Fig. 2

Predicted mean values and 95% confidence intervals of the survival rates for different equine cells. eRGO1 and MelDuWi = primary equine melanoma cells, PriFi1 and PriFi2 = primary equine dermal fibroblasts. Cytotoxic effects investigated by MTS assay, antiproliferative effects determined by CVS assay. Data represent predicted mean values and 95% confidence intervals of 6–8 independent experiments for each combination of cell type, incubation time and concentration as given by the generalized additive models. BA had a stronger cytotoxic effect when cells were exposed for 24, 48 and 96 h compared to 5 h (P < 0.001 each). While there was a highly significant difference in cytotoxicity between 24 h and 96 h (P < 0.001), cytotoxic effects differed less between 24 h and 48 h (P < 0.01) and 48 h and 96 h (P < 0.05). Equally, there was a statistically significant difference in the cell proliferation between a treatment duration of 5 h compared to 24, 48 and 96 h (P < 0.001 each). A treatment duration of 24 h compared to 48 h, 24 h compared to 96 h and 48 h compared to 96 h revealed a high significance in cell proliferation (P < 0.001 each). A pairwise comparison of all cell types revealed PriFi1 as the most sensitive cell type in MTS assay (P < 0.001 for PriFi1 vs. all other cell types), whereas it was the most resistant one in CVS (P < 0.001 for PriFi1 vs. all other cell types). MelDuWi was the most resistant cell type towards BA’s cytotoxic effects (P < 0.001 for MelDuWi vs. all other cell types). In conclusion, betulinic acid did not show a selectivity to equine melanoma cells compared to normal cells