Inhibition of Yin Yang 1-dependent repressor activity of DR5 transcription and expression by the novel proteasome inhibitor NPI-0052 contributes to its TRAIL-enhanced apoptosis in cancer cells

Cancer resistance via the downregulation of the tumor suppressors RKIP and PTEN expressions: therapeutic implications

The Raf kinase inhibitor protein (RKIP) has been reported to be underexpressed in many cancers and plays a role in the regulation of tumor cells' survival, proliferation, invasion, and metastasis, hence, a tumor suppressor. RKIP also regulates tumor cell resistance to cytotoxic drugs/cells. Likewise, the tumor suppressor, phosphatase and tensin homolog (PTEN), which inhibits the phosphatidylinositol 3 kinase (PI3K)/AKT pathway, is either mutated, underexpressed, or deleted in many cancers and shares with RKIP its anti-tumor properties and its regulation in resistance. The transcriptional and posttranscriptional regulations of RKIP and PTEN expressions and their roles in resistance were reviewed. The underlying mechanism of the interrelationship between the signaling expressions of RKIP and PTEN in cancer is not clear. Several pathways are regulated by RKIP and PTEN and the transcriptional and post-transcriptional regulations of RKIP and PTEN is significantly altered in cancers. In addition, RKIP and PTEN play a key role in the regulation of tumor cells response to chemotherapy and immunotherapy. In addition, molecular and bioinformatic data revealed crosstalk signaling networks that regulate the expressions of both RKIP and PTEN. These crosstalks involved the mitogen-activated protein kinase (MAPK)/PI3K pathways and the dysregulated nuclear factor-kappaB (NF-κB)/Snail/Yin Yang 1 (YY1)/RKIP/PTEN loop in many cancers. Furthermore, further bioinformatic analyses were performed to investigate the correlations (positive or negative) and the prognostic significance of the expressions of RKIP or PTEN in 31 different human cancers. These analyses were not uniform and only revealed that there was a positive correlation between the expression of RKIP and PTEN only in few cancers. These findings demonstrated the existence of signaling cross-talks between RKIP and PTEN and both regulate resistance. Targeting either RKIP or PTEN (alone or in combination with other therapies) may be sufficient to therapeutically inhibit tumor growth and reverse the tumor resistance to cytotoxic therapies.

Marine-derived pipeline anticancer natural products: a review of their pharmacotherapeutic potential and molecular mechanisms

Background

Cancer is a complex and most widespread disease and its prevalence is increasing worldwide, more in countries that are witnessing urbanization and rapid industrialization changes. Although tremendous progress has been made, the interest in targeting cancer has grown rapidly every year. This review underscores the importance of preventive and therapeutic strategies.

Main text

Natural products (NPs) from various sources including plants have always played a crucial role in cancer treatment. In this growing list, numerous unique secondary metabolites from marine sources have added and gaining attention and became potential players in drug discovery and development for various biomedical applications. Many NPs found in nature that normally contain both pharmacological and biological activity employed in pharmaceutical industry predominantly in anticancer pharmaceuticals because of their enormous range of structure entities with unique functional groups that attract and inspire for the creation of several new drug leads through synthetic chemistry. Although terrestrial medicinal plants have been the focus for the development of NPs, however, in the last three decades, marine origins that include invertebrates, plants, algae, and bacteria have unearthed numerous novel pharmaceutical compounds, generally referred as marine NPs and are evolving continuously as discipline in the molecular targeted drug discovery with the inclusion of advanced screening tools which revolutionized and became the component of antitumor modern research.

Conclusions

This comprehensive review summarizes some important and interesting pipeline marine NPs such as Salinosporamide A, Dolastatin derivatives, Aplidine/plitidepsin (Aplidin®) and Coibamide A, their anticancer properties and describes their mechanisms of action (MoA) with their efficacy and clinical potential as they have attracted interest for potential use in the treatment of various types of cancers.

Marine Power on Cancer: Drugs, Lead Compounds, and Mechanisms

Worldwide, 19.3 million new cancer cases and almost 10.0 million cancer deaths occur each year. Recently, much attention has been paid to the ocean, the largest biosphere of the earth that harbors a great many different organisms and natural products, to identify novel drugs and drug candidates to fight against malignant neoplasms. The marine compounds show potent anticancer activity in vitro and in vivo, and relatively few drugs have been approved by the U.S. Food and Drug Administration for the treatment of metastatic malignant lymphoma, breast cancer, or Hodgkin's disease. This review provides a summary of the anticancer effects and mechanisms of action of selected marine compounds, including cytarabine, eribulin, marizomib, plitidepsin, trabectedin, zalypsis, adcetris, and OKI-179. The future development of anticancer marine drugs requires innovative biochemical biology approaches and introduction of novel therapeutic targets, as well as efficient isolation and synthesis of marine-derived natural compounds and derivatives.

Recent insights how combined inhibition of immuno/proteasome subunits enables therapeutic efficacy

The proteasome is a multicatalytic protease in the cytosol and nucleus of all eukaryotic cells that controls numerous cellular processes through regulated protein degradation. Proteasome inhibitors have significantly improved the survival of multiple myeloma patients. However, clinically approved proteasome inhibitors have failed to show efficacy against solid tumors, neither alone nor in combination with other therapies. Targeting the immunoproteasome with selective inhibitors has been therapeutically effective in preclinical models for several autoimmune diseases and colon cancer. Moreover, immunoproteasome inhibitors prevented the chronic rejection of allogeneic organ transplants. In recent years, it has become apparent that inhibition of one single active center of the proteasome is insufficient to achieve therapeutic benefits. In this review we summarize the latest insights how targeting multiple catalytically active proteasome subunits can interfere with disease progression in autoimmunity, growth of solid tumors, and allograft rejection.

RKIP as an Inflammatory and Immune System Modulator: Implications in Cancer

Raf kinase inhibitor protein (RKIP), an important modulator of intracellular signalling pathways, is commonly downregulated in multiple cancers. This reduction, or loss of expression, is correlated not only with the presence of metastasis, contributing to RKIP’s classification as a metastasis suppressor, but also with tumour aggressiveness and poor prognosis. Recent findings suggest a strong involvement of RKIP in the modulation of tumour microenvironment components, particularly by controlling the infiltration of specific immune cells and secretion of pro-metastatic factors. Additionally, RKIP interaction with multiple signalling molecules seems to potentiate its function as a regulator of inflammatory processes, mainly through stimulation of anti- or pro-inflammatory cytokines. Furthermore, RKIP is involved in the modulation of immunotherapeutic drugs response, through diverse mechanisms that sensitize cells to apoptosis. In the present review, we will provide updated information about the role of RKIP as an inflammatory and immune modulator and its potential implications in cancer will be addressed.

The Two Sides of YY1 in Cancer: A Friend and a Foe

Yin Yang 1 (YY1), a dual function transcription factor, is known to regulate transcriptional activation and repression of many genes associated with multiple cellular processes including cellular differentiation, DNA repair, autophagy, cell survival vs. apoptosis, and cell division. Owing to its role in processes that upon deregulation are linked to malignant transformation, YY1 has been implicated as a major driver of many cancers. While a large body of evidence supports the role of YY1 as a tumor promoter, recent reports indicated that YY1 also functions as a tumor suppressor. The mechanism by which YY1 brings out opposing outcome in tumor growth vs. suppression is not completely clear and some of the recent reports have provided significant insight into this. Likewise, the mechanism by which YY1 functions both as a transcriptional activator and repressor is not completely clear. It is likely that the proteins with which YY1 interacts might determine its function as an activator or repressor of transcription as well as its role as a tumor suppressor or promoter. Hence, a collection of YY1-protein interactions in the context of different cancers would help us gain an insight into how YY1 promotes or suppresses cancers. This review focuses on the YY1 interacting partners and its target genes in different cancer models. Finally, we discuss the possibility of therapeutically targeting the YY1 in cancers where it functions as a tumor promoter.

