A binary adenoviral vector system for expressing high levels of the proapoptotic gene bax

BCL-2 family isoforms in apoptosis and cancer

The BCl-2 family has long been identified for its role in apoptosis. Following the initial discovery of BCL-2 in the context of B-cell lymphoma in the 1980s, a number of homologous proteins have since been identified. The members of the Bcl-2 family are designated as such due to their BCL-2 homology (BH) domains and involvement in apoptosis regulation. The BH domains facilitate the family members’ interactions with each other and can indicate pro- or anti-apoptotic function. Traditionally, these proteins are categorised into one of the three subfamilies; anti-apoptotic, BH3-only (pro-apoptotic), and pore-forming or ‘executioner’ (pro-apoptotic) proteins. Each of the BH3-only or anti-apoptotic proteins has a distinct pattern of activation, localisation and response to cell death or survival stimuli. All of these can vary across cell or stress types, or developmental stage, and this can cause the delineation of the roles of BCL-2 family members. Added to this complexity is the presence of relatively uncharacterised isoforms of many of the BCL-2 family members. There is a gap in our knowledge regarding the function of BCL-2 family isoforms. BH domain status is not always predictive or indicative of protein function, and several other important sequences, which can contribute to apoptotic activity have been identified. While therapeutic strategies targeting the BCL-2 family are constantly under development, it is imperative that we understand the molecules, which we are attempting to target. This review, discusses our current knowledge of anti-apoptotic BCL-2 family isoforms. With significant improvements in the potential for splicing therapies, it is important that we begin to understand the distinctions of the BCL-2 family, not limited to just the mechanisms of apoptosis control, but in their roles outside of apoptosis.

Generation of apoptosis-resistant HEK293 cells with CRISPR/Cas mediated quadruple gene knockout for improved protein and virus production

Apoptosis has important functions during pathophysiologic processes. However, from a biopharmaceutical point of view, active apoptosis of host cells is undesirable during viral packaging or protein expression, because it decreases the efficiency of viral or protein production. Here we used the CRISPR/Cas technique to knock out four pro-apoptotic genes, Caspase3, Caspase6, Caspase7 and AIF1, in HEK293 cells, and successfully produced an apoptosis-resistant cell line. Furthermore, this cell line showed higher expression levels of pro-apoptotic proteins and higher packaging efficiency for the virus carrying these proteins than control HEK293 cells. This study not only produced an apoptosis-resistant cell line that is useful in producing apoptosis-inducing proteins or viruses expressing these proteins, but also provides a methodology to build other apoptosis-resistant cell lines.

Apoptotic activity of 5-fluorouracil in breast cancer cells transformed by low doses of ionizing α-particle radiation

Globally, breast cancer in women is the leading cause of cancer death. This fact has generated an interest to obtain insight into breast tumorigenesis and also to develop drugs to control the disease. Ras is a proto-oncogene that is activated as a response to extracellular signals. As a member of the Ras GTPase superfamily, Rho-A is an oncogenic and a critical component of signaling pathways leading to downstream gene regulation. In chemotherapy, apoptosis is the predominant mechanism by which cancer cells die. However, even when the apoptotic machinery remains intact, survival signaling may antagonize the cell death by signals. The aim of this study was to evaluate 5-fluorouracil (5-FU) in cells transformed by low doses of ionizing α-particle radiation, in breast cancer cell lines on these genes, as well as apoptotic activity. We used two cell lines from an in vitro experimental breast cancer model. The MCF-10F and Tumor2 cell lines. MCF-10F was exposed to low doses of high linear energy transfer (LET) α-particles radiation (150 keV/µm). Tumor2, is a malignant and tumorigenic cell line obtained from Alpha5 (60cGy+E/60cGy+E) injected into the nude mice. Results indicated that 5-FU decreased H-ras, Rho-A, p53, Stat1 and increased Bax gene expression in Tumor2 and decreased Rac1, Rho-A, NF-κB and increased Bax and caspase-3 protein expression in Tumor2. 5-FU decreased H-ras, Bcl-xL and NF-κB and increased Bax gene expression. 5-FU decreased Rac1, Rho-A protein expression and increased Bax and caspase-3 protein expression in MDA-MB-231. Flow cytometry indicated 21.5% of cell death in the control MCF-10F and 80% in Tumor2 cell lines. It can be concluded that 5-FU may exert apoptotic activity in breast cancer cells transformed by low doses of ionizing α-particles in vitro regulating genes of Ras family and related to apoptosis such as Bax, Bcl-xL and NF-κB expression.

Doxorubicin Changes Bax /Bcl-xL Ratio, Caspase-8 and 9 in Breast Cancer Cells

PURPOSE

Doxorubicin is administrated as a single agent in first-line therapy of breast cancer to induce apoptosis in tumor cells. Bax, Bcl-xL, Caspase-8 and 9 proteins are involved in induction of apoptosis. The present study describes Bax, Bcl-xL gene expression and Caspase-8 and 9 protein levels in MCF-7 cells incubated with doxorubicin at different doses an incubation times.

METHODS

The cytotoxic effects of doxorubicin were studied using MTT assay. MCF-7 cells were treated with three concentrations of doxorubicin (0.1, 0.5, 1 μM) and incubated for 24, 48 and 72 hours then expression levels of Bax and Bcl-xL genes were elucidated by Real-time RT-PCR technique and protein levels of caspase-8 and caspase-9 proteins were measured using ELISA method. Morphological modifications of the cells were also monitored via light microscopic images.

RESULTS

Doxorubicin decreased the anti-apoptotic Bcl-xL and increased pro-apoptotic Bax mRNA levels. Doxorubicin induced a significant increase in Bax /Bcl-xL ratio in all doses and incubation times (p<0.05). Highest (more than 10 fold) increase in Bax /Bcl-xL ratio was revealed after 48 h incubation of the cells with in all doses of doxorubicin. Doxorubicin also increased caspase-9 level in a time and dose-dependent manner, while caspase-8 level didn't follow time and dose dependency pattern.

CONCLUSION

Our results confirm that doxorubicin induces mitochondrial-dependent apoptosis by down-regulation of Bcl-xL and up- regulation of Bax and caspase-9 expressions.

Curcumin conjugates induce apoptosis via a mitochondrion dependent pathway in MCF-7 and MDA-MB-231 cell lines

In order to enhance the bioavailability of curcumin its conjugates with piperic acid and glycine were synthesized by esterifying the 4 and 4' phenolic hydroxyls, the sites of metabolic conjugation. Antiproliferative and apoptotic efficacy of synthesized conjugates was investigated in MCF-7 and MDA-MB-231 cell lines. IC50 values of di-O-glycinoyl (CDG) and di-O-piperoyl (CDP) esters of curcumin were found to be comparable with that of curcumin. Both conjugates induced chromatin condensation fragmentation and apoptotic body formation. CDP exposure to MCF-7 cells induced apoptosis initiating loss of mitochondrial membrane potential (Δψm) followed by inhibition of translocation of transcription factor NF-kB and release of Cytochrome-C. Reactive oxygen species (ROS) production was evaluated by fluorescent activated cell sorter. Change in ratio of Bcl2/ Bclxl was observed, suggesting permeablization of mitochondrial membrane leading to the release of AIF, Smac and other apoptogenic molecules. DNA fragmentation as a hallmark for apoptosis was monitored by TUNEL as well as agrose gel electrophoresis. Thus, it was proven that conjugation does not affect the therapeutic potential of parent molecule in vitro, while these could work in vivo as prodrugs with enhanced pharmacokinetic profile. Pharmacokinetics of these molecules under in vivo conditions is a further scope of this study.

