Caspase-8 gene therapy using the human telomerase reverse transcriptase promoter for malignant glioma cells

Cell membrane breakage and triggering T cell infiltration are involved in human telomerase reverse transcriptase (hTERT) promoter-driven novel peptide KK-64 for liver cancer gene therapy

Liver cancer is an aggressive malignancy with exhibits both high mortality and morbidity. The current treatment options are associated with several limitations, novel specific anti-cancer drugs are urgently needed to improve liver cancer treatment. In this study, a new peptide KK-64 was designed, and it showed strong cytotoxicity against liver cancer cells. To obtain the tumor targeting property, a plasmid that contains KK-64 DNA fragment and driven by human telomerase reverse transcriptase (hTERT) promoter was constructed. pcTERT-kk-64 plasmid was found to specifically inhibit the viability of liver cancer cells HepG2, induce substantial apoptosis as well as damage to the cell membranes, but had minimal effects toward normal liver HL-7702 cells. Furthermore, pcTERT-kk-64 plasmids was also noted to significantly attenuate migration and invasion of HepG2 cells. The anti-tumor effect of pcTERT-kk-64 plasmid was also observed in H22 cell-bearing mice, and it appeared to cause significant tumor regression, trigger tumor cell apoptosis, and infiltrate cytotoxicity T cells to the tumor tissues after plasmids injection. Thus, pcTERT-kk-64 plasmids showed both strong cytotoxicity and tumor selectivity in vitro and in tumor-bearing mice in liver cancer models.

Telomerase-positive circulating tumor cells are associated with poor prognosis via a neutrophil-mediated inflammatory immune environment in glioma

BACKGROUND

Gliomas are the most common aggressive cancer in the central nervous system. Considering the difficulty in monitoring glioma response and progression, an approach is needed to evaluate the progression or survival of patients with glioma. We propose an application to facilitate clinical detection and treatment monitoring in glioma patients by using telomerase-positive circulating tumor cells (CTCs) and to further evaluate the relationship between the immune microenvironment and CTCs in glioma patients.

METHODS

From October 2014 to June 2017, 106 patients newly diagnosed with glioma were enrolled. We used the telomerase reverse transcriptase CTC detection method to detect and analyze the CTC statuses of glioma patients before and after surgery. FlowSight and FISH confirmed the CTCs detected by the telomerase-based method. To verify the correlation between CTCs and the immune response, peripheral white blood cell RNA sequencing was performed.

RESULTS

CTCs were common in the peripheral blood of glioma patients and were not correlated with the pathological classification or grade of patients. The results showed that the presence of postoperative CTCs but not preoperative CTCs in glioma patients was a poor prognostic factor. The level of postoperative CTCs, which predicts a poor prognosis after surgery, may be associated with neutrophils. RNA sequencing suggested that postoperative CTCs were positively correlated with innate immune responses, especially the activation of neutrophils and the generation of neutrophil extracellular traps, but negatively correlated with the cytotoxic response.

CONCLUSIONS

Our results showed that telomerase-positive CTCs can predict a poor prognosis of patients with glioma. Our results also showed a correlation between CTCs and the immune macroenvironment, which provides a new perspective for the treatment of glioma.

A human Myogenin promoter modified to be highly active in alveolar rhabdomyosarcoma drives an effective suicide gene therapy

Rhabdomyosarcoma is a rare childhood soft tissue cancer whose cells resemble poorly differentiated skeletal muscle, expressing myogenic proteins including MYOGENIN. Alveolar rhabdomyosarcoma (ARMS) accounts for ~40% of cases and is associated with a poorer prognosis than other rhabdomyosarcoma variants, especially if containing the chromosomal translocation generating the PAX3-FOXO1 hybrid transcription factor. Metastasis is commonly present at diagnosis, with a five-year survival rate of <30%, highlighting the need for novel therapeutic approaches. We designed a suicide gene therapy by generating an ARMS-targeted promoter to drive the herpes simplex virus thymidine kinase (HSV-TK) suicide gene. We modified the minimal human MYOGENIN promoter by deleting both the NF1 and MEF3 transcription factor binding motifs to produce a promoter that is highly active in ARMS cells. Our bespoke ARMS promoter driving HSV-TK efficiently killed ARMS cells in vitro, but not skeletal myoblasts. Using a xenograft mouse model, we also demonstrated that ARMS promoter-HSV-TK causes apoptosis of ARMS cells in vivo. Importantly, combining our suicide gene therapy with standard chemotherapy agents used in the treatment of rhabdomyosarcoma, reduced the effective drug dose, diminishing deleterious side effects/patient burden. This modified, highly ARMS-specific promoter could provide a new therapy option for this difficult-to-treat cancer.

The role of telomerase and viruses interaction in cancer development, and telomerase-dependent therapeutic approaches

Human telomerase reverse transcriptase (hTERT) is an enzyme that is critically involved in elongating and maintaining telomeres length to control cell life span and replicative potential. Telomerase activity is continuously expressed in human germ-line cells and most cancer cells, whereas it is suppressed in most somatic cells. In normal cells, by reducing telomerase activity and progressively shortening the telomeres, the cells progress to the senescence or apoptosis process. However, in cancer cells, telomere lengths remain constant due to telomerase's reactivation, and cells continue to proliferate and inhibit apoptosis, and ultimately lead to cancer development and human death due to metastasis. Studies demonstrated that several DNA and RNA oncoviruses could interact with telomerase by integrating their genome sequence within the host cell telomeres specifically. Through the activation of the hTERT promoter and lengthening the telomere, these cells contributes to cancer development. Since oncoviruses can activate telomerase and increase hTERT expression, there are several therapeutic strategies based on targeting the telomerase of cancer cells like telomerase-targeted peptide vaccines, hTERT-targeting dendritic cells (DCs), hTERT-targeting gene therapy, and hTERT-targeting CRISPR/Cas9 system that can overcome tumor-mediated toleration mechanisms and specifically apoptosis in cancer cells. This study reviews available data on the molecular structure of telomerase and the role of oncoviruses and telomerase interaction in cancer development and telomerase-dependent therapeutic approaches to conquest the cancer cells.

