A new type of adenovirus vector that utilizes homologous recombination to achieve tumor-specific replication

Potent inhibition of OKT3-induced T cell proliferation and suppression of CD147 cell surface expression in HeLa cells by scFv-M6-1B9

CD147, a multifunctional type I transmembrane glycoprotein, has been implicated in various physiological and pathological processes. It is involved in signal transduction pathways and also plays a crucial role in the invasive and metastatic activity of malignant tumor cells. Diminished expression of this molecule has been shown to be beneficial in suppression of tumor progression. In a previous study, we generated and characterized a recombinant antibody fragment, scFv, which reacted specifically to CD147. In the present study, we further investigated the biological properties, function and the effect of generated scFv on CD147 expression. The in vitro study showed that soluble scFv-M6-1B9 produced from E. coli HB2151 bound to CD147 surface molecule and inhibited OKT3-induced T cell proliferation. Furthermore, soluble lysate of scFv-M6-1B9 from 293A cells, transduced with a scFv-M6-1B9 expressing adenovirus vector, recognized both recombinant and native CD147. These results indicate that scFv-M6-1B9 binds with high efficiency and specificity. Importantly, scFv-M6-1B9 intrabody reduced the expression of CD147 on the cell surface of HeLa cells suggesting that scFv-M6-1B9 is biologically active. In conclusion, our present study demonstrated that scFv-M6-1B9 has a great potential to target both the intracellular and the extracellular CD147. The generated scFv-M6-1B9 may be an effective agent to clarify the cellular function of CD147 and may aid in efforts to develop a novel treatment in various human carcinomas.

Epithelial Junction Opener Improves Oncolytic Adenovirus Therapy in Mouse Tumor Models

A central resistance mechanism in solid tumors is the maintenance of epithelial junctions between malignant cells that prevent drug penetration into the tumor. Human adenoviruses (Ads) have evolved mechanisms to breach epithelial barriers. For example, during Ad serotype 3 (Ad3) infection of epithelial tumor cells, massive amounts of subviral penton-dodecahedral particles (PtDd) are produced and released from infected cells to trigger the transient opening of epithelial junctions, thus facilitating lateral virus spread. We show here that an Ad3 mutant that is disabled for PtDd production is significantly less effective in killing of epithelial human xenograft tumors than the wild-type Ad3 virus. Intratumoral spread and therapeutic effect of the Ad3 mutant was enhanced by co-administration of a small recombinant protein (JO; produced in Escherichia coli) that incorporated the minimal junction opening domains of PtDd. We then demonstrated that co-administration of JO with replication-competent Ads that do not produce PtDd (Ad5, Ad35) resulted in greater attenuation of tumor growth than virus injection alone. Furthermore, we genetically modified a conditionally replicating Ad5-based oncolytic Ad (Ad5Δ24) to express a secreted form of JO upon replication in tumor cells. The JO-expressing virus had a significantly greater antitumor effect than the unmodified AdΔ24 version. Our findings indicate that epithelial junctions limit the efficacy of oncolytic Ads and that this problem can be address by co-injection or expression of JO. JO has also the potential for improving cancer therapy with other types of oncolytic viruses.

Homologous recombination-based adenovirus vector system for tumor cell-specific gene delivery

Cancer gene therapy requires tumor-specific delivery and expression of a transgene to maximize antitumor efficacy and minimize side effects. In this study, we developed a new tumor-targeting, homologous recombination-based adenovirus vector system, HRAVS. HRAVS is composed of two adenovirus vectors, Ad.CMV.IR containing reverse sequence (IR) and a CMV promoter and Ad.IR.EGFP comprising the report gene EGFP and IR. For improved viral DNA replication and transgene expression, the E1a gene was added to HRAVS to generate the enhanced HRAVS, EHRAVS, which consists of Ad.CMV.IR and Ad.IR.EGFP/E1a. The optimal vector composition ratio of Ad.CMV.IR to Ad.IR.EGFP or Ad.IR.EGFP/E1a was identified as 30:70 based on EGFP expression efficiency in tumor cells. The transgene expression of HRAVS and EHRAVS was efficiently and specifically activated in tumor cells only and not in normal cells. Moreover, compared with HRAVS, EHRAVS infection led to higher virus yields and transgene expression and higher toxicity to tumor cells, and these results could be related to the involvement of E1a genes. The results in present study suggest the need for in vivo antitumor study using these new dual-Ad vector systems based on the homologous recombination.

