Noninvasive visualization of adenovirus replication with a fluorescent reporter in the E3 region

Expanding the adenovirus toolbox: reporter viruses for studying the dynamics of human adenovirus replication

To streamline standard virological assays, we developed a suite of nine fluorescent or bioluminescent replication competent human species C5 adenovirus reporter viruses that mimic their parental wild-type counterpart. These reporter viruses provide a rapid and quantitative readout of various aspects of viral infection and replication based on EGFP, mCherry, or NanoLuc measurement. Moreover, they permit real-time non-invasive measures of viral load, replication dynamics, and infection kinetics over the entire course of infection, allowing measurements that were not previously possible. This suite of replication competent reporter viruses increases the ease, speed, and adaptability of standard assays and has the potential to accelerate multiple areas of human adenovirus research.IMPORTANCEIn this work, we developed a versatile toolbox of nine HAdV-C5 reporter viruses and validated their functions in cell culture. These reporter viruses provide a rapid and quantitative readout of various aspects of viral infection and replication based on EGFP, mCherry, or NanoLuc measurement. The utility of these reporter viruses could also be extended for use in 3D cell culture, organoids, live cell imaging, or animal models, and provides a conceptual framework for the development of new reporter viruses representing other clinically relevant HAdV species.

Cancer imaging and therapy utilizing a novel NIS-expressing adenovirus: The role of adenovirus death protein deletion

Encoding the sodium iodide symporter (NIS) by an adenovirus (Ad) is a promising strategy to facilitate non-invasive imaging and radiotherapy of pancreatic cancer. However, insufficient levels of NIS expression in tumor cells have limited its clinical translation. To optimize Ad-based radiotherapy and imaging, we investigated the effect of Ad death protein (ADP) deletion on NIS expression. We cloned two sets of oncolytic NIS-expressing Ads that differed only in the presence or absence of ADP. We found that ADP expression negatively affected NIS membrane localization and inhibited radiotracer uptake. ADP deletion significantly improved NIS-based imaging in pancreatic cancer models including patient-derived xenografts, where effective imaging was possible for up to 6 weeks after a single virus injection. This study demonstrates that improved oncolysis may hinder the therapeutic effect of oncolytic viruses designed to express NIS. In vivo studies in combination with ¹³¹I showed potential for effective radiotherapy. This also highlights the need for further investigation into optimal timing of ¹³¹I administration and suggests that repeated doses of ¹³¹I should be considered to improve efficacy in clinical trials. We conclude that ADP deletion is essential for effective NIS-based theranostics in cancer.

Site-directed modification of adenoviral vector with combined DNA assembly and restriction-ligation cloning

Commonly used and well accepted approaches are lacking for site-directed modification of adenoviral vectors. Here, we attempt to introduce an easy-to-implement strategy for such purpose with an example of establishing a replication competent adenoviral vector system from pKAd5 plasmid, an infectious clone of human adenovirus 5 (HAdV-5). PCR products of GFP expression cassette and plasmid backbone were fused with the EcoRI/NdeI-digested fragment of pKAd5 to generate a modified intermediate plasmid pMDXE3GA by DNA assembly. NdeI-digested fragment of pMDXE3GA was brought back to pKAd5 to form the adenoviral plasmid pKAd5XE3GA by restriction-ligation cloning. Recombinant adenovirus HAdV5-XE3GA was rescued, amplified and purified. The expression of GFP and the propagation of virus in adherent HEp-2 and suspension K562 cells were investigated. Expression of target gene was significantly enhanced in both cell lines infected with HAdV5-XE3GA due to virus replication. However, propagation of virus could not sustain in culture of K562 cells. Shuttle plasmid pSh5RC-GFP was constructed to facilitate exchange of transgene. In summary, the strategy of combined DNA assembly and restriction-ligation cloning is functional, cost-effective and suitable for genetic modification of adenovirus.

MT1-MMP silencing by an shRNA-armed glioma-targeted conditionally replicative adenovirus (CRAd) improves its anti-glioma efficacy in vitro and in vivo

