Effect and Mechanism of Tanshinone I on the Radiosensitivity of Lung Cancer Cells.

ABSTRACT

BACKGROUND: Resistance to radiotherapy is one of the main obstacles to improving cancer prognoses. To effectively destroy cancer cells, novel radiation sensitizers are needed. Recently, several natural products have been shown to exhibit promising tumor-killing properties. However, little is known about the specific mechanisms of these natural compounds on cancer treatment. In this study, after screening a high-throughput natural product library, we identified tanshinone I (Tan I) as a potential radiation sensitizer in lung cancer cells. METHODS: Lung cancer radioresistant cell lines, H358-IR and H157-IR, were first established to confirm the radioresistant phenotypes. After that, a natural product library was used to screen the potential radiation sensitizer. We further examined the inhibition functions of Tan I on radioresistant cancer cells via a series of experiments. RESULTS: Tan I significantly inhibited cell proliferation and clone formation, consequently enhancing radiosensitivity in radioresistant lung cancer cells, H358-IR and H157-IR. Stable isotope labeling of amino acids in cell culture (SILAC)-based quantitative proteomics indicated that Tan I downregulates expression of pro-oncogenic protein phosphoribosyl pyrophosphate aminotransferase (PPAT) in both H358-IR and H157-IR cells. Further analysis of molecular docking showed that Tan I is well-docked into the active pocket of the structure of PPAT, serving as a potential PPAT inhibitor. CONCLUSIONS: Taken together, these findings suggest that inhibition of the tumor promoter PPAT by Tan I exerts marked inhibitory effects on radioresistant lung cancer cells, improving radiation efficacy.