Induction of CEMIP in Chondrocytes by Inflammatory Cytokines: Underlying Mechanisms and Potential Involvement in Osteoarthritis

In patients with osteoarthritis (OA), there is a decrease in both the concentration and molecular size of hyaluronan (HA) in the synovial fluid and cartilage. Cell migration-inducing hyaluronidase 1 (CEMIP), also known as hyaluronan (HA)-binding protein involved in HA depolymerization (HYBID), was recently reported as an HA depolymerization-related molecule expressed in the cartilage of patients with OA. However, the underlying mechanism of CEMIP regulation is not well understood. We found that CEMIP expression was transiently increased by interleukine-1β (IL-1β) stimulation in chondrocytic cells. We also observed that ERK activation and NF-κB nuclear translocation were involved in the induction of CEMIP by IL-1β. In addition, both administration of HA and mechanical strain attenuated the CEMIP induction in IL-1β-stimulated chondrocytes. In conclusion, we clarified the regulatory mechanism of CEMIP in chondrocytes by inflammatory cytokines and suggested the potential involvement in osteoarthritis development.

Promoter-Operating Targeted Expression of Gene Therapy in Cancer: Current Stage and Prospect

The technique of targeted expression of interesting genes, including distinct delivery systems and specific gene promoter-operating expression, is an important strategy for gene therapy against cancers. Up to now, extensive literature documented the efficacy of distinct delivery systems, such as the liposome system, nano-particle system, polyetherimide (PEI) system, and so on, in cancer gene therapy. However, a related document on the potential value of using a specific gene promoter, such as a tumor suppressor, in cancer gene therapy was still scary. The main obstacle might be that the selection of an ideal gene promoter to operate interesting gene expression in cancer gene therapy is still not fully understood. Therefore, many efforts need to be done in order to make it a real power tool for the human clinical treatment of cancer patients. The purpose of this review is to clarify the current state and some problematics in development of promoter-operating targeted expression of interesting genes and highlight its potential in cancer gene therapy.

Gene therapy using the human telomerase catalytic subunit gene promoter enables targeting of the therapeutic effects of vesicular stomatitis virus matrix protein against human lung adenocarcinoma

The catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), is highly active in immortalized cells and more than 90% of human cancer cells, but is quiescent in the majority of normal somatic cells. Thus, the hTERT promoter has been extensively used in targeted cancer gene therapy. Vesicular stomatitis virus (VSV) matrix protein (MP) induces the apoptosis of tumor cells in the absence of other viral components. In our previous studies, we successfully constructed the pVAX-M plasmid from the pVAX plasmid, which expressed wild-type VSV MP (VSV MP is under the control of the CMV promoter) and demonstrated that pVAX-M efficiently suppresses the growth of malignant tumors via the induction of apoptosis in vitro and in vivo. The present study was designed to construct the plasmid phTERTM (VSV MP is under the control of the hTERT promoter) and investigate whether it had a targeted antitumor effect in nude mice bearing human lung adenocarcinoma. In vitro, A549 human lung adenocarcinoma cells were treated with NS, Lip-null, etoposide, Lip-pVAX-M or Lip-phTERT-M, and examined for cell viability through MTT assays or for apoptosis by flow cytometry and TUNEL assays. In vivo, A549 human lung carcinoma models in nude mice were established. Mice were treated with 10 4-weekly intravenous administrations of NS, Lip-null, etoposide (2 mg/kg), Lip-pVAX-M or Lip-phTERT-M. Subsequently, Lip-phTERT-M was found to be the most efficient inhibitor of tumor growth and inducer of tumor cell apoptosis when compared with the other groups in vivo and in vitro (P<0.05). Notably, immunohistochemical staining showed that Lip-phTERT-M significantly limited the overexpression of VSV MP to the tumor tissues and reduced VSV MP expression in other organs in comparison with Lip-pVAX-M (P<0.05). Therefore, it can be concluded that phTERT-M demonstrates a targeted antitumor effect on A549 human lung adenocarcinoma cells. These observations suggest that phTERT-M gene therapy may be a novel and potent strategy for targeting human lung adenocarcinoma.

Eukaryotic expression vectors bearing genes encoding cytotoxic proteins for cancer gene therapy

Cancer gene therapy is a promising direction for the treatment of cancer patients. A primary goal of all cancer therapies is to selectively target and kill tumour cells. Such therapies are administered via different approaches, including both viral and non-viral delivery; however, both methods have advantages and disadvantages. Transcriptional targeting enables genes encoding toxic proteins to be expressed directly in cancer cells. Numerous vectors have been created with the purpose of killing cancer cells, and some have successfully suppressed malignant tumours. Data concerning the function of vectors bearing genes that encode cytotoxic proteins under the control of different promoters, including tissue/tumour specific and constitutive promoters, is summarised here. This review focuses on vectors that bear genes encoding diphtheria toxin, Pseudomonas exotoxin A, caspases, gef, streptolysin, and melittin. Data describing the efficacy of such vectors have been summarised. Notably, there are vectors that killed cancer cell lines originating from the same type of cancer with differential efficiency. Thus, there is differential inhibition of cancer cell growth dependent on the cell line. In this review, the constructs employing genes whose expression induces cell death and the efficiency with which they suppress cancer cell growth will be summarised.