Knockdown of Yin Yang 1 enhances anticancer effects of cisplatin through protein phosphatase 2A-mediated T308 dephosphorylation of AKT

Cisplatin is still one of the first-line drugs for chemotherapy of head and neck squamous cell carcinoma (HNSCC) and shows a survival advantage for HNSCC. However, a substantial proportion of HNSCC eventually becomes resistance to cisplatin and the underlying mechanisms remain to be fully understood. Yin Yang 1 (YY1) is a multifunctional protein regulating both gene transcription and protein modifications and also plays a role in chemotherapy resistance. Here, we reported that knockdown of YY1 by lentivirus-mediated short hairpin RNA or tetracycline-inducible short hairpin RNA enhanced cisplatin-induced apoptosis and inhibition of cell proliferation, migration and invasion in the HNSCC cell lines, and inhibition of the xenograft tumor growth. The underlying mechanisms were revealed that knockdown of YY1 downregulated both S473 and T308 phosphorylation of AKT (protein kinase B), which was mainly responsible for cisplatin resistance, whereas overexpression of YY1 upregulated both S473 and T308 phosphorylation. Cisplatin upregulated YY1 mRNA and protein expression and both S473 and T308 phosphorylation of AKT. In the presence of cisplatin, knockdown of YY1 not only blocked cisplatin-induced increase in S473 and T308 phosphorylation of AKT, but still downregulated T308 phosphorylation. Moreover, protein phosphatase 2A (PP2A) antagonist, okadaic acid, upregulated T308, but not S473, phosphorylation, and simultaneously abolished YY1 knockdown-mediated enhancement of cisplatin-induced inhibition of cell proliferation. In addition, knockdown of YY1 promoted PP2A activity through upregulating mRNA and protein expressions of PP2A catalytic subunit alpha (PPP2CA) through the binding of YY1 in the promoter of PPP2CA. Conversely, activating PP2A by forskolin also promoted YY1 degradation and subsequently inhibited T308 phosphorylation. These results suggested that knockdown of YY1 enhanced anticancer effects of cisplatin through PP2A mediating T308 dephosphorylation of AKT, and that targeting YY1 or PP2A would enhance the efficiency of cisplatin chemotherapy in treatment of HNSCC.

NanoTRAIL-Oncology: A Strategic Approach in Cancer Research and Therapy

TRAIL is a member of the tumor necrosis factor superfamily that can largely trigger apoptosis in a wide variety of cancer cells, but not in normal cells. However, insufficient exposure to cancer tissues or cells and drug resistance has severely impeded the clinical application of TRAIL. Recently, nanobiotechnology has brought about a revolution in advanced drug delivery for enhanced anticancer therapy using TRAIL. With the help of materials science, immunology, genetic engineering, and protein engineering, substantial progress is made by expressing fusion proteins with TRAIL, engineering TRAIL on biological membranes, and loading TRAIL into functional nanocarriers or conjugating it onto their surfaces. Thus, the nanoparticle-based TRAIL (nanoTRAIL) opens up intriguing opportunities for efficient and safe bioapplications. In this review, the mechanisms of action and biological function of TRAIL, as well as the current status of TRAIL treatment, are comprehensively discussed. The application of functional nanotechnology combined with TRAIL in cancer therapy is also discussed.

c-Abl phosphorylation of Yin Yang 1's conserved tyrosine 254 in the spacer region modulates its transcriptional activity

Yin Yang 1 (YY1) is a multifunctional transcription factor that can activate or repress transcription depending on the promotor and/or the co-factors recruited. YY1 is phosphorylated in various signaling pathways and is critical for different biological functions including embryogenesis, apoptosis, proliferation, cell-cycle regulation and tumorigenesis. Here we report that YY1 is a substrate for c-Abl kinase phosphorylation at conserved residue Y254 in the spacer region. Pharmacological inhibition of c-Abl kinase by imatinib, nilotinib and GZD824, knock-down of c-Abl using siRNA, and the use of c-Abl kinase-dead drastically reduces tyrosine phosphorylation of YY1. Both radioactive and non-radioactive in vitro kinase assays, as well as co-immunoprecipitation in different cell lines, show that the target of c-Abl phosphorylation is tyrosine residue 254. c-Abl phosphorylation has little effect on YY1 DNA binding ability or cellular localization in asynchronous cells. However, functional studies reveal that c-Abl mediated phosphorylation of YY1 regulates YY1's transcriptional ability in vivo. In conclusion, we demonstrate the novel role of c-Abl kinase in regulation of YY1's transcriptional activity, linking YY1 regulation with c-Abl tyrosine kinase signaling pathways.

Lambertianic Acid Sensitizes Non-Small Cell Lung Cancers to TRAIL-Induced Apoptosis via Inhibition of XIAP/NF-κB and Activation of Caspases and Death Receptor 4

Lambertianic acid (LA) is a biologically active compound from the leaves of Pinus koraiensis. In the present study, apoptotic mechanisms of LA plus TNF-related apoptosis-inducing ligand (TRAIL) were elucidated in non-small cell lung cancer cells (NSCLCs). Cytotoxicity assay, flow cytometry, immunoprecipitation, and Western blotting were performed. Here, combined treatment of LA and TRAIL increased cytotoxicity, sub-G1 population, cleaved poly (ADP-ribose) polymerase (PARP), and caspase3/8/9 in A549 and H1299 cells compared to LA or TRAIL alone. Furthermore, combined treatment of LA and TRAIL significantly decreased antiapoptotic proteins such as B-cell lymphoma 2 (Bcl-2), Fas-like inhibitor protein (FLIP), and X-linked inhibitor of apoptosis protein (XIAP), and enhanced the activation of proapoptotic proteins Bid compared to LA or TRAIL alone. In addition, combined treatment of LA and TRAIL upregulated the expression of Death receptor 4 (DR4) and downregulated phosphorylation of nuclear factor κ-light-chain-enhancer of activated B cells (p-NF-κB), inhibitory protein of kB family (p-IκB), and FLIP in A549 and H1299 cells along with disrupted binding of XIAP with caspase3 or NF-κB. Overall, these findings suggest that lambertianic acid enhances TRAIL-induced apoptosis via inhibition of XIAP/NF-κB in TRAIL resistant NSCLCs.

Linking Autophagy and the Dysregulated NFκB/ SNAIL/YY1/RKIP/PTEN Loop in Cancer: Therapeutic Implications

The role of autophagy in the pathogenesis of various cancers has been well documented in many reports. Autophagy in cancer cells regulates cell proliferation, viability, invasion, epithelial-to-mesenchymal transition (EMT), metastasis, and responses to chemotherapeutic and immunotherapeutic treatment strategies. These manifestations are the result of various regulatory gene products that govern autophagic, biochemical, and molecular mechanisms. In several human cancer cell models, the presence of a dysregulated circuit-namely, NFκB/SNAIL/YY1/RKIP/PTEN-that plays a major role in the regulation of tumor cell unique characteristics just listed for autophagy-regulated activities. Accordingly, the autophagic mechanism and the dysregulated circuit in cancer cells share many of the same properties and activities. Thus, it has been hypothesized that there must exist a biochemical/molecular link between the two. The present review describes the link and the association of each gene product of the dysregulated circuit with the autophagic mechanism and delineates the presence of crosstalk. Crosstalk between autophagy and the dysregulated circuit is significant and has important implications in the development of targeted therapies aimed at either autophagy or the dysregulated gene products in cancer cells.

