Late viral RNA export, rather than p53 inactivation, determines ONYX-015 tumor selectivity

Significant antitumor activity of oncolytic adenovirus expressing human interferon-beta for hepatocellular carcinoma

BACKGROUND

Human interferon-beta (IFN-beta) has been widely used in gene therapy for its antitumor activity but its therapeutic effect is limited. The conditionally replicative adenovirus ONYX-015 (a E1B-55-kDa-deleted adenovirus) targets well to tumor cells, but is not potent enough to cause significant tumor regression. To solve these problems, a tumor-selective replicating adenovirus expressing IFN-beta was constructed in this study.

METHODS

The oncolytic adenoviruses were generated by homologous recombination in packaging cells. The expression of the IFN-beta protein was detected by enzyme-linked immunosorbent assay (ELISA). The antitumor efficacy of ZD55-IFN-beta was evaluated in cell lines and human hepatocellular carcinoma xenografts in nude mice.

RESULTS

ZD55-IFN-beta can express much more IFN-beta than Ad-IFN-beta because of the replication of the ZD55 vector. Our data showed that ZD55-IFN-beta could exert a strong cytopathic effect on tumor cells (about 100-fold higher than Ad-IFN-beta or ONYX-015). Moreover, no obvious cytotoxic or apoptotic effects were detected in normal cells infected with ZD55-IFN-beta.

CONCLUSIONS

The antitumor efficacy of IFN-beta could be significantly improved due to the increased gene expression level from the tumor-selective replicating vector. The oncolytic adenovirus expressing IFN-beta may provide a novel approach for cancer gene therapy.

A phase I trial of intratumoral administration of recombinant oncolytic adenovirus overexpressing HSP70 in advanced solid tumor patients

Our pre-clinical studies demonstrated that intratumoral vaccination with a recombinant oncolytic type 2 adenovirus overexpressing the heat shock protein (HSP)70 protein, designated as H103, can inhibit primary and metastatic tumors through enhanced oncolytic activity and HSP-mediated immune responses against shared and mutated tumor antigens. In the pre-clinical studies of local H103 administration, no significant toxicity was observed in the animal trials with mice, cavy or rhesus monkeys. A phase I clinical trial of intratumoral injection of H103 was conducted in the patients with advanced solid tumors. A total of 27 patients were injected intratumorally with H103 in a dose-escalation study from a dose of 2.5 x 10(7) to 3.0 x 10(12) viral particles (VPs). The maximum tolerated dose of H103 was not defined. Two patients developed dose-limiting toxicities of grade III fever at the dose of 1.5 x 10(12) VP and transient grade IV thrombocytopenia at the dose of 3.0 x 10(12) VP. The common adverse events were mainly mild to moderate (grade I/II) in nature, including fever, mild injection-site reaction, leucopenia, lymphopenia, thrombocytopenia and hypochromia. The objective response (complete response+partial response) to H103-injected tumors was 11.1% (3/27), and the clinical benefit rate (complete response+partial response+minor response+stable disease) was 48.1%. Interestingly, transient and partial regression of distant, uninjected tumors was observed in three patients. The numbers of immune cells (CD4(+) and CD8(+) T cells, and natural killer cells) were elevated after H103 administration, but without statistical significance. This phase I trial demonstrates that intratumoral administration of H103 can be safely applied to cancer patients and shows promising clinical antitumor activity, warranting a further clinical investigation.

Comparison of molecular strategies for breast cancer virotherapy using oncolytic adenovirus

Oncolytic viruses are regulated by the tumor phenotype to replicate and lyse cancer cells selectively. To identify optimal strategies for breast cancer we compared five adenoviruses with distinct regulatory mechanisms: Ad-dl922-947 (targets G1-S checkpoint); Ad-Onyx-015 and Ad-Onyx-017 (target p53/mRNA export); Ad-vKH1 (targets Wnt pathway), and AdEHE2F (targets estrogen receptor/G1-S checkpoint/hypoxic signaling). The quantity of virus required to kill 50% of breast cancer cells after 6 days (EC(50), plaque-forming units per cell) was measured. The most potent virus was Ad-dl922-947 (EC(50), 0.01-5.4 in SkBr3, MDA-231, MDA-468, MCF7, and ZR75.1 cells), followed by wild-type (Ad-WT; EC(50), 0.3-5.5) and AdEHE2F (EC(50), 1.4-3.9). Ad-vKH1 (EC(50), 7.2-72.1), Ad-Onyx-017 (EC(50), 8.4-167), and Ad-Onyx-015 (EC(50), 17.7-377) showed less activity. Most viruses showed limited cytotoxicity in normal human cells, including breast epithelium MCF10A (EC(50), >722) and fibroblasts (EC(50), >192) and only moderate cytotoxicity in normal microvascular endothelial cells (HMVECs; EC(50), 42.8-149), except Ad-dl922-947, which was active in HMVECs (EC(50), 1.6). After injection into MDA-231 xenografts, Ad-WT, AdEHE2F, and Ad-dl922-947 showed replication, assessed by hexon staining and quantitative polymerase chain reaction measurement of viral DNA, and significantly inhibited tumor growth, leading to extended survival. After intravenous injection Ad-dl922-947 showed DNA replication (233% of the injected dose was measured in liver after 3 days) whereas AdEHE2F did not. Overall, AdEHE2F showed the best combination of low toxicity in normal cells and high activity in breast cancer in vitro and in vivo, suggesting that molecular targeting using estrogen response elements, hypoxia response elements, and a dysregulated G1-S checkpoint is a promising strategy for virotherapy of breast cancer.

Generation of a conditionally replicating adenovirus based on targeted destruction of E1A mRNA by a cell type-specific MicroRNA

MicroRNAs have emerged as important players in tissue-specific mammalian gene regulation and have also been exploited in experimental targeting of gene expression. We have constructed a recombinant adenovirus that contains sequences complementary to the liver-specific microRNA 122 (miR122) in the 3' untranslated region of the E1A gene. In Huh7 cells, which resemble normal hepatocytes in expressing high levels of miR122, this feature resulted in strongly reduced levels of E1A mRNA and protein. This property allowed us to generate a novel recombinant adenovirus that was severely attenuated in cells of hepatic origin but replicated normally in other cells. This strategy may be useful in circumventing liver toxicity associated with the systemic delivery of oncolytic adenoviruses. These data provide the first example of exploiting differential microRNA expression patterns to alter the natural tropism of a DNA virus. In addition, these results suggest that other microRNAs expressed in a tissue- or transformation-specific manner may also be used for the targeting of adenoviral replication and that the same principle may be applied to other viruses that have shown promise as oncolytic or gene delivery platforms.

Development of targeted oncolytic virotherapeutics through translational research

BACKGROUND

Oncolytic virotherapeutics is a promising platform for cancer treatment but the product class has yet been successful. The key to success is integration of bidirectional translational research to rapidly address issues encountered in the laboratory and the clinics.

