A Smac-mimetic sensitizes prostate cancer cells to TRAIL-induced apoptosis via modulating both IAPs and NF-kappaB

Background  

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising agent for human cancer therapy, prostate cancer still remains resistant to TRAIL. Both X-linked inhibitor of apoptosis (XIAP) and nuclear factor-kappaB function as key negative regulators of TRAIL signaling. In this study, we evaluated the effect of SH122, a small molecule mimetic of the second mitochondria-derived activator of caspases (Smac), on TRAIL-induced apoptosis in prostate cancer cells.     

Smac mimetic reverses resistance to TRAIL and chemotherapy in human urothelial cancer cells

Purpose

Inhibitors of apoptosis proteins (IAP s) have been shown to contribute to resistance of neoplastic cells to chemotherapy and to biologic antineoplastic agents. Consequently, new agents are being developed targeting this family of proteins. In a panel of bladder cancer cell lines, we evaluated a Smac mimetic that antagonizes several IAPs for its suitability for bladder cancer therapy.

Results

Single-agent compound-A had little effect, but compound-A augmented TRAIL- and chemotherapy-induced apoptosis. Immunoblotting showed that combination treatment with compound-A and TRAIL resulted in cleavage of procaspase-3 and procaspase-7, activation of which irreversibly commits cells to apoptosis. Immunoprecipitation of XIAP showed displacement of active caspase-3 fragments from XIAP, supporting the proposed mechanism of action. Furthermore, siRNA-mediated silencing of XIAP similarly sensitized these cells to apoptosis.

Experimental design

A panel of seven bladder cancer cell lines were evaluated for sensitivity to the Smac mimetic compound-A alone, TRAIL alone, chemotherapy alone, compound-A plus TRAIL and compound-A plus chemotherapy by DNA fragmentation analysis. IAP levels and caspase activation were examined by western blotting. Release of caspase-3 from X-linked inhibitor of apoptosis protein (XIAP), the most effective IAP, was assessed by immunoprecipitation and western blotting. Finally, siRNA knockdown of XIAP was correlated with the sensitivity of cells to apoptosis induced by compound-A plus TRAIL by DNA fragmentation and western blotting.

Conclusion

Our results suggest that targeting of XIAP with the Smac mimetic compound-A has the potential to augment the effects of a variety of chemotherapeutic and biologic therapies in bladder cancer.Key words: bladder cancer, smac mimetic, IAP antagonist, chemotherapy, TRAIL     

Novel SMAC-mimetics synergistically stimulate melanoma cell death in combination with TRAIL and Bortezomib

Background:

XIAP (X-linked inhibitor of apoptosis protein) is an anti-apoptotic protein exerting its activity by binding and suppressing caspases. As XIAP is overexpressed in several tumours, in which it apparently contributes to chemoresistance, and because its activity in vivo is antagonised by second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis-binding protein with low pI, small molecules mimicking SMAC (so called SMAC-mimetics) can potentially overcome tumour resistance by promoting apoptosis.

Methods:

Three homodimeric compounds were synthesised tethering a monomeric SMAC-mimetic with different linkers and their affinity binding for the baculoviral inhibitor repeats domains of XIAP measured by fluorescent polarisation assay. The apoptotic activity of these molecules, alone or in combination with tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and/or Bortezomib, was tested in melanoma cell lines by MTT viability assays and western blot analysis of activated caspases.

Results:

We show that in melanoma cell lines, which are typically resistant to chemotherapeutic agents, XIAP knock-down sensitises cells to TRAIL treatment in vitro, also favouring the accumulation of cleaved caspase-8. We also describe a new series of 4-substituted azabicyclo[5.3.0]alkane monomeric and dimeric SMAC-mimetics that target various members of the IAP family and powerfully synergise at submicromolar concentrations with TRAIL in inducing cell death. Finally, we show that the simultaneous administration of newly developed SMAC-mimetics with Bortezomib potently triggers apoptosis in a melanoma cell line resistant to the combined effect of SMAC-mimetics and TRAIL.

