TW-37, a small-molecule inhibitor of Bcl-2, inhibits cell growth and invasion in pancreatic cancer

Therapeutic Targeting of Regulated Signaling Pathways of Non-Small Cell Lung Carcinoma

Non-small cell lung carcinoma (NSCLC) is the most common cancer globally. Phytochemicals and small molecule inhibitors significantly prevent varying types of cancers, including NSCLC. These therapeutic molecules serve as important sources for new drugs that interfere with cellular proliferation, apoptosis, metastasis, and angiogenesis by regulating signaling pathways. These molecules affect several cellular signaling cascades, including p53, NF-κB, STAT3, RAS, MAPK/ERK, Wnt, and AKT/PI3K, and are thus implicated in the therapeutic management of cancers. This review aims to describe the bioactive compounds and small-molecule inhibitors, their anticancer action, and targeting cellular signaling cascades in NSCLC. We highlighted the therapeutic potential of Epigallocatechin gallate (EGCG), Perifosine, ABT-737, Thymoquinine, Quercetin, Venetoclax, Gefitinib, and Genistein. These compounds are implicated in the therapeutic management of NSCLC. This review further offers deeper mechanistic insights into different signaling pathways that could be targeted for NSCLC therapy by phytochemicals and small-molecule inhibitors.

Molecular Research in Pancreatic Cancer: Small Molecule Inhibitors, Their Mechanistic Pathways and Beyond

Pancreatic enzymes assist metabolic digestion, and hormones like insulin and glucagon play a critical role in maintaining our blood sugar levels. A malignant pancreas is incapable of doing its regular functions, which results in a health catastrophe. To date, there is no effective biomarker to detect early-stage pancreatic cancer, which makes pancreatic cancer the cancer with the highest mortality rate of all cancer types. Primarily, mutations of the KRAS, CDKN2A, TP53, and SMAD4 genes are responsible for pancreatic cancer, of which mutations of the KRAS gene are present in more than 80% of pancreatic cancer cases. Accordingly, there is a desperate need to develop effective inhibitors of the proteins that are responsible for the proliferation, propagation, regulation, invasion, angiogenesis, and metastasis of pancreatic cancer. This article discusses the effectiveness and mode of action at the molecular level of a wide range of small molecule inhibitors that include pharmaceutically privileged molecules, compounds under clinical trials, and commercial drugs. Both natural and synthetic small molecule inhibitors have been counted. Anti-pancreatic cancer activity and related benefits of using single and combined therapy have been discussed separately. This article sheds light on the scenario, constraints, and future aspects of various small molecule inhibitors for treating pancreatic cancer-the most dreadful cancer so far.

GADRP: graph convolutional networks and autoencoders for cancer drug response prediction

Drug response prediction in cancer cell lines is of great significance in personalized medicine. In this study, we propose GADRP, a cancer drug response prediction model based on graph convolutional networks (GCNs) and autoencoders (AEs). We first use a stacked deep AE to extract low-dimensional representations from cell line features, and then construct a sparse drug cell line pair (DCP) network incorporating drug, cell line, and DCP similarity information. Later, initial residual and layer attention-based GCN (ILGCN) that can alleviate over-smoothing problem is utilized to learn DCP features. And finally, fully connected network is employed to make prediction. Benchmarking results demonstrate that GADRP can significantly improve prediction performance on all metrics compared with baselines on five datasets. Particularly, experiments of predictions of unknown DCP responses, drug-cancer tissue associations， and drug-pathway associations illustrate the predictive power of GADRP. All results highlight the effectiveness of GADRP in predicting drug responses, and its potential value in guiding anti-cancer drug selection.

Bax/Bcl-2 Cascade Is Regulated by the EGFR Pathway: Therapeutic Targeting of Non-Small Cell Lung Cancer

Non-small cell lung carcinoma (NSCLC) comprises 80%-85% of lung cancer cases. EGFR is involved in several cancer developments, including NSCLC. The EGFR pathway regulates the Bax/Bcl-2 cascade in NSCLC. Increasing understanding of the molecular mechanisms of fundamental tumor progression has guided the development of numerous antitumor drugs. The development and improvement of rationally planned inhibitors and agents targeting particular cellular and biological pathways in cancer have been signified as a most important paradigm shift in the strategy to treat and manage lung cancer. Newer approaches and novel chemotherapeutic agents are required to accompany present cancer therapies for improving efficiency. Using natural products as a drug with an effective delivery system may benefit therapeutics. Naturally originated compounds such as phytochemicals provide crucial sources for novel agents/drugs and resources for tumor therapy. Applying the small-molecule inhibitors (SMIs)/phytochemicals has led to potent preclinical discoveries in various human tumor preclinical models, including lung cancer. In this review, we summarize recent information on the molecular mechanisms of the Bax/Bcl-2 cascade and EGFR pathway in NSCLC and target them for therapeutic implications. We further described the therapeutic potential of Bax/Bcl-2/EGFR SMIs, mainly those with more potent and selectivity, including gefitinib, EGCG, ABT-737, thymoquinone, quercetin, and venetoclax. In addition, we explained the targeting EGFR pathway and ongoing in vitro and in vivo and clinical investigations in NSCLC. Exploration of such inhibitors facilitates the future treatment and management of NSCLC.

B Cell Lymphoma 2: A Potential Therapeutic Target for Cancer Therapy

Defects in the apoptosis mechanism stimulate cancer cell growth and survival. B cell lymphoma 2 (Bcl-2) is an anti-apoptotic molecule that plays a central role in apoptosis. Bcl-2 is the founding constituent of the Bcl-2 protein family of apoptosis controllers, the primary apoptosis regulators linked with cancer. Bcl-2 has been identified as being over-expressed in several cancers. Bcl-2 is induced by protein kinases and several signaling molecules which stimulate cancer development. Identifying the important function played by Bcl-2 in cancer progression and development, and treatment made it a target related to therapy for multiple cancers. Among the various strategies that have been proposed to block Bcl-2, BH3-mimetics have appeared as a novel group of compounds thanks to their favorable effects on many cancers within several clinical settings. Because of the fundamental function of Bcl-2 in the regulation of apoptosis, the Bcl-2 protein is a potent target for the development of novel anti-tumor treatments. Bcl-2 inhibitors have been used against several cancers and provide a pre-clinical platform for testing novel therapeutic drugs. Clinical trials of multiple investigational agents targeting Bcl-2 are ongoing. This review discusses the role of Bcl-2 in cancer development; it could be exploited as a potential target for developing novel therapeutic strategies to combat various types of cancers. We further highlight the therapeutic activity of Bcl-2 inhibitors and their implications for the therapeutic management of cancer.

Synergistic Effects of TW-37 and ABT-263 on Renal Cell Carcinoma Cells

Background

Renal cell carcinoma (RCC) is a common urological system malignancy lack of effective therapeutic options. Upregulation of the Bcl-2 proteins was correlated with poor prognosis of RCC, suggesting that BH-3 mimetics may be a promising treatment option. ABT-263 is a BH3 mimetic that possesses anti-tumor effects. TW-37 is another inhibitor of Bcl-2 family protein with potential anti-tumor activities. However, since their effect as single agent is limited, combination treatment represents a strategy to improve the efficiency. We studied the ABT-263 in combination with TW-37 and analyzed the molecular mechanisms of action in RCC cells.

Methods

MTT and colony formation assays were used to measure the proliferation of RCC cells. Transwell assay was used to assay the migration and invasion of RCC cells. Cell cycle distribution and apoptosis were measured using the flow cytometry and apoptotic nucleosome assay, respectively. Western blotting was performed to measure the change of proteins. The anti-tumor effects of ABT-263, TW-37 and their combination were also evaluated in vivo.

