Variation in adenovirus receptor expression and adenovirus vector-mediated transgene expression at defined stages of the cell cycle

Synergistic antitumor immune response mediated by paclitaxel-conjugated nanohybrid oncolytic adenovirus with dendritic cell therapy

Dendritic cell (DC)-based vaccines have emerged as a promising strategy in cancer immunotherapy due to low toxicity. However, the therapeutic efficacy of DC as a monotherapy is insufficient due to highly immunosuppressive tumor environment. To address these limitations of DC as immunotherapeutic agent, we have developed a polymeric nanocomplex incorporating (1) oncolytic adenovirus (oAd) co-expressing interleukin (IL)-12 and granulocyte-macrophage colony-stimulating factor (GM-CSF) and (2) arginine-grafted bioreducible polymer with PEGylated paclitaxel (APP) to restore antitumor immune surveillance function in tumor milieu and potentiate immunostimulatory attributes of DC vaccine. Nanohybrid complex (oAd/APP) in combination with DC (oAd/APP+DC) induced superior expression level of antitumor cytokines (IL-12, GM-CSF, and interferon gamma) than either oAd/APP or DC monotherapy in tumor tissues, thus resulting in superior intratumoral infiltration of both endogenous and exogenous DCs. Furthermore, oAd/APP+DC treatment led superior migration of DC to secondary lymphoid organs, such as draining lymph nodes and spleen, in comparison with either monotherapy. Superior migration profile of DCs in oAd/APP+DC treatment group resulted in more prolific activation of tumor-specific T cells in these lymphoid organs and greater intratumoral infiltration of T cells. Additionally, oAd/APP+DC treatment led to lower subset of tumor infiltrating lymphocytes and splenocytes being immunosuppressive regulatory T cells than any other treatment groups. Collectively, oAd/APP+DC led to superior induction of antitumor immune response and amelioration of immunosuppressive tumor microenvironment to elicit potent tumor growth inhibition than either monotherapy.

Current clinical landscape of oncolytic viruses as novel cancer immunotherapeutic and recent preclinical advancements

Oncolytic viruses (OVs) have been gaining attention in the pharmaceutical industry as a novel immunotherapeutic and therapeutic adjuvant due to their ability to induce and boost antitumor immunity through multiple mechanisms. First, intrinsic mechanisms of OVs that enable exploitation of the host immune system (e.g., evading immune detection) can nullify the immune escape mechanism of tumors. Second, many types of OVs have been shown to cause direct lysis of tumor cells, resulting in an induction of tumor-specific T cell response mediated by release of tumor-associated antigens and danger signal molecules. Third, armed OV-expressing immune stimulatory therapeutic genes could be highly expressed in tumor tissues to further improve antitumor immunity. Last, these OVs can inflame cold tumors and their microenvironment to be more immunologically favorable for other immunotherapeutics. Due to these unique characteristics, OVs have been tested as an adjuvant of choice in a variety of therapeutics. In light of these promising attributes of OVs in the immune-oncology field, the present review will examine OVs in clinical development and discuss various strategies that are being explored in preclinical stages for the next generation of OVs that are optimized for immunotherapy applications.

In Vivo Tracking for Oncolytic Adenovirus Interactions with Liver Cells

Hepatotoxicity remains an as yet unsolved problem for adenovirus (Ad) cancer therapy. The toxic effects originate both from rapid Kupffer cell (KCs) death (early phase) and hepatocyte transduction (late phase). Several host factors and capsid components are known to contribute to hepatotoxicity, however, the complex interplay between Ad and liver cells is not fully understood. Here, by using intravital microscopy, we aimed to follow the infection and immune response in mouse liver from the first minutes up to 72 h post intravenous injection of three Ads carrying delta-24 modification (Ad5-RGD, Ad5/3, and Ad5/35). At 15–30 min following the infusion of Ad5-RGD and Ad5/3 (but not Ad5/35), the virus-bound macrophages demonstrated signs of zeiosis: the formation of long-extended protrusions and dynamic membrane blebbing with the virus release into the blood in the membrane-associated vesicles. Although real-time imaging revealed interactions between the neutrophils and virus-bound KCs within minutes after treatment, and long-term contacts of CD8+ T cells with transduced hepatocytes at 24–72 h, depletion of neutrophils and CD8+ T cells affected neither rate nor dynamics of liver infection. Ad5-RGD failed to complete replicative cycle in hepatocytes, and transduced cells remained impermeable for propidium iodide, with a small fraction undergoing spontaneous apoptosis. In Ad5-RGD-immune mice, the virus neither killed KCs nor transduced hepatocytes, while in the setting of hepatic regeneration, Ad5-RGD enhanced liver transduction. The clinical and biochemical signs of hepatotoxicity correlated well with KC death, but not hepatocyte transduction. Real-time in vivo tracking for dynamic interactions between virus and host cells provides a better understanding of mechanisms underlying Ad-related hepatotoxicity.

A pH- and Bioreducible Cationic Copolymer with Amino Acids and Piperazines for Adenovirus Delivery

Adenoviruses (Ads) are attractive nonviral vectors and show great potential in cancer gene therapy. However, inherent properties of Ads, including immunogenicity, nonspecific toxicity, and coxsackie and adenovirus receptor (CAR)-dependent cell uptake, limit their clinical use. To surmount these issues, we developed a pH- and glutathione-responsive poly(ethylene glycol)-poly(ꞵ-aminoester)-polyethyleneimine (PPA) for conjugation with Ad. The pH sensitivity of the PPA copolymer was elegantly tuned by substitution with different amino acids (arginine, histidine, and tryptophan), piperazines (Pip1, Pip2, and Pip3), and guanidine residues in the backbone of the PPA conjugate. PPA copolymer was further functionalized with short-chain cross-linker succinimidyl 3-(2-pyridyldithio)propionate) (SPDP) to obtain PPA-SPDP for facile conjugation with Ad. The PPA-conjugated Ad (PPA-Ad) conjugate was obtained by reacting PPA-SPDP conjugate with thiolated Ad (Ad-SH). Ad-SH was prepared by reacting Ad with 2-iminothiolane. The size distribution and zeta potential results of PPA-Ad conjugate showed an increasing trend with an increase in copolymer dose. From in vitro test, it was found that the transduction efficiency of PPA-Ad conjugate in CAR-positive cells (A549 and H460 cells) was remarkably increased at the acidic pH condition (pH 6.2) when compared with PPA-Ad conjugate incubated under the physiological condition (pH 7.4). Interestingly, the increase in transduction efficiency was evidenced in CAR-negative cells (MDA-MB-231 and T24 cells). These results demonstrated that biocompatible and biodegradable PPA copolymers can efficiently cover the surface of Ad and can increase the transduction efficiency, and hence PPA copolymers can be a useful nanomaterial for viral vector delivery in cancer therapy.

Virus Infection Variability by Single-Cell Profiling

Cell-to-cell variability of infection has long been known, yet it has remained one of the least understood phenomena in infection research. It impacts on disease onset and development, yet only recently underlying mechanisms have been studied in clonal cell cultures by single-virion immunofluorescence microscopy and flow cytometry. In this review, we showcase how single-cell RNA sequencing (scRNA-seq), single-molecule RNA-fluorescence in situ hybridization (FISH), and copper(I)-catalyzed azide-alkyne cycloaddition (click) with alkynyl-tagged viral genomes dissect infection variability in human and mouse cells. We show how the combined use of scRNA-FISH and click-chemistry reveals highly variable onsets of adenoviral gene expression, and how single live cell plaques reveal lytic and nonlytic adenovirus transmissions. The review highlights how scRNA-seq profiling and scRNA-FISH of coxsackie, influenza, dengue, zika, and herpes simplex virus infections uncover transcriptional variability, and how the host interferon response tunes influenza and sendai virus infections. We introduce the concept of "cell state" in infection variability, and conclude with advances by single-cell simultaneous measurements of chromatin accessibility and mRNA counts at high-throughput. Such technology will further dissect the sequence of events in virus infection and pathology, and better characterize the genetic and genomic stability of viruses, cell autonomous innate immune responses, and mechanisms of tissue injury.

Oncolytic virotherapy reverses chemoresistance in osteosarcoma by suppressing MDR1 expression

BACKGROUND

Osteosarcoma (OS) is a malignant bone tumor primarily affecting children and adolescents. The prognosis of chemotherapy-refractory OS patients is poor. We developed a tumor suppressor p53-expressing oncolytic adenovirus (OBP-702) that exhibits antitumor effects against human OS cells. Here, we demonstrate the chemosensitizing effect of OBP-702 in human OS cells.