Homoharringtonine-Induced Apoptosis of Human Leukemia HL-60 Cells is Associated with Down-Regulation of Telomerase

Homoharringtonine (HHT), first isolated from the Chinese evergreen Cephalotaxus Harringtonia, has been shown inhibiting activity in leukemia in initial studies in China and in later studies in the US, but the detailed mechanism of action is still unclear. The goal of the experiments shown here is to explore the effect of HHT on the telomerase activity and apoptosis of human leukemia HL-60 cells. The telomerase activity of HL-60 cells was examined by the telomeric repeat amplification protocol (TRAP) — an enzyme-linked immunosorbent assay (ELISA). Apoptosis was analyzed by morphological observation, DNA agarose gel electrophoresis, flow cytometry (FCM), and TdT-mediated dUTP-biotin nick end labeling (TUNEL). After treatment with HHT at 5–500 μg/l for 48 hours, the level of telomerase activity in HL-60 cells decreased in a dose-and time-dependent manner. Simultaneously, HL-60 cells underwent apoptosis. In conclusion, our data suggest that HHT can inhibit the telomerase content of HL-60 cells effectively and induce apoptosis.

Targeting different types of human meningioma and glioma cells using a novel adenoviral vector expressing GFP-TRAIL fusion protein from hTERT promoter

Objective

The objective of this study was to evaluate the anti-tumor effects of Ad/gTRAIL (an adenoviral vector in which expression of GFP and TRAIL is driven by a human telomerase reverse transcriptase promoter, hTERT) on malignant meningiomas and gliomas.

Background

Gliomas and meningiomas are the two most common types of human brain tumors. Currently there is no effective cure for recurrent malignant meningiomas or for gliomas. Ad/gTRAIL has been shown to be effective in killing selected lung, colon and breast cancer cells, but there have been no studies reporting its antitumor effects on malignant meningiomas. Therefore, we tested the antitumor effect of Ad/gTRAIL for the first time in human malignant meningioma and glioma cell lines, and in intracranial M6 and U87 xenografts.

Methods

Materials and Methods: Human malignant meningioma and glioma cells were infected with adenoviruses, Ad/gTRAIL and Ad/CMV-GFP. Cell viability was determined by proliferation assay. FACS analysis and quantification of TRAIL were used to measure apoptosis in these cells. We injected Ad/gTRAIL viruses in intracranial M6 and U87 xenografts, and measured the brain tumor volume, quantified apoptosis by TUNEL assay in the brain tumor tissue.

Results

Our studies demonstrate that in vitro/in vivo treatment with Ad/gTRAIL virus resulted in significant increase of TRAIL activity, and elicited a greater tumor cell apoptosis in malignant brain tumor cells as compared to treatment with the control, Ad/CMV-GFP virus without TRAIL activity.

Conclusions

We showed for the first time that adenovirus Ad/gTRAIL had significant antitumor effects against high grade malignant meningiomas as well as gliomas. Although more work needs to be done, our data suggests that Ad/gTRAIL has the potential to be useful as a tool against malignant brain tumors.

Noninvasive and real-time monitoring of the therapeutic response of tumors in vivo with an optimized hTERT promoter

BACKGROUND

Telomerase is commonly recognized as an effective anticancer target. The human telomerase reverse transcriptase (hTERT), the rate-limiting component of telomerase, is expressed in most malignant tumors, but it is not found in most normal somatic cells. Here, we report a real-time and noninvasive method to monitor tumor response to a lentivirus-based hTERT-conditional suicidal gene therapy.

METHODS

In this study, we constructed a lentivirus system in which an optimized hTERT promoter was used to drive the expression of the cytosine deaminase (CD) gene, one of the suicide genes, and a green fluorescent protein (GFP) reporter gene (pLenti-CD/GFP). The lentivirus was used to infect telomerase-positive or telomerase-negative cell lines. In vitro and in vivo experiments were conducted to analyze the dynamic processes of exogenous gene expression noninvasively in cell culture and living animals in real time via optical imaging.

RESULTS

The lentivirus was able to express the CD gene and GFP in telomerase-positive tumor cells and significantly decrease cell proliferation after the use of prodrug 5-flucytosine. However, it could not express GFP and CD in telomerase-negative cell lines, nor could it induce any suicidal effect in those cells. The in vivo study showed that telomerase-positive tumors can be visualized after intratumor injection of the lentivirus in tumor-bearing nude mice via an optical imaging system. Significant tumor growth suppression was observed in telomerase-positive tumors.

CONCLUSIONS

Collectively, this technology provides a valuable, noninvasive method to evaluate the real-time therapeutic response of tumors in vivo.

Cotransfected sodium iodide symporter and human tyroperoxidase genes following human telomerase reverse transcriptase promoter for targeted radioiodine therapy of malignant glioma cells

INTRODUCTION

Radioiodine is a routine therapy for differentiated thyroid cancers. In principle, undifferentiated thyroid cancers as well as nonthyroid cancers can concentrate and, thus, be treated with radioiodine after transfection with the human sodium iodide symporter (hNIS) gene. The human telomerase reverse transcriptase (hTERT) promoter is an effective tumor-specific promoter of gene expression and, thus, may be useful in targeted gene therapy of cancer.

