Design and evaluation of chemically synthesized siRNA targeting the NPM-ALK fusion site in anaplastic large cell lymphoma (ALCL)

pH-responsive DNA nanomicelles for chemo-gene synergetic therapy of anaplastic large cell lymphoma

Chemo-gene therapy is an emerging synergetic modality for the treatment of cancers. Herein, we developed pH-responsive multifunctional DNA nanomicelles (DNMs) as delivery vehicles for controllable release of doxorubicin (Dox) and anaplastic lymphoma kinase (ALK)-specific siRNA for the chemo-gene synergetic therapy of anaplastic large cell lymphoma (ALCL).

Methods: DNMs were synthesized by performing in situ rolling circle amplification (RCA) on the amphiphilic primer-polylactide (PLA) micelles, followed by functionalization of pH-responsive triplex DNA via complementary base pairing. The anticancer drug Dox and ALK-specific siRNA were co-loaded to construct Dox/siRNA/DNMs for chemo-gene synergetic cancer therapy. When exposed to the acidic microenvironment (pH below 5.0), C-G·C⁺ triplex structures were formed, leading to the release of Dox and siRNA for gene silencing to enhance the chemosensitivity in ALCL K299 cells. The chemo-gene synergetic anticancer effect of Dox/siRNA/DNMs on ALCL was evaluated in vitro and in vivo.

Results: The pH-responsive DNMs exhibited good monodispersity at different pH values, good biocompatibility, high drug loading capacity, and excellent stability even in the human serum. With the simultaneous release of anticancer drug Dox and ALK-specific siRNA in response to pH in the tumor microenvironment, the Dox/siRNA/DNMs demonstrated significantly higher treatment efficacy for ALCL compared with chemotherapy alone, because the silencing of ALK gene expression mediated by siRNA increased the chemosensitivity of ALCL cells. From the pathological analysis of tumor tissue, the Dox/siRNA/DNMs exhibited the superiority in inhibiting tumor growth, low toxic side effects and good biosafety.

Conclusion: DNMs co-loaded with Dox and ALK-specific siRNA exhibited significantly enhanced apoptosis of ALCL K299 cells in vitro and effectively inhibited tumor growth in vivo without obvious toxicity, providing a potential strategy in the development of nanomedicines for synergetic cancer therapy.

Aptamer-Equipped Protamine Nanomedicine for Precision Lymphoma Therapy

Anaplastic large cell lymphoma (ALCL) is the most common T-cell lymphoma in children. ALCL cells characteristically express surface CD30 molecules and carry the pathogenic ALK oncogene, both of which are diagnostic biomarkers and are also potential therapeutic targets. For precision therapy, we report herein a protamine nanomedicine incorporated with oligonucleotide aptamers to selectively target lymphoma cells, a dsDNA/drug payload to efficiently kill targeted cells, and an siRNA to specifically silence ALK oncogenes. The aptamer-equipped protamine nanomedicine was simply fabricated through a non-covalent charge-force reaction. The products had uniform structure morphology under an electron microscope and a peak diameter of 103 nm by dynamic light scattering measurement. Additionally, flow cytometry analysis demonstrated that under CD30 aptamer guidance, the protamine nanomedicine specifically bound to lymphoma cells, but did not react to off-target cells in control experiments. Moreover, specific cell targeting and intracellular delivery of the nanomedicine were also validated by electron and confocal microscopy. Finally, functional studies demonstrated that, through combined cell-selective chemotherapy using a drug payload and oncogene-specific gene therapy using an siRNA, the protamine nanomedicine effectively killed lymphoma cells with little toxicity to off-target cells, indicating its potential for precision therapy.

Aptamer technology: a new approach to treat lymphoma?

Oligonucleotide aptamers are a class of small-molecule ligands. Functionally similar to protein antibodies, aptamers can specifically bind to their targets with high affinity. Biomedical studies have revealed the potential clinical value of aptamer technology for disease diagnosis and targeted therapy. Lymphoma is a group of cancers originating from the lymphatic system. Currently, chemotherapy is the primary treatment for lymphoma, although it may cause serious side effects in patients due to lack of target specificity. Here, we selectively discuss the recent development of potential applications of aptamer technology for precision lymphoma therapy, which are able to not only achieve high therapeutic efficacy but also do not cause off-target side effects.

