Adenovirus expressing nc886, an anti-interferon and anti-apoptotic non-coding RNA, is an improved gene delivery vector

Recombinant adenovirus (rAdV) vector is the most promising vehicle to deliver an exogenous gene into target cells and is preferred for gene therapy. Exogenous gene expression from rAdV is often too inefficient to induce phenotypic changes and the amount of administered rAdV must be very high to achieve a therapeutic dose. However, it is often hampered because a high dose of rAdV is likely to induce cytotoxicity by activating immune responses. nc886, a 102-nucleotide non-coding RNA that is transcribed by RNA polymerase III, acts as an immune suppressor and a facilitator of AdV entry into the nucleus. Therefore, in this study, we have constructed an rAdV expressing nc886 (AdV:nc886) to explore whether AdV:nc886 overcomes the aforementioned drawbacks of conventional rAdV vectors. When infected into mouse cell lines and mice, AdV:nc886 expresses a sufficient amount of nc886, which suppresses the induction of interferon-stimulated genes and apoptotic pathways triggered by AdV infection. As a result, AdV:nc886 is less cytotoxic and produces more rAdV-delivered gene products, compared with the parental rAdV vector lacking nc886. In conclusion, this study demonstrates that the nc886-expressing rAdV could become a superior gene delivery vehicle with greater safety and higher efficiency for in vivo gene therapy.

Adenoviral Gene Therapy Vectors in Clinical Use-Basic Aspects with a Special Reference to Replication-Competent Adenovirus Formation and Its Impact on Clinical Safety

Adenoviral vectors are commonly used in clinical gene therapy. Apart from oncolytic adenoviruses, vector replication is highly undesired as it may pose a safety risk for the treated patient. Thus, careful monitoring for the formation of replication-competent adenoviruses (RCA) during vector manufacturing is required. To render adenoviruses replication deficient, their genomic E1 region is deleted. However, it has been known for a long time that during their propagation, some viruses will regain their replication capability by recombination in production cells, most commonly HEK293. Recently developed RCA assays have revealed that many clinical batches contain more RCA than previously assumed and allowed by regulatory authorities. The clinical significance of the higher RCA content has yet to be thoroughly evaluated. In this review, we summarize the biology of adenovirus vectors, their manufacturing methods, and the origins of RCA formed during HEK293-based vector production. Lastly, we share our experience using minimally RCA-positive serotype 5 adenoviral vectors based on observations from our clinical cardiovascular gene therapy studies.

Cell transformation by the adenovirus oncogenes E1 and E4

Extensive studies on viral-mediated oncogenic transformation by human adenoviruses have revealed much of our current understanding on the molecular mechanisms that are involved in the process. To date, these studies have shown that cell transformation is a multistep process regulated by the cooperation of several adenoviral gene products encoded in the early regions 1 (E1) and 4 (E4). Early region 1A immortalizes primary rodent cells, whereas co-expression of early region protein 1B induces full manifestation of the transformed phenotype. Beside E1 proteins, also some E4 proteins have partial transforming activities through regulating many cellular pathways. Here, we summarize recent data of how adenoviral oncoproteins may contribute to viral transformation and discuss the challenge of pinpointing the underlying mechanisms.

Interregional Coevolution Analysis Revealing Functional and Structural Interrelatedness between Different Genomic Regions in Human Mastadenovirus D

Human mastadenovirus D (HAdV-D) is exceptionally rich in type among the seven human adenovirus species. This feature is attributed to frequent intertypic recombination events that have reshuffled orthologous genomic regions between different HAdV-D types. However, this trend appears to be paradoxical, as it has been demonstrated that the replacement of some of the interacting proteins for a specific function with other orthologues causes malfunction, indicating that intertypic recombination events may be deleterious. In order to understand why the paradoxical trend has been possible in HAdV-D evolution, we conducted an interregional coevolution analysis between different genomic regions of 45 different HAdV-D types and found that ca. 70% of the genome has coevolved, even though these are fragmented into several pieces via short intertypic recombination hot spot regions. Since it is statistically and biologically unlikely that all of the coevolving fragments have synchronously recombined between different genomes, it is probable that these regions have stayed in their original genomes during evolution as a platform for frequent intertypic recombination events in limited regions. It is also unlikely that the same genomic regions have remained almost untouched during frequent recombination events, independently, in all different types, by chance. In addition, the coevolving regions contain the coding regions of physically interacting proteins for important functions. Therefore, the coevolution of these regions should be attributed at least in part to natural selection due to common biological constraints operating on all types, including protein-protein interactions for essential functions. Our results predict additional unknown protein interactions.

IMPORTANCE

Human mastadenovirus D, an exceptionally type-rich human adenovirus species and causative agent of different diseases in a wide variety of tissues, including that of ocular region and digestive tract, as well as an opportunistic infection in immunocompromised patients, is known to have highly diverged through frequent intertypic recombination events; however, it has also been demonstrated that the replacement of a component protein of a multiprotein system with a homologous protein causes malfunction. The present study solved this apparent paradox by looking at which genomic parts have coevolved using a newly developed method. The results revealed that intertypic recombination events have occurred in limited genomic regions and been avoided in the genomic regions encoding proteins that physically interact for a given function. This approach detects purifying selection against recombination events causing the replacement of partial components of multiprotein systems and therefore predicts physical and functional interactions between different proteins and/or genomic elements.