Bax and Bak function as the outer membrane component of the mitochondrial permeability pore in regulating necrotic cell death in mice

A critical event in ischemia-based cell death is the opening of the mitochondrial permeability transition pore (MPTP). However, the molecular identity of the components of the MPTP remains unknown. Here, we determined that the Bcl-2 family members Bax and Bak, which are central regulators of apoptotic cell death, are also required for mitochondrial pore-dependent necrotic cell death by facilitating outer membrane permeability of the MPTP. Loss of Bax/Bak reduced outer mitochondrial membrane permeability and conductance without altering inner membrane MPTP function, resulting in resistance to mitochondrial calcium overload and necrotic cell death. Reconstitution with mutants of Bax that cannot oligomerize and form apoptotic pores, but still enhance outer membrane permeability, permitted MPTP-dependent mitochondrial swelling and restored necrotic cell death. Our data predict that the MPTP is an inner membrane regulated process, although in the absence of Bax/Bak the outer membrane resists swelling and prevents organelle rupture to prevent cell death.

DOI:http://dx.doi.org/10.7554/eLife.00772.001

In all multicellular plants and animals, cells are continuously dying and being replaced. There are a number of different types of cell death, but two of the best studied are apoptosis and necrosis. Apoptosis, sometimes referred to as ‘cell suicide’, is a form of programmed cell death that is generally beneficial to the organism. Necrosis, however, occurs whenever cells are damaged—for example, due to a lack of oxygen—and can trigger harmful inflammation in surrounding tissue. Although the processes leading up to apoptosis and necrosis are very different, they both involve regulated changes in mitochondria—the organelles that supply cells with chemical energy.

Mitochondria have a distinctive appearance, being enclosed by two membranes, the innermost of which is highly folded. During apoptosis, large pores form in the outer membranes of mitochondria. These pores are generated by two proteins—Bax and Bak—and they enable the mitochondrion to release proteins that activate processes involved in apoptosis. Pores also form in the mitochondrial membrane during necrosis. However, these mitochondrial permeability transition pores (MPTPs) occur simultaneously in both the inner and outer membranes and are thought to lead to swelling and rupture of mitochondria.

Now, Karch et al. have shown that Bax and Bak are also involved in the formation of these permeability pores that underlie necrosis. When mouse cells that had been genetically modified to lack Bak and Bax were grown in cell culture, they were found to be resistant to substances that normally induce necrosis. Instead, their mitochondria continued to function normally, suggesting that MPTPs cannot form in the absence of Bak and Bax.

Karch et al. then generated mice with heart cells that lack Bax and Bak, and deprived their hearts of oxygen to simulate a heart attack. Compared to normal mice, the genetically modified animals experienced less damage to their heart muscle, suggesting that the absence of Bax and Bak prevents cell death due to necrosis. If Bax and Bak are involved in both apoptosis and necrosis, inhibiting them could be a powerful therapeutic approach for preventing all forms of cell death during heart attacks or in certain degenerative diseases.

DOI:http://dx.doi.org/10.7554/eLife.00772.002

Data-driven modeling of SRC control on the mitochondrial pathway of apoptosis: implication for anticancer therapy optimization

Src tyrosine kinases are deregulated in numerous cancers and may favor tumorigenesis and tumor progression. We previously described that Src activation in NIH-3T3 mouse fibroblasts promoted cell resistance to apoptosis. Indeed, Src was found to accelerate the degradation of the pro-apoptotic BH3-only protein Bik and compromised Bax activation as well as subsequent mitochondrial outer membrane permeabilization. The present study undertook a systems biomedicine approach to design optimal anticancer therapeutic strategies using Src-transformed and parental fibroblasts as a biological model. First, a mathematical model of Bik kinetics was designed and fitted to biological data. It guided further experimental investigation that showed that Bik total amount remained constant during staurosporine exposure, and suggested that Bik protein might undergo activation to induce apoptosis. Then, a mathematical model of the mitochondrial pathway of apoptosis was designed and fitted to experimental results. It showed that Src inhibitors could circumvent resistance to apoptosis in Src-transformed cells but gave no specific advantage to parental cells. In addition, it predicted that inhibitors of Bcl-2 antiapoptotic proteins such as ABT-737 should not be used in this biological system in which apoptosis resistance relied on the deficiency of an apoptosis accelerator but not on the overexpression of an apoptosis inhibitor, which was experimentally verified. Finally, we designed theoretically optimal therapeutic strategies using the data-calibrated model. All of them relied on the observed Bax overexpression in Src-transformed cells compared to parental fibroblasts. Indeed, they all involved Bax downregulation such that Bax levels would still be high enough to induce apoptosis in Src-transformed cells but not in parental ones. Efficacy of this counterintuitive therapeutic strategy was further experimentally validated. Thus, the use of Bax inhibitors might be an unexpected way to specifically target cancer cells with deregulated Src tyrosine kinase activity.

Targeting the Bcl-2 family for cancer therapy

INTRODUCTION

Programmed cell death is well-orchestrated process regulated by multiple pro-apoptotic and anti-apoptotic genes, particularly those of the Bcl-2 gene family. These genes are well documented in cancer with aberrant expression being strongly associated with resistance to chemotherapy and radiation.

AREAS COVERED

This review focuses on the resistance induced by the Bcl-2 family of anti-apoptotic proteins and current therapeutic interventions currently in preclinical or clinical trials that target this pathway. Major resistance mechanisms that are regulated by Bcl-2 family proteins and potential strategies to circumvent resistance are also examined. Although antisense and gene therapy strategies are used to nullify Bcl-2 family proteins, recent approaches use small molecule inhibitors (SMIs) and peptides. Structural similarity of the Bcl-2 family of proteins greatly favors development of inhibitors that target the BH3 domain, called BH3 mimetics.

EXPERT OPINION

Strategies to specifically identify and inhibit critical determinants that promote therapy resistance and tumor progression represent viable approaches for developing effective cancer therapies. From a clinical perspective, pretreatment with novel, potent Bcl-2 inhibitors either alone or in combination with conventional therapies hold significant promise for providing beneficial clinical outcomes. Identifying SMIs with broader and higher affinities for inhibiting all of the Bcl-2 pro-survival proteins will facilitate development of superior cancer therapies.

BAX gene over-expression via nucleofection to induce apoptosis in human lens epithelial cells

Despite significant advances in cataract surgery techniques, posterior capsule opacification (PCO) remains a common complication. In PCO, remaining epithelial cells cloud the lens capsule and impair postoperative vision. This in vitro study was designed to investigate the potential of a gene-based approach, specifically over-expression of the proapoptotic BAX gene, to prevent PCO. Human lens epithelial cells (HLECs) were transfected by nucleofection with a plasmid encoding a fusion protein of green fluorescent protein and human BAX. The expression levels of BAX and its antiapoptotic counterpart BCL2 were determined by realtime reverse transcription polymerase chain reaction, Western blotting and immunofluorescence. BAX over-expression-induced cell death was analyzed by fluorescence-activated cell sorting using the Annexin V antibody. Fluorescence microscopy and transmission electron microscopy were used to assess changes in morphology and ultrastructure. Differential expression of the downstream apoptosis-related factor, caspase 3, was detected by Western blotting. Nucleofection efficiency was high (nearly 80%). BAX-transfected HLECs showed remarkably enhanced BAX gene expression and BAX:BCL2 ratio, but relatively little change in endogenous BCL2 expression. BAX over-expression also led to significant cytotoxicity, induction of apoptosis-related characteristics and activation of caspase 3. In conclusion, our results indicate that BAX gene over-expression can trigger cell death in HLECs via an apoptotic pathway. Thus, BAX may be a promising candidate for human gene therapy to treat PCO.

