Combination effect of oncolytic adenovirotherapy and TRAIL gene therapy in syngeneic murine breast cancer models

Oncolytic Viruses and Cancer, Do You Know the Main Mechanism?

The global rate of cancer has increased in recent years, and cancer is still a threat to human health. Recent developments in cancer treatment have yielded the understanding that viruses have a high potential in cancer treatment. Using oncolytic viruses (OVs) is a promising approach in the treatment of malignant tumors. OVs can achieve their targeted treatment effects through selective cell death and induction of specific antitumor immunity. Targeting tumors and the mechanism for killing cancer cells are among the critical roles of OVs. Therefore, evaluating OVs and understanding their precise mechanisms of action can be beneficial in cancer therapy. This review study aimed to evaluate OVs and the mechanisms of their effects on cancer cells.

Synergistic effect of bladder cancer-specific oncolytic adenovirus in combination with chemotherapy

Gene therapy with adenoviral early region gene (E1A) may enhance the susceptibility of neoplastic cells to chemotherapy-induced cell death. Our previous study developed a urothelium-specific oncolytic serotype 5 adenovirus (Ad5) with the uroplakin II (UPII) promoter controlling E1A expression. The present study investigated whether this urothelium-specific recombinant adenovirus (Ad5-UPII-E1A) enhanced mitomycin (MMC) and hydroxycamptothecin (HCPT) sensitization and drug-induced apoptosis in bladder cancer cells. The results of the MTT assay revealed that combination therapy, using Ad5-UPII-E1A and MMC or HCPT, synergistically inhibited the viability of bladder cancer cells in a dose- and time-dependent manner when compared with either agent alone. When cells were treated with Ad5-UPII-E1A alone they arrested in the G1 phase, but cell cycle analysis by flow cytometry revealed S phase arrest when treated with combined therapy. Treatment with MMC or HCPT enhanced Ad5-UPII-E1A-induced apoptosis in 5,637 cells, observed by transmission electron microscopy. Western blot analysis revealed that MMC and HCPT enhanced the E1A expression of the Ad5-UPII-E1A vectorin a dose-dependent manner. The present study demonstrated that Ad5-UPII-E1A combined with MMC or HCPT resulted in synergistic cytotoxicity in a process which involved the promotion of apoptosis in bladder cancer cell lines. MMC and HCPT also promoted the oncolytic effect of Ad5-UPII-E1A. Thus, treatment using Ad5-UPII-E1A combined with MMC or HCPT may be an attractive strategy for the sensitization of bladder cancer to chemotherapy.

Combinatorial treatment with oncolytic adenovirus and helper-dependent adenovirus augments adenoviral cancer gene therapy

Oncolytic adenoviruses (Onc.Ads) produce significant antitumor effects but as single agents they rarely eliminate tumors. Investigators have therefore incorporated sequences into these vectors that encode immunomodulatory molecules to enhance antitumor immunity. Successful implementation of this strategy requires multiple tumor immune inhibitory mechanisms to be overcome, and insertion of the corresponding multiple functional genes reduces the titer and replication of Onc.Ads, compromising their direct ant-tumor effects. By contrast, helper-dependent (HD) Ads are devoid of viral coding sequences, allowing inclusion of multiple transgenes. HDAds, however, lack replicative capacity. Since HDAds encode the adenoviral packaging signal, we hypothesized that the coadministration of Onc.Ad with HDAd would allow to be amplified and packaged during replication of Onc.Ad in transduced cancer cells. This combination could provide immunostimulation without losing oncolytic activity. We now show that coinfection of Onc.Ad with HDAd subsequently replicates HDAd vector DNA in trans in human cancer cell lines in vitro and in vivo, amplifying the transgenes the HDAd encode. This combinatorial treatment significantly suppresses the tumor growth compared to treatment with a single agent in an immunocompetent mouse model. Hence, combinatorial treatment of Onc.Ad with HDAd should overcome the inherent limitations of each agent and provide a highly immunogenic oncolytic therapy.

