The polyamine transport system as a target for anticancer drug development

The vast majority of anticancer drugs in clinical use are limited by systemic host toxicity due to their non-specific side effects. These shortcomings have led to the development of tumour specific drugs which target a single-deregulated pathway or over expressed receptor in cancer cells. Whilst this approach has achieved clinical success, we have also learnt that targeting a single entity in cancer is rarely curative due to the large number of deregulated pathways, receptors and kinases which are also present, in addition to the target. An attractive alternative to improve targeting would be to harness the already established activity of known anticancer drugs by attaching them to a molecule that is transported into cancer cells via a selective transport system. One possibility for this approach is the polyamine pathway. This review provides a brief overview of the polyamine pathway and how, over the years, it has proved an exciting target for the development of novel anticancer agents. However, the focus of this article will be on the properties of the polyamine transport system and how these features could potentially be exploited to develop a novel and selective anticancer drug delivery system.     

Restoration of antitumor immunity through selective inhibition of myeloid derived suppressor cells by anticancer therapies

Accumulating evidence suggests that the success of some anticancer therapies not only relies on their direct cytotoxicity on tumor cells but also on their ability to promote anticancer immune responses. However, immunosuppressive cells such as Myeloid Derived Suppressor Cells (MDSC) that are generated during tumor progression blunt antitumor immune responses and thus represent a major obstacle to the clinical implementation of immunotherapy protocols. We have recently identified 5-Fluorouracil (5-FU) as an anticancer agent that selectively induced MDSC apoptotic cell death in vitro and in vivo. The elimination of MDSC by 5-FU increased IFNγ secretion by tumor specific CD8(+) T cells infiltrating the tumor and promoted T-cell dependent antitumor responses in vivo, suggesting that some anticancer therapies can reverse tumor-mediated immunosuppression. Here, we review the molecular pathways leading to the induction of MDSC in cancer and discuss how different anticancer agents successfully target these cells in vivo, thereby restoring potent anticancer immunity.     

Statins,stem cells,and cancer

The statins (3‐hydroxy‐3‐methylglutaryl coenzyme A reductase inhibitors) were proven to be effective antilipid agents against cardiovascular disease. Recent reports demonstrate an anticancer effect induced by the statins through inhibition of cell proliferation, induction of apoptosis, or inhibition of angiogenesis. These effects are due to suppression of the mevalonate pathway leading to depletion of various downstream products that play an essential role in cell cycle progression, cell signaling, and membrane integrity. Recent evidence suggests a shared genomic fingerprint between embryonic stem cells, cancer cells, and cancer stem cells. Activation targets of NANOG, OCT4, SOX2, and c‐MYC are more frequently overexpressed in certain tumors. In the absence of bona fide cancer stem cell lines, human embryonic stem cells, which have similar properties to cancer and cancer stem cells, have been an excellent model throwing light on the anticancer affects of various putative anticancer agents. It was shown that key cellular functions in karyotypically abnormal colorectal and ovarian cancer cells and human embryonic stem cells are inhibited by the statins and this is mediated via a suppression of this stemness pathway. The strategy for treatment of cancers may thus be the targeting of a putative cancer stem cell within the tumor with specific agents such as the statins with or without chemotherapy. The statins may thus play a dual prophylactic role as a lipid‐lowering drug for the prevention of heart disease and as an anticancer agent to prevent certain cancers. This review examines the relationship between the statins, stem cells, and certain cancers. J. Cell. Biochem. 106: 975–983, 2009. © 2009 Wiley‐Liss, Inc.     

Mithramycin inhibits etoposide resistance in glucose-deprived HT-29 human colon carcinoma cells

Physiological cell conditions such as glucose deprivation and hypoxia play roles in the development of drug resistance in solid tumors. These tumor-specific conditions cause decreased expression of DNA topoisomerase IIalpha, rendering cells resistant to topo II target drugs such as etoposide. Thus, targeting tumor-specific conditions such as a low glucose environment may be a novel strategy in the development of anticancer drugs. On this basis, we established a novel screening program for anticancer agents with preferential cytotoxic activity in cancer cells under glucose-deprived conditions. We recently isolated an active compound, AA-98, from Streptomyces sp. AA030098 that can prevent stress-induced etoposide resistance in vitro. Furthermore, LC-MS and various NMR spectroscopic methods identified AA-98 as mithramycin, which belongs to the aureolic acid group of antitumor compounds. We found that mithramycin prevents the etoposide resistance that is induced by glucose deprivation. The etoposide-chemosensitive action of mithramycin was just dependent on strict low glucose conditions, and resulted in the selective cell death of etoposide-resistant HT-29 human colon cancer cells.     

