Oncolytic adenoviruses targeted to cancer stem cells: Table 1

Alpha-1 antitrypsin deficiency: current therapy and emerging targets

INTRODUCTION

Alpha1 antitrypsin deficiency (AATD), a common hereditary disorder affecting mainly lungs, liver and skin has been the focus of some of the most exciting therapeutic approaches in medicine in the past 5 years. In this review, we discuss the therapies presently available for the different manifestations of AATD and new therapies in the pipeline.

AREAS COVERED

We review therapeutic options for the individual lung, liver and skin manifestations of AATD along with approaches which aim to treat all three. Along with this renewed interest in treating AATD come challenges. How is AAT best delivered to the lung? What is the desired level of AAT in the circulation and lungs which therapeutics should aim to provide? Will treating the liver disease increase the potential for lung disease? Are there treatments to target the underlying genetic defect with the potential to prevent all aspects of AATDrelated disease?

EXPERT OPINION

With a relatively small population able to participate in clinical studies, increased awareness and diagnosis of AATD is urgently needed. Better, more sensitive clinical parameters will assist in the generation of acceptable and robust evidence of therapeutic effect for current and emerging treatments.

Evaluation of tumor immunity after administration of conditionally replicative adenoviral vector in canine osteosarcoma patients

Osteosarcoma is one among the most common neoplasms in dogs. Current treatments show limited efficacy and fail to prevent metastasis. Conditionally replicative adenoviruses (CRAd) replicate exclusively in targeted tumor cells and release new virus particles to infect additional cells. We proposed that OC-CAVE1 (CAV2 with the E1A promoter replaced with the osteocalcin promotor) may also enhance existing immunity against tumors by overcoming immune tolerance via exposure of new epitopes and cytokine signaling. Eleven client-owned dogs with spontaneously occurring osteosarcomas were enrolled in a pilot study. All dogs were injected with OC-CAVE1 following amputation of the affected limb or limb-sparing surgery. Dogs were monitored for viremia and viral shedding. There was minimal virus shedding in urine and feces by the 6th day and no virus was present in blood after 4 weeks. CAV-2 antibody-titers increased in all of the patients, post-CRAd injection. Immunological assays were performed to monitor 1) humoral response against tumors, 2) levels of circulatory CD11c + cells, 3) levels of regulatory T cells, and 4) cytotoxic activity of tumor specific T cells against autologous tumor cells between pre-CRAd administration and 4 weeks post-CRAd administration samples. Administration of the CRAd OC-CAVE1 resulted in alteration of some immune response parameters but did not appear to result in increased survival duration. However, 2 dogs in the study achieved survival times in excess of 1 year. Weak replication of OC-CAVE1 in metastatic cells and delay of chemotherapy following CRAd treatment may contribute to the lack of immune response and improvement in survival time of the clinical patients.

Oncolytic Viruses and Hematological Malignancies: A New Class of Immunotherapy Drugs

The use of viruses for tumour treatment has been imagined more than one hundred years ago, when it was reported that viral diseases were occasionally leading to a decrease in neoplastic lesions. Oncolytic viruses (OVs) seem to have a specific tropism for tumour cells. Previously, it was hypothesised that OVs’ antineoplastic actions were mainly due to their ability to contaminate, proliferate and destroy tumour cells and the immediate destructive effect on cells was believed to be the single mechanism of action of OVs’ action. Instead, it has been established that oncolytic viruses operate via a multiplicity of systems, including mutation of tumour milieu and a composite change of the activity of immune effectors. Oncolytic viruses redesign the tumour environment towards an antitumour milieu. The aim of our work is to evaluate the findings present in the literature about the use of OVs in the cure of haematological neoplastic pathologies such as multiple myeloma, acute and chronic myeloid leukaemia, and lymphoproliferative diseases. Further experimentations are essential to recognize the most efficient virus or treatment combinations for specific haematological diseases, and the combinations able to induce the strongest immune response.

