Gene silencing in androgen-responsive prostate cancer cells from the tissue-specific prostate-specific antigen promoter

A novel conditional gene silencing method using a tumor-specific and heat-inducible siRNA system

RNAi technology is an invaluable tool for investigating gene function. However, the non-temporal and non-spatial control is the primary limitation, which leads to siRNA leakiness and off-target effects. In this study, we inserted three kinds of HSE into tumor specific promoter hTERT, which aims to construct a temperature-inducible and tumor-specific RNAi plasmid vector. In our system, the expression of mature siRNA is tightly controlled by the heat shock-inducible and tumor-specific promoters. From the expression level of RNA and protein, we determined the efficiency of the inducible siRNA system by targeting SNCG gene in HepG2 and MCF-7 cells. Results showed that the controllable siRNA system could be induced to initiate siRNA expression by heat-induce. The silencing effect of SNCG is on a relative low level (10 %) at 37 °C, while it is significantly increased to 50 or 60 % after heat inducing at 43 °C. This new conditional siRNA system provides a novel approach to drive the siRNA expression by heat-inducible and tumor-specific promoter.

Strategies for siRNA navigation to desired cells

Whilst small interfering (si) RNAs have emerged as a promising therapeutic modality for treating a diversity of human diseases, delivery constitutes the most serious obstacle to siRNA drug development. As the most used delivery agents can enter all cell types, specificity must be built into the delivery agents or directly attached to the siRNA molecules. The use of antibodies, peptides, Peptide-Fc fusions, aptamers, and other targeting ligands has now enabled efficient gene silencing in the desired cell populations/tissues in vitro and in vivo. The present review summarizes these current innovations, which are important for the design of safe therapeutic siRNAs.

Targeted polymeric nanoparticles for cancer gene therapy

In this article, advances in designing polymeric nanoparticles for targeted cancer gene therapy are reviewed. Characterization and evaluation of biomaterials, targeting ligands, and transcriptional elements are each discussed. Advances in biomaterials have driven improvements to nanoparticle stability and tissue targeting, conjugation of ligands to the surface of polymeric nanoparticles enable binding to specific cancer cells, and the design of transcriptional elements has enabled selective DNA expression specific to the cancer cells. Together, these features have improved the performance of polymeric nanoparticles as targeted non-viral gene delivery vectors to treat cancer. As polymeric nanoparticles can be designed to be biodegradable, non-toxic, and to have reduced immunogenicity and tumorigenicity compared to viral platforms, they have significant potential for clinical use. Results of polymeric gene therapy in clinical trials and future directions for the engineering of nanoparticle systems for targeted cancer gene therapy are also presented.

Embedding siRNA sequences targeting apolipoprotein B100 in shRNA and miRNA scaffolds results in differential processing and in vivo efficacy

Overexpression of short hairpin RNA (shRNA) often causes cytotoxicity and using microRNA (miRNA) scaffolds can circumvent this problem. In this study, identically predicted small interfering RNA (siRNA) sequences targeting apolipoprotein B100 (siApoB) were embedded in shRNA (shApoB) or miRNA (miApoB) scaffolds and a direct comparison of the processing and long-term in vivo efficacy was performed. Next generation sequencing of small RNAs originating from shApoB- or miApoB-transfected cells revealed substantial differences in processing, resulting in different siApoB length, 5' and 3' cleavage sites and abundance of the guide or passenger strands. Murine liver transduction with adeno-associated virus (AAV) vectors expressing shApoB or miApoB resulted in high levels of siApoB expression associated with strong decrease of plasma ApoB protein and cholesterol. Expression of miApoB from the liver-specific LP1 promoter was restricted to the liver, while the H1 promoter-expressed shApoB was ectopically present. Delivery of 1 × 10(11) genome copies AAV-shApoB or AAV-miApoB led to a gradual loss of ApoB and plasma cholesterol inhibition, which was circumvented by delivering a 20-fold lower vector dose. In conclusion, incorporating identical siRNA sequences in shRNA or miRNA scaffolds results in differential processing patterns and in vivo efficacy that may have serious consequences for future RNAi-based therapeutics.

Optimization and comparison of knockdown efficacy between polymerase II expressed shRNA and artificial miRNA targeting luciferase and Apolipoprotein B100

Background

Controlling and limiting the expression of short hairpin RNA (shRNA) by using constitutive or tissue-specific polymerase II (pol II) expression can be a promising strategy to avoid RNAi toxicity. However, to date detailed studies on requirements for effective pol II shRNA expression and processing are not available. We investigated the optimal structural configuration of shRNA molecules, namely: hairpin location, stem length and termination signal required for effective pol II expression and compared it with an alternative strategy of avoiding toxicity by using artificial microRNA (miRNA) scaffolds.

