Antioncogenic effect of adenovirus E1A in human tumor cells

Microbial cancer therapeutics: A promising approach

The success of conventional cancer therapeutics is hindered by associated dreadful side-effects of antibiotic resistance and the dearth of antitumor drugs' selectivity and specificity. Hence, the conceptual evolution of anti-cancerous therapeutic agents that selectively target cancer cells without impacting the healthy cells or tissues, has led to a new wave of scientific interest in microbial-derived bioactive molecules. Such strategic solutions may pave the way to surmount the shortcomings of conventional therapies and raise the potential and hope for the cure of wide range of cancer in a selective manner. This review aims to provide a comprehensive summary of anti-carcinogenic properties and underlying mechanisms of bioactive molecules of microbial origin, and discuss the current challenges and effective therapeutic application of combinatorial strategies to attain minimal systemic side-effects.

Cancer Treatment Goes Viral: Using Viral Proteins to Induce Tumour-Specific Cell Death

Cell death is a tightly regulated process which can be exploited in cancer treatment to drive the killing of the tumour. Several conventional cancer therapies including chemotherapeutic agents target pathways involved in cell death, yet they often fail due to the lack of selectivity they have for tumour cells over healthy cells. Over the past decade, research has demonstrated the existence of numerous proteins which have an intrinsic tumour-specific toxicity, several of which originate from viruses. These tumour-selective viral proteins, although from distinct backgrounds, have several similar and interesting properties. Though the mechanism(s) of action of these proteins are not fully understood, it is possible that they can manipulate several cell death modes in cancer exemplifying the intricate interplay between these pathways. This review will discuss our current knowledge on the topic and outstanding questions, as well as deliberate the potential for viral proteins to progress into the clinic as successful cancer therapeutics.

An oncolytic adenovirus 11p vector expressing adenovirus death protein in the E1 region showed significant apoptosis and tumour-killing ability in metastatic prostate cells

The usefulness for cancer therapy of replication-competent adenoviral vectors expressing therapeutic genes from the E3 region has been evaluated, but few reports have described replication-competent adenoviruses with insertions at the E1 region in the full viral genome. We investigated in different prostate cancer cells the oncolytic efficacy of the replication-competent adenovirus 11p vectors expressing adenovirus death (RCAd11pADP) and red fluorescence (RCAd11pRFP) proteins from the upstream E1 region. ADP/RFP gene expression was 2-3 logs higher in PC3 and DU145 cells than in LNCaP and RWPE-1 cells. E1A protein expression in PC3 and DU145 cells was notably increased after infection with the RCAd11pADP or RCAd11pRFP vector compared with the Ad11pwt virus. Toxicity assays revealed 2-5-fold greater oncolytic effects of RCAd11pADP compared to Ad11pwt. Although all three viruses suppressed subcutaneous PC3 tumour growth in nude mice, RCAd11pRFP had greater oncolytic effects than did the Ad11pwt virus, and RCAd11pADP exhibited significant anti-tumour effects via apoptosis in a xenograft model. Interestingly, the apoptosis triggered by RCAd11pADP was markedly enhanced in comparison to that by the vector expressing ADP from E3 region. Taken together, our findings suggest that RCAd11pADP can potentially be used for the treatment of prostate metastases in clinical settings.

Overexpression of Adenoviral E1A Sensitizes E1A+Ras-Transformed Cells to the Action of Histone Deacetylase Inhibitors

The adenoviral E1A protein induces cell proliferation, transformation, and tumor formation in rodents, on the one hand. On the other hand, E1A expression increases cell sensitivity to a number of cytotoxic agents. Therefore, E1A is a candidate for use as a component of combination therapy for malignant tumors. The highest augmentation in the cytotoxic effect was achieved by a combined use of E1A expression and histone deacetylases (HDAC) inhibitors. However, HDAC inhibitors do not induce apoptosis in cells transformed with E1A and cHa-ras oncogenes. In this study, it was shown that HDAC inhibitors reduce the expression of adenoviral E1A. However, under unregulated E1A overexpression, these cells undergo apoptosis in the presence of HDAC inhibitors. Treatment with a HDAC inhibitor, sodium butyrate (NaBut), was shown to activate the anti-apoptotic factor NF-kB in control cells. However, NaBut was unable to modulate the NF-kB activity in E1A overexpressed cells. Therefore, it is fair to postulate that cells transformed with E1A and cHa-ras oncogenes avoid the apoptosis induced by HDAC inhibitors thanks to a NaBut-dependent decrease in E1A expression.

PIDD-dependent activation of caspase-2-mediated mitochondrial injury in E1A-induced cellular sensitivity to macrophage nitric oxide-induced apoptosis

Expression of the adenovirus E1A oncogene sensitizes tumor cells to innate immune rejection by apoptosis induced by macrophage-produced tumor necrosis factor (TNF)-α and nitric oxide (NO). E1A sensitizes cells to TNF-α and NO through two distinct mechanisms, by repressing NF-κB-dependent antiapoptotic responses and enhancing caspase-2 activation and mitochondrial injury, respectively. The mechanisms through which E1A enhances caspase-2 activation in response to NO were unknown. Here, we report that E1A-induced sensitization to NO-induced apoptosis is dependent on expression of PIDD (p53-inducible protein with a death domain) and enhancement of primary immunodeficiency diseases (PIDD) processing for formation of the PIDDosome, the core component of the caspase-2 activation complex. NO-induced apoptosis in E1A-expressing cells did not require expression Bak or Bax, indicating that NO-induced caspase-2-mediated mitochondrial injury does not proceed through the activities of typical, proapoptotic Bcl-2 family members that induce mitochondrial cytochrome C release. These results define a PIDD-dependent pathway, through which E1A enhances casapse-2-mediated mitochondrial injury, resulting in increased sensitivity of mammalian cells to macrophage-induced, NO-mediated apoptosis.

E1A enhances cellular sensitivity to DNA-damage-induced apoptosis through PIDD-dependent caspase-2 activation

Expression of the adenoviral protein, E1A, sensitizes mammalian cells to a wide variety of apoptosis-inducing agents through multiple cellular pathways. For example, E1A sensitizes cells to apoptosis induced by TNF-superfamily members by inhibiting NF-kappa B (NF-κB)-dependent gene expression. In contrast, E1A sensitization to nitric oxide, an inducer of the intrinsic apoptotic pathway, is not dependent upon repression of NF-κB-dependent transcription but rather is dependent upon caspase-2 activation. The latter observation suggested that E1A-induced enhancement of caspase-2 activation might be a critical factor in cellular sensitization to other intrinsic apoptosis pathway-inducing agents. Etoposide and gemcitabine are two DNA damaging agents that induce intrinsic apoptosis. Here we report that E1A-induced sensitization to both of these agents, like NO, is independent of NF-κB activation but dependent on caspase-2 activation. The results show that caspase-2 is a key mitochondrial-injuring caspase during etoposide and gemcitabine-induced apoptosis of E1A-positive cells, and that caspase-2 is required for induction of caspase-3 activity by both chemotherapeutic agents. Expression of PIDD was required for caspase-2 activation, mitochondrial injury and enhanced apoptotic cell death. Furthermore, E1A-enhanced sensitivity to injury-induced apoptosis required PIDD cleavage to PIDD-CC. These results define the PIDD/caspase-2 pathway as a key apical, mitochondrial-injuring mechanism in E1A-induced sensitivity of mammalian cells to chemotherapeutic agents.

