Transcriptional repression of the neu protooncogene by the adenovirus 5 E1A gene products

The Breast Cancer Protooncogenes HER2, BRCA1 and BRCA2 and Their Regulation by the iNOS/NOS2 Axis

The expression of inducible nitric oxide synthase (iNOS; NOS2) and derived NO in various cancers was reported to exert pro- and anti-tumorigenic effects depending on the levels of expression and the tumor types. In humans, the breast cancer level of iNOS was reported to be overexpressed, to exhibit pro-tumorigenic activities, and to be of prognostic significance. Likewise, the expression of the oncogenes HER2, BRCA1, and BRCA2 has been associated with malignancy. The interrelationship between the expression of these protooncogenes and oncogenes and the expression of iNOS is not clear. We have hypothesized that there exist cross-talk signaling pathways between the breast cancer protooncogenes, the iNOS axis, and iNOS-mediated NO mutations of these protooncogenes into oncogenes. We review the molecular regulation of the expression of the protooncogenes in breast cancer and their interrelationships with iNOS expression and activities. In addition, we discuss the roles of iNOS, HER2, BRCA1/2, and NO metabolism in the pathophysiology of cancer stem cells. Bioinformatic analyses have been performed and have found suggested molecular alterations responsible for breast cancer aggressiveness. These include the association of BRCA1/2 mutations and HER2 amplifications with the dysregulation of the NOS pathway. We propose that future studies should be undertaken to investigate the regulatory mechanisms underlying the expression of iNOS and various breast cancer oncogenes, with the aim of identifying new therapeutic targets for the treatment of breast cancers that are refractory to current treatments.

Gospel of malignant Glioma: Oncolytic virus therapy

Glioma accounts for nearly 80% of all intracranial malignant tumors. It is a major challenge to society as it is causes to impaired brain function in many patients. Currently, gliomas are mainly treated with surgery, postoperative radiotherapy, and chemotherapy. However, the curative effects of these treatments are not satisfactory. Oncolytic virus (OV) is a novel treatment which works by activating the immune functions and inducing apoptosis of tumor cells. The OV propagates indefinitely in the host cell, eventually leading to the death of host cell. Subsequently, a large number of antigens and signal molecules are released which exert antitumor immunity. Several preclinical and clinical studies have shown that G207, DNX2401, Zika and other viruses have important roles in malignant tumors. For example, these viruses can reduce the growth of tumor cells without causing severe complications. However, the known OVs have not been clearly classified. Herein, we divided OVs into neurotropic and non-neurophilic OVs based on whether the OVs are naturally neurotropic or not. The therapeutic effects of each group were compared. Finally, challenges encountered in the clinical application of OVs in the treatment of malignant gliomas were summarized.

Use of Nanoparticles in Delivery of Nucleic Acids for Melanoma Treatment

Melanoma accounts for 4% of all skin cancer malignancies, with only 14% of diagnosed patients surviving for more than 5 years after diagnosis. Until now, there is no clear understanding of the detailed molecular contributors of melanoma pathogenesis. Accordingly, more research is needed to understand melanoma development and prognosis.All the treatment approaches that are currently applied have several significant limitations that prevent effective use in melanoma. One major limitation in the treatment of cancer is the acquisition of multidrug resistance (MDR). The MDR results in significant treatment failure and poor clinical outcomes in several cancers, including skin cancer. Treatment of melanoma is especially retarded by MDR. Despite the current advances in targeted and immune-mediated therapy, treatment arms of melanoma are severely limited and stand as a significant clinical challenge. Further, the poor pharmacokinetic profile of currently used chemotherapeutic agents is another reason for treatment failure. Therefore, more research is needed to develop novel drugs and carrier tools for more effective and targeted treatment.Nucleic acid therapy is based on nucleic acids or chemical compounds that are closely related, such as antisense oligonucleotides, aptamers, and small-interfering RNAs that are usually used in situations when a specific gene implicated in a disorder is deemed a therapeutically beneficial target for inhibition. However, the proper application for nucleic acid therapies is hampered by the development of an effective delivery system that can maintain their stability in the systemic circulation and enhance their uptake by the target cells. In this chapter, the prognosis of the different types of melanoma along with the currently used medications is highlighted, and the different types of nucleic acids along with the currently available nanoparticle systems for delivering these nucleic acids into melanoma cells are discussed. We also discuss recently conducted research on the use of different types of nanoparticles for nucleic acid delivery into melanoma cells and highlight the most significant outcomes.

Etoposide enhances antitumor efficacy of MDR1-driven oncolytic adenovirus through autoupregulation of the MDR1 promoter activity

Conditionally replicating adenoviruses (CRAds), or oncolytic adenoviruses, such as E1B55K-deleted adenovirus, are attractive anticancer agents. However, the therapeutic efficacy of E1B55K-deleted adenovirus for refractory solid tumors has been limited. Environmental stress conditions may induce nuclear accumulation of YB-1, which occurs in multidrug-resistant and adenovirus-infected cancer cells. Overexpression and nuclear localization of YB-1 are associated with poor prognosis and tumor recurrence in various cancers. Nuclear YB-1 transactivates the multidrug resistance 1 (MDR1) genes through the Y-box. Here, we developed a novel E1B55K-deleted adenovirus driven by the MDR1 promoter, designed Ad5GS3. We tested the feasibility of using YB-1 to transcriptionally regulate Ad5GS3 replication in cancer cells and thereby to enhance antitumor efficacy. We evaluated synergistic antitumor effects of oncolytic virotherapy in combination with chemotherapy. Our results show that adenovirus E1A induced E2F-1 activity to augment YB-1 expression, which shut down host protein synthesis in cancer cells during adenovirus replication. In cancer cells infected with Ad5WS1, an E1B55K-deleted adenovirus driven by the E1 promoter, E1A enhanced YB-1 expression, and then further phosphorylated Akt, which, in turn, triggered nuclear translocation of YB-1. Ad5GS3 in combination with chemotherapeutic agents facilitated nuclear localization of YB-1 and, in turn, upregulated the MDR1 promoter activity and enhanced Ad5GS3 replication in cancer cells. Thus, E1A, YB-1, and the MDR1 promoter form a positive feedback loop to promote Ad5GS3 replication in cancer cells, and this regulation can be further augmented when chemotherapeutic agents are added. In the in vivo study, Ad5GS3 in combination with etoposide synergistically suppressed tumor growth and prolonged survival in NOD/SCID mice bearing human lung tumor xenografts. More importantly, Ad5GS3 exerted potent oncolytic activity against clinical advanced lung adenocarcinoma, which was associated with elevated levels of nuclear YB-1 and cytoplasmic MDR1 expression in the advanced tumors. Therefore, Ad5GS3 may have therapeutic potential for cancer treatment, especially in combination with chemotherapy. Because YB-1 is expressed in a broad spectrum of cancers, this oncolytic adenovirus may be broadly applicable.

