Human melanoma cells expressing the alphavbeta3 integrin are partially protected from necrotic cell death induced by dynamic matrix detachment.

Anchorage-independence is a hallmark of metastatic cancer cells. In previous studies we characterized a novel model for anchorage-independence employing dynamic matrix detachment (DMD) using rotation in low shear stress conditions. We observed that in contrast to the classical apoptosis-inducing static matrix detachment (SMD) model, the venous circulation-mimicking DMD model induced necrosis in transformed cells. In the current study we revisited the mechanism of DMD-induced cell death and evaluated the contribution of alphavbeta3 integrin overexpression in human melanoma cells to anchorage-independence in DMD. DMD cell culture induced primarily necrosis in the melanoma cells studied. alphavbeta3, but not the control related alphaIIbbeta3 integrin, could confer survival advantage in DMD. While apoptosis was unaffected, constitutive, unligated alphavbeta3 overexpression was associated with attenuation of necrosis in DMD. alphavbeta3 overexpressing melanoma cells manifested AKT activation that was independent of DMD conditions. Furthermore, while a small molecular inhibitor of AKT phosphorylation induced apoptosis in adherent cells, in DMD conditions it had no effect on cell outcome. Thus, alphavbeta3-overexpressing melanoma cells are partially protected from DMD-induced cell death in an apoptosis-independent mechanism. This finding may be one of the factors accounting for anchorage-independence in circulating metastatic melanoma cells.

Evaluation of tumor-specific promoter activities in melanoma.

Gene therapy is a novel therapy for melanoma. To date, however, there is still no powerful tumor specific promoter (TSP) to restrict the transgene expression in melanoma cells. In order to define a useful TSP for targeting in the context of melanoma gene therapy, four promoters, the cyclooxygenase-2 (Cox-2), alpha-chemokine SDF-1 receptor (CXCR4), epithelial glycoprotein 2 (EGP-2), and survivin, were tested in both established melanoma cell lines and primary melanoma cells. We employed recombinant adenoviral vectors (reAds) each with a candidate TSP (the Cox-2, CXCR4, EGP-2, or survivin), a reporter luciferase gene, and a poly-A signal, all of which were inserted into the E1-deleted region. A reAdGL3Bcytomegalovirus (CMV), containing the CMV promoter and luciferase gene, was used as a positive control to normalize the luciferase activity. Luciferase activity was measured in multiple tumor cell lines and two primary melanoma cell cultures after infection with reAds. Human epithelial melanocytes, HEM, were used as normal control. In contrast to three other promoters, the survivin promoter exhibited the highest activities within both melanoma cell lines and primary melanoma cells, but not in HEMs. Additionally, the survivin promoter exhibited very low activities in major mouse organs including the liver, in vivo. EGP-2 is not active in melanoma; messenger RNA expressions were correlated to promoter activities both in melanoma cell lines and primary cell cultures. Thus, these data suggest that the survivin promoter achieved a 'tumor-on/liver-off' profile, and thus represents a potentially useful tumor-specific promoter with applications for transcriptional targeting of Ad vector-based cancer gene therapy or oncolysis to melanoma.

Combining high selectivity of replication with fiber chimerism for effective adenoviral oncolysis of CAR-negative melanoma cells.

Oncolytic adenoviruses constitute a new and promising tool for cancer treatment that has been rapidly translated into clinical trials. However, minimal or absent expression of the adenovirus serotype 5 (Ad5) receptor CAR (coxsackievirus and adenovirus receptor) on cancer cells represents a major limitation for Ad5-based oncolysis. Here, we report on the resistance of CAR-negative primary melanoma cells to cell killing by wild-type Ad5 (Ad5wt) even after high titer infection, thus underlining the need for tropism-modification of oncolytic adenoviruses. We engineered a new generation of oncolytic adenoviruses that exhibit both efficient target cell infection by swapping Ad5 fiber domains with those of Ad serotype 3, which binds to a receptor distinct from CAR, and targeted virus replication. Fiber chimerism resulted in efficient cytopathicity to primary melanoma cells, which was at least 10(4)-fold increased relative to Ad5wt. Since viral infectivity mediated by such modified viral capsids was not cell type-specific, it was pivotal to carefully restrict adenoviral replication to target cells. Towards this end, we replaced both E1A and E4 promoters of fiber chimeric viruses by tyrosinase enhancer/promoter constructs. The resulting viruses showed melanoma-specific expression of E1A and E4 and combined efficient virus replication and cell killing in melanoma cell lines and primary melanoma cells with a remarkable specificity profile that implements strong attenuation in nonmelanoma cells, including normal fibroblasts and keratinocytes.

