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Science: Viruses as cancer killers
Advanced cancer can rarely be cured. In the future, genetically modified viruses will help to fight if chemotherapy and radiation therapy do not promise success. Despite significant advances in surgical procedures and increasingly effective chemotherapy drugs, advanced cancer patients still have poor chances of survival.
Patients can gain lifetime from a few months to a few years. However, the extension usually brings with it a deterioration in the quality of life, which can severely restrict those affected. Eight out of ten patients receiving chemotherapy to treat breast cancer experience severe pain.
Tumor cells react similarly to bacteria and form resistance when they are pressurized with medication. "Resistance has been documented for all of the targeted drugs used in cancer therapy," said Charles Sawyers of the Memorial Sloan-Kettering Cancer Center in New York, one of the world's leading experts in the field.
Within a period of several months of cancer treatment, the effectiveness of a drug decreases and existing cancer cells multiply over time and the cancer comes back.
Dissolution of cancer cells The new type of virotherapy, also known as oncolytic (cancer cell dissolving) tumor therapy, with its immense advantages over conventional methods, is a new glimmer of hope. In principle, oncolytic viruses do the same as measles, mumps or chickenpox. They only do this in a more targeted and effective way.
Advantage of this treatment: They only penetrate tumor cells, multiply inside the cell and destroy it within hours or days.
The new generation of viruses released in the process attacks other tumor cells in the area. This works almost like the "pyramid scheme". The malignant cells are thereby dissolved more and more quickly. Ideally, a single administration can lead to a viral domino effect, which is sufficient to eliminate a tumor within a short time.
Additional weapons The oncolytic viruses are additionally equipped with additional "weapons" through genetic engineering. These are intended to help pinch the tumor cells from several sides. The modified microorganisms contain, for example, molecules that have a toxic effect on the tumor cell, induce the formation of messenger substances or transmit so-called tumor suppressor genes. This prevents the cancer cell from growing. The messenger substances activate the body's own defense system, which attacks the tumor cells. In order for cancer to grow, it needs a lot of oxygen and enough micronutrients. Here the “killer viruses” are supposed to interrupt the blood supply to the cancer.
Scientists from the American pharmaceutical company Jennerex recently reported in the US journal "Cancer Research" that they were able to completely shut off the blood supply to compact tumors in the liver in just five days by infusing a suitable oncolytic virus.
The result: the cancer cells that survived the direct attack of the tumor killers soon died in a second "attack wave" because they were cut off from the oxygen supply.
There are now 20 types of viruses identified. Cancer researchers around the world are currently working on this new therapy concept. The researchers have now identified more than 20 different types of virus, all of which have the ability to kill. Paralysis, herpes and chickenpox viruses can be found among them. In order for these pathogens to successfully take on the role of tumor killers, they are adapted to a specific tumor type on the molecular biological drawing board. For example, the herpes simplex virus, which usually triggers lip or genital herpes, has switched off so-called latency genes.
These enable the pathogen to survive in a host cell over a long period of time. In a second step, the disease-causing properties of the virus are isolated and cut out. As a result, the cells can no longer trigger a disease in the body. The genetic information is damaged in such a way that the microorganisms can no longer spread in the healthy body.
Research into viral infusion Recently, researchers have been trying to administer the microbial therapeutic to those affected by means of blood infusion. The theory here is that genetically modified viruses search for the tumors with extreme determination. In practice, however, other results were shown. Only a few viruses have reached the tumor because they have already been caught in the lungs, liver and spleen. This is due to the structure of the human immune system. If this has already come into contact with the virus family in the past, the intruders are neutralized using so-called antibodies and the goal is not achieved.
After all, in 30 patients the infusion was repeated three times at 14 day intervals, as the researchers report in the British journal "Nature Medicine". Patients who received the highest concentration of oncolytic viruses survived an average of 14 months. In contrast, patients who had received a small amount of pathogens were only seven months.
Research is just beginning A study from Korea shows that cancer researchers are still a long way from actually converting theoretical and experimental knowledge into an effective treatment method. So far, her focus has been on the principle of action and how the harmlessness of viral tumor therapy can be demonstrated. The best results in use were achieved by an oncolytic virus based on herpes simplex manufactured by the American pharmaceutical company Amgen. Studies on 436 patients with black skin cancer (melanoma) showed a clear advantage of oncolytic therapy compared to control patients. A final analysis of the data is still pending.
Oncolytic viruses are currently not approved as a cancer treatment drug in the United States or Europe. Only in China have the health authorities registered a genetically modified adenovirus for the treatment of tumors in the head and neck area. (fr)