Heregulin negatively regulates transcription of ErbB2/3 receptors via an AKT-mediated pathway

Despite the importance of the ErbB2/3 heterodimer in breast cancer progression, the negative regulation of these receptors is still poorly understood. We demonstrate here for the first time that the ErbB3/4 ligand heregulin (HRG) reduced both ErbB2 and ErbB3 mRNA and protein levels in human breast cancer cell lines. In contrast, EGFR levels were unaffected by HRG treatment. The effect was rapid with a decline in steady-state mRNA levels first noted 2 h after HRG treatment. HRG reduced the rate of transcription of ErbB2 and ErbB3 mRNA, but did not affect ErbB2 or ErbB3 mRNA stability. To test if ErbB2 kinase activity was required for the HRG-induced downregulation, we treated cells with the ErbB2/EGFR inhibitor lapatinib. Lapatinib diminished the HRG-induced decrease in ErbB2 and ErbB3 mRNA and protein, suggesting that the kinase activity of EGFR/ErbB2 is involved in the HRG-induced receptor downregulation. Further, HRG-mediated decreases in ErbB2/3 mRNA transcription are reversed by inhibiting the AKT but not MAPK pathway. To examine the functional consequences of HRG-mediated decreases in ErbB receptor levels, we performed cell-cycle analysis. HRG blocked cell-cycle progression and lapatinib reversed this block. Our findings support a role for HRG in the negative regulation of ErbB expression and suggest that inhibition of ErbB2/3 signaling by ErbB2 directed therapies may interfere with this process. J. Cell. Physiol. 229: 1831-1841, 2014. © 2014 Wiley Periodicals, Inc.

E1a promotes c-Myc-dependent replicative stress: implications in glioblastoma radiosensitization

The E1a gene from adenovirus is known to be a potent inducer of chemo/radiosensitivity in a wide range of tumors. However, the molecular bases of its radiosensitizer properties are still poorly understood. In an attempt to study this effect, U87MG cells, derived from a radio-resistant tumor as glioblastoma, where infected with lentivirus carrying E1a gene developing an acute sensitivity to ionizing radiation. The induction of radiosensitivity correlated with a marked G 2/M phase accumulation and a potent apoptotic response. Our findings demonstrate that c-Myc plays a pivotal role in E1a-associated radiosensitivity through the induction of a replicative stress situation, as our data support by genetic approaches, based in interference and overexpression in U87MG cells. In fact, we present evidence showing that Chk1 is a novel transcriptional target of E1a gene through the effect exerted by this adenoviral protein onto c-Myc. Moreover, c-Myc upregulation also explains the marked phosphorylation of H2AX associated to E1a expression in the absence of DNA damage. Indeed, all these observations were applicable to other experimental models, such as T98G, LN-405 and A172, rendering the same pattern in terms of radiosensitivity, cell cycle distribution, upregulation of Chk1, c-Myc, and phosphorylation pattern of H2AX. In summary, our data propose a novel mechanism to explain how E1a mediates radiosensitivity through the signaling axis E1a→c-Myc→ replicative stress situation. This novel mechanism of E1a-mediated radiosensitivity could be the key to open new possibilities in the current therapy of glioblastoma.

Expression of the Adenovirus Early Gene 1A Transcription-Repression Domain Alone Downregulates HER2 and Results in the Death of Human Breast Cancer Cells Upregulated for the HER2 Proto-Oncogene

Adenovirus (Ad) early gene 1A 243 residue protein (E1A 243R) possesses a potent transcription-repression function within the N-terminal 80 amino acids (E1A 1-80). We examined the ability of E1A 243R and E1A 1-80 to repress transcription of both an exogenous and the endogenous HER2 promoter in a human breast cancer cell line upregulated for the HER2 proto-oncogene (SK-BR-3). Both moieties repressed HER2 expression by over 90%. When E1A 1-80 was expressed from a nonreplicative Ad vector, levels of expression were lower than anticipated. Addition of nonspecific sequences to the E1A 1-80 C-terminus (E1A 1-80 C+) enhanced its expression 10- to 20-fold. Because "oncogene addiction" suggests that repression of HER2 could kill HER2 upregulated cells, we examined the ability of full-length E1A 243R and E1A 1-80 C+ delivered by an Ad vector to kill HER2 upregulated SK-BR-3 cells. Expression of both E1A 243R and E1A 1-80 C+ killed SK-BR-3 cells but not normal breast cells. E1A 1-80 C+ is a particularly effective killer of SK-BR-3 cells. At 144 h post infection, over 85% of SK-BR-3 cells were killed by a 100 moi of the Ad vector expressing E1A 1-80 C+. As controls, Ad vectors expressing E1A 243R with deletion of all known functional domains or expressing unrelated β-galactosidase had no effect. Three additional human breast cancer cells lines reported to be upregulated for HER2 or another EGF family member (EGFR) were found to be efficiently killed by expression of E1A 1-80 C+, whereas three additional "normal" cell lines (two derived from breast and one from foreskin) were not. The ability of the E1A transcription-repression domain alone to kill HER2 upregulated breast cancer cells has potential for development of therapies for treatment of aggressive human breast cancers and potentially other human cancers that overexpress HER2.

