Cancer-specific gene therapy

Polymeric nano-carriers for on-demand delivery of genes via specific responses to stimuli

Polymeric nano-carriers have been developed as a most capable and feasible technology platform for gene therapy. As vehicles, polymeric nano-carriers are obliged to possess high gene loading capability, low immunogenicity, safety, and the ability to transfer various genetic materials into specific sites of target cells to express therapeutic proteins or block a process of gene expression. To this end, various types of polymeric nano-carriers have been prepared to release genes in response to stimuli such as pH, redox, enzymes, light and temperature. These stimulus-responsive nano-carriers exhibit high gene transfection efficiency and low cytotoxicity. In particular, dual- and multi-stimulus-responsive polymeric nano-carriers can respond to a combination of signals. Markedly, these combined responses take place either simultaneously or in a sequential manner. These dual-stimulus-responsive polymeric nano-carriers can control gene delivery with high gene transfection both in vitro and in vivo. In this review paper, we highlight the recent exciting developments in stimulus-responsive polymeric nano-carriers for gene delivery applications.

Mesenchymal stem cells anchored with thymidine phosphorylase for doxifluridine-mediated cancer therapy

Many tumors express thymidine phosphorylase (TYMP) with various levels, however due to tumor heterogeneity, the amount of TYMP is usually not enough to convert prodrug doxifluridine (5'-DFUR) to toxic drug 5-fluorouracil (5-FU). Since human mesenchymal stem cells (hMSCs) have unique features of tumor-tropism and low immunogenicity, the purpose of this study is to use mesenchymal stem cells as carriers to deliver TYMP to cancer cells and then trigger their death by administrating doxifluridine. First, the TYMP gene sequence and core streptavidin (core SA) were constructed into pET-30a(+) plasmid. After bacterial transformation and colony screening, TYMP-SA fusion protein was expressed by IPTG induction and purified by immobilized metal affinity chromatography and characterized by SDS-PAGE and western blot with a clear band at 75 kDa. The characterized TYMP-SA was further anchored on the cell membrane of biotinylated hMSCs via biotin-streptavidin binding. hMSCs anchored with TYMP-SA were then co-cultured with adenocarcinoma A549 cells (with different ratios) and treated with 100 μM prodrug doxifluridine over the course of four days. Our results showed that a 2 : 1 ratio led to the eradication of A549 cells at the end of the experiment with less than 5% confluency, in comparison with the 1 : 1 and 1 : 2 ratios which still had about 13% and 20% confluency respectively. In conclusion, harnessing hMSCs as cell carriers for the delivery of TYMP enzyme to cancer cells could lead to significant cell death post-treatment of the prodrug doxifluridine.

Combination of NDRG2 overexpression, X-ray radiation and docetaxel enhances apoptosis and inhibits invasiveness properties of LNCaP cells

OBJECTIVE

N-myc downstream regulated gene 2 (NDRG2) is identified as a promising candidate tumor suppressor in several human malignancies including prostate cancer (PCa). Here, we investigated the effect of combined NDRG2 overexpression, x-ray radiation (RTX), and docetaxel (DTX) against viability and invasiveness properties of LNCaP cells.

MATERIAL AND METHODS

A plasmid harboring NDRG2 gene under transcriptional control of prostate-specific enhancing sequence regulatory element was constructed to overexpress NDRG2 in PCa cell lines. The effects of NDRG2 overexpression in combination with RTX and DTX on viability, proliferation, and apoptosis of LNCaP cells were evaluated using MTT, colony formation, and annexin V flowcytometirc assays. Migration and invasion of NDRG2-overexpressed cells as well as expression of matrix metalloproteinses-2 (MMP2) and -9 (MMP9) were also assessed using transwell chamber assay and real-time PCR.

RESULTS

The results of fluorescence microscopy and real-time PCR showed a high and specific overexpression of NDRG2 in LNCaP cells. Overexpression of NDRG2 significantly reduced cell viability and increased apoptosis of LNCaP cell. Migration, invasion, as well as the expression of MMP2 and MMP9, was decreased following NDRG2 overexpression. Combination of NDRG2 overexpression with RTX and DTX decreased the viability, invasion, and migration of LNCaP cells synergistically.

CONCLUSION

These results indicate that a combination of NDRG2 overexpression with chemotherapy and radiotherapy can be considered for effective treatment of PCa.

