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Bacteria Used Successfully in Cancer Treatment
Laura Jassowski
5/19/11
Abstract: Research has shown that bacteria has been used successfully in
treating cancer in patients. Many patients’ resistance to cancer has prompted scientists
to search for alternative methods of treating cancer. Many different bacterial species
have been studied as either a vector to deliver the tumoricidal medicine into the tumor
or as live genetically modified bacteria designed to replicate inside the tumor and kill it.
Although many of the different approaches have proven successful and look very
promising, they still need to be investigated slightly more before they can be applied
conventionally.
In a world riddled with cancer, where the body’s own cells are the disease, there
are few effective treatments available for the patients afflicted with the disease. Some of
the caners don’t respond to conventional treatment. This prompted scientists to look for
a better way to deliver medicine into the tumor and kill it without harming the patient’s
healthy living tissue around it. Scientists started looking to the world of microbiology for
the answer to their problems. The discovery of bacteria as an anticancer was
discovered about one hundred years back. The German physicians W. Busch and F.
Fehleisen separately observed when certain cancers went into regression when their
patients accidentally became infected with erysipelas (Streptococcus pyogenes).
Independently, American physician William Coley noticed that his patient’s neck cancer
began to regress when he contracted the same infection (Bacteria in Cancer Therapy,
Patyar, S). Coley began the first well- documented use of bacteria to treat cancer. He
developed a vaccine in the 1800’s that comprised of two killed bacterial species,
S.pyogenes and Serraita marcescens to stimulate the infection without the risk of the
fever. This vaccine was widely used to treat all kinds of cancers- sarcomas, carcinomas,
lymphomas. Complete, prolonged regression was documented in many cases. This
research sets the ground for anticancer research with bacteria today.
The first way scientists are trying to develop bacteria into cancer treatments are
as a tumorcide (Bacteria Successful in Cancer Treatment, Science Daily). Certain
species of anaerobic bacteria, especially from the genus Clostridium, have proven to
consume oxygen poor tumor tissue and thrive inside their anaerobic environments
(Bacteria in Cancer Therapy, Patyar, S). The only problem is the bacteria die when they
come into contact with the oxygen rich tissue of the tissue, and don’t completely
consume the tumor. Scientists then need to combine with other treatments to finish off
the tumor. There is tumor regression, but there is also a high degree of toxicity
associated with such a pathogenic bacteria and the animal falls ill or dies. Scientists
tried shifting their focus to a nonpathogenic form of Clostridium –M55 (Bacteria in
Cancer Therapy, Patyar, S). The problem with this bacterium is it was able to colonize
but there was little cancer regression. Scientists then took Clostridium novyi and
combined it with chemotherapeutic agents. This strategy is known as COBALT
(combination bacteriolytic therapy) (Bacteria in Cancer Therapy, Patyar, S). This
resulted in significant anti-tumor properties but still resulted in animal deaths. This
bacterium was exploited because of its membrane disrupting potential. This process
will be exploited further and it has proved promising because of its significant
eradication of tumors in mice. To make poorly vascularized regions of the tumor
accessible, it is used in conjunction with anti-microbial agents.
Another method is using bacteria as a vector instead of a tumorcide (Bacteria
Successful in Cancer Treatment, Science Daily). To overcome many of the problems
faced with the previous experiments, scientists are using genetically modified bacteria
as vectors to deliver therapy directly to a tumor. To do this, scientists produce a protein
of interest specifically in the tumor microenvironment and then provide strong therapy to
various cancer treatments. One example is since S.Typhimurium naturally colonizes in
the liver it is attenuated form could be used to deliver cytokines directly locally to liver to
effect hepatic metastases. (Bacteria in Cancer Therapy, Patyar, S).
Still another way for bacteria to be utilized to help treat cancer is bacterially
directed enzyme producing therapy. This form overcomes the acceptable side effects
of bacterial therapy and uses anaerobic bacteria that have been transformed with
enzymes to convert a non-toxic prodrug into a toxic drug. The enzyme from the bacteria
is solely expressed in the tumor. Although combinations of enzymes and prodrugs have
killed tumors in vitro, so far live results have been disappointing (Bacteria in Cancer
Therapy, Patyar, S).
Although the results of many of the tests from all of the many different ways to
use bacteria to treat cancer have been promising and bear further research, there are
some problems. The first is the toxicity of the bacteria at the dose required for
therapeutic use. If the dose is lowered it reduces efficiency. There is also the risk of
developing a systemic infection from the injected bacteria. Another problem is even the
removal of toxic genes like in COBALT therapy still leads to fifteen to forty- five percent
mortality in mice(Bacteria in Cancer Therapy, Patyar, S).. There is also the issue of
incomplete lysis of the tumor. Despite these setbacks, using bacteria to treat cancer
may be a promising field of research for the future.