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

Malignant function of nuclear factor-kappaB axis in prostate cancer: Molecular interactions and regulation by non-coding RNAs

Prostate carcinoma is a malignant situation that arises from genomic alterations in the prostate, leading to changes in tumorigenesis. The NF-κB pathway modulates various biological mechanisms, including inflammation and immune responses. Dysregulation of NF-κB promotes carcinogenesis, including increased proliferation, invasion, and therapy resistance. As an incurable disease globally, prostate cancer is a significant health concern, and research into genetic mutations and NF-κB function has the efficacy to facilitate the introduction of novel therapies. NF-κB upregulation is observed during prostate cancer progression, resulting in increased cell cycle progression and proliferation rates. Additionally, NF-κB endorses resistance to cell death and enhances the capacity for metastasis, particularly bone metastasis. Overexpression of NF-κB triggers chemoresistance and radio-resistance, and inhibition of NF-κB by anti-tumor compounds can reduce cancer progression. Interestingly, non-coding RNA transcripts can regulate NF-κB level and its nuclear transfer, offering a potential avenue for modulating prostate cancer progression.

Nano-TRAIL: a promising path to cancer therapy

Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand, also called apo-2 ligand (TRAIL/Apo-2L), is a cytokine that triggers apoptosis by binding to TRAIL-R1 (DR4) and TRAIL-R2 (DR5) death receptors. Apoptosis occurs through either the extrinsic or intrinsic pathway. The administration of recombinant human TRAIL (rhTRAIL) or TRAIL-receptor (TRAIL-R) agonists promotes apoptosis preferentially in cancerous cells over normal cells in vitro; this phenomenon has also been observed in clinical studies. The limited efficacy of rhTRAIL in clinical trials could be attributed to drug resistance, short half-life, targeted delivery issues, and off-target toxicities. Nanoparticles are excellent drug and gene delivery systems characterized by improved permeability and retention, increased stability and biocompatibility, and precision targeting. In this review, we discuss resistance mechanisms to TRAIL and methods to overcome TRAIL resistance by using nanoparticle-based formulations developed for the delivery of TRAIL peptides, TRAIL-R agonists, and TRAIL genes to cancer cells. We also discuss combinatorial approaches of chemotherapeutic drugs with TRAIL. These studies demonstrate TRAIL's potential as an anticancer agent.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

Behind the Adaptive and Resistance Mechanisms of Cancer Stem Cells to TRAIL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), also known as Apo-2 ligand (Apo2L), is a member of the TNF cytokine superfamily. TRAIL has been widely studied as a novel strategy for tumor elimination, as cancer cells overexpress TRAIL death receptors, inducing apoptosis and inhibiting blood vessel formation. However, cancer stem cells (CSCs), which are the main culprits responsible for therapy resistance and cancer remission, can easily develop evasion mechanisms for TRAIL apoptosis. By further modifying their properties, they take advantage of this molecule to improve survival and angiogenesis. The molecular mechanisms that CSCs use for TRAIL resistance and angiogenesis development are not well elucidated. Recent research has shown that proteins and transcription factors from the cell cycle, survival, and invasion pathways are involved. This review summarizes the main mechanism of cell adaption by TRAIL to promote response angiogenic or pro-angiogenic intermediates that facilitate TRAIL resistance regulation and cancer progression by CSCs and novel strategies to induce apoptosis.

Smac mimetics and TRAIL cooperate to induce MLKL-dependent necroptosis in Burkitt's lymphoma cell lines

Burkitt's lymphoma (BL) is a highly aggressive form of B-cell non-Hodgkin's lymphoma. The clinical outcome in children with BL has improved over the last years but the prognosis for adults is still poor, highlighting the need for novel treatment strategies. Here, we report that the combinational treatment with the Smac mimetic BV6 and TRAIL triggers necroptosis in BL when caspases are blocked by zVAD.fmk (TBZ treatment). The sensitivity of BL cells to TBZ correlates with MLKL expression. We demonstrate that necroptotic signaling critically depends on MLKL, since siRNA-induced knockdown and CRISPR/Cas9-mediated knockout of MLKL profoundly protect BL cells from TBZ-induced necroptosis. Conversely, MLKL overexpression in cell lines expressing low levels of MLKL leads to necroptosis induction, which can be rescued by pharmacological inhibitors, highlighting the important role of MLKL for necroptosis execution. Importantly, the methylation status analysis of the MLKL promoter reveals a correlation between methylation and MLKL expression. Thus, MLKL is epigenetically regulated in BL and might serve as a prognostic marker for treatment success of necroptosis-based therapies. These findings have crucial implications for the development of new treatment options for BL.

Smac mimetics LCL161 and GDC-0152 inhibit osteosarcoma growth and metastasis in mice

Background

Current therapies fail to cure over a third of osteosarcoma patients and around three quarters of those with metastatic disease. “Smac mimetics” (also known as “IAP antagonists”) are a new class of anti-cancer agents. Previous work revealed that cells from murine osteosarcomas were efficiently sensitized by physiologically achievable concentrations of some Smac mimetics (including GDC-0152 and LCL161) to killing by the inflammatory cytokine TNFα in vitro, but survived exposure to Smac mimetics as sole agents.

Methods

Nude mice were subcutaneously or intramuscularly implanted with luciferase-expressing murine 1029H or human KRIB osteosarcoma cells. The impacts of treatment with GDC-0152, LCL161 and/or doxorubicin were assessed by caliper measurements, bioluminescence, ¹⁸FDG-PET and MRI imaging, and by weighing resected tumors at the experimental endpoint. Metastatic burden was examined by quantitative PCR, through amplification of a region of the luciferase gene from lung DNA. ATP levels in treated and untreated osteosarcoma cells were compared to assess in vitro sensitivity. Immunophenotyping of cells within treated and untreated tumors was performed by flow cytometry, and TNFα levels in blood and tumors were measured using cytokine bead arrays.

Results

Treatment with GDC-0152 or LCL161 suppressed the growth of subcutaneously or intramuscularly implanted osteosarcomas. In both models, co-treatment with doxorubicin and Smac mimetics impeded average osteosarcoma growth to a greater extent than either drug alone, although these differences were not statistically significant. Co-treatments were also more toxic. Co-treatment with LCL161 and doxorubicin was particularly effective in the KRIB intramuscular model, impeding primary tumor growth and delaying or preventing metastasis. Although the Smac mimetics were effective in vivo, in vitro they only efficiently killed osteosarcoma cells when TNFα was supplied. Implanted tumors contained high levels of TNFα, produced by infiltrating immune cells. Spontaneous osteosarcomas that arose in genetically-engineered immunocompetent mice also contained abundant TNFα.

Conclusions

These data imply that Smac mimetics can cooperate with TNFα secreted by tumor-associated immune cells to kill osteosarcoma cells in vivo. Smac mimetics may therefore benefit osteosarcoma patients whose tumors contain Smac mimetic-responsive cancer cells and TNFα-producing infiltrating cells.

