studies and in vitro experiments was conducted to evaluate gene therapy as a potential future therapeutic option.

DATA SOURCES

Eligible studies were identified through searches of electronic databases Ovid MEDLINE, Ovid MEDLINE In-Process, Embase, PubMed, Biosis Previews, Scopus, ISI Web of Science, and The Cochrane Library.

STUDY SELECTION

Articles obtained from the search were independently reviewed by 2 authors using specific criteria to identify experimental animal studies and in vitro experiments conducted to evaluate gene therapy for cisplatin-induced ototoxicity. No restriction was applied to publication dates or languages.

DATA EXTRACTION

Data extracted included experiment type, cell type, species, targeted gene, gene expression, method, administration, inner ear site evaluated, outcome measures for cytotoxicity, and significant results.

RESULTS

Fourteen articles were included in this review. In vitro and in vivo experiments have been performed to evaluate the potential of gene expression manipulation for cisplatin-induced ototoxicity. Twelve different genes were targeted including NTF3, GDNF, HO-1, XIAP, Trpv1, BCL2, Otos, Nfe2l2, Nox1, Nox3, Nox4, and Ctr1. All of the included articles demonstrated a benefit of gene therapy on cytotoxicity caused by cisplatin.

CONCLUSION

Experimental animal studies and in vitro experiments have demonstrated the efficacy of gene therapy for cisplatin-induced ototoxicity. However, further investigation regarding safety, immunogenicity, and consequences of genetic manipulation in the inner ear tissues must be completed to develop future therapeutic options.

Phenethyl isothiocyanate suppresses inhibitor of apoptosis family protein expression in prostate cancer cells in culture and in vivo

BACKGROUND

Cruciferous vegetable constituent phenethyl isothiocyanate (PEITC) causes apoptosis in prostate cancer cells through mechanisms not fully understood. The present study was designed to determine the role of inhibitor of apoptosis (IAP) family proteins in PEITC-induced apoptosis induction.

METHODS

Effect of PEITC treatment on protein and mRNA expression of IAP in cells was determined by Western blotting and reverse transcription PCR, respectively. Immunohistochemistry was performed to determine the in vivo effect of PEITC administration on X-linked IAP (XIAP) and Survivin protein expression. Overexpression of desired protein was achieved by transient transfection. Cell viability was determined by trypan blue dye exclusion assay, whereas apoptosis was quantified by measurement of histone-associated DNA fragment release into the cytosol. Transwell chamber assay was used to determine cell migration.

RESULTS

Exposure of PC-3 and LNCaP human prostate cancer cells to PEITC resulted in downregulation of XIAP and Survivin proteins and Survivin mRNA. PEITC administration to transgenic adenocarcinoma of mouse prostate mice caused modest but significant downregulation of XIAP and Survivin proteins in the dorsolateral prostate. Proapoptotic response to PEITC was significantly attenuated by ectopic expression of XIAP and Survivin proteins. Survivin overexpression also conferred modest but significant protection against PEITC-mediated inhibition of PC-3 cell migration.

CONCLUSIONS

The present study demonstrates that cellular responses to PEITC, including apoptosis induction and inhibition of cell migration, in prostate cancer cells are mediated by downregulation of XIAP and/or Survivin, which may serve as valid biomarkers of PEITC response in future clinical investigations.

Survivin inhibition by an interacting recombinant peptide, derived from the human ferritin heavy chain, impedes tumor cell growth

BACKGROUND

Proteins involved in the aberrant regulation of signaling pathways and their downstream effectors are promising targets for cancer therapy. Survivin is an anti-apoptotic and cell cycle-promoting protein, which is consistently overexpressed in cancer cells. In normal cells, its expression is tightly controlled by signaling pathways and their associated transcriptional activators and repressors. In cancer cells, its expression is enhanced as a consequence of oncogenic signaling. We investigated the potential of a novel, peptide-based survivin inhibitor in breast cancer (SK-BR-3, MDA-MB-468) and glioblastoma (Tu9648) cells. These cells express high levels of survivin.

MATERIALS AND METHODS

We downregulated survivin expression in tumor cells with a lentiviral gene transfer vector encoding a specific shRNA and a recombinant fusion protein, rSip, comprising the FTH1-derived survivin interaction domain, the human thioredoxin and a protein transduction domain.