Evaluation of apoptogenic adenovirus type 5 oncolytic vectors in a Syrian hamster head and neck cancer model

Human adenovirus (HAdV) vectors are intensely investigated for virotherapy of a wide variety of human cancers. Here, we have evaluated the effect of two apoptogenic HAdV5 vectors in an immunocompetent Syrian hamster animal model of head and neck cancer. We established two cell lines of hamster cheek pouch squamous cell carcinomas, induced by treatment with 9, 10-dimethyl-1, 2-benzanthracene (DMBA). These cell lines, when infected with HAdV5 mutants lp11w and lp11w/Δ55K (which are defective in the expression of either E1B-19K alone or both E1B-19K and E1B-55K proteins) exhibited enhanced apoptotic and cytotoxic responses. The cheek pouch tumor cells transplanted either subcutaneously at the flanks or in the cheek pouches of hamsters readily formed tumors. Intra-tumoral administration of HAdV5 E1B mutants efficiently suppressed the growth of tumors at both sites. Histological examination of orthotopic tumors revealed reduced vascularity and the expression of the viral fiber antigen in virus-administered cheek pouch tumors. These tumors also exhibited increased caspase-3 levels, suggesting virus-induced apoptosis may contribute to tumor growth suppression. Our results suggest that the apoptogenic HAdV5 vectors may have utility for the treatment of human head and neck cancers.

Intertypic modular exchanges of genomic segments by homologous recombination at universally conserved segments in human adenovirus species D

Human adenovirus species D (HAdV-D), which is composed of clinically and epidemiologically important pathogens worldwide, contains more taxonomic "types" than any other species of the genus Mastadenovirus, although the mechanisms accounting for the high level of diversity remain to be disclosed. Recent studies of known and new types of HAdV-D have indicated that intertypic recombination between distant types contributes to the increasing diversity of the species. However, such findings raise the question as to how homologous recombination events occur between diversified types since homologous recombination is suppressed as nucleotide sequences diverge. In order to address this question, we investigated the distribution of the recombination boundaries in comparison with the landscape of intergenomic sequence conservation assessed according to the synonymous substitution rate (dS). The results revealed that specific genomic segments are conserved between even the most distantly related genomes; we call these segments "universally conserved segments" (UCSs). These findings suggest that UCSs facilitate homologous recombination, resulting in intergenomic segmental exchanges of UCS-flanking genomic regions as recombination modules. With the aid of such a mechanism, the haploid genomes of HAdV-Ds may have been reshuffled, resulting in chimeric genomes out of diversified repertoires in the HAdV-D population analogous to the MHC region reshuffled via crossing over in vertebrates. In addition, some HAdVs with chimeric genomes may have had the opportunity to avoid host immune responses thereby causing epidemics.

Control of human adenovirus type 5 gene expression by cellular Daxx/ATRX chromatin-associated complexes

Death domain-associated protein (Daxx) cooperates with X-linked α-thalassaemia retardation syndrome protein (ATRX), a putative member of the sucrose non-fermentable 2 family of ATP-dependent chromatin-remodelling proteins, acting as the core ATPase subunit in this complex, whereas Daxx is the targeting factor, leading to histone deacetylase recruitment, H3.3 deposition and transcriptional repression of cellular promoters. Despite recent findings on the fundamental importance of chromatin modification in host-cell gene regulation, it remains unclear whether adenovirus type 5 (Ad5) transcription is regulated by cellular chromatin remodelling to allow efficient virus gene expression. Here, we focus on the repressive role of the Daxx/ATRX complex during Ad5 replication, which depends on intact protein-protein interaction, as negative regulation could be relieved with a Daxx mutant that is unable to interact with ATRX. To ensure efficient viral replication, Ad5 E1B-55K protein inhibits Daxx and targets ATRX for proteasomal degradation in cooperation with early region 4 open reading frame protein 6 and cellular components of a cullin-dependent E3-ubiquitin ligase. Our studies illustrate the importance and diversity of viral factors antagonizing Daxx/ATRX-mediated repression of viral gene expression and shed new light on the modulation of cellular chromatin remodelling factors by Ad5. We show for the first time that cellular Daxx/ATRX chromatin remodelling complexes play essential roles in Ad gene expression and illustrate the importance of early viral proteins to counteract cellular chromatin remodelling.

Adenovirus type 5 early region 1B 55K oncoprotein-dependent degradation of cellular factor Daxx is required for efficient transformation of primary rodent cells

Early region 1B 55K (E1B-55K) from adenovirus type 5 (Ad5) is a multifunctional regulator of lytic infection and contributes in vitro to complete cell transformation of primary rodent cells in combination with Ad5 E1A. Inhibition of p53 activated transcription plays a key role in processes by which E1B-55K executes its oncogenic potential. Nevertheless, additional functions of E1B-55K or further protein interactions with cellular factors of DNA repair, transcription, and apoptosis, including Mre11, PML, and Daxx, may also contribute to the transformation process. In line with previous results, we performed mutational analysis to define a Daxx interaction motif within the E1B-55K polypeptide. The results from these studies showed that E1B-55K/Daxx binding is not required for inhibition of p53-mediated transactivation or binding and degradation of cellular factors (p53/Mre11). Surprisingly, these mutants lost the ability to degrade Daxx and showed reduced transforming potential in primary rodent cells. In addition, we observed that E1B-55K lacking the SUMO-1 conjugation site (SCS/K104R) was sufficient for Daxx interaction but no longer capable of E1B-55K-dependent proteasomal degradation of the cellular factor Daxx. These results, together with the observation that E1B-55K SUMOylation is required for efficient transformation, provides evidence for the idea that SUMO-1-conjugated E1B-55K-mediated degradation of Daxx plays a key role in adenoviral oncogenic transformation. We assume that the viral protein contributes to cell transformation through the modulation of Daxx-dependent pathways. This further substantiates the assumption that further mechanisms for efficient transformation of primary cells can be separated from functions required for the inhibition of p53-stimulated transcription.