METHODS

We used hTERT promoter-modulated expression of the hNIS and human thyroperoxidase (hTPO) genes in an experimental model of radioiodine-based treatment of malignant glioma. Cells were cotransfected by adenovirus in which the hNIS gene had been coupled to the hTERT promoter and the hTPO gene had been coupled to the human cytomegalovirus (CMV) promoter (Ad-hTERT-hNIS and Ad-CMV-hTPO, respectively), and they were evaluated in cells thus transfecting transgene expression by western blots, (125)I uptake and influx, and clonogenecity after (131)I treatment.

RESULTS

After cotransfection with two adenovirus, cells showed about 31-34 times higher (125)I uptake than the control cells transfected with Ad-CMV-EGFP (enhanced green fluorescent protein) and almost 1.3-1.4 times higher (125)I uptake than cells only transfected with Ad-hTERT-hNIS. Western blots revealed two bands of ∼70 and 110 kDa, respectively. The in vitro clonogenic assay indicated that, after exposure to 100-1000 μCi of (131)I-iodide for 12 hours, 91%-94% of cells cotransfected with the hNIS and hTPO genes, 88%-93% of cells transfected with the hNIS gene, and only 62%-68% of control (nontransfected) cells were killed.

CONCLUSIONS

The experiments demonstrated that an effective therapy of (131)I was achieved in malignant glioma cell lines after induction of tumor-specific iodide uptake activity by the hTERT promoter-directed NIS expression in vitro. Cotransfection of the hNIS and hTPO genes can lead to longer retention of radioiodide, but did not increase cell killing over that achieved with transfection with the hNIS gene alone.

Proteases as therapeutics

Proteases are an expanding class of drugs that hold great promise. The U.S. FDA (Food and Drug Administration) has approved 12 protease therapies, and a number of next generation or completely new proteases are in clinical development. Although they are a well-recognized class of targets for inhibitors, proteases themselves have not typically been considered as a drug class despite their application in the clinic over the last several decades; initially as plasma fractions and later as purified products. Although the predominant use of proteases has been in treating cardiovascular disease, they are also emerging as useful agents in the treatment of sepsis, digestive disorders, inflammation, cystic fibrosis, retinal disorders, psoriasis and other diseases. In the present review, we outline the history of proteases as therapeutics, provide an overview of their current clinical application, and describe several approaches to improve and expand their clinical application. Undoubtedly, our ability to harness proteolysis for disease treatment will increase with our understanding of protease biology and the molecular mechanisms responsible. New technologies for rationally engineering proteases, as well as improved delivery options, will expand greatly the potential applications of these enzymes. The recognition that proteases are, in fact, an established class of safe and efficacious drugs will stimulate investigation of additional therapeutic applications for these enzymes. Proteases therefore have a bright future as a distinct therapeutic class with diverse clinical applications.

FasL and FADD delivery by a glioma-specific and cell cycle-dependent HSV-1 amplicon virus enhanced apoptosis in primary human brain tumors

BACKGROUND

Glioblastoma multiforme is the most malignant cancer of the brain and is notoriously difficult to treat due to the highly proliferative and infiltrative nature of the cells. Herein, we explored the combination treatment of pre-established human glioma xenograft using multiple therapeutic genes whereby the gene expression is regulated by both cell-type and cell cycle-dependent transcriptional regulatory mechanism conferred by recombinant HSV-1 amplicon vectors.

RESULTS

We demonstrated for the first time that Ki67-positive proliferating primary human glioma cells cultured from biopsy samples were effectively induced into cell death by the dual-specific function of the pG8-FasL amplicon vectors. These vectors were relatively stable and exhibited minimal cytotoxicity in vivo. Intracranial implantation of pre-transduced glioma cells resulted in better survival outcome when compared with viral vectors inoculated one week post-implantation of tumor cells, indicating that therapeutic efficacy is dependent on the viral spread and mode of viral vectors administration. We further showed that pG8-FasL amplicon vectors are functional in the presence of commonly used treatment regimens for human brain cancer. In fact, the combined therapies of pG8-FasL and pG8-FADD in the presence of temozolomide significantly improved the survival of mice bearing intracranial high-grade gliomas.

CONCLUSION

Taken together, our results showed that the glioma-specific and cell cycle-dependent HSV-1 amplicon vector is potentially useful as an adjuvant therapy to complement the current gene therapy strategy for gliomas.

Targeted gene therapy of nasopharyngeal cancer in vitro and in vivo by enhanced thymidine kinase expression driven by human TERT promoter and CMV enhancer

Background/Aim

To explore the therapeutic effects of thymidine kinase (TK) expressed by enhanced vector pGL3-basic- hTERTp-TK-EGFP-CMV driven by human telomerase reverse transcriptase promoter (hTERTp) as well as cytomegalovirus immediate early promoter enhancer (CMV).

Materials/Methods

Enhanced TK-EGFP expression was confirmed by fluorescent microscopy, real time PCR and telomerase activity. Its effects were examined by survival of tumor cells NPC 5-8F and MCF-7, index of xenograft implanted in nude mice and histology.

Results

Compared with non-enhanced vector pGL3-basic-TK-hTERTp-EGFP, TK expressed by the enhanced vector significantly decreased NPC 5-8F and MCF-7 cell survival rates after ganciclovir (GCV) treatment (p < 0.001) and tumor progress in nude mice with NPC xenograft and treated with GCV, without obvious toxicity to mouse liver and kidney.

Conclusion

The enhanced TK expression vector driven by hTERTp with CMV enhancer has brighter clinical potentials in nasopharyngeal carcinoma therapy than the non-enhanced vector.