Transcriptional targeting of adenoviral vector through the CXCR4 tumor-specific promoter.

Adenoviral vectors are considered to be good gene delivery vectors for cancer gene therapy due to their wide host tissue range and cell cycle-independent infectivity. However, the disadvantages include the lack of specificity for cancer cells and the high liver accumulation in vivo. The human CXCR4 gene is expressed at high levels in many types of cancers, but is repressed in the liver. We explored the CXCR4 promoter as a candidate to restrict adenoviral transgene expression to tumor cells with a low expression in host tissues. The luciferase activities in multiple cancer cell lines infected with recombinant adenovirus reAdGL3BCXCR4 or the control vector reAdGL3BCMV revealed that the CXCR4 promoter exhibited relatively high transcriptional activity in a breast cancer cell line, MDA-MB-361, and two ovarian cancer cell lines, OVCAR-3 and SKOV3. ip1, 65% (P=0.0087), 16.7% (P=0.1) and 20% (P=0.0079) compared to that of the CMV promoter, respectively, and low expression, 4.9 and 0.1%, respectively, in both normal cell lines HFBC and HMEC. In addition, CXCR4 had a low expression of luciferase (0.32%) compared to that of the CMV promoter in mouse liver in vivo. The data also revealed that the CXCR4 promoter was a stronger tumor-specific promoter (TSP) than the Cox-2M promoter in primary melanomas obtained from two patients. The CXCR4 promoter is shown to have a 'tumor-on' and 'liver-off' status in vitro and in vivo, and CXCR4 may prove to be a good candidate TSP for cancer gene therapy approaches for melanoma and breast cancers.

Combined transcriptional and transductional targeting improves the specificity and efficacy of adenoviral gene delivery to ovarian carcinoma.

Adenoviruses are efficient gene delivery vehicles but have broad native tropism. To this end, finding ways to target this virus specifically to carcinomas has become an important focus of cancer gene therapy. Transductional and transcriptional forms of targeting have been used with promising results in ovarian carcinoma. Therefore, we combined both forms of targeting to investigate the effect on the specificity and efficiency of transgene expression in this disease. We used the tissue-specific SLPI promoter and the ovarian cancer associated targeting adaptor protein, sCARfC6.5. This bispecific protein contains the coxsackie-adenovirus receptor ectodomain and a single-chain antibody specific for c-erbB-2. Viruses containing the SLPI or the ubiquitously expressed CMV promoter, with or without sCARfC6.5, were used for infection of ovarian cancer cell lines, primary ovarian tumor cells, and in an orthotopic model of disseminated ovarian carcinoma. This dual-targeting strategy increased the efficiency and specificity of transgene expression in vitro in reporter and cell-killing assays, and in vivo. By using both the SLPI promoter and sCARfC6.5, transgene expression was increased in ovarian tumors and decreased in normal tissues, including the liver. Thus, we show that combining transcriptional and transductional targeting can increase the efficacy and specificity of adenoviral gene therapy for ovarian carcinoma.

Cyclooxygenase-2 promoter for tumour-specific targeting of adenoviral vectors to melanoma.

