Cordycepin, extracted from the medicinal mushroom Cordyceps militaris, was shown to induce cancer cell apoptosis. Yet its anticancer function was limitedly evaluated, and the mechanism was not entirely elucidated. In this study, we demonstrated the effectiveness of cordycepin in inducing apoptosis in HeLa cells and investigated its apoptosis-inducing mechanism through label-free surface-enhanced Raman spectroscopy (SERS). SERS spectral changes revealed detailed molecular changes in both early and late stages of apoptosis. Importantly, SERS characteristic peaks at 805 and 1438 cm−1, which were assigned to RNA, continued to decrease significantly from early to late apoptosis stages. It indicated that cordycepin induced HeLa cell apoptosis mainly through interfering with RNA production, potentially by restraining the translation of RNA encoding ribosomal proteins. Meanwhile, apoptotic cells and their apoptosis stage could be easily differentiated by SERS-based principal component analysis (PCA). Furthermore, the morphological changes of early and late-stage apoptotic cells were illustrated by differential interference contrast and fluorescence microscopic imaging. Therefore, the natural ingredient, cordycepin, could serve as a promising anticancer candidate. Our biological model of cell apoptosis in vitro, the non-invasive and rapid SERS technique, combined with PCA analysis, could be a powerful tool in the investigation of cell apoptosis mechanisms and anticancer drug screening.
Raman observation of a molecular signaling pathway of apoptotic cells induced by photothermal therapy
