Multidomain Bcl-2 homolog Bax but not Bak mediates synergistic induction of apoptosis by TRAIL and 5-FU through the mitochondrial apoptosis pathway

Oral administration of Limonin (LM) exerts neuroprotective effects by inhibiting neuron autophagy and microglial activation in 6-OHDA-injected rats

Parkinson's disease (PD) is a neurodegenerative disorder that occurs most frequently in middle-aged and elderly people. It is characterized by an insidious onset and a complex etiology, and no effective treatment has been developed. The primary characteristic of PD is the degenerative death of midbrain dopaminergic neurons. The excessive autophagy of neurons and hyperactivation of microglia were shown to be involved in the apoptosis of dopaminergic neurons. Limonin (LM), a type of pure natural compound present in grapefruit or citrus fruits (e. g., lemon, orange) has been reported to inhibit apoptosis and inflammation. However, its role and mechanism of action in PD are unclear. In this study, we explored the effect and mechanism of action of LM in PD. In vivo experiments revealed that LM ameliorated 6-OHDA-induced reduced motor activity and PD-related pathological damage in rats. In vitro experiments revealed that LM inhibited the 6-OHDA-induced apoptosis of PC12 cells by inhibiting the excessive autophagy of neurons. In addition, LM inhibited microglial inflammation by activating the AKT/Nrf-2/HO-1 pathway and protected neurons against microglial inflammation-mediated neurotoxicity. In conclusion, the findings of this experiment demonstrated that LM exerted neuroprotective effects by inhibiting neuronal autophagy-mediated apoptosis and microglial activation in 6-OHDA-injected rats, thus indicating that LM can serve as a candidate for PD by targeting neuroinflammation and neuronal autophagy to inhibit neuronal apoptosis.

Sublethal cytochrome c release generates drug-tolerant persister cells

Drug-tolerant persister cells (persisters) evade apoptosis upon targeted and conventional cancer therapies and represent a major non-genetic barrier to effective cancer treatment. Here, we show that cells that survive treatment with pro-apoptotic BH3 mimetics display a persister phenotype that includes colonization and metastasis in vivo and increased sensitivity toward ferroptosis by GPX4 inhibition. We found that sublethal mitochondrial outer membrane permeabilization (MOMP) and holocytochrome c release are key requirements for the generation of the persister phenotype. The generation of persisters is independent of apoptosome formation and caspase activation, but instead, cytosolic cytochrome c induces the activation of heme-regulated inhibitor (HRI) kinase and engagement of the integrated stress response (ISR) with the consequent synthesis of ATF4, all of which are required for the persister phenotype. Our results reveal that sublethal cytochrome c release couples sublethal MOMP to caspase-independent initiation of an ATF4-dependent, drug-tolerant persister phenotype.

Tenacissoside G synergistically potentiates inhibitory effects of 5-fluorouracil to human colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is one of the most malignant tumors worldwide with poor prognosis and low survival rate. Since the clinical efficacy of the commonly used 5-fluorouracil (5-FU) based chemotherapy in CRC patients is limited because of its intolerable adverse effects, there is an urgent need to explore agents that can enhance the anti-cancer activity of 5-FU, reduce adverse effects and prevent resistance.

PURPOSE

This study aims to investigate Tenacissoside G (TG)'s synergistic potentiation with 5-FU in inhibitory activity to colorectal cancer cells.

METHODS

The anti-proliferation effect of TG on 5 colorectal cancer cell lines was assessed by CCK-8 assay. The isobologram analysis and combination index methods were used to detect the synergistic effect of TG and 5-FU by the CompuSyn software using the T.C. Chou Method. The effects of TG/5-FU combination on cell cycle distribution and apoptosis induction were detected by flow cytometry. DNA damage degrees of cells treated with TG, 5-FU and their combination were evaluated by the alkaline comet assay. Protein expression regulated by the TG/5-FU combination was investigated by western blotting. Furthermore, a xenograft mouse model was established to investigate the synergistic anti-tumor effect in vivo.

RESULTS

In this work, we observed a dose-dependent growth inhibitory activity and cell cycle arrest induction of TG, a monomeric substance originated from Marsdenia tenacissima (Roxb.) Wight et Arn, in colorectal cancer cells. It was found that TG potentiated the anticancer effects of 5-FU with a synergism for the first time. And the co-treatment effects were also validated by in vivo experiments. The underlying mechanisms involved in the synergistic effects were probably included: (1) increased activation of caspase cascade; (2) enhancement of DNA damage degree and (3) induction of p53 phosphorylation at Serine 46.

CONCLUSION

TG potentiated 5-FU's inhibitory activity to human colorectal cancer through arresting cell cycle progression and inducing p53-mediated apoptosis, which may present a novel strategy in CRC therapies and contribute to the optimizing clinical application of 5-FU.

Simultaneous microRNA-612 restoration and 5-FU treatment inhibit the growth and migration of human PANC-1 pancreatic cancer cells

Despite the recent advances in the treatment of other cancers, the 5-year survival rate of pancreatic cancer remains under 9 %. Chemotherapy and surgical resection are the most common therapy methods. The regulatory role of microRNAs in different types of cancer has given them therapeutic importance. miR-612 has been downregulated in colorectal, bladder, liver, and some other types of cancer and could be considered a tumor-suppressor miRNA. 5-FU is one of the most common chemotherapeutic agents used in pancreatic cancer treatment, which is used in multiple drug regimens and combinatorial therapy methods. The aim of this study is the evaluation of miR-612 restoration in the PANC-1 cell line and using the tumor-suppressive effect of it in combination with 5-FU on cell growth and migration. MiR-612 mimic was transfected to PANC-1 cells through electroporation. Following the transfection, expression levels of miR-612 and BAX, BCL-2, Caspase-3, MMP9, and PD-L1 genes were measured by qRT-PCR. MTT assay was used to determine the cytotoxicity of miR-612 and 5-FU on PANC-1 cell viability. To confirm MTT results and to evaluate the quantitative effect of apoptosis induction flow cytometry test was used and in order to confirm apoptosis test results and cell cycle arrest evaluation DAPI staining and cell, cycle tests were conducted, respectively. Finally, to assess the inhibitory effect of miR-612 in combination with 5-FU on migration and growth wound healing and colony formation assays were used, respectively. Results demonstrated that miR-612 alongside 5-FU has an important role in the inhibition of migration and growth and also apoptosis induction in PANC-1 cells and could be considered as a supporting agent of chemotherapy and a novel therapeutic modality in pancreatic cancer treatment.

Countering TRAIL Resistance in Melanoma

Melanoma of the skin has become a prime example for demonstrating the success of targeted cancer therapy. Nevertheless, high mortality has remained, mainly related to tumor heterogeneity and inducible therapy resistance. But the development of new therapeutic strategies and combinations has raised hope of finally defeating this deadly disease. TNF-related apoptosis-inducing ligand (TRAIL) represents a promising antitumor strategy. The principal sensitivity of melanoma cells for TRAIL was demonstrated in previous studies; however, inducible resistance appeared as a major problem. To address this issue, combination strategies were tested, and survival pathway inhibitors were shown to sensitize melanoma cells for TRAIL-induced apoptosis. Finally, cell cycle inhibition was identified as a common principle of TRAIL sensitization in melanoma cells. Mitochondrial apoptosis pathways, pro- and antiapoptotic Bcl-2 proteins as well as the rheostat consisted of Smac (Second mitochondria-derived activator of caspase) and XIAP (X-linked inhibitor of apoptosis protein) appeared to be of particular importance. Furthermore, the role of reactive oxygen species (ROS) was recognized in this setting. Inducible TRAIL resistance in melanoma can be explained by (i) high levels of antiapoptotic Bcl-2 proteins, (ii) high levels of XIAP, and (iii) suppressed Bax activity. These hurdles have to be overcome to enable the use of TRAIL in melanoma therapy. Several strategies appear as particularly promising, including new TRAIL receptor agonists, Smac and BH3 mimetics, as well as selective kinase inhibitors.

Associations of Genetic Variations in MicroRNA Seed Regions With Acute Adverse Events and Survival in Patients With Rectal Cancer Receiving Postoperative Chemoradiation Therapy

PURPOSE

The aim of this study was to investigate the associations between single nucleotide polymorphisms (SNPs) in the seed regions of microRNAs and acute adverse events (AEs) and survival in patients with rectal cancer receiving postoperative chemoradiation therapy.