Adenovirus-mediated intratumoral expression of immunostimulatory proteins in combination with systemic Treg inactivation induces tumor-destructive immune responses in mouse models

Tumor-associated antigens (TAAs) include overexpressed self-antigens (e.g. Her2/neu) and tumor-virus antigens (e.g. HPV-16 E6/E7). Although in cancer patients, TAA-specific CD4+ and CD8+ cells are often present, they are not able to control tumor growth. In recent studies it became apparent that tumor-site located immune-evasion mechanisms contribute to this phenomenon and that regulatory T-cells play a major role. We tested in Her2/neu+ breast cancer and HPV-16 E6/E7+ cervical cancer mouse models, whether intratumoral expression of immunostimulatory proteins (ISPs), e.g. recombinant antibodies (αCTLA-4, αCD137, αCD3), cyto/chemokines (IL-15, LIGHT, mda-7), and costimulatory ligands (CD80), via adenovirus(Ad)-mediated gene transfer would overcome resistance. In both the breast and cervical cancer model, none of the Ad.ISP vectors displayed a significant therapeutic effect when compared with an Ad vector that lacked a transgene (Ad.zero). However, the combination of Ad.ISP vectors with systemic Treg depletion, using anti-CD25 mAb (breast cancer model) or low-dose cyclophosphamide (cervical cancer model) resulted in a significant delay of tumor growth in mice treated with Ad.αCTLA4. In the cervical cancer model we also demonstrated the induction of a systemic anti-tumor immune response that was able to delay the growth of distant tumors. Ad.αCTLA4 mediated tumor-destructive immune responses involved NKT- and CD8+ T-cells. In both models no auto-immune reactions were observed. The study shows that Ad.αCTLA4 in combination with systemic Treg depletion has potentials in the immunotherapy of cancer.

Applying genomic and bioinformatic resources to human adenovirus genomes for use in vaccine development and for applications in vector development for gene delivery

Technological advances and increasingly cost-effect methodologies in DNA sequencing and computational analysis are providing genome and proteome data for human adenovirus research. Applying these tools, data and derived knowledge to the development of vaccines against these pathogens will provide effective prophylactics. The same data and approaches can be applied to vector development for gene delivery in gene therapy and vaccine delivery protocols. Examination of several field strain genomes and their analyses provide examples of data that are available using these approaches. An example of the development of HAdV-B3 both as a vaccine and also as a vector is presented.

[SiRNA technology, the gene therapy of the future?]

A new era in genetics started 17 years ago, when co-suppression in petunia was discovered. Later, co-suppression was identified as RNA interference (RNAi) in many plant and lower eukaryote animals. Although an ancient antiviral host defense mechanism in plants, the physiologic role of RNAi in mammals is still not completely understood. RNAi is directed by short interfering RNAs (siRNAs), one subtype of short double stranded RNAs. In this review we summarize the history and mechanisms of RNAi. We also aim to highlight the correlation between structure and efficacy of siRNAs. Delivery is the most important obstacle for siRNA based gene therapy. Viral and nonviral deliveries are discussed. In vivo delivery is the next obstacle to clinical trials with siRNAs. Although hydrodynamic treatment is effective in animals, it cannot be used in human therapy. One possibility is organ selective catheterization. The known side effects of synthesized siRNAs are also discussed. Although there are many problems to face in this new field of gene therapy, successful in vitro and in vivo experiments raise hope for treating human disease with siRNA.

