Oral USC-093, a novel homoserinamide analogue of the tyrosinamide (S)-HPMPA prodrug USC-087 has decreased nephrotoxicity while maintaining antiviral efficacy against human adenovirus infection of Syrian hamsters

Adenovirus infections of immunocompromised humans are a significant source of morbidity and mortality. Presently, there is no drug specifically approved for the treatment of adenovirus infections by the FDA. The state-of-the-art treatment of such infections is the off-label use of cidofovir, an acyclic nucleotide phosphonate. While cidofovir inhibits adenovirus replication, it has dose-limiting kidney toxicity. There is an apparent need for a better compound to treat adenovirus infections. To this end, we have been developing acyclic nucleotide phosphonate prodrugs that utilize an amino acid scaffold equipped with a lipophilic modifier. Here, we compare the antiviral potential of two prodrugs of HPMPA that differ only in the amino acid-based promoiety: USC-087, based on an N-hexadecyl tyrosinamide, and USC-093, based on an N-hexadecyl serinamide. Oral administration of both compounds was very efficacious against disseminated HAdV-C6 infection in immunosuppressed Syrian hamsters, suppressing virus replication and mitigating pathology even when treatment was withheld until 4 days after challenge. We saw only marginal efficacy after respiratory infection of hamsters, which may reflect suboptimal distribution to the lung. Importantly, neither compound induced intestinal toxicity, which was observed as the major adverse effect in clinical trials of brincidofovir, a prodrug of cidofovir which also contains a C-16 modifier. Notably, we found that there was a significant difference in the nephrotoxicity of the two compounds: USC-087 caused significant kidney toxicity while USC-093 did not, at effective doses. These findings will be valuable guidepoints in the future evolution of this new class of potential prodrugs to treat adenovirus infections.

NPP-669, a Novel Broad-Spectrum Antiviral Therapeutic with Excellent Cellular Uptake, Antiviral Potency, Oral Bioavailability, Preclinical Efficacy, and a Promising Safety Margin

DNA viruses are responsible for many diseases in humans. Current treatments are often limited by toxicity, as in the case of cidofovir (CDV, Vistide), a compound used against cytomegalovirus (CMV) and adenovirus (AdV) infections. CDV is a polar molecule with poor bioavailability, and its overall clinical utility is limited by the high occurrence of acute nephrotoxicity. To circumvent these disadvantages, we designed nine CDV prodrug analogues. The prodrugs modulate the polarity of CDV with a long sulfonyl alkyl chain attached to one of the phosphono oxygens. We added capping groups to the end of the alkyl chain to minimize β-oxidation and focus the metabolism on the phosphoester hydrolysis, thereby tuning the rate of this reaction by altering the alkyl chain length. With these modifications, the prodrugs have excellent aqueous solubility, optimized metabolic stability, increased cellular permeability, and rapid intracellular conversion to the pharmacologically active diphosphate form (CDV-PP). The prodrugs exhibited significantly enhanced antiviral potency against a wide range of DNA viruses in infected human foreskin fibroblasts. Single-dose intravenous and oral pharmacokinetic experiments showed that the compounds maintained plasma and target tissue levels of CDV well above the EC₅₀ for 24 h. These experiments identified a novel lead candidate, NPP-669. NPP-669 demonstrated efficacy against CMV infections in mice and AdV infections in hamsters following oral (p.o.) dosing at a dose of 1 mg/kg BID and 0.1 mg/kg QD, respectively. We further showed that NPP-669 at 30 mg/kg QD did not exhibit histological signs of toxicity in mice or hamsters. These data suggest that NPP-669 is a promising lead candidate for a broad-spectrum antiviral compound.

Filociclovir Is a Potent In Vitro and In Vivo Inhibitor of Human Adenoviruses

Human adenovirus (HAdV) infection is common in the general population and can cause a range of clinical manifestations, among which pneumonia and keratoconjunctivitis are the most common. Although HAdV infections are mostly self-limiting, infections in immunocompromised individuals can be severe. No antiviral drug has been approved for treating adenoviruses. Filociclovir (FCV) is a nucleoside analogue which has successfully completed phase I human clinical safety studies and is now being developed for treatment of human cytomegalovirus (HCMV)-related disease in immunocompromised patients. In this report, we show that FCV is a potent broad-spectrum inhibitor of HAdV types 4 to 8, with 50% effective concentrations (EC50s) ranging between 1.24 and 3.6 μM and a 50% cytotoxic concentration (CC50) of 100 to 150 μM in human foreskin fibroblasts (HFFs). We also show that the prophylactic oral administration of FCV (10 mg/kg of body weight) 1 day prior to virus challenge and then daily for 14 days to immunosuppressed Syrian hamsters infected intravenously with HAdV6 was sufficient to prevent morbidity and mortality. FCV also mitigated tissue damage and inhibited virus replication in the liver. The 10-mg/kg dose had similar effects even when the treatment was started on day 4 after virus challenge. Furthermore, FCV administered at the same dose after intranasal challenge with HAdV6 partially mitigated body weight loss but significantly reduced pathology and virus replication in the lung. These findings suggest that FCV could potentially be developed as a pan-adenoviral inhibitor.

Generation and characterization of an Il2rg knockout Syrian hamster model for XSCID and HAdV-C6 infection in immunocompromised patients

Model animals are indispensable for the study of human diseases, and in general, of complex biological processes. The Syrian hamster is an important model animal for infectious diseases, behavioral science and metabolic science, for which more experimental tools are becoming available. Here, we describe the generation and characterization of an interleukin-2 receptor subunit gamma (Il2rg) knockout (KO) Syrian hamster strain. In humans, mutations in IL2RG can result in a total failure of T and natural killer (NK) lymphocyte development and nonfunctional B lymphocytes (X-linked severe combined immunodeficiency; XSCID). Therefore, we sought to develop a non-murine model to study XSCID and the infectious diseases associated with IL2RG deficiency. We demonstrated that the Il2rg KO hamsters have a lymphoid compartment that is greatly reduced in size and diversity, and is impaired in function. As a result of the defective adaptive immune response, Il2rg KO hamsters developed a more severe human adenovirus infection and cleared virus less efficiently than immune competent wild-type hamsters. Because of this enhanced virus replication, Il2rg KO hamsters developed more severe adenovirus-induced liver pathology than wild-type hamsters. This novel hamster strain will provide researchers with a new tool to investigate human XSCID and its related infections.

Adenovirus and Oxaliplatin cooperate as agnostic sensitizers for immunogenic cell death in colorectal carcinoma

Treatments with cytotoxic agents or viruses may cause Immunogenic Cell Death (ICD) that immunize tumor-bearing hosts but do not cause complete regression of tumor. We postulate that combining two ICD inducers may cause durable regression in immunocompetent mice. ICD was optimized in vitro by maximizing calreticulin externalization in human colorectal carcinoma (CRC) cells by exposure to mixtures of Oxaliplatin (OX) and human adenovirus (AdV). Six mm diameter CT26 or 4T1 carcinomas in flanks of BALB/c mice were injected once intratumorally (IT) with OX, AdV or their mixture. Tumor growth, Tumor-Infiltrating Lymphocytes (TIL), nodal cytotoxicity, and rejection of a viable cell challenge were measured. Tumors injected IT once with an optimum mixture of 80 µM OX - AdV 25 Multiplicity of Infection (MOI) in PBS buffer were 17-29% the volume of control tumors. When buffer was changed from PBS to 5% dextrose in water (D5W), volumes of tumors injected IT with 80 µM OX-AdV 25 MOI were 10% while IT OX or AdV alone were 32% and 40% the volume of IT buffer-treated tumors. OX-AdV IT increased CD3+ TIL by 4-fold, decreased CD8+ PD-1+ TIL from 79% to 19% and induced cytotoxicity to CT26 cells in draining node lymphocytes while lymphocytes from CT26-bearing untreated mice were not cytotoxic. OX-AdV IT in D5W caused complete regression in 40% of mice. Long-term survivors rejected a contralateral challenge of CT26. The buffer for Oxaliplatin is critical. The two ICD inducer mixture is promising as an agnostic sensitizer for carcinomas like colorectal carcinoma.

