Progression Elevated Gene-3 Research Articles

Adenovirus‐mediated hPNPaseold‐35 gene transfer as a therapeutic strategy for neuroblastoma

Current treatment options for neuroblastoma fail to eradicate the disease in the majority of high-risk patients, clearly mandating development of innovative therapeutic strategies. Gene therapy represents a promising approach for reversing the neoplastic phenotype or driving tumor cells to self-destruction. We presently studied the effects of adenovirus-mediated gene transfer of human polynucleotide phosphorylase (hPNPase(old-35)), a 3',5'-exoribonuclease with growth-inhibitory properties, in neuroblastoma cells. Transgene expression was driven by either the cytomegalovirus (CMV) promoter or by a tumor-selective promoter derived from progression elevated gene-3 (PEG-3). Our data demonstrate that efficient adenoviral transduction of neuroblastoma cells and robust transgene expression are feasible objectives, that the PEG-3 promoter is capable of selectively targeting gene expression in the majority of neuroblastoma cells, and that hPNPase(old-35) induces profound growth suppression and apoptosis of malignant neuroblastoma cells, while exerting limited effects on normal neural crest-derived melanocytes. These findings support future applications of hPNPase(old-35) for targeted gene-based therapy of neuroblastoma and suggest that combination with the PEG-3 promoter holds promise for creating a potent and selective neuroblastoma therapeutic. J. Cell. Physiol. 219: 707-715, 2009. (c) 2009 Wiley-Liss, Inc.

A cancer terminator virus eradicates both primary and distant human melanomas

The prognosis and response to conventional therapies of malignant melanoma inversely correlate with disease progression. With increasing thickness, melanomas acquire metastatic potential and become inherently resistant to radiotherapy and chemotherapy. These harsh realities mandate the design of improved therapeutic modalities, especially those targeting metastases. To develop an approach to effectively treat this aggressive disease, we constructed a conditionally replication-competent adenovirus in which expression of the adenoviral E1A gene, necessary for replication, is driven by the cancer-specific promoter of progression-elevated gene-3 (PEG-3) and which simultaneously expresses mda-7/IL-24 in the E3 region of the adenovirus (Ad.PEG-E1A-mda-7), a cancer terminator virus (CTV). This CTV produces large quantities of MDA-7/IL-24 protein as a function of adenovirus replication uniquely in cancer cells. Infection of Ad.PEG-E1A-mda-7 (CTV) in normal human immortal melanocytes and human melanoma cells demonstrates cancer cell-selective adenoviral replication, mda-7/IL-24 expression, growth inhibition and apoptosis induction. Injecting Ad.PEG-E1A-mda-7 CTV into xenografts derived from MeWo human metastatic melanoma cells in athymic nude mice completely eliminated not only primary treated tumors but also distant non-treated tumors (established in the opposite flank), thereby implementing a cure. These provocative findings advocate potential therapeutic applications of this novel virus for treating patients with advanced melanomas with metastases.

ASCR-008 Suppression of teratocarcinoma growth by soluble TRAIL gene from progression-elevated gene-3 promoter

ASCR-008 Suppression of teratocarcinoma growth by soluble TRAIL gene from progression-elevated gene-3 promoter

ASCR-016 Comparison of the effect of soluble TRAIL from progression-elevated gene-3 promoter on EC and ES cells

ASCR-016 Comparison of the effect of soluble TRAIL from progression-elevated gene-3 promoter on EC and ES cells

Progression elevated gene‐3 promoter (PEG‐Prom) confers cancer cell selectivity to human polynucleotide phosphorylase (hPNPaseold‐35)‐mediated growth suppression