A capsid-modified, conditionally replicating oncolytic adenovirus vector expressing TRAIL Leads to enhanced cancer cell killing in human glioblastoma models

Glioblastoma multiforme (GBM) is the most aggressive brain tumor, and patients rarely survive for more than 2 years. Gene therapy may offer new treatment options and improve the prognosis for patients with GBM. Adenovirus-mediated gene therapy strategies for brain tumors have been limited by inefficient gene transfer due to low expression of the adenovirus serotype 5 (Ad5) receptor. We have used an adenovirus vector that specifically replicates in tumor cells and uses an Ad5 capsid and the adenovirus serotype (Ad35) fiber for efficient infection of malignant tumor cells. This vector also expresses adenovirus E1A and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in a tumor-specific manner. Here, we show that this oncolytic vector (Ad5/Ad35.IR-E1A/TRAIL) efficiently infects the GBM tumor cell lines SF767, T98G, and U-87 MG. Tumor cell killing was markedly enhanced with Ad5/Ad35.IR-E1A/TRAIL compared with wild-type Ad5 and Ad35 virus or Ad5/Ad35.IR-E1A- vectors without TRAIL expression in vitro. In vivo experiments using s.c. xenografted U-87 MG cells in NOD/SCID mice showed a significant growth delay of tumors after i.t. injection of Ad5/Ad35.IR-E1A/TRAIL, whereas adenovirus wild-type injections showed only marginal or no effect. Our findings indicate that the use of a capsid-modified adenoviral vector, in combination with TRAIL expression, is a promising novel approach for gene therapy of glioblastoma.

A tumor-specific conditionally replicative adenovirus vector expressing TRAIL for gene therapy of hepatocellular carcinoma

We constructed a novel hepatocellular carcinoma-specific conditionally replicative adenovirus (CRAd). This adenovirus, designated Ad.HS4.AFP.E1A/TRAIL, expresses E1A to mediate viral replication and TRAIL to enhance HCC-killing efficacy under the control of a modified AFP promoter. An insulator HS-4 was placed in front of the AFP promoter to enhance the fidelity of the heterologous promoter. This virus was shown to have specific cytolytic activity in AFP-expressing HCC cells in vitro. Furthermore, the replication efficiency of Ad.HS4.AFP.E1A/TRAIL correlated well with AFP expression of the host cells, showing a 100-fold and 1 000 000-fold decrease in the low-and non-AFP-expressing HCC cells, respectively, compared to the high AFP-expressing HCC cells. An increase in mRNA of TRAIL and the elevated Caspase-3 activity were also observed in Ad.HS4.AFP.E1A/TRAIL-infected HCC cells. These results indicated that TRAIL expression from the viral vector activated the Caspase-3 enzymatic capacity and the HCC cells were sensitive to TRAIL. In vivo, Ad.HS4.AFP.E1A/TRAIL effectively prevented the growth of low AFP-expressing BEL-7404 xenografts. These results indicate that Ad.HS4.AFP.E1A/TRAIL could provide a new strategy of gene therapy for HCC.

A new group B adenovirus receptor is expressed at high levels on human stem and tumor cells

CD46 is used by human group B adenoviruses (Ads) as a high-affinity attachment receptor. Here we show evidence that several group B Ads utilize an additional receptor for infection of human cells, which is different from CD46. We tentatively named this receptor receptor X. Competition studies with unlabeled and labeled Ads, recombinant Ad fiber knobs, and soluble CD46 and CD46 antibodies revealed three different subgroups of group B Ads, in terms of their receptor usage. Group I (Ad16, -21, -35, and -50) nearly exclusively uses CD46. Group II (Ad3, -7p, and -14) utilizes receptor X and not CD46. Group III (Ad11p) uses both CD46 and the alternative receptor X. Interaction of group II and III Ads with receptor X occurs via the fiber knob. Receptor X is an abundantly expressed glycoprotein that interacts with group II and III Ads at relatively low affinity in a Ca(2+)-dependent manner. This receptor is expressed at high levels on human mesenchymal and undifferentiated embryonic stem cells, as well as on human cancer cell lines. These findings have practical implications for stem cell and gene therapy.

