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Here kitty, kitty! A feline parasite could be an effective cancer treatment

You'll never look at your cat's litter box the same way again.

By Cassidy Ward
Cassidy Cat Getty

Cats might hold the keys to treating some stubborn tumors, and it’s in the form of a common parasite — one with which you might already be infected. New research involving novel treatment of tumors utilizing injected genetically modified parasites has shown reduction in size and increased response to other more-common therapies. The results of this study were published in the Journal for ImmunoTherapy of Cancer.

Toxoplasma gondii is a common protozoan parasite which infects all manner of warm-blooded animals including mammals and birds. Humans can acquire infection through undercooked meat or through exposure to infected cats — mostly commonly when cleaning litter boxes. Gross, we know, but what are you going to do?

Previous studies have shown that the parasite might assist cats in the hunting of rodents. Infection with the parasite causes mice to lose their fear of cats, a potentially fatal behavioral change if we’ve ever heard of one. In fact, mice are usually averse to the scent of cats — that scent usually preceding a swift and violent death — but those infected with toxoplasma gondii are slightly attracted to the scent, making them easy targets for prowling feline predators.

While cats have weaponized this parasite to attack mice, researchers are doing the same thing on a cellular level, using a genetically modified version of the parasite to attack “cold” tumors. The parasite was modified to reduce its ability to cause disease while retaining its ability to impact immune response.

A tumor is considered cold when it shows no signs of inflammation. This is an indication that for one reason or another, the tumor is not eliciting an immune response and is likewise not responsive to immunotherapies. Conversely, hot tumors are so called because they do elicit a response and are being invaded by T cells which are fighting back. This makes hot tumors more easily treatable with some therapies.

This study does not represent the first time pathogens have been tested as potential therapies for fighting cancers. Bacteria, viruses, and parasites have all been researched to determine their potential to disrupt tumor development, but there are challenges. Prior infections and existing or resulting immune responses can minimize the body’s ability to make use of these weaponized microbes, so the need to continue studying additional pathogens remains.

Toxoplasma gondii parasite

Toxoplasma gondii is estimated to have infected a large portion of the human population. Estimates have a wide range but it’s estimated that 11% of the U.S. population over the age of 6 have been infected. Some global regions, mostly those with hot and humid climates, have higher infection rates upward of 60%. Most infected individuals never experience any symptoms and those who do usually recover quickly.

The parasite is capable of infiltrating most cell types, making it a good candidate for tumor treatment study. Researchers injected the modified parasite into cold tumors of mice and measured the impact. Once inside the tissues, the protozoa secreted proteins which instigated an immune response in the body. In essence, they were able to flip a switch in the body, turning the tumor from cold to hot.

In the tested mice, the injection of toxoplasma gondii affected the tumor directly, causing decreased growth but also improved immune response, making the tumors more receptive to existing immunotherapies.

These treatments significantly improved survival rates in mice in various tumor types, including melanoma, Lewis lung carcinoma, and colon adenocarcinoma. Moreover, the benefits were seen not only in the injected tumors but also in distant tumors elsewhere in the body.

Importantly, unlike some other pathogens which have been studied for this type of treatment, preexisting infection with the parasite does not appear to inhibit its effectiveness. Instead, injection of the parasite kickstarted innate immune responses and made the tumors more receptive to immunotherapies. Using the toxoplasma gondii in partnership with existing therapies showed a marked improvement in tumor growth attenuation and survival rates.

Improvements in genetic research and technologies are allowing us to better understand the mechanics of biological processes in order to aim them like missiles at diseases. This study represents just one example of that research.

It’s true that success in mice does not always equate to success in humans, but the response elicited by this common parasite opens up new avenues of research for potential future cancer treatments.

Cats may pretend not to like us, but when push comes to shove, they’ve got our backs, even if in the form of their disgusting parasites.