MATERIALS AND METHODS

The in vitro and in vivo antitumor activities of doxorubicin (DOX) and OBP-702 were assessed using parental and DOX-resistant OS cells (U2OS, MNNG/HOS) and a DOX-resistant MNNG/HOS xenograft tumor model.

RESULTS

DOX-resistant OS cells exhibited high multidrug resistant 1 (MDR1) expression, which was suppressed by OBP-702 or MDR1 siRNA, resulting in enhanced DOX-induced apoptosis. Compared to monotherapy, OBP-702 and DOX combination therapy significantly suppressed tumor growth in the DOX-resistant MNNG/HOS xenograft tumor model.

CONCLUSION

Our results suggest that MDR1 is an attractive therapeutic target for chemoresistant OS. Tumor-specific virotherapy is thus a promising strategy for reversing chemoresistance in OS patients via suppression of MDR1 expression.

Enhanced expression of coxsackievirus and adenovirus receptor in lipopolysaccharide-induced inflammatory macrophages is through TRIF-dependent innate immunity pathway

AIMS

Inflammatory macrophages have been proposed as a therapeutic target for joint disorders caused by inflammation. This study aimed to investigate the expression and regulation of coxsackievirus-adenovirus receptor (CAR) in lipopolysaccharide (LPS)-stimulated inflammatory macrophages whereby to evaluate the feasibility of virus-directed enzyme prodrug therapy (VDEPT).

MAIN METHODS

Macrophage cell lines (RAW264.7 and J774A.1) and primary macrophage cells derived from rat spleen were used to evaluate the expression of CAR protein or CAR mRNA. Specific inhibitors for TLR4 pathway were used to investigate the regulation of CAR expression. CAR expression in rat joints was documented by immunohistochemistry. Conditionally replicating adenovirus, CRAd-EGFP(PS1217L) or CRAd-NTR(PS1217H6), and non-replicating adenovirus CTL102 were used to transduce genes for enhanced green fluorescent protein (EGFP) or nitroreductase (NTR), respectively. The expression of EGFP, NTR, and the toxicity induced by CB1954 activation were evaluated.

KEY FINDINGS

The in vitro experiments revealed that CAR upregulation was mediated through the TLR4/TRIF/IRF3 pathway in LPS-stimulated inflammatory macrophage RAW264.7 and J774A.1 cells. The inflammatory RAW264.7 cells upregulated CAR expression following LPS stimulation, leading to higher infectability, increased NTR expression, and enhanced sensitization to CB1954. In animal experiments, the induction of CAR expression was observed in the CD68-expressing primary macrophages and in the CD68-expressing macrophages within joints following LPS stimulation.

SIGNIFICANCE

In conclusion, we report an enhanced CAR expression in inflammatory macrophages in vitro and in vivo through the immune response elicited by LPS. Thus, the TLR4/TRIF/IRF3 pathway of macrophages, when activated, could facilitate the therapeutic application of adenovirus-mediated VDEPT.

Advantages of Using Paclitaxel in Combination with Oncolytic Adenovirus Utilizing RNA Destabilization Mechanism

Oncolytic virotherapy is a novel approach to cancer therapy. Ad-fosARE is a conditionally replicative adenovirus engineered by inserting AU-rich elements (ARE) in the 3'-untranslated region of the E1A gene. In this study, we examined the oncolytic activity of Ad-fosARE and used it in a synergistic combination with the chemotherapeutic agent paclitaxel (PTX) for treating cancer cells. The expression of E1A was high in cancer cells due to stabilized E1A-ARE mRNA. As a result, the efficiency of its replication and cytolytic activity in cancer cells was higher than in normal cells. PTX treatment increased the cytoplasmic HuR relocalization in cancer cells, enhanced viral replication through elevated E1A expression, and upregulated CAR (Coxsackie-adenovirus receptor) required for viral uptake. Furthermore, PTX altered the instability of microtubules by acetylation and detyrosination, which is essential for viral internalization and trafficking to the nucleus. These results indicate that PTX can provide multiple advantages to the efficacy of Ad-fosARE both in vitro and in vivo, and provides a basis for designing novel clinical trials. Thus, this virus has a lot of benefits that are not found in other oncolytic viruses. The virus also has the potential for treating PXT-resistant cancers.

Influence of cell physiological state on gene delivery to T lymphocytes by chimeric adenovirus Ad5F35

Adoptive transfer of genetically-modified T cells is a promising approach for treatment of both human malignancies and viral infections. Due to its ability to efficiently infect lymphocytes, the chimeric adenovirus Ad5F35 is potentially useful as an immunotherapeutic for the genetic modification of T cells. In previous studies, it was found that the infection efficiency of Ad5F35 was significantly increased without enhanced expression of the viral receptor after T cell stimulation; however, little is known about the underlying mechanism. Nonetheless, cell physiology has long been thought to affect viral infection. Therefore, we aimed to uncover the physiologic changes responsible for the increased infection efficiency of Ad5F35 following T cell stimulation. Given the complexity of intracellular transport we analyzed viral binding, entry, and escape using a Jurkat T cell model and found that both cell membrane fluidity and endosomal escape of Ad5F35 were altered under different physiological states. This, in turn, resulted in differences in the amount of virus entering cells and reaching the cytoplasm. These results provide additional insight into the molecular mechanisms underlying Ad5F35 infection of T cells and consequently, will help further the clinical application of genetically-modified T cells for immunotherapy.

Synergistic cytotoxicity against human tumor cell lines by oncolytic adenovirus dl1520 (ONYX-015) and melphalan

AIMS AND BACKGROUND

In light of the need for more selective anticancer therapy, much work has been directed at developing compounds or biological agents that target functions specific to cancer cells. To this end, numerous viruses have been engineered to exploit the dependence of cancer cells on particular anomalies that contribute to their rogue proliferative activity, such as dysfunctional p53, overactive mitogenic signaling, or a defective interferon response. The oncolytic human adenovirus dl1520 (ONYX-015) was engineered to propagate specifically in p53-deficient tumors, which comprise over half of all tumors. Based on successes in clinical trials, the full potential of dl1520 and other oncolytic viruses may be even better realized by using them in combination with conventional chemotherapy drugs.

METHODS

As a model system in which to test this potential, representative cell lines from 2 common cancer types, oral squamous cell carcinoma (HN-5a) and colon adenocarcinoma (HT-29), were chosen, as well as platinum-drug-resistant variants of each.

RESULTS

Following preliminary screening of virus and drug combinations, dl1520 and melphalan were found to synergistically inhibit proliferation of all the cancer cell lines. Melphalan pretreatment or cotreatment with dl1520 enhanced inhibition of proliferation by dl1520 by up to 60% and increased apoptosis by up to 25%. The tight-junction protein CAR (coxsackie and adenovirus receptor), via which adenovirus enters cells, was not upregulated by treatment with melphalan, suggesting that other mechanisms contribute to synergy.

CONCLUSIONS

The synergy between melphalan and dl1520 suggests that tumor-selective cell killing by oncolytic viruses may be augmented by combining with cytotoxic drugs.

Paclitaxel resistance increases oncolytic adenovirus efficacy via upregulated CAR expression and dysfunctional cell cycle control

Resistance to paclitaxel chemotherapy frequently develops in ovarian cancer. Oncolytic adenoviruses are a novel therapy for human malignancies that are being evaluated in early phase trials. However, there are no reliable predictive biomarkers for oncolytic adenovirus activity in ovarian cancer. We investigated the link between paclitaxel resistance and oncolytic adenovirus activity using established ovarian cancer cell line models, xenografts with de novo paclitaxel resistance and tumour samples from two separate trials. The activity of multiple Ad5 vectors, including dl922-947 (E1A CR2-deleted), dl1520 (E1B-55K deleted) and Ad5 WT, was significantly increased in paclitaxel resistant ovarian cancer in vitro and in vivo. This was associated with greater infectivity resulting from increased expression of the primary receptor for Ad5, CAR (coxsackie adenovirus receptor). This, in turn, resulted from increased CAR transcription secondary to histone modification in resistant cells. There was increased CAR expression in intraperitoneal tumours with de novo paclitaxel resistance and in tumours from patients with clinical resistance to paclitaxel. Increased CAR expression did not cause paclitaxel resistance, but did increase inflammatory cytokine expression. Finally, we identified dysregulated cell cycle control as a second mechanism of increased adenovirus efficacy in paclitaxel-resistant ovarian cancer. Ad11 and Ad35, both group B adenoviruses that utilise non-CAR receptors to infect cells, are also significantly more effective in paclitaxel-resistant ovarian cell models. Inhibition of CDK4/6 using PD-0332991 was able both to reverse paclitaxel resistance and reduce adenovirus efficacy. Thus, paclitaxel resistance increases oncolytic adenovirus efficacy via at least two separate mechanisms - if validated further, this information could have future clinical utility to aid patient selection for clinical trials.

