Utility of TK/GCV in the context of highly effective oncolysis mediated by a serotype 3 receptor targeted oncolytic adenovirus

Bioreductive prodrug PR-104 improves the tumour distribution and titre of the nitroreductase-armed oncolytic adenovirus ONYX-411NTR leading to therapeutic benefit

Advances in the field of cancer immunotherapy have stimulated renewed interest in adenoviruses as oncolytic agents. Clinical experience has shown that oncolytic adenoviruses are safe and well tolerated but possess modest single-agent activity. One approach to improve the potency of oncolytic viruses is to utilise their tumour selectivity to deliver genes encoding prodrug-activating enzymes. These enzymes can convert prodrugs into cytotoxic species within the tumour; however, these cytotoxins can interfere with viral replication and limit utility. In this work, we evaluated the activity of a nitroreductase (NTR)-armed oncolytic adenovirus ONYX-411^NTR in combination with the clinically tested bioreductive prodrug PR-104. Both NTR-expressing cells in vitro and xenografts containing a minor population of NTR-expressing cells were highly sensitive to PR-104. Pharmacologically relevant prodrug exposures did not interfere with ONYX-411^NTR replication in vitro. In vivo, prodrug administration increased virus titre and improved virus distribution within tumour xenografts. Colonisation of tumours with high ONYX-411^NTR titre resulted in NTR expression and prodrug activation. The combination of ONYX-411^NTR with PR-104 was efficacious against HCT116 xenografts, whilst neither prodrug nor virus were active as single agents. This work highlights the potential for future clinical development of NTR-armed oncolytic viruses in combination with bioreductive prodrugs.

Understanding and addressing barriers to successful adenovirus-based virotherapy for ovarian cancer

Ovarian cancer is the leading cause of death among women with gynecological cancer, with an overall 5-year survival rate below 50% due to a lack of specific symptoms, late stage at time of diagnosis and a high rate of recurrence after standard therapy. A better understanding of heterogeneity, genetic mutations, biological behavior and immunosuppression in the tumor microenvironment have allowed the development of more effective therapies based on anti-angiogenic treatments, PARP and immune checkpoint inhibitors, adoptive cell therapies and oncolytic vectors. Oncolytic adenoviruses are commonly used platforms in cancer gene therapy that selectively replicate in tumor cells and at the same time are able to stimulate the immune system. In addition, they can be genetically modified to enhance their potency and overcome physical and immunological barriers. In this review we highlight the challenges of adenovirus-based oncolytic therapies targeting ovarian cancer and outline recent advances to improve their potential in combination with immunotherapies.

Methods for Modification of Therapeutic Viruses

The optimal clinical exploitation of viruses as gene therapy or oncolytic vectors will require them to be administered intravenously. Strategies must therefore be deployed to enable viruses to survive the harsh neutralizing environment of the bloodstream and achieve deposition within and throughout target tissues or tumor deposits. This chapter describes the genetic and chemical engineering approaches that are being developed to overcome these challenges.

Synergistic antitumor effect of adenovirus armed with Drosophila melanogaster deoxyribonucleoside kinase and nucleoside analogs for human breast carcinoma in vitro and in vivo

Background

Suicide gene therapy in cancer can selectively kill tumors without damaging normal tissues. Drosophila melanogaster multisubstrate deoxyribonucleoside kinase (Dm-dNK), an original suicide kinase, makes use of the carcinomatous suicide gene therapy for broader substrate specificity and a higher catalytic rate.

Methods

To enhance the anti-tumor efficacy of Dm-dNK and maintain its substrate specificity and safety control in the meantime, the conditionally replicative gene–viral system, ZD55–dNK (which contains the selective replication adenovirus, ZD55, encoded with Dm-dNK), was investigated in pushing a deeper development of this strategy. Selective replication, cell killing efficacy, and cytotoxicity, in combination with chemotherapy, were applied to two breast cell lines (MDA231 and MCF7 cells), two normal cell lines (WI38 and MRC5 cells), and the MCF7 xenograft model in vivo.

Results

The preclinical study showed that ZD55–dNK, combined with 2′,2′-difluorodeoxycytidine (DFDC), synergistically inhibited adenovirus replication in vitro but maintained specifically cancer cell killing efficacy. ZD55–dNK also greatly improved the antineoplastic effect in vitro and in breast cancer xenograft in vivo.