Potent antitumor activity of oncolytic adenovirus expressing Beclin-1 via induction of autophagic cell death in leukemia

An attractive strategy among adenovirus-based oncolytic systems is to design adenoviral vectors to express pro-apoptotic genes, in which this gene-virotherapy approach significantly enhances tumor cell death by activating apoptotic pathways. However, the existence of cancer cells with apoptotic defects is one of the major obstacles in gene-virotherapy. Here, we investigated whether a strategy that combines the oncolytic effects of an adenoviral vector with simultaneous expression of Beclin-1, an autophagy gene, offers a therapeutic advantage for leukemia. A Beclin-1 cDNA was cloned in an oncolytic adenovirus with chimeric Ad5/11 fiber (SG511-BECN). SG511-BECN treatment induced significant autophagic cell death, and resulted in enhanced cell killing in a variety of leukemic cell lines and primary leukemic blasts. SG511-BECN effects were seen in chronic myeloid leukemia and acute myeloid leukemia with resistance to imatinib or chemotherapy, but exhibited much less cytotoxicity on normal cells. The SG511-BECN-induced autophagic cell death could be partially reversed by RNA interference knockdown of UVRAG, ATG5, and ATG7. We also showed that SG511-BECN strongly inhibited the growth of leukemic progenitors in vitro. In murine leukemia models, SG511-BECN prolonged the survival and decreased the xenograft tumor size by inducing autophagic cell death. Our results suggest that infection of leukemia cells with an oncolytic adenovirus overexpressing Beclin-1 can induce significant autophagic cell death and provide a new strategy for the elimination of leukemic cells via a unique mechanism of action distinct from apoptosis.

Trojan horse at cellular level for tumor gene therapies

Among innovative strategies developed for cancer treatments, gene therapies stand of great interest despite their well-known limitations in targeting, delivery, toxicity or stability. The success of any given gene-therapy is highly dependent on the carrier efficiency. New approaches are often revisiting the mythic trojan horse concept to carry therapeutic nucleic acid, i.e. DNAs, RNAs or small interfering RNAs, to pathologic tumor site. Recent investigations are focusing on engineering carrying modalities to overtake the above limitations bringing new promise to cancer patients. This review describes recent advances and perspectives for gene therapies devoted to tumor treatment, taking advantage of available knowledge in biotechnology and medicine.

Intravenous administration of adenoviruses targeting transforming growth factor beta signaling inhibits established bone metastases in 4T1 mouse mammary tumor model in an immunocompetent syngeneic host

We have examined the effect of adenoviruses expressing soluble transforming growth factor receptorII-Fc (sTGFβRIIFc) in a 4T1 mouse mammary tumor bone metastasis model using syngeneic BALB/c mice. Infection of 4T1 cells with a non-replicating adenovirus, Ad(E1-).sTβRFc, or with two oncolytic adenoviruses, Ad.sTβRFc and TAd.sTβRFc, expressing sTGFβRIIFc (the human TERT promoter drives viral replication in TAd.sTβRFc) produced sTGFβRIIFc protein. Oncolytic adenoviruses produced viral replication and induced cytotoxicity in 4T1 cells. 4T1 cells were resistant to the cytotoxic effects of TGFβ-1 (up to 10 ng ml(-1)). However, TGFβ-1 induced the phosphorylation of SMAD2 and SMAD3, which were inhibited by co-incubation with sTGFβRIIFc protein. TGFβ-1 also induced interleukin-11, a well-known osteolytic factor. Intracardiac injection of 4T1-luc2 cells produced bone metastases by day 4. Intravenous injection of Ad.sTβRFc (on days 5 and 7) followed by bioluminescence imaging (BLI) of mice on days 7, 11 and 14 in tumor-bearing mice indicated inhibition of bone metastasis progression (P<0.05). X-ray radiography of mice on day 14 showed a significant reduction of the lesion size by Ad.sTβRFc (P<0.01) and TAd.sTβRFc (P<0.05). Replication-deficient virus Ad(E1-).sTβRFc expressing sTGFβRIIFc showed some inhibition of bone metastasis, whereas Ad(E1-).Null was not effective in inhibiting bone metastases. Thus, systemic administration of Ad.sTβRFc and TAd.sTβRFc can inhibit bone metastasis in the 4T1 mouse mammary tumor model, and can be developed as potential anti-tumor agents for breast cancer.