Conclusion:

Hence, the newly developed SMAC-mimetics effectively synergise with TRAIL and Bortezomib in inducing cell death. These findings warrant further preclinical studies in vivo to verify the anticancer effectiveness of the combination of these agents.     

Tumor suppressor XIAP‐Associated factor 1 (XAF1) cooperates with tumor necrosis factor‐related apoptosis‐inducing ligand to suppress colon cancer growth and trigger tumor regression

BACKGROUND:

XIAP‐associated factor 1 (XAF1) antagonizes the anticaspase activity of XIAP (X‐linked inhibitor of apoptosis) and functions as a tumor suppressor in colon cancer. The tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL) is known as a potential anticancer agent. In this study, the synergistic effect of XAF1 and TRAIL on colon cancer growth was investigated.

METHODS:

Adeno‐XAF1 virus was generated and purified. Cell apoptosis was detected by flow‐cytometry and terminal deoxynucleotidyl transferase‐mediated dUTP nick‐end labeling assay. Protein expression of the different genes was determined by Western blot analysis. Tumorigenesis and tumor growth were assessed in subcutaneous nude mouse xenograft experiments.

RESULTS:

Stable overexpression of XAF1‐sensitized colon cancer cells to TRAIL‐induced apoptosis significantly increased the activity of caspase 3, 7, 8, and 9; released cytochrome c; and down‐regulated XIAP, survivin, and c‐IAP‐2. The restoration of XAF1 expression mediated by adenovirus (adeno‐XAF1) directly induced apoptosis, and synergized TRAIL‐induced apoptosis in colon cancer cells. Ex vivo transduction of adeno‐XAF1 suppressed colon cancer formation in vivo. Furthermore, adeno‐XAF1 treatment of mice significantly inhibited tumor growth, strongly enhanced TRAIL‐induced apoptosis and antitumor activity in colon cancer xenograft models in vivo, and markedly prolonged the survival. Notably, the combined treatment with adeno‐XAF1 and TRAIL completely eradicated the established tumors without detectable toxicity in normal tissue.

CONCLUSIONS:

The combined restoration of XAF1 expression and TRAIL treatment may be a potent strategy for colon cancer therapy. Cancer 2010. © 2010 American Cancer Society.     

Loss of XIAP protein expression by RNAi and antisense approaches sensitizes cancer cells to functionally diverse chemotherapeutics

Stable expression of short-hairpin RNAs (shRNAs) directed against the X-linked inhibitor of apoptosis (XIAP) resulted in the generation of three MDA-MB-231 cell lines (XIAP shRNA cells) with reductions in XIAP mRNA and protein levels > 85% relative to MDA-MB-231 cells stably transfected with the U6 RNA polymerase III promoter alone (U6 cells). This RNA interference (RNAi) approach dramatically sensitized these cells to killing by the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Importantly, loss of XIAP also sensitized the cells to killing by taxanes but had no additional effects on killing by carboplatin and doxorubicin. The increased sensitivity of the XIAP shRNA cells to killing by TRAIL and taxanes correlated with enhanced caspase cleavage and activation, including caspase-8, and robust processing of poly(ADP-ribose) polymerase and BID compared to U6 cells. Additionally, increasing XIAP levels by adenovirus-mediated expression protected both XIAP shRNA and U6 cells from TRAIL killing in a dose-dependent manner. The effects observed by stable RNAi with respect to TRAIL sensitization were also achieved following downregulation of XIAP in Panc-1 cells treated with a second-generation, mixed-backbone antisense oligonucleotide, AEG 35156/GEM640. These data indicate that reducing XIAP protein expression by either RNAi or antisense approaches increases cancer cell susceptibility to functionally diverse chemotherapeutic agents and supports the notion that downregulation of XIAP in vivo may synergize with disease-relevant chemotherapeutic regimes, including TRAIL and taxanes, to increase the effectiveness of antineoplastic agents.     

