Current Gene Therapy, Volume 4, No. 1, 2004
Contents
Transductional and Transcriptional Targeting
of Adenovirus for Clinical Applications Pp.1-14
J.N.
Glasgow, G.J. Bauerschmitz, D.T. Curie1 and A. Hemminki
Exploiting Internal Ribosome Entry Sites in
Gene Therapy Vector Design Pp.15-31
S.M.
Ngoi, A.C. Chien and C.G.L. Lee
Fas Ligand Gene Therapy for Vascular Intimal
Hyperplasia Pp.33-39
Canwen
Jiang, Yi-Feng Yang and Seng H. Cheng
Replicative Oncolytic Herpes Simplex Viruses
in Combination Cancer Therapies Pp.41-51
Dawn
E. Post, Giulia Fulci, E. Antonio Chiocca, and Erwin G. Van Meir
Cancer Prevention and Therapy in a
Preclinical Mouse Model: Impact of FHIT Viruses Pp.53-63
Hideshi
Ishii, Andrea Vecchione, Louise Y.Y. Fong, Nicola Zanesi, Francesco Trapasso,
Yusuke Furukawa, Raffaele Baffa, Kay Huebner and Carlo M. Croce
Can the Use of HIV-1 Derived Gene Transfer
Vectors for Clinical Application be Justified? Pp.65-77
M.
Fuller and D.S. Anson
Potential of Gene Therapy for the Treatment
of Pituitary Tumors Pp.79-89
R.G.
Goya, D.K. Sarkar, O.A. Brown and C.B. Herenu
Promoters and Control Elements: Designing
Expression Cassettes for Gene Therapy Pp.89-113
E.D.
Papadakis, S.A. Nicklin, A.H. Baker and S.J. White
Gene Therapy: How to Target the Kidney.
Promises and Pitfalls Pp.115-122
S.
Tomasoni and A. Benigni
TGF-b:
A Fibrotic Factor in Wound Scarring and a Potential Target for Anti- Scarring
Gene Therapy Pp.123-136
W.
Liu, D.R. Wang and Y.L. Cao
[Back to top] Transductional and Transcriptional Targeting
of Adenovirus for Clinical Applications
J.N. Glasgow, G.J. Bauerschmitz, D.T. Curie1 and A.
Hemminki
Adenovirus (Ad)
targeting is a novel approach for the design and administration of therapeutic
agents wherein the agent is rationally designed to localize and restrict
transgene expression to the site of disease in a self-directed manner, usually
via exploitation of unique biophysical and genetic properties specific to the
diseased tissue. The ablation of promiscuous native Ad tropism coupled with
active targeting modalities has demonstrated that innate gene delivery
efficiency may be retained while circumventing Ad dependence on its primary
cellular receptor, the coxsackie and adenovirus receptor (CAR), to achieve
CAR-independent vector tropism. Herein, we describe advances in Ad targeting
that are predicated not only on fundamental understanding of vector/cell
interplay, but also on the specific transcriptional profiles of target tissues.
Further, targeting is discussed in the context of improving the safety and
efficacy of clinical approaches utilizing adenoviral vectors and replication
competent oncolytic agents. In summary, existing results suggest a critical
linkage between targeted agents and increases in therapeutic utility.
[Back to top] Exploiting Internal Ribosome Entry Sites in
Gene Therapy Vector Design
S.M.
Ngoi, A.C. Chien and C.G.L. Lee
Efficient and
regulated co-expression of multiple genes is an important consideration in the
design of gene therapy vectors. While the augmentation of a single therapeutic
gene is often sufficient for gene therapy of simple mendelian disorders,
strategies for the treatment of complex disorders and infectious diseases
necessitate the introduction of multiple genes into the cell. Complex disorders
such as cancer often involve mutations in multiple genes and a combination
strategy targeting different defective genes simultaneously are often more
effective than any single strategy. Likewise, approaches for treating
infectious diseases such as HIV-1 (human immunodeficiency virus) often involve
the blocking of multiple steps of the viral replication pathway simultaneously
to prevent the emergence of resistant strains of the virus. Even for the
treatment of single gene defects, the additional incorporation of a selectable
marker gene is often necessary to achieve sustained expression of the
therapeutic gene in the cells. Among the several different strategies to
co-express multiple genes, the incorporation of an IRES (internal ribosome
entry site) into gene therapy vector design represents one of the more
promising strategies. IRES functions as a ribosome-landing pad for the
efficient internal initiation of translation ensuring coordinate expression of
several genes and are located at the 5’UTR (5’ untranslated regions) of these
genes. Currently, the most popular IRES utilized for gene therapy is the IRES
from the EMCV (encephalomyocarditis virus). However, the major caveat with
present vector systems utilizing this IRES is that the expression of the
downstream gene is significantly less efficient than the upstream gene. This
review will examine the growing list of naturally occurring and synthetic
IRESes and how they can be exploited for human gene therapy.