Down-regulation of multiple cell survival proteins in head and neck cancer cells by an apoptogenic mutant of adenovirus type 5

Head and neck squamous cell carcinomas (HNSCC) are one of the leading causes of cancer deaths world wide. Up-regulation of the epidermal growth factor receptor (EGFR) and BCL-2 family anti-apoptosis proteins in these cancers is linked to aggressive tumor growth, metastasis and chemoresistance. Infection of two HNSCC cell lines, SCC25 and CAL27 by an Ad5 mutant (lp11w) defective in coding for the viral anti-apoptosis protein, E1B-19K efficiently induced apoptotic cell death. In cells infected with lp11w there was a dramatic down-regulation of EGFR by apoptosis-dependent and -independent mechanisms. The levels of the anti-apoptotic proteins BCL-2, BCL-xL and MCL-1 were also down-regulated in lp11w-infected cells compared to uninfected or Ad5-RM infected cells. Infection with lp11w also enhanced sensitivity of the HNSCC cells to the chemotherapeutic drug cisplatin. Our results suggest that adenoviral vectors defective in E1B-19K would be valuable for efficient down-regulation of cell survival proteins and EGFR in epithelial cancers and could be exploited as oncolytic agents to treat HNSCCs.

Suppression of FasL expression in tumor cells and preventing tumor necrosis factor-induced apoptosis by adenovirus 14.7K is an effective escape mechanism for immune cells

To elucidate if the Fas/FasL signal pathway participates in the immune escape of tumor cells, and if contemporary Fas/FasL and tumor necrosis factor (TNF))-induced apoptosis is better for immune cell survival than just blocking Fas/FasL-induced apoptotic signal. FasL expression in mouse H22 hepatocellular cancer cells was suppressed by the siRNA technique. The wild-type Ad5 14.7K gene was amplified by polymerase chain reaction and transduced into Jurkat T-cells. Apoptosis of target Jurkat cells was detected by flow cytometry. TNF-alpha in the culture supernatant of H22 cells by ELISA was seen. FasL and 14.7K gene expression in stably transfected or transduced clones were determined by Western blotting. As a result, FasL expression in H22 cells was down-regulated after stable transfection with a plasmid encoding antisense FasL cDNA. Down-regulation of FasL expression in H22 cells had no effect on tumor growth in vitro. There was an apparent decrease in the number of apoptotic Jurkat T-cells after coculture with transfected H22 cells, relative to coculture with FasL-expressing untransfected cells. Compared with untransduced Jurkat cells, apoptotic rates in 14.7K-transduced Jurkat cells were significantly reduced in three different E/T ratios (P < 0.01), respectively. We conclude that Fas/FasL signal pathway participates in the immune escape of tumor cells by inducing immune cells apoptosis. Reducing the expression of FasL in tumor cells can decrease the apoptotic rate of immune cells, further blocking the apoptotic signal pathway of immune cells by preventing TNF-induced apoptosis can increase the survival of immune cells.

Evidence for involvement of BH3-only proapoptotic members in adenovirus-induced apoptosis

Mammalian cells infected with human adenoviruses (Ads) undergo an apoptotic response as a result of expression of the viral E1A proteins, and this process is suppressed by the viral E1B-19K protein. The intermediary steps in the Ad-induced apoptosis pathway are not fully resolved. The apical step in the canonical mammalian apoptosis pathway involves functional activation of one or more of the BH3-only BCL-2 family proapoptotic proteins. Previous reports have suggested that Ad-induced apoptosis may be initiated at checkpoints downstream of the BH3-only proteins. Here, we undertook genetic and biochemical studies to determine the roles of BH3-only proteins in Ad-induced apoptosis. We examined the activities of the cellular antiapoptosis protein BCL-xL and its mutants expressed from the E1B region of the Ad5 genome. Our results showed efficient suppression of Ad-induced apoptosis by a BCL-xL mutant (mt1) deficient in interaction with multidomain proapoptotic proteins BAX and BAK but proficient in interaction with BH3-only proteins, suggesting a role for BH3-only proteins in the initiation of Ad-induced apoptosis. Further, the antiapoptotic activity of BCL-xL mt1 in Ad-infected cells was observed in spite of BAK activation as a consequence of MCL-1 degradation. Analysis of the mRNA levels of various BH3-only members by reverse transcription-PCR revealed prominent activation of the Bik gene. Further, the BIK protein was also modified into an apoptotically enhanced phosphorylated form during the viral infection. In addition to BIK, enhanced level of BIM was observed in Ad-infected cells. Between the two major E1A proteins coded by the 12S and 13S mRNAs, the 13S product appeared to contribute to the activation of these BH3-only members and apoptosis during viral infection. Depletion of BIK by the use of small interfering RNA reduced the level of Ad-induced apoptosis. Our results are consistent with a model that activation of the BH3-only members may initiate Ad-induced apoptosis.

