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Safety and Cost Concerns Cloud Early Promise of New Cancer Drugs
A new wave of experimental cancer drugs that directly recruit the immune system's powerful T cells are proving to be highly effective weapons against tumors, but top oncology researchers are concerned about the two emerging technologies, citing dangers seen repeatedly in clinical trials, including the potentially fatal buildup of toxic debris from killed tumor cells and damage to healthy tissues, according to a new report from Reuters. Such adverse effects could block regulatory approval if they aren’t controlled, researchers and drug company executives told Reuters reporters.
In some trials, the two new approaches –– chimeric antigen receptor (CAR) T cells and bispecific antibodies –– have eliminated blood cancers in 40% to 90% of patients who had no remaining options.
CAR T cells are T cells that have been removed from the body and attached through genetic engineering to an antibody fragment that recognizes a specific tumor protein. The result is a drug with the killing power of a greatly enhanced T cell, combined with the tumor-spotting ability of an antibody.
Bispecific antibodies are a twist on conventional antibodies, Y-shaped proteins whose two arms grasp for the same protein target found on cancer cells. With bispecifics, one arm of the antibody typically grasps a cancer cell while the other arm takes hold of T cells, bringing the mortal enemies into contact. The T cell punches holes into the adjacent tumor cell and injects deadly enzymes. Conventional antibodies, by contrast, don’t directly recruit T cells.
If approved, CAR T cells could cost $300,000 to $500,000 per patient, making them among the world’s most expensive drugs and testing the ability of insurers to pay for them, said Les Funtleyder of the hedge fund E Squared Asset Management. Bispecific antibodies could command prices of $200,000 or more, he said.
In addition, the potency of the experimental drugs comes with some dangerous potential adverse effects, Reuters says.
Most CAR T cells and bispecific antibodies currently in development identify blood cancer cells by a specific protein, CD19, found on the surfaces of lymphomas and leukemias. But since the same protein can also be found on non-cancerous cells, the drugs can go off track and attack healthy tissues.
“Our biggest concern would be an off-target toxicity that wasn’t expected, and we didn’t know the cause of it,” said Dr. George Bindu, team leader of the FDA’s Office of Cellular, Tissue, and Gene Therapies. In that case, “we might have to ask [the drug-maker] for additional information, how the toxicity happened, what organ it was, and literally go back to the drawing board.”
At least 30 bispecific antibodies are believed to be in development, including ones from Roche, Johnson & Johnson, AbbVie, and Eli Lilly. A growing number of drug-makers, including Kite, Novartis, Juno, Cellectis/Pfizer, and Bluebird/Celgene, are also racing to develop the first CAR T therapies.
In December 2014, the FDA approved the first bispecific treatment, Amgen’s $178,000 Blincyto for patients with acute lymphoblastic leukemia (ALL) that did not respond to previous treatment. The cancer, prevalent in children, is diagnosed each year in an estimated 6,020 Americans, killing about 25% of them. A main hope for Blincyto is that it will keep patients alive until they can receive stem cell transplants, their best chance of a possible cure.
Roche’s Genentech unit is conducting a mid-stage trial of a bispecific antibody to treat head-and-neck cancer and colorectal cancer. The company is also studying a dozen others in preclinical trials against cancer, Alzheimer’s disease, and inflammatory diseases.
CAR technology may also come to the rescue where few options remain. In a Novartis-sponsored trial, 90% (27/30) of children and adults with ALL had no signs of the disease after being treated with the company’s CAR T drug. About 78% of the patients were still alive 6 months after treatment, while some sustained remission for up to 2 years.
Source: Reuters; January 26, 2015.