Anti-Colorectal Cancer Effects of Probiotic-Derived p8 Protein

Recently, we reported a novel therapeutic probiotic-derived protein, p8, which has anti-colorectal cancer (anti-CRC) properties. In vitro experiments using a CRC cell line (DLD-1), anti-proliferation activity (about 20%) did not improve after increasing the dose of recombinant-p8 (r-p8) to >10 μM. Here, we show that this was due to the low penetrative efficiency of r-p8 exogenous treatment. Furthermore, we found that r-p8 entered the cytosol through endocytosis, which might be a reason for the low penetration efficiency. Therefore, to improve the therapeutic efficacy of p8, we tried to improve delivery to CRC cells. This resulted in endogenous expression of p8 and increased the anti-proliferative effects by up to 2-fold compared with the exogenous treatment (40 μM). Anti-migration activity also increased markedly. Furthermore, we found that the anti-proliferation activity of p8 was mediated by inhibition of the p53-p21-Cyclin B1/Cdk1 signal pathway, resulting in growth arrest at the G2 phase of the cell cycle. Taken together, these results suggest that p8 is toxic to cancer cells, shows stable expression within cells, and shows strong cancer suppressive activity by inducing cell cycle arrest. Therefore, p8 is a strong candidate for gene therapy if it can be loaded onto cancer-specific viruses.

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

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

Complex of TNF-α and Modified Fe3O4 Nanoparticles Suppresses Tumor Growth by Magnetic Induction Hyperthermia

BACKGROUND

Magnetic nanoparticles are increasingly applied in clinical area for drug delivery, also in magnetic induction hyperthermia (MIH), and so on. The present research would prepare appropriately modified superparamagnetic iron oxide nanoparticles (SPIONs) to conduct MIH and transfect the anticancer cytokine TNF-α into cells.

MATERIALS AND METHODS

The SPIONs were surface-modified by 3-aminopropyltriethoxysilane (APTS) and/or protamine sulfate (PRO). The combined MIH using SPIONs and gene therapy were applied to treat Hep G2 cells and tumor model transplanted in nude mice.

RESULTS

The PRO-SPIONs (the surfaces were sequentially modified by APTS and PRO) showed high transfection efficiency for TNF-α gene with no obvious cytotoxicity. It also exhibited great temperature rising performance under alternating current magnetic field. The combined MIH and gene therapy using PRO-SPIONs/TNF-α complex could reduce cell variability of Hep G2 cells and tumor size transplanted in nude mice.

CONCLUSIONS

The PRO-SPIONs efficiently transfect the TNF-α gene into Hep G2 cells. Cells expressed more TNF-α when they were exposed to alternating current magnetic field only once. Combined MIH and gene therapy for treatment in vivo exhibited better effects than MIH or gene therapy alone. The combined MIH and gene therapy is promising in liver cancer treatment.

Digesting a Path Forward: The Utility of Collagenase Tumor Treatment for Improved Drug Delivery

Collagen and hyaluronan are the most abundant components of the extracellular matrix (ECM) and their overexpression in tumors is linked to increased tumor growth and metastasis. These ECM components contribute to a protective tumor microenvironment by supporting a high interstitial fluid pressure and creating a tortuous setting for the convection and diffusion of chemotherapeutic small molecules, antibodies, and nanoparticles in the tumor interstitial space. This review focuses on the research efforts to deplete extracellular collagen with collagenases to normalize the tumor microenvironment. Although collagen synthesis inhibitors are in clinical development, the use of collagenases is contentious and clinically untested in cancer patients. Pretreatment of murine tumors with collagenases increased drug uptake and diffusion 2-10-fold. This modest improvement resulted in decreased tumor growth, but the benefits of collagenase treatment are confounded by risks of toxicity from collagen breakdown in healthy tissues. In this review, we evaluate the published in vitro and in vivo benefits and limitations of collagenase treatment to improve drug delivery.

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.

Use of the XRCC2 promoter for in vivo cancer diagnosis and therapy

The homologous recombination (HR) pathway is a promising target for cancer therapy as it is frequently upregulated in tumors. One such strategy is to target tumors with cancer-specific, hyperactive promoters of HR genes including RAD51 and RAD51C. However, the promoter size and the delivery method have limited its potential clinical applications. Here we identified the ~2.1 kb promoter of XRCC2, similar to ~6.5 kb RAD51 promoter, as also hyperactivated in cancer cells. We found that XRCC2 expression is upregulated in nearly all types of cancers, to a degree comparable to RAD51 while much higher than RAD51C. Further study demonstrated that XRCC2 promoter is hyperactivated in cancer cell lines, and diphtheria toxin A (DTA) gene driven by XRCC2 promoter specifically eliminates cancer cells. Moreover, lentiviral vectors containing XRCC2 promoter driving firefly luciferase or DTA were created and applied to subcutaneous HeLa xenograft mice. We demonstrated that the pXRCC2-luciferase lentivirus is an effective tool for in vivo cancer visualization. Most importantly, pXRCC2-DTA lentivirus significantly inhibited the growth of HeLa xenografts in comparison to the control group. In summary, our results strongly indicate that virus-mediated delivery of constructs built upon the XRCC2 promoter holds great potential for tumor diagnosis and therapy.

