Specific down-regulation of HER-2/neu mediated by a chimeric U6 hammerhead ribozyme results in growth inhibition of human ovarian carcinoma

Therapeutic Potential of Ribozymes

Recent advances in RNA engineering during the last two decades have supported the development of RNA-based therapeutics targeting a variety of human diseases. The broad scope of these emerging drugs clearly demonstrates the versatility of RNA. Ribozymes have been seen as promising candidates in this area. However, efficient intracellular application of ribozymes remains challenging, and other strategies appear to have outperformed ribozymes as molecular drugs. Nevertheless, trans-cleaving ribozymes have been applied for specific cleavage of target mRNAs in order to inhibit undesired gene expression. Furthermore, ribozymes have been engineered to allow site-directed RNA sequence alterations, enabling the correction of genetic misinformation at the RNA level. This chapter provides an overview of ribozyme-based strategies, highlighting the promises and pitfalls for potential therapeutic applications.

TP53-induced glycolysis and apoptosis regulator promotes proliferation and invasiveness of nasopharyngeal carcinoma cells

The TP53-induced glycolysis and apoptosis regulator (TIGAR) is the protein product of the p53 target gene, C12orf5. TIGAR blocks glycolysis and promotes cellular metabolism via the pentose phosphate pathway; it promotes the production of cellular nicotinamide adenine dinucleotide phosphate (NADPH), which leads to enhanced scavenging of intracellular reactive oxygen species, and inhibition of oxidative stress-induced apoptosis in normal cells. Our previous study identified a novel nucleoside analog that inhibited cellular growth and induced apoptosis in nasopharyngeal carcinoma (NPC) cell lines via downregulation of TIGAR expression. Furthermore, the growth inhibitory effects of c-Met tyrosine kinase inhibitors were ameliorated by the overexpression of TIGAR in the NPC cell lines. These results indicate a significant role for TIGAR expression in the survival of NPCs. The present study aimed to further define the function of TIGAR expression in NPC cells. In total, 36 formalin-fixed, paraffin-embedded NPC tissue samples were obtained for the immunohistochemical determination of TIGAR expression. The effects of TIGAR expression on cell proliferation, NADPH production and cellular invasiveness were also assessed in NPC cell lines. Overall, TIGAR was overexpressed in 27/36 (75%) of the NPC tissues compared with the adjacent non-cancer epithelial cells. Similarly, TIGAR overexpression was also observed in a panel of six NPC cell lines compared with normal NP460 hTert and Het1A cell lines. TIGAR overexpression led to increased cellular growth, NADPH production and invasiveness of the NPC cell lines, whereas a knockdown of TIGAR expression resulted in significant inhibition of cellular growth and invasiveness. The expression of the two mesenchymal markers, fibronectin and vimentin, was increased by TIGAR overexpression, but reduced following TIGAR-knockdown. The present study revealed that TIGAR overexpression led to increased cellular growth, NADPH production and invasiveness, and the maintenance of a mesenchymal phenotype, in NPC tissues.

EGFR/HER-targeted therapeutics in ovarian cancer

Despite decades of research and evolving treatment modalities, survival among patients with epithelial ovarian cancer has improved only incrementally. During this same period, the development of biologically targeted therapeutics has improved survival for patients with diverse malignancies. Many of these new drugs target the human epidermal growth factor receptor (EGFR/HER/ErbB) family of tyrosine kinases, which play a major role in the etiology and progression of many carcinomas, including epithelial ovarian cancer. While several HER-targeted therapeutics are US FDA approved for the treatment of various malignancies, none have gained approval for the treatment of ovarian cancer. Here, we review the published literature on HER-targeted therapeutics for the treatment of ovarian cancer, including novel HER-targeted therapeutics in various stages of clinical development, as well as the challenges that have limited the use of these inhibitors in clinical settings.