Bioactive food components and cancer risk reduction

Research over the last three decades has provided convincing evidence to support the premise that diets rich in fruits and vegetables may be protective against the risk of different types of cancers. Initial evidence for protective effect of fruits and vegetables against cancer risk came from population-based case-control studies, which prompted intense research aimed at (a) identification of bioactive component(s) responsible for the anticancer effects of fruits and vegetables, (b) elucidation of the mechanisms by which bioactive food components may prevent cancer, and (c) determination of their efficacy for prevention of cancer in animal models. The bioactive components responsible for cancer chemopreventive effects of various edible plants have now been identified. For instance, anticancer effect of Allium vegetables including garlic is attributed to organosulfur compounds (e.g., diallyl trisulfide). Interestingly, unlike cancer chemotherapy drugs, many bioactive food components selectively target cancer cells. Molecular basis for selectivity of anticancer bioactive food components towards cancer cells remains elusive, but these agents appear promiscuous and target multiple signal transduction pathways to inhibit cancer cell growth in vitro and in vivo. Despite convincing observational and experimental evidence, however, limited effort has been directed towards clinical investigations to determine efficacy of bioactive food components for prevention of human cancers. This article reviews current knowledge on cancer chemopreventive effects of a few highly promising dietary constituents, including garlic-derived organosulfides, berry compounds, and cruciferous vegetable-derived isothiocyanates, and serves to illustrate complexity of the signal transduction mechanisms in cancer chemoprevention by these promising bioactive food components.     

Exploiting death receptor signaling pathways for tumor therapy

Apoptosis or programmed cell death is a key regulator of physiological growth control and regulation of tissue homeostasis. Tipping the balance between cell death and proliferation in favor of cell survival may result in tumor formation. Moreover, current cancer therapies, e.g. chemotherapy, gamma-irradiation, immunotherapy or suicide gene therapy, primarily exert their antitumor effect by triggering an evolutionary conserved apoptosis program in cancer cells. For example, death receptor signaling has been implied to contribute to the efficacy of cancer therapy. Thus, failure to undergo apoptosis in response to anticancer therapy because of defects in death receptor pathways may result in resistance. Further insights into the mechanisms regulating apoptosis in response to anticancer therapy and how cancer cells evade cell death may provide novel opportunities for targeted therapeutics. Thus, agents designed to selectively activate death receptor pathways may enhance the efficacy of conventional therapies and may even overcome some forms of cancer resistance.     

Design,Synthesis, and In Vitro and In Vivo Biological Studies of a 3′-Deoxythymidine Conjugate that Potentially Kills Cancer Cells Selectively

Thymidine kinases (TKs) have been considered one of the potential targets for anticancer therapeutic because of their elevated expressions in cancer cells. However, nucleobase analogs targeting TKs have shown poor selective cytotoxicity in cancer cells despite effective antiviral activity. 3′-Deoxythymidine phenylquinoxaline conjugate (dT-QX) was designed as a novel nucleobase analog to target TKs in cancer cells and block cell replication via conjugated DNA intercalating quinoxaline moiety. In vitro cell screening showed that dT-QX selectively kills a variety of cancer cells including liver carcinoma, breast adenocarcinoma and brain glioma cells; whereas it had a low cytotoxicity in normal cells such as normal human liver cells. The anticancer activity of dT-QX was attributed to its selective inhibition of DNA synthesis resulting in extensive mitochondrial superoxide stress in cancer cells. We demonstrate that covalent linkage with 3′-deoxythymidine uniquely directed cytotoxic phenylquinoxaline moiety more toward cancer cells than normal cells. Preliminary mouse study with subcutaneous liver tumor model showed that dT-QX effectively inhibited the growth of tumors. dT-QX is the first molecule of its kind with highly amendable constituents that exhibits this selective cytotoxicity in cancer cells.     