Recent updates in utilizing prodrugs in drug delivery (2013-2015)

INTRODUCTION

Utilizing the prodrug approach as a method to overcome various pharmaceutical and pharmacokinetic barriers to drug delivery is significantly accelerating and achieving successes. In contrast to the older traditional prodrugs which suffer from decreased bioavailability and a high profile of side effects, due to activation at undesired sites, the targeted prodrug approach utilizes delivery systems to improve delivery for a wide range of therapeutics including anti-cancer, anti-bacterial and anti-inflammatory drugs.

AREAS COVERED

Recent updates in utilization of prodrugs in drug delivery between 2013 and 2015 are discussed. Targeted prodrugs against cancer, solid tumors, microbial infections, inflammation and other diseases using advanced delivery systems such as theranostic approaches, siRNA, DOX immunoconjugate, C 60-ser carrier vector, biotinylated prodrug, human serum albumin (HSA) carrier and others are presented.

EXPERT OPINION

Recent research efforts have been directed at developing targeted prodrugs to replace the classical prodrugs. The use of this approach has accelerated following the emergence of encouraging results from several studies on targeted prodrugs that have highlighted their higher efficiency and improved safety profiles. Targeted prodrug delivery is now considered more than a chemical modification method. It is an applicable and promising approach and, in the future, better knowledge and wide application of this approach may be attained which may pave the way for more forward-thinking and creative techniques.

Image-aided Suicide Gene Therapy Utilizing Multifunctional hTERT-targeting Adenovirus for Clinical Translation in Hepatocellular Carcinoma

Trans-splicing ribozyme enables to sense and reprogram target RNA into therapeutic transgene and thereby becomes a good sensing device for detection of cancer cells, judging from transgene expression. Previously we proposed PEPCK-Rz-HSVtk (PRT), hTERT targeting trans-splicing ribozyme (Rz) driven by liver-specific promoter phosphoenolpyruvate carboxykinase (PEPCK) with downstream suicide gene, herpes simplex virus thymidine kinase (HSVtk) for hepatocellular carcinoma (HCC) gene therapy. Here, we describe success of a re-engineered adenoviral vector harboring PRT in obtaining greater antitumor activity with less off-target effect for clinical application as a theranostics. We introduced liver-selective apolipoprotein E (ApoE) enhancer to the distal region of PRT unit to augment activity and liver selectivity of PEPCK promoter, and achieved better transduction into liver cancer cells by replacement of serotype 35 fiber knob on additional E4orf1-4 deletion of E1&E3-deleted serotype 5 back bone. We demonstrated that our refined adenovirus harboring PEPCK/ApoE-Rz-HSVtk (Ad-PRT-E) achieved great anti-tumor efficacy and improved ability to specifically target HCC without damaging normal hepatocytes. We also showed noninvasive imaging modalities were successfully employed to monitor both how well a therapeutic gene (HSVtk) was expressed inside tumor and how effectively a gene therapy took an action in terms of tumor growth. Collectively, this study suggests that the advanced therapeutic adenoviruses Ad-PRT-E and its image-aided evaluation system may lead to the powerful strategy for successful clinical translation and the development of clinical protocols for HCC therapy.

Killing of cancer cells through the use of eukaryotic expression vectors harbouring genes encoding nucleases and ribonuclease inhibitor

Cancer gene therapy vectors are promising tools for killing cancer cells with the purpose of eradicating malignant tumours entirely. Different delivery methods of vectors into the cancer cells, including both non-viral and viral, as well as promoters for the targeted expression of genes encoding anticancer proteins were developed for effective and selective killing of cancer cells without harming healthy cells. Many vectors have been created to kill cancer cells, and some vectors suppress malignant tumours with high efficiency. This review is focused on vectors bearing genes for nucleases such as deoxyribonucleases (caspase-activated DNase, deoxyribonuclease I-like 3, endonuclease G) and ribonucleases (human polynucleotide phosphorylase, ribonuclease L, α-sarcin, barnase), as well as vectors harbouring gene encoding ribonuclease inhibitor. The data concerning the functionality and the efficacy of such vectors are presented.

Gene-directed enzyme prodrug therapy

As one targeting strategy of prodrug delivery, gene-directed enzyme prodrug therapy (GDEPT) promises to realize the targeting through its three key features in cancer therapy-cell-specific gene delivery and expression, controlled conversion of prodrugs to drugs in target cells, and expanded toxicity to the target cells' neighbors through bystander effects. After over 20 years of development, multiple GDEPT systems have advanced into clinical trials. However, no GDEPT product is currently marketed as a drug, suggesting that there are still barriers to overcome before GDEPT becomes a standard therapy. In this review, we first provide a general introduction of this prodrug targeting strategy. Then, we utilize the four most thoroughly studied systems to illustrate components, mechanisms, preclinical and clinical results, and further development directions of GDEPT. These four systems are herpes simplex virus thymidine kinase/ganciclovir, cytosine deaminase/5-fluorocytosine, cytochrome P450/oxazaphosphorines, and nitroreductase/CB1954 system. Later, we focus our discussion on bystander effects including local and distant bystander effects. Lastly, we discuss carriers that are used to deliver genes for GDEPT including virus carriers and non-virus carriers. Among these carriers, the stem cell-based gene delivery system represents one of the newest carriers under development, and may brought about a breakthrough to the gene delivery issue of GDEPT.