SV40 T/t-common polypeptide enhances the sensitivity of HER2-overexpressing human cancer cells to anticancer drugs cisplatin and doxorubicin

HER2-overexpressing cancer cells are resistant to cisplatin (CDDP) and doxorubicin (DXR). Here we report that SV40 T/t-common polypeptide could specifically sensitize HER2-overexpressing cancer cells to CDDP and DXR and specifically enhance CDDP- or DXR-induced apoptosis in these cells. This activity of T/t-common may be attributed to its ability to inhibit Bcl-2 and Bcl-XL and to suppress ERK activity in CDDP- or DXR-treated HER2-overexpressing cancer cells. T/t-common could enhance the antitumor activity of DXR on HER2-overexpressing ovarian tumor in NOD/SCID mice, suggesting that combination therapy using T/t-common and chemotherapeutic agents may provide a new approach for treating HER2-overexpressing cancers.

Steroid-coupled liposomes for targeted delivery to tumor

The steroidal receptors play a key role in protein synthesis and maintain the homeostasis in normal and diseased state, including tumorigenesis at the target tissues when overactivated. Thus steroidal receptors may act as potential targets for selective delivery of different therapeutic agents as they are overexpressed by a number of endocrinal tumors. The selective delivery of these agents may be a better treatment strategy for endocrinal cancer as it may also result in cytosolic and nuclear delivery of cytotoxic agents. In this review, the targeting potential of steroidal receptors for the drug or bioactive(s) delivery is discussed. The ligands that have been proven to be effective for specific steroidal receptors can be used as vectors for carrying the drug or drug-delivery system to the desired site of drug action in an optimum concentration. This strategy will not only minimize the undesired side effects associated with nonspecific delivery of drug, but will also maximize the drug utilization. Ligand-conjugated liposomes as a carrier of bioactives prevent passive diffusion of the encapsulated drug to normal cells, increase the time of circulation and reduce the undesirable side effects of a drug.

The N-terminal domain of EBNA1 acts as a suppressor of the HER2/neu oncogene

HER2/neu oncogene-mediated malignancy is clearly associated with various human cancers. Therefore, HER2/neu targeting is an effective approach to cancer therapy. We have previously demonstrated that Epstein-Barr virus nuclear antigen-1 (EBNA1) can suppress HER2/neu oncogene expression, although EBNA1 itself has oncogenic potential. Here, we found that the N-terminal domain of EBNA1 alone, named EBNA1-NT, which contains the N-terminal region of amino acid residues 1-86 of EBNA1, is required and sufficient to suppress HER2/neu oncogene expression at the transcriptional level. Furthermore, in EBNA1-NT-transfected HER2/neu-overexpressing cells, we found EBNA1-NT could down-regulate the endogenous production of p185(HER2/neu), lower transformation ability, sensitize paclitaxel-induced apoptosis and decrease tumorigenic potential. These data suggest that EBNA1-NT may act as a repressor of the HER2/neu oncogene.

The effect of emodin on VEGF receptors in human colon cancer cells

AIMS

This study was designed to evaluate the antiangiogenic properties of emodin and its ability to inhibit tyrosine-kinase-mediated phosphorylation of vascular endothelial growth factor (VEGF) receptors in colon cancer cells.

METHODS

The effects of emodin on VEGF-receptor (VEGFR) phosphorylation were determined by assaying the tyrosine kinase activity and by Western blot analysis. The antiproliferative and proapoptotic activities of emodin were evaluated by soft agar colony formation, flow cytometric analysis of cell cycle, and by apoptotic assay.

RESULTS

Emodin causes a dose-dependent inhibition of VEGFR phosphorylation in colon cancer cells. Treatment with 40 muM of emodin decreased the relative activity of VEGFR-1 to 22.4%, when compared to the control group (assigned a value of 100%); VEGFR-2 and -3 showed a similar reduction in relative activity at 58.5% and 31.6%, respectively (p < 0.01, in each case). Treatment with emodin reduced VEGFR phosphorylation, as evidenced by Western blot analysis. Flow cytometric analysis showed that, upon treatment with emodin, the HCT116 cell cycle was blocked at the G2/M phase. Emodin also increased the apoptosis of HCT116 cells in a dose-dependent manner; treatment with 40 muM emodin increased the apoptotic rate from 8.1% +/- 2.7% in the control group to 27.8% +/- 10.9% in the treated group (p < 0.01).

CONCLUSIONS

These studies demonstrate that emodin may inhibit cancer-cell growth by blocking VEGFR signaling and indicate that emodin can be used as a potential inhibitor for tumor angiogenesis.

Prevalence and characteristics of the MMTV-like associated breast carcinomas in Tunisia

The involvement of a retrovirus homologous to the mouse mammary tumor virus (MMTV) in the pathogenesis of human breast cancer (BC) has long been assumed, but has never been proven. Previous studies have reported the detection of MMTV-like env sequences in variable proportions that did not exceed 40% of BC cases in several countries. However, these viral sequences have been found in higher proportion (74%) in Tunisian diagnosed with BC during the seventies. This study is an attempt to evaluate the current prevalence of MMTV-like env gene in BC in Tunisian women. We used semi-nested PCR that amplify a 190-bp MMTV-like env sequence, followed by direct sequencing to screen a series of 122 cases of BC randomly selected. The findings were correlated to clinicopathological data and immunohistochemical expression status of progesterone and oestrogen receptors, HER2, and P53. Specific MMTV-like env sequences were found in 17 (13.9%) cases of breast carcinomas, whereas the same sequences were not detected in matched normal breast tissues. The presence of the viral sequences correlates inversely with progesterone receptor expression (6.8% versus 20.3%; P=0.03) and HER2 overexpression (3.1% versus 17.7%; P=0.04). This present study confirms the presence of MMTV-like env sequences in BC in Tunisian women but describes an important decrease in the prevalence of the viral sequences compared with previous studies. This reduction may be due to some changes in the virological characteristics or exposure to the virus.

