Photodynamic therapy (PDT):

PDT=PHOTODYNAMIC THERAPY
Photodynamic therapy (PDT) is a
treatment that uses a drug, called a
photosensitizer, and a particular type
of light. When photosensitizers are
exposed to a specific wavelength of
light, they produce a form of oxygen
that kills nearby cells.
In the first step of PDT for cancer
treatment, a photosensitizing agent is
injected into the bloodstream. The
agent is absorbed by cells all over the
body but stays in cancer cells longer
than it does in normal cells.
Approximately 24 to 72 hours after
injection  when most of the agent has
left normal cells but remains in cancer
cells, the tumor is exposed to light. The
photosensitizer in the tumor absorbs
the light and produces an active form
of oxygen that destroys nearby cancer
cells.


NEW DRUG USED FOR SENTISIZING
IN PHOTODYNAMIC THERAPY
Earlier PDT drugs meant that the
patient's entire body was sensitive to
light for up to three months, increasing
the risk of sunburn. But a new drug
called 5-aminolaevulinic acid (ALA) is
only light sensitive for around a day
and so carries far less risk of sunburn.
The drug is made by Biosynth.


HEAD AND NECK CANCER STUDY
USING PHOTODYNAMIC THERAPY
In Phase 1 trial Doctors at University
College Hospital in London have
tested the latest form of photodynamic
therapy on 11 patients with advanced
head and neck cancers, all of whose
tumors have shrunk or died away.
During photodynamic therapy a drug is
injected into the patient’s bloodstream
that makes the cancer cells extremely
sensitive to light. Those involved in the
trial were injected with a new drug —
known as Amphinex, a photosensitising
agent — three to four days before
being given standard chemotherapy.
Because tumors have high metabolic
activity and are surrounded by a
proliferation of new blood vessels, the
drug accumulates in cancer cells in
preference to healthy tissue. When a
low-powered red laser is shone on the
tumor, directly or through the skin, the
light triggers a chemical reaction that
disrupts the harmful cells and boosts
the action of a chemotherapy drug,
bleomycin.
The results are quite impressive. You
can see the tumor turn black and die,
not quite before your eyes, but over a
matter of days.


PHOTODYNAMIC THERAPY'S USE  IN
DERMATOLOGY
PDT is successfully utilized in
dermatology in the treatment of actinic
keratoses (lesions that can develop
after years of exposure to UV light),
Bowen's disease (the growth of
abnormal cells that can turn into skin
cancer and that is partly due to long-
term exposure to the sun); and basal
cell carcinoma (the most
common form of skin cancer);


OTHER DEVELOPMENTS
PDT trials are already underway for
cancers of the prostate, breast, bile
duct and pancreas;

Glowing plaster by Polymetronics (UK)
in trial;