A hypoxia- and {alpha}-fetoprotein-dependent oncolytic adenovirus exhibits specific killing of hepatocellular carcinomas

Modifying oncolytic virotherapy to overcome the barrier of the hypoxic tumor microenvironment. Where do we stand?

Viruses are completely dependent on host cell machinery for their reproduction. As a result, factors that influence the state of cells, such as signaling pathways and gene expression, could determine the outcome of viral pathogenicity. One of the important factors influencing cells or the outcome of viral infection is the level of oxygen. Recently, oncolytic virotherapy has attracted attention as a promising approach to improving cancer treatment. However, it was shown that tumor cells are mostly less oxygenated compared with their normal counterparts, which might affect the outcome of oncolytic virotherapy. Therefore, knowing how oncolytic viruses could cope with stressful environments, particularly hypoxic environments, might be essential for improving oncolytic virotherapy.

Strategies to Develop Potent Oncolytic Viruses and Enhance Their Therapeutic Efficacy

Despite advancements in cancer therapy that have occurred over the past several decades, successful treatment of advanced malignancies remains elusive. Substantial resources and significant efforts have been directed toward the development of novel therapeutic modalities to improve patient outcomes. Oncolytic viruses (OVs) are emerging tools with unique characteristics that have attracted great interest in developing effective anticancer treatment. The original attraction was directed toward selective replication and cell-specific toxicity, two unique features that are either inherent to the virus or could be conferred by genetic engineering. However, recent advancements in the knowledge and understanding of OVs are shifting the therapeutic paradigm toward a greater focus on their immunomodulatory role. Nonetheless, there are still significant obstacles that remain to be overcome to enhance the efficiency of OVs as effective therapeutic modalities and potentially establish them as part of standard treatment regimens. In this review, we discuss advances in the design of OVs, strategies to enhance their therapeutic efficacy, functional translation into the clinical settings, and various obstacles that are still encountered in the efforts to establish them as effective anticancer treatments.

A novel oncolytic adenovirus inhibits hepatocellular carcinoma growth

OBJECTIVE

To evaluate the inhibitory role of a novel oncolytic adenovirus (OA), GP73-SphK1sR-Ad5, on the growth of hepatocellular carcinoma (HCC).

METHODS

GP73-SphK1sR-Ad5 was constructed by integrating Golgi protein 73 (GP73) promoter and sphingosine kinase 1 (SphK1)-short hairpin RNA (shRNA) into adenovirus serotype 5 (Ad5), and transfecting into HCC Huh7 cells and normal human liver HL-7702 cells. The expression of SphK1 and adenovirus early region 1 (E1A) was detected by quantitative real-time PCR (qRT-PCR) and western blot, respectively. Cell viability was detected by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, and apoptotic rate was determined by flow cytometry. An Huh7 xenograft model was established in mice injected intratumorally with GP73-SphK1sR-Ad5. Twenty days after injection, the tumor volume and weight, and the survival time of the mice were recorded. The histopathological changes in tumor tissues were observed by hematoxylin-eosin (HE) staining and transmission electron microscopy (TEM).

RESULTS

Transfection of GP73-SphK1sR-Ad5 significantly upregulated E1A and downregulated SphK1 in Huh7 cells, but not in HL7702 cells. GP73-SphK1sR-Ad5 transfection significantly decreased the viability and increased the apoptotic rate of Huh7 cells, but had no effect on HL7702 cells. Intratumoral injection of GP73-SphK1sR-Ad5 into the Huh7 xenograft mouse model significantly decreased tumor volume and weight, and prolonged survival time. It also significantly decreased the tumor infiltration area and blood vessel density, and increased the percentages of cells with nucleus deformation and cells with condensed chromatin in tumor tissues.

CONCLUSIONS

GP73-SphK1sR-Ad5 serves as a novel OA and can inhibit HCC progression with high specificity and efficacy.

Efficacy of an Oncolytic Adenovirus Driven by a Chimeric Promoter and Armed with Decorin Against Renal Cell Carcinoma

Virus-targeted therapy for tumors can effectively prolong the survival rate of patients and has become a new trend for cancer biotherapy. Oncolytic adenovirus (OAd) can specifically replicate in tumor cells, allowing the therapeutic genes carried to be rapidly copied. As known, solid tumors are always hypoxic, and researchers often overlook a key point, the replication of OAd depends not only on its own activity but also on the cellular hypoxic environment in which the virus replicates. In this study, we constructed an OAd carrying Decorin, HRE-Ki67-Decorin, combining the Ki67 promoter upstreamed with hypoxia-response element (HRE) sequences to drive adenoviral E1A. The OAd HRE-Ki67-Decorin had better replication ability under hypoxic conditions, downregulated cellular immunosuppressed growth factor TGF-β. In addition, HRE-Ki67-Decorin was potent in suppressing tumor growth and participated in the assembly of tumor extracellular matrix by expressing Decorin in subcutaneous renal cancer cell tumor models. Tumor sections from HRE-Ki67-Decorin-treated tissues had less collagen fibers and more spread of virus among tumor tissues. These results indicated that chimeric HRE-Ki67 promoter-regulated OAd carrying Decorin might be an effective anticancer treatment strategy.

Mesenchymal Stem Cell-Mediated Delivery of an Oncolytic Adenovirus Enhances Antitumor Efficacy in Hepatocellular Carcinoma

Oncolytic virotherapy is a promising alternative to conventional treatment, yet systemic delivery of these viruses to tumors remains a major challenge. In this regard, mesenchymal stem cells (MSC) with well-established tumor-homing property could serve as a promising systemic delivery tool. We showed that MSCs could be effectively infected by hepatocellular carcinoma (HCC)-targeted oncolytic adenovirus (HCC-oAd) through modification of the virus' fiber domain and that the virus replicated efficiently in the cell carrier. HCC-targeting oAd loaded in MSCs (HCC-oAd/MSC) effectively lysed HCC cells in vitro under both normoxic and hypoxic conditions as a result of the hypoxia responsiveness of HCC-oAd. Importantly, systemically administered HCC-oAd/MSC, which were initially infected with a low viral dose, homed to HCC tumors and resulted in a high level of virion accumulation in the tumors, ultimately leading to potent tumor growth inhibition. Furthermore, viral dose reduction and tumor localization of HCC-oAd/MSC prevented the induction of hepatotoxicity by attenuating HCC-oAd hepatic accumulation. Taken together, these results demonstrate that MSC-mediated systemic delivery of oAd is a promising strategy for achieving synergistic antitumor efficacy with improved safety profiles. SIGNIFICANCE: Mesenchymal stem cells enable delivery of an oncolytic adenovirus specifically to the tumor without posing any risk associated with systemic administration of naked virions to the host.

Transcatheter arterial embolization combined with hypoxia-replicative oncolytic adenovirus perfusion enhances the therapeutic effect of hepatic carcinoma

Purpose

Transcatheter arterial embolization or transcatheter arterial chemoembolization has become a critical therapy for unresectable hepatocarcinoma. Although hypoxia caused by embolization can induce apoptosis and necrosis of the majority of tumor cells, a small proportion of cells can survive with hypoxia and chemotherapy resistance. HIF-1α induced by hypoxia is the key factor rendering surviving tumor cells invasive and metastatic properties. Thus, we generated a synthetic hypoxia-replicative oncolytic adenovirus (HYAD) expecting to further eliminate the surviving tumor cells, which expressed HIF-1α.