MMP14 (MT1-MMP) is a cell membrane-associated proteinase of the extracellular matrix, whose biological roles vary from angiogenesis to cell proliferation and survival. We recently found a direct correlation between MMP14 expression levels in brain tumors of glioma patients and the disease progression. By using gene silencing as an experimental approach we found that MMP14 knockdown decreases production of pro-angiogenic factors such as VEGF and IL8 and thereby suppresses angiogenesis in glioma tumors. Although the clinical relevance of MMP14 down-regulation and its possible implications for glioma therapy in humans remain unclear, we observed a significant improvement in animal survival upon down-regulation of MMP14 in murine intracranial glioma xenografts infected with MMP14 shRNA-expressing CRAd. We further found that down-regulation of MMP14 in gliomas by combinational treatment with CRAd-S-5/3 and Marimastat, a chemical inhibitor of metalloproteinases, augments suppression of pro-angiogenic factors, caused by the replication-competent adenovirus. We also demonstrated that delivery of MMP14-targeting shRNA by a fiber-modified adenoviral vector to the glioma cells effectively suppresses their proliferation in vitro and in vivo. Thus our data indicate that inhibition of MMP14 expression in tumors in combination with glioma virotherapy could be effectively utilized to suppress angiogenesis and neovascularization of glioma tumors by decreasing production of pro-angiogenic factors.

Oncolytic adenovirus expressing interferon alpha in a syngeneic Syrian hamster model for the treatment of pancreatic cancer

BACKGROUND

The addition of interferon (IFN) alpha to adjuvant chemoradiotherapy regimens resulted in remarkable improvements in survival for pancreatic cancer patients. However, systemic toxicities and insufficient levels of IFN at the tumor sites have limited its widespread adoption in treatment schemes. We have previously developed an IFN-expressing conditionally replicative oncolytic adenovirus and demonstrated its therapeutic effects both in vitro and in vivo. Here, the same vectors were tested in a syngeneic and immunocompetent Syrian hamster model to better understand the roles of adenoviral replication and of the pleiotropic effects of IFN on pancreatic tumor growth suppression.

METHODS

Oncolytic adenoviruses expressing human or hamster IFN were designed and generated. Viral vectors were tested in vitro to determine qualitative and quantitative cell viability, cyclooxygenase 2 (Cox2) promoter activity, and IFN production. For the in vivo studies, subcutaneous hamster pancreatic cancer tumors were treated with 1 intratumoral dose of virus. Similarly, 1 intraperitoneal dose of virus was used to prolong survival in a carcinomatosis model.

RESULTS

All cell lines tested demonstrated Cox2 promoter activity. The oncolytic potential of a replication competent adenovirus expressing the IFN cytokine was clearly demonstrated. These viruses resulted in significant tumor growth suppression and survival increases compared with controls in a hamster model.

CONCLUSION

The profound therapeutic potential of an IFN-expressing oncolytic adenovirus for the treatment of pancreatic cancer was demonstrated in a syngeneic Syrian hamster model. These results strongly suggest the potential application of our viruses as part of combination regimens with other therapeutics.

A novel approach for detecting viable and tissue-specific circulating tumor cells through an adenovirus-based reporter vector

BACKGROUND

Circulating tumor cells (CTCs) hold great promise as biomarkers and are a direct source of tumor cells through a simple blood draw. However, CTCs are rare and their detection requires sensitive and specific methods to overcome the overwhelming hematocyte population. Therefore, CTC detection remains technically challenging.

METHODS

An assay was developed for detecting viable and tissue-specific CTCs using a tropism-enhanced and conditionally replicating reporter adenovirus (CTC-RV). Adenoviral replication was made prostate-specific by placing the E1A gene under the control of the probasin promoter and prostate-specific antigen enhancer (PSE-PBN). Viral tropism was expanded through capsid-displayed integrin targeting peptides. A secreted reporter, humanized Metridia Luciferase (hMLuc), was engineered for expression during the major late phase of viral replication. The assay involves red blood cell lysis, cell collection, viral infection, and subsequent quantification of reporter activity from cellular media. Assay and reporter stability, cell specificity and sensitivity were evaluated in cell dilution models in human blood.

RESULTS

A conditionally replicating prostate-selective adenovirus reporter and CTC assay system were generated. The secreted reporter, MLuc, was found to be stable for at least 3 days under assay conditions. CTC detection, modeled by cell dilution in blood, was selective for androgen receptor positive prostate cancer (PCa) cells. Serial dilution demonstrated assay linearity and sensitivity to as few as three cells. Prostate cancer cell viability declined after several hours in anticoagulated blood at ambient temperatures.

CONCLUSIONS

Conditionally replicative adenoviral vectors and secreted reporters offer a functional method to detect viable CTCs with cell specificity and high sensitivity.