Nanopharmacology in translational hematology and oncology

Nanoparticles have displayed considerable promise for safely delivering therapeutic agents with miscellaneous therapeutic properties. Current progress in nanotechnology has put forward, in the last few years, several therapeutic strategies that could be integrated into clinical use by using constructs for molecular diagnosis, disease detection, cytostatic drug delivery, and nanoscale immunotherapy. In the hope of bringing the concept of nanopharmacology toward a viable and feasible clinical reality in a cancer center, the present report attempts to present the grounds for the use of cell-free nanoscale structures for molecular therapy in experimental hematology and oncology.

NPM-ALK: The Prototypic Member of a Family of Oncogenic Fusion Tyrosine Kinases

Anaplastic lymphoma kinase (ALK) was first identified in 1994 with the discovery that the gene encoding for this kinase was involved in the t(2;5)(p23;q35) chromosomal translocation observed in a subset of anaplastic large cell lymphoma (ALCL). The NPM-ALK fusion protein generated by this translocation is a constitutively active tyrosine kinase, and much research has focused on characterizing the signalling pathways and cellular activities this oncoprotein regulates in ALCL. We now know about the existence of nearly 20 distinct ALK translocation partners, and the fusion proteins resulting from these translocations play a critical role in the pathogenesis of a variety of cancers including subsets of large B-cell lymphomas, nonsmall cell lung carcinomas, and inflammatory myofibroblastic tumours. Moreover, the inhibition of ALK has been shown to be an effective treatment strategy in some of these malignancies. In this paper we will highlight malignancies where ALK translocations have been identified and discuss why ALK fusion proteins are constitutively active tyrosine kinases. Finally, using ALCL as an example, we will examine three key signalling pathways activated by NPM-ALK that contribute to proliferation and survival in ALCL.

Novel therapeutic options in anaplastic large cell lymphoma: molecular targets and immunological tools

Anaplastic large cell lymphoma (ALCL) is a CD30-positive, aggressive T-cell lymphoma, and about half of the patients with this disease harbor the t(2;5)(p21;q35) translocation. This chromosomal aberration leads to fusion of the NPM gene with the ALK tyrosine kinase, leading to its constitutive activation. To date, treatment options include polychemotherapy (e.g., cyclophosphamide, doxorubicin, vincristine, and prednisone), which is sometimes combined with radiation in the case of bulky disease, leading to remission rates of ∼80%. However, the remaining patients do not respond to therapy, and some patients experience chemo-resistant relapses, making the identification of new and better treatments imperative. The recent discovery of deregulated ALK in common cancers such as non-small cell lung cancer and neuroblastoma has reinvigorated industry interest in the development of ALK inhibitors. Moreover, it has been shown that the ALK protein is an ideal antigen for vaccination strategies due to its low expression in normal tissue. The characterization of microRNAs that are deregulated in ALCL will yield new insights into the biology of ALCL and open new avenues for therapeutic approaches in the future. Also, CD30 antibodies that have been tested in ALCL for quite a while will probably find a place in forthcoming treatment strategies.

A nanocomplex that is both tumor cell-selective and cancer gene-specific for anaplastic large cell lymphoma

Background

Many in vitro studies have demonstrated that silencing of cancerous genes by siRNAs is a potential therapeutic approach for blocking tumor growth. However, siRNAs are not cell type-selective, cannot specifically target tumor cells, and therefore have limited in vivo application for siRNA-mediated gene therapy.