RESULTS

Downregulation of survivin expression decreased the growth and viability of tumor cells in culture and reduced growth of the cancer cells upon transplantation into immunodeficient mice. rSip selectively targets the anti-apoptotic function of survivin and causes tumor cell death. Non-transformed NIH/3T3 and MCF10A cells remain unaffected.

CONCLUSIONS

rSip provides a lead structure for the development of drugs targeting the tumor cell "addiction protein" survivin.

Peptides mimicking the unique ARTS-XIAP binding site promote apoptotic cell death in cultured cancer cells

PURPOSE

XIAP [X-linked inhibitor of apoptosis (IAP) protein] is the best characterized mammalian caspase inhibitor. XIAP is frequently overexpressed in a variety of human tumors, and genetic inactivation of XIAP in mice protects against lymphoma. Therefore, XIAP is an attractive target for anticancer therapy. IAP antagonists based on a conserved IAP-binding motif (IBM), often referred to as "Smac-mimetics," are currently being evaluated for cancer therapy in the clinic. ARTS (Sept4_i2) is a mitochondrial proapoptotic protein which promotes apoptosis by directly binding and inhibiting XIAP via a mechanism that is distinct from all other known IAP antagonists. Here, we investigated the ability of peptides derived from ARTS to antagonize XIAP and promote apoptosis in cancer cell lines.

EXPERIMENTAL DESIGN

The ability of synthetic peptides, derived from the C-terminus of ARTS, to bind to XIAP, stimulate XIAP degradation, and induce apoptosis was examined. We compared the response of several cancer cell lines to different ARTS-derived peptides. Pull-down assays were used to examine binding to XIAP, and apoptosis was evaluated using terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, caspase activation, and Western blot analyses of caspase substrates.

RESULTS

The C-terminus of ARTS contains a unique sequence, termed ARTS-IBM (AIBM), which is important for binding to XIAP and cell killing. AIBM peptides can bind to XIAP-BIR3, penetrate cancer cells, reduce XIAP levels, and promote apoptosis.

CONCLUSIONS

Short synthetic peptides derived from the C-terminus of ARTS are sufficient for binding to XIAP and can induce apoptosis in cancer cells. These results provide proof-of-concept for the feasibility of developing ARTS-based anticancer therapeutics.

ARTS-based anticancer therapy: taking aim at cancer stem cells

Apoptosis related protein in TGF-β signaling pathway (ARTS/septin 4 isoform 2) hereforth referred to as ARTS, was originally found to promote apoptosis induced by TGF-β, but later was shown to promote apoptosis induced by a wide variety of apoptotic stimuli. In vivo and in vitro studies revealed that ARTS-induced apoptosis is mainly executed through direct binding and antagonizing XIAP. High levels of XIAP are found in many types of cancers and often correlate with poor prognosis. ARTS was shown to function as a tumor-suppressor protein in human patients and mouse-tumor models. In particular, Septin 4/ARTS-deficient mice have increased tumor susceptibility and contain increased numbers of stem cells (SCs) and progenitor cells, apparently owing to their resistance towards apoptosis. Based on these results we propose that loss of proapoptotic ARTS may act as the 'first hit' initiating tumorigenesis in two distinct ways. First, loss of ARTS-mediated apoptosis leads to increased numbers of normal SCs. Elevated numbers of normal SCs may lead to increased cancer risk due to higher numbers of cellular targets available for transforming mutations. Second, after these SCs acquire additional transforming mutations and become cancer SC (CSCs), they are more likely to survive in the absence of ARTS owing to increased resistance toward apoptosis. A combination of these two mechanisms, over time, is expected to significantly increase tumor risk. Because CSCs appear to share phenotypic markers with normal SCs, targeting the signaling pathways that affect normal SC development and maintenance can serve as a useful approach towards true eradication of cancer. In this article we describe the role of ARTS in apoptosis and cancer, with focus on its potential role as a CSC marker and as a potential target for anticancer and anti-CSC therapy.

Rational design, synthesis and characterization of potent, drug-like monomeric Smac mimetics as pro-apoptotic anticancer agents

A set of phenyl-substituted Smac mimetics/IAP inhibitor analogues of lead compound 2a was synthesized, aiming to retain its strong cell-free potency while increasing its bioavailability. Seventeen compounds 2b-r were prepared and characterized in vitro, using cell-free and cellular assays. Among them, the p-CF(3) substituted analogue 2m showed the best permeability through cell membranes, and was selected for further in vitro and in vivo studies due to its strong, sub-micromolar cellular potency.