Suppression of autophagy by FIP200 deletion impairs DNA damage repair and increases cell death upon treatments with anticancer agents

Autophagy is a lysosomal bulk degradation process for intracellular protein and organelles. FIP200 (200 kDa FAK-family interacting protein) is an essential component of mammalian autophagy that is implicated in breast cancer in recent studies. Here we show that inactivation of FIP200 resulted in deficient repair of DNA damage induced by ionizing radiation and anticancer agents in mouse embryonic fibroblasts (MEF). The persistent DNA damage correlated to increased apoptosis and reduced survival of FIP200 knockout (KO) MEFs after treatments with camptothecin (CPT), a topoisomerase I inhibitor and chemotherapeutic agent. Reexpression of FIP200 in FIP200 KO MEFs restored both efficient DNA damage repair and cell survival. Furthermore, knockdown of the increased p62 expression in FIP200 KO MEFs rescued the impaired DNA damage repair and CPT-induced cell death. In contrast, treatment of cells with N-acetyl cysteine did not affect these defects in FIP200 KO MEFs. Finally, FIP200 KO MEFs also showed deficient DNA damage repair and increased cell death compared with control MEFs, when treated with etoposide, a topoisomerase II inhibitor and another anticancer agent. Together, these results identify a new function for FIP200 in the regulation of DNA damage response and cell survival through its activity in autophagy and suggest the possibility of FIP200 or other autophagy proteins as a potential target for treatment to enhance the efficiency of cancer therapy using DNA damage-inducing agents.     

Teratogen screening using transcriptome profiling of differentiating human embryonic stem cells

Teratogens are substances that may cause defects in normal embryonic development while not necessarily being toxic in adults. Identification of possible teratogenic compounds has been historically beset by the species‐specific nature of the teratogen response. To examine teratogenic effects on early human development we performed non‐biased expression profiling of differentiating human embryonic and induced pluripotent stem cells treated with several drugs – ethanol, lithium, retinoic acid (RA), caffeine and thalidomide, which is known to be highly species specific. Our results point to the potency of specific teratogens and their affected tissues and pathways. Specifically, we could show that ethanol caused dramatic increase in endodermal differentiation, RA caused misregulation of neural development and thalidomide affected both these processes. We thus propose this method as a valuable addition to currently available animal screening approaches.     

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

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

Enhanced suppression of proliferation and migration in highly-metastatic lung cancer cells by combination of valproic acid and coumarin-3-carboxylic acid and its molecular mechanisms of action

Valproic acid (VPA) as a broad-spectrum inhibitor of histone deacetylase, has been used in cancer therapy. Recently, the combination of VPA with other anticancer agents has been considered as a useful and necessary strategy to inhibit tumor growth and progression. The coumarin derivates from natural plants have been shown to be the promising natural anticancer agents. However, no literature is available on the anticancer effects of the combination of VPA and coumarin-3-carboxylic acid (HCCA). Here we show that this combination significantly increases inhibitory effects against the proliferation and migration in highly-metastatic lung cancer cells by inducing apoptosis and cell cycle arrest as well as regulating related protein expressions. Our results indicate that this combination of VPA with HCCA not only enhances the protein levels of Bax, cytosolic cytochrome c, caspase-3 and PARP-1 but also reduces the protein expressions of Bcl-2, cyclin D1 and NF-κB as well as inhibits the phosphorylation and expressions of Akt, EGFR, VEGFR2 and c-Met in the cancer cells. Our results suggest that the combination of VPA with HCCA suppresses the proliferation and migration of lung cancer cells via EGFR/VEGFR2/c-Met-Akt-NF-κB signaling pathways; this combination may have a wide therapeutic and/or adjuvant therapeutic application in the treatment of lung cancer.     

Selective cytotoxicity of squamocin on T24 bladder cancer cells at the S-phase via a Bax-, Bad-, and caspase-3-related pathways

Annonaceous acetogenins are a group of potential anti-neoplastic agents isolated from Annonaceae plants. We purified squamocin, a cytotoxic bis-tetrahydrofuran acetogenin, from the seeds of Annona reticulata and analyzed its biologic effects on cancer cells. We showed that squamocin was cytotoxic to all the cancer lines tested. Furthermore, squamocin arrested T24 bladder cancer cells at the G1 phase and caused a selective cytotoxicity on S-phase-enriched T24 cells. It induced the expression of Bax and Bad pro-apoptotic genes, enhanced caspase-3 activity, cleaved the functional protein of PARP and caused cell apoptosis. These results suggest that squamocin is a potentially promising anticancer compound.     