Results

Highly effective shRNAs targeting luciferase (shLuc) or Apolipoprotein B100 (shApoB1 and shApoB2) were placed under the control of the pol II CMV promoter and expressed at +5 or +6 nucleotides (nt) with reference to the transcription start site (TSS). Different transcription termination signals (TTS), namely minimal polyadenylation (pA), poly T (T5) and U1 were also used. All pol II- expressed shRNA variants induced mild inhibition of Luciferase reporters carrying specific targets and none of them showed comparable efficacy to their polymerase III-expressed H1-shRNA controls, regardless of hairpin position and termination signal used. Extending hairpin stem length from 20 basepairs (bp) to 21, 25 or 29 bp yielded only slight improvement in the overall efficacy. When shLuc, shApoB1 and shApoB2 were placed in an artificial miRNA scaffold, two out of three were as potent as the H1-shRNA controls. Quantification of small interfering RNA (siRNA) molecules showed that the artificial miRNA constructs expressed less molecules than H1-shRNAs and that CMV-shRNA expressed the lowest amount of siRNA molecules suggesting that RNAi processing in this case is least effective. Furthermore, CMV-miApoB1 and CMV-miApoB2 were as effective as the corresponding H1-shApoB1 and H1-shApoB2 in inhibiting endogenous ApoB mRNA.

Conclusion

Our results demonstrate that artificial miRNA have a better efficacy profile than shRNA expressed either from H1 or CMV promoter and will be used in the future for RNAi therapeutic development.

What are the key targeted delivery technologies of siRNA now?

Whilst significant advances have been made in the delivery of nucleic acids to mammalian cells, most of the used strategies do not distinguish between normal and cancer cells. The same challenge is also facing radioactive- and chemo-therapies which are highly toxic and poorly tolerated due to limited tumor specificity. Regardless of the nature of the drug, there is a need for developing a technology platform which targets drugs only to tumors cells, leaving normal cells undamaged. Among the targeting strategies, receptor-targeted delivery provides an innovative strategy to selectively direct therapeutics to cancer cells. Receptor-binding ligands (e.g., peptides, antibodies, aptamers) can be incorporated into gene delivery vesicles or directly conjugated to siRNA in the hope in promoting their localization in target cell expressing the cognate receptors. The present chapter discusses the current progress made in the specific delivery of siRNAs.

Inhibitory RNA molecules in immunotherapy for cancer

Over the past few decades, our expanding knowledge of the mammalian immune system - how it is developed, activated, and regulated - has fostered hope that it may be harnessed in the future to successfully treat human cancer. The immune system activated by cancer vaccines may have the unique ability to selectively eradicate tumor cells at multiple sites in the body without inflicting damage on normal tissue. However, progress in the development of cancer vaccines that effectively capitalize on this ability has been limited and slow. The immune system is restrained by complex, negative feedback mechanisms that evolved to protect the host against autoimmunity and may also prevent antitumor immunity. In addition, tumor cells exploit a plethora of strategies to evade detection and elimination by the immune system. For these reasons, the field of cancer immunotherapy has suffered considerable setbacks in the past and faces great challenges at the present time. Some of these challenges may be overcome through the use of RNA interference, a process by which gene expression can be efficiently and specifically "knocked down" in cells. This chapter focuses on the current status and future prospects in the application of small interfering RNA and microRNA, two main forms of RNA interference, to treat cancer by curtailing mechanisms that attenuate the host immune response.

Targeted delivery of antisense oligonucleotides and siRNAs into mammalian cells

RNA interference (RNAi) is a natural mechanism for gene silencing that can be harnessed for the development of RNA-based drugs. Although synthetic small interfering RNA (siRNAs) can be delivered in vitro to virtually all cell types using lipid-based transfection agents or electroporation, efficient strategies for achieving either systemic or targeted delivery remains one of the major in vivo challenges. Among the targeting strategies, receptor-targeted delivery provides an innovative strategy to selectively direct therapeutics to cancer cells. Receptor-binding peptides can be incorporated into gene-delivery vesicles or directly conjugated to siRNAs in the hope of promoting their localization in target cells expressing the cognate receptors. This chapter discusses the current status of siRNA-targeting strategies using either peptides identified through iterative screening of random peptide phage libraries or naturally occurring peptides. Also, transcriptional targeting strategies and detailed protocols for the selection of cancer cell-binding peptide from random peptide libraries are described.