Results

Cotreatment of TW-37 and ABT-263 synergistically repressed the proliferation of RCC cells. TW-37 and ABT-263 also synergistically inhibited the migration and invasion of RCC cells It was also showed that TW-37 and ABT-263 synergistically induced cell cycle arrest at the G2/M phase. Furthermore, increased apoptosis was observed after exposure to TW-37 and ABT-263. Mechanism investigation showed that TW-37 and ABT-263 synergistically induced apoptosis via the mitochondrial pathway and relied on the activation of Bax and caspases. Furthermore, ERK signaling pathway activation was detected after treated with TW-37 and ABT-263. Finally, TW-37 and ABT-263 also synergistically repressed the growth of RCC cells in xenograft mice.

Conclusion

In summary, our data demonstrated that combined treatment with TW-37 and ABT-263 exhibited synergistic RCC cell death and this combination may be applied as an effective therapeutic strategy against RCC.

Small molecule inhibitors in pancreatic cancer

Pancreatic cancer (PC), with a 5 year survival of <7%, is one of the most fatal of all human cancers. The highly aggressive and metastatic character of this disease poses a challenge that current therapies are failing, despite significant efforts, to meet. This review examines the current status of the 35 small molecule inhibitors targeting pancreatic cancer in clinical trials and the >50 currently under investigation. These compounds inhibit biological targets spanning protein kinases, STAT3, BET, HDACs and Bcl-2 family proteins. Unsurprisingly, protein kinase inhibitors are overrepresented. Some trials show promise; a phase I combination trial of vorinostat 11 and capecitabine 17 gave a median overall survival (MoS) of 13 months and a phase II study of pazopanib 15 showed a MoS of 25 months. The current standard of care for metastatic pancreatic ductal adenocarcinoma, fluorouracil/folic acid (5-FU, Adrucil®), and gemcitabine (GEMZAR®) afforded a MoS of 23 and 23.6 months (EPAC-3 study), respectively. In patients who can tolerate the FOLFIRINOX regime, this is becoming the standard of treatment with a MoS of 11.1 months. Clinical study progress has been slow with limited improvement in patient survival relative to gemcitabine 1 monotherapy. A major cause of low PC survival is the late stage of diagnosis, occurring in patients who consider typical early stage warning signs of aches and pains normal. The selection of patients with specific disease phenotypes, the use of improved efficient drug combinations, the identification of biomarkers to specific cancer subtypes and more effective designs of investigation have improved outcomes. To move beyond the current dire condition and paucity of PC treatment options, determination of the best regimes and new treatment options is a challenge that must be met. The reasons for poor PC prognosis have remained largely unchanged for 20 years. This is arguably a consequence of significant changes in the drug discovery landscape, and the increasing pressure on academia to deliver short term 'media' friendly short-term news 'bites'. PC research sits at a pivotal point. Perhaps the greatest challenge is enacting a culture change that recognises that major breakthroughs are a result of blue sky, truly innovative and curiosity driven research.

Discovery of Mcl-1 inhibitors from integrated high throughput and virtual screening

Protein-protein interactions (PPIs) represent important and promising therapeutic targets that are associated with the regulation of various molecular pathways, particularly in cancer. Although they were once considered “undruggable,” the recent advances in screening strategies, structure-based design, and elucidating the nature of hot spots on PPI interfaces, have led to the discovery and development of successful small-molecule inhibitors. In this report, we are describing an integrated high-throughput and computational screening approach to enable the discovery of small-molecule PPI inhibitors of the anti-apoptotic protein, Mcl-1. Applying this strategy, followed by biochemical, biophysical, and biological characterization, nineteen new chemical scaffolds were discovered and validated as Mcl-1 inhibitors. A novel series of Mcl-1 inhibitors was designed and synthesized based on the identified difuryl-triazine core scaffold and structure-activity studies were undertaken to improve the binding affinity to Mcl-1. Compounds with improved in vitro binding potency demonstrated on-target activity in cell-based studies. The obtained results demonstrate that structure-based analysis complements the experimental high-throughput screening in identifying novel PPI inhibitor scaffolds and guides follow-up medicinal chemistry efforts. Furthermore, our work provides an example that can be applied to the analysis of available screening data against numerous targets in the PubChem BioAssay Database, leading to the identification of promising lead compounds, fuelling drug discovery pipelines.

Effect of TW37 on the growth of H1975 EGFR‑TKI‑resistant lung cancer cells and its underlying mechanisms

Previous studies have suggested that the B‑cell lymphoma 2 (Bcl‑2) inhibitor, TW37, may induce apoptosis of the non‑small cell lung cancer cell line, H1975/epidermal growth factor receptor‑tyrosine kinase inhibitor (EGFR‑TKI), which exhibits secondary resistance to EGFR‑TKI. However, the effects of TW37 on H1975/EGFR‑TKI cells remain unclear. The aim of the present study was to investigate the effects of TW37 on the growth of H1975/EGFR‑TKI cells and explore the underlying mechanisms. An in vitro study was performed, whereby H1975/EGFR‑TKI cells were treated with serially increasing concentrations of TW37. MTT, flow cytometry, migration and transwell invasion assays were preformed to investigate the proliferation, apoptosis, migration and invasion of H1975/EGFR‑TKI cells, respectively. In addition, reverse transcription‑polymerase chain reaction and western blot analyses were performed to detect the mRNA and protein expression levels of apoptosis‑associated factors, respectively. An enzyme‑linked immunosorbent assay was performed to detect phosphatidylinositol [3,4,5] tris‑phosphate (PIP3) expression. The results suggested that the mRNA and protein expression levels of Bcl‑2 were significantly decreased in TW37‑treated cells when compared with the untreated control group. Following treatment with TW37, the proliferation, migration and invasion ability of H1975/EGFR‑TKI cells decreased in a dose‑dependent manner, while the percentage of apoptotic cells increased. In addition, the results demonstrated that TW37 reduced the expression of PIP3 and the phosphorylation of AKT serine/threonine kinase 1 (AKT) in H1975/EGFR‑TKI cells in a dose‑dependent manner. In conclusion, TW37 inhibited H1975/EGFR‑TKI cell growth and induced cell apoptosis potentially via suppression of AKT signaling pathway activation.

The preclinical analysis of TW-37 as a potential anti-colorectal cancer cell agent

TW-37 is a novel, potent and non-peptide Bcl-2 small-molecule inhibitor. Its activity in colorectal cancer (CRC) cells is studied. In both HCT-116 cells and primary human colon cancer cells, treatment with TW-37 at only nM concentration efficiently inhibited cell survival and proliferation. TW-37 also induced caspase-3/9 and apoptosis activation in CRC cells. Feedback autophagy activation was observed in TW-37-treated CRC cells. Reversely pharmacological autophagy inhibition or Beclin-1 knockdown by targeted-shRNA potentiated TW-37-induced apoptosis and killing of CRC cells. In vivo, intravenous injection of TW-37 inhibited HCT-116 tumor growth in mice. TW-37’s anti-tumor activity was further potentiated against Beclin-1-silenced HCT-116 tumors. Together, targeting Bcl-2 family protein by TW-37 efficiently inhibits CRC cell growth in vitro and in vivo. Inhibition of feedback autophagy activation could further sensitize TW-37.

Targeting cancer cell mitochondria as a therapeutic approach: recent updates

Mitochondria play a key role in ATP generation, redox homeostasis and regulation of apoptosis. Due to the essential role of mitochondria in metabolism and cell survival, targeting mitochondria in cancer cells is considered as an attractive therapeutic strategy. However, metabolic flexibility in cancer cells may enable the upregulation of compensatory pathways, such as glycolysis to support cancer cell survival when mitochondrial metabolism is inhibited. Thus, compounds capable of both targeting mitochondria and inhibiting glycolysis may be particularly useful to overcome such drug-resistant mechanism. This review provides an update on recent development in the field of targeting mitochondria and novel compounds that impact mitochondria, glycolysis or both. Key challenges in this research area and potential solutions are also discussed.