Conclusion

The concomitant use of ZD55–dNK and DFDC is possibly a novel and promising approach to breast cancer treatment, and further investigation on the safe control of excessive virus replication and the efficacy of this approach in humans is warranted.

Overcoming tumor resistance by heterologous adeno-poxvirus combination therapy

Successful cancer control relies on overcoming resistance to cell death and on activation of host antitumor immunity. Oncolytic viruses are particularly attractive in this regard, as they lyse infected tumor cells and trigger robust immune responses during the infection. However, repeated injections of the same virus promote antiviral rather than antitumor immunity and tumors may mount innate antiviral defenses to restrict oncolytic virus replication. In this article, we have explored if alternating the therapy virus could circumvent these problems. We demonstrate in two virus-resistant animal models a substantial delay in antiviral immune- and innate cellular response induction by alternating injections of two immunologically distinct oncolytic viruses, adenovirus, and vaccinia virus. Our results are in support of clinical development of heterologous adeno-/vaccinia virus therapy of cancer.

An armed, YB-1-dependent oncolytic adenovirus as a candidate for a combinatorial anti-glioma approach of virotherapy, suicide gene therapy and chemotherapeutic treatment

We investigated the novel recombinant oncolytic adenovirus Ad-delo-sr39TK-RGD, armed with a mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39TK) as a suicide gene, and explored its antitumor efficacy in combination with HSV1-sr39TK/ganciclovir (GCV) gene therapy and temozolomide (TMZ). Ad-delo-sr39TK-RGD is an E1-mutated conditionally replicating adenovirus dependent on the human Y-box binding protein 1 (YB-1). Thus, we utilized the YB-1 dependency of the vector to target human glioma cells in vitro, using two-dimensional cell culture and three-dimensional multicellular spheroids, and demonstrated the strong replication competence and oncolytic potential of the virus. The cytotoxicity mediated by HSV1-sr39TK and its prodrug GCV enhanced the oncolytic effect even at <0.1 μg ml(-1) GCV and induced cell killing of > 95% after adding GCV 0-1 days following infection. An increased bystander effect of viral replication and GCV in co-cultured infected and uninfected cells was observed. Co-administrating Ad-delo-sr39TK-RGD with TMZ and GCV, spheroid growth was reduced drastically. Gamma counting of infected spheroids demonstrated successful accumulation of the radiotracer (18)F-labeled 9-[4-fluoro-3-(hydroxymethyl)butyl]guanine mediated by HSV1-sr39TK. Hence, our results show that the combination of YB-1-dependent virotherapy with suicide genes and TMZ effectively induces glioma cell killing and may allow for in vivo non-invasive imaging within a limited time frame.

Serotype chimeric oncolytic adenovirus coding for GM-CSF for treatment of sarcoma in rodents and humans

Sarcomas are a relatively rare cancer, but often incurable at the late metastatic stage. Oncolytic immunotherapy has gained attention over the past years, and a wide range of oncolytic viruses have been delivered via intratumoral injection with positive safety and promising efficacy data. Here, we report preclinical and clinical results from treatment of sarcoma with oncolytic adenovirus Ad5/3-D24-GMCSF (CGTG-102). Ad5/3-D24-GMCSF is a serotype chimeric oncolytic adenovirus coding for human granulocyte-macrophage colony-stimulating factor (GM-CSF). The efficacy of Ad5/3-D24-GMCSF was evaluated on a panel of soft-tissue sarcoma (STS) cell lines and in two animal models. Sarcoma specific human data were also collected from the Advanced Therapy Access Program (ATAP), in preparation for further clinical development. Efficacy was seen in both in vitro and in vivo STS models. Fifteen patients with treatment-refractory STS (13/15) or primary bone sarcoma (2/15) were treated in ATAP, and treatments appeared safe and well-tolerated. A total of 12 radiological RECIST response evaluations were performed, and two cases of minor response, six cases of stable disease and four cases of progressive disease were detected in patients progressing prior to virus treatment. Overall, the median survival time post treatment was 170 days. One patient is still alive at 1,459 days post virus treatment. In summary, Ad5/3-D24-GMCSF appears promising for the treatment of advanced STS; a clinical trial for treatment of refractory injectable solid tumors including STS is ongoing.

Oncolytic immunotherapy: where are we clinically?