Establishment of CXCR4-small interfering RNA retrovirus vector driven by human prostate-specific antigen promoter and its biological effects on prostate cancer in vitro and in vivo

PURPOSE

CXC chemokine receptor-4 (CXCR4) is closely involved in bone metastasis of prostate cancer, and CXCR4 levels are frequently increased in prostate cancer cells and tissues. In the present study, its biological effects on prostate cancer in vitro and in vivo and feasibility to be a therapy target were investigated using a RNA interfering retrovirus vector targeting CXCR4 gene driven by human prostate-specific antigen promoter (pPSA).

METHODS

We established a pPSA-siCXCR4 retrovirus vector and transfected prostate cancer cell PC-3m, LNCaP and breast cancer cell MCF-7, respectively. The expression of CXCR4 mRNA and protein was detected by RT-PCR and western blot, and the ability of adhesion, migration, invasion of prostate cancer cells was assessed using Transwell chamber. A metastasizing model using BALB/cA mice with human bone tissue implantation was established too, and transfected prostate cancer cells were via caudal vein. Survival time of mice suffering bone metastatic tumor as well as the weight and volume of these tumors were recorded and analyzed.

RESULTS

The expression of CXCR4 mRNA and protein in androgen-responsive LNCaP cells was blocked by the pPSA-siCXCR4 vector, but it could not work in non androgen-responsive PC-3m cell and breast cancer cell MCF-7. The results of experiments in vitro also showed that the adhesion, transendothelial migration and invasive ability of transfected LNCaP cells were impaired, while there was no change in PC-3m and MCF-7 cells after transfection. pPSA-siCXCR4 represented a similar inhibitory effect in fluorescent bone metastasis model of LNCaP cells compared with PC-3m cells.

CONCLUSION

These results suggest that the downstream siRNA controlled by PSA promoter in retrovirus system can express selectively in androgen-responsive prostate cancer in vitro and in vivo, and CXCR4 plays an important role in prostate cancer metastasis. We believe that the pPSA-siCXCR4 retrovirus vector is a potential choice in gene therapy for androgen-responsive prostate cancer.

Conditional gene silencing in mammalian cells mediated by a stress-inducible promoter

MicroRNAs (miRNAs) are endogenous non-coding small RNAs, which negatively regulate gene expression in a sequence-specific manner through the RNA interference (RNAi) pathway. Here we describe a new miRNA-based conditional RNAi expression system that relies on cellular stress-response mechanisms in mammalian cells. In our constructs, expression of miRNA mimics is tightly controlled by a heat shock-inducible promoter. This system is highly effective in silencing permanently or conditionally expressed luciferase. The stress inducible vectors also effectively deplete co-expressed pro-apoptotic protein CHOP with heat shock. Furthermore, we demonstrate cloning of a protein-coding sequence between the stress-inducible promoter and the miRNA expression cassette allows simultaneous silencing of a target gene and activation of synthesis of a protein of choice in response to stress stimulation. This new conditional gene silencing approach could be an invaluable tool for various areas of basic and applied research and for therapeutic intervention.

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.

Immunotherapeutic strategies employing RNA interference technology for the control of cancers

The human immune system is comprised of several types of cells that have the potential to eradicate tumors without inflicting damage on normal tissue. Over the past decade, progress in the understanding of tumor biology and immunology has offered the exciting possibility of treating malignant disease with vaccines that exploit the capacity of T cells to effectively and selectively kill tumor cells. However, the immune system frequently fails to mount a successful defense against cancers despite vaccination with tumor-associated antigens. The ability of these vaccines to generate an abundant supply of armed effector T cells is often limited by immunoregulatory signaling pathways that suppress T cell activation. In addition, many tumors create a local microenvironment that inhibits the function of T cells. The attenuation of these pathways, which facilitate the evasion of tumors from immune surveillance, thus represents a potentially effective approach for cancer immunotherapy. Specifically, it may be of interest to modify the properties of dendritic cells, T cells, and tumor cells to downregulate the expression of proteins that diminish the immune response to cancers. RNA interference (RNAi) techniques have developed into a highly effective means of intracellular gene 'knockdown' and may be successfully employed in this way to improve cancer immunotherapies. This strategy has recently been explored both in vitro and in vivo, and has generated significantly enhanced antitumor immunity in numerous studies. Nevertheless, several practical concerns remain to be resolved before RNAi technology can be implemented safely and efficiently in humans. As novel developments and discoveries in molecular biology rapidly continue to unfold, it is likely that this technology may soon translate into a potent form of gene silencing in the clinic with profound applications to cancer immunotherapy.

