Fig. 1

Bright-field images of 3D colon cancer tumoroids after being exposed to different concentrations of melatonin (A). An inner compact zone is evident at the center of each tumoroids. 48-hour treatment with melatonin did not affect the integrity of spheroids. Measuring survival rate using an MTT assay (B). The survival rate was reduced by increasing the melatonin concentration from 0.005 to 0.8 mM (n = 12). As shown in panel A, melatonin at this range did not affect the integrity of tumoroids. Measuring survival rate using an LDH leakage assay (C; n = 12). Tumoriods were treated with higher melatonin concentrations, 4 to 10 mM, for 48 h. Data confirmed the significant increase of supernatant LDH compared to the control tumoroids, indicating reduced cell membrane integrity in the presence of melatonin. Bright-field images of tumoroids 48 h after being treated with melatonin (D). In non-treated tumoroids, dense and compact tumoroids structures with flattened cells (arrowheads) at the periphery zone are evident. In melatonin-treated groups, cells within the tumoroids parenchyma are disaggregated and these features were more evident in group melatonin 10 mM. Calculation of mean tumoroids diameter (E; n = 12). Melatonin can significantly reduce the diameter of 3D colon cancer tumoroids after 48 h in in vitro conditions. One-Way ANOVA with Tukey post-hoc analysis. *p < 0.05; **p < 0.01; ***p < 0.001; and ****p < 0.0001