Adenoviral transduction efficiency of ovarian cancer cells can be limited by loss of integrin beta3 subunit expression and increased by reconstitution of integrin alphavbeta3

Of vascular defense, hemostasis, cancer, and platelet biology: an evolutionary perspective

We have established considerable expertise in studying the role of platelets in cancer biology. From this expertise, we were keen to recognize the numerous venous-, arterial-, microvascular-, and macrovascular thrombotic events and immunologic disorders are caused by severe, acute-respiratory-syndrome coronavirus 2 (SARS-CoV-2) infections. With this offering, we explore the evolutionary connections that place platelets at the center of hemostasis, immunity, and adaptive phylogeny. Coevolutionary changes have also occurred in vertebrate viruses and their vertebrate hosts that reflect their respective evolutionary interactions. As mammals adapted from aquatic to terrestrial life and the heavy blood loss associated with placentalization-based live birth, platelets evolved phylogenetically from thrombocytes toward higher megakaryocyte-blebbing-based production rates and the lack of nuclei. With no nuclei and robust RNA synthesis, this adaptation may have influenced viral replication to become less efficient after virus particles are engulfed. Human platelets express numerous receptors that bind viral particles, which developed from archetypal origins to initiate aggregation and exocytic-release of thrombo-, immuno-, angiogenic-, growth-, and repair-stimulatory granule contents. Whether by direct, evolutionary, selective pressure, or not, these responses may help to contain virus spread, attract immune cells for eradication, and stimulate angiogenesis, growth, and wound repair after viral damage. Because mammalian and marsupial platelets became smaller and more plate-like their biophysical properties improved in function, which facilitated distribution near vessel walls in fluid-shear fields. This adaptation increased the probability that platelets could then interact with and engulf shedding virus particles. Platelets also generate circulating microvesicles that increase membrane surface-area encounters and mark viral targets. In order to match virus-production rates, billions of platelets are generated and turned over per day to continually provide active defenses and adaptation to suppress the spectrum of evolving threats like SARS-CoV-2.

Recent Progress of RGD Modified Liposomes as Multistage Rocket Against Cancer

Cancer is a life-threatening disease, contributing approximately 9.4 million deaths worldwide. To address this challenge, scientific researchers have investigated molecules that could act as speed-breakers for cancer. As an abiotic drug delivery system, liposomes can hold both hydrophilic and lipophilic drugs, which promote a controlled release, accumulate in the tumor microenvironment, and achieve elongated half-life with an enhanced safety profile. To further improve the safety and impair the off-target effect, the surface of liposomes could be modified in a way that is easily identified by cancer cells, promotes uptake, and facilitates angiogenesis. Integrins are overexpressed on cancer cells, which upon activation promote downstream cell signaling and eventually activate specific pathways, promoting cell growth, proliferation, and migration. RGD peptides are easily recognized by integrin over expressed cells. Just like a multistage rocket, ligand anchored liposomes can be selectively recognized by target cells, accumulate at the specific site, and finally, release the drug in a specific and desired way. This review highlights the role of integrin in cancer development, so gain more insights into the phenomenon of tumor initiation and survival. Since RGD is recognized by the integrin family, the fate of RGD has been demonstrated after its binding with the acceptor’s family. The role of RGD based liposomes in targeting various cancer cells is also highlighted in the paper.

Epigenetic silencing of the LDOC1 tumor suppressor gene in ovarian cancer cells

PURPOSE

Due to very unspecific symptoms ovarian cancer often is diagnosed only at a late stage of the disease. Thus, morbidity and mortality of the patients are high. Even the established tumor marker CA12-5 shows only low specificity, rising the need for alternative biomarkers capable of detecting early stages of ovarian cancer. We analyzed the expression of the tumor suppressor candidate gene LDOC1 (leucine zipper downregulated in cancer 1) as a potential early biomarker in ovarian cancer cell lines.

METHODS

A total of seven ovarian cancer cell lines were analyzed by RT-PCR (reverse transcriptase polymerase chain reaction) and real-time PCR for expression of LDOC1. Verification of promoter methylation was performed using methylation-specific primers on bisulfite-modified genomic DNA.

RESULTS

Three out of seven ovarian cancer cell lines showed a complete loss of LDOC1 gene expression. LDOC1 silencing was caused neither by gene deletion nor gene rearrangements, but by methylation and subsequent inactivation of the concerned promoter as proofed by methylation specific primers. Similarly, promoter methylation could be inhibited by adding AdC (5-aza-2'-deoxycytidine), an inhibitor of DNA methyltransferases. As a result, a reactivation of the LDOC1 gene was seen.

CONCLUSIONS

The tumor suppressor gene LDOC1 in ovarian cancer cell lines is downregulated by promoter methylation and thus may serve as an early biomarker. Further investigation will show if detection of methylated LDOC1 in peripheral blood has both adequate sensitivity and specificity for a timely non-invasive detection of ovarian cancer.