[Back to top] Fas Ligand Gene Therapy for Vascular Intimal
Hyperplasia
Canwen Jiang, Yi-Feng Yang and Seng H. Cheng
Fas, a member of
the tumor necrosis factor receptor super-family, is expressed in all cell types
examined, while physiologic expression of Fas ligand (FasL) is found
predominantly in activated T-lymphocytes, vascular endothelial cells, and
“immune-privileged” tissues. Activation of Fas following FasL binding activates
caspases, which results in apoptosis. In the vasculature, there may be a
delicate balance between cell proliferation and apoptosis in vascular smooth
muscle cells. Shifts in this balance could account for the accumulation of
vascular smooth muscle cells in response to arterial injury, a major feature of
vascular intimal hyperplasia. Intimal hyperplasia occurs in more than a third
of patients receiving percutaneous transluminal balloon angioplasty. Stenting
with or without coating significantly reduces the incidence rate of
angiographic restenosis and that of target vessel revascularization. However,
“in-stent” intimal hyperplasia/restenosis remains a challenge for clinical
cardiologists. Although both the cell types and mechanisms that contribute to
intimal hyperplasia in response to vascular injury remain controversial,
vascular smooth muscle cell migration and proliferation appear to play an
important role in the process. In animal models, cytotoxic and cytostatic gene
therapy strategies targeted at the vascular smooth muscle cells have shown
therapeutic potential for the treatment of vascular intimal hyperplasia.
However, Fas ligand-based gene therapy appears to offer several advantages. In
this review article, we will discuss the mode of FasL/Fas signaling in vascular
smooth muscle cells and its therapeutic implications. We will also compare the
relative merits of FasL with other cytotoxic and cytostatic gene therapy
approaches for the treatment of intimal hyperplasia.
[Back to top] Replicative Oncolytic Herpes Simplex Viruses
in Combination Cancer Therapies
Dawn
E. Post, Giulia Fulci, E. Antonio Chiocca, and Erwin G. Van Meir
Viruses that kill
the host cell during their replication cycle have attracted much interest for
the specific killing of tumor cells and this oncolytic virotherapy is being
evaluated in clinical trials. The rationale for using replicative oncolytic
viruses is that viral replication in infected tumor cells will permit in situ
viral multiplication and spread of viral infection throughout the tumor mass
thus overcoming the delivery problems of gene therapy. Improved understanding
of the life cycle of viruses has evidenced multiple interactions between viral
and cellular gene products, which have evolved to maximize the ability of
viruses to infect and multiply within cells. Differences in viral-cell
interactions between normal and tumor cells have emerged that have led to the
design of a number of genetically engineered viral vectors that selectively
kill tumor cells while sparing normal cells. These viruses have undergone
further modifications to carry adjunct therapy genes to increase their
anti-cancer abilities. Since these viruses kill cells by oncolytic mechanisms
differing from standard anticancer therapies, there is an opportunity that
synergistic interactions with other therapies might be found with the use of
combination therapy. In this review, we focus on the oncolytic Herpes Simplex
Virus-1 (HSV-1) vectors that have been examined in preclinical and clinical
cancer models and their use in combination with chemo-, radio-, and gene
therapies.