Combination of bladder cancer-specific oncolytic adenovirus gene therapy with cisplatin on bladder cancer in vitro

Bladder cancer-specific oncolytic adenovirus Ad/PSCAE/UPII/E1A, carrying E1A gene regulated by human Uroplakin II (UPII) promoter and prostate stem cell antigen enhancer (PSCAE), could kill bladder tumor cells preferentially. The aim of this study was to examine the effects of Ad/PSCAE/UPII/E1A combined with cisplatin on human bladder cancer cells and to identify the underlying mechanisms. The combined effects of Ad/PSCAE/UPII/E1A and cisplatin on EJ, 5637, and BIU-87 bladder cancer cells were evaluated by MTT cell proliferation assay. Cell apoptosis was detected by flow cytometry with fluorescein isothiocyanate-conjugated annexin V (annexin V-FITC) and propidium iodide staining. The activation of the caspase pathway and the expression of Bcl-2 family proteins were determined by western blot assay. Ad/PSCAE/UPII/E1A adenovirus vector could infect bladder cancer cell lines selectively and induce growth inhibition effectively. Of note, the combination treatment of cisplatin and Ad/PSCAE/UPII/E1A could inhibit the proliferation of bladder cancer cells significantly compared with the "alone" treatment. Furthermore, Ad/PSCAE/UPII/E1A plus cisplatin combined treatment resulted in enhanced apoptosis in bladder cancer cells. The enhanced antitumor effects in vitro elicited by Ad/PSCAE/UPII/E1A plus cisplatin were closely related to the increased Fas expression and cleavage of caspase-8 and Bid and decrease in the ratio of anti- to pro-apoptotic proteins followed by activation of caspase-9 and caspase-3, which may contribute to the activation of extrinsic and intrinsic apoptotic pathways. Our results indicate that the combination of Ad/PSCAE/UPII/E1A with cisplatin exerts a synergistic antitumor effect on human bladder cancer cells and is a potential combined treatment strategy for bladder cancer.

Ionizing radiation enhances dl922-947-mediated cell death of anaplastic thyroid carcinoma cells

dl922-947 is an oncolytic adenovirus potentially suitable for the treatment of aggressive localized tumors, such as anaplastic thyroid carcinoma (ATC). In this study, we have analyzed the effects of dl922-947 in combination with ionizing radiations, testing different schedules of administration and observing synergistic effects only when ATC cells were irradiated 24 h prior to viral infection. Cells undergoing combined treatment exhibited a marked increase in cell death and viral replication, suggesting that irradiation blocks cells in a more permissive state for viral life cycle. We also show that dl922-947 triggers a DNA damage response, characterized by mobilization of the MRN complex (composed by Mre11-Rad50-Nbs1), accumulation of γH2AX, and activation of the checkpoint kinases ataxia telangiectasia mutated (ATM) and Chk1. Based on these observations, we speculate that the DNA damage response acts as a cellular protective mechanism to hinder viral infection and replication. To confirm this hypothesis, we demonstrate that the ATM inhibitor KU55933 increased the oncolytic activity of dl922-947 and its replication. Finally, we validate the potential therapeutic use of this approach by showing in vivo that the combined treatment slows tumor xenograft growth more potently than either irradiation or infection alone.

A tumor-stroma targeted oncolytic adenovirus replicated in human ovary cancer samples and inhibited growth of disseminated solid tumors in mice

Targeting the tumor stroma in addition to the malignant cell compartment is of paramount importance to achieve complete tumor regression. In this work, we modified a previously designed tumor stroma-targeted conditionally replicative adenovirus (CRAd) based on the SPARC promoter by introducing a mutated E1A unable to bind pRB and pseudotyped with a chimeric Ad5/3 fiber (Ad F512v1), and assessed its replication/lytic capacity in ovary cancer in vitro and in vivo. AdF512v1 was able to replicate in fresh samples obtained from patients: (i) with primary human ovary cancer; (ii) that underwent neoadjuvant treatment; (iii) with metastatic disease. In addition, we show that four intraperitoneal (i.p.) injections of 5 × 10(10) v.p. eliminated 50% of xenografted human ovary tumors disseminated in nude mice. Moreover, AdF512v1 replication in tumor models was enhanced 15-40-fold when the tumor contained a mix of malignant and SPARC-expressing stromal cells (fibroblasts and endothelial cells). Contrary to the wild-type virus, AdF512v1 was unable to replicate in normal human ovary samples while the wild-type virus can replicate. This study provides evidence on the lytic capacity of this CRAd and highlights the importance of targeting the stromal tissue in addition to the malignant cell compartment to achieve tumor regression.

Combination of oncolytic adenovirus and dacarbazine attenuates antitumor ability against uveal melanoma cells via cell cycle block

Uveal melanoma is the most common primary intraocular malignancy in adults; however, current therapeutic modalities, including chemotherapy, have not been successful. Oncolytic viruses serve as an emerging gene therapy tool for cancer treatment because they specifically kill tumor cells while sparing normal cells. The oncolytic virus H101 has been approved by the Chinese State Food and Drug Administration for the treatment of certain malignancies. Unfortunately, the monotherapy of adenovirus has demonstrated limited efficacy in a clinical setting. Thus, novel treatment strategies in which an oncolytic virus is combined with existing chemicals are advancing toward potential clinical use. In this study, we chose the combination of oncolytic virus H101 and the alkylating agent dacarbazine (DTIC) to treat uveal melanoma cells in vitro. Our results demonstrated that the combination exerted a synergistic antitumor effect without enhanced toxicity to normal cells via a type of cell cycle block other than the induction of apoptosis. Further investigation is warranted to elucidate the specific underlying mechanisms of this co-treatment therapy. Our study suggests the viro-chemo combination therapy is feasible and is a potentially promising approach for the treatment of uveal melanoma.

A simple detection system for adenovirus receptor expression using a telomerase-specific replication-competent adenovirus

Adenovirus serotype 5 (Ad5) is frequently used as an effective vector for induction of therapeutic transgenes in cancer gene therapy or of tumor cell lysis in oncolytic virotherapy. Ad5 can infect target cells through binding with the coxsackie and adenovirus receptor (CAR). Thus, the infectious ability of Ad5-based vectors depends on the CAR expression level in target cells. There are conventional methods to evaluate the CAR expression level in human target cells, including flow cytometry, western blotting and immunohistochemistry. Here, we show a simple system for detection and assessment of functional CAR expression in human tumor cells, using the green fluorescent protein (GFP)-expressing telomerase-specific replication-competent adenovirus OBP-401. OBP-401 infection induced detectable GFP expression in CAR-expressing tumor cells, but not in CAR-negative tumor cells, nor in CAR-positive normal fibroblasts, 24 h after infection. OBP-401-mediated GFP expression was significantly associated with CAR expression in tumor cells. OBP-401 infection detected tumor cells with low CAR expression more efficiently than conventional methods. OBP-401 also distinguished CAR-positive tumor tissues from CAR-negative tumor and normal tissues in biopsy samples. These results suggest that GFP-expressing telomerase-specific replication-competent adenovirus is a very potent diagnostic tool for assessment of functional CAR expression in tumor cells for Ad5-based antitumor therapy.

Radiation-induced upregulation of gene expression from adenoviral vectors mediated by DNA damage repair and regulation

PURPOSE

In the present study, we evaluated the combination of replication-deficient adenoviruses and radiotherapy in vitro. The purpose of the present study was to analyze the mechanism of radiation-mediated upregulation of adenoviral transgene expression.

METHODS AND MATERIALS

Adenoviral transgene expression (luciferase or green fluorescent protein) was studied with and without radiation in three cell lines: breast cancer M4A4-LM3, prostate cancer PC-3MM2, and lung cancer LNM35/enhanced green fluorescent protein. The effect of the radiation dose, modification of the viral capsid, and five different transgene promoters were studied. The cellular responses were studied using mass spectrometry and immunofluorescence analysis. Double strand break repair was modulated by inhibitors of heat shock protein 90, topoisomerase-I, and DNA protein kinase, and transgene expression was measured.

RESULTS

We found that a wide range of radiation doses increased adenoviral transgene expression regardless of the cell line, transgene, promoter, or viral capsid modification. Treatment with adenovirus, radiation, and double strand break repair inhibitors resulted in persistence of double strand breaks and subsequent increases in adenovirus transgene expression.