Lung-cancer chemoprevention by induction of synthetic lethality in mutant KRAS premalignant cells in vitro and in vivo

Lung cancer is the leading cause of cancer death in both men and women in the United States, with a low 5-year survival rate despite improved treatment strategies. These data underscore the great need for effective chemoprevention of this cancer. Mutations and activation of KRAS occur frequently in, and are thought to be a primary driver of the development of, non-small cell lung cancers (NSCLC) of the adenocarcinoma subtype. In this study, we developed a new approach for the chemoprevention of NSCLC involving specific targeting of apoptosis in mutant KRAS cells. This approach is based on a synthetic lethal interaction among TNF-related apoptosis-inducing ligand (TRAIL), the second mitochondria-derived activator of caspase Smac/DIABLO (Smac), and KRAS. Mutational activation of KRAS modulated the expression of TRAIL receptors by upregulating death receptors and downregulating decoy receptors. Furthermore, oncogenic KRAS repressed cellular FADD-like interleukin 1β-converting enzyme (FLICE)-like inhibitory protein (c-FLIP) expression through activation of Erk/mitogen-activated protein kinase (MAPK)-mediated activation of c-Myc. Smac overcame KRAS-induced cell-survival signaling by antagonizing X-linked inhibitor of apoptosis protein (XIAP). Therefore, the combination of TRAIL and a small molecule mimic of Smac induced apoptosis specifically in mutant KRAS cells without harming normal cells. We further showed that short-term, intermittent in vivo treatment with TRAIL and Smac mimic induced apoptosis in tumor cells and reduced tumor burden in a murine model of KRAS-induced lung cancer. These results reflect the potential benefit of a selective therapeutic approach for the chemoprevention of NSCLC.

Design, synthesis and evaluation of monovalent Smac mimetics that bind to the BIR2 domain of the anti-apoptotic protein XIAP

We report the systematic rational design and synthesis of new monovalent Smac mimetics that bind preferentially to the BIR2 domain of the anti-apoptotic protein XIAP. Characterization of compounds in vitro (including 9i; ML101) led to the determination of key structural requirements for BIR2 binding affinity. Compounds 9h and 9j sensitized TRAIL-resistant breast cancer cells to apoptotic cell death, highlighting the value of these probe compounds as tools to investigate the biology of XIAP.

Garlic constituent diallyl trisulfide suppresses x-linked inhibitor of apoptosis protein in prostate cancer cells in culture and in vivo

We have shown previously that garlic constituent diallyl trisulfide (DATS) inhibits growth of cultured and xenografted human prostate cancer cells in association with apoptosis induction, but the mechanism of cell death is not fully understood. The present study systematically investigates the role of inhibitor of apoptosis (IAP) family proteins in the regulation of DATS-induced apoptosis using cultured PC-3 and LNCaP human prostate cancer cells and dorsolateral prostate from control and DATS-treated transgenic adenocarcinoma of mouse prostate (TRAMP) mice. Level of X-linked inhibitor of apoptosis (XIAP) protein was decreased on 8-hour treatment with 20 and 40 μmol/L DATS, but this effect was partially attenuated at the 16-hour time point. DATS-mediated decline in XIAP protein level was partially reversible in the presence of proteasomal inhibitor MG132. In contrast, DATS-treated PC-3 and LNCaP cells exhibited marked induction of survivin and cellular inhibitor of apoptosis protein 1 (cIAP1) proteins. Induction of survivin protein expression resulting from DATS exposure was associated with an increase in its mRNA level. Dorsolateral prostates from DATS-treated TRAMP mice exhibited statistically significant downregulation of XIAP and induction of survivin protein compared with those of control mice. Ectopic expression of XIAP conferred partial but significant protection against DATS-induced apoptosis. On the other hand, DATS-induced apoptosis was only marginally affected by RNA interference of survivin or cIAP1. In conclusion, the present study indicates that the DATS-induced apoptosis in prostate cancer cells is mediated in part by suppression of XIAP protein expression, and that XIAP represents a viable biomarker of DATS response for future clinical investigations.

