Gene therapy for genetic diseases

Lentivirus-mediated RNAi knockdown of prostate-specific membrane antigen suppresses growth, reduces migration ability and the invasiveness of prostate cancer cells

Prostate-specific membrane antigen is a type II membrane protein with folate hydrolase activity produced by prostatic epithelium. It has been demonstrated that prostate-specific membrane antigen over-expression may be correlated with prostate cancer, particularly in advanced cancer. The aim of the current study was to explore the possibility of prostate-specific membrane antigen as a therapeutic target for the treatment of prostate cancer. To address this problem, lentivirus-mediated small interfering RNA was employed to reduce endogenous prostate-specific membrane antigen expression in prostate cancer cell lines—LNCaP and DU-145. Then, the tumorigenesis, migration ability and invasiveness of prostate-specific membrane antigen-reduced prostate cancer cell lines were also examined. The prostate-specific membrane antigen expression in LNCaP and DU-145 cells was persistently and markedly reduced by lentivirus-mediated RNA interference. Down-regulation of prostate-specific membrane antigen expression significantly suppressed the growth rates of LNCaP and DU-145 cells. Moreover, the specific down-regulation arrested cells in G0/G1 phase of cell cycle. Furthermore, we also observed that the silence of prostate-specific membrane antigen could decrease the migration ability and the invasiveness of LNCaP and DU-145 cells. Our investigation demonstrated that lentivirus-mediated RNA interference silencing targeting prostate-specific membrane antigen might reduce the proliferation, and induce potent antitumor activity of LNCaP and DU-145 cells. Prostate-specific membrane antigen has considerable potential as a new therapeutic target for the treatment of prostate cancer.

Lentivirus-mediated RNAi knockdown of insulin-like growth factor-1 receptor inhibits growth, reduces invasion, and enhances radiosensitivity in human osteosarcoma cells

The type 1 insulin-like growth factor receptor (IGF-1R) is essential for tumorigenicity, tumor proliferation, and protection from apoptosis. IGF-1R overexpression has been found in many human cancers including osteosarcoma. To explore its possibility as a therapeutic target for the treatment of osteosarcoma, lentivirus-mediated siRNA was employed to downregulate endogenous IGF-1R expression to study the function of IGF-1R in tumorigenesis and radioresistance of osteosarcoma cells. The IGF-1R expression was persistently and markedly reduced by lentivirus-mediated RNAi. Downregulation of IGF-1R expression in osteosarcoma cells significantly suppressed their growth rates in vitro and reduced the potential of tumorigenicity in vivo. Moreover, the specific downregulation arrested cells in G(0)/G(1) phase of cell cycle and also induced apoptosis which correlated with the activation of Caspase-3. Furthermore, we also observed that suppression of IGF-1R could reduce the invasiveness of osteosarcoma cells and enhance their radiosensitivity. Our study suggested that lentivirus-mediated RNAi silencing targeting IGF-1R could induce potent antitumor activity and radiosensitizing activity in human osteosarcomas.

A new solution for improving gene delivery

Intense research has focused on methods for overcoming the various barriers to DNA delivery while simultaneously reducing toxicity. Recently, Yuan and colleagues discovered a 'leakage route', whereby viral vectors escaped the injection site and entered the systemic circulation and contributed to the systemic toxicity in cancer gene therapy. They also demonstrated that alginate solution sealed this leak. Although their work focused on intratumoral injection of viral vectors, the findings can be extended to drug delivery in general, particularly DNA delivery.

Lysine: Is it worth more?

Lysine, an essential cationic amino acid, has a positively charged R group. The structure of lysine is given as (H(3)N(+)-)CH(-COO(-))-CH(2)-CH(2)-CH(2)-CH(2)-N(+)H(3).While the anabolic role(s) of the molecule has been in focus for quite a few decades now, its biological properties, e.g. role in cellular proliferation in vitro (both anchorage dependent and anchorage independent) and in vivo, its ability to induce strong inflammatory and immune responses - both humoral and cell mediated, its role in augmented healing of all types of wounds in animal models as well as in human subjects (both acute and chronic), as well as its role in inducing extensive angiogenic responses, have never received reasonable attention so far. In the current brief and indicative review (rather than exhaustive reviews of each area), we intend to bring these biological properties of the molecule to focus while discussing a few other interesting aspects - lysine as a food preservative as well as its possible role(s) in immune therapy. While the areas look extremely divergent, we propose a common denominator in the form of a possible molecular mechanism of action of the molecule in all these diverse situations.

