Viruses help to destroy malignant tumors

Science: Viruses as a cancer killer

09/10/2013

Cancer in advanced stages can rarely be cured. In the future, genetically modified viruses should help fight the disease if chemotherapy and radiotherapy do not promise success. Despite significant advances in surgical procedures and increasingly effective chemotherapeutic agents, advanced cancer patients still have poor survival rates.

Between a few months to a few years, patients can gain in life. The extension, however, usually brings a deterioration in the quality of life with it, which can severely restrict those affected. In eight out of ten patients who receive chemotherapy for the treatment of breast cancer, the therapy causes severe pain.

Tumor cells react in a similar way to bacteria and form resistance when drugged. "Resistances are well documented in all targeted drugs used in cancer," says Charles Sawyers of the Memorial Sloan-Kettering Cancer Center in New York, one of the world's leading experts in this field.

Within a few months of cancer treatment, the effectiveness of a drug decreases increasingly and remaining cancer cells multiply over time and the cancer comes back.

Dissolution of cancer cells
There is the novel virotherapy, also called oncolytic (cancer cell dissolving) tumor therapy, with its immense advantages over conventional procedures, a new glimmer of hope. Oncolytic viruses act in principle as well as measles, mumps or chickenpox. They only do this more purposefully and effectively.

Advantage of this treatment: they penetrate only into tumor cells, multiply inside the cell and destroy it within hours or days.

The released new generation of viruses attacks other tumor cells in the environment. This works after the quasi „The malignant cells are increasingly and faster being dissolved, so ideally, a single administration can lead to a viral domino effect that is sufficient to eliminate a tumor within a short period of time.

Additional weapons
The oncolytic viruses are additionally equipped by genetic engineering with other "weapons". These should help to take the tumor cells from several sides in the forceps. The altered microorganisms contain, for example, molecules which have a toxic effect on the tumor cell, induce the formation of messenger substances or transmit so-called tumor suppressor genes. The cancer cell is thereby prevented from growing. The messenger substances activate the body's own defense system, which attacks the tumor cells. For cancer to grow it needs a lot of oxygen and enough micronutrients. Here are the „killer virus“ interrupt the blood supply of the cancer.

Recently, scientists from the American pharmaceutical company Jennerex reported in the US journal "Cancer Research" that they succeeded in completely interrupting the blood supply of compact tumors in the liver within just five days by infusing a suitable oncolytic virus.

The Ergenbis: the cancer cells that survived the direct onslaught of the tumor killers soon died on a second "wave of attack" because they were cut off from the oxygen supply.

Meanwhile, 20 types of viruses have been identified
Cancer researchers around the world are currently working on this new therapy concept. More than 20 dissimilar virus species, all of which have the ability to kill, have now been determined by the researchers. Poliomyelitis, herpes and chickenpox are found among them. So that these pathogens successfully take over the task as tumor killers, they are adapted to the molecular biology drawing board for a specific tumor type. For example, with the herpes simplex virus, which normally causes a lip or genital herpes, so-called latency genes have been eliminated.

These allow the pathogen to survive for a long time in a host cell. In a second step, the disease-causing properties of the virus are isolated and cut out. As a result, the cells can no longer cause illness in the body. The genetic information is damaged so that the microorganisms in the healthy body can no longer spread.

Research for the virus infusion
Recently, researchers have been attempting to administer the microbial therapeutic to those affected by infusion via the blood. The theory is that genetically modified viruses are searching for the tumors with extreme determination. In practice, however, showed different results. Few viruses have reached the tumor because they have been trapped in the lungs, liver and spleen. This is due to the buildup of the human immune system. If this has already been in contact with the virus family in the past, the invaders are neutralized by means of so-called antibodies and the target is not reached.

After all, in 30 patients, the infusion was repeated three times at intervals of 14 days, as the researchers in the British journal Nature Medicine report. Patients who received the highest concentration of oncolytic viruses survived for an average of 14 months. Patients who had a low level of pathogens, but only seven months.

Research is still in its infancy
A study from Korea shows that cancer researchers are still a long way from translating theoretical and experimental knowledge into effective treatment. So far, their attention has been focused on the mode of action and how an harmlessness of viral tumor therapy can be demonstrated. The best results in the application were obtained from an oncolytic virus based on herpes simplex produced by the American pharmaceutical company Amgen. Investigations 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.

Neither in the US nor in Europe are oncolytic viruses currently approved as a drug for cancer treatment. Only in China have the health authorities registered a genetically modified adenovirus for the treatment of head and neck cancer. (Fr)