[Back to
top] Cancer Prevention and Therapy in a
Preclinical Mouse Model: Impact of FHIT Viruses
Hideshi Ishii, Andrea Vecchione, Louise Y.Y. Fong,
Nicola Zanesi, Francesco Trapasso, Yusuke Furukawa, Raffaele Baffa, Kay Huebner
and Carlo M. Croce
A link between common chromosome fragile sites and frequent chromosomal deletions in cancer was observed two decades ago and led to the hypothesis that genes at fragile sites may play a role in tumor development. In 1996, the human fragile histidine triad gene, FHIT, was identified by positional cloning of the chromosome region spanning the carcinogen-sensitive, common fragile site, FRA3B at 3p14.2. Loss or inactivation of the FHIT gene in a large fraction of human tumors results in absence or reduction of Fhit protein. In vitro analyses and in vivo tumorigenicity studies show that restoration of Fhit protein induces tumor suppression in 50% of tumor cell lines tested. Viral vector-mediated FHIT gene transfer to Fhit-deficient mice not only prevents but reverses the carcinogen-induced tumor development in vivo, in accordance with the oncosuppressive properties of Fhit protein. The strong proapoptotic activity following Fhit infection of cancer cells strengthens the case for further exploration of FHIT gene therapy in cancer prevention and treatment.
[Back to top] Can the Use of HIV-1 Derived Gene Transfer Vectors for Clinical
Application be Justified?
M.
Fuller and D.S. Anson
Vectors derived from human immunodeficiency virus type 1 (HIV-1) are an attractive option for many gene therapy applications as they can transduce non-cycling cell populations, and can integrate their genome into the host cell chromosome. The rationale underlying the design of most retroviral vector systems is to segregate the viral cis sequences, which are required for transfer of the viral genome, from the trans sequences that encode viral proteins. This allows the efficient production of replication incompetent virus and has been successfully applied to the generation of HIV-1 vectors. Nonetheless, the possibility that recombination events in the vector production system can generate replication-competent virus, combined with the pathogenic nature of HIV-1, raises major bio-safety issues. Numerous HIV-1 vectors have now been reported, with each generation significantly improved in ways designed to reduce the risk of replication-competent virus being produced. However, progress in vector design needs to be complemented by the development of methods for the quantitation of the probability of replication competent virus being produced. Assaying individual events in the multi-step pathway that can lead to the production of replication-competent virus, rather than relying on the detection of replication-competent virus per se, will be important for quality control purposes. This review will specifically examine the approaches to HIV-1 vector design that have been postulated as increasing bio-safety, possible methods for evaluating bio-safety and whether these approaches are likely to be sufficient to overcome resistance to the use of HIV-1 for clinical application. In addition, we discuss the possible justifications for developing vectors from lentiviruses other than HIV-1.
[Back to top] Potential of Gene Therapy for the Treatment of Pituitary Tumors
R.G. Goya, D.K. Sarkar, O.A. Brown and C.B. Herenu
Pituitary adenomas
constitute the most frequent neuroendocrine pathology, comprising up to 15% of
primary intracranial tumors. Current therapies for pituitary tumors include
surgery and radiotherapy, as well as pharmacological approaches for some types.
Although all of these approaches have shown a significant degree of success,
they are not devoid of unwanted side effects, and in most cases do not offer a
permanent cure. Gene therapy—the transfer of genetic material for therapeutic
purposes—has undergone an explosive development in the last few years. Within
this context, the development of gene therapy approaches for the treatment of
pituitary tumors emerges as a promising area of research. We begin by
presenting a brief account of the genesis of prolactinomas, with particular
emphasis on how estradiol induces prolactinomas in animals. In so doing, we
discuss the role of each of the recently discovered growth inhibitory and
growth stimulatory substances and their interactions in estrogen action. We
also evaluate the cell-cell communication that may govern these growth factor
interactions and subsequently promote the growth and survival of prolactinomas.
Current research efforts to implement gene therapy in pituitary tumors include
the treatment of experimental prolactinomas or somatomammotropic tumors with
adenoviral vector-mediated transfer of the suicide gene for the herpes simplex
type 1 (HSV1) thymidine kinase, which converts the prodrug ganciclovir into a
toxic metabolite. In some cases, the suicide transgene has been placed under
the control of pituitary cell-type specific promoters, like the human prolactin
or human growth hormone promoters. Also, regulatable adenoviral vector systems
are being assessed in gene therapy approaches for experimental pituitary
tumors. In a different type of approach, an adenoviral vector, encoding the
human retinoblastoma suppressor oncogene, has been successfully used to rescue
the phenotype of spontaneous pituitary tumors of the pars intermedia in mice.