Evaluation of adenovirus vectors containing serotype 35 fibers for tumor targeting

There is growing evidence from in vitro studies that subgroup B adenoviruses (Ad) can overcome the limitations in safety and tumor transduction efficiency seen with commonly used subgroup C serotype 5-based vectors. In this study, we confirm that the expression level of the B-group Ad receptor, CD46, correlates with the grade of malignancy of cervical cancer in situ. We also demonstrate the in vivo properties of Ad5-based vectors that contain the B-group Ad serotype 35 fiber (Ad5/35) in transgenic mice that express CD46 in a pattern and at a level similar to humans. Upon intravenous and intraperitoneal injection, an Ad5/35 vector did not efficiently transduce normal tissue, but was able to target metastatic or intraperitoneal tumors that express CD46 at levels comparable to human tumors. When an oncolytic Ad5/35-based vector was employed, in both tumor models antitumor effects were observed. Furthermore, injection of Ad5/35 vectors into CD46 transgenic mice caused less innate toxicity than Ad5 vectors. Our data demonstrate that Ad vectors that target CD46 offer advantages over Ad5-based vectors for treatment of cancer.

Effect of adenovirus-mediated heat shock protein expression and oncolysis in combination with low-dose cyclophosphamide treatment on antitumor immune responses

Heat shock proteins such as gp96 have the ability to chaperone peptides and activate antigen-presenting cells. In this study, we tested whether adenovirus-mediated overexpression of secreted or membrane-associated forms of gp96 in tumor cells would stimulate an antitumor immune response. Studies were carried out in C57Bl/6 mice bearing aggressively growing s.c. tumors derived from syngeneic TC-1 cells, a cell line that expresses HPV16 E6 and E7 proteins. We found that secreted gp96 can induce protective and therapeutic antitumor immune responses. Our data also indicate that the antitumor effect of sgp96 expression seems to be limited by the induction of suppressive regulatory T cells (Treg). TC-1 tumor transplantation increased the number of splenic and tumor-infiltrating Tregs. Importantly, treatment of mice with low-dose cyclophosphamide decreased the number of Tregs and enhanced the immunostimulatory effect of sgp96 expression. We also tested whether an oncolytic vector (Ad.IR-E1A/TRAIL), that is able to induce tumor cell apoptosis and, potentially, release cryptic tumor epitopes in immunogenic form, could stimulate antitumor immune responses. Although tumor cells infected ex vivo with Ad.IR-E1A/TRAIL had no antitumor effect when used as a vaccine alone, the additional treatment with low-dose cyclophosphamide resulted in the elimination of pre-established tumors. This study gives a rationale for testing approaches that suppress Tregs in combination with oncolytic or immunostimulatory vectors.

Evaluation of adenovirus vectors containing serotype 35 fibers for vaccination

In contrast to commonly used serotype 5-based adenovirus (Ad) vectors, Ad's containing fibers derived from B-group serotype 35 (Ad5/35) efficiently transduce human DCs ex vivo and appear to target antigen-presenting cells after intravenous injection into baboons. Based on this, Ad5/35 vectors could be valuable tools for immunotherapy and vaccination. On the other hand, a number of studies indicate that signaling through the B-group Ad receptor, CD46, can cause tolerance or immunosuppression. Since mice do not express CD46 in a human-like pattern, we studied the in vivo properties of Ad5/35 in transgenic mice that express CD46 in a pattern and at a level similar to those of humans. Hypersensitivity assays and analyses of frequencies of regulatory T cells and T cell responses did not indicate that Ad5/35 injection exerts detrimental effects on the host's immune system. An Ad5/35 vector expressing a model antigen was able to trigger a strong T cell response against the test antigen after intramuscular injection. Overall, compared to Ad5 vectors, Ad5/35 vectors had a better safety profile, reflected by lower serum levels of proinflammatory cytokines.