Transcriptional targeting of small interfering RNAs into cancer cells

Small interfering RNAs (siRNAs) are widely used for analyzing gene function and have the potential to be developed into human therapeutics. However, persistent siRNA expression in normal cells may cause toxic side effects. Therefore, the therapeutic applications of RNAi in cancer require either the specific delivery of synthetic siRNAs into cancer cells or the control of siRNA expression. Accordingly, we have developed a cancer-specific vector that expresses siRNAs from the human survivin promoter. A plasmid vector expressing siRNAs under this promoter enabled efficient gene silencing of gene expression in different cancer cell lines. The levels of inhibition were comparable to that obtained with the constitutively active U6 promoter. By contrast to U6 promoter, no significant gene silencing was obtained with the Survivin promoter in normal mammary epithelial cells. Collectively, these data indicate that the survivin promoter is suitable for directing siRNA expression in cancer cells, but not normal cells.

Stable RNA interference: comparison of U6 and H1 promoters in endothelial cells and in mouse brain

BACKGROUND

RNA interference (RNAi) is a post-transcriptional RNA degradation process, which has become a very useful tool in gene function studies and gene therapy applications. Long-term cellular expression of small interfering RNA (siRNA) molecules required for many gene therapy applications can be achieved by lentiviral vectors (LVs). The two most commonly used promoters to drive the short hairpin RNA (shRNA) expression are the human U6 small nuclear promoter (U6) and the human H1 promoter (H1).

METHODS

We investigated whether there is any significant difference between the efficiencies of U6 and H1 in LV-mediated RNAi using green fluorescent protein (GFP) as a target gene by flow cytometry and real-time reverse-transcription polymerase chain reaction (RT-PCR) in endothelial cells. Also, we compared the efficiencies of U6 and H1 in the GFP transgenic mouse brain after stereotactic LV injection.

RESULTS

We show that the U6 promoter is more efficient than H1 in GFP silencing in vitro, leading to 80% GFP knockdown at an average of one integrated vector genome per target cell genome. The silencing is persistent for several months. In addition, the U6 promoter is superior to H1 in vivo and leads to stable GFP knockdown in mouse brain for at least 9 months.

CONCLUSIONS

These results show that LV-mediated RNAi is a powerful gene-silencing method for the long-term inhibition of gene expression in vitro and in vivo.

Prospects of RNA interference therapy for cancer

RNA interference (RNAi) is a powerful gene-silencing process that holds great promise in the field of cancer therapy. The discovery of RNAi has generated enthusiasm within the scientific community, not only because it has been used to rapidly identify key molecules involved in many disease processes including cancer, but also because RNAi has the potential to be translated into a technology with major therapeutic applications. Our evolving understanding of the molecular pathways important for carcinogenesis has created opportunities for cancer therapy employing RNAi technology to target the key molecules within these pathways. Many gene products involved in carcinogenesis have already been explored as targets for RNAi intervention, and RNAi targeting of molecules crucial for tumor-host interactions and tumor resistance to chemo- or radiotherapy has also been investigated. In most of these studies, the silencing of critical gene products by RNAi technology has generated significant antiproliferative and/or proapoptotic effects in cell-culture systems or in preclinical animal models. Nevertheless, significant obstacles, such as in vivo delivery, incomplete suppression of target genes, nonspecific immune responses and the so-called off-target effects, need to be overcome before this technology can be successfully translated into the clinical arena. Significant progress has already been made in addressing some of these issues, and it is foreseen that early phase clinical trials will be initiated in the very near future.

Gene therapy for gastric cancer: Is it promising?

Gastric cancer is one of the most common tumors worldwide. The therapeutic outcome of conventional therapies is inefficient. Thus, new therapeutic strategies are urgently needed. Gene therapy is a promising molecular alternative in the treatment of gastric cancer, including the replacement of defective tumor suppressor genes, the inactivation of oncogenes, the introduction of suicide genes, genetic immunotherapy, anti-angiogenetic gene therapy, and virotherapy. Improved molecular biological techniques and a better understanding of gastric carcinogenesis have allowed us to validate a variety of genes as molecular targets for gene therapy. This review provides an update of the new developments in cancer gene therapy, new principles, techniques, strategies and vector systems, and shows how they may be applied in the treatment of gastric cancer.