Results

In this study, we tested a functional RNA nanocomplex which exclusively targets and affects human anaplastic large cell lymphoma (ALCL) by taking advantage of the abnormal expression of CD30, a unique surface biomarker, and the anaplastic lymphoma kinase (ALK) gene in lymphoma cells. The nanocomplexes were formulated by incorporating both ALK siRNA and a RNA-based CD30 aptamer probe onto nano-sized polyethyleneimine-citrate carriers. To minimize potential cytotoxicity, the individual components of the nanocomplexes were used at sub-cytotoxic concentrations. Dynamic light scattering showed that formed nanocomplexes were ~140 nm in diameter and remained stable for more than 24 hours in culture medium. Cell binding assays revealed that CD30 aptamer probes selectively targeted nanocomplexes to ALCL cells, and confocal fluorescence microscopy confirmed intracellular delivery of the nanocomplex. Cell transfection analysis showed that nanocomplexes silenced genes in an ALCL cell type-selective fashion. Moreover, exposure of ALCL cells to nanocomplexes carrying both ALK siRNAs and CD30 RNA aptamers specifically silenced ALK gene expression, leading to growth arrest and apoptosis.

Conclusions

Taken together, our findings indicate that this functional RNA nanocomplex is both tumor cell type-selective and cancer gene-specific for ALCL cells.

Transfection of shRNA-encoding Minivector DNA of a few hundred base pairs to regulate gene expression in lymphoma cells

This work illustrates the utility of Minivector DNA, a non-viral, supercoiled gene therapy vector incorporating short hairpin RNA from an H1 promoter. Minivector DNA is superior to both plasmid DNA and small interfering RNA (siRNA) in that it has improved biostability while maintaining high cell transfection efficiency and gene silencing capacity. Minivector DNAs were stable for over 48 h in human serum, as compared with only 0.5 and 2 h for siRNA and plasmid, respectively. Although all three nucleic acids exhibited similar transfection efficiencies in easily transfected adhesion fibroblasts cells, only Minivector DNAs and siRNA were capable of transfecting difficult-to-transfect suspension lymphoma cells. Minivector DNA and siRNA were capable of silencing the gene encoding anaplastic lymphoma kinase, a key pathogenic factor of human anaplastic large cell lymphoma, and this silencing caused inhibition of the lymphoma cells. Based on these results, Minivector DNAs are a promising new gene therapy tool.

RNA-mediated gene silencing in hematopoietic cells

In the past few years, the discovery of RNA-mediated gene silencing mechanisms, like RNA interference (RNAi), has revolutionized our understanding of eukaryotic gene expression. These mechanisms are activated by double-stranded RNA (dsRNA) and mediate gene silencing either by inducing the sequence-specific degradation of complementary mRNA or by inhibiting mRNA translation. RNAi now provides a powerful experimental tool to elucidate gene function in vitro and in vivo, thereby opening new exciting perspectives in the fields of molecular analysis and eventually therapy of several diseases such as infections and cancer. In hematology, numerous studies have described the successful application of RNAi to better define the role of oncogenic fusion proteins in leukemogenesis and to explore therapeutic approaches in hematological malignancies. In this review, we highlight recent advances and caveats relating to the application of this powerful new methodology to hematopoiesis.

Synergistic growth inhibition of anaplastic large cell lymphoma cells by combining cellular ALK gene silencing and a low dose of the kinase inhibitor U0126

Abnormal expression of anaplastic lymphoma kinase (ALK) gene is an important pathogenic factor for anaplastic large cell lymphoma (ALCL). To study the function of ALK, an inducible short hairpin RNA (shRNA) system was stably introduced into cultured human ALCL cells. Inducing shRNA expression in the generated cells resulted in cellular ALK gene silencing and led to inactivation of multiple signaling pathways and growth arrest. Interestingly, a combination of ALK gene silencing with U0126, a kinase inhibitor specific for the extracellular signal-regulated kinases 1/2 pathway, resulted in an augmented reduction in cellular JunB expression. Functional studies indicated that combining ALK gene silencing with U0126 treatment provided a synergistic growth inhibition, which occurred faster and was more profound than with either treatment alone. This synergistic effect was also observed when measuring cell proliferation, apoptosis, and in vitro cell colony formation. Importantly, the combination of ALK gene silencing and U0126 had a prolonged inhibitory effect, preventing recovery of ALCL cell growth even after treatments were removed. Moreover, this synergistic inhibitory effect was confirmed in vivo using a mouse model with xenografted ALCL tumors. Our findings indicate that combining cellular ALK gene silencing with a low dose of U0126 may prove to be an effective and more specific therapeutic approach to treating ALCL.

