Dogs, cats may show way to better treatments for human cancers

Cujo romps around the room, seemingly unaware he is missing a front leg, before snuggling in for a caress and reaching up to bestow a canine kiss on his owner Valeria Martinez.

GUELPH, Ont. — Cujo romps around the room, seemingly unaware he is missing a front leg, before snuggling in for a caress and reaching up to bestow a canine kiss on his owner Valeria Martinez.

Being a dog, the nine-year-old Rottweiler is also unaware he is part of a series of cutting-edge studies that researchers at the Ontario Veterinary College in Guelph, Ont., hope might one day help humans with the same kind of cancer that led to his amputation.

“Good boy. Good boy, baby,” Martinez coos as Cujo rolls on his back, then rights himself to continue his three-legged perambulation around the visitors’ room at the OVC’s Mona Campbell Centre for Animal Cancer.

It was here that the canine had his right front leg surgically removed in December after a painful lump in the limb was diagnosed as osteosarcoma, the same type of bone cancer that affected Terry Fox and ended his Marathon of Hope when the malignancy recurred in his lungs. The 22-year-old died in June 1981.

Osteosarcoma in dogs is almost identical to the disease that occurs in teens and young adults, with a similar progression. But canines are 10 times more likely to develop the cancer than humans.

“Just like in people, osteosarcoma in dogs is a highly metastatic disease, meaning it comes back,” says Dr. Paul Woods, a veterinary medical oncologist at the OVC, which is part of the University of Guelph.

In dogs, osteosarcoma occurs most often in large breeds like mastiffs, greyhounds and wolfhounds, although smaller dogs can develop the disease. Standard treatment includes amputating the affected limb, then treating the pet with chemotherapy.

“We do chemotherapy similar to chemotherapy they use in people, and the idea is we’re trying to delay or prevent recurrence of this metastatic disease,” Woods explains.

He concedes, however, that the regimen typically only extends the animal’s life, with most eventually succumbing to the cancer.

But as part of a multicentre trial headed by the U.S. National Institutes of Health, Guelph researchers are testing a drug called rapamycin, which they hope might stop the bone cancer from recurring.

About 160 dogs will be included in the eight- to 12-month study being conducted by the NIH’s Comparative Oncology Trials Consortium at about 20 U.S. sites along with Guelph, with funding from the Morris Animal Foundation, an international non-profit organization that supports veterinary research.

All the animals will get standard care for their cancer, then half will be randomized to receive rapamycin. The drug is used to prevent organ rejection in transplant patients but is being repurposed as a potential anti-cancer medication.

One of those getting the drug is Cujo.

When Martinez first brought her pet to the centre from her home in Barrie, Ont., she was “looking for a miracle” but worried how Cujo would fare with a missing limb.

Three weeks after the operation, Cujo “started to live normally,” she says. While he can no longer manage the daily three-kilometre walks the pair took before he lost his leg, he can run and play in the backyard, “no problem.”

Following the operation, Cujo underwent four rounds of chemotherapy, which Martinez says didn’t seem to bother him beyond being tired the first day of treatment.

The pet is now being monitored to see if his cancer is being held at bay.

“What we’re wondering is will that delay or at best stop the metastatic disease from coming back,” says Woods. “Hopefully it will help dogs, but it may also translate to helping people as well.”

That’s also the goal of another OVC osteosarcoma research project, this one in the lab of viral immunologist Byram Bridle.

With a $450,000 grant from the Terry Fox Foundation, Bridle is laying the groundwork for a three-year study that will test two novel virus-based therapies in dogs with the bone cancer.

One uses a non-disease-causing “oncolytic” virus that has been engineered to target and destroy osteosarcoma cells without harming surrounding healthy cells. The second is a virus-based vaccine that boosts and harnesses the power of the immune system in a bid to wipe out the cancer cells — delivering a one-two punch against the tumour.

“So the concept here is the oncolytic virus will get in and quickly replicate and destroy a lot of the cancer cells, debulking the tumour, and then this overwhelming immune response will come in as a second wave and hopefully kill the remaining cancer cells,” says Bridle, who as a child was inspired by Fox and chose the study of cancer as a career path.

“What kills these animals is when some of the (cancer) cells migrate to other parts of the body,” he says. But because the experimental viruses distribute throughout the body, “we don’t need to know where these tumour cells are — the viruses can seek them out and find them.”

Researchers are in the process of producing clinical batches of the therapies for the trial, which is expected to enrol at least 45 dogs and last about two years once regulatory approval is granted.

“If we can show that the experimental therapy is better … it will allow us to design an optimal therapy to test in human patients,” says Bridle, who is working with collaborators at McMaster University and the Ottawa Hospital Research Institute.

A trial using a similar approach is already underway for cats with the feline version of breast cancer, and researchers hope the results may point to a new way to treat some forms of the disease in humans.

The study is funded by the Canadian Breast Cancer Foundation, the first time the charitable organization has invested in research involving companion animals, says Bridle, who is working on the project with Woods and Brian Lichty of McMaster.

So far, 12 cats have been treated with immunotherapy designed to target feline mammary carcinoma, which typically occurs in older animals that have not been spayed.

Among them is Tabby, a stray adopted 13 years ago by Millie Daley of Hamilton, who also has one of her kittens.

When her local vet discovered Tabby had mammary cancer, Daley turned to the OVC, which agreed to take her pet into the immunotherapy trial.

Over a period of weeks, the cat received one of the vaccines, the tumour was surgically removed and then the second vaccine was administered.

“She had no reaction to either of the vaccines, she just sailed through them,” says Daley, who has brought Tabby in for a followup appointment. “She runs around the house, she has more energy now than she had before all this started.

“It’s a triple win all the way around. She’s getting excellent care and I win because I’m not going bankrupt … and down the road it may even help me or other humans to deal with breast cancer in another way that’s less invasive and may (have) a better result.”

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