Genetic identification of adenovirus type 5 genes that influence viral spread

The mechanisms that control cell-to-cell spread of human adenoviruses (Ad) are not well understood. Two early viral proteins, E1B-19K and E3-ADP, appear to have opposing effects since viral mutants that are individually deficient in E1B-19K produce large plaques (G. Chinnadurai, Cell 33:759-766, 1983), while mutants deficient in E3-ADP produce small plaques (A. E. Tollefson et al., J. Virol. 70:2296-2306, 1996) on infected cell monolayers. We have used a genetic strategy to identify different viral genes that influence adenovirus type 5 (Ad5) spread in an epithelial cancer cell line. An Ad5 mutant (dl327; lacking most of the E3 region) with the restricted-spread (small-plaque) phenotype was randomly mutagenized with UV, and 27 large-plaque (lp) mutants were isolated. A combination of analyses of viral proteins and genomic DNA sequences have indicated that 23 mutants contained lesions in the E1B region affecting either 19K or both 19K and 55K proteins. Four other lp mutants contained lesions in early regions E1A and E4, in the early L1 region that codes for the i-leader protein, and in late regions that code for the viral structural proteins, penton base, and fiber. Our results suggest that the requirement of E3-ADP for Ad spread could be readily compensated for by abrogation of the functions of E1B-19K and provide genetic evidence that these two viral proteins influence viral spread in opposing manners. In addition to E1B and E3 proteins, other early and late proteins that regulate viral replication and infectivity also influence lateral viral spread. Our studies have identified novel mutations that could be exploited in designing efficient oncolytic Ad vectors.

Viruses with deletions in antiapoptotic genes as potential oncolytic agents

Replication-selective oncolytic viruses have emerged as a new treatment platform for cancers. However, selectivity and potency need to be improved before virotherapy can become a standard treatment modality. In addition, mechanisms that can be incorporated to enable targeting a broad range of cancer types are highly desirable. Cancer cells are well known to have multiple blocks in apoptosis pathways. On the other hand, viruses have evolved to express numerous antiapoptotic genes to antagonize apoptosis induced upon infection. Viruses with deletions in antiapoptotic genes can therefore be complemented by antiapoptotic genetic changes in cancer cells for efficient replication and oncolysis. In this review, we summarize the recent development of this concept, the potential obstacles, and future directions for optimization.

Novel molecular approaches to cystic fibrosis gene therapy

Gene therapy holds promise for the treatment of a range of inherited diseases, such as cystic fibrosis. However, efficient delivery and expression of the therapeutic transgene at levels sufficient to result in phenotypic correction of cystic fibrosis pulmonary disease has proved elusive. There are many reasons for this lack of progress, both macroscopically in terms of airway defence mechanisms and at the molecular level with regard to effective cDNA delivery. This review of approaches to cystic fibrosis gene therapy covers these areas in detail and highlights recent progress in the field. For gene therapy to be effective in patients with cystic fibrosis, the cDNA encoding the cystic fibrosis transmembrane conductance regulator protein must be delivered effectively to the nucleus of the epithelial cells lining the bronchial tree within the lungs. Expression of the transgene must be maintained at adequate levels for the lifetime of the patient, either by repeat dosage of the vector or by targeting airway stem cells. Clinical trials of gene therapy for cystic fibrosis have demonstrated proof of principle, but gene expression has been limited to 30 days at best. Results suggest that viral vectors such as adenovirus and adeno-associated virus are unsuited to repeat dosing, as the immune response reduces the effectiveness of each subsequent dose. Nonviral approaches, such as cationic liposomes, appear more suited to repeat dosing, but have been less effective. Current work regarding non-viral gene delivery is now focused on understanding the mechanisms involved in cell entry, endosomal escape and nuclear import of the transgene. There is now increasing evidence to suggest that additional ligands that facilitate endosomal escape or contain a nuclear localization signal may enhance liposome-mediated gene delivery. Much progress in this area has been informed by advances in our understanding of the mechanisms by which viruses deliver their genomes to the nuclei of host cells.

Mitochondrial localization of p53 during adenovirus infection and regulation of its activity by E1B-19K

Recent results have revealed that the p53 tumor suppressor protein possesses a direct transcription-independent apoptotic activity. During apoptosis induced by genotoxic stress, a small fraction of p53 is targeted to mitochondria where it initiates apoptosis by causing mitochondrial dysfunction. In adenovirus-infected cells, the expression of E1A protein enhances the accumulation of p53 during early phases of infection and during late times after infection, it is targeted for degradation by the combined action of E1B-55K and E4-orf6 proteins. The functional significance of E1A-mediated accumulation of p53 during early phases of viral replication is not known. Our studies with isogenic epithelial cell lines that differ only on the status of p53 indicate that Ad infection induces apoptosis by p53-dependent and -independent pathways and both pathways are suppressed by E1B-19K. We show that during early phase of Ad infection, a fraction of p53 is targeted to the mitochondria. In virus infected cells, a large fraction of the viral antiapoptosis protein E1B-19K is also localized in mitochondria during early and late phases of infection. Coimmunoprecipitation analysis has revealed that p53 and E1B-19K form a complex in mitochondria. The interaction of 19K involves two noncontiguous regions located around amino-acid residues 14-15 and 123-124. On p53, the mutations within the DNA-binding domain reduce interaction with E1B-19K. Our studies also suggest that 19K may additionally complex with the multidomain mitochondrial proapoptotic protein BAK, thereby reducing the level of p53 interaction with BAK. We suggest that p53-induced apoptosis may be important for efficient cell lysis and viral spread and that E1B-19K may neutralize the apoptotic activity of p53 at multiple levels.