Drug development against human adenoviruses and its advancement by Syrian hamster models

The symptoms of human adenovirus infections are generally mild and self-limiting. However, these infections have been gaining importance in recent years because of a growing number of immunocompromised patients. Solid organ and hematopoietic stem cell transplant patients are subjected to severe immunosuppressive regimes and cannot efficaciously eliminate virus infections. In these patients, adenovirus infections can develop into deadly multi-organ disseminated disease. Presently, in the absence of approved therapies, physicians rely on drugs developed for other purposes to treat adenovirus infections. As there is a need for anti-adenoviral therapies, researchers have been developing new agents and repurposing existing ones to treat adenovirus infections. There are several small molecule drugs that are being tested for their efficacy against human adenoviruses; some of these have reached clinical trials, while others are still in the preclinical phase. Besides these compounds, research on immunotherapy against adenoviral infection has made significant progress, promising another modality for treatment. The availability of an animal model confirmed the activity of some drugs already in clinical use while proving that others are inactive. This led to the identification of several lead compounds that await further development. In the present article, we review the current status of anti-adenoviral therapies and their advancement by in vivo studies in the Syrian hamster model.

Characterization of an N-Terminal Non-Core Domain of RAG1 Gene Disrupted Syrian Hamster Model Generated by CRISPR Cas9

The accumulating evidence demonstrates that Syrian hamsters have advantages as models for various diseases. To develop a Syrian hamster (Mesocricetus auratus) model of human immunodeficiency caused by RAG1 gene mutations, we employed the CRISPR/Cas9 system and introduced an 86-nucleotide frameshift deletion in the hamster RAG1 gene encoding part of the N-terminal non-core domain of RAG1. Histological and immunohistochemical analyses demonstrated that these hamsters (referred herein as RAG1-86nt hamsters) had atrophic spleen and thymus, and developed significantly less white pulp and were almost completely devoid of splenic lymphoid follicles. The RAG1-nt86 hamsters had barely detectable CD3⁺ and CD4⁺ T cells. The expression of B and T lymphocyte-specific genes (CD3γ and CD4 for T cell-specific) and (CD22 and FCMR for B cell-specific) was dramatically reduced, whereas the expression of macrophage-specific (CD68) and natural killer (NK) cell-specific (CD94 and KLRG1) marker genes was increased in the spleen of RAG1-nt86 hamsters compared to wildtype hamsters. Interestingly, despite the impaired development of B and T lymphocytes, the RAG1-86nt hamsters still developed neutralizing antibodies against human adenovirus type C6 (HAdV-C6) upon intranasal infection and were capable of clearing the infectious viruses, albeit with slower kinetics. Therefore, the RAG1-86nt hamster reported herein (similar to the hypomorphic RAG1 mutations in humans that cause Omenn syndrome), may provide a useful model for studying the pathogenesis of the specific RAG1-mutation-induced human immunodeficiency, the host immune response to adenovirus infection and other pathogens as well as for evaluation of cell and gene therapies for treatment of this subset of RAG1 mutation patients.

USC-087 protects Syrian hamsters against lethal challenge with human species C adenoviruses

Human adenoviruses (AdV) cause generally mild infections of the respiratory and GI tracts as well as some other tissues. However, AdV can cause serious infection in severely immunosuppressed individuals, especially pediatric patients undergoing allogeneic hematopoietic stem cell transplantation, where mortality rates are up to 80% with disseminated disease. Despite the seriousness of AdV disease, there are no drugs approved specifically to treat AdV infections. We report here that USC-087, an N-alkyl tyrosinamide phosphonate ester prodrug of HPMPA, the adenine analog of cidofovir, is highly effective against multiple AdV types in cell culture. USC-087 is also effective against AdV-C6 in our immunosuppressed permissive Syrian hamster model. In this model, hamsters are immunosuppressed by treatment with high dose cyclophosphamide. Injection of AdV-C6 (or AdV-C5) intravenously leads to a disseminated infection that resembles the disease seen in humans, including death. We have tested the efficacy of orally-administered USC-087 against the median lethal dose of intravenously administered AdV-C6. USC-087 completely prevented or significantly decreased mortality when administered up to 4 days post challenge. USC-087 also prevented or significantly decreased liver damage caused by AdV-C6 infection, and suppressed virus replication even when administered 4 days post challenge. These results imply that USC-087 is a promising candidate for drug development against HAdV infections.

Male Syrian hamsters are more susceptible to intravenous infection with species C human adenoviruses than are females

Recently, increasing attention has been focused on the influence of sex on the course of infectious diseases. Thus far, the best-documented examples point toward an immune-mediated mechanism: the generally stronger immune response in females can result in a faster clearance of the pathogen or, conversely, a more severe immune-mediated pathology. Here, we report that human species C adenoviruses replicate more and cause more pathology in male Syrian hamsters than in females. We also show that this sex disparity is not caused by a stronger immune response to the infection by the female hamsters. Rather, the liver of male hamsters is more susceptible to adenovirus infection: after intravenous injection, more hepatocytes become infected in male animals than in females. We hypothesize that Kupffer cells (hepatic tissue macrophages) of female animals are more active in sequestering circulating virions, and thus protect hepatocytes more efficiently than those of males.

Tristetraprolin induces cell cycle arrest in breast tumor cells through targeting AP-1/c-Jun and NF-κB pathway

The main characteristic of cancers, including breast cancer, is the ability of cancer cells to proliferate uncontrollably. However, the underlying mechanisms of cancer cell proliferation, especially those regulated by the RNA binding protein tristetraprolin (TTP), are not completely understood. In this study, we found that TTP inhibits cell proliferation in vitro and suppresses tumor growth in vivo through inducing cell cycle arrest at the S phase. Our studies demonstrate that TTP inhibits c-Jun expression through the C-terminal Zn finger and therefore increases Wee1 expression, a regulatory molecule which controls cell cycle transition from the S to the G2 phase. In contrast to the well-known function of TTP in regulating mRNA stability, TTP inhibits c-Jun expression at the level of transcription by selectively blocking NF-κB p65 nuclear translocation. Reconstitution of NF-κB p65 completely abolishes the inhibition of c-Jun transcription by TTP. Moreover, reconstitution of c-Jun in TTP-expressing breast tumor cells diminishes Wee1 overexpression and promotes cell proliferation. Our results indicate that TTP suppresses c-Jun expression that results in Wee1 induction which causes cell cycle arrest at the S phase and inhibition of cell proliferation. Our study provides a new pathway for TTP function as a tumor suppressor which could be targeted in tumor treatment.

Correction: STAT2 Knockout Syrian Hamsters Support Enhanced Replication and Pathogenicity of Human Adenovirus, Revealing an Important Role of Type I Interferon Response in Viral Control

[This corrects the article DOI: 10.1371/journal.ppat.1005084.].

New drug on the horizon for treating adenovirus

Human adenoviruses can cause serious disseminated infections including death in immunosuppressed patients, especially pediatric allogeneic hematopoietic stem cell transplant (allo-HSCT) patients. There are no drugs approved to treat such infections. Cidofovir is used intravenously in many transplant clinics, probably with some effect, but controlled trials have not been completed. Cidofovir is an acyclic nucleoside phosphonate analog of cytidine monophosphate. Following conversion to its diphosphate form within cells, cidofovir is a preferred substrate for the adenovirus DNA polymerase, leading to viral DNA chain termination. Problems with cidofovir include poor cellular uptake and nephrotoxicity. Brincidofovir, a lipid-linked derivative of cidofovir which is active against five families of double-stranded DNA viruses, represents a major advance in anti-adenovirus therapy. It is administered orally, taken up readily by cells followed by release of cidofovir within cells, and is not nephrotoxic. Brincidofovir, under development by Chimerix, Inc., is being evaluated against adenovirus infections in transplant patients including allo-HSCT patients in a phase III clinical trial (AdVise Study). Preliminary results indicate that brincidofovir is safe and very effective at decreasing adenovirus viremia and adenovirus-induced pathogenicity and mortality. Anti-adenovirus adoptive T cell therapy is another very promising approach to treating allo-HSCT patients as demonstrated in clinical studies.