Target gene therapy of glioma: overexpression of BAX gene under the control of both tissue-specific promoter and hypoxia-inducible element

Glioma-specific transcription of tumor-killing genes has been exploited as a promising gene therapeutic modality in glioma patients. Musashi1 (Msi1) and GFAP gene promoters are both cancer-specific promoters. Optimized HIF-binding site (optHBS) sequence was newly found as efficient as EPO HREs used as enhancer in cancer gene therapy. We constructed 4optHBS-Msi1/GFAP promoters and tested their ability to mediate BAX expression to induce apoptosis in glioma cell lines. Our results demonstrated that 4optHBS-Msi1/GFAP promoters are apparently strong and glioma-selective promoters with potential application in targeted glioma gene therapy, and 4optHBS-Msi1/GFAPBAXa are valuable tools for glioma gene therapy.

Adenoviral virotherapy for malignant brain tumors

Glioblastoma multiforme is the most common form of primary brain cancer. In the past decade, virotherapy of tumors has gained credence, particularly in glioma management, as these tumors are not completely resectable and tend to micro-metastasize. Adenoviral vectors have an advantage over other viral vectors in that they are relatively non-toxic and do not integrate in the genome. However, the lack of coxsackie and adenovirus receptors on surface of gliomas provides for inefficient transduction of wild-type adenoviral vectors in these tumors. By targeting receptors that are overexpressed in gliomas, modified adenoviral constructs have been shown to efficiently infect glioma cells. In addition, by taking advantage of tumor-specific promoter elements, oncolytic adenoviral vectors offer the promise of selective tumor-specific replication. This dual targeting strategy has enabled specificity in both laboratory and pre-clinical settings. This review examines current trends in adenoviral virotherapy of gliomas, with an emphasis on targeting modalities and future clinical applications.

Molecular strategies for the treatment of malignant glioma--genes, viruses, and vaccines

The standard treatment paradigm of surgery, radiation, and chemotherapy for malignant gliomas has only a modest effect on survival. It is well emphasized in the literature that despite aggressive multimodal therapy, most patients survive approximately 1 year after diagnosis, and less than 10% survive beyond 2 years. This dismal prognosis provides the impetus for ongoing investigations in search of improved therapeutics. Standard multimodal therapy has largely reached a plateau in terms of effectiveness, and there is now a growing body of literature on novel molecular approaches for the treatment of malignant gliomas. Gene therapy, oncolytic virotherapy, and immunotherapy are the major investigational approaches that have demonstrated promise in preclinical and early clinical studies. These new molecular technologies each have distinct advantages and limitations, and none has yet demonstrated a significant survival benefit in a phase II or III clinical trial. Molecular approaches may not lead to the discovery of a "magic bullet" for these aggressive tumors, but they may ultimately prove synergistic with more conventional approaches and lead to a broadening of the multimodal approach that is the current standard of care. This review will discuss the scientific background, therapeutic potential, and clinical limitations of these novel strategies with a focus on those that have made it to clinical trials.

Telomeres and telomerase: Biological and clinical importance in dogs

In recent years in human oncology the enzyme telomerase has emerged as an ideal target for cancer therapy. This has led to the assessment of telomerase in cancers in companion animals, mainly dogs and these studies confirm that in dogs, like humans, telomere maintenance by telomerase is the primary mechanism by which cancer cells overcome their mortality and extend their lifespan. This review aims to provide an introduction to the biology of telomeres and telomerase and to discuss some of the telomere/telomerase directed therapeutic methodologies currently under development which may be of benefit to the canine cancer patient.

Tumor-specific expression of the RGD-alpha3(IV)NC1 domain suppresses endothelial tube formation and tumor growth in mice

Angiogenesis plays an essential role in tumor growth. This study investigated expression of the noncollagenous domain of alpha3(IV) collagen (alpha3(IV)NC1) transduced into tumors and its inhibition of tumor growth. We hypothesized that if a human telomerase reverse transcriptase (hTERT) promoter-driven RGD motif containing alpha3(IV)NC1 (hTERT/RGD-alpha3(IV)NC1) were expressed in telomerase-expressing tumor cells, it would inhibit tumor growth by its anti-angiogenic property. Adenoviral transduction of hTERT/RGD-alpha3(IV)NC1 expressed RGD-alpha3(IV)NC1 in hTERT-positive tumor cell lines. However, hTERT/RGD-alpha3(IV)NC1 did not express RGD-alpha3(IV)NC1 in hTERT-negative cells such as keratinocytes and fibroblasts. The secreted RGD-alpha3(IV)NC1 in the conditioned medium from tumor cells inhibited cell proliferation as well as tube formation in cultured endothelial cells, but had no effect on other types of cells. In an in vivo model, adenoviral hTERT/RGD-alpha3(IV)NC1 gene therapy showed limited expression of RGD-alpha3(IV)NC1 in tumors and resulted in a significant decrease of vessel density in tumors. The growth of subcutaneous (s.c.) tumors in nude mice was significantly suppressed by treatment with hTERT/RGD-alpha3(IV)NC1. In addition, long-term inhibition of tumor growth was achieved by intermittent administration of hTERT/RGD-alpha3(IV)NC1. In conclusion, our findings demonstrate that tumor-specific anti-angiogenic gene therapy utilizing RGD-alpha3(IV)NC1 under the hTERT promoter inhibited angiogenesis in tumors, resulting in an antitumor effect.