A genetic strategy to treat sickle cell anemia by coregulating globin transgene expression and RNA interference

The application of RNA interference (RNAi) to stem cell-based therapies will require highly specific and lineage-restricted gene silencing. Here we show the feasibility and therapeutic potential of coregulating transgene expression and RNAi in hematopoietic stem cells. We encoded promoterless small-hairpin RNA (shRNA) within the intron of a recombinant gamma-globin gene. Expression of both gamma-globin and the lariat-embedded small interfering RNA (siRNA) was induced upon erythroid differentiation, specifically downregulating the targeted gene in tissue- and differentiation stage-specific fashion. The position of the shRNA within the intron was critical to concurrently achieve high-level transgene expression, effective siRNA generation and minimal interferon induction. Lentiviral transduction of CD34(+) cells from patients with sickle cell anemia led to erythroid-specific expression of the gamma-globin transgene and concomitant reduction of endogenous beta(S) transcripts, thus providing proof of principle for therapeutic strategies that require synergistic gene addition and gene silencing in stem cell progeny.

On the delivery of small interfering RNAs into mammalian cells

RNA interference is becoming the technique of choice for analysing gene function and drug target validation. In this process, sequence-specific gene inhibition is initiated by small RNA duplexes, known as small interfering RNAs (siRNAs). The possibility that exogenously delivered siRNAs or endogenously expressed hairpin siRNAs can cause the destruction of specific target mRNA in vitro and in animal models has been demonstrated. However, the key challenges for the development of siRNAs as human therapeutics is largely dependent on the development of suitable delivery agents and improved siRNA specificity. This review highlights recent advances in siRNA delivery, as well as challenging problems related to immune stimulation.

Towards high-throughput functional target discovery in angiogenesis research

Angiogenesis is a hallmark of malignancies and other proliferative diseases, and inhibition of this process is considered to be a promising treatment strategy. Classical gene-expression analyses performed during the past decade have generated vast lists of genes associated with disease but have so far yielded only limited novel therapeutic targets for clinical applications. Recently, the focus has shifted from target identification, based on gene-expression analysis, to identification of genes, based on the function of the encoded protein. Disease-target genes can now be identified in a high-throughput fashion based on functional properties that are directly related to the disease phenotype. This new approach significantly shortens the time span for the development of therapeutic applications from the laboratory bench to the hospital bedside.

Probing tumor phenotypes using stable and regulated synthetic microRNA precursors

RNA interference is a powerful method for suppressing gene expression in mammalian cells. Stable knock-down can be achieved by continuous expression of synthetic short hairpin RNAs, typically from RNA polymerase III promoters. But primary microRNA transcripts, which are endogenous triggers of RNA interference, are normally synthesized by RNA polymerase II. Here we show that RNA polymerase II promoters expressing rationally designed primary microRNA-based short hairpin RNAs produce potent, stable and regulatable gene knock-down in cultured cells and in animals, even when present at a single copy in the genome. Most notably, by tightly regulating Trp53 knock-down using tetracycline-based systems, we show that cultured mouse fibroblasts can be switched between proliferative and senescent states and that tumors induced by Trp53 suppression and cooperating oncogenes regress upon re-expression of Trp53. In practice, this primary microRNA-based short hairpin RNA vector system is markedly similar to cDNA overexpression systems and is a powerful tool for studying gene function in cells and animals.

Epigenetic manipulation of gene expression: a toolkit for cell biologists

Cell biologists have been afforded extraordinary new opportunities for experimentation by the emergence of powerful technologies that allow the selective manipulation of gene expression. Currently, RNA interference is very much in the limelight; however, significant progress has also been made with two other approaches. Thus, antisense oligonucleotide technology is undergoing a resurgence as a result of improvements in the chemistry of these molecules, whereas designed transcription factors offer a powerful and increasingly convenient strategy for either up- or down-regulation of targeted genes. This mini-review will highlight some of the key features of these three approaches to gene regulation, as well as provide pragmatic guidance concerning their use in cell biological experimentation based on our direct experience with each of these technologies. The approaches discussed here are being intensely pursued in terms of possible therapeutic applications. However, we will restrict our comments primarily to the cell culture situation, only briefly alluding to fundamental differences between utilization in animals versus cells.