Mechanisms of chemoresistance and poor prognosis in ovarian clear cell carcinoma

Clear cell carcinoma (CCC) accounts for 4% to 12% of epithelial ovarian cancer in Western countries and, for some unknown reasons, it comprises more than 20% of such cancers in Japan. CCC shows unique clinical features such as a high incidence of stage I disease, a large pelvic mass, an increased incidence of vascular thromboembolic complications, and hypercalcemia. It is frequently associated with endometriosis. Compared to serous adenocarcinoma (SAC), CCC is relatively resistant to conventional platinum, or taxane-based chemotherapy which is associated with its poor prognosis. However, the mechanisms underlying CCC's resistance to chemotherapy have not been understood. Although several mechanisms involved in drug resistance exist in CCC, including decreased drug accumulation, increased drug detoxification, and an increased DNA repair activity; however, no particular chemoresistance system has been identified. On the other hand, an in vitro study revealed that low cell proliferation may cause the insensitivity of CCC to cisplatin. The Ki-67 labeling index in CCC tumors was significantly lower than SAC. The Ki-67 labeling index for responders was significantly higher than that for non-responders in both tumor types. A multivariable analysis revealed that Ki-67 labeling index and residual tumor size were independent prognostic factors in CCC. Therefore, lower proliferation of the tumor cells may contribute to their resistance to chemotherapy. However, further investigation into the molecular biology and genetics of CCC is warranted. This review discusses the current state of knowledge of the chemoresistance mechanism in CCC and novel treatment strategies for CCC.

Adenovirus E1A negatively regulates E1AF, an ets family of the protein

E1AF was first identified as a transcription factor that binds to enhancer motifs of the adenovirus E1A gene and is thought to be a human homologue of mouse PEA3, one of the ets oncoprotein families. Here we show the effect of E1A on the gene expression and function of E1AF. E1A repressed the activity of E1AF promoter, and the N-terminal region of E1A, which is involved in the oncogenic activity of E1A, was essential for this repression. The ability as a transcription factor of E1AF, as well as those of the other PEA3 subfamily members ER81 and ERM, was also repressed by E1A via the same oncogenic domain. Furthermore, E1AF repressed the transformation activity of E1A cooperating with E1B, whereas the other ets family Ets-1 enhanced this activity. These results suggest that E1AF is one of the targets of E1A.

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.

Advances in targeting human epidermal growth factor receptor-2 signaling for cancer therapy

Human epidermal growth factor receptor (HER)-2 is a member of the HER tyrosine kinase family, which regulates cell growth and proliferation. HER-2 is overexpressed in 20% to 30% of breast cancers and has been associated with an aggressive phenotype and a poorer prognosis, making it an appealing therapeutic target. Since 1998, the anti-HER-2 antibody trastuzumab has been used for the treatment of women with HER-2-positive metastatic breast cancer. Results from large trials have established a role for trastuzumab in the adjuvant setting for the treatment of high-risk primary breast cancer as well. Tyrosine kinase inhibitors that target HER-2 are also very promising therapies and are likely to be incorporated into clinical practice in the near future. HER-2-targeted therapies represent a major step forward in achieving our goal of delivering individualized targeted therapy for breast cancer. However, there are many unanswered questions about the optimal use of these agents. Ongoing research will better elucidate the best combination therapies to overcome resistance to HER-2-targeted agents and will help identify patients at high enough risk to warrant their toxicity.

Development of a Conditionally Replicating Pseudorabies Virus for HER-2/neu-overexpressing Bladder Cancer Therapy

Overexpression of the HER-2/neu oncogene, a frequent molecular event in a variety of cancers including bladder cancer, is associated with tumor progression and poor prognosis. Therapeutic strategies to targeting HER-2/neu-overexpressing cancer cells have shown promise. Pseudorabies virus (PrV), a herpesvirus of swine, may be exploited as an oncolytic agent for human cancer. Herein, we generated a conditionally replicating glycoprotein E-defective PrV mutant carrying glycoprotein D and herpes simplex virus type 1 thymidine kinase genes, which are essential for viral entry and replication, under the transcriptional control of the HER-2/neu promoter. The recombinant PrV, designated YP2, selectively replicated in and lysed HER-2/neu-overexpressing human bladder, mouse bladder, and hamster oral cancer cells in vitro. Notably, YP2 retarded MBT-2 bladder tumor growth in mice by more than 50% and more than half of the mice survived for over 50 days, whereas all the control mice survived less than 30 days. Taken together, our results suggest that YP2 may have therapeutic potential for the treatment of invasive bladder cancer. Furthermore, because HER-2/neu is overexpressed in a broad spectrum of cancers, this conditionally replicating PrV may be broadly applicable.

Antitumor activity of an Ets protein, PEA3, in breast cancer cell lines MDA-MB-361DYT2 and BT474M1

Polyomavirus enhancer activator 3 (PEA3) is a member of the Ets family of transcription factors. We demonstrated in a previous study that, by downregulating the HER-2/neu oncogene at the transcriptional level, PEA3 can inhibit the growth and development into tumors of HER-2/neu-overexpressing ovarian cancer cells. Here, we establish stable clones of the human breast cancer cell line MDA-MB-361DYT2 that express PEA3 under the control of a tetracycline-inducible promoter. Ectopic expression of PEA3 in this cell line inhibited cell growth and resulted in cell cycle accumulation in the G1 phase. We demonstrate that expression of PEA3 in an orthotopic breast cancer model inhibited tumor growth and prolonged the survival of tumor-bearing mice. In a parallel experiment with another breast cancer cell line, BT474M1, we were unable to obtain stable PEA3-inducible transfectants, suggesting that PEA3 may exert a strong growth inhibition effect in this cell line. Indeed, PEA3 coupled with the liposome SN2 demonstrated therapeutic effects in mice bearing tumors induced by BT474M1. These results provide evidence for the antitumor activity of PEA3 in human breast cancers.