CONCLUSIONS

Radiation-induced enhancement of adenoviral transgene expression is linked to DNA damage recognition and repair. Radiation induces a global cellular response that results in increased production of RNA and proteins, including adenoviral transgene products. This study provides a mechanistic rationale for combining radiation with adenoviral gene delivery.

Low-dose paclitaxel synergizes with oncolytic adenoviruses via mitotic slippage and apoptosis in ovarian cancer

The microtubule-stabilizing drug paclitaxel has activity in relapsed ovarian cancer. dl922-947, an oncolytic adenovirus with a 24-bp deletion in E1A CR2, replicates selectively within and lyses cells with a dysregulated Rb pathway and has efficacy in ovarian cancer. In the aggressive A2780CP xenograft, combination treatment with weekly dl922-947 and paclitaxel has significantly greater efficacy than either treatment alone and can produce complete tumor eradication in some animals. We investigated the mechanisms of paclitaxel's synergy with dl922-947 in ovarian cancer. The host-cell microtubule network is grossly rearranged and stabilized following adenovirus infection, but paclitaxel does not increase this significantly. Paclitaxel does not synergize by increasing infectivity, viral protein expression or virus release. However, destabilizing the microtubule network with nocodazole reduces viral exit, revealing a novel microtubule-dependent pathway for non-lytic adenoviral exit. dl922-947 can override multiple cell cycle checkpoints but induces cell death by a non-apoptotic mechanism. In combination, dl922-947 and low-dose paclitaxel induces aberrant, multipolar mitoses, mitotic slippage and multinucleation, triggering an apoptotic cell death.

Retargeting of adenovirus vectors through genetic fusion of a single-chain or single-domain antibody to capsid protein IX

Adenovirus (Ad) vectors are the most commonly used system for gene therapy applications, due in part to their ability to infect a wide array of cell types and tissues. However, many therapies would benefit from the ability to target the Ad vector only to specific cells, such as tumor cells for cancer gene therapy. In this study, we investigated the utility of capsid protein IX (pIX) as a platform for the presentation of single-chain variable-fragment antibodies (scFv) and single-domain antibodies (sdAb) for virus retargeting. We show that scFv can be displayed on the capsid through genetic fusion to native pIX but that these molecules fail to retarget the virus, due to improper folding of the scFv. Redirecting expression of the fusion protein to the endoplasmic reticulum (ER) results in correct folding of the scFv and allows it to recognize its epitope; however, ER-targeted pIX-scFv was incorporated into the Ad capsid at a very low level which was not sufficient to retarget virus infection. In contrast, a pIX-sdAb construct was efficiently incorporated into the Ad capsid and enhanced virus infection of cells expressing the targeted receptor. Taken together, our data indicate that pIX is an effective platform for presentation of large targeting polypeptides on the surface of the virus capsid, but the nature of the ligand can significantly affect its association with virions.

Docetaxel increases antitumor efficacy of oncolytic prostate-restricted replicative adenovirus by enhancing cell killing and virus distribution

BACKGROUND

We explored multiple molecular mechanisms of the combination of docetaxel and an oncolytic prostate-restricted replication competent adenovirus (Ad) (PRRA) in advanced prostate cancer (PCa) models. The combinational therapy has potential to overcome the therapeutic limitations of poor virus distribution inside solid tumors.

METHODS

We evaluated the effect of docetaxel on the antitumor efficacy and efficiency of virus transduction, transgene expression and virus distribution of PRRA in a prostate-specific antigen/prostate-specific membrane antigen-positive tumor xenograft model. We also evaluated the effect of docetaxel on apoptosis induction, cell killing and the efficiency of transgene expression and virus replication in vitro.

RESULTS

Tumor growth inhibition was significantly enhanced when docetaxel was administrated before intratumor injection of PRRA. In vivo dual-photon microscopy and ex vivo fluorescence microscopy and immunohistochemistry showed that docetaxel increased transgene expression and expanded virus distribution. The combination of docetaxel and PRRA also increased cell apoptosis. In vitro, docetaxel significantly increased cell killing in PRRA-treated PCa cells. Docetaxel significantly increased Ad-mediated trangene expression independent of Ad binding receptors and replication capability. Docetaxel increased the activity of cytomegalovirus (CMV) promoter but not of a chimeric prostate-specific enhancer, resulting in higher transgene expression. The enhanced CMV promoter activity resulted from activation of p38 mitogen-activated protein kinase (MAPK) because inhibition of p38 MAPK blocked the docetaxel-induced increase in CMV promoter activity.

CONCLUSIONS

Combining docetaxel with an oncolytic PRRA improved therapeutic potential by expanding virus distribution and enhancing cell apoptosis and killing. These studies suggested a novel mechanism for enhancing the effect of therapeutic genes delivered by a PRRA.

The non-essential left end region of the fowl adenovirus 9 genome is suitable for foreign gene insertion/replacement

The goals of this study were to demonstrate that a non-essential region at the left end of the fowl adenovirus 9 (FAdV-9) genome could be used to generate recombinant viruses, examine their in vitro growth characteristics and determine their ability to transduce non-avian cells. Three FAdV-9 vectors (rFAdV-9s) were generated carrying the enhanced-green fluorescent protein (EGFP) gene: FAdV-9inEGFP, FAdV-9 Delta 1-EGFP and FAdV-9 Delta 4-EGFP. FAdV-9inEGFP carried the EGFP cassette inserted into the non-essential region without deletion resulting in an increase of the genome size to 103.7% of the wild-type. FAdV-9 Delta 1-EGFP and FAdV-9 Delta 4-EGFP (rFAdV-9 Delta s) carried the EGFP cassette replacing the non-essential sequences at nucleotides 1194-2342 and 491-2782, respectively. All rFAdV-9s had wild-type growth kinetics and plaque morphology. The rFAdV-9 Delta s replicated in CH-SAH cells with the same titers as the wild-type virus. The FAdV-9inEGFP titers were approximately 1 log lower than those of rFAdV-9 Delta s and wt FAdV-9 at 36 and 48 h post-infection (h.p.i.). EGFP was expressed in avian and mammalian cells infected with rFAdV-9s. EGFP expression, based on spectrofluorometry, was significantly higher in chicken hepatoma cells infected with FAdV-9inEGFP than in those with rFAdV-9 Delta s at 18 and 24h.p.i, suggesting a functional role of some or all non-essential ORFs on foreign gene expression. This study demonstrated the suitability of the non-essential region as an insertion/replacement site for foreign genes to generate FAdV-9-based vectors that can be applied as recombinant vaccines for poultry or gene delivery vehicles for mammalian systems.

Inhibition of repair of radiation-induced DNA damage enhances gene expression from replication-defective adenoviral vectors

Radiation has been shown to up-regulate gene expression from adenoviral vectors in previous studies. In the current study, we show that radiation-induced dsDNA breaks and subsequent signaling through the mitogen-activated protein kinase (MAPK) pathway are responsible, at least in part, for this enhancement of transgene expression both in vitro and in vivo. Inhibitors of ataxia-telangiectasia-mutated, poly(ADP-ribose) polymerase-mutated, and DNA-dependent protein kinase (DNA-PK)-mediated DNA repair were shown to maintain dsDNA breaks (gammaH2AX foci) by fluorescence-activated cell sorting and microscopy. Inhibition of DNA repair was associated with increased green fluorescent protein (GFP) expression from a replication-defective adenoviral vector (Ad-CMV-GFP). Radiation-induced up-regulation of gene expression was abrogated by inhibitors of MAPK (PD980059 and U0126) and phosphatidylinositol 3-kinase (LY294002) but not by p38 MAPK inhibition. A reporter plasmid assay in which GFP was under the transcriptional control of artificial Egr-1 or cytomegalovirus promoters showed that the DNA repair inhibitors increased GFP expression only in the context of the Egr-1 promoter. In vivo administration of a water-soluble DNA-PK inhibitor (KU0060648) was shown to maintain luciferase expression in HCT116 xenografts after intratumoral delivery of Ad-RSV-Luc. These data have important implications for therapeutic strategies involving multimodality use of radiation, targeted drugs, and adenoviral gene delivery and provide a framework for evaluating potential advantageous combinatorial effects.