Regulation of Rad51 promoter

The DNA double-strand break repair and homologous recombination protein Rad51 is overexpressed in the majority of human cancers. This correlates with therapy resistance and decreased patient survival. We previously showed that constructs containing Rad51 promoter fused to a reporter gene are, on average, 850-fold more active in cancer cells than in normal cells. It is not well understood what factors and sequences regulate the Rad51 promoter and cause its high activity in cancerous cells. Here we characterized regulatory regions and examined genetic requirements for oncogenic stimulation of the Rad51 promoter. We identified specific regions responsible for up- and downregulation of the Rad51 promoter in cancerous cells. Furthermore, we show that Rad51 expression is positively regulated by EGR1 transcription factor. We then modeled the malignant transformation process by expressing a set of oncoproteins in normal human fibroblasts. Expression of different combinations of SV40 large T antigen, oncogenic Ras and SV40 small T antigen resulted in step-wise increase in Rad51 promoter activity, with all the 3 oncoproteins together leading to a 47-fold increase in expression. Cumulatively, these results suggest that Rad51 promoter is regulated by multiple factors, and that its expression is gradually activated as cells progress toward malignancy.

Functional analysis of human cancer-associated genes and their association with the testes and epididymis

Human cancer-associated UniGene sets (NCBI GeneBank) provide a platform for identifying differentially-expressed genes in human cancers. The present study identified and characterized a set of human cancer-associated genes using the Digital Differential Display (DDD) and functional analysis tools. A total of 1,904 genes were differentially expressed in 15 cancer types, including genes that had been previously shown to be specific in certain human cancers. A total of 274 genes were uniquely expressed in certain cancer types, including 37 genes that were highly expressed in the human testes and epididymis. These genes mainly functioned as ribosomal proteins, enzymes, receptors, secretory proteins and cell adhesion molecules. The most common domains that were encoded by the cancer-associated genes were those of cytochrome P450 CYP2D6, serpin and apolipoprotein A-I. A further gene ontology (GO) enrichment analysis revealed seven major functional clusters, which corresponded to the enriched pathways involved in cancer. The present study provides a source of cancer-associated genes and their functions. The results provide new insights into cancer biology and the involvement of highly-expressed epididymal genes in cancer biomarkers.

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.

Intratumoral versus intravenous gene therapy using a transcriptionally targeted viral vector in an orthotopic hepatocellular carcinoma rat model

PURPOSE

To evaluate the feasibility of intratumoral delivery of adenoviral vector carrying a bidirectional two-step transcriptional amplification (TSTA) system to amplify transcriptional strength of cancer-specific Survivin promoter in a hepatocellular carcinoma model.

MATERIALS AND METHODS

MCA-RH7777 cells were implanted in rat liver, and tumor formation was confirmed with [(18)F]fluorodeoxyglucose (18F-FDG) positron emission tomography (PET). The adenoviral vector studied had Survivin promoter driving a therapeutic gene (tumor necrosis factor-α-related apoptosis-inducing ligand [TRAIL]) and a reporter gene (firefly luciferase [FL]; Ad-pSurvivin-TSTA-TRAIL-FL). Tumor-bearing rats were administered Ad-pSurvivin-TSTA-TRAIL-FL intravenously (n = 7) or intratumorally (n = 8). For control groups, adenovirus FL under cytomegalovirus (CMV) promoter (Ad-pCMV-FL) was administered intravenously (n = 3) or intratumorally (n = 3). One day after delivery, bioluminescence imaging was performed to evaluate transduction. At 4 and 7 days after delivery, 18F-FDG-PET was performed to evaluate therapeutic efficacy.

RESULTS

With intravenous delivery, Ad-pSurvivin-TSTA-TRAIL-FL showed no measurable liver tumor FL signal on day 1 after delivery, but showed better therapeutic efficacy than Ad-pCMV-FL on day 7 (PET tumor/liver ratio, 3.5 ± 0.58 vs 6.0 ± 0.71; P = .02). With intratumoral delivery, Ad-pSurvivin-TSTA-TRAIL-FL showed positive FL signal from all tumors and better therapeutic efficacy than Ad-pCMV-FL on day 7 (2.4 ± 0.50 vs 5.4 ± 0.78; P = .01). In addition, intratumoral delivery of Ad-pSurvivin-TSTA-TRAIL-FL demonstrated significant decrease in tumoral viability compared with intravenous delivery (2.4 ± 0.50 vs 3.5 ± 0.58; P = .03).