The poor prognosis of pancreatic cancer patients using currently available therapies mandates novel therapeutics that combine anti-neoplastic potency with toxicity-minimizing cancer specificity. Employing an overlapping pathway screen to identify genes exhibiting coordinated expression as a consequence of terminal cell differentiation and replicative senescence, we identified human polynucleotide phosphorylase (hPNPase(old-35)), a 3',5'-exoribonuclease that exhibits robust growth-suppressing effects in a wide spectrum of human cancers. A limitation to the anti-neoplastic efficacy of hPNPase(old-35) relates to its lack of cancer specificity. The promoter of Progression Elevated Gene-3 (PEG-Prom), discovered in our laboratory via subtraction hybridization in a transformation progression rodent tumor model functions selectively in a diverse array of human cancer cells, with limited activity in normal cells. An adenovirus constructed with the PEG-Prom driving expression of hPNPase(old-35) containing a C-terminal Hemaglutinin (HA)-tag (Ad.PEG.hPNPase(old-35)) was shown to induce robust transgene expression, growth suppression, apoptosis, and cell-cycle arrest in a broad panel of pancreatic cancer cells, with minimal effects in normal immortalized pancreatic cells. hPNPase(old-35) expression correlated with arrest in the G(2)/M phase of the cell cycle and up-regulation of the cyclin-dependent kinase inhibitors (CDKI) p21(CIP1/WAF-1/MDA-6) and p27(KIP1). In a nude mouse xenograft model, Ad.PEG.hPNPase(old-35) injections effectively inhibited growth of human pancreatic cancer cells in vivo. These findings support the potential efficacy of combining a cancer-specific promoter, such as the PEG-Prom, with a novel anti-neoplastic agent, such as hPNPase(old-35), to create a potent, targeted cancer therapeutic, especially for a devastating disease like pancreatic cancer.

Eradication of Therapy-Resistant Human Prostate Tumors Using a Cancer Terminator Virus

Terminal prostate cancer is refractory to conventional anticancer treatments because of frequent overexpression of antiapoptotic proteins Bcl-2 and/or Bcl-x(L). Adenovirus-mediated delivery of melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), a secreted cytokine having cancer-selective apoptosis-inducing properties, profoundly inhibits prostate cancer cell growth. However, forced overexpression of Bcl-2 or Bcl-x(L) renders prostate cancer cells resistant to Ad.mda-7. We constructed a conditionally replication-competent adenovirus in which expression of the adenoviral E1A gene, necessary for replication, is driven by the cancer-specific promoter of progression elevated gene-3 (PEG-3) and which simultaneously expresses mda-7/IL-24 in the E3 region of the adenovirus (Ad.PEG-E1A-mda-7), a cancer terminator virus (CTV). This CTV generates large quantities of MDA-7/IL-24 as a function of adenovirus replication uniquely in cancer cells. Infection of Ad.PEG-E1A-mda-7 (CTV) in normal prostate epithelial cells and parental and Bcl-2- or Bcl-x(L)-overexpressing prostate cancer cells confirmed cancer cell-selective adenoviral replication, mda-7/IL-24 expression, growth inhibition, and apoptosis induction. Injecting Ad.PEG-E1A-mda-7 (CTV) into xenografts derived from DU-145-Bcl-x(L) cells in athymic nude mice completely eradicated not only primary tumors but also distant tumors (established in the opposite flank), thereby implementing a cure. These provocative findings advocate potential therapeutic applications of this novel virus for advanced prostate cancer patients with metastatic disease.

Ionizing radiation enhances adenoviral vector expressing mda‐7/IL‐24‐mediated apoptosis in human ovarian cancer

Ovarian cancer is the fifth most common cause of cancer-related death in women. Current interventional approaches, including debulking surgery, chemotherapy, and/or radiation have proven minimally effective in preventing the recurrence and/or mortality associated with this malignancy. Subtraction hybridization applied to terminally differentiating human melanoma cells identified melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), whose unique properties include the ability to selectively induce growth suppression, apoptosis, and radiosensitization in diverse cancer cells, without causing any harmful effects in normal cells. Previously, it has been shown that adenovirus-mediated mda-7/IL-24 therapy (Ad.mda-7) induces apoptosis in ovarian cancer cells, however, the apoptosis induction was relatively low. We now document that apoptosis can be enhanced by treating ovarian cancer cells with ionizing radiation (IR) in combination with Ad.mda-7. Additionally, we demonstrate that mda-7/IL-24 gene delivery, under the control of a minimal promoter region of progression elevated gene-3 (PEG-3), which functions selectively in diverse cancer cells with minimal activity in normal cells, displays a selective radiosensitization effect in ovarian cancer cells. The present studies support the use of IR in combination with mda-7/IL-24 as a means of augmenting the therapeutic benefit of this gene in ovarian cancer, particularly in the context of tumors displaying resistance to radiation therapy.