Materials and methods

In our study, we detected protein expression, proliferation, apoptosis, and necrosis of hepatic tumor cell line when infected with HYAD under hypoxia and normoxia. And we constructed VX2 hepatic cancer rabbit models to explore the therapeutic effect of transcatheter arterial embolization combined with HYAD perfusion under digital subtraction angiography. Inhibition of tumor growth and invasion was detected by histopathological examination and contrast-enhanced CT scan.

Results

Experiments in vitro verified that HYAD expressed and replicated along with HIF-1α expression or hypoxia. Compared with wild adenovirus type 5 (WT), HYAD expressed much more under hypoxia, which was the main principle of HYAD killing surviving tumor cells posttransarterial embolization. In vivo experiment of VX2 models, HYAD perfusion combined with polyvinyl alcohol (PVA) embolization achieved the highest expression quantity and the longest expression duration compared with simple HYAD perfusion, WT perfusion combined with PVA embolization, and simple WT perfusion. Because adenovirus expression protein E1A had the properties of promoting apoptosis, inhibiting invasion, and inhibiting metastasis, HYAD perfusion combined with PVA embolization group efficiently repressed tumor growth and intrahepatic metastases compared to other processing groups.

Conclusion

HYAD can overcome the hypoxic tumor microenvironment postembolization and target the surviving tumor cells with specificity. In turn, HYAD perfusion combined with PVA embolization can bring out the best effect in each other.

Physically crosslinked injectable hydrogels for long-term delivery of oncolytic adenoviruses for cancer treatment

A dual pH- and temperature-responsive physically crosslinked and injectable hydrogel system was developed for efficient and long-term delivery of oncolytic adenoviruses (Ads).

Transcriptional control of the MUC16 promoter facilitates follicle-stimulating hormone peptide-conjugated shRNA nanoparticle-mediated inhibition of ovarian carcinoma in vivo

Ovarian cancer is the leading cause of cancer death among gynecological malignancies. The high mortality rate has not been significantly reduced despite advances in surgery and chemotherapy. Gene therapy shows therapeutic potential, but several key issues must be resolved before clinical application. To minimize toxicity in noncancerous tissues, tumor-specific ligands are conjugated to vectors to increase the selectivity of drug delivery. The expression pattern of follicle-stimulating hormone (FSH) receptor in normal and cancer tissues provides an opportunity for highly selective drug delivery in ovarian cancer. Furthermore, tumor-specific promoters can conditionally regulate therapeutic gene expression in tumor or normal tissues. The mucin 16 (MUC16) promoter might be a potential tool to drive ovarian cancer-localized gene expression since MUC16/CA125 is overexpressed in most ovarian carcinomas. Here, we screened the possible MUC16 promoter sequences and constructed MUC16 promoter-driven gro-α shRNA plasmid vectors. The vectors were specifically delivered into ovarian cancer cells via FSH peptide-conjugated nanoparticles. The predicted promoter sequence with TAAA repeats showed high transcriptional activity. The nanoparticle complex containing MUC16 promoter-driven gro-α shRNA and FSH peptides had the ability to decrease gro-α protein secretion in ovarian cancer cells and block tumor growth without obvious toxic effects in a nude mouse model bearing ovarian cancer. Our study provides a novel gene delivery system using a MUC16 promoter trigger and FSH peptide-mediated active targeting in ovarian cancer, and this system may be a promising strategy for specific genetic therapeutic delivery.

Osthole attenuates angiogenesis in an orthotopic mouse model of hepatocellular carcinoma via the downregulation of nuclear factor-κB and vascular endothelial growth factor

Osthole has been demonstrated to have antitumor activity. Previous studies by our group indicated that osthole effectively inhibited tumor growth in hepatocellular carcinoma (HCC) through the induction of apoptosis and enhancement of antitumor immune responses in mice. The importance of angiogenesis in the proliferation, invasion and metastasis of tumor cells in HCC is well established. The present study aimed to investigate the effects of osthole on angiogenesis in an orthotopic mouse model of HCC. Orthotopic HCC in mice was established, and osthole at 61, 122 and 244 mg/kg was administered intraperitoneally once daily to the tumor-bearing mice for 14 consecutive days. Immunohistochemistry was performed to analyze the microvessel density (MVD) of tissues, and the level of vascular endothelial growth factor (VEGF) was measured by ELISA. The protein levels of nuclear factor-κB (NF-κB) p65 and IκB-α were also detected by western blotting. MVD was positively correlated with tumor weight in the orthotopic mouse model of HCC. Osthole administration significantly decreased MVD in tumor and adjacent tissues, and inhibited tumor growth. Furthermore, osthole downregulated the expression of VEGF and NF-κB p65, and upregulated IκB-α expression in tumor and adjacent tissues. To the best of our knowledge, the results of the present study demonstrated for the first time that osthole inhibits angiogenesis in an orthotopic mouse model of HCC, which may be one of the mechanisms underlying the anti-HCC activity of osthole, which in turn may be mediated by the NF-κB/VEGF signaling pathway. Therefore, osthole, a potential angiogenesis inhibitor and immune system enhancer, may be a promising lead compound for the treatment of HCC.

Hepatocellular carcinoma-targeting oncolytic adenovirus overcomes hypoxic tumor microenvironment and effectively disperses through both central and peripheral tumor regions

Cancer-specific promoter driven replication of oncolytic adenovirus (Ad) is cancer-specific, but shows low transcriptional activity. Thus, we generated several chimeric α-fetoprotein (AFP) promoter variants, containing reconstituted enhancer and silencer regions, to preferentially drive Ad replication in hepatocellular carcinoma (HCC). Modified AFP promoter, containing 2 enhancer A regions and a single enhancer B region (a2bm), showed strong and HCC-specific transcription. In AFP-positive HCCs, gene expression was 43- to 456-fold higher than those of control AFP promoter lacking enhancers. a2bm promoter was further modified by inserting multiple hypoxia-responsive elements (HRE) to generate Ha2bm promoter, which showed stronger transcriptional activity than a2bm promoter under hypoxic conditions. Ha2bm promoter-regulated oncolytic Ad (Ha2bm-d19) showed a stronger antitumor and proapoptotic effect than did a2bm promoter-regulated oncolytic Ad (a2bm-d19) in HCC xenograft tumors. Systemically administered Ha2bm-d19 caused no observable hepatotoxicity, whereas control replication-competent Ad, lacking cancer specificity (d19), induced significant hepatic damage. Ha2bm-d19 caused significantly lower expression of interleukin-6 than d19, showing that HCC-targeted delivery of Ad attenuates induction of the innate immune response against Ad. This chimeric AFP promoter enabled Ad to overcome the hypoxic tumor microenvironment and target HCC with high specificity, rendering it a promising candidate for the treatment of aggressive HCCs.