Silibinin sensitizes TRAIL-mediated apoptosis by upregulating DR5 through ROS-induced endoplasmic reticulum stress-Ca2+-CaMKII-Sp1 pathway

In this study, we addressed how silibinin enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in various cancer cells. Combined treatment with silibinin and TRAIL (silibinin/TRAIL) induced apoptosis accompanied by the activation of caspase-3, caspase-8, caspase-9, and Bax, and cytosolic accumulation of cytochrome c. Anti-apoptotic proteins such as Bcl-2, IAP-1, and IAP-2 were inhibited as well. Silibinin also triggered TRAIL-induced apoptosis in A549 cells through upregulation of death receptor 5 (DR5). Pretreatment with DR5/Fc chimeric protein and DR5-targeted small interfering RNA (siRNA) significantly blocked silibinin/TRAIL-mediated apoptosis in A549 cells. Furthermore, silibinin increased the production of reactive oxygen species (ROS), which led to the induction of TRAIL-mediated apoptosis through DR5 upregulation. Antioxidants such as N-acetyl-L-cysteine and glutathione reversed the apoptosis-inducing effects of TRAIL. Silibinin further induced endoplasmic reticulum (ER) stress as was indicated by the increase in ER marker proteins such as PERK, eIF2α, and ATF-4, which stimulate the expression of CCAAT/enhancer binding protein homologous protein (CHOP). CHOP-targeted siRNA eliminated the induction of DR5 and resulted in a significant decrease in silibinin/TRAIL-mediated apoptosis. We also found that silibinin/TRAIL-induced apoptosis was accompanied with intracellular influx of Ca²⁺, which was stimulated by ER stress and the Ca²⁺ chelator, ethylene glycol tetraacetic acid (EGTA). Ca²⁺/calmodulin-dependent protein kinase (CaMKII) inhibitor, K252a, blocked silibinin/TRAIL-induced DR5 expression along with TRAIL-mediated apoptosis. Accordingly, we showed that ROS/ER stress-induced CaMKII activated Sp1, which is an important transcription factor for DR5 expression. Our results showed that silibinin enhanced TRAIL-induced apoptosis by upregulating DR5 expression through the ROS-ER stress-CaMKII-Sp1 axis.

Novel Proteasome Inhibitors and Histone Deacetylase Inhibitors: Progress in Myeloma Therapeutics

The unfolded protein response is responsible for the detection of misfolded proteins and the coordination of their disposal and is necessary to maintain the cellular homoeostasis. Multiple myeloma cells secrete large amounts of immunoglobulins, proteins that need to be correctly folded by the chaperone system. If this process fails, the misfolded proteins have to be eliminated by the two main garbage-disposal systems of the cell: proteasome and aggresome. The blockade of either of these systems will result in accumulation of immunoglobulins and other toxic proteins in the cytoplasm and cell death. The simultaneous inhibition of the proteasome, by proteasome inhibitors (PIs) and the aggresome, by histone deacetylase inhibitors (HDACi) results in a synergistic increase in cytotoxicity in myeloma cell lines. This review provides an overview of mechanisms of action of second-generation PIs and HDACi in multiple myeloma (MM), the clinical results currently observed with these agents and assesses the potential therapeutic impact of the different agents in the two classes. The second-generation PIs offer benefits in terms of increased efficacy, reduced neurotoxicity as off-target effect and may overcome resistance to bortezomib because of their different chemical structure, mechanism of action and biological properties. HDACi with anti-myeloma activity in clinical development discussed in this review include vorinostat, panobinostat and selective HDAC6 inhibitor, ricolinostat.

Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer

Pancreatic cancer is highly malignant with limited therapy and a poor prognosis. TRAIL-activating therapy has been promising, however, clinical trials have shown resistance and limited responses of pancreatic cancers. We investigated the effects of calmodulin(CaM) antagonists, trifluoperazine(TFP) and tamoxifen(TMX), on TRA-8-induced apoptosis and tumorigenesis of TRA-8-resistant pancreatic cancer cells, and underlying mechanisms. TFP or TMX alone did not induce apoptosis of resistant PANC-1 cells, while they dose-dependently enhanced TRA-8-induced apoptosis. TMX treatment enhanced efficacy of TRA-8 therapy on tumorigenesis in vivo. Analysis of TRA-8-induced death-inducing-signaling-complex (DISC) identified recruitment of survival signals, CaM/Src, into DR5-associated DISC, which was inhibited by TMX/TFP. In contrast, TMX/TFP increased TRA-8-induced DISC recruitment/activation of caspase-8. Consistently, caspase-8 inhibition blocked the effects of TFP/TMX on TRA-8-induced apoptosis. Moreover, TFP/TMX induced DR5 expression. With a series of deletion/point mutants, we identified CaM antagonist-responsive region in the putative Sp1-binding domain between -295 to -300 base pairs of DR5 gene. Altogether, we have demonstrated that CaM antagonists enhance TRA-8-induced apoptosis of TRA-8-resistant pancreatic cancer cells by increasing DR5 expression and enhancing recruitment of apoptotic signal while decreasing survival signals in DR5-associated DISC. Our studies support the use of these readily available CaM antagonists combined with TRAIL-activating agents for pancreatic cancer therapy.

Nitric oxide-mediated sensitization of resistant tumor cells to apoptosis by chemo-immunotherapeutics

The generation of NO by the various NO synthases in normal and malignant tissues is manifested by various biological effects that are involved in the regulation of cell survival, differentiation and cell death. The role of NO in the cytotoxic immune response was first revealed by demonstrating the induction of iNOS in target cells by immune cytokines (e.g. IFN-γ, IL-1, TNF-α, etc.) and resulting in the sensitization of resistant tumor cells to death ligands-induced apoptosis. Endogenous/exogenous NO mediated its immune sensitizing effect by inhibiting NF-κΒ activity and downstream, inactivating the repressor transcription factor YY1, which inhibited both Fas and DR5 expressions. In addition, NO-mediated inhibition of NF-κΒ activity and inhibition downstream of its anti-apoptotic gene targets sensitized the tumor cells to apoptosis by chemotherapeutic drugs. We have identified in tumor cells a dysregulated pro-survival/anti-apoptotic loop consisting of NF-κB/Snail/YY1/RKIP/PTEN and its modification by NO was responsible, in large, for the reversal of chemo and immune resistance and sensitization to apoptotic mechanisms by cytotoxic agents. Moreover, tumor cells treated with exogenous NO donors resulted in the inhibition of NF-κΒ activity via S-nitrosylation of p50 and p65, inhibition of Snail (NF-κΒ target gene), inhibition of transcription repression by S-nitrosylation of YY1 and subsequent inhibition of epithelial-mesenchymal transition (EMT), induction of RKIP (inhibition of the transcription repressor Snail), and induction of PTEN (inhibition of the repressors Snail and YY1). Further, each gene product modified by NO in the loop was involved in chemo-immunosensitization. These above findings demonstrated that NO donors interference in the regulatory circuitry result in chemo-immunosensitization and inhibition of EMT. Overall, these observations suggest the potential anti-tumor therapeutic effect of NO donors in combination with subtoxic chemo-immuno drugs. This combination acts on multiple facets including reversal of chemo-immune resistance, and inhibition of both EMT and metastasis.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Spatial dynamics of TRAIL death receptors in cancer cells

TNF-related apoptosis inducing ligand (TRAIL) selectively induces apoptosis in cancer cells without harming most normal cells. Currently, multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL (rhTRAIL) and agonistic antibodies that target death receptors (DRs) 4 or 5. It is encouraging that these products have shown a tolerated safety profile in early phase studies. However, their therapeutic potential is likely limited by the emergence of tumor drug resistance phenomena. Increasing evidence indicates that TRAIL DRs are deficient on the plasma membrane of some cancer cells despite their total protein expression. Notably, the lack of surface DR4/DR5 is sufficient to render cancers resistant to TRAIL-induced apoptosis, regardless of the status of other apoptosis signaling components. The current review highlights recent findings on the dynamic expression of TRAIL death receptors, including the regulatory roles of endocytosis, autophagy, and Ras GTPase-mediated signaling events. This information could aid in the identification of novel predictive biomarkers of tumor response as well as the development of combinational drugs to overcome or bypass tumor drug resistance to TRAIL receptor-targeted therapies.