CONCLUSIONS

Intratumoral delivery of a transcriptionally targeted therapeutic vector for amplifying tumor-specific effect demonstrated better transduction efficiency and therapeutic efficacy for liver cancer than systemic delivery, and may lead to improved therapeutic outcome for future clinical practice.

Rad51 promoter-targeted gene therapy is effective for in vivo visualization and treatment of cancer

Rad51 protein is overexpressed in a wide range of human cancers. Our previous in vitro studies demonstrated that a construct comprised Rad51 promoter driving expression of the diphtheria toxin A gene (pRad51-diphtheria toxin A (DTA)) destroys a variety of human cancer cell lines, with minimal to no toxicity to normal human cells. Here we delivered Rad51 promoter-based constructs in vivo using linear polyethylenimine nanoparticles, in vivo jetPEI, to visualize and treat tumors in mice with HeLa xenografts. For tumor detection, we used pRad51-Luc, a construct containing the firefly luciferase under the Rad51 promoter, administered by intraperitoneal (IP) injection. Tumors were detected with an in vivo bioluminescent camera. All mice with cancer displayed strong bioluminescence, while mice without cancer displayed no detectable bioluminescence. Treatment with pRad51-DTA/jetPEI decreased tumor mass of subcutaneous (SC) and IP tumors by sixfold and fourfold, respectively, along with the strong reduction of malignant ascites. Fifty percent of the mice with SC tumors were cancer-free after six pRad51-DTA/jetPEI injections, and for the mice with IP tumors, mean survival time increased by 90% compared to control mice. This study demonstrates the clinical potential of pRad51-based constructs delivered by nanoparticles for the diagnostics and treatment of a wide range of cancers.

A reconstituted telomerase-immortalized human corneal epithelium in vivo: a pilot study

PURPOSE

Telomerase-immortalized human corneal epithelial cells have been reported to stratify and differentiate in vitro similar to native tissue. The purpose of this study was to assess the ability of a telomerase-immortalized human corneal epithelial cell line to generate a full thickness epithelium in vivo in athymic mice.

METHODS

Telomerized corneal epithelial cells were transduced with a retroviral vector encoding the herpes simplex thymidine kinase gene. Efficacy of the thymidine kinase suicide gene was confirmed using a live/dead assay. The epithelium was mechanically removed from athymic nude mice and remaining cells were treated with mitomycin C to prevent re-epithelialization. Telomerized corneal epithelial cells were seeded onto the denuded cornea and allowed to adhere for 4 and 24 hours. Cellular attachment was assessed using a fluorescent cell tracker. Stratification and differentiation were assessed after 7 days using phalloidin and a mouse monoclonal antibody to K3.

RESULTS

Telomerized corneal epithelial cells were visualized across the denuded stromal surface at 4 and 24 hours, with multi-layering evident at the latter time point. No epithelium was present in the non-treated eye. After 7 days post-transplantation cells stratified into a multilayered epithelium, with positive K3 expression in basal and suprabasal cells. Treatment with ganciclovir induced significant loss of viability in vitro.

CONCLUSIONS

The findings in this pilot study demonstrate that telomerized corneal epithelial cells possess the capacity to reconstitute a stratified corneal epithelium in vivo. The introduction of thymidine kinase allowed for the successful induction of cell death in proliferating cells in vitro. Collectively, these data suggest that a telomerase-immortalized corneal epithelial cell line transduced with thymidine kinase represents a potential model for studying differentiation and epithelial-niche interactions in vivo with potential applications in tissue engineering.

Potent, tumor-specific gene expression in an orthotopic hepatoma rat model using a Survivin-targeted, amplifiable adenoviral vector

Ideal cancer gene therapies should have high tumor specificity and efficacy, and allow systemic administration to target metastases. We recently developed a bi-directional, two-step transcriptional amplification (TSTA) system driven by the tumor-specific Survivin promoter (pSurv) to amplify the correlated expression of both the reporter gene firefly luciferase (FL) and therapeutic gene tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Here, we compare the specificity and potency of an adenovirus carrying this system (Ad-pSurv-TSTA-TRAIL-FL) to a nonspecific vector (Ad-pCMV-FL) in an orthotopic hepatocellular carcinoma (HCC) rat model after systemic administration. At 24 h after injection of Ad-pCMV-FL, bioluminescence imaging revealed a trend (P=0.30) towards greater FL expression in liver versus tumor. In striking contrast, Ad-pSurv-TSTA-TRAIL-FL showed increased FL activity within the tumor compared with the liver (P<0.01), a strong trend towards reduced liver expression compared with Ad-pCMV-FL (P=0.07), and importantly, similar FL levels within tumor compared with Ad-pCMV-FL (P=0.32). Hence, this vector shows potent, tumor-specific transgene expression even after extensive liver transduction and may be of significant value in avoiding hepatotoxicity in HCC patients. Future studies will explore the benefits of tumor-specific TRAIL expression in this model, the potential to target metastases and the extension of this vector for the treatment of other Survivin-positive tumors is warranted.

