AAV-mediated TRAIL gene expression driven by hTERT promoter suppressed human hepatocellular carcinoma growth in mice

CPEB3 suppresses gastric cancer progression by inhibiting ADAR1-mediated RNA editing via localizing ADAR1 mRNA to P bodies

Deciphering the crosstalk between RNA-binding proteins and corresponding RNAs will provide a better understanding of gastric cancer (GC) progression. The comprehensive bioinformatics study identified cytoplasmic polyadenylation element-binding protein 3 (CPEB3) might play a vital role in GC progression. Then we found CPEB3 was downregulated in GC and correlated with prognosis. In addition, CPEB3 suppressed GC cell proliferation, invasion and migration in vitro, as well as tumor growth and metastasis in vivo. Mechanistic study demonstrated CPEB3 interacted with 3'-UTR of ADAR1 mRNA through binding to CPEC nucleotide element, and then inhibited its translation by localizing it to processing bodies (P bodies), eventually leading to the suppression of ADAR1-mediated RNA editing. Microscale thermophoresis assay further revealed that the direct interaction between CPEB3 and GW182, the P-body's major component, was through the 440-698AA region of CPEB3 binding to the 403-860AA region of GW182. Finally, AAV9-CPEB3 was developed and administrated in mouse models to assess its potential value in gene therapy. We found AAV9-CPEB3 inhibited GC growth and metastasis. Besides, AAV9-CPEB3 induced hydropic degeneration in mouse liver, but did not cause kidney damage. These findings concluded that CPEB3 suppresses GC progression by inhibiting ADAR1-mediated RNA editing via localizing ADAR1 mRNA to P bodies.

Hepatocellular Carcinoma Is a Natural Target for Adeno-Associated Virus (AAV) 2 Vectors

Simple Summary

Gene therapy is a novel approach to treat diseases by introducing corrective genetic information into target cells. Adeno-associated virus vectors are the most frequently applied gene delivery tools for in vivo gene therapy and are also studied as part of innovative anticancer strategies. Here, we report on the natural preference of AAV2 vectors for hepatocellular carcinoma (HCC) compared to nonmalignant liver cells in mice and human tissue. This preference in transduction is due to the improved intracellular processing of AAV2 vectors in HCC, resulting in significantly more vector genomes serving as templates for transcription in the cell nucleus. Based on this natural tropism for HCC, novel therapeutic strategies can be designed or existing therapeutic approaches can be strengthened as they currently result in only a minor improvement of the poor prognosis for most liver cancer patients.

Abstract

Although therapeutic options are gradually improving, the overall prognosis for patients with hepatocellular carcinoma (HCC) is still poor. Gene therapy-based strategies are developed to complement the therapeutic armamentarium, both in early and late-stage disease. For efficient delivery of transgenes with antitumor activity, vectors demonstrating preferred tumor tropism are required. Here, we report on the natural tropism of adeno-associated virus (AAV) serotype 2 vectors for HCC. When applied intravenously in transgenic HCC mouse models, similar amounts of vectors were detected in the liver and liver tumor tissue. In contrast, transduction efficiency, as indicated by the level of transgene product, was moderate in the liver but was elevated up to 19-fold in mouse tumor tissue. Preferred transduction of HCC compared to hepatocytes was confirmed in precision-cut liver slices from human patient samples. Our mechanistic studies revealed that this preference is due to the improved intracellular processing of AAV2 vectors in HCC, resulting, for example, in nearly 4-fold more AAV vector episomes that serve as templates for gene transcription. Given this background, AAV2 vectors ought to be considered to strengthen current—or develop novel—strategies for treating HCC.

The role of telomeres and telomerase in cirrhosis and liver cancer

Telomerase is a key enzyme for cell survival that prevents telomere shortening and the subsequent cellular senescence that is observed after many rounds of cell division. In contrast, inactivation of telomerase is observed in most cells of the adult liver. Absence of telomerase activity and shortening of telomeres has been implicated in hepatocyte senescence and the development of cirrhosis, a chronic liver disease that can lead to hepatocellular carcinoma (HCC) development. During hepatocarcinogenesis, telomerase reactivation is required to enable the uncontrolled cell proliferation that leads to malignant transformation and HCC development. Part of the telomerase complex, telomerase reverse transcriptase, is encoded by TERT, and several mechanisms of telomerase reactivation have been described in HCC that include somatic TERT promoter mutations, TERT amplification, TERT translocation and viral insertion into the TERT gene. An understanding of the role of telomeres and telomerase in HCC development is important to develop future targeted therapies and improve survival of this disease. In this Review, the roles of telomeres and telomerase in liver carcinogenesis are discussed, in addition to their potential translation to clinical practice as biomarkers and therapeutic targets.