Mad1 suppresses bladder cancer cell proliferation by inhibiting human telomerase reverse transcriptase transcription and telomerase activity

OBJECTIVES

To study the effects and possible mechanisms of mitosis arrest deficiency 1 (Mad1), the heterodimerizer of Max and a transcriptional repressor, on cell proliferation of bladder cancer in vitro and in vivo.

METHODS

Combining methyl thiazolyl tetrazolium (MTT) assay, flow cytometry, luciferase assay, telomeric repeat amplification protocol-enzyme-linked immunosorbent assay, real-time reverse transcriptase polymerase chain reaction, experimental animal models, and other assays, we detected the alterations of cell proliferation, cell cycle, promoter activity and expression of human telomerase reverse transcriptase (hTERT), and telomerase activity in different treated bladder cells and xenograft tissues.

RESULTS

Mad1 inhibited cell proliferation, increased G0/G1 accumulation in cell cycle distribution, decreased the transcription and expression of hTERT, and reduced telomerase activity compared with controls in T24 and EJ cells. Mad1 also arrested tumor growth and downregulated hTERT expression and telomerase activity in bladder cancer xenograft BALB/c nude mice.

CONCLUSIONS

Mad1 inhibited the proliferation of human bladder cancer cells by inhibiting hTERT transcription and telomerase activity. Mad1 could be a potentially useful candidate for inhibition of bladder cancer growth.

Use of replication-competent retroviral vectors in an immunocompetent intracranial glioma model

OBJECT

The authors had previously reported on a replication-competent retrovirus (RCR) that has been demonstrated to be stable, capable of effective transduction, and able to prolong survival in an intracranial tumor model in nude mice. The purpose of this study was further investigation of this gene therapy option.

METHODS

The transduction efficiency of RCR in RG2, an immunocompetent intracranial tumor model, was tested in Fischer 344 rats. The immune response to the RCR vector was expressed by the quantification of CD4, CD8, and CD11/b in tumors. The pharmaceutical efficacy of the suicide gene CD in converting prodrug 5-fluorocytosine (5-FC) to 5-fluorouracil (5-FU) was measured using fluorine-19 nuclear magnetic resonance (19F-NMR) spectroscopy. Animal survival data were plotted on Kaplan-Meier survival curves. Finally, the biodistribution of RCR was determined using quantitative real-time polymerase chain reaction (RT-PCR) for the detection of retroviral env gene. There was no evidence of viral transduction in normal brain cells. Neither severe inflammation nor immunoreaction occurred after intracranial injection of RCR-green fluorescent protein compared with phosphate-buffered saline (PBS). The 19F-NMR spectroscopy studies demonstrated that RCR-CD was able to convert 5-FC to 5-FU effectively in vitro. The infection of RG2 brain tumors with RCR-CD and their subsequent treatment with 5-FC significantly prolonged survival compared with that in animals with RG2 transduced tumors treated with PBS. In contrast to the nude mouse model, evidence of virus dissemination to the systemic organs after intracranial injection was not detected using RT-PCR.

CONCLUSIONS

The RCR-mediated suicide gene therapy described in this paper effectively transduced malignant gliomas in an immunocompetent in vivo rodent model, prolonging survival, without evidence of severe intracranial inflammation, and without local transduction of normal brain cells or systemic organs.

The human survivin promoter: a novel transcriptional targeting strategy for treatment of glioma

Object

Malignant brain tumors have been proved to be resistant to standard treatments and therefore require new therapeutic strategies. Survivin, a recently described member of the inhibitor of apoptosis protein family, is overexpressed in several human brain tumors, primarily gliomas, but is downregulated in normal tissues. The authors hypothesized that the expression of tumor-specific survivin could be exploited for treatment of gliomas by targeting the tumors with gene therapy vectors.

Methods

Following confirmation of survivin expression in glioma cell lines, an adenoviral vector containing the survivin promoter and the reporter gene luciferase was tested in established and primary glioma cells, normal astrocytic cells, and normal human brain tissues. High levels of reporter gene expression were observed in established tumor and primary tumor cell lines and low levels of expression in astrocytes and normal human brain tissue. To test oncolytic potency, the authors constructed survivin promoter–based conditionally replicative adenoviruses (CRAds), composed of survivin promoter–regulated E1 gene expression and an RGD-4C capsid modification. These CRAds could efficiently replicate within and kill a variety of established glioma tumor cells, but were inactive in a normal human liver organ culture. Finally, survivin promoter–based CRAds significantly inhibited the growth of glioma xenografts in vivo.

Conclusions

Together these data indicate that the survivin promoter is a promising tumor-specific promoter for transcriptional targeting of adenovirus-based vectors and CRAds for malignant gliomas. The strategy of using survivin–CRAds may thus translate into an experimental therapeutic approach that can be used in human clinical trials.

Telomeres and telomerase as targets for anticancer drug development

In most human cancers, the telomere erosion problem has been bypassed through the activation of a telomere maintenance system (usually activation of telomerase). Therefore, telomere and telomerase are attractive targets for anti-cancer therapeutic interventions. Here, we review a large panel of strategies that have been explored to date, from small inhibitors of the catalytic sub-unit of telomerase to anti-telomerase immunotherapy and gene therapy. The many positive results that are reported from anti-telomere/telomerase assays suggest a prudent optimism for a possible clinical application in a close future. However, we discuss some of the main limits for these approaches of antitumour drug development and why significant work remains before a clinically useful drug can be proposed to patients.