Targeting oncogenic signaling pathways by exploiting nanotechnology

Two scientific areas have recently emerged that can revolutionize cancer chemotherapy. First, an understanding of the different cellular signaling pathways implicated in the development and progression of cancer resulting in poor prognosis and drug resistance, have identified potential drug targets. Inhibitors of signal transduction pathways are currently in the clinics. Secondly, nanotechnology has emerged as an exciting multidisciplinary field promising to provide breakthrough solutions to the problems of optimizing the efficacy or therapeutic index of anticancer agents. The promise of nanotechnology lies in the ability to engineer customizable nanoscale constructs that can be loaded with one or more payloads such as chemotherapeutics, targeting units, imaging and diagnostic agents. This review addresses the potential integration of these two approaches to engineer nanoparticles that can target various signal transduction pathways in cancer.     

Daidzein Synergizes with Gefitinib to Induce ROS/JNK/c-Jun Activation and Inhibit EGFR-STAT/AKT/ERK Pathways to enhance Lung Adenocarcinoma cells chemosensitivity

Lung cancer is the major cause of cancer associated mortality. Mutations in EGFR have been implicated in lung cancer pathogenesis. Gefitinib (GF) is a RTKI (receptor tyrosine kinase inhibitor) first-choice drug for EGFR mutated advanced lung cancer. However, drug toxicity and cancer cell resistance lead to treatment failure. Consequently, new therapeutic strategies are urgently required. Therefore, this study was aimed at identifying tumor suppressive compounds that can synergistically improve Gefitinib chemosensitivity in the lung cancer treatment. Medicinal plants offer a vast platform for the development of novel anticancer agents. Daidzein (DZ) is an isoflavone compound extracted from soy plants and has been shown to possess many medicinal benefits. The anticancer potential of GF and DZ combination treatment was investigated using MTT, western blot, fluorescent microscopy imaging, flow cytometry and nude mice tumor xenograft techniques. Our results demonstrate that DZ synergistically induces c-Jun nuclear translocation through ROS/ASK1/JNK and downregulates EGFR-STAT/AKT/ERK pathways to activate apoptosis and a G0/G1 phase cell cycle blockade. In in-vivo, the combination treatment significantly suppressed A549 lung cancer cells tumor xenograft growth without noticeable toxicity. Daidzein supplements with current chemotherapeutic agents may well be an alternative strategy to improve the treatment efficacy of lung adenocarcinoma.     

Enhancement of Auranofin-Induced Apoptosis in MCF-7 Human Breast Cells by Selenocystine,a Synergistic Inhibitor of Thioredoxin Reductase

Thioredoxin system plays an important role in regulation of intracellular redox balance and various signaling pathways. Thioredoxin reductase (TrxR) is overexpressed in many cancer cells and has been identified as a potential target of anticancer drugs. Auranofin (AF) is potent TrxR inhibitor with novel in vitro and in vivo anticancer activities. Selenocystine (SeC) is a nutritionally available selenoamino acid with selective anticancer effects through induction of apoptosis. In the present study, we demonstrated the synergistic effects and the underlying molecular mechanisms of SeC in combination with AF on MCF-7 human breast cancer cells. The results showed that SeC and AF synergistically inhibited the cancer cell growth through induction of ROS-dependent apoptosis with the involvement of mitochondrial dysfunction. DNA damage-mediated p53 phosphorylation and down-regulation of phosphorylated AKT and ERK also contributed to cell apoptosis. Moreover, we demonstrated the important role of TrxR activity in the synergistic action of SeC and AF. Taken together, our results suggest the strategy to use SeC and AF in combination could be a highly efficient way to achieve anticancer synergism by targeting TrxR.     

