3-7-dihydroxyflavone and baicalein

Fourteen baicalein and 3,7-dihydroxyflavone derivatives were synthesized and evaluated for their inhibitory activity against the in vitro growth of three human tumor cell lines. The synthetic approaches were based on the reaction with prenyl or geranyl bromide in alkaline medium, followed by cyclization of the respective monoprenylated derivative. Dihydropyranoflavonoids were also obtained by one-pot synthesis, using Montmorillonite K10 clay as catalyst combined with microwave irradiation. In vitro screening of the compounds for cell growth inhibitory activity revealed that the presence of one geranyl group was associated with a remarkable increase in the inhibitory activity. Moreover, for the 3,7-dihydroxyflavone derivatives a marked increase in growth inhibitory effect was also observed for compounds with furan and pyran fused rings. The most active compounds were also studied regarding their effect on cell cycle profile and induction of apoptosis. Overall the results point to the relevant role of the prenylation of flavone scaffold in the growth inhibitory activity of cancer cells.

Topics: Antineoplastic Agents; Apoptosis; Cell Cycle; Cell Proliferation; Crystallography, X-Ray; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Flavanones; Flavonoids; Humans; Models, Molecular; Molecular Structure; Stereoisomerism; Structure-Activity Relationship; Tumor Cells, Cultured

Prolyl oligopeptidase is a cytosolic serine peptidase that hydrolyzes proline-containing peptides at the carboxy terminus of proline residues. It has been associated with schizophrenia, bipolar affective disorder, and related neuropsychiatric disorders and therefore may have important clinical implications. In a previous work, we used (19)F NMR to search for new prolyl oligopeptidase inhibitors from a library of traditional Chinese medicine plant extracts, and identified several extracts as powerful inhibitors of this peptidase. Here, the flavonoid baicalin was isolated as the active component of an extract of Scutellaria baicalensis roots having prolyl oligopeptidase inhibitory activity. Baicalin inhibited prolyl oligopeptidase in a dose-dependent manner. Inhibition experiments using baicalin analogs showed that the sugar moiety was not necessary for activity. The IC(50)s of baicalin and its aglycone derivative baicalein were rather similar, showing that the sugar moiety was not involved in the interaction of baicalin with POP. These results were confirmed by saturation transfer difference NMR experiments. To further understand the absorption and transport mechanisms of baicalin and baicalein, we evaluated their transport in vitro through the gastrointestinal tract and the blood-brain barrier using a Parallel Artificial Membrane Permeability Assay. The molecule which potentially crosses both barriers was identified as baicalein, the aglycone moiety of baicalin. Our results show that baicalin is a new prodrug able to inhibit prolyl oligopeptidase. As baicalin is a natural compound with a long history of safe administration to humans, it is a highly attractive base from which to develop new treatments for schizophrenia, bipolar affective disorder, and related neuropsychiatric diseases.

Topics: Dose-Response Relationship, Drug; Enzyme Inhibitors; Flavanones; Flavonoids; Prolyl Oligopeptidases; Serine Endopeptidases; Structure-Activity Relationship