Gene transfer: the challenge of regulated gene expression

Gene therapy is expected to have a major impact on human healthcare in the future. However, precise regulation of therapeutic gene expression in vivo is still a challenge. Natural and synthetic enhancer-promoters (EPs) can be utilized to drive gene transcription in a temporal, spatial or environmental signal-inducible manner in response to heat shock, hypoxia, radiation, chemotherapy, epigenetic agents or viral infection. To allow tightly regulated expression, a regulatable gene-expression system can also be implemented. Most of these systems are based on small molecule (drug)-responsive artificial transactivators. In this review, we aim to provide a brief overview of the classes of EPs and regulatable systems, along with lessons learned from these studies. We highlight the potential applications in gene transfer, gene therapy for cancer and genetic disease and the future challenges for clinical applications.

Improving the titer of recombinant adenovirus by suppressing problematic transgene transcription during packaging

A new strategy to package "problematic" transgenes in adenovirus was developed that was based on modifications of the tetracycline-inducible system. This strategy used two components: the adenoviral genome containing the transgene under control of a hybrid TRE promoter/SV40 enhancer and a trans-encoded tTS suppressor Using luciferase reporters, expression of tTS in 293A cells reduced transcription from the promoter/enhancer 25-fold. Procaspase 8 adenovirus was then tested, since it is known to package poorly with standard adenoviral systems. Expression of tTS in 293A cells increased the titer of procaspase 8 adenovirus by 22-fold in initial viral packaging (using transiently transfected tTS) and 9-fold in subsequent viral reamplification (using 293A cells stably expressing tTS). The Tac antigen gene (i.e., CD25), which packages in adenovirus without difficulty, was also tested as a control. In contrast to that observed with procaspase 8, tTS expression did not alter the titer obtained when packaging the CD25 gene, thus excluding nonspecific effects of tTS expression on adenoviral titer Since tTS was provided in trans and did not package in the resulting adenoviruses, strong transcription of the transgenes occurred in transducted cells without the need of additional reagents.

Adenovirus-mediated small hairpin RNA targeting Bcl-XL as therapy for colon cancer

Bcl-XL, an anti-apoptotic protein of Bcl-2 family, is overexpressed in colon cancers. To determine Bcl-XL's potential feasibility as a therapeutic target, we constructed a recombinant adenovirus that expressed a U6 promoter-driven small hairpin RNA (shRNA) targeting Bcl-XL (Ad/Bcl-XL shRNA) and evaluated the vector's ability to induce RNA interference in vivo and alter apoptosis induction in colon cancer cells and tumours. Ad/Bcl-XL shRNA effectively knocked down Bcl-XL expression in colon cancer cells and decreased their viability. Treatment with Ad/Bcl-XL shRNA but not control vectors led to dramatically increased cleavage of cellular apoptosis-related enzymes caspase-9, caspase-3 and poly(ADP-ribose) polymerase. Ad/Bcl-XL shRNA also significantly suppressed the growth of subcutaneous tumours derived from DLD1 cells in a nude mouse model and did so without causing any obvious damage to normal tissues or normal human fibroblasts. Together, our results support the feasibility of using adenovirus-mediated RNA interference therapy targeting Bcl-XL against colon cancers and warrant further studies of its safety and efficacy.

Mitochondrial medicine: pharmacological targeting of mitochondria in disease

Mitochondria play a central role in cell life and death and are known to be important in a wide range of diseases including the cancer, diabetes, cardiovascular disease, and the age-related neurodegenerative diseases. The unique structural and functional characteristics of mitochondria enable the selective targeting of drugs designed to modulate the function of this organelle for therapeutic gain. This review discusses mitochondrial drug targeting strategies and a variety of novel mitochondrial drug targets including the electron transport chain, mitochondrial permeability transition, Bcl-2 family proteins and mitochondrial DNA. Mitochondrial drug-targeting strategies will open up avenues for manipulating mitochondrial functions and allow for selective protection or eradication of cells for therapeutic gain in a variety of diseases.

Voltage-dependent anion channels are dispensable for mitochondrial-dependent cell death

Mitochondria are critically involved in necrotic cell death induced by Ca(2+) overload, hypoxia and oxidative damage. The mitochondrial permeability transition (MPT) pore - a protein complex that spans both the outer and inner mitochondrial membranes - is considered the mediator of this event and has been hypothesized to minimally consist of the voltage-dependent anion channel (Vdac) in the outer membrane, the adenine-nucleotide translocase (Ant) in the inner membrane and cyclophilin-D in the matrix. Here, we report the effects of deletion of the three mammalian Vdac genes on mitochondrial-dependent cell death. Mitochondria from Vdac1-, Vdac3-, and Vdac1-Vdac3-null mice exhibited a Ca(2+)- and oxidative stress-induced MPT that was indistinguishable from wild-type mitochondria. Similarly, Ca(2+)- and oxidative-stress-induced MPT and cell death was unaltered, or even exacerbated, in fibroblasts lacking Vdac1, Vdac2, Vdac3, Vdac1-Vdac3 and Vdac1-Vdac2-Vdac3. Wild-type and Vdac-deficient mitochondria and cells also exhibited equivalent cytochrome c release, caspase cleavage and cell death in response to the pro-death Bcl-2 family members Bax and Bid. These results indicate that Vdacs are dispensable for both MPT and Bcl-2 family member-driven cell death.

Novel system uses probasin-based promoter, transcriptional silencers and amplification loop to induce high-level prostate expression

BACKGROUND

Despite several effective treatment options available for prostate cancer, it remains the second leading cause of cancer death in American men. Thus, there is a great need for new treatments to improve outcomes. One such strategy is to eliminate cancer through the expression of cytotoxic genes specifically in prostate cells by gene therapy vectored delivery. To prevent systemic toxicity, tissue- and/or cancer-specific gene expression is required. However, the use of tissue- or cancer-specific promoters to target transgene expression has been hampered by their weak activity.

RESULTS

To address this issue, we have developed a regulation strategy that includes feedback amplification of gene expression along with a differentially suppressible tetracycline regulated expression system (DiSTRES). By differentially suppressing expression of the tetracycline-regulated transcriptional activator (tTA) and silencer (tTS) genes based on the cell origin, this leads to the activation and silencing of the TRE promoter, respectively. In vitro transduction of LNCaP cells with Ad/GFPDiSTRES lead to GFP expression levels that were over 30-fold higher than Ad/CMV-GFP. Furthermore, Ad/FasL-GFPDiSTRES demonstrated cytotoxic effects in prostate cancer cells known to be resistant to Fas-mediated apoptosis.

CONCLUSION

Prostate-specific regulation from the DiSTRES system, therefore, serves as a promising new regulation strategy for future applications in the field of cancer gene therapy and gene therapy as a whole.

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery due to the usual finding of advanced disease at diagnosis. Attempts to improve survival in advanced disease using various combinations of chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Techniques have been developed that allow transfer of functional genes into mammalian cells, such as those that block activated tumor-promoting oncogenes and/or those that replace inactivated tumor-suppressing or apoptosis-promoting genes. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas, and will then review the status of gene therapies for treatment of lung cancer.