OBJECTIVE

We highlight the hurdles identified for the targeted oncolytic virotherapy approach, specifically those identified in clinical trials with wild-type viruses and first-generation targeted agents. We also analyze the translational research and development that has been applied to overcome these hurdles, including virus engineering and design improvements for next-generation virotherapeutics.

RESULTS/CONCLUSION

The iterative loop between the clinic and the lab can function as a major driving force to optimize products from this platform.

Enhanced combined tumor-specific oncolysis and suicide gene therapy for prostate cancer using M6 promoter

Enzyme pro-drug suicide gene therapy has been hindered by inefficient viral delivery and gene transduction. To further explore the potential of this approach, we have developed AdIU1, a prostate-restricted replicative adenovirus (PRRA) armed with the herpes simplex virus thymidine kinase (HSV-TK). In our previous Ad-OC-TK/ACV phase I clinical trial, we demonstrated safety and proof of principle with a tissue-specific promoter-based TK/pro-drug therapy using a replication-defective adenovirus for the treatment of prostate cancer metastases. In this study, we aimed to inhibit the growth of androgen-independent (AI), PSA/PSMA-positive prostate cancer cells by AdIU1. In vitro the viability of an AI- PSA/PSMA-expressing prostate cancer cell line, CWR22rv, was significantly inhibited by treatment with AdIU1 plus GCV (10 microg ml(-1)), compared with AdIU1 treatment alone and also cytotoxicity was observed following treatment with AdIU1 plus GCV only in PSA/PSMA-positive CWR22rv and C4-2 cells, but not in the PSA/PSMA-negative cell line, DU-145. In vivo assessment of AdIU1 plus GCV treatment revealed a stronger therapeutic effect against CWR22rv tumors in nude mice than treatment with AdIU1 alone, AdE4PSESE1a alone or in combination with GCV. Our results demonstrate the therapeutic potential of specific-oncolysis and suicide gene therapy for AI-PSA/PSMA-positive prostate cancer gene therapy.

Oncolytic Viruses: A New Weapon to Fight Cancer

Remission from cancer after viral infection was first noted in the beginning of the 20th century, and with advances in virotherapy and genetic engineering, the advent of an approved viral therapeutic in North America is fast approaching. Mechanisms of tumour selectivity and killing, along with information obtained from clinical trials are reviewed here. Although oncolytic viruses are generally safe and well tolerated, their overall anti-tumour efficacy has varied. This article outlines strategies to improve the efficacy of the oncolytic platform without compromising its impressive safety profile. It will highlight new methods being developed to quantify the activity of oncolytic viruses in real time. Harnessing the factors that control the tumour microenvironment and the immune system are the key to enhancing the oncolytic activity. The purpose of this article is to introduce and provide an overview of the current state of cancer killing of oncolytic viruses. The reader will acquire knowledge of the basic principles of oncolytic viruses and their use in the clinical setting. This review summarizes articles retrieved from Medline using key words such as "virus," "oncolytic virus," "virotherapy," "cancer," and "clinical trials." Review articles published in the English language from 2005 onward were read and corroborating data and conclusions were summarized. When appropriate, cited references were also reviewed and incorporated. The reader is directed to references we found most concise.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

An early function of the adenoviral E1B 55 kDa protein is required for the nuclear relocalization of the cellular p53 protein in adenovirus-infected normal human cells

It is well established that the human subgroup C adenovirus type 5 (Ad5) E1B 55 kDa protein can regulate the activity and concentration of the cellular tumor suppressor, p53. However, the contribution(s) of these functions of the E1B protein to viral reproduction remains unclear. To investigate this issue, we examined properties of p53 in normal human cells infected by E1B mutant viruses that display defective entry into the late phase or viral late mRNA export. The steady-state concentrations of p53 were significantly higher in cells infected by the E1B 55 kDa null mutant Hr6 or three mutants carrying small insertions in the E1B 55 kDa protein coding sequence than in Ad5-infected cells. Nevertheless, none of the mutants induced apoptosis in infected cells. Rather, the localization of p53 to E1B containing nuclear sites observed during infection by Ad5 was prevented by mutations that impair interaction of the E1B protein with p53 and/or with the E4 Orf6 protein. These results indicate that the E1B protein fulfills an early function that correlates efficient entry into the late phase with the localization of E1B and p53 in the nucleus of Ad5-infected normal human cells.

Synergistic antitumor activity of XIAP-shRNA and TRAIL expressed by oncolytic adenoviruses in experimental HCC

RNA interference (RNAi) induced by small interfering RNA (siRNA) can trigger sequence-specific gene silencing in mammalian cells. It has been proposed that siRNA can be developed as a novel strategy for cancer therapy. However effective delivery of therapeutically active siRNAs into the target tissue/cells in vivo is still a major obstacle for successful application. Oncolytic adenoviral vector mediated RNAi provides the potential advantages of minimizing the harm of normal cells, regenerating siRNAs within the tumor microenvironment and inspiring an additive antitumor outcome through viral oncolysis. Hepatocellular carcinoma (HCC) displays a high resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated cell death, partially due to high expression levels of the X-linked Inhibitor-of-Apoptosis protein (XIAP). Here, we utilized an oncolytic adenovirus (ZD55) for expressing short hairpin RNA (shRNA), a precursor of siRNA, to knockdown XIAP. To increase sensitivity of HCC cells to TRAIL, we have used ZD55 to deliver both XIAP-shRNA and TRAIL into HCC cells. The results showed that the combination of ZD55-XIAP-shRNA and ZD55-TRAIL resulted in significant reduction of XIAP expression and potent antitumor activity both in HCC cells and in animal model with tumor. This pilot study offers a promise of using oncolytic adenovirus to deliver siRNA targeting overexpressed oncogenes and a novel strategy for cancer therapy by regulating the equilibrium between the proapoptotic and antiapoptotic factors.

Reprogrammed viruses as cancer therapeutics: targeted, armed and shielded

Virotherapy is currently undergoing a renaissance, based on our improved understanding of virus biology and genetics and our better knowledge of many different types of cancer. Viruses can be reprogrammed into oncolytic vectors by combining three types of modification: targeting, arming and shielding. Targeting introduces multiple layers of cancer specificity and improves safety and efficacy; arming occurs through the expression of prodrug convertases and cytokines; and coating with polymers and the sequential usage of different envelopes or capsids provides shielding from the host immune response. Virus-based therapeutics are beginning to find their place in cancer clinical practice, in combination with chemotherapy and radiation.

