Multivalent & multifunctional ligands to β-amyloid

Ligands selectively targeting β-amyloid in the living brain are promising candidates of therapeutics and early diagnosis tools for Alzheimer's disease. Among the major stages of β-amyloid aggregation, monomers and oligomers are excellent targets to reduce neurotoxic brain damages for prevention of the disease progression, while oligomers and fibrils, abundant in the late stage of the disease, are pathological objectives to develop reliable imaging probes. So far, there have been many efforts to develop a wide variety of monovalent β-amyloid ligands such as thioflavin T, PIB, FDDNP, curcumin, and tramiprosate. However, pathology of Alzheimer's disease is not fully understood yet so that there is currently no cure and further investigations on Alzheimer's disease are needed. For past several years, multivalent β-amyloid ligands have offered an alternative route by enhancing binding affinity of drug candidates. In addition, it has been revealed that not only neurotoxicity due to the protein misfolding but also other factors are involved in the β-amyloid cascade such as oxidative stress, inflammation, metal chelation, and several types of neurotransmitters. Thus, there have been numerous studies to improve binding affinities of single β-amyloid ligands via adopting multivalent effects or to develop drug candidates targeting multiple stages of the pathological cascade. In this review, multivalent and multifunctional β-amyloid ligands and their promising aspects as an alternative approach to Alzheimer's disease are discussed.