Advances in Alpha-1 Antitrypsin Gene Therapy

AAT (alpha-1 antitrypsin) deficiency (AATD), characterized by low levels of circulating serine protease inhibitor AAT, results in emphysematous destruction of the lung. Inherited serum deficiency disorders, such as hemophilia and AATD, have been considered ideal candidates for gene therapy. Although viral vector-meditated transduction of the liver has demonstrated utility in hemophilia, similar success has not been achieved for AATD. The challenge for AAT gene therapy is achieving protective levels of AAT locally in the lung and mitigating potential liver toxicities linked to systemically administered viral vectors. Current strategies with ongoing clinical trials involve different routes of adeno-associated virus administrations, such as intramuscular and intrapleural injections, to provide consistent therapeutic levels from nonhepatic organ sites. Nevertheless, exploration of alternative methods of nonhepatic sourcing of AAT has been of great interest in the field. In this regard, pulmonary endothelium-targeted adenovirus vector could be a key technical mandate to achieve local augmentation of AAT within the lower respiratory tract, with the potential benefit of circumventing liver toxicities. In addition, incorporation of the CRISPR/Cas9 (CRISPR-associated protein 9) nuclease system into gene-delivery technologies has provided adjunctive technologies that could fully realize a one-time treatment for sustained, lifelong expression of AAT in patients with AATD. This review will focus on the adeno-associated virus- and adenoviral vector-mediated gene therapy strategies for the pulmonary manifestations of AATD and show that endeavoring to use genome-editing techniques will advance the current strategy to one fully compatible with direct human translation.

Differentiation of Cancer Stem Cells by Using Synthetic Small Molecules: Toward New Therapeutic Strategies against Therapy Resistance

Despite the existing arsenal of anti-cancer drugs, 10 million people die each year worldwide due to cancers; this highlights the need to discover new therapies based on innovative modes of action against these pathologies. Current chemotherapies are based on the use of cytotoxic agents, targeted drugs, monoclonal antibodies or immunotherapies that are able to reduce or stop the proliferation of cancer cells. However, tumor eradication is often hampered by the presence of resistant cells called cancer stem-like cells or cancer stem cells (CSCs). Several strategies have been proposed to specifically target CSCs such as the use of CSC-specific antibodies, small molecules able to target CSC signaling pathways or drugs able to induce CSC differentiation rendering them sensitive to classical chemotherapy. These latter compounds are the focus of the present review, which aims to report recent advances in anticancer-differentiation strategies. This therapeutic approach was shown to be particularly promising for eradicating tumors in which CSCs are the main reason for therapeutic failure. This general view of the chemistry and mechanism of action of compounds inducing the differentiation of CSCs could be particularly useful for a broad range of researchers working in the field of anticancer therapies as the combination of compounds that induce differentiation with classical chemotherapy could represent a successful approach for future therapeutic applications.

Synergistic antitumor activity of triple-regulated oncolytic adenovirus with VSTM1 and daunorubicin in leukemic cells

V-set and transmembrane domain-containing 1 (VSTM1), which is downregulated in bone marrow cells from leukemia patients, may provide a diagnostic and treatment target. Here, a triple-regulated oncolytic adenovirus was constructed to carry a VSTM1 gene expression cassette, SG611-VSTM1, and contained the E1a gene with a 24-nucleotide deletion within the CR2 region under control of the human telomerase reverse transcriptase promoter, E1b gene directed by the hypoxia response element, and VSTM1 gene controlled by the cytomegalovirus promoter. Real-time quantitative PCR and Western blot analyses showed that SG611-VSTM1 expressed VSTM1 highly efficiently in the human leukemic cell line K562 compared with SG611. In Cell Counting Kit-8 and flow cytometric assays, SG611-VSTM1 exhibited more potent anti-proliferative and pro-apoptotic effects in leukemic cells compared with SG611 and exerted synergistic cytotoxicity with low-dose daunorubicin (DNR) in vitro. In xenograft models, SG611-VSTM1 intratumorally injected at a dose of 1 × 10(9) plaque forming units combined with intraperitoneally injected low-dose DNR displayed significantly stronger antitumor effects than either treatment alone. Histopathologic examination revealed that SG611-VSTM1 induced apoptosis of leukemic cells. These results implicate an important role for VSTM1 in the pathogenesis of leukemia, and SG611-VSTM1 may be a promising agent for enhancing chemosensitivity in leukemia therapy.