METHODS AND MATERIALS

Eighteen SNPs were genotyped in 365 patients with rectal cancer receiving postoperative chemoradiation therapy. The associations between genotypes and AEs were estimated by odds ratios and 95% confidence intervals (CIs), which were computed by using multivariate logistic regression models. The hazard ratios and 95% CIs to assess the death of patients for different genotypes were calculated by Cox proportional regression models. Overall survival and disease-free survival of patients with different genotypes were estimated by Kaplan-Meier plots, and the statistical significance was determined by using the log-rank test.

RESULTS

In these patients, the most common grade ≥2 AEs were diarrhea (44.1%), leukopenia (29.6%), and dermatitis (18.9%). With false discovery rate correction, SNP rs2273626 was significantly associated with a decreased risk of grade ≥2 leukopenia (odds ratio, 0.48; 95% CI, 0.31-0.74; P = .0009). In addition, SNP rs202195689 was associated with overall survival and disease-free survival in patients receiving postoperative chemoradiation therapy, with the hazard ratios for death being 2.02 (95% CI, 1.36-3.01; P = .0006) and 1.91 (95% CI, 1.36-2.70; P = .0002), respectively. However, no significant association between these SNPs and diarrhea and dermatitis was observed.

CONCLUSIONS

These results suggest that rs2273626 and rs202195689 in microRNA seed regions might serve as independent biomarkers for predicting AEs and prognosis in patients with rectal cancer receiving postoperative chemoradiation therapy. Independent replication of these findings is required to confirm these results.

The oncolytic peptide LTX-315 kills cancer cells through Bax/Bak-regulated mitochondrial membrane permeabilization

LTX-315 has been developed as an amphipathic cationic peptide that kills cancer cells. Here, we investigated the putative involvement of mitochondria in the cytotoxic action of LTX-315. Subcellular fractionation of LTX-315-treated cells, followed by mass spectrometric quantification, revealed that the agent was enriched in mitochondria. LTX-315 caused an immediate arrest of mitochondrial respiration without any major uncoupling effect. Accordingly, LTX-315 disrupted the mitochondrial network, dissipated the mitochondrial inner transmembrane potential, and caused the release of mitochondrial intermembrane proteins into the cytosol. LTX-315 was relatively inefficient in stimulating mitophagy. Cells lacking the two pro-apoptotic multidomain proteins from the BCL-2 family, BAX and BAK, were less susceptible to LTX-315-mediated killing. Moreover, cells engineered to lose their mitochondria (by transfection with Parkin combined with treatment with a protonophore causing mitophagy) were relatively resistant against LTX-315, underscoring the importance of this organelle for LTX-315-mediated cytotoxicity. Altogether, these results support the notion that LTX-315 kills cancer cells by virtue of its capacity to permeabilize mitochondrial membranes.

Negative prognostic impact of regulatory T cell infiltration in surgically resected esophageal cancer post-radiochemotherapy

Ever accumulating evidence indicates that the long-term effects of radiotherapy and chemotherapy largely depend on the induction (or restoration) of an anticancer immune response. Here, we investigated this paradigm in the context of esophageal carcinomas treated by neo-adjuvant radiochemotherapy, in a cohort encompassing 196 patients. We found that the density of the FOXP3⁺ regulatory T cell (Treg) infiltrate present in the residual tumor (or its scar) correlated with the pathological response (the less Tregs the more pronounced was the histological response) and predicted cancer-specific survival. In contrast, there was no significant clinical impact of the frequency of CD8⁺ cytotoxic T cells. At difference with breast or colorectal cancer, a loss-of-function allele of toll like receptor 4 (TLR4) improved cancer-specific survival of patients with esophageal cancer. While a loss-of-function allele of purinergic receptor P2X, ligand-gated ion channel, 7 (P2RX7) failed to affect cancer-specific survival, its presence did correlate with an increase in Treg infiltration. Altogether, these results corroborate the notion that the immunosurveillance seals the fate of patients with esophageal carcinomas treated with conventional radiochemotherapy.

Selective activation of TNFR1 and NF-κB inhibition by a novel biyouyanagin analogue promotes apoptosis in acute leukemia cells

BACKGROUND

Acquired resistance towards apoptosis is a hallmark of cancer. Elimination of cells bearing activated oncogenes or stimulation of tumor suppressor mediators may provide a selection pressure to overcome resistance. KC-53 is a novel biyouyanagin analogue known to elicit strong anti-inflammatory and anti-viral activity. The current study was designed to evaluate the anticancer efficacy and molecular mechanisms of KC-53 against human cancer cells.

METHODS

Using the MTT assay we examined initially how KC-53 affects the proliferation rates of thirteen representative human cancer cell lines in comparison to normal peripheral blood mononuclear cells (PBMCs) and immortalized cell lines. To decipher the key molecular events underlying its mode of action we selected the human promyelocytic leukemia HL-60 and the acute lymphocytic leukemia CCRF/CEM cell lines that were found to be the most sensitive to the antiproliferative effects of KC-53.

RESULTS

KC-53 promoted rapidly and irreversibly apoptosis in both leukemia cell lines at relatively low concentrations. Apoptosis was characterized by an increase in membrane-associated TNFR1, activation of Caspase-8 and proteolytic inactivation of the death domain kinase RIP1 indicating that KC-53 induced mainly the extrinsic/death receptor apoptotic pathway. Regardless, induction of the intrinsic/mitochondrial pathway was also achieved by Caspase-8 processing of Bid, activation of Caspase-9 and increased translocation of AIF to the nucleus. FADD protein knockdown restored HL-60 and CCRF/CEM cell viability and completely blocked KC-53-induced apoptosis. Furthermore, KC-53 administration dramatically inhibited TNFα-induced serine phosphorylation on TRAF2 and on IκBα hindering therefore p65/NF-κΒ translocation to nucleus. Reduced transcriptional expression of pro-inflammatory and pro-survival p65 target genes, confirmed that the agent functionally inhibited the transcriptional activity of p65.

CONCLUSIONS

Our findings demonstrate, for the first time, the selective anticancer properties of KC-53 towards leukemic cell lines and provide a detailed understanding of the molecular events underlying its dual anti-proliferative and pro-apoptotic properties. These results provide new insights into the development of innovative and targeted therapies for the treatment of some forms of leukemia.

5-Fluorouracil preferentially sensitizes mutant KRAS non-small cell lung carcinoma cells to TRAIL-induced apoptosis

Mutations in the KRAS gene are very common in non-small cell lung cancer (NSCLC), but effective therapies targeting KRAS have yet to be developed. Interest in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a potent inducer of cell death, has increased following the observation that TRAIL can selectively kill a wide variety of human cancer cells without killing normal cells both in vitro and in xenograft models. However, results from clinical trials of TRAIL-based therapy are disappointingly modest at best and many have demonstrated a lack of therapeutic benefit. Current research has focused on selecting a subpopulation of cancer patients who may benefit from TRAIL-based therapy and identifying best drugs to work with TRAIL. In the current study, we found that NSCLC cells with a KRAS mutation were highly sensitive to treatment with TRAIL and 5-fluorouracil (5FU). Compared with other chemotherapeutic agents, 5FU displayed the highest synergy with TRAIL in inducing apoptosis in mutant KRAS NSCLC cells. We also found that, on a mechanistic level, 5FU preferentially repressed survivin expression and induced expression of TRAIL death receptor 5 to sensitize NSCLC cells to TRAIL. The combination of low-dose 5FU and TRAIL strongly inhibited xenograft tumor growth in mice. Our results suggest that the combination of TRAIL and 5FU may be beneficial for patients with mutant KRAS NSCLC.

Bak and Mcl-1 are essential for Temozolomide induced cell death in human glioma

Temozolomide (TMZ) is an alkylating agent used for the treatment of glioblastoma multiforme (GBM), the main form of human brain tumours in adults. It has been reported that TMZ induced DNA lesions that subsequently trigger cell death but the actual mechanisms involved in the process are still unclear. We investigated the implication of major proteins of the Bcl-2 family in TMZ-induced cell death in GBM cell lines at concentrations closed to that reached in the brain during the treatments. We did not observe modulation of autophagy at these concentrations but we found an induction of apoptosis. Using RNA interference, we showed that TMZ induced apoptosis is dependent on the pro-apoptotic protein Bak but independent of the pro-apoptotic protein Bax. Apoptosis was not enhanced by ABT-737, an inhibitor of Bcl-2/Bcl-Xl/Bcl-W but not Mcl-1. The knock-down of Mcl-1 expression increased TMZ induced apoptosis. Our results identify a Mcl-1/Bak axis for TMZ induced apoptosis in GBM and thus unravel a target to overcome therapeutic resistance toward TMZ.