Tumor antigen LRRC15 impedes adenoviral infection: implications for virus-based cancer therapy

Adenoviruses for gene or oncolytic therapy are under development. Notable among these strategies is adenoviral delivery of the tumor suppressor p53. Since all therapeutics have limitations in certain settings, we have undertaken retroviral suppressor screens to identify genes conferring resistance to adenovirus-delivered p53. These studies identified the tumor antigen LRRC15, which is frequently overexpressed in multiple tumor types, as a repressor of cell death due to adenoviral p53. LRRC15, however, does not impede p53 function per se but impedes adenoviral infection. Specifically, LRRC15 causes redistribution of the coxsackievirus-adenovirus receptor away from the cell surface. This effect is manifested in less adenoviral binding to the surfaces of LRRC15-expressing cells. This discovery, therefore, not only is important for understanding adenoviral biology but also has potentially important implications for adenovirus-based anticancer therapeutics.

Treatment of metastatic renal cancer with capsid-modified oncolytic adenoviruses

Renal cancer is a common and deadly disease that lacks curative treatments when metastatic. Here, we have used oncolytic adenoviruses, a promising developmental approach whose safety has recently been validated in clinical trials. Although preliminary clinical efficacy data exist for selected tumor types, potency has generally been less than impressive. One important reason may be that expression of the primary receptor, coxsackie-adenovirus receptor, is often low on many or most advanced tumors, although not evaluated in detail with renal cancer. Here, we tested if fluorescence-assisted cell sorting could be used to predict efficacy of a panel of infectivity-enhanced capsid-modified marker gene expressing adenoviruses in renal cancer cell lines, clinical specimens, and subcutaneous and orthotopic murine models of peritoneally metastatic renal cell cancer. The respective selectively oncolytic adenoviruses were tested for killing of tumor cells in these models, and biodistribution after locoregional delivery was evaluated. In vivo replication was analyzed with noninvasive imaging. Ad5/3-Delta24, Ad5-Delta24RGD, and Ad5.pK7-Delta24 significantly increased survival of mice compared with mock or wild-type virus and 50% of Ad5/3-Delta24 treated mice were alive at 320 days. Because renal tumors are often highly vascularized, we investigated if results could be further improved by adding bevacizumab, a humanized antivascular endothelial growth factor antibody. The combination was well tolerated but did not improve survival, suggesting that the agents may be best used in sequence instead of together. These results set the stage for clinical testing of oncolytic adenoviruses for treatment of metastatic renal cancer currently lacking other treatment options.

Development of lipid particles targeted via sugar-lipid conjugates as novel nuclear gene delivery system

Efficient nuclear gene delivery is essential for successful gene therapy. This study developed a novel system that mimics the mechanism of nuclear entry of adenovirus (Ad) by means of a Multifunctional Envelope-type Nano Device (MEND). In this system, plasmid DNA (pDNA) was condensed with polycation, followed by encapsulation in a lipid membrane. To target MEND to the nuclear pore complex (NPC), sugar served as a NPC-mediated nuclear targeting device was modified on the surface of the lipid envelope. This was accomplished via synthesis of a sugar-cholesterol conjugate. After binding of the MEND to the NPC, the pDNA core was transferred into the nucleus in conjunction with a breakdown of the lipid envelope. Sugar-modified MEND showed higher transfection efficiency compared with unmodified MEND, in non-dividing and dividing cells. Confocal microscopy confirmed that nuclear transfer of pDNA was improved by sugar modification of MEND. Furthermore, destabilization of the lipid envelope significantly enhanced transfection activity: therefore, nuclear-delivery efficiency was closely related to lipid envelope stability. Moreover, quantitative evaluation of cellular uptake and nuclear transfer processes by real-time PCR confirmed that the surface sugars affected nuclear transfer, but not cellular uptake. In summary, a novel system for the nuclear delivery of pDNA was successfully developed by using a sugar-modified MEND and by optimizing the lipid envelope stability.

The histone deacetylase inhibitor FK228 given prior to adenovirus infection can boost infection in melanoma xenograft model systems

A major limitation of adenovirus type 5-mediated cancer gene therapy is the inefficient infection of many cancer cells. Previously, we showed that treatment with low doses of the histone deacetylase inhibitor FK228 (FR901228, depsipeptide) increased coxsackie adenovirus receptor (CAR) levels, histone H3 acetylation, and adenovirus infection efficiencies as measured by viral transgene expression in cancer cell lines but not in cultured normal cells. To evaluate FK228 in vivo, the effects of FK228 therapy in athymic mice bearing LOX IMVI or UACC-62 human melanoma xenografts were examined. Groups of mice were treated with FK228 using several dosing schedules and the differences between treated and control animals were determined. In mice with LOX IMVI xenografts (n = 6), maximum CAR induction was observed 24 h following a single FK228 dose of 3.6 mg/kg with a 13.6 +/- 4.3-fold (mean +/- SD) increase in human CAR mRNA as determined by semiquantitative reverse transcription-PCR analysis. By comparison, mouse CAR levels in liver, kidney, and lung from the same animals showed little to no change. Maximum CAR protein induction of 9.2 +/- 4.8-fold was achieved with these treatment conditions and was associated with increased histone H3 acetylation. Adenovirus carrying a green fluorescent protein (GFP) transgene (2 x 10(9) viral particles) was injected into the xenografts and GFP mRNA levels were determined. A 7.4 +/- 5.2-fold increase in GFP mRNA was found 24 h following adenovirus injection into optimally FK228-treated mice (n = 10). A 4-fold increase in GFP protein-positive cells was found following FK228 treatment. These studies suggest that FK228 treatment prior to adenovirus infection could increase the efficiency of adenovirus gene therapy in xenograft model systems.

Endogenous low-level expression of the coxsackievirus and adenovirus receptor enables coxsackievirus B3 infection of RD cells

Cells in which the appropriate viral receptor cannot be detected may paradoxically act as a host to the virus. For example, RD cells are often considered to be non-permissive for infection with coxsackievirus and adenovirus receptor (CAR)-dependent group B coxsackieviruses (CVB), insofar as inoculated cell monolayers show little or no cytopathic effect (CPE) and immunohistological assays for CAR have been consistently negative. Supernatants recovered from RD cells exposed to CVB, however, contained more virus than was added in the initial inoculum, indicating that productive virus replication occurred in the monolayer. When infected with a recombinant CVB type 3 (CVB3) chimeric strain expressing S-Tag within the viral polyprotein, 4–11 % of RD cells expressed S-Tag over 48 h. CAR mRNA was detected in RD cells by RT-PCR, and CAR protein was detected on Western blots of RD lysates; both were detected at much lower levels than in HeLa cells. Receptor blockade by an anti-CAR antibody confirmed that CVB3 infection of RD cells was mediated by CAR. These results show that some RD cells in the culture population express CAR and can thereby be infected by CVB, which explains the replication of CAR-dependent CVB in cell types that show little or no CPE and in which CAR has not previously been detected. Cells within cultures of cell types that have been considered non-permissive may express receptor transiently, leading to persistent replication of virus within the cultured population.

Adenovirus dodecahedron cell attachment and entry are mediated by heparan sulfate and integrins and vary along the cell cycle

The adenovirus penton base is a strategic protein involved in the virus internalisation pathway through interaction between its RGD sequences and integrin. In some human adenovirus serotypes, this pentameric protein features the ability of interacting together by twelve, leading to the formation of a symmetric nanoparticle called dodecahedron (Dd). This non-infectious adenovirus-like particle exhibiting sixty RGD sequences interacts with integrin but also with heparan sulfate proteoglycans (HSPGs) expressed at the cell surface. In this study, we discriminate the respective importance of HSPGs and integrin on human adenovirus serotype 3 dodecahedron attachment and entry. Using different cell lines and a specific integrin inhibitor, we have determined that HSPGs are mainly responsible for particle attachment to the cell surface, favouring a strictly required interaction with integrin that triggers internalisation. No other receptors are involved in Dd entry and integrins on their own can mediate the particle entry in HSPGs-deficient cells. Moreover, integrin recognition by Dd is highly susceptible to cations and particularly to manganese that enhances particle binding by 4- to 7-fold compared to calcium. Interestingly, investigations on Dd receptors along the cell cycle revealed an enhanced particle targeting to mitotic cells and a loss of internalisation at this stage. This phenomenon observed with both HeLa- and HSPGs-deficient cells, depends on integrin remodelling during mitosis. This provides new clues for the use of this adenovirus nanoparticle as a delivery vector and sheds light on the integrin and HSPGs relationship in both resting and dividing cells.