Therapy-induced apoptosis in primary tumors

An enormous body of literature has accumulated over the past 15 years implicating apoptosis (programmed cell death) in breast cancer cell death induced by conventional and investigational cancer therapies in preclinical models. As a result, new therapeutic approaches that directly target key components of apoptotic pathways are either entering or will soon enter clinical trials in patients, raising hopes that the information gained from the preclinical studies can be translated to improve patient care. However, there is a new appreciation for the fact that apoptosis is not the only relevant pathway that mediates physiological cell death, and many investigators are challenging the notion that targeting apoptosis is the best means of optimizing therapeutic efficacy in primary tumors. Here I will review some of the basic concepts that have emerged from the study of apoptosis in preclinical models, the evidence that apoptosis does or does not mediate the effects of current front line therapies in patients, and the new strategies that are emerging that are designed to more directly target apoptotic pathways.

Mitochondria: a target for cancer therapy

Mitochondria, the cells powerhouses, are essential for maintaining cell life, and they also play a major role in regulating cell death, which occurs upon permeabilization of their membranes. Once mitochondrial membrane permeabilization (MMP) occurs, cells die either by apoptosis or necrosis. Key factors regulating MMP include calcium, the cellular redox status (including levels of reactive oxygen species) and the mobilization and targeting to mitochondria of Bcl-2 family members. Contemporary approaches to targeting mitochondria in cancer therapy use strategies that either modulate the action of Bcl-2 family members at the mitochondrial outer membrane or use specific agents that target the mitochondrial inner membrane and the mitochondrial permeability transition (PT) pore. The aim of this review is to describe the major mechanisms regulating MMP and to discuss, with examples, mitochondrial targeting strategies for potential use in cancer therapy.

Gene therapy for lung cancer

Lung cancer patients suffer a 15% overall survival despite advances in chemotherapy, radiation therapy, and surgery. This unacceptably low survival rate is due to the usual finding of advanced disease at diagnosis. However, multimodality strategies using conventional therapies only minimally improve survival rates even in early stages of lung cancer. Attempts to improve survival in advanced disease using various combinations of platinum-based chemotherapy have demonstrated that no regimen is superior, suggesting a therapeutic plateau and the need for novel, more specific, and less toxic therapeutic strategies. Over the past three decades, the genetic etiology of cancer has been gradually delineated, albeit not yet completely. Understanding the molecular events that occur during the multistep process of bronchogenic carcinogenesis may make these tasks more surmountable. During these same three decades, techniques have been developed which allow transfer of functional genes into mammalian cells. For example, blockade of activated tumor-promoting oncogenes or replacement of inactivated tumor-suppressing or apoptosis-promoting genes can be achieved by gene therapy. This article will discuss the therapeutic implications of these molecular changes associated with bronchogenic carcinomas and will then review the status of gene therapies for treatment of lung cancer.

Proteolytic cleavage of Livin (ML-IAP) in apoptotic melanoma cells potentially mediated by a non-canonical caspase

BACKGROUND

Several inhibitor of apoptosis proteins (IAPs) are cleaved during apoptosis. Studies of the melanoma-associated IAP (ML-IAP) Livin, using recombinant molecules, have implicated both caspases 3/7 and the serine protease Omi/HtrA2 in its proteolytic cleavage.

OBJECTIVE

To characterize the apoptotic cleavage of Livin in melanocytic cells, and evaluate the role of known proteases.

METHODS

We assessed the capacity of a variety of stimuli to induce Livin cleavage in human melanoma cell lines and normal human melanocytes. The role of caspases and Omi was examined using caspase inhibitors and RNAi, respectively. A potential caspase substrate was further examined by site-directed mutagenesis. Deletion mapping was used to identify the cleavage site.

RESULTS

Livin cleavage was observed in multiple human melanoma cell lines in response to a variety of apoptotic stimuli (UVB, 4-TBP, cisplatin, TNF, Bax), and not affected by the addition of various protease inhibitors or RNAi-mediated silencing of Omi/HtrA2. Livin cleavage induced by 4-TBP, but not UVB or cisplatin, was blocked by the pan-caspase inhibitor zVAD-fmk. Mutation of Asp52 to Glu in Livin did not affect cleavage, while either mutation of Asp52 to Ala, deletion of Asp52, or deletion of the adjacent region (residues 53-61) abrogated cleavage.

CONCLUSION

Livin cleavage, induced by multiple apoptotic stimuli in melanoma cells, likely occurs in an Omi-independent fashion at residue 52 within its potential caspase substrate (DHVD52). However, relative insensitivity of the apoptotic cleavage to zVAD-fmk, or Asp52 to Glu mutation, suggests the involvement of a non-canonical caspase.

Prevention of posterior capsule opacification by the induction of therapeutic apoptosis of residual lens cells

Posterior capsule opacification (PCO) is a common complication of cataract surgery. Using adenovirus(Ad)-mediated gene transfer, we overexpressed the proapoptotic molecules p53, procaspase 3, Bax, and TRAIL to induce therapeutic programmed cell death of residual lens cells to prevent PCO. Overexpressed TRAIL did not induce apoptosis in cultured rabbit lens cells or in human lens cells. Overexpressed p53 induced apoptosis of lens cells in vitro and ex vivo, but was unable to prevent PCO in vivo. Overexpressed procaspase 3 was associated with engagement of many components of the apoptotic pathway, including cleavage of intracellular caspase targets such as PARP and inter-nucleosome DNA fragmentation. Even when only slightly overexpressed, Bax caused apoptosis of transduced rabbit and human lens cells by engaging the mitochondrial pathway, including catalytic activation of the caspases. A single in vivo injection of Ad vectors expressing either Bax or procaspase 3 into the capsular bag at the end of phacoemulsification prevented PCO in rabbits. These experiments show that Ad-mediated Bax or procaspase 3 overexpression is capable of inducing therapeutic programmed cell death in vitro and in vivo in residual lens cells and preventing PCO in a rabbit model of PCO. Manipulation of proapoptotic molecule expression could be a novel gene therapy approach for prevention of PCO.

Transcriptional targeting of adenovirus vectors with the squamous cell carcinoma-specific antigen-2 promoter for selective apoptosis induction in lung cancer

Squamous cell carcinoma antigens SCCA1 and SCCA2 are highly homologous serine proteinase inhibitors which have been widely utilized as serological markers for squamous cell cancers, but it has recently been demonstrated that only SCCA2 is truly specific for certain forms of lung cancer. Using a construct containing the 5'-flanking region of the SCCA2 gene between -460 and +0 bp and the luciferase reporter gene, SCCA2 promoter activity was detected in SCCA2-producing SCC cell lines (LK-2, LC-1), but not in SCCA2-nonproducing lung adenocarcinoma cell lines (A549, ABC-1, and RERF-LC-MS) or normal cells (WI-38, SAEC, and NHEK-Adult). Infection with a recombinant adenovirus vector, Ad-SCCA2-DsRed, resulted in cell-specific expression of the SCCA2 promoter-driven DsRed marker gene only in LK-2 and LC-1 cells. The same strategy was used for SCCA2-driven expression of a proapoptotic gene, (KLAKLAK)2, which can cause mitochondrial disruption by triggering mitochondrial permeabilization and swelling, resulting in the release of cytochrome c and induction of apoptosis. Infection with Ad-SCCA2-KLAKLAK2 specifically reduced the growth of the two human lung SCC cell lines compared to the SCCA2 nonproducing cell lines both in vitro and in vivo, suggesting that the SCCA2 promoter had a tumor-specific effect. These results suggest that transduction of SCCA2 promoter-controlled suicide genes by adenoviral vectors can confer transcriptionally targeted cytotoxicity in SCCA2-producing lung SCC cells, and represents a novel strategy for gene transfer specifically targeted to SCC in the lung.