Reducing off target viral delivery in ovarian cancer gene therapy using a protease-activated AAV2 vector platform

Gene therapy is a promising strategy for treating metastatic epithelial ovarian cancer (EOC). However, efficient vector targeting to tumors is difficult and off-target effects can be severely detrimental. Most vector targeting approaches rely on surface receptors overexpressed on some subpopulation of cancer cells. Unfortunately, there is no universally expressed cell surface biomarker for tumor cells. As an alternative, we developed an adeno-associated virus (AAV) based "Provector" whose cellular transduction can be activated by extracellular proteases, such as matrix metalloproteinases (MMP) that are overexpressed in the tumor microenvironments of the most aggressive forms of EOC. In a non-tumor bearing mouse model, the Provector demonstrates efficient de-targeting of healthy tissues, especially the liver, where viral delivery is <1% of AAV2. In an orthotopic HeyA8 tumor model of EOC, the Provector maintains decreased off-target delivery in the liver and other tissues but with no loss in tumor delivery. Notably, approximately 10% of the injected Provector is still detected in the blood at 24 h while >99% of injected AAV2 has been cleared from the blood by 1 h. Furthermore, mouse serum raised against the Provector is 16-fold less able to neutralize Provector transduction compared to AAV2 serum neutralizing AAV2 transduction (1:200 vs 1:3200 serum dilution, respectively). Thus, the Provector appears to generate less neutralizing antibodies than AAV2. Importantly, serum against AAV2 does not neutralize the Provector as well as AAV2, suggesting that pre-existing antibodies against AAV2 would not negate the clinical application of Provectors. Taken together, we present an EOC gene delivery vector platform based on AAV with decreased off-target delivery without loss of on-target specificity, and greater immunological stealth over the traditional AAV2 gene delivery vector.

EFLDO sensitizes liver cancer cells to TNFSF10‑induced apoptosis in a p53‑dependent manner

Ent‑3α‑formylabieta‑8(14),13(15)‑dien‑16,12β‑olide (EFLDO) is a compound extracted from Euphorbia lunulata Bge exhibiting anti‑proliferative activity in vitro. In the present study, EFLDO was identified to sensitize HepG2 cells to tumor necrosis factor (TNF) superfamily member 10 (TNFSF10)‑induced apoptosis. Liver cancer cells were resistant to TNFSF10; however, EFLDO increased TNFSF10‑induced cancer cell viability inhibition and cell apoptosis induction as assessed by MTT assay and Annexin V‑fluorescein isothiocyanate (FITC)/propidium iodide assay, respectively. The western blotting results suggested that treatment with EFLDO increased TNFSF10‑induced upregulation of the protein expression levels of pro‑apoptotic proteins, including BCL2 associated agonist of cell death, BCL2 associated X, apoptosis regulator, caspase‑3 (CASP3) and CASP8. Furthermore, treatment with EFLDO increased TNFSF10‑mediated downregulation of the protein expression level of the anti‑apoptotic protein BCL2 apoptosis regulator. Notably, the increase in the activity of CASP3 was consistent with the western blotting results. Treatment with EFLDO sensitized liver cancer cells to TNFSF10, and apoptosis was induced via the upregulation of TNF receptor superfamily member 10a (TNFRSF10A) and TNFRSF10B in a tumor protein p53 (p53)‑dependent manner, as detected by reverse transcription‑quantitative polymerase chain reaction and western blot analyses. In addition, p53 was identified to be necessary for EFLDO‑induced sensitivity to TNFSF10, as assessed by western blotting and Annexin V‑FITC assay. Collectively, the present results suggested a novel mechanism underlying EFLDO function in liver cancer. Treatment with EFLDO was able to increase the antitumor effect of TNFSF10 in liver cancer cells in a p53‑dependent manner.

Telomerase reverse transcriptase interference synergistically promotes tumor necrosis factor‑related apoptosis‑inducing ligand‑induced oral squamous cell carcinoma apoptosis and suppresses proliferation in vitro and in vivo

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is known to induce cell apoptosis in many types of cancer cells. However, some malignant cells still exhibit anti-apoptosis features induced by TRAIL; thus the underlying mechanisms that regulate sensitivity and resistance of tumor cells to TRAIL-induced apoptosis remain unclear. Human telomerase reverse transcriptase (hTERT) is overexpressed in most types of human tumors and is mostly inactive in somatic cells. The present study aimed to investigate the endogenous effects and mechanisms of hTERT inhibition and TRAIL overexpression on TRAIL-induced apoptosis of human oral squamous cell carcinoma (OSCC) cells. The effects of adeno-associated virus (AAV)-mediated TRAIL and hTERT gene silencing by RNA interference were investigated on the proliferation and apoptosis of human OSCC cells in vitro and in vivo. The present results suggest that knockdown of hTERT expression accelerated TRAIL-resistant OSCC cells to TRAIL-induced apoptosis and impaired OSCC cell proliferation. In addition, this process is accompanied by the upregulation of caspase-3, caspase-8 and caspase-9, and downregulation of B cell lymphoma-2. Additionally, the possible mechanisms underlying the association between TRAIL expression and hTERT silencing were explored. The results demonstrated that TRAIL expression levels were elevated when the hTERT gene was silenced, and notable anti-tumor effects were observed when TRAIL upregulation and hTERT gene silencing were carried out simultaneously. The present findings provide experimental evidence for the combined use of TRAIL and hTERT as a possible gene therapy strategy in oral cancer.