HDAC inhibitor valproic acid upregulates CAR in vitro and in vivo

Background

The presence of CAR in diverse tumor types is heterogeneous with implications in tumor transduction efficiency in the context of adenoviral mediated cancer gene therapy. Preliminary studies suggest that CAR transcriptional regulation is modulated through histone acetylation and not through promoter methylation. Furthermore, it has been documented that the pharmacological induction of CAR using histone deacetylase inhibitor (iHDAC) compounds is a viable strategy to enhance adenoviral mediated gene delivery to cancer cells in vitro. The incorporation of HDAC drugs into the overall scheme in adenoviral based cancer gene therapy clinical trials seems rational. However, reports using compounds with iHDAC properties utilized routinely in the clinic are pending. Valproic acid, a short chained fatty acid extensively used in the clinic for the treatment of epilepsy and bipolar disorder has been recently described as an effective HDAC inhibitor at therapeutic concentrations.

Methods

We studied the effect of valproic acid on histone H3 and H4 acetylation, CAR mRNA upregulation was studied using semiquantitative PCR and adenoviral transduction on HeLa cervical cancer cells, on MCF-7 breast cancer cells, on T24 transitional cell carcinoma of the bladder cells. CAR mRNA was studied using semiquantitative PCR on tumor tissue extracted from patients diagnosed with cervical cancer treated with valproic acid.

Results

CAR upregulation through HDAC inhibition was observed in the three cancer cell lines with enhancement of adenoviral transduction. CAR upregulation was also observed in tumor samples obtained from patients with cervical cancer treated with therapeutic doses of valproic acid. These results support the addition of the HDAC inhibitor valproic acid to adenoviral mediated cancer gene therapy clinical trials to enhance adenoviral mediated gene delivery to the tumor cells.

Identification of HI-like loop in CELO adenovirus fiber for incorporation of receptor binding motifs

Vectors based on the chicken embryo lethal orphan (CELO) avian adenovirus (Ad) have two attractive properties for gene transfer applications: resistance to preformed immune responses to human Ads and the ability to grow in chicken embryos, allowing low-cost production of recombinant viruses. However, a major limitation of this technology is that CELO vectors demonstrate decreased efficiency of gene transfer into cells expressing low levels of the coxsackie-Ad receptor (CAR). In order to improve the efficacy of gene transfer into CAR-deficient cells, we modified viral tropism via genetic alteration of the CELO fiber 1 protein. The alphav integrin-binding motif (RGD) was incorporated at two different sites of the fiber 1 knob domain, within an HI-like loop that we identified and at the C terminus. Recombinant fiber-modified CELO viruses were constructed containing secreted alkaline phosphatase (SEAP) and enhanced green fluorescent protein genes as reporter genes. Our data show that insertion of the RGD motif within the HI-like loop of the fiber resulted in significant enhancement of gene transfer into CAR-negative and CAR-deficient cells. In contrast, CELO vectors containing the RGD motif at the fiber 1 C terminus showed reduced transduction of all cell lines. CELO viruses modified with RGD at the HI-like loop transduced the SEAP reporter gene into rabbit mammary gland cells in vivo with an efficiency significantly greater than that of unmodified CELO vector and similar to that of Ad type 5 vector. These results illustrate the potential for efficient CELO-mediated gene transfer into a broad range of cell types through modification of the identified HI-like loop of the fiber 1 protein.

Combining high selectivity of replication via CXCR4 promoter with fiber chimerism for effective adenoviral oncolysis in breast cancer

Conditionally replicative adenoviruses (CRAds) represent novel therapeutic agents that have been recently applied in the context of breast cancer therapy. However, deficiencies in the ability of the adenovirus to infect target tumor cells and to specifically replicate within the tumor target represent key deficiencies preventing the realization of the full potential of this therapeutic approach. Minimal expression of the adenovirus serotype 5 (Ad5) receptor CAR (coxsackie and adenovirus receptor) on breast cancer cells represents a major limitation for Ad5-based virotherapy. Genetic fiber chimerism is a method to alter the tropism of Ad5-based CRAds to achieve CAR-independent infectivity of tumor cells. Here, we describe the use of a CRAd with cancer specific transcriptional control of the essential Ad5 E1A gene using the human CXCR4 gene promoter. We further modified the fiber protein of this agent by switching the knob domain with that of the adenovirus serotype 3. The oncolytic activity of this 5/3 fiber-modified CRAd was studied in breast cancer cell lines, primary breast cancer and human liver tissue slices from patients, and in a xenograft breast cancer mouse model. This infectivity enhanced CRAd agent showed improved replication and killing in breast cancer cells in vitro and in vivo with a remarkable specificity profile that was strongly attenuated in nonbreast cancer cells, as well as in normal human breast and liver tissues. In conclusion, utilization of a CRAd that combined infectivity enhancement strategies and transcriptional targeting improved the CRAd-based antineoplastic effects for breast cancer therapy.

Baculovirus transduction of rat articular chondrocytes: roles of cell cycle

BACKGROUND

We have previously demonstrated highly efficient baculovirus transduction of primary rat articular chondrocytes, thus implicating the possible applications of baculovirus in gene-based cartilage tissue engineering. However, baculovirus-mediated gene expression in the chondrocytes is transient.

METHODS

In this study, we attempted to prolong the expression by supertransduction, but uncovered that after long-term culture the chondrocytes became more refractory to baculovirus transduction. Therefore, the correlation between baculovirus-mediated enhanced green fluorescent protein (EGFP) expression and cell cycle was investigated by comparing the cycling chondrocytes and chondrocytes rich in quiescent cells, in terms of EGFP expression, virus uptake, cell cycle distribution, nuclear import and methylation of viral DNA.

RESULTS

We demonstrated, for the first time, that baculovirus-mediated transduction of chondrocytes is correlated with the cell cycle. The chondrocytes predominantly in G2/M phase were approximately twice as efficient in EGFP expression as the cycling cells, while the cells in S and G1 phases expressed EGFP as efficiently as the cycling cells. Notably, the chondrocyte populations rich in quiescent cells resulted in efficient virus uptake, but less effective nuclear transport of baculoviral DNA and higher degree of methylation, and hence poorer transgene expression.

CONCLUSIONS

These findings unravel the practical limitations when employing baculovirus in cartilage tissue engineering. The implications and possible solutions are discussed.

Cell cycle dependent transcription, a determinant factor of heterogeneity in cationic lipid-mediated transgene expression

BACKGROUND

Heterogeneity of transgene expression, the presence or absence (below the limit of detection) of transgene expression on a cell-by-cell basis, is a severe disadvantage in the use of cationic lipid-mediated gene vectors for gene therapy and experiments in molecular biology. Understandings of intracellular trafficking and the function (transgene expression) of vectors related to cellular physiology are essential in terms of clarifying the mechanism underlying the heterogeneity.

METHODS

To distinguish the contribution of nuclear transfer efficiency and subsequent intranuclear transcription efficiency to the overall heterogeneity in transgene expression, a novel imaging system was established for the dual visualization of the nuclear transfer of pDNA and marker gene expression (lacZ) in single cells.

RESULTS

The expression of LacZ occurred in only approximately 30% of HeLa cells of the nuclear pDNA-positive cells, indicating that intranuclear transcription efficiency contributed to the heterogeneity. Dual imaging against synchronized cells further revealed that the efficiency of nuclear delivery was comparable irrespective of cell cycle status, which is contrary to the generally accepted hypothesis that nuclear import of pDNA is enhanced during cell division when the nuclear membrane structure is perturbed. The most significant finding in the present study is that nuclear transcription efficiency in terms of the ratio of LacZ-positive cells to nuclear pDNA-positive cells drastically increased in the late S and G2/M phase.

CONCLUSIONS

This is the first demonstration to show that cell cycle dependent intranuclear transcription appears to be responsible for the overall heterogeneity of transgene expression.

Replication-deficient adenovirus induces host topoisomerase I activity: implications for adenovirus-mediated gene expression

Replication-deficient adenoviruses are useful vectors for the transfer of therapeutic transgenes to malignant and non-malignant tissues. Yet their clinical application is limited by the potential toxicity of viral infection and the transient nature of transgene expression. Although transgene expression from adenovirus vectors is initially higher than expression of transgenes transduced by other viral or non-viral vectors, it is often insufficient to generate a significant therapeutic effect. We addressed this issue by searching for DNA-targeted viral-induced host responses potentially restricting transgene expression. Nuclear protein extracts from livers of rats systemically infected with replication-deficient adenovirus exhibited enhanced topoisomerase I activity compared with extracts from uninfected animals. Consequently, the inhibition of topoisomerase I by the anti-cancer drug topotecan greatly enhanced transgene expression in adenovirus-infected hepatic cells, colon cancer and prostate cancer cell cultures, mouse liver, human ex vivo tumor specimens, and mouse tumor in vivo. The enhancement could not be ascribed to non-specific genotoxic stress, cell death, or cell-cycle perturbation. These findings are significant for gene therapy as they reveal novel aspects of the host anti-adenovirus response and set the stage for the development of a rational molecular-pharmacological approach to increase the effectiveness, and safety, of adenovirus-mediated cancer therapeutics.

