Abstract
Hepatocellular carcinoma (HCC) is refractory to chemotherapies, necessitating novel effective agents. The lysosome inhibitor Bafilomycin A1 (BafA1) at high concentrations displays cytotoxicity in a variety of cancers. Here we show that BafA1 at nanomolar concentrations suppresses HCC cell growth in both 2 dimensional (2D) and 3D cultures. BafA1 induced cell cycle arrest in the G1 phase and triggered Cyclin D1 turnover in HCC cells in a dual-specificity tyrosine phosphorylation-regulated kinase 1B (DYRK1B) dependent manner. Notably, BafA1 induced caspase-independent cell death in HCC cells by impairing autophagy flux as demonstrated by elevated LC3 conversion and p62/SQSTM1 levels. Moreover, genetic ablation of LC3 significantly attenuated BafA1-induced cytotoxicity of HCC cells. We further demonstrate that pharmacological down-regulation or genetic depletion of p38 MAPK decreased BafA1-induced cell death via abolishment of BafA1-induced upregulation of Puma. Notably, knockdown of Puma impaired BafA1-induced HCC cell death, and overexpression of Puma enhanced BafA1-mediated HCC cell death, suggesting a role for Puma in BafA1-mediated cytotoxicity. Interestingly, pharmacological inhibition of JNK with SP600125 enhanced BafA1-mediated cytotoxicity both in vitro and in xenografts derived from HCC cells. Taken together, our data suggest that BafA1 may offer potential as an effective therapy for HCC.
Highlights
In order to achieve the effective inhibitory effects on cancer cell growth and/or autophagic degradation, Bafilomycin A1 (BafA1) is usually required at high concentrations (>0.1 μM), which may induce severe acidosis and secondary adverse effects in normal cells, thereby hindering its application in clinical trials
Large amounts of the cells from BafA1treated BEL7402 and HepG2 spheroids were stained with the cell-death dye propidium iodide (PI), indicative of cell death (Fig. 1F)
These results indicate that BafA1, at low concentration (5 nM), is sufficient to inhibit HCC cell growth in vitro
Summary
In order to achieve the effective inhibitory effects on cancer cell growth and/or autophagic degradation, BafA1 is usually required at high concentrations (>0.1 μM), which may induce severe acidosis and secondary adverse effects in normal cells, thereby hindering its application in clinical trials. In this investigation, we show that BafA1 at nanomolar concentrations substantially inhibits the growth of HCC cells in both 2D and 3D cultures and in mouse models. We further demonstrate that BafA1 induces caspase-independent HCC cell death via targeting of autophagy and MAPK pathways. Our data supports further exploration of BafA1 as a drug candidate in the treatment of HCC
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