Therapeutic effect of targeted Fas-expressing adenoviruses method combining γδ T cells in a mouse model of human ovarian carcinoma

The present study aimed to investigate the therapeutic effect and safety of targeted use of Fas-expressing adenoviruses combined with γδ T cell-mediated killing to treat human ovarian cancer xenografts in BALB/c mice. Shuttle plasmids containing control elements of human telomerase reverse transcriptase promoter and two-step transcriptional amplification system were constructed and packaged into adenovirus-5 vectors to generate expression of an exogenous Fas gene. A mouse xenograft model of human ovarian carcinoma was constructed. A total of 35 BALB/c mice were randomly divided into five groups, which were injected with PBS, γδ T cells, Fas-expressing adenoviruses, taxol, or Fas-expressing adenovirus and γδ T cells. The weight and volume of tumors in mice in each group was monitored. Tissue sections of the various tissues of mice in the Fas-expressing adenovirus and γδ T cells group was compared with those in the PBS group to evaluate the safety of Fas-expressing adenovirus and γδ T cells in the treatment of human ovarian cancer xenograft tumors. The results of the present study indicated that mice in all treatment groups were alive at the end of the treatment course. Tumor weight and volume was the highest in the PBS group, followed successively by the adenovirus group, the γδ T cell group, the adenovirus and γδ T cell group, and the taxol group. The weight and volume inhibition rate in adenovirus and γδ T cell group were significantly higher compared with in the PBS group (P<0.05). Pathological observation of tissue samples revealed that none of vital organs in the adenovirus and γδ T cell group developed any evident morphological changes during treatment, when compared with healthy controls. In conclusion, the combined therapy with Fas-expressing adenoviruses and γδ T cells is efficient and safe for the treatment of mouse human ovarian carcinoma xenografts.

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.

Combination of AAV-TRAIL with miR-221-Zip Therapeutic Strategy Overcomes the Resistance to TRAIL Induced Apoptosis in Liver Cancer

TNF-related apoptosis-inducing ligand (TRAIL) possesses the capacity to induce apoptosis in a wide variety of tumor cells without affecting most normal cells. However, it has now emerged that many primary cancer cells are resistant to TRAIL monotherapy. Overcoming the intrinsic or acquired TRAIL resistance is desirable for TRAIL-mediated cancer therapy. In this study, we found that the miR-221/222 cluster was up-regulated in TRAIL-resistant liver cancer cells. Specific inhibitors of miR-221 and/or miR-222, called sponge, TuD and miR-Zip were constructed, and their ability to overcome TRAIL resistance was compared. Among them, AAV-mediated gene therapy using co-expression of TRAIL with miR-221-Zip showed the most synergistic activity in the induction of apoptosis in vitro. In vivo treatment of nude mice bearing human TRAIL-resistant liver cancer xenografts with AAV-TRAIL-miR-221-Zip also led to growth inhibition. This sensitizing effect of miR-221-Zip was associated with increased expression of PTEN, the miR-221 target, as well as with decreasing levels of Survivin. Moreover, miR-221 expression was concomitant with promotion of Survivin expression and suppression of PTEN expression. TRAIL sensitivity of cancer cells isolated from liver cancer tissues or from patients was significantly correlated with miR-221 expression. And miR-221 blood expression levels in liver cancer patients were correlated with TRAIL sensitivity, thus it had the potential to be a predictor of TRAIL sensitivity in liver cancer. These data suggested the potential of combining AAV-TRAIL with miR-221-Zip as a therapeutic intervention for liver cancer.

Seek and destroy: targeted adeno-associated viruses for gene delivery to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common form of primary liver cancer with high incidence globally. Increasing mortality and morbidity rates combined with limited treatment options available for advanced HCC press for novel and effective treatment modalities. Gene therapy represents one of the most promising therapeutic options. With the recent approval of herpes simplex virus for advanced melanoma, the field of gene therapy has received a major boost. Adeno-associated virus (AAV) is among the most widely used and effective viral vectors today with safety and efficacy demonstrated in a number of human clinical trials. This review identifies the obstacles for effective AAV based gene delivery to HCC which primarily include host immune responses and off-target effects. These drawbacks could be more pronounced for HCC because of the underlying liver dysfunction in most of the patients. We discuss approaches that could be adopted to tackle these shortcomings and manufacture HCC-targeted vectors. The combination of transductional targeting by modifying the vector capsid and transcriptional targeting using HCC-specific promoters has the potential to produce vectors which can specifically seek HCC and deliver therapeutic gene without significant side effects. Finally, the identification of novel HCC-specific ligands and promoters should facilitate and expedite this process.