Restituting intestinal epithelial cells exhibit increased transducibility by adenoviral vectors

BACKGROUND AND AIMS

While mature enterocytes are resistant to transduction by adenovirus type 5 (Ad5) vectors, undifferentiated cells are transduced much more efficiently. Our purpose was to study enterocyte transduction in models of intestinal wound healing.

METHODS

Transduction was studied ex vivo using cultures of endoscopic biopsies and in vitro utilizing Caco-2 cells in models of mucosal wound healing. Vectors carried either the LacZ or the luciferase gene. CAR (coxsackievirus and adenovirus receptor) and integrins were studied with transduction inhibition and immunofluorescent staining.

RESULTS

Increased transduction efficiency was observed for a subset of enterocytes with a flattened de-differentiated phenotype present at the edge of cultured biopsies. In the in vitro systems, expanding Caco-2 cell monolayers exhibited increased transducibility that was time- and dose-dependent, reaching virtually 100% in cells along the leading edge at high viral load. Bioluminescence activity of transduced expanding monolayers was up to 3-fold greater than that of non-expanding monolayers ('fence' system, 48 h, MOI 1000, p < 0.05). Mitomycin C pre-treatment did not affect levels of transduction in expanding monolayers. At the highest viral load tested, CAR or integrin blocking prior to virus application resulted in 39.4% and 45.4% reduction in transduction levels (p < 0.05). Immunofluorescence revealed altered expression of CAR on the migrating edge of the Caco-2 cultures and the expression of CAR on the apical membrane of biopsy enterocytes.

CONCLUSIONS

Increased CAR and integrin accessibility in migrating enterocytes mediates increased transduction by Ad5 vectors. This subset of enterocytes provides a target for the delivery of genes of interest for both research and gene therapy applications.

Combining adenoviral oncolysis with temozolomide improves cell killing of melanoma cells

Oncolytic adenoviruses are emerging agents for treatment of cancer by tumor-restricted virus replication, cell lysis and virus spread. Clinical studies with first generation oncolytic adenoviruses have revealed that an increased potency is warranted in order to achieve therapeutic efficacy. One approach towards this end is to combine adenoviral oncolysis with chemotherapy. Here, a fundamental requirement is that chemotherapy does not interfere with adenovirus replication in cancer cells. We have previously developed a melanoma-targeted oncolytic adenovirus, Ad5/3.2xTyr, which features tyrosinase promoter regulated replication and enhanced cell entry into melanoma cells. In this study, we investigated a combination treatment of melanoma cells with Ad5/3.2xTyr and temozolomide (TMZ), which produces the same active metabolite as Dacarbazine/DTIC, the standard chemotherapy for advanced melanoma. We report that TMZ does not inhibit adenovirus replication in melanoma cells. Additive or synergistic cell killing of melanoma cells, dependent on the cell line used, was observed. Enhanced cell binding was not responsible for synergism of adenoviral oncolysis and TMZ treatment. We rather observed that higher numbers of virus genomes are produced in TMZ-treated cells, which also showed a cell cycle arrest in the G2 phase. Our results have important implications for the clinical implementation of adenoviral oncolysis for treatment of malignant melanoma. It suggests that such studies are feasible in the presence of TMZ or DTIC chemotherapy and recommends the investigation of a viro-chemo combination therapy.

Neutralized adenovirus-immune complexes can mediate effective gene transfer via an Fc receptor-dependent infection pathway

Neutralization of adenovirus (Ad) by anti-Ad neutralizing antibodies in serum involves formation of Ad-immune complexes that prevent the virus from interacting with target cells. We hypothesized that Ad-immune complexes likely contain viable Ad vectors which, although no longer capable of gaining access to receptors on target cells, may be able to express transgenes in cells bearing Fc receptors for immunoglobulins, i.e., that antibody-based "neutralization" of Ad vectors may be circumvented by the Fc receptor pathway. To test this hypothesis, we expressed the Fcgamma receptor IIA (FcgammaR) in A549 lung epithelial cells or human dermal fibroblasts and evaluated gene transfer in the presence of human neutralizing anti-Ad serum. FcgammaR-expressing cells bound and internalized copious amounts of Ad, with a distinct population of internalized Ad trafficking to the nucleus. The dose-response curves for inhibition of gene transfer revealed that FcgammaR-expressing cells required a more-than-10-fold higher concentration of anti-Ad serum to achieve 50% inhibition of Ad-encoded beta-galactosidase expression compared with non-FcgammaR-expressing cells. The discrepancy between neutralization of Ad during infection of FcgammaR-expressing cells and neutralization of Ad during infection of non-FcgammaR-expressing cells occurred with either heat-inactivated or non-heat-inactivated sera, was blocked by addition of purified Fc domain protein, and did not require the cytoplasmic domain of FcgammaR, suggesting that immune complex internalization proceeded via endocytosis rather than phagocytosis. FcgammaR-mediated infection by Ad-immune complexes did not require expression of the coxsackie virus-Ad receptor (CAR) since similar data were obtained when CAR-deficient human dermal fibroblasts were engineered to express FcgammaR. However, interaction of the Ad penton base with cell surface integrins contributed to the difference in neutralization between FcgammaR-expressing and non-FcgammaR-expressing cells. The data indicate that complexes formed from Ad and anti-Ad neutralizing antibodies, while compromised with respect to infection of non-FcgammaR-expressing target cells, maintain the potential to transfer genes to FcgammaR-expressing cells, with consequent expression of the transgene. The formation of Ad-immune complexes that can target viable virus to antigen-presenting cells may account for the success of Ad-based vaccines administered in the presence of low levels of neutralizing anti-Ad antibody.

A novel system to study adenovirus tropism to normal and malignant colon tissues

We describe here a new organ culture system for the evaluation of viral tropism to colon carcinomas and normal colon tissues. Organ cultures of mouse and human colon retained viability for several days and thus facilitated studies of viral tropism. Two adenoviral vectors (AD) were compared in the study: AD5, that utilizes the CAR receptor, demonstrated poor infectivity to both normal and carcinoma tissues, while a capsid-modified-AD, recognizing haparan-sulfate receptor, demonstrated efficient infectivity of both tissues. Immunohistochemistry analysis demonstrated different viral tropism; while AD5 infected only the colon epithelia, the capsid-modified-adeno infected both the epithelia and mesothelial layers. To investigate other determinants in the tissue that influence viral tropism, human cancer tissues were pretreated with collagenase and infected with the AD viruses. Increased infectivity and altered tropism were noted in the treated tumor tissue. Taken together, this ex vivo system indicated that receptor utilization and extracellular-matrix components influence AD viral tropism in solid tissues.

Paclitaxel and vincristine potentiate adenoviral oncolysis that is associated with cell cycle and apoptosis modulation, whereas they differentially affect the viral life cycle in non-small-cell lung cancer cells

Chemotherapy, including microtubule (MT)-interacting agents, can enhance the tumor-eradicating activity of replication-competent adenoviruses. The purpose of this study was to obtain more insight into the mechanism underlying this enhancement that may be exploited for the development of improved therapy. Two MT-interacting agents with opposite activity, paclitaxel (PTX) that stabilizes and vincristine (VCR) that destabilizes MTs, were found to synergistically enhance adenoviral oncolysis in non-small-cell lung cancer (NSCLC) cells. To explore the possibility that these drugs affect the viral life cycle by modulating adenoviral gene expression, we used a quantitative reverse transcription-polymerase chain reaction assay and found that PTX, but not VCR, increased the expression of E1A13S, ADP and Penton genes, which correlated with an increase in viral particle assembly and release. Next, the effect of combined treatment on cell-cycle progression was studied. Both drugs suppressed adenovirus-induced S-phase arrest and instead caused G2/M arrest, which was accompanied by an increase in apoptotic cells. Taken together, the enhancement of oncolysis by MT-interacting drugs appears not to require specific MT transport or scaffold functions. Our findings suggest that MT-interacting drug-induced cellular signals that modulate cell-cycle arrest and apoptosis are primarily on the basis of their oncolysis-enhancing activity.