Osteogenesis imperfecta: prospects for molecular therapeutics

Osteogenesis Imperfecta (OI) is a dominant negative disorder of connective tissue. OI patients present with bone fragility and skeletal deformity within a broad phenotypic range. Defects in the COL1A1 or COL1A2 genes, coding, respectively, for the alpha1 and alpha2 chains of type I collagen, are the causative mutations. Over 150 mutations have been characterized. Both quantitative defects, such as null COL1A1 alleles, and qualitative defects, such as glycine substitutions, exon skipping, deletions, and insertions, have been described in type I collagen. Quantitative and structural mutations are associated with the milder and more severe forms of OI, respectively. A more detailed relationship between genotype and phenotype is still incompletely understood; several models have been proposed and are being tested. Transgenic and knock-out murine models for OI have previously been created. We have recently generated a knock-in murine model (the Brittle mouse) carrying a typical glycine substitution in type I collagen. This mouse will permit a better understanding of OI pathophysiology and phenotypic variability. It will also be used for gene therapeutic approaches to OI, especially mutation suppression by hammerhead ribozymes. The present review will provide an update of OI clinical and molecular data and outline gene therapeutic approaches being tested on OI murine models for this disorder.

Latest developments in gene transfer technology: achievements, perspectives, and controversies over therapeutic applications

Over the last decade, more than 300 phase I and phase II gene-based clinical trials have been conducted worldwide for the treatment of cancer and monogenic disorders. Lately, these trials have been extended to the treatment of AIDS and, to a lesser extent, cardiovascular diseases. There are 27 currently active gene therapy protocols for the treatment of HIV-1 infection in the USA. Preclinical studies are currently in progress to evaluate the possibility of increasing the number of gene therapy clinical trials for cardiopathies, and of beginning new gene therapy programs for neurologic illnesses, autoimmuno diseases, allergies, regeneration of tissues, and to implement procedures of allogeneic tissues or cell transplantation. In addition, gene transfer technology has allowed for the development of innovative vaccine design, known as genetic immunization. This technique has already been applied in the AIDS vaccine programs in the USA. These programs aim to confer protective immunity against HIV-1 transmission to individuals who are at risk of infection. Research programs have also been considered to develop therapeutic vaccines for patients with AIDS and generate either preventive or therapeutic vaccines against malaria, tuberculosis, hepatitis A, B and C viruses, influenza virus, La Crosse virus, and Ebola virus. The potential therapeutic applications of gene transfer technology are enormous. However, the effectiveness of gene therapy programs is still questioned. Furthermore, there is growing concern over the matter of safety of gene delivery and controversy has arisen over the proposal to begin in utero gene therapy clinical trials for the treatment of inherited genetic disorders. From this standpoint, despite the latest significant achievements reported in vector design, it is not possible to predict to what extent gene therapeutic interventions will be effective in patients, and in what time frame.

Gene transfer technology in therapy: current applications and future goals

Gene therapy has attracted much interest since the first submissions of phase I clinical trials in the early 1990s, for the treatment of inherited genetic diseases. Preliminary results were very encouraging and prompted many investigators to submit protocols for phase I and phase II clinical trials for the treatment of inherited genetic diseases and cancer. The possible application of gene transfer technology to treat AIDS, cardiopathies, and neurologic diseases is under evaluation. Some viral vectors have already been used to deliver HIV-1 subunits to immunize volunteers who are participating in the AIDS vaccine programs in the USA. However, gene delivery systems still need to be optimized in order to achieve effective therapeutic interventions. The purpose of this review is to summarize the latest achievements in improving gene delivery systems, their current application in preclinical studies and in therapy, and the most pressing issues that must be addressed in the area of vector design.

