Discovery of isoplumbagin as a novel NQO1 substrate and anti-cancer quinone

Isoplumbagin (5-hydroxy-3-methyl-1,4-naphthoquinone), a naturally occurring quinone from Lawsonia inermis and Plumbago europaea, that has been reported to have anti-inflammatory and anti-microbial activity. Inflammation has long been implicated in cancer progression. In this study, we examined the anti-cancer effect of chemically-synthesized isoplumbagin. Our results revealed that isoplumbagin treatment suppressed cell viability and invasion of highly invasive oral squamous cell carcinoma (OSCC) OC3-IV2 cells, glioblastoma U87 cells, non-small cell lung carcinoma H1299 cells, prostate cancer PC3 cells, and cervical cancer Hela cells by using MTT and Boyden chamber assays. In vivo studies demonstrate the inhibitory effect of 2 mg/kg isoplumbagin on the growth of orthotopic xenograft tumors derived from OSCC cells. Mechanistically, isoplumbagin exerts its cytotoxic effect through acting as a substrate of NAD(P)H quinone dehydrogenase 1 (NQO1) to generate hydroquinone, which reverses mitochondrial fission phenotype, reduces mitochondrial complex IV activity and thus compromises mitochondrial function. Collectively, this work reveals an anti-cancer activity of isoplumbagin mainly through modulating mitochondrial dynamics and function. Chemical compounds: Isoplumbagin (PubChem CID: 375105)