Disulfiram/copper causes redox-related proteotoxicity and concomitant heat shock response in ovarian cancer cells that is augmented by auranofin-mediated thioredoxin inhibition

A valuable strategy to develop new therapeutic options for a variety of diseases has been the identification of new targets and applications for already approved drugs, the so-called drug repositioning. Recurrent ovarian cancer is a nearly incurable malignancy for which new and effective treatments are urgently needed. The alcohol-deterring drug disulfiram has been shown to cause preferential cell death in a variety of cancer cells. In this study, it is shown that disulfiram mediates effective cell death in ovarian cancer cells by promoting a pro-oxidative intracellular environment in a copper-dependent mechanism. Within few hours of application, disulfiram caused irreversible cell damage associated with pronounced induction of the inducible heat shock proteins HSP70, HSP40, and HSP32. The small heat shock protein HSP27 was found to be covalently dimerized via oxidized disulfide bonds and precipitated in para-nuclear protein aggregates. Simultaneous inhibition of the cellular thioredoxin system by auranofin further enhanced the cytotoxic effect of disulfiram. These data indeed indicate that the combination of two approved drugs, the anti-alcoholic disulfiram and the anti-rheumatic auranofin, may be of interest for the treatment of recurrent and genotoxic drug-resistant ovarian cancer by inducing a proteotoxic cell death mechanism.

Adenovirus serotype 11 causes less long-term intraperitoneal inflammation than serotype 5: implications for ovarian cancer therapy

In a phase II/III clinical trial intraperitoneal (i.p.) administration of a group C adenovirus vector (Ad5) caused bowel adhesion formation, perforation and obstruction. However, we had found that i.p. group B, in contrast to group C adenoviruses, did not cause adhesions in nude BALB/c ovarian cancer models, prompting further investigation. Ex vivo, group B Ad11 caused lower inflammatory responses than Ad5 on BALB/c peritoneal macrophages. In vivo, i.p. Ad11 triggered short-term cytokine and cellular responses equal to Ad5 in both human CD46-positive and -negative mice. In contrast, in a long-term study of repeated i.p. administration, Ad11 caused no/mild, whereas Ad5 induced moderate/severe adhesions and substantial liver toxicity accompanied by elevated levels of IFNγ and VEGF and loss of i.p. macrophages, regardless of CD46 expression. It appears that, although i.p. Ad11 evokes immediate inflammation similar to Ad5, repeated administration of Ad11 is better tolerated and long-term fibrotic tissue remodelling is reduced.

Role of cell surface molecules and autologous ascitic fluid in determining efficiency of adenoviral transduction of ovarian cancer cells

Adenovirus is the most frequently used virus in gene therapy clinical trials. There have been conflicting reports on the ability of adenovirus to transduce primary ovarian cancer samples and the expression of relevant cell surface molecules. These factors were examined using primary ovarian cancer cells cultured from ascites and solid tumor to gain insights into the clinical use of adenovirus in ovarian cancer. The level of transduction of primary cultures was much higher than uncultured cells and established cell lines, and correlated with higher levels of coxsackie-adenovirus receptor (CAR) and integrin expression. Growth of primary cultures in autologous ascitic fluid prevented an increase in CAR expression and inhibited transduction compared with cells treated in supplemented RPMI. Cells at the periphery of solid tumor samples were transduced using a replication-incompetent virus and correlated with CAR expression. However, transduction was abolished by autologous ascitic fluid, despite the expression of CAR. We conclude that the use of adenoviruses for ovarian cancer gene therapy will require testing in the presence of inhibitory factors in ascitic fluid. The clinical use of adenoviral vectors may require circumvention of such inhibitory factors and the use of replication competent adenovirus to enable efficient viral penetration of the cancer.

Coxsackie adenovirus receptor (CAR) regulates integrin function through activation of p44/42 MAPK

The coxsackie B virus and adenovirus receptor (CAR) is an attachment receptor for Adenovirus serotype 5 (Ad5) and in many cell types forms homodimers with neighbouring cells as part of a cell adhesion complex. CAR co-operates with cell surface integrin receptors to enable efficient viral entry, but little is known about the mechanism of crosstalk between these two receptor types. Here we show that overexpression of CAR in human epithelial cells leads to increased basal activation of p44/42 MAPK and this is required for efficient Ad5 infection. We demonstrate that CAR forms homodimers in cis and that this dimerisation is enhanced in the presence of Ad5 in a phospho-p44/42-dependent manner. CAR-induced p44/42 activation also leads to increased activation of beta1 and beta3 integrins. Analysis of CAR mutants demonstrates that the cyto domain of CAR is required for CAR-induced p44/42 activation, integrin activation and localisation to cell junctions. This data for the first time demonstrates that signalling downstream of CAR can have a dual effect on integrins and CAR itself in order to promote efficient viral binding to cell membranes.