Following a century of preclinical and clinical work, oncolytic viruses are now proving themselves in randomized phase 3 trials. Interestingly, human data indicates that these agents have potent immunostimulatory activity, raising the possibility that the key consequence of oncolysis might be induction of antitumor immunity, especially in the context of viruses harboring immunostimulatory transgenes. While safety and efficacy of many types of oncolytic viruses, including adenovirus, herpes, reo, and vaccinia seem promising, few mechanisms of action studies have been performed with human substrates. Thus, the relative contribution of "pure" oncolysis, the immune response resulting from oncolysis, and the added benefit of adding a transgene remain poorly understood. Here, the available clinical data on oncolytic viruses is reviewed, with emphasis on immunological aspects.

Oncolytic virotherapy for ovarian cancer

In the past two decades, more than 20 viruses with selective tropism for tumor cells have been developed as oncolytic viruses (OVs) for treatments of a variety of malignancies. Of these viruses, eleven have been tested in human ovarian cancer models in preclinical studies. So far, nine phase I or II clinical trials have been conducted or initiated using four different types of OVs in patients with recurrent ovarian cancers. In this article, we summarize the different OVs that are being assessed as therapeutics for ovarian cancer. We also present an overview of recent advances in identification of key genetic or immune-response pathways involved in tumorigenesis of ovarian cancer, which provides a better understanding of the tumor specificities and oncolytic properties of OVs. In addition, we discuss how next-generation OVs could be genetically modified or integrated into multimodality regimens to improve clinical outcomes based on recent advances in ovarian cancer biology.

Polymer coatings for delivery of nucleic acid therapeutics

Gene delivery remains the greatest challenge in applying nucleic acid therapeutic for a broad range of diseases. Combining stability during the delivery phase with activation and transgene expression following arrival at the target site requires sophisticated vectors that can discriminate between cell types and respond to target-associated conditions to trigger expression. Efficient intravenous delivery is the greatest single hurdle, with synthetic vectors frequently found to be unstable in the harsh conditions of the bloodstream, and viral vectors often recognized avidly by both the innate and the adaptive immune system. Both types of vectors benefit from coating with hydrophilic polymers. Self-assembling polyelectrolyte non-viral vectors can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Both types of vectors may also have their tropism changed following chemical linkage of novel ligands to the polymer coating. These families of vectors go some way towards realizing the goal of efficient systemic delivery of genes and should find a range of important uses in bringing this still-emerging field to fruition.

Oncolytic virotherapy of glioma: what does it need to make it work?

Oncolytic virotherapy is a highly promising approach, with diverse viruses currently under development as therapeutic agents to treat malignant glioma. Although the first clinical trials did not show toxicity or serious adverse events related to intracerebral administration, overall the antitumor efficacy has fallen short of expectations. This article discusses multiple options on how to improve and maximize the effectiveness of oncolytic virus therapy in brain cancer, including strategies to enhance safety by attenuating neurovirulence via cancer-specific cell-targeting, increasing antitumor potency by transgene-arming and integrating the ability to trigger an effective antitumoral immune response, as well as developing optimized delivery routes in order to boost intratumoral viral distribution. Eventually, it will highlight the use of multipronged approaches, combining multiple modes of action of different agents.

Oncolytic adenovirus research and applications

Cancer treatments have improved steadily, but still only few metastatic solid tumors can be cured. Apoptosis-resistant clones frequently develop following standard treatments. Resistance factors are shared between different treatment regimens and, therefore, loss of response can occur rapidly, despite changing the drug, and there is a tendency for crossresistance between modalities. Therefore, new agents with novel mechanisms of action are desperately needed. Oncolytic adenoviruses, featuring cancer-selective cell lysis and spread, constitute an interesting drug platform aimed towards the goals of tumor specificity, and have been engineered in a variety of ways to improve their selectivity and efficacy. They allow rational drug development by the genetic incorporation of targeting mechanisms that can exert their function at different stages of the viral replication cycle. Owing to their immunogenicity, adenoviruses are particularly attractive for immunostimulatory purposes.

Systemic adenoviral gene delivery to orthotopic murine breast tumors with ablation of coagulation factors, thrombocytes and Kupffer cells

BACKGROUND

Rapid clearance of adenoviruses from blood by macrophage lineage cells of the liver and spleen, and binding to platelets, hinder their successful systemic use for cancer gene therapy. Vitamin K dependent coagulation factors are important mediators for the adenovirus liver tropism. Here we aim to determine the effects of coagulation factor, thrombocyte and liver macrophage (Kupffer cell) ablation on biodistribution of serotype 5 adenoviruses in mice with orthotopic breast tumors.

