Lung cancer and gene therapy Diana Zamora vila

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Lung cancer and gene therapyDiana Zamora Ávila
Paul R EarlImmunology and Virology
DepartmentBiosecurity Laboratory, Level
3Facultad de Ciencias BiológicasUniversidad
Autónoma de Nuevo LeónSan Nicolás, 66451 NL,
Mexico
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Lung cancer is the most common cancer worldwide
in both the indices of prevalence and mortality.
Smoking is a risk factor highly associated with
this type of cancer (85-90 ), and the exposure
to tobacco smoke in the environment can cause
cancer in nonsmokers. Certain agents like
arsenic, asbestos, chromium, nickel and vinyl
chloride encountered in the work environment
increase the risk and also can cause cancer. In
addition, the effects of smoking may be additive
with some hazardous agents.
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ClassificationThe 2 main types of lung
cancer are small cell and nonsmall cell
neoplasms.1/ Small cell pulmonary cancer
constitutes 20 of all these cancers, the cells
multiplying rapidly and are able to metastisize
into major organs like lymphatic ganglia, bones,
brain, adrenal glands and liver. The primary
tumor usually generates near the bronchi and
expands to the center of the lungs. The main
cause of this type of cancer is smoking.
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Small-cell lung cancer
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2/ Nonsmall-cell pulmonary cancer represents
almost 80 of all lung cancer. It diffuses more
slowly than the small cell type. The 3
subtypes are 1/ carcinoma of
squamous or epidermoid cells (30 ),
2/ adenocarcinoma (40 )
y 3/
undifferentiated carcinoma with large cells (10
). Some cancers start in the bronchioles and
evolve from there through several
years.
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Nonsmall-cell lung cancer
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Lung cancer is a very aggressive disease in
which less than 15 (10-13 ) of the patients
survive over 5 years. This is the lowest rate of
all types of cancer. More, 80 of cases do not
respond favorably to chemotherapy or radiation.
The main cause of poor or no recovery from lung
cancer is the high rate of metastasis existing
before diagnosis. In nonsmall cell lung
cancer, about 2/3rds of the pacients are
inoperable as a result of metastasis. In small
cell lung cancer, metastases are present in most
patients. The liver has 1/3rd cases, and the
brain is the first site.
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Genetic therapyIn genic therapy one
procedure is introducing a gene(s) into somatic
human cells. Two general strategies exist 1/
genic therapy in vivo in which the target cells
are introduced directly into the body, and 2/
therapy ex vivo in which the target cells are
modified in vitro and later replaced.The genetic
treatment of lung cancer is difficult as it is a
multifactor disease. Thus various alternatives
have been proposed for stimulating the immune
system, including the transfer of suicidal cells,
inactivation of oncogenes, gene replacement,
tumor repressers and the transfer of
pro-apoptotic genes.
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A promising target for the development of novel
anticancer strategies is telomerase, a
ribonucleoprotein reverse transcriptase that
extends human telomeres by a terminal transferase
activity. Telomerase is highly active in the vast
majority of human tumors, known since 1994. Its
essential genes are hTR and hTER. However,
telomerase has not yet advanced from the
laboratory to the clinic.
See
www.nature.com/clinicalpractice/onc.
See also methioninase gene therapy and
apoptosis as given by Yamamoto et al. (Cancer
Gene Therapy 10, 445450, 2003).
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STIMULATION OF THE IMMUNE SYSTEMTumor regression
has been demonstrated in animal models that was
mediated by the administration of cytokines such
as interleukines (IL) 2, 4 , 6, 7, 1 2,
stimulating factor of colonies of granulocytic
macrophages (GM-CSF), tumor necrosis factor -?
(TNF-?), interferon-? (IFN-?) IFN-?,
nonetheless use in humans has been limited due to
toxicity.The strategies based on cytokines can
lead to the development of tumor cell vaccines
that genetically incorporate modified fibroblasts
or tumor cells that secrete cytokines.
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TRANSFER OF KILLER GENES This type of genic
therapy is based on the transduction of a gene
able to convert a nontoxic compound into a toxic
metabolite able to selectively kill tumor cells
upon administration of the appropriate prodrug.
The 2 genes used most for this type of therapy
are thymidine kinase of herpes simplex virus
HSV-tk and the gene of cytosine deaminase.
Cytosine deaminase converts 5-fluorocytosine into
an antimetabolite cytotoxic 5-fluoroacyl. HSV-tk
converts the gancyclovir into a toxic trifosfate
metabolite. An adenoviral transduction in
nonsmall cancer cells with HSV-tk followed by the
administration of gancyclovir selectively kills
the tumor cells.
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INHIBITION OF ONCOGENESThis type of therapy
is based on the identicifation and inhibition of
those genes critical for carcinogenesis.
Oncogenes of the ras family are some of the more
common oncogenes that are activated in lung
cancer and therefore are targets for this type of
therapy.In preclinical studies mediated by a
plasmid with an antisense sequence with k-ras the
mRNA is selectively blocked by mutation, and
tumor growth is reduced both in vivo and in vitro
in murine models.
