Showing papers on "Cancer cell published in 2004"

In vivo activation of the p53 pathway by small-molecule antagonists of MDM2.

Abstract: MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.

Integrin signalling during tumour progression.

Abstract: During progression from tumour growth to metastasis, specific integrin signals enable cancer cells to detach from neighbouring cells, re-orientate their polarity during migration, and survive and proliferate in foreign microenvironments. There is increasing evidence that certain integrins associate with receptor tyrosine kinases (RTKs) to activate signalling pathways that are necessary for tumour invasion and metastasis. The effect of these integrins might be especially important in cancer cells that have activating mutations, or amplifications, of the genes that encode these RTKs.

Akt stimulates aerobic glycolysis in cancer cells

Abstract: Cancer cells frequently display high rates of aerobic glycolysis in comparison to their nontransformed counterparts, although the molecular basis of this phenomenon remains poorly understood. Constitutive activity of the serine/threonine kinase Akt is a common perturbation observed in malignant cells. Surprisingly, although Akt activity is sufficient to promote leukemogenesis in nontransformed hematopoietic precursors and maintenance of Akt activity was required for rapid disease progression, the expression of activated Akt did not increase the proliferation of the premalignant or malignant cells in culture. However, Akt stimulated glucose consumption in transformed cells without affecting the rate of oxidative phosphorylation. High rates of aerobic glycolysis were also identified in human glioblastoma cells possessing but not those lacking constitutive Akt activity. Akt-expressing cells were more susceptible than control cells to death after glucose withdrawal. These data suggest that activation of the Akt oncogene is sufficient to stimulate the switch to aerobic glycolysis characteristic of cancer cells and that Akt activity renders cancer cells dependent on aerobic glycolysis for continued growth and survival.

Cytokines in cancer pathogenesis and cancer therapy

Abstract: The mixture of cytokines that is produced in the tumour microenvironment has an important role in cancer pathogenesis. Cytokines that are released in response to infection, inflammation and immunity can function to inhibit tumour development and progression. Alternatively, cancer cells can respond to host-derived cytokines that promote growth, attenuate apoptosis and facilitate invasion and metastasis. A more detailed understanding of cytokine–tumour-cell interactions provides new opportunities for improving cancer immunotherapy.

A high-affinity conformation of Hsp90 confers tumor selectivity on Hsp90 inhibitors

Abstract: 5628 Heat shock protein 90 (Hsp90) is a molecular chaperone that plays a key role in the conformational maturation of oncogenic signaling proteins including HER-2, Akt, Raf-1, Bcr-Abl, and mutated p53. The Hsp90 inhibitor 17-allylaminogeldanamycin (17-AAG) binds Hsp90 and induces proteasomal degradation of Hsp90 ‘client’ proteins. Although Hsp90 is highly expressed in most cells, Hsp90 inhibitors selectively kill cancer cells, and 17-AAG is currently in Phase I clinical trials. However, the molecular basis of the tumor selectivity of Hsp90 inhibitors is unknown. The selective retention of 17-AAG in subcutaneous tumor masses in vivo suggests the existence of a drug ‘sink’ in tumor cells. Here we report that Hsp90 derived from tumor cells and clinical cancer biopsies has a 100-fold higher binding affinity for 17-AAG than does Hsp90 from normal cells and tissues. Furthermore, the cytotoxic activity of 17-AAG correlates closely with the binding affinity of the drug to Hsp90 isolated from different cells. This binding affinity change is induced by association of Hsp90 with it’s co-chaperone proteins since tumor Hsp90 is present entirely in multi-chaperone complexes with high ATPase activity, whereas Hsp90 from normal tissues is in a latent, uncomplexed state. In vitro reconstitution of chaperone complexes with Hsp90 resulted in increased binding affinity to 17-AAG, and increased ATPase activity. Additional experiments addressing the relative contribution of cell cycling, oncoprotein overexpression and stress to the activation of Hsp90 will also be presented. We propose a model of Hsp90-dependent malignant progression in which, as tumor cells gradually accumulate mutant and overexpressed signaling proteins, Hsp90 becomes engaged in active chaperoning and stabilization of oncoproteins, and adopts a novel high-affinity form induced by bound co-chaperone proteins. Interestingly, dependence on the activated, high affinity chaperone could make Hsp90 an ’Achilles heel’ of tumor cells, driving the selective accumulation and bioactivity of pharmacological Hsp90 inhibitors, and making tumor Hsp90 a unique cancer target.

