Dimebon Development for Huntington Disease, Alzheimer Disease Progresses
The defunct Russian antihistamine Dimebon may (may) improve cognition in Huntington disease, according to newly published results of a short-term, but well-controlled, trial in the Archives of Neurology. However, the efficacy outcome—which was just 1 of 3 efficacy measures made in the trial—was not the primary endpoint of this company-sponsored phase 2 study of the drug’s tolerability.
Among 91 ambulatory enrollees with HD,* 90-day treatment with Dimebon, 20 mg tid, significantly improved the mean score on the 30-point MMSE by less than 1 point (0.97; P = .03, vs placebo). No significant differences between Dimebon and placebo treatment were noted, however, on the Unified Huntington’s Disease Rating Scale (which assesses motor function, as well as cognition) or the 13-item ADAS-cog. Tolerability of Dimebon, the primary outcome measure, was comparable to that of placebo: 87% and 82% of patients, respectively, completed treatment. No significant treatment differences were noted with regard to the most commonly reported adverse events (eg, falls, headache, and dizziness).
The rationale for studying Dimebon in HD and other neurodegenerative disorders, like Alzheimer disease, is based on the drug’s ability in the laboratory to stabilize mitochondrial membranes and possibly promote neuronal stability or even regeneration. According to the study authors, “Abnormal mitochondrial depolarization, which can lead to collapse of the mitochondrial membrane and ultimately neuronal apoptosis, has been implicated in the pathophysiologic progression of HD and other neurodegenerative diseases.”
A placebo-controlled study of Dimebon in AD revealed significant improvement in cognition, behavior, and general function at 6 and 12 months. Results of this study evidently motivated Pfizer to give Medivation $725 million in 2008 for worldwide marketing rights to the drug. Corporate-funded phase 3 studies of Dimebon are currently recruiting patients with HD (here) or AD (for instance, here or here).
News of the phase 2 results was associated with a bump in Medivation’s share price (but not Pfizer’s).
N.B.–Dimebon is the trade name for dimebolin HCl or latrepirdine.
ADAS-cog = Alzheimer’s Disease Assessment Scale, cognitive subscale; MMSE = Mini-Mental State Examination.
* Study-eligible patients were allowed to take antipsychotic agents (at stable dosages), but they could not take cholinesterase inhibitors (eg, Aricept) or N-methyl-D-aspartate antagonists (eg, Namenda).
Image of Dimebon structure from Wikipedia.