Mutation of the fiber shaft heparan sulphate binding site of a 5/3 chimeric adenovirus reduces liver tropism.

Natural tropism to the liver is a major obstacle in systemic delivery of adenoviruses in cancer gene therapy. Adenovirus binding to soluble coagulation factors and to cellular heparan sulphate proteoglycans via the fiber shaft KKTK domain are suggested to cause liver tropism. Serotype 5 adenovirus constructs with mutated KKTK regions exhibit liver detargeting, but they also transduce tumors less efficiently, possibly due to altered fiber conformation. We constructed Ad5/3lucS*, a 5/3 chimeric adenovirus with a mutated KKTK region. The fiber knob swap was hypothesized to facilitate tumor transduction. This construct was studied with or without additional coagulation factor ablation. Ad5/3lucS* exhibited significantly reduced transduction of human hepatic cells in vitro and mouse livers in vivo. Combination of coagulation factor ablation by warfarinization to Ad5/3lucS* seemed to further enhance liver detargeting. Cancer cell transduction by Ad5/3lucS* was retained in vitro. In vivo, viral particle accumulation in M4A4-LM3 xenograft tumors was comparable to controls, but Ad5/3lucS* transgene expression was nearly abolished. Coagulation factor ablation did not affect tumor transduction. These studies set the stage for further investigations into the effects of the KKTK mutation and coagulation factor ablation in the context of 5/3 serotype chimerism. Of note, the putative disconnect between tumor transduction and transgene expression could prove useful in further understanding of adenovirus biology.

An oncolytic adenovirus enhanced for toll-like receptor 9 stimulation increases antitumor immune responses and tumor clearance.

Oncolytic viruses represent a multifaceted tool for cancer treatment. In addition to specific killing of cancer cells (oncolysis), these agents also provide danger signals prompting the immune system to stimulate an antitumor immune response. To increase adenovirus adjuvancy, we engineered the genome of Ad5D24 by inserting 18 immunostimulatory islands (Ad5D24-CpG). The toxicity and immunogenicity profile of Ad5D24-CpG showed that the safety of the maternal virus was retained. The efficacy of the CpG-enriched virus was assessed in a xenograft model of lung cancer where a significant increase in antitumor effect was seen in comparison with controls. When the experiment was repeated in animal depleted of natural killer (NK) cells, Ad5D24-CpG lost its advantage. The same was seen when Toll-like receptor (TLR)9 was blocked systemically. In a syngeneic model of melanoma (B16-OVA), we observed a significant increase of OVA-specific T cells and a decrease of activation of myeloid-derived suppressor cells in Ad5D24-CpG-treated mice. In conclusion, we have generated the first genetically modified oncolytic adenovirus backbone able to enhance TLR9-stimulation for increased antitumor activity.

Immune response is an important aspect of the antitumor effect produced by a CD40L-encoding oncolytic adenovirus.

Oncolytic adenovirus is an attractive platform for immunotherapy because virus replication is highly immunogenic and not subject to tolerance. Although oncolysis releases tumor epitopes and provides costimulatory danger signals, arming the virus with immunostimulatory molecules can further improve efficacy. CD40 ligand (CD40L, CD154) induces apoptosis of tumor cells and triggers several immune mechanisms, including a T-helper type 1 (T(H)1) response, which leads to activation of cytotoxic T cells and reduction of immunosuppression. In this study, we constructed a novel oncolytic adenovirus, Ad5/3-hTERT-E1A-hCD40L, which features a chimeric Ad5/3 capsid for enhanced tumor transduction, a human telomerase reverse transcriptase (hTERT) promoter for tumor selectivity, and human CD40L for increased efficacy. Ad5/3-hTERT-E1A-hCD40L significantly inhibited tumor growth in vivo via oncolytic and apoptotic effects, and (Ad5/3-hTERT-E1A-hCD40L)-mediated oncolysis resulted in enhanced calreticulin exposure and HMGB1 and ATP release, which were suggestive of immunogenicity. In two syngeneic mouse models, murine CD40L induced recruitment and activation of antigen-presenting cells, leading to increased interleukin-12 production in splenocytes. This effect was associated with induction of the T(H)1 cytokines IFN-γ, RANTES, and TNF-α. Tumors treated with Ad5/3-CMV-mCD40L also displayed an enhanced presence of macrophages and cytotoxic CD8(+) T cells but not B cells. Together, our findings show that adenoviruses coding for CD40L mediate multiple antitumor effects including oncolysis, apoptosis, induction of T-cell responses, and upregulation of T(H)1 cytokines.