Locally-delivered T-cell-derived cellular vehicles efficiently track and deliver adenovirus delta24-RGD to infiltrating glioma

Oncolytic adenoviral vectors are a promising alternative for the treatment of glioblastoma. Recent publications have demonstrated the advantages of shielding viral particles within cellular vehicles (CVs), which can be targeted towards the tumor microenvironment. Here, we studied T-cells, often having a natural capacity to target tumors, for their feasibility as a CV to deliver the oncolytic adenovirus, Delta24-RGD, to glioblastoma. The Jurkat T-cell line was assessed in co-culture with the glioblastoma stem cell (GSC) line, MGG8, for the optimal transfer conditions of Delta24-RGD in vitro. The effect of intraparenchymal and tail vein injections on intratumoral virus distribution and overall survival was addressed in an orthotopic glioma stem cell (GSC)-based xenograft model. Jurkat T-cells were demonstrated to facilitate the amplification and transfer of Delta24-RGD onto GSCs. Delta24-RGD dosing and incubation time were found to influence the migratory ability of T-cells towards GSCs. Injection of Delta24-RGD-loaded T-cells into the brains of GSC-bearing mice led to migration towards the tumor and dispersion of the virus within the tumor core and infiltrative zones. This occurred after injection into the ipsilateral hemisphere, as well as into the non-tumor-bearing hemisphere. We found that T-cell-mediated delivery of Delta24-RGD led to the inhibition of tumor growth compared to non-treated controls, resulting in prolonged survival (p = 0.007). Systemic administration of virus-loaded T-cells resulted in intratumoral viral delivery, albeit at low levels. Based on these findings, we conclude that T-cell-based CVs are a feasible approach to local Delta24-RGD delivery in glioblastoma, although efficient systemic targeting requires further improvement.

Conditionally replicative adenoviral vectors for imaging the effect of chemotherapy on pancreatic cancer cells

Pancreatic cancer has a poor prognosis after complete macroscopic resection combined with chemotherapy. Even after neoadjuvant chemotherapy, R0 resection is often not possible. Moreover, current imaging techniques cannot reliably distinguish viable cancer cells from scar tissue at the resectional margin. We investigated the use of a conditionally replicative adenovirus (CRAd), Ad5/3Cox2CRAd-ΔE3ADP-Luc, for imaging the effects of chemotherapy. The CRAd infectivity of pancreatic cancer cells was enhanced by a chimeric Ad5/3 fiber, E1A expression was under the control of the Cox2 promoter, and the luciferase gene was inserted adjacent to the adenovirus death protein (ADP) gene. Subcutaneous xenografts of the pancreatic cancer cell line MiaPaCa-2 were established in 24 BALB/c nu/nu mice. When xenografts reached a diameter of 4-6 mm (day 1), the mice were injected i.p. with either PBS (group A; n = 12) or 1000 mg/kg gemcitabine (group B; n = 12), weekly. On days 19, 26, 33, and 40, CRAd were injected intratumorally into three mice in groups A and B. Bioluminescence was imaged 72 h after CRAd injection, and gross tumor volumes were measured then tumors were removed for ex vivo histopathology using H&E and Ki-67 staining. Correlations between gross tumor volume, pathological evaluation of the percentage of viable tumor area, and CRAd bioluminescence were analyzed. Bioluminescence correlated closely with the percentage of viable tumor area (R = 0.96), but not with gross tumor volume (R = 0.31). Therefore, CRAds might be reliable imaging tools for monitoring chemotherapy in pancreatic cancer, and could improve our ability to distinguish viable tumor cells from scar tissue.

Effect of increased viral replication and infectivity enhancement on radioiodide uptake and oncolytic activity of adenovirus vectors expressing the sodium iodide symporter

Our laboratory has investigated replicating adenovirus-human sodium iodide symporter (Ad-hNIS) vectors in a combinatorial oncolytic approach known as radiovirotherapy. However, hNIS-mediated iodide sequestration requires an intact cell membrane, and the enhancement of infectivity may alter the radioiodide accumulation in vivo. To assess these effects, we constructed Ad-NIS vectors expressing NIS from the major late promoter. Viral tropism was altered using a hybrid Ad5/3 fiber, and rates of viral spread altered through expression of the Ad death protein (ADP). The hybrid 5/3 fiber enhanced Ad-mediated cytolysis and radioisotope uptake in vitro. Replicating ADP-lacking viral vectors showed levels of uptake similar to non-replicating vectors that declined as cells lysed. ADP expression enhanced the rate of cell lysis and viral release, but reduced the peak and duration of radioiodide uptake. SPECT-computed tomography imaging showed the Ad5/3-noADP-hNIS vector induced significantly more isotope uptake than other vector structures, indicating that viral spread may not always make up for the reduced NIS expression as in our work with prostate cancer. These results indicate that replicating, infectivity-enhanced Ad-NIS vectors provide superior overall efficacy, but also indicate that the effect of replication speed requires tumor and model-specific testing.