A hypoxia- and telomerase-responsive oncolytic adenovirus expressing secretable trimeric TRAIL triggers tumour-specific apoptosis and promotes viral dispersion in TRAIL-resistant glioblastoma

Glioblastoma is a highly aggressive and malignant type of cancer that is apoptosis resistant and difficult to cure by conventional cancer therapies. In this regard, an oncolytic adenovirus that selectively targets the tumour tissue and induces tumour cell lysis is a promising treatment option. We designed and constructed a hypoxia-responsive and cancer-specific modified human telomerase reverse transcriptase (H5CmTERT) promoter to drive replication of an oncolytic adenovirus (H5CmTERT-Ad). To enhance the anti-tumour efficacy of H5CmTERT-Ad against malignant glioblastoma, we also generated an H5CmTERT-Ad expressing secretable trimeric tumour necrosis factor-related apoptosis-inducing ligand (H5CmTERT-Ad/TRAIL). H5CmTERT promoter-regulated oncolytic adenoviruses showed cancer-specific and superior cell-killing effect in contrast to a cognate control oncolytic adenovirus replicating under the control of the endogenous adenovirus promoter. The cancer cell-killing effects of H5CmTERT-Ad and H5CmTERT-Ad/TRAIL were markedly higher during hypoxia than normoxia owing to hypoxia responsiveness of the promoter. H5CmTERT-Ad/TRAIL showed more potent anti-tumour efficacy than H5CmTERT-Ad did in a xenograft model of TRAIL-resistant subcutaneous and orthotopic glioblastoma through superior induction of apoptosis and more extensive virus distribution in the tumour tissue. Altogether, our findings show that H5CmTERT-Ad/TRAIL can promote dispersion of an oncolytic adenovirus through robust induction of apoptosis in a highly TRAIL-resistant glioblastoma.

Potent antitumor effect of tumor microenvironment-targeted oncolytic adenovirus against desmoplastic pancreatic cancer

Pancreatic cancer is a leading cause of cancer-related death. Desmoplastic pancreatic tumors exhibit excessive extracellular matrix (ECM) and are thus highly resistant to anticancer therapeutics, since the ECM restricts drug penetration and dispersion. Here, we designed and generated two hypoxia-responsive and cancer-specific hybrid promoters, H(mT)E and H(E)mT. Transgene expression driven by each hybrid promoter was markedly higher under hypoxic conditions than normoxic conditions. Moreover, H(E)mT-driven transgene expression was highly cancer-specific and was superior to that of H(mT)E-driven expression. A decorin-expressing oncolytic adenovirus (Ad; oH(E)mT-DCN) replicating under the control of the H(E)mT promoter induced more potent and highly cancer-specific cell death compared with its cognate control oncolytic Ad, which harbored the endogenous Ad E1A promoter. Moreover, oH(E)mT-DCN exhibited enhanced antitumor efficacy compared with both the clinically approved oncolytic Ad ONYX-015 and its cognate control oncolytic Ad lacking DCN. oH(E)mT-DCN treatment also attenuated the expression of major ECM components, such as collagen I/III, elastin and fibronectin and induced tumor cell apoptosis, leading to extensive viral dispersion within orthotopic pancreatic tumors and pancreatic cancer patient-derived tumor spheroids. Collectively, these findings demonstrate that oH(E)mT-DCN exhibits potent antitumor efficacy by degrading the ECM and inducing apoptosis in a multifunctional process. This process facilitates the dispersion and replication of oncolytic Ad, making it an attractive candidate for the treatment of aggressive and desmoplastic pancreatic cancer.

Efficacy of combining ING4 and TRAIL genes in cancer-targeting gene virotherapy strategy: first evidence in preclinical hepatocellular carcinoma

Current treatments of hepatocellular carcinoma (HCC) are ineffective and unsatisfactory in many aspects. Cancer-targeting gene virotherapy using oncolytic adenoviruses (OAds) armed with anticancer genes has shown efficacy and safety in clinical trials. Nowadays, both inhibitor of growth 4 (ING4), as a multimodal tumor suppressor gene, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), as a potent apoptosis-inducing gene, are experiencing a renaissance in cancer gene therapy. Herein we investigated the antitumor activity and safety of mono- and combined therapy with OAds armed with ING4 (Ad-ΔB/ING4) and TRAIL (Ad-ΔB/TRAIL) gene, respectively, on preclinical models of human HCC. OAd-mediated expression of ING4 or TRAIL transgene was confirmed. Ad-ΔB/TRAIL and/or Ad-ΔB/ING4 exhibited potent killing effect on human HCC cells (HuH7 and Hep3B) but not on normal liver cells. Most importantly, systemic therapy with Ad-ΔB/ING4 plus Ad-ΔB/TRAIL elicited more eradicative effect on an orthotopic mouse model of human HCC than their monotherapy, without causing obvious overlapping toxicity. Mechanistically, Ad-ΔB/ING4 and Ad-ΔB/TRAIL were remarkably cooperated to induce antitumor apoptosis and immune response, and to repress tumor angiogenesis. This is the first study showing that concomitant therapy with Ad-ΔB/ING4 and Ad-ΔB/TRAIL may provide a potential strategy for HCC therapy and merits further investigations to realize its possible clinical translation.

Combined therapy with oncolytic adenoviruses encoding TRAIL and IL-12 genes markedly suppressed human hepatocellular carcinoma both in vitro and in an orthotopic transplanted mouse model

BACKGROUND

Gene-based virotherapy mediated by oncolytic viruses is currently experiencing a renaissance in cancer therapy. However, relatively little attention has been given to the potentiality of dual gene virotherapy strategy as a novel therapeutic approach to mediate triplex anticancer combination effects, particularly if the two suitable genes are well chosen. Both tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and interleukin-12 (IL-12) have been emerged as promising pharmacological candidates in cancer therapy; however, the combined efficacy of TRAIL and IL-12 genes for treatment of human hepatocellular carcinoma (HCC) remains to be determined.

METHODS

Herein, we investigated the therapeutic efficacy of concurrent therapy with two armed oncolytic adenoviruses encoding human TRAIL gene (Ad-ΔB/TRAIL) and IL-12 gene (Ad-ΔB/IL-12), respectively, on preclinical models of human HCC, and also elucidated the possible underlying mechanisms. The effects of Ad-ΔB/TRAIL+Ad-ΔB/IL-12 combination therapy were assessed both in vitro on Hep3B and HuH7 human HCC cell lines and in vivo on HCC-orthotopic model established in the livers of athymic nude mice by intrahepatic implantation of human Hep3B cells.

RESULTS

Compared to therapy with non-armed control Ad-ΔB, combined therapy with Ad-ΔB/TRAIL+Ad-ΔB/IL-12 elicited profound anti-HCC killing effects on Hep3B and HuH7 cells and on the transplanted Hep3B-orthotopic model. Efficient viral replication and TRAIL and IL-12 expression were also confirmed in HCC cells and the harvested tumor tissues treated with this combination therapy. Mechanistically, co-therapy with Ad-ΔB/TRAIL+Ad-ΔB/IL-12 exhibited an enhanced effect on apoptosis promotion, activation of caspase-3 and-8, generation of anti-tumor immune response evidenced by upregulation of interferon gamma (IFN-γ) production and infiltration of natural killer-and antigen presenting cells, and remarkable repression of intratumor vascular endothelial growth factor (VEGF) and cluster of differentiation 31 (CD31) expression and tumor microvessel density.