RNA-binding protein HuR mediates cytoprotection through stimulation of XIAP translation

Expression of the intrinsic cellular caspase inhibitor XIAP is regulated primarily at the level of protein synthesis. The 5' untranslated region harbours an Internal Ribosome Entry Site (IRES) motif that supports cap-independent translation of XIAP mRNA during conditions of cellular stress. In this study, we show that the RNA-binding protein HuR, which is known to orchestrate an antiapoptotic cellular program, stimulates translation of XIAP mRNA through XIAP IRES. We further show that HuR binds to XIAP IRES in vitro and in vivo, and stimulates recruitment of the XIAP mRNA into polysomes. Importantly, protection from the apoptosis-inducing agent etoposide by overexpression of HuR requires the presence of XIAP, suggesting that HuR-mediated cytoprotection is partially executed through enhanced XIAP translation. Our data suggest that XIAP belongs to the HuR-regulated RNA operon of antiapoptotic genes, which, along with Bcl-2, Mcl-1 and ProTα, contributes to the regulation of cell survival.

p53-Independent apoptosis by benzyl isothiocyanate in human breast cancer cells is mediated by suppression of XIAP expression

We have shown previously that cruciferous vegetable constituent benzyl isothiocyanate (BITC) suppresses viability of cultured MCF-7 and MDA-MB-231 human breast cancer cells and retards mammary cancer development in MMTV-neu mice by causing apoptosis, but the mechanism of cell death is not fully understood. We now show that whereas p53 is dispensable for BITC-induced cell death, proapoptotic response to this promising chemopreventive agent is mediated by suppression of X-linked inhibitor of apoptosis (XIAP) protein expression. The BITC treatment increased levels of total and Ser(15)-phosphorylated p53 protein in MCF-7 cells, but the proapoptotic response to this agent was maintained even after knockdown of the p53 protein level. Exposure of MCF-7 and MDA-MB-231 cells to BITC resulted in a marked decrease in protein level of XIAP as early as 8 hours after treatment. Ectopic expression of XIAP conferred statistically significant protection against BITC-mediated cytoplasmic histone-associated apoptotic DNA fragmentation in both cell lines. Moreover, inhibition of MDA-MB-231 cell growth in vivo in female athymic mice by BITC administration correlated with a modest but statistically significant decrease in XIAP protein level in the tumor xenograft. The BITC treatment also resulted in induction as well as nuclear translocation of survivin only in the MCF-7 cells. The BITC-induced apoptosis was modestly but statistically significantly augmented by RNA interference of survivin in MCF-7 cells. In conclusion, the present study provides novel insight into the molecular circuitry of BITC-induced apoptosis to indicate suppression of XIAP expression as a critical mediator of this process.

Phenethyl isothiocyanate sensitizes androgen-independent human prostate cancer cells to docetaxel-induced apoptosis in vitro and in vivo

PURPOSE

The present study was undertaken to determine efficacy of phenethyl isothiocyanate (PEITC) for sensitization of androgen-independent human prostate cancer cells (AIPC) to Docetaxel-induced apoptosis using cellular and xenograft models.

METHODS

Cell viability was determined by trypan blue dye exclusion assay. Microscopy and DNA fragmentation assay were performed to quantify apoptotic cell death in cultured cells. Protein levels were determined by immunoblotting. PC-3 prostate cancer xenograft model was utilized to determine in vivo efficacy of the PEITC and/or Docetaxel treatments.

RESULTS

Pharmacologic concentrations of PEITC augmented Docetaxel-induced apoptosis in PC-3 and DU145 cells in association with suppression of Bcl-2 and XIAP protein levels and induction of Bax and Bak. The PEITC-Docetaxel combination was markedly more efficacious against PC-3 xenograft in vivo compared with PEITC or Docetaxel alone. Significantly higher counts of apoptotic bodies were also observed in tumor sections from mice treated with the PEITC-Docetaxel combination compared with PEITC or Docetaxel alone. The PEITC and/or Docetaxel-mediated changes in the levels of apoptosis regulating proteins in the tumor were generally consistent with the molecular alterations observed in cultured cells.

CONCLUSION

These results offer obligatory impetus to test PEITC-Docetaxel combination for the treatment of AIPC in a clinical setting.