PI3K-Akt pathway: its functions and alterations in human cancer.

Abstract: Phosphatidylinositol-3-kinase (PI3K) is a lipid kinase and generates phosphatidylinositol-3,4,5-trisphosphate (PI(3, 4, 5)P3). PI(3, 4, 5)P3 is a second messenger essential for the translocation of Akt to the plasma membrane where it is phosphorylated and activated by phosphoinositide-dependent kinase (PDK) 1 and PDK2. Activation of Akt plays a pivotal role in fundamental cellular functions such as cell proliferation and survival by phosphorylating a variety of substrates. In recent years, it has been reported that alterations to the PI3K-Akt signaling pathway are frequent in human cancer. Constitutive activation of the PI3K-Akt pathway occurs due to amplification of the PIK3C gene encoding PI3K or the Akt gene, or as a result of mutations in components of the pathway, for example PTEN (phosphatase and tensin homologue deleted on chromosome 10), which inhibit the activation of Akt. Several small molecules designed to specifically target PI3K-Akt have been developed, and induced cell cycle arrest or apoptosis in human cancer cells in vitro and in vivo. Moreover, the combination of an inhibitor with various cytotoxic agents enhances the anti-tumor efficacy. Therefore, specific inhibition of the activation of Akt may be a valid approach to treating human malignancies and overcoming the resistance of cancer cells to radiation or chemotherapy.

Persistence of a small subpopulation of cancer stem-like cells in the C6 glioma cell line

Abstract: Both stem cells and cancer cells are thought to be capable of unlimited proliferation. Paradoxically, however, some cancers seem to contain stem-like cells (cancer stem cells). To help resolve this paradox, we investigated whether established malignant cell lines, which have been maintained for years in culture, contain a subpopulation of stem cells. In this article, we show that many cancer cell lines contain a small side population (SP), which, in many normal tissues, is thought to contain the stem cells of the tissue. We demonstrate that in the absence of serum the combination of basic fibroblast growth factor and platelet-derived growth factor maintains SP cells in the C6 glioma cell line. Moreover, we show that C6 SP cells, but not non-SP cells, can generate both SP and non-SP cells in culture and are largely responsible for the in vivo malignancy of this cell line. Finally, we provide evidence that C6 SP cells can produce both neurons and glial cells in vitro and in vivo. We propose that many cancer cell lines contain a minor subpopulation of stem cells that is enriched in an SP, can be maintained indefinitely in culture, and is crucial for their malignancy.

Targeted cancer therapy

Abstract: Disruption of the normal regulation of cell-cycle progression and division lies at the heart of the events leading to cancer. Complex networks of regulatory factors, the tumour microenvironment and stress signals, such as those resulting from damaged DNA, dictate whether cancer cells proliferate or die. Recent progress in understanding the molecular changes that underlie cancer development offer the prospect of specifically targeting malfunctioning molecules and pathways to achieve more effective and rational cancer therapy.

Hedgehog signaling in prostate regeneration neoplasia and metastasis

Abstract: Elevated Hedgehog (Hh) pathway activity, including ligand stimulated Hh pathway activity, was detected in prostate tumors, and determined to be associated with growth and proliferation of the cancer cells. Accordingly, methods are provided for treating a prostate cancer associated with elevated Hh pathway activity by reducing or inhibiting the Hh pathway activity. Also provided are methods of determining the responsiveness of a prostate tumor to treatment with an Hh pathway antagonist.

Self-renewal and solid tumor stem cells

Abstract: Solid tumors arise in organs that contain stem cell populations. The tumors in these tissues consist of heterogeneous populations of cancer cells that differ markedly in their ability to proliferate and form new tumors. In both breast cancers and central nervous system tumors, cancer cells differ in their ability to form tumors. While the majority of the cancer cells have a limited ability to divide, a population of cancer stem cells that has the exclusive ability to extensively proliferate and form new tumors can be identified based on marker expression. Growing evidence suggests that pathways that regulate the self-renewal of normal stem cells are deregulated in cancer stem cells resulting in the continuous expansion of self-renewing cancer cells and tumor formation. This suggests that agents that target the defective self-renewal pathways in cancer cells might lead to improved outcomes in the treatment of these diseases.