CONCLUSIONS

Overall, our data showed a favorable therapeutic effect of Ad-ΔB/TRAIL+Ad-ΔB/IL-12 combination therapy against human HCC, and may therefore constitute a promising and effective therapeutic strategy for treating human HCC. However, further studies are warranted for its reliable clinical translation.

Antitumor effect and safety profile of systemically delivered oncolytic adenovirus complexed with EGFR-targeted PAMAM-based dendrimer in orthotopic lung tumor model

Adenovirus (Ad)-mediated cancer gene therapy has been proposed as a promising alternative to conventional therapy for cancer. However, success of systemically administered naked Ad has been limited due to the immunogenicity of Ad and the induction of hepatotoxicity caused by Ad's native tropism. In this study, we synthesized an epidermal growth factor receptor (EGFR)-specific therapeutic antibody (ErbB)-conjugated and PEGylated poly(amidoamine) (PAMAM) dendrimer (PPE) for complexation with Ad. Transduction of Ad was inhibited by complexation with PEGylated PAMAM (PP) dendrimer due to steric hindrance. However, PPE-complexed Ad selectively internalized into EGFR-positive cells with greater efficacy than either naked Ad or Ad complexed with PP. Systemically administered PPE-complexed oncolytic Ad elicited significantly reduced immunogenicity, nonspecific liver sequestration, and hepatotoxicity than naked Ad. Furthermore, PPE-complexed oncolytic Ad demonstrated prolonged blood retention time, enhanced intratumoral accumulation of Ad, and potent therapeutic efficacy in EGFR-positive orthotopic lung tumors in comparison with naked Ad. We conclude that ErbB-conjugated and PEGylated PAMAM dendrimer can efficiently mask Ad's capsid and retarget oncolytic Ad to be efficiently internalized into EGFR-positive tumor while attenuating toxicity induced by systemic administration of naked oncolytic Ad.

Cell-specific expression of artificial microRNAs targeting essential genes exhibit potent antitumor effect on hepatocellular carcinoma cells

To achieve specific and potent antitumor effect of hepatocyte carcinoma cells, replication defective adenoviral vectors, namely rAd/AFP-amiRG, rAd/AFP-amiRE and rAd/AFP-amiRP, were constructed which were armed with artificial microRNAs (amiRs) targeting essential functional genes glyceraldehyde-3-phosphate dehydrogenase, eukaryotic translation initiation factor 4E and DNA polymerase α respectively under the control of a recombinant promoter comprised of human α-fetoprotein enhancer and basal promoter. The AFP enhancer/promoter showed specific high transcription activity in AFP-positive HCC cells Hep3B, HepG2 and SMMC7721, while low in AFP-negative cell Bcap37. All artificial microRNAs exhibited efficient knockdown of target genes. Decreased ATP production and protein synthesis was observed in rAd/AFP-amiRG and rAd/AFP-amiRE treated HCC cells. All three recombinant adenoviruses showed efficient blockage of cell cycle progression and significant suppression of HCC cells in vitro. In nude mice model bearing Hep3B xenograft, administration of rAd/AFP-amiRG showed potent antitumor effect. The strategy of tumor-specific knockdown of genes essential for cell survival and proliferation may suggest a novel promising approach for HCC gene therapy.

Polymeric oncolytic adenovirus for cancer gene therapy

Oncolytic adenovirus (Ad) vectors present a promising modality to treat cancer. Many clinical trials have been done with either naked oncolytic Ad or combination with chemotherapies. However, the systemic injection of oncolytic Ad in clinical applications is restricted due to significant liver toxicity and immunogenicity. To overcome these issues, Ad has been engineered physically or chemically with numerous polymers for shielding the Ad surface, accomplishing extended blood circulation time and reduced immunogenicity as well as hepatotoxicity. In this review, we describe and classify the characteristics of polymer modified oncolytic Ad following each strategy for cancer treatment. Furthermore, this review concludes with the highlights of various polymer-coated Ads and their prospects, and directions for future research.

Potent antitumor effect of neurotensin receptor-targeted oncolytic adenovirus co-expressing decorin and Wnt antagonist in an orthotopic pancreatic tumor model

Pancreatic cancer is highly aggressive, malignant, and notoriously difficult to cure using conventional cancer therapies. These conventional therapies have significant limitations due to excessive extracellular matrix (ECM) of pancreatic cancer and poor cancer specificity. The excess ECM prevents infiltration of drugs into the inner layer of the solid tumor. Therefore, novel treatment modalities that can specifically target the tumor and degrade the ECM are required for effective therapy. In the present study, we used ECM-degrading and Wnt signal-disrupting oncolytic adenovirus (oAd/DCN/LRP) to achieve a desirable therapeutic outcome against pancreatic cancer. In addition, to overcome the limitations in systemic delivery of oncolytic Ad (oAd) and to specifically target pancreatic cancer, neurotensin peptide (NT)-conjugated polyethylene glycol (PEG) was chemically crosslinked to the surface of Ad, generating a systemically injectable hybrid system, oAd/DCN/LRP-PEG-NT. We tested the targeting and therapeutic efficacy of oAd/DCN/LRP-PEG-NT toward neurotensin receptor 1 (NTR)-overexpressing pancreatic cancer cells, both in vitro and in vivo. The oAd/DCN/LRP-PEG-NT elicited increased NTR-selective cancer cell killing and transduction efficiency when compared with a cognate control lacking NT (oAd/DCN/LRP-PEG). Furthermore, systemic administration of oAd/DCN/LRP-PEG-NT significantly decreased induction of innate and adaptive immune responses against Ad, and blood retention time was markedly prolonged by PEGylation. Moreover, NTR-targeting oAd elicited greater in vivo tumor growth suppression when compared with naked oAd and 9.5 × 10(6)-fold increased tumor-to-liver ratio. This significantly enhanced antitumor effect of oAd/DCN/LRP-PEG-NT was mediated by active viral replication and viral spreading, which was facilitated by ECM degradation and inhibition of Wnt signaling-related factors (Wnt, β-catenin, and/or vimentin) in the tumor tissues. Taken together, these results demonstrate that oAd/DCN/LRP-PEG-NT has strong therapeutic potential for systemic treatment of NTR-overexpressing pancreatic cancer due to its NTR-targeting ability, enhanced therapeutic efficacy, and safety.

Oncolytic adenovirus targeting cyclin E overexpression repressed tumor growth in syngeneic immunocompetent mice

Background

Clinical trials have indicated that preclinical results obtained with human tumor xenografts in mouse models may overstate the potential of adenovirus (Ad)-mediated oncolytic therapies. We have previously demonstrated that the replication of human Ads depends on cyclin E dysregulation or overexpression in cancer cells. ED-1 cell derived from mouse lung adenocarcinomas triggered by transgenic overexpression of human cyclin E may be applied to investigate the antitumor efficacy of oncolytic Ads.

Methods

Ad-cycE was used to target cyclin E overexpression in ED-1 cells and repress tumor growth in a syngeneic mouse model for investigation of oncolytic virotherapies.