Doxorubicin increases the effectiveness of Apo2L/TRAIL for tumor growth inhibition of prostate cancer xenografts

Background  

Prostate cancer is a significant health problem among American men. Treatment strategies for androgen-independent cancer are currently not available. Tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) is a death receptor ligand that can induce apoptosis in a variety of cancer cell lines, including androgen-independent PC3 prostate carcinoma cells. In vitro, TRAIL-mediated apoptosis of prostate cancer cell lines can be enhanced by doxorubicin and correlates with the downregulation of the anti-apoptotic protein c-FLIP. This study evaluated the effects of doxorubicin on c-FLIP expression and tumor growth in combination with Apo2L/TRAIL in a xenograft model.     

Targeting inhibitor of apoptosis proteins in combination with ErbB antagonists in breast cancer

Introduction

Inhibitor of apoptosis (IAPs) proteins are a family of proteins that can block apoptosis in normal cells and have been suggested to cause resistance to apoptosis in cancer. Overexpression of oncogenic receptor tyrosine kinases is common in breast cancer; in particular 20% of all cases show elevated Her2. Despite clinical success with the use of targeted therapies, such as Trastuzumab, only up to 35% of Her2-positive patients initially respond. We reasoned that IAP-mediated apoptosis resistance might contribute to this insensitivity to receptor tyrosine kinase therapy, in particular ErbB antagonists. Here we examine the levels of IAPs in breast cancer and evaluate whether targeting IAPs can enhance apoptosis in response to growth factor receptor antagonists and TRAIL.

Methods

IAP levels were examined in a breast cancer cell line panel and in patient samples. IAPs were inhibited using siRNA or cell permeable mimetics of endogenous inhibitors. Cells were then exposed to TRAIL, Trastuzumab, Lapatinib, or Gefitinib for 48 hours. Examining nuclear morphology and staining for cleaved caspase 3 was used to score apoptosis. Proliferation was examined by Ki67 staining.

Results

Four members of the IAP family, Survivin, XIAP, cIAP1 and cIAP2, were all expressed to varying extents in breast cancer cell lines or tumours. MDAMB468, BT474 and BT20 cells all expressed XIAP to varying extents. Depleting the cells of XIAP overcame the intrinsic resistance of BT20 and MDAMB468 cells to TRAIL. Moreover, siRNA-based depletion of XIAP or use of a Smac mimetic to target multiple IAPs increased apoptosis in response to the ErbB antagonists, Trastuzumab, Lapatinib or Gefitinib in Her2-overexpressing BT474 cells, or Gefitinib in EGFR-overexpressing MDAMB468 cells.

Conclusions

The novel findings of this study are that multiple IAPs are concomitantly expressed in breast cancers, and that, in combination with clinically relevant Her2 treatments, IAP antagonists promote apoptosis and reduce the cell turnover index of breast cancers. We also show that combination therapy of IAP antagonists with some pro-apoptotic agents (for example, TRAIL) enhances apoptosis of breast cancer cells. In some cases (for example, MDAMB468 cells), the enhanced apoptosis is profound.     

A galectin-3 sequence polymorphism confers TRAIL sensitivity to human breast cancer cells

BACKGROUND:

A common polymorphism, rs4644, coding for Pro64 or His64 of the carbohydrate‐binding protein galectin‐3, influences the susceptibility of galectin‐3 to cleavage by matrix metalloproteinases and is associated with breast cancer incidence. Because forced expression of galectin‐3 in a galectin‐3 null breast cancer cell line confers sensitivity to tumor necrosis factor‐related apoptosis‐inducing ligand (TRAIL), the authors sought to determine whether the His64/Pro64 polymorphism of galectin‐3 affects the sensitivity to TRAIL.

METHODS:

Genomic DNA of breast cell lines was analyzed for the single nucleotide polymorphism rs4644, and cytotoxicity was determined with the MTT assay.

