PC12 Cell Conditional Medium Prepared after Latroeggtoxin-VI Treatment Suppresses Glioma Cells

Latroeggtoxin-VI (LETX-VI) is a proteinaceous toxin found in the eggs of spider Latrodectus tredecimguttatus and was previously shown to promote the synthesis and release of dopamine that has been shown to be an endogenous tumor modulator. Here, the anticancer activity of LETX-VI was investigated from both direct and indirect aspects. LETX-VI was shown to have no obvious direct effects on the tested cancer cell lines including B16-F10, Hela, MDA-MB-231, SMMC7721, A549, U251 and U87-MG cells, but has indirect inhibitory effects on the glioma cells U87-MG and U251 by stimulating the synthesis and release of dopamine and cancer-inhibitory proteins from PC12 cells. Culture of U251 and U87-MG cells with the PC12 cell conditional medium (CM) prepared after LETX-VI treatment remarkably inhibited the proliferation and migration ability of the glioma cells. Dopamine quantitative determination and exogenous dopamine addition experiment demonstrated that the inhibitory effect of the CM on U87-MG and U251 cells was at least partially mediated by the LETX-VI-induced increase in dopamine of the CM. Besides, proteomics analysis of the exosomes secreted from PC12 cells into the CM after LETX-VI treatment suggested that some cancer-inhibitory proteins in the exosomes, particularly the proteins encoded by ROCK2, PIK3R1 and TGFβ1 genes, respectively, might synergize with dopamine to mediate the inhibitory effect of CM on glioma cells. All the observations not only increased our understanding of the biological properties and application prospects of LETX-VI, but also provided new ideas for the prevention and treatment of brain gliomas via the endogenous pathways.