Understanding Apoptosis and Apoptotic Pathways Targeted Cancer Therapeutics

Various physiological processes involve appropriate tissue developmental process and homeostasis - the pathogenesis of several diseases connected with deregulatory apoptosis process. Apoptosis plays a crucial role in maintaining a balance between cell death and division, evasion of apoptosis results in the uncontrolled multiplication of cells leading to different diseases such as cancer. Currently, the development of apoptosis targeting anticancer drugs has gained much interest since cell death induced by apoptosis causes minimal inflammation. The understanding of complexities of apoptosis mechanism and how apoptosis is evolved by tumor cells to oppose cell death has focused research into the new strategies designed to induce apoptosis in cancer cells. This review focused on the underlying mechanism of apoptosis and the dysregulation of apoptosis modulators involved in the extrinsic and intrinsic apoptotic pathway, which include death receptors (DRs) proteins, cellular FLICE inhibitory proteins (c-FLIP), anti-apoptotic Bcl-2 proteins, inhibitors of apoptosis proteins (IAPs), tumor suppressor (p53) in cancer cells along with various current clinical approaches aimed to selectively induce apoptosis in cancer cells.

Oncolytic viro-chemotherapy exhibits antitumor effect in laryngeal squamous cell carcinoma cells and mouse xenografts

Background: Oncolytic virus can specifically replicate in and then lyse tumor cells, but seldom in normal cells. Further studies have shown the significant therapeutic effect of oncolytic virotherapy combining with other strategies, such as chemo-, radio-, and immunotherapy et al. In this study, we investigated the combinational effect of oncolytic virus ZD55-TRAIL and chemotherapy drug doxorubicin (DOX) on human laryngeal squamous cell carcinoma (LSCC).

Methods: The effect of ZD55-TRAIL combined with DOX on cell growth was assessed in LSCC Hep2 cells and normal cells by MTT assay. Hochest 33342 staining was performed to observe cell morphological changes. Western blot was used to detect the expression of apoptotic activation proteins. The in vivo antitumor efficacy of combination treatment was estimated in laryngeal cancer xenograft models.

Results: The combination of ZD55-TRAIL and DOX exhibited enhanced inhibitory effects on laryngocarcinoma cell growth, and had few side effects to normal cells in vitro. Chemotherapy drug increased the inducement of tumor cell apoptosis mediated by oncolytic virus. In vivo experiment confirmed that the combination treatment significantly inhibited Hep2 laryngocarcinoma xenografts growth in mice.

Conclusion: The oncolytic viro-chemotherapy is a potent therapeutic approach for in vitro cytotoxicity evaluation of Hep2 cells and xenograft growth in vivo.

Aconitine inhibits the proliferation of hepatocellular carcinoma by inducing apoptosis

Hepatocellular carcinoma (HCC) is the primary liver cancer that occurs with a high incidence in Asia. Owing to the poor prognosis of the disease, the mortality rate remains high, making HCC the third most common cause of cancer-related mortality worldwide. Studies on current therapies have generated little empirical evidence in improving the survival rate of patients with advanced HCC. Certain agents have exhibited promising results in molecular targeted therapy, but they remain in clinical trials. Aconitine, a main bioactive constituent of a traditional Chinese herb, Wutou, and belonging to the Aconitum genus, has been demonstrated to inhibit the growth of certain tumors, including HCC, but the underlying molecular mechanism by which aconitine inhibits tumor growth is largely unknown. In the present study, aconitine was applied to two types of hepatic carcinoma cells and normal hepatic cells at various concentrations, and it was found to specifically inhibit the proliferation of cancer cells in a dose-dependent manner. Further study found that aconitine activated the production of reactive oxygen species, leading to an increased release of cytochrome c from mitochondria and the activation of apoptosis. This is demonstrated by the increased cleavage of caspases 3 and 7, as well as an increased B-cell lymphoma 2 (Bcl-2)-associated X protein level and a decreased Bcl-2 level in cancer cells. An in vivo study also found that aconitine was able to inhibit the growth of tumors in mice. The results of the present study suggest that aconitine has the potential to be developed into an effective anti-HCC agent.

Overcoming chemotherapy drug resistance by targeting inhibitors of apoptosis proteins (IAPs)

Inhibitors of apoptosis (IAPs) are a family of proteins that play a significant role in the control of programmed cell death (PCD). PCD is essential to maintain healthy cell turnover within tissue but also to fight disease or infection. Uninhibited, IAPs can suppress apoptosis and promote cell cycle progression. Therefore, it is unsurprising that cancer cells demonstrate significantly elevated expression levels of IAPs, resulting in improved cell survival, enhanced tumor growth and subsequent metastasis. Therapies to target IAPs in cancer has garnered substantial scientific interest and as resistance to anti-cancer agents becomes more prevalent, targeting IAPs has become an increasingly attractive strategy to re-sensitize cancer cells to chemotherapies, antibody based-therapies and TRAIL therapy. Antagonism strategies to modulate the actions of XIAP, cIAP1/2 and survivin are the central focus of current research and this review highlights advances within this field with particular emphasis upon the development and specificity of second mitochondria-derived activator of caspase (SMAC) mimetics (synthetic analogs of endogenously expressed inhibitors of IAPs SMAC/DIABLO). While we highlight the potential of SMAC mimetics as effective single agent or combinatory therapies to treat cancer we also discuss the likely clinical implications of resistance to SMAC mimetic therapy, occasionally observed in cancer cell lines.

IAP Antagonists Enhance Cytokine Production from Mouse and Human iNKT Cells

Inhibitor of apoptosis protein (IAP) antagonists are in clinical trials for a variety of cancers, and mouse models show synergism between IAP antagonists and anti-PD-1 immunotherapy. Although IAP antagonists affect the intrinsic signaling of tumor cells, their most pronounced effects are on immune cells and the generation of antitumor immunity. Here, we examined the effects of IAP antagonism on T-cell development using mouse fetal thymic organ culture and observed a selective loss of iNKT cells, an effector cell type of potential importance for cancer immunotherapy. Thymic iNKT-cell development probably failed due to increased strength of TCR signal leading to negative selection, given that mature iNKT cells treated with IAP antagonists were not depleted, but had enhanced cytokine production in both mouse and human ex vivo cultures. Consistent with this, mature mouse primary iNKT cells and iNKT hybridomas increased production of effector cytokines in the presence of IAP antagonists. In vivo administration of IAP antagonists and α-GalCer resulted in increased IFNγ and IL-2 production from iNKT cells and decreased tumor burden in a mouse model of melanoma lung metastasis. Human iNKT cells also proliferated and increased IFNγ production dramatically in the presence of IAP antagonists, demonstrating the utility of these compounds in adoptive therapy of iNKT cells. Cancer Immunol Res; 6(1); 25-35. ©2017 AACR.

KATP channel block inhibits the Toll-like receptor 2-mediated stimulation of NF-κB by suppressing the activation of Akt, mTOR, JNK and p38-MAPK

Changes in the K_ATP channel activity have been shown to regulate inflammation and immune responses. Using human keratinocytes, we investigated the effect of K_ATP channel inhibition on inflammatory mediator production in relation to the Toll like receptor-2-mediated-Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK, which regulate the transcription genes involved in immune and inflammatory responses. 5-Hydroxydecanoate (a selective K_ATP channel blocker), glibenclamide (a cell surface and mitochondrial K_ATP channel inhibitor), the Akt inhibitor, rapamycin, Bay 11-7085 and N-acetylcysteine reduced the lipoteichoic acid- or peptidoglycan-induced production of cytokines and chemokines, and production of reactive oxygen species and increased the levels and activities of Kir 6.2, NF-κB, phosphorylated-Akt and mTOR, and the activation of JNK and p38-MAPK in keratinocytes. Inhibitors of c-JNK (SP600125) and p38-MAPK (SB203580) attenuated the lipoteichoic acid- or peptidoglycan-induced production of inflammatory mediators, the activation of the JNK and p38-MAPK, and the production of reactive oxygen species in keratinocytes. The results show that K_ATP channel blockers may reduce the bacterial component-stimulated production of inflammatory mediators in keratinocytes by suppressing the Toll-like receptor-2-mediated activation of the Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK. The suppressive effect of K_ATP channel blockers appears to be achieved by the inhibition of reactive oxygen species production.