842. Novel Oncolytic Adenoviruses for Cancer Gene Therapy

Top of pageAbstract Conditionally replication competent adenoviruses (CRCA) are being stringently evaluated for their ability to replicate selectively in cancer cells and induce oncolysis. However, recent clinical trials in different cancer indications demonstrate that oncolytic adenoviruses alone are not sufficient to significantly deter the precipitous course of the disease suggesting that additional approaches are necessary to bolster oncolysis by these agents. For replication competent adenoviruses to be successful for cancer treatment, they must replicate only in cancer cells with minimal toxicity to normal tissues. The promoter region of Progression Elevated Gene-3 (PEG-Prom) has the unique ability to function selectively in cancer cells with minimum to no activity in normal cells. We have created several CRCA in which the expression of the E1A gene of Ad, necessary for replication, is under the control of PEG-Prom and which simultaneously express a cancer-specific tumor suppressor/immunomodulatory gene in the E3 region of the Ad. We have demonstrated that these CRCA display cancer cell specific replication, transgene expression and induction of apoptosis and necrosis without harming normal cells. Intratumoral injection of these CRCA completely eradicates both primary and distant (representative of metastasis) tumors in established human cancer xenografts in athymic nude mice. These novel CRCA might thus be effective tools to induce complete remission of cancers and need to be stringently evaluated in immunocompetent animal models of cancer and Phase I/II clinical trials for their effective translation for the actual treatment of cancer patients.

Targeted Virus Replication Plus Immunotherapy Eradicates Primary and Distant Pancreatic Tumors in Nude Mice

Pancreatic cancer is an aggressive neoplasm with no current viable, effective treatment options. In the majority of cases, at first diagnosis, pancreatic cancer has already become metastatic so that conventional treatment regimens provide minimal, if any, clinical benefit in prolonging life or ameliorating the negative prognosis of this disease. These harsh realities underscore the need for developing improved treatment paradigms for this cancer, with gene therapy and immunotherapy currently being evaluated as potential therapeutic options. We currently describe an adenovirus-based therapy for successfully managing pancreatic cancer, the cancer terminator virus (CTV), which is founded on targeted induction of viral replication from a cancer-specific progression elevated gene-3 (PEG-3) promoter (PEG-Prom) and immune modulation by IFN-gamma. The PEG-Prom functions selectively in cancer cells of diverse lineages compared with their normal cellular counterparts. In the CTV, the PEG-Prom drives expression of the adenoviral early region 1A (E1A) gene, necessary for virus replication, with IFN-gamma simultaneously being expressed from the E3 region. Infection of normal cells and pancreatic cancer cells with the CTV confirmed cancer cell-selective adenoviral replication, robust IFN-gamma production coupled with virus replication, growth inhibition, and apoptosis induction. Infection of established pancreatic tumors in nude mice with the CTV promoted viral replication, IFN-gamma production, and activation of antitumor immunity resulting in complete eradication of both primary and distant tumors, curing animals of disease. The CTV provides a novel reagent for treating pancreatic and other human cancers with potential for eliminating both primary tumors and metastatic disease.

Dual cancer-specific targeting strategy cures primary and distant breast carcinomas in nude mice.