Adenovirus 5 E1A enhances histone deacetylase inhibitors-induced apoptosis through Egr-1-mediated Bim upregulation

Histone deacetylase inhibitors (HDACi) are potent anti-cancer agents for variety of cancer types. Suberoylanilide hydroxamic acid (SAHA) has been approved as a drug to treat cutaneous T cell lymphoma, and the combination of HDACi and other agents have been actively tested in many clinical trials. Adenovirus 5 early region 1A (E1A) has been shown to exhibit high tumor suppressor activity, and gene therapy using E1A has been tested in clinical trials. Here, we showed that proapoptotic activity of HDACi was robustly enhanced by E1A in multiple cancer cells, but not in normal cells. Moreover, we showed that combination of E1A gene therapy and SAHA showed high therapeutic efficacy with low toxicity in vivo ovarian and breast xenograft models. SAHA downregulated Bcl-XL and upregulated proapoptotic BH3-only protein Bim, whose expression was further enhanced by E1A in cancer cells. These alterations of Bcl-2 family proteins were critical for apoptosis induced by the combination in cancer cells. SAHA enhanced acetylation of histone H3 in Bim promoter region, while E1A upregulated Egr-1, which was directly involved in Bim transactivation. Together, our results provide not only a novel insight into the mechanisms underlying anti-tumor activity of E1A, but also a rationale for the combined HDACi and E1A gene therapy in future clinical trials.

Targeted killing effects of double CD and TK suicide genes controlled by survivin promoter on gastric cancer cell

Suicide genes such as cytosine deaminase (CD) and herpes simplex virus thymidine kinase (TK) encode products that convert nontoxic substances (prodrugs) into toxic metabolites. Studies in recent years indicated that survivin(sur) expression was associated with the biological behaviors of gastric carcinoma. In the present study, targeted killing effects of double CD and TK suicide genes controlled by survivin promoter on gastric cancer cell were investigated, the recombinant pSCT vector containing CD and TK genes driven by sur promoter was constructed and transfected into SGC-7901 cells. After adding the CCV and 5-FC, the effects of double suicide genes on cell growth, cell cycle and proliferation were determined by MTT assay and flow cytometry (FCM). The results showed that sur promoter could specifically drive the expression of double CD/TK gene in SGC-7901 cells, whereas not in the normal GES-1 cell. After using CCV and 5-FC, the growth of SGC-7901 cells was inhibited. G1 phase proportion was significantly higher in SGC-7901 cells transfected with double suicide genes than the untransfected cells. These results suggest that CD and TK double suicide genes driven by sur promoter could provide a new approach for enhancing selective suicide gene therapy of CD/5-FC for the treatment of advanced gastric carcinoma.

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.

Bioengineered viral vectors for targeting and killing prostate cancer cells

Enabling the transduction of therapeutic gene expression exclusively in diseased sites is the key to developing more effective treatments for advanced prostate cancer using viral-based therapy. While prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by lentiviruses with envelope proteins engineered to bind to this therapeutic antibody. More importantly, after intravenous injection, this trastuzumab-bound lentivirus is able to target castration-resistant prostate tumor xenografts, albeit with low efficiency. This proof of principle opens up multiple possibilities for the prevention and treatment of prostate cancer using a viral-based therapy. However, to be safe and more effective, the viral vectors must target prostate cancer cells more selectively and efficiently. A higher degree of specificity and efficiency of cancer cell targeting can be achieved by engineering viral vectors to bind to a specific cell surface marker and by controlling the expression of the therapeutic payload at transcriptional level, with a tissue-specific promoter, and at the translational level, with a regulatory sequences inserted into either the 5'UTR or 3'UTR regions of the therapeutic gene(s). The latter would be designed to ensure that translation of this mRNA occurs exclusively in malignant cells. Furthermore, in order to obtain a potent anti-tumor effect, viral vectors would be engineered to express pro-apoptotic genes, intra-cellar antibodies/nucleotide aptamers to block critical proteins, or siRNAs to knockdown essential cellular mRNAs. Alternatively, controlled expression of an essential viral gene would restore replication competence to the virus and enable selective oncolysis of tumor cells. Successful delivery of such bioengineered viruses may provide a more effective way to treat advanced prostate cancer.