Meeting product development challenges in manufacturing clinical grade oncolytic adenoviruses

Oncolytic adenoviruses have been considered for use as anticancer therapy for decades, and numerous means of conferring tumor selectivity have been developed. As with any new therapy, the trip from the laboratory bench to the clinic has revealed a number of significant development hurdles. Viral therapies are subject to specific regulations and must meet a variety of well-defined criteria for purity, potency, stability, and product characterization prior to their use in the clinic. Published regulatory guidelines, although developed specifically for biotechnology-derived products, are applicable to the production of oncolytic adenoviruses and other cell-based products, and they should be consulted early during development. Most importantly, both the manufacturing process and the development of characterization and release assays should be science-driven, use the best available science and technology, and must consider the unique nature of the product: a living, and mutatable, virus. Potentially significant impacts on product quality and safety stem from the possibility of genetic instability related to over-engineering the viruses (as evidenced by their recombination and/or occasional reversion to wild-type virus during manufacturing). This report provides examples of some of the critical components affecting the development and production of clinical grade material and summarizes the significant progress made in recent years.

Evaluation of biodistribution and safety of adenovirus vectors containing group B fibers after intravenous injection into baboons

Vectors containing group B adenovirus (Ad) fibers are able to efficiently transduce gene therapy targets that are refractory to infection with standard Ad serotype 5 (Ad5) vectors, including malignant tumor cells, hematopoietic stem cells, and dendritic cells. Preliminary studies in mice indicate that, after intravenous injection, B-group fiber-containing Ads do not efficiently transduce most organs and cause less acute toxicity than Ad5 vectors. However, biodistribution and safety studies in mice are of limited value because the mouse analog of the B-group Ad receptor, CD46, is expressed only in the testis, whereas in humans, CD46 is expressed on all nucleated cells. Unlike mice, baboons have CD46 expression patterns and levels that closely mimic those in humans. We conducted a biodistribution and toxicity study of group B Ad fiber-containing vectors in baboons. Animals received phosphate-buffered saline, Ad5-bGal (a first-generation Ad5 vector), or B-group fiber-containing Ads (Ad5/35-bGal and Ad5/11-bGal) at a dose of 2 x 10(12) VP/kg, and vector biodistribution and safety was analyzed over 3 days. The amount of Ad5/35-bGal and Ad5/11-bGal vector genomes was in most tissues one to three orders of magnitude below that of Ad5. Significant Ad5/35- and Ad5/11-mediated transgene (beta-galactosidase) expression was seen only in the marginal zone of splenic follicles. Compared with the animal that received Ad5-bGal, all animals injected with B-group fiber-containing Ad vectors had lower elevations in serum proinflammatory cytokine levels. Gross and histopathology were normal in animals that received B-group Ad fiber-containing Ads, in contrast to the Ad5-infused animal, which showed widespread endothelial damage and inflammation. In a further study, a chimeric Ad5/35 vector carrying proapoptotic TRAIL and Ad E1A genes under tumor-specific regulation was well tolerated in a 30-day toxicity study. No major clinical, serologic, or pathologic abnormalities were noticed in this animal.

Assessment of a combined, adenovirus-mediated oncolytic and immunostimulatory tumor therapy