Structural and Dynamic Characterization of the Molecular Hub Early Region 1A (E1A) from Human Adenovirus

The small-DNA human adenovirus encodes one of the most versatile molecular hubs, the E1A protein. This protein is essential for productive viral infection in human cells and a vast amount of biologically relevant data are available on its interactions with host proteins. Up to now, however, no high-resolution structural and dynamic information on E1A is available despite its important biological role. Among the different spliced variants of E1A, two are expressed at high level in the early stage of infection. These are 243 and 289 residues isoforms. Herein, we present their NMR characterization, showing that they are both highly disordered, but also demonstrate a certain heterogeneous behavior in terms of structural and dynamic properties. Furthermore, we present the characterization of the isolated domain of the longer variant, known as CR3. This study opens the way to understanding at the molecular level how E1A functions.

Complete replication-competent adenovirus 11p vectors with E1 or E3 insertions show improved heat stability

Conventional adenovirus vectors harboring E1 or E3 deletions followed by the insertion of an exogenous gene show considerably reduced virion stability. Here, we report strategies to generate complete replication-competent Ad11p(RCAd11p) vectors that overcome the above disadvantage. A GFP cassette was successfully introduced either upstream of E1A or in the E3A region. The resulting vectors showed high expression levels of the hexon and E1genes and also strongly induced the cytopathic effect in targeted cells. When harboring oversized genomes, the RCAd11pE1 and RCAd11pE3 vectors showed significantly improved heat stability in comparison to Ad11pwt;of the three, RCAd11pE3 was the most tolerant to heat treatment. Electron microscopy showed that RCAd11pE3, RCAd11pE1, Ad11pwt, and Ad11pE1 Delmanifested dominant, moderate, minimum, or no full virus particles after heat treatment at 47°C for 5h. Our results demonstrated that both genome size and the insertion site in the viral genome affect virion stability.

miR-137 suppresses the invasion and procedure of EMT of human breast cancer cell line MCF-7 through targeting CtBP1

Distant metastasis is the predominant site of gastric cancer recurrence and the most common cause of death. Recently, accumulating evidence has established that aberrant epithelial-mesenchymal transition activation plays a crucial role in the genesis, invasion, and metastasis of various cancers, including breast cancer. In this paper, we found that miR-137, which has been reported to function as a tumor suppressor in a variety of cancers, could significantly suppress the migration and invasion of MCF-7 cells, which might be correlated with its suppressive effects on the EMT procedure. Upon transfection, the epithelial marker, E-cadherin, was up-regulated, and the mesenchymal markers, N-cadherin and Vimentin, were suppressed. Moreover, we also found that carboxyl-terminal binding protein 1 (CtBP1) was a putative target gene of miR-137 in MCF-7 cells, and might be involved in the suppressive effects, which might provide novel diagnostic and therapeutic options for human breast cancer in the future.

The anti-tumor activity of E1A and its implications in cancer therapy

The adenovirus type 5 E1A protein (E1A) plays a critical role in anti-cancer gene therapy and has been tested in clinical trials. The expression of E1A significantly reduces tumorigenesis, promotes cell death, and inhibits cancer cell mobility. Chemosensitization is one of the anti-tumor effects of E1A, increasing in vitro and in vivo sensitization of anti-cancer drugs, including cisplatin, gemcitabine, etoposide, doxorubicin, paclitaxel, and tumor necrosis factor-related apoptosis-inducing ligand and histone deacetylase inhibitors in different types of cancer cells. E1A also demonstrates anti-metastasis activity through various molecular mechanisms such as the repression of protease expression, suppression of HER2/neu and downregulation of microRNA (miR-520h). Moreover, E1A has been reported to reprogram transcription in tumor cells and stabilize tumor suppressors such as PP2A/C, p21 and p53. Because E1A plays a potentially significant role in anti-tumor therapy, there exists an urgent need to study the anti-cancer activities of E1A. This paper presents a review of our current understanding of the tumor-suppressive functions and molecular regulation of E1A, as well as the potential clinical applications of E1A.

CtBP1 is involved in epithelial-mesenchymal transition and is a potential therapeutic target for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly invasive type of cancer. Metastasis is the leading cause of mortality of advanced HCC patients. In the metastasis cascade, cancer cells undergo epithelial-mesenchymal transition resulting in the loss of cell‑to‑cell adhesion, migration and invasion into the stroma. Loss of E-cadherin expression is a key molecular event in epithelial-mesenchymal transition through several regulatory mechanisms including epigenetic modification, regulation by inhibitory transcriptional factors and deletion of chromosome 16q24 locus. C-terminal binding protein 1 (CtBP1) functions as a corepressor binding to several transcriptional factors and suppresses E-cadherin expression. We found that CtBP1 was upregulated in HCC when compared with paired normal liver tissues and was inversely correlated with E-cadherin expression in HCC by immunohistochemical assay using tissue array. Western blot analysis confirmed the results of the immunohistochemical assays. When CtBP1 was knocked down by siRNA in HepG2 cells (a human HCC cell line), E-cadherin was upregulated and the invasive ability of HepG2 cells was inhibited. In addition, following CtBP1 knockdown, the cell viability was decreased along with increased apoptosis rather than cell cycle arrest. These data suggest a pivotal role of CtBP1 in EMT of HCC, and its potential as a therapeutic target in human disease.

Evolutionary functional analysis and molecular regulation of the ZEB transcription factors

ZEB1 and ZEB2, which are members of the ZEB family of transcription factors, play a pivotal role in the development of the vertebrate embryo. However, recent evidence shows that both proteins can also drive the process of epithelial-mesenchymal transition during malignant cancer progression. The understanding of how both ZEBs act as transcription factors opens up new possibilities for future treatment of advanced carcinomas. This review gives insight into the molecular mechanisms that form the basis of the multitude of cellular processes controlled by both ZEB factors. By using an evolutionary approach, we analyzed how the specific organization of the different domains and regulatory sites in ZEB1 and ZEB2 came into existence. On the basis of this analysis, a detailed overview is provided of the different cofactors and post-translational mechanisms that are associated with ZEB protein functionality.

Opposing oncogenic activities of small DNA tumor virus transforming proteins

The E1A gene of species C human adenovirus is an intensely investigated model viral oncogene that immortalizes primary cells and mediates oncogenic cell transformation in cooperation with other viral or cellular oncogenes. Investigations using E1A proteins have illuminated important paradigms in cell proliferation and about the functions of cellular proteins such as the retinoblastoma protein. Studies with E1A have led to the unexpected discovery that E1A also suppresses cell transformation and oncogenesis. Here, I review our current understanding of the transforming and tumor-suppressive functions of E1A, and how E1A studies led to the discovery of a related tumor-suppressive function in benign human papillomaviruses. The potential role of these opposing functions in viral replication in epithelial cells is also discussed.

Adenovirus 5 E1A enhances histone deacetylase inhibitors-induced apoptosis through Egr-1-mediated Bim upregulation

Histone deacetylase inhibitors (HDACi) are potent anti-cancer agents for variety of cancer types. Suberoylanilide hydroxamic acid (SAHA) has been approved as a drug to treat cutaneous T cell lymphoma, and the combination of HDACi and other agents have been actively tested in many clinical trials. Adenovirus 5 early region 1A (E1A) has been shown to exhibit high tumor suppressor activity, and gene therapy using E1A has been tested in clinical trials. Here, we showed that proapoptotic activity of HDACi was robustly enhanced by E1A in multiple cancer cells, but not in normal cells. Moreover, we showed that combination of E1A gene therapy and SAHA showed high therapeutic efficacy with low toxicity in vivo ovarian and breast xenograft models. SAHA downregulated Bcl-XL and upregulated proapoptotic BH3-only protein Bim, whose expression was further enhanced by E1A in cancer cells. These alterations of Bcl-2 family proteins were critical for apoptosis induced by the combination in cancer cells. SAHA enhanced acetylation of histone H3 in Bim promoter region, while E1A upregulated Egr-1, which was directly involved in Bim transactivation. Together, our results provide not only a novel insight into the mechanisms underlying anti-tumor activity of E1A, but also a rationale for the combined HDACi and E1A gene therapy in future clinical trials.