RESULTS:

When a collection of 9 breast cancer cell lines that express galectin‐3 was examined for lectin, galactoside‐binding, soluble, 3 (LGALS3) genotype and sensitivity to doxorubicin and TRAIL, doxorubicin sensitivity was not found to be related to LGALS3 genotype. In contrast, none of the 5 cell lines that were homozygous for Pro64 galectin‐3 were found to be sensitive to TRAIL, but 2 of 2 homozygous His64 cell lines and 1 of 2 heterozygous His64 cell lines were sensitive to TRAIL. Forced expression of galectin‐3 of defined genotype in galectin‐3 null cells was used to more directly test the effect of the Pro64His mutation on TRAIL sensitivity. High levels of expression of His64 galectin‐3 rendered BT549 cells sensitive to TRAIL and resistant to doxorubicin, but cells expressing Pro64 galectin‐3 remained resistant to TRAIL and sensitive to doxorubicin.

CONCLUSIONS:

The results of the current study indicate that the naturally occurring Pro64His mutation in galectin‐3 increases sensitivity to death receptor‐mediated apoptosis. This finding could be relevant to disparities in breast cancer outcomes across population groups, and could guide the design of future clinical trials of TRAIL‐based therapies. Cancer 2011;. © 2011 American Cancer Society.     

The novel thymidylate synthase inhibitor trifluorothymidine (TFT) and TRAIL synergistically eradicate non-small cell lung cancer cells

Purpose

TRAIL, a tumor selective anticancer agent, may be used for the treatment of non-small cell lung cancer (NSCLC). However, TRAIL resistance is frequently encountered. Here, the combined use of TRAIL with trifluorothymidine (TFT), a thymidylate synthase inhibitor, was examined for sensitizing NSCLC cells to TRAIL.

Methods

Interactions between TRAIL and TFT were studied in NSCLC cells using growth inhibition and apoptosis assays. Western blotting and flow cytometry were used to investigate underlying mechanisms.

Results

The combined treatment of TFT and TRAIL showed synergistic cytotoxicity in A549, H292, H322 and H460 cells. For synergistic activity, the sequence of administration was important; TFT treatment followed by TRAIL exposure did not show sensitization. Combined TFT and TRAIL treatment for 24 h followed by 48 h of TFT alone was synergistic in all cell lines, with combination index values below 0.9. The treatments affected cell cycle progression, with TRAIL inducing a G1 arrest and TFT, a G2/M arrest. TFT activated Chk2 and reduced Cdc25c levels known to cause G2/M arrest. TRAIL-induced caspase-dependent apoptosis was enhanced by TFT, whereas TFT alone mainly induced caspase-independent death. TFT increased the expression of p53 and p21/WAF1, and p53 was involved in the increase of TRAIL-R2 surface expression. TFT also caused downregulation of cFLIP and XIAP and increased Bax expression.

Conclusions

TFT enhances TRAIL-induced apoptosis in NSCLC cells by sensitizing the apoptotic machinery at different levels in the TRAIL pathway. Our findings suggest a possible therapeutic benefit of the combined use of TFT and TRAIL in NSCLC.     

XIAP siRNA对TRAIL诱导结肠癌细胞SW620凋亡能力的影响

 目的
研究XIAP siRNA对肿瘤坏死因子相关的凋亡诱导配体(Tumor Necrosis Factor-related Apoptosis-Inducing Ligand,TRAIL)诱导结
肠癌细胞SW620凋亡的影响。方法SW620细胞分为转染XIAP siRNA组、空转染对照组或者siRNA阴性对照组,然后给予TRAIL处理。XIAP
表达水平的变化、细胞增殖抑制、Caspase-3活性分别由Western blot、MTT法和Caspase-3荧光测定来检测。切割PARP的表达水平由
Western blot来测定。结果XIAP siRNA转染以后显著下调XIAP蛋白表达水平。和空转染对照组、siRNA阴性对照组相比,XIAP siRNA
显著增强10、100、1 000 ng/ml等浓度的TRAIL作用以后SW620细胞的增殖抑制、Caspase-3活性和激活PARP。结论 XIAP siRNA能显
著增强TRAIL诱导结肠癌细胞SW620的凋亡。     

