Plumbagin-induced anticancer effects are associated with mitochondrial-encoded respiratory gene downregulation in oral squamous cell carcinoma

Abstract

Plumbagin (PL) is a known quinoid (5-hydroxyl-2-methyl-1,4-napthoquinone) initially isolated from the roots of Plumbago zeylanica L. It is reported to exert anti-proliferative effects in oral squamous cell carcinoma (OSCC) cells, suggesting that PL would be a promising therapeutic anti-cancer drug for OSCC; however, the molecular basis by which PL suppresses cell survival signaling is poorly understood. In this study, we conducted a comprehensive gene expression analysis to identify the molecular basis by which PL suppresses cell survival signaling. Human OSCC cell lines HSC-3 and SAS were used in this study. Comprehensive gene expression analysis was performed with an Agilent Whole Human Genome DNA microarray 4 × 44 format. Gene Set Enrichment Analysis was conducted to investigate the effect of PL on the oncogenic signaling pathway in the OSCC cells. cDNA microarray and subsequent gene set enrichment analyses showed that PL readily downregulates oxidative phosphorylation, MYC-target genes, and MTORC signaling at 4 h after treatment in HSC-3 and SAS cells. Semi-quantitative PCR analysis showed that gene expression levels of mitochondrial (Mt)-encoded COX-2, COX-3, and ND1 genes are significantly lower in the PL-treated OSCC cells than those in the untreated cells. In addition, an ROS scavenger, NAC, reversed the PL-induced downregulation of expression of Mt-encoded genes. Accordingly, intracellular ATP levels significantly decreased after PL treatment. Collectively, PL downregulates both oxidative phosphorylation and oncogenic signatures and decreases the survival of OSCC cells, thus highlighting its application as a potent treatment for patients with OSCC.