Control of mRNA export by adenovirus E4orf6 and E1B55K proteins during productive infection requires E4orf6 ubiquitin ligase activity

During the adenovirus infectious cycle, the early proteins E4orf6 and E1B55K are known to perform several functions. These include nuclear export of late viral mRNAs, a block of nuclear export of the bulk of cellular mRNAs, and the ubiquitin-mediated degradation of selected proteins, including p53 and Mre11. Degradation of these proteins occurs via a cellular E3 ubiquitin ligase complex that is assembled through interactions between elongins B and C and BC boxes present in E4orf6 to form a cullin 5-based ligase complex. E1B55K, which has been known for some time to associate with the E4orf6 protein, is thought to bind to specific substrate proteins to bring them to the complex for ubiquitination. Earlier studies with E4orf6 mutants indicated that the interaction between the E4orf6 and E1B55K proteins is optimal only when E4orf6 is able to form the ligase complex. These and other observations suggested that most if not all of the functions ascribed to E4orf6 and E1B55K during infection, including the control of mRNA export, are achieved through the degradation of specific substrates by the E4orf6 ubiquitin ligase activity. We have tested this hypothesis through the generation of a virus mutant in which the E4orf6 product is unable to form a ligase complex and indeed have found that this mutant behaves identically to an E4orf6(-) virus in production of late viral proteins, growth, and export of the late viral L5 mRNA.

Oncolytic virotherapy: molecular targets in tumor-selective replication and carrier cell-mediated delivery of oncolytic viruses

Tremendous advances have been made in developing oncolytic viruses (OVs) in the last few years. By taking advantage of current knowledge in cancer biology and virology, specific OVs have been genetically engineered to target specific molecules or signal transduction pathways in cancer cells in order to achieve efficient and selective replication. The viral infection and amplification eventually induce cancer cells into cell death pathways and elicit host antitumor immune responses to further help eliminate cancer cells. Specifically targeted molecules or signaling pathways (such as RB/E2F/p16, p53, IFN, PKR, EGFR, Ras, Wnt, anti-apoptosis or hypoxia) in cancer cells or tumor microenvironment have been studied and dissected with a variety of OVs such as adenovirus, herpes simplex virus, poxvirus, vesicular stomatitis virus, measles virus, Newcastle disease virus, influenza virus and reovirus, setting the molecular basis for further improvements in the near future. Another exciting new area of research has been the harnessing of naturally tumor-homing cells as carrier cells (or cellular vehicles) to deliver OVs to tumors. The trafficking of these tumor-homing cells (stem cells, immune cells and cancer cells), which support proliferation of the viruses, is mediated by specific chemokines and cell adhesion molecules and we are just beginning to understand the roles of these molecules. Finally, we will highlight some avenues deserving further study in order to achieve the ultimate goals of utilizing various OVs for effective cancer treatment.

Oncolytic viruses: do they have a role in anti-cancer therapy?

Oncolytic viruses are replication competent, tumor selective and lyse cancer cells. Their potential for anti-cancer therapy is based upon the concept that selective intratumoral replication will produce a potent anti-tumor effect and possibly bystander or remote cell killing, whilst minimizing normal tissue toxicity. Viruses may be naturally oncolytic or be engineered for oncolytic activity, and possess a host of different mechanisms to provide tumor selectivity. Clinical use of live replicating viruses is associated with a unique set of safety issues. Clinical experience has so far provided evidence of limited efficacy and a favourable toxicity profile. The interaction with the host immune system is complex. An anti-viral immune response may limit efficacy by rapidly clearing the virus. However, virally-induced cell lysis releases tumor associated antigens in a 'dangerous' context, and limited evidence suggests that this can lead to the generation of a specific anti-tumor immune response. Combination therapy with chemotherapy or radiotherapy represents a promising avenue for ongoing translation of oncolytic viruses into clinical practice. Obstacles to therapy include highly effective non-specific host mechanisms to clear virus following systemic delivery, immune-mediated clearance, and intratumoral barriers limiting virus spread. A number of novel strategies are now under investigation to overcome these barriers. This review provides an overview of the potential role of oncolytic viruses, highlighting recent progress towards developing effective therapy and asks if they are a realistic therapeutic option at this stage.

Oncolytic adenovirus-mediated shRNA against Apollon inhibits tumor cell growth and enhances antitumor effect of 5-fluorouracil

Apollon, a membrane-associated inhibitor of apoptosis protein, protects cells against apoptosis and is upregulated in certain tumor cells. In this study, the effects of Apollon protein knockdown by RNA interference on the growth of human HeLa, HT-1080 and MCF-7 cells in vitro and in vivo were investigated. An oncolytic adenovirus (ZD55) containing the RNA polymerase III-dependent U6 promoter to express short hairpin RNA (shRNA) directed against Apollon (ZD55-siApollon) was constructed. Our data show that ZD55-siApollon successfully exerts a gene knockdown effect and causes the inhibition of tumor cell growth both in culture and in athymic mice in vivo. Cell cycle analysis, 4',6-diamidino-2-phenylindole staining and western blot analysis reveal that ZD55-siApollon-mediated suppression of Apollon induces apoptosis. Intratumoral injection of ZD55-siApollon significantly inhibits tumor growth in HT-1080 xenograft mice. Furthermore, ZD55-siApollon enhances the antitumor effect of 5-fluorouracil, a chemotherapeutic agent. In conclusion, these results suggest that the depletion of Apollon by oncolytic adenovirus-shRNA delivery system provides a promising method for cancer therapy.

Adenovirus E1B55K region is required to enhance cyclin E expression for efficient viral DNA replication

Adenoviruses (Ads) with E1B55K mutations can selectively replicate in and destroy cancer cells. However, the mechanism of Ad-selective replication in tumor cells is not well characterized. We have shown previously that expression of several cell cycle-regulating genes is markedly affected by the Ad E1b gene in WI-38 human lung fibroblast cells (X. Rao, et al., Virology 350:418-428, 2006). In the current study, we show that the Ad E1B55K region is required to enhance cyclin E expression and that the failure to induce cyclin E overexpression due to E1B55K mutations prevents viral DNA from undergoing efficient replication in WI-38 cells, especially when the cells are arrested in the G(0) phase of the cell cycle by serum starvation. In contrast, cyclin E induction is less dependent on the function encoded in the E1B55K region in A549 and other cancer cells that are permissive for replication of E1B55K-mutated viruses, whether the cells are in the S phase or G(0) phase. The small interfering RNA that specifically inhibits cyclin E expression partially decreased viral replication. Our study provides evidence suggesting that E1B55K may be involved in cell cycle regulation that is important for efficient viral DNA replication and that cyclin E overexpression in cancer cells may be associated with the oncolytic replication of E1B55K-mutated viruses.