Downregulation of NPM-ALK by siRNA Causes Anaplastic Large Cell Lymphoma Cell Growth Inhibition and Augments the Anti Cancer Effects of Chemotherapy In Vitro

The fusion protein, nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), results from the chromosome translocation t(2;5)(p23;q25) and is present in 50-70 percent of anaplastic large-cell lymphomas (ALCLs). NPM-ALK is a constitutively activated kinase that transforms cells through stimulating several mitogenic signaling pathways. To examine if the NPM-ALK is a potential therapeutic target in ALCL, we used siRNA to specifically downregulate the expression of the NPM-ALK in ALCL cell lines. In this report, we demonstrated viability loss in t(2;5)-positive ALCL cell lines, SUDHL-1 and Karpas 299 cells, but not in lymphoma cell lines without the chromosome translocation, Jurkat and Granta 519 cells. Further study demonstrated that the downregulation of NPM-ALK resulted in decreased cell proliferation and increased cell apoptosis. When used in combination with chemotherapeutic agents, such as doxorubicin, the inhibition of the NPM-ALK augments the chemosensitivity of the tumor cells. These results revealed the importance of continuous expression of NPM-ALK in maintaining the growth of ALCL cells. Our data also suggested that the repression of the fusion gene might be a potential novel therapeutic strategy for NPM-ALK positive ALCLs.

Targeting oncogenes with siRNAs

Current cancer chemotherapies heavily rely on the unspecific inhibition of proliferating cells. This lack of tumour cell specificity results in severe toxic side effects and may only hardly affect quiescent cancer stem cells consequently leading to relapse. Since oncogenes are exclusively expressed in malignant and pre-malignant cells, they may provide unique, cancer cell specific targets for therapeutic strategies. However, their role in maintaining the malignant phenotype is frequently unknown. Furthermore, oncogenic transcription factors are generally considered to be "undruggable" with conventional small molecule approaches. Oncogene-specific RNA interference offers here new and exciting options to analyse oncogene functions directly in the malignant environment. Moreover, such approaches may permit the targeting of oncogenic transcription factors, thereby considerably extending the number of cancer-specific target structures. In this chapter, several rationales and practical aspects of oncogene targeting with siRNAs are discussed. Special emphasis is given to the application of RNA interference to haematopoietic cells, which are generally hard to transfect. In particular, solving the problem of systemic siRNA/shRNA delivery will greatly advance the inclusion of RNA interference strategies into more efficient and specific therapeutic strategies.

Development of anaplastic lymphoma kinase (ALK) small-molecule inhibitors for cancer therapy

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase (RTK) involved in the genesis of several human cancers; indeed, ALK was initially identified in constitutively activated and oncogenic fusion forms--the most common being nucleophosmin (NPM)-ALK--in a non-Hodgkin's lymphoma (NHL) known as anaplastic large-cell lymphoma (ALCL) and subsequent studies identified ALK fusions in the human sarcomas called inflammatory myofibroblastic tumors (IMTs). In addition, two recent reports have suggested that the ALK fusion, TPM4-ALK, may be involved in the genesis of a subset of esophageal squamous cell carcinomas. While the cause-effect relationship between ALK fusions and malignancies such as ALCL and IMT is very well established, more circumstantial links implicate the involvement of the full-length, normal ALK receptor in the genesis of additional malignancies including glioblastoma, neuroblastoma, breast cancer, and others; in these instances, ALK is believed to foster tumorigenesis following activation by autocrine and/or paracrine growth loops involving the reported ALK ligands, pleiotrophin (PTN) and midkine (MK). There are no currently available ALK small-molecule inhibitors approved for clinical cancer therapy; however, recognition of the variety of malignancies in which ALK may play a causative role has recently begun to prompt developmental efforts in this area. This review provides a succinct summary of normal ALK biology, the confirmed and putative roles of ALK fusions and the full-length ALK receptor in the development of human cancers, and efforts to target ALK using small-molecule kinase inhibitors.