Functional interactions of antiapoptotic proteins and tumor necrosis factor in the context of a replication-competent adenovirus

Replication-selective oncolytic adenoviruses hold promise, but novel mechanisms must be identified to maximize intratumoral virus persistence, spread and therapeutic transgene-carrying capacity while maintaining safety. One of the main approaches to engineering cancer-selectivity has been to delete a viral gene that is theoretically expendable in cancer cells. Results with this approach have been mixed, however, as evidenced by controversy over Onyx-015 (E1B-55kD(-)) selectivity. We hypothesized that the functional redundancy between viral gene products might limit selectivity and/or potency with this approach. Antiviral immune inducers of apoptosis (eg TNF-alpha) have not been thoroughly investigated in previous studies. We therefore explored whether deletion of functionally redundant viral genes, E1B-19kD and E3B, both independently antagonize TNF-alpha, could lead to enhanced oncolytic potency while maintaining selectivity. Since tumors have numerous blocks in apoptotic pathways, we hypothesized that deletion of one or both gene regions would result in cancer-selectivity in the presence of TNF-alpha. We have previously shown that the E1B-19kD deletion resulted in enhanced viral spread in vitro and in immunocompetent tumor models in vivo. In contrast, the impact of E3B deletion, especially its in vitro selectivity and potency, was not thoroughly characterized, although it resulted in rapid immune-mediated viral clearance in vivo. Furthermore, previous publications indicated that double-deleted mutants have selectivity but unsatisfactory efficacy. We compared the selectivity and potency of E1B-19kD(-), E3B(-) and E1B-19kD(-)/E3B(-) mutants to wild-type adenovirus. In cancer cells, the E1B-19kD(-) mutant had superior replication, spread and cytolysis (+) or (-) TNF-alpha; deletion of both E1B-19kD and E3B was relatively deleterious. In normal cells without TNF-alpha, similar results were obtained. In contrast, all three mutants were significantly inhibited in the presence of TNF-alpha. In immunocompetent mice, all three mutants were significantly inhibited in normal tissue. In tumors, only the E1B-19kD(-) mutant demonstrated enhanced replication, spread and antitumoral efficacy. Therefore, E1B-19kD deletion and E3B retention should be incorporated in oncolytic adenoviruses for enhanced safety and efficacy. In addition, functional redundant viral genes and their biological mediators/targets need to be carefully examined for the next generation of gene-deleted oncolytic viruses.

Transport across a polarized monolayer of Caco-2 cells by transferrin receptor-mediated adenovirus transcytosis

Adenoviral vectors have a poor record of transgene delivery efficiency through physical barriers such as the epithelium or endothelium. We report here the construction of an adenoviral vector that has the capability to be transported across polarized epithelial monolayers of Caco-2 cells (a colon carcinoma cell line) by transcytosis. This transcytosis is transferrin receptor (TfR)-mediated with use of a bifunctional adaptor, soluble coxsackie adenovirus receptor (sCAR)-Tf, and is both temperature and iron dependent. Under experimental conditions, the adenoviral transcytosis was inhibited by pretreatment of Caco-2 cells with colchicine, an inhibitor of transcytosis, and was not enhanced by pretreatment with Brefeldin A (BFA), an enhancer of transcytosis. In these Caco-2 cells, the transcytosis rate was 0.3 +/- 1.3% (SD). The transcytosed adenoviruses remain biologically functional. These data suggest the potential clinical benefit under conditions where drug delivery is a challenge, such as within the airway epithelium, at the bladder lumen urothelial cell interface, and across the blood-brain barrier for clinical treatment of lung, urogenital, and brain disorders, respectively, by adenoviral transcytosis of transgene delivery.

An E1B-19 kDa gene deletion mutant adenovirus demonstrates tumor necrosis factor-enhanced cancer selectivity and enhanced oncolytic potency

Oncolytic adenoviruses hold promise as a new treatment platform for cancer, but limitations have been identified, including limited spread and potency. The adenoviral protein E1B-19 kDa is a Bcl-2 homologue that blocks apoptosis induction via the intrinsic and extrinsic pathways, specifically including tumor necrosis factor-mediated cell death. We demonstrate that an E1B-19 kDa gene deletion mutant had tumor necrosis factor-enhanced cancer selectivity, in vitro and in vivo, due to genetic blocks in apoptosis pathways in cancer cells. In addition, this mutant demonstrated significantly enhanced viral spread and antitumoral potency relative to dl1520 (aka Onyx-015) and wild-type adenovirus in vitro. Significant antitumoral efficacy was demonstrated in vivo by intratumoral and intravenous routes of administration. E1B-19 kDa deletion should be considered as a feature of oncolytic adenoviruses to enhance their safety, spread, and efficacy.

Oncolytic virotherapy as a novel strategy for pancreatic cancer

We have developed a novel gene therapy that targets genetic alterations in pancreatic cancer using oncolytic replication-selective adenoviruses in tumor cells. E1B-55kDa-deleted adenovirus (AxE1AdB) can selectively replicate in TP53-deficient human cancer cells but not cells with functional TP53. Consecutive injection with AxE1AdB markedly inhibited the growth of human pancreatic tumors in severe combined immunodeficiency disease mice. Furthermore, AxE1AdB displayed the ability to enhance gene expression as a virus vector. It is reported that uracil phosphoribosyl transferase (UPRT) overcomes 5-FU resistance. The therapeutic advantage of a replication-selective adenovirus that expresses UPRT (AxE1AdB-UPRT) was thus evaluated in an intraperitoneum-disseminated tumor model. Combined treatment with 5-FU and AxE1AdB-UPRT dramatically reduced the disseminated tumor burden without causing toxicity in normal tissues. We also clarified the process of AxE1AdB-inhibited tumor angiogenesis through the preserved E1A region: an adenoviral E1A protein binds to pRB, forcing the quiescent cell into the S phase. We constructed a double-mutant, replication-selective adenovirus (AxdAdB-3) containing a mutation in the RB-binding motif of the E1A region and a deletion of large E1B-55kDa. AxdAdB-3 swiftly induced cancer cell death in vitro and showed a potent antitumor effect in vivo. These results strongly suggest that AxdAdB-3 possesses a wider therapeutic potential than previously believed, given that most pancreatic cancers have abnormalities in both the TP53 and RB pathways.