Integrin targeted oncolytic adenoviruses Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of patients with advanced chemotherapy refractory solid tumors.

The safety of oncolytic viruses for treatment of cancer has been shown in clinical trials while antitumor efficacy has often remained modest. As expression of the coxsackie-adenovirus receptor may be variable in advanced tumors, we developed Ad5-D24-RGD, a p16/Rb pathway selective oncolytic adenovirus featuring RGD-4C modification of the fiber. This allows viral entry through alpha-v-beta integrins frequently highly expressed in advanced tumors. Advanced tumors are often immunosuppressive which results in lack of tumor eradication despite abnormal epitopes being present. Granulocyte-macrophage colony stimulating factor (GMCSF) is a potent activator of immune system with established antitumor properties. To stimulate antitumor immunity and break tumor associated immunotolerance, we constructed Ad5-RGD-D24-GMCSF, featuring GMCSF controlled by the adenoviral E3 promoter. Preliminary safety of Ad5-D24-RGD and Ad5-RGD-D24-GMCSF for treatment of human cancer was established. Treatments with Ad5-D24-RGD (N = 9) and Ad5-RGD-D24-GMCSF (N = 7) were well tolerated. Typical side effects were grade 1-2 fatigue, fever and injection site pain. 77% (10/13) of evaluable patients showed virus in circulation for at least 2 weeks. In 3 out of 6 evaluable patients, disease previously progressing stabilized after a single treatment with Ad5-RGD-D24-GMCSF. In addition, 2/3 patients had stabilization or reduction in tumor marker levels. All patients treated with Ad5-D24-RGD showed disease progression in radiological analysis, although 3/6 had temporary reduction or stabilization of marker levels. Induction of tumor and adenovirus specific immunity was demonstrated with ELISPOT in Ad5-RGD-D24-GMCSF treated patients. RGD modified oncolytic adenoviruses with or without GMCSF seem safe for further clinical development.

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.

Optimized mouse model for the imaging of tumor metastasis upon experimental therapy.

Development of new cancer treatments focuses increasingly on the relation of cancer tissue with its microenvironment. A major obstacle for the development of new anti-cancer therapies has been the lack of relevant animal models that would reproduce all the events involved in disease progression from the early-stage primary tumor until the development of mature metastatic tissue. To this end, we have developed a readily imageable mouse model of colorectal cancer featuring highly reproducible formation of spontaneous liver metastases derived from intrasplenic primary tumors. We optimized several experimental variables, and found that the correct choice of cell line and the genetic background, as well as the age of the recipient mice, were critical for establishing a useful model system. Among a panel of colorectal cancer cell lines tested, the epithelial carcinoma HT29 line was found to be the most suitable in terms of producing homogeneous tumor growth and metastases. In our hands, SCID mice at the age of 125 days or older were the most suitable in supporting consistent HT29 tumor growth after splenic implantation followed by reproducible metastasis to the liver. A magnetic resonance imaging (MRI) protocol was optimized for use with this mouse model, and demonstrated to be a powerful method for analyzing the antitumor effects of an experimental therapy. Specifically, we used this system to with success to verify by MRI monitoring the efficacy of an intrasplenically administered oncolytic adenovirus therapy in reducing visceral tumor load and development of liver metastases. In summary, we have developed a highly optimized mouse model for liver metastasis of colorectal cancer, which allows detection of the tumor load at the whole body level and enables an accurate timing of therapeutic interventions to target different stages of cancer progression and metastatic development.

Induction of interferon pathways mediates in vivo resistance to oncolytic adenovirus.

Oncolytic adenoviruses are an emerging experimental approach for treatment of tumors refractory to available modalities. Although preclinical results have been promising, and clinical safety has been excellent, it is also apparent that tumors can become virus resistant. The resistance mechanisms acquired by advanced tumors against conventional therapies are increasingly well understood, which has allowed development of countermeasures. To study this in the context of oncolytic adenovirus, we developed two in vivo models of acquired resistance, where initially sensitive tumors eventually gain resistance and relapse. These models were used to investigate the phenomenon on RNA and protein levels using two types of analysis of microarray data, quantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry. Interferon (IFN) signaling pathways were found upregulated and Myxovirus resistance protein A (MxA) expression was identified as a marker correlating with resistance, while transplantation experiments suggested a role for tumor stroma in maintaining resistance. Furthermore, pathway analysis suggested potential therapeutic targets in oncolytic adenovirus-resistant cells. Improved understanding of the antiviral phenotype causing tumor recurrence is of key importance in order to improve treatment of advanced tumors with oncolytic adenoviruses. Given the similarities between mechanisms of action, this finding might be relevant for other oncolytic viruses as well.