Chapter five--The development of transcription-regulated adenoviral vectors with high cancer-selective imaging capabilities

A clear benefit of molecular imaging is to enable noninvasive, repetitive monitoring of intrinsic signals within tumor cells as a means to identify the lesions as malignant or to assess the ability of treatment to perturb key pathways within the tumor cells. Due to the promising utility of molecular imaging in oncology, preclinical research to refine molecular imaging techniques in small animals is a blossoming field. We will first discuss the several imaging modalities such as fluorescent imaging, bioluminescence imaging, and positron emission tomography that are now commonly used in small animal settings. The indirect imaging approach, which can be adapted to a wide range of imaging reporter genes, is a useful platform to develop molecular imaging. In particular, reporter gene-based imaging is well suited for transcriptional-targeted imaging that can be delivered by recombinant adenoviral vectors. In this review, we will summarize transcription-regulated strategies used in adenoviral-mediated molecular imaging to visualize metastasis and monitor oncolytic therapy in preclinical models.

Characterization of infectivity-enhanced conditionally replicating adenovectors for prostate cancer radiovirotherapy

Prostate cancer (PCa) is the second most commonly diagnosed and sixth leading cause of cancer death in American men and one for which no curative therapy exists after metastasis. To meet this need for novel therapies, our laboratory has previously generated conditionally replicating adenovirus (CRAd) vectors expressing the sodium iodide symporter (hNIS). This virus transduced PCa cells and induced functional NIS expression, allowing for noninvasive tumor imaging and combination therapy with radioiodide, referred to as radiovirotherapy. We have now generated two new modified vectors to further improve efficacy. Ad5/3PB-ADP-hNIS and Ad5/3PB-hNIS include a hybrid Ad5/3 fiber knob to improve transduction efficiency, and express NIS from the endogenous major late promoter to restrict NIS expression to target cells. Additionally, Ad5/3PB-ADP-hNIS includes the adenovirus death protein (ADP), which hastens the release of viral particles after assembly. These two vectors specifically induce radioisotope uptake, cytopathic effect, and viral replication in androgen receptor-expressing PCa cell lines with Ad5/3PB-ADP-hNIS showing earlier (131)I uptake and cytolysis at low multiplicity of infection. SPECT-CT imaging of xenograft tumors infected with Ad5/3PB-hNIS showed steady uptake, whereas infection with Ad5/3PB-ADP-hNIS led to increasing uptake, indicating viral spread. Radiovirotherapy of xenograft LNCaP tumors with Ad5/3PB-ADP-hNIS showed the most significant survival extension versus control tumors (p=0.001), but the benefit of radiovirotherapy was not statistically significant compared with virotherapy alone in this model. These results show the potential of Ad5/3PB-ADP-hNIS as a vector for treatment of prostate cancer.

Generation of a novel, cyclooxygenase-2-targeted, interferon-expressing, conditionally replicative adenovirus for pancreatic cancer therapy

BACKGROUND

Oncolytic adenoviruses provide a promising alternative for cancer treatment. Recently, adjuvant interferon (IFN)-alfa has shown significant survival benefits for pancreatic cancer, yet was impeded by systemic toxicity. To circumvent these problems adenovirus with high-level targeted IFN-alfa expression can be generated.

METHODS

Conditionally replicative adenoviruses (CRAds) with improved virulence and selectivity for pancreatic cancer were generated. The vectors were tested in vitro, in vivo, and in human pancreatic cancer and normal tissue specimens.

RESULTS

Adenoviral death protein and fiber modifications significantly improved oncolysis. CRAds selectively replicated in vitro, in vivo and showed persistent spread in cancer xenografts. They showed high-level replication in human pancreatic cancer specimens, but not in normal tissues. Improved IFN-CRAd oncolytic efficiency was shown.

CONCLUSIONS

Optimized cyclooxygenase-2 CRAds show highly favorable effects in vitro and in vivo. We report a pancreatic cancer-specific, highly virulent, IFN-expressing CRAd, and we believe that adenovirus-based IFN therapy offers a new treatment opportunity for pancreatic cancer patients.

Delivery of interferon alpha using a novel Cox2-controlled adenovirus for pancreatic cancer therapy

BACKGROUND

Combination therapy with interferon alpha (IFN) is correlated with improved survival in patients with pancreatic ductal adenocarcinoma (PDAc) but frequently presents side effects. We designed a novel targeted adenovirus with replication restricted to cyclooxygenase 2 (Cox2)-overexpressing PDAcs and hypothesize that the locally delivered therapeutic gene IFN can augment oncolytic effects while minimizing systemic toxicity.