Second-generation HIF-activated oncolytic adenoviruses with improved replication, oncolytic, and antitumor efficacy

There is a need to develop more potent oncolytic adenoviruses (Ads) that show increased antitumor activity in patients. The HYPR-Ads are targeted oncolytic Ads that specifically kill tumor cells, which express active hypoxia-inducible factor (HIF). While therapeutically efficacious, the HYPR-Ads showed attenuated replication and oncolytic activity. To overcome these deficiencies and improve antitumor efficacy, we created new HIF-activated oncolytic Ads, HIF-Ad and HIF-Ad-IL4, which have two key changes: (i) a modified HIF-responsive promoter to regulate the E1A replication gene and (ii) insertion of the E3 gene region. The HIF-Ads showed conditional activation of E1A expression under hypoxia. Importantly, the HIF-Ads show hypoxia-dependent replication, oncolytic and cellular release activities, and potent antitumor efficacy, all of which are significantly greater than that of the HYPR-Ads. Notably, HIF-Ad-IL4 treatment led to regressions in tumor size by 70% and extensive tumor infiltration by leukocytes resulting in an antitumor efficacy that is up to six-fold greater than that of the HYPR-Ads, HIF-Ad and wild-type Ad treatment. These studies show that treatment with an HIF-activated oncolytic Ad leads to a measurable therapeutic response. The novel design of the HIF-Ads represents a significant improvement compared with first-generation oncolytic Ads and has great potential to increase the efficacy of this cancer therapy.

Efficacy of oncolytic mutants targeting pRb and p53 pathways is synergistically enhanced when combined with cytotoxic drugs in prostate cancer cells and tumor xenografts

Replication-selective oncolytic adenoviruses have proven safety records with promising clinical outcomes. However, strategies to improve efficacy are still required. Here we report greatly improved antitumor efficacy for both attenuated (dl1520) and highly potent (dl922–947) oncolytic mutants in combination with the current standard of care for late-stage hormone-independent prostate cancers, mitoxantrone or docetaxel. In agreement with previous reports, dl922–947 had superior potency compared with dl1520 both as a single agent and in combination with cytotoxic drugs. The dl922–947 mutant caused significant synergistic cell killing in both drug-insensitive and -sensitive prostate cancer cell lines, PC3 and DU145, respectively, when combined with docetaxel or mitoxantrone. The magnitude of the synergistic response was greatest for dl1520 whereas overall efficacy was greatest for dl922–947, and the latter was also more efficacious in vivo in prostate cancer models. In DU145 and PC3 cells increased viral uptake (up to 9- and 8-fold, respectively), E1A expression, and altered cell cycle progression contributed to the synergistic cell killing. A similar trend was also detected in LNCaP cells. Potent E1A expression was essential for the response. In murine xenograft models (DU145 and PC3) tumor growth inhibition was improved when suboptimal doses of docetaxel and viral mutants were combined. These findings demonstrate that the efficacy of highly potent oncolytic mutants such as dl922–947 that target the retinoblastoma protein (pRb) pathway could be further enhanced even with low drug doses, and support the deletion of the E1ACR2 region in future candidate adenoviruses for treatment of hormone-independent prostate cancers.

Analysis of adenovirus trans-complementation-mediated gene expression controlled by melanoma-specific TETP promoter in vitro

BACKGROUND

Human adenoviruses (Ads) have substantial potential for clinical applications in cancer patients. Conditionally replicating adenoviruses (CRAds) include oncolytic adenoviruses in which expression of the immediate early viral transactivator protein E1A is controlled by a cancer cell-selective promoter. To enhance efficacy, CRAds are further armed to contain therapeutic genes. Due to size constraints of the capsid geometry, the capacity for packaging transgenes into Ads is, however, limited. To overcome this limitation, the employment of E1A-deleted replication-deficient viruses carrying therapeutic genes in combination with replication-competent CRAd vectors expressing E1A in trans has been proposed. Most trans-complementing studies involved transgene expressions from strong ubiquitous promoters, and thereby relied entirely on the cancer cell specificity of the CRAd vector.

RESULTS

Here we tested the trans-complementation of a CRAd and a replication-deficient transgene vector containing the same cancer cell-selective promoter. Hereto, we generated two new vectors expressing IL-2 and CD40L from a bicistronic expression cassette under the control of the melanoma/melanocyte-specific tyrosinase enhancer tyrosinase promoter (TETP), which we previously described for the melanoma-specific CRAd vector AdDeltaEP-TETP. These vectors gave rise to tightly controlled melanoma-specific transgene expression levels, which were only 5 to 40-fold lower than those from vectors controlled by the nonselective CMV promoter. Reporter analyses using Ad-CMV-eGFP in combination with AdDeltaEP-TETP revealed a high level of trans-complementation in melanoma cells (up to about 30-fold), but not in non-melanoma cells, unlike the AdCMV-eGFP/wtAd5 binary vector system, which was equally efficient in melanoma and non-melanoma cells. Similar findings were obtained when replacing the transgene vector AdCMV-eGFP with AdCMV-IL-2 or AdCMV-CD40L. However, the combination of the novel AdTETP-CD40L/IL-2 vector with AdDeltaEP-TETP or wtAd5 gave reproducible moderate 3-fold enhancements of IL-2 by trans-complementation only.