Immunological effects of low-dose cyclophosphamide in cancer patients treated with oncolytic adenovirus.

Patients with advanced solid tumors refractory to and progressing after conventional therapies were treated with three different regimens of low-dose cyclophosphamide (CP) in combination with oncolytic adenovirus. CP was given with oral metronomic dosing (50 mg/day, N = 21), intravenously (single 1,000 mg dose, N = 7) or both (N = 7). Virus was injected intratumorally. Controls (N = 8) received virus without CP. Treatments were well tolerated and safe regardless of schedule. Antibody formation and virus replication were not affected by CP. Metronomic CP (oral and oral + intravenous schedules) decreased regulatory T cells (T(regs)) without compromising induction of antitumor or antiviral T-cell responses. Oncolytic adenovirus given together with metronomic CP increased cytotoxic T cells and induced Th1 type immunity on a systemic level in most patients. All CP regimens resulted in higher rates of disease control than virus only (all P < 0.0001) and the best progression-free (PFS) and overall survival (OS) was seen in the oral + intravenous group. One year PFS and OS were 53 and 42% (P = 0.0016 and P < 0.02 versus virus only), respectively, both which are unusually high for chemotherapy refractory patients. We conclude that low-dose CP results in immunological effects appealing for oncolytic virotherapy. While these first-in-human data suggest good safety, intriguing efficacy and extended survival, the results should be confirmed in a randomized trial.

Switching the fiber knob of oncolytic adenoviruses to avoid neutralizing antibodies in human cancer patients.

BACKGROUND: Oncolytic adenoviruses are an attractive strategy for treating cancers resistant to conventional treatments. However, their systemic utility could be limited as a result of the high prevalence of pre-existing immunity towards the vector. Furthermore, neutralizing antibodies (NAbs) may prevent successful intravenous readministration of the same agent. Previous preclinical reports indicate that the NAb response can be partially overcome by modifying the adenoviral fiber knob. However, to date, this strategy has not been evaluated in human patients. METHODS: Twenty-four human patients with advanced cancer were treated with two cycles of oncolytic adenoviruses, featuring three capsid variants: unmodified adenovirus serotype 5 (Ad5), serotype 5 with RGD motif in the HI-loop of the fiber knob (Ad5-RGD) and serotype 5 carrying fiber knob from serotype 3 (Ad5/3). A virus with different fiber structure was used for the second round of treatment and patient serum was analyzed for a neutralizing effect. RESULTS: All patients developed NAbs against the virus that they were treated with. However, the magnitude and velocity of the response varied considerably. When measured just before the second treatment cycle, a differential in serum NAb titer against the first versus second virus was seen in 83% of cases, suggesting that even minor changes in the fiber knob can circumvent neutralization in cancer patients. No correlation between NAb titers and outcome variables was observed. CONCLUSIONS: The results obtained in the present study extend previous preclinical reports into human cancer patients and suggest that modification of the fiber knob is a feasible strategy for circumventing the NAb response in patients receiving multiple rounds of oncolytic adenoviruses.

In vivo and in vitro distribution of type 5 and fiber-modified oncolytic adenoviruses in human blood compartments.

BACKGROUND: Successful tumor targeting of systemically administered oncolytic adenoviruses may be hindered by interactions with blood components. MATERIALS AND METHODS: Blood distribution of oncolytic adenoviruses featuring type 5 adenovirus fiber, 5/3 capsid chimerism, or RGD-4C in the fiber knob was investigated in vitro and in patients with refractory solid tumors. RESULTS: Virus titers and prevalence in serum of patients increased over the first post-treatment week, suggesting replication. Detection of low virus loads was more sensitive in blood clots than in serum, although viral levels > 500 viral particles/mL did not differ significantly between both sample types. While adenovirus bound to erythrocytes, platelets, granulocytes, and peripheral blood mononuclear cells in vitro, the virus was mainly detectable in erythrocytes and granulocytes in cancer patients. Taken together with a temporary post-treatment decrease in thrombocyte counts, platelet activation by adenovirus and subsequent clearance seem likely to occur in humans. Fiber modifications had limited observed effect on virus distribution in blood cell compartments. Neutrophils, monocytes and cytotoxic T lymphocytes were the major leukocyte subpopulations interacting with adenoviruses. CONCLUSION: Serum and blood clots are relevant to estimate oncolytic adenovirus replication. Insight into viral interactions with blood cells may contribute to the development of new strategies for tumor delivery.