Transcriptome sequencing and development of an expression microarray platform for liver infection in adenovirus type 5-infected Syrian golden hamsters

The Syrian golden hamster is an attractive animal for research on infectious diseases and other diseases. We report here the sequencing, assembly, and annotation of the Syrian hamster transcriptome. We include transcripts from ten pooled tissues from a naïve hamster and one stimulated with lipopolysaccharide. Our data set identified 42,707 non-redundant transcripts, representing 34,191 unique genes. Based on the transcriptome data, we generated a custom microarray and used this new platform to investigate the transcriptional response in the Syrian hamster liver following intravenous adenovirus type 5 (Ad5) infection. We found that Ad5 infection caused a massive change in regulation of liver transcripts, with robust up-regulation of genes involved in the antiviral response, indicating that the innate immune response functions in the host defense against Ad5 infection of the liver. The data and novel platforms developed in this study will facilitate further development of this important animal model.

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Syrian hamster transcriptome; 42,707 transcripts representing 34,191 unique genes

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Syrian hamster custom expression microarray platform

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Ad5 intravenous infection of the Syrian hamster liver

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Ad5 upregulation of hamster liver genes involved in innate antiviral response.

Valganciclovir inhibits human adenovirus replication and pathology in permissive immunosuppressed female and male Syrian hamsters

Adenovirus infections of immunocompromised pediatric hematopoietic stem cell transplant patients can develop into serious and often deadly multi-organ disease. There are no drugs approved for adenovirus infections. Cidofovir (an analog of 2-deoxycytidine monophosphate) is used at times but it can be nephrotoxic and its efficacy has not been proven in clinical trials. Brincidofovir, a promising lipid-linked derivative of cidofovir, is in clinical trials. Ganciclovir, an analog of 2-deoxyguanosine, has been employed occasionally but with unknown efficacy in the clinic. In this study, we evaluated valganciclovir against disseminated adenovirus type 5 (Ad5) infection in our permissive immunosuppressed Syrian hamster model. We administered valganciclovir prophylactically, beginning 12 h pre-infection or therapeutically starting at Day 1, 2, 3, or 4 post-infection. Valganciclovir significantly increased survival, reduced viral replication in the liver, and mitigated the pathology associated with Ad5 infection. In cultured cells, valganciclovir inhibited Ad5 DNA replication and blocked the transition from early to late stage of infection. Valganciclovir directly inhibited Ad5 DNA polymerase in vitro, which may explain, at least in part, its mechanism of action. Ganciclovir and valganciclovir are approved to treat infections by certain herpesviruses. Our results support the use of valganciclovir to treat disseminated adenovirus infections in immunosuppressed patients.

The effects of radiation on antitumor efficacy of an oncolytic adenovirus vector in the Syrian hamster model

We report that radiation enhances the antitumor efficacy of the oncolytic adenovirus vector VRX-007 in Syrian hamster tumors. We used tumor-specific irradiation of subcutaneous tumors and compared treatment options of radiation alone or combined with VRX-007 and cyclophosphamide (CP). Radiation therapy further augmented the VRX-007-mediated inhibition of tumor growth, in both CP-treated and non-CP-treated hamsters, even though radiation did not lead to increased viral replication in tumors when compared to those treated with VRX-007 alone. Moreover, tumor growth inhibition was similar in tumors irradiated either one week before or after injection with VRX-007, which suggests that radiation exerts its antitumor effect independently from vector therapy. Thus, our results demonstrate that these two therapies do not have to be provided simultaneously to enhance their combined effectiveness against subcutaneous hamster tumors.

Chapter three--Syrian hamster as an animal model to study oncolytic adenoviruses and to evaluate the efficacy of antiviral compounds

The Syrian (golden) hamster (Mesocricetus auratus) has served as a useful model for different aspects of biology for at least 50 years, and its use has been expanding recently. In earlier years, among other things, it was a model for cancer development. More recently, it has become a model for many different infectious diseases. It has also become an alternative model for the study of oncolytic adenovirus vectors for cancer gene therapy. Among several other human pathogens, the hamster is permissive for the replication of human species C adenoviruses, which are the parental virus for the majority of adenovirus vectors in use today. These vectors replicate in some of the established hamster tumor cell lines that can be used to generate tumors in vivo, that is, one can study oncolytic (replication competent) adenoviruses in a permissive, immunocompetent model. This has afforded the opportunity to study the effect of the host immune system on the vector-infected tumor and has allowed the use of a more relevant animal model to determine the safety and biodistribution of replication-competent adenoviruses. The hamster has also been used to evaluate antiviral compounds and vaccines against many viruses, including adenoviruses, flaviviruses, alphaviruses, arenaviruses, bunyaviruses, and paramyxoviruses.

A fully replication-competent adenovirus vector with enhanced oncolytic properties

We have studied the oncolytic efficacy of two adenovirus vectors named KD3 and INGN 007, which differ from each other only in that whereas KD3 has two small deletions in its e1a gene that restrict its replication to rapidly cycling cells, INGN 007 has wild-type e1a gene. Both vectors overexpress the adenovirus death protein (ADP). Both KD3 and INGN 007 effectively suppressed the growth of subcutaneous human A549 and Hep3B tumors in nude mice upon intratumoral injection, and contained the growth of subcutaneous LNCaP tumors after intravenous injection, making some tumors shrink or disappear. However, in a more demanding model, intravenous injections of neither KD3 nor wild-type Ad5 were effective against subcutaneous A549 tumors, whereas INGN 007 increased the mean survival time by 35%. INGN 007 was also effective in suppressing tumor growth in a challenging A549 orthotopic lung cancer model. INGN 007 was superior to dl1520 (ONYX-015) in repressing subcutaneous A549 tumors. Our results suggest that vectors such as INGN 007 might provide better antitumor efficacy in the clinic as well.

Oncolytic (replication-competent) adenoviruses as anticancer agents

IMPORTANCE OF THE FIELD

Whilst therapies for neoplasies have advanced tremendously in the last few decades, there is still a need for new anti-cancer treatments. One option is genetically-engineered oncolytic adenovirus (Ad) 'vectors'. These kill cancer cells via the viral replication cycle, and amplify the anti-tumor effect by producing progeny virions able to infect neighboring tumor cells.

AREAS COVERED IN THIS REVIEW

We provide a description of basic Ad biology and summarize the literature for oncolytic Ads from 1996 to the present.

WHAT THE READER WILL GAIN

An overall view of oncolytic Ads, the merits and drawbacks of the various features of these vectors, and obstacles to further development and future directions for research.

TAKE HOME MESSAGE

Ads are attractive for gene therapy because they are relatively innocuous, easy to produce in large quantities, genetically stable, and easy to manipulate. A variety of have been constructed and tested, in pre-clinical and clinical experiments. Oncolytic Ads proved to be remarkably safe; no dose-limiting toxicity was observed in any clinical trial, and the maximum tolerated dose was not reached. At present, the major challenge for researchers is to increase the efficacy of the vectors, and to incorporate oncolytic virotherapy into existing treatment protocols.

Adenovirus E1A and E1B-19K proteins protect human hepatoma cells from transforming growth factor beta1-induced apoptosis

Primary and some transformed hepatocytes undergo apoptosis in response to transforming growth factor beta1 (TGFbeta). We report that infection with species C human adenovirus conferred resistance to TGFbeta-induced apoptosis in human hepatocellular carcinoma cells (Huh-7). Protection against TGFbeta-mediated cell death in adenovirus-infected cells correlated with the maintenance of normal nuclear morphology, lack of pro-caspases 8 and 3 processing, maintenance of the mitochondrial membrane potential, and lack of cellular DNA degradation. The TGFbeta pro-apoptotic signaling pathway was blocked upstream of mitochondria in adenovirus-infected cells. Both the N-terminal sequences of the E1A proteins and the E1B-19K protein were necessary to protect infected cells against TGFbeta-induced apoptosis.