Adeno-associated virus (AAV) vectors in cancer gene therapy

Gene delivery vectors based on adeno-associated virus (AAV) have been utilized in a large number of gene therapy clinical trials, which have demonstrated their strong safety profile and increasingly their therapeutic efficacy for treating monogenic diseases. For cancer applications, AAV vectors have been harnessed for delivery of an extensive repertoire of transgenes to preclinical models and, more recently, clinical trials involving certain cancers. This review describes the applications of AAV vectors to cancer models and presents developments in vector engineering and payload design aimed at tailoring AAV vectors for transduction and treatment of cancer cells. We also discuss the current status of AAV clinical development in oncology and future directions for AAV in this field.

Systemically administered AAV9-sTRAIL combats invasive glioblastoma in a patient-derived orthotopic xenograft model

Adeno-associated virus (AAV) vectors expressing tumoricidal genes injected directly into brain tumors have shown some promise, however, invasive tumor cells are relatively unaffected. Systemic injection of AAV9 vectors provides widespread delivery to the brain and potentially the tumor/microenvironment. Here we assessed AAV9 for potential glioblastoma therapy using two different promoters driving the expression of the secreted anti-cancer agent sTRAIL as a transgene model; the ubiquitously active chicken β-actin (CBA) promoter and the neuron-specific enolase (NSE) promoter to restrict expression in brain. Intravenous injection of AAV9 vectors encoding a bioluminescent reporter showed similar distribution patterns, although the NSE promoter yielded 100-fold lower expression in the abdomen (liver), with the brain-to-liver expression ratio remaining the same. The main cell types targeted by the CBA promoter were astrocytes, neurons and endothelial cells, while expression by NSE promoter mostly occurred in neurons. Intravenous administration of either AAV9-CBA-sTRAIL or AAV9-NSE-sTRAIL vectors to mice bearing intracranial patient-derived glioblastoma xenografts led to a slower tumor growth and significantly increased survival, with the CBA promoter having higher efficacy. To our knowledge, this is the first report showing the potential of systemic injection of AAV9 vector encoding a therapeutic gene for the treatment of brain tumors.

Targeting adeno-associated virus and adenoviral gene therapy for hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) heavily endangers human heath worldwide. HCC is one of most frequent cancers in China because patients with liver disease, such as chronic hepatitis, have the highest cancer susceptibility. Traditional therapeutic approaches have limited efficacy in advanced liver cancer, and novel strategies are urgently needed to improve the limited treatment options for HCC. This review summarizes the basic knowledge, current advances, and future challenges and prospects of adeno-associated virus (AAV) and adenoviruses as vectors for gene therapy of HCC. This paper also reviews the clinical trials of gene therapy using adenovirus vectors, immunotherapy, toxicity and immunological barriers for AAV and adenoviruses, and proposes several alternative strategies to overcome the therapeutic barriers to using AAV and adenoviruses as vectors.

Adeno-associated virus-mediated cancer gene therapy: current status

Gene therapy is one of the frontiers of modern medicine. Adeno-associated virus (AAV)-mediated gene therapy is becoming a promising approach to treat a variety of diseases and cancers. AAV-mediated cancer gene therapies have rapidly advanced due to their superiority to other gene-carrying vectors, such as the lack of pathogenicity, the ability to transfect both dividing and non-dividing cells, low host immune response, and long-term expression. This article reviews and provides up to date knowledge on AAV-mediated cancer gene therapy.

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.

MicroRNA-regulated non-viral vectors with improved tumor specificity in an orthotopic rat model of hepatocellular carcinoma

In hepatocellular carcinoma (HCC), tumor specificity of gene therapy is of utmost importance to preserve liver function. MicroRNAs (miRNAs) are powerful negative regulators of gene expression and many are downregulated in human HCC. We identified seven miRNAs that are also downregulated in tumors in a rat hepatoma model (P<0.05) and attempted to improve tumor specificity by constructing a panel of luciferase-expressing vectors containing binding sites for these miRNAs. Attenuation of luciferase expression by the corresponding miRNAs was confirmed across various cell lines and in mouse liver. We then tested our vectors in tumor-bearing rats and identified two miRNAs, miR-26a and miR-122, that significantly decreased expression in liver compared with the control vector (6.40 and 0.26%, respectively; P<0.05). In tumor, miR-122 had a nonsignificant trend towards decreased (∼50%) expression, whereas miR-26 had no significant effect on tumor expression. To our knowledge, this is the first work using differentially expressed miRNAs to de-target transgene expression in an orthotopic hepatoma model and to identify miR-26a, in addition to miR-122, for de-targeting liver. Considering the heterogeneity of miRNA expression in human HCC, this information will be important in guiding development of more personalized vectors for the treatment of this devastating disease.