Mechanisms of disease: understanding resistance to HER2-targeted therapy in human breast cancer

Trastuzumab is a monoclonal antibody targeted against the human epidermal growth factor receptor (HER) 2 tyrosine kinase receptor, which is overexpressed in approximately 25% of invasive breast cancers. The majority of patients with metastatic breast cancer who initially respond to trastuzumab, however, demonstrate disease progression within 1 year of treatment initiation. Preclinical studies have indicated several molecular mechanisms that could contribute to the development of trastuzumab resistance. Increased signaling via the phosphatidylinositol 3-kinase/Akt pathway could contribute to trastuzumab resistance because of activation of multiple receptor pathways that include HER2-related receptors or non-HER receptors such as the insulin-like growth factor 1 receptor, which appears to be involved in a cross-talk with HER2 in resistant cells. Additionally, loss of function of the tumor suppressor PTEN gene, the negative regulator of Akt, results in heightened Akt signaling that leads to decreased sensitivity to trastuzumab. Decreased interaction between trastuzumab and its target receptor HER2, which is due to steric hindrance of HER2 by cell surface proteins such as mucin-4 (MUC4), may block the inhibitory actions of trastuzumab. Novel therapies targeted against these aberrant molecular pathways offer hope that the effectiveness and duration of response to trastuzumab can be greatly improved.

Expression of PEA3 and lack of correlation between PEA3 and HER-2/neu expression in breast cancer

The ETS protein PEA3 functions as a transcription factor to regulate gene expression. Although members of the ETS family have been reported to be involved in tumor progression, ectopic expression of PEA3 has been shown to suppress tumor formation. Despite several studies demonstrated frequent expression of PEA3 and its high association with HER-2/neu and have suggested a potential role of PEA3 in breast cancer, contradictory result has shown that the PEA3 was associated with better survival rate in breast cancer. In the current study, we address this discrepancy by examining the expression of PEA3 and HER-2/neu on 289 archived breast cancer tumor tissues and their correlation with clinicopathologic factors and prognosis. The staining of PEA3 was further validated by in situ hybridization for PEA3 mRNA. We found PEA3 was positive in 22.2% (64/289) of all cases and only 25.6% (21/82) of HER-2/neu-overexpressing cases showed co-expression of PEA3. In contrast to HER-2/neu, PEA3 expression was not correlated with prognosis or major clinicopathologic factors, except for a negative correlation with lymphovascular permeation ( p=0.007). This study demonstrates that PEA3 expression is not correlated with HER-2/neu expression in breast cancer tumor tissues, nor is it associated with adverse clinicopathologic factors or prognosis.

Mutational and functional analysis of an essential subdomain of the adenovirus E1A N-terminal transcription repression domain

Adenovirus early gene 1A (E1A) possesses a potent transcriptional repression function within the first 80 amino acids (E1A 1-80). Our previous analysis of subdomain 1 (residues 1 to 30) revealed strong correlations between residues required for repression and for disruption of TBP-TATA complexes. Here, we report a functional analysis of subdomain 2 (48 to 60) by alanine-scanning mutagenesis. 53Ala, 54Pro, 55Glu, and 56Asp are required for repression in vitro and in vivo and for efficient interaction with p300 but not for disruption of TBP-TATA. These combined results suggest a model for E1A transcription repression. E1A through subdomains 1 and 2 uses coactivators like p300 as scaffolds to access E1A repressible promoters. At the promoter, subdomain 1 interacts with TBP to disrupt TBP-TATA and abort transcription initiation. In further support of this model, we show that E1A 1-80 bound to the p300-binding site retains the ability to interact with TBP.

Herceptin: mechanisms of action and resistance

HER-2 is overexpressed in 20-25% of invasive breast cancers and is associated with an aggressive tumor phenotype and reduced survival rate. The HER-2 status of a tumor is the critical determinant of response to the HER-2-targeted antibody Herceptin. Thus, accurate assessment of HER-2 expression levels is essential for identifying breast cancer patients who will benefit from HER-2-targeted therapy. Herceptin combined with chemotherapy increases response rates, time to disease progression, and survival. However, the majority of cancers that initially respond to Herceptin begin to progress again within 1 year. This review describes mechanisms by which Herceptin inhibits cell growth in breast cancers that overexpress HER-2 and highlights possible mechanisms contributing to Herceptin resistance.

Bcl-2 antisense oligonucleotide overcomes resistance to E1A gene therapy in a low HER2-expressing ovarian cancer xenograft model

We are currently conducting clinical trials of E1A gene therapy for patients with ovarian cancer. The adenovirus type 5 E1A gene suppresses growth of ovarian cancer cells that overexpress HER-2/neu (HER2) and growth of some--but not all--that express low HER2. In HER2-overexpressing cells, suppression by E1A is predominantly by down-regulation of HER2, but the mechanism in low HER2-expressing cells is not fully understood. The adenoviral E1B protein has sequential and functional homology to Bcl-2 and prolongs the viability of adenovirus host cells by inhibiting E1A-induced apoptosis. Bcl-2 is overexpressed in ovarian cancer and participates in chemoresistance; we hypothesized that Bcl-2 inhibits E1A-induced apoptosis leading to resistance to E1A gene therapy. E1A suppressed colony formation of ovarian cancer cells that express low levels of Bcl-2 and HER2 (OVCAR-3 and OVCA 433), but enhanced colony formation in low HER2-, high Bcl-2-expressing ovarian cancer cells (2774 and HEY). Treating 2774 or HEY cells with antisense oligonucleotide Bcl-2 (Bcl-2-ASO) did not reduce cell viability. E1A combined with Bcl-2-ASO led to significant decreases in cell viability resulting from increased apoptosis relative to cells treated with E1A alone (P < 0.05). The increase in apoptosis was partly due to cytochrome c release and subsequently caspase-9 activation by Bcl-2-ASO. Finally, in an ovarian cancer xenograft model, treatment with Bcl-2-ASO did not prolong survival, but E1A plus Bcl-2-ASO did (P < 0.001). In conclusion, ovarian tumors overexpressing Bcl-2 may not respond well to E1A gene therapy, but treatment with a combination of E1A and Bcl-2-ASO may overcome this resistance.