Results

Murine ED-1 cells were permissive for human Ad replication and Ad-cycE repressed ED-1 tumor growth in immunocompetent FVB mice. ED-1 cells destroyed by oncolytic Ads in tumors were encircled in capsule-like structures, while cells outside the capsules were not infected and survived the treatment.

Conclusion

Ad-cycE can target cyclin E overexpression in cancer cells and repress tumor growth in syngeneic mouse models. The capsule structures formed after Ad intratumoral injection may prevent viral particles from spreading to the entire tumor.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1731-x) contains supplementary material, which is available to authorized users.

Gene therapy targeting hepatocellular carcinoma by a dual-regulated oncolytic adenovirus harboring the focal adhesion kinase shRNA

Cancer targeting gene-viro-therapy (CTGVT) approach has become a hotspot and a trend in the field of cancer biotherapy and oncolytic adenovirus is an ideal vector to carry the targeting genes. In this study, we used human telomerase reverse transcriptase (hTERT) promoter to control the adenovirus early region 1a (E1A) and the human α-fetoprotein (AFP) promoter integrated with hypoxia response element (HRE) to control the adenovirus early region 1b (E1B). Then the novel double-regulated adenovirus Ad-hTERT-HREAF (named SG505) was engineered. The short-hairpin RNA against focal adhesion kinase (FAK) was inserted into SG505 and thus forming Ad-hTERT-HREAF-shRNA (called SG505‑siFAK). Then various oncolytic adenoviruses were examined to verify whether they could suppress liver cancer cells selectively and efficiently both in vitro and in vivo. Both replicative and replication-defective adenoviruses carrying FAK-shRNA significantly inhibited the expression of FAK in Hep3B and SMMC-7721 cell lines and efficiently suppressed the growth of liver cancer cell lines with minor effect to normal cells. Furthermore, the recombined oncolytic adenoviruses, SG505-siFAK, SG505-EGFP and SG505 were able to selectively propagate in AFP-positive liver cancer cells in vitro and the SG505-siFAK efficiently suppressed the expression of FAK. SG505-siFAK showed the most potent tumor inhibition capability among the three recombined adenovirus with IC50 levels of 0.092±0.009 and 0.424±0.414 pfu/cell in the Hep3B and HepG2 cell line, respectively. Animal experiment further confirmed that SG505-siFAK achieved the most significant tumor inhibition of Hep3B liver cancer xenografted growth by intratumoral injection comparing to the intravenous injection among the three recombined viruses. Immunohistochemical results indicated that FAK expression was downregulated significantly in the tumors treated with SG505-siFAK. The dual-regulated oncolytic adenovirus SG505-siFAK was proven to inhibit the growth of liver cancer cells selectively and efficiently, therefore SG505-siFAK could be a potential agent for future clinical trials of hepatocellular carcinoma.

Current concepts of immune based treatments for patients with HCC: from basic science to novel treatment approaches

The recent approval of two immune checkpoint inhibitors for the treatment of malignant melanoma has sparked great interest by physicians and basic scientists searching for novel therapeutics for GI cancer. Chronic inflammation is recognised as a major risk factor for the development of hepatocellular carcinoma (HCC) and makes this type of cancer a potentially ideal target for an immune based treatment approach. Further evidence for a critical role of immune responses in patients with HCC is derived from the fact that immune signatures and profiles predict patients' outcome as well as the fact that tumour-induced spontaneous antitumour immunity can be detected. In addition ablative therapies can lead to changes in the number, phenotype and function of different immune cell subsets, which correlate with patients' survival. Various HCC-specific mouse models have been developed, which improve our understanding of hepatocarcinogenesis and tumour-immune cell interactions, and lead to the development of novel immune based treatment approaches, which are currently being evaluated in preclinical and in early clinical settings. Immune checkpoint blockade along with adoptive immune cell therapy and vaccine approaches are currently being evaluated either alone or in combination with other treatments. Here, we provide an overview for the rationale of immunotherapy in HCC, summarise ongoing studies and provide a perspective for immune based approaches in patients with HCC.

Dual tumor targeting with pH-sensitive and bioreducible polymer-complexed oncolytic adenovirus

Oncolytic adenoviruses (Ads) have shown great promise in cancer gene therapy but their efficacy has been compromised by potent immunological, biochemical, and specific tumor-targeting limitations. To take full advantage of the innate cancer-specific killing potency of oncolytic Ads but also exploit the subtleties of the tumor microenvironment, we have generated a pH-sensitive and bio-reducible polymer (PPCBA)-coated oncolytic Ad. Ad-PPCBA complexes showed higher cellular uptake at pH 6.0 than pH 7.4 in both high and low coxsackie and adenovirus receptor-(CAR)-expressing cells, thereby demonstrating Ad-PPCBA's ability to target the low pH hypoxic tumor microenvironment and overcome CAR dependence for target cell uptake. Endocytic mechanism studies indicated that Ad-PPCBA internalization is mediated by macropinocytosis instead of the CAR-dependent endocytic pathway that internalizes naked Ad. VEGF-specific shRNA-expressing oncolytic Ad complexed with PPCBA (RdB/shVEGF-PPCBA) elicited much more potent suppression of U87 human brain cancer cell VEGF gene expression in vitro, and human breast cancer MCF7 cell/Matrigel plug vascularization in a mouse model, when cancer cells had been previously infected at pH 6.0 versus pH 7.4. Moreover, intratumorally and intravenously injected RdB/shVEGF-PPCBA nanocomplexes elicited significantly higher therapeutic efficacy than naked virus in U87-tumor mouse xenograft models, reducing IL-6, ALT, and AST serum levels. These data demonstrated PPCBA's biocompatibility and capability to shield the Ad surface to prevent innate immune response against Ad after both intratumoral and systemic administration. Taken together, these results demonstrate that smart, tumor-specific, oncolytic Ad-PPCBA complexes can be exploited to treat both primary and metastatic tumors.

Virotherapy targeting cyclin E overexpression in tumors with adenovirus-enhanced cancer-selective promoter

Oncolytic virotherapy can selectively destroy cancer cells and is a potential approach in cancer treatment. A strategy to increase tumor-specific selectivity is to control the expression of a key regulatory viral gene with a tumor-specific promoter. We have previously found that cyclin E expression is augmented in cancer cells after adenovirus (Ad) infection. Thus, the cyclin E promoter that is further activated by Ad in cancer cells may have unique properties for enhancing oncolytic viral replication. We have shown that high levels of viral E1a gene expression are achieved in cancer cells infected with Ad-cycE, in which the endogenous Ad E1a promoter was replaced with the cyclin E promoter. Ad-cycE shows markedly selective oncolytic efficacy in vitro and destroys various types of cancer cells, including those resistant to ONYX-015/dl1520. Furthermore, Ad-cycE shows a strong capacity to repress A549 xenograft tumor growth in nude mice and significantly prolongs survival. This study suggests the potential of Ad-cycE in cancer therapy and indicates the advantages of using promoters that can be upregulated by virus infection in cancer cells in development of oncolytic viruses. Key messages: Cyclin E promoter activity is high in cancer cells and enhanced by adenovirus infection. Cyclin E promoter is used to control the E1a gene of a tumor-specific oncolytic adenovirus. Ad-cycE efficiently targets cancer cells and induces oncolysis. Ad-cycE significantly repressed xenograft tumor and prolonged survival.