CONCLUSIONS

The cancer cell-selective TETP tested here did not give the expected enforceable transgene expression typically achieved in the Ad trans-complementing system. Reasons for this could include virus-mediated down regulation of limiting transcription factors, and/or competition for such factors by different promoters. Whether this finding is unique to the particular promoter system tested here, or also occurs with other promoters warrants further investigations.

TRAIL gene-armed oncolytic poxvirus and oxaliplatin can work synergistically against colorectal cancer

We have explored a unique combination therapy for metastatic colorectal cancer. This strategy combines a potent and new oncolytic poxvirus expressing a membrane-bound tumor necrosis factor-related apoptosis-inducing ligand (TRAIL or TNFSF10) and oxaliplatin (Ox) chemotherapy. We hypothesized that TRAIL expression would increase the efficacy of the oncolytic poxvirus, and that the therapeutic efficacy would be further enhanced by combination with chemotherapy. The cytotoxicity to cancer cells by Ox, oncolytic vaccinia virus (VV) and trail gene-armed VV alone or in combination was tested in vitro. The trail gene armed oncolytic VV-expressed high levels of TRAIL in infected cancer cells and had greater potency as a cytotoxic agent compared with the parent VV. Ox alone exerted concentration-dependent cytotoxicity. In vitro, the combination of the two agents applied at suboptimal concentrations for individual therapy displayed synergy in inducing cancer cells into enhanced levels of apoptosis/necrosis. Western blot analyses were consistent with the notion that TRAIL induced cancer cell death mainly through apoptosis, whereas Ox and vJS6 induced cell death more through non-apoptotic death pathways. In two aggressive colorectal carcinomatosis models derived from human HCT116 and murine MC38 cells, the combination therapy displayed synergistic or additive antitumor activity and prolonged the survival of the tumor-bearing mice compared with either Ox chemotherapy or vvTRAIL-mediated oncolytic gene therapy alone. This combination strategy may provide a new avenue to treating peritoneal carcinomatosis and other types of metastases of colorectal cancer.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

E1A-expressing adenoviral E3B mutants act synergistically with chemotherapeutics in immunocompetent tumor models

The majority of clinical trials evaluating replication-selective oncolytic adenoviruses utilized mutants with immunomodulatory E3B genes deleted, likely contributing to the attenuated efficacy. We investigated whether an intact immune response could contribute to the observed improved efficacy in response to combinations with chemotherapeutics. Seven carcinoma cell lines were evaluated by combining viral mutants; dl309 (DeltaE3B), dl704 (DeltaE3gp19K), dl312 (DeltaE1A) or wild-type Ad5 with the commonly used clinical drugs cisplatin and paclitaxel. Synergistic effects on cell death were determined by generation of combination indexes in cultured cells. In vivo tumor growth inhibition was achieved by virotherapy alone and was most efficacious with wild-type virus and least with the DeltaE3B mutant. Significantly higher efficacy was observed when the viruses were combined with drugs. The greatest enhancement of tumor inhibition was in combination with the DeltaE3B mutant restoring potency to that of Ad5 wild-type levels, observed only in animals with intact immune response. Increases in infectivity, viral gene expression and replication were identified as potential mechanisms contributing to the synergistic effects. Our results suggest that the attenuation of DeltaE3B mutants can be overcome by low doses of chemotherapeutics only in the presence of an intact immune response indicating a role for T-cell-mediated functions.

Anticancer activity of oncolytic adenovirus vector armed with IFN-alpha and ADP is enhanced by pharmacologically controlled expression of TRAIL