Repression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) but not its receptors during oral cancer progression

Background  

TRAIL plays an important role in host immunosurveillance against tumor progression, as it induces apoptosis of tumor cells but not normal cells, and thus has great therapeutic potential for cancer treatment. TRAIL binds to two cell-death-inducing (DR4 and DR5) and two decoy (DcR1, and DcR2) receptors. Here, we compare the expression levels of TRAIL and its receptors in normal oral mucosa (NOM), oral premalignancies (OPM), and primary and metastatic oral squamous cell carcinomas (OSCC) in order to characterize the changes in their expression patterns during OSCC initiation and progression.     

A small molecule inhibitor of XIAP induces apoptosis and synergises with vinorelbine and cisplatin in NSCLC

Background:

Evasion of apoptosis contributes to the pathogenesis of solid tumours including non-small cell lung cancer (NSCLC). Malignant cells resist apoptosis through over-expression of inhibitor of apoptosis proteins (IAPs), such as X-linked IAP (XIAP).

Methods:

A phenylurea-based small molecule inhibitor of XIAP, XIAP antagonist compound (XAC) 1396-11, was investigated preclincally to determine its ability to sensitise to clinically relevant cytotoxics, potentially allowing dose reduction while maintaining therapeutic efficacy.

Results:

XIAP protein expression was detected in six NSCLC cell lines examined. The cytotoxicity of XAC 1396-11 against cultured NSCLC cell lines in vitro was concentration- and time-dependent in both short-term and clonogenic assays. XAC 1396-11-induced apoptosis was confirmed by PARP cleavage and characteristic nuclear morphology. XAC 1396-11 synergised with vinorelbine±cisplatin in H460 and A549 NSCLC cells. The mechanism of synergy was enhanced apoptosis, shown by increased cleavage of caspase-3 and PARP and by the reversal of synergy by a pan-caspase inhibitor. Synergy between XAC 1396-11 and vinorelbine was augmented by optimising drug scheduling with superior effects when XAC 1396-11 was administered before vinorelbine.

Conclusion:

These preclinical data suggest that XIAP inhibition in combination with vinorelbine holds potential as a therapeutic strategy in NSCLC.     

Ex vivo purging of leukemia cells using tumor-necrosis-factor-related apoptosis-inducing ligand in hematopoietic stem cell transplantation.

The aim of this study was to evaluate the potential of tumor-necrosis-factor-related apoptosis-inducing ligand TRAIL to eradicate leukemia cell lines, while sparing normal hematopoietic stem cells. Human Jurkat and Molt-4 cell lines were used to optimize the purging process in umbilical cord blood (UCB) mononuclear cells. The Jurkat cell line was TRAIL sensitive and TRAIL-resistant Molt-4 cell line became sensitive after being treated with TRAIL and a low dose of doxorubicin (0.1 micro M), but UCB mononuclear cells remained resistant. DR4 expression was increased when Jurkat cells were treated with TRAIL, and DR5 expression increased after exposing Molt-4 cells to TRAIL plus a low dose of doxorubicin for 24 h. The expression of DR4 and DR5 in UCB mononuclear cells was unchanged after treatment with TRAIL, a low-dose doxorubicin, or TRAIL plus a low dose of doxorubicin. In TRAIL-sensitive Jurkat cells, caspases 8, 9, 3, and 7 were activated by TRAIL treatment and activation of caspases was augmented by TRAIL plus a low dose of doxorubicin than TRAIL or a low dose of doxorubicin alone in Molt-4 cells. Experiments involving mixture of UCB mononuclear cells and Jurkat or Molt-4 cells showed a marked eradication of leukemia cells and the limiting dilution assay demonstrated an eradication rate of more than 4 logs after 24 h incubation with 100 ng/ml of TRAIL in Jurkat cells. In the case of Molt-4 cells, the eradication rate was about 3 logs when TRAIL was used in combination with a low dose of doxorubicin. No significant decrease in the number of granulocyte-macrophage colony-forming unit) (CFU-GM) colonies was detected when UCB mononuclear cells were treated with TRAIL in combination with a low dose of doxorubicin. These results suggest that TRAIL offers the possibility of being used as an ex vivo purging agent for autologous transplantation in hematologic malignancies.     