METHODS

IFN-expressing vectors were tested in vitro with the use of 4 PDAc cell lines with cytocidal effect measured by crystal violet and colorimetrically and IFN production assayed by ELISA. Cox2 promoter activity was checked by a luciferase reporter assay. In vivo, subcutaneous tumor xenografts with 2 PDAc cell lines in nude mice were treated with a single intratumoral viral dose.

RESULTS

All PDAc cell lines were Cox2-positive. Oncolysis from the novel Cox2-controlled virus was comparable or superior to Adwt, the wild-type virus without safety features. The absence of cytocidal effect in Cox2-negative cells with the novel virus indicated cancer specificity. In vivo, stronger tumor suppression from the novel virus was seen when compared with nonreplicating IFN-expressing vectors.

CONCLUSION

We demonstrated the potent therapeutic effects of a novel tumor-specific conditionally replicative IFN-expressing adenovirus. With potential to locally deliver IFN and avoid systemic toxicity, this strategy may therefore expand the application of this robust and promising therapy.

Early infection and spread of a conditionally replicating adenovirus under conditions of plaque formation

Conditionally-replicating adenoviruses (CRAds) and other oncolytic viruses replicate selectively in tumor cells, presenting a potential cancer treatment approach. To optimize application of these viruses, understanding of early spread of these viruses in target cells is important. Here we used a recombinant adenovirus expressing enhanced jellyfish green fluorescent protein (EGFP) in place of the EIA and EIB genes (AdEGFPuci). Infection of susceptible cells (AD-293) under plaque formation conditions (MOI<<1) on gridded culture dishes and daily monitoring allowed visualization of initially infected cells, as well as spread to neighboring cells. We determined key parameters of early infection, including the rate and efficiency of spread from the initially infected cell to other cells. It was noteworthy that a minority of initially infected cells ultimately resulted in plaques. The approaches elucidated here will be useful for determining early infection parameters for CRAds of therapeutic interest.

A cathepsin-cleavage site between the adenovirus capsid protein IX and a tumor-targeting ligand improves targeted transduction

Human adenoviruses have a great potential as anticancer agents. One strategy to improve their tumor-cell specificity and anti-tumor efficacy is to include tumor-specific targeting ligands in the viral capsid. This can be achieved by fusion of polypeptide-targeting ligands with the minor capsid protein IX. Previous research suggested that protein IX-mediated targeting is limited by inefficient release of protein IX-fused ligands from their cognate receptors in the endosome. This thwarts endosomal escape of the virus particles. Here we describe that the targeted transduction of tumor cells is augmented by a cathepsin-cleavage site between the protein IX anchor and the HER2/neu-binding ZH Affibody molecule as ligand. The cathepsin-cleavage site did not interfere with virus production and incorporation of the Affibody molecules in the virus capsid. Virus particles harboring the cleavable protein IX-ligand fusion in their capsid transduced the HER2/neu-positive SKOV-3 ovarian carcinoma cells with increased efficiency in monolayer cultures, three-dimensional spheroid cultures and in SKOV-3 tumors grown on the chorioallantoic membrane of embryonated chicken eggs. These data show that inclusion of a cathepsin-cleavage sequence between protein IX and a high-affinity targeting ligand enhances targeted transduction. This modification further augments the applicability of protein IX as an anchor for coupling tumor-targeting ligands.

Enhanced transduction of CAR-negative cells by protein IX-gene deleted adenovirus 5 vectors

In human adenoviruses (HAdV), 240 copies of the 14.3-kDa minor capsid protein IX stabilize the capsid. Three N-terminal domains of protein IX form triskelions between hexon capsomers. The C-terminal domains of four protein IX monomers associate near the facet periphery. The precise biological role of protein IX remains enigmatic. Here we show that deletion of the protein IX gene from a HAdV-5 vector enhanced the reporter gene delivery 5 to 25-fold, specifically to Coxsackie and Adenovirus Receptor (CAR)-negative cell lines. Deletion of the protein IX gene also resulted in enhanced activation of peripheral blood mononuclear cells. The mechanism for the enhanced transduction is obscure. No differences in fiber loading, integrin-dependency of transduction, or factor-X binding could be established between protein IX-containing and protein IX-deficient particles. Our data suggest that protein IX can affect the cell tropism of HAdV-5, and may function to dampen the innate immune responses against HAdV particles.