We have previously described oncolytic adenovirus (Ad) vectors KD3 and KD3-interferon (IFN) that were rendered cancer-specific by mutations in the E1A region of Ad; these mutations abolish binding of E1A proteins to p300/CBP and pRB. The antitumor activity of the vectors was enhanced by overexpression of the Adenovirus Death Protein (ADP, E3-11.6K) and by replication-linked expression of IFN-alpha. We hypothesized that the anticancer efficacy of the KD3-IFN vector could be further improved by expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). E1-deleted Ad vectors were constructed carrying reporter genes for enhanced green fluorescent protein or secreted placental alkaline phosphatase (SEAP) and a therapeutic gene for TRAIL under control of the TetON system. Expression of the genes was increased in the presence of a helper virus and the inducer doxycycline such that up to 231-fold activation of expression for the TetON-SEAP vector was obtained. Coinfection with TetON-TRAIL augmented oncolytic activity of KD3 and KD3-IFN in vitro. Induction of TRAIL expression did not reduce the yield of progeny virus. Combination of TetON-TRAIL and KD3-IFN produced superior antitumor activity in vivo as compared with either vector alone demonstrating the efficacy of a four-pronged cancer gene therapy approach, which includes Ad oncolysis, ADP overexpression, IFN-alpha-mediated immunotherapy, and pharmacologically controlled TRAIL activity.

Targeted cancer gene therapy using a hypoxia inducible factor dependent oncolytic adenovirus armed with interleukin-4

There is a need for novel therapies targeting hypoxic cells in tumors. These cells are associated with tumor resistance to therapy and express hypoxia inducible factor-1 (HIF-1), a transcription factor that mediates metabolic adaptation to hypoxia and activates tumor angiogenesis. We previously developed an oncolytic adenovirus (HYPR-Ad) for the specific killing of hypoxic/HIF-active tumor cells, which we now armed with an interleukin-4 gene (HYPR-Ad-IL4). We designed HYPR-Ad-IL4 by cloning the Ad E1A viral replication and IL-4 genes under the regulation of a bidirectional hypoxia/HIF-responsive promoter. The IL-4 cytokine was chosen for its ability to induce a strong host antitumor immune response and its potential antiangiogenic activity. HYPR-Ad-IL4 induced hypoxia-dependent IL-4 expression, viral replication, and conditional cytolysis of hypoxic, but not normoxic cells. The treatment of established human tumor xenografts with HYPR-Ad-IL4 resulted in rapid and maintained tumor regression with the same potency as that of wild-type dl309-Ad. HYPR-Ad-IL4-treated tumors displayed extensive necrosis, fibrosis, and widespread viral replication. Additionally, these tumors contained a distinctive leukocyte infiltrate and prominent hypoxia. The use of an oncolytic Ad that locally delivers IL-4 to tumors is novel, and we expect that HYPR-Ad-IL4 will have broad therapeutic use for all solid tumors that have hypoxia or active HIF, regardless of tissue origin or genetic alterations.

Oncolytic adenovirus-mediated E1A gene therapy induces tumor-cell apoptosis and reduces tumor angiogenesis leading to inhibition of hepatocellular carcinoma growth in animal model

Oncolytic adenovirus (rAd)-mediated E1A gene therapy of cancer has become a novel therapeutic modality. In this study, we constructed a recombinant oncolytic adenovirus (rAd-E1A) expressing the tumor suppressor E1A gene. We demonstrated that the rAd-E1A replicated in HepG2 and SMMC-7721 human hepatocellular carcinoma (HCC) cells but attenuated in the normal liver cell line HL-7702. It induced HCC cell apoptosis through upregulation of apoptosis-associated Bax, caspase-3, and Fas and downregulation of survivin and Bcl-2 in a p53-dependent pathway. It also downregulated the expression of angiogenesis- associated vascular endothelial growth factor (VEGF) and CD34 genes and reduced tumor vessel formation and angiogenesis. In mice bearing SMMC-7721 tumors, intratumoral injections of rAd- E1A significantly inhibited HCC growth. Therefore, the oncolytic adenovirus-mediated E1A gene therapy may be a useful therapeutic approach for HCC treatment.

Adenoviral vectors--how to use them in cancer gene therapy?

Gene therapy is most often described as a technique for introducing the foreign genetic material into cells with a correction of a dysfunctional gene as its final goal. Today, it is well known that cancer is one of the leading causes of mortality in the world. Besides classical methods for cancer treatment new strategies against cancer are needed. Although originally being designed as a treatment for monogenetic illness, soon after, gene therapy appeared as a potential new strategy in cancer therapy. One of the widely used vectors for cancer gene therapy is adenovirus. In this review we have described molecular biology of adenoviruses and basis for construction of adenoviral vectors. We have also described concepts for cancer gene therapy including their in vitro and in vivo application. Special attention is drawn toward retargeting of adenovirus as a new approach in vector design for cancer gene therapy, in order to restrict transgene expression in tumor tissue. This approach uses biophysical as well as genetic characteristics of tumor itself and its supporting tissue, allowing new "bypass" in cancer gene therapy.