Adenovirus type 5 E1A and E6 proteins of low-risk cutaneous beta-human papillomaviruses suppress cell transformation through interaction with FOXK1/K2 transcription factors

The adenovirus (Adv) oncoprotein E1A stimulates cell proliferation and inhibits differentiation. These activities are primarily linked to the N-terminal region (exon 1) of E1A, which interacts with multiple cellular protein complexes. The C terminus (exon 2) of E1A antagonizes these processes, mediated in part through interaction with C-terminal binding proteins 1 and 2 (CtBP1/2). To identify additional cellular E1A targets that are involved in the modulation of E1A C-terminus-mediated activities, we undertook tandem affinity purification of E1A-associated proteins. Through mass spectrometric analysis, we identified several known E1A-interacting proteins as well as novel E1A targets, such as the forkhead transcription factors, FOXK1/K2. We identified a Ser/Thr-containing sequence motif in E1A that mediated interaction with FOXK1/K2. We demonstrated that the E6 proteins of two beta-human papillomaviruses (HPV14 and HPV21) associated with epidermodysplasia verruciformis also interacted with FOXK1/K2 through a motif similar to that of E1A. The E1A mutants deficient in interaction with FOXK1/K2 induced enhanced cell proliferation and oncogenic transformation. The hypertransforming activity of the mutant E1A was suppressed by HPV21 E6. An E1A-E6 chimeric protein containing the Ser/Thr domain of the E6 protein in E1A interacted efficiently with FOXK1/K2 and inhibited cell transformation. Our results suggest that targeting FOXK1/K2 may be a common mechanism for certain beta-HPVs and Adv5. E1A exon 2 mutants deficient in interaction with the dual-specificity kinases DYRK1A/1B and their cofactor HAN11 also induced increased cell proliferation and transformation. Our results suggest that the E1A C-terminal region may suppress cell proliferation and oncogenic transformation through interaction with three different cellular protein complexes: FOXK1/K2, DYRK(1A/1B)/HAN11, and CtBP1/2.

The c-MYC-interacting proapoptotic tumor suppressor BIN1 is a transcriptional target for E2F1 in response to DNA damage

The E2F1 transcription factor, which was originally identified as a cell-cycle initiator, mediates apoptosis in response to DNA damage. As E2F1-induced apoptosis is an attractive mechanism for cancer therapy, it is critical to fully elucidate its effector pathways. Here, we show that the c-MYC-interacting proapoptotic tumor suppressor, BIN1, is transcriptionally activated by E2F1 and mediates E2F1-induced apoptosis in response to DNA damage. Acting through the DNA-binding and transactivation domains, ectopically expressed E2F1 activated the human BIN1 promoter, which contains canonical E2F-recognition sites. Conversely, depletion of E2F1 by small interfering RNA or germline deletion led to BIN1 deficiency. DNA-damaging agents (which included etoposide) increased BIN1 levels, unless E2F1 was deficient. Moreover, endogenous E2F1 protein interacted directly with the BIN1 gene promoter in chromatin, particularly after etoposide treatment. Notably, suppression of BIN1 expression using an antisense (AS) technique attenuated the cell death mediated by E2F1 and etoposide. Although the p53 tumor suppressor, its sibling protein p73, and caspases are well-known E2F1 effectors for DNA damage-induced apoptosis, AS-BIN1 did not compromise their apoptotic functions. Our results collectively suggest that BIN1 is a novel transcriptional target of E2F1 that triggers a unique mode of cell death in response to DNA damage.

The transcriptional corepressor CtBP: a foe of multiple tumor suppressors

CtBP1 and CtBP2 are closely related and evolutionarily conserved transcriptional corepressors. There is strong evidence linking CtBPs to tumorigenesis and tumor progression. CtBPs promote epithelial-mesenchymal transition and function as apoptosis antagonists. Also, CtBPs mediate repression of several tumor suppressor genes. Certain tumor suppressors also target CtBPs to restrain their tumor-promoting activity. Down-regulation of CtBPs mediated by some tumor suppressors results in p53-independent apoptosis and reduced tumor cell migration and invasion. The role of CtBPs in modulating the activities of different tumor suppressors is reviewed here. The results discussed here suggest that CtBPs may constitute a novel p53-independent anticancer target.

E1A oncogene enhancement of caspase-2-mediated mitochondrial injury sensitizes cells to macrophage nitric oxide-induced apoptosis

The adenovirus E1A oncogene induces innate immune rejection of tumors by sensitizing tumor cells to apoptosis in response to injuries, such as those inflicted by macrophage-produced TNF alpha and NO. E1A sensitizes cells to TNF by repressing its activation of NF-kappaB-dependent, antiapoptotic defenses. This suggested the hypothesis that E1A blockade of the NF-kappaB activation response might be the central mechanism of E1A induced cellular sensitivity to other proapoptotic injuries, such as macrophage-produced NO. However, creation of E1A-positive NIH-3T3 mouse cell variants with high-level, NF-kappaB-dependent resistance to TNF did not coselect for resistance to apoptosis induced by either macrophage-NO or chemical-NO, as the hypothesis would predict. E1A expression did block cellular recovery from NO-induced mitochondrial injury and converted the reversible, NO-induced cytostasis response of cells to an apoptotic response. This viral oncogene-induced phenotypic conversion of the cellular injury response of mouse and human cells was mediated by an E1A-related increase in NO-induced activation of caspase-2, an apical initiator of intrinsic apoptosis. Blocking caspase-2 activation or expression eliminated the NO-induced apoptotic response of E1A-positive cells. These results define an NF-kappaB-independent pathway through which the E1A gene of human adenovirus sensitizes mouse and human cells to apoptosis by enhancement of caspase-2-mediated mitochondrial injury.

Interaction of Adenovirus E1A with the HHV8 Promoter of Latent Genes: E1A Proteins are Able to Activate the HHV-8 LANAp in MV3 Reporter Cells

Human herpesvirus 8 (HHV-8) is associated with Kaposi's sarcoma, body cavity-based lymphoma, and Castleman's disease. Adenoviral (Ad) E1A proteins regulate the activity of cellular and viral promoters/enhancers and transcription factors and can suppress tumorigenicity of human cancers. As (i) HHV-8 and Ad may co-exist in immunocompromised patients and (ii) E1A might be considered as therapeutic transgene for HHV-8-associated neoplasms we investigated whether the promoter of the latency-associated nuclear antigen (LANAp) controlling expression of vCyclin, vFLIP, and LANA proteins required for latent type infection is regulated by E1A. Transfection experiments in MV3 melanoma cells revealed activation of the LANAp by Ad5 E1A constructs containing an intact N terminus (aa 1-119). In particular, an Ad12 E1A mutant, Spm2, lacking six consecutive alanine residues in the "spacer" region activated the HHV-8 promoter about 15-fold compared to vector controls. In summary, we report the activation of the LANAp by E1A as a novel interaction of E1A with a viral promoter. These data may have relevance for the management of viral infections in immunocompromised patients. A role for E1A as a therapeutic in this context remains to be defined.