G-Quadruplex surveillance in BCL-2 gene: a promising therapeutic intervention in cancer treatment

Recently, therapeutic implications of BCL-2 quadruplex invigorated the field of clinical oncology. This Keynote review discusses how a BCL-2 quadruplex-selective approach circumvents the limitations of existing therapeutics; and which improvisations might ameliorate the recent trends of quadruplex-based treatment.

Binding affinity of pro-apoptotic BH3 peptides for the anti-apoptotic Mcl-1 and A1 proteins: Molecular dynamics simulations of Mcl-1 and A1 in complex with six different BH3 peptides

The anti-apoptotic members of Bcl-2 family of proteins bind to their pro-apoptotic counterparts to induce or prevent cell death.Based on the distinct binding profiles for specific pro-apoptotic BH3 peptides, the anti-apoptotic Bcl-2 proteins can be divided into at least two subclasses. The subclass that includes Bcl-X_L binds strongly to Bad BH3 peptide while it has weak binding affinity for the second subclass of Bcl-2 proteins such as Mcl-1 and A1. Anti-apoptotic Bcl-2 proteins are considered to be attractive drug targets for anti-cancer drugs. BH3-mimetic inhibitors such as ABT-737 have been shown to be specific to Bcl-X_L subclass while Mcl-1 and A1 show resistance to the same drug. An efficacious inhibitor should target all the anti-apoptotic Bcl-2 proteins. Hence, development of inhibitors selective to Mcl-1 and A1 is of prime importance for targeted cancer therapeutics. The first step to achieve this goal is to understand the molecular basis of high binding affinities of specific pro-apoptotic BH3 peptides for Mcl-1 and A1. To understand the interactions between the BH3 peptides and Mcl-1/A1, we performed multi-nanosecond molecular dynamics (MD) simulations of six complex structures of Mcl-1 and A1. With the exception of Bad, all complex structures were experimentally determined. Bad complex structures were modeled. Our simulation studies identified specific pattern of polar interactions between Mcl-1/A1 and high-affinity binding BH3 peptides. The lack of such polar interactions in Bad peptide complex is attributed to specific basic residues present before and after the highly conserved Leu residue. The close approach of basic residues in Bad and Mcl-1/A1 is hypothesized to be the cause of weak binding affinity. To test this hypothesis, we generated in silico mutants of these basic residues in Bad peptide and Mcl-1/A1 proteins. MD simulations of the mutant systems established the pattern of stable polar interactions observed in high-affinity binding BH3 peptides. We have thus identified specific residue positions in Bad and Mcl-1/A1 responsible for the weak binding affinity. Results from these simulation studies will aid in the development of inhibitors specific to Mcl-1 and A1 proteins.

DRP-1 is required for BH3 mimetic-mediated mitochondrial fragmentation and apoptosis

The concept of using BH3 mimetics as anticancer agents has been substantiated by the efficacy of selective drugs, such as Navitoclax and Venetoclax, in treating BCL-2-dependent haematological malignancies. However, most solid tumours depend on MCL-1 for survival, which is highly amplified in multiple cancers and a major factor determining chemoresistance. Most MCL-1 inhibitors that have been generated so far, while demonstrating early promise in vitro, fail to exhibit specificity and potency in a cellular context. To address the lack of standardised assays for benchmarking the in vitro binding of putative inhibitors before analysis of their cellular effects, we developed a rapid differential scanning fluorimetry (DSF)-based assay, and used it to screen a panel of BH3 mimetics. We next contrasted their binding signatures with their ability to induce apoptosis in a MCL-1 dependent cell line. Of all the MCL-1 inhibitors tested, only A-1210477 induced rapid, concentration-dependent apoptosis, which strongly correlated with a thermal protective effect on MCL-1 in the DSF assay. In cells that depend on both MCL-1 and BCL-XL, A-1210477 exhibited marked synergy with A-1331852, a BCL-XL specific inhibitor, to induce cell death. Despite this selectivity and potency, A-1210477 induced profound structural changes in the mitochondrial network in several cell lines that were not phenocopied following MCL-1 RNA interference or transcriptional repression, suggesting that A-1210477 induces mitochondrial fragmentation in an MCL-1-independent manner. However, A-1210477-induced mitochondrial fragmentation was dependent upon DRP-1, and silencing expression levels of DRP-1 diminished not just mitochondrial fragmentation but also BH3 mimetic-mediated apoptosis. These findings provide new insights into MCL-1 ligands, and the interplay between DRP-1 and the anti-apoptotic BCL-2 family members in the regulation of apoptosis.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Inhibition of Bcl-2 or IAP proteins does not provoke mutations in surviving cells

Chemotherapy and radiotherapy can cause permanent damage to the genomes of surviving cells, provoking severe side effects such as second malignancies in some cancer survivors. Drugs that mimic the activity of death ligands, or antagonise pro-survival proteins of the Bcl-2 or IAP families have yielded encouraging results in animal experiments and early phase clinical trials. Because these agents directly engage apoptosis pathways, rather than damaging DNA to indirectly provoke tumour cell death, we reasoned that they may offer another important advantage over conventional therapies: minimisation or elimination of side effects such as second cancers that result from mutation of surviving normal cells. Disappointingly, however, we previously found that concentrations of death receptor agonists like TRAIL that would be present in vivo in clinical settings provoked DNA damage in surviving cells. In this study, we used cell line model systems to investigate the mutagenic capacity of drugs from two other classes of direct apoptosis-inducing agents: the BH3-mimetic ABT-737 and the IAP antagonists LCL161 and AT-406. Encouragingly, our data suggest that IAP antagonists possess negligible genotoxic activity. Doses of ABT-737 that were required to damage DNA stimulated Bax/Bak-independent signalling and exceeded concentrations detected in the plasma of animals treated with this drug. These findings provide hope that cancer patients treated by BH3-mimetics or IAP antagonists may avoid mutation-related illnesses that afflict some cancer survivors treated with conventional DNA-damaging anti-cancer therapies.

Selectivity by small-molecule inhibitors of protein interactions can be driven by protein surface fluctuations

Small-molecules that inhibit interactions between specific pairs of proteins have long represented a promising avenue for therapeutic intervention in a variety of settings. Structural studies have shown that in many cases, the inhibitor-bound protein adopts a conformation that is distinct from its unbound and its protein-bound conformations. This plasticity of the protein surface presents a major challenge in predicting which members of a protein family will be inhibited by a given ligand. Here, we use biased simulations of Bcl-2-family proteins to generate ensembles of low-energy conformations that contain surface pockets suitable for small molecule binding. We find that the resulting conformational ensembles include surface pockets that mimic those observed in inhibitor-bound crystal structures. Next, we find that the ensembles generated using different members of this protein family are overlapping but distinct, and that the activity of a given compound against a particular family member (ligand selectivity) can be predicted from whether the corresponding ensemble samples a complementary surface pocket. Finally, we find that each ensemble includes certain surface pockets that are not shared by any other family member: while no inhibitors have yet been identified to take advantage of these pockets, we expect that chemical scaffolds complementing these “distinct” pockets will prove highly selective for their targets. The opportunity to achieve target selectivity within a protein family by exploiting differences in surface fluctuations represents a new paradigm that may facilitate design of family-selective small-molecule inhibitors of protein-protein interactions.