Cellular genetic tools to control oncolytic adenoviruses for virotherapy of cancer

Key challenges facing cancer therapy are the development of tumor-specific drugs and the implementation of potent multimodal treatment regimens. Oncolytic adenoviruses, featuring cancer-selective viral cell lysis and spread, constitute a particularly interesting drug platform towards both goals. First, as complex biological agents, adenoviruses allow for rational drug development by genetic incorporation of targeting mechanisms that exert their function at different stages of the viral replication cycle. Secondly, therapeutic genes implementing diverse cancer cell-killing activities can be inserted into the oncolytic adenovirus genome without loss of replication potential, thus deriving a "one-agent combination therapy". This article reviews an intriguing approach to derive oncolytic adenoviruses, which is to insert cellular genetic regulatory elements into adenovirus genomes for control of virus replication and therapeutic gene expression. This approach has been thoroughly investigated and optimized during the last decade for transcriptional targeting of adenovirus replication and gene expression to a wide panel of tumor types. More recently, further cellular regulatory mechanisms, such as mRNA stability and translation regulation, have been reported as tools for virus control. Consequently, oncolytic adenoviruses with a remarkable specificity profile for prostate cancer, gastrointestinal cancers, liver cancer, breast cancer, lung cancer, melanoma, and other cancers were derived. Such specificity profiles allow for the engineering of new generations of oncolytic adenoviruses with improved potency by enhancing viral cell binding and entry or by expressing therapeutic genes. Clearly, genetic engineering of viruses has great potential for the development of innovative antitumor drugs--towards targeted and multimodal cancer therapy.

E1A-expressing adenoviral E3B mutants act synergistically with chemotherapeutics in immunocompetent tumor models

The majority of clinical trials evaluating replication-selective oncolytic adenoviruses utilized mutants with immunomodulatory E3B genes deleted, likely contributing to the attenuated efficacy. We investigated whether an intact immune response could contribute to the observed improved efficacy in response to combinations with chemotherapeutics. Seven carcinoma cell lines were evaluated by combining viral mutants; dl309 (DeltaE3B), dl704 (DeltaE3gp19K), dl312 (DeltaE1A) or wild-type Ad5 with the commonly used clinical drugs cisplatin and paclitaxel. Synergistic effects on cell death were determined by generation of combination indexes in cultured cells. In vivo tumor growth inhibition was achieved by virotherapy alone and was most efficacious with wild-type virus and least with the DeltaE3B mutant. Significantly higher efficacy was observed when the viruses were combined with drugs. The greatest enhancement of tumor inhibition was in combination with the DeltaE3B mutant restoring potency to that of Ad5 wild-type levels, observed only in animals with intact immune response. Increases in infectivity, viral gene expression and replication were identified as potential mechanisms contributing to the synergistic effects. Our results suggest that the attenuation of DeltaE3B mutants can be overcome by low doses of chemotherapeutics only in the presence of an intact immune response indicating a role for T-cell-mediated functions.

Myxoma virus and oncolytic virotherapy: a new biologic weapon in the war against cancer

Oncolytic virotherapy is an innovative alternative to more conventional cancer therapies. The ability of some viruses to specifically target and kill malignant cancerous cells while leaving normal tissue unscathed has opened a large repertoire of new and selective cancer killing therapeutic candidates. Poxviruses, such as vaccinia virus, have a long history of use in humans as live vaccines and have more recently been studied as potential platforms for delivery of immunotherapeutics and attenuated variants of vaccinia have been explored as oncolytic candidates. In contrast, the poxvirus myxoma virus is a novel oncolytic candidate that has no history of use in humans directly, as it has a distinct and absolute host species tropism to lagomorphs (rabbits). Myxoma virus has been recently shown to be able to also selectively infect and kill human tumor cells, a unique tropism that is linked to dysregulated intracellular signalling pathways found in the majority of human cancers. This review outlines the existing knowledge on the tropism of myxoma virus for human cancer cells, as well as preclinical data exhibiting its ability to infect and clear tumors in animal models of cancer. This is an exciting new therapeutic option for treating cancer, and myxoma virus joins a growing group of oncolytic virus candidates that are being developed as a new class of cancer therapies in man.

A phase I trial of intravenous infusion of ONYX-015 and enbrel in solid tumor patients

ONYX-015 is an attenuated chimeric human group C adenovirus, which preferentially replicates in and lyses tumor cells that are p53 negative. The purpose of this phase I, dose-escalation study was to determine the safety and feasibility of intravenous infusion with ONYX-015 in combination with enbrel in patients with advanced carcinoma. Enbrel is a recombinant dimer of human tumor-necrosis factor (TNF)-alpha receptor, previously shown to reduce the level of functional TNF. Nine patients, three in each cohort received multiple cycles of ONYX-015 infusion (1 x 10(10), 1 x 10(11) and 1 x 10(12) vp weekly for 4 weeks/cycle) in addition to subcutaneous enbrel (only during cycle 1) injections per FDA-indicated dosing. Of the nine patients, four had stable disease. No significant adverse events were attributed to the experimental regimen, confirming that enbrel can be safely administered along with oncolytic virotherapy. Two of the three patients in cohort 3 had detectable viral DNA at days 3 and 8 post-ONYX-015 infusion. Their detectable circulating viral DNA was markedly higher during cycle 1 (with enbrel coadministration) as compared with cycle 2 (without enbrel) at the same time points. Area under the curve determinations indicate a marked higher level of TNF-alpha induction and accelerated clearance at cycle 2 in the absence of enbrel. Further assessment is recommended.

Critical role for arginine methylation in adenovirus-infected cells

During the late stages of adenovirus infection, the 100K protein (100K) inhibits the translation of cellular messages in the cytoplasm and regulates hexon trimerization and assembly in the nucleus. However, it is not known how it switches between these two functions. Here we show that 100K is methylated on arginine residues at its C terminus during infection and that this region is necessary for binding PRMT1 methylase. Methylated 100K is exclusively nuclear. Mutation of the third RGG motif (amino acids 741 to 743) prevents localization to the nucleus during infection, suggesting that methylation of that sequence is important for 100K shuttling. Treatment of infected cells with methylation inhibitors inhibits expression of late structural proteins. These data suggest that arginine methylation of 100K is necessary for its localization to the nucleus and is a critical cellular function necessary for productive adenovirus infection.

Lysis of Dysplastic but not Normal Oral Keratinocytes and Tissue-Engineered Epithelia with Conditionally Replicating Adenoviruses

There is no effective medical treatment for oral precancer, and surgery to remove these lesions is imprecise because abnormal mucosa extends beyond the visible lesion. Development of vectors for tumor-selective viral replication has been a significant advance, and viral lysis is well suited to destruction of oral precancerous mucosa. To facilitate evaluation of new treatments, we engineered dysplastic oral epithelium using keratinocytes isolated from dysplastic lesions. We show that these model systems recapitulate the key characteristics of the clinical lesions closely, and that topical delivery of the conditionally replicating adenovirus (CRAd) dl922-947 can lyse tissue-engineered epithelia that show mild, moderate, or severe dysplasia, but normal oral epithelia are very resistant to this treatment. The lytic effect is determined by various factors, including the grade and proliferation index of the dysplastic epithelia. The presence of suprabasal cycling cells, expression of the coxsackie adenovirus receptor (CAR), the transcription cofactor p300, and other aberrations that affect the regulation of the cell cycle or apoptosis and promote viral replication may also be important. The ability of dl922-947 to destroy engineered oral dysplasia was significantly greater than that observed using wild-type adenovirus, d/1520, or viruses modified to bypass cell entry dependent on the presence of CAR. Evidence of infection in clinical dysplastic lesions was also shown ex vivo using tissue explants. We conclude that dl922-947 may provide an efficient molecular cytotoxic to dissolve oral dysplastic lesions.