Cetuximab retargeting of adenovirus via the epidermal growth factor receptor for treatment of intraperitoneal ovarian cancer

Gene and virotherapy of ovarian cancer, using type 5 adenovirus (Ad5), has demonstrated good activity in preclinical animal studies, particularly after intraperitoneal administration of virus; however, success in clinical trials has been limited by poor infectivity of ovarian cancer cells and inflammatory responses to Ad5. We previously demonstrated that covalent modification of Ad5 with reactive copolymers on the basis of poly(hydroxypropylmethacrylamide) can shield the virus, offering protection from neutralizing antibodies and enabling retargeting to cancer-upregulated receptors with peptide ligands (basic fibroblast growth factor [bFGF] and murine epidermal growth factor [EGF]). These ligands may be less than ideal for clinical use, however, because they are potential mitogens. Accordingly, in this study we investigated the use of an anti-EGF receptor (EGFR) antibody, cetuximab, to retarget adenoviral transduction of EGFR-positives in vitro and in vivo. Cetuximab retargeting altered the physicochemical characteristics of Ad5, although it did not cause particle aggregation. Although cetuximab stimulated internalization of EGFR, similarly to EGF, it inhibited EGFR phosphorylation. Adenoviral transduction was inhibited after polymer coating, but was rescued in EGFR-positive cells (and not in EGFR-negative cells) by cetuximab retargeting. Cetuximab retargeting of wild-type adenovirus serotype 5 (Ad5WT) prolonged survival in an animal model of human ovarian cancer, similar to unmodified Ad5WT, but polymer coating ameliorated stimulation of adhesion formation. We conclude that polymer coating and covalent attachment of cetuximab successfully retargeted adenovirus to EGFR-positive cells, retained in vivo efficacy of an oncolytic adenovirus, and ameliorated side effects caused by unmodified adenovirus.

Integrin beta3 down-regulates invasive features of ovarian cancer cells in SKOV3 cell subclones

PURPOSE

To investigate the role of integrin beta3 in invasive features of ovarian cancer SKOV3 cells, by comparing different metastatic subclones.

METHODS

In the present study, two cell subclones, termed as S1 and S21, which possessed high and low metastatic potential, respectively, were isolated and established from human ovarian cancer parental cell line SKOV3 by the limited dilution method. The expressions of integrin alphav, integrin alphavbeta3, integrin beta3, E-cadherin, FAK and ILK in the two cell subclones were compared by means of real-time RT-PCR or flow cytometry. Subsequently, S21 was transfected with siRNA for integrin beta3 and the effects of transfection were examined by methyl thiazolyl tetrazolium (MTT) assay, colony formation assay, Matrigel invasion assay and cell migration assay.

RESULTS

The expressions of integrin alphavbeta3, integrin beta3 and E-cadherin were markedly down-regulated in S1; however, there were no significant differences in the expressions of integrin alphav, FAK and ILK beta. Of note, more than 70% knockdown of integrin beta3 expression was obtained by siRNA technique. The integrin beta3-siRNA-transfected cells showed significant increases in cell proliferation, cell migration and invasive activity in contrast with the mock-transfected cells. The expressions of integrin alphavbeta3 and E-cadherin were lower in the integrin beta3-siRNA-transfected cells compared to the mock control.

CONCLUSION

Integrin beta3, like E-cadherin, may be also a suppressor gene down-regulating invasive features of ovarian cancer cells in SKOV3 cell subclones.

Systemic therapy for cervical cancer with potentially regulatable oncolytic adenoviruses

Clinical trials have confirmed the safety of selectively oncolytic adenoviruses for treatment of advanced cancers. However, increasingly effective viruses could result in more toxicity and therefore it would be useful if replication could be abrogated if necessary. We analyzed viruses containing the cyclooxygenase-2 (Cox-2) or vascular endothelial growth factor (VEGF) promoter for controlling replication. Anti-inflammatory agents can lower Cox-2 protein levels and therefore we hypothesized that also the promoter might be affected. As Cox-2 modulates expression of VEGF, also the VEGF promoter might be controllable. First, we evaluated the effect of anti-inflammatory agents on promoter activity or adenovirus infectivity in vitro. Further, we analyzed the oncolytic potency of the viruses in vitro and in vivo with and without the reagents. Moreover, the effect of on virus replication was analyzed. We found that RGD-4C or Ad5/3 modified fibers improved the oncolytic potency of the viruses in vitro and in vivo. We found that both promoters could be downregulated with dexamethasone, sodium salicylate, or salicylic acid. Oncolytic efficacy correlated with the promoter activity and in vitro virus production could be abrogated with the substances. In vivo, we saw good therapeutic efficacy of the viruses in a model of intravenous therapy of metastatic cervical cancer, but the inhibitory effect of dexamethasone was not strong enough to provide significant differences in a complex in vivo environment. Our results suggest that anti-inflammatory drugs may affect the replication of adenovirus, which might be relevant in case of replication associated side effects.