Protein kinase C inhibition and x-linked inhibitor of apoptosis protein degradation contribute to the sensitization effect of luteolin on tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in cancer cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is an important member of the TNF superfamily with great potential in cancer therapy. Luteolin is a dietary flavonoid commonly found in some medicinal plants. Here we found that pretreatment with a noncytotoxic concentration of luteolin significantly sensitized TRAIL-induced apoptosis in both TRAIL-sensitive (HeLa) and TRAIL-resistant cancer cells (CNE1, HT29, and HepG2). Such sensitization is achieved through enhanced caspase-8 activation and caspase-3 maturation. Further, the protein level of X-linked inhibitor of apoptosis protein (XIAP) was markedly reduced in cells treated with luteolin and TRAIL, and ectopic expression of XIAP protected against cell death induced by luteolin and TRAIL, showing that luteolin sensitizes TRAIL-induced apoptosis through down-regulation of XIAP. In search of the molecular mechanism responsible for XIAP down-regulation, we found that luteolin and TRAIL promoted XIAP ubiquitination and proteasomal degradation. Next, we showed that protein kinase C (PKC) activation prevented cell death induced by luteolin and TRAIL via suppression of XIAP down-regulation. Moreover, luteolin inhibited PKC activity, and bisindolylmaleimide I, a general PKC inhibitor, simulated luteolin in sensitizing TRAIL-induced apoptosis. Taken together, these results present a novel anticancer effect of luteolin and support its potential application in cancer therapy in combination with TRAIL. In addition, our data reveal a new function of PKC in cell death: PKC activation stabilizes XIAP and thus suppresses TRAIL-induced apoptosis.     

Chetomin induces degradation of XIAP and enhances TRAIL sensitivity in urogenital cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the most promising anti-cancer agents, but some tumor types develop resistance to TRAIL. Here, we report that chetomin, an inhibitor of hypoxia-inducible factors, is a potent enhancer of TRAIL-induced apoptosis. TRAIL or chetomin alone weakly induced apoptosis, but the combination of chetomin and TRAIL synergistically induced apoptosis in prostate cancer PC-3 cells. The combination of chetomin and TRAIL induces the activation of caspase-3, -8, -9 and -10. Among the apoptotic factors related to the TRAIL pathway, chetomin markedly decreased the X-linked inhibitor of apoptosis (XIAP) protein levels in a dose-dependent manner, but other IAP family members, TRAIL receptors and Bcl-2 family members were not altered by chetomin. Using XIAP siRNA instead of chetomin, down-regulation of XIAP sensitized PC-3 cells to TRAIL-induced apoptosis. Conversely, transient transfection of XIAP reduced the apoptotic response to combined treatment with chetomin and TRAIL. Treatment with chetomin induced a rapid decrease in XIAP protein levels but had no effect on XIAP mRNA levels. Since chetomin-mediated XIAP down-regulation was completely prevented by proteasome inhibitors, it was suggested that chetomin induces the degradation of the XIAP protein in a proteasome-dependent manner. Additionally, chetomin also sensitized renal cancer Caki-1 cells and bladder cancer UM-UC-3 cells to TRAIL-induced apoptosis via down-regulation of XIAP. Co-treatment of chetomin and TRAIL did not enhance apoptosis in normal peripheral blood mononuclear cells (PBMC). Taken together, these findings suggest that TRAIL and chetomin synergistically induce apoptosis in human urogenital cancer cells through a mechanism that involves XIAP down-regulation by chetomin.     

