KS-619-1

Alzheimer's disease (AD) causes cognitive impairment in the elderly and is a severe problem worldwide. One of the major reasons for the pathogenesis of AD is thought to be due to the accumulation of amyloid beta (Aβ) peptides that result in neuronal cell death in the brain. In this study, bioassay-guided fractionation was performed to develop seed compounds for anti-AD drugs that can act as dual inhibitors of BACE1 and Aβ aggregation from secondary metabolites produced by Streptomyces sp. To improve the solubility, the crude extracts were methylated with trimethylsilyl (TMS) diazomethane and then purified to yield polyketides 1-5, including the new compound 1. We synthesized the compounds 6 and 7 (original compounds 2 and 3, respectively), and their activities were evaluated. KS-619-1, the demethylated form of 4 and 5, was isolated and evaluated for its inhibitory activity. The IC50 values for BACE1 and Aβ aggregation were found to be 0.48 and 1.1 μM, respectively, indicating that KS-619-1 could be a lead compound for the development of therapeutic agents for AD.

K-259-2 and KS-619-1, novel anionic anthraquinone metabolites isolated from culture broth of microorganisms, inhibited activation of bovine brain phosphodiesterase induced by calmodulin (CaM), sodium oleate, or limited proteolysis with almost equal potency. The inhibition of calmodulin-activated phosphodiesterase (CaM-PDE) by K-259-2 or KS-619-1 was overcome by a higher concentration of CaM. Direct interaction of K-259-2 and KS-619-1 with CaM was confirmed through use of hydrophobic fluorescent probes. Kinetic analysis revealed that the inhibition of the trypsin-activated phosphodiesterase was competitively inhibited by K-259-2 or KS-619-1 with respect to cAMP. Addition of a lower amount of either phosphatidylserine or sodium oleate to the reaction mixture was efficacious in attenuating the inhibition of the CaM-PDE by W-7, chlorpromazine, trifluoperazine, compound 48/80, or R-24571 but, in contrast, had little or no effect on the inhibition by K-259-2 or KS-619-1. In conclusion, K-259-2 and KS-619-1, unlike so-called CaM antagonists, do not interact with phosphatidylserine or sodium oleate and it appears that these novel anthraquinone compounds inhibit the enzyme not only via CaM antagonism but possibly also by interacting directly with the enzyme.

The structure of KS-619-1, a potent inhibitor of Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase, was determined to be 8,13-dioxo-3-(2-oxopropyl)-5,6,8,13-tetrahydro-1,7,9,11- tetrahydroxybenz[a]naphtacene-2-carboxylic acid by spectral studies of KS-619-1 and its methyl derivative.