Death receptor 5 expression is inversely correlated with prostate cancer progression

Prostate carcinoma (PCa) is one of the most common cancers in men. Prostate-specific antigen (PSA) has been widely used to predict the outcome of PCa and screening with PSA has resulted in a decline in mortality. However, PSA is not an optimal prognostic tool as its sensitivity may be too low to reduce morbidity and mortality. Consequently, there is a demand for additional robust biomarkers for prostate cancer. Death receptor 5 (DR5) has been implicated in the prognosis of several cancers and it has been previously shown that it is negatively regulated by Yin Yang 1 (YY1) in prostate cancer cell lines. The present study investigated the clinical significance of DR5 expression in a prostate cancer patient cohort and its correlation with YY1 expression. Immunohistochemical analysis of protein expression distribution was performed using tissue microarray constructs from 54 primary PCa and 39 prostatic intraepithelial neoplasia (PIN) specimens. DR5 expression was dramatically reduced as a function of higher tumor grade. By contrast, YY1 expression was elevated in PCa tumors as compared with that in PIN, and was increased with higher tumor grade. DR5 had an inverse correlation with YY1 expression. Bioinformatic analyses corroborated these data. The present findings suggested that DR5 and YY1 expression levels may serve as progression biomarkers for prostate cancer.

Two death-inducing human TRAIL receptors to target in cancer: similar or distinct regulation and function?

The emergence during evolution of two tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) receptors, receptor-1/DR4 and -2/DR5, able to induce apoptosis has raised the question whether they differ in function and regulation, which is of key importance for selecting either DR4 or DR5 selective pro-apoptotic agents for cancer treatment. In this review we found practically no information regarding possible differences in DR4 and DR5 function based on structural differences. On the other hand, a panel of different DR4 or DR5 selective pro-apoptotic agonists have been developed that were explored for efficacy in different tumour types in a large number of studies. Leukemic cells appear mainly sensitive for DR4-induced apoptosis, contrasting the situation in other tumour types that show heterogeneity in receptor preference and, in some cases, a slight overall preference for DR5. Both receptors were found to mediate intracellular stress-induced apoptosis, although this is most frequently reported for DR5. Interestingly, DR5 was also found to transmit non-apoptotic signalling in resistant tumour cells and recently nuclear localization and a role in microRNA maturation has been described. DR4 expression is most heavily regulated by promoter methylation, intracellular trafficking and post-translational modifications. DR5 expression is predominantly regulated at the transcriptional level, which may reflect its ability to respond to cellular stressors. It will be important to further increase our understanding of the mechanisms determining TRAIL receptor preference in order to select the appropriate TRAIL receptor selective agonists for therapy, and to develop novel strategies to enhance apoptosis activation in tumours.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

New orally active proteasome inhibitors in multiple myeloma

Bortezomib is the first proteasome inhibitor approved for the therapy of multiple myeloma (MM). Although Bortezomib has renovated the treatment of MM, a considerable proportion of subjects fail to respond to Bortezomib treatment and almost all patients relapse from this drug either alone or when used in combination therapies. However, the good clinical outcome of Bortezomib treatment in MM patients gave impulsion for the development of second generation proteasome inhibitors with the ambition of improving efficacy of proteasome inhibition, enhancing antitumor activity, and decreasing toxicity, as well as providing flexible dosing schedules and patient convenience. This review provides an overview of the role of oral proteasome inhibitors including Marizomib, Oprozomib, Delanzomib, chemical proteasome inhibitors, and cinnabaramides, in the therapy of MM, focusing on developments over the past five years. These emerging drugs with different mechanisms of action have exhibited promising antitumor activity in patients with relapsed/refractory MM, and they are creating chances to target multiple pathways, overcome resistance, and improve clinical outcomes, mainly for those subjects who are refractory to approved agents. Future steps in the clinical development of oral inhibitors include the optimization of the schedule and the definition of their antitumor activity in MM.

Phosphorylation of signal transducer and activator of transcription 1 reduces bortezomib-mediated apoptosis in cancer cells

The potent and selective proteasome inhibitor bortezomib has shown remarkable antitumor activity and is now entering clinical trials for several cancers. However, the molecular mechanisms by which bortezomib induces cytotoxicity in ovarian cancer cells still remain unclear. In this study, we show that bortezomib induced apoptosis, which was demonstrated by the downregulation of antiapoptotic molecules (Bcl-2, Bcl-XL, p-Bad, and p-AKT) and the upregulation of proapoptotic proteins (p21, p27, and cleaved-Bid) in ovarian cancer cell lines. Moreover, bortezomib stimulates Janus kinase (JAK) phosphorylation and activates heat-shock transcription factor-1 (HSF-1) and heat-shock protein 70 (HSP70), ultimately leading to signal transducer and activator of transcription 1 (STAT1) phosphorylation. Phosphorylated STAT1 partially counteracted apoptosis induced by bortezomib in cancer cells. These findings suggest that the antitumor activity of bortezomib in ovarian cancer can be improved by inhibiting bortezomib-induced STAT1 phosphorylation. This effect can be achieved by STAT1 knockdown, HSP70 knockdown, JAK inhibition, or the addition of cisplatin, one of the most commonly used anticancer drugs. These results provide the first evidence that STAT1 phosphorylation can play a role in bortezomib resistance by exerting antiapoptotic effects. They also suggest the possibility to abolish or reduce bortezomib chemoresistance in ovarian cancer by the addition of cisplatin or JAK inhibitors.

Roles Each of Snail, Yin Yang 1 and RKIP in the Regulation of Tumor Cells Chemo-immuno-resistance to Apoptosis

The current anti-cancer therapeutic armamentarium consists of surgery, chemotherapy, radiation, hormonal therapy, immunotherapy, and combinations thereof. Initial treatments usually result in objective clinical responses with prolongation of overall survival (OS) and progression-free survival (PFS) in a large subset of the treated patients. However, at the onset, there is a subset of patients who does not respond and another subset that initially responded but experiences relapses and recurrences. These latter subsets of patients develop a state of cross-resistance to a variety of unrelated therapies. Therefore, there is an urgent need to first unravel the underlying mechanisms of resistance and associated gene products that regulate the cross-resistance. Such gene products are potential therapeutic targets as well as potential prognostic/diagnostic biomarkers. In this context, we have identified three interrelated gene products involved in resistance, namely, Snail, YY1, and RKIP that are components of the dysregulated NF-κB/Snail/YY1/RKIP loop in many cancers. In this review, we will discuss the roles each of Snail, YY1 and RKIP in the regulation of tumor cell resistance to chemo and immunotherapies. Since these same gene products have also been shown to be involved in the regulation of the EMT phenotype and metastasis, we suggest that targeting any of these three gene products can simultaneously inhibit tumor cell resistance and metastasis.

Bortezomib and TRAIL: a perfect match for apoptotic elimination of tumour cells?

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine that selectively eradicates tumour cells via specific cell surface receptors and is intensively explored for use as a novel anticancer approach. To enhance the efficacy of TRAIL receptor agonists the proteasome inhibitor bortezomib is one of the most potent sensitizers. Here we review the main mechanisms underlying bortezomib-dependent TRAIL sensitization, including stimulation of apoptosis by increasing expression of TRAIL receptors, reduction of cFLIP and enhancement of caspase 8 activation, and modulation of Bcl-2 family proteins and inhibitor of apoptosis proteins (IAPs). Concomitantly, pro-survival signals are suppressed such as elicited by NF-κB and Akt. The different preclinical tumour models explored with this combination, including primary tumour (stem) cells, stroma co-culture and mice models, are discussed, as well as possible hurdles for clinical activity. Collectively, anticipating a solid rationale for bortezomib-TRAIL combination and very promising preclinical results, its clinical activity remains to be demonstrated.