Energy Substrate Modulates Mitochondrial Structure and Oxidative Capacity in Cancer Cells

Abstract: Comparative analysis of cytoplasmic organelles in a variety of tumors relative to normal tissues generally reveals a strong diminution in mitochondrial content and in oxidative phosphorylation capacity. However, little is known about what triggers these modifications and whether or not they are physiologically reversible. We hypothesized that energy substrate availability could play an important role in this phenomenon. The physiological effects of a change in substrate availability were examined on a human cancer cell line (HeLa), focusing specifically on its ability to use glycolysis versus oxidative phosphorylation, and the effect that energy substrate type has on mitochondrial composition, structure, and function. Changes in oxidative phosphorylation were measured in vivo by a variety of techniques, including the use of two novel ratiometric green fluorescent protein biosensors, the expression level of oxidative phosphorylation and some glycolytic enzymes were determined by Western blot, mitochondrial DNA content was measured by real-time PCR, and mitochondrial morphology was monitored by both confocal and electron microscopy. Our data show that the defective mitochondrial system described in cancer cells can be dramatically improved by solely changing substrate availability and that HeLa cells can adapt their mitochondrial network structurally and functionally to derive energy by glutaminolysis only. This could also provide an explanation for the enhancement of oxidative phosphorylation capacity observed after tumor regression or removal. Our work demonstrates that the pleomorphic, highly dynamic structure of the mitochondrion can be remodeled to accommodate a change in oxidative phosphorylation activity. We compared our finding on HeLa cells with those for nontransformed fibroblasts to help distinguish the regulatory pathways.

The membrane-cytoskeleton linker ezrin is necessary for osteosarcoma metastasis.

Abstract: Metastatic cancers, once established, are the primary cause of mortality associated with cancer. Previously, we used a genomic approach to identify metastasis-associated genes in cancer. From this genomic data, we selected ezrin for further study based on its role in physically and functionally connecting the actin cytoskeleton to the cell membrane. In a mouse model of osteosarcoma, a highly metastatic pediatric cancer, we found ezrin to be necessary for metastasis. By imaging metastatic cells in the lungs of mice, we showed that ezrin expression provided an early survival advantage for cancer cells that reached the lung. AKT and MAPK phosphorylation and activity were reduced when ezrin protein was suppressed. Ezrin-mediated early metastatic survival was partially dependent on activation of MAPK, but not AKT. To define the relevance of ezrin in the biology of metastasis, beyond the founding mouse model, we examined ezrin expression in dogs that naturally developed osteosarcoma. High ezrin expression in dog tumors was associated with early development of metastases. Consistent with this data, we found a significant association between high ezrin expression and poor outcome in pediatric osteosarcoma patients.

Cancer: An inflammatory link

Abstract: The NF-κB protein is a key player in inflammation. It now seems that it might also activate signalling pathways, in both cancer cells and tumour-associated inflammatory cells, that promote malignancy.

