Phenanthroquinolizidine Alkaloids from the Roots of Boehmeria pannosa Potently Inhibit Hypoxia-Inducible Factor-1 in AGS Human Gastric Cancer Cells

A bioassay-guided phytochemical investigation on the methanol extract of Boehmeria pannosa, using a HIF-1-mediated reporter gene assay, led to the isolation of two phenanthroquinolizidine alkaloids, (−)-cryptopleurine (1) and (−)-(15R)-hydroxycryptopleurine (2). The structure of the new compound 2 was determined by spectroscopic methods. Compounds 1 and 2 potently inhibited the hypoxia-induced expression of a reporter gene under the control of a hypoxia response element (HRE) with IC50 values of 8.7 and 48.1 nM, respectively. Furthermore, 1 and 2 suppressed the accumulation of HIF-1α protein in a dose-dependent manner, but not the HIF-1β protein and inhibited expression of vascular endothelial growth factor (VEGF) by hypoxia.