Evasion of the immune system by adenoviruses

Human adenoviruses (Ads) have the ability to transform primary cells, and certain Ads, the subgenus A adenoviruses such as Ad12, induce tumours in immunocompetent rodents. The oncogenic phenotype of the subgenus A adenoviruses is determined by the viral E1A oncogene. In order to generate tumours, Ad12-transformed cells must evade the cellular immune system of the host. Ad12 E1A gene products mediate transcriptional repression of several genes in the major histocompatibility complex (MHC) involved in antigen processing and presentation, resulting in evasion of cytotoxic T lymphocyte (CTL) killing of transformed cells. In this review, the molecular mechanisms of E1A-mediated transcriptional repression of MHC gene expression are described. In addition, evasion of natural killer (NK) cell killing by Ad-transformed cells is also considered.

Subversion of host defense mechanisms by adenoviruses

Adenoviruses (Ads) cause acute and persistent infections. Alike the much more complex herpesviruses, Ads encode numerous immunomodulatory functions. About a third of the viral genome is devoted to counteract both the innate and the adaptive antiviral immune response. Immediately upon infection, E1A blocks interferon-induced gene expression and the VA-RNA inhibits interferon-induced PKR activity. At the same time, E1A reprograms the cell for DNA synthesis and induces the intrinsic cellular apoptosis program that is interrupted by E1B/19K and E1B/55K proteins, the latter inhibits p53-mediated apoptosis. Most other viral stealth functions are encoded by a separate transcription units, E3. Several E3 products prevent death receptor-mediated apoptosis. E3/14.7K seems to interfere with the cytolytic and pro-inflammatory activities of TNF while E3/10.4K and 14.5K proteins remove Fas and TRAIL receptors from the cell surface by inducing their degradation in lysosomes. These and other functions that may afect granule-mediated cell death might drastically limit lysis by NK cells and cytotoxic T cells (CTL). Moreover, Ads interfere with recognition of infected cell by CTL. The paradigmatic E3/19K protein subverts antigen presentation by MHC class I molecules by inhibiting their transport to the cell surface. In concert, these viral countermeasures ensure prolonged survival in the infected host and, as a consequence, facilitate transmission. Elucidating the molecular mechanisms of Ad-mediated immune evasion has stimulated corresponding research on other viruses. This knowledge will also be instrumental for designing better vectors for gene therapy and vaccination, and may lead to a more rational treatment of life-threatening Ad infections, e.g. in transplantation patients.

Requirement of BAX for efficient adenovirus-induced apoptosis

Infection of human epithelial cells with adenoviruses induces an apoptosis paradigm that is efficiently suppressed by the expression of viral E1B-19K protein, which is a functional homolog of the cellular antiapoptosis protein BCL-2. The mechanisms of adenovirus (Ad)-induced apoptosis appear to involve the cellular BCL-2 family proapoptotic proteins. Recent genetic studies with fibroblasts derived from mutant mouse embryos indicate that a class of the BCL-2 family proapoptotic proteins (designated BH-123 or multidomain proteins) such as BAX and BAK constitutes an essential component of the core apoptosis machinery in animal cells. We have examined the role of BAX in Ad-induced apoptosis in human epithelial cells using two colon cancer cell lines, HCT116Bax (Bax(+/-)) and HCT116BaxKO (Bax(-/-)) (L. Zhang, J. Yu, B. H. Park, K. W. Kinzler, and B. Vogelstein, Science 290:989-992, 2000). Infection of Bax(+/-) cells with an Ad type 2 mutant (dl250) defective in expression of the E1B-19K protein resulted in enhanced cytopathic effect, large plaques on cell monolayers, fragmentation of cellular DNA, and enhanced cell death. These mutant phenotypes were not efficiently expressed in Bax(-/-) cells, suggesting that BAX is essential for Ad-induced apoptosis. Infection of Bax(+/-) cells with dl250 induced increased levels of an N-terminally processed form of BAX. Cells infected with the 19K mutant also contained enhanced levels of truncated BAX in membrane-inserted form. Our results suggest that at least a part of the mechanism utilized by E1B-19K to suppress apoptosis during Ad infection may involve modulation of the activities of BAX.

Caspase-mediated cleavage of adenovirus early region 1A proteins

Adenovirus 2 and 12 early region 1A (Ad2 and Ad12 E1A) proteins were cleaved during cisplatin-induced apoptosis of Ad-transformed rat and human cells. Cleavage was inhibited in the presence of caspase inhibitors such as Z-VAD-FMK. In Ad12 transformants both 13S and 12S E1A proteins were cleaved at a similar rate. In Ad2 transformants the E1A 13S component was appreciably less stable than the 12S component. In in vitro studies Ad2 and Ad12 E1A 13S and Ad2 12S proteins were rapidly cleaved by caspase 3 whereas Ad12 12S E1A and Ad12 13S E1A were rapidly degraded by caspase 7. Cleavage sites in Ad12 13S proteins for caspase 3 have been determined. Initial cleavage occurred at D24 and D150; this was followed by cleavage at D204 and D242. Caspase-3-mediated cleavage of Ad12 13S E1A destroyed its ability to bind to CBP and TBP but interaction between C terminal E1A polypeptides and CtBP was observed. During viral infection Ad5 and Ad12 E1A 12S proteins were markedly more stable than 13S proteins but no difference was observed in Ad E1A levels in the absence or presence of the caspase inhibitors Z-VAD-FMK or Z-D(OMe)-E(OMe)-V-D(OMe)-CH(2)F. Limited caspase 3 and 10 activation occurred during infection with the E1B 19K(-) virus Ad2 pm1722 but little or no activation of caspase 3 was observed during wt virus infection. Examination of protein cleavage during viral infection of A549 cells showed proteolysis of lamin B and PARP in response to Ad5 wt and Ad2 pm1722. Protein degradation in response to both viruses was partially inhibited by Z-VAD-FMK. Following infection of human skin fibroblasts lamin B was degraded, although only limited changes in PARP levels were observed. We have concluded that Ad E1A is cleaved by caspases during apoptosis but not during viral infection. However, some of the processes commonly associated with apoptosis occur during viral infection, particularly with E1B 19K(-) mutants, although apoptosis per se is not evident.