Novel therapeutic strategies are warranted for the treatment of metastatic melanoma as conventional therapies are inefficient. Conceptually, these strategies should be systemic and tumour-targeted. Gene therapy and viral oncolysis represent promising new approaches for cancer treatment that allow for the incorporation of molecular targeting strategies. In this regard, we analysed cyclooxygenase-2 (cox-2) expression as a potential new target for melanoma gene therapy. By reverse transcription polymerase chain reaction analysis, we showed cox-2 mRNA expression in all of the six tested melanoma cell lines, thus establishing cox-2 as a tumour marker for melanoma of potential interest for targeted therapeutics. Next, we analysed the activity and specificity of the cox-2 promoter within adenoviral vectors by luciferase assays. For this purpose, melanoma cell lines, primary melanoma cells and normal melanocytes were infected with adenoviruses containing cox-2 promoter sequences driving the luciferase reporter gene. The results demonstrated activity of the cox-2 promoter in melanoma cell lines and primary melanoma cells, but not in non-malignant primary epidermal melanocytes. Thus, we established herein the tumour specificity of the cox-2 promoter with potential applications for transcriptional targeting of adenoviral vector-based cancer gene therapy or virotherapy to melanoma.

Effective single chain antibody (scFv) concentrations in vivo via adenoviral vector mediated expression of secretory scFv.

Single chain antibodies (scFv) represent powerful interventional agents for the achievement of targeted therapeutics. The practical utility of these agents have been limited, however, by difficulties related to production of recombinant scFv and the achievement of effective and sustained levels of scFv in situ. To circumvent these limitations, we have developed an approach to express scFv in vivo. An anti-erbB2 scFv was engineered for secretion by eukaryotic cells. The secreted scFv could bind to its target and specifically suppress cell growth of erbB2-positive cells in vitro. Adenoviral vectors expressing the cDNA for the secretory scFv likewise could induce target cells to produce an anti-tumor anti-erbB2 scFv. In vivo gene transfer via the anti-erbB2 scFv encoding adenovirus also showed anti-tumor effects. Thus, by virtue of engineering a secreted version of the anti-tumor anti-erbB-2 scFv, and in vivo expression via adenoviral vector, effective concentrations of scFv were achieved. In vivo gene transfer clearly represents a powerful means to realize effective scFv-based approaches. This method will likely have applicability for a range of disorders amenable to targeted therapeutic approaches.

Transcriptional targeting for ovarian cancer gene therapy.

Ovarian carcinoma is a leading cause of cancer death in women. Though advances in conventional therapies have been achieved, long-term survival rates for most patients diagnosed with ovarian cancer are still low. Therefore, novel molecular therapeutic strategies such as gene therapy are being intensively pursued. Such approaches are based on the enormous progress that has been achieved in the elucidation of the molecular foundations of ovarian cancer. In this regard transcriptional control elements (promoters) of genes frequently upregulated or specifically expressed in tumors can be applied in a heterologous context to drive expression of therapeutic genes in targeted gene therapy strategies. This review discusses transcriptional targeting strategies in ovarian cancer gene therapy and gives an overview of tumor-specific promoters (TSPs) that have been applied for this purpose.

Adenovirus-mediated soluble FLT-1 gene therapy for ovarian carcinoma.

PURPOSE: We hypothesized that adenovirus-mediated soluble fms-like tyrosine kinase receptor (sFLT-1) gene therapy can inhibit the ovarian tumor growth and increase survival of mice in the context of ovarian carcinoma. EXPERIMENTAL DESIGN: We constructed an infectivity-enhanced recombinant adenovirus (AdRGDGFPsFLT-1) expressing soluble FLT-1 and green fluorescent protein (GFP). An adenovirus AdRGDGFP expressing GFP alone was used as control. The functional validation of adenovirus-mediated sFLT-1 was determined by an in vitro human umbilical vein endothelial cell proliferation inhibition assay. To evaluate the therapeutic potential of adenovirus-expressed sFLT-1 to inhibit the growth of ovarian tumors and to increase the survival duration of mice with ovarian tumors, two tumor models were used. First, SKOV3.ip1 ovarian carcinoma cells were infected ex vivo with either AdRGDGFPsFLT-1 or AdRGDGFP or uninfected and then inoculated s.c. into BALB/c nude mice, and tumor growth was monitored. Second, SKOV3.ip1 cells were inoculated i.p. into CB17 SCID mice and then treated with two doses of either AdRGDGFPsFLT-1 or AdRGDGFP or with PBS on days 1 and 14 after inoculation of cells, and the survival duration was monitored. RESULTS: Treatment with adenovirus-expressed sFLT-1 significantly inhibited the proliferation of human umbilical vein endothelial cells. The s.c. tumor nodules in mice derived from cells infected with AdRGDGFPsFLT-1 were significantly smaller than those infected with either AdRGDGFP or uninfected. In addition, i.p. administration of the AdRGDGFPsFLT-1 resulted in a significant increase in the survival times of mice compared with AdRGDGFP- or PBS-treated mice. CONCLUSIONS: Our results suggest that adenovirus-mediated sFLT-1 gene therapy can effectively inhibit ovarian tumor growth and increase survival in a murine model of ovarian carcinoma.

