Gene therapy may offer birth control for cats

By | June 6, 2023

For all the cats who share our homes as pets, there is a vast dark world of strays, a sprawling, rapidly reproducing mob.

Their lives are plagued by the threat of infectious disease, predators, and fast-moving machines. And they are themselves the main predators, preying on millions of birds and small mammals every year.

In the United States, volunteers are especially active in capturing cats, taking them to clinics to be surgically neutered, and then returning them to their colonies. But controlling stray cat populations is expensive and logistically cumbersome. Many communities, especially in countries outside the United States and Europe, lack the veterinary and economic resources to coordinate such efforts.

Finding an alternative to surgery has been a goal for many people for decades, and there has simply been nothing else that has proven effective, said William Swanson, director of animal research at the New York Zoo and Botanical Garden. Cincinnati.

Such a method may finally be on the horizon. In a study published Tuesday in the journal Nature Communications, a single shot of a gene therapy prevented pregnancy in cats for at least two years. The study was extremely small: Six female cats who received the gene therapy shot were compared with three who didn’t.

By limiting the study size to a few cats, the researchers were able to extensively track each of them, analyzing 15,220 freeze-dried poop samples for estrogen and progesterone levels and examining 1,200 hours of video of mating behavior, said Dr. Swanson.

The contraceptive injection releases a gene that enters muscle cells, enabling them to pump out a substance called anti-Mllerian hormone, or AMH, which interferes with the development of ovarian follicles in the ovaries.

The researchers warned that much more research would be needed to test the preliminary findings. And if larger studies confirm that the first gene therapy treatment developed specifically for animals is safe and effective throughout the life of the cat, controlling cat populations won’t require the surgical expertise of veterinarians, Dr. Swanson said.

David Ppin, a reproductive biologist at Massachusetts General Hospital in Boston, was initially studying AMH as a potential therapy for ovarian cancer, but decided to look into its effects on the ovaries. When he injected mice with the hormone, their ovaries shrank to the size of newborns, suggesting that AMH may have contraceptive properties.

Dr. Ppin is studying the potential use of AMH in people, not as a gene therapy but as a pill or injection that must be taken continuously. Most contraceptives today prevent ovulation, but AMH would act earlier, blocking the maturation of the follicles.

She thinks it could be useful for women who can’t take birth control pills with progesterone or estrogen for medical reasons, or that it could help women undergoing cancer treatment preserve their fertility. It’s a hormone that we haven’t gotten to play with before that potentially has many different applications in women’s health, she said.

As a gene therapy that could be permanent, use of AMH in people is unlikely. But it’s actually the perfect tool for controlling cat overpopulation, he said. Four of the cats in the study exhibited no behavior that indicated they were ready to mate, and two allowed male cats to mate with them, but did not ovulate.

Dr. Ppin and Dr. Swanson, a feline reproduction expert (and scientific advisory board member of the Michelson Found Animals Foundation, which funded the work), are planning a larger study that could support an application to the Food and Drug Administration for consider approving therapy to be marketed for use in cats.

They are also testing the therapy in kittens, which can be treated from eight weeks of age, as well as dogs, which also have huge stray populations, particularly in other countries.

This is really exciting and I hope it pans out, said Julie Levy, a veterinarian at the University of Florida College of Veterinary Medicine in Gainesville, who was not involved in the study. Wouldn’t it be great if we could send a field technician to inject cats and then let them go?

The study is an example of the Michelson Foundations’ practice of throwing big money at the problem of finding nonsurgical contraception for stray dogs and cats, said Dr. Levy, who works with cats in outdoor colonies and shelters, both in US and abroad.

But he cautioned that there was still a lot to learn from a larger study, such as how long the injection lasts, whether it’s as safe as it appears and what percentage of cats it will actually protect against pregnancy, because it probably won’t be 100 percent.

Others note that it may not be that easy. If the injection is effective, long-lasting, and inexpensive compared to spaying and neutering, it could be very valuable, said Autumn Davidson, a veterinarian at Cornells College of Veterinary Medicine in Ithaca, New York. But to receive the injection, the animals must be captured, and queens who are adept at evading people’s traps could still make population control a struggle.

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