Fighting cancer with bacteria

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Could common everyday bacteria be the key to fighting cancer? A Caltech research team lead by Professor Mikhail Shapiro think it could. Using ultrasound controlled bacteria they have managed to create a way of effectively killing cancerous cells without harming healthy tissues. This may prove to be a potential alternative to the often painful and arduous treatments currently in place such as chemotherapy and radiotherapy.

So how does this work? The technique uses E. coli bacteria, which are injected into the body to kill cancerous cells. Bacteria destroy cells in two ways; either by multiplying and surrounding the cells tightly until they burst and die or by releasing toxins which destroy the cells. The idea is to apply this to specifically tumour cells and avoid the healthy ones. But first things first — wouldn’t the immune system kick in and kill our bacteria before it has a chance to work? Actually no! Tumours are highly immunosuppressive, meaning that the immune system is weakened in their vicinity. This is a very favourable condition for our cancer killing bacteria. Once injected into the body the bacteria begin to kill tumour cells and, as a knock-on effect, the presence of the bacteria will stimulate the immune system to attack the tumour, while the working bacteria are protected safely in the immunosuppressive tumour core. This is called immunotherapy, the treatment of disease by the stimulation of the body’s own immune system.

This is a remarkable step forward in oncology

This is actually not a new idea; using pathogens to kill cancerous cells has been an active area of research for many decades. It actually began in the 1890s when William Coley, the ‘father of immunotherapy’, noticed that a patient with an inoperable neck tumour actually went into remission after he developed a skin infection. The new breakthrough that Shapiro and his team have made here comes in how we control the bacteria once they are inside the body.

Bacteria are rapidly dividing and rapidly spreading pathogens, so how can we be sure that they will not spread through the body and damage our healthy cells instead of the tumour? How can we be sure this will not make us ill? The bacteria Shapiro’s team are working with have been engineered so that they are dormant until they are warmed to temperatures of around 42 degrees Celsius (around five degrees warmer than body temperature).

These engineered bacteria are then injected into the body and are allowed to circulate. A beam of focused ultrasound is pointed at the tumour which heats the area to the correct temperature. This activates the bacteria solely within that area and allows them to start destroying the tumour without the risk of damaging healthy tissue. Testing done by the research team have found that patients would need to be treated with ultrasound rays for approximately an hour per session, with sessions occurring every few days for the duration of the treatment to allow the treatment to work the most efficiently.

Shapiro’s team tested this method on a series of mice. Out of the ten tested, six of the mice showed bacterial activation via the focused ultrasound rays. Of those six mice, five showed significant slowing in tumour growth and one mouse even showed the tumour disappearing altogether (although it was noted that this was not a typical result and that other factors may be involved). Overall though it was found that the endpoint tumour volume of the mice treated with this technique was much smaller than the endpoint of the tumours in the control mice who did not receive the treatment.

This shows very promising results. It could in time be developed into an alternative to chemotherapy and radiation therapy, which are very harsh and unpleasant treatments for patients. This form of immunotherapy could be used as a method of slowing or delaying tumour growth while other methods, such as surgery, remove it altogether. Alternatively, it could potentially be used to destroy tumours directly. However, this kind of application in humans is potentially years away. Animal trials may have been successful, but trials in humans have not begun yet and although we can hope the results of the treatment on humans are the same, we cannot be sure. There have been many cases of medicine which is successful in animal trials being ineffective in humans.

In any case, this is a remarkable step forward in oncology. Hopefully, we could soon see this approved by the agency which approves new medicines and medical practice in the UK, the Medicines and Healthcare products Regulatory Agency. Shapiro’s new immunotherapy method could be an effective and gentler treatment, giving patients all over the world relief.

Image: NCI

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