Despite intense interest and considerable effort, there are few examples of small molecules that directly inhibit protein-protein interactions. Crystal structures of early successes have highlighted the plasticity of the protein surface, as some inhibitor-bound proteins are captured in conformations that are distinct from both their unbound and their protein-bound conformations. The lack of a single well-defined structure presents a challenge for predicting the members of a protein family to which a given compound will show activity (ligand selectivity). Here we generate ensembles of conformations from simulation, and show that we can predict ligand selectivity based on which family members sample conformations complementary to the ligand. This approach may present a new avenue for designing highly-selective inhibitors of protein-protein interactions.

Targeting BCL2-Proteins for the Treatment of Solid Tumours

Due to their central role in the regulation of apoptosis, the antiapoptotic BCL2-proteins are highly promising targets for the development of novel anticancer treatments. To this end, several strategies have been developed to inhibit BCL2, BCL-XL, BCL-w, and MCL1. While early clinical trials in haematological malignancies demonstrated exciting single-agent activity of BCL2-inhibitors, the response in solid tumours was limited, indicating that, in solid tumours, different strategies have to be developed in order to successfully treat patients with BCL2-inhibitors. In this review, the function of the different antiapoptotic BCL2-proteins and their role in solid tumours will be discussed. In addition, a comprehensive analysis of current small molecules targeting these antiapoptotic BCL2-proteins (e.g., ABT-737, ABT-263, ABT-199, TW-37, sabutoclax, obatoclax, and MIM1) will be provided including a discussion of the results of any clinical trials. This analysis will summarise the potential of BCL2-inhibitors for the treatment of solid tumours and will unravel novel approaches to utilise these inhibitors in clinical applications.

Small molecule inhibitors of bcl-2 family proteins for pancreatic cancer therapy

Pancreatic cancer (PC) has a complex etiology and displays a wide range of cellular escape pathways that allow it to resist different treatment modalities. Crucial signaling molecules that function downstream of the survival pathways, particularly at points where several of these pathways crosstalk, provide valuable targets for the development of novel anti-cancer drugs. Bcl-2 family member proteins are anti-apoptotic molecules that are known to be overexpressed in most cancers including PC. The anti-apoptotic machinery has been linked to the observed resistance developed to chemotherapy and radiation and therefore is important from the targeted drug development point of view. Over the past ten years, our group has extensively studied a series of small molecule inhibitors of Bcl-2 against PC and provide solid preclinical platform for testing such novel drugs in the clinic. This review examines the efficacy, potency, and function of several small molecule inhibitor drugs targeted to the Bcl-2 family of proteins and their preclinical progress against PC. This article further focuses on compounds that have been studied the most and also discusses the anti-cancer potential of newer class of Bcl-2 drugs.

Angiogenesis inhibitors in cancer therapy: mechanistic perspective on classification and treatment rationales

Angiogenesis, a process of new blood vessel formation, is a prerequisite for tumour growth to supply the proliferating tumour with oxygen and nutrients. The angiogenic process may contribute to tumour progression, invasion and metastasis, and is generally accepted as an indicator of tumour prognosis. Therefore, targeting tumour angiogenesis has become of high clinical relevance. The current review aimed to highlight mechanistic details of anti-angiogenic therapies and how they relate to classification and treatment rationales. Angiogenesis inhibitors are classified into either direct inhibitors that target endothelial cells in the growing vasculature or indirect inhibitors that prevent the expression or block the activity of angiogenesis inducers. The latter class extends to include targeted therapy against oncogenes, conventional chemotherapeutic agents and drugs targeting other cells of the tumour micro-environment. Angiogenesis inhibitors may be used as either monotherapy or in combination with other anticancer drugs. In this context, many preclinical and clinical studies revealed higher therapeutic effectiveness of the combined treatments compared with individual treatments. The proper understanding of synergistic treatment modalities of angiogenesis inhibitors as well as their wide range of cellular targets could provide effective tools for future therapies of many types of cancer.

MiR-148a regulates the growth and apoptosis in pancreatic cancer by targeting CCKBR and Bcl-2

Our previous studies have revealed that miR-148a is downregulated in pancreatic cancer. Bioinformatics analysis has shown cholecystokinin-B receptor (CCKBR) and B cell lymphoma (Bcl-2) to be potential targets of miR-148a. But the pathophysiologic role of miR-148a and its relevance to the growth and development of pancreatic cancer are yet to be investigated. The purpose of this study is to elucidate the molecular mechanisms where miR-148a acts as a tumor suppressor in pancreatic cancer. Our results showed significant downregulation of miR-148a in 28 pancreatic cancer tissue samples and five pancreatic cancer cell lines, compared with their non-tumor counterparts by qRT-PCR. MiR-148a was found to not only inhibit the proliferation of pancreatic cancer cells (PANC-1 and AsPC-1) in vitro by MTT assay and colony formation assay, but also to promote cells apoptosis in vitro by Annexin V-FITC apoptosis detection and caspase activity assay. Using western blot and luciferase activity assay, CCKBR and Bcl-2 were identified as targets of miR-148a. Moreover, we also found that the expression of Bcl-2 lacking in 3'UTR could abrogate the pro-apoptosis function of miR-148a. These findings suggest the importance of miR-148a's targeting of CCKBR and Bcl-2 in the regulation of pancreatic cancer growth and apoptosis.

Evaluation and critical assessment of putative MCL-1 inhibitors

High levels of BCL-2 family proteins are implicated in a failed/ineffective apoptotic programme, often resulting in diseases, including cancer. Owing to their potential as drug targets in cancer therapy, several inhibitors of BCL-2 family proteins have been developed. These primarily target specific members of the BCL-2 family, particularly BCL-2 and BCL-XL but are ineffective against MCL-1. Major efforts have been invested in developing inhibitors of MCL-1, which is commonly amplified in human tumours and associated with tumour relapse and chemoresistance. In this report, the specificity of several BCL-2 family inhibitors (ABT-263, UCB-1350883, apogossypol and BH3I-1) was investigated and compared with putative MCL-1 inhibitors designed to exhibit improved or selective binding affinities for MCL-1 (TW-37, BI97C1, BI97C10, BI112D1, compounds 6 and 7, and MCL-1 inhibitor molecule (MIM-1)). ABT-263, BI97C1, BI112D1, MIM-1 and TW-37 exhibited specificity in inducing apoptosis in a Bax/Bak- and caspase-9-dependent manner, whereas the other agents showed no killing activity, or little or no specificity. Of these inhibitors, only ABT-263 and UCB-1350883 induced apoptosis in a BCL-2- or BCL-XL-dependent system. In cells that depend on MCL-1 for survival, ABT-263 and TW-37 induced extensive apoptosis, suggesting that at high concentrations these inhibitors have the propensity to inhibit MCL-1 in a cellular context. TW-37 induced apoptosis, assessed by chromatin condensation, caspase processing and phosphatidylserine externalisation, in a BAK-dependent manner and in cells that require MCL-1 for survival. TW-37-mediated apoptosis was also partly dependent on NOXA, suggesting that derivatives of TW-37, if engineered to exhibit better selectivity and efficacy at low nanomolar concentrations, may provide useful lead compounds for further synthetic programmes. Expanded medicinal chemistry iteration, as performed for the ABT series, may likewise improve the potency and specificity of the evaluated MCL-1 inhibitors.

