Studies of the anticancer drug bexarotene have shown that, in mice, the drug quickly reverses the physiological, cognitive, and memory deficits which are characteristic of Alzheimer's. More than half of the amyloid beta plaques associated with Alzheimer's were cleared from the brain within hours, and normal behavioral patterns which had been blocked by the plaques were restored within 72 hours.
Alzheimer's is a devastating degenerative disease that kills the person before it kills the body. The most common form of dementia, it usually begins with disturbance of short-term memory. As the disease progresses, additional symptoms can comprise confusion, trouble with language, mood swings, irritability, aggression, and long-term memory loss. Eventually bodily functions are lost, leading to the ultimate symptom of death. It is a disease of families, as great burdens are generally taken up by a sufferer's caregivers. Tens of millions of people worldwide suffer from Alzheimer's, a number which is expected to quadruple by 2050.
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In the search for treatments for Alzheimer's, extensive use is made of genetically engineered mice. Such mice are engineered to express mutant human genes for the amyloid beta precursor protein APP, as well as enzymes that control APP cleavage. The result is that amyloid beta peptides, which are coexistent with Alzheimer's in humans, are also present in the mouse models.
In such mutant transgenic mice, diffuse deposition of amyloid beta in the brain is observed by six months of age, and the deposition is progressive. By nine months of age all mutant transgenic mice exhibit plaques in the brain, along with the characteristic deficits associated with Alzheimer's - at least so far as we can read cognitive deficits and neurological symptoms in mice.
In the Case Western studies, a team lead by Professor of Neurosciences Gary Landreth has long been studying the mechanism of Alzheimer's in humans. Recently one of his graduate students, Paige Cramer, suggested studying the effects of bexarotene on Alzheimer's mouse models. As part of this study, mice were given mega-doses of the drug, which is FDA approved to treat cutaneous T-cell lymphoma. Within 72 hours, the mice's ability to form new memories and construct nests was restored, and 75 percent of amyloid beta plaques had been removed from the brain. No candidate drug has previously exhibited such dramatic activity toward the neurodegeneration associated with Alzheimer's.
Landreth's group intends to carry out a preliminary human trial of bexarotene in the next few months. This is made possible because the drug is already FDA approved as an anticancer drug, so safety of the drug has already been approved, at least at doses used for cancer treatment. This first human study will focus on such doses. Although much smaller than the mega-doses used in the study, we have no idea what might be effective and tolerable doses in treating human Alzheimer's, so future clinical studies will work up from what we presently know about bexarotene toxicity.
It is important to note that previous potential Alzheimer's treatments have had encouraging results in mouse models without producing a similar effect in humans with Alzheimer's. All physicians who have commented publicly on the study have emphasized that use of the drug as a treatment for Alzheimer's is premature to the point of folly.
Physicians are receiving a huge influx of calls from caretakers and relatives requesting that bexarotene be used off-label as a Hail Mary pass to treat their loved ones who suffer from Alzheimer's. The drug is extremely expensive, costing roughly US$100 per day in the dosage used for cancer treatment. This dose is far smaller than the mega doses used in Prof. Landreth's study, which might presently cost two or three thousand dollars per day. Despite the cost and cautions, there is little question that the efficacy of bexarotene as a treatment for Alzheimer's will be known long before the medical profession and the FDA concur on the use of bexarotene as an Alzheimer's treatment.
Source: Case Western University