Pre-existing immunity and passive immunity to adenovirus 5 prevents toxicity caused by an oncolytic adenovirus vector in the Syrian hamster model

We have used Syrian hamsters to examine the role of pre-existing immunity to adenovirus (Ad) 5 in the toxicity of the oncolytic Ad vector INGN 007. Groups of hamsters were or were not immunized with Ad5. Half the hamsters were immunosuppressed using cyclophosphamide (CP), then injected intravenously (i.v.) with 3x the maximum tolerated dose (MTD) of INGN 007 (in immunocompetent hamsters), and toxicity and vector replication in the liver were quantitated. In nonimmunized immunocompetent hamsters, toxicity was observed early but the hamsters recovered by day 6 after vector injection. In nonimmunized immunosuppressed hamsters, the vector was lethal by 3 days. Pre-existing neutralizing antibody (NAb) prevented liver infection and hepatotoxicity in both immunocompetent and immunosuppressed hamsters. In another study, passive immunization of immunosuppressed hamsters 1 day before a lethal dose (1x MTD) of INGN 007 prevented liver infection and replication, but immunization 1 day after vector administration was barely effective. When immunosuppressed hamsters were passively immunized 1 day after injection of 1/3rd the MTD of INGN 007, then significant protection was observed against liver infection and toxicity. Therefore, serum NAb are sufficient to prevent oncolytic Ad vector liver infection and toxicity. We saw no evidence that pre-existing immunity was associated with increased vector toxicity.

New pancreatic carcinoma model for studying oncolytic adenoviruses in the permissive Syrian hamster

Syrian hamster is a practical animal model for studying the systemic effects of oncolytic vectors derived from adenovirus serotype 5 (Ad5). Ad5 replicates well in Syrian hamster tissues, and Syrian hamster cell lines are available that are known to support Ad5 replication. In this study, we established four new Syrian hamster cell lines from transplantable pancreatic, renal, hepatic and lung tumors. The pancreatic cell line (SHPC6) and the renal cell line were highly permissive for Ad5 replication. The SHPC6 cell line formed disseminated intraperitoneal tumors when cells were injected into the peritoneal cavity. INGN 007, an oncolytic Ad5-based vector, completely reversed the growth of disseminated intraperitoneal SHPC6 tumor nodules following intraperitoneal injection of the vector, leading to 100% survival of the treated animals. SHPC6 cells also formed subcutaneous tumors, whose growth was suppressed by INGN 007 following intratumoral injection. INGN 007 replicated in both the intraperitoneal and subcutaneous SHPC6 tumors. Following intraperitoneal injection, INGN 007 did not replicate in the livers of hamsters with intraperitoneal SHPC6 tumors, and was not hepatotoxic. These studies suggest that the SHPC6 cell line may be useful as a model for disseminated pancreatic cancer, and that INGN 007 may be a safe and effective vector to treat these tumors.

INGN 007, an oncolytic adenovirus vector, replicates in Syrian hamsters but not mice: comparison of biodistribution studies

Preclinical biodistribution studies with INGN 007, an oncolytic adenovirus (Ad) vector, supporting an early stage clinical trial were conducted in Syrian hamsters, which are permissive for Ad replication, and mice, which are a standard model for assessing toxicity and biodistribution of replication-defective (RD) Ad vectors. Vector dissemination and pharmacokinetics following intravenous administration were examined by real-time PCR in nine tissues and blood at five time points spanning 1 year. Select organs were also examined for the presence of infectious vector/virus. INGN 007 (VRX-007), wild-type Ad5 and AdCMVpA (an RD vector) were compared in the hamster model, whereas only INGN 007 was examined in mice. DNA of all vectors was widely disseminated early after injection, but decayed rapidly in most organs. In the hamster model, DNA of INGN 007 and Ad5 was more abundant than that of the RD vector AdCMVpA at early times after injection, but similar levels were seen later. An increased level of INGN 007 and Ad5 DNA but not AdCMVpA DNA in certain organs early after injection, and the presence of infectious INGN 007 and Ad5 in lung and liver samples at early times after injection, strongly suggests that replication of INGN 007 and Ad5 occurred in several Syrian hamster organs. There was no evidence of INGN 007 replication in mice. In addition to providing important information about INGN 007, the results underscore the utility of the Syrian hamster as a permissive immunocompetent model for Ad5 pathogenesis and oncolytic Ad vectors.

Immunosuppression enhances oncolytic adenovirus replication and antitumor efficacy in the Syrian hamster model

We recently described an immunocompetent Syrian hamster model for oncolytic adenoviruses (Ads) that permits virus replication in tumor cells as well as some normal tissues. This model allows exploration of interactions between the virus, tumor, normal organs, and host immune system that could not be examined in the immunodeficient or nonpermissive animal models previously used in the oncolytic Ad field. Here we asked whether the immune response to oncolytic Ad enhances or limits antitumor efficacy. We first determined that cyclophosphamide (CP) is a potent immunosuppressive agent in the Syrian hamster and that CP alone had no effect on tumor growth. Importantly, we found that the antitumor efficacy of oncolytic Ads was significantly enhanced in immunosuppressed animals. In animals that received virus therapy plus immunosuppression, significant differences were observed in tumor histology, and in many cases little viable tumor remained. Notably, we also determined that immunosuppression allowed intratumoral virus levels to remain elevated for prolonged periods. Although favorable tumor responses can be achieved in immunocompetent animals, the rate of virus clearance from the tumor may lead to varied antitumor efficacy. Immunosuppression, therefore, allows sustained Ad replication and oncolysis, which leads to substantially improved suppression of tumor growth.

West Nile 25A virus infection of B-cell-deficient ((micro)MT) mice: characterization of neuroinvasiveness and pseudoreversion of the viral envelope protein

The attenuated West Nile virus 25A strain (WN25A) was investigated for its neuroinvasive properties in B-cell-deficient (microMT) mice. After peripheral inoculation, WN25A caused fatal encephalitis in the majority of 6-8-week-old mice, characterized by a systemic infection with viraemia, moderate virus burdens in peripheral tissues and a high titre of brain-associated virus. Mice generally succumbed to infection within a few weeks of infection. However, others survived for as long as 10 weeks, and some for even longer. Normal age-matched C57BL/6 mice showed no signs of illness after inoculation with WN25A virus. Nucleotide sequencing of WN25A viruses recovered from the brains of B-cell-deficient mice revealed that the conserved N-linked glycosylation site in the viral envelope protein was abolished by substitution of a serine residue at position 155. This was found to be a pseudoreversion relative to the wild-type WN-Israel strain, based on virulence testing of one such brain-associated virus in both B-cell-deficient and normal C57BL/6 mice. This study provides further characterization of the mouse virulence properties of the attenuated WN25A virus in the context of B-cell deficiency. Replication in these mice does not involve rapid neuroadaptation or reversion of WN25A virus to a neuroinvasive phenotype. Molecular modelling studies suggest a difference in local structure of the E protein associated with either an asparagine or serine residue at position 155 compared with the tyrosine found in the virulent parental WN-Israel virus.

Anticancer activity of oncolytic adenovirus vector armed with IFN-alpha and ADP is enhanced by pharmacologically controlled expression of TRAIL

We have previously described oncolytic adenovirus (Ad) vectors KD3 and KD3-interferon (IFN) that were rendered cancer-specific by mutations in the E1A region of Ad; these mutations abolish binding of E1A proteins to p300/CBP and pRB. The antitumor activity of the vectors was enhanced by overexpression of the Adenovirus Death Protein (ADP, E3-11.6K) and by replication-linked expression of IFN-alpha. We hypothesized that the anticancer efficacy of the KD3-IFN vector could be further improved by expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). E1-deleted Ad vectors were constructed carrying reporter genes for enhanced green fluorescent protein or secreted placental alkaline phosphatase (SEAP) and a therapeutic gene for TRAIL under control of the TetON system. Expression of the genes was increased in the presence of a helper virus and the inducer doxycycline such that up to 231-fold activation of expression for the TetON-SEAP vector was obtained. Coinfection with TetON-TRAIL augmented oncolytic activity of KD3 and KD3-IFN in vitro. Induction of TRAIL expression did not reduce the yield of progeny virus. Combination of TetON-TRAIL and KD3-IFN produced superior antitumor activity in vivo as compared with either vector alone demonstrating the efficacy of a four-pronged cancer gene therapy approach, which includes Ad oncolysis, ADP overexpression, IFN-alpha-mediated immunotherapy, and pharmacologically controlled TRAIL activity.