TNF-related apoptosis-inducing ligand (TRAIL) for bone sarcoma treatment: Pre-clinical and clinical data

Bone sarcomas are rare, highly malignant mesenchymal tumours that affect teenagers and young adults, as well as older patients. Despite intensive, multimodal therapy, patients with bone sarcomas have poor 5-year survival, close to 50%, with lack of improvement over recent decades. TNF-related apoptosis-inducing ligand (TRAIL), a member of the tumour necrosis factor (TNF) ligand superfamily (TNFLSF), has been found to induce apoptosis in cancer cells while sparing nontransformed cells, and may therefore offer a promising new approach to treatment. We cover the existing preclinical and clinical evidence about the use of TRAIL and other death receptor agonists in bone sarcoma treatment. In vitro studies indicate that TRAIL and other death receptor agonists are generally potent against bone sarcoma cell lines. Ewing's sarcoma cell lines present the highest sensitivity, whereas osteosarcoma and chondrosarcoma cell lines are considered less sensitive. In vivo studies also demonstrate satisfactory results, especially in Ewing's sarcoma xenograft models. However, the few clinical trials in the literature show only low or moderate efficacy of TRAIL in treating bone sarcoma. Potential strategies to overcome the in vivo resistance reported include co-administration with other drugs and the potential to deliver TRAIL on the surface of primed mesenchymal or immune cells and the use of targeted single chain antibodies such as scFv-scTRAIL.

IAP antagonists sensitize murine osteosarcoma cells to killing by TNFα

Outcomes for patients diagnosed with the bone cancer osteosarcoma have not improved significantly in the last four decades. Only around 60% of patients and about a quarter of those with metastatic disease survive for more than five years. Although DNA-damaging chemotherapy drugs can be effective, they can provoke serious or fatal adverse effects including cardiotoxicity and therapy-related cancers. Better and safer treatments are therefore needed. We investigated the anti-osteosarcoma activity of IAP antagonists (also known as Smac mimetics) using cells from primary and metastatic osteosarcomas that arose spontaneously in mice engineered to lack p53 and Rb expression in osteoblast-derived cells. The IAP antagonists SM-164, GDC-0152 and LCL161, which efficiently target XIAP and cIAPs, sensitized cells from most osteosarcomas to killing by low levels of TNFα but not TRAIL. RIPK1 expression levels and activity correlated with sensitivity. RIPK3 levels varied considerably between tumors and RIPK3 was not required for IAP antagonism to sensitize osteosarcoma cells to TNFα. IAP antagonists, including SM-164, lacked mutagenic activity. These data suggest that drugs targeting XIAP and cIAP1/2 may be effective for osteosarcoma patients whose tumors express abundant RIPK1 and contain high levels of TNFα, and would be unlikely to provoke therapy-induced cancers in osteosarcoma survivors.

TRAIL Promotes Tumor Growth in a Syngeneic Murine Orthotopic Pancreatic Cancer Model and Affects the Host Immune Response

OBJECTIVES

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is currently being evaluated as a possible biological agent for cancer treatment. However, many tumor cells are resistant to TRAIL-induced apoptosis. In these cases, TRAIL may activate different pathways promoting tumor growth as well as showing different interactions with the immunological tumor microenvironment. In this study, the impact of TRAIL on tumor growth and survival in a syngeneic model of TRAIL-resistant pancreatic cancer cells was investigated.

METHODS

Murine 6606PDA pancreatic cancer cells were injected into the pancreatic heads of TRAIL mice and their littermates. To examine a direct effect of TRAIL on tumor cells, cultures of 6606PDA were TRAIL stimulated.

RESULTS

The TRAIL mice displayed significantly decreased tumor volumes and an enhanced overall survival in pancreatic cancer. The decreased tumor growth in TRAIL mice was accompanied by a decrease of regulatory CD4 cells within tumors. Concordantly, TRAIL treatment of wild-type mice enhanced tumor growth and increased the fraction of regulatory CD4 cells. Yet, a direct effect of TRAIL on 6606PDA cells was not detected.

CONCLUSIONS

Thus, TRAIL can promote tumor growth in TRAIL-resistant tumor cells. This may restrict possible future clinical applications of TRAIL in pancreatic cancer.

Potential of apoptotic pathway-targeted cancer therapeutic research: Where do we stand?

Underneath the intricacy of every cancer lies mysterious events that impel the tumour cell and its posterity into abnormal growth and tissue invasion. Oncogenic mutations disturb the regulatory circuits responsible for the governance of versatile cellular functions, permitting tumour cells to endure deregulated proliferation, resist to proapoptotic insults, invade and erode normal tissues and above all escape apoptosis. This disruption of apoptosis has been highly implicated in various malignancies and has been exploited as an anticancer strategy. Owing to the fact that apoptosis causes minimal inflammation and damage to the tissue, apoptotic cell death-based therapy has been the centre of attraction for the development of anticancer drugs. Increased understanding of the molecular pathways underlying apoptosis has enabled scientists to establish unique approaches targeting apoptosis pathways in cancer therapeutics. In this review, we reconnoitre the two major pathways (intrinsic and extrinsic) targeted cancer therapeutics, steering toward chief modulators of these pathways, such as B-cell lymphoma 2 protein family members (pro- and antiapoptotic), inhibitor of apoptosis proteins, and the foremost thespian of extrinsic pathway regulator, tumour necrosis factor-related apoptosis-inducing agent. Together, we also will have a look from clinical perspective to address the agents (drugs) and therapeutic strategies adopted to target these specific proteins/pathways that have entered clinical trials.

Molecular mechanisms of apoptosis and roles in cancer development and treatment

Programmed cell death (PCD) or apoptosis is a mechanism which is crucial for all multicellular organisms to control cell proliferation and maintain tissue homeostasis as well as eliminate harmful or unnecessary cells from an organism. Defects in the physiological mechanisms of apoptosis may contribute to different human diseases like cancer. Identification of the mechanisms of apoptosis and its effector proteins as well as the genes responsible for apoptosis has provided a new opportunity to discover and develop novel agents that can increase the sensitivity of cancer cells to undergo apoptosis or reset their apoptotic threshold. These novel targeted therapies include those targeting anti-apoptotic Bcl-2 family members, p53, the extrinsic pathway, FLICE-inhibitory protein (c-FLIP), inhibitor of apoptosis (IAP) proteins, and the caspases. In recent years a number of these novel agents have been assessed in preclinical and clinical trials. In this review, we introduce some of the key regulatory molecules that control the apoptotic pathways, extrinsic and intrinsic death receptors, discuss how defects in apoptotic pathways contribute to cancer, and list several agents being developed to target apoptosis.

