New Drug Clears Cancer Cells Through Immune System Judo

For years, scientists have been probing various immune response proteins in the hopes of finding a new way to target and destroy cancer cells. Yesterday, two months ahead of schedule, the FDA approved a drug that does just that, targeting the protein “programmed cell death 1,” or PD-1. While not the first drug to use the immune system to fight cancer, it may be the most promising to date.

Pembrolizumab is currently approved for advanced melanoma patients who have no other treatment options left. In clinical trials, tumors shrank in 24% of patients, and in one particular trial, 69% of patients were alive after one year of pembrolizumab treatment, a number that shocked the doctors in charge.

melanoma-cell
A three-dimensional illustration of a melanoma cell

Pembrolizumab works by suppressing the expression of PD-1. In a healthy cell, PD-1 is active and present on the surface of a cell. But when a cell is nearing the end of it’s life, PD-1 expression tapers off. Immune cells recognize this signal and come in to clear away the dead or dying cell. Researchers have discovered that, in many tumors, PD-1 continues to be expressed. By preventing PD-1 from appearing on the surface of a cell, they predicted that cancer cells would be eliminated by the body’s own defenses.

Doctors are hopeful that therapies which target PD-1 will give patients new options with fewer side effects than traditional chemotherapy. Andrew Pollack, reporting for the New York Times:

“This is really opening up a whole new avenue of effective therapies previously not available,” said Dr. Louis M. Weiner, director of the Georgetown Lombardi Comprehensive Cancer Center in Washington and a spokesman for the American Association for Cancer Research. “It allows us to see a time when we can treat many dreaded cancers without resorting to cytotoxic chemotherapy.”

Pembrolizumab is being marketed as Keytruda by Merck, the drug’s developer. Priced at $12,500 per month or $150,000 per year, the drug is apparently more expensive than other cancer drugs. Pollack reports that some cancer doctors have expressed concern that the high price tag will be too dear for some patients.

Pembrolizumab is an antibody that specifically targets PD-1, so side effects tend to be less severe than with more general chemotherapy. Patients still run the risk of a potentially harmful inflammatory response—a sign of a runaway immune system, though most tolerated the drug well.

For now, pembrolizumab is limited to patients with advanced melanoma that doesn’t respond to other treatments, but Merck has seen promising results with lung and kidney cancers. Other pharmaceutical companies are racing to get their PD-1 drugs approved, too. As more drugs come on the market, and new ones are calibrated for different cancers, the next few years could be the beginning of a new era in clinical cancer treatments.