We close the
article by discussing the future of molecular therapies. We point out that
although, gene therapy represents a key step in the development of molecular
medicine, it has inherent limitations. As a consequence, it is our view that at
some point, genetic therapies will have to move from exogenous gene transfer
(i.e. gene therapy) to endogenous gene repair. This approach will call for
radically new technologies, such as nanotechnology, whose present state of
development is outlined.
[Back to top] Promoters and Control Elements: Designing Expression Cassettes for Gene
Therapy
E.D. Papadakis, S.A. Nicklin, A.H. Baker and S.J. White
It has become
apparent that the clinical success anticipated in the field of gene therapy has
been limited by progress in several of the fundamental areas of genetics, molecular
and cellular biology relevant to its application. Whilst a great deal of effort
has been made in the evaluation of transgenes, it is only more recently with
the advance of vector systems that attention has begun to be focused upon the
means and control of transgene expression. Until recently, the majority of
constructs have employed ubiquitous viral promoters to drive expression from
simple gene expression cassettes using viral promoters and lacking introns, 3’
untranslated regions (UTRs), locus control regions (LCR’s), matrix attachment
regions (MAR’s) and other such genetic components. It has consequently emerged
that these elements may have a key role in determining the levels and longevity
of gene expression attainable in vivo, irrespective of the vector system
utilised. The majority of gene therapy applications would also benefit from the
specific optimisation of ‘tailor-made’ expression cassettes to optimise their
therapeutic efficacy. In conjunction with modification of vector tropism and
strategies to limit their immunogenicity, this should create vectors suitable
for the clinical application of gene therapy. This review aims to highlight
some of the principle considerations of gene expression in vivo, and the means
by which it may most effectively be achieved, whether this is via the minimal
modification of an existing eukaryotic promoter or by the more extensive design
of a novel promoter and associated elements.
[Back to top] Gene Therapy: How to Target the Kidney. Promises and Pitfalls
S. Tomasoni and A. Benigni
The success of
gene therapy strongly depends on an efficient delivery system to allow local
transfer and expression of the therapeutic gene in the target organ or tissue.
Vector systems have been improved and many show promise. There are two
different categories of delivery vehicles: non-viral and viral vectors, both
with advantages and disadvantages that must be taken into consideration in view
of the final aim.
Compared to other
solid organs, the kidney offers the main advantage of access by different
routes that dictate different sites of transfection. Thus, the choice of the
delivery vehicle and administration route has to take account which cells are
to be specifically targeted by the gene transfer approach. This concept will be
discussed in the first part of the review.
Using a gene
therapy approach, improvements of renal function and interstitial inflammation
have been achieved in experimental models of glomerulonephritis and
tubulo-interstitial damage. Gene therapy applied to renal transplantation has
shown promising results in rodents, almost controlling acute rejection.
Finally, the development of animal models resembling the clinical features of
human genetic renal disorders offers a first step towards new treatments among
which gene therapy could become reality in the near future. The main findings
concerning the suitability of gene therapy for slowing the progression of
kidney diseases, and preventing acute renal graft rejection, or treating
genetic disorders, are discussed.
[Back to top] TGF-b: A Fibrotic
Factor in Wound Scarring and a Potential Target for Anti- Scarring Gene Therapy
W. Liu, D.R. Wang and Y.L. Cao
Hypertrophic scar
and keloid are common and difficult to treat diseases in plastic surgery.
Results of wound healing research over the past decades have demonstrated that
transforming growth factor-b (TGF-b) plays an essential role in cutaneous scar
formation. In contrast, fetal wounds, which heal without scarring, contain a
lower level of TGF-b than adult wounds. How to translate the discovery of basic scientific
research into the clinical treatment of wound scarring has become an important
issue to both clinicians and basic researchers. The development of gene therapy
techniques offers the potential to genetically modify adult wound healing to a
healing process similar to fetal wounds, and thus reduces wound scarring. This
article intends to review the roles of TGF-b in the formation of wound scarring, the
possible strategies of antagonizing wound TGF-b, and our preliminary results of scar gene
therapy, which show that wound scarring can be significantly reduced by
targeting wound TGF-b.