The oncoprotein NPM-ALK of anaplastic large-cell lymphoma induces JUNB transcription via ERK1/2 and JunB translation via mTOR signaling

Anaplastic large cell lymphomas (ALCLs) are highly proliferating tumors that commonly express the AP-1 transcription factor JunB. ALK fusions occur in approximately 50% of ALCLs, and among these, 80% have the t(2;5) translocation with NPM-ALK expression. We report greater activity of JunB in NPM-ALK-positive than in NPM-ALK-negative ALCLs. Specific knockdown of JUNB mRNA using small interfering RNA and small hairpin RNA in NPM-ALK-expressing cells decreases cellular proliferation as evidenced by a reduced cell count in the G2/M phase of the cell cycle. Expression of NPM-ALK results in ERK1/2 activation and transcriptional up-regulation of JUNB. Both NPM-ALK-positive and -negative ALCL tumors demonstrate active ERK1/2 signaling. In contrast to NPM-ALK-negative ALCL, the mTOR pathway is active in NPM-ALK-positive lymphomas. Pharmacological inhibition of mTOR in NPM-ALK-positive cells down-regulates JunB protein levels by shifting JUNB mRNA translation from large polysomes to monosomes and ribonucleic particles (RNPs), and decreases cellular proliferation. Thus, JunB is a critical target of mTOR and is translationally regulated in NPM-ALK-positive lymphomas. This is the first study demonstrating translational control of AP-1 transcription factors in human neoplasia. In conjunction with NPM-ALK, JunB enhances cell cycle progression and may therefore represent a therapeutic target.

Pathobiology of ALK+ anaplastic large-cell lymphoma

Anaplastic large-cell lymphoma (ALCL) was initially recognized on the basis of morphologic features and the consistent expression of CD30. It then became evident that the majority of these tumors are derived from lymphoid cells of T or null immunophenotype. The subsequent finding that t(2;5)(p23;q35) occurs in 40% to 60% of ALCL patients established a distinct clinicopathologic entity. This chromosomal translocation induces the formation of the chimeric protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), which possesses significant oncogenic potential resulting from the constitutive activation of the tyrosine kinase ALK. In addition to its specific pathophysiologic events, NPM-ALK-expressing lymphoma presents with consistent clinical manifestations. Only 13 years after the identification of NPM-ALK, tremendous progress has been made in our understanding of this molecule because of the relentless efforts of multiple investigators who have dissected its biologic roles using in vitro and in vivo experimental models. Several upstream modulators, cross-reacting oncogenes, and downstream effectors of NPM-ALK have been identified and characterized. Understanding these interacting oncogenic systems is expected to facilitate the design of new therapeutic strategies and agents. In this review, we briefly discuss ALCL and focus on NPM-ALK.

Anaplastic lymphoma kinase and its signalling molecules as novel targets in lymphoma therapy

A crucial issue in the development of molecularly-targeted anticancer therapies is the identification of appropriate molecules whose targeting would result in tumour regression with a minimal level of systemic toxicity. Anaplastic lymphoma kinase (ALK) is a transmembrane receptor tyrosine kinase, normally expressed at low levels in the nervous system. As a consequence of chromosomal translocations involving the alk gene (2p23), ALK is also aberrantly expressed and constitutively activated in approximately 60% of CD30+ anaplastic large cell lymphomas (ALCLs). Due to the selective overexpression of ALK in tumour cells, its direct involvement in the process of malignant transformation and its frequent expression in ALCL patients, the authors recognise ALK as a suitable candidate for the development of molecularly targeted strategies for the therapeutic treatment of ALK-positive lymphomas. Strategies targeting ALK directly or indirectly via the inhibition of the protein networks responsible for ALK oncogenic signalling are discussed.

