BBC News reports that an experimental therapy hides “cancer killing viruses inside the immune system in order to sneak them into a tumour” and that this “Trojan-horse therapy ‘completely eliminates’ cancer in mice”.
This news is based on early stage research into a new type of cancer treatment, using viruses to target and attack cancerous tumours. Several research teams have adopted this approach in recent years. The current study took advantage of large immune system cells called macrophages that increase in number in the tumour after standard chemotherapy and radiation treatment.
The scientists treated mice that had prostate cancer with chemotherapy, and then used these immune system cells to deliver a virus to the remaining tumour. This virus then multiplied and attacked the tumour cells. Compared to mice who received the chemotherapy only, those who received the additional treatment lived longer and did not experience any spreading of the tumour beyond the prostate.
This research provides early evidence that using the immune system’s existing cells may offer a mechanism by which to deliver novel cancer treatments. This research is still in its early stages, and trials in people will be needed to ensure that the approach is safe and effective for treating human prostate cancer.
Where did the story come from?
The study was carried out by researchers from the University of Sheffield Medical School and Uppsala University, and was funded by the Prostate Cancer Charity and Yorkshire Cancer Research. The study was published in the peer-reviewed journal Cancer Research.
The research was covered well by the BBC. The broadcaster not only emphasised that the research was conducted in mice in the body of its story, but in the headline as well. Throughout the story, it also outlined the limitations of the research, mentioning that this is still early in the process and will require further trials in humans, and that promising results in animal studies have been known to have no effect in people.
What kind of research was this?
This was an animal study that assessed the effectiveness of a virus (called an oncolytic virus, or OV) that specifically targets, infects and destroys cancer cells at treating prostate cancer in mice. The researchers used a type of immune cell called a macrophage to hide the virus and deliver it to the tumour. These cells are necessary to hide the virus from other cells in the immune system that would normally seek out and destroy any viruses in the body.
Macrophages are drawn to tumour sites after chemotherapy and radiation treatment, and the researchers were interested in exploiting this natural process to deliver further cancer therapies. They thought that by doing so the effectiveness of treatment would be improved and that the tumours would not regrow or spread.
Animal studies are often used in the early stages of new treatment research. Results of animal studies should be interpreted cautiously as they may not hold when the treatment is used in human clinical trials. They are, however, an important step in the development of new treatments, and provide necessary proof-of-concept evidence to support future studies in people.
What did the research involve?
The researchers conducted two main sets of experiments. In the first, two groups of mice were treated with chemotherapy. Two days after the treatment ended, the researchers injected one group of mice with the macrophages housing the tumour-attacking virus and provided no further treatment to the other group (which acted as a chemotherapy-alone control group).
The researchers used a similar approach with radiation therapy, with all mice receiving radiation treatment and, two days after the end of treatment, injecting one group with the macrophage-virus combination, and discontinuing treatment in the radiation-only control group.
The researchers then monitored tumour regrowth, spread and mouse survival for 42 days, and compared these outcomes between the two groups of mice.
What were the basic results?
The researchers found that, compared to chemotherapy alone, mice treated with the macrophage delivered virus prevented tumour regrowth for 35 days. The tumours in these mice also did not spread (metastasise) to the lungs, although some of the virus was detected in the lung tissue.
When compared to radiation alone, mice treated with the macrophage-virus therapy had a significantly longer period of time without any tumour regrowth, with none evident at the end of the experiment (day 42). The macrophage-virus treated group also had better survival rates, and had significantly fewer metastases in the lungs, although some of the virus was detected in the lung tissue.
How did the researchers interpret the results?
The researchers concluded that it is possible to take advantage of the increase in macrophages after chemo and radiation therapy to deliver a cancer-fighting virus directly to the tumour. They say that this treatment kept the tumour from regrowing and spreading.
Conclusion
This is exciting, but early stage, research into a possible new cancer treatment.
Researchers have been investigating novel methods to get therapies directly into tumorous cells for a number of years, as such targeted approaches may offer better outcomes compared to systemic approaches alone. Getting the therapy into the tumours has proven difficult however, and the potential of using the body’s immune system to accomplish this is quite intriguing.
Given the preliminary nature of this study, however, it may be quite some time before we know whether such approaches are safe and effective for treating human disease. The researchers say that further research is needed to see if this combined treatment “approach will be equally effective in prostate cancer patients”. According to the BBC coverage, such trials may get under way as early as next year.
For now this is an interesting approach to treating prostate tumours, but we will have to wait and see whether the promise of this early stage animal study bears promise for the treatment of advanced prostate cancer in people.
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