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.

E1ASpecifically Enhances Sensitivity to Topoisomerase IIα Targeting Anticancer Drug by Up-Regulating the Promoter Activity

DNA topoisomerases I and II (topo I and II) are nuclear enzymes involved in cellular replication and are targets for several anticancer drugs. We showed previously that E1A gene transfer enhanced the sensitivity of Ewing's sarcoma cells to the topo IIalpha targeting agents etoposide and Adriamycin in vitro and in vivo. To determine whether this effect was specific for topo IIalpha, we investigated the effect of E1A gene transfer on cell sensitivity to agents that target topo I and IIbeta. Transfecting TC71 human Ewing's sarcoma cells with an adenoviral vector containing the E1A gene enhanced their sensitivity to the topo IIalpha targeting agents etoposide (16-fold) and Adriamycin (8-fold). By contrast, E1A gene transfer did not affect cellular sensitivity to either amsacrine or camptothecin. Western blot analysis indicated that topo IIalpha protein levels increased 3.1-fold after E1A gene transfer, but topo I and IIbeta protein levels did not change. A plasmid containing topo IIalpha gene promoter with luciferase reporter gene was constructed to determine the effects of E1A gene transfer on the activity of the topo IIalpha promoter. E1A increased the activity of the topo IIalpha gene promoter by 3.5-fold relative to that of cells transfected with Ad-beta-gal. These results suggest that elevated topo IIalpha protein levels and enhanced sensitivity to topo IIalpha targeting agents were secondary to a direct effect of E1A on the topo IIalpha promoter. Combining E1A gene therapy with topo IIalpha targeting anticancer drugs may therefore have therapeutic benefit by increasing tumor cell sensitivity.

Absence of amplification of HER-2/neu (c-erbB-2) gene in Ewing's sarcoma: a real-time polymerase chain reaction method

Amplification and overexpression of the HER-2/neu (c-erbB-2) oncogene have been observed in many cancers and are associated with a poor prognosis particularly in breast cancer. The human epidermal growth factor (HER)-2 receptor has recently been implicated in Ewing's sarcoma tumor cell line growth and chemosensitivity. The present study evaluates the amplification of HER-2/neu gene in paraffin sections from 42 cases of Ewing's sarcoma by a real-time quantitative polymerase reaction method using LightCycler system (Roche diagnostics, GmbH Mannheim, Germany). The relative copy number of HER-2/neu versus beta-globin was calculated at the crossing point. The mean calculated copy number in these cases of Ewing's sarcoma and normal controls was 26.43 and 26.93, respectively. The p value was 0.215 (p<0.05). Our results demonstrated an absence of HER-2/neu oncogene amplification in Ewing's sarcomas, and we suggest that HER-2/neu is not a biologically or therapeutically important pathway in Ewing's sarcoma.

Designing a HER2/neu promoter to drive alpha1,3galactosyltransferase expression for targeted anti-alphaGal antibody-mediated tumor cell killing

Introduction

Our goal was to specifically render tumor cells susceptible to natural cytolytic anti-αGal antibodies by using a murine α1,3galactosyltransferase (mαGalT) transgene driven by a designed form of HER2/neu promoter (pNeu), the transcription of which is frequently observed to be above basal in breast tumors. Indeed, the αGalT activity that promotes Galα1,3Galβ1,4GlcNAc-R (αGal) epitope expression has been mutationally disrupted during the course of evolution, starting from Old World primates, and this has led to the counter-production of large amounts of cytotoxic anti-αGal antibodies in recent primates, including man.

Method

Expression of the endogenous c-erbB-2 gene was investigated in various cell lines by northern blotting. A mαGalT cDNA was constructed into pcDNA3 vector downstream of the original CMV promoter (pCMV/mαGalT) and various forms of pNeu were prepared by PCR amplification and inserted in the pCMV/mαGalT construct upstream of the mαGalT cDNA, in the place of the CMV promoter. These constructs were transferred into HEK-293 control and breast tumor cell lines. Stably transfected cells were analyzed by northern blotting for their expression of αGalT and c-erbB-2, and by flow cytometry for their binding with fluorescein isothiocyanate-conjugated Griffonia simplicifolia/isolectin B4.

Results

We show that expression of the mαGalT was up- or down-modulated according to the level of endogenous pNeu activity and the particular form of constructed pNeu. Among several constructs, two particular forms of the promoter, pNeu250 containing the CCAAT box and the PEA3 motif adjacent to the TATAA box, and pNeu664, which has three additional PEA3 motifs upstream of the CCAAT box, were found to promote differential αGalT expression.

Conclusion

Our results strengthen current concepts about the crucial role played by the proximal PEA3 motif of pNeu, and may represent a novel therapeutic approach for the development of targeted transgene expression.

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.