Carbon-ion beams effectively induce growth inhibition and apoptosis in human neural stem cells compared with glioblastoma A172 cells

Carbon-ion radiotherapy (CIRT) holds promise in the treatment of glioblastoma, an aggressive X-ray-resistant brain tumor. However, since glioblastoma cells show a highly invasive nature, carbon-ion (C-ion) irradiation of normal tissues surrounding the tumor is inevitable. Recent studies have revealed the existence of neural stem cells in the adult brain. Therefore, the damaging effect of C-ion beams on the neural stem cells has to be carefully considered in the treatment planning of CIRT. Here, we investigated the growth and death mode of human neural stem cells (hNSCs) and glioblastoma A172 cells after X-ray or C-ion beam irradiation. The X-ray dose resulting in a 50% growth rate (D(50)) was 0.8 Gy in hNSCs and 3.0 Gy in A172 cells, while the D(50) for C-ion beams was 0.4 Gy in hNSCs and 1.6 Gy in A172 cells; the relative biological effectiveness value of C-ion beams was 2.0 in hNSCs and 1.9 in A172 cells. Importantly, both X-rays and C-ion beams preferentially induced apoptosis, not necrosis, in hNSCs; however, radiation-induced apoptosis was less evident in A172 cells. The apoptosis-susceptible nature of the irradiated hNSCs was associated with prolonged upregulation of phosphorylated p53, whereas the apoptosis-resistant nature of A172 cells was associated with a high basal level of nuclear factor kappa B expression. Taken together, these data indicate that apoptosis is the major cell death pathway in hNSCs after irradiation. The high sensitivity of hNSCs to C-ion beams underscores the importance of careful target volume delineation in the treatment planning of CIRT for glioblastoma.

3,4,5-Tricaffeoylquinic Acid Attenuates TRAIL-induced Apoptosis in Human Keratinocytes by Suppressing Apoptosis-related Protein Activation

Caffeoyl derivatives exhibit antiinflammatory and antioxidant effects. However, the effect of 3,4,5-tricaffeoylquinic acid on the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in keratinocytes that may be involved in skin diseases has not been studied. In this respect, we investigated the effect of 3,4,5-tricaffeoylquinic acid on TRAIL-induced apoptosis in human keratinocytes. 3,4,5-Tricaffeoylquinic acid and oxidant scavengers attenuated the decrease in the cytosolic levels of Bid, Bcl-2, and survivin proteins; the increase in the levels of cytosolic Bax, p53, and phosphorylated p53; the increase in the levels of phosphorylated p38; the increase in the mitochondrial levels of the voltage-dependent anion channel; loss of the mitochondrial transmembrane potential; the release of cytochrome c; activation of caspases (8, 9, and 3); cleavage of poly [ADP-ribose] polymerase-1; production of reactive oxygen species; the depletion of glutathione (GSH); nuclear damage; and cell death in keratinocytes treated with TRAIL. These results suggest that 3,4,5-tricaffeoylquinic acid may reduce TRAIL-induced apoptosis in human keratinocytes by suppressing the activation of the caspase-8 and Bid pathways and the mitochondria-mediated cell death pathway. The effect appears to be associated with the inhibitory effect on the production of reactive oxygen species and depletion of GSH. 3,4,5-Tricaffeoylquinic acid appears to be effective in the prevention of TRAIL-induced apoptosis-mediated skin diseases.

High levels of X-linked Inhibitor-of-Apoptosis Protein (XIAP) are indicative of radio chemotherapy resistance in rectal cancer

BACKGROUND

The mainstay of treatment in rectal cancer is neoadjuvant radio chemotherapy prior to surgery, in an attempt to downstage the tumour, allowing for more complete removal during surgery. In 40 % of cases however, this neoadjuvant radio chemotherapy fails to achieve tumour regression, partly due insufficient apoptosis signaling. X-linked Inhibitor of Apoptosis Protein (XIAP) is an anti-apoptotic protein that has been reported to contribute to disease progression and chemotherapy resistance.

METHODS

We obtained rectal biopsy normal and matched tumour tissue from 29 rectal cancer patients with varying degrees of tumour regression, and using Western blot, examined anti-apoptotic XIAP and pro-apoptotic Smac protein levels in these tissues, with the aim to examine whether disturbed XIAP/Smac levels may be an indicator of neoadjuvant radio chemotherapy resistance. Expression of inhibitor of apoptosis proteins cIAP-1 and cIAP-2 was also examined.

RESULTS

We found that levels of XIAP increased in accordance with the degree of radio chemotherapy resistance of the tissue. Levels of this protein were also significantly higher in tumour tissue, compared to matched normal tissue in highly resistant tissue. In contrast, Smac protein levels did not increase with radio chemotherapy resistance, and the protein was similarly expressed in normal and tumour tissue, indicating a shift in the balance of these proteins. Post treatment surgical resection tissue was available for 8 patients. When we compared matched tissue pre- and post- radio chemotherapy we found that XIAP levels increased significantly during treatment in both normal and tumour tissue, while Smac levels did not change. cIAP-1 and cIAP-2 levels were not differentially expressed in varying degrees of radio chemotherapy resistance, and neoadjuvant therapy did not alter expression of these proteins.

CONCLUSION

These data indicate that disturbance of the XIAP/Smac balance may be a driver of radio chemotherapy resistance, and hence high levels of XIAP may be a useful indicator of neoadjuvant radio chemotherapy resistance in rectal cancer. Moreover, as XIAP levels increase with radio chemotherapy it is possible that a subset of more resistant tumour cells survive this treatment and may be resistant to further adjuvant treatment. Patients with resistant tumours highly expressing XIAP may benefit from alternative treatment strategies, such as Smac mimetics post neoadjuvant radio chemotherapy.

Mechanism of Arctigenin-Induced Specific Cytotoxicity against Human Hepatocellular Carcinoma Cell Lines: Hep G2 and SMMC7721

Arctigenin (ARG) has been previously reported to exert high biological activities including anti-inflammatory, antiviral and anticancer. In this study, the anti-tumor mechanism of ARG towards human hepatocellular carcinoma (HCC) was firstly investigated. We demonstrated that ARG could induce apoptosis in Hep G2 and SMMC7721 cells but not in normal hepatic cells, and its apoptotic effect on Hep G2 was stronger than that on SMMC7721. Furthermore, the following study showed that ARG treatment led to a loss in the mitochondrial out membrane potential, up-regulation of Bax, down-regulation of Bcl-2, a release of cytochrome c, caspase-9 and caspase-3 activation and a cleavage of poly (ADP-ribose) polymerase in both Hep G2 and SMMC7721 cells, suggesting ARG-induced apoptosis was associated with the mitochondria mediated pathway. Moreover, the activation of caspase-8 and the increased expression levels of Fas/FasL and TNF-α revealed that the Fas/FasL-related pathway was also involved in this process. Additionally, ARG induced apoptosis was accompanied by a deactivation of PI3K/p-Akt pathway, an accumulation of p53 protein and an inhibition of NF-κB nuclear translocation especially in Hep G2 cells, which might be the reason that Hep G2 was more sensitive than SMMC7721 cells to ARG treatment.