E1A inhibits the proliferation of human cervical cancer cells (HeLa cells) by apoptosis induction through activation of HER-2/Neu/Caspase-3 pathway

OBJECTIVE

This study is to investigate the inhibitory effect of E1A gene on the cell proliferation of HeLa cells and its mechanism related to apoptosis.

METHODS

MTT assay and soft agar colony formation assay were employed to justify the inhibition activity of E1A on the proliferation of HeLa cells transfected with E1A gene. Western Blot, RT-PCR and Real-time quantitative RT-PCR were used to detect the gene expression of E1A, HER-2/Neu and Caspase-3 in HeLa cells, respectively. The Caspase-3 activity was monitored by ApoAlert Caspase-3 Assay. The redistribution of cell cycles and apoptosis of HeLa cells regulated by E1A expression were evaluated by flow cytometry.

RESULTS

E1A expression significantly inhibits the cell proliferation and anchorage-independent cell growth of HeLa, with the respective highest inhibition rate of 40.7% and 43.4% (P < 0.01). HER-2/Neu expression in HeLa was significantly down-regulated by E1A, while the protein expression and activity of Caspase-3 was up-regulated by E1A expression. Flow cytometry revealed that E1A transfection in HeLa increased the cell number at G1 stage and simultaneously decreased the cell number at S stage. E1A transfection induced 8.71% of HeLa cells at apoptosis status.

CONCLUSIONS

E1A significantly inhibits the cell proliferation of HeLa by the apoptosis induction through HER-2/Neu/Caspase-3 pathway. These results encourage us to continue an in-vivo study and preclinical development of LPD-E1A as a novel gene therapeutic agent for human cervical cancer.

Adenovirus type 5 E1A gene therapy for ovarian clear cell carcinoma: a potential treatment strategy

Resistance of ovarian clear cell carcinoma (CCC) to platinum-based chemotherapy is associated with poor prognosis, and an effective treatment for advanced disease is urgently needed. HER2/neu is up-regulated more often in CCC than in other histologic types of epithelial ovarian cancer. The purpose of this study was to assess possible treatment for ovarian CCC with the anti-HER2 antibody trastuzumab or human adenovirus type 5 E1A. We treated 10 CCC cell lines with trastuzumab or E1A and assessed cell viability, proliferation, and colony formation and the expression of HER2 and wild-type p53 proteins and molecules downstream of those signaling pathways. HER2 protein was detected at various levels in all 10 cell lines by Western blotting and in 5 CCC cell lines by immunohistochemical staining; HER2 gene amplification was detected (by fluorescence in situ hybridization) in only one cell line (RMG-I). Trastuzumab did not inhibit proliferation in any of the four CCC cell lines tested (RMG-I, SKOV-2, OVTOKO, and OVSAYO). However, transfection with E1A (as compared with control vectors) reduced colony formation in all 10 CCC cell lines regardless of HER2 expression level. Infection of RMG-I and SMOV-2 cells with an adenoviral vector encoding E1A led to significant (P < 0.05) suppression of proliferation and enhancement of cell death; this effect required stabilization of p53 (but not p73) protein and was associated with the up-regulation of Bax and the cleavage of caspase-9. Other mechanisms, such as p53-independent apoptosis, may also be involved in E1A-mediated cell death in CCC. Finally, treatment with E1A prolonged survival in a CCC xenograft model (P < 0.001). E1A gene therapy, because of its ability to stabilize wild-type p53, is worth exploring as a treatment modality for women with ovarian CCC, which typically expresses wild-type p53.

Matching complementing functions of transformed cells with stable expression of selected viral genes for production of E1-deleted adenovirus vectors

Production of E1-deleted adenovirus (rAd) vectors requires complementation by E1A and E1B functions provided by the production cell line. The two cell lines most commonly used for production of rAd vectors, 293 and Per.C6, were derived from human primary cells and contain contiguous E1A and E1B sequences from the Ad genome. As an alternative system, we tested complementation of rAd vectors using sequential transfection of individual E1A and E1B expression cassettes into A549 human lung tumor cells, which support highly efficient replication of wild type adenovirus. We found that E1A function could be complemented in A549 cells by the mutant E1Adl01/07, and that E1B function could be provided in such cells using only the 55K E1B gene. Production yields in the resulting producer cell line, designated SL0003, were similar to those obtained from 293 cells without generation of detectable recombinant replication competent adenovirus.

Intrathecal administration of Y-27632, a specific rho-associated kinase inhibitor, for rat neoplastic meningitis

The small GTP-binding protein Rho and its target Rho-associated kinase trigger an intracellular signaling cascade that controls actin cytoskeleton and plays an essential role in cell motility and adhesion. A specific Rho-associated kinase inhibitor, Y-27632, has been reported to inhibit cancer invasion. Clinically, disseminated tumor cells in the cerebrospinal fluid invade the intraparenchymal region, damaging the brain and nerves, resulting in fatal brain stem dysfunction, despite intrathecal chemotherapy. To expand therapeutic options for this devastating neoplastic meningitis, we evaluated the potential use of intrathecal Y-27632 administration by employing Walker 256 cells, a rat mammary cancer cell line. Y-27632 dose-dependently inhibited chemotactic and invasive activity of Walker 256 cells. Y-27632 also inhibited the phosphorylation level of regulatory myosin light chain in vitro, but the effect was temporary and was considerably diminished within 16 hours. Y-27632 induced striking morphologic changes in Walker 256 cells, as evidenced by decreased cell-matrix adhesion in culture dishes and three-dimensional collagen I gels, and slightly inhibited colony formation in soft agar. Nevertheless, this drug treatment did not affect Walker 256 cell growth rate. We were able to administer continuous delivery of this inhibitor using an osmotic pump and maintaining drug concentration of 10 mumol/L within the brain. Importantly, this concentration of Y-27632 showed minimal neurotoxicity both in vitro and in vivo. We found that an intrathecal therapy, combining 5-fluoro-2'-deoxyuridine with Y-27632, significantly increased the survival time of rats bearing meningeal carcinomatosis in comparison with animals treated with 5-fluoro-2'-deoxyuridine alone. Taken together, our findings indicate that continuous intrathecal administration of Y-27632 could be a promising therapeutic method when combined with chemotherapy for treating human neoplastic meningitis.

Cancer-specific gene therapy

Cancer cells transcriptionally activate many genes that are important for uncontrolled proliferation and cell death. Deregulated transcriptional machinery in tumor cells usually consists of increased expression/activity of transcription factors. Ideally, cancer-specific killing can be achieved by delivering a therapeutic gene under the control of the DNA elements that can be activated by transcription factors that are overexpressed and/or constitutively activated in cancer cells. Additionally, tumor-specific translation of tumor-killing genes has been also exploited in cancer gene therapy. Based on these rationales, cancer-specific expression of a therapeutic gene has emerged as a potentially successful approach for cancer gene therapy. To achieve tumor-specific expression, cancer-specific vectors are generally composed of promoters, enhancers, and/or 5'-UTR that are responsive to tumor-specific transcription factors. A number of cancer-specific promoters have been reported, such as those of probasin, human telomerase reverse transcriptase, survivin, ceruloplasmin, HER-2, osteocalcin, and carcinoembryonic antigen. Evidences suggest that the enhancer element targeted by beta-catenin can be useful to target colon cancer cells. The 5'-UTR of the basic fibroblast growth factor-2 has been reported to provide tumor specificity. Moreover, a variety of therapeutic genes demonstrated direct antitumor effects such as those encoding proapoptotic proteins p53, E1A, p202, PEA3, BAX, Bik, and prodrug metabolizing enzymes, namely thymidine kinase and cytosine deaminase. As cancerous cells of different origins vary significantly in their genetic, transcriptional/translational, and cellular profiles, the success of a cancer gene therapy will not be promised unless it is carefully designed based on the biology of a specific tumor type. Thus, tremendous research efforts have been focused on the development of non-viral vectors that selectively target various tumors resulting in minimal toxicity in the normal tissues. Significant progresses were also made in the exploitation of various novel apoptotic, cytotoxic genes as therapeutic tools that suppress the growth of different tumors. Together, these recent advances provide rationales for future clinical testing of transcriptionally targeted non-viral vectors in cancer patients.

