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Dimebon disappointment.

ABSTRACT: Dimebon (latrepirdine) has received widespread publicity as a potential therapy for Alzheimer's disease following a very positive phase 2 study carried out in Russia and published in the Lancet in 2008. In this study there were improvements over 6 months in all endpoints (cognitive, global, daily function and behaviour), with continuing improvement at 12 months in cognition and daily function. A more recent multinational phase 3 study, however, showed no improvements whatsoever and no difference between the two drug-treated groups and the placebo group. Of note, there was little deterioration in any of the groups after 6 months in contrast to the placebo group in the phase 2 study. The potential reasons for these disappointing results are discussed, as well as the implication for dimebon and drug treatment in Alzheimer's disease.

SUBMITTER: Jones RW

PROVIDER: S-EPMC2983434 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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Dimebon disappointment.

Jones Roy W RW

Alzheimer's research & therapy 20100913 5

Dimebon (latrepirdine) has received widespread publicity as a potential therapy for Alzheimer's disease following a very positive phase 2 study carried out in Russia and published in the Lancet in 2008. In this study there were improvements over 6 months in all endpoints (cognitive, global, daily function and behaviour), with continuing improvement at 12 months in cognition and daily function. A more recent multinational phase 3 study, however, showed no improvements whatsoever and no difference ...[more]

PMID: 20836898

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Project description:BackgroundDimebon is an antihistamine compound with a long history of clinical use in Russia. Recently, Dimebon has been proposed to be useful for treating neurodegenerative disorders. It has demonstrated efficacy in phase II Alzheimer's disease (AD) and Huntington's disease (HD) clinical trials. The mechanisms responsible for the beneficial actions of Dimebon in AD and HD remain unclear. It has been suggested that Dimebon may act by blocking NMDA receptors or voltage-gated Ca2+ channels and by preventing mitochondrial permeability pore transition.ResultsWe evaluated the effects of Dimebon in experiments with primary striatal neuronal cultures (MSN) from wild type (WT) mice and YAC128 HD transgenic mice. We found that Dimebon acts as an inhibitor of NMDA receptors (IC50 = 10 muM) and voltage-gated calcium channels (IC50 = 50 muM) in WT and YAC128 MSN. We further found that application of 50 muM Dimebon stabilized glutamate-induced Ca2+ signals in YAC128 MSN and protected cultured YAC128 MSN from glutamate-induced apoptosis. Lower concentrations of Dimebon (5 muM and 10 muM) did not stabilize glutamate-induced Ca2+ signals and did not exert neuroprotective effects in experiments with YAC128 MSN. Evaluation of Dimebon against a set of biochemical targets indicated that Dimebon inhibits alpha-Adrenergic receptors (alpha1A, alpha1B, alpha1D, and alpha2A), Histamine H1 and H2 receptors and Serotonin 5-HT2c, 5-HT5A, 5-HT6 receptors with high affinity. Dimebon also had significant effect on a number of additional receptors.ConclusionOur results suggest that Ca2+ and mitochondria stabilizing effects may, in part, be responsible for beneficial clinical effects of Dimebon. However, the high concentrations of Dimebon required to achieve Ca2+ stabilizing and neuroprotective effects in our in vitro studies (50 muM) indicate that properties of Dimebon as cognitive enhancer are most likely due to potent inhibition of H1 histamine receptors. It is also possible that Dimebon acts on novel high affinity targets not present in cultured MSN preparation. Unbiased evaluation of Dimebon against a set of biochemical targets indicated that Dimebon efficiently inhibited a number of additional receptors. Potential interactions with these receptors need to be considered in interpretation of results obtained with Dimebon in clinical trials.

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Dimebon disappointment.

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Dimebon disappointment.

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