In this study, we identified murine breast cancer cell lines that support DNA replication of E1-deleted adenovirus vectors and which can be killed by an oncolytic adenovirus expressing adenovirus E1A and tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL) in a replication-dependent manner (Ad.IR-E1A/TRAIL). We showed that systemic or intratumoral (i.t.) injection of adenovirus vectors into mice increases plasma levels of proinflammatory cytokines and chemokines, including TNF-alpha, INF-gamma, and MCP-1, which are potent inducers of dendritic cell maturation. Furthermore, we showed that in vivo expression of Flt3L from an adenovirus vector increases the number of CD11b+ and CD11c+ cells (populations that include dendritic cells) in the blood circulation. Based on these findings, we tested whether Ad.IR-E1A/TRAIL induced killing of tumor cells in combination with dendritic cell mobilization by Ad.Flt3L or, for comparison, Ad.GM-CSF would have an additive antitumor effect. As a model, we used immunocompetent C3H mice with syngeneic s.c. tumors derived from C3L5 cells. We found that vaccination of mice with C3L5 cells that underwent viral oncolysis in combination with Flt3L or granulocyte-macrophage colony-stimulating factor (GM-CSF) expression induces a systemic antitumor immune response. I.t. injection of the oncolytic and Flt3L expressing vectors into established tumors delayed tumor growth but did not cause efficient tumor elimination. This study shows the effectiveness of a combined oncolytic/immunostimulatory tumor therapy approach.

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

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

Xenograft models for liver metastasis: Relationship between tumor morphology and adenovirus vector transduction

The improvement of initial tumor cell transduction with viral vectors is a major task in tumor gene therapy. We have developed mouse tumor models with hepatic metastases to study transduction of tumor cells after systemic adenovirus vector application. The tumor models were established by intraportal transplantation of human tumor cell lines into immunodeficient mice. Liver metastases derived from cervix, colon, breast, and liver cancer lines were analyzed for distribution of extracellular matrix, vascularization, and transgene expression after tail vein injection of adenovirus vectors. Overall, xenografts resembled the morphology of corresponding tumors in cancer patients. Adenovirus-mediated gene delivery depended on tumor vascularization and direct contact between blood vessels and tumor cells. These models represent important tools for studying and improving tumor gene therapy approaches.

A tumor-targeted and conditionally replicating oncolytic adenovirus vector expressing TRAIL for treatment of liver metastases

We have constructed a new capsid-modified adenovirus (Ad) vector that specifically replicates in tumor cells and expresses TNF-related apoptosis-inducing ligand (TRAIL). The Ad capsid contains short-shafted fibers derived from Ad serotype 35, which allow for efficient infection of malignant tumor cells, and largely avoids innate toxicity after intravenous application. Replication-dependent homologous recombination in Ad genomes was used to achieve tumor-specific expression of Ad E1a (to mediate viral replication) and TRAIL (to mediate apoptosis and enhance release of progeny virus from infected cells). We demonstrated that our oncolytic vector (Ad5/35.IR-E1A/TRAIL) induced apoptosis in human tumor cell lines derived from colorectal, lung, prostate, and liver cancer. Both in vitro and in vivo tumor models showed efficient intratumoral spread of this vector. In a model for metastatic colon cancer, tail vein infusion of Ad5/35.IR-E1A/TRAIL resulted in elimination of preestablished liver metastases. Intravenous injection of this vector caused a transient elevation of serum glutamic pyruvic transaminase in tumor-bearing mice, which we attributed to factors released from apoptotic tumor cells. Liver histology analyzed at day 14 after virus injection did not show signs of hepatocellular damage. This new oncolytic vector represents a potentially efficient means for gene therapy of metastatic cancer.

Analyses of melanoma-targeted oncolytic adenoviruses with tyrosinase enhancer/promoter-driven E1A, E4, or both in submerged cells and organotypic cultures