MCL1 and BCL-xL levels in solid tumors are predictive of dinaciclib-induced apoptosis

Dinaciclib is a potent CDK1, 2, 5 and 9 inhibitor being developed for the treatment of cancer. Additional understanding of antitumor mechanisms and identification of predictive biomarkers are important for its clinical development. Here we demonstrate that while dinaciclib can effectively block cell cycle progression, in vitro and in vivo studies, coupled with mouse and human pharmacokinetics, support a model whereby induction of apoptosis is a main mechanism of dinaciclib's antitumor effect and relevant to the clinical duration of exposure. This was further underscored by kinetics of dinaciclib-induced downregulation of the antiapoptotic BCL2 family member MCL1 and correlation of sensitivity with the MCL1-to-BCL-xL mRNA ratio or MCL1 amplification in solid tumor models in vitro and in vivo. This MCL1-dependent apoptotic mechanism was additionally supported by synergy with the BCL2, BCL-xL and BCL-w inhibitor navitoclax (ABT-263). These results provide the rationale for investigating MCL1 and BCL-xL as predictive biomarkers for dinaciclib antitumor response and testing combinations with BCL2 family member inhibitors.

BID preferentially activates BAK while BIM preferentially activates BAX, affecting chemotherapy response

Apoptosis is a highly regulated form of cell death that controls normal homeostasis as well as the antitumor activity of many chemotherapeutic agents. Commitment to death via the mitochondrial apoptotic pathway requires activation of the mitochondrial pore-forming proteins BAK or BAX. Activation can be effected by the activator BH3-only proteins BID or BIM, which have been considered to be functionally redundant in this role. Herein, we show that significant activation preferences exist between these proteins: BID preferentially activates BAK while BIM preferentially activates BAX. Furthermore, we find that cells lacking BAK are relatively resistant to agents that require BID activation for maximal induction of apoptosis, including topoisomerase inhibitors and TRAIL. Consequently, patients with tumors that harbor a loss of BAK1 exhibit an inferior response to topoisomerase inhibitor treatment in the clinic. Therefore, BID and BIM have nonoverlapping roles in the induction of apoptosis via BAK and BAX, affecting chemotherapy response.

p14ARF induces apoptosis via an entirely caspase-3-dependent mitochondrial amplification loop

The p14(ARF) tumor suppressor triggers cell death or cell cycle arrest upon oncogenic stress. In MCF-7 breast carcinoma cells, expression of the tumor suppressor gene p14(ARF) fails to trigger apoptosis but induces an arrest in the G1 and, to a lesser extent, in the G2 phase in the cell division cycle. Here, inhibition of cell cycle arrest resulted in apoptosis induction in caspase-3 proficient MCF-7 cells upon expression of p14(ARF) . This occurred in the absence of S-phase progression or mitotic entry. In contrast, syngeneic, caspase-3-deficient MCF-7 cells remained entirely resistant to p14(ARF) -induced apoptosis. Thus, cell cycle checkpoint abrogation overcomes resistance to p14(ARF) -induced cell death and promotes cell death via a caspase-3-dependent pathway. Cell death coincided with dissipation of the mitochondrial membrane potential, release of cytochrome c, and was inhibitable by pan-caspase inhibitors and the caspase-3/7 inhibitor zDEVD-fmk. Of note, mitochondrial events of apoptosis execution depended entirely on caspase-3 proficiency indicating that caspase-3 either acts "up-stream" of the mitochondria in a "non-canonical" pathway or mediates a mitochondrial feedback loop to amplify the apoptotic caspase signal in p14(ARF) -induced stress signaling.

Death receptors as targets in cancer

Anti-tumour therapies based on the use pro-apoptotic receptor agonists, including TNF-related apoptosis-inducing ligand (TRAIL) or monoclonal antibodies targeting TRAIL-R1 or TRAIL-R2, have been disappointing so far, despite clear evidence of clinical activity and lack of adverse events for the vast majority of these compounds, whether combined or not with conventional or targeted anti-cancer therapies. This brief review aims at discussing the possible reasons for the lack of apparent success of these therapeutic approaches and at providing hints in order to rationally design optimal protocols based on our current understanding of TRAIL signalling regulation or resistance for future clinical trials.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

Targeting FLIP and Mcl-1 using a combination of aspirin and sorafenib sensitizes colon cancer cells to TRAIL

The multikinase inhibitor sorafenib is highly effective against certain types of cancer in the clinic and prevents colon cancer cell proliferation in vitro. Non-steroidal anti-inflammatory drugs, such as acetylsalicylic acid (aspirin), have shown activity against colon cancer cells. The aims of this study were to determine whether the combination of aspirin with sorafenib has enhanced anti-proliferative effects and increases recombinant human tumour necrosis factor-related apoptosis-inducing ligand (rhTRAIL)-induced apoptosis in the human SW948, Lovo, Colo205, Colo320, Caco-2 and HCT116 colon cancer cell lines. In four cell lines, aspirin strongly stimulated the anti-proliferative effects of sorafenib (∼four-fold enhancement) by inducing cell cycle arrest. Furthermore, combining low doses of aspirin (≤ 5 mm) and sorafenib (≤ 2.5 µm) greatly sensitized TRAIL-sensitive and TRAIL-resistant colon cancer cells to rhTRAIL, much more potently than either drug combined with rhTRAIL. The increase in rhTRAIL sensitivity was due to inhibition of FLIP and Mcl-1 protein expression following aspirin and sorafenib co-treatment, as confirmed by knock-down studies. Next, the clinical relevance of targeting FLIP and Mcl-1 in colon cancer was examined. Using immunohistochemistry, we found that Mcl-1 expression was significantly increased in colon adenoma and carcinoma patient material compared to healthy colonic epithelium, similar to the enhanced FLIP expression we recently observed in colon cancer. These results underscore the potential of combining low doses of aspirin with sorafenib to inhibit proliferation and target the anti-apoptotic proteins FLIP and Mcl-1 in colon cancer cells.

Treatment of malignant melanoma by downregulation of XIAP and overexpression of TRAIL with a conditionally replicating oncolytic adenovirus

BACKGROUND AND AIM

Currently available systemic therapies for malignant melanoma produce low response rates in patients, and more effective treatment modalities are clearly needed. The tumor necrosis factor (TNF)- related apoptosis-inducing ligand has a significant impact on therapy for patients with X-linked inhibitor of apoptosis protein-downregulation malignant melanoma. The primary objective of this study was to assess its therapeutic potential.

MATERIALS AND METHODS

We employed a conditionally replicating oncolytic adenoviral vector, named CRAd5.TRAIL/siXIAP, with the characteristics of over-expression of the therapeutic gene TRAIL and downregulation of XIAP in one vector. B16F10-luc cells were employed to detect anti-tumor activity of CRAd5.TRAIL/siXIAP in vitro and in vivo.

RESULTS

CRAd5.TRAIL/siXIAP enhanced caspase-8 activation and caspase-3 maturation in B16F10 cells in vitro. Furthermore, it more effectively infected and killed melanoma cells in vitro and in vivo than other adenoviruses.

CONCLUSION

Taken together, the combination of upregulation of TRAIL and downregulation of siXIAP with one oncolytic adenoviral vector holds promise for development of an effective therapy for melanomas and other common cancers.

Taxifolin enhances andrographolide-induced mitotic arrest and apoptosis in human prostate cancer cells via spindle assembly checkpoint activation

Andrographolide (Andro) suppresses proliferation and triggers apoptosis in many types of cancer cells. Taxifolin (Taxi) has been proposed to prevent cancer development similar to other dietary flavonoids. In the present study, the cytotoxic and apoptotic effects of the addition of Andro alone and Andro and Taxi together on human prostate carcinoma DU145 cells were assessed. Andro inhibited prostate cancer cell proliferation by mitotic arrest and activation of the intrinsic apoptotic pathway. Although the effect of Taxi alone on DU145 cell proliferation was not significant, the combined use of Taxi with Andro significantly potentiated the anti-proliferative effect of increased mitotic arrest and apoptosis by enhancing the cleavage of poly(ADP-ribose) polymerase, and caspases-7 and -9. Andro together with Taxi enhanced microtubule polymerization in vitro, and they induced the formation of twisted and elongated spindles in the cancer cells, thus leading to mitotic arrest. In addition, we showed that depletion of MAD2, a component in the spindle assembly checkpoint (SAC), alleviated the mitotic block induced by the two compounds, suggesting that they trigger mitotic arrest by SAC activation. This study suggests that the anti-cancer activity of Andro can be significantly enhanced in combination with Taxi by disrupting microtubule dynamics and activating the SAC.