Combing oncolytic adenovirus expressing Beclin-1 with chemotherapy agent doxorubicin synergistically enhances cytotoxicity in human CML cells in vitro

Cancer virotherapy provides a new strategy to treat cancer that can directly kill cancer cells by oncolysis. Insertion of therapeutic genes into the genome of a modified adenovirus, thereby creating a so-called gene-virotherapy that shares the advantages of gene therapy and virotherapy. In this study we investigated whether a strategy that combines the oncolytic effects of an adenoviral vector with the simultaneous expression of the autophagy gene Beclin-1 offered a therapeutic advantage for chronic myeloid leukemia (CML) cells with resistance to chemotherapy and evaluated the synergistic effects of SG511-BECN and doxorubicin (Dox) in human CML cells in vitro. Oncolytic virus SG511-BECN was constructed through introducing the Beclin-1 gene into the oncolytic adenoviral backbone. SG511-BECN displayed significantly improved antileukemia activity on multidrug-resistant CML cell line K562/A02, which was mediated via induction of autophagic cell death. Furthermore, Dox could synergize with SG511-BECN to kill the CML cells by improving the infectious efficiency of the oncolytic adenovirus without causing significant damage to normal human mononuclear cells. The results demonstrate that targeting the autophagic cell death pathway and combination of a chemotherapy agent with oncolytic adenovirus may be a novel strategy for the treatment of leukemia with chemotherapy resistance.

Inhibition of Epithelial-Mesenchymal Transition and Metastasis by Combined TGFbeta Knockdown and Metformin Treatment in a Canine Mammary Cancer Xenograft Model

Epithelial mesenchymal transition (EMT) is a process by which epithelial cells acquire mesenchymal properties, generating metastases. Transforming growth factor beta (TGF-β) is associated with this malignancy by having the ability to induce EMT. Metformin, has been shown to inhibit EMT in breast cancer cells. Based on this evidence we hypothesize that treatment with metformin and the silencing of TGF-β, inhibits the EMT in cancer cells. Canine metastatic mammary tumor cell line CF41 was stably transduced with a shRNA-lentivirus, reducing expression level of TGF-β1. This was combined with metformin treatment, to look at effects on cell migration and the expression of EMT markers. For in vivo study, unmodified or TGF-β1sh cells were injected in the inguinal region of nude athymic female mice followed by metformin treatment. The mice's lungs were collected and metastatic nodules were subsequently assessed for EMT markers expression. The migration rate was lower in TGF-β1sh cells and when combined with metformin treatment. Metformin treatment reduced N-cadherin and increased E-cadherin expression in both CF41 and TGF-β1sh cells. Was demonstrated that metformin treatment reduced the number of lung metastases in animals bearing TGF-β1sh tumors. This paralleled a decreased N-cadherin and vimentin expression, and increased E-cadherin and claudin-7 expression in lung metastases. This study confirms the benefits of TGF-β1 silencing in addition to metformin as potential therapeutic agents for breast cancer patients, by blocking EMT process. To the best of our knowledge, we are the first to report metformin treatment in cells with TGF-β1 silencing and their effect on EMT.

CD44-shRNA recombinant adenovirus inhibits cell proliferation, invasion, and migration, and promotes apoptosis in HCT116 colon cancer cells

The cell-surface glycoprotein CD44 is closely associated with cell proliferation, tumor invasion, and metastasis. Previous studies have reported that knockdown of CD44 with short hairpin RNA (shRNA) reduced cell proliferation and migration, and induced apoptosis. However, more efficient means of delivering small interference RNA are still necessary. We developed an in vitro model of CD44-shRNA recombinant adenovirus (Ad-CD44-shRNA) and evaluated its ability to alter tumor invasion, migration, and apoptosis in human colon cancer cells. An shRNA against CD44 was used for knockdown of CD44 expression, and recombinant adenovirus was constructed using AD293 cells. The Ad-CD44-shRNA-treated HCT116 colon cancer cells showed a significant decrease in cell proliferation, migration, and invasion, while apoptosis was increased. The Ad-CD44-shRNA also decreased the phosphorylation of Akt and GSK-3β. The levels of Bcl-2 and Bcl-xL expression were downregulated, whereas the expression levels of Bax, cleaved caspase‑3 and -9, and PARP were increased in Ad-CD44-shRNA-treated colon cancer cells. These results support the feasibility of an adenovirus-mediated RNA interference therapy targeting human colon cancer via the CD44 as a potential future therapeutic intervention.

Redirecting adenovirus tropism by genetic, chemical, and mechanical modification of the adenovirus surface for cancer gene therapy

INTRODUCTION

Despite remarkable advancements, clinical evaluations of adenovirus (Ad)-mediated cancer gene therapies have highlighted the need for improved delivery and targeting.