Melanoma-associated Chondroitin Sulfate Proteoglycan (MCSP)-targeted delivery of soluble TRAIL potently inhibits melanoma outgrowth <Emphasis Type="Italic">in vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis>

Background  

Advanced melanoma is characterized by a pronounced resistance to therapy leading to a limited patient survival of ~6 - 9 months. Here, we report on a novel bifunctional therapeutic fusion protein, designated anti-MCSP:TRAIL, that is comprised of a melanoma-associated chondroitin sulfate proteoglycan (MCSP)-specific antibody fragment (scFv) fused to soluble human TRAIL. MCSP is a well-established target for melanoma immunotherapy and has recently been shown to provide important tumorigenic signals to melanoma cells. TRAIL is a highly promising tumoricidal cytokine with no or minimal toxicity towards normal cells. Anti-MCSP:TRAIL was designed to 1. selectively accrete at the cell surface of MCSP-positive melanoma cells and inhibit MCSP tumorigenic signaling and 2. activate apoptotic TRAIL-signaling.     

High susceptibility of metastatic cells derived from human prostate and colon cancer cells to TRAIL and sensitization of TRAIL-insensitive primary cells to TRAIL by 4,5-dimethoxy-2-nitrobenzaldehyde

Background  

Tumor recurrence and metastasis develop as a result of tumors' acquisition of anti-apoptotic mechanisms and therefore, it is necessary to develop novel effective therapeutics against metastatic cancers. In this study, we showed the differential TRAIL responsiveness of human prostate adenocarcinoma PC3 and human colon carcinoma KM12 cells and their respective highly metastatic PC3-MM2 and KM12L4A sublines and investigated the mechanism underlying high susceptibility of human metastatic cancer cells to TRAIL.     

The histone deacetylase inhibitor valproic acid sensitizes human and canine osteosarcoma to doxorubicin

Purpose

Osteosarcoma (OS) remains an incurable and ultimately fatal disease in many patients, and novel forms of therapy are needed. Improved models of OS that more closely mimic human disease would provide more robust information regarding the utility of novel therapies. Spontaneous OS in dogs may provide such a model. Pharmacologic inhibition of histone deacetylase (HDAC) enzymes has a variety of anti-tumor effects but may demonstrate the most utility when utilized in combination with standard cytotoxic therapies. We sought to determine the in vitro and in vivo effects of the HDAC inhibitor valproic acid (VPA) on doxorubicin (DOX) sensitivity in canine and human OS.

Methods

We evaluated the in vitro anti-proliferative and apoptotic effects of VPA/DOX combination treatment, alterations in histone acetylation and nuclear DOX accumulation resulting from VPA treatment, and the in vivo efficacy of combination therapy in a xenograft model.

Results

Treatment of canine and human OS cell lines with clinically achievable VPA concentrations resulted in increased histone acetylation but modest anti-proliferative effects. Pre-incubation with VPA followed by doxorubicin (DOX) resulted in significant growth inhibition and potentiation of apoptosis, associated with a dose-dependent increase in nuclear DOX accumulation. The combination of VPA and DOX was superior to either monotherapy in a canine OS xenograft model.

Conclusion

These results demonstrate a rationale for the addition of HDAC inhibitors to current protocols for the treatment of OS and illustrate the similarities in response to HDAC inhibitors between human and canine OS, lending further credibility to the canine OS model.     

ABT-263 sensitizes TRAIL-resistant hepatocarcinoma cells by downregulating the Bcl-2 family of anti-apoptotic protein

Purpose  

Tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent due to its selective cytotoxicity to transformed cells. However, most human hepatocellular carcinomas (HCC) develop resistance to TRAIL. Thus, there is an urgent need to investigate the molecular targets and the underlying mechanisms that may be involved in overriding the resistance of tumor cells to TRAIL.