Expression of coxsackie and adenovirus receptor reduces the lung metastatic potential of murine tumor cells

The coxsackie and adenovirus receptor (CAR) is involved in the epithelial cell tight junction, the downregulated expression of which is observed in different cancer types. In the present study, we examined CAR's role in tumor metastasis using a B16 melanoma and CT26 colon adenocarcinoma model of experimental metastasis. In lung metastasis, the colony number of B16 cells stably expressing CAR (B16CAR) was significantly lower than that of the control CAR-negative B16 cells. B16 and CT26 cells transiently expressing CAR, which were transduced with adenovirus (Ad) vector expressing CAR, also reduced lung metastasis, suggesting that CAR plays a role in the early stage of metastasis. CAR expression significantly decreased the accumulation of B16 cells in the lung after i.v. injection and the migration in vitro. CAR expression reduced expression of alpha(v), alpha(4), beta(3) and beta(1) integrin, which play important roles in attachment to cells or basement membrane. Thus, CAR expression likely acts as a metastatic suppressor.

p53 as a target for anti-cancer drug development

Loss of p53 function compromises genetic homeostasis in cells exhibiting deregulated DNA replication and/or DNA damage, and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Progress has recently been made in the clinical use of replication-deficient virus carrying wt-TP53 (Ad5CMV-p53) and/or cancer-selective oncolytic adenoviruses (ONYX-015). These strategies demonstrated clinical activity as monotherapy and were synergistic with traditional chemotherapy agents in the treatment of some types of cancer. In addition, pharmacological methods are under development to either stimulate wild-type p53 protein function, or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3) or single-chain Fv antibody fragments corresponding to defined p53 domains. Here, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

Glucocorticoids inhibit cell death in ovarian cancer and up-regulate caspase inhibitor cIAP2

PURPOSE

Almost all patients with epithelial ovarian cancer receive chemotherapy and, concurrently, the synthetic steroid hormone dexamethasone to alleviate the side effects. This study aims to test the impact of steroid hormones on the apoptosis of epithelial ovarian cancer cells and to identify its mediators.

EXPERIMENTAL DESIGN

Tumor cell lines from 19 patients with advanced epithelial ovarian cancer were analyzed for glucocorticoid receptor, estrogen receptor, progesterone receptor, and androgen receptor expression. Cells were incubated with corresponding steroid hormones at serum-equivalent doses in hormone-depleted medium. Apoptosis was induced by application of tumor necrosis factor-related apoptosis-inducing ligand or staurosporine and determined by poly(ADP-ribose)polymerase cleavage and cell survival. Microarray with 8K cDNA chips including apoptosis-relevant genes was used to study genes regulated by glucocorticoids.

RESULTS

In cell culture, tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in OV-MZ-30 and OV-MZ-31 cells was reduced after treatment with dexamethasone or cortisol, but not with estradiol, progesterone, or androstenedione. Microarray analysis revealed a 7-fold up-regulation of the caspase inhibitor cIAP2 by dexamethasone in OV-MZ-30 and OV-MZ-31 cells. cIAP2 up-regulation by glucocorticoids was confirmed by RT-PCR and Western blot analysis in OV-MZ-30, OV-MZ-31, OV-CAR3, and SK-OV-3 cells. Down-regulation of cIAP2 expression by small interfering RNA sensitized SK-OV-3 cells to apoptosis inducer staurosporine. Under clinical conditions, treatment with dexamethasone was associated with significant up-regulation of cIAP2 in the ascites cells.

CONCLUSIONS

Activation of the glucocorticoid receptor in epithelial ovarian cancer cells caused an anti-apoptotic effect associated with the enhanced cellular expression level of cIAP2. Dexamethasone pretreatment of epithelial ovarian cancer patients receiving apoptosis-inducing chemotherapy raises questions about a negative effect on antitumor efficacy.

Variable expression of coxsackie-adenovirus receptor in thyroid tumors: implications for adenoviral gene therapy

Adenoviral gene therapy represents a novel approach for the treatment of aggressive thyroid carcinomas. Both coxsackie-adenovirus receptor (CAR) and integrins have been shown to be the major determinants for adenoviral infectivity in many types of cancer cells, yet conflicting results have been reported. In this report we examine these factors mediating adenoviral infection in thyroid cells and to evaluate CAR expression in various types of thyroid cancer. We found that neither expression levels of CAR nor integrins are solely predictive of adenoviral infectivity in thyroid cells. However, the absence of CAR was associated with poor adenoviral infectivity in immortalized rat FRTL-5 cells. Moreover, preincubation with alpha-CAR antibody decreased infectivity in FTC 238 cells, a human thyroid tumor line. These results indicate that CAR does play a role in adenoviral infection of thyroid cells. Immunohistochemical analysis revealed that CAR is expressed at the cell surface in the majority of malignant thyroid tumors. We further show that adenoviral infectivity in some thyroid cancer cells can be improved by poly-L-lysine. Our study warrants a functional method to evaluate adenoviral infectivity should be developed and instituted prior to clinical trials of adenoviral gene therapy in patients with advanced thyroid cancer.

Coxsackie and adenovirus receptor promotes adenocarcinoma cell survival and is expressionally activated after transition from preneoplastic precursor lesions to invasive adenocarcinomas

PURPOSE

The cell adhesion protein, coxsackie and adenovirus receptor (CAR), is differentially expressed in various human adenocarcinomas. We analyzed the role of differential CAR expression during tumorigenesis and in cell survival of adenocarcinomas.