Indole-3-carbinol (I3C) increases apoptosis, represses growth of cancer cells, and enhances adenovirus-mediated oncolysis

Epidemiological studies suggest that high intake of cruciferous vegetables is associated with a lower risk of cancer. Experiments have shown that indole-3-carbinol (I3C), a naturally occurring compound derived from cruciferous vegetables, exhibits potent anticarcinogenic properties in a wide range of cancers. In this study, we showed that higher doses of I3C (≥400 μM) induced apoptotic cancer cell death and lower doses of I3C (≤200 μM) repressed cancer cell growth concurrently with suppressed expression of cyclin E and its partner CDK2. Notably, we found that pretreatment with low doses of I3C enhanced Ad-mediated oncolysis and cytotoxicity of human carcinoma cells by synergistic upregulation of apoptosis. Thus, the vegetable compound I3C as a dietary supplement may benefit cancer prevention and improve Ad oncolytic therapies.

Dual‑sensitive HRE/Egr1 promoter regulates Smac overexpression and enhances radiation‑induced A549 human lung adenocarcinoma cell death under hypoxia

The aim of this study was to construct an expression vector carrying the hypoxia/radiation dual‑sensitive chimeric hypoxia response element (HRE)/early growth response 1 (Egr‑1) promoter in order to overexpress the therapeutic second mitochondria‑derived activator of caspases (Smac). Using this expression vector, the present study aimed to explore the molecular mechanism underlying radiotherapy‑induced A549 human lung adenocarcinoma cell death and apoptosis under hypoxia. The plasmids, pcDNA3.1‑Egr1‑Smac (pE‑Smac) and pcDNA3.1‑HRE/Egr-1‑Smac (pH/E‑Smac), were constructed and transfected into A549 human lung adenocarcinoma cells using the liposome method. CoCl2 was used to chemically simulate hypoxia, followed by the administration of 2 Gy X‑ray irradiation. An MTT assay was performed to detect cell proliferation and an Annexin V‑fluorescein isothiocyanate apoptosis detection kit was used to detect apoptosis. Quantitative polymerase chain reaction and western blot analyses were used for the detection of mRNA and protein expression, respectively. Infection with the pE‑Smac and pH/E‑Smac plasmids in combination with radiation and/or hypoxia was observed to enhance the expression of Smac. Furthermore, Smac overexpression was found to enhance the radiation‑induced inhibition of cell proliferation and promotion of cycle arrest and apoptosis. The cytochrome c/caspase‑9/caspase‑3 pathway was identified to be involved in this regulation of apoptosis. Plasmid infection in combination with X‑ray irradiation was found to markedly induce cell death under hypoxia. In conclusion, the hypoxia/radiation dual‑sensitive chimeric HRE/Egr‑1 promoter was observed to enhance the expression of the therapeutic Smac, as well as enhance the radiation‑induced inhibition of cell proliferation and promotion of cycle arrest and apoptosis under hypoxia. This apoptosis was found to involve the mitochondrial pathway.

Efficient lung orthotopic tumor-growth suppression of oncolytic adenovirus complexed with RGD-targeted bioreducible polymer

Oncolytic adenoviruses (Ad) have been developed for the eradication of tumors. Although they hold much promise as a cancer therapy, they have a short blood circulation time and high liver toxicity. An effective strategy to overcome these problems has been complexing Ad with shielding materials. However, the therapeutic efficacy of the Ad complexes has also been an issue because passive accumulation does not allow for sufficient delivery of Ad to the cancer cells. To enhance the therapeutic efficacy of the polymer-coated Ads, the attachment of a targeting moiety to polymer-coated Ad vectors is inescapable. Our lab has previously reported the potential use of Arg-Gly-Asp (RGD)-targeted bioreducible polymers with a polyethylene glycol (PEG) linker for delivering oncolytic Ads. We have shown the enhanced in vitro transduction efficiency and increased cancer-killing effect with producing progeny oncolytic Ad particles. In addition, we have shown significant tumor-growth inhibition of the polymer-shielded Ad in an in vivo lung orthotopic tumor model. The shielding effect of the Ad surface with the polymers allowed evasion of host immune responses and reduction of liver toxicity. This data demonstrates that the RGD-conjugated bioreducible polymer for delivering the oncolytic Ad vectors could be utilized for cancer therapy via systemic administration.

Utilizing adenovirus vectors for gene delivery in cancer

INTRODUCTION

Adenovirus (Ad) is a promising candidate vector for cancer gene therapy because of its unique characteristics, which include efficient infection, high loading capacity and lack of insertional mutagenesis. However, systemic administration of Ad is hampered by the host's immune response, hepatocytoxicity, short half-life of the vector and low accumulation at the target site. For these reasons, clinical applications of Ad are currently restricted.

AREAS COVERED

In this review, we focus on recent developments in Ad nanocomplex systems that improve the transduction and targeting efficacy of Ad vectors in cancer gene therapy. We discuss the development of different Ad delivery systems, including surface modification of Ad, smart Ad/nanohybrid systems and hydrogels for sustained release of Ad.

EXPERT OPINION

The fusion of bioengineering and biopharmaceutical technologies can provide solutions to the obstacles encountered during systemic delivery of Ads. The in vivo transgene expression efficiency of Ad nanocomplex systems is typically high, and animal tumor models demonstrate that systemic administration of these Ad complexes can arrest tumor growth. However, further optimization of these smart Ad nanocomplex systems is needed to increase their effectiveness and safety for clinical application in cancer gene therapy.

Suppression of orthotopically implanted hepatocarcinoma in mice by umbilical cord-derived mesenchymal stem cells with sTRAIL gene expression driven by AFP promoter

Mesenchymal stem cells (MSCs) are promising vehicles for delivering therapeutic agents in tumor therapy. Human umbilical cord-derived mesenchymal stem cells (HUMSCs) resemble bone marrow-derived MSCs with respect to hepatic differentiation potential in injured livers in animals, while their hepatic differentiation under the hepatocarcinoma microenvironment is unclear. In this study, HUMSCs were isolated and transduced by lentiviral vectors coding the soluble human tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) gene driven by alpha-fetoprotein (AFP) promoter to investigate the therapeutic effects of these HUMSC against orthotopically implanted hepatocarcinoma in mice. We showed that HUMSCs can be transduced by lentivirus efficiently. HUMSCs developed cuboidal morphology, and expressed AFP and albumin in a two-step protocol. HUMSCs were capable of migrating to hepatocarcinoma in vitro as well as in vivo. In the orthotopical hepatocarcinoma microenvironment, the AFP promoter was activated during the early hepatic differentiation of HUMSCs. After intravenous injected, MSC.AFPILZ-sTRAIL expressed sTRAIL exclusively at the tumor site, and exhibited significant antitumor activity. This effect was stronger when in combination with 5-FU. The treatment was tolerated well in mice. Collectively, our results provide a potential strategy for targeted tumor therapy relying on the use of the tumor tropism and specific differentiation of HUMSCs as vehicles.