Non-apoptotic roles of Bcl-2 family: the calcium connection

The existence of the bcl-2 (B-cell lymphoma-2) gene was reported nearly 30 years ago. Yet, Bcl-2 family group of proteins still surprises us with their structural and functional diversity. Since the discovery of the Bcl-2 family of proteins as one of the main apoptosis judges, the precise mechanism of their action remains a hot topic of intensive scientific research and debates. Although extensive work has been performed on the role of mitochondria in apoptosis, more and more studies point out an implication of the endoplasmic reticulum in this process. Interestingly, Bcl-2 family proteins could be localized to both the mitochondria and the endoplasmic reticulum highlighting their crucial role in apoptosis control. In particular, in these organelles Bcl-2 proteins seem to be involved in calcium homeostasis regulation although the mechanisms underlying this function are still misunderstood. We now assume with high degree of certainty that the majority of Bcl-2 family members take part not only in apoptosis regulation but also in other processes important for the cell physiology briefly denominated as "non-apoptotic" functions. Drawing a complete and comprehensive image of Bcl-2 family requires the understanding of their implications in all cellular processes. Here, we review the current knowledge on the control of calcium homeostasis by the Bcl-2 family at the endoplasmic reticulum and at the mitochondria. Then we focus on the non-apoptotic functions of the Bcl-2 proteins in relation with the regulation of this versatile intracellular messenger. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

MUC5AC protects pancreatic cancer cells from TRAIL-induced death pathways

We have previously reported that a specific siRNA transfected MUC5AC could knockdown MUC5AC expression and suppress in vivo tumor growth and metastasis, although it had no effects on in vitro cell growth, cell survival, proliferation and morphology. In the present study, we investigated which host immune cells induced these effects and how the effects were induced using immunocyte-depleted animal models. The tumor growth of SW1990/si-MUC5AC cells, which show no tumor growth when implanted subcutaneously into a nude mouse, was recovered when neutrophils were removed by anti-Gr-1 mAb administration. This result suggests that MUC5AC may suppress the antitumor effects of neutrophils by allowing tumor cells to escape the host immune system. Subsequently, we investigated the effects of MUC5AC on apoptosis induction mediated by TNF-related apoptosis-inducing ligand (TRAIL), one of the antitumor mechanisms of neutrophils. SW1990/si-MUC5AC cells showed significantly increased active caspase 3 expression after the addition of TRAIL. On the other hand, SW1990/si-mock cells showed no such changes. Our results indicate that MUC5AC inhibits TRAIL‑induced apoptosis in human pancreatic cancer and may serve as an important indicator in diagnosis and prognosis.

Targeting the Bcl-2 family for cancer therapy

INTRODUCTION

Programmed cell death is well-orchestrated process regulated by multiple pro-apoptotic and anti-apoptotic genes, particularly those of the Bcl-2 gene family. These genes are well documented in cancer with aberrant expression being strongly associated with resistance to chemotherapy and radiation.

AREAS COVERED

This review focuses on the resistance induced by the Bcl-2 family of anti-apoptotic proteins and current therapeutic interventions currently in preclinical or clinical trials that target this pathway. Major resistance mechanisms that are regulated by Bcl-2 family proteins and potential strategies to circumvent resistance are also examined. Although antisense and gene therapy strategies are used to nullify Bcl-2 family proteins, recent approaches use small molecule inhibitors (SMIs) and peptides. Structural similarity of the Bcl-2 family of proteins greatly favors development of inhibitors that target the BH3 domain, called BH3 mimetics.

EXPERT OPINION

Strategies to specifically identify and inhibit critical determinants that promote therapy resistance and tumor progression represent viable approaches for developing effective cancer therapies. From a clinical perspective, pretreatment with novel, potent Bcl-2 inhibitors either alone or in combination with conventional therapies hold significant promise for providing beneficial clinical outcomes. Identifying SMIs with broader and higher affinities for inhibiting all of the Bcl-2 pro-survival proteins will facilitate development of superior cancer therapies.

Apoptosis sensitizers enhance cytotoxicity in hepatoblastoma cells

PURPOSE

Drug resistance remains a major challenge for the treatment of high-risk hepatoblastoma (HB). To enhance effectiveness of chemotherapy we modulate apoptosis in HB cells in vitro.

METHODS

Viability was monitored in HB cells (HuH6, HepT1) and fibroblasts in monolayer and spheroid cultures treated with ABT-737, obatoclax, HA14-1, and TW-37 and each in combination with CDDP, etoposide, irinotecan, paclitaxel, and DOXO in a MTT assay. Western blot analyses were performed to determine expressions of pro- and anti-apoptotic proteins.

RESULTS

Obatoclax and ABT-737 led to a dose-dependent decrease of viability in HB cells at concentrations above 0.3 μM. TW-37 and HA14-1 were less effective. ABT-737 and obatoclax had additive effects when combined with CDDP, etoposide, irinotecan, paclitaxel, or DOXO. This was also observed for fibroblast, however, for higher drug concentrations. In spheroid cultures, relative expression of Bcl-XL was increased, Bax was decreased, Mcl-1 was low, and Bcl-2 was not detected compared to 2D cultures, denoting an anti-apoptotic state in spheroids. Obatoclax and ABT-737 have overcome the resistance to CDDP. HuH6 cells have shown higher susceptability for apoptosis sensitizers than HepT1.

CONCLUSION

The data provide evidence that ABT-737 and obatoclax might improve treatment results in children with HB.

Inhibitors of the anti-apoptotic Bcl-2 proteins: a patent review

INTRODUCTION

The B-cell lymphoma-2 (Bcl-2) family of proteins is central to the regulation of apoptosis, which is vital for proper tissue development and cellular homeostasis. Anti-apoptotic proteins, members of the Bcl-2 family, are an important survival factor for many cancers and their overexpression has been associated with tumor initiation, progression, and resistance to current anticancer therapies. Therefore, strategies seeking to antagonize the function of Bcl-2 anti-apoptotic proteins have been extensively studied for developing a novel cancer therapy.

AREAS COVERED

This review covers research and patent literature of the last 15 years dealing with the discovery and development of inhibitors of the Bcl-2 protein family.

EXPERT OPINION

The feasibility of disrupting protein-protein interactions between anti-apoptotic and pro-apoptotic proteins, members of the Bcl-2 family, using peptidomimetics and small-molecule inhibitors has been successfully established. Three small-molecule inhibitors have entered human clinical trials, which will allow the evaluation of this potential therapeutic approach in cancer patients. It will be important to gain a better understanding of pan and selective Bcl-2 inhibitors in order to facilitate future drug design efforts.

Bcl-2: a prime regulator of mitochondrial redox metabolism in cancer cells

SIGNIFICANCE

Mitochondria play a critical role as death amplifiers during drug-induced apoptosis in cancer cells by providing pro-apoptotic factors that are released from the mitochondrial inter-membranous space upon the induction of mitochondrial outer membrane permeabilization. This intrinsic death signaling pathway is the preferred mechanism employed by most anticancer compounds, and as such, resistance to drug-induced apoptosis is invariably associated with inhibition of mitochondrial death signaling network. The latter is a function of a balance between the pro- and the anti-apoptotic members of the Bcl-2 family. Bcl-2 is the prototype anti-apoptotic protein that localizes to the mitochondria and blocks the recruitment and activation of pro-apoptotic proteins, such as Bax, to the mitochondria.

RECENT ADVANCES AND CRITICAL ISSUES

Recent evidence has highlighted a novel mechanism of anti-apoptotic activity of Bcl-2 in addition to its canonical activity in regulating mitochondrial outer membrane permeabilization. This novel activity is a function of cellular redox regulation, in particular, mitochondrial metabolism in cancer cells.

FUTURE DIRECTIONS

Here we review the current state of our understanding of the death inhibitory activity of Bcl-2 and provide insight into the novel functional biology of this remarkable protein, which could have implications for designing innovative strategies to overcome the problem of drug resistance in the clinical settings.