Adeno-associated virus-mediated doxycycline-regulatable TRAIL expression suppresses growth of human breast carcinoma in nude mice

Background

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) functions as a cytokine to selectively kill various cancer cells without toxicity to most normal cells. Numerous studies have demonstrated the potential use of recombinant soluble TRAIL as a cancer therapeutic agent. We have showed previous administration of a recombinant adeno-associated virus (rAAV) vector expressing soluble TRAIL results in an efficient suppression of human tumor growth in nude mice. In the present study, we introduced Tet-On gene expression system into the rAAV vector to control the soluble TRAIL expression and evaluate the efficiency of the system in cancer gene therapy.

Methods

Controllability of the Tet-On system was determined by luciferase activity assay, and Western blotting and enzyme-linked immunoabsorbent assay. Cell viability was determined by MTT assay. The breast cancer xenograft animal model was established and recombinant virus was administrated through tail vein injection to evaluate the tumoricidal activity.

Results

The expression of soluble TRAIL could be strictly controlled by the Tet-On system in both normal and cancer cells. Transduction of human cancer cell lines with rAAV-TRE-TRAIL&rAAV-Tet-On under the presence of inducer doxycycline resulted in a considerable cell death by apoptosis. Intravenous injection of the recombinant virus efficiently suppressed the growth of human breast carcinoma in nude mice when activated by doxycycline.

Conclusion

These data suggest that rAAV-mediated soluble TRAIL expression under the control of the Tet-On system is a promising strategy for breast cancer therapy.

Discovery of cationic polymers for non-viral gene delivery using combinatorial approaches

Gene therapy is an attractive treatment option for diseases of genetic origin, including several cancers and cardiovascular diseases. While viruses are effective vectors for delivering exogenous genes to cells, concerns related to insertional mutagenesis, immunogenicity, lack of tropism, decay and high production costs necessitate the discovery of non-viral methods. Significant efforts have been focused on cationic polymers as non-viral alternatives for gene delivery. Recent studies have employed combinatorial syntheses and parallel screening methods for enhancing the efficacy of gene delivery, biocompatibility of the delivery vehicle, and overcoming cellular level barriers as they relate to polymer-mediated transgene uptake, transport, transcription, and expression. This review summarizes and discusses recent advances in combinatorial syntheses and parallel screening of cationic polymer libraries for the discovery of efficient and safe gene delivery systems.

The adeno-associated virus-mediated HSV-TK/GCV suicide system: a potential strategy for the treatment of bladder carcinoma

Novel treatment strategies such as gene therapy are warranted in view of the failure of current treatment approaches to cure a high percentage of patients with advanced bladder cancers. The emergence of cancer gene therapy potentially offers a number of exciting treatments. The majority of approaches involve strategies to suppress the function of activated oncogenes to restore the expression of functional tumour suppressor genes or to initiate tumour self-destruction. One gene therapy approach against tumours that holds great promise is suicide gene therapy. Herpes simplex virus thymidine kinase (HSV-TK) phosphorylates ganciclovir (GCV), which in turn interacts with cellular DNA polymerase and interferes with DNA synthesis to cause death of rapidly dividing cells. The development of an effective delivery system is absolutely critical to the usefulness and safety of gene therapy. At present, the adeno-associated virus (AAV) vector has the most promising potential in view of its non-pathogenicity, wide tropisms and long-term transgene expression in vivo. Gene therapy studies using different serotypes of recombinant AAV (rAAV) as delivery vehicles have proved rAAVs to be an effective modality of cancer gene therapy. In the present study, we investigated the suppression effect of AAV-mediated HSV-TK/GCV system on the bladder cancer cells and in mice xenograft models of bladder cancer. Our data demonstrate that rAAV-HSV-TK system controlled tumour cell growth and achieves strong antitumour efficacy in vivo. These findings provide a foundation for the development of potential targeted clinical therapies for bladder cancer in humans.

Development of optimized AAV3 serotype vectors: mechanism of high-efficiency transduction of human liver cancer cells

Our recent studies have revealed that among the 10 different commonly used adeno-associated virus (AAV) serotypes, AAV3 vectors transduce human liver cancer cells extremely efficiently because these cells express high levels of human hepatocyte growth factor receptor (hHGFR), and AAV3 utilizes hHGFR as a cellular co-receptor for viral entry. In this report, we provide further evidence that both extracellular as well as intracellular kinase domains of hHGFR are involved in AAV3 vector entry and AAV3-mediated transgene expression. We also document that AAV3 vectors are targeted for degradation by the host cell proteasome machinery, and that site-directed mutagenesis of surface-exposed tyrosine (Y) to phenylalanine (F) residues on AAV3 capsids significantly improves the transduction efficiency of Y701F, Y705F and Y731F mutant AAV3 vectors. The transduction efficiency of the Y705+731F double-mutant vector is significantly higher than each of the single mutants in liver cancer cells in vitro. In immunodeficient mouse xenograft models, direct intratumoral injection of AAV3 vectors also led to high-efficiency transduction of human liver tumor cells in vivo. We also document here that the optimized tyrosine-mutant AAV3 vectors lead to increased transduction efficiency following both intratumoral and tail-vein injections in vivo. The optimized tyrosine-mutant AAV3 serotype vectors containing proapoptotic genes should prove useful for the potential gene therapy of human liver cancers.