AREA COVERED

Genetic modification of Ad capsid proteins has been extensively attempted. Although genetic modification enhances the therapeutic potential of Ad, it is difficult to successfully incorporate extraneous moieties into the capsid and the engineering process is laborious. Recently, chemical modification of the Ad surface with nanomaterials and targeting moieties has been found to enhance Ad internalization into the target by both passive and active mechanisms. Alternatively, external stimulus-mediated targeting can result in selective accumulation of Ad in the tumor and prevent dissemination of Ad into surrounding nontarget tissues. In the present review, we discuss various genetic, chemical, and mechanical engineering strategies for overcoming the challenges that hinder the therapeutic efficacy of Ad-based approaches.

EXPERT OPINION

Surface modification of Ad by genetic, chemical, or mechanical engineering strategies enables Ad to overcome the shortcomings of conventional Ad and enhances delivery efficiency through distinct and unique mechanisms that unmodified Ad cannot mimic. However, although the therapeutic potential of Ad-mediated gene therapy has been enhanced by various surface modification strategies, each strategy still possesses innate limitations that must be addressed, requiring innovative ideas and designs.

RGD-modifided oncolytic adenovirus exhibited potent cytotoxic effect on CAR-negative bladder cancer-initiating cells

Cancer-initiating cell (CIC) is critical in cancer development, maintenance and recurrence. The reverse expression pattern of coxsackie and adenovirus receptor (CAR) and α_ν integrin in bladder cancer decreases the infection efficiency of adenovirus. We constructed Arg-Gly-Asp (RGD)-modified oncolytic adenovirus, carrying EGFP or TNF-related apoptosis-inducing ligand (TRAIL) gene (Onco^Ad.RGD-hTERT-EGFP/TRAIL), and applied them to CAR-negative bladder cancer T24 cells and cancer-initiating T24 sphere cells. Onco^Ad.RGD-hTERT-EGFP had enhanced infection ability and cytotoxic effect on T24 cells and T24 sphere cells, but little cytoxicity on normal urothelial SV-HUC-1 cells compared with the unmodified virus Onco^Ad.hTERT-EGFP. Notably, Onco^Ad.RGD-hTERT-TRAIL induced apoptosis in T24 cells and T24 sphere cells. Furthermore, it completely inhibited xenograft initiation established by the oncolytic adenovirus-pretreated T24 sphere cells, and significantly suppressed tumor growth by intratumoral injection. These results provided a promising therapeutic strategy for CAR-negative bladder cancer through targeting CICs.

Targeting tumor suppressor networks for cancer therapeutics

Cancer is a consequence of mutations in genes that control cell proliferation, differentiation and cellular homeostasis. These genes are classified into two categories: oncogenes and tumor suppressor genes. Together, overexpression of oncogenes and loss of tumor suppressors are the dominant driving forces for tumorigenesis. Hence, targeting oncogenes and tumor suppressors hold tremendous therapeutic potential for cancer treatment. In the last decade, the predominant cancer drug discovery strategy has relied on a traditional reductionist approach of dissecting molecular signaling pathways and designing inhibitors for the selected oncogenic targets. Remarkable therapies have been developed using this approach; however, targeting oncogenes is only part of the picture. Our understanding of the importance of tumor suppressors in preventing tumorigenesis has also advanced significantly and provides a new therapeutic window of opportunity. Given that tumor suppressors are frequently mutated, deleted, or silenced with loss-of-function, restoring their normal functions to treat cancer holds tremendous therapeutic potential. With the rapid expansion in our knowledge of cancer over the last several decades, developing effective anticancer regimens against tumor suppressor pathways has never been more promising. In this article, we will review the concept of tumor suppression, and outline the major therapeutic strategies and challenges of targeting tumor suppressor networks for cancer therapeutics.