Dacarbazine and the agonistic TRAIL receptor-2 antibody lexatumumab induce synergistic anticancer effects in melanoma

Mapatumumab and lexatumumab (targeting death receptor 4 (DR4) and 5 (DR5), respectively) are agonistic TRAIL receptor antibodies that induce apoptosis in a wide range of cancer cells. The potency of mapatumumab and lexatumumab was assessed in mono therapy protocols, and the ability to sensitize for dacarbazine (DTIC) treatment was explored in ten different melanoma cell lines. Our data indicated that melanoma cell lines tend to be resistant to mapatumumab, most likely due to low expression of DR4, while a dose dependent response to lexatumumab was observed. Combining DTIC and lexatumumab induced an additive or synergistic effect on cell death in the various melanoma cell lines. The synergistic effect observed in the FEMX-1 cell line was related to enhanced cleavage of Bid in parallel with elevated expression of the pro-apoptotic proteins Bim, Bax and Bak. Furthermore, the anti-apoptotic proteins Bcl-XL, cIAP-1, XIAP and livin were down regulated. Cleavage of Bid and down regulation of cIAP-2 and livin were observed in vivo. Altogether, these data suggest a change in the balance between pro- and anti-apoptotic proteins favoring induction of apoptosis. In the more therapy resistant cell line, HHMS, no changes in the pro- and anti-apoptotic proteins were observed. FEMX-1 xenografts treated with DTIC and lexatumumab showed reduced growth and increased level of apoptosis compared to the control groups, providing arguments for further evaluation of this combination in melanoma patients.

p14(ARF)-induced apoptosis in p53 protein-deficient cells is mediated by BH3-only protein-independent derepression of Bak protein through down-regulation of Mcl-1 and Bcl-xL proteins

The p14(ARF) tumor suppressor plays a central role in regulating cell cycle arrest and apoptosis. We reported previously that p14(ARF) is capable of triggering apoptosis in a p53-independent manner. However, the mechanism remained unclear. Here we demonstrate that the p53-independent activation of the mitochondrial apoptosis pathway by p14(ARF) is primarily mediated by the pro-apoptotic Bax-homolog Bak. Expression of p14(ARF) exclusively triggers a N-terminal conformational switch of Bak, but not Bax, which allows for mitochondrial permeability shift, release of cytochrome c, activation of caspases, and subsequent fragmentation of genomic DNA. Although forced expression of Bak markedly sensitizes toward p14(ARF)-induced apoptosis, re-expression of Bax has no effect. Vice versa, knockdown of Bak by RNA interference attenuates p14(ARF)-induced apoptosis, whereas down-regulation of Bax has no effect. Bak activation coincides with a prominent, caspase-independent deprivation of the endogenous Bak inhibitors Mcl-1 and Bcl-x(L). In turn, mitochondrial apoptosis is fully blocked by overexpression of either Mcl-1 or Bcl-x(L). Taken together, these data indicate that in the absence of functional p53 and Bax, p14(ARF) triggers mitochondrial apoptosis signaling by activating Bak, which is facilitated by down-regulating anti-apoptotic Mcl-1 and Bcl-x(L). Moreover, our data suggest that the simultaneous inhibition of two central endogenous Bak inhibitors, i.e. Mcl-1 and Bcl-x(L), may be sufficient to activate mitochondrial apoptosis in the absence of BH3-only protein regulation.

Resveratrol induces apoptosis via a Bak-mediated intrinsic pathway in human lung adenocarcinoma cells

Our recent study have shown that resveratrol (RV), a natural plant polyphenol found in red grape skins as well as other food product, induced apoptosis via the downstream factors, caspase-independent AIF and to lesser extent caspase-9, of intrinsic apoptosis pathway in human lung adenocarcinoma (ASTC-a-1) cells. This report is designed to explore the roles of the upstream mediators of the intrinsic pathway, such as Bak/Bax, Bim, Puma and Noxa, during RV-induced apoptosis in human lung adenocarcinoma (ASTC-a-1 and A549) cell lines. RV treatment remarkably induced the activation of Bak but not Bax, and silencing Bak but not Bax by shRNA almost completely prevented RV-induced cell death, mitochondrial dysfunction and also largely prevented RV-induced AIF release, demonstrating the preferential engagement of Bak but not Bax during RV-induced apoptosis. In addition, although RV treatment induced a significant degradation of Mcl-1, knockdown of Mcl-1 by shRNA only modestly increased RV-induced Bak activation. Interestingly, silencing Bim but not Puma and Noxa remarkably attenuated RV-induced cell death, loss of mitochondrial membrane potential, and Bak activation, suggesting the important roles of Bim. Collectively, our findings for the first time demonstrate that RV induces apoptosis dominantly via a Bak- but not Bax-mediated AIF-dependent mitochondrial apoptotic signaling pathway in which Bim but not Puma and Noxa may supply the force to trigger Bak activation and subsequent apoptosis in both ASTC-a-1 and A549 cell lines.

Luteolin enhances TNF-related apoptosis-inducing ligand's anticancer activity in a lung cancer xenograft mouse model

Sensitization of cancer cells to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by luteolin has been suggested by in vitro studies. However, no in vivo experiment has been reported to validate the potentiation effect of luteolin on TRAIL's anticancer activity. In this report, we first confirmed that luteolin potentiates TRAIL-induced cytotoxicity in A549 cells and HeLa cells in association with increased activation of apoptosis. Then we performed an in vivo experiment with a non-small cell lung cancer xenograft mouse model, which showed for the first time that the in vivo anticancer activity of TRAIL was greatly enhanced by luteolin. Compared with that in untreated control or treatment with TRAIL or luteolin alone, inhibition of tumor growth and apoptotic cell death in xenograft tumors were significantly increased in animals receiving combination treatment with TRAIL and luteolin. Data from this study thus provide strong in vivo evidence supporting that luteolin is a potential sensitizer for TRAIL in anticancer therapy.

Predominant requirement of Bax for apoptosis in HCT116 cells is determined by Mcl-1's inhibitory effect on Bak

The intrinsic mitochondrial apoptotic pathway acts through two core pro-apoptotic proteins Bax (Bcl2-associated X protein) and Bak (Bcl2-antagonist/killer 1). Although Bax and Bak seem to have redundant roles in apoptosis, accumulating evidence also suggests that they might not be interchangeable under certain conditions, at least in some human cell lines. Here we report the generation of Bak knockout as well as BaxBak double knockout HCT116 human colon carcinoma cells. We show that Bak is dispensable for apoptosis induced by a variety of stimuli including ABT-737 but not for fluorouracil-induced apoptosis. In addition, Bax deficiency only provides partial protection against camptothecin and cisplatin-induced apoptosis and no protection against killing by Puma or ABT-737 plus Noxa overexpression. Moreover, Bak is activated normally in response to many chemotherapeutic drugs in the presence of Bax, but remains kept in check by Mcl-1 in the absence of Bax. Our data suggest that Bax and Bak are functionally redundant, but they are counteracted by distinct anti-apoptotic Bcl-2 family proteins in different species.

Ethanol enhances susceptibility to apoptotic cell death via down-regulation of autophagy-related proteins

BACKGROUND

Alcohol induces cellular stress and promotes cell death in immune cells. Molecular mechanisms by which ethanol impairs the function of immune cells are largely unknown. Autophagy is a degradation pathway, acting either as a pro-survival or pro-death mechanism activated during stress conditions. We examined whether ethanol influences autophagy in monocytic human U937, CD4 Jurkat, and MCF-7 cells.

METHODS

Effects of ethanol during starvation-induced autophagy were investigated, treating cells with ethanol alone and in combination with activation of autophagy by rapamycin or inhibition by wortmannin. Apoptotic and necrotic cell death features such as the breakdown of the mitochondrial membrane potential, DNA fragmentation, and cell permeability were assessed using FACS analyses. Expression level of Beclin-1, LC3-II, Bcl-2, and the activation of caspase-3, and PARP-1 were determined using Western blot analyses. Influence of ethanol on formation of LC3-II complexes was assessed using fluorescence microscopy in MCF-7 cells stable transfected with a GFP-LC3-II-expression vector.