Limitations of current viral-based gene therapies for malignant tumors include lack of cancer-specific targeting and insufficient tumor delivery. To ameliorate these problems and develop a truly effective adenovirus gene-based therapy for cancer, we constructed a conditionally replication competent adenovirus (CRCA) manifesting the unique properties of tumor-specific virus replication in combination with production of a cancer-selective cytotoxic cytokine, melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24), which embodies potent bystander antitumor activity. Cancer cell selective tropism was ensured by engineering the expression of the adenoviral E1A protein, necessary for viral replication, under the control of a minimal promoter region of progression elevated gene-3 (PEG-3), which functions selectively in diverse cancer cells with minimal activity in normal cells. In the E3 region of this CRCA, we introduced the mda-7/IL-24 gene, thereby mediating robust production of this cytokine as a function of adenovirus replication. Infection of this CRCA (designated Ad.PEG-E1A-mda-7) in normal mammary epithelial cells and breast cancer cells confirmed cancer cell selective adenoviral replication, mda-7/IL-24 expression, growth inhibition, and apoptosis induction. Injecting Ad.PEG-E1A-mda-7 into human breast cancer xenografts in athymic nude mice completely eradicated not only the primary tumor but also distant tumors (established on the opposite flank of the animal) thereby implementing a cure. This dual cancer-specific targeting strategy provides an effective approach for treating breast and other human neoplasms with the potential for eradicating both primary tumors and metastatic disease. Additionally, these studies support the potential use of mda-7/IL-24 in the therapy of malignant cancers.

Potential molecular mechanism for rodent tumorigenesis: mutational generation of Progression Elevated Gene-3 (PEG-3)

Progression Elevated Gene-3 (PEG-3) was cloned using subtraction hybridization as an upregulated transcript associated with transformation and tumor progression of rat embryo fibroblast cells. PEG-3 is a unique gene facilitating tumor progression by modulating multiple pathways in transformed cells, including genomic stability, angiogenesis and invasion. PEG-3 originates from mutation in the growth arrest and DNA damage inducible gene GADD34. A one base deletion in rat GADD34 results in a frame-shift and premature appearance of a stop-codon resulting in a C-terminally truncated molecule that is PEG-3. We now document that mutation in the GADD34 gene is a frequent event during transformation and/or immortalization of rodent cells. Sequencing of the GADD34 gene in a number of independent rat tumor cell lines revealed that in a majority of these the GADD34 gene is mutated to either PEG-3 or a PEG-3-like gene with similar C-terminal truncations. An important function of GADD34 is to inhibit cell growth, predominantly by apoptosis, and we demonstrate that PEG-3 or C-terminal truncations of human GADD34 resembling PEG-3 prevent growth inhibition by both human and rat GADD34. Phosphorylation of p53 by GADD34 is one mechanism by which it inhibits growth and PEG-3 could prevent GADD34-induced p53 phosphorylation. In contrast, PEG-3 was unable to block other GADD34-induced changes, including eIF2 alpha dephosphorylation, indicating that its effects on GADD34 may be related more to its effect on cell growth rather than a global inhibitor of all GADD34 functions. We hypothesize that mutational generation of PEG-3 or a similar molecule is a critical event during rodent carcinogenesis. The inherent property of PEG-3 to function as a dominant negative of the growth inhibitory property of GADD34 might rescue cells from DNA damage-induced apoptosis leading to growth independence and tumorigenesis.

Targeting gene expression selectively in cancer cells by using the progression-elevated gene-3 promoter.

One impediment to effective cancer-specific gene therapy is the rarity of regulatory sequences targeting gene expression selectively in tumor cells. Although many tissue-specific promoters are recognized, few cancer-selective gene promoters are available. Progression-elevated gene-3 (PEG-3) is a rodent gene identified by subtraction hybridization that displays elevated expression as a function of transformation by diversely acting oncogenes, DNA damage, and cancer cell progression. The promoter of PEG-3, PEG-Prom, displays robust expression in a broad spectrum of human cancer cell lines with marginal expression in normal cellular counterparts. Whereas GFP expression, when under the control of a CMV promoter, is detected in both normal and cancer cells, when GFP is expressed under the control of the PEG-Prom, cancer-selective expression is evident. Mutational analysis identifies the AP-1 and PEA-3 transcription factors as primary mediators of selective, cancer-specific expression of the PEG-Prom. Synthesis of apoptosis-inducing genes, under the control of the CMV promoter, inhibits the growth of both normal and cancer cells, whereas PEG-Prom-mediated expression of these genes kills only cancer cells and spares normal cells. The efficacy of the PEG-Prom as part of a cancer gene therapeutic regimen is further documented by in vivo experiments in which PEG-Prom-controlled expression of an apoptosis-inducing gene completely inhibited prostate cancer xenograft growth in nude mice. These compelling observations indicate that the PEG-Prom, with its cancer-specific expression, provides a means of selectively delivering genes to cancer cells, thereby providing a crucial component in developing effective cancer gene therapies.

