How a nasty, brain-eating parasite could help us fight cancer

August 26, 2016 by Hany Elsheikha, The Conversation
Meet Toxoplasma gondii. Credit: Ke Hu and John M. Murray/wikimedia, CC BY-SA

We've known since the turn of the 20th century that some infectious diseases are a major risk for developing specific cancers. More worryingly, about one-sixth of cancers worldwide are attributable to infectious agents. Globally, more than 2m cancer cases are linked to certain carcinogenic viral, bacterial or parasitic agents. Two-thirds of these occur in developing countries.

Although we've been aware of the connection between parasites and since before the 18th century, we're increasingly linking certain parasites to an increased risk of developing specific forms of cancer. For example, the fish-borne parasitic worms Opisthorchis viverrini and Clonorchis sinensis have been linked to increased risk of developing cancer of the bile duct (the tube that connects the liver to the intestines). Also, infection with the parasitic worm Schistosoma haematobium can cause bladder cancer. Worldwide, these three parasitic infections accounted for 8,300 new cancer cases in 2012.

Infections can lead to cancer by directly manipulating the genes that control growth of the affected – causing the cell to grow out of control. They can also cause cancer through long-term inflammation that leads to changes in the affected cells and in nearby immune cells or by suppressing a person's immune system that normally helps protect the body from some cancers. But we also know that the body's own immune defences can be used to fight tumour cells. And now a new study suggests that a brain-eating parasite that has been incriminated in cases of brain cancer can be reprogrammed to treat .

The team of investigators behind the new study set out to harness the immune system's reaction to the presence of the parasite Toxoplasma gondii (T. gondii), which can be found in cat faeces, as a tool to cure ovarian cancer. Specifically, they identified specific proteins secreted by T. gondii that enable the immune system to attack established ovarian tumours in mice. This involved uncovering parasite specific proteins and associated host mechanisms that are important for the development of potent antitumor responses. The researchers deleted genes for proteins that the parasite injects into a host cell to modulate cell functions and immune response during infection. They also used the genetically altered parasites to vaccinate mice with aggressive ovarian cancer.

Toxoplasma gondii tissue cyst in mouse brain. Credit: Jitinder P. Dubey

The results showed that active parasite invasion along with specific proteins secreted before and after penetration of mouse cells elicited an antitumour response and increased survival by at least 40 days (mice only live a couple of years) compared to non-vaccinated mice. While surviving a longer period with cancer can be considered as an improvement, these results should be handled carefully because vaccinated mice didn't get rid of the cancer completely and we do not know how this treatment could affect tumour regression in humans.

Terrifying bug

In the field of parasitology no single parasite is as popular as T. gondii. This single-cell parasite, which affects one third of the world's human population, is best known for its ability to invade and damage the brain and alter the behaviour of affected individuals. Long before the Zika virus became a serious concern for expectant mothers, infection with T. gondii was terrifying not only to pregnant women, but also to individuals with seriously compromised immune systems, such as HIV/AIDS patients or patients on cancer therapies. This parasite can be passed along from mothers to the fetus, putting the developing babies at risk of severe neurological and vision disorders. It is very intriguing that what used to be a disturbing infection could potentially now be the remedy for an even more terrifying disease.

The idea of turning , elicited by parasitic infection, against illnesses is not new. Some worms have been shown to lessen susceptibility to type 1 diabetes and other autoimmune and inflammatory diseases, as well as to promote wound healing. However, the potential of exploiting the immune responses associated with T. gondii to help the immune system recognise and attack ovarian cancer, which is difficult to treat, is definitely out-of-the-box thinking and deserves to be commended. The same group of investigators has previously shown that the use of attenuated T. gondii can generate longlasting immunity that protects against the recurrence of disseminated pancreatic cancer. But it is early days and much more work needs to be done to determine if a similar mechanism happens in humans.

As more is learned about the dynamic cross-talks between this parasite, cells and tumours it may be possible that T. gondii or some of its proteins can one day become a real remedy that can be used to cure ovarian cancer and hopefully other forms of cancer, too.

Explore further: Parasite proteins prompt immune system to fight off ovarian tumors in mice

Related Stories

Parasite proteins prompt immune system to fight off ovarian tumors in mice

July 22, 2016
Scientists identified the specific proteins secreted by the parasite Toxoplasma gondii that cause the immune system in mice to attack established ovarian tumors. The study, led by David Bzik of the Geisel School of Medicine ...

New study brings long-sought vaccines for deadly parasite closer to reality

December 13, 2012
One major cause of illness from food-borne diseases is the parasite Toxoplasma gondii (T. gondii). New insights into how the immune system combats T. gondii are provided in a study published by Cell Press December 13th in ...

Toxoplasma gondii can stop cancer in its tracks as a vaccine

July 18, 2014
Toxoplasma gondii (T. gondii) is a single-celled parasite that is happiest in a cat's intestines, but it can live in any warm blooded animal. Found worldwide, T. gondii affects about one-third of the world's population, 60 ...

Increased risk from toxoplasmosis

February 25, 2015
A third of all humans carry the parasite that causes toxoplasmosis—a disease commonly associated with cats, HIV-AIDS patients and pregnant women—with scientists long believing healthy immune systems control the parasite ...

Cancer-like forms of parasites may lead to new approaches to curing diseases

November 3, 2015
A study in the Proceedings of the National Academy of Sciences shows that some forms of the single celled parasites, Trypanosoma brucei and Toxoplasma gondii behave like cancer cells.

Recommended for you

Research could change how doctors treat leukemia and other cancers fed by fat

February 21, 2018
Obesity and cancer risk have a mysterious relationship, with obesity increasing the risk for 13 types of cancer. For some cancers—including pediatric cancers—obesity affects survival rates, which are lower for people ...

Similarities found in cancer initiation in kidney, liver, stomach, pancreas

February 21, 2018
Recent research at Washington University School of Medicine in St. Louis demonstrated that mature cells in the stomach sometimes revert back to behaving like rapidly dividing stem cells. Now, the researchers have found that ...

Genes activated in metastasis also drive the first stages of tumour growth

February 21, 2018
In spite of the difference between the cell functions responsible for giving rise to a tumour and that give rise to metastasis, studies at IRB Barcelona using the fly Drosophila melanogaster reveal that some genes can drive ...

Researchers discover novel mechanism linking changes in mitochondria to cancer cell death

February 20, 2018
To stop the spread of cancer, cancer cells must die. Unfortunately, many types of cancer cells seem to use innate mechanisms that block cancer cell death, therefore allowing the cancer to metastasize. While seeking to further ...

Stem cell vaccine immunizes lab mice against multiple cancers

February 15, 2018
Stanford University researchers report that injecting mice with inactivated induced pluripotent stem cells (iPSCs) launched a strong immune response against breast, lung, and skin cancers. The vaccine also prevented relapses ...

Induced pluripotent stem cells could serve as cancer vaccine, researchers say

February 15, 2018
Induced pluripotent stem cells, or iPS cells, are a keystone of regenerative medicine. Outside the body, they can be coaxed to become many different types of cells and tissues that can help repair damage due to trauma or ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.