EXPERIMENTAL DESIGN

In a murine mammary cancer model, a syngenic preneoplastic mammary tissue was implanted into the mammary fat pads of syngenic female BALB/c mice. CAR expression was determined by semiquantitative reverse transcription-PCR in the preneoplastic noninvasive precursor lesions and the developing invasive adenocarcinomas. Cell clones overexpressing CAR were generated and tested for their response to apoptotic factors and for the expression of apoptosis relevant proteins by reverse transcription-PCR and Western blot analysis.

RESULTS

In comparison of preneoplastic precursor lesions with established adenocarcinomas, CAR expression was enhanced 2- to 5-fold in all six tissues which had survived and transformed into invasive adenocarcinomas. When stable CAR-overexpressing cell clones of the human cancer cell lines HeLa, CaSki, and A2780 were compared with the parental cell lines, 1.5- to 6-fold more cells survived application of tumor necrosis factor-related apoptosis-inducing ligand or growth factor withdrawal. CAR-enhanced cell survival was accompanied by reduced activation of caspase 3 and enhanced expression of bcl-2 or bcl-XL, depending on the cell type tested. Up-regulation of bcl-2 was found in all CAR-expressing adenocarcinomas of the murine cancer model.

CONCLUSIONS

CAR expression is enhanced after transition from preneoplastic precursor lesions to neoplastic mammary cancer outgrowths. Enhanced CAR expression can promote cancer cell survival. These data suggest differential expression of CAR as a new factor in tumorigenesis.

Potential of equine herpesvirus 1 as a vector for immunization

Key problems using viral vectors for vaccination and gene therapy are antivector immunity, low transduction efficiencies, acute toxicity, and limited capacity to package foreign genetic information. It could be demonstrated that animal and human cells were efficiently transduced with equine herpesvirus 1 (EHV-1) reconstituted from viral DNA maintained and manipulated in Escherichia coli. Between 13 and 23% of primary human CD3+, CD4+, CD8+, CD11b+, and CD19+ cells and more than 70% of CD4+ MT4 cells or various human tumor cell lines (MeWo, Huh7, HeLa, 293T, or H1299) could be transduced with one infectious unit of EHV-1 per cell. After intranasal instillation of EHV-1 into mice, efficient transgene expression in lungs was detectable. Successful immunization using EHV-1 was shown after delivery of the human immunodeficiency virus type 1 Pr55gag precursor by the induction of a Gag-specific CD8+ immune response in mice. Because EHV-1 was not neutralized by human sera containing high titers of antibodies directed against human herpesviruses 1 to 5, it is concluded that this animal herpesvirus has enormous potential as a vaccine vector, because it is able to efficiently transduce a variety of animal and human cells, has high DNA packaging capacity, and can conveniently be maintained and manipulated in prokaryotic cells.

Oncolytic herpes simplex virus mutants are more efficacious than wild-type adenovirus Type 5 for the treatment of high-risk neuroblastomas in preclinical models

BACKGROUND

High-risk neuroblastoma (Nb) is incurable using current treatment regimens in the majority of patients. Oncolytic virotherapy is a novel approach being tested for several types of adult cancers.

OBJECTIVES

To compare the susceptibility of Nb tumor models to oncolytic adenovirus and HSV mutants and delineate the mechanisms of resistance or sensitivity.

METHODS

Human Nb cell lines were used to determine susceptibility to adenovirus type 5 wild-type and HSV1 mutant (NV1066) infection, adenovirus receptor expression, support of NV1066 replication, and induction of apoptosis. Human xenograft tumors in immunodeficient mice were evaluated for histological effects and tumor response to intratumoral injection of an oncolytic HSV mutant.

RESULTS

All eight Nb cell lines tested in culture were relatively resistant to infection with wild type and attenuated adenoviruses. Cells expressed the cocksackie-adenovirus attachment receptor (CAR) but had low or absent expression of the internalization receptors (alphavbeta3, alphavbeta5 integrins). In contrast, all cells were uniformly sensitive to infection with the attenuated HSV mutant, NV1066. Productive virus replication and induction of apoptosis were observed in HSV-infected cells. CHLA-20 and LAN-5 xenograft tumors injected with a single dose of NV1066 showed a significant antitumor response, and the animals had a prolonged survival post infection in comparison to the PBS-treated control group. HSV injected tumors showed extensive areas of necrosis and morphologic evidence of apoptosis.

CONCLUSIONS

Nb tumor models are resistant to adenovirus mediated oncolysis but highly sensitive to HSV mediated oncolysis. Further studies of HSV virotherapy as a novel treatment for Nb are warranted.