Liver-specific microRNA-122 target sequences incorporated in AAV vectors efficiently inhibits transgene expression in the liver

Vectors based on adeno-associated virus (AAV) are effective in gene delivery in vivo. Tissue-specific gene expression is often needed to minimize ectopic expression in unintended cells and undesirable consequences. Here we investigated if incorporation of target sequences of tissue-specific microRNA (miRNA) into AAV vectors could inhibit ectopic expression in tissues such as the liver and hematopoietic cells. First we inserted liver-specific miR-122 target sequences (miR-122T) into the 3′ untranslated region (UTR) of a number of AAV vectors. After intravenous delivery in mice, we found that 5 copies of the 20mer miR-122T reduced liver expression of luciferase by 50-fold and β-galactosidase (LacZ) by 70-fold. Five copies of miR-122T also reduced mRNA levels of a secretable protein (myostatin propeptide) from the AAV vector plasmid by 23–fold in the liver. However, gene expression in other tissues including the heart was not inhibited. Similarly, we inserted 4 copies of miR-142-3pT or miR-142-5pT, both hematopoietic lineage-specific, into the 3′ UTR of the AAV-luciferase vector. We wished to see if they could prolong transgene expression by inhibiting expression in antigen-presenting cells. However, in vivo luciferase gene expression in major tissues declined with time regardless of the miR-142 target sequences used. Quantitative analysis of the vector DNA in various tissues revealed that the decline of transgene expression in vivo was mainly due to promoter shut-off other than loss of AAV-transduced cells by immune destruction. Moreover, transgene expression was not detected in circulating mononuclear cells after delivering AAV9 vector with or without miR142T. These results demonstrate that live-specific miR-122 target sequence in AAV vectors was highly efficient in reducing liver expression, whereas hematopoietic miR-142 target sequences were ineffective in preventing decline of AAV vector gene expression in non-hematopoietic tissues resulted from promoter shut-off.

Novel cytotoxic vectors based on adeno-associated virus

Vectors based on adeno-associated virus (AAV) are promising tools for gene therapy. The production of strongly toxic vectors, for example for cancer-directed gene transfer, is often unfeasible due to uncontrolled expression of toxic genes in vector-producing cells. Using an approach based on transcriptional repression, we have created novel AAV vectors carrying the genes coding for diphtheria toxin A (DTA) and the pro-apoptotic PUMA protein. The DTA vector had a significant toxic effect on a panel of tumor cell lines, and abrogation of protein synthesis could be shown. The PUMA vector had a toxic effect on HeLa and RPMI 8226 cells, and sensitized transduced cells to doxorubicin. To permit targeted gene transfer, we incorporated the DTA gene into a genetically modified AAV-2 capsid previously developed by our group that mediates enhanced transduction of murine breast cancer cells in vitro. This vector had a stronger cytotoxic effect on breast cancer cells than DTA vectors with wildtype AAV capsid or vectors with a random capsid modification. The vector production and application system presented here allows for easy exchange of promotors, transgenes and capsid specificity for certain target cells. It will therefore be of great possible value in a broad range of applications in cytotoxic gene therapy and significantly broadens the spectrum of available tools for AAV-based gene therapy.

The human and canine TERT promoters function equivalently in human and canine cells

Telomerase targeted cancer gene therapy is being exploited for treatment of human cancer. The high incidence and many comparative aspects of human and canine cancer and the compliance and dedication of dog owners to treat cancer makes the canine pet population a good clinical model for investigating and developing new cancer therapeutics. Here, we report that the human telomerase promoter operates in canine cells, suggesting that human telomerase promoter-driven cancer therapy can be used to treat cancer in canines. Therefore, the canine pet population can act as a clinical model for new drug development based on telomerase therapeutics.