Adenoviral E1A Targets Mdm4 to Stabilize Tumor Suppressor p53

The adenoviral protein E1A associates with multiple anticancer activities, including stabilization of p53 tumor suppressor, and has been tested through gene therapy approaches in clinical trials. To identify potential E1A-binding proteins involved in E1A's anticancer activities, we screened a yeast two-hybrid library and identified Mdm4, an Mdm2-related p53-binding protein, as a novel E1A-binding protein. The NH(2)-terminal region of Mdm4 and the CR1 domain of E1A were required for the interaction between E1A and Mdm4. E1A preferentially bound to Mdm4 rather than Mdm2 and formed a complex with p53 in the presence of Mdm4, resulting in the stabilization of p53 in a p14(ARF)-independent manner. E1A failed to stabilize p53 in the absence of Mdm4, showing that Mdm4 was required for p53 stabilization by E1A. Moreover, E1A-mediated stabilization of p53 occurred in nucleus. Although it had no effect on the p53-Mdm2 interaction, E1A facilitated Mdm4 binding to p53 and inhibited Mdm2 binding to Mdm4, resulting in decreased nuclear exportation of p53. Thus, our findings highlighted a novel mechanism, whereby E1A stabilized the p53 tumor suppressor through Mdm4.

ErbB2 is required for ductal morphogenesis of the mammary gland

The ERBB2/HER2/NEU receptor tyrosine kinase gene is amplified in up to 30% of human breast cancers. The frequent and specific selection of this receptor kinase gene for amplification in breast cancer implies that it has important normal functions in the mammary gland. To investigate the functions of ErbB2 during normal mouse mammary gland development, we transplanted mammary buds from genetically rescued ErbB2(-/-) embryos that express ErbB2 in the cardiac muscle. ErbB2(-/-) mammary buds transplanted to a wild-type mammary fat pad support outgrowth of an epithelial tree that advances only slowly through the mammary fat pad at puberty. This penetration defect is associated with structural defects in terminal end buds, characterized by a decrease in body cell number, an increased presence of cap-like cells in the prelumenal compartment, and the presence of large luminal spaces. Lobuloalveolar development was not affected in glands that developed from ErbB2(-/-) transplanted tissue. The results may have implications for the aggressive phenotypes associated with ERBB2-overexpressing mammary carcinomas.

E1A activates transcription of p73 and Noxa to induce apoptosis

p73, a member of the p53 family of proteins, transcriptionally activates a number of genes involved in the control of cell cycle and apoptosis. Overexpression of p73 was detected in a large number of primary head and neck cancers, and in the established cell lines examined, these all contained inactivating p53 mutations. The significance of p73 overexpression in the pathogenesis of head and neck cancer is currently unclear. We have shown that the expression of adenovirus 5 E1A in a panel of head and neck cancer cell lines induces apoptosis independently of their p53 status. In this study we examined the role of p73 and its transcriptional targets in E1A-mediated induction of apoptosis. E1A expression resulted in significant activation of the TAp73 promoter but had no effect on the alternative, DeltaNp73 promoter. E1A also increased expression of endogenous TAp73 mRNA and protein. E1A mutants lacking the p300- and/or pRB-binding sites showed reduced ability to activate the TAp73 promoter. Additionally, mutations in the E2F1-binding sites in the TAp73 promoter impaired activation by E1A. Importantly, expression of the 13S isoform of E1A substantially induced the p53 apoptotic target Noxa in several p53-deficient cancer cell lines. Our results indicate that E1A activation of p73 and the p53 apoptotic target Noxa can occur in the absence of a functional p53. This activation is likely to play a key role in the mechanism of p53-independent apoptosis induced by E1A in some cancers and may provide an avenue for future cancer therapies.

Endocrine aspects of cancer gene therapy

The field of cancer gene therapy is in continuous expansion, and technology is quickly moving ahead as far as gene targeting and regulation of gene expression are concerned. This review focuses on the endocrine aspects of gene therapy, including the possibility to exploit hormone and hormone receptor functions for regulating therapeutic gene expression, the use of endocrine-specific genes as new therapeutic tools, the effects of viral vector delivery and transgene expression on the endocrine system, and the endocrine response to viral vector delivery. Present ethical concerns of gene therapy and the risk of germ cell transduction are also discussed, along with potential lines of innovation to improve cell and gene targeting.

EBNA1 may prolong G(2)/M phase and sensitize HER2/neu-overexpressing ovarian cancer cells to both topoisomerase II-targeting and paclitaxel drugs

We have shown previously that the Epstein-Barr virus nuclear antigen-1 (EBNA1) can act as a transforming suppressor in the HER2/neu-overexpressing ovarian cancer cells. In the present study, by using flow cytometric analysis, we demonstrate that EBNA1 could prolong G(2)/M phase and sensitize to Taxol-induced apoptosis in the EBNA1-expressing ovarian cancer cell stable transfectants. In addition, EBNA1 could also significantly increase topoisomerase IIalpha protein expression, indicating that the up-regulation of topoisomerase IIalpha may be one of the mechanisms by which EBNA1 enhances the sensitivity of ovarian cancer cells to topoisomerase II-targeting anticancer drugs, such as VP-16 and Adriamycin. These data suggest that EBNA1 not only prolongs cell cycle at G(2)/M phase and up-regulates topoisomerase IIalpha expression in HER2/neu-overexpressing ovarian cancer cells, but also increases cellular apoptosis through sensitization of cancer cells to topoisomerase II-directing anticancer drugs.

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.

The epidermal growth factor receptor HER2 is not a major therapeutic target in Ewing sarcoma

BACKGROUND

Although chimeric EWS gene and Ets gene fusions are pathognomonic of Ewing sarcoma (ES) and primitive neuroectodermal tumors (PNET), the molecular pathogenesis of these pediatric malignancies is poorly understood. Recently, the human epidermal growth factor (HER)-2 receptor, which plays an important role in the biology of certain epithelial cancers, has been implicated in ES tumor cell line growth and chemosensitivity.

MATERIALS

To investigate whether HER2 might be a rational target for ES/PNET therapy, five ES cell lines and 13 archival primary ES/PNET samples were examined by immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) for evidence of HER2 overexpression.