METHODS

Prior to intravenous injection of adenoviruses, mice bearing orthotopic breast tumors were pretreated with warfarin to inhibit vitamin K dependent coagulation factor synthesis, an anti-platelet antibody causing thrombocytopenia or an inhibitor of the Kupffer cell scavenger receptor or their combination. Virus availability in blood after injection was determined from blood samples and transgene expression in tissues analyzed 72 hours afterwards with In Vivo Imaging and luciferase assays.

RESULTS

Warfarin pretreatment reduced gene delivery to liver, spleen and lung. Kupffer cell ablation increased persistence of adenoviruses in blood but didn't affect biodistribution significantly. Depletion of Kupffer cells combined with thrombocytopenia doubled the systemic gene delivery of 5/3 chimeric adenovirus to tumors (p < 0.05). Triple ablation of platelets, Kupffer cells and coagulation factors increased the tumor to liver ratio of systemic adenovirus gene delivery by 81% (p < 0.05).

CONCLUSIONS

Depletion of coagulation factors can reduce transduction of liver, spleen and lung. Kupffer cell depletion is the most feasible method of increasing amount adenovirus in systemic blood flow and in combination with ablation of thrombocytes can increase the transduction of adenovirus to tumors.

Intelligent design: combination therapy with oncolytic viruses

Metastatic cancer remains an incurable disease in the majority of cases and thus novel treatment strategies such as oncolytic virotherapy are rapidly advancing toward clinical use. In order to be successful, it is likely that some type of combination therapy will be necessary to have a meaningful impact on this disease. Although it may be tempting to simply combine an oncolytic virus with the existing standard radiation or chemotherapeutics, the long-term goal of such treatments must be to have a rational, potentially synergistic combination strategy that can be safely and easily used in the clinical setting. The combination of oncolytic virotherapy with existing radiotherapy and chemotherapy modalities is reviewed along with novel biologic therapies including immunotherapies, in order to help investigators make intelligent decisions during the clinical development of these products.

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.

Targeted radiotherapy for prostate cancer with an oncolytic adenovirus coding for human sodium iodide symporter

PURPOSE

Oncolytic adenoviruses are promising tools for cancer therapy. Although several clinical reports have indicated both safety and promising antitumor capabilities for these viruses, there are only a few examples of complete tumor eradication. Thus, the antitumor efficacy of oncolytic adenoviruses needs to be improved. One potentially useful approach is combination with radiotherapy.

EXPERIMENTAL DESIGN

To target systemically administered radioiodide to tumors, we created Ad5/3-Delta24-human sodium iodide symporter (hNIS), a Rb-p16 pathway selective infectivity enhanced oncolytic adenovirus encoding hNIS.

RESULTS

Ad5/3-Delta24-hNIS replication effectively killed prostate cancer cells in vitro and in vivo. Also, the virus-mediated radioiodide uptake into prostate cancer cells in vitro and into tumors in vivo. Furthermore, Ad5/3-Delta24-hNIS with radioiodide was significantly more effective than virus alone in mice with prostate cancer xenografts.

CONCLUSIONS

These results suggest that oncolytic adenovirus-mediated targeted radiotherapy might be a potentially useful option for enhancing the efficacy or adenoviral virotherapy.

Ad5/3-9HIF-Delta24-VEGFR-1-Ig, an infectivity enhanced, dual-targeted and antiangiogenic oncolytic adenovirus for kidney cancer treatment

Despite good safety data in clinical trials, oncolytic adenoviruses have not been efficient enough to make them a viable treatment alternative for cancers. As more potent viruses are being made, transcriptional and transductional targeting to tumor tissues becomes increasingly appealing. To improve antitumor efficacy, oncolytic adenoviruses can be armed with therapeutic transgenes, such as the antiangiogenic soluble vascular endothelial growth factor receptor 1-Ig fusion protein. We hypothesized that an infectivity enhanced, targeted, vascular endothelial growth factor receptor 1-Ig armed oncolytic adenovirus would exhibit improved specificity and antitumor effect in murine kidney cancer models. Two hypoxia inducible factor-sensitive promoters were evaluated for renal cancer specificity using a novel in vivo dual luciferase-imaging system. Earlier data had shown usefulness of the 5/3-serotype chimera capsid modification for kidney cancer. Therefore, we constructed Ad5/3-9HIF-Delta24-VEGFR-1-Ig, which showed good specificity and oncolytic effect on renal cancer cells in vitro and resulted in antitumor efficacy in a subcutaneous in vivo model, in which vascular endothelial growth factor receptor 1-Ig expression and a concurrent antiangiogenic effect were confirmed. In an intraperitoneally disseminated kidney cancer model, significantly enhanced survival was observed when compared with control viruses. These results suggest that a targeted, antiangiogenic, oncolytic adenovirus might be a valuable agent for testing in kidney cancer patients.