Antitumor effect of E1A in ovarian cancer by cytoplasmic sequestration of activated ERK by PEA15

The adenovirus type 5 gene E1A is known to suppress tumorigenicity by transcriptionally downregulating HER-2/neu (HER2) or by inducing apoptosis. We show here that E1A also suppressed the tumorigenicity of the low-HER2-expressing ovarian cancer cell line OVCAR-3 by decreasing cell proliferation. We further found that the mechanism responsible for this reduced proliferation is the presence of PEA15 (phosphoprotein enriched in astrocytes), which is upregulated by E1A in ovarian cancer; PEA15 promotes translocation of ERK from the nucleus to the cytoplasm, leading to inhibition of ERK-dependent transcription and proliferation. Indeed, siRNA-mediated knockdown of PEA15 expression in OVCAR-3 stable E1A transfectants resulted in a nuclear accumulation of the active form of ERK, followed by an increase in Elk-1 activity, DNA synthesis, and anchorage-independent growth. Finally, PEA15 by itself suppressed colony formation in breast and ovarian cancer cell lines, in which E1A is known to have antitumor activity. We conclude that part of the antitumor effect of E1A in ovarian cancer results from cytoplasmic sequestration of the activated form of ERK by PEA15.

E1A-induced apoptosis does not prevent replication of adenoviruses with deletion of E1b in majority of infected cancer cells

Apoptotic pathways are initiated as a cellular defense mechanism to eliminate adenovirus-infected cells. We have investigated how E1A-induced apoptosis interferes with viral replication in cancer cells. We found that E1B19K alone can efficiently suppress E1A-induced apoptosis in cancer cells. Viruses deleted for both E1B19K and E1B55K resulted in cellular DNA degradation. However, less than 20% of human lung cancer cells infected with a virus deleted for both E1B19K and E1B55 K had evidence of chromatin condensation and multiple-micronuclei formation (apoptotic hallmarks); these cells could not produce infectious viral particles. The majority of cancer cells infected with viruses deleted for the entire E1b gene did not undergo extended apoptosis and produced abundant viral progeny. Thus, only a fraction of cancer cells underwent apoptosis and did not allow E1b-deleted viruses to replicate, while the majority of cancer cells were resistant to E1A-induced apoptosis and could support virus-selective replication. The results of this study imply that, in addition to inhibiting E1A-induced apoptosis, E1B proteins may contribute other important roles in the viral life cycle. Our results also suggest that combining virus-induced apoptosis and selective viral replication into one vector will be a novel approach to destroy cancer cells.

Macrophages kill human papillomavirus type 16 E6-expressing tumor cells by tumor necrosis factor alpha- and nitric oxide-dependent mechanisms

The expression of adenovirus serotype 2 or 5 (Ad2/5) E1A sensitizes cells to killing by NK cells and activated macrophages, a property that correlates with the ability of E1A to bind the transcriptional coadaptor proteins p300-CBP. The E6 oncoproteins derived from the high-risk human papillomaviruses (HPV) interact with p300 and can complement mutant forms of E1A that cannot interact with p300 to induce cellular immortalization. Therefore, we determined if HPV type 16 (HPV16) E6 could sensitize cells to killing by macrophages and NK cells. HPV16 E6 expression sensitized human (H4 and C33A) and murine (MCA-102) cell lines to lysis by macrophages but not by NK cells. The lysis of cells that expressed E6 by macrophages was p53 independent but dependent on the production of tumor necrosis factor alpha (TNF-alpha) or nitric oxide (NO) by macrophages. Unlike cytolysis assays with macrophages, E6 expression did not significantly sensitize cells to lysis by the direct addition of NO or TNF-alpha. Like E1A, E6 has been reported to sensitize cells to lysis by TNF-alpha by inhibiting the TNF-alpha-induced activation of NF-kappaB. We found that E1A, but not E6, blocked the TNF-alpha-induced activation of NF-kappaB, an activity that correlated with E1A-p300 binding. In summary, Ad5 E1A and HPV16 E6 sensitized cells to lysis by macrophages. Unlike E1A, E6 did not block the ability of TNF-alpha to activate NF-kappaB or sensitize cells to lysis by NK cells, TNF-alpha, or NO. Thus, there appears to be a spectrum of common and unique biological activities that result as a consequence of the interaction of E6 or E1A with p300-CBP.

Enhanced paclitaxel cytotoxicity and prolonged animal survival rate by a nonviral-mediated systemic delivery of E1A gene in orthotopic xenograft human breast cancer

Paclitaxel (Taxol) is a promising frontline chemotherapeutic agent for the treatment of human breast and ovarian cancers. The adenoviral type 5 E1A gene has been tested in multiple clinical trials for its anticancer activity. E1A has also been shown to sensitize paclitaxel-induced killing in E1A-expressing cells. Here, we show that E1A can sensitize paclitaxel-induced apoptosis in breast cancer cells in a gene therapy setting by an orthotopic mammary tumor model. We first showed that expression of E1A enhanced in vitro paclitaxel cytotoxicity, as compared to the control cells. We then compared the therapeutic efficacy of paclitaxel between orthotopic tumor models established with vector-transfected MDA-MB-231 (231-Vect) versus 231-E1A stable cells, using tumor weight and apoptotic index (TUNEL assay) as the parameters. We found paclitaxel was more effective in shrinking tumors and inducing apoptosis in tumor models established with stable 231-E1A cells than the control 231-Vect cells. We also tested whether E1A could directly enhance paclitaxel-induced killing in nude mice, by using a nonviral, surface-protected cationic liposome to deliver E1A gene via the mouse tail vein. We compared the therapeutic effects of E1A gene therapy with or without Taxol chemotherapy in the established orthotopic tumor model of animals inoculated with MDA-MB-231 cells, and found that a combination of systemic E1A gene therapy and paclitaxel chemotherapy significantly enhanced the therapeutic efficacy and dramatically repressed tumor growth (P < .01). In addition, survival rates were significantly higher in animals treated with combination therapy than in the therapeutic control groups (both P < .0001). Thus, the E1A gene therapy indeed enhances the sensitivity of tumor cells to chemotherapy in a gene therapy setting and, the current study provides preclinical data to support combination therapy between E1A gene and chemotherapy for future clinical trials.

The Rac exchange factor Tiam1 is required for the establishment and maintenance of cadherin-based adhesions

Rho family proteins are essential for the formation of adherens junctions, which are required for the maintenance of epithelial integrity. Activated Rac and the Rac exchange factor Tiam1 have been shown to promote the formation of adherens junctions and the accompanying induction of an epithelioid phenotype in a number of cell lines. Here we show that Madin-Darby canine kidney II cells in which Tiam1 was down-regulated using short interfering RNA disassembled their cadherin-based adhesions and acquired a flattened, migratory, and mesenchymal morphology. In addition, the expression of E1A in mesenchymal V12Ras-transformed Madin-Darby canine kidney II cells led simultaneously to the up-regulation of the Tiam1 protein, the activation of Rac, the formation of cadherin-based adhesions, and reversion to an epithelial phenotype. This finding suggests that E1A induces an epithelial morphology through the up-regulation of Tiam1 and, thereby, the activation of Rac and the formation of cadherin-based adhesions. Indeed, we found that E1A is able to induce an epithelial-like morphology accompanied by the formation of cadherin-based adhesions only in wild-type but not in Tiam1-deficient primary mouse embryonic fibroblasts. These studies indicate that the Rac activator Tiam1 is essential for the formation as well as the maintenance of cadherin-based adhesions.

