Because so many of the patients in the early testing showed significant long-lasting responses, the study was continued and the FDA granted the drug “breakthrough therapy” status, allowing it to be fast-tracked for approval. The largest Phase 1 study in the history of oncology, the research was conducted at UCLA and 11 other sites in the U.S., Europe and Australia.
Keytruda, formerly known as MK-3475, is an antibody that targets a protein called PD-1 that is expressed by immune cells. The protein puts the immune system’s brakes on, keeping its T cells from recognizing and attacking cancer cells, said Dr. Antoni Ribas, the study’s principal investigator and a professor of medicine in the division of hematology–oncology at the David Geffen School of Medicine at UCLA.
For many years, when using immunotherapy to fight cancer, doctors’ strategy has been to bolster the immune system so it could kill the cancer cells. But the approach had limited success because PD-1 prevented the immune system from becoming active enough to attack the cancer.
Keytruda, in effect, cuts the brake lines, freeing up the immune system to attack the cancer.
“This drug is a game changer, a very significant advance in the treatment of melanoma,” said Ribas, who also is a researcher at UCLA’s Jonsson Comprehensive Cancer Center. “For patients who have not responded to prior therapies, this drug now provides a very real chance to shrink their tumors and the hope of a lasting response to treatment.”
Judith Gasson, senior associate dean for research at the David Geffen School of Medicine at UCLA and director of the Jonsson Cancer Center, said researchers have long hoped to develop an effective and lasting immunotherapy to fight cancer.
“We have long believed that harnessing the power of our own immune systems would dramatically alter cancer treatment,” she said. “Based upon work conducted over the past two decades, we are beginning to see the clinical benefits of this research in some of the most challenging cancers.”
Generally, about 1 in 10 patients responded to previous immunotherapy drugs. Some of those who responded, however, exhibited long-lived benefits, which sustained scientists’ interest in the method as an effective mechanism to fight cancer.
The response and duration rates for Keytruda were much greater than for previous drugs, Ribas said. In the new study, 72 percent of patients responded to the drug, meaning that their tumors shrank to some degree. Overall, 34 percent of patients showed an objective response, meaning that their tumors shrank by more than 30 percent, and did not re-grow.
Ribas said Keytruda has the potential to be used to treat other cancers that the immune system can recognize, including cancers of the lung, bladder, head and neck.
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