New Polymethoxyflavones from Hottonia palustris Evoke DNA Biosynthesis-Inhibitory Activity in An Oral Squamous Carcinoma (SCC-25) Cell Line.

Four new compounds, 5-hydroxy-2',6'-dimethoxyflavone ( 4 ), 5-hydroxy-2',3',6'-trimethoxyflavone ( 5 ), 5-dihydroxy-6-methoxyflavone ( 6 ), and 5,6'-dihydroxy-2',3'-dimethoxyflavone ( 7 ), and three known compounds, 1,3-diphenylpropane-1,3-dione ( 1 ), 5-hydroxyflavone ( 2 ), and 5-hydroxy-2'-methoxyflavone ( 3 ), were isolated from the aerial parts of Hottonia palustris . Their chemical structures were determined through the use of spectral, spectroscopic and crystallographic methods. The quantitative analysis of the compounds ( 1-7 ) and the zapotin ( ZAP ) in methanol ( HP1 ), petroleum ( HP6 ), and two chloroform extracts ( HP7 and HP8 ) were also determined using HPLC-PDA. The biological activity of these compounds and extracts on the oral squamous carcinoma cell (SCC-25) line was investigated by considering their cytotoxic effects using the MTT assay. Subsequently, the most active compounds and extracts were assessed for their effect on DNA biosynthesis. It was found that all tested samples during 48 h treatment of SCC-25 cells induced the DNA biosynthesis-inhibitory activity: compound 1 (IC 50 , 29.10 ± 1.45 µM), compound 7 (IC 50 , 40.60 ± 1.65 µM) and extracts ZAP (IC 50 , 20.33 ± 1.01 µM), HP6 (IC 50 , 14.90 ± 0.74 µg), HP7 (IC 50 , 16.70 ± 0.83 µg), and HP1 (IC 50 , 30.30 ± 1.15 µg). The data suggest that the novel polymethoxyflavones isolated from Hottonia palustris evoke potent DNA biosynthesis inhibitory activity that may be considered in further studies on experimental pharmacotherapy of oral squamous cell carcinoma.