The pharmacogenomics of sex hormone metabolism: breast cancer risk in menopausal hormone therapy

With women in western countries spending nearly one-third of their lifetime beyond menopause and a substantial number of these women facing severe menopausal symptoms, the goal of sex hormone pharmacogenomics is to promote the safe use of hormone replacement therapy (HRT). This could be achieved by providing molecular predictors for the upfront stratification of women in need of relief from menopausal symptoms into those with a likely benefit from HRT and those with a contraindication due to an HRT-associated breast cancer risk or other adverse effects. An increasing knowledge base of sex hormone metabolism and its variability, HRT outcomes and breast cancer susceptibility, as well as emerging examples of pharmacogenomic predictors, underscore the potential relevance of genetic variations for HRT outcome. The genes responsible for the metabolism, signaling and action of sex hormones are at the heart of this research; however, pharmacogenomic investigation of their therapeutic effects due to the enormous complexity of the biological pathways involved is still in its infancy. This article discusses the current knowledge, challenges and potential future directions towards the goal of genotype-guided safer HRT use.

Artepillin C (3,5-diprenyl-4-hydroxycinnamic acid) sensitizes LNCaP prostate cancer cells to TRAIL-induced apoptosis

Naturally occurring phenolic compounds have been shown to sensitize prostate cancer cells to tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. TRAIL is a potent stimulator of apoptosis in cancer cells and an important immune effector molecule in the surveillance and elimination of developing tumours. However, many cancer cells are resistant to TRAIL-mediated death. In this study, we aimed to determine the mechanisms by which TRAIL resistance can be overcome in prostate cancer cells by 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C). Artepillin C is a bioactive component of Brazilian green propolis that possesses antitumour and chemopreventive activities. TRAIL-resistant LNCaP prostate cancer cells were treated with TRAIL and artepillin C. Cytotoxicity was measured by MTT and lactate dehydrogenase (LDH) assays. Apoptosis was detected using Annexin V-FITC staining by flow cytometry and fluorescence microscopy. Death receptor (DR) (TRAIL-R1/DR4 and TRAIL-R2/DR5) expression was analyzed using flow cytometry. Mitochondrial membrane potential (ΔΨm) was evaluated using DePsipher staining by fluorescence micro scopy. The inhibition of NF-κB (p65) activation was confirmed with the ELISA-based TransAM NF-κB kit. Caspase-8 and caspase-3 activities were determined by colorimetric protease assays. The results showed that artepillin C sensitized the TRAIL-resistant LNCaP cells by engaging the extrinsic (receptor-mediated) and intrinsic (mitochondrial) apoptotic pathways. Artepillin C increased the expression of TRAIL-R2 and decreased the activity of NF-κB. Co-treatment with TRAIL and artepillin C induced the significant activation of caspase-8 and caspase-3, as well as the disruption of ΔΨm. These findings show that prostate cancer cells can be sensitized to TRAIL-mediated immunoprevention by artepillin C and confirm the role of phenolic compounds in prostate cancer immunochemoprevention.

YY1 overexpression is associated with poor prognosis and metastasis-free survival in patients suffering osteosarcoma

Background

The polycomb transcription factor Yin Yang 1 (YY1) overexpression can be causally implicated in experimental tumor growth and metastasization. To date, there is no clinical evidence of YY1 involvement in outcome of patients with osteosarcoma. Prognosis of osteosarcoma is still severe and only few patients survive beyond five years. We performed a prospective immunohistochemistry analysis to correlate YY1 immunostaining with metastatic development and survival in a selected homogeneous group of patients with osteosarcoma.

Methods

We studied 41 patients suffering from osteosarcoma (stage II-IVa). Multivariate analysis was performed using Cox proportional hazard regression to evaluate the correlation between YY1 expression and both metastasis development and mortality.

Results

YY1 protein is not usually present in normal bone; in contrast, a high number of patients (61%) showed a high score of YY1 positive cells (51-100%) and 39% had a low score (10-50% positive cells). No statistical difference was found in histology, anatomic sites, or response to chemotherapy between the two degrees of YY1 expression. Cox regression analysis demonstrated that the highest score of YY1 expression was predictive of both low metastasis-free survival (HR = 4.690, 95%CI = 1.079-20.396; p = 0.039) and poor overall survival (HR = 8.353, 95%CI = 1.863-37.451 p = 0.006) regardless of the effects of covariates such as age, gender, histology and chemonecrosis.

Conclusion

Overexpression of YY1 in primary site of osteosarcoma is associated with the occurrence of metastasis and poor clinical outcome.

Mcl-1 and YY1 inhibition and induction of DR5 by the BH3-mimetic Obatoclax (GX15-070) contribute in the sensitization of B-NHL cells to TRAIL apoptosis

The pan Bcl-2 family antagonist Obatoclax (GX15-070), currently in clinical trials, was shown to sensitize TRAIL-resistant tumors to TRAIL-mediated apoptosis via the release of Bak and Bim from Mcl-1 or Bcl-2/Bcl-XL complexes or by the activation of Bax, though other mechanisms were not examined. Herein, we hypothesize that Obatoclax-mediated sensitization to TRAIL apoptosis may also result from alterations of the apoptotic pathways. The TRAIL-resistant B-cell line Ramos was used as a model for investigation. Treatment of Ramos cells with Obatoclax significantly inhibited the expression of several members of the Bcl-2 family, dissociated Bak from Mcl-1 and inhibited the NFκB activity. Cells treated with Mcl-1 siRNA were sensitized to TRAIL apoptosis. We examined whether the sensitization of Ramos to TRAIL by Obatoclax resulted from signaling of the DR4 and/or DR5. Transfection with DR5 siRNA, but not with DR4 siRNA, sensitized the cells to apoptosis following treatment with Obatoclax and TRAIL. The signaling via DR5 correlated with Obatoclax-induced inhibition of the DR5 repressor Yin Yang 1 (YY1). Transfection with YY1 siRNA sensitized the cells to TRAIL apoptosis following treatment with Obatoclax and TRAIL. Overall, the present findings reveal a new mechanism of Obatoclax-induced sensitization to TRAIL apoptosis and the involvement of the inhibition of NFκB activity and downstream Mcl-1 and YY1 expressions and activities.

Marizomib, a proteasome inhibitor for all seasons: preclinical profile and a framework for clinical trials

The proteasome has emerged as an important clinically relevant target for the treatment of hematologic malignancies. Since the Food and Drug Administration approved the first-in-class proteasome inhibitor bortezomib (Velcade) for the treatment of relapsed/refractory multiple myeloma (MM) and mantle cell lymphoma, it has become clear that new inhibitors are needed that have a better therapeutic ratio, can overcome inherent and acquired bortezomib resistance and exhibit broader anti-cancer activities. Marizomib (NPI-0052; salinosporamide A) is a structurally and pharmacologically unique β-lactone-γ-lactam proteasome inhibitor that may fulfill these unmet needs. The potent and sustained inhibition of all three proteolytic activities of the proteasome by marizomib has inspired extensive preclinical evaluation in a variety of hematologic and solid tumor models, where it is efficacious as a single agent and in combination with biologics, chemotherapeutics and targeted therapeutic agents. Specifically, marizomib has been evaluated in models for multiple myeloma, mantle cell lymphoma, Waldenstrom's macroglobulinemia, chronic and acute lymphocytic leukemia, as well as glioma, colorectal and pancreatic cancer models, and has exhibited synergistic activities in tumor models in combination with bortezomib, the immunomodulatory agent lenalidomide (Revlimid), and various histone deacetylase inhibitors. These and other studies provided the framework for ongoing clinical trials in patients with MM, lymphomas, leukemias and solid tumors, including those who have failed bortezomib treatment, as well as in patients with diagnoses where other proteasome inhibitors have not demonstrated significant efficacy. This review captures the remarkable translational studies and contributions from many collaborators that have advanced marizomib from seabed to bench to bedside.

Yin yang 1 is a novel regulator of pulmonary fibrosis

RATIONALE

The differentiation of fibroblasts into myofibroblasts is a cardinal feature of idiopathic pulmonary fibrosis (IPF). The transcription factor Yin Yang 1 (YY1) plays a role in the proliferation and differentiation of diverse cell types, but its role in fibrotic lung diseases is not known.