Rejuvenating the immune system in rheumatoid arthritis

In rheumatoid arthritis (RA), the aging process of the immune system is accelerated. Formerly, this phenomenon was suspected to be a consequence of chronic inflammatory activity. However, newer data strongly suggest that deficiencies in maintaining telomeres and overall DNA stability cause excessive apoptosis of RA T cells, imposing proliferative pressure and premature aging on the system. Already during the early stages of their life cycle, and long before they participate in the inflammatory process, RA T cells are lost owing to increased apoptotic susceptibility. A search for underlying mechanisms has led to the discovery of defective pathways of repairing broken DNA and elongating and protecting telomeric sequences at the chromosomal ends. Two enzymatic machineries devoted to DNA repair and maintenance have been implicated. RA T cells fail to induce sufficient amounts of the telomeric repair enzyme telomerase, leaving telomeric ends uncapped and thus susceptible to damage. Of equal importance, RA T cells produce low levels of the DNA repair enzyme ataxia telangiectasia mutated and the complex of nucleoproteins that sense and fix DNA double-strand breaks. The inability to repair damaged DNA renders naive T cells vulnerable to apoptosis, exhausts T-cell regeneration and reshapes the T cell repertoire. Therapeutic attempts to reset the immune systems of patients with RA and prevent premature immunosenescence should include restoration of DNA repair capability.

Improved nonviral cancer suicide gene therapy using survivin promoter-driven mutant Bax

Suicide gene vectors are being developed in many laboratories as an attractive approach to cancer therapy. However, the development of these therapies is hampered by safety concerns and limitations of efficacy. The use of tumor-specific promoters, such as survivin promoter, can provide much needed specificity to target tumor cells. However, the expression levels from these promoters is often suboptimal and hence it is imperative to enhance the activity of the cytotoxic gene of interest. We tested apoptotic activity of several mutants of proapoptotic gene bax that constitutively translocate to the mitochondria and induce apoptosis. One of these mutants with deletion of serine at position S184 (S184del) was found to be most active and showed significant antitumor activity when expressed by the survivin promoter. In vitro testing shows that this vector (Sur-BaxS184del) induces cell killing in a variety of tumor cell lines of different origin with significantly higher efficacy than wild-type bax (Sur-BaxWT). The increase in cytotoxicity was a result of enhanced induction of apoptosis in tumor cells. In contrast to cytomegalovirus (CMV) promoter-driven bax (CMV-Bax), Sur-BaxS184del caused minimum toxicity in normal human dermal fibroblasts validating its specificity and safety. In a mouse tumor model (DA-3, murine breast cancer cells), we show that intratumoral injection of Sur-BaxS184del resulted in tumor growth retardation to the same level as CMV-Bax. This study highlights the effectiveness of using bax mutants in combination with survivin promoter for tumor-targeted suicide gene therapy in a nonviral vector.

Transcriptional targeting of gene expression in breast cancer by the promoters of protein regulator of cytokinesis 1 and ribonuclease reductase 2

For cancer gene therapy, cancer-specific over- expression of a therapeutic gene is required to reduce side effects derived from expression of the gene in normal cells. To develop such an expression vector, we searched for genes over-expressed and/or specifically expressed in cancer cells using bioinformatics and have selected genes coding for protein regulator of cytokinesis 1 (PRC1) and ribonuclease reductase 2 (RRM2) as candidates. Their cancer-specific expressions were confirmed in both breast cancer cell lines and patient tissues. We compared each promoter's cancer-specific activity in the breast normal and cancer cell lines using the luciferase gene as a reporter and confirmed cancer-specific expression of both PRC1 and RRM2 promoters. To test activities of these promoters in viral vectors, the promoters were also cloned into an adeno-associated viral (AAV) vector containing green fluorescence protein (GFP) as the reporter. The GFP expression levels by these promoters were various depending on cell lines tested and, in MDA-MB-231 cells, GFP activities derived from the PRC1 and RRM2 promoters were as strong as that from the cytomegalovirus (CMV) promoter. Our result showed that a vector containing the PRC1 or RRM2 promoter could be used for breast cancer specific overexpression in gene therapy.

Use of the Rad51 promoter for targeted anti-cancer therapy

Rad51 protein, involved in homologous recombination, is overexpressed in a variety of tumors, and its expression is correlated with a poor prognosis. Here we propose to exploit the overexpression of Rad51 in cancer cells to design a Rad51 promoter-based anticancer therapy. On average, Rad51 mRNA and protein levels are increased in cancer cells four- and sixfold, respectively. Serendipitously, we discovered that when the Rad51 ORF is replaced with another ORF, the difference in promoter activity between normal and cancer cells increases to an average of 840-fold with a maximum difference of 12,500-fold. This dramatic difference in activity has high therapeutic potential. We demonstrate that the fusion of Rad51 promoter to diphtheria toxin A (DTA) gene kills a variety of cancer cell types, including breast cancer, fibrosarcoma, and cervical cancer cells, with minimal effect on normal breast epithelial cells and normal fibroblasts. Our results suggest that therapies based on the Rad51 promoter will be highly tumor specific and open new avenues for targeting a broad range of cancers.