Overcoming tumor immune evasion with an unique arbovirus

Combining dendritic cell vaccination with the adjuvant effect of a strain of dengue virus may be a way to overcome known tumor immune evasion mechanisms. Dengue is unique among viruses as primary infections carry lower mortality than the common cold, but secondary infections carry significant risk of hypovolemic shock. While current immuno-therapies rely on a single axis of attack, this approach combines physiological (hyperthermic reduction of tumor perfusion), immunological (activation of effector cells of the adaptive and innate immune system), and apoptosis-inducing pathways (sTRAIL) to destroy tumor cells. The premise of using multiple mechanisms of action in synergy with a decline in the ability of the tumor cells to employ resistance methods suggests the potential of this combination approach in cancer immunotherapy.

Bortezomib sensitizes non-small cell lung cancer to mesenchymal stromal cell-delivered inducible caspase-9-mediated cytotoxicity

Delivery of suicide genes to solid tumors represents a promising tumor therapy strategy. However, slow or limited killing by suicide genes and ineffective targeting of the tumor has reduced effectiveness. We have adapted a suicide system based on an inducible caspase-9 (iC9) protein that is activated using a specific chemical inducer of dimerization (CID) for adenoviral-based delivery to lung tumors via mesenchymal stromal cells (MSCs). Four independent human non-small cell lung cancer (NSCLC) cell lines were transduced with adenovirus encoding iC9, and all underwent apoptosis when iC9 was activated by adding CID. However, there was a large variation in the percentage of cell killing induced by CID across the different lines. The least responsive cell lines were sensitized to apoptosis by combined inhibition of the proteasome using bortezomib. These results were extended to an in vivo model using human NSCLC xenografts. E1A-expressing MSCs replicated Ad.iC9 and delivered the virus to lung tumors in SCID mice. Treatment with CID resulted in some reduction of tumor growth, but addition of bortezomib led to greater reduction of tumor size. The enhanced apoptosis and anti-tumor effect of combining MSC-delivered Ad.iC9, CID and bortezomib appears to be due to increased stabilization of active caspase-3, as proteasomal inhibition increased the levels of cleaved caspase-9 and caspase-3. Knockdown of X-linked inhibitor of apoptosis protein (XIAP), a caspase inhibitor that targets active caspase-3 to the proteasome, also sensitized iC9-transduced cells to CID, suggesting that blocking the proteasome counteracts XIAP to permit apoptosis. Thus, MSC-based delivery of the iC9 suicide gene to human NSCLC effectively targets lung cancer cells for elimination. Combining this therapy with bortezomib, a drug that is otherwise inactive in this disease, further enhances the anti-tumor activity of this strategy.

Differential response of head and neck cancer cell lines to TRAIL or Smac mimetics is associated with the cellular levels and activity of caspase-8 and caspase-10

Background:

Current treatment strategies for head and neck cancer are associated with significant morbidity and up to 50% of patients relapse, highlighting the need for more specific and effective therapeutics. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) and Smac mimetics (SMs) are promising anticancer agents, but their effect on head and neck squamous cell carcinoma (HNSCC) remains unknown.

Methods:

We examined the response of a panel of nine HNSCC cell lines to TRAIL and SMs and investigated the mechanism of cell type-specific response by functional analysis.

Results:

Head and neck cancer cell lines revealed a converse response pattern with three cell lines being highly sensitive to Smac-164 (SM) but resistant to TRAIL, whereas the other six were sensitive to TRAIL but resistant to SM. Distinct protein expression and activation patterns were found to be associated with susceptibility of HNSCC cell lines to TRAIL and SM. Tumour necrosis factor-related apoptosis-inducing ligand sensitivity was associated with high caspase-8 and Bid protein levels, and TRAIL-sensitive cell lines were killed via the type II extrinsic apoptotic pathway. Smac mimetic-sensitive cells expressed low levels of caspase-8 and Bid but had high TNF-α expression. Smac mimetic-induced cell death was associated with caspase-10 activation, suggesting that in the absence of caspase-8, caspase-10 mediates response to SM. Cotreatment with TNF-α sensitised the resistant cells to SM, demonstrating a decisive role for TNF-α-driven feedback loop in SM sensitivity.

Conclusions:

Tumour necrosis factor-related apoptosis-inducing ligand and SMs effectively kill HNSCC cell lines and therefore represent potential targeted therapeutics for head and neck cancer. Distinct molecular mechanisms determine the sensitivity to each agent, with levels of TNF-α, caspase-8, Bid and caspase-10 providing important predictive biomarkers of response to these agents.

Rotundarpene prevents TRAIL-induced apoptosis in human keratinocytes by suppressing the caspase-8- and Bid-pathways and the mitochondrial pathway

The extract and hemiterpene glycosides of Ilex rotunda Thunb have demonstrated antioxidant and anti-inflammatory effects. Nevertheless, the effect of rotundarpene on the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis in keratinocytes that may be involved in skin diseases has not been studied. In this respect, we investigated the effect of rotundarpene on TRAIL-induced apoptosis in human keratinocytes. TRAIL triggers apoptosis by inducing a decrease in the cytosolic levels of Bid, Bcl-2, Bcl-xL, and survivin proteins, increase in the cytosolic levels of Bax, and increase in the mitochondrial levels of VDAC1, loss of the mitochondrial transmembrane potential, release of cytochrome c, activation of caspases (-8, -9, and -3), cleavage of PARP-1, and an increase in the tumor suppressor p53 levels. Treatment with rotundarpene prevented TRAIL-induced changes in the levels of apoptosis-related proteins, formations of reactive oxygen species and nitric oxide, nuclear damage, and cell death. These results suggest that rotundarpene may reduce TRAIL-induced apoptosis in human keratinocytes by suppressing the activation of the caspase-8- and Bid-pathways and the mitochondria-mediated cell death pathway, which is associated with the formation of reactive oxygen species and reactive nitrogen species. These data suggest that rotundarpene appears to be effective in the prevention of TRAIL-induced apoptosis-mediated skin diseases.

Identification of DR5 as a critical, NF-κB-regulated mediator of Smac-induced apoptosis

Smac mimetic promotes apoptosis by neutralizing inhibitor of apoptosis (IAP) proteins and is considered as a promising cancer therapeutic. Although an autocrine/paracrine tumor necrosis factor-α (TNFα) loop has been implicated in Smac mimetic-induced cell death, little is yet known about additional factors that determine sensitivity to Smac mimetic. Using genome-wide gene expression analysis, we identify death receptor 5 (DR5) as a novel key mediator of Smac mimetic-induced apoptosis. Although several cell lines that are sensitive to the Smac mimetic BV6 die in a TNFα-dependent manner, A172 glioblastoma cells undergo BV6-induced apoptosis largely independently of TNFα/TNFR1, as the TNFα-blocking antibody Enbrel or TNFR1 knockdown provide little protection. Yet, BV6-stimulated nuclear factor-κB (NF-κB) activation is critically required for apoptosis, as inhibition of NF-κB by overexpression of dominant-negative IκBα superrepressor (IκBα-SR) blocks BV6-induced apoptosis. Unbiased genome-wide gene expression studies in IκBα-SR-overexpressing cells versus vector control cells reveal that BV6 increases DR5 expression in a NF-κB-dependent manner. Importantly, this BV6-stimulated upregulation of DR5 is critically required for apoptosis, as transient or stable knockdown of DR5 significantly inhibits BV6-triggered apoptosis. In addition, DR5 silencing attenuates formation of a RIP1/FADD/caspase-8 cytosolic cell death complex and activation of caspase-8, -3 and -9. By identifying DR5 as a critical mediator of Smac mimetic-induced apoptosis, our findings provide novel insights into the determinants that control susceptibility of cancer cells to Smac mimetic.

