By Mark M. Green
(Abstracted from “A Scientist’s View of Almost Everything,” by Mark M. Green, 2019)
Cancer patients in the 1800s were observed, too often to be chance, to be relieved of their cancerous tumors when they were ill with respiratory problems. When viruses were discovered later in that century, it was hypothesized that viral particles were responsible for the effect on the cancerous tumors. The discovery of viruses arose from the fact that infectious fluids remained infectious when transferred from one animal or plant to another even after processes were used that were known to kill or remove bacteria.
Soon after the discovery of viruses, doctors began to experiment with using viruses to treat cancer, but with mixed results. It’s interesting that the greatest successes were in the treatment of patients whose immune systems were depressed, which was understood as arising from the fact that the virus, which was therapeutic against cancer, had not been removed from the blood of the patient by their immune system.
In the middle years of the twentieth century, doctors tried to use viruses to treat cancer with some success, although too often the viral infection killed the patient. This treatment strategy was therefore mostly abandoned, returning cancer treatment to use of radiation and chemotherapy, which are still primarily used today.
However, in recent decades the ability to alter the genetic material of viruses has given rise to their use in battling cancer by removing the viral characteristics that cause human disease. Nevertheless, serious major problems remain to be solved in suppressing the immune system of the patient to allow the therapeutic virus to get to the tumor. Another problem involves delivering the virus to the tumor, since the virus cannot be used systemically. Some success does appear to be in the wings, with the Food and Drug Administration of the United States and the European Medicines Agency recommending and allowing use of a genetically modified virus (T-VEC) to attack certain cancers—a virus that in its unmodified form causes herpes.
One specific example of the effort to move forward on viral therapy for cancer treatment is based on work at the University of Calgary, which led to the formation of a company called Oncolytics Biotech located in Calgary. The company’s work is focused on the fact that many metastatic cancers arise from a mutated protein, Ras protein, which is responsible for cell growth. When a particular type of mutation occurs in this protein, the protein’s function can be turned on permanently so that cell growth occurs without limit, giving rise to cancerous tumors.
A virus commonly encountered in human beings, reovirus, which causes infections that are subclinical—in other words they give rise to no or very slight symptoms—has been discovered to preferentially infect cells in which the Ras protein is “turned on.” Infection of certain tumors by a reovirus causes cancerous cells to produce more reovirus, and causes lysis of cancerous cell walls, killing the cancerous cells and releasing more of the reovirus, which can then go on to kill more cancerous cells.
At Oncolytics Biotech, products based on the reovirus are currently being used in trials that could lead to their wide use in cancer therapy. In an article written by Heidi Ledford published in Nature/News, Brad Thompson of Oncolytics Biotech described the general idea behind viral therapy for cancer succinctly by pointing out that cancerous cells in their high growth, leading to tumors, are far more susceptible to infection than normal cells: “Malignancy can suppress normal antiviral responses, and sometimes the mutations that drive tumor cells also make cells more susceptible to infection. Viral infection can thus ravage a tumor while leaving healthy cells untouched.”
It appears that the infectious characteristics of viruses might lead to important new medical procedures for dealing with cancer.