YOU would have thought the last thing dying patients needed was a dose of
herpes. But researchers in Scotland have shown that a strain of this potentially
lethal virus can safely be used to tackle otherwise untreatable brain
cancers.
Of nine patients given only months to live, four are still alive up to three
years after the virus was injected into their tumours in a preliminary safety
trial. If further trials are successful, the treatment could be applied to other
aggressive cancers, such as skin and ovarian cancer.
The team, led by Moira Brown of the University of Glasgow, used a strain of
herpes simplex virus (HSV)鈥攖he virus that causes cold sores鈥攖o
selectively kill tumour cells in glioma, the most aggressive form of brain
cancer. Normal HSV can cause fatal encephalitis if it infects the brain. But a
strain called HSV 1716 homes in on tumour cells, leaving healthy tissue
unharmed.
Advertisement
Because of the risks, only a few groups worldwide are working on viral
therapies that depend on 鈥渓ive鈥� viruses. The viruses used to deliver drugs or
genes to tumours are normally altered so that they can鈥檛 replicate and spread
through the body. HSV 1716 can replicate, but because it lacks a key gene it can
only do so in rapidly dividing cells such as cancer cells.
None of the nine patients who took part in the initial trial had adverse
reactions. The virus did not establish a permanent infection or spread through
their bodies, and scans suggest that the tumours in the four surviving patients
have stopped growing. Encouraged by this, the researchers plan to start further
trials by the end of the year. They are also testing the therapy on patients
with the skin cancer melanoma.
Brown expects that HSV 1716 therapy would be used in combination with
conventional treatments. She also hopes to deliver a double whammy to tumours by
engineering HSV to target their cells with toxins. This approach could also be
used to make cancers more sensitive to chemotherapy.
Although it鈥檚 early days yet, Brown is excited about the prospects: 鈥淚鈥檓
delighted that we鈥檝e actually put something into patients and that, so far,
everything looks very encouraging.鈥�
The results are hopeful, agrees Tony Minson, a virologist at Cambridge
University. 鈥淪ome people worry slightly about the fact that the virus can grow
and replicate,鈥� he says. 鈥淚t is the risky end of the game. But that鈥檚 OK as long
as you are treating patients for whom there is no other option.鈥�
Because HSV 1716 can infect any actively growing cells, its use is likely to
be limited. So Calydon, a California-based company, is developing viruses that
can replicate only in specific types of tissues, such as prostate tissue. But
vice-president David Karpf welcomes Brown鈥檚 work: 鈥淭he more groups working on
this, the greater the likelihood that one of us will find a virus that is
tolerated and effective.鈥