Safety of glucocorticoids in cancer patients treated with oncolytic adenoviruses.

Oncolytic adenoviruses are an emerging treatment option for advanced and refractory cancer. Such patients are often treated with corticosteroids to ameliorate tumor associated symptoms. Thus, it is important to evaluate whether safety is affected by immunosuppression possibly induced by corticosteroids. Concurrent low-dose cyclophosphamide, appealing for its immunomodulatory effects, could also impact safety. In a retrospective case-control study, we evaluated the effect of systemic corticosteroid use in cancer patients receiving oncolytic virotherapy. Four treatment groups were identified: (1) oncolytic adenovirus with oral glucocorticoids, (2) virus alone, (3) virus with glucocorticoids and cyclophosphamide and (4) virus with cyclophosphamide. Adverse events, neutralizing antibody titers, viral DNA in circulation and tumor responses were evaluated. The most common adverse effects were grade 1-2 fatigue, nausea, fever and abdominal pain. Common asymptomatic findings included self-limiting grade 1-3 hyponatremia and aspartate aminotransferase increase. Safety was good and no significant differences were observed between the groups. All patients had an increase in neutralizing antibody titers post-treatment, and no trends for differences between groups were observed. There were fewer post-treatment virus genomes circulating in patients receiving glucocorticoids when compared to their control groups. Overall, glucocorticoid use in cancer patients receiving oncolytic adenovirus, with or without low-dose cyclophosphamide, seems safe.

Defects in innate immunity render breast cancer initiating cells permissive to oncolytic adenovirus.

BACKGROUND: Cancer stem cells/initiating cells (CSC/CIC), are thought to exist as a small population in malignant tissues. They are resistant to conventional cancer treatments and possibly underlie post-treatment relapse. The CIC population can be targeted with capsid modified oncolytic adenoviruses. METHODOLOGY/PRINCIPAL FINDINGS: We studied the mechanisms of innate immunity to oncolytic adenovirus Ad5/3-Delta24 in conventional treatment resistant non-CIC breast cancer cells, breast cancer CD44(+)/CD24(-/low) CIC population and normal breast tissue CD44(+)/CD24(-/low) stem cells. We compared virus recognition by pattern recognition receptors for adenovirus, Toll-like receptors (TLR) 2 and 9 and virus induced type I interferon (IFN) response regulation in these cell types. We show TLR mediated virus recognition in these non-immune cell types. Normal tissue stem cells have intact type I IFN signaling. Furthermore, TLR9 and TLR2 reside constantly in recognition sites, implying constant activation. In contrast, breast cancer CD44(+)/CD24(-/low) CIC have dysregulated innate immune responses featuring dysfunctional virus recognition caused by impaired trafficking of TLR9 and cofactor MyD88 and the absence of TLR2, having a deleterious impact on TLR pattern recognition receptor signaling. Furthermore, the CIC have increased inhibitory signaling via the suppressor of cytokine signaling/Tyro3/Axl/Mer receptor tyrosine kinase (SOCS/TAM) pathway. These defects in contribute to dysfunctional induction of type I IFN response in CIC and therefore permissivity to oncolytic adenovirus. CONCLUSIONS/SIGNIFICANCE: CICs may underlie the incurable nature of relapsed or metastatic cancers and are therefore an important target regarding diagnostic and prognostic aspects as well as treatment of the disease. This study addresses the mechanisms of innate infection immunity in stem cells deepening the understanding of stem cell biology and may benefit not only virotherapy but also immunotherapy in general.

Adenoviruses with an αvß integrin targeting moiety in the fiber shaft or the HI-loop increase tumor specificity without compromising antitumor efficacy in magnetic resonance imaging of colorectal cancer metastases.