The tumor suppressor gene TP53: implications for cancer management and therapy

The p53 protein is an inducible transcription factor with multiple anti-proliferative roles in response to genotoxic damage; unprogrammed proliferative stimuli; and deprivation of oxygen, nutrients, or ribonucleotides. Inactivation of the TP53 gene by mutation or deletion is the most common event in human cancer. Loss of p53 function compromises genetic homeostasis in cells exposed to mutagens and prevents normal cytotoxic responses to cancer therapies. Genetic and pharmacological approaches are being developed with the ultimate goal of restoring or controlling p53 functions in cancer patients. Genetic interventions aiming at expressing wild-type TP53 in cancer cells, either by retroviral or adenoviral transfer, have met limited clinical success. However, recently, the use of a defective adenovirus (ONYX-015) that selectively kills p53-incompetent cells has shown promising effects in pre-clinical and clinical studies. Pharmacological methods are under development to either stimulate wild-type p53 protein function or induce p53 mutant proteins to resume wild-type functions. These methods are based on small chemicals (CP-31388, PRIMA-1), peptides (CDB3), or single-chain Fv antibody fragments corresponding to defined p53 domains. In addition, detection of mutant TP53 may also serve as a marker for early cancer detection, prediction, and prognosis. In this review, we discuss the mechanisms underlying these approaches and their perspectives for cancer therapy.

The coxsackie adenovirus receptor inhibits cancer cell migration

The coxsackie and adenovirus receptor (CAR) is a key factor in adenoviral cancer gene therapy. Reduced expression of CAR during progression of prostate and bladder cancer has been reported. In embryonic development and tissue differentiation, CAR is also differentially expressed. This study suggests a role of CAR expression in cell adhesion and cell motility of human cancer cells. Stable CAR-expressing clones from E-cadherin-deficient A2780 ovarian and CaSki cervical cancer cells with originally low and high CAR expression levels, respectively, were established. CAR reexpression in otherwise singularly growing A2780 parental cells resulted in formation of cell-cell contacts and aggregation in cell clusters. CAR overexpression in cell adhesion-forming CaSki cells did not result in morphological changes. Migration of the A2780 CAR clones was strongly reduced as characterized by using spread-off assays. Using migration chambers, formation of satellite colonies was reduced by 97% in CAR-expressing A2780 cell clones and by 23% in CAR-expressing CaSki cell clones. Parental A2780 and CaSki cells selected for high migratory ability by using migration chambers expressed endogenous CAR on lower levels associated with lower adenoviral transduction efficiency. Our data suggest CAR as a new inhibitory factor for cancer cell migration.

Efficient internalization into low-passage glioma cell lines using adenoviruses other than type 5: an approach for improvement of gene delivery to brain tumours

There is a need for improvement of the commonly used adenovirus vectors based on serotype 5. This study was performed on three adenovirus serotypes with a CAR-binding motif (Ad4p, Ad5p and Ad17p) and three non-CAR-binding serotypes (Ad11p, Ad16p and Ad21p). The capacity of these alternative adenovirus vector candidates to deliver DNA into low-passage glioma cell lines from seven different donors was evaluated. The non-CAR-binding serotype Ad16p was the most efficient serotype with regard to import of its DNA, as well as initiation of hexon protein expression. Ad16p established hexon expression in 60–80 % of the cell population in gliomas from all donors tested. The other non-CAR-binding serotypes, Ad11p and Ad21p, showed hexon expression in 25–60 and 40–80 % of cells, respectively. The corresponding figure for the best CAR-binding serotype, Ad5p, was only 25–65 %, indicating greater variability between cells from different donors than serotype Ad16p had. The other CAR-binding serotypes, Ad4p and Ad17p, were refractory to some of the gliomas, giving a maximum of only 45 and 40 % hexon expression, respectively, in the most permissive cells. Interestingly, the transduction capacity of the CAR-binding serotypes was not correlated to the level of CAR expression on the cells.

Increased adenoviral transduction efficacy in human laryngeal carcinoma cells resistant to cisplatin is associated with increased expression of integrin alphavbeta3 and coxsackie adenovirus receptor

In our study, we investigated molecular mechanisms of increased adenoviral transduction efficacy in cisplatin-resistant human laryngeal carcinoma cells CA3ST as compared to parental cells HEp2. Using reverse transcription-PCR, the genes potentially implicated in adenoviral entry were screened. In cisplatin-resistant cells, only upregulation of alphavbeta3 integrin was detected, which was additionally confirmed by flow cytometry. Moderately increased expression of CAR was determined in cisplatin-resistant CA3ST cells using flow cytometry and measurement of wild-type adenovirus Ad5CMVbetagal attachment. In order to test the implication of alphavbeta3 integrin in transduction efficacy, 6 HEp2-derived alphavbeta3-expressing clones with graded expression of alphavbeta3 were isolated. To a certain degree of density, expression of alphavbeta3 positively correlated with Ad5CMVbetagal transduction efficacy (i.e., increased viral transduction), suggesting a role of alphavbeta3 in transduction efficacy. However, HEp2 clones with the highest alphavbeta3) expression were negatively correlated with transduction efficacy (i.e., decreased viral transduction). This was shown to be associated with downregulation of alphavbeta5 integrin, also involved in viral transduction, in clones with the highest alphavbeta3 expression. The implication of CAR in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells was further assessed by transduction experiments using adenoviral mutant Ad5FbDelta639 whose entry is only to a very small extent dependent on the presence of CAR. Indeed, Ad5FbDelta639 infected 2.5-fold more, in comparison to wild-type adenovirus, which infected 5-fold more efficiently resistant CA3ST cells than parental HEp2 cells, indicating that increased expression of CAR contributes to increased efficacy of adenoviral transduction. Thus, the data presented provide evidence that both alphavbeta3 integrin and CAR are involved in increased adenoviral transduction efficacy in cisplatin resistant CA3ST cells. These findings may have significant implications in human gene therapy using adenoviruses, especially in patients after unsuccessful cisplatin treatment.