Identification of a new human adenovirus protein encoded by a novel late l-strand transcription unit

A short open reading frame named the "U exon," located on the adenovirus (Ad) l-strand (for leftward transcription) between the early E3 region and the fiber gene, is conserved in mastadenoviruses. We have observed that Ad5 mutants with large deletions in E3 that infringe on the U exon display a mild growth defect, as well as an aberrant Ad E2 DNA-binding protein (DBP) intranuclear localization pattern and an apparent failure to organize replication centers during late infection. Mutants in which the U exon DNA is reconstructed have a reversed phenotype. Chow et al. (L. T. Chow et al., J. Mol. Biol. 134:265-303, 1979) described mRNAs initiating in the region of the U exon and spliced to downstream sequences in the late DBP mRNA leader and the DBP-coding region. We have cloned this mRNA (as cDNA) from Ad5 late mRNA; the predicted protein is 217 amino acids, initiating in the U exon and continuing in frame in the DBP leader and in the DBP-coding region but in a different reading frame from DBP. Polyclonal and monoclonal antibodies generated against the predicted U exon protein (UXP) showed that UXP is approximately 24K in size by immunoblot and is a late protein. At 18 to 24 h postinfection, UXP is strongly associated with nucleoli and is found throughout the nucleus; later, UXP is associated with the periphery of replication centers, suggesting a function relevant to Ad DNA replication or RNA transcription. UXP is expressed by all four species C Ads. When expressed in transient transfections, UXP complements the aberrant DBP localization pattern of UXP-negative Ad5 mutants. Our data indicate that UXP is a previously unrecognized protein derived from a novel late l-strand transcription unit.

Preparation and titration of CsCl-banded adenovirus stocks

Adenovirus research often requires purified high-titer virus stocks and accurate virus titers for use in experiments. Accurate titers are important for quantitative, interpretable, and reproducible results. This is especially true when there are comparisons of different mutant viruses following infection. This chapter details the large-scale preparation of adenovirus (either replication-competent or replication-defective) in spinner cultures (e.g., KB, HeLa, or 293 cells). Protocols for harvesting cells and isolation of adenovirus by CsCl banding are presented. Methods for titering adenovirus by plaque assay are presented along with a discussion of how plaque assays can be used to determine the kinetics of cell killing and cytolysis by adenoviruses.

Immunocompetent, semi-permissive cotton rat tumor model for the evaluation of oncolytic adenoviruses

Oncolytic adenovirus (Ad) vectors belong to a new class of cancer therapy agents that destroy cancer cells as part of the virus's lytic infectious cycle. In this chapter we describe an immunocompetent, semi-permissive cotton rat tumor model to evaluate the safety and efficacy of oncolytic Ad vectors. With this model one can investigate the effect of the host immune system on the vector-tumor interaction as well as the vector's effect on normal host cells in vivo. This chapter describes procedures for analyzing the growth and cytolytic properties of oncolytic Ad vectors in cotton rat cells in vitro. We discuss handling and husbandry issues and techniques for subcutaneous, intratumoral, and intravenous injection of cotton rats. We present methods for generating subcutaneous tumors in cotton rats and assessing the efficacy of Ad vectors upon intratumoral injection. Also, we discuss procedures for determining the biodistribution of a replicating Ad in cotton rats.

A real-time PCR method to rapidly titer adenovirus stocks

A critical step in working with adenovirus (Ad) and its vectors is the accurate, reproducible, sensitive, and rapid measurement of the amount of virus present in a stock. Titration methods fall into one of two categories: determination of either the infectious or the particle (infectious plus noninfectious) titer. Determining the infectious titer of a virus stock by plaque assay has important limitations, including cell line-, researcher-, and laboratory-dependent variation in titer, and the length of time required to perform the assay (2-4 wk). A major drawback of particle titration methods is the lack of consistent correlation between the resultant titer and the infectious titer. To overcome these problems, a rapid, sensitive, and reproducible real-time polymerase chain reaction (PCR) assay was developed that detects encapsidated full-length genomes. Importantly, there is a linear correlation between the titer determined by the realtime PCR assay and the infectious titer determined by a plaque assay. This chapter provides step-by-step guidance for preparing viral DNA, conducting the real-time PCR assay, and using the resultant data to calculate a viral titer.

Use of the Syrian hamster as an animal model for oncolytic adenovirus vectors

Oncolytic adenoviruses (Ads) are promising candidates for cancer therapy. However, current animal models to evaluate these vectors have substantial limitations. Because Ad replication is generally species-specific, oncolytic Ads are usually examined in immunodeficient mice bearing human xenograft tumors. However, this model suffers because the animals are immunodeficient and normal and cancerous mouse tissues are poorly permissive to human Ad replication. We have recently developed a Syrian hamster model that is both immunocompetent and permissive to human Ad replication in normal and cancerous tissues. The Syrian hamster is also permissive for Ad5 replication in the lung, which is the natural site of infection in humans. Human Ads replicate well in vitro in the Syrian hamster cell lines examined and demonstrate significant antitumor efficacy following injection into Syrian hamster tumors in vivo. In this chapter we describe the maintenance of these Syrian hamster cell lines in culture and how to assess oncolytic Ad vector replication in these cells in vitro. We also describe detailed methods for growth of these cell lines as subcutaneous tumors, for intravenous and intratumoral injections in hamsters, and for evaluation of the efficacy, replication, and biodistribution of oncolytic Ad vectors following administration in hamsters. In addition, we describe how to assess replication in normal tissues such as the lungs and give helpful tips on handling, anesthesia, and general care of Syrian hamsters.

JE Nakayama/JE SA14-14-2 virus structural region intertypic viruses: biological properties in the mouse model of neuroinvasive disease

A molecular clone of Japanese encephalitis (JE) virus Nakayama strain was used to create intertypic viruses containing either the 5'-C-prM-E or the prM-E region of the attenuated JE SA14-14-2 virus in the JE Nakayama background. These two intertypic JE viruses, JE-X/5'CprME(S) and JE-X/prME(S), respectively, generally resembled the parental JE virus in cell culture properties. Similar to virus derived from the JE Nakayama molecular clone (JE-XJN), JE-X/prME(S) was highly neuroinvasive and neurovirulent for young adult mice, whereas JE-X/5'CprME(S) was attenuated for neuroinvasiveness and only partially attenuated for neurovirulence. Immunization of young mice with JE-X/5'CprME(S) virus elicited neutralizing antibodies against JE Nakayama virus and conferred protection against encephalitis following challenge with JE Nakayama virus. The sequence of the JE-X/5'CprME(S) virus differed from that of JE-X/prME(S) virus at two nucleotides in the 5' UTR, 3 amino acid positions in the capsid protein, 4 positions in the prM protein and 1 in the envelope protein. For JE-X/prME(S) virus, the 4 differences in prM and the single substitution in the envelope represented reversions to the sequence of JE Nakayama virus. Overall, this study reveals that molecular determinants associated with the prM-E region of the attenuated JE SA14-14-2 virus are insufficient by themselves to confer an attenuation phenotype upon JE Nakayama virus. This suggests a role for determinants in the 5' UTR and/or the capsid protein of the JE SA 14-14-2 virus genome in influencing the virulence properties of the JE Nakayama virus in the mouse model.