BACKGROUND: Colorectal cancer is often a deadly disease and cannot be cured at metastatic stage. Oncolytic adenoviruses have been considered as a new therapeutic option for treatment of refractory disseminated cancers, including colorectal cancer. The safety data has been excellent but tumor transduction and antitumor efficacy especially in systemic administration needs to be improved. METHODS: Here, the utility of αvß integrin targeting moiety Arg-Gly-Asp (RGD) in the Lys-Lys-Thr-Lys (KKTK) domain of the fiber shaft or in the HI-loop of adenovirus serotype 5 for increased tumor targeting and antitumor efficacy was evaluated. To this end, novel spleen-to-liver metastatic colorectal cancer mouse model was used and the antitumor efficacy was evaluated with magnetic resonance imaging (MRI). RESULTS: Both modifications (RGD in the HI-loop or in the fiber shaft) increased gene transfer efficacy in colorectal cancer cell lines and improved tumor-to-normal ratio in systemic administration of the vector. CONCLUSIONS: Antitumor potency was not compromised with RGD modified viruses suggesting increased safety profile and tumor specificity.

Treatment of cancer patients with a serotype 5/3 chimeric oncolytic adenovirus expressing GMCSF.

Augmenting antitumor immunity is a promising way to enhance the potency of oncolytic adenoviral therapy. Granulocyte-macrophage colony-stimulating factor (GMCSF) can mediate antitumor effects by recruiting natural killer cells and by induction of tumor-specific CD8(+) cytotoxic T-lymphocytes. Serotype 5 adenoviruses (Ad5) are commonly used in cancer gene therapy. However, expression of the coxsackie-adenovirus receptor is variable in many advanced tumors and preclinical data have demonstrated an advantage for replacing the Ad5 knob with the Ad3 knob. Here, a 5/3 capsid chimeric and p16-Rb pathway selective oncolytic adenovirus coding for GMCSF was engineered and tested preclinically. A total of 21 patients with advanced solid tumors refractory to standard therapies were then treated intratumorally and intravenously with Ad5/3-D24-GMCSF, which was combined with low-dose metronomic cyclophosphamide to reduce regulatory T cells. No severe adverse events occurred. Analysis of pretreatment samples of malignant pleural effusion and ascites confirmed the efficacy of Ad5/3-D24-GMCSF in transduction and cell killing. Evidence of biological activity of the virus was seen in 13/21 patients and 8/12 showed objective clinical benefit as evaluated by radiology with Response Evaluation Criteria In Solid Tumors (RECIST) criteria. Antiadenoviral and antitumoral immune responses were elicited after treatment. Thus, Ad5/3-D24-GMCSF seems safe in treating cancer patients and promising signs of efficacy were seen.

Oncolytic adenovirus ICOVIR-7 in patients with advanced and refractory solid tumors.

PURPOSE: Twenty-one patients with cancer were treated with a single round of oncolytic adenovirus ICOVIR-7. EXPERIMENTAL DESIGN: ICOVIR-7 features an RGD-4C modification of the fiber HI-loop of serotype 5 adenovirus for enhanced entry into tumor cells. Tumor selectivity is mediated by an insulator, a modified E2F promoter, and a Rb-binding site deletion of E1A, whereas replication is optimized with E2F binding hairpins and a Kozak sequence. ICOVIR-7 doses ranged from 2 x 10(10) to 1 x 10(12) viral particles. All patients had advanced and metastatic solid tumors refractory to standard therapies. RESULTS: ICOVIR-7 treatment was well tolerated with mild to moderate fever, fatigue, elevated liver transaminases, chills, and hyponatremia. One patient had grade 3 anemia but no other serious side effects were seen. At baseline, 9 of 21 of patients had neutralizing antibody titers against the ICOVIR-7 capsid. Treatment resulted in neutralizing antibody titer induction within 4 weeks in 16 of 18 patients. No elevations of serum proinflammatory cytokine levels were detected. Viral genomes were detected in the circulation in 18 of 21 of patients after injection and 7 of 15 of the samples were positive 2 to 4 weeks later suggesting viral replication. CONCLUSIONS: Overall, objective evidence of antitumor activity was seen in 9 of 17 evaluable patients. In radiological analyses, 5 of 12 evaluable patients had stabilization or reduction in tumor size. These consisted of one partial response, two minor responses and two cases of stable disease, all occurring in patients who had progressive disease before treatment. In summary, ICOVIR-7 treatment is apparently safe, resulting in anticancer activity, and is therefore promising for further clinical testing.

Oncolytic adenovirus coding for granulocyte macrophage colony-stimulating factor induces antitumoral immunity in cancer patients.