Targeting of adenovirus to endothelial cells by a bispecific single-chain diabody directed against the adenovirus fiber knob domain and human endoglin (CD105).

The use of adenoviruses for antivascular cancer gene therapy is limited by their low transduction efficiency for endothelial cells. We have developed a recombinant bispecific antibody as a molecular bridge, linking the adenovirus capsid to the endothelial cell surface protein endoglin, for vascular targeting of adenoviruses. Endoglin (CD105), a component of the transforming growth factor beta receptor complex, represents a promising target for antivascular cancer therapy. Endoglin is expressed predominantly on endothelial cells and is upregulated in angiogenic areas of tumors. We isolated single-chain Fv fragments directed against human endoglin from a human semisynthetic antibody library. One of the isolated scFv fragments (scFv C4) bound specifically to various proliferating primary endothelial cells or cell lines including HUVEC, HDMEC, HMVEC, and HMEC. ScFv C4 was therefore used to construct a bispecific single-chain diabody directed against endoglin and the adenovirus fiber knob domain (scDb EDG-Ad). This bispecific molecule mediated enhanced and selective adenovirus transduction of HUVECs, which was independent from binding to the coxsackievirus and adenovirus receptor (CAR) and alpha(v)-integrins. Thus, adenovirus infection was redirected to a new cellular receptor (CD105) and cell entry pathway. These results demonstrate the utility of bispecific single-chain diabodies, which can be produced in large quantities in bacteria, for the retargeting of adenoviruses in cancer gene therapy.

Gene therapy: designer promoters for tumour targeting.

One of the biggest challenges facing cancer therapy is to generate tumour-specific treatment strategies. Gene therapy hopes to achieve this by directing the activity of therapeutic genes specifically to the sites of disease. Of paramount importance for the success of this approach is the availability of tumour-specific delivery systems: both the transductional targeting of the vector vehicle and the restriction of transgene expression to the tumour are promising strategies towards this goal. This review will focus on the recent achievements in the field of transcriptional targeting and the different strategies to improve or design promoters with the desired specificities.

Generation of angiostatin-like fragments from plasminogen by prostate-specific antigen.

Angiostatin, a potent inhibitor of angiogenesis, tumour growth and metastasis, is a biologically active fragment of plasminogen, containing the kringle domains 1-4. It is generated from plasminogen by limited proteolysis. We show that prostate-specific antigen (PSA), a serine proteinase secreted by human prostate and human prostate cancer cells, is able to convert Lys-plasminogen to biologically active angiostatin-like fragments, containing kringles 1-4, by limited proteolysis of peptide bond Glu439-Ala440 in vitro. In an in vitro morphogenesis assay, the purified angiostatin-like fragments inhibited proliferation and tubular formation of human umbilical vein endothelial cells with the same efficacy as angiostatin. This finding might help to understand growth characteristics of prostate cancer, which usually has low microvessel density and slow proliferation.

A dual specificity promoter system combining cell cycle-regulated and tissue-specific transcriptional control.

