Hepatocellular carcinoma is the third most common cause of
cancer-related deaths worldwide. Furthermore, the existing pharmacological-based treatments are insufficiently effective and generate many side effects.
Hispidulin (6-methoxy-5,7,4'-trihydroxyflavone) is a
flavonoid found in various medicinal herbs that present
antineoplastic properties. Here we evaluated how modulation of
reactive oxygen species (ROS) and alterations of
antioxidant defenses could be associated to the antiproliferative effects of
hispidulin in HepG2 cells. In addition, we studied the inhibitory activity of
hispidulin on the efflux of drugs mediated by
ABC transporters involved in multidrug resistance. In order to understand the increase of intracellular ROS promoted by
hispidulin, we investigated the
mRNA expression levels and activities of
antioxidant enzymes, and the GSH/
GSSG ratio. We showed that
hispidulin significantly down-regulated the transcription levels of
catalase, leading to reduction of
enzyme activity and decrease of the GSH content. We also observed that, in the presence of
N-acetylcysteine or exogenous
catalase, the proliferation was lowered back to the control levels. These data clearly indicate a strong involvement of intracellular ROS levels for triggering the antiproliferative effects. We also demonstrated that the inhibition produced by
hispidulin on
drug efflux was specific for ABCG2, since no effects were observed with ABCB1 and ABCC1. Furthermore, HepG2 cells were more sensitive to
hispidulin-mediated cell death than immortalized L929 fibroblasts, suggesting a differential toxicity of this compound between
tumor and non-tumor cell lines. Our results suggest that
hispidulin constitutes a promising candidate to sensitize chemoresistant
cancer cells overexpressing ABCG2.