Hypoxia- and radiation-induced overexpression of Smac by an adenoviral vector and its effects on cell cycle and apoptosis in MDA-MB-231 human breast cancer cells

A conditionally replicative adenoviral (CRAd) vector, designated as CRAd.pEgr-1-Smac, that promotes the overexpression of second mitochondria-derived activator of caspase (Smac) when stimulated by hypoxia and radiation was constructed. MDA-MB-231 cells were transfected with CRAd.pEgr-1-Smac and treated with 4-Gy X-rays. The hypoxic status in cancer cells was mimicked with the chemical reagent CoCl₂. Smac protein expression was measured by a western blotting assay and cell proliferation was detected with the MTT assay. The cell cycle progression and apoptotic percentage were measured by flow cytometry with PI and Annexin V-FITC staining kits, respectively, following the irradiation of the transfected cells with 4-Gy X-rays. The results showed that CRAd.pEgr-1-Smac was able to increase the Smac protein expression induced by hypoxia and radiation, inhibit cell proliferation and promote apoptosis. Therefore, this method of gene-radiotherapy is indicated to be an ideal strategy for the treatment of breast cancer.

Combination of autophagy inducer rapamycin and oncolytic adenovirus improves antitumor effect in cancer cells

Background

Combination of oncolytic adenoviruses (Ads) and chemotherapy drugs has shown promising therapeutic results and is considered as a potential approach for cancer therapy. We previously have shown that autophagy may generate decomposed cellular molecules that can be used as nutrition to support virus replication in cancer cells. In this study, we evaluated a unique combination of the novel oncolytic Ad-cycE with rapamycin, an autophagy inducer and first-line chemotherapeutic drug.

Methods

The combination of oncolytic Ad-cycE and the autophagy inducer rapamycin was assessed for enhanced antitumor effect. We also evaluated the combined effects of rapamycin and Ad-cycE on cancer cell viability. The interaction between Ad-cycE and rapamycin was analyzed with Calcusyn (Biosoft, Ferguson, MO).

Results

We show that rapamycin induces autophagy, enhances Ad E1A expression and increases Ad oncolytic replication. Combination of rapamycin and Ad-cycE elicits stronger cytotoxicity than single treatment alone. The analyzed data indicates that the Ad-cycE and rapamycin combination has a significantly synergistic antitumor effect.

Conclusions

Our study provides a new insight into vector development and demonstrates the novel roles of autophagy in adenovirus replication. The combination of autophagy-induced chemotherapy and oncolytic virotherapy may be a new approach to improve future cancer treatment.

An oncolytic adenovirus expressing interleukin-24 enhances antitumor activities in combination with paclitaxel in breast cancer cells

Oncolytic adenoviruses are a novel class of anticancer treatment, based upon their ability to replicate selectively within malignant cells resulting in cell lysis. The replication‑selective adenovirus, ZD55‑IL‑24, was constructed by harboring an E1B‑55 kDa deletion and arming with interleukin-24 (IL-24). The microtubule‑stabilizing drug paclitaxel (PTX) exhibits activity in relapsed cancer. In the present study, the synergistic antitumor effects of the combination of PTX and ZD55‑IL‑24 on breast cancer cells was investigated. The results demonstrated that there were different roles for PTX in the expression of transgenic mRNA and protein. ZD55‑IL‑24 combined with PTX induced marked growth inhibition of MDA‑MB‑231 and Bcap‑37 cells. PTX increased viral uptake and appeared not to alter the replication of ZD55‑IL‑24 in breast cancer cells. Annexin V‑fluorescein isothiocyanate/propidium iodide staining and the Hoechst 33258 assay indicated that ZD55‑IL‑24 induced an increase in the number of apoptotic cells when administered in combination with PTX. It was demonstrated that ZD55‑IL‑24 conjugated with PTX was highly concomitant, and increased proapoptotic proteins levels, activated caspase‑3, -7 and -9 and downregulated anti‑apoptotic proteins. These results suggested that ZD55‑IL‑24 in combination with PTX exhibited a markedly increased cytotoxic and apoptosis‑inducing effect in breast cancer cells. Thus, this chemo‑gene‑viro therapeutic strategy was demonstrated to be superior to conventional chemotherapy or gene‑viro therapy alone.

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.

Local sustained delivery of oncolytic adenovirus with injectable alginate gel for cancer virotherapy

Adenoviruses (Ad) have been investigated for their efficacy in reducing primary tumors after local intratumoral administration. Despite high Ad concentrations and repetitive administration, the therapeutic efficacy of Ad has been limited because of rapid dissemination of the Ad into the surrounding normal tissues and short maintenance of Ad biological activity in vivo. To maximize the therapeutic potential of Ad-mediated gene therapeutics, we investigated the efficacy of local, sustained Ad delivery, using an injectable alginate gel matrix system. The biological activity of Ad loaded in alginate gel was prolonged compared with naked Ad, as evidenced by the high green fluorescent protein gene transduction efficiency over an extended time period. Moreover, oncolytic Ad encapsulated in alginate gel elicited 1.9- to 2.4-fold greater antitumor activity than naked Ad in both C33A and U343 human tumor xenograft models. Histological and quantitative PCR analysis confirmed that the oncolytic Ad/alginate gel matrix system significantly increased preferential replication and dissemination of oncolytic Ad in a larger area of tumor tissue in vivo. Taken together, these results show that local sustained delivery of oncolytic Ad in alginate gel augments therapeutic effect through selective infection of tumor cells, sustained release and prolonged maintenance of Ad activity.

The hTERT promoter enhances the antitumor activity of an oncolytic adenovirus under a hypoxic microenvironment

Hypoxia is a microenvironmental factor that contributes to the invasion, progression and metastasis of tumor cells. Hypoxic tumor cells often show more resistance to conventional chemoradiotherapy than normoxic tumor cells, suggesting the requirement of novel antitumor therapies to efficiently eliminate the hypoxic tumor cells. We previously generated a tumor-specific replication-competent oncolytic adenovirus (OBP-301: Telomelysin), in which the human telomerase reverse transcriptase (hTERT) promoter drives viral E1 expression. Since the promoter activity of the hTERT gene has been shown to be upregulated by hypoxia, we hypothesized that, under hypoxic conditions, the antitumor effect of OBP-301 with the hTERT promoter would be more efficient than that of the wild-type adenovirus 5 (Ad5). In this study, we investigated the antitumor effects of OBP-301 and Ad5 against human cancer cells under a normoxic (20% oxygen) or a hypoxic (1% oxygen) condition. Hypoxic condition induced nuclear accumulation of the hypoxia-inducible factor-1α and upregulation of hTERT promoter activity in human cancer cells. The cytopathic activity of OBP-301 was significantly higher than that of Ad5 under hypoxic condition. Consistent with their cytopathic activity, the replication of OBP-301 was significantly higher than that of Ad5 under the hypoxic condition. OBP-301-mediated E1A was expressed within hypoxic areas of human xenograft tumors in mice. These results suggest that the cytopathic activity of OBP-301 against hypoxic tumor cells is mediated through hypoxia-mediated activation of the hTERT promoter. Regulation of oncolytic adenoviruses by the hTERT promoter is a promising antitumor strategy, not only for induction of tumor-specific oncolysis, but also for efficient elimination of hypoxic tumor cells.