RESULTS

Although several ES cell lines demonstrated modest constitutive HER2 expression by immunoblot, none of the ES cell lines or primary tumor samples showed evidence of HER2 overexpression by IHC or HER2 gene amplification by FISH. Moreover, treatment of human ES cell lines with the HER2-targeted agent trastuzumab (Herceptin) had little effect on cell survival, proliferation, or growth in semi-solid medium.

CONCLUSIONS

These results suggest that HER2 is not a biologically or therapeutically important pathway in ES/PNET.

Zonula occludens-1 and Her-2/neu expression in invasive breast carcinoma

A subset of breast carcinomas shows unexplained overexpression of HER-2/neu protein without HER-2/neu gene amplification. These tumors are often scored 2+ by immunohistochemistry (DAKO HercepTest). In vitro, Zonula occludens-1 (ZO-1), a tight junction protein, can upregulate HER-2/neu expression by sequestering a repressor of the HER-2/neu gene promoter. To assess this relation in vivo, we examined the expression of ZO-1 in 2 series of breast carcinomas. In group 1, 35 invasive breast carcinomas previously scored by HercepTest for HER-2/neu status (negative [n = 12], 2+ [n = 13], 3+ [n = 10]) were examined by immunohistochemistry for expression of ZO-1. ZO-1 expression was then correlated with HER-2/neu expression status. Twenty-four of 35 carcinomas (69%) were positive for ZO-1 expression. Frequency of ZO-1 expression did not differ between HER-2/neu-negative carcinomas (67%) and 2+ positive carcinomas (77%). Carcinomas with 3+ HER-2/neu expression were less commonly positive for ZO-1 (60%), but this difference was not significant. Twenty tumors contained ductal carcinoma in situ (DCIS); 18 of 20 DCIS (90%) were positive for ZO-1. Interestingly, in those tumors with ZO-1-positive DCIS, 4 of 18 (22%) were negative for ZO-1 expression in the invasive tumor. In group 2, 31 of 42 (74%) fluorescent in situ hybridization-nonamplified breast carcinomas showed ZO-1 expression, also with no significant difference in frequency between HER-2/neu-positive (by immunohistochemistry) and negative cases. ZO-1 expression does not correlate with HER-2/neu expression in breast carcinomas. Other causes of HER-2/neu protein overexpression should be sought in cases without HER-2/neu gene amplification.

Regulation of Her2/neu promoter activity by the ETS transcription factor, ER81

Overexpression of the HER2/Neu receptor is correlated to a poor prognosis in tumor patients and leads to stimulation of mitogen-activated protein kinase (MAPK) signaling pathways, which in turn activate transcription factors, such as the ETS protein ER81. Here, we have analyzed whether, on the other hand, ER81 may regulate the Her2/neu gene. Indeed, ER81, together with its co-activators, p300 and CBP, activates the Her2/neu promoter, and this activation is enhanced upon stimulation of MAPK pathways as well as by oncogenic HER2/Neu protein. Furthermore, ER81 interacts with one ETS binding site in the Her2/neu promoter, whose mutation decreases ER81-mediated transcription. Activation of the Her2/neu promoter is also diminished upon mutation of MAPK-dependent phosphorylation sites in ER81 or upon deletion of ER81 transactivation domains. In addition, the ER81 DNA-binding domain on its own functions as a dominant-negative molecule, effectively repressing any stimulation of the Her2/neu promoter. Altogether, our results show that ER81 is a component of a positive regulatory feedback loop, in which the HER2/Neu protein activates ER81, as well as p300/CBP via MAPKs causing the upregulation of the Her2/neu gene.

The Epstein-Barr virus nuclear antigen-1 may act as a transforming suppressor of the HER2/neu oncogene

It is known that the HER2/neu proto-oncogene is associated with a wide variety of human cancers and considered to be an attractive target for developing anti-cancer agents. We report here for the first time that the Epstein-Barr virus nuclear antigen-1 (EBNA1) suppresses the HER2/neu oncogene expression at the transcriptional level. Recombinant clones of EBNA1 were subcloned and stably transfected into HER2/neu-overexpressing human ovarian cancer SKOV3.ip1 cells. These EBNA1-containing clones down-regulated the endogenous production of p185(HER2/neu). In addition, the EBNA1-expressing stable transfectants showed reduced growth rate, low soft agarose colony-forming ability and tumorigenic potential as compared with the parental line. These data suggest that EBNA1 may act as a transforming suppressor of the HER2/neu oncogene.

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.

Modulation of PI3K/Akt pathway by E1a mediates sensitivity to cisplatin

In order to investigate the molecular mechanisms implicated in the induction of chemo sensitivity by adenovirus E1a gene expression, we decided to investigate which signal transduction pathways could be affected by the E1a gene in Human Normal Fibroblast (IMR90). No effect was observed in SAPK pathways (p38MAPK and JNK), but E1a was able to affect the Akt activation mediated by insulin. This result was confirmed by transient transfection experiments performed in Cos-7 cells and also observed in other transformed cell lines such as A431. Furthermore, E1a expression induces a decrease in the basal status of Akt activity. Finally we demonstrated that E1a is able to block the Akt activation mediated by cisplatin and correlates with a sensitive phenotype. In summary, our data demonstrate that specific inhibition of the PI3K/Akt pathway mediates some of the biological properties of E1a such as induction of chemosensitivity.

Trastuzumab: designer drug or fashionable fad?

Trastuzumab (Herceptin) is the first monoclonal antibody to be approved for the treatment of a solid tumour and is directed against the c-erb-B2 receptor. c-erb-B2 is a member of the epidermal growth factor family and approximately 25% of breast cancers express such receptors, which appear to confer a poorer prognosis and may be an indicator of resistance to cytotoxic chemotherapy. This review assesses the mechanisms of action of trastuzumab, discusses the measurement of the HER-2/neu gene and its products, and describes the preclinical and clinical studies that have been instrumental to date in the emergence of trastuzumab in clinical practice.

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.

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.