Baicalein, a component of Scutellaria baicalensis, induces apoptosis by Mcl-1 down-regulation in human pancreatic cancer cells

Scutellaria baicalensis (SB) and SB-derived polyphenols possess anti-proliferative activities in several cancers, including pancreatic cancer (PaCa). However, the precise molecular mechanisms have not been fully defined. SB extract and SB-derived polyphenols (wogonin, baicalin, and baicalein) were used to determine their anti-proliferative mechanisms. Baicalein significantly inhibited the proliferation of PaCa cell lines in a dose-dependent manner, whereas wogonin and baicalin exhibited a much less robust effect. Treatment with baicalein induced apoptosis with release of cytochrome c from mitochondria, and activation of caspase-3 and -7 and PARP. The general caspase inhibitor zVAD-fmk reversed baicalein-induced apoptosis, indicating a caspase-dependent mechanism. Baicalein decreased expression of Mcl-1, an anti-apoptotic member of the Bcl-2 protein family, presumably through a transcriptional mechanism. Genetic knockdown of Mcl-1 resulted in marked induction of apoptosis. The effect of baicalein on apoptosis was significantly attenuated by Mcl-1 over-expression, suggesting a critical role of Mcl-1 in this process. Our results provide evidence that baicalein induces apoptosis in pancreatic cancer cells through down-regulation of the anti-apoptotic Mcl-1 protein.

Targeting apoptosis signaling in pancreatic cancer

The ability to escape apoptosis or programmed cell death is a hallmark of human cancers, for example pancreatic cancer. This can promote tumorigenesis, since too little cell death by apoptosis disturbs tissue homeostasis. Additionally, defective apoptosis signaling is the underlying cause of failure to respond to current treatment approaches, since therapy-mediated antitumor activity requires the intactness of apoptosis signaling pathways in cancer cells. Thus, the elucidation of defects in the regulation of apoptosis in pancreatic carcinoma can result in the identification of novel targets for therapeutic interference and for exploitation for cancer drug discovery.

Small-molecule inhibitors reveal a new function for Bcl-2 as a proangiogenic signaling molecule

Cancer has a complex etiology and displays a wide range of cellular escape pathways that allow it to circumvent treatment. Signaling molecules functionally downstream of the circumvented pathways, and particularly at checkpoints where several of these pathways intersect, provide valuable targets for the development of novel anti-cancer drugs. Bcl-2, a pro-survival signaling molecule, is one such protein. This review examines the efficacy, potency, and function of several small molecule inhibitor drugs targeted to the Bcl-2 family of proteins. The review focuses on the compounds with most available data within the literature and discusses both the anti-cancer and the recently unveiled anti-angiogenic potential of this new class of drugs.

Emerging Bcl-2 inhibitors for the treatment of cancer

INTRODUCTION

Bcl-2 family proteins are a component of the antiapoptotic machinery and are overexpressed in different malignancies. Accordingly, their enhanced expression has been attributed to the observed chemoresistance in most of the cancers. Therefore, targeting Bcl-2 family members becomes an important and attractive approach towards cancer therapy and is currently a very rapidly evolving area of research. This article highlights the numerous advancements that have been made in the design and synthesis of small molecule inhibitors (SMI) of pro-survival Bcl-2 proteins.

AREAS COVERED

This review comprehensively describes the progress made over the last 2 decades on this subject, including the clinical status of SMIs of Bcl-2 family proteins. Newer insights on the status of our knowledge on SMIs of Bcl-2 family proteins, their most beneficial application as well as current and future directions in this field are discussed.

EXPERT OPINION

Targeting Bcl-2 family proteins using SMI strategies is gaining momentum, with the emergence of certain new classes of inhibitors in Phase I and II clinical settings. In view of the tremendous progress toward the development of such inhibitors, this innovative approach certainly holds promise and has the potential to become a future mainstay for cancer therapy. The stage is set for the next generation of SMIs, for not only Bcl-2 proteins but also for Mcl-1. Other emerging molecules in the apoptotic machinery will also be explored and targeted.

The marine compound spongistatin 1 targets pancreatic tumor progression and metastasis

Treatment of pancreatic cancer remains a major challenge and new anticancer drugs are urgently required. Our study presents the marine natural compound spongistatin 1 as a promising experimental drug. Spongistatin 1 was applied in an orthotopic in vivo model of human pancreatic cancer. Spongistatin 1 significantly reduced tumor growth, which correlates with a strong apoptosis induction (DNA-fragmentation) and long-term effects on clonogenic survival of pancreatic tumor cells (L3.6pl) in vitro. In addition, the formation of metastasis was reduced in spongistatin 1-treated mice, which is in line with a diminished MMP-9 activity in tumor tissue determined by zymography. Based on the pronounced efficacy of spongistatin 1, the underlying mechanisms were studied in more detail. In vitro adhesion, as well as migration, and invasion assays showed spongistatin 1 to influence these critical steps in the metastatic cascade. Furthermore, spongistatin 1 induced anoikis in L3.6pl cells. Exposure to spongistatin 1 leads to phosphorylation, and thus inactivation of the antiapoptotic protein Bcl-2 in pancreatic tumor cells. siRNA experiments silencing Bcl-2 suggest a role of Bcl-2 in anoikis and cell migration. Taken together, spongistatin 1 not only proved to be a potent experimental drug but also served as a chemical tool to examine the role of the antiapoptotic protein Bcl-2 in pancreas carcinoma, thereby supporting the hypothesis of a link between apoptosis signaling and metastasis.

PAR-4 as a possible new target for pancreatic cancer therapy

IMPORTANCE OF THE FIELD

Pancreatic cancer (PC) is a deadly disease that is intractable to currently available treatment regimens. Although well described in different tumors types, the importance of apoptosis inducer prostate apoptosis response-4 (Par-4) in PC has not been appreciated. PC is an oncogenic kras driven disease, which is known to downregulate Par-4. Therefore, this review highlights its significance and builds a strong case supporting the role of Par-4 as a possible therapeutic target in PC.

AREAS COVERED IN THIS REVIEW

Literature-based evidence spanning the last 15 years on Par-4 and its significance in PC.

WHAT THE READER WILL GAIN

This review provides comprehensive knowledge of the significance of Par-4 and its association with kras status in PC, along with the crosstalk with crucial resistance and survival molecules NF-kappaB and Bcl-2 that ultimately are responsible for the overall poor outcome of different therapeutic approaches in this disease.

TAKE HOME MESSAGE

Par-4 holds promise as a potential therapeutic target that can be induced by chemopreventive agents and small-molecule inhibitors either alone or in combination with standard chemotherapeutics leading to selective apoptosis in PC cells. It also acts as a chemosensitizer and therefore warrants further clinical investigations in this disease.

Metronomic small molecule inhibitor of Bcl-2 (TW-37) is antiangiogenic and potentiates the antitumor effect of ionizing radiation

PURPOSE

To investigate the effect of a metronomic (low-dose, high-frequency) small-molecule inhibitor of Bcl-2 (TW-37) in combination with radiotherapy on microvascular endothelial cells in vitro and in tumor angiogenesis in vivo.

METHODS AND MATERIALS

Primary human dermal microvascular endothelial cells were exposed to ionizing radiation and/or TW-37 and colony formation, as well as capillary sprouting in three-dimensional collagen matrices, was evaluated. Xenografts vascularized with human blood vessels were engineered by cotransplantation of human squamous cell carcinoma cells (OSCC3) and human dermal microvascular endothelial cells seeded in highly porous biodegradable scaffolds into the subcutaneous space of immunodeficient mice. Mice were treated with metronomic TW-37 and/or radiation, and tumor growth was evaluated.