A rapid and efficient method for purification of recombinant adenovirus with arginine-glycine-aspartic acid-modified fibers

Recombinant adenoviral vectors (adenovectors) have been subject to various genetic modifications to improve their transduction efficiency and targeting capacity. Production and purification of adenovectors with modified capsid proteins can be problematic using conventional two-cycle CsCl gradient ultracentrifugation. We have developed a new method for purifying recombinant adenovectors in two steps: iodixanol discontinuous density gradient ultracentrifugation and size exclusion column chromatography. The purity and infectious activity of adenovectors isolated by the two methods were comparable. The new method yielded three to four times more adenovectors with arginine-glycine-aspartic acid (RGD)-modified fiber proteins than did the conventional CsCl method. For other fiber-modified and wild-type adenovectors, the yields of the two methods were comparable. Thus, the iodixanol-based method can be used not only to improve the production of RGD-modified adenovectors but also to purify adenovectors with or without fiber modifications. Moreover, the whole procedure can be completed in 3h. Therefore, this method is rapid and efficient for production of recombination adenovectors, especially those with RGD-modified fibers.

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.

Cancer gene therapy

The prognosis of patients with some kinds of cancers whose patients are often found unresectable upon diagnosis is still dismal. In these fields, development of a new therapeutic modality is needed and gene therapy represents one promising strategy. So far, numerous cancer gene therapy clinical trials based on these principles have been carried out and have shown the safety of such modalities, but have fallen short of the initial expectations to cure cancers. In this review, we would like to make a problem-oriented discussion of current status of cancer gene therapy research by using mainly gastrointestinal cancers as an example. In order to overcome obstacles for full realization of cancer gene therapy, numerous researches have been conducted by many researchers. Various cancer-selective and non-selective genes, as well as lytic viruses themselves have been employed for gene therapy. In the context of gene delivery method, different kinds of viral and non-viral strategies have been utilized. In addition, surrogate assays, such as soluble markers and imaging, have been developed for safer and more informative clinical trials. Many experiments and clinical trials to date have figured out current obstacles for the realization of an effective cancer gene therapy modality. Tireless efforts to overcome such hurdles and continuous infusion of novel concepts into this field should lead to break through technologies and the cure of the patients.

Loss of cyclophilin D reveals a critical role for mitochondrial permeability transition in cell death

Mitochondria play a critical role in mediating both apoptotic and necrotic cell death. The mitochondrial permeability transition (mPT) leads to mitochondrial swelling, outer membrane rupture and the release of apoptotic mediators. The mPT pore is thought to consist of the adenine nucleotide translocator, a voltage-dependent anion channel, and cyclophilin D (the Ppif gene product), a prolyl isomerase located within the mitochondrial matrix. Here we generated mice lacking Ppif and mice overexpressing cyclophilin D in the heart. Ppif null mice are protected from ischaemia/reperfusion-induced cell death in vivo, whereas cyclophilin D-overexpressing mice show mitochondrial swelling and spontaneous cell death. Mitochondria isolated from the livers, hearts and brains of Ppif null mice are resistant to mitochondrial swelling and permeability transition in vitro. Moreover, primary hepatocytes and fibroblasts isolated from Ppif null mice are largely protected from Ca2+-overload and oxidative stress-induced cell death. However, Bcl-2 family member-induced cell death does not depend on cyclophilin D, and Ppif null fibroblasts are not protected from staurosporine or tumour-necrosis factor-alpha-induced death. Thus, cyclophilin D and the mitochondrial permeability transition are required for mediating Ca2+- and oxidative damage-induced cell death, but not Bcl-2 family member-regulated death.

Overcoming acquired resistance to TRAIL by chemotherapeutic agents and calpain inhibitor I through distinct mechanisms

We recently found that repeated application of adenovectors expressing the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or recombinant TRAIL proteins to TRAIL-susceptible cancer cells resulted in selection and expansion of TRAIL-resistant cells. Overcoming this acquired resistance to TRAIL is desirable for TRAIL-mediated cancer therapy. Here we demonstrate that several chemotherapeutic agents, including 5-fluorouracil (5-FU) and mitomycin, and calpain inhibitor I, an NFkappaB inhibitor, can overcome acquired resistance to TRAIL in DLD1 colon cancer cells. The combination of TRAIL (approved gene symbol TNFSF10) gene therapy and 5-FU enhanced tumor suppression in vivo in nude mice bearing subcutaneous tumors established from TRAIL-resistant colon cancer cells. Whereas treatment with the combination of TRAIL and 5-FU or mitomycin led to enhanced activation of caspase-3, the combination of TRAIL and calpain inhibitor I resulted in enhanced activation of both caspase-8 and caspase-3. Moreover, mitomycin, but not 5-FU or calpain inhibitor I, induced overexpression of the BAX gene, which was correlated with enhanced TRAIL-induced cell killing in TRAIL-resistant DLD1 cells. Together, these results suggest that acquired resistance to TRAIL can be overcome by different mechanisms and that combinations of TRAIL gene therapy and chemotherapy may be a useful approach for cancer treatment.

Differential involvement of Bax and Bak in TRAIL-mediated apoptosis of leukemic T cells

TRAIL-induced apoptosis has been considered a promising therapeutic approach for tumors that are resistant to chemotherapy, which is usually mediated via mitochondrial apoptotic cascades. Recent studies have shown that in certain cancer cells, TRAIL-mediated apoptosis is also dependent on mitochondrial involvement, suggesting that similar mechanisms of resistance to chemotherapy might be implicated in the resistance of tumor cells to TRAIL. We have used TRAIL-resistant leukemic cells that are deficient in both Bax and Bak to determine the roles of these Bcl-2 members in TRAIL-mediated apoptosis. Exposure of these cells to TRAIL did not have an impact on cell viability, although it induced the processing of caspase-3 to its active p20 subunit. The activity of the p20 caspase-3 appeared to be inhibited as no autoprocessing of this p20 subunit or cleavage of known caspase-3 substrates were detected. Also, in the absence of Bax and Bak, no release of mitochondrial apoptogenic proteins was observed following TRAIL treatment. Adenoviral transduction of the Bax, but not the Bak gene, to the Bax/Bak-deficient leukemic cells rendered them TRAIL-sensitive as assessed by enhanced apoptotic death and caspase-3 processing. These findings demonstrate preferential utilization of Bax over Bak in leukemic cell response to specific apoptotic stimulation.

Gene therapy for sarcoma utilizing adenoviral transfer of the β-glucuronidase and bax genes and an anthracyline prodrug

BACKGROUND

When acted on by beta-glucuronidase (BG), HMR1826 is metabolized to doxorubicin. Use of this prodrug with adenoviral transfer of beta-glucuronidase (AdBG) is limited by the drug's inability to enter cells and intracellular retention of BG after transduction. We evaluated a system combining AdBG, transfer of the proapoptotic gene bax (AdBax) at a low multiplicity of infection, and HMR1826 administration.

MATERIALS AND METHODS

Fibrosarcoma cells were treated with AdBG alone, AdBG plus HMR1826, AdBG followed by beta-galactosidase (AdLacZ) plus HMR1826, and AdBG followed by AdBax with no prodrug. In the experimental group, cells were transfected with AdBG, followed by AdBax plus HMR1826. Viability was measured 24 h after transfection and prodrug administration. Western blots for BG were performed on cell lysates and supernatants.