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GENES SUPPRESSERS OF TUMORSAnother genic therapy
strategy based on work with gene tumor
suppressers, in contrast to oncogenes, is with
the 2 alleles of a tumor suppresser gen that
should be eliminated or inactivated by inducing
tumor growth. Theoretically, replacement of only
one copy of the tumor supresser gene in cells
with a loss of homozygotic function can restore
the ways of normal growth and cellular
proliferation. One of the genes most commonly
mutated (50-70 of cases) is p53 that can be
inactivated by overexpression of MdM-2.
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TRANSFER OF PRO-APOPTOTIC GENESCells with
multiple genetic alterations are usually
eliminated by apoptosis. For survival, they
depend upon the overexpression of antiapoptotic
molecules like bcl-2, bcl-xL or survivin. The
downregulation of such proteins may reduce the
apoptotic threshold of cells. The 2 major
apoptotic signaling pathways are 1/ the
mitochrondrial pathway and 2/ the death receptor
pathway. Cells having condensed and fragmented
chromatin demonstrate apoptotosis.
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TRANSFER OF GENESMany systems have been
used for the administration of genes in the
treatment of cancer such as use of adenovirus and
associated viruses, poxvirus, herpes simplex, but
all of these can provoke an immune responce
against the vector, in the manner required to use
different strains or different routes of
administration. An ideal technique for genic
transfer should be nontoxic and have great
efficiency for various types of cells with 1 or
more genes for which the transfer process is
selective.
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NONVIRAL SYSTEMS Due to the low
efficiency of the transfection of naked DNA,
various methods have been used for increasing the
efficiency like microinjection, electroporation
and precipitation with calcium, but unfortunately
these methods are usually inapplicible in vivo
and generally result in a transient expression of
the gene. The efficiency can be raised by using a
gen gun to incorporate the DNA by bombarding the
skin.
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VIRAL SYSTEMS In comparison with
the previous systems, this type of system shows
an efficiency of better tranduction both in vitro
and in vivo. The viral
vectors used the most are defective retroviruses,
adenoviruses and ones associated with
adenoviruses. Others are herpes simplex,
vaccinia, avipox baculoviruses. Among the
disadvantages encountered in the use of viruses
as vectors are toxicity, the production of
foreign transient proteins and limitations in the
size of the gene to be transferred. The virus
vectors most widely used with adenoviruses are
easy to produce in vitro efficiently and with
surety.
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TRANSFER OF GENES IN LUNG CANCER
AEROSOL TECHNIQUEMost drugs and DNA complexes
have been administered by conventional routes
oral or intravenous. The biodistribution of drugs
by means of these strategies are diseminated and
the quantity that is deposited in the lung is
small. Another important aspect to consider in
these types of systems is the toxicity that is
observed after injection. The ability to express
trangenes in the lung in a selective manner can
facilitate the development of genic therapy for a
variety of human diseases.
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Polyethylene amine (PEI) is a polycation able to
condense DNA and to protect against the
degradation of DNAases así como de liberarlo in
vitro and in vivo, this polymer forms polyionic
complexes with DNA to establish electrostatic
cooperative interactions with its ammonium groups
and the phosphate groups of the DNA. More, it is
possible to reach high levels of gene expression
if human albumin, albumin from mouse serum or
ovialbumin and human igG are added to this
compound.
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Furthermore, liposomes formulated with
9-nitrocamptotecine (9NC-DLPC), which
is an inhibitor of topoisomerase 1 and inhibits
the growth of subcutaneously induced tumors like
the metastasis of lung cancer in the murine
model, observing a synergistic effect through
the combination of the administration of
gene p53 and PEI. Recently, the expression of
Wilms' tumor gene (WT1) has been encountered in
lines lung cancer cells in 5/11 (45 ) by the
test for reverse transcriptase polymerase chain
reaction (RT-PCR), 2/5 (40 ) in SLCL and in 3/6
of NSCLC. In another study, WT1 overexpression
was found in 12/15 cell lines of lung cancer. The
protein of WT1 is an attractive target for
immunotherapy.
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STIMULATION OF THE IMMUNE SYSTEM BY WT1Recent
advances in immunology and molecular biology have
permitted the identification of many antigens
associated with tumors (TAAs), and the episomes
that are recognized by cytotoxic HLA class I T
lymphocytes in different kinds of neoplasms. One
of the TAAs identified is the product of gene WT1
that allows the possibility of slowing down the
cancer based on administration of this peptide.
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In a phase I clinical study, Tsuboi et al.
(Microbiol Immunol 48 175-84, 2004) applied
immunotherapy based upon WT1 by intradermal
injection of 3 mg of the peptide of WT1 of 9
bases that stimulated HLA-A2402, the vaccination
in an interval of 2 weeks, resulting in the
reduction of the CEA and xSLX tumor markers and a
transient decrease in the tumor size being the
primary clinical evidence that shows that
vaccines against WT1 are an alternative for
pulmonary cancer patients.
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The futureLung cancer is one of
the most aggressive and fatal neoplasms. Today
it is possible to diagnose earlie, and we have an
improved panel of anticancer drugs. Nevertheless,
less than 15 of patients survive more than 5
years. The most recent trend is to explore genic
therapy and therapeutic vaccines as alternatives
for treatment. With these new tools perhaps the
patient's life can be prolonged reducing the cost
of treatment.