Cooperative effect of adenoviral p53 gene therapy and standard chemotherapy in ovarian cancer cells independent of the endogenous p53 status

Clinical adenoviral p53 gene therapy has been shown by us and others to inhibit tumor growth of ovarian cancer with endogenous mutant p53. This study was designed to test the cooperative antitumor effect of standard combination chemotherapy using paclitaxel and carboplatin together with adenoviral p53 gene transfer in the presence of wild-type and mutant p53. Seven ovarian cancer cell lines with mutant p53 and seven ovarian cancer cell lines with wild-type p53 were tested. An E1-deleted adenovirus type 5 expressing p53 (ACNp53) was used for p53 gene transfer. p53 gene transfer at 50% transduction efficiency significantly reduced IC50 of carboplatin chemotherapy up to 49-fold, of paclitaxel chemotherapy up to six-fold, and of paclitaxel/carboplatin chemotherapy up to 19-fold in the wild-type p53 cell line OV-MZ-5. Synergism between ACNp53 and chemotherapy calculated by median-effect analysis was found at low drug concentrations in all cell lines independent of the p53 mutational status. In conclusion, adenoviral p53 gene transfer significantly increased the sensitivity of ovarian tumor cells to paclitaxel, to carboplatin and/or to the combination of both.

Comparative transductions of breast cancer cells by three DNA viruses

Defining the ideal vectors to transduce breast cancer using viruses is currently under intense pre-clinical evaluation. Our study constitutes the first direct comparison of the infection efficiencies of a human serotype 5 (Ad5), a canine serotype 2 (CAV-2) adenovirus, and a human serotype 2 adeno-associated virus (AAV-2) in breast cancer cells. We observed an excellent infection efficiency for Ad5 vector, whereas both CAV-2 and AAV-2 vectors lead to low infection of these cells. Real-time PCR, flow cytometry, and antibody blocking studies suggest that Ad5 and CAV-2 infection ability is not strictly dependent on coxsackie adenovirus receptor (CAR) or alpha(v) integrin levels. In conclusion, our data suggest that human adenoviruses are excellent transducers of breast cancer cells, though it may be difficult to predict the extent of infection solely on CAR or alpha(v) integrin levels.

Why did p53 gene therapy fail in ovarian cancer?

Promising preclinical and clinical data led to the initiation of an international randomised phase II/III trial of p53 gene-therapy trial for first-line treatment of patients with ovarian cancer. In that trial, replication-deficient adenoviral vectors carrying wild-type p53 were given intraperitoneally in combination with standard chemotherapy to patients with ovarian cancers harbouring p53 mutations. The study was closed after the first interim analysis because an adequate therapeutic benefit was not shown. In this review, we discuss the possible reasons for failure of p53 gene therapy, which include the multiple genetic changes in cancer and epigenetic dysregulations leading to aberrant silencing of genes. These complex interactions lead us to conclude that repair of single genes might not be a suitable strategy for the treatment of cancer. Moreover, dominant negative cross talk between ectopic wild-type p53 and recently identified dominant p53 mutants and splice variants of p63 and p73--which are frequently overexpressed in ovarian cancers--could seriously compromise the effectiveness of p53 gene therapy. Other substantial problems in targeting tumour cells with adenoviral vectors are the heterogeneity or lack of expression of coxsackie-adenovirus receptors and integrin co-receptors in ovarian tumours and the presence of adenovirus-neutralising antibodies in ovarian cancer-related ascites.

CAR is a cell-cell adhesion protein in human cancer cells and is expressionally modulated by dexamethasone, TNFalpha, and TGFbeta

The coxsackie adenovirus receptor (CAR) has become of interest for gene therapy due to its crucial function in adenoviral cell entry. In clinical trials with adenoviral vectors, dexamethasone is applied to reduce side effects such as inflammatory reactions or emesis. By using a beta-galactosidase-expressing adenovirus (AdGal), we observed that dexamethasone treatment resulted in decreased adenoviral gene transfer into human cancer cells. Expression of CAR and integrin alpha5beta1 was transcriptionally downregulated by dexamethasone as shown for HeLa cervical cancer cells and U87MG glioblastoma cells. TNFalpha increased CAR expression in HeLa and ovarian cancer cells but decreased CAR expression in U87MG cells. In all tested cancer cell lines, TNFalpha induced a significant increase in the expression of adenovirus-binding integrins alpha5beta1, alphavbeta3 and alphavbeta5. Pretreatment with TNFalpha increased AdGal gene transfer into cancer cells and enhanced the cytotoxic effect of a p53-expressing adenovirus. In contrast, TGFbeta reduced CAR expression level and adenoviral gene transfer into OV-UL-2 ovarian cancer cells. Confocal immunofluorescence analysis revealed localization of CAR at cell-cell adhesions in several human cancer cell lines and disruption of cell-cell contacts increased adenoviral gene transfer into human cancer cells. In clinical cancer gene therapy, efficiency of adenoviral gene delivery could be altered by cell adhesion, TNFalpha, TGFbeta, and dexamethasone.