RESULTS

Minimal cellular killing was noted in the AdBG alone, AdBG plus HMR 1826, or AdBG:AdLacZ plus HMR 1826 groups, and Western blot did not demonstrate BG in the supernatant even though all AdBG-transfected cell lysates were positive. Cell killing was noted in the AdBG:AdBax group, but less than in the AdBG:AdBax plus HMR 1826 group (without prodrug versus with prodrug: 1:1 to 55.5% versus 75.9%, 5:1 to 10.0% versus 75.9%, 10:1 7.6% versus 49.0%, 20:1 4.6% versus 24.9%, P = 0.037). Western blot demonstrated BG in the supernatant of the AdBG:AdBax groups.

CONCLUSIONS

We have devised a novel enzyme prodrug method of killing tumor cells and engendering a bystander effect. AdBax leads to BG release from dying cells after AdBG transduction and conversion of HMR1826 to an active anthracycline.

Co-delivery of pro-apoptotic BAX with a DNA vaccine recruits dendritic cells and promotes efficacy of autoimmune diabetes prevention in mice

Genetic vaccines encoding pancreatic beta cell antigens can prevent autoimmune (type 1) diabetes when delivered into murine model systems, but there is a need to improve their efficacy. Here, we investigated the effects of intramuscular delivery of DNA coding for the pro-apoptotic protein BAX together with an intracellular or a secreted form of the beta cell antigen glutamic acid decarboxylase (GAD) on diabetes onset and immune responses in non-obese diabetic (NOD) mice. We hypothesized that induction of apoptosis in vaccine-containing cells could lead to GAD tolerance and disease suppression. Remarkably, monitoring of spontaneous diabetes onset indicated that only delivery of DNA coding for secreted GAD and BAX resulted in significant prevention of the disease. Using GFP as a model plasmid-encoded antigen revealed that co-delivery of BAX resulted in the recruitment of GFP-containing dendritic cells (DCs) in the draining lymph nodes and spleen of NOD mice. Furthermore, data indicated that subcellular localization of GAD had an effect on both the number and function of antigen presenting cells (APCs) recruited by BAX as well as on IFN-gamma secretion, and that diabetes suppression was unlikely to be caused by increased T helper 2 (Th2)-like activity. Our results indicate that, under certain conditions, co-delivery of DNA encoding BAX can improve the efficacy of genetic vaccination for prevention of pathogenic autoimmunity via a mechanism likely to involve modulation of antigen presenting cell function. In addition, our data also suggest that properties associated with subcellular localization of an antigen in apoptotic cells can have a significant effect on induced immune responses.

GSH depletion enhances adenoviral bax-induced apoptosis in lung cancer cells

The utility of dominant acting proapoptotic molecules to induce cell death in cancer cells is being evaluated in preclinical studies and clinical trials. We recently developed a binary adenoviral expression system to enable the efficient gene transfer of Bax and other proapoptotic molecules. Using this system, overexpression of Bax protein in four non-small-cell lung cancer (NSCLC) cell lines, H1299, A549, H226 and H322, was evaluated. The H322 line exhibited significant resistance to Bax-induced cell death compared to the other cell lines. H322 cells had the highest level of glutathione (GSH). GSH levels were significantly decreased following buthionine sulfoximine treatment and this coincided with enhanced apoptosis induction by Ad-Bax in H322 cells. GSH depletion enhanced Bax protein translocation to mitochondrial membranes. These findings suggest that the redox status may be a determinant of Bax-mediated cell death and that manipulation of intracellular thiols may sensitize cells to apoptosis by facilitating Bax insertion into mitochondrial membranes.

Tumor necrosis factor-related apoptosis-inducing ligand gene on human colorectal cancer cell line HT29

AIM: To evaluate the therapeutic efficiency of Tumor Necrosis Factor-related Apoptosis-inducing Ligand (TRAIL) gene on human colorectal cancer cell line HT29.

METHODS: Human embryonal kidney cells transformed by introducing sheared fragments of Ad5 DNA (293 cell) were used for amplification of adenoviral vectors: Ad/GT-TRAIL, Ad/GT-Bax, Ad/GT-LacZ and Ad/PGK-GV16. Human colorectal cancer cell line HT29 was transfected with binary adenovirus-mediated TRAIL gene. Bax gene was used as positive control, LacZ gene was used as the vector control, and cells treated with PBS only were used as a mock control. The morphological changes, cell growth and apoptosis were measured by reversmicroscope, MTT method and flow cytometry.

RESULTS: All adenoviral vectors titer determined by optical absorbency at A260nm were 1 × 10¹⁰ viral particle/ml(vp/ml). Obviously morphological changes of HT29 cells were observed when infected with Ad/GT-TRAIL, and these changes were much more obviously when Ad/PGK-GV16 was coinfected. The cell suppression percentage and the percentage of apoptotic cells were 52.5% and 16.5% respectively when infected with Ad/GT-TRAIL alone, while combining with Ad/PGK-GV16, the growth of HT29 was suppressed by 85.2% and the percentage of apoptotic cells was 35.9%. It showed a significantly enhanced therapeutic efficiency with binary system (P < 0.05).

CONCLUSION: A binary adenoviral vector system provides an effective approach to amplify viral vectors that express potentially toxic gene, TRAIL. Ad/GT-TRAIL showed a significantly enhanced therapeutic efficiency for HT29 when coinfected with Ad/PGK-GV16. Ad/GT-TRAIL could induce apoptosis of HT29 and inhibit its growth.

N-terminal deletion augments the cell-death-inducing activity of BAX in adenoviral gene delivery to nonsmall cell lung cancers

Therapeutic modalities that overcome the antiapoptotic function of Bcl-2 that is often overexpressed in cancer cells are expected to be a novel strategy for cancer treatment. We previously reported that the leukemic cell death induced by an N-terminally truncated Bax (deltaN Bax: corresponding to amino acid 112-192 of full-length Bax) was not blocked by Bcl-2 or Bcl-x(L) owing to the lack of the BH3 domain needed to interact with the antiapoptotic Bcl-2 family molecules. In this study, we used the Cre-loxP system that allowed us to propagate adenoviruses expressing deltaN Bax, and investigated the effects of the deltaN Bax gene transfer into A549 and NCI-H1299 nonsmall cell lung cancer cell lines. deltaN Bax showed more cell-death-inducing activity in both cells than did the full-length Bax in vitro. It was found that the deltaN Bax-induced cell death was not inhibited by the pan-caspase inhibitor z-VAD-fmk, suggesting that deltaN Bax induces cell death through a caspase-independent mechanism. Intratumoral injection of adenoviruses expressing deltaN Bax into A549 tumors in Balb/c nude mice showed a significantly stronger suppression of tumor growth (74%) than full-length Bax (25%) compared to the control. Our results suggest that deltaN Bax may provide a better alternative than currently used cytotoxic genes in cancer gene therapy trials.

Restoring apoptosis as a strategy for cancer gene therapy: focus on p53 and mda-7

Understanding the molecular and genetic determinants of cancer will provide unique opportunities for developing rational and effective therapies. Malignant cells are frequently resistant to chemotherapy and radiation induced programmed cell death (apoptosis). This resistance can occur by mutations in the tumor suppressor gene p53. Strategies designed to replace this defective tumor suppressor protein, as well as forced expression of a novel cancer specific apoptosis inducing gene, melanoma differentiation associated gene-7 (mda-7), offer promise for restoring apoptosis in tumor cells. Conditional-replicating viruses that selectively induce cytolysis in tumor cells provides an additional means of targeting cancer cells for destruction. Although these approaches represent works in progress, future refinements will in all likelihood result in the next generation of cancer therapies.