Apoptosis meets proteasome, an invaluable therapeutic target of anticancer drugs

This report reviews the current status of extensive efforts directed towards the interpretation of crosstalk between apoptosis and proteasome to understanding the molecular mechanism of anticancer agents targeting proteasome, with particular focus on MG132 and PS-341. The discovery that all cancer cells have retained the apoptotic death program has offered to the researchers new biochemical targets to design anticancer drugs. Moreover, the demonstration that proteasome inhibition induces apoptosis and sensitizes cancer cells to traditional tumoricidal agents has proposed the proteasome as an attractive target for development of new anticancer drugs. Since then, a number of both naturally occurring and synthetic inhibitors of the proteasome have been identified. The best characterized and most widely used inhibitors of the proteasome are the peptide aldehydes; among these MG132, due to its broad spectrum of action, low cost and rapid reversibility of action, still remains the first choice to study proteasome function in cell and tissue cultures. Recently, a very potent new class of selective and reversible proteasome inhibitors which contains an inhibitory boronate group has been described. PS-341 represent the first of this promising class of agents that could have application in cancer therapy and it is the only that has progressed to clinical trials.     

Autophagy and mTOR pathways in mouse embryonic stem cell,lung cancer and somatic fibroblast cell lines

Embryonic developmental stages and regulations have always been one of the most intriguing aspects of science. Since the cancer stem cell discovery, striking for cancer development and recurrence, embryonic stem cells and control mechanisms, as well as cancer cells and cancer stem cell control mechanisms become important research materials. It is necessary to reveal the similarities and differences between somatic and cancer cells which are formed of embryonic stem cells divisions and determinations. For this purpose, mouse embryonic stem cells (mESCs), mouse skin fibroblast cells (MSFs) and mouse lung squamous cancer cells (SqLCCs) were grown in vitro and the differences between these three cell lines signalling regulations of mechanistic target of rapamycin (mTOR) and autophagic pathways were demonstrated by immunofluorescence and real-time polymerase chain reaction. Expressional differences were clearly shown between embryonic, cancer and somatic cells that mESCs displayed higher expressional level of Atg10, Hdac1 and Cln3 which are related with autophagic regulation and Hsp4, Prkca, Rhoa and ribosomal S6 genes related with mTOR activity. LC3 and mTOR protein levels were lower in mESCs than MSFs. Thus, the mechanisms of embryonic stem cell regulation results in the formation of somatic tissues whereas that these cells may be the causative agents of cancer in any deterioration.     

A novel role of DNA polymerase eta in modulating cellular sensitivity to chemotherapeutic agents

Genetic defects in polymerase eta (pol eta; hRad30a gene) result in xeroderma pigmentosum variant syndrome (XP-V), and XP-V patients are sensitive to sunlight and highly prone to cancer development. Here, we show that pol eta plays a significant role in modulating cellular sensitivity to DNA-targeting anticancer agents. When compared with normal human fibroblast cells, pol eta-deficient cells derived from XP-V patients were 3-fold more sensitive to beta-d-arabinofuranosylcytosine, gemcitabine, or cis-diamminedichloroplatinum (cisplatin) single-agent treatments and at least 10-fold more sensitive to the gemcitabine/cisplatin combination treatment, a commonly used clinical regimen for treating a wide spectrum of cancers. Cellular and biochemical analyses strongly suggested that the higher sensitivity of XP-V cells to these agents was due to the inability of pol eta-deficient cells to help resume the DNA replication process paused by the gemcitabine/cisplatin-introduced DNA lesions. These results indicated that pol eta can play an important role in determining the cellular sensitivity to therapeutic agents. The findings not only illuminate pol eta as a potential pharmacologic target for developing new anticancer agents but also provide new directions for improving future chemotherapy regimen design considering the use of nucleoside analogues and cisplatin derivatives.     

A new science-business paradigm in anticancer drug development

Studies into the molecular mechanisms of cancer have revealed that, with a few exceptions, the disease lacks a specific drug target. Therefore, new anticancer drugs not only take many years and much money to develop but also might not outperform existing drugs. However, what are assumed to be unfavorable hallmarks of cancer, for example drug resistance, can be exploited for selective anticancer therapy and for protection of normal cells. Based on this paradigm, the drug discovery can be complemented by novel use of existing agents and even "failed" drugs. The pharmacological industry could develop low cost, effective therapeutic modalities, by "re-using" already marketed and late-stage products in cancer-selective therapeutic kits.