Mass Spectrometry-based Proteomic Studies of Human Anaplastic Large Cell Lymphoma

Malignant lymphomas are a diverse group of malignant neoplasms that arise as a result of a complex interplay of multiple factors including genetic aberrations, immunosuppression, and exposure to noxious agents such as ionizing radiation and chemical agents. Anaplastic large cell lymphoma (ALCL) is an aggressive T-lineage lymphoma harboring chromosomal translocations involving the anaplastic lymphoma kinase (ALK) tyrosine kinase. The most common translocation in ALCL is the t(2;5)(p23;q35). This results in the formation of a chimeric fusion kinase, nucleophosmin/ALK. Nucleophosmin/ALK activates numerous downstream signaling pathways resulting in enhanced survival and proliferation. Using a variety of mass spectrometry-driven proteomic strategies, we have studied several aspects of the ALCL proteome. In this review, we provide a summary of mass spectrometry-based proteomic studies that expands the current understanding of the molecular pathogenesis of ALCL and provides the basis for the identification of biomarkers and targets for novel therapeutic agents.

RNA interference as a potential tool in the treatment of leukaemia

Leukaemias are often characterised by nonrandom chromosomal translocations that, at the molecular level, induce the activation of specific oncogenes or create novel chimeric genes. They have frequently been regarded as optimal targets for gene silencing approaches, as these single abnormalities may directly initiate or maintain the malignant process. Since the ground-breaking discovery that double-stranded RNA molecules 21 - 23 nucleotides in length, named small interfering RNAs (siRNAs), are able to elicit gene-specific inhibition also in mammalian cells, the interest of the scientific community has rapidly been drawn to the potential of these siRNAs for targeting oncogenic fusion genes in leukaemic cells. There has been a flurry of reports describing overexpressed or mutated genes that may also serve as attractive targets for therapeutic intervention by RNA silencing methods. Although this approach seems to be relatively straightforward, many problems remain to be solved before siRNAs may become clinically implemented as 'leukaemia drugs'. Difficulties in delivering siRNAs into the leukaemic cell, inefficient target mRNA cleavage, prolonged protein half-life in cancer cells, nonspecific side effects caused by targeting other genes than those originally thought, immunological reactions of the host organism against the siRNAs, such as interferon responses, or even acquired resistance mechanisms, such as escape mutants, should be overcome. This paper reviews the current knowledge regarding the use of siRNAs, either chemically synthesised or intracellular-generated via specialised expression constructs, in order to suppress the falsely activated oncogenes in haematopoietic malignancies.

Targeting leukemic fusion proteins with small interfering RNAs: recent advances and therapeutic potentials

RNA interference has become an indispensable research tool to study gene functions in a wide variety of organisms. Because of their high efficacy and specificity, RNA interference-based approaches may also translate into new therapeutic strategies to treat human diseases. In particular, oncogenes such as leukemic fusion proteins, which arise from chromosomal translocations, are promising targets for such gene silencing approaches, because they are exclusively expressed in precancerous and cancerous tissues, and because they are frequently indispensable for maintaining the malignant phenotype. This review summarizes recent developments in targeting leukemia-specific genes and discusses problems and approaches for possible clinical applications.

Lymphoproliferative disorders: prospects for gene therapy

The lymphoproliferative disorders represent a large group of diseases with a significant variation in presentation and clinical course. There has been a trend of increasing incidence for some of these disorders, and despite advances in therapies, a significant number of patients either respond poorly or have early relapses. For this reason there is a need to investigate novel therapies to be used either alone or as adjunct treatment in combination with conventional therapies. Gene therapy is a relatively new field that takes advantage of our increased understanding of molecular biology with the aim of treating a variety of diseases including cancer. It is defined as the introduction of genetic material into cells for therapeutic intent. Methods to improve gene delivery efficiency have been the focus of a large amount of research and to date the optimal procedure uses viruses such as oncoretroviruses, lentiviruses, adenoviruses, adeno-associated viruses and herpes simplex viruses. There are four main gene therapy strategies that might be used for the treatment of lymphoproliferative disorders. First, immunotherapy using tumour vaccines or techniques to enhance the function of immune effector cells has been investigated with some success in patients with B-cell malignancies. Second, the introduction of prodrug-activated 'suicide' genes into cells has been explored, in particular in patients with post-transplantation lymphoproliferative disease. Third, direct lysis of tumour cells using viruses shows some early promise, especially in the treatment of B-cell disorders by manipulating the measles virus to target the CD20 antigen. Finally, anti-gene strategies such as anti-sense therapy, ribozymes, and most recently RNA interference, could be used to suppress expression of specific target genes. RNA interference in particular has tremendous potential and has been studied in the context of anaplastic large cell lymphoma as well as Epstein-Barr virus-associated malignancies. Whilst we are still in the early days of this field and to date results have been modest, there is still a significant potential for gene therapy to play a role in the future treatment of these disorders.

