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Radioactive Bacteria Can Kill Tumor Cells
It’s a classic story line, straight from comic books. An ordinary, everyday person is exposed to radiation, thereby gaining super powers. This irradiated super hero is then able to go out and stop criminals, protecting the city. While the story is familiar, the players have changed. Recently, researchers have found that a strain of Listeria monocytogenes bacteria, the new super hero, can deliver radiation to pancreatic cancer metastasis, killing the tumor cells and saving the world from the evil cancer.

Pancreatic cancer is an extremely lethal form of cancer, with a very low 5 year survival rate and poor prognosis for patients. Metastasis of the primary pancreatic cancer tumor, which is when tumor cells move to and colonize other parts of the body, is one of many reasons why pancreatic cancer is so lethal. While removal of the pancreatic tumor may help slow down the damaged caused by the cancer, metastatic tumors can be more difficult to find, may not develop until after the primary tumor has been removed, and may not be as susceptible to standard treatments as primary tumor cells.

The use of microbes to fight cancer is not a new field of research. Many researchers have used bacteria to either directly kill tumor cells, or as a vector to deliver vaccines or medications. In fact, an immune factor known as Tumor Necrosis Factor was first discovered over one hundred years ago by a practitioner who injected cancer patients with live bacteria. The live bacteria helped incite an immune response that was effective against the tumors. Unfortunately, many of the patients succumbed to the bacterial infection and the extremely strong immune response that followed. In the past hundred years, research into this type of anticancer therapeutic has come a long way. Bacteria and viruses can more easily target and kill damaged cells, such as a cancer cells. By utilizing attenuated strains of bacteria or viruses, which are not as pathogenic as normal strains, scientists can target defective cells while leaving healthy cells unharmed by the microbe. In addition, bacteria and virus expressing tumor cell antigens have been used to help train the immune system to fight cancer cells.

Previously, an attenuated strain of L. monocytogenes was able to selectively kill breast cancer cells, without harming normal cells. This inspired researchers at the Albert Einstein College of Medicine to test whether the attenuated Listeria could be effective against metastatic pancreatic cancer cells. The researchers believed that the Listeria bacteria could be used either to directly kill the cancer cells, or to target the cells and bring medicine or radiation to the metastatic tumors. A study performed in a mouse model of pancreatic cancer indeed showed that the attenuated L. monocytogenes could effectively target metastatic tumor cells.

The researchers found that the attenuated L. monocytogenes replicated strongly in metastatic pancreatic cancer cells. The bacteria replicated less efficiently in primary tumor cells, and very poorly in normal cells. This suggested that the bacteria could be used to specifically target metastases, which are normally very difficult to find and treat. The researchers loaded the Listeria bacteria with a radioactive compound to deliver to the metastatic cancer cells. The metastatic pancreatic cancer tumors in mice treated with this combination therapy of bacterial killing and radiation therapy resulted in tumors shrinking 90% compared to tumors in mice treated with saline injections. The effects of killing by the attenuated L. monocytogenes bacteria was significantly enhanced by the radiation delivered to the tumor cells.

While the researcher suggests that the bacteria can be used to target and kill metastatic cancer cells, the results are not as straightforward as they seem. The radioactive L. monocytogenes bacteria were not given to the mice after the formation of metastasis. Rather, the treatment was provided while the metastases were being formed. Even though the research does not demonstrate that the treatment can destroy metastatic tumors that have already become established, it is potentially usable as a preventative treatment. Preventing metastasis of tumors from many types of cancer would be extremely beneficial. The L. monocytogenes treatment could also potentially be used therapeutically after a patient has completed preliminary anticancer chemotherapy, as a preventative measure against future metastases to prevent recurrence of the cancer.

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There was a similar study which was started last year. The research was conducted by doctors from Johns Hopkins Hospital where they tested patients having Chordoma. It is a rare cancerous tumor that grows fairly slow at any parts of the spine, from the tailbone to the base of the skull. Since it is a solid type of tumor, it contains portions low in oxygen. This happens since tumors grow rapidly, so the supply of blood and oxygen are being out spaced. For most cases, such tumors do not respond to standard radiation and chemotherapies.

Knowing this, patients with chordoma then are the right candidates for their test.

Using bacteria as agents to kill tumor cells have been an idea in circulation for the past century. Since these types of tumors have areas of hypoxia, the kinds of bacteria will then come into the picture. Anaerobic bacteria are microbes that thrive in (and look for) areas that are low in oxygen. These bacteria can target the chordoma and leave normal tissue cells unharmed. Once the bacteria are done destroying the tumor cells, they can then be easily eradicated using common antibiotics.

Such an idea was inspired by Dr. William Coley in 1980s where he noticed patients with cancer who underwent surgeries and later developed some bacterial infection eventually became cured of their tumors completely.

Not just that, by the time 1950s and 1960s came, the anaerobic bacteria, Clostridium butyricum, was also used to fight cancer. The test worked; however, there were difficulties in controlling the bacteria and patients became sick of infection, because Clostridium went on producing toxins to nearby tissues.

During the early 2000, scientists from Johns Hopkins University genetically engineered the bacteria to lack the ability in producing toxic proteins. They tested it on mice and 30% were cured of the cancer. Not only that, the mice’s immune system also soon recognized the cancer cells and destroyed them even before they could grow.

Another study, sponsored by the BioMed Valley Discoveries, Inc, was launched in 2010-2011 where the same type of engineered bacteria was used to patients with solid tumors. Patients enrolled in the study were those that did not respond to standard cancer treatment. The experiment is estimated to be completed by December of 2014.
Lyka Candelario, RN
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