Arming a replicating adenovirus with osteoprotegerin reduces the tumor burden in a murine model of osteolytic bone metastases of breast cancer

Most patients with advanced breast cancer develop osteolytic bone metastases, which have numerous complications. Because current therapies are not curative, new treatments are needed. Conditionally replicating adenoviruses (CRAds) are anticancer agents designed to infect and lyse tumor cells. However, in spite of their promise as selective cancer therapeutics, replicating adenoviruses have shown limited efficacy in the clinical setting. We hypothesized that a CRAd armed with osteoprotegerin (OPG) would eradicate bone metastases of breast cancer both directly, by oncolysis, and indirectly, by inhibiting osteoclastic bone resorption and thus reducing the tumor burden. We constructed an armed CRAd (Ad5-Δ24-sOPG-Fc-RGD) by replacing viral E3B genes with a fusion of the ligand-binding domains of OPG and the Fc portion of human IgG1. Conditional replication was conferred by a 24-base pair deletion within E1A (Δ24), which prevents the binding of E1A to the retinoblastoma tumor suppressor/cell cycle regulator protein and limits replication in normal cells. Enhanced infection of cells expressing low levels of the primary Ad5 receptor was conferred by incorporating an RGD peptide sequence into the fiber knob to mediate binding to α_v integrins. After characterization of the armed CRAd, we demonstrated that infection of breast cancer cells by Ad-Δ24-sOPG-Fc-RGD both killed the infected cells by oncolysis and inhibited the formation of osteoclasts in an in vitro co-culture model. In a murine model of osteolytic bone metastases of breast cancer, the CRAd armed with sOPG-Fc reduced tumor burden in the bone and inhibited osteoclast formation more effectively than an unarmed CRAd.

Evaluation of adenovirus capsid labeling versus transgene expression

Adenoviral vectors have been utilized for a variety of gene therapy applications. Our group has incorporated bioluminescent, fluorographic reporters, and/or suicide genes within the adenovirus genome for analytical and/or therapeutic purposes. These molecules have also been incorporated as capsid components. Recognizing that incorporations at either locale yield potential advantages and disadvantages, our report evaluates the benefits of transgene incorporation versus capsid incorporation. To this end, we have genetically incorporated firefly luciferase within the early region 3 or at minor capsid protein IX and compared vector functionality by means of reporter readout.

Current issues and future directions of oncolytic adenoviruses

Oncolytic adenoviruses (Ads) constitute a promising new class of anticancer agent. They are based on the well-studied adenoviral vector system, which lends itself to concept-driven design to generate oncolytic variants. The first oncolytic Ad was approved as a drug in China in 2005, although clinical efficacy observed in human trials has failed to reach the high expectations that were based on studies in animal models. Current obstacles to the full realization of efficacy of this class of anticancer agent include (i) limited efficiency of infection and specific replication in tumor cells, (ii) limited vector spread within the tumor, (iii) imperfect animal models and methods of in vivo imaging, and (iv) an incomplete understanding of the interaction of these agents with the host. In this review, we discuss recent advances in the field of oncolytic Ads and potential ways to overcome current obstacles to their clinical application and efficacy.

Targeted radionuclide therapy using a Wnt-targeted replicating adenovirus encoding the Na/I symporter

PURPOSE

The Na/I symporter (hNIS) promotes concentration of iodine in cells. In cancer gene therapy, this transgene has potential as a reporter gene for molecular imaging of viral biodistribution and as a therapeutic protein promoting (131)I-mediated radiotherapy. Here, we combined the imaging and therapeutic potential of hNIS in an oncolytic adenoviruses targeting colorectal cancer cells.

EXPERIMENTAL DESIGN

We generated an adenovirus (AdIP2) encoding hNIS and capable of selective replication in colorectal carcinoma cells. The selectivity of this virus was verified in vitro and in vivo. Its spread in tumors was monitored in vivo using single-photon emission computed tomography/CT imaging upon (99m)TcO(4)(-) injection and confirmed by immunohistochemistry. Metabolic radiotherapy was done through injection of therapeutic doses of (131)I(-).

RESULTS

We showed in vitro and in vivo the selectivity of AdIP2 and that hNIS expression is restricted to the target cells. Imaging and immunohistochemical data showed that viral spread is limited and that the point of maximal hNIS expression is reached 48 hours after a single intratumoral injection. Administration of a single therapeutic dose of (131)I at this time point led to a dramatic reduction in tumor size not observed in hNIS-negative viruses.

CONCLUSIONS

This report showed for the first time that the combination of the imaging and therapeutic potentials of hNIS can be applied to oncolytic adenoviruses in experimental models of cancer.