RESULTS

Ethanol down regulated autophagy proteins such as Beclin-1 and LC3-II. Apoptosis was enhanced as shown by breakdown of mitochondrial potential, up-regulation of cleaved caspase-3 and PARP-1 and down-regulation of anti-apoptotic protein Bcl-2. Formation of LC3-II complexes was inhibited by ethanol in caspase-3 deficient MCF-7 cells. Stimulation of autophagy by rapamycin prevented ethanol-induced apoptotic cell death. Inhibition of autophagy by wortmannin aggravated ethanol-mediated necrotic cell death.

CONCLUSION

Inhibition of autophagy via ethanol enhances susceptibility to cell death.

Combined modality therapy with TRAIL or agonistic death receptor antibodies

Molecularly targeted therapies, such as antibodies and small molecule inhibitors have emerged as an important breakthrough in the treatment of many human cancers. One targeted therapy under development is tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) due to its ability to induce apoptosis in a variety of human cancer cell lines and xenografts, while lacking toxicity in most normal cells. TRAIL and apoptosis-inducing agonistic antibodies to the TRAIL death receptors have been the subject of many preclinical and clinical studies in the past decade. However, the sensitivity of individual cancer cell lines of a particular tumor type to these agents varies from highly sensitive to resistant. Various chemotherapy agents have been shown to enhance the apoptosis-inducing capacity of TRAIL receptor-targeted therapies and induce sensitization of TRAIL-resistant cells. This review provides an overview of the mechanisms associated with chemotherapy enhancement of TRAIL receptor-targeted therapies including modulation of the apoptotic (death receptor expression, FLIP, and Bcl-2 or inhibitors of apoptosis (IAP) families) as well as cell signaling (NFκB, Akt, p53) pathways. These mechanisms will be important in establishing effective combinations to pursue clinically and in determining relevant targets for future cancer therapies.

Restoration of the immunogenicity of cisplatin-induced cancer cell death by endoplasmic reticulum stress

In contrast to other cytotoxic agents including anthracyclins and oxaliplatin (OXP), cisplatin (CDDP) fails to induce immunogenic tumor cell death that would allow to stimulate an anticancer immune response and hence to amplify its therapeutic efficacy. This failure to induce immunogenic cell death can be attributed to CDDP's incapacity to elicit the translocation of calreticulin (CRT) from the lumen of the endoplasmic reticulum (ER) to the cell surface. Here, we show that, in contrast to OXP, CDDP is unable to activate the protein kinase-like ER kinase (PERK)-dependent phosphorylation of the eukaryotic translation initiation factor 2α (eIF2α). Accordingly, CDDP also failed to stimulate the formation of stress granules and macroautophagy, two processes that only occur after eIF2α phosphorylation. Using a screening method that monitors the voyage of CRT from the ER lumen to the cell surface, we identified thapsigargin (THAPS), an inhibitor of the sarco/ER Ca(2+)-ATPase as a molecule that on its own does not stimulate CRT exposure, yet endows CDDP with the capacity to do so. The combination of ER stress inducers (such as THAPS or tunicamycin) and CDDP effectively induced the translocation of CRT to the plasma membrane, as well as immunogenic cell death, although ER stress or CDDP alone was insufficient to induce CRT exposure and immunogenic cell death. Altogether, our results underscore the contribution of the ER stress response to the immunogenicity of cell death.

Ethanol changes gene expression of transcription factors and cytokine production of CD4+ T-cell subsets in PBMCs stimulated with LPS

BACKGROUND

Acute ethanol intoxication has the potential to alter immune reactivity by various pathways. The aim of this study was to investigate T-helper cell subsets transcription factors and cytokines in human peripheral blood mononuclear cells (PBMCs) following a single dose of lipopolysaccharide (LPS) with or without ethanol exposure.

METHODS

Human PBMCs were cultured in the presence of 100 mM ethanol and/or 100 ng/ml LPS for various time periods (1, 3, 8, and 24 hours) and analyzed for the kinetics of gene expression by quantitative real-time PCR of selected transcription factors (T-bet, GATA3, Foxp3, and RORγt) and cytokines (TNF-α, IL-6, IL-10, and IFN-γ). The proportion of Th17 and Treg cells was identified 24 hours after treatment with ethanol and LPS by multiparameter flow cytometry. Viability and amount of dead cells were analyzed after 24 and 48 hours by MTT assay and flow cytometry.

RESULTS

  Following LPS challenge, gene expression of Foxp3 increased, whereas RORγt decreased after 3 hours, GATA3 decreased within 1 hour, whereas expression of T-bet did not change at any time. Gene expression of TNF-α, interferon-γ (IFN-γ), and IL-6 peaked after 3 hours, expression of IL-10 peaked after 8 hours. Ethanol suppressed the LPS-induced gene expression of Foxp3, RORγt, and T-bet after 8 hours, expression of TNF-α and IFN-γ was also suppressed after 3 and 8 hours. Markers of inflammation including TNF-α and IL-1β in supernatant of PBMCs were significantly decreased, while levels of IL-10 and IL-6 remained unchanged following ethanol exposure. Furthermore, ethanol-treated cells alone or in combination with LPS had significantly fewer IL-17- and IFN-γ-secreting CD4+ T cells but constant proportion of Treg cells when compared to control cells. Proliferation and viability of the cells were not influenced under these conditions.

CONCLUSIONS

Alcohol interferes with the kinetics of Foxp3, RORγt, and T-bet gene expression and the production of TNF-α and IL-1ß and influences the balance of Treg/Th17 cells following LPS exposure.

Chemotherapy overcomes TRAIL-R4-mediated TRAIL resistance at the DISC level

TNF-related apoptosis-inducing ligand or Apo2L (Apo2L/TRAIL) is a promising anti-cancer drug owing to its ability to trigger apoptosis by binding to TRAIL-R1 or TRAIL-R2, two membrane-bound receptors that are often expressed by tumor cells. TRAIL can also bind non-functional receptors such as TRAIL-R4, but controversies still exist regarding their potential to inhibit TRAIL-induced apoptosis. We show here that TRAIL-R4, expressed either endogenously or ectopically, inhibits TRAIL-induced apoptosis. Interestingly, the combination of chemotherapeutic drugs with TRAIL restores tumor cell sensitivity to apoptosis in TRAIL-R4-expressing cells. This sensitization, which mainly occurs at the death-inducing signaling complex (DISC) level, through enhanced caspase-8 recruitment and activation, is compromised by c-FLIP expression and is independent of the mitochondria. Importantly, TRAIL-R4 expression prevents TRAIL-induced tumor regression in nude mice, but tumor regression induced by TRAIL can be restored with chemotherapy. Our results clearly support a negative regulatory function for TRAIL-R4 in controlling TRAIL signaling, and unveil the ability of TRAIL-R4 to cooperate with c-FLIP to inhibit TRAIL-induced cell death.

Pseudomonas exotoxin A-mediated apoptosis is Bak dependent and preceded by the degradation of Mcl-1

Pseudomonas exotoxin A (PE) is a bacterial toxin that arrests protein synthesis and induces apoptosis. Here, we utilized mouse embryo fibroblasts (MEFs) deficient in Bak and Bax to determine the roles of these proteins in cell death induced by PE. PE induced a rapid and dose-dependent induction of apoptosis in wild-type (WT) and Bax knockout (Bax(-/-)) MEFs but failed in Bak knockout (Bak(-/-)) and Bax/Bak double-knockout (DKO) MEFs. Also a loss of mitochondrial membrane potential was observed in WT and Bax(-/-) MEFs, but not in Bak(-/-) or in DKO MEFs, indicating an effect of PE on mitochondrial permeability. PE-mediated inhibition of protein synthesis was identical in all 4 cell lines, indicating that differences in killing were due to steps after the ADP-ribosylation of EF2. Mcl-1, but not Bcl-x(L), was rapidly degraded after PE treatment, consistent with a role for Mcl-1 in the PE death pathway. Bak was associated with Mcl-1 and Bcl-x(L) in MEFs and uncoupled from suppressed complexes after PE treatment. Overexpression of Mcl-1 and Bcl-x(L) inhibited PE-induced MEF death. Our data suggest that Bak is the preferential mediator of PE-mediated apoptosis and that the rapid degradation of Mcl-1 unleashes Bak to activate apoptosis.