IAPs on the move: role of inhibitors of apoptosis proteins in cell migration

Inhibitors of Apoptosis Proteins (IAPs) are a class of highly conserved proteins predominantly known for the regulation of caspases and immune signaling. However, recent evidence suggests a crucial role for these molecules in the regulation of tumor cell shape and migration by controlling MAPK, NF-κB and Rho GTPases. IAPs directly control Rho GTPases, thus regulating cell shape and migration. For instance, XIAP and cIAP1 function as the direct E3 ubiquitin ligases of Rac1 and target it for proteasomal degradation. IAPs are differentially expressed in tumor cells and have been targeted by several cancer therapeutic drugs that are currently in clinical trials. Here, we summarize the current knowledge on the role of IAPs in the regulation of cell migration and discuss the possible implications of these observations in regulating tumor cell metastases.

Physiologically based pharmacokinetic and pharmacodynamic modeling of an antagonist (SM-406/AT-406) of multiple inhibitor of apoptosis proteins (IAPs) in a mouse xenograft model of human breast cancer

The inhibitors of apoptosis proteins (IAPs) are a class of key apoptosis regulators overexpressed or dysregulated in cancer. SM-406/AT-406 is a potent and selective small molecule mimetic of Smac that antagonizes the inhibitor of apoptosis proteins (IAPs). A physiologically based pharmacokinetic and pharmacodynamic (PBPK-PD) model was developed to predict the tissue concentration-time profiles of SM-406, the related onco-protein levels in tumor, and the tumor growth inhibition in a mouse model bearing human breast cancer xenograft. In the whole body physiologically based pharmacokinetic (PBPK) model for pharmacokinetics characterization, a well stirred (perfusion rate-limited) model was used to describe SM-406 pharmacokinetics in the lung, heart, kidney, intestine, liver and spleen, and a diffusion rate-limited (permeability limited) model was used for tumor. Pharmacodynamic (PD) models were developed to correlate the SM-406 concentration in tumor to the cIAP1 degradation, pro-caspase 8 decrease, CL-PARP accumulation and tumor growth inhibition. The PBPK-PD model well described the experimental pharmacokinetic data, the pharmacodynamic biomarker responses and tumor growth. This model may be helpful to predict tumor and plasma SM-406 concentrations in the clinic.

Licochalcone A enhances geldanamycin-induced apoptosis through reactive oxygen species-mediated caspase activation

BACKGROUND AND PURPOSE

Geldanamycin and licochalcone A induce apoptosis in cancer cells. However, whether the combination of geldanamycin and licochalcone A-induced apoptosis in epithelial ovarian cancer cells is mediated by the formation of reactive oxygen species, leading to the activation of apoptotic caspase, has not been studied.

EXPERIMENTAL APPROACH

Using the human epithelial ovarian carcinoma cell lines OVCAR-3 and SK-OV-3, we investigated the promoting effect of licochalcone A on geldanamycin-induced apoptosis.

RESULTS

Geldanamycin induced changes in apoptosis-related protein levels, loss of the mitochondrial transmembrane potential, release of cytochrome c, activation of caspases, cleavage of PARP-1, formation of reactive oxygen species and depletion of glutathione (GSH). Licochalcone A enhanced geldanamycin-induced apoptosis-related protein activation, formation of reactive oxygen species, caspase activation and cell death. The combined effect was inhibited by the addition of oxidant scavengers.

CONCLUSIONS

Licochalcone A may potentiate the apoptotic effect of geldanamycin on ovarian carcinoma cell lines by the activation of the caspase-8- and Bid-dependent pathways and the mitochondria-mediated apoptotic pathway. The apoptosis-promoting effect of licochalcone A may be mediated by its stimulatory action on the formation of reactive oxygen species and the depletion of GSH, which results in the activation of caspases.

Brefeldin a induces apoptosis by activating the mitochondrial and death receptor pathways and inhibits focal adhesion kinase-mediated cell invasion

Brefeldin A induces apoptosis in various cancer cells; however, the apoptotic process in cancer cells exposed to brefeldin A remains unclear. In addition, it is unclear whether brefeldin A-induced apoptosis is mediated by the formation of reactive oxygen species. Furthermore, the effect of brefeldin A on the invasion and migration of human epithelial ovarian cancer cells has not been studied. Therefore, we investigated the effect of brefeldin A on apoptosis, cell adhesion and migration using the human epithelial ovarian carcinoma cell lines OVCAR-3 and SK-OV-3. The results suggest that brefeldin A may induce apoptotic cell death in ovarian carcinoma cell lines by activating the mitochondrial pathway and the caspase-8- and Bid-dependent pathways. The apoptotic effect of brefeldin A seems to be mediated by formation of reactive oxygen species and depletion of GSH, which results in the activation of apoptotic caspases. Brefeldin A inhibited foetal bovine serum-induced adhesion and migration of OVCAR-3 cells. Brefeldin A may prevent the foetal bovine serum-induced cell adhesion and migration by limiting the focal adhesion kinase-dependent activation of cytoskeletal-associated components.

Inhibitor of apoptosis protein (IAP) antagonists demonstrate divergent immunomodulatory properties in human immune subsets with implications for combination therapy

Inhibitor of apoptosis proteins (IAPs) are critical in regulating apoptosis resistance in cancer. Antagonists of IAPs, such as LCL161, are in clinical development and show promise as anti-cancer agents for solid and hematological cancers, with preliminary data suggesting they may act as immunomodulators. IAP antagonists hypersensitize tumor cells to TNF-α-mediated apoptosis, an effect that may work in synergy with that of cancer vaccines. This study aimed to further investigate the immunomodulatory properties of LCL161 on human immune subsets. T lymphocytes treated with LCL161 demonstrated significantly enhanced cytokine secretion upon activation, with little effect on CD4 and CD8 T-cell survival or proliferation. LCL161 treatment of peripheral blood mononuclear cells significantly enhanced priming of naïve T cells with synthetic peptides in vitro. Myeloid dendritic cells underwent phenotypic maturation upon IAP antagonism and demonstrated a reduced capacity to cross-present a tumor antigen-based vaccine. These effects are potentially mediated through an observed activation of the canonical and non-canonical NF-κB pathways, following IAP antagonism with a resulting upregulation of anti-apoptotic molecules. In conclusion, this study demonstrated the immunomodulatory properties of antagonists at physiologically relevant concentrations and indicates their combination with immunotherapy requires further investigation.

Ethanol promotes cytotoxic effects of tumor necrosis factor-related apoptosis-inducing ligand through induction of reactive oxygen species in prostate cancer cells

BACKGROUND

Effective treatment of prostate cancer (PCa) remains a major challenge due to chemoresistance to drugs including tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Ethanol and ethanol extracts are known apoptosis inducers. However, cytotoxic effects of ethanol on PCa cells are unclear.

METHODS

In this study we utilized PC3 and LNCaP cell culture models. We used immunohistochemical analysis, western blot analysis, reactive oxygen species (ROS) measurement, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) Cell Proliferation Assay, Annexin-V staining and flow cytometry for quantification of apoptosis. In vitro soft agar colony formation and Boyden chamber invasion assays were used. Tumorigenicity was measured in a xenotransplantation mouse model.