RESULTS

Low-dose TW-37 sensitized primary endothelial cells to radiation-induced inhibition of colony formation. Low-dose TW-37 or radiation partially inhibited endothelial cell sprout formation, and in combination, these therapies abrogated new sprouting. Combination of metronomic TW-37 and low-dose radiation inhibited tumor growth and resulted in significant increase in time to failure compared with controls, whereas single agents did not. Notably, histopathologic analysis revealed that tumors treated with TW-37 (with or without radiation) are more differentiated and showed more cohesive invasive fronts, which is consistent with less aggressive phenotype.

CONCLUSIONS

These results demonstrate that metronomic TW-37 potentiates the antitumor effects of radiotherapy and suggest that patients with head and neck cancer might benefit from the combination of small molecule inhibitor of Bcl-2 and radiation therapy.

Bmi-1 is related to proliferation, survival and poor prognosis in pancreatic cancer

B-cell-specific Moloney murine leukemia virus insertion site 1 (BMI1) is a member of the polycomb group of transcriptional repressors. Until now, its expression and functional significance in pancreatic carcinogenesis was unknown. In the present study, we demonstrated that expression of BMI1 was markedly up-regulated in pancreatic cancer cell lines and surgically resected cancer specimens. In addition, BMI1 expression levels correlated positively with the presence of lymph node metastases and negatively with patient survival rates, suggesting a role for BMI1 in the progression of pancreatic cancer. Furthermore, stable down-regulation of BMI1 suppressed cell growth, delayed the G1/S transition, and enhanced the susceptibility of different pancreatic cell lines to apoptosis following expression of a lentiviral-mediated shRNA targeted for BMI1. Expression of the short-hairpin RNA also correlated with the up-regulation of p21 and Bax and the down-regulation of cyclin D1, cyclin-dependent kinase (CDK)-2 and -4, Bcl-2, and phospho-Akt. Finally, growth suppression following BMI1 depletion was confirmed in a nude mouse model. In conclusion, our findings indicate that BMI1 plays an important role in the late progression of pancreatic cancer and may represent a novel therapeutic target for the treatment of pancreatic cancer.

New potential anti-cancer agents synergize with bortezomib and ABT-737 against prostate cancer

BACKGROUND

We previously described the identification of a transcriptional inhibitor ARC and FoxM1 inhibitors, thiazole antibiotics, Siomycin A and thiostrepton that were able to induce potent p53-independent apoptosis in cancer cell lines of different origin. Here, we report the characterization of these drugs individually or in combination with ABT-737 and bortezomib on a panel of prostate cancer cell lines.

METHODS

DU 145, LNCaP and PC-3 prostate cancer cells were treated with ARC, Siomycin A and thiostrepton to evaluate their activity as single agents or in combination with ABT-737 and bortezomib to measure their synergistic potential in anti-proliferative and cell cycle assays. Chou-Talalay method was used to quantitate the synergistic interaction. Western blot method was used to determine Mcl-1 and FoxM1 expression and caspase-3 cleavage.

RESULTS

We show that ARC inhibited the viability of prostate cancer cells and induced apoptosis in low nanomolar concentration. It potently downregulated the expression of Mcl-1 and showed synergistic combination effect with Bcl-2 inhibitor ABT-737. Thiazole antibiotics, Siomycin A and thiostrepton inhibited growth, FoxM1 expression and induced cell death in prostate cancer cells in low micromolar concentrations. In addition, thiostrepton and ARC synergistically induced apoptosis in prostate cancer cells following combination treatment with proteasome inhibitor bortezomib. Furthermore, we found that all tested drug combinations were able to induce apoptosis selectively in transformed, but not normal cells of the same origin.

CONCLUSIONS

Based on their in vitro activity as single or combination agents, ARC, Siomycin A and thiostrepton represent potential candidates for drug development against prostate cancer.

The role of Bcl-2 family proteins in chronic lymphocytic leukaemia

Bcl-2 family proteins have long been implicated in the pathology of chronic lymphocytic leukaemia (CLL). Indeed, a number of these proteins have been shown to have prognostic importance in this disease. The precise ways in which these proteins impact upon CLL and the ways in which they are regulated remain incompletely resolved. However, significant advances have been recently made in our understanding of how these proteins are controlled by genetic, epigenetic and microenvironmental cues. Furthermore, major progress has been made in trying to target these proteins therapeutically. Here we review the current knowledge about this family of apoptosis-regulating proteins and how they impact upon drug resistance and disease progression. We also summarise evolution in the development of Bcl-2 family inhibitors for the treatment of CLL and other cancers.

Mimicking the BH3 domain to kill cancer cells

Cancer cells show deviant behavior that induces apoptotic signaling. To survive, cancer cells typically acquire changes enabling evasion of death signals. One way they do this is by increasing the expression of anti-apoptotic BCL-2 proteins. Anti-apoptotic BCL-2 family proteins antagonize death signaling by forming heterodimers with pro-death proteins. Heterodimer formation occurs through binding of the pro-apoptotic protein's BH3 domain into the hydrophobic cleft of anti-apoptotic proteins. The BH3 mimetics are small molecule antagonists of the anti-apoptotic BCL-2 members that function as competitive inhibitors by binding to the hydrophobic cleft. Under certain conditions, antagonism of anti-apoptotic BCL-2 family proteins can unleash pro-death molecules in cancer cells. Thus, the BH3 mimetics are a new class of cancer drugs that specifically target a mechanism of cancer cell survival to selectively kill cancer cells.

Regulated cell death pathways: new twists in modulation of BCL2 family function

A number of cell death pathways have been recognized. Though apoptosis and autophagy have been well characterized, programmed necrosis has recently received attention and may provide clinical alternatives to suppress resistant tumors. Necrosis is primarily characterized by large-scale permeabilization, swelling, and rupture of cell membranes and the release of pro-inflammatory cytokines. Traditionally, necrosis in cancer cells has been indicative of poor prognoses, as chronic inflammation was found to encourage tumor growth. Yet, many antitumor effects associated with necrosis have been discovered in certain settings, such as the formation of an effective antitumor immune response. In this way, finding ways to attenuate the pro-tumor effects of necrosis while engaging the antitumor pathways via drugs, radiation, and sensitization may prove valuable as a clinical focus for the future. We hypothesize that the use of Bcl-2 inhibitors may enhance necrotic death characterized by inflammation and antitumor immunity. In this article, we briefly review apoptosis and autophagy and reason how necrosis may be a suitable alternative therapeutic endpoint. We then highlight novel inhibitors of Bcl-2 that may provide clinical application of our hypothesis in the future.

TW-37, a small-molecule inhibitor of Bcl-2, mediates S-phase cell cycle arrest and suppresses head and neck tumor angiogenesis

Members of the Bcl-2 family play a major role in the pathobiology of head and neck cancer. We have shown that Bcl-2 orchestrates a cross talk between tumor cells and endothelial cells that have a direct effect on the progression of head and neck squamous cell carcinoma (HNSCC). Notably, Bcl-2 is significantly up-regulated in the tumor-associated endothelial cells compared with the endothelial cells of normal oral mucosa in patients with HNSCC. Here, we evaluated the effect of TW-37, a small-molecule inhibitor of Bcl-2, on the cell cycle and survival of endothelial cells and HNSCC and on the progression of xenografted tumors. TW-37 has an IC50 of 1.1 micromol/L for primary human endothelial cells and averaged 0.3 micromol/L for head and neck cancer cells (OSCC3, UM-SCC-1, and UM-SCC-74A). The combination of TW-37 and cisplatin showed enhanced cytotoxic effects for endothelial cells and HNSCC in vitro, compared with single drug treatment. Notably, whereas cisplatin led to an expected G2-M cell cycle arrest, TW-37 mediated an S-phase cell cycle arrest in endothelial cells and in HNSCC. In vivo, TW-37 inhibited tumor angiogenesis and induced tumor apoptosis without significant systemic toxicities. Combination of TW-37 and cisplatin enhanced the time to tumor failure (i.e., 4-fold increase in tumor volume), compared with either drug given separately. Collectively, these data reveal that therapeutic inhibition of Bcl-2 function with TW-37 is sufficient to arrest endothelial cells and HNSCC in the S phase of the cell cycle and to inhibit head and neck tumor angiogenesis.