Construction and characterization of E1-minus replication-defective adenovirus vectors that express E3 proteins from the E1 region

Previous research has indicated that the adenovirus protein complex named RID, derived from the E3 transcription unit, functions to remove the receptors named Fas/Apo1/CD95 (Fas) and epidermal growth factor receptor (EGFR) from the surface of cells. (The RID complex is composed of the RIDalpha and RIDbeta polypeptides, previously named 10.4K and 14.5K, respectively.) In response to RID, Fas and EGFR appear to be internalized into endosomes and degraded in lysosomes. Fas is a death receptor in the tumor necrosis factor (TNF) receptor superfamily. RID inhibits apoptosis via the Fas pathway, presumably because RID gets rid of Fas. Earlier work further showed that another adenovirus E3-coded protein, E3-14.7K, inhibits apoptosis induced by TNF. Most of the above studies have been conducted using viable virus mutants that lack one or more of the genes for RID, E3-14.7K, or E1B-19K (this protein, coded by the E1B transcription unit, also inhibits apoptosis via the TNF and Fas pathways). Some studies have also been conducted with the genes for RID or E3-14.7K transiently or stably transfected into cells. We now report a new approach to studying the E3 genes. We have constructed four E1-minus replication-defective vectors that have all the E3 genes deleted from their natural position and then reinserted, in different permutations, into the deleted E1 region under control of the cytomegalovirus immediate early promoter. Vector Ad/RID only has the genes for RIDalpha and RIDbeta. Vector Ad/14.7K only has the gene for E3-14.7K. Vector Ad/RID/14.7K only has the genes for RIDalpha, RIDbeta, and E3-14.7K. Vector Ad/E3 has all E3 genes, but there are two missense mutations in the gene for Adenovirus Death Protein. These vectors expressed RID and/or E3-14.7K, as expected. The RID-expressing vectors forced the internalization and degradation of Fas and EGFR, and they inhibited apoptosis induced through the Fas pathway. These vectors should be useful reagents to study the E3 proteins.

Gene therapy for pancreatic cancer targeting the genomic alterations of tumor suppressor genes using replication-selective oncolytic adenovirus

In order to develop an effective therapeutic intervention for patients with pancreatic cancer, we examined the genetic alternations of pancreatic cancer. Based on these results, we are developing a new gene therapy targeting the genetic character of pancreatic cancer using mutant adenoviruses selectively replication-competent in tumor cells. Loss of heterozygosity (LOH) of 30% or more were observed on chromosome arms 17p (47%), 9p (45%), 18q (43%), 12q (34%), and 6q (30%). LOH of 12q, 17p, and 18q showed the significant association with poor prognosis. These data strongly suggest that mutation of the putative suppressor genes, TP53 and SMAD4 play significant roles in the disease progression. Based on this rationale, we are developing a new gene therapy targeting tumors without normal TP53 function. E1B-55kDa-deleted adenovirus (AxE1AdB) can selectively replicate in TP53-deficient human tumor cells but not cells with functional TP53. We evaluated the therapeutic effect of this AxE1AdB on pancreatic cancer without normal TP53 function. The growth of human pancreatic tumor in SCID mice model was markedly inhibited by the consecutive injection of AxE1AdB. Furthermore, AxE1AdB is not only the strong weapon but also useful carrier of genes possessing anti-tumor activities as a virus vector specific to tumors without normal TP53 function. It was reported that uracil phosphoribosyl transferase (UPRT) overcomes 5FU resistance. UPRT catalyzes the synthesis of 5-fluorouridine monophosphate (FUMP) from Uracil and phosphoribosylpyrophosphate (PRPP). The antitumor effect of 5FU is enhanced by augmenting 5-fluorodeoxyuridine monophosphate (FdUMP) converted from FUMP, which inhibits Thymidylate Synthetase (TS). The therapeutic advantage of restricted replication competent adenovirus that expresses UPRT (AxE1AdB-UPRT) was evaluatedin an intra-peritoneal disseminated tumor model. To study the anti-tumor effect of AxE1AdB-UPRT/5FU, mice with disseminated AsPC-1 tumors were administered the adenovirus, followed by the 5FU treatment. It was shown that the treatment with AxE1AdB-UPRT/5FU caused a dramatic reduction of the disseminated tumor burden without toxicity in normal tissues. These results revealed thatthe AxE1AdB-UPRT/5FU system is a promising tool for intraperitoneal disseminated pancreatic cancer.

Adenovirus infection of primary malignant lymphoid cells

Adenovirus infection represents a cellular stress that induces host cell pro-apoptotic responses. To overcome this barrier to productive infection, viral polypeptides modulate a variety of host cell pathways. The interface of these early viral gene products with key cellular regulatory proteins has provided considerable information concerning basic cellular mechanisms operative in cell cycle regulation, transcriptional control and apoptosis. The overlap of these mechanisms with those impacted during oncogenesis provides the opportunity to use adenoviruses and adenovirus mutants to characterize the state of key regulatory pathways in specific malignant cells. For example, adenoviruses mediate cytotoxicity after infection of chronic lymphocytic leukemia (CLL) cells, mantle cell lymphoma (MCL) cells and multiple myeloma cell lines. Specific adenovirus mutants demonstrate enhanced cytotoxicity and, in many cases, apoptosis is not the primary mechanism of cell death. Analysis of these infections with respect to both the features of the primary malignant cell and the mechanisms of adenovirus-mediated cytotoxicity holds the prospect of providing novel insights into the status of key regulatory pathways in individual patient malignant cells. These studies also hold the prospect of supporting the development of specific attenuated adenoviruses as therapeutic agents with selective cytotoxicity for specific primary lymphoid malignancies.