Progression elevated gene-3 (PEG-3) induces pleiotropic effects on tumor progression: modulation of genomic stability and invasion.

Progression elevated gene-3 (PEG-3) is a novel rodent gene, identified and cloned by subtraction hybridization, that associates with transformation progression in virus- and oncogene-transformed rat embryo (RE) cells. Previous reports document that ectopic expression of PEG-3 in rodent or human tumor cells produces an aggressive transformed/tumorigenic phenotype. Moreover, PEG-3 expression in rodent tumor cells correlates directly with genomic instability, as indicated by chromosomal alterations and gene amplification, and it promotes angiogenesis. The present studies were designed to further elucidate the functional significance and role of PEG-3 in cancer progression with a specific focus on genomic instability and cancer invasion. Genomic instability was assessed by micronucleus assays and staining of centrosomes to define centrosomal amplification. Immunocytochemical observations revealed that overexpression of PEG-3 in transformed rodent cells induced a loss of chromosomes as established by the appearance of micronuclei and staining of the centrosomes with gamma-tubulin antibody, thereby confirming centrosome amplification. Overexpression of PEG-3 modulated the expression of several genes involved in centrosomal duplication, such as p21CIP1/WAF1/MDA-6, nucleophosmin (NPM), and aurora-A kinase. In vitro invasion of transformed rodent cells was augmented by PEG-3, which correlated with an increase in the transcription and activity of matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9), which play important roles in local invasion during cancer progression. These findings demonstrate that PEG-3 plays a central role in augmenting tumor progression by modulating several critical parameters of the carcinogenic process, such as genomic stability and local tumor cell invasion.

Progression elevated gene-3, PEG-3, induces genomic instability in rodent and human tumor cells.

Genomic instability is a fundamental component of cancer progression. Subtraction hybridization identified a novel rodent gene, progression elevated gene-3 (PEG-3) whose expression directly correlates with cancer aggressiveness and progression. Moreover, ectopic expression of PEG-3 in rodent or human tumor cells produces an aggressive transformed phenotype. We demonstrate that PEG-3 expression in rodent tumor cells correlates directly with genomic instability as characterized by alterations in chromosome composition and structure. Additionally, elevated endogenous or ectopic expression of PEG-3 in rodent and human tumor cells, respectively, enhances gene amplification, as monitored by resistance to methothrexate (MTX) and amplification of the dihydrofolate reductase (dhfr) gene. Stable expression of PEG-3 in normal cloned rat embryo fibroblast (CREF) cells marginally elevates MTX resistance, but morphology remains unaltered and anchorage independence is not induced, suggesting that these phenotypes are separable in immortal cells and gene amplification may precede the acquisition of morphological and oncogenic transformation. The present studies document that stable, inducible, and transient expression of PEG-3 in cancer cells augments genomic instability. In these contexts, one mechanism by which PEG-3 influences cancer progression may be by preferentially facilitating the development of genomic changes in evolving cancer cells.

Ionizing radiation modulates vascular endothelial growth factor (VEGF) expression through multiple mitogen activated protein kinase dependent pathways.