Baculovirus transduction of human mesenchymal stem cell-derived progenitor cells: variation of transgene expression with cellular differentiation states

We have previously demonstrated that baculovirus can efficiently transduce human mesenchymal stem cells (MSCs). In this study, we further demonstrated, for the first time, that baculovirus can transduce adipogenic, chondrogenic and osteogenic progenitors originating from MSCs. The transduction efficiency (21-90%), transgene expression level and duration (7-41 days) varied widely with the differentiation lineages and stages of the progenitors, as determined by flow cytometry. The variation stemmed from differential transgene transcription (as revealed by real-time reverse transcription-polymerase chain reaction), rather than from variability in virus entry or cell cycle (as determined by quantitative real-time PCR and flow cytometry). Nonetheless, the baculovirus-transduced cells remained capable of differentiating into adipogenic, osteogenic and chondrogenic pathways. The susceptibility to baculovirus transduction was higher for adipogenic and osteogenic progenitors, but was lower for chondrogenic progenitors. In particular, the duration of transgene expression was prolonged in the transduced adipogenic and osteogenic progenitors (as opposed to the MSCs), implicating the possibility of extending transgene expression via a proper transduction strategy design. Taken together, baculovirus may be an attractive alternative to genetically modify adipogenic and osteogenic progenitors in the ex vivo setting for cell therapy or tissue engineering.

Transductional targeting of adenovirus vectors for gene therapy

Cancer gene therapy approaches will derive considerable benefit from adenovirus (Ad) vectors capable of self-directed localization to neoplastic disease or immunomodulatory targets in vivo. The ablation of native Ad tropism coupled with active targeting modalities has demonstrated that innate gene delivery efficiency may be retained while circumventing Ad dependence on its primary cellular receptor, the coxsackie and Ad receptor. Herein, we describe advances in Ad targeting that are predicated on a fundamental understanding of vector/cell interplay. Further, we propose strategies by which existing paradigms, such as nanotechnology, may be combined with Ad vectors to form advanced delivery vehicles with multiple functions.

Histone Deacetylase Inhibitors Modulate the Sensitivity of Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand–Resistant Bladder Tumor Cells

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of tumors are superficial at diagnosis and, after local surgical therapy, have a high rate of local recurrence and progression. Current treatments extend time to recurrence but do not alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein tumor necrosis factor-related apoptosis inducing ligand (TRAIL) with histone deacetylase inhibitors (HDACi) against TRAIL-resistant bladder tumor cells. Pretreatment with HDACi at nontoxic doses, followed by incubation with TRAIL, resulted in a marked increase in TRAIL-induced apoptosis of T24 cells but showed no significant increase in toxicity to SV40 immortalized normal human uroepithelial cell-1. HDAC inhibition, especially with sodium butyrate and trichostatin A, led to increased TRAIL-R2 gene transcription that correlated with increased TRAIL-R2 surface expression. The increased TRAIL-R2 levels also resulted in accelerated death-inducing signaling complex (DISC) formation, caspase activation, and loss of mitochondrial membrane potential, which all contributed to the increase in tumor cell death. Collectively, these results show the therapeutic potential of combining HDAC inhibition with TRAIL as an alternative treatment for bladder cancer.

Loss of coxsackie and adenovirus receptor expression is associated with features of aggressive bladder cancer

OBJECTIVES

To examine whether loss of coxsackie and adenovirus receptor (CAR) expression is associated with bladder cancer characteristics and clinical outcomes and with expression of p53 and E-cadherin. Low levels of CAR are associated with decreased efficiency of adenovirus-mediated gene transduction of bladder transitional cell carcinoma.

METHODS

Immunohistochemical staining for CAR and p53 was carried out on tissue microarrays from 62 patients who had undergone radical cystectomy. We also examined 30 specimens for E-cadherin expression.

RESULTS

CAR expression was lost in 17 (27%) of 62 tumors. Loss of CAR expression was associated with metastases to regional lymph nodes (P = 0.049), muscle-invasive disease (P = 0.025), grade 3 disease (P = 0.038), altered p53 status (P = 0.041), and loss of E-cadherin expression (P = 0.042). With a median follow-up of 60 months, loss of CAR expression was associated with decreased bladder cancer-specific survival (P = 0.029) but not disease progression. When adjusted for the effects of standard pathologic features, only lymph node metastasis was associated with bladder transitional cell carcinoma progression and mortality.

CONCLUSIONS

Loss of CAR expression is associated with established markers of biologically aggressive bladder transitional cell carcinoma. The association of CAR with E-cadherin and p53 suggests a potential role for CAR in the regulation of urothelium integrity and the cell cycle.

A real-time RT-PCR assay for the quantitative determination of adenoviral gene expression in tumor cells

Oncolytic adenoviruses are exploited as possible anticancer agents in clinical trails. To monitor adenoviral gene expression, a real-time RT-PCR method with a LightCycler was developed that allows the rapid and easy quantification of a number of early and late adenoviral genes in infected tumor cells. Primers were designed that can amplify the spliced forms of the genes encoding E1A13S, DNA polymerase (Pol), pre-terminal protein (pTP), adenoviral death protein (ADP), Hexon (Hex) and Penton (Pent) genes. Standard curves were generated using two-fold serial dilutions of cDNAs derived from non-small cell lung cancer (NSCLC) H460 cells infected for 24h with wild-type adenovirus serotype 5. For all genes correlation coefficients of the standard curves of 0.984 or higher were obtained. The dynamic range of the assay was sufficient to allow the quantitative determination of adenoviral gene expression during a lytic cycle. This RT-PCR assay could be used as a research tool to study the effect of host-cell factors or exogenous treatments on adenoviral gene expression. As example, it is shown that the procedure is suitable to detect changes in adenoviral gene expression in infected H460 cells treated with paclitaxel that is known to enhance the antitumor effect of oncolytic adenoviruses.

Ionizing radiation-induced adenovirus infection is mediated by Dynamin 2

Specific viral targeting into intrahepatic tumors remains critical for adenovirus gene therapy in liver cancer. We previously showed that ionizing radiation increases adenovirus uptake and transgene expression in cells and colon cancer xenografts. Here, we tested whether radiation induces viral uptake through virus-cell membrane interaction. We found that radiation (8 Gy) induced adenoviral gene transfer in rat hepatocytes (WB) and human colon carcinoma cells (LoVo). This induction (24.4- and 6.5-fold, respectively) and viral uptake were significantly diminished by preincubation with antibody for Dynamin 2 but not for Coxsackie adenovirus receptor or for integrin alpha(v). Radiation-induced Dynamin 2 expression was detected by immunohistochemical staining and by increased mRNA levels for Dynamin 2 in WB (1.5-fold) and LoVo (2.2-fold) cells. Specific small interference RNA (siRNA) transfection significantly inhibited Dynamin 2 expression in various tumor cell lines (LoVo, D54, and MCF-7) and abolished the radiation induction of Dynamin 2. Likewise, radiation-induced viral gene transfer in these cells (6.5-, 5.5-, and 9.0-fold, respectively) was significantly reduced in siRNA-transfected cells (2.7-, 3.7-, and 5.0-fold, respectively). Moreover, viral uptake in LoVo tumor xenografts was significantly increased in s.c. tumors (10.9-fold) when adenovirus was given i.v. at 24 hours after tumor irradiation, coincident with an elevated Dynamin 2 expression in irradiated tumors. These data suggest that ionizing radiation induces adenovirus gene transfer in cells and tumor xenografts by regulating viral uptake, potentially through interaction with cellular Dynamin 2 and thus should provide insight into improving adenovirus targeting in tumors.

Molecular and cellular insights into the coxsackie-adenovirus receptor: role in cellular interactions in the stem cell niche

In recent years, progress has been made in characterizing the molecular and cellular elements that are responsible for the regeneration in the damaged brain and highlighting the key role of the stromal-vascular 'environment' to orchestrate secondary neurogenesis and repair. Indeed, the ability of the stem cells to self-renew and differentiate is tightly regulated by stromal ependymal cells and endothelial cells expressing molecular cues that constitute the extracellular stem cell 'niche'. Several soluble growth factors such as EGF, TGFbeta, FGF2, SDF-1alpha and Noggin are important signals for the stem cell niche but little is known about the role of membrane-bound molecules in intercellular communications between the niche and the stem cells. In this mini-review, we highlight the emerging role of a family of adhesion molecules in the control of secondary neurogenesis. The coxsackie-adenovirus receptor (CAR) is a 46 kDa transmembrane protein and a member of the immunoglobulin super family. It is close structurally and evolutionary to other adhesion molecules involved in cell-cell interactions during embryogenesis, broadly expressed in the developing central nervous system but restricted to ependymal cells in the adult brain. This unique location and its newly established signalling properties further support the role of CAR in intercellular communications. Elucidating the other signalling molecules and manipulating the stromal-vascular niche for example by adenovirus gene therapy remain important goals for future clinical applications.