In vivo bioimaging tracks conditionally replicative adenoviral replication and provides an early indication of viral antitumor efficacy

In vivo monitoring of conditionally replicative adenovirus (CRAd) replication and assessing its correlation to CRAd biological effects are necessary for the clinical development of gene therapy. Noninvasive bioimaging is one current approach which can monitor in vivo CRAd replication and functional effect. Here we describe a novel cyclooxygenase-2 (Cox2) promoter-controlled CRAd that was modified to contain firefly luciferase in its E3 region; this modification permitted serial bioluminescence imaging of viral replication in vitro and in vivo. In vitro luciferase expression correlated with viral replication and cytolytic effect. In vivo bioluminescence imaging showed dynamic representation of the viral replication level in athymic nude mice bearing subcutaneous tumor xenografts. Importantly, in vivo luciferase bioluminescence measured 6 days after viral administration significantly correlated with CRAd antitumor effect at day 36. Thus, our system could detect viral replication and predict in vivo therapeutic outcome based on early imaging. Further development of this approach may improve patient safety, enhance clinical trial conduct, and provide mechanistic insight into CRAd function in vivo. (Cancer Sci 2009; 00: 000–000)

Novel Infectivity-Enhanced Oncolytic Adenovirus with a Capsid-Incorporated Dual-Imaging Moiety for Monitoring Virotherapy in Ovarian Cancer

We sought to develop a cancer-targeted, infectivity-enhanced oncolytic adenovirus that embodies a capsid-labeling fusion for non-invasive dual-modality imaging of ovarian cancer virotherapy. A functional fusion protein composed of fluorescent and nuclear imaging tags was genetically incorporated into the capsid of an infectivity-enhanced conditionally replicative adenovirus. Incorporation of herpes simplex virus thymidine kinase (HSV-tk) and monomeric red fluorescent protein 1 (mRFP1) into the viral capsid and its genomic stability were verified by molecular analyses. Replication and oncolysis were evaluated in ovarian cancer cells. Fusion functionality was confirmed by in vitro gamma camera and fluorescent microscopy imaging. Comparison of tk-mRFP virus to single-modality controls revealed similar replication efficiency and oncolytic potency. Molecular fusion did not abolish enzymatic activity of HSV-tk as the virus effectively phosphorylated thymidine both ex vivo and in vitro. In vitro fluorescence imaging demonstrated a strong correlation between the intensity of fluorescent signal and cytopathic effect in infected ovarian cancer cells, suggesting that fluorescence can be used to monitor viral replication. We have in vitro validated a new infectivity-enhanced oncolytic adenovirus with a dual-imaging modality-labeled capsid, optimized for ovarian cancer virotherapy. The new agent could provide incremental gains toward climbing the barriers for achieving conditionally replicated adenovirus efficacy in human trials.

Advancements in adenoviral based virotherapy for ovarian cancer

Ovarian cancer is a leading gynecologic malignancy with relatively grim survival statistics. There is a significant need for the development of new treatment options for this malignancy. The development of virotherapy as a treatment option for ovarian cancer has the potential to improve patient survival. Adenoviruses have multiple advantages as vectors for virotherapy including a well-understood structure and the ability to infect cells easily. We will outline the advances in virotherapy in the treatment of ovarian cancer, with particular attention directed toward adenoviral vectors.

Armed replicating adenoviruses for cancer virotherapy

Conditionally replicating adenoviruses (CRAds) have many advantages as agents for cancer virotherapy and have been safely used in human clinical trials. However, replicating adenoviruses have been limited in their ability to eliminate tumors by oncolysis. Thus, the efficacy of these agents must be improved. To this end, CRAds have been engineered to express therapeutic transgenes that exert antitumor effects independent of direct viral oncolysis. These transgenes can be expressed under native gene control elements, in which case placement within the genome determines the expression profile, or they can be controlled by exogenous promoters. The therapeutic transgenes used to arm replicating adenoviruses can be broadly classified into three groups. There are those that mediate killing of the infected cell, those that modulate the tumor microenvironment and those with immunomodulatory functions. Overall, the studies to date in animal models have shown that arming a CRAd with a rationally chosen therapeutic transgene can improve its antitumor efficacy over that of an unarmed CRAd. However, a number of obstacles must be overcome before the full potential of armed CRAds can be realized in the human clinical context. Hence, strategies are being developed to permit intravenous delivery to disseminated cancer cells, overcome the immune response and enable in vivo monitoring of the biodistribution and activity of armed CRAds.