A Multicenter Phase I Gene Therapy Clinical Trial Involving Intraperitoneal Administration of E1A-Lipid Complex in Patients with Recurrent Epithelial Ovarian Cancer Overexpressing HER-2/neuOncogene

PURPOSE

HER-2/neu oncogene is overexpressed in 10-30% of epithelial ovarian cancers and is associated with a poor prognosis. The E1A gene product of adenovirus type 5 down-regulates HER-2/neu and causes tumor regression in animal models. In the current study, we sought to determine the toxicity and biological activity of E1A-lipid complex in ovarian cancer patients.

EXPERIMENTAL DESIGN

A Phase I trial involving intraperitoneal (i.p.) administration of E1A-lipid complex was initiated in ovarian cancer patients to assess biological activity (E1A gene transfer/transcription/translation and HER-2/neu expression) and to determine the maximum tolerated dose. Successive cohorts received E1A-lipid complex at doses of 1.8, 3.6, and 7.2 mg DNA/m(2), given as weekly i.p. infusions for 3 of 4 weeks (each cycle) up to a maximum of six cycles. Peritoneal fluid was sampled at baseline and twice monthly for cellularity, cytology, CA-125, and biological activity

RESULTS

Fifteen patients, with a median age of 57 years (range, 43-81) were recruited. Three (1.8 mg DNA/m(2)), 4 (3.6 mg DNA/m(2)), and 8 patients (7.2 mg DNA/m(2)) received i.p. E1A. A total of 91 infusions (range, 1-18) was administered. Abdominal pain was the dose-limiting toxicity, and the maximum-tolerated dose was 3.6 mg DNA/m(2). E1A gene transfer and expression was observed in all of the patients and at all of the dose levels. HER-2/neu down-regulation could be demonstrated in the tumor cells of 2 patients (18%). There was no correlation between dose and biological activity.

CONCLUSIONS

I.P. EIA-lipid complex gene therapy is feasible and safe. Future studies, either alone or in combination with chemotherapy, particularly in patients with minimal residual disease, should be evaluated.

Expression of an E1A/E7 chimeric protein sensitizes tumor cells to killing by activated macrophages but not NK cells

Adenovirus (Ad) E1A and human papillomavirus (HPV) E7 express homologous conserved regions (CRs) that mediate their shared biological functions. Despite their similarities, the expression of E1A sensitizes tumor cells to killing by NK cells and macrophages but the expression of E7 does not, a factor that may contribute to the dissimilar oncogenicities of Ad and HPV. This study was undertaken to define molecular differences between E1A and E7 that are responsible for the ability of E1A and the inability of E7 to sensitize cells to killing by NK cells and macrophages. Genetic mapping studies using human fibrosarcoma cells (H4) that stably expressed mutant forms of E1A showed that only those forms of E1A that interacted with the transcriptional coadaptor protein p300 sensitized cells to killing by NK cells and macrophages. E7 lacks the N-terminal p300-binding region present in E1A. Therefore, a chimeric E1A/E7 gene was constructed that included the N terminus and the CR1 (p300-binding) domain of E1A fused to CR2 and the C-terminal sequences of E7. The E1A/E7 protein interacted with p300 and pRb and immortalized primary mouse embryo fibroblasts (MEF). The expression of E1A/E7 sensitized H4 and MEF cells to killing by activated macrophages but not to killing by NK cells. Therefore, N-terminal differences between E1A and E7 that map to the E1A-p300 binding region accounted for differences in their abilities to sensitize cells to killing by macrophages. However, regions in addition to the E1A-p300 binding region are required to sensitize cells to killing by NK cells.

Emerging roles of DNA tumor viruses in cell proliferation: new insights into genomic instability

The small DNA virus proteins E1A and E1B from human Adenovirus, E6 and E7 from human papillomavirus, and large T and small T antigens from SV40, are multifaceted molecular tools that can carry out an impressive number of tasks in the host cell. These viral factors, collectively termed 'oncoproteins' for their ability to induce cancer, can be viewed as paradigmatic oncogenic factors which can disrupt checkpoint controls at multiple levels--they interfere with both 'gatekeeper' cellular functions, including major control pathways of cell cycle and apoptosis, and with 'caretaker' functions, thereby inducing mitotic abnormalities and increasing genomic instability. Both E1A and E7 have been recently found to interact physically with the Ran GTPase. This interaction is key in uncoupling the centrosome cycle from the cell cycle, highlighting a direct link between viral infection and the induction of genomic instability. Further expanding our current knowledge in this field will be crucial to elucidate viral strategies leading to cellular transformation and cancer progression, as well as design novel preventive or therapeutic approaches to human cancer.

Strategies to target HER2/neu overexpression for cancer therapy

Amplification or overexpression of the HER2/neu (also known as erbB-2) gene has been noted in various types of human cancers. In addition to malignant transformation, the activation of signaling pathways of HER2/neu enhances various metastasis-associated properties and may render cancer cells resistant to conventional therapies. This, at least partially, contributes to the poor prognosis and lower survival rate of patients. Many studies have demonstrated that repression of HER2/neu overexpression suppresses the malignant phenotypes of cancer cells. Therefore, various novel HER2/neu-blocking agents have been developed, several of which have been tested in clinical trials with satisfactory results, including trastuzumab, a HER2/neu monoclonal antibody that has been approved by the FDA in the treatment of HER2/neu-overexpressing breast cancer patients. In this article, we intend to discuss the biological relevance and significance of HER2/neu overexpression in tumorigenesis, metastasis, and resistance to conventional therapy. We also summarize the currently available strategies and combination therapies targeting HER2/neu-overexpressing cancer cells. Although the optimal treatment for HER2/neu-overexpressing cancer patients remains elusive, the initial success of trastuzumab indicates that HER2/neu is a good target for cancer therapy. Further elucidation of HER2/neu-mediated pathways and downstream molecules is critical to provide alternative therapies, overcome drug resistance, and improve the therapeutic outcome for HER2/neu-overexpressing cancer patients.

Adenovirus E1A, not human papillomavirus E7, sensitizes tumor cells to lysis by macrophages through nitric oxide- and TNF-alpha-dependent mechanisms despite up-regulation of 70-kDa heat shock protein

Expression of adenovirus (Ad) serotype 2 or 5 (Ad2/5) E1A or human papillomavirus (HPV)16 E7 reportedly sensitizes cells to lysis by macrophages. Macrophages possess several mechanisms to kill tumor cells including TNF-alpha, NO, reactive oxygen intermediates (ROI), and Fas ligand (FasL). E1A sensitizes cells to apoptosis by TNF-alpha, and macrophages kill E1A-expressing cells, in part through the elaboration of TNF-alpha. However, E1A also up-regulates the expression of 70-kDa heat shock protein, a protein that inhibits killing by TNF-alpha and NO, thereby protecting cells from lysis by macrophages. Unlike E1A, E7 does not sensitize cells to killing by TNF-alpha, and the effector mechanism(s) used by macrophages to kill E7-expressing cells remain undefined. The purpose of this study was to further define the capacity of and the effector mechanisms used by macrophages to kill tumor cells that express Ad5 E1A or HPV16 E7. We found that Ad5 E1A, but not HPV16 E7, sensitized tumor cells to lysis by macrophages. Using macrophages derived from mice unable to make TNF-alpha, NO, ROI, or FasL, we determined that macrophages used NO, and to a lesser extent TNF-alpha, but not FasL or ROI, to kill E1A-expressing cells. Through the use of S-nitroso-N-acetylpenicillamine, which releases NO upon exposure to an aqueous environment, E1A was shown to directly sensitize tumor cells to NO-induced death. E1A sensitized tumor cells to lysis by macrophages despite up-regulating the expression of 70-kDa heat shock protein. In summary, E1A, but not E7, sensitized tumor cells to lysis by macrophages. Macrophages killed E1A-expressing cells through NO- and TNF-alpha-dependent mechanisms.