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.

uPAR-controlled oncolytic adenoviruses eliminate cancer stem cells in human pancreatic tumors

Pancreatic tumors contain cancer stem cells highly resistant to chemotherapy. The identification of therapies that can eliminate this population of cells might provide with more effective treatments. In the current work we evaluated the potential of oncolytic adenoviruses to act against pancreatic cancer stem cells (PCSC). PCSC from two patient-derived xenograft models were isolated from orthotopic pancreatic tumors treated with saline, or with the chemotherapeutic agent gemcitabine. An enrichment in the number of PCSC expressing the cell surface marker CD133 and a marked enhancement on tumorsphere formation was observed in gemcitabine treated tumors. No significant increase in the CD44, CD24, and epithelial-specific antigen (ESA) positive cells was observed. Neoplastic sphere-forming cells were susceptible to adenoviral infection and exposure to oncolytic adenoviruses resulted in elevated cytotoxicity with both Adwt and the tumor specific AduPARE1A adenovirus. In vivo, intravenous administration of a single dose of AduPARE1A in human-derived pancreatic xenografts led to a remarkable anti-tumor effect. In contrast to gemcitabine AduPARE1A treatment did not result in PCSC enrichment. No enrichment on tumorspheres neither on the CD133(+) population was detected. Therefore our data provide evidences of the relevance of uPAR-controlled oncolytic adenoviruses for the elimination of pancreatic cancer stem cells.

Oncolytic adenovirus encoding tumor necrosis factor-related apoptosis inducing ligand (TRAIL) inhibits the growth and metastasis of triple-negative breast cancer

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is a promising cancer therapeutic target due to its selective apoptosis-inducing effect in cancer cells. To efficiently deliver TRAIL to the tumor cells, an oncolytic adenovirus (p55-hTERT-HRE-TRAIL) carrying the TRAIL coding sequence was constructed. In the present study, we aimed to investigate the effect of p55-hTERT-HRE-TRAIL on the growth and metastasis of triple-negative breast cancer (TNBC). We observed that infection of the recombinant adenovirus resulted in expression of TRAIL and massive cell death in a TNBC cell line MDA-MB-231. This effect is much weaker in MCF-10A, which is a normal breast cell line. Administration of P55-HTERT-HRE-TRAIL significantly reduced orthotopic breast tumor growth and extended survival in a metastatic model. Our results suggest the oncolytic adenovirus armed with P55-HTERT-HRE-TRAIL, which exhibited enhanced anti-tumor activity and improved survival, is a promising candidate for virotherapy of TNBC.

Cisplatin induces differentiation of breast cancer cells

Breast tumors are heterogeneous including cells with stem cell properties and more differentiated cells. This heterogeneity is reflected into the molecular breast cancer subtypes. Breast cancer stem cells are resistant to chemotherapy, thus recent efforts are focusing on identifying treatments that shift them toward a more differentiated phenotype, making them more susceptible to chemotherapy. We examined whether the drug cisplatin induces differentiation in breast cancer cell lines that represent different breast cancer subtypes. We used three cell lines representing triple-negative breast cancers, BT-549 and MDA-MB-231 (claudin-low), and MDA-MB-468 (basal-like), along with estrogen and progesterone receptor positive MCF-7 cells (luminal). Cisplatin was applied at 2.5, 5, 10, and 20 μM, and cell viability and proliferation were measured using MTS and BrdU assays, respectively. The effect of cisplatin on the cellular hierarchy was examined by flow cytometry, immunofluorescence and qRT-PCR. Cisplatin treatment of 10 and 20 μM reduced cell viability by 36–51% and proliferation capacity by 36–67%. Treatment with cisplatin resulted in 12–67% down-regulation of stem cell markers (CD49f, SSEA4) and 10–130% up-regulation of differentiation markers (CK18, SMA, β-tubulin). At the mRNA level, CD49f was down-regulated whilst β-tubulin was up-regulated in the claudin-low cell lines. SSEA4 protein expression decreased upon cisplatin treatment, but SSEA4 mRNA expression increased indicating a differential regulation of cisplatin at the post-transcriptional level. It is concluded that cisplatin reduces breast cancer cell survival and induces differentiation of stem/progenitor cell subpopulations within breast cancer cell lines. These effects indicate the potential of this drug to target specific chemotherapy-resistant cells within a tumor.