The Role of Apoptosis-Related Genes in non—small-Cell Lung Cancer

Both intrinsic and acquired resistance to chemotherapeutic drugs are major obstacles in the treatment of non-small-cell lung cancer. Apart from classical drug resistance mechanisms, the failure of tumor cells to undergo apoptosis also plays an important role in drug resistance. Mutations and defects in the apoptotic pathway are, therefore, additional factors that determine drug resistance. The tumor suppressor gene p53, the retinoblastoma gene, and the bcl-2 family members are important factors in this pathway. Recently much attention has been drawn to different apoptotic pathways induced by naturally occurring death receptor ligands (such as tumor necrosis factor, Fas ligand, and tumor necrosis factor-related apoptosis-inducing ligand) or induced by drugs that affect the downstream pathway from the epidermal growth factor receptor. Insight regarding the proteins that determine sensitivity for chemotherapeutic drugs could provide new targets for cancer treatment, which may help to at least partly overcome drug resistance in non-small-cell lung cancer

Combined TRAIL and Bax gene therapy prolonged survival in mice with ovarian cancer xenograft

We evaluated the antitumor activity of the Bax gene and green fluorescent protein/tumor necrosis factor-related apoptosis-inducing ligand (GFP/TRAIL) fusion gene driven by the human telomerase reverse transcriptase promoter both separately and combined in the human ovarian cancer lines SKOV3ip and DOV13 and human lung cancer line H1299. In vitro study showed that both TRAIL- and Bax-expressing vectors elicited significant cell killing in H1299 and SKOV3ip cells, but only the GFP/TRAIL gene elicited significant cell killing in DOV13 cells. Combined TRAIL and Bax therapy also produced more profound cell killing in SKOV3ip and H1299 cells, but not DOV13 cells without escalation of the vector doses. To further evaluate the combined effects of Bax and TRAIL, abdominally spread tumors were established in nude mice via intraperitoneal inoculation of SKOV3ip cells followed by that of adenoviral vectors. Tumor growth, ascites formation, survival duration and toxicity were evaluated after treatment. We found that treatment using the Bax- or TRAIL-expressing vector alone significantly suppressed tumor growth and ascites formation, and prolonged animal survival when compared with that of using PBS or a control vector. Combined TRAIL and Bax therapy further prolonged survival significantly when compared with therapy using the TRAIL or Bax gene alone. Transgene expression and apoptosis induction were not detected in normal human ovarian epithelial cells in vitro or normal mouse tissues in vivo after intraperitoneal vector administration. Also, liver toxicity was not detected after either treatment. Thus, combined TRAIL and Bax gene therapy may be useful for treatment of abdominally spread tumors.

Mechanisms involved in development of resistance to adenovirus-mediated proapoptotic gene therapy in DLD1 human colon cancer cell line

To evaluate resistance that develops in cancer cells during treatment with adenoviral vectors expressing proapoptotic genes, we repeatedly treated the human colon cancer cell line DLD1 with adenoviral vectors expressing the human Bax gene and the human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene. DLD1 cells resistant to the Bax- or TRAIL-expressing adenoviral vectors were then selected and designated as DLD1/Bax-R or DLD1/TRAIL-R cells, respectively. Further study showed that resistance in DLD1/Bax-R cells was caused by resistance to adenoviral infection, which can be overcome by dose escalation of the adenoviral vectors. However, resistance in DLD1/TRAIL-R cells was caused by resistance to the TRAIL gene. Therefore, different mechanisms are involved in the development of resistance during adenovirus-mediated proapoptotic gene therapy. A survey of molecules involved in TRAIL- or Bax-mediated apoptotic pathways showed no significant change in expression of death receptors, death decoy receptors; FLIP; Bcl-2; Bcl-xS; Bax; Bak; XIAP or caspase-2, -7, -8, or -9 in either DLD1/Bax-R or DLD1/TRAIL-R cells. Bcl-xL expression detected in both mRNA and protein level assays was three times higher in DLD1/TRAIL-R cells than in parental or DLD1/Bax-R cells. However, transfection of DLD1 cells with the Bcl-xL gene showed that overexpression of Bcl-xL is not sufficient for the resistance. Moreover, DLD1/Bax-R cells were sensitive to adenoviral vectors that expressed the TRAIL gene, but resistant to adenoviral vectors that expressed the Bak gene. In contrast, DLD1/TRAIL-R cells were sensitive to adenoviral vectors that expressed either Bax or Bak gene. Thus, alternative application of adenoviral vectors that expressed proapoptotic genes in different pathways or different cell killing models may delay or prevent development of resistance in adenovirus-mediated proapoptotic gene therapy.

Bax-induction gene therapy of pancreatic cancer

BACKGROUND

Bax is a strong pro-apoptotic gene that induces programmed cell death when expressed. Human telomerase reverse transcriptase (hTERT) is the catalytic subunit for telomerase, an enzyme found to be active in more than 85% of human cancers. Recently, a binary adenoviral system (Ad/GT-Bax + Ad/hTERT-GV16) was constructed using the hTERT promoter to induce Bax gene expression in tumor cells.

METHODS

To test whether human pancreatic tumor cells would respond to this system of Bax-induced apoptosis, we compared the effects of Bax gene induction with that of LacZ gene induction using the same binary system.

RESULTS

Lysates of the human pancreatic cell lines PANC-28, MIA PaCa-2, and BxPC-3 showed significantly elevated levels of human telomerase using the PCR-based TRAP assay. As early as 24 h after treatment with Bax-induction gene therapy, growth inhibition was observed. Overexpression of the Bax protein was confirmed by Western blotting. Extensive apoptosis on FACS analysis at 48 h was seen after Bax induction. In addition, cytosolic cytochrome c levels increased compared to mitochondrial levels after Bax induction. Levels of caspase-3, a key downstream enzyme involved in apoptosis, also increased significantly compared to controls after treatment. None of these effects were seen with LacZ.

CONCLUSION

Our results suggest that the binary adenoviral vector system, Ad/GT-Bax + Ad/hTERT-GV16, induces high levels of Bax expression that induce apoptosis in human pancreatic cancer cells.

Clinical update of Ad-p53 gene therapy for lung cancer

These preliminary Phase I and II gene therapy trials in NSCLC have demonstrated that Ad-p53 gene transfer is associated with low toxicity and evidence of antitumoral activity at the locoregional site. Effort to enhance antitumoral efficacy with chemotherapy and radiation therapy have not increased Ad-p53 toxicity and appear to be feasible. Randomized Phase III studies are now needed to determine the potential of Ad-p53 to improve overall survival in selected subsets of NSCLC patients. Future gene therapy research is required to develop systemic delivery systems and to overcome p53 tumor resistance. It is hoped that these efforts will ultimately lead to a novel mode of therapy to complement conventional chemotherapy, radiation therapy, and surgical treatment strategies.

From castration-induced apoptosis of prostatic epithelium to the use of apoptotic genes in the treatment of prostate cancer

Current knowledge of the mechanisms regulating androgen-ablation-induced apoptosis is reviewed, and our efforts to develop a system in which genes of the apoptotic pathway are used to induce therapeutic apoptosis in experimental models of prostate cancer are described.