Therapeutic potential of siRNA-mediated combined knockdown of the IAP genes (Livin, XIAP, and Survivin) on human bladder cancer T24 cells

Livin, X-linked inhibitor of apoptosis (XIAP), and Survivin are three well-known inhibitors of apoptosis almost exclusively over-expressed in cancer cells and are considered potent targets for cancer treatment. In the present study, we found that Livin, XIAP, and Survivin were simultaneously expressed in bladder cancer cells. We speculated that Livin, XIAP, and Survivin might have synergistic effects on cell growth and apoptosis. Our results confirmed that combined knockdown of all these three genes can synergistically inhibit the proliferation and transformation ability of high-grade bladder cancer T24 cells and promote the cell apoptotic sensitivity to chemotherapy. Furthermore, combined knockdown of Livin, XIAP, and Survivin can markedly increase the abundance of active caspase-3, active caspase-7, active caspase-9, and cytosolic Smac. Our findings imply that combined silencing of Livin, XIAP, and Survivin may be a potent multitargeted gene therapy for bladder cancer.

Expression of X-linked inhibitor of apoptosis protein in human colorectal cancer and its correlation with prognosis

BACKGROUND

X-linked inhibitor of apoptosis protein (XIAP) is a member of the inhibitor of apoptosis family of proteins and deregulation of XIAP can result in tumorigenicity. The objective of this study was to evaluate the prognostic significance of XIAP expression in colorectal cancer (CRC).

METHODS

RT-PCR was performed to detect the expression of XIAP mRNA in CRC cells and tissues. The expression of XIAP protein in tissues was measured by immunohistochemistry. The correlation of XIAP expression with clinicopathologic factors and prognosis of CRC patients was evaluated.

RESULTS

CRC cells showed significantly higher levels of XIAP mRNA expression than normal human intestinal epithelial cell. The expression level of XIAP mRNA in CRC samples was significantly higher than that in corresponding non-tumor samples. XIAP staining was positive in the cytoplasm of CRC cells. Higher XIAP protein expression was significantly correlated with tumor differentiation (P = 0.016), venous invasion (P = 0.039), and Duke's staging (P = 0.002). Moreover, XIAP-high group showed lower disease-free (P = 0.0136) and overall survival (P = 0.0084) rates than XIAP-low group. Multivariate analysis indicated that the status of XIAP expression was an independent prognostic factor for CRC (P = 0.0206; HR: 2.730; 95% CI: 1.226-5.445).

CONCLUSION

The status of XIAP expression might become an independent prognostic marker for CRC.

Phase I trial of AEG35156 administered as a 7-day and 3-day continuous intravenous infusion in patients with advanced refractory cancer

PURPOSE

To establish the maximum-tolerated dose and evaluate tolerability, pharmacokinetics, pharmacodynamic effects, and antitumor activity of AEG35156, a second-generation antisense to X-linked inhibitor of apoptosis (XIAP) protein, in patients with advanced refractory malignant tumors.

PATIENTS AND METHODS

This was a first-in-man, open-label, phase I dose-escalation study. AEG35156 was administered by continuous intravenous infusion over 7 days (7DI) or 3 days (3DI) of a 21-day treatment cycle. Dose escalation started at 48 mg/m(2)/d and continued until consistent dose-limiting toxicity (DLT) was observed.

RESULTS

Thirty-eight patients were entered in seven cohorts. Grade 3 to 4 adverse events were uncommon and were predominantly abnormal laboratory values: elevated ALT, thrombocytopenia, and lymphopenia. DLTs comprised elevated hepatic enzymes, hypophosphatemia, and thrombocytopenia. The maximum-tolerated doses were defined as 125 mg/m(2)/d for the 7DI regimen and < or = 213 mg/m(2)/d for the 3DI schedule. AEG35156 area under the plasma concentration curve and peak plasma concentration increased proportionally with dose. Suppression of XIAP mRNA levels was maximal at 72 hours (mean suppression, 21%), and this coincided with a dramatic decrease in circulating tumor cells in a patient with non-Hodgkin's lymphoma. Two further patients had unconfirmed partial responses. Circulating biomarkers of cell death and apoptosis altered in association with drug infusion and toxicity.

CONCLUSION

In this first-in-man study, AEG35156 was well tolerated, with predictable toxicities, pharmacokinetic properties, and clinical evidence of antitumor activity in patients with refractory lymphoma, melanoma, and breast cancer. Phase I/II trials of AEG35156 chemotherapy combinations are ongoing in patients with pancreatic, breast, non-small-cell lung cancer, acute myeloid leukemia, lymphoma, and solid tumors for which docetaxel is indicated.