Cleavage of collagen RNA transcripts by hammerhead ribozymes in vitro is mutation-specific and shows competitive binding effects

We report here the in vitro use of hammerhead ribozymes as an approach to the gene therapy of osteogenesis imperfecta (OI). Our strategy for the treatment of this dominant genetic disorder is based on selective reduction of the level of the mRNA transcripts from the mutant allele. We studied the in vitro cleavage activity of five different hammerhead ribozymes targeted against synthetic transcripts of two naturally occurring human collagen mutations and against a point mutation introduced into a construct containing a portion of the mouse COL1A1 gene. This is the first demonstration that ribozyme cleavage is absolutely dependent on the presence of the ribozyme cleavage site introduced by the disease-causing mutation. Cleavage specificity and activity were unchanged when the cleavage site was located in transcripts of progressively longer length. Cleavage efficiency depended directly on the ratio of ribozyme/substrate, as well as on the time and temperature of incubation. We investigated the competitive effects of both total RNA and normal synthetic transcripts on ribozyme cleavage activity. The ribozyme was able to localize and cleave its specific target even in the presence of a vast excess of total RNA. However, cleavage efficiency was linearly inhibited by the presence of a non- cleavable competitor substrate which contained a ribozyme binding site identical to the site present in the cleavable target. Although this competition could be eliminated by introducing a mismatch into one ribozyme binding arm, the presence of the mismatch decreased ribozyme cleavage efficiency. The mutation- specificity of ribozyme cleavage demonstrated in this work provides support for in vivo studies aimed at ribozyme development as a treatment for dominant negative genetic disorders.

T lymphocyte-directed gene therapy for ADA- SCID: initial trial results after 4 years

In 1990, a clinical trial was started using retroviral-mediated transfer of the adenosine deaminase (ADA) gene into the T cells of two children with severe combined immunodeficiency (ADA- SCID). The number of blood T cells normalized as did many cellular and humoral immune responses. Gene treatment ended after 2 years, but integrated vector and ADA gene expression in T cells persisted. Although many components remain to be perfected, it is concluded here that gene therapy can be a safe and effective addition to treatment for some patients with this severe immunodeficiency disease.

Retroviral vector particles displaying the antigen-binding site of an antibody enable cell-type-specific gene transfer

Retroviral vectors are the most efficient tool for stably introducing genes into vertebrate cells. However, their use is limited by the host range of the retrovirus from which they are derived. To alter the host range, we recently constructed retrovirus vector particles, derived from spleen necrosis virus, that display a single-chain antigen-binding site of an antibody (scA) on the viral surface (T.-H. T. Chu, I. Martinez, W. Sheay, and R. Dornburg, Gene Ther. 1:292-299, 1994). Using a hapten (2,4-dinitrophenol) model system, we showed that such particles are competent for infection. In this study, we repeated our experiments using an scA directed against a cell surface protein expressed on various human carcinoma cell lines. We found that such scA-displaying particles can efficiently infect human cells that express the corresponding antigen. Particles with wild-type spleen necrosis virus envelope are minimally infectious on such cells. The addition of the original monoclonal antibody to the viral vector particle solution prior to infection inhibited infection. This competition assay showed that the infection is mediated by the antibody moiety and, therefore, is antibody specific. These data indicate that retroviral vectors with antibody-envelope fusion proteins may be a valuable tool for selectively introducing genes into any target cell.

Further studies on targeted DNA transfer to cells using a highly efficient delivery system of biotinylated transferrin and biotinylated polylysine complexed to streptavidin

Conjugates consisting of biotinylated transferrin and biotinylated poly-L-lysine attached to streptavidin have been prepared and found to transfer luciferase plasmid DNA very efficiently to HeLa cells in the presence of chloroquine. Transfection was dependent on (i) use of biotinylated short chain polylysine containing 70 lysine residues, (ii) biotinylated transferrin containing 1-2 biotin moieties, (iii) reaction of biotinylated transferrin with streptavidin followed by isolation of the resulting conjugate on Sephadex G-200 and (iv) interaction of streptavidin-biotinylated transferrin with biotinylated polylysine giving a complex suitable for DNA transfection. It was found that if the above sequence of steps resulting in the formation of streptavidin-biotinylated transferrin/biotinylated polylysine was followed without isolation of intermediate conjugates by Sephadex G-200 chromatography, pRSVL DNA transfer was still very efficient. Transfer of luciferase DNA by the streptavidin conjugates and subsequent expression of luciferase activity was almost completely inhibited by excess free transferrin, showing that gene transfer was through the transferrin receptor pathway via receptor-mediated endocytosis. The streptavidin (bio2-transferrin) bio10-pLys70 conjugate used in the present experiments was approximately one hundred times more efficient in pRSVL DNA transfection with the HeLa cells than the previously described avidin-pLys460 (bio-transferrin) complex.