The therapeutic efficacy of adenoviral vectors for cancer gene therapy is limited by a low level of primary adenovirus receptors on tumour cells

Replication-defective adenoviral vectors are currently being employed as gene delivery vehicles for cancer gene therapy. To address the hypothesis that the therapeutic efficacy of adenoviral vectors is restricted by their inability to infect tumour cells expressing low levels of the primary cellular receptor for adenoviruses, the coxsackievirus and adenovirus receptor (CAR), we have employed a pair of ovarian cancer cell lines differing only in the expression of a primary receptor for Ad5. This novel system thus allowed the direct evaluation of the relationship between the efficacy of an adenoviral vector and the primary receptor levels of the host cancer cell, without the confounding influence of other variable cellular factors. We demonstrate that a deficiency of the primary cellular receptor on the tumour cells restricts the efficacy of adenoviral vectors in two distinct cancer gene therapy approaches, TP53 gene replacement therapy and herpes simplex virus thymidine kinase/ganciclovir suicide gene therapy. Moreover, we show that a deficiency of the primary receptor on the tumour cells limits the efficiency of adenovirus-mediated gene transfer in vivo. Since a number of studies have reported that primary cancer cells express only low levels of CAR, our results suggest that strategies to redirect adenoviruses to achieve CAR-independent infection will be necessary to realize the full potential of adenoviral vectors in the clinical setting.

Determination of molecules regulating gene delivery using adenoviral vectors in ovarian carcinomas

Gene therapeutic approaches currently favor adenoviral vectors over alternatively available vector systems. Ovarian cancer represents an attractive model for an intraperitoneal adenovirus-based gene therapy, which is now under intensive clinical investigation. Adenovirus-mediated gene transfer depends on adequate virus uptake and thus on the presence of sufficient amounts of high-affinity coxsackie-adenovirus receptor (CAR) and alphavbeta3- and alphavbeta5 integrins on target cells. This fact has been ignored in most ongoing clinical trials. This investigation, therefore, determined expression of CAR by immunohistochemistry in 37 ovarian carcinomas and compared it with that of alphavbeta3 and alphavbeta5 integrins. In all samples, except one undifferentiated carcinoma, CAR was immunohistochemically demonstrable. Grade 1 tumors exhibited stronger CAR immunostaining as compared with higher-grade cancers (P < 0.03). Integrins alphavbeta3 and alphavbeta5 were detectable in 62% and 65% of carcinomas, respectively, and staining for both classes correlated positively (P < 0.005). Cancers classified as undifferentiated completely lacked alphavbeta3 expression. Furthermore, in undifferentiated and grade 3 carcinomas the three molecules studied exhibited marked distributional heterogeneity with regard to focal positivity and negativity within the same tumor. Either the absence of CAR, alphavbeta3 and alphavbeta5 or the pronounced heterogeneity in their expression might seriously compromise the efficiency of adenovirus-based gene therapy in ovarian cancer.

The Promise of Integrins as Effective Targets for Anticancer Agents

This review will briefly describe integrin function, address why integrins are attractive targets for chemotherapeutic drug design, and discuss some ongoing studies aimed at inhibiting integrin activity. Integrins are cell surface heterodimeric receptors. They modulate many cellular processes including: growth, death (apoptosis), adhesion, migration, and invasion by activating several signaling pathways. Many potential chemotherapeutic agents target integrins directly (eg, polypeptides, monoclonal antibodies, adenovirus vectors). These agents may be clinically useful in controlling the metastatic spread of cancer.

Ribozyme-mediated telomerase inhibition induces immediate cell loss but not telomere shortening in ovarian cancer cells

Telomerase is a promising target for human cancer gene therapy. Its inhibition allows telomere shortening to occur in cancer cells, which in turn is thought to trigger delayed senescence and/or apoptosis. We tested whether telomerase inhibition might have additional, immediate effects on tumor cell growth. Ovarian cancer cell lines with widely differing telomere lengths were efficiently transduced with an adenovirus expressing a ribozyme directed against the T motif of the catalytic subunit of human telomerase, hTERT. Three days after transduction, telomerase activity was significantly reduced and massive cell loss was induced in mass cultures from all four ovarian cancer cell lines tested, whereas transduction of telomerase-negative human fibroblasts did not attenuate their growth. The kinetics of induction of cell death in cancer cells was not significantly dependent on telomere length, and telomeres did not shorten measurably before the onset of apoptosis. The data suggest the existence of a "fast-track" mechanism by which diminution of telomerase can interfere with cancer cell growth and induce cell death, presumably by apoptosis. This phenomenon might be a consequence of the telomere capping function provided by telomerase in tumor cells. Uncapping of telomeres by ribozyme-mediated inhibition of telomerase bears therapeutic potential for ovarian cancer.