Novel strategies to augment genetically delivered immunotoxin molecular therapy for cancer therapy

Immunotoxin therapy is a promising molecular cancer treatment strategy. Its main advantage is seletive cytotoxicity towards tumor cells and minimal toxicity in normal tissues. However, a short half-life and rapid clearance severely hampers its clinical application. We report here a novel genetic approach in which a recombinant adenovirus vector was used to deliver an immunotoxin gene e23(scFv)-PE40 targeted to the oncogene c-erbB-2 (also known as Her2/neu). This vector, when combined with a low dose of a conditionally replicative adenovirus vector (CRAd), has enhanced tumor-killing ability either alone or in combination with the chemotherapeutic agent etoposide. Our data show that low-dose CRAd facilitated the replication of replication-deficient Ad-e23(scFv)-PE40 up to 6-20 times and the transcription of e23(scFv)-PE40 gene up to 12 times. Moreover, etoposide increased the e23(scFv)-PE40 transcription up to 8.5 times. Furthermore, we show that systemic application of Ad-e23(scFv)-PE40 and enhanced expression of the immunotoxin gene was well tolerated as determined by serum biochemical markers and histological examination of most vital organs. Taken together, our data support a novel genetic immunotoxin delivery approach that may yield enhanced efficacy against a variety of Her2/neu-expressing tumors.

pcDNA3.1(-)-mediated ribozyme targeting of HER-2 suppresses breast cancer tumor growth

The HER-2 proto-oncogene (also called c-erbB-2/neu) encodes the protein, p185, which is closely related to the growth and metastasis of adenocarcinoma, and is overexpressed in 25-30% of human breast cancers. In this study, we attempt to reverse the malignant phenotype of the breast cancer cell line, MCF-7, using a HER-2-specific hammerhead ribozyme. Two anti-HER-2 hammerhead ribozymes, RZ1 and RZ2, were synthesized, inserted separately into the nonviral eukaryotic expression vector, pcDNA3.1(-), and transfected into MCF-7 cells. Analyses showed that the HER-2 mRNA and p185, as well as oncogene k-ras were down-regulated remarkably in the ribozyme-transfected cells, while the onco-suppressor gene, p53, was up-regulated. Furthermore, the tumorigenicity of the RZ1-stably transfected MCF-7 cells was decreased dramatically in nude mice. These results demonstrate that the use of anti-HER-2 ribozymes may be a beneficial strategy for gene therapy of breast cancer.

A construct with fluorescent indicators for conditional expression of miRNA

BACKGROUND

Transgenic RNAi holds promise as a simple, low-cost, and fast method for reverse genetics in mammals. It may be particularly useful for producing animal models for hypomorphic gene function. Inducible RNAi that permits spatially and temporally controllable gene silencing in vivo will enhance the power of transgenic RNAi approach. Furthermore, because microRNA (miRNA) targeting specific genes can be expressed simultaneously with protein coding genes, incorporation of fluorescent marker proteins can simplify the screening and analysis of transgenic RNAi animals.

RESULTS

We sought to optimally express a miRNA simultaneously with a fluorescent marker. We compared two construct designs. One expressed a red fluorescent protein (RFP) and a miRNA placed in its 3' untranslated region (UTR). The other expressed the same RFP and miRNA, but the precursor miRNA (pre-miRNA) coding sequence was placed in an intron that was inserted into the 3'-UTR. We found that the two constructs expressed comparable levels of miRNA. However, the intron-containing construct expressed a significantly higher level of RFP than the intron-less construct. Further experiments indicate that the 3'-UTR intron enhances RFP expression by its intrinsic gene-expression-enhancing activity and by eliminating the inhibitory effect of the pre-miRNA on the expression of RFP. Based on these findings, we incorporated the intron-embedded pre-miRNA design into a conditional expression construct that employed the Cre-loxP system. This construct initially expressed EGFP gene, which was flanked by loxP sites. After exposure to Cre recombinase, the transgene stopped EGFP expression and began expression of RFP and a miRNA, which silenced the expression of specific cellular genes.

CONCLUSION

We have designed and tested a conditional miRNA-expression construct and showed that this construct expresses both the marker genes strongly and can silence the target gene efficiently upon Cre-mediated induction of the miRNA expression. This construct can be used to increase the efficiency of making cell lines or transgenic animals that stably express miRNA targeting specific genes.