Targeting Interferon-α Increases Antitumor Efficacy and Reduces Hepatotoxicity of E1A-mutated Spread-enhanced Oncolytic Adenovirus

Novel approaches are needed to improve the antitumor potency and to increase the cancer specificity of oncolytic adenoviruses (Ad). We hypothesized that the combination of interferon-alpha (IFN-alpha) expression with a specific mutation in the e1a gene of Ad could target vector replication to genetic defects in the IFN-alpha pathway resulting in both improved antitumor efficacy and reduced toxicity. The conditionally replicative Ad vector KD3-IFN carries the dl1101/1107 mutation in the e1a gene that eliminates binding of E1A proteins to p300/CBP and pRb. KD3-IFN expresses human IFN-alpha in concurrence with vector replication and overexpresses the adenovirus death protein (ADP; E3-11.6K). The antitumor activity of KD3-IFN was significantly higher than that of a control vector in established human hepatocellular carcinoma tumors in immunodeficient mice and in hamster kidney cancer tumors in immunocompetent Syrian hamsters. The dl1101/1107 mutation rendered Ad replication sensitive to the antiviral effect of IFN-alpha in normal as opposed to cancer cells. These results translated to reduced vector toxicity upon systemic administration to C57BL/6 mice. The combination of Ad oncolysis, ADP overexpression, and IFN-alpha-mediated immunotherapy represents a three-pronged approach for increasing the anticancer efficacy of replicative Ads. Exploiting the dl1101/1107 mutation provides a mechanism for additional selectivity of IFN-alpha-expressing replication-competent Ads.

Chimeric Japanese encephalitis virus/dengue 2 virus infectious clone: biological properties, immunogenicity and protection against dengue encephalitis in mice

A molecular clone of Japanese encephalitis virus (JE virus) was derived from the JE virus Nakayama strain and used to produce infectious JE virus in cell culture. The engineered JE virus resembled the parental JE virus in cell-culture properties and was related closely to other JE virus strains based on nucleotide sequence analysis. The JE virus clone was used as a genetic background for construction of a chimeric virus containing the structural proteins prM and E of Dengue virus, serotype 2. The chimeric JE/dengue 2 virus generated authentic dengue 2 structural proteins as assessed by immunoassays for the dengue E protein. It exhibited a small plaque size and less efficient growth in various cell lines than the parental JE virus. JE/dengue 2 virus was non-neuroinvasive for young adult mice, but displayed partial neurovirulence at doses up to 4 log p.f.u. given intracerebrally. Immunization of 3-week-old mice with JE/dengue 2 virus yielded neutralizing-antibody titres against dengue 2 virus and conferred protection against dengue encephalitis caused by neuroadapted dengue 2 virus. A rise in post-challenge neutralizing-antibody titres against dengue 2 virus in surviving mice suggests that immunization is associated with establishment of a memory antibody response in this model. This study demonstrates the capacity of JE virus to serve as a vector for expression of heterologous flavivirus structural proteins. Similar to previous studies with other chimeric flaviviruses, this approach may be useful as a genetic system for engineering experimental vaccines against Dengue virus and other medically important flaviviruses.

Syrian hamster as a permissive immunocompetent animal model for the study of oncolytic adenovirus vectors

Oncolytic adenoviruses represent an innovative approach to cancer therapy. These vectors are typically evaluated in immunodeficient mice with human xenograft tumors. However, in addition to being immunodeficient, this model is limited because normal and cancerous mouse tissues are poorly permissive for human adenovirus replication. This prompted us to search for a model that more accurately reflects the use of oncolytic adenoviruses in cancer patients. To this end, we developed a novel Syrian hamster model that is both immunocompetent and replication-permissive. We found that human adenovirus replicates well in Syrian hamster cell lines and confirmed replication in the lungs. Oncolytic adenovirus injection showed efficacy in three different hamster tumor models. Furthermore, i.t. oncolytic adenovirus injection resulted in suppression of primary and metastatic lesions, i.t. replication and necrosis, vector entrance into the bloodstream, replication in the liver and lungs, and anti-adenovirus antibody induction. Our findings show that the Syrian hamster is a promising immunocompetent model that is permissive to human adenovirus replication in tumors as well as normal tissues. Therefore, the Syrian hamster model may become a valuable tool for the field of oncolytic adenovirus vectors in which vector safety and efficacy can be evaluated.

Oncolytic adenovirus that overproduces ADP and replicates selectively in tumors due to hTERT promoter-regulated E4 gene expression

We have constructed a novel oncolytic adenovirus (Ad) vector, named VRX-011, in which the replication of the vector is targeted to cancer cells by the replacement of the wild-type Ad E4 promoter with the human telomerase reverse transcriptase (hTERT) promoter. Genes in the Ad E4 transcription unit are essential for Ad replication; therefore, VRX-011 will grow efficiently only in cells in which the hTERT promoter is active, that is, in a wide range of cancer and immortalized cells but not in most somatic cells. Consistent with these expectations, VRX-011 replicated efficiently in all cancer cell lines examined, while its growth was restricted in various primary and normal cells. VRX-011 overexpresses ADP (also known as E3-11.6K), an Ad protein required for efficient cell lysis and release of virions from cells at late stages of infection. This overexpression enhances cell-to-cell spread and could significantly increase antitumor efficacy. In a xenograft model in nude mice, both intratumoral and intravenous administration of VRX-011 effectively suppressed the growth of subcutaneous Hep3B human liver tumors. Also, intravenous delivery of VRX-011 greatly reduced the number and size of A549 human lung cancer cell nodules in a disseminated lung tumor model in nude mice. Importantly, tail vein administration of different doses of VRX-011 in C57BL/6 mice showed minimal liver toxicity. Considering its broad range of lytic replication in cancer cells, its attenuated phenotype in primary cells, its efficacy in suppressing xenografts, and its low toxicity in mouse liver, VRX-011 is a promising candidate for further evaluation as an anticancer therapeutic.

Adenovirus immunoregulatory E3 proteins prolong transplants of human cells in immunocompetent mice

The majority of proteins encoded in the early 3 (E3) region of human subgroup C adenoviruses function to modulate the host immune response. For example, gp19K, one of these E3 proteins, prevents the major histocompatibility complex type I (MHC-I) from presenting viral antigens on the surface of the infected cell. Other E3 proteins, such as the RID and 14.7K proteins, counteract the effector phase of the cellular immune response. In order to study further the effects of these proteins, we constructed an E1-/E3- adenovirus vector, Ad/E3, that contains all the E3 genes with the exception of the cytolytic adp gene, inserted into the deleted E1 region. The transcription of the E3 genes in this vector is driven by a CMV promoter in place of the native E3 promoter. Ad/E3 expressed close to wild-type adenovirus levels of all E3 proteins, and these proteins appear to function normally in cell culture. For example, in Ad/E3-infected cells, surface expression of MHC-I was down-regulated, as was cell surface display of death receptors Fas and TRAIL Receptor 1. A human cell line of lung origin (A549), which was rapidly rejected after transplantation into C57BL/6 mice, was protected for an extended time from the host immune response after infection with an Ad/E3, and went through a number of divisions in immunocompetent mice. These latter results indicate that the E3 proteins protect cells from destruction by the immune system.

Cotton Rat Tumor Model for the Evaluation of Oncolytic Adenoviruses

Oncolytic human adenovirus (Ad) vectors exert their antitumor effect by replicating in and lysing tumor cells. These vectors are commonly evaluated in immunodeficient mice bearing human tumor xenografts. However, this model suffers because the mice are immunodeficient and are not permissive for human Ads. We have developed a cotton rat model to test the selectivity, immunogenicity, and efficacy of oncolytic Ad vectors. The cotton rat is a rodent species that is semipermissive for human Ads. We show that the cotton cancer rat cell line LCRT supports the replication of human Ad in tissue culture and that the cells are destroyed on virus replication. When injected subcutaneously, LCRT cells formed tumors in immunocompetent cotton rats, and the growth of these tumors was delayed by the injection of an oncolytic Ad vector. Replication of the Ad vector in the tumor was demonstrated by sampling tumor tissue and isolating infectious virus particles at various times after intratumoral injection of the virus. We propose that the cotton rat can be used as an animal model to evaluate oncolytic Ad vectors.