Design and synthesis of a gossypol derivative with improved antitumor activities

A novel chemical process has been devised for the synthesis of a new derivative of gossypol, 6,7,6',7'-tetrahydroxy-5,5'-diisopropyl-3,3'-dimethyl-[2,2']binaphthalenyl-1,4,1',4'-tetraone (Apogossypolone). This new process has only four steps, with a shorter synthesis span, a simple purification process, and improved yield and quality. The structure of apogossypolone was characterized by( 1)H-nuclear magnetic resonance, (13)C-nuclear magnetic resonance, mass spectroscopy, infrared spectroscopy, and elemental analysis. Cell-cytotoxicity assay demonstrates that apogossypolone is three- to six-fold more potent than the parent compound, (-)-gossypol, in inhibiting the human prostate tumor cell lines PC-3 and DU-145 as well as the human breast cancer cell line MDA-MB-231. The colony-formation assay with DU-145 cells showed that apogossypolone inhibited more than 70% of colony formation at 1 muM, whereas (-)-gossypol at 10 muM only inhibited less than 50% of colony formation. The results indicate that apogossypolone exerts strong antitumor activities in human prostate and breast cancer cells, and thus represents a promising cancer therapeutic.

Corticotropin Releasing Factor promotes breast cancer cell motility and invasiveness

INTRODUCTION

Cancer cells secrete bioactive peptides that act in an autocrine or paracrine fashion affecting tumor growth and metastasis. Corticotropin-releasing factor (CRF), a hypothalamic neuropeptide that controls the response to stress, has been detected in breast cancer tissues and cell lines. CRF can affect breast cancer cells in an autocrine or paracrine manner via its production from innervating sympathetic neurons or immune cells.

METHODS

In the present study we report our findings regarding the impact of CRF on breast cancer cell motility and invasiveness. For this purpose we used the MCF7 breast cancer cell line and evaluated the effect of CRF on motility and invasiveness using the wound-healing and boyden-chamber assays. In addition, we measured the effect of CRF on molecules that mediate motility by western blot, immunofluorescence, ELISA and RT-PCR.

RESULTS

Our findings show that: 1. CRF transiently inhibited the apoptosis of MCF7 cells. 2. CRF enhanced MCF7 cell motility in a wound healing assay and their invasiveness through extracellular matrix. 3. CRF increased actin polymerization, phosphorylation of Focal Adhesion Kinase (FAK), providing a potential mechanism for the observed induction of MCF7 motility. 4. CRF induced the expression of Cox-1 but not Cox-2 in MCF7 cells as well as the production of prostaglandins, factors known to promote invasiveness and metastasis.

CONCLUSION

Overall, our data suggest that CRF stimulates cell motility and invasiveness of MCF7 cells most probably via induction of FAK phosphorylation and actin filament reorganization and production of prostaglandins via Cox1. Based on these findings we postulate that the stress neuropeptide CRF present in the vicinity of tumors (either produced locally by the tumor cells themselves or by nearby normal cells or secreted from the innervations of surrounding tissues) may play an important role on breast tumor growth and metastatic capacity, providing a potential link between stress and tumor progression.

Apoptosis pathways and their therapeutic exploitation in pancreatic cancer

Resistance to apoptosis (programmed cell death) is a characteristic feature of human malignancies including pancreatic cancer, which is one of the leading causes of cancer deaths in the western world. Defects in this intrinsic cell death program can contribute to the multistep process of tumorigenesis, because too little cell death can disturb tissue homeostasis. Further, blockade of apoptosis pathways can cause treatment failure, because intact apoptosis signalling cascades largely mediate therapy-induced cytotoxicity. The elucidation of apoptosis pathways in pancreatic carcinoma over the last decade has resulted in the identification of various molecular defects. How apoptosis pathways can be exploited for the treatment of pancreatic cancer will be discussed in this review.

TW-37, a small-molecule inhibitor of Bcl-2, inhibits cell growth and induces apoptosis in pancreatic cancer: involvement of Notch-1 signaling pathway

Overexpression of Bcl-2 family proteins has been found in a variety of aggressive human carcinomas, including pancreatic cancer, suggesting that specific agents targeting Bcl-2 family proteins would be valuable for pancreatic cancer therapy. We have previously reported that TW-37, a small-molecule inhibitor of Bcl-2 family proteins, inhibited cell growth and induced apoptosis in pancreatic cancer. However, the precise role and the molecular mechanism of action of TW-37 have not been fully elucidated. In our current study, we found that TW-37 induces cell growth inhibition and S-phase cell cycle arrest, with regulation of several important cell cycle-related genes like p27, p57, E2F-1, cdc25A, CDK4, cyclin A, cyclin D1, and cyclin E. The cell growth inhibition was accompanied by increased apoptosis with concomitant attenuation of Notch-1, Jagged-1, and its downstream genes such as Hes-1 in vitro and in vivo. We also found that down-regulation of Notch-1 by small interfering RNA or gamma-secretase inhibitors before TW-37 treatment resulted in enhanced cell growth inhibition and apoptosis. Our data suggest that the observed antitumor activity of TW-37 is mediated through a novel pathway involving inactivation of Notch-1 and Jagged-1.

Non-peptidic small molecule inhibitors against Bcl-2 for cancer therapy

A critical regulator of the apoptotic machinery is the Bcl-2 family proteins whose over expression confers a protective effect on malignant cells against death signals of apoptosis. Cancer cells that are resistant to various anti-cancer drugs and treatment regimen are found to over express these Bcl-2 proteins such as Bcl-2, Bcl-X(L), Mcl-1, Bcl-w, and A1/Bfl1. In recent years there has been an exponential growth in the identification as well as synthesis of non-peptidic cell permeable small-molecule inhibitors (SMIs) of protein-protein interaction. The focus of this article is on inhibitors of anti-apoptotic protein Bcl-2. This review summarizes an up to date knowledge of the available SMIs, their mode of action as well as their current status in preclinical as well as clinical development.

The effect of targeted magnetic nanopaticles on hepatoma and the expression of bcl-2/bax protein

The effect of targeted magnetic nanoparticles on hepatoma and the underlying mechanism were examined. Nude mice transplanted with a human hepatoma cell line (HepG2 cells) were randomized into 5 groups, including: (1) group A, receiving normal saline, (2) group B, receiving 5-fluorouracil (5-Fu), (3) group C, receiving magnetic nanoparticles containing 5-Fu, (4) group D, consisting of treatment with magnetic nanoparticles containing 5-Fu and inside magnetic field and (5) group E, receiving pure magnetic nanoparticles and inside magnetic field. Morphological features of transplanted tumors in mice in each group were observed under transmission electron microscope (TEM). The expression of bcl-2/bax protein was immunohistochemically detected by SABC method. The results showed that a large number of apoptotic tumor cells were found in group B and group D under TEM. The expression of bcl-2 protein was significantly decreased and the expression of bax protein increased significantly in both group B and D as compared with those in group A, C and E (P<0.01 for all). The decrease in bcl-2 and the increase in bax were more in group D as compared with group B (P<0.01). It is concluded that the targeted magnetic nanoparticles containing 5-Fu can improve the chemotherapeutic effect of 5-Fu by decreasing bcl-2 expression, increasing bax expression and inducing apoptosis of the liver cancer cells.