Oncolytic virotherapy: the questions and the promise

Oncolytic virotherapy is a new strategy to reduce tumor burden through selective virus replication in rapidly proliferating cells. Oncolytic viruses are members of at least ten virus families, each with its advantages and disadvantages. Here, I briefly review the recent advances and key challenges, as exemplified by the best-studied platforms. Recent advances include preclinical proof of feasibility, clinical evidence of tolerability and effectiveness, and the development of new strategies to improve efficacy. These include engineered tumor selectivity and expression of antitumorigenic genes that could function independently of virus replication, identification of combinatorial therapies that accelerate intratumoral virus propagation, and modification of immune responses and vascular delivery for treatment of metastatic disease. Key challenges are to select "winners" from the distinct oncolytic platforms that can stimulate anti-cancer immunity without affecting virus replication and can lyse cancer stem cells, which are most likely responsible for tumor maintenance, aggressiveness, and recurrence. Preventing the emergence of resistant tumor cells during virotherapy through the activation of multiple death pathways, the development of a better understanding of the mechanisms of cancer stem-cell lysis, and the development of more meaningful preclinical animal models are additional challenges for the next-generation of engineered viruses.

An adenovirus vector incorporating carbohydrate binding domains utilizes glycans for gene transfer

BACKGROUND

Vectors based on human adenovirus serotype 5 (HAdV-5) continue to show promise as delivery vehicles for cancer gene therapy. Nevertheless, it has become clear that therapeutic benefit is directly linked to tumor-specific vector localization, highlighting the need for tumor-targeted gene delivery. Aberrant glycosylation of cell surface glycoproteins and glycolipids is a central feature of malignant transformation, and tumor-associated glycoforms are recognized as cancer biomarkers. On this basis, we hypothesized that cancer-specific cell-surface glycans could be the basis of a novel paradigm in HAdV-5-based vector targeting.

METHODOLOGY/PRINCIPAL FINDINGS

As a first step toward this goal, we constructed a novel HAdV-5 vector encoding a unique chimeric fiber protein that contains the tandem carbohydrate binding domains of the fiber protein of the NADC-1 strain of porcine adenovirus type 4 (PAdV-4). This glycan-targeted vector displays augmented CAR-independent gene transfer in cells with low CAR expression. Further, we show that gene transfer is markedly decreased in cells with genetic glycosylation defects and by inhibitors of glycosylation in normal cells.

CONCLUSIONS/SIGNIFICANCE

These data provide the initial proof-of-concept for HAdV-5 vector-mediated gene delivery based on the presence of cell-surface carbohydrates. Further development of this new targeting paradigm could provide targeted gene delivery based on vector recognition of disease-specific glycan biomarkers.

Treatment of malignant melanoma by downregulation of XIAP and overexpression of TRAIL with a conditionally replicating oncolytic adenovirus

BACKGROUND AND AIM

Currently available systemic therapies for malignant melanoma produce low response rates in patients, and more effective treatment modalities are clearly needed. The tumor necrosis factor (TNF)- related apoptosis-inducing ligand has a significant impact on therapy for patients with X-linked inhibitor of apoptosis protein-downregulation malignant melanoma. The primary objective of this study was to assess its therapeutic potential.

MATERIALS AND METHODS

We employed a conditionally replicating oncolytic adenoviral vector, named CRAd5.TRAIL/siXIAP, with the characteristics of over-expression of the therapeutic gene TRAIL and downregulation of XIAP in one vector. B16F10-luc cells were employed to detect anti-tumor activity of CRAd5.TRAIL/siXIAP in vitro and in vivo.

RESULTS

CRAd5.TRAIL/siXIAP enhanced caspase-8 activation and caspase-3 maturation in B16F10 cells in vitro. Furthermore, it more effectively infected and killed melanoma cells in vitro and in vivo than other adenoviruses.

CONCLUSION

Taken together, the combination of upregulation of TRAIL and downregulation of siXIAP with one oncolytic adenoviral vector holds promise for development of an effective therapy for melanomas and other common cancers.

Cancer stem cells, microRNAs, and therapeutic strategies including natural products

Embryonic stem cells divide continuously and differentiate into organs through the expression of specific transcription factors at specific time periods. Differentiated adult stem cells on the other hand remain in quiescent state and divide by receiving cues from the environment (extracellular matrix or niche), as in the case of wound healing from tissue injury or inflammation. Similarly, it is believed that cancer stem cells (CSCs), forming a smaller fraction of the tumor bulk, also remain in a quiescent state. These cells are capable of initiating and propagating neoplastic growth upon receiving environmental cues, such as overexpression of growth factors, cytokines, and chemokines. Candidate CSCs express distinct biomarkers that can be utilized for their identification and isolation. This review focuses on the known and candidate cancer stem cell markers identified in various solid tumors and the promising future of disease management and therapy targeted at these markers. The review also provides details on the differential expression of microRNAs (miRNAs), and the miRNA- and natural product-based therapies that could be applied for the treatment of cancer stem cells.