Combination effect of oncolytic adenovirus therapy and herpes simplex virus thymidine kinase/ganciclovir in hepatic carcinoma animal models

AIM

Oncolytic adenovirus, also called conditionally replicating adenovirus (CRAD), can selectively propagate in tumor cells and cause cell lysis. The released viral progeny can infect neighboring cancer cells, initiating a cascade that can lead to the ultimate destruction of the tumor. Suicide gene therapy using herpes simplex virus thymidine kinase (HSV-TK) and ganciclovir (GCV) offers a potential treatment strategy for cancer and is undergoing preclinical trials for a variety of tumors. We hypothesized that HSV-TK gene therapy combined with oncolytic adenoviral therapy would have an enhanced effect compared with the individual effects of the therapies and is a potential novel therapeutic strategy to treat liver cancer.

METHODS

To address our hypothesis, a novel CRAD was created, which consisted of a telomerase-dependent oncolytic adenovirus engineered to express E1A and HSV-TK genes (Ad-ETK). The combined effect of Ad-ETK and GCV was assessed both in vitro and in vivo in nude mice bearing HepG2 cell-derived tumors. Expression of the therapeutic genes by the transduced tumor cells was analyzed by RT-PCR and Western blotting.

RESULTS

We confirmed that Ad-ETK had antitumorigenic effects on human hepatocellular carcinoma (HCC) both in vitro and in vivo, and the TK/GCV system enhanced oncolytic adenoviral therapy. We confirmed that both E1A and HSV-TK genes were expressed in vivo.

CONCLUSION

The Ad-ETK construct should provide a relatively safe and selective approach to killing cancer cells and should be investigated as an adjuvant therapy for hepatocellular carcinoma.

Lentiviruses with trastuzumab bound to their envelopes can target and kill prostate cancer cells

In this study, we took advantage of the overexpression of human epidermal growth factor receptor 2 (HER-2) in prostate cancers to design lentiviruses with modified envelope proteins that bind antibodies to specific cell-surface antigens. When bound to trastuzumab (Herceptin, Genentech, CA), lentiviruses were able to selectively infect androgen-sensitive LNCaP and castration-resistant C4-2 human prostate cancer cell lines, both of which express high levels of HER-2. To test for a therapeutic effect, we engineered our antibody-binding lentiviruses to express thymidine kinase, which can convert the non-toxic pro-drug ganciclovir (GCV) into a cytotoxic form. LNCaP and C4-2 cells infected by these viruses were sensitive to GCV killing. In vivo, C4-2 xenograft tumors treated either intratumorally or i.v. with trastuzumab-bound lentivirus expressed luciferase, although the latter route was less tumor specific. When a prostate-specific promoter for governing luciferase expression was combined with trastuzumab-mediated delivery, there was a further enrichment in targeting viral gene expression in prostate tumors. In conclusion, we found that although prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by viruses with envelope proteins engineered to bind this antibody.

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.

Imaging of viral thymidine kinase gene expression by replicating oncolytic adenovirus and prediction of therapeutic efficacy

PURPOSE

We have used a genetically attenuated adenoviral vector which expresses HSVtk to assess the possible additive role of suicidal gene therapy for enhanced oncolytic effect of the virus. Expression of TK was measured using a radiotracer-based molecular counting and imaging system.

MATERIALS AND METHODS

Replication-competent recombinant adenoviral vector (Ad-DeltaE1B19/55) was used in this study, whereas replication-incompetent adenovirus (Ad-DeltaE1A) was generated as a control. Both Ad-DeltaE1B19/55-TK and Ad-DeltaE1A-TK comprise the HSVtk gene inserted into the E3 region of the viruses. YCC-2 cells were infected with the viruses and incubated with 2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-iodouracil (I-131 FIAU) to measure amount of radioactivity. The cytotoxicity of the viruses was determined, and gamma ray imaging of HSVtk gene was performed. MTT assay was also performed after GCV treatment.