Stem cell origin of cancer and differentiation therapy

Abstract: Our forefathers in pathology, on observing cancer tissue under the microscope in the mid-19th century, noticed the similarity between embryonic tissue and cancer, and suggested that tumors arise from embryo-like cells [1] , [2] [Recherches dur le Traitement du Cancer, etc. Paris. (1829); Editoral Archiv fuer pathologische Anatomie und Physiologie und fuer klinische Medizin 8 (1855) 23]. The concept that adult tissues contain embryonic remnants that generally lie dormant, but that could be activated to become cancer was later formalized by Cohnheim [3] , [4] [Path. Anat. Physiol. Klin. Med. 40 (1867) 1–79; Virchows Arch. 65 (1875) 64] and Durante [5] [Arch. Memori ed Osservazioni di Chirugia Practica 11 (1874) 217–226], as the “embryonal rest” theory of cancer. An updated version of the embryonal rest theory of cancer is that cancers arise from tissue stem cells in adults. Analysis of the cellular origin of carcinomas of different organs indicates that there is, in each instance, a determined stem cell required for normal tissue renewal that is the most likely cell of origin of carcinomas [6] [Lab. Investig. 70 (1994) 6–22]. In the present review, the nature of normal stem cells (embryonal, germinal and somatic) is presented and their relationships to cancer are further expanded. Cell signaling pathways shared by embryonic cells and cancer cells suggest a possible link between embryonic cells and cancer cells. Wilm’s tumors (nephroblastomas) and neuroblastomas are presented as possible tumors of embryonic rests in children. Teratocarcinoma is used as the classic example of the totipotent cancer stem cell which can be influenced by its environment to differentiate into a mature adult cell. The observation that “promotion” of an epidermal cancer may be accomplished months or even years after the initial exposure to carcinogen (“initiation”), implies that the original carcinogenic event occurs in a long-lived epithelial stem cell population. The cellular events during hepatocarcinogenesis illustrate that cancers may arise from cells at various stages of differentiation in the hepatocyte lineage. Examples of genetic mutations in epithelial and hematopoietic cancers show how specific alterations in gene expression may be manifested as maturation arrest of a cell lineage at a specific stage of differentation. Understanding the signals that control normal development may eventually lead us to insights in treating cancer by inducing its differentiation (differentiation therapy). Retinoid acid (RA) induced differentiation therapy has acquired a therapeutic niche in treatment of acute promyelocytic leukemia and the ability of RA to prevent cancer is currently under examination.

Disruption of Cancer Cell Replication by Alternating Electric Fields

Abstract: Low-intensity, intermediate-frequency (100–300 kHz), alternating electric fields, delivered by means of insulated electrodes, were found to have a profound inhibitory effect on the growth rate of a variety of human and rodent tumor cell lines (Patricia C, U-118, U-87, H-1299, MDA231, PC3, B16F1, F-98, C-6, RG2, and CT-26) and malignant tumors in animals. This effect, shown to be nonthermal, selectively affects dividing cells while quiescent cells are left intact. These fields act in two modes: arrest of cell proliferation and destruction of cells while undergoing division. Both effects are demonstrated when such fields are applied for 24 h to cells undergoing mitosis that is oriented roughly along the field direction. The first mode of action is manifested by interference with the proper formation of the mitotic spindle, whereas the second results in rapid disintegration of the dividing cells. Both effects, which are frequency dependent, are consistent with the computed directional forces exerted by these specific fields on charges and dipoles within the dividing cells. In vivo treatment of tumors in C57BL/6 and BALB/c mice (B16F1 and CT-26 syngeneic tumor models, respectively), resulted in significant slowing of tumor growth and extensive destruction of tumor cells within 3–6 days. These findings demonstrate the potential applicability of the described electric fields as a novel therapeutic modality for malignant tumors.

Alkylating DNA damage stimulates a regulated form of necrotic cell death

Abstract: Necrosis has been considered a passive form of cell death in which the cell dies as a result of a bioenergetic catastrophe imposed by external conditions. However, in response to alkylating DNA damage, cells undergo necrosis as a self-determined cell fate. This form of death does not require the central apoptotic mediators p53, Bax/Bak, or caspases and actively induces an inflammatory response. Necrosis in response to DNA damage requires activation of the DNA repair protein poly(ADP-ribose) polymerase (PARP), but PARP activation is not sufficient to determine cell fate. Cell death is determined by the effect of PARP-mediated β-nicotinamide adenine dinucleotide (NAD) consumption on cellular metabolism. Cells using aerobic glycolysis to support their bioenergetics undergo rapid ATP depletion and death in response to PARP activation. In contrast, cells catabolizing nonglucose substrates to maintain oxidative phosphorylation are resistant to ATP depletion and death in response to PARP activation. Because most cancer cells maintain their ATP production through aerobic glycolysis, these data may explain the molecular basis by which DNA-damaging agents can selectively induce tumor cell death independent of p53 or Bcl-2 family proteins.