Elucidation of the molecular mechanism underlying tumor-selective replication of the oncolytic adenovirus mutant ONYX-015

Tumor-selective replicating viruses offer appealing advantages over conventional cancer therapy. ONYX-015 (dl1520) is the prototype for oncolytic adenoviral therapy. It has undergone extensive clinical testing with proven safety and evidence of promising clinical efficacy. The strategy underlying its tumor-selective cell killing is based on deletion of the viral E1B-55K gene, which is crucial for efficient viral replication in normal cells but dispensable in tumor cells. Originally, the successful replication of ONYX-015 was thought to strictly depend on deregulated p53 signaling in tumor cells. However, recent preclinical as well as clinical evidence questions this mechanism. The study by O'Shea and colleagues is of immense importance as it sheds new light into the molecular mechanism underlying the tumor-selective replication of ONYX-015. Based on these findings, modulation of the proposed molecular mechanism by pharmacologic agents or hyperthermia may largely enhance the therapeutic index of ONYX-015 for tumor cells versus normal tissue and improve clinical efficacy. Finally, new strategies to allow successful patient stratification for future clinical trials appear to be in reach, based on the reported results.

Ras transformation mediates reovirus oncolysis by enhancing virus uncoating, particle infectivity, and apoptosis-dependent release

Reovirus, a potential cancer therapy, replicates more efficiently in Ras-transformed cells than in non-transformed cells. It was presumed that increased translation was the mechanistic basis of reovirus oncolysis. Analyses of each step of the reovirus life cycle now show that cellular processes deregulated by Ras transformation promote not one but three viral replication steps. First, in Ras-transformed cells, proteolytic disassembly (uncoating) of the incoming virions, required for onset of infection, occurs more efficiently. Consequently, threefold more Ras-transformed cells become productively infected with reovirus than non-transformed cells, which accounts for the observed increase of reovirus proteins in Ras-transformed cells. Second, Ras transformation increases the infectious-to-noninfectious virus particle ratio, as virions purified from Ras-transformed cells are fourfold more infectious than those purified from non-transformed cells. Progeny assembled in non- and Ras-transformed cells appear similar by electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, suggesting that Ras transformation introduces a subtle change necessary for virus infectivity. Finally, reovirus release, mediated by caspase-induced apoptosis, is ninefold more efficient in Ras-transformed cells. The combined effects of enhanced virus uncoating, infectivity, and release result in >100-fold differences in virus titers within one round of replication. Our analysis reveals previously unrecognized mechanisms by which Ras transformation mediates selective viral oncolysis.

Advances in preclinical investigation of prostate cancer gene therapy

Treating recurrent prostate cancer poses a great challenge to clinicians. Research efforts in the last decade have shown that adenoviral vector-based gene therapy is a promising approach that could expand the arsenal against prostate cancer. This maturing field is at the stage of being able to translate many preclinical discoveries into clinical practices. At this juncture, it is important to highlight the promising strategies including prostate-targeted gene expression, the use of oncolytic vectors, therapy coupled to reporter gene imaging, and combined treatment modalities. In fact, the early stages of clinical investigation employing combined, multimodal gene therapy focused on loco-regional tumor eradication and showed promising results. Clinicians and scientists should seize the momentum of progress to push forward to improve the therapeutic outcome for the patients.

Recent developments in the use of adenoviruses and immunotoxins in cancer gene therapy

Despite setbacks in the past and apparent hurdles ahead, gene therapy is advancing toward reality. The past several years have witnessed this new field of biomedicine developing rapidly both in breadth and depth, especially for the treatment of cancer, thanks largely to the better understanding of molecular and genetic basis of oncogenesis and the development of new and improved vectors and technologies for gene delivery and targeting. This article is intended to provide a brief review of recent advances in cancer gene therapy using adenoviruses, both as vectors and as oncolytic agents, and some of the recent progress in the development of immunotoxins for use in cancer gene therapy.

Intranuclear targeting and nuclear export of the adenovirus E1B-55K protein are regulated by SUMO1 conjugation

We have investigated the requirements for CRM1-mediated nuclear export and SUMO1 conjugation of the adenovirus E1B-55K protein during productive infection. Our data show that CRM1 is the major export receptor for E1B-55K in infected cells. Functional inactivation of the E1B-55K CRM1-dependent nuclear export signal (NES) or leptomycin B treatment causes an almost complete redistribution of the viral protein from the cytoplasm to the nucleus and its accumulation at the periphery of the viral replication centers. Interestingly, however, this nuclear restriction imposed on the wild type and the NES mutant protein is fully compensated by concurrent inactivation of the adjacent SUMO1 conjugation site. Moreover, the same mutation fully reverses defects of the NES mutant in the nucleocytoplasmic transport of Mre11 and proteasomal degradation of p53. These results show that nuclear export of E1B-55K in infected cells occurs via CRM1-dependent and -independent pathways and suggest that SUMO1 conjugation and deconjugation provide a molecular switch that commits E1B-55K to a CRM1-independent export pathway.

Novel therapies targeting signaling pathways in lung cancer

Despite advances in chemotherapy, the prognosis for advanced non-small-cell lung cancer (NSCLC) remains dismal. Increasing understanding of the biological processes responsible for lung carcinogenesis has led to development of new therapeutic strategies targeting this disease at a molecular level. This article examines the molecular events believed to lead to cellular changes in lung cancer, and how knowledge of these is used to develop new agents used individually or in combination with available cytotoxic drugs to improve survival. Finally, it explores how a deeper understanding of the embryonic signaling pathways responsible for airway epithelial repair and tumorogenesis, such as Hedgehog (Hh), Notch, and Wingless (Wnt), can lead to the development of newer and more specific therapies for lung cancer.

p53 gene in treatment of hepatic carcinoma: status quo

Hepatocellular carcinoma (HCC) is one of the 10 most common cancers worldwide. There is no ideal treatment for HCC yet and many researchers are trying to improve the effects of treatment by changing therapeutic strategies. As the majority of human cancers seem to exhibit either abnormal p53 gene or disrupted p53 gene activation pathways, intervention to restore wild-type p53 (wt-p53) activities is an attractive anti-cancer therapy including HCC. Abnormalities of p53 are also considered a predisposition factor for hepatocarcinogenesis. p53 is frequently mutated in HCC. Most HCCs have defects in the p53-mediated apoptotic pathway although they carry wt-p53. High expression of p53 in vivo may exert therapeutic effects on HCC in two aspects: (1) High expression of exogenous p53 protein induces apoptosis of tumor cells by inhibiting proliferation of cells through several biologic pathways and (2) Exogenous p53 renders HCC more sensitive to some chemotherapeutic agents. Several approaches have been designed for the treatment of HCC via the p53 pathway by restoring the tumor suppression function from inactivation, rescuing the mutated p53 gene from instability, or delivering therapeutic exogenous p53. Products with p53 status as the target have been studied extensively in vitro and in vivo. This review elaborates some therapeutic mechanisms and advances in using recombinant human adenovirus p53 and oncolytic virus products for the treatment of HCC.

