Monoclonal antibodies show promise as new therapy for veterinary patients

In 1986, the Food and Drug Administration (FDA) approved the first monoclonal antibody for human medical therapy. Today more than 100 monoclonal antibodies (mAb), which are designed to bind to specific target proteins, are available for humans, including those intended to treat cancer and autoimmune disorders.

The power of mAbs is now being unleashed for debilitating diseases in dogs and cats. mAbs for veterinary patients may be regulated as an animal biologic or a new animal drug, depending on their mechanism of action.

Specifically, the drug’s therapeutic target determines which regulatory agency reviews and approves it. The U.S. Department of Agriculture (USDA) approves mAbs that target the immune system, while the FDA approves mAbs that have other targets.

The USDA Animal and Plant Health Inspection Service’s (APHIS) Center for Veterinary Biologics (CVB) and FDA have a joint committee that coordinates regulatory responsibility.

In 2016, the USDA APHIS CVB granted a license to Zoetis for its monoclonal antibody to treat allergic dermatitis and atopic dermatitis in dogs, Cytopoint. In May 2023, the USDA APHIS CVB also granted a conditional license to Elanco for its Canine Parvovirus Monoclonal Antibody (CPMA).

In January 2022, the FDA granted its first approval for a mAb for animals: Zoetis’s Solensia, to control pain associated with osteoarthritis in cats. More recently, in May, the FDA approved Zoetis’s Librela, an mAb to control osteoarthritis (OA) in dogs, which will be commercially available this fall.

These mAbs are just the beginning, notes Robert Polzer, PhD, executive vice president and president of research and development at Zoetis. Allergies, dermatological conditions, renal diseases, cardiac diseases, and cancer are five key disease categories for research into new mAb therapies, he says.

“We have 50 biological targets for which we are generating monoclonal antibodies,” Dr. Polzer says. “We anticipate more drugs will be rolling out in these areas.”

Catching up to human mAb advances

The 30-year gap between the development of mAbs for humans and those for animals is partly because while some human medications can be easily adopted to use in animals, mAb therapy is species specific.

“We have to do a lot of research to understand what a dog antibody looks like, what a cat antibody looks like,” says Dr. Polzer. “It took several years for that science and technology to mature.”

But now that they are here, the approved mAb therapies are having a significant impact on veterinary care, says Dr. Ken Pawlowski, clinical director of Insight Veterinary Wellness Center in El Dorado, California. He often prescribes Cytopoint to treat seasonal and environmental allergies in dogs.

Cytopoint works by binding to and neutralizing the cytokine interleukin 31, which is a cytokine involved in causing itchiness, and thus inhibits pruritus and reduces skin lesions. Like other naturally occurring antibodies and antibody-antigen complexes, elimination is via normal protein degradation pathways. Dr. Pawlowski said the mAb has provided significant relief to dogs he sees in his practice that are suffering from allergies.

“It works really well for most dogs. If they have serious allergies, they may need something in addition to that or may do better on the oral medications,” he said.

Recently, he began prescribing Solensia for cats with osteoarthritis, which is given as a monthly subcutaneous injection. It is an especially welcome therapy for treating osteoarthritis in cats, he notes, because, until now, few treatments were available for cats with osteoarthritis. NSAIDS such as meloxicam can cause kidney damage, making them unsuitable for long-term use, and oral medications are difficult to administer to cats.

Solensia, however, as with Librela, works in a different way than NSAIDS. It blocks nerve growth factor, a neuropeptide that blocks pain signals and reduces inflammation.

In a randomized, double-blind clinical study, owners of cats treated with Solensia reported a significant improvement in their cats’ activity levels compared with cats given a placebo. Reported side effects were mild with dermatitis, alopecia, and diarrhea as the most common ones.

Dr. Michelle Meyer, a veterinarian at Serenity Animal hospital in Sterling Heights, Michigan, has also had good results with Solensia.

“It is an immense help,” says Dr. Meyer. “Does it help every patient? No. But the amount of good that I have seen come from this—the number of phone calls from clients with praise, that it has turned back the clock and their cat is playing again—it is amazing.”

Side effects have been minimal, she adds, including vomiting and itching at the injection site. The cost is reasonable, she adds, noting that the drugs costs about $75 for treating a cat under 15.4lb and $115 for treating a cat over 15.4 lb although costs may vary from clinic to clinic.

While Librela, Zoetis’s mAb osteoarthritis treatment for dogs, is just being rolled out this fall in the U.S., it was approved in 2020 in the European Union. Data on its usage in Europe has shown that, among veterinarians who have used it to treat osteoarthritis in dogs, they rated it an 8.6 out of 10 for effectiveness at treating OA pain.

First treatment to stop CPV replication

When it comes to treating canine parvovirus (CPV), a disease that afflicts about 330,000 dogs in the U.S annually, Elanco’s CPMA therapy, which began shipping to veterinary clinics in July, is a breakthrough, veterinarians say. It is the first therapy to treat parvovirus that targets the virus itself, instead of treating the resulting clinical signs, notes Dr. Jennifer Miller, a veterinarian with Elanco. The mAb, given in a single intravenous dose, works by blocking the virus from entering the gastrointestinal tract, thus preventing it from replicating in host cells and damaging the intestines.

Without treatment, up to 91% of puppies who contract CPV die. Even with treatment, mortality can approach 50%, depending on the severity of the disease and the type of supportive care, points out Dr. Miller.

In a clinical study of CPMA efficacy—presented as an abstract at the 2023 American College of Veterinary Internal Medicine Forum—none of the 21 dogs who received a dose of CPMA died from CPV, and their symptoms were less severe and resolved more quickly than the control group of dogs.

When CPMA became commercially available this summer, the first dog treated was Cookie, an 8-week-old pit bull mix puppy brought to the Fix Project animal clinic in Long Beach, California. The 4 1/2 lb pup, who had not been vaccinated, tested positive for CPV.

Within 48 hours of receiving CPMA, Cookie “was eating, doing very well with normal puppy behavior,” says Dr. Miller. “She did overall very well and was able be reunited with her family. The Fix Project has continued to use CPMA in their treatment protocol. And overall, they are seeing that the puppies are not needing to stay in the hospital as long as without CPMA, and it’s been awesome to see that in action.”

At Colorado State University's (CSU) Veterinary Teaching Hospital, 18 dogs with CPV have received CPMA, says Dr. Kristin Zersen, assistant professor of emergency and critical care at CSU’s College of Veterinary Medicine & Biomedical Sciences. CPMA is given in addition to supportive care, such as IV fluids and anti-nausea medication.

“It’s a little too soon to tell overall benefits, but there have been no concerns or side effects that I’ve noticed. It’s very well tolerated and easy to implement,” she says.

The cost of treatment will vary from clinic to clinic, but it is cheaper than an extended hospitals stay, she says.

Impact just beginning

Already, the handful of mAbs approved for treatment in animals is dramatically helping dogs and cats suffering from allergies, osteoarthritis, and CPV. As more mAbs are developed and approved, these therapies hold the promise of improving the ability of veterinarians to treat diseases that they now can treat only with supportive care or by managing the animal’s clinical signs.

“We may be actually able to treat them, stop the progression, and not let some of these diseases ravage our patients the way they have,” says Dr. Pawlowski.

“It’s an exciting field,” Dr. Polzer says. “We’ve seen how this has really taken off in the human health space in the past few decades, and we have just begun to see the positive impact that biological therapies can have in the animal health space. We definitely see a bright future for this.”

A version of this story appears in the January 2024 print issue of JAVMA