Ablation of oncogenic ALK is a viable therapeutic approach for anaplastic large-cell lymphomas

Anaplastic large-cell lymphomas (ALCLs) carry chromosome translocations in which the anaplastic lymphoma kinase (ALK) gene is fused to several partners, most frequently, the NPM1 gene. We have demonstrated that the constitutive activation of ALK fusion proteins results in cellular transformation and lymphoid neoplasia. Herein, we specifically down-regulated ALK protein expression by using small hairpin RNA (shRNA) targeting a sequence coding for the catalytic domain of ALK. The ablation of ALK leads to the down-modulation of known ALK downstream effectors, cell growth arrest, and reversion of the transformed phenotype of ALK(+) mouse embryonic fibroblasts in vitro and in vivo. In human ALCL cells lentiviral-mediated ALK knock-down leads to G(1) cell-cycle arrest and apoptosis in vitro and tumor growth inhibition and regression in vivo. Using a specific approach we have demonstrated that the survival and growth of ALK(+) ALCLs are strictly dependent on ALK activation and signaling. Therefore, ALK is a viable target for therapeutic intervention and its inactivation might represent a pivotal approach for the treatment of ALK lymphomas and other ALK-dependent human tumors.

Rnai as an experimental and therapeutic tool to study and regulate physiological and disease processes

Over the past four years RNA interference (RNAi) has exploded onto the research scene as a new approach to manipulate gene expression in mammalian systems. More recently, RNAi has garnered much interest as a potential therapeutic strategy. In this review, we briefly summarize the current understanding of RNAi biology and examine how RNAi has been used to study the genetic basis of physiological and disease processes in mammalian systems. We also explore some of the new developments in the use of RNAi for disease therapy and highlight the key challenges that currently limit its application in the laboratory, as well as in the clinical setting.

Potential applications of RNA interference technology in the treatment of cancer

Inhibition of growth and progression of cancer cells is a challenge with major potential impact. RNA interference (RNAi) technology has been rapidly developed as a laboratory tool for the downregulation of the expression of a gene of interest. Moreover, RNAi offers a new potential for gene therapy of particular neoplasms by the specific inhibition of a cancer-associated target. This article will briefly describe the mechanism and application possibilities of RNAi, and illustrate the therapeutic potential in cancer gene therapy. The utilization of RNAi technology as a potential therapeutic tool for the treatment of cancer will be discussed in detail for two specific targets; the Bcr-Abl tyrosine kinase and the multidrug transporter MDR1/P-glycoprotein.

Development of gene-specific double-stranded RNA drugs

A relatively recent entrant into molecular biology--double-stranded RNA (dsRNA)--as a class exhibits a unique set of properties: relative stability, affinity for specific proteins and enzymes, ability to activate the interferon pathway and finally, RNA interference (RNAi). In RNAi, unique double-stranded short interfering RNA molecules (siRNA) destroy the corresponding target RNA with exquisite potency and selectivity, thus causing post-transcriptional gene silencing (PTGS). An understanding of the design of gene-specific dsRNA and development of techniques to deliver dsRNA in the cell and in live animals has heralded a new age of gene therapy without gene knockout. This review first summarizes the biological synthesis, metabolism and effect of the dsRNA with special emphasis on siRNA and RNAi. This is followed by the clinical, pharmacological and pharmaceutical prospects of the development of the dsRNA as a drug. It is clear that the dsRNA holds an enormous promise in the treatment of a large number of metabolic and infectious diseases including but not limited to cancer, macular degeneration, diabetic retinopathy, Alzheimer's and other neural disorders, autoimmune diseases, and all viral infections including AIDS (acquired immune deficiency syndrome), hepatitis and respiratory syncytial virus (RSV).