Developing New Drug Treatments

The most crucial prerequisite for successful drug development to treat any disease is to have identified specific targets against which therapies can be directed. In the last two decades, scientists have identified a number of therapeutic targets specific to Alzheimer's disease. The discovery of the three genes that invariably cause early-onset AD and of ApoE-ε4, the first and most significant susceptibility gene for late-onset AD, have lent a great deal of strength to the amyloid hypothesis. The importance of these genetic findings resides in the fact that these four genes all act on the same cascade of events. Through various mechanisms, they all lead to an increase in the buildup of beta-amyloid and neurofibrillary tangles in the brain, which eventually causes neurons to die. This convergence of evidence pointed toward beta-amyloid as a major therapeutic target.

Hundreds of laboratories around the world are contributing knowledge about the role of beta-amyloid in AD. Each, in a multitude of increasingly understood steps in the beta-amyloid cascade, might become a site to target with promising therapeutic compounds.

Dr. Paul Aisen, director of the Alzheimer's Disease Cooperative Study—a long-standing, National Institute on Aging-backed initiative to coordinate clinical trials of promising drugs that may be outside the purview of pharmaceutical companies—described the encouraging tenor of this era in AD drug development: "Everybody's coming together now. It's a huge endeavor, but we're working together to make progress, so that now we have candidate drugs that target the specific process that's initiating Alzheimer's disease, we have brought them into human trials, and we are perhaps close to success."

Like many others in the field, Dr. Aisen believes that researchers are well on track toward reaching their goals. "We need to optimize the treatment of the symptoms, but even more importantly, we need to slow the disease process. We need to halt it. We need to be able to prevent the development of Alzheimer's disease. We need to promote healthy aging—aging without memory impairment, without Alzheimer's disease."

These are undoubtedly ambitious objectives. Many drug targets are being investigated. Clinical trials of ninety-one drugs were underway as of 2008. More drug candidates are awaiting Food and Drug Administration approval to enter human testing. Promising drugs may help people with AD maintain their mental functioning. Others may slow, delay, or even prevent AD. Inside the world of AD drug research today, the optimism is palpable, but scientists also realize that significant challenges remain to be overcome.

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Excerpted from THE ALZHEIMER'S PROJECT: MOMENTUM IN SCIENCE, published by Public Affairs, www.publicaffairsbooks.com.

Alzheimer's Disease (AD)

A progressive degenerative disease of the brain that causes impairment of memory and other cognitive abilities.

Amyloid Precursor Protein (APP)

The larger protein from which beta-amyloid is formed.

ApoE Gene

A gene that codes for a protein that carries cholesterol to and within cells; different forms of the ApoE gene are associated with differing risks for late-onset Alzheimer's disease. This gene may be referred to as a risk factor gene or a "susceptibility gene" because one form of the gene, called APOE4, is associated with the risk of developing late onset AD.

Beta-Amyloid

Derived from the amyloid precursor protein and found in plaques, the insoluble deposits outside neurons. May also be called A-beta.

Beta-Amyloid Plaque

A largely insoluble deposit found in the space between nerve cells in the brain. The plaques in Alzheimer's disease are made of beta-amyloid and other molecules, surrounded by non-nerve cells (glia) and damaged axons and dendrites from nearby neurons.

Cognitive Reserve

The brain's ability to operate effectively even when some damage to cells or brain cell communications has occurred.

Dementia

A broad term referring to a decline in cognitive function that interferes with daily life and activities. Alzheimer's disease is one form of dementia.

Functional MRI (fMRI)

An adaptation of an MRI (see magnetic resonance imaging) technique that measures brain activity during a mental task, such as one involving memory, language, or attention.

Hippocampal Formation

A structure in the brain that plays a major role in learning and memory and is involved in converting short-term to long-term memory. Also called the hippocampus.

Inflammation

The process by which the body responds to cellular injury by attempting to eliminate foreign matter and damaged tissue.

Insulin Resistance

A condition in which the pancreas makes enough insulin, but the cells do not respond properly to it; characterizes and precedes type 2 diabetes.

Magnetic Resonance Imaging (MRI)

A diagnostic and research technique that uses magnetic fields to generate a computer image of internal structures in the body.

Mild Cognitive Impairment (MCI)

A condition in which a person has cognitive problems greater than those expected for his or her age. Amnestic MCI includes memory problems, but not the personality or other cognitive problems that characterize AD.

Neurodegenerative Disease

A disease characterized by a progressive decline in the structure and function of brain tissue. These diseases include AD, Parkinson's disease, frontotemporal lobar degeneration, and dementia with Lewy bodies. They are usually more common in older people.

Oligomers

Clusters of a small number of beta-amyloid peptides.

Oxidative Damage

Damage that can occur to cells when they are exposed to too many free radicals.

Pittsburgh Compound B (PiB)

The radioactive tracer compound used during a PET (see Positron Emission Tomography) scan of the brain to show beta-amyloid deposits.

Pittsburgh Compound B (PiB)

The radioactive tracer compound used during a PET (see Positron Emission Tomography) scan of the brain to show beta-amyloid deposits.

Synapse

The tiny gap between nerve cells across which neurotransmitters and nerve signals pass.

Tau

A protein that helps to maintain the structure of microtubules in normal nerve cells. Abnormal tau is a principal component of the paired helical filaments in neurofibrillary tangles.

Tangles

A protein that helps to maintain the structure of microtubules in normal nerve cells. Abnormal tau is a principal component of the paired helical filaments in neurofibrillary tangles.

Memory

Normal Aging

Genetic Risk Factor

Dominant and Recessive Genes

Genes and Proteins

Protein-Misfolding Disease

Cholesterol

Biomarkers

Disease-Modifying Drug

Transgenic Mice

An animal that has had a gene (such as the human APP gene) inserted into its chromosomes for the purpose of research. Mice carrying a mutated human APP gene often develop plaques in their brains as they age.

Pathology

Microglia

Insulin & Insulin Resistance

Susceptibility Gene

A variant in a cell's DNA that does not cause a disease by itself but may increase the chance that a person will develop a disease.

Susceptibility Genes

A variant in a cell's DNA that does not cause a disease by itself but may increase the chance that a person will develop a disease.

Genome-Wide Association Study

Vascular Disease

Genetics

Genetics

Normal Aging