We investigated the role of radiation-induced mitogen activated protein kinase (MAPK) pathway activity in the regulation of proliferation, cell survival and vascular endothelial growth factor (VEGF) production in primary astrocytes and in T9 and RT2 glioblastoma cells derived from Fisher 344 rats. In these cells, ionizing radiation (2 Gy) caused activation of the MAPK pathway which was blocked by specific inhibitor drugs. Blunting of radiation-induced MAPK activity weakly enhanced radiation-induced apoptosis 24 h after exposure in RT2 cells. Furthermore, blunting of MAPK activation weakly enhanced the ability of radiation to reduce RT2 cell growth in clonogenic growth assays. These findings argue that inhibition of MAPK signaling reduces proliferation and enhances cell killing by ionizing radiation in transformed astrocytes. Proliferation and survival of cancer cells has been linked in vivo to enhanced expression of angiogenic growth factors. Recently we demonstrated that the gene product of a novel rodent radiation-responsive gene, progression elevated gene 3 (PEG-3), could enhance vascular endothelial growth factor (VEGF) promoter activity in rodent fibroblasts, leading to increased VEGF protein levels and tumorigenic behavior in vivo. Thus PEG-3 and VEGF expression could be expected to directly correlate with the oncogenic potential of transformed cells. RT2 cells expressed more PEG-3 and VEGF protein than T9 cells, and were more tumorigenic in vivo than T9 cells. Radiation activated the PEG-3 promoter via MAPK signaling and ectopic over-expression of PEG-3 enhanced both basal MAPK activity and basal VEGF promoter activity. Basal MAPK activity partially correlated with basal VEGF promoter activity and VEGF protein levels in primary astrocytes, T9 and RT2 cells. Radiation increased the activity of the VEGF promoter and VEGF protein levels in primary astrocytes, T9 and RT2 cells which were dependent upon MAPK function. Furthermore, inhibition of AP-1 transcription factor signaling by dominant negative c-Jun (TAM67) also significantly reduced basal, and to a lesser extent radiation-induced, VEGF promoter function in RT2 cells. Collectively, our data demonstrate that radiation-induced MAPK signaling can both protect cells from radiation-induced cell death as well as enhance protein levels of pro-angiogenic factors such as VEGF. Enhanced VEGF expression in RT2 cells may be mediated via MAPK and JNK pathway signaling which converges upon the AP-1 transcription factor complex.

Cooperation between AP1 and PEA3 sites within the progression elevated gene-3 (PEG-3) promoter regulate basal and differential expression of PEG-3 during progression of the oncogenic phenotype in transformed rat embryo cells.

Cancer is a progressive disease in which a tumor cell temporally develops qualitatively new transformation related phenotypes or a further elaboration of existing transformation associated properties. Subtraction hybridization identified a novel gene associated with transformation progression in mutant adenovirus type 5, H5ts125, transformed rat embryo cells, progression elevated gene-3 (PEG-3). To define the mechanism by which expression of PEG-3 is enhanced as a function of cancer progression a 5'-flanking promoter region of approximately 2.0-kb, PEG-Prom, was isolated, cloned and characterized. The full-length and various mutated regions of the PEG-Prom were linked to a luciferase reporter construct and evaluated for promoter activity during cancer progression. These assays demonstrate a requirement for AP1 and PEA3 sites adjacent to the TATA box region of PEG-3 in mediating basal promoter activity and the enhanced expression of PEG-3 in progressed H5ts125-transformed rat embryo cells. An involvement of AP1 and PEA3 in PEG-3 regulation was also confirmed by electrophoretic mobility shift assays (EMSA) and transfection studies with cJun and PEA3 expression vectors. Our findings document the importance of both AP1 and PEA3 transcription factors in mediating basal and elevated expression of PEG-3 in H5ts125-transformed rat embryo cells displaying an aggressive and progressed cancer phenotype.

PEG-3, a nontransforming cancer progression gene, is a positive regulator of cancer aggressiveness and angiogenesis.