OBJECTIVES

To elucidate the mechanism by which YY1 regulates fibroblast differentiation and lung fibrosis.

METHODS

Lung fibroblasts were cultured with transforming growth factor (TGF)-β or tumor necrosis factor-α. Nuclear factor (NF)-κB, YY1, and α-smooth muscle actin (SMA) were determined in protein, mRNA, and promoter reporter level. Lung fibroblasts and lung fibrosis were assessed in a partial YY1-deficient mouse and a YY1(f/f) conditional knockout mouse after being exposed to silica or bleomycin.

MEASUREMENTS AND MAIN RESULTS

TGF-β and tumor necrosis factor-α up-regulated YY1 expression in lung fibroblasts. TGF-β-induced YY1 expression was dramatically decreased by an inhibitor of NF-κB, which blocked I-κB degradation. YY1 is significantly overexpressed in both human IPF and murine models of lung fibrosis, including in the aggregated pulmonary fibroblasts of fibrotic foci. Furthermore, the mechanism of fibrogenesis is that YY1 can up-regulate α-SMA expression in pulmonary fibroblasts. YY1-deficient (YY1(+/-)) mice were significantly protected from lung fibrosis, which was associated with attenuated α-SMA and collagen expression. Finally, decreasing YY1 expression through instilled adenovirus-cre in floxed-YY1(f/f) mice reduced lung fibrosis.

CONCLUSIONS

YY1 is overexpressed in fibroblasts in both human IPF and murine models in a NF-κB-dependent manner, and YY1 regulates fibrogenesis at least in part by increasing α-SMA and collagen expression. Decreasing YY1 expression may provide a new therapeutic strategy for pulmonary fibrosis.

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.

A potential mechanism of rituximab-induced inhibition of tumor growth through its sensitization to tumor necrosis factor-related apoptosis-inducing ligand-expressing host cytotoxic cells

Rituximab (anti-CD20 mAb) mediates antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis in B-NHL cells. The contribution of other host-mediated cytotoxic effects has not been examined. The expression of death-inducing ligands (e.g. TRAIL) by host effector cells may contribute to the mechanism of tumor cell destruction in vivo by rituximab-mediated sensitization of resistant B-cell non-Hodgkin lymphoma (B-NHL) cells. We have examined the sensitizing activity of rituximab on B-NHL cell lines resistant to TRAIL (as model) and natural killer (NK)-induced apoptosis. Treatment of TRAIL-resistant B-NHL cell lines with rituximab sensitized the cells to TRAIL apoptosis and synergy was achieved via activation of the type II mitochondrial pathway for apoptosis. Further, rituximab (Fab')(2)-treated tumor cells were killed by purified peripheral blood-derived NK cells via TRAIL. Treatment of B-NHL cells with rituximab inhibited both YY1 DNA-binding activity and expression. Rituximab-mediated sensitization to TRAIL apoptosis was due, in large part, to rituximab-mediated inhibition of the transcription factor Yin Yang 1 (YY1). The direct role of YY1 in TRAIL sensitization by rituximab was shown in cells transfected with YY1 siRNA, and such cells mimicked rituximab and became sensitive to TRAIL-induced apoptosis. These data suggest that, in vivo, host effector cells expressing TRAIL may contribute to rituximab-mediated depletion of B-NHL cells.

Salinosporamide natural products: Potent 20 S proteasome inhibitors as promising cancer chemotherapeutics

Proteasome inhibitors are rapidly evolving as potent treatment options in cancer therapy. One of the most promising drug candidates of this type is salinosporamide A from the bacterium Salinispora tropica. This marine natural product possesses a complex, densely functionalized γ-lactam-β-lactone pharmacophore, which is responsible for its irreversible binding to its target, the β subunit of the 20S proteasome. Salinosporamide A entered phase I clinical trials for the treatment of multiple myeloma only three years after its discovery. The strong biological activity and the challenging structure of this compound have fueled intense academic and industrial research in recent years, which has led to the development of more than ten syntheses, the elucidation of its biosynthetic pathway, and the generation of promising structure-activity relationships and oncological data. Salinosporamide A thus serves as an intriguing example of the successful interplay of modern drug discovery and biomedical research, medicinal chemistry and pharmacology, natural product synthesis and analysis, as well as biosynthesis and bioengineering.

2-Tellurium-bridged β-cyclodextrin, a thioredoxin reductase inhibitor, sensitizes human breast cancer cells to TRAIL-induced apoptosis through DR5 induction and NF-κB suppression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) exhibits potent antitumor activity via membrane receptors on cancer cells without deleterious side effects for normal tissue. Unfortunately, breast cancer cells, as many other cancer types, develop resistance to TRAIL; therefore, TRAIL sensitizing agents are currently being explored. 2-Tellurium-bridged β-cyclodextrin (2-TeCD) is a synthetic organotellurium compound, with both glutathione peroxidase-like catalytic ability and thioredoxin reductase inhibitor activity. In the present study, we reported that 2-TeCD sensitized TRAIL-resistant human breast cancer cells and xenograft tumors to undergo apoptosis. In vitro, 2-TeCD efficiently sensitized MDA-MB-468 and T47D cells, but not untransformed human mammary epithelial cells, to TRAIL-mediated apoptosis, as evidenced by enhanced caspase activity and poly (adenosine diphosphate-ribose) polymerase cleavage. From a mechanistic standpoint, we showed that 2-TeCD treatment of breast cancer cells significantly upregulated the messenger RNA and protein levels of TRAIL receptor, death receptor (DR) 5, in a transcription factor Sp1-dependent manner. 2-TeCD treatment also suppressed TRAIL-induced nuclear factor-κB (NF-κB) prosurvival pathways by preventing cytosolic IκBα degradation, as well as p65 nuclear translocation. Consequently, the combined administration suppressed anti-apoptotic molecules that are transcriptionally regulated by NF-κB. In vivo, 2-TeCD and TRAIL were well tolerated in mice and their combination significantly inhibited growth of MDA-MB-468 xenografts and promoted apoptosis. Upregulation of DR5 and downregulation of NF-κB by the dual treatment were also observed in tumor tissues. Overall, 2-TeCD sensitizes resistant breast cancer cells to TRAIL-based apoptosis in vitro and in vivo. These findings provide strong evidence for the therapeutic potential of this combination against breast cancers.

Dual role of NO donors in the reversal of tumor cell resistance and EMT: Downregulation of the NF-κB/Snail/YY1/RKIP circuitry

Several studies have implicated the role of Nitric Oxide (NO) in the regulation of tumor cell behavior and have shown that NO either promotes or inhibits tumorigenesis. These conflicting findings have been resolved, in part, by the levels of NO used such that low levels promote tumor growth and high levels inhibit tumor growth. Our studies have focused on the use of high levels of NO provided primarily by the NO donor, DETANONOate. We have shown that treatment of resistant tumor cells with DETANONOate sensitizes them to apoptosis by both chemotherapeutic drugs and cytotoxic immunotherapeutic ligands. The underlying mechanisms by which NO sensitizes tumor cells to apoptosis were shown to be regulated, in part, by NO-mediated inhibition of the NF-κB survival/anti-apoptotic pathways and downstream of NF-κB by inhibition of the transcription factor Yin Yang 1 (YY1). In addition to NO-induced sensitization to apoptosis, we have also shown that NO induced the expression of the metastasis-suppressor/immunosurveillance cancer gene product, Raf-1 kinase inhibitor protein (RKIP). Overexpression of RKIP mimics NO in tumor cells-induced sensitization to apoptosis. The induction of RKIP by NO was the result of the inhibition of the RKIP repressor, Snail, downstream of NF-κB. These findings established the presence of a dysregulated NF-κB/Snail/YY1/ RKIP circuitry in resistance and that treatment with NO modifies this loop in tumor cells in favor of the inhibition of tumor cell survival and the response to cytotoxic drugs. Noteworthy, the NF-κB/Snail/YY1/RKIP loop consists of gene products that regulate the epithelial to mesenchymal transition (EMT) and, thus, tumor metastasis. Hence, we have found that treatment of metastatic cancer cell lines with DETANONOate inhibited the EMT phenotype, through both the inhibition of the metastasis-inducers, NF-κB and Snail and the induction of the metastasis-suppressor, RKIP. Altogether, the above findings establish, for the first time, the dual role of high levels of NO in the sensitization of tumor cells to apoptotic stimuli as well as inhibition of EMT. Hence, NO donors may be considered as novel potential therapeutic agents with dual roles in the treatment of patients with refractory cancer and in the prevention of the initiation of the metastatic cascade via EMT.