RESULTS

Here, we demonstrate that ethanol enhances the apoptosis-inducing potential of TRAIL in androgen-resistant PC3 cells and sensitizes TRAIL-resistant, androgen sensitive LNCaP cells to apoptosis through caspase activation, and a complete cleavage of poly (ADP)-ribose polymerase, which was in association with increased production of ROS. The cytotoxicity of ethanol was suppressed by an antioxidant N-acetyl cystein pretreatment. Furthermore, ethanol in combination with TRAIL increased the expression of cyclin-dependent kinase inhibitor p21 and decreased the levels of Bcl-2 and phosphorylated-AKT. These molecular changes were accompanied by decreased proliferation, anchorage-independent growth and invasive potential of PC3 and LNCaP cells. In vivo studies using a xenotransplantation mouse model with PC3 cells demonstrated significantly increased apoptosis in tumors treated with ethanol and TRAIL in combination.

CONCLUSIONS

Taken together, use of ethanol in combination with TRAIL may be an effective strategy to augment sensitivity to TRAIL-induced apoptosis in PCa cells.

A small molecule SMAC mimic LBW242 potentiates TRAIL- and anticancer drug-mediated cell death of ovarian cancer cells

Background

Ovarian cancer remains a leading cause of death in women and development of new therapies is essential. Second mitochondria derived activator of caspase (SMAC) has been described to sensitize for apoptosis. We have explored the pro-apoptotic activity of LBW242, a mimic of SMAC/DIABLO, on ovarian cancer cell lines (A2780 cells and its chemoresistant derivative A2780/ADR, SKOV3 and HEY cells) and in primary ovarian cancer cells. The effects of LBW242 on ovarian cancer cell lines and primary ovarian cancer cells was determined by cell proliferation, apoptosis and biochemical assays.

Principal Findings

LBW242 added alone elicited only a moderate pro-apoptotic effect; however, it strongly synergizes with tumor necrosis factor-related apoptosis inducing ligand (TRAIL) or anticancer drugs in inducing apoptosis of both ovarian cancer cell lines and primary ovarian cancer cells. Mechanistic studies show that LBW242-induced apoptosis in ovarian cancer cells is associated with activation of caspase-8. In line with this mechanism, c-FLIP overexpression inhibits LBW242-mediated apoptosis.

Conclusion

LBW242 sensitizes ovarian cancer cells to the antitumor effects of TRAIL and anticancer drugs commonly used in clinic. These observations suggest that the SMAC/DIABLO mimic LBW242 could be of value for the development of experimental strategies for treatment of ovarian cancer.

Combined effect of Hsp90 inhibitor geldanamycin and parthenolide via reactive oxygen species-mediated apoptotic process on epithelial ovarian cancer cells

Hsp90 inhibitor geldanamycin and parthenolide have been shown to induce apoptosis in cancer cells. However, the combined effect of geldanamycin and parthenolide on epithelial ovarian cancer cells has not been studied. In respect of cell death process, we investigated the promoting effect of parthenolide on geldanamycin-induced apoptosis in the human epithelial ovarian carcinoma cell lines OVCAR-3 and SK-OV-3. Geldanamycin induced a decrease in Bid, Bcl-2, Bcl-xL and survivin protein levels; an increase in Bax and tumour suppressor p53 levels; loss of the mitochondrial transmembrane potential; cytochrome c release; activation of caspases (-8, -9 and -3); cleavage of PARP-1; and increase in the reactive oxygen species formation. Parthenolide enhanced geldanamycin-induced changes in the apoptosis-related protein levels, reactive oxygen species formation, nuclear damage and cell death. The combined effect was inhibited by the addition of oxidant scavengers. The results suggest that parthenolide may potentiate the apoptotic effect of geldanamycin on ovarian carcinoma cell lines by the activation of the caspase-8- and Bid-dependent pathway and the mitochondria-mediated apoptotic pathway. The apoptosis-promoting effect seems to be mediated by the stimulatory effect on the formation of reactive oxygen species.

Guanylate cyclase activator YC-1 potentiates apoptotic effect of licochalcone A on human epithelial ovarian carcinoma cells via activation of death receptor and mitochondrial pathways

Natural phenol licorice compounds have been shown to induce apoptosis in cancer cells. 3-(5'-Hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) may enhance the sensitivity of cancer cells to anticancer drugs. However, the combined effect of licochalcone A and YC-1 on cell death in ovarian cancer cells has not been studied. We assessed the combined effect of licochalcone A and YC-1 on apoptosis in human epithelial ovarian carcinoma cell lines in relation to the cell death process. In the OVCAR-3 and SK-OV-3 cell lines, licochalocone A induced a decrease in Bid, Bcl-2, Bcl-xL and survivin protein levels; an increase in Bax levels; loss of the mitochondrial transmembrane potential; cytochrome c release; activation of caspases (-8, -9 and -3); cleavage of PARP-1; and an increase in the tumor suppressor p53 levels. YC-1 enhanced licochalcone A-induced apoptosis-related protein activation, nuclear damage and cell death. These results suggest that YC-1 may potentiate the apoptotic effect of licochalcone A on ovarian carcinoma cell lines by increasing the activation of the caspase-8- and Bid-dependent pathway and the mitochondria-mediated apoptotic pathway, leading to caspase activation. The combination of licochalcone A and YC-1 may confer a benefit in the treatment of human epithelial ovarian adenocarcinoma.

Targeting IAP proteins for therapeutic intervention in cancer

Evasion of apoptosis is one of the crucial acquired capabilities used by cancer cells to fend off anticancer therapies. Inhibitor of apoptosis (IAP) proteins exert a range of biological activities that promote cancer cell survival and proliferation. X chromosome-linked IAP is a direct inhibitor of caspases - pro-apoptotic executioner proteases - whereas cellular IAP proteins block the assembly of pro-apoptotic protein signalling complexes and mediate the expression of anti-apoptotic molecules. Furthermore, mutations, amplifications and chromosomal translocations of IAP genes are associated with various malignancies. Among the therapeutic strategies that have been designed to target IAP proteins, the most widely used approach is based on mimicking the IAP-binding motif of second mitochondria-derived activator of caspase (SMAC), which functions as an endogenous IAP antagonist. Alternative strategies include transcriptional repression and the use of antisense oligonucleotides. This Review provides an update on IAP protein biology as well as current and future perspectives on targeting IAP proteins for therapeutic intervention in human malignancies.