Gene therapy using retroviral vectors

Gene therapy is a novel approach for treating various congenital and acquired genetic disorders, including cancer, heart disease, and acquired immune deficiency syndrome. Amongst possible gene delivery systems, retroviral vector mediated gene transfer has been the most extensively studied and has been approved for use in over 40 current Phase I/II clinical trials for the treatment of various disorders, primarily cancers. Recent technological improvements include the optimization of vector production by concentration and lyophilization, resulting in high titers of vectors, as well as the large-scale production of vector-produced cells for the treatment of brain cancer. Present clinical protocols require specialized care centers with expertise in molecular biology and cell transplantation. Considerable effort is under way to develop retroviral vectors that can be both injected directly into the body and targeted to specific cell types within the body. Such vectors could be administered to patients by physicians in their offices. Successful development of this new technology would greatly expand the clinical potential of gene therapy.

Improved self-inactivating retroviral vectors derived from spleen necrosis virus

Self-inactivating (SIN) retroviral vectors contain a deletion spanning most of the right long terminal repeat's (LTR's) U3 region. Reverse transcription copies this deletion to both LTRs. As a result, there is no transcription from the 5' LTR, preventing further replication. Many previously developed SIN vectors, however, had reduced titers or were genetically unstable. Earlier, we reported that certain SIN vectors derived from spleen necrosis virus (SNV) experienced reconstitution of the U3-deleted LTR at high frequencies. This reconstitution occurred on the DNA level and appeared to be dependent on defined vector sequences. To study this phenomenon in more detail, we developed an almost completely U3-free retroviral vector. The promoter and enhancer of the left LTR were replaced with those of the cytomegalovirus immediate-early genes. This promoter swap did not impair the level of transcription or alter its start site. Our data indicate that SNV contains a strong initiator which resembles that of human immunodeficiency virus. We show that the vectors replicate with efficiencies similar to those of vectors possessing two wild-type LTRs. U3-deleted vectors carrying the hygromycin B phosphotransferase gene did not observably undergo LTR reconstitution, even when replicated in helper cells containing SNV-LTR sequences. However, vectors carrying the neomycin resistance gene did undergo LTR reconstitution with the use of homologous helper cell LTR sequences as template. This supports our earlier finding that sequences within the neomycin resistance gene can trigger recombination.

Gene therapy utilizing drug resistance genes: a review

The generation of drug resistant bone marrow may facilitate the development of aggressive chemotherapeutic regimens that might otherwise be lethal due to marrow toxicity. With the availability of technology that permits in vitro manipulation of human marrow and peripheral blood stem cells, it is now possible to introduce genes that confer drug resistance to these hematopoietic progenitors. Animal models and in vitro work with human progenitors using drug resistance genes are reviewed.

Cerebral transplantation for Parkinson's disease: current progress and future prospects

Cerebral transplantation has received considerable attention from both the medical community and lay press as a potential treatment for Parkinson's disease. Animal models have demonstrated feasibility, although the experience in subhuman primates was very limited when the first human trials were initiated in the mid-1980s. The dramatic success reported for adrenal-to-brain transplantation in some initial trials could not be consistently replicated by other centers. Occasionally, however, patients benefited. Failure of the adrenal medullary graft to survive may have been a major factor in the poor outcomes. Recently, several US and European centers reported substantial clinical improvement after fetal dopaminergic mesencephalon was grafted into the striatum of patients with Parkinson's disease. Although many outcomes were impressive, in some cases the improvement was marginal; in no case was the condition completely reversed, and all but one patient still required levodopa therapy. Before this technique can be considered for routine use, further refinement is necessary, and many technical issues must be addressed. Certain animal studies have suggested that transplantation-related improvement may be derived from graft neurotrophic factors rather than from secretion of dopamine into the dopamine-depleted brain of patients with Parkinson's disease. Preliminary investigations in animals indicate that several other tissues, besides fetal mesencephalon, may also prove appropriate for grafting. Ultimately, advances in molecular biology may allow either transplantation of genetically engineered cells or direct modification of existing brain cells by transfection with viral vectors. The favorable preliminary experience with cerebral transplantation in patients with Parkinson's disease has resulted in the consideration of this strategy for other neurologic disorders.

