The findings, presented at a European neurology meeting in Stockholm, followed the companies' announcement last month that they were scrapping large-scale clinical trials of the drug after it failed to improve memory or thinking skills in patients with mild to moderate Alzheimer's.
Many researchers had long expected bapineuzumab to fail this test because they believe Alzheimer's starts years before memory problems become apparent.
But they have been eagerly awaiting the so-called biomarker results - measurements of fluids and tissues in the body - to see if the drug hit its biological targets, suggesting it could work in at an earlier stage of the disease.
These biomarker results show that compared with the subjects who were give a placebo, bapineuzumab significantly reduced the amount of the protein beta amyloid on the brain scans of patients with a gene mutation that increases their risk of Alzheimer's.
The drug also significantly reduced the amount of a toxic form of the protein tau in spinal fluid, a sign of brain cell death, compared with patients who were given a placebo.
However, MRI tests showed patients in the treatment and placebo groups had a similar loss of brain volume.
Dr. Reisa Sperling of Harvard Medical School and Brigham and Women's Hospital, who presented results of a study of patients who carry the ApoE4 gene mutation, said the findings were not a "home run in biomarkers," but they are encouraging.
"I am happy there is evidence that we are having some effect on the disease process in the brain," she said in a telephone interview from Stockholm.
"I am very interested in moving towards a much earlier stage of Alzheimer's disease in which we might be able to impact the biology at time when we might prevent symptoms."
The results of a second trial of patients who were not carriers of the ApoE4 mutation, presented by Dr. Stephen Salloway of Brown University in Providence, Rhode Island, showed no improvements in any of these biomarkers. However, the follow-up study only included 39 patients and was likely too small to show much of an effect, Salloway said.
"WHOLE NEW AVENUE" Dr. Ronald Petersen, an Alzheimer's researcher at the Mayo Clinic in Rochester, Minnesota, who had not yet seen the results, said the biomarker data are much more interesting than the clinical results, which were not "very likely to see something."
Petersen said that, if the results were "flat, dead negative," enthusiasm for this drug would wane. But if there is a signal there, it opens "a whole new avenue for what might be possible."
Researchers will be comparing these findings to those of Eli Lilly and Co's similar drug, solanezumab. Although the Lilly drug also failed to meet its study's main goals in mild to moderate patients, the company did see a slight benefit when they just looked at results in mild patients.
Biomarker results for Lilly's drug are expected to be released on October 8 at a neurology meeting in Boston.
Salloway said researchers have yet to analyze pooled data on mild patients in the bapineuzumab studies.
Executives at Pfizer and Johnson & Johnson said in an interview that the biomarker results did show underlying activity.
"I think now it is just a matter of refining it and finding a way to use that to help the patient," said Dr. Ron Black, an assistant vice president of clinical research and development at Pfizer.
Although the companies have discontinued all studies involving the intravenous form of this drug, they still have an ongoing phase 2 study testing the treatment in a shot form.
Dr. Eric Yuen of Johnson & Johnson's Janssen Alzheimer Immunotherapy said the newer formulation may offer a smoother exposure to the drug than the IV version, which could help reduce some of the side effects.
The companies are also testing two other compounds that target amyloid. One, known as AAB-003, is an antibody drug similar to bapineuzumab and the other, ACC-001, is a vaccine or immunotherapy that is already being tested in earlier stage Alzheimer's patients.
Sperling said side effects will play a role in the future of bapineuzumab.
"I think it will be important to see whether we will get a better side effect profile that will allow us to dose higher," Sperling said.
"The other hope I have is if we went much earlier, before people have a head full of amyloid, we might be able to have less of a side effect profile. That is obviously something we're going to have to look at carefully."
Several studies, including one proposed by Sperling, will be testing drugs such as bapineuzumab in patients with normal memories who are likely to develop Alzheimer's, either because they are genetically predisposed to it or because biomarker tests suggest it is already forming.
Salloway, who is also helping to organize a study known as DIAN in patients with an inherited form of the disease, said researchers will examine all available data in order to pick compounds likely to influence the disease process early on.
(Editing by Andre Grenon)
Reserve your seat now for MedCity CONVERGE, to be held July 9-10 in Philadelphia. Discover strategies, solutions and startups in healthcare innovation. Be a part of this gathering where the entire healthcare ecosystem converges.