The Future of Cancer Clinical Trials Hold Promise Thanks To Viruses

Chemotherapy has always and continues to be an important line of defense against cancer, but is not for the faint of heart. Some form of chemotherapy is still routinely prescribed for most types of the disease, and most treatments work by targeting fast-growing cells, like those typically found in rapidly growing tumors. But while chemotherapy can shrink tumors, they often grow back and become resistant to treatment.

To combat this resistance, chemotherapy is now often used in combination with other treatments that have different mechanisms for attacking and killing cancer cells. Doctors must be cautious when combining treatments to ensure that the regimen does not become too toxic for patients to tolerate. The goal is to introduce drugs that can be used with chemotherapy to not only enhance anti-tumor activity and extend survival, but to improve quality of life while undergoing treatment.

One approach that has proven quite promising is harnessing viruses to infect, multiply within and subsequently destroy cancer cells, ideally with virus constructs targeting tumors without affecting normal tissue.

Several types of these viruses have been developed to date, with names like adenovirus, poxvirus, and picornavirus. Even the herpes simplex virus is under consideration for this type of use, though in a modified form that does not confer the disease that the naturally-occurring virus confers.

Some researchers consider a different class of viruses, known as reoviruses, to be among the most promising for the task of battling cancer cells. Reoviruses are found everywhere in nature and have been isolated from rivers and stagnant waters throughout the world. These viruses choose to colonize cancer cells that exhibit enhanced activity in a pathway controlling cellular growth (the so-called Ras pathway), while sparing normal cells in which the virus cannot grow as rapidly.  Approximately one-third of human cancers have the mutation that makes them a prime target for reoviruses.

Studies have shown that reovirus, used in conjunction with immune suppressive drugs, can effectively prolong the survival of various cancer-stricken animals in the laboratory.
This suggests that immune suppressive drugs can be combined with reovirus in the treatment of human cancers, and clinical studies designed to test this are already ongoing.

Calgary-based Oncolytics Biotech has developed a modified reolysin form that it calls Reolysin. In preclinical studies using a wide variety of cancer cell lines, investigators found that when used together, reovirus and chemotherapy resulted in more efficient anti-cancer activity than when each agent was used on its own, plus co-administering Reolysin with other drugs seemed to enhance virus delivery to tumor cells and lessen the body’s immune response to it.

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Source: Clinical Leader