Suppression of bladder cancer growth in mice by adeno-associated virus vector-mediated endostatin expression

Novel treatment strategies such as gene therapy are warranted in view of the failure of current treatment approaches to cure a high percentage of patients with advanced bladder cancers. Testing of the hypothesis that blocking the angiogenic switch may keep tumour growth in check has been facilitated by the discovery of endogenous inhibitors of angiogenesis and has also added another research dimension to the field of cancer gene therapy. Consequently, the concept of targeting the tumour vasculature with anti-angiogenic agents has emerged as an attractive new strategy in the treatment of cancer. Targeted biological therapies that selectively interfere with tumour angiogenesis could improve survival among patients with bladder cancer. Endostatin is a tumour-derived angiogenesis inhibitor and is the first endogenous inhibitor of angiogenesis to be indentified in a matrix protein. Gene therapy represents an attractive approach to treat cancers and other chronic diseases. The development of an effective delivery system is absolutely critical to the usefulness and safety of gene therapy. At present, the adeno-associated virus (AAV) vector has the most promising potential in view of its non-pathogenicity, wide tropisms and long-term transgene expression in vivo. Gene therapy studies using different serotypes of recombinant AAV (rAAV) as delivery vehicles have proved rAAVs to be an effective modality of cancer gene therapy. In the present study, an IgG fragment was inserted at the start of the sequence coding for endostatin with the aim of enabling continuous secretion of endostatin the serum. We also investigated the suppression effect of AAV-mediated endostatin expression on endothelial cells and in mice xenograft models of bladder cancer. Our data demonstrates that rAAV-endostatin controlled tumour cell growth and achieves strong anti-tumour efficacy in vivo.

AAV's anatomy: roadmap for optimizing vectors for translational success

Adeno-Associated Virus based vectors (rAAV) are advantageous for human gene therapy due to low inflammatory responses, lack of toxicity, natural persistence, and ability to transencapsidate the genome allowing large variations in vector biology and tropism. Over sixty clinical trials have been conducted using rAAV serotype 2 for gene delivery with a number demonstrating success in immunoprivileged sites, including the retina and the CNS. Furthermore, an increasing number of trials have been initiated utilizing other serotypes of AAV to exploit vector tropism, trafficking, and expression efficiency. While these trials have demonstrated success in safety with emerging success in clinical outcomes, one benefit has been identification of issues associated with vector administration in humans (e.g. the role of pre-existing antibody responses, loss of transgene expression in non-immunoprivileged sites, and low transgene expression levels). For these reasons, several strategies are being used to optimize rAAV vectors, ranging from addition of exogenous agents for immune evasion to optimization of the transgene cassette for enhanced therapeutic output. By far, the vast majority of approaches have focused on genetic manipulation of the viral capsid. These methods include rational mutagenesis, engineering of targeting peptides, generation of chimeric particles, library and directed evolution approaches, as well as immune evasion modifications. Overall, these modifications have created a new repertoire of AAV vectors with improved targeting, transgene expression, and immune evasion. Continued work in these areas should synergize strategies to improve capsids and transgene cassettes that will eventually lead to optimized vectors ideally suited for translational success.

Targeted knockdown of Bcl2 in tumor cells using a synthetic TRAIL 3'-UTR microRNA

Targeting tumor-related overexpression of anti-apoptotic Bcl2 protein by RNAi has been suggested as a potential treatment for cancer. However, the stability of RNAi and its delivery are still major obstacles to the clinical testing of Bcl2 RNAi. Here, we explore a novel strategy of expressing a synthetic Bcl2 microRNA (smRNA) in the 3' untranslated region (UTR) of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), an apoptosis-inducing protein without apparent toxic effects in normal cells. TRAIL was specifically expressed from the human telomerase reverse transcriptase promoter (pTRT) that is active in many human tumors. Using this approach, we demonstrated that pTRT drove the tumor-specific expression of Bcl2 smRNA, which was processed by the host RNAi machinery and silenced endogenous Bcl2 expression in tumor cells. Bcl2 smRNA induced tumor cell apoptosis by activating caspase-3 and led to significant sensitization of tumor cells to TRAIL-induced apoptosis, while normal cells were spared. We also showed that the combined therapy of TRAIL-induced apoptosis and Bcl2 downregulation was superior to the mono-therapy of TRAIL or Bcl2 smRNA alone. This study proves a general paradigm for cancer therapy by using 3' UTR microRNA technology.

Antiangiogenesis gene armed tumor-targeting adenovirus yields multiple antitumor activities in human HCC xenografts in nude mice

AIM

Gene therapy represents a promising therapeutic strategy for hepatocellular carcinoma (HCC). To improve the ratio of killing efficacy on tumor cells to side-effect on normal cells, we constructed an oncolytic adenovirus vector, AdSu-hE, expressing the human endostatin (hE) gene, in which the chimeric promoter of human epidermal growth factor receptor 2 enhancer and human telomerase reverse transcriptase promoter was used to control the adenoviral E1a gene.

METHODS

Tumor-selective replication of adenovirus AdSu-hE and its concomitant expression of endostatin were measured by 50% tissue culture infective dose method, fluorescent protein expression, Western blot and enzyme linked immunosorbent assay in cancer and normal cell lines. The antitumor efficacy was observed in nude mice bearing human HCCs.