Viral vector-mediated delivery of competing glycosyltransferases modifies epitope expression cell specifically

The glycoconjugate epitopes 3-fucosyl-N-acetyllactosamine (CD15) and sulfoglucuronylcarbohydrate (SGC) mediate cell adhesion events in several systems, and are regulated both spatially and temporally during cerebellar development. In cotransfection studies using COS-1 cells, competition between glycosyltransferases that utilize a common precursor involved in the final synthetic steps of these epitopes, can modulate epitope expression. For example, cotransfection of rat alpha1,3-fucosyltransferase IV (Fuc-TIV) and either rat glucuronic acid transferase P (GlcAT) or pig alpha1,3-galactosyltransferase (GalT) resulted in the dominance of either SGC or GalalphaGal epitope expression, respectively, with blockage of CD15 epitope expression. Viral vectors expressing these glycosyltransferases were used to determine whether competition plays a role in establishing epitope dominance in cerebellar cells, and whether overexpression of competing glycosyltransferases could be used to block epitope expression. Infection of cerebellar astrocytes with viral vectors expressing either Fuc-TIV, or Fuc-TIX, caused dramatic increases in CD15 expression in the presence of continued endogenous SGC epitope expression. Likewise, viral transduction with GalT resulted in GalalphaGal expression without affecting endogenous CD15 or SGC expression. Thus, competition between these enzymes does not appear to play a role in establishing epitope expression in astrocytes, and transduction of these enzymes does not provide a method of blocking the expression of endogenous epitopes. In contrast to what was observed for astrocytes, infection with viral vectors expressing either Fuc-T, GlcAT, or GalT did not result in significant expression of the relevant epitopes (CD15, SGC or GalalphaGal, respectively) on granule neurons. These results suggest a different complement of precursors are present in granule neurons and astrocytes, presumably due to the presence of different complements of glycosyltransferases in these cells.

Transient suppression of transgene expression by means of antisense oligonucleotides: a method for the production of toxin-transducing recombinant viruses

Some of the therapeutic genes to be delivered by means of recombinant adenoviruses code for toxic compounds. Expression of these sequences can be deleterious to the complementation cells used for vector production, making it often difficult to generate high-titer stocks of toxin-transducing recombinant adenoviruses. In this work, we present a novel strategy for the transient post-transcriptional down-regulation of toxic transgene expression during the vector production phase, through the administration of phosphorothioate-modified antisense oligodeoxyribonucleotides. This method was successfully applied to the production of hybrid adenoviruses that contain the gene encoding the cytotoxic parvoviral protein NS1. The generation of recombinant adenoviruses in 293T cells was found to be fully suppressed as a result of adding of the NS gene to the vector genome. Yet, the production of NS-harboring hybrid adenoviruses could be rescued by treating the producer cells with antisense oligonucleotides specific for the translation initiation region of the NS transcript. This rescue correlated with a striking reduction of NS RNA and protein levels in the complementation cells. These data provide proof of principle of the suitability of the antisense oligonucleotides strategy for overcoming the interference of harmful transgenes with the production of adenoviral and other vectors.

Prostate cancer gene therapy and the role of radiation

Even though prostate cancer is detected earlier than in the pre-PSA era, prostate cancer is the second leading cause of cancer mortality in the American male. Prostate cancer therapy is not ideal, especially for high-risk localized and metastatic cancer; therefore, investigators have sought new therapeutic modalities such as angiogenesis inhibitors, inhibitors of the cell signaling pathway, vaccines, and gene therapy. Gene therapy has emerged as potential therapy for both localized and systemic prostate cancer. Gene therapy has been shown to work supra-additively with radiation in controlling prostate cancer in vivo. With further technological advances in radiation therapy, gene therapy, and the understanding of prostate cancer biology, gene therapy will potentially have an important role in prostate cancer therapy.

hTERT promoter induces tumor-specific Bax gene expression and cell killing in syngenic mouse tumor model and prevents systemic toxicity

We recently showed that the human telomerase reverse transcriptase (hTERT) promoter induces tumor-specific Bax gene expression and selectively kills various human cancer cells both in vitro and in xenograft tumors. However, it remains unclear whether the hTERT promoter can be used to induce transgene expression in syngenic tumors in mice and whether Bax gene expression driven by the hTERT promoter will cause long-term, stem cell-related toxicity. To address these questions, we tested hTERT promoter-driven, adenovirus-mediated Bax transgene expression in an established syngenic mouse tumor model and its effects on tumor and normal murine tissues. The hTERT promoter was highly active in several murine tumor cell lines and a transformed cell line, but not in non-transformed and normal murine cell lines. The hTERT promoter induced tumor-specific Bax gene expression in mouse UV-2237m fibrosarcoma cells both in vitro and in vivo and suppressed syngenic tumor growth in immune-competent mice with no obvious acute or long-term toxic effects. Moreover, hTERT promoter-driven transgene expression in human CD34(+) bone marrow progenitor cells had effects similar to those observed in other normal human cells, suggesting that the hTERT promoter is much less active in CD34(+) cells than in tumor cells. Together, our data demonstrate that the hTERT promoter may allow the use of proapoptotic genes for cancer treatment without noticeable effects on progenitor cells.

Use of the probasin promoter ARR2PB to express Bax in androgen receptor-positive prostate cancer cells

BACKGROUND

Adenovirus-mediated overexpression of the apoptosis-inducing protein Bax can induce apoptosis in prostate cancer cell lines. Constitutive overexpression of Bax could result in unwanted apoptosis in every site of accidental Bax accumulation in vivo. Therefore, we developed an adenoviral construct (Av-ARR2PB-Bax) in which the probasin promoter, modified to contain two androgen response elements, drives Bax expression. This promoter would be expected to limit expression of Bax to cells expressing the androgen receptor.

METHODS

A variety of androgen receptor (AR)-positive and -negative cell lines of prostatic or nonprostatic origin were infected with Av-ARR2PB-Bax or a control virus, Av-ARR2PB-CAT, in which the same promoter drives expression of the chloramphenicol acetyl transferase-reporter gene. Bax expression and apoptosis in vitro were assessed by western blot analysis. Tumor size and apoptosis in vivo were assessed after four weekly injections of Av-ARR2PB-Bax or Av-ARR2PB-CAT into subcutaneous LNCaP xenografts growing in uncastrated male mice. All statistical tests were two-sided.

RESULTS

Bax was overexpressed in an androgen-dependent way in AR-positive cell lines of prostatic origin but not in AR-positive cells of nonprostatic origin or in AR-negative cell lines of either prostatic or nonprostatic origin. The androgen dihydrotestosterone activated apoptosis in LNCaP cells infected with Av-ARR2PB-Bax but not in those infected with Av-ARR2PB-CAT. Av-ARR2PB-Bax-injected LNCaP xenograft tumors decreased in tumor size from 34.1 mm3 (95% confidence interval [CI] = 25.1 mm3 to 43.1 mm3) to 24.6 mm3 (95% CI = -2.5 mm3 to 51.7 mm3), but the difference was not statistically significant (P =.5). Tumors injected with Av-ARR2PB-CAT increased in size, from 28.9 mm3 (95% CI = 12.7 mm3 to 45.1 mm3) to 206 mm3 (95% CI = 122 mm3 to 290 mm3) (P =.002) and contained statistically significant more apoptotic cells (23.3% [95% CI = 21.1% to 25.6%] versus 9.5% [95% CI = 8.0% to 11.1]) (P<.001).

CONCLUSIONS

Av-ARR2PB-Bax induces androgen-dependent therapeutic apoptosis in vitro and in vivo by activating apoptosis in AR-positive cells derived specifically from prostatic epithelium and does not affect nonprostatic cells.