Scientists could soon start testing cancer drugs on pet dogs, giving them access to treatments not ordinarily available to our four-legged friends, while simultaneously providing us with data on therapies that might be beneficial to us.
“We have a lot of dogs in the United States, approximately 70 million of them, and it’s believed that about 25 percent of pet dogs will develop some form of cancer in their lifetime,” explains Professor Timothy Fan, from the University of Illinois. “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.”
The idea was backed by fifteen other experts in the field at a meeting sponsored by the National Cancer Policy Forum of the National Academies’ Institute of Medicine in Washington, D.C. They argue that using pet dogs to trial new medicines has many advantages over using mice and rats in the lab as is normally done these days. Advantages which also extend to the dogs in question.
For a start, pet dogs naturally develop cancer as they age, meaning that no two cancers are the same, just like in people, says Fan. They also develop at a similar speed and grow to a similar size as they do in humans. This has advantages over using mice since cancer studies in these animals often involves inducing tumor formation, meaning development is virtually identical. This means that while it allows researchers to work out exactly how a drug functions, it often means that it doesn't translate into human studies particularly well.
“We've relied almost exclusively on murine [mouse] preclinical models, and we've been able to show that investigational agents are very good at fighting cancer in these models,” says Fan. “But only about one in ten of the agents that show great activity in mice will show similar activity in humans. So the question that we begin to ask is: why is the hit rate so low?”
Some cancer drug studies have already been performed on dogs and have started to show promise. One such trial, looking at the effects of an anti-cancer drug called PAC-1 on lymphomas and osteosarcomas, was so successful on the dogs that it has moved into a Phase 1 human clinical trial.
“Another example in which dogs have been important in demonstrating drug activity was [with another] anti-cancer compound,” Fan said, “[a] pro-drug, which must be activated by a naturally occurring enzyme in human leukocytes before it can become effective. Mice and rats lack this enzyme, but dogs have it, so the compound was tested in dogs.”
But not all canine cancers will be of use. Differences in diet, for example, mean that dogs don’t often get colon cancer, so there is limited opportunity for study here. It’s also likely that rats and mice will still be favored most of the time as they’re cheaper to raise, have shorter lifespans, and can be genetically manipulated.