Gene therapy is a novel approach to treat, cure, and
ultimately prevent disease by correcting defective genes in the body.
It's main aim is to correct the defects at the DNA level and prevent
further recurrence.
There are essentially two forms of gene therapy
- Somatic gene therapy. This involves changes in the
somatic cells of the recipient's genome in which the
modification cannot be inherited by the next
generation.
- Germ-line gene therapy. Here gene manipulations are made in
the gametes, where the changes can be passed to the
next generation.
Delivery
The fundamental task for gene therapy is to
devise methods for delivering the genetic material into the target
cells
in a specific, efficient, sustainable and safe manner. Only the cancer
cells
must be targeted and the healthy cells must remain unaffected. The problem
of "drug delivery", where the gene is the drug, is particularly
challenging
for genes that are large and complex and require targeting to the nuclei
of cells.
Gene delivery vehicles called "vectors" are being employed for therapeutic
gene delivery to the cells. Viruses are currently employed as vectors.The
virulent part of the virus is removed and is replaced with therapeutic
recombinant genes. However, the
immune and inflammatory
responses of the
patient often interfere with this method of delivery.
In another approach, naked DNA, proteins or lipids are used for
delivering the genetic material.
Gene therapy is still in its infancy with most human clinical trials in
the research stages. The approaches which are currently employed
in cancer gene therapy are:
- Re-activation of tumour suppressor genes
- Blocking the expression of oncogene
- Delivery of suicide genes to cancerous cells
- Immunogene therapy
A detailed account of every approach is given in the
following external
link.
RESEARCH - IN TRIAL
- In cancer cells, telomerase (an enzyme) prevents apoptosis leading to
uncontrolled proliferation. A research group at university of
Brunel have identified a way to switch off this enzyme. [60]
- Canadian scientists have discovered a new virus called reovirus,
which kills only the cancerous cells leaving the normal cells
intact. Normally
cells are protected against the reovirus. In cancerous cells, this protection
is lost by mutations in the RAS oncogene. Hence this virus targets and infects
cancer cells leading to their destruction.
[61]
- Scientists in Northern Ireland have found that nitric oxide, when
used in conjunction with radiotherapy, destroys cancer cells without affecting
normal cells. Nitric Oxide injection sensitizes cancerous cells
such that subsequent radiotherapy, kills only the sensitized
malignant cells and
spares the surrounding healthy cells. The same group have used RBCs as
delivering vehicles of toxic drugs to cancer cells.
[62]
- Normal cells contain a protective coating of sugars around their
core whereas this coating is missed in the breast cancer cells. Scientists
have developed a vaccine that targets one of these sugars known as
STn. Antibodies can then target the cancer cells and kill them. [63]