RESULTS

On gamma counter-analyses, counts/ minute (cpm)/microg of protein showed MOIs dependency with DeltaE1B19/55-TK infection. On MTT assay, Ad-DeltaE1B19/55-TK led to more efficient cell killing than Ad-DeltaE1A-TK. On plate imaging by gamma camera, both Ad-DeltaE1B19/55-TK and Ad-DeltaE1A-TK infected cells showed increased I-131 FIAU uptake in a MOI dependent pattern, and with GCV treatment, cell viability of DeltaE1B19/55-TK infection was remarkably reduced compared to that of Ad-DeltaE1A-TK infection.

CONCLUSION

Replicating Ad-DeltaE1B19/55-TK showed more efficient TK expression even in the presence of higher-cancer cell killing effects compared to non-replicating Ad-DeltaE1A-TK. Therefore, GCV treatment still possessed an additive role to oncolytic effect of Ad-DeltaE1B19/55-TK. The expression of TK by oncolytic viruses could rapidly be screened using a radiotracer-based counting and imaging technique.

Extended release of adenovirus from silica implants in vitro and in vivo

Despite promising preclinical results, the clinical benefits of cancer gene therapy have been modest heretofore. The main obstacle continues to be the level and persistence of gene delivery to sufficiently large areas of the tumor. One approach for overcoming this might entail extended local virus release. We studied the utility of silica gel monoliths for delivery of adenovirus to advanced orthotopic gastric and pancreatic cancer tumors. Initially, the biochemical properties of the silica-virus matrix were studied and nearly linear release as a function of time was detected. Virus stayed infective for weeks at +37 degrees C and months at +4 degrees C, which may facilitate storage and distribution. In vivo, extended release of functional replication deficient and also replication-competent, capsid-modified oncolytic viruses was seen. Treatment of mice with pancreatic cancer doubled their survival (P<0.001). Also, silica gel-based delivery slowed the development of antiadenovirus antibodies.

Novel strategies in tailoring human adenoviruses into therapeutic cancer gene therapy vectors

Gene therapy is a novel approach for the treatment of cancer that has so far not been realized. The scope of this review is to try to define the remaining barriers to the successful use of adenovirus vectors for gene and viral therapy of human tumors and to suggest solutions whereby these barriers can be bypassed. It is the conviction of the authors that too many studies have been performed in animal models that are not sufficiently comprehensive to allow conclusions to be drawn for application in humans. For example, in the case of the murine experimental model, in which most studies have been performed, mice are devoid of circulating antibodies to adenovirus type 5 and adenovirus cannot replicate in mouse cells. While the problems are real enough, as witnessed by the quite limited success in human trials, some of the solutions that will be suggested here are hypothetical and have not as yet been tried, even in animals. The review has no ambition to be exhaustive but is intended as a contribution in order to forward the field of gene therapy vectors for systemic clinical application.

Oncolytic adenoviruses kill breast cancer initiating CD44+CD24-/low cells

Cancer stem cells have been indicated in the initiation of tumors and are even found to be responsible for relapses after apparently curative therapies have been undertaken. In breast cancer, they may reside in the CD44(+)CD24(-/low) population. The use of oncolytic adenoviruses presents an attractive anti-tumor approach for eradication of these cells because their entry occurs through infection and they are, therefore, not susceptible to those mechanisms that commonly render stem cells resistant to many drugs. We isolated CD44(+)CD24(-/low) cells from patient pleural effusions and confirmed stem cell-like features including oct4 and sox2 expression and Hoechst 33342 exclusion. CD44(+)CD24(-/low) cells, including the Hoechst excluding subpopulation, could be effectively killed by oncolytic adenoviruses Ad5/3-Delta24 and Ad5.pk7-Delta24. In mice, CD44(+)CD24(-/low) cells formed orthotopic breast tumors but virus infection prevented tumor formation. Ad5/3-Delta24 and Ad5.pk7-Delta24 were effective against advanced orthotopic CD44(+)CD24(-/low)-derived tumors. In summary, Ad5/3-Delta24 and Ad5.pk7-Delta24 can kill CD44(+)CD24(-/low), and also committed breast cancer cells, making them promising agents for treatment of breast cancer.