Cellular genetic tools to control oncolytic adenoviruses for virotherapy of cancer

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

SPECT/CT imaging of oncolytic adenovirus propagation in tumours in vivo using the Na/I symporter as a reporter gene

Oncolytic adenoviruses have shown some promise in cancer gene therapy. However, their efficacy in clinical trials is often limited, and additional therapeutic interventions have been proposed to increase their efficacies. In this context, molecular imaging of viral spread in tumours could provide unique information to rationalize the timing of these combinations. Here, we use the human sodium iodide symporter (hNIS) as a reporter gene in wild-type and replication-selective adenoviruses. By design, hNIS cDNA is positioned in the E3 region in a wild-type adenovirus type 5 (AdIP1) and in an adenovirus in which a promoter from the human telomerase gene (RNA component) drives E1 expression (AdAM6). Viruses show functional hNIS expression and replication in vitro and kinetics of spread of the different viruses in tumour xenografts are visualized in vivo using a small animal nano-SPECT/CT camera. The time required to reach maximal spread is 48 h for AdIP1 and 72 h for AdAM6 suggesting that genetic engineering of adenoviruses can affect their kinetics of spread in tumours. Considering that this methodology is potentially clinically applicable, we conclude that hNIS-mediated imaging of viral spread in tumours may be an important tool for combined anticancer therapies involving replicating adenoviruses

Androgen receptor attenuation of Ad5 replication: implications for the development of conditionally replication competent adenoviruses

Conditionally replication competent adenoviruses (CRAds) represent one of the most intensely studied gene therapy strategies for a variety of malignancies, including prostate cancer. These viruses can be generated by placing a tissue or cancer-specific promoter upstream of one or more of the viral genes required for replication (e.g., E1A, E1B). We report here that E1A inhibits androgen receptor (AR) target gene induction and, correspondingly, activated AR inhibits adenoviral replication. This mutual inhibition appears to be an indirect effect, possibly through competition for shared transcriptional co-activators. The net effect is that the oncolytic effect of prostate-specific CRAds is attenuated by these interactions. Fusion of the E1A to AR ameliorates this inhibition, while enhancing specificity. These findings have significant implications in the development of prostate-specific CRAd therapies.

Luciferase imaging for evaluation of oncolytic adenovirus replication in vivo

Oncolytic viruses kill cancer cells by tumor-selective replication. Clinical data have established the safety of the approach but also the need of improvements in potency. Efficacy of oncolysis is linked to effective infection of target cells and subsequent productive replication. Other variables include intratumoral barriers, access to target cells, uptake by non-target organs and immune response. Each of these aspects relates to the location and degree of virus replication. Unfortunately, detection of in vivo replication has been difficult, labor intensive and costly and therefore not much studied. We hypothesized that by coinfection of a luciferase expressing E1-deleted virus with an oncolytic virus, both viruses would replicate when present in the same cell. Photon emission due to conversion of D-Luciferin is sensitive and penetrates tissues well. Importantly, killing of animals is not required and each animal can be imaged repeatedly. Two different murine xenograft models were used and intratumoral coinjections of luciferase encoding virus were performed with eight different oncolytic adenoviruses. In both models, we found significant correlation between photon emission and infectious virus production. This suggests that the system can be used for non-invasive quantitation of the amplitude, persistence and dynamics of oncolytic virus replication in vivo, which could be helpful for the development of more effective and safe agents.

Quantifying the Activity of Adenoviral E1A CR2 Deletion Mutants Using Renilla Luciferase Bioluminescence and 3′-Deoxy-3′-[18F]Fluorothymidine Positron Emission Tomography Imaging

The adenoviral E1A CR2 mutant dl922-947 has potent activity in ovarian cancer. We have used Renilla luciferase bioluminescence imaging to monitor viral E1A expression and replication and [18F]fluorothymidine positron emission tomography ([18F]FLT-PET) to quantify the activity of dl922-947 in vivo. We created dlCR2 Ren, with the same E1A CR2 deletion as dl922-947 and the luciferase gene from Renilla reniformis downstream of E1. Light emitted from s.c. and i.p. IGROV1 ovarian carcinoma xenografts was measured following treatment with dlCR2 Ren. Mice bearing s.c. IGROV1 xenografts were injected with 2.96 to 3.7 MBq of [18F]FLT 48 and 168 hours following i.t. injection of dl922-947 or control virus Ad LM-X. The presence of Renilla luciferase in dlCR2 Ren did not reduce in vitro nor in vivo potency compared with dl922-947. Light emission correlated closely with E1A expression in vitro and peaked 48 hours after dlCR2 Ren injection in both s.c. and i.p. IGROV1 xenografts. It diminished by 168 hours in s.c. tumors but persisted for at least 2 weeks in i.p. models. Normalized tumor [18F]FLT uptake at 60 minutes (NUV60), fractional retention, and area under radioactivity curve all decreased marginally 48 hours after dl922-947 treatment and significantly at 168 hours compared with controls. There was a close linear correlation between NUV60 and both tumor proliferation (Ki67 labeling index) and thymidine kinase 1 expression. Renilla luciferase bioluminescence and [18F]FLT-PET imaging are capable of quantifying the activity and effectiveness of E1A CR2-deleted adenoviral mutants in ovarian cancer.