We have generated novel conditionally replicative adenoviruses (CRAds) targeted to melanoma cells. In these adenoviruses, the E4 region (AdΔ24TyrE4) or both E1 and E4 regions (Ad2xTyr) were controlled by a synthetic tyrosinase enhancer/promoter (Tyr2E/P) specific for melanocytes. The properties of these CRAds were compared with wild-type adenovirus (Adwt) and our previous CRAd with a targeted E1A CRII mutation (AdTyrΔ24) in submerged cultures of melanoma cells and nonmelanoma control cells. We showed that AdΔ24TyrE4 had a cell type selectivity similar to AdTyrΔ24 but had a distinct block in viral reproduction in nonmelanoma cells and that Ad2xTyr had an augmented selectivity for melanoma cells. These viruses were additionally tested in organotypic cultures of melanoma cell lines, primary human keratinocytes (PHKs), or mixed cell populations. Unexpectedly, the CRAds exhibited somewhat different cell type selectivity profiles in these cultures relative to those observed in submerged cultures, demonstrating the importance of multiple assay systems. Specifically, AdTyrΔ24 and Ad2xTyr were selective for melanoma cells, whereas AdΔ24TyrE4 exhibited no selectivity, similar to Adwt. AdTyrΔ24 and Ad2xTyr were strongly attenuated in their ability to lyse PHKs in organotypic cultures. Furthermore, Ad2xTyr had a superior melanoma selectivity in organotypic cultures of cocultivated melanoma cells and PHKs. The enhanced selectivity for melanoma cells exhibited by Ad2xTyr provides a window of opportunity for therapeutic application. These studies also demonstrate that organotypic cultures derived from mixtures of tumor and normal cells represent a promising new model for analysis of CRAd specificity and toxicity.

The effect of sequestration by nontarget tissues on anti-tumor efficacy of systemically applied, conditionally replicating adenovirus vectors

Avoiding transduction of normal tissue after intravenous application of oncolytic adenoviruses (Ad) is an important strategy to improve the safety and efficacy of these vectors in gene therapy. As a model for a targeted vector, we used Ad vectors with type 35 fibers (Ad5/35), which efficiently transduce human cervical carcinoma cells but not liver cells. In an in vitro model of liver metastases, in which small nests of HeLa cells were surrounded by mouse hepatocytes, we showed that an Ad5/35-based conditionally replicating vector regulated by DNA replication-dependent recombination conferred increased gene transfer to tumor cells and enhanced viral replication and tumor cell lysis compared to the nontargeted Ad5 vector. Intravenous injection of Ad5/35 vectors into mice bearing liver metastases derived from HeLa cells caused markedly less hepatotoxicity than Ad5 vectors; however, it did not result in enhanced tumor cell transduction, viral replication, or oncolysis. Apparently, other factors, including the stability of virus in the blood, trapping within the liver sinusoids, transendothelial transfer, and/or vector diffusion of viral particles to tumor cells, limit tumor transduction, even if the vector is not taken up by liver cells.

Insulation from viral transcriptional regulatory elements enables improvement to hepatoma-specific gene expression from adenovirus vectors

We previously reported that the HS-4 insulator, derived from the chicken beta-globin locus, was able to shield a downstream inducible promoter from viral enhancers or silencers present in the genome of adenovirus vectors. In this study, we constructed two recombinant adenoviruses (Ad) that express an alkaline phosphatase (AP) reporter gene driven by an alpha-fetoprotein (AFP) enhancer/promoter with and without HS-4 insulator (Ad.HS4.AFP-AP and Ad.AFP-AP). The insulated vector, Ad.HS4.AFP-AP, conferred significantly higher AP expression than Ad.AFP-AP in all AFP-producing hepatocellular carcinoma cell lines (HepG2, Hep3B, and HuH7) examined. AP expression from Ad.HS4.AFP-AP was specific to hepatoma cells and barely detectable in AFP-negative tumor cell lines and normal human cells, including human hepatocytes. Intravenous infusion of viral vectors into mice with liver metastasis derived from Hep3B hepatoma cells resulted in AP expression exclusively localized to tumor cells. The number of tumor cells with detectable AP expression was significantly higher in mice infused with Ad.HS4.AFP-AP than in mice that received the non-insulated vector. This study demonstrates that the HS-4 insulator in the context of an Ad vector can increase the activity of the AFP promoter, while maintaining its tumor-specificity in vitro and in vivo. Considering that the anti-tumor activity of oncolytic vectors often depends on the level of pro-apoptotic or suicide gene expression, insulators might be a useful tool to improve the efficacy and specificity of these vectors.