Adenovirus E3-6.7K protein is required in conjunction with the E3-RID protein complex for the internalization and degradation of TRAIL receptor 2

Adenoviruses (Ads) encode several proteins within the early region 3 (E3) transcription unit that help protect infected cells from elimination by the immune system. Among these immunomodulatory proteins, the receptor internalization and degradation (RID) protein complex, which is composed of the RIDalpha (formerly E3-10.4K) and RIDbeta (formerly E3-14.5K) subunits, stimulates the internalization and degradation of certain members of the tumor necrosis factor (TNF) receptor superfamily, thus blocking apoptosis initiated by Fas and TNF-related apoptosis-inducing ligand (TRAIL). The experiments reported here show that TRAIL receptor 2 (TR2) is cleared from the cell surface in Ad-infected cells. Virus mutants containing deletions that span E3 were used to show that the RID and E3-6.7K proteins are both necessary for the internalization and degradation of TR2, whereas only the RID protein is required for TRAIL receptor 1 downregulation. In addition, replication-defective Ad vectors that express individual E3 proteins were used to establish that the RID and E3-6.7K proteins are sufficient to clear TR2. These data demonstrate that E3-6.7K is an important component of the antiapoptosis arsenal encoded by the E3 transcription unit of subgroup C Ads.

Experimental infections of humans with wild-type adenoviruses and with replication-competent adenovirus vectors: replication, safety, and transmission

Replication-competent (RC) adenoviruses (Ads) are increasingly being developed as oncolytic vectors and as vehicles for delivering vaccine antigens. Although the safety of such vectors in humans is of paramount importance, these vectors pose additional special concerns. Specifically, the prospect of causing Ad-mediated disease in the patient, the amount and sites of Ad replication, the possibility of virus shedding leading to unintended transmission to patient contacts, and the potential for persistence in the inoculated individual must be evaluated. Previous experience with administration of wild-type and RC recombinant Ads to humans may shed light on some of these issues. Experimental infections of humans with natural Ad isolates and RC recombinant vectors show that in adults Ads cause mild or no disease, particularly with Ad serotypes 2 and 5, the serotypes most often used to make recombinant constructs. Other studies show that Ad can replicate in experimentally infected persons, that in some situations Ads can be shed and transmitted to close contacts, and that there is evidence for persistent/latent Ad infection in naturally infected individuals. Overall, these studies indicate that Ads can be safely administered to humans for the treatment of cancer and as antigen delivery vehicles suggesting that the continued development of RC oncolytic and vaccine vectors should be pursued.

An oncolytic adenovirus vector combining enhanced cell-to-cell spreading, mediated by the ADP cytolytic protein, with selective replication in cancer cells with deregulated wnt signaling

We have constructed a novel oncolytic adenovirus (Ad) vector named VRX-009 that combines enhanced cell spread with tumor-specific replication. Enhanced spread, which could significantly increase antitumor efficacy, is mediated by overexpression of the Ad cytolytic protein named ADP (also known as E3-11.6K). Replication of VRX-009 is restricted to cells with a deregulated wnt signal transduction pathway by replacement of the wild-type Ad E4 promoter with a synthetic promoter consisting of five consensus binding sites for the T-cell factor transcription factor. Tumor-selective replication is indicated by several lines of evidence. VRX-009 expresses E4ORF3, a representative Ad E4 protein, only in colon cancer cell lines. Furthermore, VRX-009 replicates preferentially in colon cancer cell lines as evidenced by virus productivity 2 orders of magnitude higher in SW480 colon cancer cells than in A549 lung cancer cells. Replication in primary human bronchial epithelial cells and human umbilical vein endothelial cells was also significantly lower than in SW480 cells. When tested in human tumor xenografts in nude mice, VRX-009 effectively suppressed the growth of SW480 colon tumors but not of A549 lung tumors. VRX-009 may provide greater level of antitumor efficacy than standard oncolytic Ad vectors in tumors in which a defect in wnt signaling increases the level of nuclear beta-catenin.

Functions and mechanisms of action of the adenovirus E3 proteins

In the evolutionary battle between viruses and their hosts, viruses have armed themselves with weapons to defeat the host's attacks on infected cells. Various proteins encoded in the adenovirus (Ad) E3 transcription unit protect cells from killing mediated by cytotoxic T cells and death-inducing cytokines such as tumor necrosis factor (TNF), Fas ligand, and TNF-related apoptosis-inducing ligand (TRAIL). The viral protein E3-gp19 K blocks MHC class-I-restricted antigen presentation, which diminishes killing by cytotoxic T cells. The receptor internalization and degradation (RID) complex (formerly E3-10.4 K/14.5 K) stimulates the clearance from the cell surface and subsequent degradation of the receptors for Fas ligand and TRAIL, thereby preventing the action of these important immune mediators. RID also downmodulates the epidermal growth factor receptor (EGFR), although what role, if any, this function has in immune regulation is uncertain. In addition, RID antagonizes TNF-mediated apoptosis and inflammation through a mechanism that does not primarily involve receptor downregulation. E3-6.7 K functions together with RID in downregulating some TRAIL receptors and may block apoptosis independently of other E3 proteins. Furthermore, E3-14.7 K functions as a general inhibitor of TNF-mediated apoptosis and blocks TRAIL-induced apoptosis. Finally, after expending great effort to maintain cell viability during the early part of the virus replication cycle, Ads lyse the cell to allow efficient virus release and dissemination. To perform this task subgroup C Ads synthesize a protein late in infection named ADP (formerly E3-11.6 K) that is required for efficient virus release. This review focuses on recent experiments aimed at discovering the mechanism of action of these critically important viral proteins.

Distinct domains in the adenovirus E3 RIDalpha protein are required for degradation of Fas and the epidermal growth factor receptor

Adenovirus (Ad) types 2 and 5 encode at least five proteins within the E3 transcription unit that help the virus evade the immune system. Two such proteins, RIDalpha (formerly E3-10.4K) and RIDbeta (formerly E3-14.5K), form the RID (receptor internalization and degradation) complex (formerly E3-10.4K/14.5K). RID mediates clearance from the cell surface and lysosomal degradation of a number of important members in the tumor necrosis factor receptor (TNFR) superfamily and the receptor tyrosine kinase receptor family. Affected receptors include Fas, TRAIL (TNF-related apoptosis-inducing ligand) receptor 1 (TR1), TR2, and epidermal growth factor receptor (EGFR). Degradation of Fas and TRAIL receptors protects Ad-infected cells from apoptosis. To investigate the mechanism of action of RIDalpha, 14 mutant RIDalpha proteins, each containing a three- to five-amino-acid deletion, were constructed and then expressed from the E3 region of a replication-competent recombinant Ad in the same context as wild-type RIDalpha. Each mutant protein was characterized with regard to five physical properties associated with wild-type RIDalpha, namely, protein stability, proteolytic cleavage, insertion into the membrane, complex formation with RIDbeta, and transport to the cell surface. Additionally, the mutant proteins were tested for their ability to mediate internalization and degradation of EGFR and Fas and to protect cells from Fas-mediated apoptosis. The majority of mutant RIDalpha proteins (8 out of 14) were physically similar to wild-type RIDalpha. With regard to functional characteristics, the cytoplasmic domain of RIDalpha is largely unimportant for receptor internalization and degradation and the extracellular domain of RIDalpha is important for down-regulation of EGFR but not Fas.

Transforming growth factor beta1 receptor II is downregulated by E1A in adenovirus-infected cells

Transforming growth factor beta1 (TGF-beta1) signaling is compromised in many tumors, thereby allowing the tumor to escape the growth-inhibitory and proapoptotic activities of the cytokine. Human adenoviruses interfere with a number of cellular pathways involved in cell cycle regulation and apoptosis, initially placing the cell in a "tumor-like" state by forcing quiescent cells into the cell cycle and also inhibiting apoptosis. We report that adenovirus-infected cells resemble tumor cells in that TGF-beta1 signaling is inhibited. The levels of TGF-beta1 receptor II (TbetaRII) in adenovirus-infected cells were decreased, and this decrease was mapped, by using virus mutants, to the E1A gene and to amino acids 2 to 36 and the C-terminal binding protein binding site in the E1A protein. The decrease in the TbetaRII protein was accompanied by a decrease in TbetaRII mRNA. The decrease in TbetaRII protein levels in adenovirus-infected cells was greater than the decrease in TbetaRII mRNA, suggesting that downregulation of the TbetaRII protein may occur through more than one mechanism. Surprisingly in this context, the half-lives of the TbetaRII protein in infected and uninfected cells were similar. TGF-beta1 signaling was compromised in cells infected with wild-type adenovirus, as measured with 3TP-lux, a TGF-beta-sensitive reporter plasmid expressing luciferase. Adenovirus mutants deficient in TbetaRII downregulation did not inhibit TGF-beta1 signaling. TGF-beta1 pretreatment reduced the relative abundance of adenovirus structural proteins in infected cells, an effect that was potentiated when cells were infected with mutants incapable of modulating the TGF-beta signaling pathway. These results raise the possibility that inhibition of TGF-beta signaling by E1A is a means by which adenovirus counters the antiviral defenses of the host.

