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ABSTRACT:-
Nanoparticles of gold, which are in the size range 10-100 nm, undergo
plasmon resonance with light. This is a process whereby the electrons of gold
resonate in response to incoming radiation causing them to both scatter and
absorb light. This effect can be harnessed to either destroy tissue by local
heating or release payload molecules of therapeutic importance. Gold
nanoparticles can also be conjugated to biologically active moieties, providing
possibilities for targeting to particular tissues. Here, we review the progress
made in the exploitation of the plasmon resonance of gold nanoparticles in
photo-thermal therapeutic medicine.
CANCER AND ITS STATUS:-
From
the 1960s, when cancer was considered incurable and invariably to we talk not
only of cure and long-term survival but of prevention and control.
The common
cancers in
India
are:-
Men: the mouth, the throat and the stomach.
Women: the uterine cervix and the breast
Receptor Logic is developing a new class of antibodies that
mimic T cell receptors (TCR mimics) and can identify and attack tumor-specific
human leukocyte antigen complexes (HLA). HLA are present on virtually all cells
and display cancer targets on tumor cell surfaces.
Tragically, every 13 minutes a woman dies of breast cancer. It
costs $10,000 - $15,000 to treat breast cancer when detected early compared to
$60,000 - $145,000 when it is detected in more advanced stages. Early detection
also saves lives. The survival rate for localized breast cancers is 96%, as
compared to 21% when the cancer has spread to other areas and organs.
Cancer prevention- primary or secondary:-
Primary prevention
- removal of carcinogenic or implicated causative factors. Most of these
involve a change in lifestyle.
Secondary
prevention -
identification and treatment of asymptomatic individuals with either
pre-clinical or early cancer by health screening.
Screening:
- A step in cancer
control, detection at the pre-cancer stage so that pre-cancerous lesions do not
progress into cancer as in cervical cancer. In case of very early detection of
cancer in the pre-palpable, pre-visual stage, cure to the extent of 80 per cent
to 90 per cent is possible.
The
identification of familial risk in colon cancer and PSA (prostate specific
antigen) for prostatic cancer is also possible. Today, early detection is that
which is done only cytologically, or better, at the molecular level.
The cancers detected through screening programmes are uterine cervix, breast,
colorectum and prostate. Their greatest impact has been on cervical cancer and
breast cancer.
Cancers of the colorectum, breast, stomach, ovary,
endometrium, lungs and so on are influenced by dietary factors. Chemoprevention
attempts to block the initial initiation of the carcinogenic process or to
arrest or reverse the progress of premalignant lesion before it becomes
invasive. Cruciferous vegetables such as broccoli and yellow and green
vegetables such as carrot and greens contain agents that block the activation
of carcinogens and thus prevent DNA damage. These help protect people against
cancer.
Screening
mammography is effective in detection in the early and very early
stages, sometimes even before it is palpable to the most experienced fingers.
The lesion can be detected when its a few millimeters in size. Cancer
so detected has a cure rate of over 95 per cent. The benefit is not just
in terms of cure and survival but cure without morbidity. The lesions are
excised by sterotaxic surgery without causing any mutilation. Computerized
Tomography (CT) Scan, nuclear imaging, magnetic resonance imaging (MRI),
ultrasound scan, fiber optic endoscopy, and so on that are routine
investigations today.The
discovery of tumor markers, biological markers and genetic markers
along with immunophenotyping and immuno histochemistry, polymerase chain
reaction (PCR) to study minimal residual disease have enhanced diagnostic
capabilities multifold. Achievement of chemotherapy and multimodal therapy is
through organ conservation. Radical surgery is replaced by more
conservative surgery, with stress on organ preservation and functional
rehabilitation in cancer management.
INTRODUCTION:-
Metallic gold, either in the form
of bulk substances or as nanoparticleswidely
used in the emerging and highly interdisciplinary field of nanotechnology. Many
biodiagnostic applications of gold nanoparticles, or electrodes, have been
developed since 1970s; however, the rational application of gold nanoparticles
in therapeutic situations is largely undeveloped field. Two properties of gold
nanoparticles make them particularly suitable for therapeutic applications:
(1) antibodies and
other biological molecules can be readily attached to surface of gold
nanoparticles, and (2) the plasmon resonances of gold nanoparticles of certain
shapes cause them to have photon capture cross-sections that are four to five
orders of magnitude greater than those of photo thermal dyes. These attributes
are exploited to obtain the localized heating, or drug release, underlying the
therapeutic applications.
Harnessing
gold nanoparticles:-
Excellent
reviews of basic physical, chemical and optical properties of gold
nanoparticles, and their other applications, are available, and the medical
uses of soluble gold compounds have been discussed by Shaw .The general medical
applications of gold nanoparticles have been reviewed by Salat, while Moghimi
et al. have reviewed the use of nanoparticles in drug-delivery schemes
not involving light. However, while the medical applications of one kind of
gold particle, the nanoshell, have been widely discussed, no broad synopsis
of the recent developments in the photo-thermal, therapeutic applications of
gold nanoparticles exists in the literature at this time and we address this
topic here.
Relevant properties of gold nanoparticles:-
The chemical and physical properties of gold have been reviewed recently
by Pyykko. From a therapeutic point of view, there are two properties of gold
that are most relevant: resistance to oxidation and plasmon resonance with
light. The plasmon resonance for ordinary gold nanospheres is at ~520nm, in
middle of the visible spectrum, but this can be red-shifted into the near
infrared (NIR), with excitation wavelengths of 800-1200nm required for more
complex shapes, such as nanorods. This is useful because body tissue is
moderately transparent to NIR light, thereby providing an opportunity for
therapeutic effects in deep tissues.
Gold or silver metallo-dielectric core-shell
particles offer another route for spectral
control of both absorption and scattering of light, particularly if the core is
dielectric (most commonly gold sulfide, silica and polystyrene) and the shell
is a metal. The spectral properties of such shapes can be controlled by varying
the relative dimensions of the core and the shell (Figure 1). Several groups
have reported methods for the synthesis of these shapes, notably Halas
et al.
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