Recombinant immunoproapoptotic proteins with furin site can translocate and kill HER2-positive cancer cells

We previously reported the selective killing of HER2-positive tumor cells by a class of immunoproapoptotic proteins containing single-chain antibody, translocation domain of Pseudomonas exotoxin A (domain II; PEA II), and constitutively active human apoptotic molecules. In this study, a novel class of antitumor immunoproapoptotic proteins was explored to mediate tumor-specific apoptosis both in vitro and in vivo. Three furin cleavage sequences, including a synthetic polyarginine tract, and two furin cleavable sequences from PEA and diphtheria toxin were respectively used to replace PEA II in the previously constructed immunoproapoptotic protein. When produced and secreted by the genetically modified Jurkat cells, the novel targeted proapoptotic proteins selectively bound to HER2, which is often overexpressed on tumor cell surface. Followed by receptor-mediated endocytosis and furin cleavage in the endosome, the recombinant proteins could translocate into the cytosol, leading to irreversible cell death. Moreover, delivery of these proteins by either i.m. plasmid injection or i.v. injection of plasmid-expressing Jurkat cells led to tumor regression and prolonged animal survival in a nude mouse xenograft tumor model, indicating in vivo antitumor activity of the recombinant proteins. We conclude that the new class of immunoproapoptotic proteins show comparable activity with PEA II-containing counterpart and provide an attractive therapeutic alternative as they contain much less exogenous fragments.

[Carcinogenesis: defect control systems and options for molecular therapy]

DNA mutations lead to multiple defects of different control systems necessary to regulate cell growth, cell death and cell invasion, thus resulting in the development of a malignant tumor. While the loss of single control systems can still be compensated by others, the destruction of the whole network on a molecular level will cause tumor growth. Knowledge about these control systems and their defects during carcinogenesis may it possible to design new therapeutic strategies. Among them, gene therapy offers promising treatment options.

Reference Systems for Kinase Drug Discovery: Chemical Genetic Approaches to Cell-Based Assays

Protein kinases play key roles in a number of diseases, including cancer, inflammation, and diabetes. Disregulation of kinase-based signal transduction networks results in aberrant cell differentiation, activation, proliferation, and invasion. The growing importance of kinases as a major class of drug targets across multiple large clinical indications, together with the large number of kinases in the genome (~518), has generated a critical need for technologies that enable the identification of potent and selective kinase inhibitors with good drug-like properties. In this review, we describe methods used for developing cell-based assays for kinase inhibitors, discuss advantages and disadvantages of each approach, and describe new chemical genetic methods as reference systems for establishing cell-based assays and their use for functional selectivity profiling of kinase inhibitors.

Gene therapy for ovarian cancer: progress and potential

Gene therapy remains a promising therapeutic modality for ovarian cancer. Yet much work remains to be done to see gene therapy realize its full potential in elucidating the complex genetic interactions of delivered genes within target cancer cells and in the development of improved vector systems. Because most neoplasms involve multiple mutations, the targeting of a single mutation is unlikely to achieve total tumor control: gene therapy strategies that target multiple cellular processes or invoke various antitumor approaches need to be investigated. Additionally, current vector systems do not transduce ovarian cancer cells efficiently and are hampered by immune responses that further limit their efficacy. Additionally, limitations in vector specificity lead to transduction of normal cells and subsequent toxicity. Investigators are developing refinements to current gene therapy approaches that would address these limitations and that are soon to be incorporated into clinical trials. It is hoped that these advances will lead to improvements in the therapeutic index for ovarian cancer gene therapy and provide another effective therapeutic tool for this deadly disease.

Maxizyme-mediated specific inhibition on mutant-type p53 in vitro

AIM

To evaluate the specific inhibition of maxizyme directing against mutant-type p53 gene (mtp53) at codon 249 in exon 7 (AGG-AGT) in vitro.

METHODS

Two different monomers of anti-mtp53 maxizyme (maxizyme right MzR, maxizyme left MzL) and control mutant maxizyme (G(5)-A(5)) were designed by computer and cloned into vector pBSKU6 (pBSKU6MzR, pBSKU6MzL). After being sequenced, the restrictive endonuclease site in pBSKU6MzR was changed by PCR and then U6MzR was inserted into pBSKU6MzL, the recombinant vector was named pU6Mz and pU6asMz (mutant maxizyme). Mtp53 and wild-type p53 (wtp53) gene fragments were cloned into pGEM-T vector under the T7 promoter control. The (32)p-labeled mtp53 transcript was the target mRNA. Cold maxizyme transcripts were incubated with (32)p-labeled target RNA in vitro and radioautographed after denaturing polyacrylamide gel electrophoresis.