Adenovirus ADP protein (E3-11.6K), which is required for efficient cell lysis and virus release, interacts with human MAD2B

The human subgroup C adenovirus (Ad) protein named adenovirus death protein (ADP) (previously named E3-11.6K) is synthesized at very late stages of infection when it mediates efficient lysis of cells and release of adenovirus to infect other cells. ADP is an integral membrane N-linked, O-linked palmitoylated glycoprotein of 101 amino acids (aa) that localizes to the nuclear membrane, endoplasmic reticulum (ER), and Golgi. It has a single membrane spanning region (roughly aa 40-60) and is oriented with aa 1-40 in the lumen and aa 61-101 in the nucleoplasm and cytoplasm. Using aa 61-101 of Ad2 ADP as bait in a yeast two-hybrid screen, we isolated a cDNA for a 211-aa protein that initially was not in the database but has now been published by others with the names human MAD2B, MAD2L2, and REV7. ADP binds strongly to human MAD2B not only in yeast but also in GST pull-down experiments and in coimmunoprecipitations of ADP and MAD2B synthesized in vitro or in vivo. ADP mutants with deletions throughout the bait region do not interact with human MAD2B, whereas a Pro69Pro70 to Ala69Ala70 mutant in the "basic-proline" domain of ADP does interact. Northern blot analyses indicate that human MAD2B is expressed ubiquitously. Human MAD2B is about 25% identical to human MAD2, a spindle assembly checkpoint protein. Two human A549 cell lines were made that constitutively overexpress MAD2B. Wild-type adenovirus lyses these cells significantly more slowly than it lyses parental A549 cells, raising the possibility that ADP and MAD2B act in opposition and suggesting that the ADP-MAD2B interaction is biologically relevant.

Mutations within the ADP (E3-11.6K) protein alter processing and localization of ADP and the kinetics of cell lysis of adenovirus-infected cells

ADP (also known as E3-11.6K protein) is synthesized abundantly in late adenovirus infection and is required for efficient lysis of infected cells and release of viral progeny at the end of the viral replication cycle. ADP is a type III bitopic N(endo)C(exo) nuclear membrane and Golgi glycoprotein that is produced at high levels in late adenovirus infection (>24 h postinfection). We show pulse-chase and other studies indicating that ADP undergoes a complex process of N- and O-linked glycosylation and proteolytic cleavage. In order to further characterize ADP, a series of 23 deletion and point mutations has been constructed in the adenovirus serotype 2 adp gene and then built into a wild-type adenovirus background. These mutants were analyzed for processing and intracellular localization of ADP. Mutation of the single predicted N glycosylation site eliminated N glycosylation. Deletion of a region in ADP rich in serine and threonine residues reduced O glycosylation. In general, mutations within the lumenal domain of ADP resulted in lower protein stability; immunofluorescence assays indicated that these ADPs were primarily present in the Golgi apparatus. Viruses with mutations within the cytoplasmic-nucleoplasmic domain of ADP showed normal glycosylation patterns and protein abundance for ADP, but the protein was often found throughout cellular membranes rather than being localized specifically to the nuclear membrane and Golgi apparatus. The ADP virus mutants were analyzed by cell viability assays to determine the kinetics of cell lysis following infection of human A549 cells. In general, viruses with mutations within the lumenal domain of ADP display greatly reduced efficiencies of cell lysis. Viruses with large deletions in the cytoplasmic-nucleoplasmic domain of ADP retain much of their ability to lyse infected cells.

Radiation increases the activity of oncolytic adenovirus cancer gene therapy vectors that overexpress the ADP (E3-11.6K) protein

We have described three potential adenovirus type 5 (Ad5)-based replication-competent cancer gene therapy vectors named KD1, KD3, and VRX-007. All three vectors overexpress an Ad5 protein named Adenovirus Death Protein (ADP, also named E3-11.6 K protein). ADP is required for efficient lysis of Ad5-infected cells and spread of virus from cell to cell, and thus its overexpression increases the oncolytic activity of the vectors. KD1 and KD3 contain mutations in the Ad5 E1A gene that knock out binding of the E1A proteins to cellular p300/CBP and pRB; these mutations allow KD1 and KD3 to grow well in cancer cells but not in normal cells. VRX-007 has wild-type E1A. Here we report that radiation increases the oncolytic activity of KD1, KD3, and VRX-007. This increased activity was observed in cultured cells, and it was not because of radiation-induced replication of the vectors. The combination of radiation plus KD3 suppressed the growth of A549 lung adenocarcinoma xenografts in nude mice more efficiently than radiation alone or KD3 alone. The combination of ADP-overexpressing vectors and radiation may have potential in treating cancer.

Overexpression of the ADP (E3-11.6K) protein increases cell lysis and spread of adenovirus

Adenoviruses replicate in the nucleus and induce lytic cell death. We have shown previously that efficient cell lysis and release of adenovirus from infected cells requires an 11.6-kDa protein named Adenovirus Death Protein (ADP). The adp gene is located in the early E3 transcription unit, but the gene is expressed primarily at very late stages of infection. The putative function of ADP was discerned previously from the use of virus mutants that lack functional ADP. Here we describe two adenovirus mutants, named VRX-006 and VRX-007, that overexpress ADP. VRX-006 lacks all other genes in the E3 region, and VRX-007 lacks all other E3 genes except 12.5K. VRX-006 and VRX-007 display the phenotype predicted by the proposed function for ADP: they produce early cytopathic effect, early cell lysis, large plaques, and increased cell-to-cell spread. They grow as well in cultured cells as does adenovirus type 5. These results are consistent with the conclusion that ADP functions in adenovirus infections to promote virus release from cells at the culmination of infection.

Adenovirus RIDbeta subunit contains a tyrosine residue that is critical for RID-mediated receptor internalization and inhibition of Fas- and TRAIL-induced apoptosis

The adenovirus-encoded receptor internalization and degradation (RID) protein (previously named E3-10.4K/14.5K), which is composed of RIDalpha and RIDbeta subunits, down-regulates a number of cell surface receptors in the tumor necrosis factor (TNF) receptor superfamily, namely Fas, TRAIL receptor 1, and TRAIL receptor 2. Down-regulation of these "death" receptors protects adenovirus-infected cells from apoptosis induced by the death receptor ligands Fas ligand and TRAIL. RID also down-regulates certain tyrosine kinase cell surface receptors, especially the epidermal growth factor receptor (EGFR). RID-mediated Fas and EGFR down-regulation occurs via endocytosis of the receptors into endosomes followed by transport to and degradation within lysosomes. However, the molecular interactions underlying this function of RID are unknown. To investigate the molecular determinants of RIDbeta that are involved in receptor down-regulation, mutations within the cytoplasmic tail of RIDbeta were constructed and the mutant proteins were analyzed for their capacity to internalize and degrade Fas and EGFR and to protect cells from death receptor ligand-induced apoptosis. The results demonstrated the critical nature of a tyrosine residue near the RIDbeta C terminus; mutation of this residue to alanine abolished RID function. Mutating the tyrosine to phenylalanine did not abolish the function of RID, arguing that phosphorylation of the tyrosine is not required for function. These data suggest that this tyrosine residue forms part of a tyrosine-based sorting signal (Yxxphi). Additional mutations that target another potential sorting motif and several possible protein-protein interaction motifs had no discernible effect on RID function. It was also demonstrated that mutation of serine 116 to alanine eliminated phosphorylation of RIDbeta but did not affect any of the functions of RID that were examined. These results suggest a model in which the tyrosine-based sorting signal in RID plays a role in RID's ability to down-regulate receptors.