No abstract

Two cytotoxic rocaglate derivatives possessing an unusual dioxanyloxy unit, silvestrol (1) and episilvestrol (2), were isolated from the fruits and twigs of Aglaia silvestris by bioassay-guided fractionation monitored with a human oral epidermoid carcinoma (KB) cell line. Additionally, two new baccharane-type triterpenoids, 17,24-epoxy-25-hydroxybaccharan-3-one (3) and 17,24-epoxy-25-hydroxy-3-oxobaccharan-21-oic acid (4), as well as eleven known compounds, 1beta,6alpha-dihydroxy-4(15)-eudesmene (5), ferulic acid (6), grasshopper ketone (7), apigenin, cabraleone, chrysoeriol, 1beta,4beta-dihydroxy-6alpha,15alpha-epoxyeudesmane, 4-hydroxy-3-methoxyacetophenone, 4-hydroxyphenethyl alcohol, ocotillone, and beta-sitosterol 3-O-beta-D-glucopyranoside, were also isolated and characterized. The structures of compounds 1-4 were elucidated by spectroscopic studies and by chemical transformation. The absolute stereochemistry of silvestrol (1) was established by a X-ray diffraction study of its di-p-bromobenzoate derivative, and the structure of 3 was also confirmed by single-crystal X-ray diffraction. The isolates and chemical transformation products were evaluated for cytotoxicity against several human cancer cell lines, and silvestrol (1) and episilvestrol (2) exhibited potent in vitro cytotoxic activity. Silvestrol (1) was further evaluated in vivo in the hollow fiber test and in the murine P-388 leukemia model.

Tau is a microtubule (MT)-stabilizing protein that is altered in Alzheimer's disease (AD) and other tauopathies. It is hypothesized that the hyperphosphorylated, conformationally altered, and multimeric forms of tau lead to a disruption of MT stability; however, direct evidence is lacking in vivo. In this study, an in vivo stable isotope-mass spectrometric technique was used to measure the turnover, or dynamicity, of MTs in brains of living animals. We demonstrated an age-dependent increase in MT dynamics in two different tau transgenic mouse models, 3xTg and rTg4510. MT hyperdynamicity was dependent on tau expression, since a reduction of transgene expression with doxycycline reversed the MT changes. Treatment of rTg4510 mice with the epothilone, BMS-241027, also restored MT dynamics to baseline levels. In addition, MT stabilization with BMS-241027 had beneficial effects on Morris water maze deficits, tau pathology, and neurodegeneration. Interestingly, pathological and functional benefits of BMS-241027 were observed at doses that only partially reversed MT hyperdynamicity. Together, these data suggest that tau-mediated loss of MT stability may contribute to disease progression and that very low doses of BMS-241027 may be useful in the treatment of AD and other tauopathies.

A fundamental challenge in chemical biology and medicine is to understand and expand the fraction of the human proteome that can be targeted by small molecules. We recently described a strategy that integrates fragment-based ligand discovery with chemical proteomics to furnish global portraits of reversible small-molecule/protein interactions in human cells. Excavating clear structure-activity relationships from these 'ligandability' maps, however, was confounded by the distinct physicochemical properties and corresponding overall protein-binding potential of individual fragments. Here, we describe a compelling solution to this problem by introducing a next-generation set of fully functionalized fragments differing only in absolute stereochemistry. Using these enantiomeric probe pairs, or 'enantioprobes', we identify numerous stereoselective protein-fragment interactions in cells and show that these interactions occur at functional sites on proteins from diverse classes. Our findings thus indicate that incorporating chirality into fully functionalized fragment libraries provides a robust and streamlined method to discover ligandable proteins in cells.