Breast cancer stem cells: new therapeutic approaches

SUMMARY Breast cancer stem cells are defined as a small subset of cells within a cancer that constitutes a reservoir of self-sustaining cells; they are low-dividing, have a reduced ability to undergo apoptosis and a higher ability of DNA repair, making them more resistant to conventional radiation and chemotherapy. The recent better understanding of the mechanisms of resistance to therapy related to stem cells has opened new scenarios and perspectives for therapeutic approaches. Some drugs active against breast cancer stem cells have been used in cancer therapy for years, other approaches are currently under clinical trials and many drugs are still in a preclinical phase. Only controlled clinical trials will answer the question whether or not these new therapeutical approaches alone or combined with the ongoing treatments significantly improve the outcome of breast cancer patients.

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.

Oncolytic adenovirus armed with IL-24 inhibits the growth of breast cancer in vitro and in vivo

Background

Interleukin-24 (IL-24) is a cytokine that belongs to the IL-10 family. It can selectively induce cancer cell apoptosis which has been utilized as a cancer gene therapy strategy.

Methods

A recombinant type five adenovirus containing IL-24 gene (designated CNHK600-IL24) was constructed, whose replication is activated only in tumor cells. The replication of CNHK600-IL24 in breast tumor cells and fibroblasts were assessed by TCID50 and MTT assay; the secretion of IL-24 was measured by ELISA and western blotting. The in vivo anti-tumor effect of CNHK600-IL24 was investigated in nude mice carrying orthotopic or metastatic breast tumor.

Results

We observed that CNHK600-IL24 could replicate efficiently and resulted in high level IL-24 expression and massive cell death in human breast cancer cell MDA-MB-231 but not in normal fibroblast cell MRC-5. In addition, orthotopic breast tumor growth in the nude mice model was significantly suppressed when CNHK600-IL24 was administered. In the metastatic model generated by tail vein injection, CNHK600-IL24 virotherapy significantly improved survival compared with the same virus expressing EGFP (median survival CNHK600-IL24, 55 days vs. CNHK600-EGFP, 41 day, p < 0.05 Mantal-Cox test). A similar phenomenon was observed in the metastatic model achieved by left ventricular injection as suggested by in vivo luminescence imaging of tumor growth.

Conclusion

The oncolytic adenovirus armed with IL-24, which exhibited enhanced anti-tumor activity and improved survival, is a promising candidate for virotherapy of breast cancer.

Targeting pediatric cancer stem cells with oncolytic virotherapy

Cancer stem cells (CSCs), also termed "cancer-initiating cells" or "cancer progenitor cells," which have the ability to self-renew, proliferate, and maintain the neoplastic clone, have recently been discovered in a wide variety of pediatric tumors. These CSCs are thought to be responsible for tumorigenesis and tumor maintenance, aggressiveness, and recurrence due to inherent resistance to current treatment modalities such as chemotherapy and radiation. Oncolytic virotherapy offers a novel, targeted approach for eradicating pediatric CSCs using mechanisms of cell killing that differ from conventional therapies. Moreover, oncolytic viruses have the ability to target specific features of CSCs such as cell-surface proteins, transcription factors, and the CSC microenvironment. Through genetic engineering, a wide variety of foreign genes may be expressed by oncolytic viruses to augment the oncolytic effect. We review the current data regarding the ability of several types of oncolytic viruses (herpes simplex virus-1, adenovirus, reovirus, Seneca Valley virus, vaccinia virus, Newcastle disease virus, myxoma virus, vesicular stomatitis virus) to target and kill both CSCs and tumor cells in pediatric tumors. We highlight advantages and limitations of each virus and potential ways in which next-generation engineered viruses may target resilient CSCs.

