An Example of a Targeted Viral Cancer Therapy

The present standards for cancer treatment are poorly targeted in comparison to prototype work taking place in the labs and clinical trials. Chemotherapy, radiotherapy, and the like have a detrimental impact on the rest of the body, and their effectiveness is limited by the degree to which they hurt the patient in the process of impacting cancer cells. Their days are numbered, however. A broad range of next generation targeted treatments have been demonstrated in recent years, with few side-effects because they affect only cancer cells and their nearest neighbors. A number of these therapies use existing biological systems as a means of targeting cancer cells, such as viruses:

The patient suffered from multiple myeloma, a cancer of the bone marrow. Last June, [doctors] injected her bloodstream with a form of measles that was genetically re-engineered to attack myeloma cells. The measles therapy followed a decade of unsuccessful treatments from numerous courses of chemotherapy to two stem cell transplants. But the cancer returned time and time again - until now. A year after the measles injections, she's still cancer-free. The idea of using viruses to defeat cancer - called oncolytic virotherapy - is not a new idea. [But] her case is the "first well-documented instance of a patient who has received an intravenously administered virus that has caused complete remission of disseminating cancer. We've known for a long time that this is possible in mice, but we had not known that it's possible in people. We now know it's possible and this should energize the field - but we have a lot of work to do."

Oncolytic virotherapy works by exploiting the fact that cancer cells usually have weak ability to fight off infections. Viruses can infect normal cells, but it's a self-limiting infection, so normal cells can easily overpower these viruses and get rid of the infection. But in the weakened cancer cells, the virus can replicate, destroy cancer cells [and] make more new virus, which can then go and kill more cancer cells around it. [The] treatment is different from a vaccine. "When you administer a vaccine, you give the minimum dose you can give in order to alert the immune system. We are using the virus as a weapon. We give it into a vein and we ask those viruses to seek and destroy the cancer cells. There are a large number of cancer cells in the body, so you need to give a massive dose of virus."

The [researchers] used a strain of the measles virus that has been used in vaccinations since 1954 and "taught it to grow on human cancer cells ... That's how it became specific for cancer." [Researchers] have given this treatment to six patients, but only one of them had a complete response to the treatment. One had a partial response and the others no response at all. One of the barriers to successful virotherapy treatment is the body's own immune system. If an antibody to a virus is present in the patient's blood stream, it will negate the benefit of giving the virus. [The] hope is to have a variety of viruses to use so that doctors can always find ones patients aren't already immune to.


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