Poliovirus protein 3A inhibits tumor necrosis factor (TNF)-induced apoptosis by eliminating the TNF receptor from the cell surface

Viral infections often trigger host defensive reactions by activating intrinsic (intracellular) and extrinsic (receptor-mediated) apoptotic pathways. Poliovirus is known to encode an antiapoptotic function(s) suppressing the intrinsic pathway. Here, the effect of poliovirus nonstructural proteins on cell sensitivity to tumor necrosis factor (TNF)-induced (i.e., receptor-mediated) apoptosis was studied. This sensitivity is dramatically enhanced by the viral proteinase 2A, due, most likely, to inhibition of cellular translation. On the other hand, cells expressing poliovirus noncapsid proteins 3A and 2B exhibit strong TNF resistance. Expression of 3A neutralizes the proapoptotic activity of 2A and results in a specific suppression of TNF signaling, including the lack of activation of NF-kappaB, due to elimination of the TNF receptor from the cell surface. In agreement with this, poliovirus infection results in a dramatic decrease in TNF receptor abundance on the surfaces of infected cells as early as 4 h postinfection. Poliovirus proteins that confer resistance to TNF interfere with endoplasmic reticulum-Golgi protein trafficking, and their effect on TNF signaling can be imitated by brefeldin A, suggesting that the mechanism of poliovirus-mediated resistance to TNF is a result of aberrant TNF receptor trafficking.

Inhibition of TRAIL-induced apoptosis and forced internalization of TRAIL receptor 1 by adenovirus proteins

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis through two receptors, TRAIL-R1 (also known as death receptor 4) and TRAIL-R2 (also known as death receptor 5), that are members of the TNF receptor superfamily of death domain-containing receptors. We show that human adenovirus type 5 encodes three proteins, named RID (previously named E3-10.4K/14.5K), E3-14.7K, and E1B-19K, that independently inhibit TRAIL-induced apoptosis of infected human cells. This conclusion was derived from studies using wild-type adenovirus, adenovirus replication-competent mutants that lack one or more of the RID, E3-14.7K, and E1B-19K genes, and adenovirus E1-minus replication-defective vectors that express all E3 genes, RID plus E3-14.7K only, RID only, or E3-14.7K only. RID inhibits TRAIL-induced apoptosis when cells are sensitized to TRAIL either by adenovirus infection or treatment with cycloheximide. RID induces the internalization of TRAIL-R1 from the cell surface, as shown by flow cytometry and indirect immunofluorescence for TRAIL-R1. TRAIL-R1 was internalized in distinct vesicles which are very likely to be endosomes and lysosomes. TRAIL-R1 is degraded, as indicated by the disappearance of the TRAIL-R1 immunofluorescence signal. Degradation was inhibited by bafilomycin A1, a drug that prevents acidification of vesicles and the sorting of receptors from late endosomes to lysosomes, implying that degradation occurs in lysosomes. RID was also shown previously to internalize and degrade another death domain receptor, Fas, and to prevent apoptosis through Fas and the TNF receptor. RID was shown previously to force the internalization and degradation of the epidermal growth factor receptor. E1B-19K was shown previously to block apoptosis through Fas, and both E1B-19K and E3-14.7K were found to prevent apoptosis through the TNF receptor. These findings suggest that the receptors for TRAIL, Fas ligand, and TNF play a role in limiting virus infections. The ability of adenovirus to inhibit killing through these receptors may prolong acute and persistent infections.

Consequences of disruption of the interaction between p53 and the larger adenovirus early region 1B protein in adenovirus E1 transformed human cells

The adenovirus early region 1B (Ad E1B) genes have no transforming capability of their own but markedly increase the transformation frequency of Ad E1A following co-transfection into mammalian cells. The larger E1B proteins of both Ad2/5 and Ad12 bind to p53 and inhibit its ability to transcriptionally activate other genes. We have previously demonstrated that synthetic peptides identical to the binding sites for p53 on both the Ad2 and Ad12 E1B proteins will disrupt the interaction in vivo and in vitro. In the work presented here we have examined the effects of complex dissociation on Ad E1-transformed human cells. It has been shown, using confocal microscopy, that when the peptide identical to the p53 binding site was added to Ad5 E1-transformed cells it initally located in the cytoplasmic dense bodies where it caused disruption of the p53/E1B complex. Peptide and p53 then translocated to the nucleus. In Ad12 E1-transformed cells the peptide localized in the nucleus directly and there caused a reorganization of p53 staining from a highly organized, 'flecked' distribution to one in which nuclear staining was homogeneous and diffuse. Peptides added to either Ad5 E1 or Ad12 E1 transformed cells resulted in the release of transcriptionally active p53. Interestingly, the level of p53 then fell presumably as a result of proteasomal action - this was probably a reflection of the short half-life of 'free' (i.e. dissociated) p53 compared to that of the bound protein. Free p53 did not cause apoptosis in target cells probably due to the presence of the smaller (19K) E1B proteins. However, addition of peptide leads to a significant reduction in cell growth rate. We have further demonstrated that a significant proportion of those cells which had taken up peptide had ceased DNA synthesis, probably due to a p53-induced cell cycle arrest. The role of the larger EIB protein during transformation is considered in view of these data.