CXCR4/YY1 inhibition impairs VEGF network and angiogenesis during malignancy

Tumor growth requires neoangiogenesis. VEGF is the most potent proangiogenic factor. Dysregulation of hypoxia-inducible factor (HIF) or cytokine stimuli such as those involving the chemokine receptor 4/stromal-derived cell factor 1 (CXCR4/SDF-1) axis are the major cause of ectopic overexpression of VEGF in tumors. Although the CXCR4/SDF-1 pathway is well characterized, the transcription factors executing the effector function of this signaling are poorly understood. The multifunctional Yin Yang 1 (YY1) protein is highly expressed in different types of cancers and may regulate some cancer-related genes. The network involving CXCR4/YY1 and neoangiogenesis could play a major role in cancer progression. In this study we have shown that YY1 forms an active complex with HIF-1alpha at VEGF gene promoters and increases VEGF transcription and expression observed by RT-PCR, ELISA, and Western blot using two different antibodies against VEGFB. Long-term treatment with T22 peptide (a CXCR4/SDF-1 inhibitor) and YY1 silencing can reduce in vivo systemic neoangiogenesis (P < 0.01 and P < 0.05 vs. control, respectively) during metastasis. Moreover, using an in vitro angiogenesis assay, we observed that YY1 silencing led to a 60% reduction in branches (P < 0.01) and tube length (P < 0.02) and a 75% reduction in tube area (P < 0.001) compared with control cells. A similar reduction was observed using T22 peptide. We demonstrated that T22 peptide determines YY1 cytoplasmic accumulation by reducing its phosphorylation via down-regulation of AKT, identifying a crosstalk mechanism involving CXCR4/YY1. Thus, YY1 may represent a crucial molecular target for antiangiogenic therapy during cancer progression.

Celastrol, a triterpene, enhances TRAIL-induced apoptosis through the down-regulation of cell survival proteins and up-regulation of death receptors

Whether celastrol, a triterpene from traditional Chinese medicine, can modulate the anticancer effects of TRAIL, the cytokine that is currently in clinical trial, was investigated. As indicated by assays that measure plasma membrane integrity, phosphatidylserine exposure, mitochondrial activity, and activation of caspase-8, caspase-9, and caspase-3, celastrol potentiated the TRAIL-induced apoptosis in human breast cancer cells, and converted TRAIL-resistant cells to TRAIL-sensitive cells. When examined for its mechanism, we found that the triterpene down-regulated the expression of cell survival proteins including cFLIP, IAP-1, Bcl-2, Bcl-xL, survivin, and XIAP and up-regulated Bax expression. In addition, we found that celastrol induced the cell surface expression of both the TRAIL receptors DR4 and DR5. This increase in receptors was noted in a wide variety of cancer cells including breast, lung, colorectal, prostate, esophageal, and pancreatic cancer cells, and myeloid and leukemia cells. Gene silencing of the death receptor abolished the effect of celastrol on TRAIL-induced apoptosis. Induction of the death receptor by the triterpenoid was found to be p53-independent but required the induction of CAAT/enhancer-binding protein homologous protein (CHOP), inasmuch as gene silencing of CHOP abolished the induction of DR5 expression by celastrol and associated enhancement of TRAIL-induced apoptosis. We found that celastrol also induced reactive oxygen species (ROS) generation, and ROS sequestration inhibited celastrol-induced expression of CHOP and DR5, and consequent sensitization to TRAIL. Overall, our results demonstrate that celastrol can potentiate the apoptotic effects of TRAIL through down-regulation of cell survival proteins and up-regulation of death receptors via the ROS-mediated up-regulation of CHOP pathway.

Variation in the FGFR2 gene and the effect of a low-fat dietary pattern on invasive breast cancer

BACKGROUND

The Women's Health Initiative dietary modification (DM) trial provided suggestive evidence of a benefit of a low-fat dietary pattern on breast cancer risk, with stronger evidence among women whose baseline diet was high in fat. Single nucleotide polymorphisms (SNP) in the FGFR2 gene relate strongly to breast cancer risk and could influence intervention effects.

METHODS

All 48,835 trial participants were postmenopausal and ages 50 to 79 years at enrollment (1993-1998). We interrogated eight SNPs in intron 2 of the FGFR2 gene for 1,676 women who developed breast cancer during trial follow-up (1993-2005). Case-only analyses were used to estimate odds ratios for the DM intervention in relation to SNP genotype.

RESULTS

Odds ratios for the DM intervention did not vary significantly with the genotype for any of the eight FGFR2 SNPs (P > or = 0.18). However, odds ratios varied (P < 0.05) with the genotype of six of these SNPs, among women having baseline percent of energy from fat in the upper quartile (> or =36.8%). This variation is most evident for SNP rs3750817, with odds ratios for the DM intervention at 0, 1, and 2 minor SNP alleles of 1.06 [95% confidence intervals (95% CI), 0.80-1.41], 0.53 (95% CI, 0.38-0.74), and 0.62 (95% CI, 0.33-1.15). The nominal significance level for this interaction is P = 0.005, and P = 0.03 following multiple testing adjustment, with most evidence deriving from hormone receptor-positive tumors.

CONCLUSION

Invasive breast cancer odds ratios for a low-fat dietary pattern, among women whose usual diets are high in fat, seem to vary with SNP rs3750817 in the FGFR2 gene.

Proteasome inhibition: a new therapeutic strategy to cancer treatment

The ubiquitin-proteasome system is a major pathway for protein degradation. Targeting this pathway using proteasome inhibitors represents a novel approach for the treatment of cancer. Proteasome inhibitors lower cell proliferation and induce apoptosis in solid and hematologic malignancies through multiple mechanisms, including stabilization of cell cycle regulators and pro-apoptotic factors, stimulation of bone morphogenetic protein signaling, inhibition of protein translation, and sensitization to ligand-induced apoptosis. In this connection, proteasome inhibition activates macroautophagy, a compensatory protein degradation system, as well as other pro-survival signaling pathways. Inhibition of these auto-protective responses sensitizes cancer cells to the anti-proliferative effects of proteasome inhibitors.

Death receptor 5-recruited raft components contributes to the sensitivity of Jurkat leukemia cell lines to TRAIL-induced cell death

In the present study we demonstrated Jurkat leukemia cell lines of TIB152 and TIB153 with different sensitivities to recombinant soluble TRAIL cytotoxicity. TRAIL receptor death receptor 5 (DR5) was constitutively localized in the rafts in both cell lines. FADD, caspase-8, and PI3K-p85 subunit were recruited into DR5 lipid rafts of TIB152 but not in TIB153 cells. The expression and enzyme activity of acid sphingomyelinase, which digests sphingomyeline to produce ceramide and plays an essential role in lipid raft assembling, were higher in the rafts of TIB152 than in TIB153. These data provide evidences that DR5-recruited raft components contribute to the different sensitivity of Jurkat leukemia cell lines to TRAIL-induced cell death and may throw some light on the development of better therapeutic strategies for the cancer cells resistant to TRAIL treatment.