Granulocyte macrophage colony-stimulating factor (GMCSF) can mediate antitumor effects by recruiting natural killer cells and by induction of tumor-specific cytotoxic T-cells through antigen-presenting cells. Oncolytic tumor cell-killing can produce a potent costimulatory danger signal and release of tumor epitopes for antigen-presenting cell sampling. Therefore, an oncolytic adenovirus coding for GMCSF was engineered and shown to induce tumor-specific immunity in an immunocompetent syngeneic hamster model. Subsequently, 20 patients with advanced solid tumors refractory to standard therapies were treated with Ad5-D24-GMCSF. Of the 16 radiologically evaluable patients, 2 had complete responses, 1 had a minor response, and 5 had disease stabilization. Responses were frequently seen in injected and noninjected tumors. Treatment was well tolerated and resulted in the induction of both tumor-specific and virus-specific immunity as measured by ELISPOT and pentamer analysis. This is the first time that oncolytic virus-mediated antitumor immunity has been shown in humans. Ad5-D24-GMCSF is promising for further clinical testing.

Human adenovirus replication in immunocompetent Syrian hamsters can be attenuated with chlorpromazine or cidofovir.

BACKGROUND: Adenoviruses can cause severe toxicity in children and in immunocompromised adults, and therefore a means to abrogate replication would be useful. With regard to cancer treatment, replication competent oncolytic adenoviruses have been safe in humans, although their efficacy has been variable. Therefore, more effective agents are now entering clinical testing and, consequently, replication-associated side effects remain a concern. Preclinical analysis of replication related toxicity has been hampered by a lack of permissive models. Therefore, it has been difficult to study modulation of human adenovirus replication in immune competent animals. METHODS: We investigated four different hamster carcinoma cell lines for transduction and cell killing potency in vitro and in vivo. Gene transfer was assessed using replication-deficient adenoviruses expressing luciferase. Cell killing was studied in vitro and in vivo using an oncolytic adenovirus that kills tumor cells by viral replication. After the most promising animal model had been selected, abrogation of virus replication was assessed in vitro and in vivo using a TCID(50) assay. RESULTS: The results obtained suggest wild-type adenovirus replication in all four tested Syrian hamster cell lines and also normal organs. Virus replication could be abrogated with chlorpromazine, cidofovir and cytosine arabinoside, and the effect occurred subsequent to nuclear delivery of the viral genome. Attenuation of virus replication also was seen in vivo both in tumors and the liver. CONCLUSIONS: Syrian hamsters may comprise a valuable immune competent model for evaluating anti-adenoviral drugs. Furthermore, chlorpromazine or cidofovir might be useful in case of adenovirus replication-associated symptoms in humans.

Targeted chemotherapy for head and neck cancer with a chimeric oncolytic adenovirus coding for bifunctional suicide protein FCU1.

PURPOSE: Transfer of prodrug activation systems into tumors by using replication-deficient viruses has been suggested to be an effective method for achieving high local and low systemic anticancer drug concentrations. However, most current suicide gene therapy strategies are still hindered by poor efficiency of in vivo gene transfer, inefficient tumor penetration, limited bystander cell killing effect, and need of large prodrug doses. We hypothesized that local amplification provided by a replication competent platform would help overcome these limitations. EXPERIMENTAL DESIGN: We generated a transductionally and transcriptionally targeted oncolytic adenovirus Ad5/3-Delta24FCU1 expressing the fusion suicide gene FCU1. FCU1 encodes a bifunctional fusion protein that efficiently catalyzes the direct conversion of 5-FC, a relatively nontoxic antifungal agent, into the toxic metabolites 5-fluorouracil and 5-fluorouridine monophosphate, bypassing the natural resistance of certain human tumor cells to 5-fluorouracil. RESULTS: We examined the efficacy of Ad5/3-Delta24FCU1 and the replication-defective control Ad5/3-FCU1 with and without 5-FC. FCU1 expression was confirmed by Western blot, whereas enzymatic conversion levels in vitro and in vivo were determined by high-performance liquid chromatography separation. Significant antitumor effect was observed in vitro and in vivo in a murine model of head and neck squamous cell carcinoma. Although we observed a decrease in viral DNA copy number in vitro and in tumors treated with Ad5/3-Delta24FCU1 and 5-FC, suggesting an effect on virus replication, the highest antitumor effect was observed for this combination. CONCLUSIONS: It seems feasible and efficacious to combine adenovirus replication to the FCU1 prodrug activation system.