Drug Trials in Dogs With Cancer May Guide New Therapies

Size and speed of tumor growth similar in dogs and humans.

Man’s best friend may soon prove to be even more beneficial to humans than just for companionship.

Experts at a meeting sponsored by the National Cancer Policy Forum discussed the benefits of treating pet dogs with naturally occurring tumors in early cancer drug trials instead of treating mice with laboratory induced tumors. The researchers noted that physiological similarities in dogs and humans, in addition to conserved genetics among some canine and human cancers, can allow pet dogs to function as useful models in studying new cancer drugs.

"We have a lot of dogs in the United States, approximately 70 million of them, and it's believed that about 25% of pet dogs will develop some form of cancer in their lifetime," said University of Illinois veterinary clinical medicine professor Timothy Fan in a press release. "We're using dogs to help guide drug development for people, but at the same time we're offering new, innovative therapies that would otherwise never be available to dogs, to help them as well."

Fan added that dogs typically develop cancer as a geriatric population similarly to humans, as tumors develop spontaneously and there is heterogeneity in the tumor population. Additionally, tumor size and growth speed are comparable in dogs and humans.

Prior studies have already begun using dogs to test new cancer therapies, including the anti-cancer drug PAC-1 in pet dogs with naturally occurring lymphomas and osteosarcomas, which contributed to the advancement of PAC-1 as a potential treatment for human cancers. The drug is currently in phase 1 human clinical trials.

Furthermore, other investigational drugs historically piloted in pet dogs with cancer include immune-stimulating agent muramyl tripeptide, which could not be tested in immune-deficient mice or rats with induced cancers.

"Because you're taking a human cancer tissue and implanting it in a mouse, that's a foreign tissue, and the mouse's immune system will reject it," Fan said. "So you have to transplant those tissues into an immunocompromised mouse. Dogs are immunocompetent, and so were an ideal study subject for testing immunomodulatory cancer therapies.”

Regardless, rodents do offer significant advantages in preclinical trials because they are cheaper to rear, have shorter lifespans, and can be genetically manipulated of for specific and uniform traits, which allows researchers to identify how a drug agent is working without dealing with confounding factors.

"But are human beings genetically identical? Absolutely not," Fan said. "There is heterogeneity in the human population and in dogs. So I would argue that if your drug agent produces positive results in dogs, that would give me greater confidence that those findings would be translatable to people."