RESULTS

The oncolytic adenovirus AdSu-hE replicated restrictedly in telomerase-positive cancer cells and resulted in oncolysis, but did not replicate in normal cell lines. Along with virus replication, AdSu-hE mediated 5-fold increased expression of endostatin in tumor cells compared with that in normal cells. Moreover, AdSu-hE expressed more endostatin in cancer cells than the non-replicative adenovirus vector Ad-hE. In vivo administration of the oncolytic adenovirus AdSu-hE into HCC-bearing nude mice produced a significant tumor reduction by synergistic effects of virus oncolysis and endostatin antiangiogenesis.

CONCLUSION

The oncolytic virus with antiangiogenesis gene driven by the chimeric promoter has an improved killing efficacy on tumor cells, and may be useful for cancer gene therapy.

Endogenous HIV-1 Vpr-mediated apoptosis and proteome alteration of human T-cell leukemia virus-1 transformed C8166 cells

HIV-1 viral protein R (Vpr) can induce cell cycle arrest and cell death, and may be beneficial in cancer therapy to suppress malignantly proliferative cell types, such as adult T-cell leukemia (ATL) cells. In this study, we examined the feasibility of employing the HIV-vpr gene, via targeted gene transfer, as a potential new therapy to kill ATL cells. We infected C8166 cells with a recombinant adenovirus carrying both vpr and GFP genes (rAd-vpr), as well as the vector control virus (rAd-vector). G(2)/M phase cell cycle arrest was observed in the rAd-vpr infected cells. Typical characteristics of apoptosis were detected in rAd-vpr infected cells, including sub-diploid peak exhibition in DNA content assay, the Hoechst 33342 accumulation, apoptotic body formation, mitochondrial membrane potential and plasma membrane integrity loss. The proteomic assay revealed apoptosis related protein changes, exhibiting the regulation of caspase-3 activity indicator proteins (vimentin and Rho GDP-dissociation inhibitor 2), mitochondrial protein (prohibitin) and other regulatory proteins. In addition, the up-regulation of anti-inflammatory redox protein, thioredoxin, was identified in the rAd-vpr infected group. Further supporting these findings, the increase of caspase 3&7 activity in the rAd-vpr infected group was observed. In conclusion, endogenous Vpr is able to kill HTLV-1 transformed C8166 cells, and may avoid the risks of inducing severe inflammatory responses through apoptosis-inducing and anti-inflammatory activities.

TNF-related apoptosis-inducing ligand (TRAIL): a new path to anti-cancer therapies

Since its discovery in 1995, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of the tumor necrosis factor super family, has been under intense focus because of its remarkable ability to induce apoptosis in malignant human cells while leaving normal cells unscathed. Consequently, activation of the apoptotic signaling pathway from the death-inducing TRAIL receptors provides an attractive, biologically-targeted approach to cancer therapy. A great deal of research has focused on deciphering the TRAIL receptor signaling cascade and intracellular regulation of this pathway, as many human tumor cells possess mechanisms of resistance to TRAIL-induced apoptosis. This review focuses on the current state of knowledge regarding TRAIL signaling and resistance, the preclinical development of therapies targeted at TRAIL receptors and modulators of the pathway, and the results of clinical trials for cancer treatment that have emerged from this base of knowledge. TRAIL-based approaches to cancer therapy vary from systemic administration of recombinant, soluble TRAIL protein with or without the combination of traditional chemotherapy, radiation or novel anti-cancer agents to agonistic monoclonal antibodies directed against functional TRAIL receptors to TRAIL gene transfer therapy. A better understanding of TRAIL resistance mechanisms may allow for the development of more effective therapies that exploit this cell-mediated pathway to apoptosis.

Suppression of cancer growth in mice by adeno-associated virus vector-mediated IFN-beta expression driven by hTERT promoter

Adeno-associated virus (AAV) has rapidly become a promising gene delivery vehicle for its excellent advantages of non-immunogenic, low pathogenicity and long-term gene expression in vivo. However, a major obstacle in development of effective AAV vector is the lack of tissue specificity, which caused low efficiency of AAV transfer to target cells. The application of human telomerase reverse transcriptase (hTERT) promoter is a prior targeting strategy for AAV in cancer gene therapy as hTERT activity is transcriptionally upregulated in most cancer cells. In the present work, we investigated whether AAV-mediated human interferon beta (IFN-beta) gene driven by hTERT promoter could specifically express in tumor cells and suppress tumor cell growth. Our data demonstrated that hTERT promoter-driven IFN-beta expression was the tumor-specific, decreased the cell viability of tumor cells but not normal cells, and induced tumor cell apoptosis via activation of caspase pathway and release of cytochrome c. AAV-mediated IFN-beta expression driven by hTERT promoter significantly suppressed the growth of colorectal cancer and lung cancer xenograft in mice and resulted in tumor cells death in vivo. These data suggested that AAVs in combination with hTERT-mediated IFN-beta expression could exert potential antitumor activity and provide a novel targeting approach to clinical gene therapy of varieties of cancers.