Bortezomib restores stroma-mediated APO2L/TRAIL apoptosis resistance in multiple myeloma

OBJECTIVES

Hematopoietic stroma promotes resistance to immune control by APO2L/TRAIL in multiple myeloma (MM) cells in part by increasing synthesis of the anti-apoptotic protein c-FLIP. Here, we tested whether bortezomib can reverse the APO2L/TRAIL environmental mediated-immune resistance (EM-IR).

MATERIAL AND METHODS

MM cell lines (RPMI 8226 and U266) and CD138+ patient's MM cells were directly adhered to HS5 stroma exposed to HS5 or bone marrow stroma of patients with MM released soluble factors in a transwell system. Cells were treated with either APO2L/TRAIL (10 ng/mL), bortezomib (10 nm) or both.

RESULTS

Pretreatment with bortezomib effectively overcomes APO2L/TRAIL apoptosis resistance in myeloma cell lines and in CD138+ cells while directly adhered or in transwell assay. Bortezomib was not cytotoxic to HS5 stroma cells and only altered monocyte chemotactic protein-2-3 and IL-10 levels in the stroma-myeloma milieu. Factors released by HS5 stroma increased expression of c-FLIP, induced STAT-3 and ERK phosphorylation and reduced DR4 receptor expression in MM cells. HS5 stroma-released factor(s) induced NF-kappaB activation after 20 h exposure in association with an enhanced c-FLIP transcription. Bortezomib effectively reduced c-FLIP protein expression without affecting other proteins. Bortezomib also increased DR4 and DR5 expression in the presence of stroma.

CONCLUSIONS

These findings provide the rationale to combine bortezomib and APO2L/TRAIL to disrupt the influence of the stroma microenvironment on MM cells.

Variation in the FGFR2 gene and the effects of postmenopausal hormone therapy on invasive breast cancer

BACKGROUND

Breast cancer concern is a major reason for the recent marked reduction in use of postmenopausal hormone therapy, although equally effective means of controlling menopausal symptoms are lacking. Single nucleotide polymorphisms (SNP) in the fibroblast growth factor receptor 2 (FGFR2) gene are substantially associated with postmenopausal breast cancer risk and could influence hormone therapy effects.

PARTICIPANTS AND METHODS

We interrogated eight SNPs in intron 2 of the FGFR2 gene for 2,166 invasive breast cancer cases from the Women's Health Initiative clinical trial and one-to-one matched controls to confirm an association with breast cancer risk. We used case-only analyses to examine the dependence of estrogen plus progestin and estrogen-alone odds ratios on SNP genotype.

RESULTS

Seven FGFR2 SNPs, including six in a single linkage disequilibrium region, were found to associate strongly (P < 10(-7)) with breast cancer risk. SNP rs3750817 (minor allele T with frequency 0.39) had an estimated per-minor-allele odds ratio of 0.78, and was not in such strong linkage disequilibrium with the other SNPs. The genotype of this SNP related significantly (P < 0.05) to hormone therapy odds ratios. For estrogen plus progestin, the odds ratios (95% confidence intervals) at 0, 1, and 2 minor SNP alleles were 1.52 (1.14-2.02), 1.33 (1.01-1.75), and 0.69 (0.41-1.17), whereas the corresponding values for estrogen alone were 0.74 (0.51-1.09), 0.99 (0.68-1.44), and 0.34 (0.15-0.76).

CONCLUSIONS

Postmenopausal women having TT genotype for SNP rs3750817 have a reduced breast cancer risk and seem to experience comparatively favorable effects of postmenopausal hormone therapy.

Pivotal roles of snail inhibition and RKIP induction by the proteasome inhibitor NPI-0052 in tumor cell chemoimmunosensitization

The novel proteasome inhibitor NPI-0052 has been shown to sensitize tumor cells to apoptosis by various chemotherapeutic drugs and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), although the mechanisms involved are not clear. We hypothesized that NPI-0052-mediated sensitization may result from NF-kappaB inhibition and downstream modulation of the metastasis inducer Snail and the metastasis suppressor/immunosurveillance cancer gene product Raf-1 kinase inhibitory protein (RKIP). Human prostate cancer cell lines were used as models, as they express different levels of these proteins. We show that NPI-0052 inhibits both NF-kappaB and Snail and induces RKIP expression, thus resulting in cell sensitization to CDDP and TRAIL. The direct role of NF-kappaB inhibition in sensitization was corroborated with the NF-kappaB inhibitor DHMEQ, which mimicked NPI-0052 in sensitization and inhibition of Snail and induction of RKIP. The direct role of Snail inhibition by NPI-0052 in sensitization was shown with Snail small interfering RNA, which reversed resistance and induced RKIP. Likewise, the direct role of RKIP induction in sensitization was revealed by both overexpression of RKIP (mimicking NPI-0052) and RKIP small interfering RNA that inhibited NPI-0052-mediated sensitization. These findings show that NPI-0052 modifies the NF-kappaB-Snail-RKIP circuitry in tumor cells and results in downstream inhibition of antiapoptotic gene products and chemoimmunosensitization. The findings also identified Snail and RKIP as targets for reversal of resistance.

Inhibition of epithelial to mesenchymal transition in metastatic prostate cancer cells by the novel proteasome inhibitor, NPI-0052: pivotal roles of Snail repression and RKIP induction

Metastasis is associated with the loss of epithelial features and the acquisition of mesenchymal characteristics and invasive properties by tumor cells, a process known as epithelial to mesenchymal transition (EMT). Snail expression, through nuclear factor (NF)-kappaB activation, is an EMT determinant. The proteasome inhibitor, NPI-0052, induces the metastasis tumor suppressor/immune surveillance cancer gene, Raf kinase inhibitor protein (RKIP), via NF-kappaB inhibition. We hypothesized that NPI-0052 may inhibit Snail expression and, consequently, the metastatic phenotype in DU-145 prostate cancer cells. Cell treatment with NPI-0052 induced E-cadherin and inhibited Snail expression and both tumor cell invasion and migration. Inhibition of Snail inversely correlated with the induction of RKIP. The underlying mechanism of NPI-0052-induced inhibition of the metastatic phenotype was corroborated by: (1) treatment with Snail siRNA in DU-145 inhibited EMT and, in contrast, overexpression of Snail in the nonmetastatic LNCaP cells induced EMT, (2) NPI-0052-induced repression of Snail via inhibition of NF-kappaB was corroborated by the specific NF-kappaB inhibitor DHMEQ and (3) RKIP overexpression mimicked NPI-0052 in the inhibition of Snail and EMT. These findings demonstrate, for the first time, the role of NPI-0052 in the regulation of EMT via inhibition of NF-kappaB and Snail and induction of RKIP.

Death receptor 5 promoter-enhancing compounds isolated from Catimbium speciosum and their enhancement effect on TRAIL-induced apoptosis

The TRAIL/death-receptor signaling pathway has been considered a promising target for selective cancer therapy, although some malignant tumors exhibit TRAIL resistance. We previously found that isoflavonoid enhanced TRAIL-induced apoptosis in TRAIL-resistant cells, which is achieved through up-regulation of death receptor 5 (DR5). In our screening program targeting DR5 promoter enhancement activity, activity-guided fractionations of the extract of Catimbium speciosum led to the isolation of six compounds. Of the isolates, cardamomin (6), the most potent compound, enhanced the expressions of DR5 and DR4 and decreased the Bcl-xL level in TRAIL-resistant DLD1 cells. The combination of 6 and TRAIL synergistically enhanced TRAIL-induced apoptosis against TRAIL-resistant cells upon the activation of caspase-8, 9, and 3. In addition, enhancement of apoptosis by 6 was inhibited by human recombinant DR5/Fc and DR4/Fc chimera proteins, TRAIL-neutralizing fusion proteins, indicating that 6 sensitize TRAIL-resistant cells to TRAIL through the induction of DR5 and DR4. Also, up-regulation of DR5 by 6 paralleled that of CCAAT/enhancer-binding protein-homologous protein (CHOP).