Treatment of inherited neurometabolic diseases: the future

The past 10 years' experience with bone marrow transplantation from normal, immunologically compatible donors indicates its possible use in various neurometabolic diseases, particularly in a patient who has not suffered irreparable brain damage. This experience may be a prelude to treatment by somatic gene therapy. This can be applied as an autologous bone marrow transplant, grafting the patient's own stem cells inserted with the normal gene. Although somatic gene therapy will be relatively easy for tissues with dividing cells, its application to target tissues with little or no cell division may pose difficulties. Meanwhile, techniques for the preservation, culture, and grafting of fetal neurons in humans have been developed and have been used in the treatment of Parkinson's disease. These procedures could readily be transferred to the treatment of other neurodegenerative diseases that cause significant morbidity, but ethical, legal, and religious considerations must be taken into account. All these efforts promise novel and improved management of inborn neurometabolic errors.

Unusually high frequency of reconstitution of long terminal repeats in U3-minus retrovirus vectors by DNA recombination or gene conversion

Recently, we described a retrovirus vector system with which to study formation of cDNA genes (R. Dornburg and H. M. Temin, Mol. Cell. Biol. 6:2328-2334, 1988; Mol. Cell. Biol. 8:64-72, 1990; J. Virol. 64:886-889, 1990). For these studies, retrovirus vectors were constructed in which the U3 region of the 3' long terminal repeat (LTR) was deleted. After one round of retrovirus replication, such vectors formed a provirus with two U3-minus LTRs. However, the insertion of some additional sequences into such vectors promoted vector rearrangements with an efficiency greater than 95%. Such rearranged vectors behaved like vectors with two wild-type LTRs. Proviruses derived from such vectors were investigated by Southern blot analysis, polymerase chain reaction, and DNA sequencing. We found that the U3 region was reconstituted, resulting in vectors with LTRs like wild-type virus. The sequences that reconstituted the U3 region of the vector LTR were derived from LTR sequences present in the helper cell. Since no retroviral protein coding sequences were detected in infected target cells, recombination of vector sequences with coencapsidated helper cell sequences during reverse transcription seems very unlikely. Thus, it appears that the recombination (or gene conversion) events leading to a vector with reconstituted LTRs occurred at the DNA level. The high frequency of this recombination (or gene conversion) was dependent on internal vector sequences.

Gene transfer into mammalian somatic cells in vivo

Direct gene transfer into mammalian somatic tissues in vivo is a developing technology with potential application for human gene therapy. During the past 2 years, extensive progress and numerous breakthroughs have been made in this area of research. Genetically engineered retroviral vectors have been used successfully to infect live animals, effecting foreign gene expression in liver, blood vessels, and mammary tissues. Recombinant adenovirus and herpes simplex virus vectors have been utilized effectively for in vivo gene transfer into lung and brain tissues, respectively. Direct injection or particle bombardment of DNA has been demonstrated to provide a physical means for in situ gene transfer, while carrier-mediated DNA delivery techniques have been extended to target specific organs for gene expression. These technological developments in conjunction with the initiation of the NIH human gene therapy trials have marked a milestone in developing new medical treatments for various genetic diseases and cancer. Various in vivo gene transfer techniques should also provide new tools for basic research in molecular and developmental genetics.

Antisense RNA therapy for CML--an hypothesis

CML, a myeloproliferative clonal disorder of myeloid stem cells, is characterized by the consistent presence of a bcr-c-abl fusion gene which is formed as a result of a translocation of the c-abl gene from chromosome 9 to downstream of the bcr gene on chromosome 22 (ph'). Current approaches to the treatment of CML are chemotherapy (conventional or aggressive with immuno-modulators) and bone marrow transplantation (BMT). Neither of the above treatment modalities results in long-term remission or cure. Hence, an alternative approach which aims at correcting the genetic defect should be considered. Taking advantage of the consistent abnormal presence of the bcr-c-abl gene in the treated and untreated CML patients at all stages, a gene therapy at the level of blocking mRNA might be considered. Such an antisense RNA therapy should include removal of patient's bone marrow, administration of the gene for constitutive expression of an antisense RNA for the bcr-c-abl fusion gene into the myeloid stem cells and reinjecting the engineered marrow into the patient. Such an approach, comparable to autologous BMT, will have the advantages of absence of graft rejection and possibility of 100% remission. The possible nature of the gene construct for such an antisense RNA therapy is discussed.