A conditionally replicative, Wnt/beta-catenin pathway-based adenovirus therapy for anaplastic thyroid cancer

Thyroid cancer affects between 10,000 and 15,000 people per year in the US. Typically, this disease can be controlled with surgical resection and radioiodide treatment. However, resistance to these conventional therapies is observed in some patients, who develop intractable anaplastic thyroid cancer (ATC), for which no effective therapies exist. Recently, a sizable fraction of undifferentiated or poorly differentiated thyroid cancers were shown to contain mutations in beta-catenin, an oncogenic protein involved in the etiology of cancers of many tissues. We developed a conditionally replicative adenovirus (named 'HILMI') which, by virtue of TCF response elements drives E1A and E1B expression, replicates specifically in cells with an active Wnt/beta-catenin pathway. We show that several thyroid cancer cell lines, derived from undifferentiated or anaplastic tissues and possessing an active Wnt/beta-catenin pathway, are susceptible to cell killing by HILMI. Furthermore, viral replication in ATC cells as xenograft tumors in nude mice was observed, and prolonged survival of mice with ATC tumors was observed following administration of the HILMI therapeutic vector. The results warrant further development of this therapeutic approach for ATC patients.

Recent clinical progress in virus-based therapies for cancer

As our knowledge of the molecular basis of cancer expands, viral vectors have been increasingly studied as potential antitumour therapeutic agents. With their ability to invade and replicate within target cells, viruses have been utilised as oncolytic agents to directly lyse tumour cells. Viruses can also deliver their genetic payload into infected cells, allowing for the repair of defective tumour suppressor genes, disruption of oncogenic pathways, and production of cytokines that activate the immune system. Finally, viruses encoding tumour-associated antigens can infect dendritic cells, triggering the development of a tumour-specific immune response. The ability to engineer viruses with high levels of tumour specificity and efficient rates of infection has enhanced the safety profile of these agents, allowing for the development of viable therapeutic options that have been examined in the clinic, either alone or in conjunction with more conventional therapies. This review highlights the principles underlying virus-based therapies for cancer, with an emphasis on recent developments from the clinic.

Gene therapy of liver cancer

The application of gene transfer technologies to the treatment of cancer has led to the development of new experimental approaches like gene directed enzyme/pro-drug therapy (GDEPT), inhibition of oncogenes and restoration of tumor-suppressor genes. In addition, gene therapy has a big impact on other fields like cancer immunotherapy, anti-angiogenic therapy and virotherapy. These strategies are being evaluated for the treatment of primary and metastatic liver cancer and some of them have reached clinical phases. We present a review on the basis and the actual status of gene therapy approaches applied to liver cancer.

Selective replication of E1B55K-deleted adenoviruses depends on enhanced E1A expression in cancer cells

E1B55K-deleted dl1520 could selectively replicate in cancer cells and has been used in clinical trials as an antitumor agent. The mechanism of virus selective replication in cancer cells, including a possible role of p53, is unclear. Studies with established cancer cell lines have demonstrated that some cancer cells are resistant to dl1520 replication, regardless of the p53 status. Hep3B cells supported the E1b-deleted adenoviruses to replicate, whereas Saos2 cells were resistant to viral replication. We applied p53-null Hep3B and Saos2 cells as models to clarify the replication ability of E1B55K-deleted adenoviruses with different expression levels of E1a. We show that lower E1A expression in Saos2 may be the reason for the poor replication in some cancer cells due to the fact that E1a promoter was less activated in Saos2 than in Hep3B. We also demonstrate that the E1B55K protein can increase E1A expression in Saos2 cells for efficient virus replication. In addition, the upstream regions of the E1a promoter have transcriptional activity in Hep3B cells but not in Saos2 cells. The viral E1B55K protein may activate cancer cellular factor(s) that targets the upstream regions of the E1a gene to increase its expression. This is the first study demonstrating that E1B55K protein affects the E1A production levels that is related to cancer selective replication. Our studies have suggested that increase of E1A expression from E1b-deleted adenoviruses may enhance killing cancer cells that otherwise are resistant to viral replication.

p53-induced apoptosis occurs in the absence of p14(ARF) in malignant pleural mesothelioma

Malignant pleural mesotheliomas (MPMs) are usually wild type for the p53 gene but contain homozygous deletions in the INK4A locus that encodes p14(ARF), an inhibitor of p53-MDM2 interaction. Previous findings suggest that lack of p14(ARF) expression and the presence of SV40 large T antigen (L-Tag) result in p53 inactivation in MPM. We did not detect SV40 L-Tag mRNA in either MPM cell lines or primary cultures, and treatment of p14(ARF)-deficient cells with cisplatin (CDDP) increased both total and phosphorylated p53 and enhanced p53 DNA-binding activity. On incubation with CDDP, levels of positively regulated p53 transcriptional targets p21(WAF), PIG3, MDM2, Bax, and PUMA increased in p14(ARF)-deficient cells, whereas negatively regulated survivin decreased. Significantly, p53-induced apoptosis was activated by CDDP in p14(ARF)-deficient cells, and treatment with p53-specific siRNA rendered them more CDDP-resistant. p53 was also activated by: 1) inhibition of MDM2 (using nutlin-3); 2) transient overexpression of p14(ARF); and 3) targeting of survivin using antisense oligonucleotides. However, it is noteworthy that only survivin downregulation sensitized cells to CDDP-induced apoptosis. These results suggest that p53 is functional in the absence of p14(ARF) in MPM and that targeting of the downstream apoptosis inhibitor survivin can sensitize to CDDP-induced apoptosis.

Gene therapeutics: the future of brain tumor therapy?

Primary glioblastoma multiforme is an aggressive brain tumor that has no cure. Current treatments include gross resection of the tumor, radiation and chemotherapy. Despite valiant efforts, prognosis remains dismal. A promising new technique involves the use of oncolytic viruses that can specifically replicate and lyse in cancers, without spreading to normal tissues. Currently, these are being tested in relevant preclinical models and clinical trials as a therapeutic modality for many types of cancer. Results from recent clinical trials with oncolytic viruses have revealed the safety of this approach, although evidence for efficacy remains elusive. Oncolytic viral strategies are summarized in this review, with a focus on therapies used in brain tumors.