Sorafenib sensitizes (-)-gossypol-induced growth suppression in androgen-independent prostate cancer cells via Mcl-1 inhibition and Bak activation

The natural BH3-mimetic (-)-gossypol shows promising efficacy in ongoing phase II/III clinical trials for human prostate cancer. Here, we show for the first time, that treatment with (-)-gossypol and multikinase inhibitor sorafenib synergistically suppresses the growth of androgen-independent prostate cancer cells (AI-PC) in vitro and in vivo. Our data suggest that sorafenib attenuates (-)-gossypol-induced Mcl-1 upregulation in AI-PCs. In this way, it serves as a potent chemosensitizer to affect cell death. Interestingly, (-)-gossypol and sorafenib induce cell death via two distinct pathways among different AI-PCs; DU145 cells via apoptosis and PC-3 via autophagy. The appointed death pathway may depend on the level of proapoptotic protein Bak, although the level of antiapoptotic protein Bcl-2 plays some role in it. DU145 cells with high Bak level prefer apoptosis induction, whereas PC-3 cells with low Bak prefer the induction of autophagy. Furthermore, inhibiting nondominant death pathways, that is, autophagy in DU145 and apoptosis in PC-3, enhances cell killing by (-)-gossypol/sorafenib combination therapy. Ultimately, our data expose a new action for sorafenib as an enhancer of (-)-gossypol-induced cell growth suppression and reveal a novel cell death mode by Bak activation manners in AI-PCs. These new insights may facilitate the rational design of clinical trials by selecting patients most likely to benefit from the Bcl-2-targeted molecular therapy.

Inhibitor of apoptosis proteins: fascinating biology leads to attractive tumor therapeutic targets

Cell death inhibition is a very successful strategy that cancer cells employ to combat the immune system and various anticancer therapies. Inhibitor of apoptosis (IAP) proteins possess a wide range of biological activities that promote cancer survival and proliferation. One of them, X-chromosome-linked IAP is a direct inhibitor of proapoptotic executioners, caspases. Cellular IAP proteins regulate expression of antiapoptotic molecules and prevent assembly of proapoptotic protein signaling complexes, while survivin regulates cell division. In addition, amplifications, mutations and chromosomal translocations of IAP genes are associated with various malignancies. Several therapeutic strategies have been designed to target IAP proteins, including a small-molecule approach that is based on mimicking the IAP-binding motif of an endogenous IAP antagonist - the second mitochondrial activator of caspases. Other strategies involve antisense nucleotides and transcriptional repression. The main focus of this article is to provide an update on IAP protein biology and perspectives on the development of IAP-targeting therapeutics.

Fas death receptor signalling: roles of Bid and XIAP

Fas (also called CD95 or APO-1), a member of a subgroup of the tumour necrosis factor receptor superfamily that contain an intracellular death domain, can initiate apoptosis signalling and has a critical role in the regulation of the immune system. Fas-induced apoptosis requires recruitment and activation of the initiator caspase, caspase-8 (in humans also caspase-10), within the death-inducing signalling complex. In so-called type 1 cells, proteolytic activation of effector caspases (-3 and -7) by caspase-8 suffices for efficient apoptosis induction. In so-called type 2 cells, however, killing requires amplification of the caspase cascade. This can be achieved through caspase-8-mediated proteolytic activation of the pro-apoptotic Bcl-2 homology domain (BH)3-only protein BH3-interacting domain death agonist (Bid), which then causes mitochondrial outer membrane permeabilisation. This in turn leads to mitochondrial release of apoptogenic proteins, such as cytochrome c and, pertinent for Fas death receptor (DR)-induced apoptosis, Smac/DIABLO (second mitochondria-derived activator of caspase/direct IAP binding protein with low Pi), an antagonist of X-linked inhibitor of apoptosis (XIAP), which imposes a brake on effector caspases. In this review, written in honour of Juerg Tschopp who contributed so much to research on cell death and immunology, we discuss the functions of Bid and XIAP in the control of Fas DR-induced apoptosis signalling, and we speculate on how this knowledge could be exploited to develop novel regimes for treatment of cancer.

Radicicol, an inhibitor of Hsp90, enhances TRAIL-induced apoptosis in human epithelial ovarian carcinoma cells by promoting activation of apoptosis-related proteins

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in various cancer cells. Hsp90 is known to be involved in cell survival and growth in tumor cells. Nevertheless, Hsp90 inhibitors exhibit a variable effect on the cytotoxicity of anticancer drugs. Furthermore, the combined effect of Hsp90 inhibitors on TRAIL-induced apoptosis in epithelial ovarian cancer cells has not been determined. To assess the ability of an inhibitor of Hsp90 inhibitor radicicol to promote apoptosis, we investigated the effect of radicicol on TRAIL-induced apoptosis in the human epithelial ovarian carcinoma cell lines OVCAR-3 and SK-OV-3. TRAIL induced a decrease in Bid, Bcl-2, Bcl-xL, and survivin protein levels, increase in Bax levels, loss of the mitochondrial transmembrane potential, cytochrome c release, activation of caspases (-8, -9, and -3), cleavage of PARP-1 and an increase in the tumor suppressor p53 levels. Radicicol enhanced TRAIL-induced apoptosis-related protein activation, nuclear damage and cell death. These results suggest that radicicol may potentiate the apoptotic effect of TRAIL on ovarian carcinoma cell lines by increasing the activation of the caspase-8- and Bid-dependent pathway and the mitochondria-mediated apoptotic pathway, leading to caspase activation. Radicicol may confer a benefit in the TRAIL treatment of epithelial ovarian adenocarcinoma.

TRAIL-mediated signaling in prostate, bladder and renal cancer

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is a death receptor ligand that has the ability to preferentially initiate apoptosis in malignant cells with minimal toxicity to normal cells. TRAIL-based therapeutics, including recombinant TRAIL, TRAIL-receptor agonistic antibodies and TRAIL gene therapy, have now entered clinical trials. Although these therapeutics are promising, concerns regarding TRAIL resistance are causing research efforts to shift towards the identification of effective combination therapies. Small-molecule inhibitors, natural compounds, and drugs approved for treatment of diseases other than cancer have been shown to affect TRAIL receptors, antiapoptotic proteins and survival pathways in prostate, bladder and renal cell lines and in preclinical models. Changes in endogenous TRAIL and TRAIL receptor expression during the development of genitourinary malignancies and the way in which the expression pattern is affected by treatment are of great interest, and understanding the biological consequences of such changes will be important to maximize the potential of TRAIL-based therapeutics.

Impact of hypoxia on the metastatic potential of human prostate cancer cells

PURPOSE

Intratumoral hypoxia is known to be associated with radioresistance and metastasis. The present study examined the effect of acute and chronic hypoxia on the metastatic potential of prostate cancer PC-3, DU145, and LNCaP cells.

METHODS AND MATERIALS

Cell proliferation and clonogenicity were tested by MTT assay and colony formation assay, respectively. "Wound-healing" and Matrigel-based chamber assays were used to monitor cell motility and invasion. Hypoxia-inducible factor 1 alpha (HIF-1α) expression was tested by Western blot, and HIF-1-target gene expression was detected by real-time polymerase chain reaction. Secretion of matrix metalloproteinases (MMPs) was determined by gelatin zymography.

RESULTS

When PC-3 cells were exposed to 1% oxygen (hypoxia) for various periods of time, chronic hypoxia (≥24 h) decreased cell proliferation and induced cell death. In contrast, prostate cancer cells exposed to acute hypoxia (≤6 h) displayed increased motility, clonogenic survival, and invasive capacity. At the molecular level, both hypoxia and anoxia transiently stabilized HIF-1α. Exposure to hypoxia also induced the early expression of MMP-2, an invasiveness-related gene. Treatment with the HIF-1 inhibitor YC-1 attenuated the acute hypoxia-induced migration, invasion, and MMP-2 activity.

CONCLUSIONS

The length of oxygen deprivation strongly affected the functional behavior of all three prostate cancer cell lines. Acute hypoxia in particular was found to promote a more aggressive metastatic phenotype.