Cancer is a progressive disease culminating in acquisition of metastatic potential by a subset of evolving tumor cells. Generation of an adequate blood supply in tumors by production of new blood vessels, angiogenesis, is a defining element in this process. Although extensively investigated, the precise molecular events underlying tumor development, cancer progression, and angiogenesis remain unclear. Subtraction hybridization identified a genetic element, progression elevated gene-3 (PEG-3), whose expression directly correlates with cancer progression and acquisition of oncogenic potential by transformed rodent cells. We presently demonstrate that forced expression of PEG-3 in tumorigenic rodent cells, and in human cancer cells, increases their oncogenic potential in nude mice as reflected by a shorter tumor latency time and the production of larger tumors with increased vascularization. Moreover, inhibiting endogenous PEG-3 expression in progressed rodent cancer cells by stable expression of an antisense expression vector extinguishes the progressed cancer phenotype. Cancer aggressiveness of PEG-3 expressing rodent cells correlates directly with increased RNA transcription, elevated mRNA levels, and augmented secretion of vascular endothelial growth factor (VEGF). Furthermore, transient ectopic expression of PEG-3 transcriptionally activates VEGF in transformed rodent and human cancer cells. Taken together these data demonstrate that PEG-3 is a positive regulator of cancer aggressiveness, a process regulated by augmented VEGF production. These studies also support an association between expression of a single nontransforming cancer progression-inducing gene, PEG-3, and the processes of cancer aggressiveness and angiogenesis. In these contexts, PEG-3 may represent an important target molecule for developing cancer therapeutics and inhibitors of angiogenesis.

Subtraction hybridization identifies a transformation progression-associated gene PEG-3 with sequence homology to a growth arrest and DNA damage-inducible gene.

Cancer is a progressive multigenic disorder characterized by defined changes in the transformed phenotype that culminates in metastatic disease. Determining the molecular basis of progression should lead to new opportunities for improved diagnostic and therapeutic modalities. Through the use of subtraction hybridization, a gene associated with transformation progression in virus- and oncogene-transformed rat embryo cells, progression elevated gene-3 (PEG-3), has been cloned. PEG-3 shares significant nucleotide and amino acid sequence homology with the hamster growth arrest and DNA damage-inducible gene gadd34 and a homologous murine gene, MyD116, that is induced during induction of terminal differentiation by interleukin-6 in murine myeloid leukemia cells. PEG-3 expression is elevated in rodent cells displaying a progressed-transformed phenotype and in rodent cells transformed by various oncogenes, including Ha-ras, v-src, mutant type 5 adenovirus (Ad5), and human papilloma virus type 18. The PEG-3 gene is transcriptionally activated in rodent cells, as is gadd34 and MyD116, after treatment with DNA damaging agents, including methyl methanesulfonate and gamma-irradiation. In contrast, only PEG-3 is transcriptionally active in rodent cells displaying a progressed phenotype. Although transfection of PEG-3 into normal and Ad5-transformed cells only marginally suppresses colony formation, stable overexpression of PEG-3 in Ad5-transformed rat embryo cells elicits the progression phenotype. These results indicate that PEG-3 is a new member of the gadd and MyD gene family with similar yet distinct properties and this gene may directly contribute to the transformation progression phenotype. Moreover, these studies support the hypothesis that constitutive expression of a DNA damage response may mediate cancer progression.

Potent anti-hepatoma efficacy of HCCS1 via dual tumor-targeting gene-virotherapy strategy

We previously demonstrated that hepatocellular carcinoma suppressor 1 (HCCS1) exerts potent anti-tumor activity. In this study, we constructed a new dual tumor-targeting oncolytic adenovirus vector, PD55-HCCS1, in which E1A was driven by the promoter of progression elevated gene-3, which is hepatoma-specific, and a CMV-HCCS1 expression cassette replaced E1B55. The PD55-HCCS1-mediated selective expression of E1A and HCCS1 in hepatoma cells and tumor-selective cytotoxicity in vitro and in vivo demonstrated the strongest inhibition of BEL-7404 cell xenografts in nude mice among a number of control Ad vectors. These data indicated the efficacy and safety of the PD55-HCCS1 system for HCC treatment.