Rational Approach To Discover Multipotent Anti-Alzheimer Drugs Michela Rosini, † Vincenza Andrisano, † Manuela Bartolini, † Maria L. Bolognesi, † Patrizia Hrelia, ‡ Anna Minarini, † Andrea Tarozzi, ‡ and Carlo Melchiorre* ,† Departments of Pharmaceutical Sciences and Pharmacology, Alma Mater Studiorum, University of Bologna, Via Belmeloro 6, 40126 Bologna, Italy Received November 4, 2004 Abstract: The coupling of two different pharmacophores, each endowed with different biological properties, afforded the hybrid compound lipocrine (7), whose biological profile was markedly improved relative to those of prototypes tacrine and lipoic acid. Lipocrine is the first compound that inhibits the catalytic activity of AChE and AChE-induced amyloid- ag- gregation and protects against reactive oxygen species. Thus, it emerged as a valuable pharmacological tool to investigate Alzheimer’s disease and as a promising lead compound for new anti-Alzheimer drugs. Alzheimer’s disease (AD), the most common cause of dementia, is a complex neurological affection that is clinically characterized by loss of memory and progres- sive deficits in different cognitive domains. The con- sistent neuropathologic hallmark of the disorder, gener- ally noted on postmortem brain examination, is a massive deposit of aggregated protein breakdown prod- ucts, amyloid- (A) plaques and neurofibrillary tangles. Even if the primary cause of AD is still speculative, A aggregates are thought to be mainly responsible for the devastating clinical effects of the disease. 1 In recent years, significant research has been devoted to the role of free radical formation, oxidative cell damage, and inflammation in the pathogenesis of AD, providing new promising targets and validated animal models. 2 To date, however, the enhancement of the central cholin- ergic function is the only clinically effective approach. 3,4 The intensive research of drugs that can improve the cholinergic transmission in AD has produced so far four approved acetylcholinesterase (AChE) inhibitors, that is, tacrine (TC), 5 donepezil, 6 rivastigmine, 7 and galan- tamine. 8 However, these drugs have been approved for the symptomatic treatment of AD because they do not address the etiology of the disease for which they are used. It is therefore necessary to discover pharmacological instruments that are able to act as far upstream as possible in the neurodegenerative cascade and, because of the multifaceted etiology of AD, able to hit different selected targets. The aim of this communication is to provide new multipotent compounds, i.e., single mol- ecules that can exhibit more pharmacological properties simultaneously, such as the enhancement of the cho- linergic transmission and inhibition of A accumulation and oxidative stress, leading to a synergic and effective treatment of AD. To this end, we applied a design strategy in which distinct pharmacophores of two different drugs were combined in the same structure leading to hybrid molecules. In principle, each pharmacophore of these new drugs should retain the ability to interact with its specific site(s) on the target and consequently to produce specific pharmacological responses that taken together should block or hopefully cure the neurodegenerative process leading to AD. To obtain proof of concept for this proposal, we chose TC and lipoic acid (LA) as prototype drugs to be combined in the same structure because of their well-established biological properties (Figure 1). In fact, LA is a universal antioxidant, 9-12 which was shown to protect neurons against cytotoxicity induced by A 13 and to stabilize cognitive functions in patients with AD, 14 whereas TC was the first AChE inhibitor approved for AD treatment. 5 AChE is the enzyme involved in the hydrolysis of the neurotransmitter acetylcholine (ACh) at cholinergic synapses in the central and peripheral nervous system. Inhibitors of AChE activity promote an increase in the concentration and the duration of action of synaptic ACh, thus causing an enhancement of the cholinergic transmission through activation of the synaptic nicotinic and muscarinic receptors. However, achievement of potent inhibitors of the AChE catalytic site would not represent a significant improvement unless there is a concomitant inhibition of the peripheral anionic site (PAS) of the enzyme, which is associated with the neurotoxic cascade of AD through AChE-induced A aggregation. 15,16 For this reason, the introduction onto the TC structure of a side chain, namely, an LA fragment following the two routes shown in Figure 1, should hopefully combine antioxidant properties with the ability to interact with PAS. Compounds 1-8 were synthesized by coupling tetra- hydroacridine intermediates 9-16 with LA in the presence of 1-(3-dimethylaminopropyl)-3-ethylcarbodi- imide hydrochloride (EDCI), according to Scheme 1 (see Supporting Information). No attempt was made to separate the enantiomers of 1-7 because it was re- ported that stereochemistry is not relevant for the protective effect of LA against oxidative cell damage. 10 In addition, concerning 8, the diastereomers were not * To whom correspondence should be addressed. Phone: +39-051- 2099706. Fax: +39-051-2099734. E-mail: carlo.melchiorre@unibo.it. † Department of Pharmaceutical Sciences. ‡ Department of Pharmacology. Figure 1. Design strategy for 1-8. 360 J. Med. Chem. 2005, 48, 360-363 10.1021/jm049112h CCC: $30.25 © 2005 American Chemical Society Published on Web 12/31/2004