Chemotherapy-Associated Oxidative Stress: Impact on Chemotherapeutic Effectiveness

Abstract: Antineoplastic agents induce oxidative stress in biological systems. During cancer chemotherapy, oxidative stress-induced lipid peroxidation generates numerous electrophilic aldehydes that can attack many cellular targets. These products of oxidative stress can slow cell cycle progression of cancer cells and cause cell cycle checkpoint arrest, effects that may interfere with the ability of anticancer drugs to kill cancer cells. The aldehydes may also inhibit drug-induced apoptosis (programmed cell death) by inactivating death receptors and inhibiting caspase activity. These effects would also diminish the efficacy of the treatment. The use of anti-oxidants during chemotherapy may enhance therapy by reducing the generation of oxidative stress-induced aldehydes.

Apoptotic and autophagic cell death induced by histone deacetylase inhibitors

Abstract: Histone deacetylase (HDAC) inhibitors can induce programmed cell death in cancer cells, although the underlying mechanism is obscure. In this study, we show that two distinct HDAC inhibitors, butyrate and suberoylanilide hydroxamic acid (SAHA), induced caspase-3 activation and cell death in multiple human cancer cell lines. The activation of caspase-3 was via the mitochondria/cytochrome c-mediated apoptotic pathway because it was abrogated in mouse embryonic fibroblasts with knockout of Apaf-1, the essential mediator of the pathway. Overexpression of Bcl-XL in HeLa cells also blocked caspase activation by the HDAC inhibitors. Nevertheless, Apaf-1 knockout, overexpression of Bcl-XL, and pharmacological inhibition of caspase activity did not prevent SAHA and butyrate-induced cell death. The cells undergoing such caspase-independent death had unambiguous morphological features of autophagic cell death. Therefore, HDAC inhibitors can induce both mitochondria-mediated apoptosis and caspase-independent autophagic cell death. Induction of autophagic cell death by HDAC inhibitors has clear clinical implications in treating cancers with apoptotic defects.

Tumor Cell Traffic through the Extracellular Matrix Is Controlled by the Membrane-anchored Collagenase MT1-MMP

Abstract: As cancer cells traverse collagen-rich extracellular matrix (ECM) barriers and intravasate, they adopt a fibroblast-like phenotype and engage undefined proteolytic cascades that mediate invasive activity. Herein, we find that fibroblasts and cancer cells express an indistinguishable pericellular collagenolytic activity that allows them to traverse the ECM. Using fibroblasts isolated from gene-targeted mice, a matrix metalloproteinase (MMP)–dependent activity is identified that drives invasion independently of plasminogen, the gelatinase A/TIMP-2 axis, gelatinase B, collagenase-3, collagenase-2, or stromelysin-1. In contrast, deleting or suppressing expression of the membrane-tethered MMP, MT1-MMP, in fibroblasts or tumor cells results in a loss of collagenolytic and invasive activity in vitro or in vivo. Thus, MT1-MMP serves as the major cell-associated proteinase necessary to confer normal or neoplastic cells with invasive activity.

Suppression of anoikis and induction of metastasis by the neurotrophic receptor TrkB

Abstract: Metastasis is a major factor in the malignancy of cancers, and is often responsible for the failure of cancer treatment. Anoikis (apoptosis resulting from loss of cell-matrix interactions) has been suggested to act as a physiological barrier to metastasis; resistance to anoikis may allow survival of cancer cells during systemic circulation, thereby facilitating secondary tumour formation in distant organs. In an attempt to identify metastasis-associated oncogenes, we designed an unbiased, genome-wide functional screen solely on the basis of anoikis suppression. Here, we report the identification of TrkB, a neurotrophic tyrosine kinase receptor, as a potent and specific suppressor of caspase-associated anoikis of non-malignant epithelial cells. By activating the phosphatidylinositol-3-OH kinase/protein kinase B pathway, TrkB induced the formation of large cellular aggregates that survive and proliferate in suspension. In mice, these cells formed rapidly growing tumours that infiltrated lymphatics and blood vessels to colonize distant organs. Consistent with the ability of TrkB to suppress anoikis, metastases--whether small vessel infiltrates or large tumour nodules--contained very few apoptotic cells. These observations demonstrate the potent oncogenic effects of TrkB and uncover a specific pro-survival function that may contribute to its metastatic capacity, providing a possible explanation for the aggressive nature of human tumours that overexpress TrkB.