Expression of adenovirus type 5 E1A in the methylotrophic yeast Pachia pastoris and the inhibitory effect on S-180 tumor growth

The human adenovirus type 5 (Ad5) early-region 1A (E1A) proteins have been shown to have strong tumor-suppressive activities in human tumor cells and to enhance the sensitivity of a variety of malignant tumors to apoptosis induced by ionizing radiation and chemotherapeutic agents. However, the inherent limitations of E1A gene therapy prevent its application, such as the efficiency of expression, precision of targeting, and toxicity of vector. This prompted us to construct an E1A expression vector (pPIC9/E1A) and express the E1A protein in the methylotrophic yeast Pichia pastoris. The E1A protein was purified using two steps of ion-exchange column chromatography on HiTrap Q and HiTrap SP. The analysis indicated that the E1A protein/liposome inhibited S-180 tumor growth and also rendered the S-180 tumor strongly susceptible to the anticancer drug bleomycin in vivo. Furthermore, tunnel assay clearly revealed that the mechanism was induction of cellular apoptosis. Importantly, the E1A protein overcame the limitations of gene therapy. Thus the E1A protein may be a useful therapeutic agent for some malignant tumors.

Tumor-specific activation of hTERT-derived promoters by tumor suppressive E1A-mutants involves recruitment of p300/CBP/HAT and suppression of HDAC-1 and defines a combined tumor targeting and suppression system

Adenovirus (Ad) E1A proteins are transcriptional regulators with antioncogenic but also transforming properties. We have previously shown that transformation-defective Ad5 E1A-derivatives are excellent tumor suppressors. For tumor-specific expression of the E1A-derivatives we intend to use tumor specific human telomerase reverse transcriptase (hTERT) core promoters. Here, we show that Spm2 and other E1A proteins with an intact amino terminus activated all hTERT constructs 10-20-fold in malignant tumor cells but not in primary fibroblasts, without affecting the activity of endogenous telomerase. The transcription rate in tumor cells was in the range of transcription from the SV40 promoter, which qualifies an E1A-hTERT system as a putative tumor targeting/expression system. The activation of the hTERT promoter by E1A was enhanced upon deletion of the Wilms' tumor 1 negative regulatory element and maintained high after deletion of the adjacent c-Myc-responsive E-box, demonstrating an important role of the remaining sequences that contain several Sp1-motifs. E1A-mediated hTERT activation was independent from the presence of the conserved region 3 (CR3) of E1A but dependent on E1A's binding to p300/CBP and recruitment of its histone acetyltransferase activity. Moreover, E1A-Spm2 and histone deacetylase-1 behaved as antagonists with respect to the regulation of transcription from the hTERT promoter. Overall, hTERT promoter/E1A-Spm2 systems may turn out to be excellent tools for transcriptionally targeted anticancer gene therapy.

Transgenic expression in mouse lung reveals distinct biological roles for the adenovirus type 5 E1A 243- and 289-amino-acid proteins

Little is known about the biological significance of human adenovirus type 5 (Ad5) E1A in vivo. However, Ad5 E1A is well defined in vitro and can be detected frequently in the lungs of patients with pulmonary disease. Transgenic expression of the Ad5 E1A gene targeted to the mouse lung reveals distinct biological effects caused by two Ad5 E1A products. Either of two Ad5 E1A proteins was preferentially expressed in vivo in the transgenic lungs. The preferential expression of the Ad5 E1A 243-amino-acid (aa) protein at a moderate level was associated with cellular hyperplasia, nodular lesions of proliferating lymphocyte-like cells, and a low level of p53-dependent apoptosis in the lungs of transgenic mice. In contrast, the preferential expression of the Ad5 E1A 289-aa protein at a moderate level resulted in a proapoptotic injury and an acute pulmonary proinflammation in the lungs of transgenic mice, mediated by multiple apoptotic pathways, as well as an enhancement of the host immune cell response. Expression of the Ad5 E1A 243-aa protein resulted in proliferation-stimulated p53 upregulation, while expression of the Ad5 E1A 289-aa protein led to DNA damage-induced p53 activation. These data suggest that the Ad5 E1A 243- and 289-aa proteins lead to distinct biological roles in vivo.

Suppression of tissue factor expression, cofactor activity, and metastatic potential of murine melanoma cells by the N-terminal domain of adenovirus E1A 12S protein

Tissue factor, the cellular initiator of blood coagulation, has been implicated as a determinant of metastatic potential in human melanoma cells. Here, we report that differential expression of tissue factor in murine melanoma cell lines of known metastatic behavior is mediated by AP-1-dependent and 12S E1A oncoprotein-repressible gene transcription. When compared to weakly metastatic C10 cells, highly metastatic M4 cells possessed elevated levels of tissue factor cofactor activity, transfected promoter activity, and heterodimeric AP-1 DNA-binding complexes containing Fra-1. Transient co-expression of the adenovirus E1A 12S oncoprotein strongly repressed transcription of an AP-1-driven tissue factor reporter gene indicating the additional requirement of N-terminal E1A-interacting coactivators. Stable expression of E1A mutants defective in CBP/p300-binding failed to suppress tissue factor expression and experimental metastasis by M4 cells while clones expressing wild type E1A exhibited greatly reduced tissue factor cofactor activity and metastatic potential in vivo. Overexpression of functional tissue factor in cells containing wild type E1A failed to restore the highly metastatic M4 phenotype suggesting that additional E1A-responsive and CBP/p300-dependent genes are required to facilitate metastasis of murine melanoma cells demonstrating high tissue factor expression and cofactor activity.

Adenovirus-5 E1A: paradox and paradigm

The adenovirus early region 1A (E1A) proteins were described originally as immortalizing oncoproteins that altered transcription in rodent cells. Surprisingly, the 243-amino-acid form of adenovirus-5 E1A was found subsequently to reverse-transform many human tumour cells. Tumour suppression apparently results from the ability of E1A to re-programme transcription in tumour cells, and the molecular basis of this intriguing effect is now beginning to emerge. These discoveries have provided a tool with which to study the regulation of fundamental cellular processes.