Evolution of oncolytic adenovirus for cancer treatment

Oncolytic adenovirus (Ad) has been used in cancer gene therapy largely due to its ability to selectively infect and replicate in tumor cells. However, because the oncolytic antitumor activity is insufficient to effectively eliminate tumors, various strategies have been devised to improve the therapeutic efficacy. Single-vector Ads "armed" with short hairpin RNA, cytokines, or matrix-modulating proteins have been developed. Two clear advantages are viral amplification of the therapeutic gene, and the additive effects of oncolytic and therapeutic gene-mediated antitumor activities. To develop systemically injectable Ad carriers, strategies to modify the Ad surface with polymers, liposomes, or nanoparticles have been shown to extend circulation time, reduce immunogenicity, and result in increased antitumor effect as well as lower accumulation and toxicity in liver. Specific targeting platforms for tumor-selective oncolytic therapies against both primary and metastatic cancers have been developed. This review will focus on updated strategies to develop potent oncolytic Ads for use in cancer treatment.

Negative regulation-resistant p53 variant enhances oncolytic adenoviral gene therapy

Intact p53 function is essential for responsiveness to cancer therapy. However, p53 activity is attenuated by the proto-oncoprotein Mdm2, the adenovirus protein E1B 55kD, and the p53 C-terminal domain. To confer resistance to Mdm2, E1B 55kD, and C-terminal negative regulation, we generated a p53 variant (p53VPΔ30) by deleting the N-terminal and C-terminal regions of wild-type p53 and inserting the transcriptional activation domain of herpes simplex virus VP16 protein. The oncolytic adenovirus vector Ad-mΔ19 expressing p53VPΔ30 (Ad-mΔ19/p53VPΔ30) showed greater cytotoxicity than Ad-mΔ19 expressing wild-type p53 or other p53 variants in human cancer cell lines. We found that Ad-mΔ19/p53VPΔ30 induced apoptosis through accumulation of p53VPΔ30, regardless of endogenous p53 and Mdm2 status. Moreover, Ad-mΔ19/p53VPΔ30 showed a greater antitumor effect and increased survival rates of mice with U343 brain cancer xenografts that expressed wild-type p53 and high Mdm2 levels. To our knowledge, this is the first study reporting a p53 variant modified at the N terminus and C terminus that shows resistance to degradation by Mdm2 and E1B 55kD, as well as negative regulation by the p53 C terminus, without decreased trans-activation activity. Taken together, these results indicate that Ad-mΔ19/p53VPΔ30 shows potential for improving p53-mediated cancer gene therapy.

Soluble vascular endothelial growth factor decoy receptor FP3 exerts potent antiangiogenic effects

The binding of vascular endothelial growth factor (VEGF) to its receptors stimulates tumor growth; therefore, modulation of VEGF would be a viable approach for antiangiogenic therapy. We constructed a series of soluble decoy receptors containing different VEGF receptor 1 (FLT1) and VEGF receptor 2 (KDR) extracellular domains fused with the Fc region of human immunoglobulin (Ig) and evaluated their antiangiogenic effects and antitumor effects. Results of in vitro binding and cell proliferation assays revealed that decoy receptor FP3 had the highest affinity to VEGF-A and -B. Compared with bevacizumab, FP3 more effectively inhibited human umbilical vein endothelial cell (HUVEC) migration and vessel sprouting from rat aortic rings. FP3 significantly reduced phosphorylation of AKT and ERK1/2, critical proteins in the VEGF-mediated survival pathway in endothelial cells. Moreover, FP3 inhibited tumor growth in human hepatocellular carcinoma (HepG2), breast cancer (MCF-7), and colorectal cancer (LoVo) tumor models, and reduced microvessel density in tumor tissues. The FP3-mediated inhibition of tumor growth was significantly higher than that of bevacizumab at the same dose. FP3 also demonstrated synergistic antitumor effects when combined with 5-fluorouracil (5-FU). Taken together, FP3 shows a high affinity for VEGF and produced antiangiogenic effects, suggesting its potential for treating angiogenesis-related diseases such as cancer.

Enhancing the therapeutic efficacy of adenovirus in combination with biomaterials

With the reason that systemically administered adenovirus (Ad) is rapidly extinguished by innate/adaptive immune responses and accumulation in liver, in vivo application of the Ad vector is strictly restricted. For achieving to develop successful Ad vector systems for cancer therapy, the chemical or physical modification of Ad vectors with polymers has been generally used as a promising strategy to overcome the obstacles. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of therapeutic Ad vectors and well accomplished to extend circulation time in blood and reduce liver toxicity. However, although polymer-coated Ads can successfully evacuate from a series of guarding systems in vivo and locate within tumors by enhanced permeability and retention (EPR) effect, the possibility to entering into the target cell is few and far between. To endow targeting moiety to polymer-coated Ad vectors, a diversity of ligands such as tumor-homing peptides, growth factors or antibodies, have been introduced with avoiding unwanted transduction and enhancing therapeutic efficacy. Here, we will describe and classify the characteristics of the published polymers with respect to Ad vectors. Furthermore, we will also compare the properties of variable targeting ligands, which are being utilized for addressing polymer-coated Ad vectors actively.

Live-attenuated measles virus vaccine confers cell contact loss and apoptosis of ovarian cancer cells via ROS-induced silencing of E-cadherin by methylation

Herein we present a novel molecular mechanism of the antitumor effects of live-attenuated measles virus (MV) vaccine in ovarian cancer. Using a 2-DE/MS-based comparative proteomics strategy, we identified 17 proteins differentially expressed in live-attenuated MV vaccine-treated SKOV-3 ovarian cancer cells, including oxidative stress-associated enzymes and cell contact-related proteins, which indicated that live-attenuated MV vaccine could induce aberrant ROS activation. It further mediated epigenetic silencing of E-cadherin via upregulating DNMT3a that conferred both cell-cell and cell-matrix contact loss and apoptosis of ovarian cancer cells. This process could be reversed through ROS inhibition. Our study lays the theoretical foundation for the clinical application of live-attenuated MV vaccine as a potential oncotherapeutic agent for ovarian cancer treatment.

Recent advances in oncolytic virus design

The cytolytic properties of viruses can be used to treat cancer. Replication of certain viruses is favoured in cancer cells, whereas others can be modified to obtain tumour specificity. This approach has evolved to become a new discipline called virotherapy. In addition, these replication-competent (oncolytic) viruses can be adapted as vectors for cancer gene therapy. The "armed" viruses show a double mechanism of action: direct destruction of cancer cells as a consequence of the lytic viral cycle, in combination with the effect of the therapeutic gene incorporated in the viral genome. Current trends in the field include strategies to increase the oncolytic potency of existing viruses; the evaluation of new candidates; the search for synergistic effects between different viruses and conventional therapies; and a rational approach to take advantage of the interplay between the viruses and the host immune system. This review summarises the most relevant achievements in recent years.