Functional proteomic screens reveal an essential extracellular role for hsp90 alpha in cancer cell invasiveness

Abstract: Tumour cell invasiveness is crucial for cancer metastasis and is not yet understood. Here we describe two functional screens for proteins required for the invasion of fibrosarcoma cells that identified the molecular chaperone heat shock protein 90 (hsp90). The hsp90 alpha isoform, but not hsp90 beta, is expressed extracellularly where it interacts with the matrix metalloproteinase 2 (MMP2). Inhibition of extracellular hsp90 alpha decreases both MMP2 activity and invasiveness. This role for extracellular hsp90 alpha in MMP2 activation indicates that cell-impermeant anti-hsp90 drugs might decrease invasiveness without the concerns inherent in inhibiting intracellular hsp90.

Carbohydrate‐mediated cell adhesion in cancer metastasis and angiogenesis

Abstract: Malignant transformation is associated with abnormal glycosylation, resulting in the synthesis and expression of altered carbohydrate determinants including sialyl Lewis a and sialyl Lewis x . The sialyl Lewis a and sialyl Lewis x determinants appear in the sera of patients with cancer, and are extensively utilized for serum diagnosis of cancers in Japan. Sialyl Lewis a and sialyl Lewis x are involved in selectin-mediated adhesion of cancer cells to vascular endothelium, and these determinants are thought to be closely associated with hematogenous metastasis of cancers. Recent progress in this area includes the following: 1. Substantial increases in solid clinical statistics that further confirm the contribution of these determinants in the progression of a wide variety of cancers; 2. Elucidation of the ligand specificity of the three family members of selectins and evaluation of the roles of these molecules in cancer cell adhesion; and 3. Advances in the study of the mechanism that leads to the enhanced expression of the sialyl Lewis a/x determinants in malignant cells. These recent results have confirmed that these determinants are not merely markers for cancers, but are functionally implicated in the malignant behavior of cancer cells. The results also suggested that the increase of these determinants in malignant cells is an inevitable consequence of the malignant transformation of cells. Considerable new knowledge has also been accumulated regarding the therapeutic implications for suppression of hematogenous metastasis targeting this cell adhesion system.

A Novel Mechanism of Chemoprotection by Sulforaphane: Inhibition of Histone Deacetylase

Abstract: Sulforaphane (SFN), a compound found at high levels in broccoli and broccoli sprouts, is a potent inducer of phase 2 detoxification enzymes and inhibits tumorigenesis in animal models. SFN also has a marked effect on cell cycle checkpoint controls and cell survival and/or apoptosis in various cancer cells, through mechanisms that are poorly understood. We tested the hypothesis that SFN acts as an inhibitor of histone deacetylase (HDAC). In human embryonic kidney 293 cells, SFN dose-dependently increased the activity of a beta-catenin-responsive reporter (TOPflash), without altering beta-catenin or HDAC protein levels. Cytoplasmic and nuclear extracts from these cells had diminished HDAC activity, and both global and localized histone acetylation was increased, compared with untreated controls. Studies with SFN and with media from SFN-treated cells indicated that the parent compound was not responsible for the inhibition of HDAC, and this was confirmed using an inhibitor of glutathione S-transferase, which blocked the first step in the metabolism of SFN, via the mercapturic acid pathway. Whereas SFN and its glutathione conjugate (SFN-GSH) had little or no effect, the two major metabolites SFN-cysteine and SFN-N-acetylcysteine were effective HDAC inhibitors in vitro. Finally, several of these findings were recapitulated in HCT116 human colorectal cancer cells: SFN dose-dependently increased TOPflash reporter activity and inhibited HDAC activity, there was an increase in acetylated histones and in p21(Cip1/Waf1), and chromatin immunoprecipitation assays revealed an increase in acetylated histones bound to the P21 promoter. Collectively, these findings suggest that SFN may be effective as a tumor-suppressing agent and as a chemotherapeutic agent, alone or in combination with other HDAC inhibitors currently undergoing clinical trials.