Silibinin Induces Both Apoptosis and Necroptosis with Potential Anti-tumor Efficacy in Lung Cancer.

BACKGROUND

The incidence of lung cancer is steadily on the rise, posing a growing threat to human health. The search for therapeutic drugs from natural active substances and elucidating their mechanism have been the focus of anti-tumor research.

OBJECTIVE

Silibinin (SiL) has been shown to be a natural product with a wide range of pharmacological activities, including anti-tumour activity. In our work, SiL was chosen as a possible substance that could inhibit lung cancer. Moreover, its effects on inducing tumor cell death were also studied.

METHODS

CCK-8 analysis and morphological observation were used to assess the cytotoxic impacts of SiL on lung cancer cells . The alterations in mitochondrial membrane potential (MMP) and apoptosis rate of cells were detected by flow cytometry. The level of lactate dehydrogenase (LDH) release out of cells was measured. The expression changes of apoptosis or necroptosis-related proteins were detected using western blotting. Protein interactions among RIPK1, RIPK3, and MLKL were analyzed using the co-immunoprecipitation (co-IP) technique. Necrosulfonamide (Nec, an MLKL inhibitor) was used to carry out experiments to assess the changes in apoptosis following the blockade of cell necroptosis. , SiL was evaluated for its antitumor effects using LLC tumor-bearing mice with mouse lung cancer.

RESULTS

With an increased dose of SiL, the proliferation ability of A549 cells was considerably inhibited, and the accompanying cell morphology changed. The results of flow cytometry showed that after SiL treatment, MMP levels decreased, and the proportion of cells undergoing apoptosis increased. There was an increase in cleaved caspase-9, caspase-3, and PARP, with a down-regulation of Bcl-2 and an up-regulation of Bax. In addition, the amount of LDH released from the cells increased following SiL treatment, accompanied by augmented expression and phosphorylation levels of necroptosis-related proteins (MLKL, RIPK1, and RIPK3), and the co-IP assay further confirmed the interactions among these three proteins, indicating the necrosome formation induced by SiL. Furthermore, Nec increased the apoptotic rate of SiL-treated cells and aggravated the cytotoxic effect of SiL, indicating that necroptosis blockade could switch cell death to apoptosis and increase the inhibitory effect of SiL on A549 cells. In LLC-bearing mice, gastric administration of SiL significantly inhibited tumor growth, and H&E staining showed significant damage to the tumour tissue. The results of the IHC showed that the expression of RIPK1, RIPK3, and MLKL was more pronounced in the tumor tissue.

CONCLUSIONS

This study confirmed the dual effect of SiL, as it can induce both biological processes, apoptosis and necroptosis, in lung cancer. SiL-induced apoptosis involved the mitochondrial pathway, as indicated by changes in caspase-9, Bcl-2, and Bax. Necroptosis may be activated due to the changes in the expression of associated proteins in tumour cells and tissues. It has been observed that blocking necroptosis by SiL increased cell death efficiency. This study helps clarify the anti-tumor mechanism of SiL against lung cancer, elucidating its role in the dual induction of apoptosis and necroptosis. Our work provides an experimental basis for the research on cell death induced by SiL and reveals its possible applications for improving the management of lung cancer.