Endogenous Bak inhibitors Mcl-1 and Bcl-xL: differential impact on TRAIL resistance in Bax-deficient carcinoma

Although both Mcl-1 and Bcl-x_L keep proapoptotic Bak in check, it is the loss of Mcl-1 that sensitizes cells to death receptor–mediated apoptosis.

Tumor necrosis factor (α)–related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent that preferentially kills tumor cells with limited cytotoxicity to nonmalignant cells. However, signaling from death receptors requires amplification via the mitochondrial apoptosis pathway (type II) in the majority of tumor cells. Thus, TRAIL-induced cell death entirely depends on the proapoptotic Bcl-2 family member Bax, which is often lost as a result of epigenetic inactivation or mutations. Consequently, Bax deficiency confers resistance against TRAIL-induced apoptosis. Despite expression of Bak, Bax-deficient cells are resistant to TRAIL-induced apoptosis. In this study, we show that the Bax dependency of TRAIL-induced apoptosis is determined by Mcl-1 but not Bcl-x_L. Both are antiapoptotic Bcl-2 family proteins that keep Bak in check. Nevertheless, knockdown of Mcl-1 but not Bcl-x_L overcame resistance to TRAIL, CD95/FasL and tumor necrosis factor (α) death receptor ligation in Bax-deficient cells, and enabled TRAIL to activate Bak, indicating that Mcl-1 rather than Bcl-x_L is a major target for sensitization of Bax-deficient tumors for death receptor–induced apoptosis via the Bak pathway.

Combined treatment with lexatumumab and irradiation leads to strongly increased long term tumour control under normoxic and hypoxic conditions

Purpose

The combination of ionizing radiation with the pro-apoptotic TRAIL receptor antibody lexatumumab has been shown to exert considerable synergistic apoptotic effects in vitro and in short term growth delay assays. To clarify the relevance of these effects on local tumour control long-term experiments using a colorectal xenograft model were conducted.

Materials and methods

Colo205-xenograft bearing NMRI (nu/nu) nude mice were treated with fractionated irradiation (5× 3 Gy, d1-5) and lexatumumab (0.75 mg/kg, d1, 4 and 8). The tumour bearing hind limbs were irradiated with graded single top up doses at d8 under normoxic (ambient) and acute hypoxic (clamped) conditions. Experimental animals were observed for 270 days. Growth delay and local tumour control were end points of the study. Statistical analysis of the experiments included evaluation of tumour regrowth and local tumour control.

Results

Combined treatment with irradiation and lexatumumab led to a pronounced tumour regrowth-delay when compared to irradiation alone. The here presented long-term experiments revealed a highly significant rise of local tumour control for normoxic (ambient) (p = 0. 000006) and hypoxic treatment (p = 0. 000030).

Conclusion

Our data show that a combination of the pro-apoptotic antibody lexatumumab with irradiation reduces tumour regrowth and leads to a highly increased local tumour control in a nude mouse model. This substantial effect was observed under ambient and more pronounced under hypoxic conditions.

Combination of the pro-apoptotic TRAIL-receptor antibody mapatumumab with ionizing radiation strongly increases long-term tumor control under ambient and hypoxic conditions

PURPOSE

Mapatumumab, an agonistic tumor necrosis factor-related apoptosis inducing ligand-receptor antibody, exerts highly synergistic apoptotic effects in vitro and in short-term growth delay assays when combined with irradiation. Because it remained unclear in how far these effects influence local tumor control, long-term experiments using a colorectal xenograft model were undertaken.

MATERIAL AND METHODS

Experiments were performed with irradiation (5 x 3 Gy, d1-5) and mapatumumab (10 mg/kg) in Colo205-xenograft-bearing NMRI (nu/nu) nude mice. Graded top up doses were delivered on the tumor-bearing hind leg under ambient and hypoxic conditions; follow-up was 270 days. Growth delay and local tumor control were end points of the study. Statistical analysis of the experiments included calculation of tumor regrowth and local tumor control.

RESULTS

After combined treatment, a pronounced tumor regrowth-delay was observed when compared with irradiation alone. Long-term experiments revealed a highly significant increase in local tumor control for ambient (p = 0.00076) and hypoxic treatment (p = 0.000069).

CONCLUSIONS

The present data demonstrate for the first time that combination of a pro-apoptotic antibody with irradiation results in evidently reduced tumor regrowth times and subsequently highly increased local tumor control under normoxic and hypoxic conditions in a xenograft mouse model.

The use of folate-PEG-grafted-hybranched-PEI nonviral vector for the inhibition of glioma growth in the rat

Combined treatment using nonviral agent-mediated enzyme/prodrug therapy and immunotherapy had been proposed as a powerful alternative method of cancer therapy. The present study was aimed to evaluate the cytotoxicity in vitro and the therapeutic efficacy in vivo when the cytosine deaminase/5-fluorocytosine (CD/5-FC) and TNF-related apoptosis-inducing ligand (TRAIL) genes were jointly used against rat C6 glioma cells. The potency of the FA-PEG-PEI used as a nonviral vector was tested in the FR-expressed C6 glioma cells and Wistar rats. The C6 glioma cells and animal model were treated by the combined application of FA-PEG-PEI/pCD/5-FC and FA-PEG-PEI/pTRAIL. The antitumor effect was evaluated by survival assays and tumor volume. This study revealed a significant increase of cytotoxicity in vitro following the combined application of FA-PEG-PEI/pCD/5-FC and FA-PEG-PEI/pTRAIL treatments in C6 glioma cells. Animal studies showed a significant growth inhibition of the C6 glioma xenografts using the combined treatment. These results demonstrated that the combined treatment generated additive cytotoxic effect in C6 glioma cells in both in vitro and in vivo conditions, and indicated that such treatment method using both enzyme/prodrug therapy and TRAIL immunotherapy might be a promising therapeutic strategy in treating glioma.

Protein kinase Cepsilon inhibits UVR-induced expression of FADD, an adaptor protein, linked to both Fas- and TNFR1-mediated apoptosis

Protein kinase C (PKC)epsilon overexpression in FVB/N transgenic mice sensitized skin to UVR-induced development of squamous cell carcinomas and suppressed formation of sunburn cells, which are DNA-damaged keratinocytes undergoing apoptosis. Here, we elucidated the mechanisms associated with the inhibition of UVR-induced appearance of sunburn cells in PKCepsilon transgenic mice. We found that the inhibition of UVR-induced sunburn cell formation in PKCepsilon transgenic mice may be the result of the inhibition of the expression of Fas, Fas ligand, and the mammalian death adaptor protein termed Fas-associated with death domain (FADD). The adaptor protein FADD is the key component of the death-inducing signaling complex of both Fas and tumor necrosis factor receptor 1. A decreased expression of epidermal FADD was observed after a single UVR exposure. However, a complete loss of FADD expression was found after four (Monday, Wednesday, Friday, and Monday) repeated UVR exposures. FADD transmits apoptotic signals from death receptors to the downstream initiator caspase-8 and connects to the mitochondrial intrinsic apoptotic signal transduction pathway by the cleavage of Bid, a Bcl-2 family member. PKCepsilon-mediated loss of FADD expression inhibited UVR signals to the activation of both extrinsic and intrinsic apoptotic pathways.