The expression of both proliferation-associated and cell type-specific genes is a hallmark of both cancer cells and tumor endothelial cells. The possibility to combine both features in a single transcriptional control unit would greatly increase the selectivity of vectors used for cancer gene therapy. Previous studies by our laboratory have shown that the transcription of several cell cycle genes is regulated by a novel cell cycle-regulated repressor, termed CDF-1. This repressor functions by blocking in resting cells the transcriptional activation by specific factors binding to the upstream activating sequence (UAS), most notably the CCAAT-box binding factor NF-Y/CBF. Based on this work we have developed a dual specificity promoter system that combines cell type specificity with cell cycle regulation. A chimeric transcription factor (Gal4/NF-Y) consisting of the transactivation domain of NF-Y and the DNA-binding domain of Gal4 is expressed from a tissue-specific promoter. Gal4/NF-Y can bind to a second promoter consisting of a minimal cyclin A promoter with multiple Gal4 binding sites replacing the normal UAS. This leads to the tissue-specific expression of Gal4/NF-Y whose stimulatory activity on the promoter is restrained in resting cells by the recruitment of the CDF-1 repressor to the promoter. The functionality of this system is demonstrated for the specific transcriptional targeting of proliferating melanoma cells, where cell cycle regulation was >20-fold and cell type specificity was >50-fold.

Cell type specificity of the human endoglin promoter.

Endoglin is a component of the transforming growth factor-beta receptor complex whose expression is limited to a small number of cell types, including endothelial cells (ECs), activated monocytes, tissue macrophages and erythroid precursors. Of particular interest is its preferential expression in the vasculature of many malignant tumors, especially in view of potential therapeutic applications. We have cloned the human endoglin promoter, analyzed its structure and demonstrate that the isolated genomic fragment shows strong promoter activity in ECs (compared to other known EC-selective promoters), but not in epithelial cells and fibroblasts. These findings suggest that the endoglin promoter may prove a useful tool for the transcriptional targeting of ECs by gene therapy. We also determined the domains that are responsible for both efficient transcription and the observed preferential activity in ECs. The region around the major site of transcription initiation was found to be essential for transcription in both ECs and non-ECs. In contrast, cell type specificity does not appear to be governed by a single mechanism, but rather seems to be due to functionally distinct regulatory mechanisms acting on different upstream sequences.

Cell cycle-independent induction of apoptosis by the anti-tumor drug Flavopiridol in endothelial cells.

The anti-tumor drug Flavopiridol is a potent inhibitor of cyclin-dependent kinases (cdks). As a consequence, Flavopiridol-treated cells arrest in both G1 and G2, but Flavopiridol has also been shown to be cytotoxic for some tumor cell lines. The underlying molecular events are, however, unclear. We now show that Flavopiridol induces apoptosis in human umbilical vein endothelial cells (HUVECs), as judged by the occurrence of classical apoptotic markers, including chromatin condensation, internucleosomal cleavage, DNA fragmentation (TUNEL assay), annexin V binding and poly(ADP-ribose) polymerase (PARP)-cleavage. Such induction of apoptosis occurs with equal efficiency in both proliferating and G0/G1-arrested cells. Because growth-arrested HUVECs lack cdk2 activity and contain high levels of the cdk inhibitor p27, our observations suggest that cell cycle regulated cdks may not be the only critical target for Flavopiridol-induced apoptosis. Surprisingly, A549 lung carcinoma cells were clearly dependent on cell proliferation for the induction of cell death, pointing to cell type-related differences in the mechanism of Flavopiridol action.

A strategy for enhancing the transcriptional activity of weak cell type-specific promoters.

Cell type- and tissue-specific promoters play an important role in the development of site-selective vectors for gene therapy. A large number of highly specific promoters has been described, but their applicability is often hampered by their inefficient transcriptional activity. In this study, we describe a new strategy for enhancing the activity of weak promoters without loss of specificity. The basic principle of this strategy is to establish a positive feedback loop which is initiated by transcription from a cell type-specific promoter. This was achieved by using a cell type-specific promoter to drive the simultaneous expression of the desired effector/reporter gene product and a strong artificial transcriptional activator which stimulates transcription through appropriate binding sites in the promoter. Using a VP16-LexA chimeric transcription factor, we show that this approach leads to a 14- to > 100-fold enhancement of both the endothelial cell-specific von Willebrand factor promoter and the gastrointestinal-specific sucrase-isomaltase promoter while maintaining approximately 30- to > 100-fold cell type specificity.