Oncolytic adenoviruses as antiglioma agents

The treatment for malignant gliomas is suboptimal. Oncolytic adenoviruses hold the promise of being effective agents for the treatment of solid tumors. Importantly, the first oncolytic viral therapy has just been approved for use in combination with chemotherapy for late-stage refractory nasopharyngeal cancer by the Chinese State FDA, following a successful Phase III randomized clinical trial. The concept underlying treatment with oncolytic adenoviruses is based on cancer selectivity by confining viral replication and infectivity to cancer cells. For this purpose, the main strategies used currently to modify the viruses include: functional deletions in essential viral genes; tumor- or tissue-specific promoters used to control the expression of these viral genes; and tropism modification to redirect adenovirus to the cancer cell surface. In the near future, oncolytic adenoviruses need to be optimized to fully realize their potential as critical anticancer tools and, thus, improve the prognosis for patients with malignant gliomas.

Gene therapy and targeted toxins for glioma

The most common primary brain tumor in adults is glioblastoma. These tumors are highly invasive and aggressive with a mean survival time of nine to twelve months from diagnosis to death. Current treatment modalities are unable to significantly prolong survival in patients diagnosed with glioblastoma. As such, glioma is an attractive target for developing novel therapeutic approaches utilizing gene therapy. This review will examine the available preclinical models for glioma including xenographs, syngeneic and genetic models. Several promising therapeutic targets are currently being pursued in pre-clinical investigations. These targets will be reviewed by mechanism of action, i.e., conditional cytotoxic, targeted toxins, oncolytic viruses, tumor suppressors/oncogenes, and immune stimulatory approaches. Preclinical gene therapy paradigms aim to determine which strategies will provide rapid tumor regression and long-term protection from recurrence. While a wide range of potential targets are being investigated preclinically, only the most efficacious are further transitioned into clinical trial paradigms. Clinical trials reported to date are summarized including results from conditionally cytotoxic, targeted toxins, oncolytic viruses and oncogene targeting approaches. Clinical trial results have not been as robust as preclinical models predicted, this could be due to the limitations of the GBM models employed. Once this is addressed, and we develop effective gene therapies in models that better replicate the clinical scenario, gene therapy will provide a powerful approach to treat and manage brain tumors.

Enhanced antitumor activity of P450 prodrug-based gene therapy using the low Km cyclophosphamide 4-hydroxylase P450 2B11

Gene therapy using the prodrug-activating enzyme P450 2B6 has shown substantial promise in preclinical and initial clinical studies with the P450 prodrugs cyclophosphamide and ifosfamide. We sought to optimize this therapy using the canine P450 enzyme 2B11, which activates cyclophosphamide and ifosfamide with Km of 80 to 160 micromol/L, approximately 10- to 20-fold lower than the Km of P450 2B6. Retrovirus encoding a P450 2B11-internal ribosome entry signal-P450 reductase expression cassette induced marked cyclophosphamide and ifosfamide cytotoxicity toward 9L gliosarcoma cells and exhibited an impressive bystander killing effect at micromolar prodrug concentrations, where P450 2B6 displayed low activity. Adeno-2B11, a replication-defective, E1/E3 region-deleted adenovirus engineered to coexpress P450 2B11 and P450 reductase, dramatically increased tumor cell-catalyzed cyclophosphamide 4-hydroxylation and cytotoxicity compared with Adeno-2B6 and effected strong bystander killing at low (20 micromol/L) cyclophosphamide concentrations. Further increases in cyclophosphamide cytotoxicity were obtained in several human cancer cell lines, including a 4-hydroperoxycyclophosphamide-resistant MCF-7 breast cancer cell line, when Adeno-2B11 was combined with Onyx-017, an E1b-55-kDa gene-deleted, tumor cell-replicating adenovirus that coamplifies and facilitates tumor cell spread of Adeno-2B11. To evaluate the therapeutic effect of P450 2B11 expression in vivo, 9L gliosarcoma cells transduced with P450-expressing retrovirus were grown as solid s.c. tumors in immunodeficient mice. Cyclophosphamide treatment on a metronomic, 6-day repeating schedule led to full regression of 9L/2B11 tumors but not P450-deficient control tumors, resulting in a tumor-free period lasting up to approximately 100 days. 9L/2B6 tumors regressed more slowly and exhibited a tumor-free period of only 21 to 39 days. Thus, P450 gene-directed enzyme prodrug therapy can be greatly improved by using the low Km P450 enzyme 2B11, which catalyzes intratumoral activation of cyclophosphamide and ifosfamide at pharmacologically relevant drug concentrations.

Use of replication-competent retroviral vectors in an immunocompetent intracranial glioma model

OBJECT

The authors had previously reported on a replication-competent retrovirus (RCR) that has been demonstrated to be stable, capable of effective transduction, and able to prolong survival in an intracranial tumor model in nude mice. The purpose of this study was further investigation of this gene therapy option.

METHODS

The transduction efficiency of RCR in RG2, an immunocompetent intracranial tumor model, was tested in Fischer 344 rats. The immune response to the RCR vector was expressed by the quantification of CD4, CD8, and CD11/b in tumors. The pharmaceutical efficacy of the suicide gene CD in converting prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) was measured using fluorine-19 nuclear magnetic resonance (19F-NMR) spectroscopy. Animal survival data were plotted on Kaplan-Meier survival curves. Finally, the biodistribution of RCR was determined using quantitative real-time polymerase chain reaction (RT-PCR) for the detection of retroviral env gene. There was no evidence of viral transduction in normal brain cells. Neither severe inflammation nor immunoreaction occurred after intracranial injection of RCR-green fluorescent protein compared with phosphate-buffered saline (PBS). The 19F-NMR spectroscopy studies demonstrated that RCR-CD was able to convert 5-FC to 5-FU effectively in vitro. The infection of RG2 brain tumors with RCR-CD and their subsequent treatment with 5-FC significantly prolonged survival compared with that in animals with RG2 transduced tumors treated with PBS. In contrast to the nude mouse model, evidence of virus dissemination to the systemic organs after intracranial injection was not detected using RT-PCR.

CONCLUSIONS

The RCR-mediated suicide gene therapy described in this paper effectively transduced malignant gliomas in an immunocompetent in vivo rodent model, prolonging survival, without evidence of severe intracranial inflammation, and without local transduction of normal brain cells or systemic organs.

p53 promotes adenoviral replication and increases late viral gene expression

The tumor suppressor protein, p53, plays a critical role in viro-oncology. However, the role of p53 in adenoviral replication is still poorly understood. In this paper, we have explored further the effect of p53 on adenoviral replicative lysis. Using well-characterized cells expressing a functional p53 (A549, K1neo, RKO) and isogenic derivatives that do not (K1scx, RKOp53.13), we show that virus replication, late virus protein expression and both wtAd5 and ONYX-015 virus-induced cell death are impaired in cells deficient in functional p53. Conversely, by transfecting p53 into these and other cells (IIICF/c, HeLa), we increase late virus protein expression and virus yield. We also show, using reporter assays in IIICF/c, HeLa and K1scx cells, that p53 can cooperate with E1a to enhance transcription from the major late promoter of the virus. Late viral protein production is enhanced by exogenous p53. Taken together, our data suggest that functional p53 can promote the adenovirus (Ad) lytic cycle. These results have implications for the use of Ad mutants that are defective in p53 degradation, such as ONYX-015, as agents for the treatment of cancers.