Targeting death-receptors in radiation therapy

The development of apoptosis resistance is a crucial step during the pathogenesis of malignant tumors. Thus, any treatment approach overcoming apoptosis resistance may be a valuable tool in oncology. Although a variety of treatments induce apoptosis, only very few specifically trigger programmed cell death. In this regard, the class of apoptosis inducing ligands may turn out to have a considerable potential in oncology. TNF-alpha-related apoptosis-inducing ligand (TRAIL/Apo2L) is the most promising candidate, either alone or in combination with established cancer therapies, since it induces apoptosis in a wide range of malignant cells while sparing most normal tissues. Since death-receptor induced apoptosis is mainly mediated via nonmitochondrial death pathways, it is possible to induce apoptosis in cancer cell systems which mainly harbor defects within the mitochondrial death cascades. Even more so it has been shown that conventional DNA damaging approaches reduced the killing threshold for receptor induced apoptosis, making TRAIL an ideal candidate for combined approaches. Thus, combined treatments might offer the chance to enhance therapeutic efficiency and overcome resistance. In combination, additive or synergistic apoptotic responses and substantially enhanced clonogenic cell kill has been documented. Furthermore, in several settings it has been shown that combined modality teatments were effective in malignant cells, which are highly resistant to either treatment, alone. Ionizing radiation is one of the most effective modalities in oncology. Thus, it is reasonable to test, how far combinations of TRAIL with ionizing radiation may increase the efficacy. Indeed, the combination of TRAIL with ionizing radiation in several in vitro settings as well as xenograft models resulted in highly increased rates of cell kill and long-term tumor control. No increase in the rate and severity of side effects has been documented, indicating that the combination really increases the therapeutic ratio. It is important to note that TRAIL and TRAIL receptor agonistic antibodies, either as single

Combined action of celecoxib and ionizing radiation in prostate cancer cells is independent of pro-apoptotic Bax

BACKGROUND AND PURPOSE

The cyclooxygenase-2-inhibitor celecoxib has been shown to inhibit cell growth and to reduce prostatic intraepithelial neoplasia in mice. The drug was suggested to increase efficacy of ionizing radiation. However, extent and mechanisms of the suggested benefit of celecoxib on the radiation response are still unclear. The aim of the present study was to analyze cytotoxic efficacy of celecoxib in combination with irradiation on human prostate cancer cell lines and to define the importance of pro-apoptotic Bax in this process.

MATERIALS AND METHODS

Induction of apoptosis and global and clonogenic cell survival upon irradation- (2-10Gy), celecoxib- (10-75microM) or combined treatment were evaluated in prostate cancer cells by fluorescence microscopy, WST-1 assay and standard colony formation assays.

RESULTS

Celecoxib <25microM caused morphological changes and growth inhibition without substantial apoptosis or radiosensitization in terms of decreased clonogenic cell survival. In contrast, celecoxib 25microM increased radiation-induced cell death and clonogenic kill. While radiation-induced clonogenic death was increased in the presence of Bax, effects of celecoxib or combined treatment were Bax independent.

CONCLUSIONS

Our findings reveal Bax-independent beneficial effects of celecoxib on radiation-induced apoptosis and eradication of clonogenic prostate cancer cells in vitro providing a rationale for clinical evaluation of high-dose celecoxib in combination with irradiation in prostate cancer patients.

Dynamin-2-dependent targeting of mannheimia haemolytica leukotoxin to mitochondrial cyclophilin D in bovine lymphoblastoid cells

Exotoxins which belong to the family containing the RTX toxins (repeats in toxin) contribute to a variety of important human and animal diseases. One example of such a toxin is the potent leukotoxin (LKT) produced by the bovine respiratory pathogen Mannheimia haemolytica. LKT binds to CD18, resulting in the death of bovine leukocytes. In this study, we showed that internalized LKT binds to the outer mitochondrial membrane, which results in the release of cytochrome c and collapse of the mitochondrial membrane potential (psi(m)). Incubation of bovine lymphoblastoid cells (BL-3 cells) with the mitochondrial membrane-stabilizing agent cyclosporine (CSA) reduced LKT-mediated cytotoxicity, cytochrome c release, and collapse of the psi(m). Coimmunoprecipitation and intracellular binding studies suggested that LKT binds to the mitochondrial matrix protein cyclophilin D. We also demonstrated that LKT mobilizes the vesicle scission protein dynamin-2 from mitochondria to the cell membrane. Incubation with CSA depleted mitochondrial dynamin-2 in BL-3 cells, making it unavailable for vesicle scission and LKT internalization. The results of this study show that LKT trafficking and LKT-mediated cell death involve dynamin-2 and cyclophilin D, in a process that can be prevented by the mitochondrial membrane-protecting function of CSA.

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.

Mcl-1 determines the Bax dependency of Nbk/Bik-induced apoptosis

B cell lymphoma 2 (Bcl-2) homology domain 3 (BH3)-only proteins of the Bcl-2 family are important functional adaptors that link cell death signals to the activation of Bax and/or Bak. The BH3-only protein Nbk/Bik induces cell death via an entirely Bax-dependent/Bak-independent mechanism. In contrast, cell death induced by the short splice variant of Bcl-x depends on Bak but not Bax. This indicates that Bak is functional but fails to become activated by Nbk. Here, we show that binding of myeloid cell leukemia 1 (Mcl-1) to Bak persists after Nbk expression and inhibits Nbk-induced apoptosis in Bax-deficient cells. In contrast, the BH3-only protein Puma disrupts Mcl-1-Bak interaction and triggers cell death via both Bax and Bak. Targeted knockdown of Mcl-1 overcomes inhibition of Bak and allows for Bak activation by Nbk. Thus, Nbk is held in check by Mcl-1 that interferes with activation of Bak. The finding that different BH3-only proteins rely specifically on Bax, Bak, or both has important implications for the design of anticancer drugs targeting Bcl-2.

The cystine/cysteine cycle: a redox cycle regulating susceptibility versus resistance to cell death

The glutathione-dependent system is one of the key systems regulating cellular redox balance, and thus cell fate. Cysteine, typically present in its oxidized form cystine in the extracellular space, is regarded as the rate-limiting substrate for glutathione (GSH) synthesis. Cystine is transported into cells by the highly specific amino-acid antiporter system xc-. Since Burkitt's Lymphoma (BL) cells display limited uptake capacity for cystine, and are thus prone to oxidative stress-induced cell death, we stably expressed the substrate-specific subunit of system xc-, xCT, in HH514 BL cells. xCT-overexpressing cells became highly resistant to oxidative stress, particularly upon GSH depletion. Contrary to previous predictions, the increase of intracellular cysteine did not affect the cellular GSH pool, but concomitantly boosted extracellular cysteine concentrations. Even though cells were depleted of bulk GSH, xCT overexpression maintained cellular integrity by protecting against lipid peroxidation, a very early event in cell death progression. Our results show that system xc- protects against oxidative stress not by elevating intracellular GSH levels, but rather creates a reducing extracellular environment by driving a highly efficient cystine/cysteine redox cycle. Our findings show that the cystine/cysteine redox cycle by itself must be viewed as a discrete major regulator of cell survival.

Cytosine deaminase/5-fluorocytosine gene therapy and Apo2L/TRAIL cooperate to kill TRAIL-resistant tumor cells

The death ligand Apo2L/TRAIL (Apo2 ligand/tumor necrosis factor-related apoptosis-inducing ligand) eradicates many tumor types while sparing most normal tissues. However, some tumors are resistant to TRAIL. We therefore determined if TRAIL cooperates with cytosine deaminase/5-fluorocytosine (CD/5-FC) gene therapy and investigated the mechanisms involved. Transfection of human LAN-5 neuroblastoma cells with CD rendered the cells (LAN-5-CD) sensitive to 5-FC-induced, caspase-dependent apoptosis. Mediated by caspase-3, CD/5-FC and TRAIL cooperated to induce apoptosis in these TRAIL-resistant cells and to cleave X-linked inhibitor of apoptosis protein (XIAP). In established LAN-5-CD tumors growing subcutaneously in mice, intratumorally applied TRAIL did not decrease tumor growth and systemically administered 5-FC only attenuated tumor growth. In contrast, 5-FC together with TRAIL dramatically decreased tumor growth and eradicated a tumor. Assuming sufficient gene transfer of CD in situ, CD/5-FC with TRAIL may be useful for the therapy of tumors resistant to TRAIL.

Noninvasive molecular imaging sheds light on the synergy between 5-fluorouracil and TRAIL/Apo2L for cancer therapy

PURPOSE

In a previous report, a recombinant luciferase reporter, activated during apoptosis via caspase-3 cleavage, was developed for imaging of apoptosis using bioluminescence. The ability to noninvasively image apoptosis in vivo could dramatically benefit the preclinical development of therapeutics targeting the apoptotic pathway. In this study, we examined the use of 5-fluorouracil (5-FU) for sensitizing D54 tumors to tumor necrosis factor alpha-related apoptosis-inducing ligand (TRAIL) therapy by monitoring apoptotic activity in vivo using bioluminescence imaging.

EXPERIMENTAL DESIGN

Using our apoptosis imaging platform and diffusion magnetic resonance imaging (MRI), we monitored the antitumor effects of 5-FU, TRAIL, and 5-FU + TRAIL using D54 xenografts. Additionally, volumetric and histologic analyses were done for correlation with findings from bioluminescence imaging and diffusion MRI.