Conditionally replicative adenoviral vectors for malignant glioma

High-grade gliomas constitute an important challenge to modern medicine, and although great effort has been made to prolong patient survival, the prognosis for this disease remains poor. Due to recent discoveries in the molecular basis of gliomas, gene therapy is becoming a promising alternative. In this review, we discuss the use of conditionally replicative adenoviral vectors (CRAd) and their applications in neuro-oncology. Such vectors, when rendered conditionally replicative via transductional and transcriptional modifications, offer great promise for patients with malignant brain tumours. We review data from preclinical and clinical studies utilising such vectors and discuss the limitations and future perspectives of CRAd oncolytic therapy for malignant glioma.

Potential utility of BimS as a novel apoptotic therapeutic molecule

We have previously demonstrated a 1000-fold induction of gene expression exclusive to Epstein-Barr virus (EBV)-positive nasopharyngeal carcinoma (NPC) cells using an adenoviral vector (ad5.oriP). This platform allows us to explore tumor-specific gene therapy with BimS (ad5.oriP.BimS), a potent proapoptotic Bcl-2 family member. Ad5.oriP.BimS (25 infectious units (ifu)/cell) reduced C666-1 viability in a time- and dose-dependent manner to 15% survival. The effect was enhanced with radiation (6 Gy). Three days after infection, the proportion of apoptotic cells increased from 3.5% (control) to 47.5% (25 ifu/cell). Confocal microscopy demonstrated Bim colocalization to the mitochondria within 18 h of ad5.oriP.BimS infection. Ad5.oriP.BimS induced a 2.8-, 2.1-, and 1.85-fold increase in caspase-3, -8, and -9 activities, respectively. When C666-1 cells were infected with ad5.oriP.BimS (20 ifu/cell), no tumors formed in 7/9 mice followed for 100 days. Six intratumoral injections of ad5.oriP.BimS (1.5 x 10(9) ifu/dose) in combination with radiation were sufficient to cause almost complete disappearance of established C666-1 or C15 xenograft tumors. Intravenous injections of ad5.oriP.BimS (10(9) ifu) induced mild perturbation in liver function tests, associated with hepatocyte apoptoses and mitoses. This vector appears to be safe and effectively cytotoxic to EBV-positive NPC cells both in vitro and in vivo, mediated primarily through the induction of apoptosis.

Therapeutic efficacy of PUMA for malignant glioma cells regardless of p53 status

Replacement of the p53 tumor suppressor gene is a rational approach to the management of malignant gliomas because p53 is frequently mutated or inactivated in these cancers. Major weaknesses of this approach are that malignant gliomas are mixtures of cells with wild-type and mutant p53, and that tumor cells exhibiting wildtype p53 are resistant to p53 gene transfer. An effective alternative is needed to overcome these difficulties. p53-upregulated modulator of apoptosis (PUMA) was identified as a p53-inducible proapoptotic molecule. Our purpose was to elucidate a role for PUMA in p53 gene therapy and to investigate whether PUMA is an efficient substitute for p53 in cancer therapy. We demonstrated that PUMA was upregulated in mutant p53 malignant glioma cells (U373-MG and T98G) undergoing apoptosis but was not upregulated in apoptosis-resistant wild-type p53 malignant glioma cells (U87-MG and D54) after adenoviral transfer of p53. Overexpression of PUMA resulted in massive apoptosis associated with mitochondrial damage and caspase-3 activation in all tumor cells tested. Use of the human telomerase reverse transcriptase (hTERT) promoter system induced apoptosis only in malignant glioma cells with telomerase activity, while sparing normal cells lacking telomerase. The ability of PUMA to induce apoptosis was greater than that of caspase-6 or caspase-8 transfer, using the same system. Moreover, exogenous expression of PUMA under the hTERT promoter system significantly suppressed the growth of subcutaneous U87-MG tumors in nude mice and did not induce apoptosis in surrounding nontumor tissues. These results indicate that PUMA, which is regulated under a tumor-specific expression system such as the hTERT promoter, may be better than p53 as a therapeutic tool for malignant gliomas.

Antitumor efficacy and tumor-selective replication with a single intravenous injection of OAS403, an oncolytic adenovirus dependent on two prevalent alterations in human cancer

A potentially promising treatment of metastatic cancer is the systemic delivery of oncolytic adenoviruses. This requires engineering viruses which selectively replicate in tumors. We have constructed such an oncolytic adenovirus, OAS403, in which two early region genes are under the control of tumor-selective promoters that play a role in two key pathways involved in tumorigenesis. The early region E1A is controlled by the promoter for the E2F-1 gene, a transcription factor that primarily upregulates genes for cell growth. The E4 region is under control of the promoter for human telomerase reverse transcriptase, a gene upregulated in most cancer cells. OAS403 was evaluated in vitro on a panel of human cells and found to elicit tumor-selective cell killing. Also, OAS403 was less toxic in human hepatocyte cultures, as well as in vivo when compared to an oncolytic virus that lacked selective E4 control. A single intravenous injection of 3 x 10(12) vp/kg in a Hep3B xenograft mouse tumor model led to significant antitumor efficacy. Additionally, systemic administration in a pre-established LNCaP prostate tumor model resulted in over 80% complete tumor regressions at a tolerable dose. Vector genome copy number was measured in tumors and livers at various times following tail vein injection and showed a selective time-dependent increase in tumors but not livers over 29 days. Furthermore, efficacy was significantly improved when OAS403 treatment was combined with doxorubicin. This virus holds promise for the treatment of a broad range of human cancers including metastatic disease.

