Hepatocellular carcinoma (HCC) is recognized as the fifth most common cancer and the third most common cause of death in Asian population. Studies reported that HCC is relatively insensitive to radiotherapy (RT); thus, considering how to sensitize HCC to RT is worth to be elucidated. Epidermal growth factor receptor (EGFR)‐mediated signalling transduction plays the important role in regulating treatment efficacy of HCC. An active compound, 18beta‐glycyrrhetinic acid (18β‐GA), has been reported to own anti‐tumour effect. However, whether 18β‐GA possess RT sensitization ability in HCC remains unclear. Here, we used RNA data from TCGA‐LIHC (Liver hepatocellular carcinoma) to identify the role between EGFR/ERK/nuclear factor kappa B (NF‐κB) signalling and RT by radiosensitivity index (RSI) analysis. We suggested that patients with activated NF‐κB signalling may show resistance to RT treatment, whereas combining 18β‐GA may reinforce RT efficacy in a Hep3B‐bearing animal model. 18β‐GA combined with RT showed superior tumour inhibition capacity as compared to monotherapy and even reached similar efficacy as erlotinib combined with RT. Treatment promotion of RT by 18β‐GA in HCC is not only through diminishing RT‐induced EGFR/ERK/NF‐κB signalling but also promoting RT‐induced apoptosis pathways. 18β‐GA may act as radiosensitizer through inactivating EGFR‐mediated HCC progression and inducing caspase‐dependent apoptosis signalling.

Abstract. Isothiocyanates (ITCs) are present as glucosinolates in various cruciferous vegetables. Allyl isothiocyanate (AITC) is one of the common naturally occurring isothiocyanates. Recent studies have shown that AITC significantly inhibited survival of leukemia HL-60, bladder cancer UM-UC-3 and colon cancer HT-29 cells in vitro. In this study, we demonstrate that AITC significantly decreased proliferation and viability of human brain malignant glioma GBM 8401 cells in a dose-dependent manner with IC 50 9.25±0.69 μM for 24 h-treatment. The analysis of cell cycle distribution also showed that AITC induced significantly G2/M arrest and sub-G1 phase (apoptotic population) in GBM 8401 cells. AITC markedly reduced the CDK1/cyclin B activity and protein levels by CDK1 activity assay and Western blot analysis. AITC-induced apoptotic cell death and this evidence was confirmed by morphological assessment and DAPI staining. Pretreatment with specific inhibitors of caspase-3 (Z-DEVE-FMK) and -9 (Z-LEHD-FMK) significantly reduced caspase-3 and -9 activity in GBM 8401 cells. Western blot analysis and colorimetric assays also displayed that AITC caused a time-dependent increase in cytosolic cytochrome c, pro-caspase-9, Apaf-1, AIF, Endo G and the stimulated caspase-9 and -3 activity. Our results suggest that AITC is a potent anti-human brain malignant glioma drug and it shows a remarkable action on cell cycle arrest before commitment for apoptosis is reached.