Pfizer's abandoned experimental drug torcetrapib failed to slow clogging of heart arteries even as it boosted "good" cholesterol levels, according to a study presented Monday.
The news raised questions about the future of similar drugs being developed by other companies.
Pfizer in December halted development of torcetrapib after a different study showed it raised the risk of death among heart patients taking it, ending the most expensive clinical drug program in history.
Researchers had hoped to demonstrate the drug's ability to slow or halt progression of plaque in coronary arteries, a potential indication of the viability of the entire class of drugs called CETP inhibitors designed to raise HDL levels.
Despite its ability to greatly boost good cholesterol and cut the "bad" LDL cholesterol variety, torcetrapib's overall performance widely missed the mark, said Steven Nissen, head of cardiology at the Cleveland Clinic who led the study.
"Whether this failure represents a problem unique to torcetrapib or suggests a lack of efficacy for the entire class of similar drugs remains to be determined," Nissen said.
"Our findings demonstrate the great difficulty in developing therapies to interrupt the atherosclerosis process," he said. "Twenty years after the introduction of statins, we are still waiting for the next breakthrough."
Pfizer spent an estimated $800 million on late-stage testing of torcetrapib with the hope that it would eventually replace its $13 billion-a-year cash cow, the cholesterol fighter Lipitor, a member of statin class of drugs that is expected to go off patent as soon as 2010.
The company had been planning to pair torcetrapib with LDL-lowering Lipitor for a potent combo cholesterol therapy.
Torcetrapib's sensational failure blew a gaping hole in Pfizer's developmental pipeline and left investors and other drugmakers to wonder if the entire class should be abandoned or if the deadly effects were specific to torcetrapib.
Roche Holding and Merck are close to having to decide whether to push forward into expensive final stage clinical testing of their own CETP inhibitors.
"Many people are trying to figure out how do we progress to the next stage -- or is this the end -- and it's really not clear, but it's not very encouraging at this point," said Dr. Christopher Cannon, a prominent cardiologist from Brigham and Women's Hospital in Boston.