Death receptor 4 (DR4) efficiently kills breast cancer cells irrespective of their sensitivity to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)

Breast cancer cells are generally resistant to induction of apoptosis by treatment with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). In this study, we demonstrate that both TRAIL-sensitive and TRAIL-resistant breast cancer cell lines can be efficiently killed by overexpression of the TRAIL receptor, death receptor 4 (DR4). The extent of cell death depended on the strength of the promoter driving DR4 expression. When driven by the strong CMV promoter, expression of DR4 killed over 90% of cells in five out of six cell lines tested in the absence of exogenous TRAIL. When driven by the relatively weak tumor-specific hTERT promoter, DR4 was less effective alone, but sensitized cells to killing by TRAIL. The extent of TRAIL sensitization depended on the magnitude of hTERT promoter activity. MCF-7 cells were relatively resistant to the action of DR4. We compared expression of the genes involved in transduction and execution of the death receptor-initiated apoptotic stimuli between MCF-7 and DR4-sensitive cell lines. We confirmed that in the panel of cell lines, MCF-7 was the only line deficient in expression of caspase 3. Bcl-2 and FLIP proteins, implicated in suppression of TRAIL-induced apoptosis, were expressed at a higher level.

Telomerase-specific replication-selective virotherapy for human cancer

PURPOSE

Replication-selective tumor-specific viruses present a novel approach for treating neoplastic disease. These vectors are designed to induce virus-mediated lysis of tumor cells after selective viral propagation within the tumor. Telomerase activation is considered to be a critical step in carcinogenesis, and its activity is closely correlated with human telomerase reverse transcriptase (hTERT) expression. We investigated the antitumor effect of the hTERT-specific replication-competent adenovirus on human cancer cells.

EXPERIMENTAL DESIGN

We constructed an adenovirus 5 vector [tumor- or telomerase-specific replication-competent adenovirus (TRAD)], in which the hTERT promoter element drives expression of E1A and E1B genes linked with an internal ribosome entry site, and we examined the selective replication and antitumor effect in human cancer cells in vitro and in vivo.

RESULTS

TRAD induced selective E1A and E1B expression in human cancer cells, but not in normal cells such as human fibroblasts. TRAD replicated efficiently and induced marked cell killing in a panel of human cancer cell lines, whereas replication as well as cytotoxicity was highly attenuated in normal human fibroblasts lacking telomerase activity. In nu/nu mice carrying s.c. human lung tumor xenografts, intratumoral injection of TRAD resulted in a significant inhibition of tumor growth. No evidence of TRAD was identified in tissues outside of the tumors, despite the presence of TRAD in the circulation. Moreover, TRAD replication in the distant, noninjected tumors was demonstrated.

CONCLUSIONS

Our results suggest that the hTERT promoter confers competence for selective replication of TRAD in human cancer cells, an outcome that has important implications for the treatment of human cancers.

Telomere maintenance in clinical medicine

Telomeres, the ends of linear chromosomes, shorten with each round of DNA replication. Loss of telomeric DNA can lead to senescence, a state in which cells no longer divide, and crisis, which triggers cell death. To prevent these phenomena, cancer and stem cells must maintain their telomeres, for example, by expressing telomerase, an enzyme that can extend telomeres. As our knowledge of telomere maintenance increases, opportunities arise for translating telomere biology into clinical medicine. Areas of current investigation include the development of diagnostic and prognostic markers for cancer; the development of chemotherapeutic agents based on telomerase inhibition, an immune response to telomerase, or telomerase-based gene therapy; and engineering rejuvenated tissues by restoring telomerase expression.

The death effector domain protein family

Apoptosis signaling is regulated and executed by specialized proteins that often carry protein/protein interaction domains. One of these domains is the death effector domain (DED) that is predominantly found in components of the death-inducing signaling complex, which forms at the members of the death receptor family following their ligation. Both proapoptotic- and antiapoptotic-DED-containing proteins have been identified, which makes these proteins exquisitely suited to the regulation of apoptosis. Aside from their pivotal role in the control of the apoptotic program, DED-containing proteins have recently been demonstrated to exert their influence on other cellular processes as well, including cell proliferation. These data highlight the multiple roles for the members of this family, suggesting that they are suited to control both life and death decisions of cells. Additionally, because they can act proapoptotically, antiapoptotically, or in the regulation of the cell cycle, this family of proteins may be excellent candidates for cancer therapy targets. Oncogene (2003) 22, 8634-8644. doi:10.1038/sj.onc.1207103

Immunotherapy and biological modifiers for the treatment of malignant brain tumors

The relative ineffectiveness of current therapies for malignant gliomas has led to the need for novel therapeutics. Therapies based on biologic modifiers are among a variety of cancer treatments currently in use or under experimental evaluation and have shown great promise, especially since several potent stimulators of the immune system have been cloned and are now available for clinical use. Early attempts at glioma therapy based on biologic modifiers, however, have failed to demonstrate significant effectiveness. In this review, we select and summarize the results of preclinical and clinical studies published during the past two years that focus on immunotherapy and biologic modifiers for treating gliomas. Despite limited clinical success, we conclude that an increased understanding of molecular biology and immunology from recent studies may pave the way for more effective approaches.

Current and Future Gene Therapy for Malignant Gliomas

Malignant gliomas are the most common neoplasm in the central nervous system. When treated with conventional treatments including surgery, irradiation, and chemotherapy, the average life expectancy of the most malignant type, glioblastoma multiforme is usually less than 1 year. Therefore, gene therapy is expected to be an effective and possibly curative treatment. Many gene therapeutic approaches have demonstrated efficacy in experimental animal models. However, the current clinical trials are disappointing. This review focuses on current therapeutic genes/vectors/delivery systems/targeting strategies in order to introduce updated trends and hopefully indicate prospective gene therapy for malignant gliomas.