Hyaluronan regulates ceruloplasmin production by gliomas and their treatment-resistant multipotent progenitors

Ceruloplasmin (glycosylphosphatidylinositol-linked ferroxidase associated with normal astrocytes) can also be secreted by glioma cells, where its function is unknown. Ceruloplasmin is not only present in glioma cells and in human glioma specimens but also is enriched in highly malignant glioma stem-like cells. Hyaluronan is a large extracellular glycosaminoglycan that enhances malignant glioma behaviors by interacting with CD44 receptors and by downstream activation of signaling proteins and transporters associated with malignancy. We examined the relationship between hyaluronan and ceruloplasmin expression in glioma stem-like cells. Antagonism of hyaluronan interactions with short-fragment hyaluronan oligomers decreased ceruloplasmin expression in parental and stem-like glioma cells in vivo and in cell culture, implying that hyaluronan regulates ceruloplasmin expression. Further gain and loss-of-function studies are needed to fully define the relationship between hyaluronan and ceruloplasmin, and ceruloplasmin's effect on malignant behaviors.

Noninvasive imaging of therapeutic gene expression using a bidirectional transcriptional amplification strategy

Promoters that limit transgene expression to tumors play a vital role in cancer gene therapy. Although tumor specific, the human Survivin promoter (pSurv) elicits low levels of transcription. A bidirectional two-step transcriptional amplification (TSTA) system was designed to enhance expression of the therapeutic gene (TG) tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL or TR) and the reporter gene firefly luciferase (FL) from pSurv. An adenoviral vector carrying the enhanced targeting apparatus (Ad-pSurv-TR-G8-FL) was tested for efficiency and specificity of gene expression in cells and in living animals. Compared to the one-step systems (Ad-pSurv-FL or Ad-pSurv-TR), the bidirectional TSTA system showed tenfold higher expression of both the therapeutic and the reporter gene and their expression correlated in cells (R(2) = 0.99) and in animals (R(2) = 0.67). Noninvasive quantitative monitoring of magnitude and time variation of TRAIL gene expression was feasible by bioluminescence imaging of the transcriptionally linked FL gene in xenograft tumors following intratumoral adenoviral injection. Moreover, the TSTA adenovirus maintained promoter specificity in nontarget tissues following tail vein administration. These studies demonstrate the potential of the bidirectional TSTA system to achieve high levels of gene expression from a weak promoter, while preserving specificity and the ability to image expression of the TG noninvasively.

NBK/BIK antagonizes MCL-1 and BCL-XL and activates BAK-mediated apoptosis in response to protein synthesis inhibition

Ribonucleases, antibiotics, bacterial toxins, and viruses inhibit protein synthesis, which results in apoptosis in mammalian cells. How the BCL-2 family of proteins regulates apoptosis in response to the shutoff of protein synthesis is not known. Here we demonstrate that an Escherichia coli toxin, MazF, inhibited protein synthesis by cleavage of cellular mRNA and induced apoptosis in mammalian cells. MazF-induced apoptosis required proapoptotic BAK and its upstream regulator, the proapoptotic BH3-only protein NBK/BIK, but not BIM, PUMA, or NOXA. Interestingly, in response to MazF induction, NBK/BIK activated BAK by displacing it from anti-apoptotic proteins MCL-1 and BCL-X(L) that sequester BAK. Furthermore, NBK/BIK- or BAK-deficient cells were resistant to cell death induced by pharmacologic inhibition of translation and by virus-mediated shutoff of protein synthesis. Thus, the BH3-only protein NBK/BIK is the apical regulator of a BAK-dependent apoptotic pathway in response to shutoff of protein synthesis that functions to displace BAK from sequestration by MCL1 and BCL-X(L). Although NBK/BIK is dispensable for development, it is the BH3-only protein targeted for inactivation by viruses, suggesting that it plays a role in pathogen/toxin response through apoptosis activation.

Suicide cancer gene therapy using pore-forming toxin, streptolysin O

We cloned the streptolysin O gene from the Streptococcus pyogenes genome and tested the possibility of using it as an anticancer reagent. Transient transfection of the streptolysin O gene efficiently killed 293T cells after 12 hours of transfection as determined by lactate dehydrogenase release and propidium iodide uptake. No caspase activity was observed and necrosis was prominent during streptolysin O-induced cell death. Biochemical analysis of streptolysin O protein revealed that the deletion of only 5 amino acids from the COOH-terminal region of streptolysin O, which is essential for cholesterol binding activity, abolished its cell-killing activity, whereas the NH2-terminal region was more resilient, i.e., up to 115 amino acids could be deleted without changing its cell-killing activity. We generated a streptolysin O-expressing adenovirus and injected it into human cervical cancer cell-derived tumors grown in a nude mouse model. Twenty-one days postinjection, the average size of tumors in the streptolysin O adenovirus-injected group was 29.3% of that of the control PBS-treated group. Our results show that the genes of pore-forming toxins, like streptolysin O protein, have the potential to establish a novel class of suicide gene therapeutic reagents.