Applications of RNA interference in cancer therapeutics as a powerful tool for suppressing gene expression

Cancer poses a tremendous therapeutic challenge worldwide, highlighting the critical need for developing novel therapeutics. A promising cancer treatment modality is gene therapy, which is a form of molecular medicine designed to introduce into target cells genetic material with therapeutic intent. The history of RNA interference (RNAi) has only a dozen years, however, further studies have revealed that it is a potent method of gene silencing that has developed rapidly over the past few years as a result of its extensive importance in the study of genetics, molecular biology and physiology. RNAi is a natural process by which small interfering RNA (siRNA) duplex directs sequence specific post-transcriptional silencing of homologous genes by binding to its complementary mRNA and triggering its elimination. RNAi has been extensively used as a novel and effective gene silencing tool for the fundamental research of cancer therapeutics, and has displayed great potential in clinical treatment.

Inhibiting XIAP expression by RNAi to inhibit proliferation and enhance radiosensitivity in laryngeal cancer cell line

OBJECTIVES

X-linked inhibitor of apoptosis protein (XIAP) is a novel member of the inhibitors of apoptosis (IAPs) family. The overexpression of XIAP is asscociated with radioresistance of human malignancies. The purpose of the present study was to investigate the effect of shRNA-targeted XIAP on the proliferation, apoptosis and radiosensitivity of human laryngeal carcinoma cells (Hep-2).

METHODS

A siRNA expression vector (pSilencer4.1-XIAPshRNA) was constructed and stably transfected into human laryngeal carcinoma cells (Hep-2). The downregulation of XIAP expression was evaluated by RT-PCR and Western blot analyses. Then, we investigated the effect of XIAP-shRNA on the proliferation, cell cycle changes and apoptosis in vitro of Hep-2 cells. Finally, the radiosensitivity of Hep-2 cells was investigated by clonogenic cell survival assay.

RESULTS

We established stably transfected cell line (Hep-2/XIAPshRNA) in which the expression of XIAP gene was downregulated. The cell viability of Hep-2/XIAP-RNA cells was obviously decreased compared with that of untransfected Hep-2 cells. Morever, XIAP-shRNA induced cell arrest in the G(0)/G(1) phase of cell cycle by flow cytometry analysis. Results of TUNEL assay indicated that Hep-2 cells stably transfected pSilencer4.1-XIAP-shRNA showed obvious apoptosis characters. Furthermore, the downregulation of XIAP expression could lead to significant radiosensitivity enhancement in laryngeal carcinoma cells.

CONCLUSIONS

RNAi-mediated downregulation of XIAP expression can inhibit proliferation, induce apoptosis and diminish the radioresistance of laryngeal carcinoma cells, so combined therapy with XIAP inhibition and radiation may be a potential strategy for the treatment of laryngeal carcinoma.

Combined inhibition of FLIP and XIAP induces Bax-independent apoptosis in type II colorectal cancer cells

Death receptors can directly (type I cells) or indirectly induce apoptosis by activating mitochondrial-regulated apoptosis (type II cells). The level of caspase 8 activation is thought to determine whether a cell is type I or II, with type II cells less efficient at activating this caspase following death receptor activation. FLICE-inhibitory protein (FLIP) blocks death receptor-mediated apoptosis by inhibiting caspase 8 activation; therefore, we assessed whether silencing FLIP could convert type II cells into type I. FLIP silencing-induced caspase 8 activation in Bax wild-type and null HCT116 colorectal cancer cells; however, complete caspase 3 processing and apoptosis were only observed in Bax wild-type cells. Bax-null cells were also more resistant to chemotherapy and tumor necrosis factor-related apoptosis inducing ligand and, unlike the Bax wild-type cells, were not sensitized to these agents by FLIP silencing. Further analyses indicated that release of second mitochondrial activator of caspases from mitochondria and subsequent inhibition of X-linked inhibitor of apoptosis protein (XIAP) was required to induce full caspase 3 processing and apoptosis following FLIP silencing. These results indicate that silencing FLIP does not necessarily bypass the requirement for mitochondrial involvement in type II cells. Furthermore, targeting FLIP and XIAP may represent a therapeutic strategy for the treatment of colorectal tumors with defects in mitochondrial-regulated apoptosis.