Adenovirus-E1A gene therapy enhances the in vivo sensitivity of Ewing's sarcoma to VP-16

This study determined the effect of Ad-E1A gene therapy in vivo. TC71 cells (2 x 10(6)) injected subcutaneously into nude mice resulted in tumor development (1-3 mm) 6 days later. Animals were then treated with Ad-E1A or Ad-beta-gal (5 x 10(9) plaque-forming units) by intratumoral injection twice weekly for 2 weeks. Animals received 8 mg/kg VP-16 given by intraperitoneal injection daily for 5 days following the first week of treatment with Ad-E1A or Ad-beta-gal. Control animals received no therapy or VP-16 only after tumor cells were injected. When tumors exceeded 2 x 2 cm, the mice were sacrificed and the tumors underwent histologic and immunohistochemical analysis. Tumors from mice treated with Ad-E1A plus VP-16 were 9.6-fold smaller than those treated with VP-16 alone and 6.3-fold smaller than those treated with Ad-E1A alone. HER2/neu p185 protein expression decreased in all tumors that received Ad-E1A therapy. TUNEL fluorescence staining revealed more apoptosis in the tumors from animals treated with Ad-E1A plus VP-16 than in those from animals treated with Ad-E1A alone, Ad-beta-gal plus VP-16, or VP-16 alone. These data demonstrated that Ad-E1A gene therapy down-regulated HER2/neu expression, increased tumor cell apoptosis induced by VP-16, and enhanced tumor cell sensitivity to VP-16. Ad-E1A may have potential in the treatment of relapsed drug-resistant Ewing's sarcoma.

Cancer therapy utilizing an adenoviral vector expressing only E1A

The human adenovirus type 5 (Ad5) early region 1A (E1A) proteins have been shown to have potent antitumor effects, due to their ability to reprogram oncogenic signalling pathways in tumor cells. The success of E1A antitumor therapy in animal models has led to its use in phase I and phase II clinical trials, where liposome-based delivery vehicles are being used to deliver a plasmid encoding E1A. To increase the efficiency of E1A delivery to tumors, we have developed an Ad vector deleted of all viral protein coding sequences (termed helper-dependent Ad vectors, hdAds) with the exception of E1A, designated hdAd-E1A. In culture, this vector mediated high-level expression of E1A gene products. A549 cells, a human lung adenocarcinoma cell line, infected with hdAd-E1A showed a reduced proliferative capacity in adherent culture, and the ability to form colonies in soft agarose was completely abolished. In contrast, A549 infected with an hdAd expressing beta-gal were able to form colonies of a similar size and frequency as uninfected cells. Under serum-depleted conditions, expression of E1A within A549 led to the induction of apoptosis. Finally, A549 cells treated with hdAd-E1A showed approximately 10-fold greater sensitivity to the chemotherapeutic drug cisplatin. Taken together, these data indicate that the use of hdAd provides a simple and effective method to deliver E1A to cancer cells, and results in reduction in the tumorigenic potential of the cells, as well as increasing the cells sensitivity to anticancer drugs.

Head and neck cancer: gene therapy approaches. Part II: genes delivered

In Part I, the review summarised the safety of adenoviral vectors and provided insight into approaches being undertaken to improve the specificity, durability and potency of adenoviral delivery vehicles. In Part II, brief discussions are held regarding results of preclinical and clinical trials with a variety of different genes, which have demonstrated antitumour activity in squamous cell carcinoma of the head and neck region (HNSCC). Studies have been performed with a variety of immune modulatory genes. Preliminary results demonstrate activity with several cytokine genes, tumour antigen genes and co-stimulatory molecule genes. Despite only preliminary results, thus far, a theoretical attractive feature for the use of gene therapy for the enhancement of immune modulation is that local injection of the gene product appears to be well tolerated. It is also successful in inducing systemic immune response, potentially providing effect to metastatic sites distal from the injected site. Animal studies have confirmed efficacy in the use of specific targeting of molecules regulating cancer growth (EGF receptor [EGFR], super oxide dismutase [SOD], cyclin D1, E1A and Bcl-2). These approaches are discussed. However, the most significant clinical advances for the use of gene therapy in advanced HNSCC involves two agents: Adp53 and ONYX-015. Preliminary Phase I and II results suggest evidence of efficacy and justify accrual Phase III trials, which are currently ongoing.

E1A: tumor suppressor or oncogene? Preclinical and clinical investigations of E1A gene therapy

In the late 1980s, we have shown that the E1A gene can downregulate HER-2/neu overexpression, thus reversing the tumorigenic and metastatic phenotype. Further, E1A can function as a tumor suppressor gene by inducing apoptosis and inhibiting metastasis. At The University of Texas M. D. Anderson Cancer Center, we have been investigating the adenovirus type 5 E1A gene as a potential therapeutic gene in breast and ovarian cancer since 1995 by using cationic liposome as gene delivery system. In this chapter, we recount our development of E1A as a therapeutic gene.

Emerging new therapies for chemotherapy-resistant cancer using adenoviral vectors

The treatment of cancer by genetic manipulation of either the tumor itself or the patient as a whole offers new avenues for the treatment of otherwise refractory cancers. Gene therapy seeks to correct underlying genetic defects in malignant tissue or to augment the host defense response or to promote selectivity of other therapies. Many innovative and exciting genetic targets have been recently identified. However, the field as a whole is still constrained by limitations of gene delivery. The most common vector for gene delivery is modified adenovirus. In this review, we survey a sampling of current therapeutic approaches that depend upon adenoviral delivery vehicles and outline the advantages and disadvantages of this vector system.

Akt is required for Axl-Gas6 signaling to protect cells from E1A-mediated apoptosis

Adenovirus type 5 E1A protein (E1A) associates with anti-tumor activities by reversing the transformed phenotype, inhibiting metastasis, and inducing apoptosis. We have previously identified that E1A suppresses the expression of Axl, a transforming tyrosine kinase and that Axl-Gas6 receptor-ligand interaction prevents E1A transfectants from apoptosis induced by serum deprivation. To determine how the Axl-Gas6 interaction prevents E1A-mediated apoptosis, we analysed the expression of anti-apoptotic molecules and found that the activated form of Akt was suppressed in the E1A transfectant ip 1-E1A and that Gas6 was able to activate Akt in ip 1-E1A cells reexpressing Axl (ip 1-E1A-Axl). To determine whether activated Akt is required to prevent E1A-mediated apoptosis, ip 1-E1A-Axl cells were treated with the phosphatidylinositol-3'-OH kinase inhibitor wortmannin or transfected with a dominant negative Akt mutant. In both cases, Gas6 no longer protected the cells from serum deprivation-induced apoptosis. Thus, we conclude that activated Akt is required for Axl-Gas6 signaling to prevent E1A-mediated apoptosis induced by serum deprivation. Downstream molecules of Akt, including NF-kappaB, Fas ligand, and BAD were examined, among which phosphorylation of BAD by Axl-Gas6 signaling is associated with the anti-apoptotic activity of Akt in our study.

Intravascular injections of a conditional replicative adenovirus (adl118) prevent metastatic disease in human breast carcinoma xenografts

We describe a study showing that the adenovirus adl118, lacking both E1B proteins, very efficiently kills human malignant cells 'in vitro' and 'in vivo'. Since many breast cancer patients do not have metastasis at the time of diagnosis, but finally develop it, we planned to study whether intravascular injections of adl118 could prevent metastatic development. We studied the effects of this mutant adenovirus in an orthotopic model of human breast carcinoma xenografts with the breast MB435-lung 2 cell line, which is highly metastatic in the lungs. In this study, all primary tumors were excised when they reached 50-100 mm3 volume in the animals. After surgery, 10(10) p.f.u. of adl118 was intravenously injected into a random group of animals, either three times during the first week only, or once every week. At death, almost all the control animals showed numerous lung metastases of large size, which were present in only 15-40% of the treated animals, depending on the size of the primary tumor at the time of excision. Overall survival was 50-70 days in control mice, and over 120 days in mice injected with adl118. Concomitant treatment with adl118 and cisplatin did not enhance the antitumor effects of adl118. With these results, we conclude that intravenous injection of conditional replicative adenovirus, after excision of the primary tumor, induces a clear decrease in the metastatic disease, and could be a new strategy in preventing tumor metastasis of breast carcinomas.