Gene therapy developments for pancreatic cancer

Treatment options for pancreatic cancer have limited success and it is therefore an appropriate target for the development of new strategies, including gene therapy. Gene therapy approaches include inhibition of activated oncogenes (KRAS, LSM1) with antisense and RNA interference strategies, replacement of inactivated tumour suppressor genes (TP53, CDKN2A, CDKN1A), targeting of cell signalling pathways, gene-directed prodrug-activation therapies and the use of replication-competent oncolytic viruses. Angiogenesis and apoptosis have also been targeted for gene therapy. Clinical trials of gene therapy have shown only moderate anti-tumour effects. As there are many genetic abnormalities in pancreatic cancer, strategies combining different targets or indeed different modalities of treatment, may be more successful. Identification of new targets and improvements in delivery and targeting may further improve the efficacy of gene therapy in pancreatic cancer.

Gene expression profiles of normal human lung cells affected by adenoviral E1B

Adenoviruses with deletion of E1b gene can selectively replicate in cancer cells. The underlying mechanisms in tumor-selective replication of E1b-deleted adenoviruses are insufficiently understood. Identifying genes with altered expression patterns caused by the E1B proteins in virus-infected cells will further increase our understanding of E1B functions and provide insight into the tumor-selective replication of E1b-mutated adenoviruses on the molecular level. An approach based on large-scale gene array was applied to analyze molecular changes affected by viral E1B. We identified a total of 345 genes with expression changes of two-fold or greater affected by wild-type adenovirus compared with its E1b-deleted counterpart. The gene array data were confirmed by quantitative real-time PCR and Western blot. E1B proteins affect the expression of a diverse range of genes involved in cell cycle regulation, apoptosis, stress responses and angiogenesis. This is the first study of the global profile of gene expression altered by the viral E1B proteins in human lung cells, and the majority of the genes were previously not known to be affected by the viral proteins. The data presented in this study will lead to more detailed analysis of E1B functions and may also lead to development of new agents and approaches for oncolytic therapy.

Late expression of nitroreductase in an oncolytic adenovirus sensitizes colon cancer cells to the prodrug CB1954

We have constructed an oncolytic adenovirus expressing the Escherichia coli nitroreductase gene nfsB from an internal ribosome entry site (IRES) in the adenovirus L5 major late transcript. The virus (Tcf-NTR) has Tcf transcription factor-binding sites in the E1A, E1B, and E4 promoters, which restrict viral replication to cells that have activation of the Wnt signaling pathway. This virus was compared with an E1B-55K-deleted virus expressing nitroreductase (NTR) from a cytomegalovirus (CMV) promoter in the E1B-55K region [CRAd-NTR(PS1217H6)]. Both viruses express NTR in colorectal cancer cell lines and show increased cytopathic effect in the presence of the prodrug CB1954. Unlike the Tcf-NTR virus, the CMV-NTR virus expresses NTR in human lung fibroblasts and sensitizes these normal cells to CB1954. The in vivo activity of the viruses was tested in SW620 xenografts in nude mice by intravenous injection of 1,011 particles of virus followed 1 week later by intraperitoneal injections of CB1954. The CMV-NTR virus produced minimal effects in this model. The median time to form 1,000-mm(3) tumors in mice treated with the Tcf-NTR virus plus CB1954 was increased from 14 to 26 days (p=0.003), but this was due mainly to the direct oncolytic effect of the virus. Combination therapy with 3 x 10(11) particles of Tcf-NTR virus (given intravenously) and the mammalian target of rapamycin (mTOR) inhibitor RAD001 (everolimus) (given orally) significantly improved survival (median, >50 days), and addition of CB1954 to this regimen further delayed tumor growth. These results show that the Tcf-NTR virus is more tumor selective and active than the CMV-NTR virus. At the level of transduction that can be achieved currently with oncolytic viruses given intravenously, drugs such as RAD001, which do not require activation by the virus, produce greater increases in efficacy than prodrugs such as CB1954.

Viral gene therapy strategies: from basic science to clinical application

A major impediment to the successful application of gene therapy for the treatment of a range of diseases is not a paucity of therapeutic genes, but the lack of an efficient non-toxic gene delivery system. Having evolved to deliver their genes to target cells, viruses are currently the most effective means of gene delivery and can be manipulated to express therapeutic genes or to replicate specifically in certain cells. Gene therapy is being developed for a range of diseases including inherited monogenic disorders and cardiovascular disease, but it is in the treatment of cancer that this approach has been most evident, resulting in the recent licensing of a gene therapy for the routine treatment of head and neck cancer in China. A variety of virus vectors have been employed to deliver genes to cells to provide either transient (eg adenovirus, vaccinia virus) or permanent (eg retrovirus, adeno-associated virus) transgene expression and each approach has its own advantages and disadvantages. Paramount is the safety of these virus vectors and a greater understanding of the virus-host interaction is key to optimizing the use of these vectors for routine clinical use. Recent developments in the modification of the virus coat allow more targeted approaches and herald the advent of systemic delivery of therapeutic viruses. In the context of cancer, the ability of attenuated viruses to replicate specifically in tumour cells has already yielded some impressive results in clinical trials and bodes well for the future of this approach, particularly when combined with more traditional anti-cancer therapies.

GC-selective DNA-binding antibiotic, mithramycin A, reveals multiple points of control in the regulation of Hdm2 protein synthesis

The primary role of the Hdm2/Mdm2 oncoprotein is to regulate the levels and activity of the transcription factor p53. Hdm2 synthesis is itself tightly controlled and, as demonstrated by a recently described SNP (SNP309) in the hdm2-P2 promoter, minor variations in Hdm2 expression have phenotypic consequences on radiation sensitivity and cancer predisposition. To further define mechanisms regulating Hdm2 expression, we have investigated the effects of the GC-selective DNA-binding drug, Mithramycin A (MA) on hdm2 mRNA transcription, trafficking, and translation. Firstly we show that the constitutive hdm2-P1 promoter is inhibited by MA. We define, for the first time, the minimal sequence elements that are required for P1-promoter activity and identify those which confer MA sensitivity. Secondly, MA induces p53-dependent transcription from the hdm2-P2 promoter. Thirdly, and critically, MA also inhibits Hdm2 synthesis at the post-transcriptional level, with negative effects on hdm2 mRNA nuclear export and translation. This study highlights the complex interplay between the pathways that regulate Hdm2 protein synthesis in cancer cells, and furthermore emphasizes the export of hdm2 mRNA from the nucleus to the cytoplasm as a key point of control in this process.