Wnt activation is implicated in glioblastoma radioresistance

Glioblastoma (GBM) patients have dismal median survival even with the most rigorous treatments currently available. Radiotherapy is the most effective non-surgical therapy for GBM patients; however, patients succumb due to tumor recurrence within a year. To develop a curative therapeutic approach, we need to better understand the underlying molecular mechanism of radiation resistance in GBM. Towards this goal, we developed an in vivo orthotopic GBM model system that mimics the radiation response of human GBM, using both established-GBM cell line and patient-derived freshly dissociated GBM specimen. In-vivo ionizing radiation (IR) treatment prolonged the survival of mice with intracranical tumor derived from U373MG, but failed to prevent tumor recurrence. U373MG and GBM578 cells isolated after in-vivo IR (U373-IR and 578-IR) were more clonogenic and enriched with stem cell-like characteristics, compared with mock-treated control tumor cells. Transcriptomic analyses and quantitative real-time reverse-transcription PCR analyses using these matched GBM cells before and after radiation treatment revealed that Wnt pathways were preferentially activated in post-IR GBM cells. U373-IR cells and 578-IR were enriched with cells positive for both active β-catenin (ABC) and Sox2 population, and this subpopulation was further increased after additional in-vitro radiation treatment, suggesting that radiation resistance of GBM is mediated due, in part, to the activation of stem cell-associated pathways including Wnt. Finally, pharmacological and siRNA inhibition of Wnt pathway significantly decreased the survival and clonogenicity of GBM cells and reduced their ABC(+)/Sox2(+) population. Together, these data suggest that Wnt activation is a molecular mechanism to confer GBM radioresistance and an important therapeutic target.

Epithelial-mesenchymal transition and breast cancer: role, molecular mechanisms and clinical impact

Epithelial-mesenchymal transition (EMT) is defined by the loss of epithelial characteristics and the acquisition of a mesenchymal phenotype. In this process, cells acquire molecular alterations that facilitate dysfunctional cell-cell adhesive interactions and junctions. These processes may promote cancer cell progression and invasion into the surrounding microenvironment. Such transformation has implications in progression of breast carcinoma to metastasis, and increasing evidences support most tumors contain a subpopulation of cells with stem-like and mesenchymal features that is resistant to chemotherapy. This review focuses on the physiological and pathological role of EMT process, its molecular related network, its putative role in the metastatic process and its implications in response/resistance to the current and/or new approaching drugs in the clinical management of breast cancer.

The emerging role of viruses in the treatment of solid tumours

There is increasing optimism for the use of non-pathogenic viruses in the treatment of many cancers. Initial interest in oncolytic virotherapy was based on the observation of an occasional clinical resolution of a lymphoma after a systemic viral infection. In many cancers, by comparison with normal tissues, the competency of the cellular anti-viral mechanism is impaired, thus creating an exploitable difference between the tumour and normal cells, as an unimpeded viral proliferation in cancer cells is eventually cytocidal. In addition to their oncolytic capability, these particular viruses may be engineered to facilitate gene delivery to tumour cells to produce therapeutic effects such as cytokine secretion and anti -tumour immune responses prior to the eventual cytolysis. There is now promising clinical experience with these viral strategies, particularly as part of multimodal studies, and already several clinical trials are in progress. The limitations of standard cancer chemotherapies, including their lack of specificity with consequent collateral toxicity and the development of cross-resistance, do not appear to apply to viral-based therapies. Furthermore, virotherapy frequently restores chemoradiosensitivity to resistant tumours and has also demonstrated efficacy against cancers that historically have a dismal prognosis. While there is cause for optimism, through continued improvements in the efficiency and safety of systemic delivery, through the emergence of alternative viral agents and through favourable clinical experiences, clinical trials as part of multimodal protocols will be necessary to define clinical utility. Significant progress has been made and this is now a major research area with an increasing annual bibliography.

Oncolytic adenovirus research and applications

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

Mesenchymal stem cell-based cellular vaccine: An efficient immunotherapeutic strategy for human malignancies

Cancer-related deaths are still the most fearsome threaten to human health. It is necessary to develop an innovative and active strategy for the prophylactic immunization against tumorigenesis. Multiple lines of evidence have demonstrated that cancer stem cells (CSCs) are the initiating cells of tumor formation, as well as the source of local recurrence and distant metastases. Mesenchymal stem cells (MSCs), the adult pluripotent progenitors of multiple mesenchymal lineages, have an unusual tropism to preclinical tumor lesions. Both MSCs and CSCs or populations of tumor-initiating cells may also have similar reactogenicity or immunogenicity. Based on the information given above, a hypothesis is generated that MSCs may possess a potential of cellular vaccine for bio-prevention against tumorigenesis via eliciting cross-immunity and inducing active antibodies.

Current issues and future directions of oncolytic adenoviruses

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