RESULTS

In cell-free systems, pU6Mz showed a specific cleavage activity against target mRNA at 37 degrees and 25 mM MgCL(2). The cleavage efficiency of pU6Mz was 42 %, while pU6asMz had no inhibitory effect. Wtp53 was not cleaved by pU6Mz either.

CONCLUSION

pU6Mz had a specific catalytic activity against mtp53 in cell-free system. These lay a good foundation for studying the effects of anti-mtp53 maxizyme in HCC cell lines. The results suggest that maxizyme may be a promising alternative approach for treating hepatocellular carcinoma containing mtp53.

Activity of HDV ribozymes to trans-cleave HCV RNA

AIM: To explore whether HDV ribozymes have the ability to trans-cleave HCV RNA.

METHODS: Three HDV genomic ribozymes were designed and named RzC1, RzC2 and RzC3. The substrate RNA contained HCV RNA 5’-noncoding region and 5'-fragment of C region (5'-NCR-C). All the ribozymes and HCV RNA 5'-NCR-C were obtained by transcription in vitro from their DNA templates, and HCV RNA 5'-NCR-C was radiolabelled at its 5’-end. Under certain pH, temperature, appropriate concentration of Mg²⁺ and deionized formamide, these ribozymes were respectively or simultaneously mixed with HCV RNA 5'-NCR-C and reacted for a certain time. The trans-cleavage reaction was stopped at different time points, and the products were separated with polyacrylamide gel electrophoresis (PAGE), displayed by autoradiography. Percentage of trans-cleaved products was measured to indicate the activity of HDV ribozymes.

RESULTS: RzC1 and RzC2 could trans-cleave 26% and 21.8% of HCV RNA 5'-NCR-C under our reaction conditions with 2.5 mol•L^-1 deionized formamide respectively. The percentage of HCV RNA 5'-NCR-C trans-cleaved by RzC1, RzC2 or combined usage of the three ribozymes increased with time, up to 24.9%, 20.3% and 37.3% respectively at 90 min point. Almost no product from RzC3 was observed.

CONCLUSION: HDV ribozymes are able to trans-cleave specifically HCV RNA at certain sites under appropriate conditions, and combination of several ribozymes aiming at different target sites can trans-cleave the substrate more efficiently than using only one of them.

Hammerhead ribozymes for target validation

Expensive failures in the pharmaceutical industry might be avoided by target validation at an early stage. Often, the full consequences of inhibiting a chosen drug target do not emerge until late in the development process. One option is to use hammerhead ribozymes as highly specific ribonucleases targeted exclusively at the mRNA encoding the target protein. The first part of this review is concerned with the mechanism and design of hammerhead ribozymes. This includes the chemistry of their action, specificity of cleavage and ability to discriminate between different mRNAs and selection of suitable cleavage sites. In considering their use for target validation, hammerhead ribozymes are divided into two categories. Endogenous ribozymes are transcribed inside the cell where they act whilst exogenous are introduced into the cell from outside. Exogenous ribozymes are synthesised chemically and must be protected against cellular nucleases. Information is provided on transfection methods and vectors that have been used with endogenous ribozymes as well as synthesis and chemical modification of exogenous ribozymes. Of proteins inhibited in cells or whole organisms, those in animal experiments are emphasised. Comparisons are made with other approaches, especially the use of antisense oligonucleotides or RNA.

Cancer gene therapy: fringe or cutting edge?

Direct targeting of cancer cells with gene therapy has the potential to treat cancer on the basis of its molecular characteristics. But although laboratory results have been extremely encouraging, many practical obstacles need to be overcome before gene therapy can fulfil its goals in the clinic. These issues are not trivial, but seem less formidable than the challenge of killing cancers selectively and rationally--a challenge that has been successfully addressed.