RESULTS

Bioluminescence imaging showed that therapy with TRAIL alone produced an initial 400% increase in apoptotic activity that rapidly diminished during the 10-day treatment period despite continued therapy. In contrast, concomitant 5-FU and TRAIL therapy elicited an apoptotic response that was sustained throughout the entire therapeutic course. Using diffusion MRI, an enhanced tumor response was detected when concomitant therapy was given versus TRAIL-alone therapy. Last, concomitant therapy resulted in a prolonged growth delay ( approximately 9 days) compared with TRAIL alone ( approximately 4 days).

CONCLUSION

We showed that concomitant 5-FU and TRAIL therapy indeed enhanced apoptotic activity in vivo, which translated into greater tumor control. Moreover, this technique sheds light on the synergy of 5-FU and TRAIL as evidenced by differences in the temporal activation of caspase-3 resulting from the different therapeutic regimens.

Targeted induction of apoptosis via TRAIL and cryoablation: a novel strategy for the treatment of prostate cancer

Adjuvant therapies contribute to the successful treatment of cancer. Our previous reports have shown that combining cryoablation with cytotoxic agents enhances cell death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytotoxic agent that preferentially induces apoptosis in a variety of human cancer cells. Human prostate cancer cells (PC-3) are resistant to many cytodestructive agents, including cryoablation and TRAIL. Here, we evaluated the effects of TRAIL combined with cryoablation on PC-3 and normal prostate (RWPE-1) cell death. Exposure of PC-3 cells to freezing (-10 degrees C) or TRAIL (500 ng/ml) results in minimal cell death, whereas a complete loss of viability is observed with the simultaneous combination. The synergistic effect was found to be due to a marked increase in apoptosis. Western blot analysis revealed a significant level of caspase-8 and -3 cleavage between 12 and 24 h post-exposure. Caspase activation assays provided similar results and also indicated a role for caspase-9. Inhibitors to caspase-8 and -9 along with a pan-caspase inhibitor were incorporated to determine which pathway was necessary for the combined efficacy. Inhibition of caspase-8 significantly blocked the combination-induced cell death compared to cells that did not receive the inhibitor (63% compared to 10% viable). The addition of the caspase-9 inhibitor resulted in only a minimal protection. Importantly, the combination was not effective when applied to normal prostate cells. The results describe a novel therapeutic model for the treatment of prostate cancer and provide support for future in vivo studies.

Inhibition of Fas expression by RNAi modulates 5-fluorouracil-induced apoptosis in HCT116 cells expressing wild-type p53

Drug resistance to 5-fluorouracil (5-FU) is still a major limitation to its clinical use. In addition, the clinical value of p53 as a predictive marker for 5-FU-based chemotherapy remains a matter of debate. Here, we used HCT116 human colorectal cancer cells expressing wild-type p53 and investigated whether inhibition of Fas expression by interference RNA modulates 5-FU-induced apoptosis. Cells were treated with 5-FU (1, 4 or 8 microM) for 8-48 h. Cell viability was evaluated by trypan blue dye exclusion. Apoptosis was assessed by changes in nuclear morphology and caspase activity. The interference RNA technology was used to silence Fas expression. Caspase activation, p53, Fas, cytochrome c, and Bcl-2 family protein expression was evaluated by immunoblotting. 5-FU was cytotoxic in HCT116 cells (p<0.001). Nuclear fragmentation and caspase-3, -8 and -9 activities were also markedly increased in HCT116 cells after 5-FU (p<0.001). In addition, wild-type p53 and Fas expression were 25- and 4-fold increased (p<0.05). Notably, when interference RNA was used to inhibit Fas, 5-FU-mediated nuclear fragmentation and caspase activity were markedly reduced in HCT116 cells. Finally, western blot analysis of mitochondrial extracts from HCT116 cells exposed to 5-FU showed a 6-fold increase in Bax, together with a 3-fold decrease in cytochrome c (p<0.001). In conclusion, 5-FU exerts its cytotoxic effects, in part, through a p53/Fas-dependent apoptotic pathway that involves Bax translocation and mitochondrial permeabilization.

Resistance of melanoma cells to TRAIL does not result from upregulation of antiapoptotic proteins by NF-κB but is related to downregulation of initiator caspases and DR4

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted considerable attention as a novel anticancer agent. However, its efficiency may be diminished by occurring resistance in cancer cells. The mechanisms of TRAIL resistance in melanoma are still unsolved. Here we show for the first time that TRAIL-induced activation of NF-kappaB occurs in apoptosis-sensitive melanoma cell lines through TRAIL receptor 1/death receptor 4 (TRAIL-R1/DR4), whereas TRAIL failed to activate nuclear factor kappa B (NF-kappaB) in melanoma cells positive only for TRAIL receptor 2/death receptor 5 (TRAIL-R2/DR5). However, activation of NF-kappaB by TRAIL was not associated with enhanced expression of antiapoptotic factors: cellular FLICE-inhibitory protein (c-FLIP), Bcl-x(L), X-linked inhibitor of apoptosis protein (XIAP), Survivin, Livin. Rather in one of the cell lines, TRAIL induced the downregulation of DR4. In an established cell culture model for TRAIL resistance and regained TRAIL sensitivity, resistance was neither associated with increased NF-kappaB activity by TRAIL nor by an increased expression of antiapoptotic proteins. However, significant downregulation of caspase-8, caspase-10 and of DR4 was characteristic for TRAIL-resistant, DR4-positive melanoma cells, and regained TRAIL sensitivity coincided with re-expression of these factors. Sensitivity was also largely retained after their exogenous overexpression. Thus, initiator caspases and DR4 rather than NF-kappaB may control melanoma cell sensitivity to TRAIL, and strategies, which result in their upregulation, may be useful for enhancement of TRAIL sensitivity.

Primary colorectal tumors fail to express the proapoptotic mediator PTAG and its reexpression augments drug-induced apoptosis

Genes implicated in tumor evolution and progression, including those in apoptotic pathways, are associated with methylation-associated gene silencing in different tumor types. By exploiting differential methylation we recently isolated a novel pituitary tumor derived apoptosis gene (PTAG) that augments drug-induced apoptosis. The importance of PTAG was determined in other tumor types, and these studies show that the majority of primary colorectal tumors fail to express the PTAG gene, indicating an important role for PTAG in colorectal tumorigenesis. The effects of expression of PTAG were examined through stable transfection of the colorectal cell lines HCT116 and SW480. Expression of PTAG, per se, had no discernible effects on cell viability or cell kinetics. In contrast to these findings, in cells subject to drug challenges that engaged either a death-receptor mediated or mitochondrial pathway, all of the experiments indicated a role for PTAG in the intrinsic pathway of apoptosis. Loss of PTAG therefore contributes to a blunted apoptotic response and is likely to predispose cells toward malignant transformation and resistance to chemotherapeutic interventions.

Combination of cytosine deaminase suicide gene expression with DR5 antibody treatment increases cancer cell cytotoxicity

Combined treatment using adenoviral-directed enzyme/prodrug therapy and immunotherapy has the potential to become a powerful alternative method of cancer therapy. We have developed adenoviral vectors encoding the cytosine deaminase gene (Ad-CD) and cytosine deaminase:uracil phosphoribosyltransferase fusion gene (Ad-CD:UPRT). A monoclonal antibody, TRA-8, specifically binds to death receptor 5, one of two death receptors bound by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The purpose of this study was to evaluate cytotoxicity in vitro and therapeutic efficacy in vivo of the combination of Ad-CD:UPRT and TRA-8 against human pancreatic cancer and glioma cell lines. The present study demonstrates that Ad-CD:UPRT infection resulted in increased 5-FC-mediated cell killing, compared with Ad-CD. Furthermore, a significant increase of cytotoxicity following Ad-CD:UPRT/5-FC and TRA-8 treatment of cancer cells in vitro was demonstrated. Animal studies showed significant inhibition of tumor growth of MIA PaCa-2 pancreatic and D54MG glioma xenografts by the combination of Ad-CD:UPRT/5-FC plus TRA-8 as compared with either agent alone or no treatment. The results suggest that the combination of Ad-CD:UPRT/5-FC with TRA-8 produces an additive cytotoxic effect in cancer cells in vitro and in vivo. These data indicate that combined treatment with enzyme/prodrug therapy and TRAIL immunotherapy provides a promising approach for cancer therapy.