Alpinum isoflavone, Methylalpinum isoflavone and Rotenone – Lonchocarpus glabrescens Metabolites that Inhibit HIF-1 Activation and Tumor Cell Migration

Hypoxia-inducible factor-1 (HIF-1) represents an important tumor-selective molecular target for anti-cancer drug discovery. The lipid extract of Lonchocarpus glabrescens (0.5 µg/mL) inhibited hypoxia-induced HIF-1 activation by 90% in a human breast carcinoma T47D cell-based reporter assay. Bioassay-guided isolation and structure elucidation yielded alpinumisoflavone (1, IC₅₀ 5µM) and 4ʹ-O-methylalpinumisoflavone (2, IC₅₀ 0.6µM), and rotenone (3, IC₅₀ 0.001µM). Rotenone (3) selectively suppressed hypoxia-induced HIF-1 activation, relative to its effect on iron chelator-induced HIF-1 activation (> 100 fold selectivity). Both 2 and 3 inhibited the hypoxic induction of HIF-1 target genes (CDKN1A, GLUT-1, and VEGF) in T47D cells. Compounds 1 and 2 suppressed tumor cell migration in a MDA-MB-231 cell-based migration assay, while 3 had no effect. Both 2 and 3 inhibited hypoxic induction of HIF-1α protein, the oxygen regulated subunit that determines HIF-1 activity. Mechanism studies indicate that 3 inhibits HIF-1 activity by suppressing mitochondrial respiration, while 2 simultaneously suppresses mitochondrial respiration and disrupts protein translation in vitro. 1 R = H 2 R = CH₃

Acknowledgements: Research Supported by NIH/NCI CA98787, NOAA/NIUST NA16RU1496, NIH C06 RR-14503–01.