*2.10. Correlation of EC50 Values with the Doubling Times of the Cell Lines*

Examination of the EC50 values for each OOP showed significant variations in the analyzed cancer cell lines of different tissue origin but also amongst cell lines of the same tissue origin but with different genetic characteristics (Table 1) To examine if the speed of proliferation of each cell line correlated to these results, the doubling time of each cell line was calculated (Table S2A) using the MTT assay (Experimental Section) which gave similar results to those obtained with the ATP assay (Figure S4). Overall, no clear correlation was detected between the EC50 values for each OOP and the doubling time of the cell lines.

In more detail, for the breast cell lines presented as representative examples (Table S2B), the slower-growing cell line SK-BR-3 was more sensitive to treatment with all OOPs as compared to the MCF-7 cell line with approximately the same doubling time. However, when compared with the faster-growing MDA-MB 231 cell line, the SK-BR-3 cells seemed to be more resistant to oleocanthal (**1**) and oleacein (**2**) treatment and more sensitive to treatment with the aglycones (i.e., (**3a,b**), (**4a,b**)). As for the skin cell lines, although they had comparable doubling times, the SK-MEL-28 was the most sensitive. It is worth mentioning that for the stomach cancer cell lines studied (i.e., the AGS and MKN-45 cells), the slower-growing cell line (i.e., AGS) seemed to be more resistant to treatment with all OOPs (higher EC50 values) as compared to the MKN-45 cells. The same trend was followed in the results for the colon cancer cell lines, but only for the treatment with the two aglycones ((**3a,b**) and (**4a,b**)) and oleomissional (**6a,b,c**) while for oleocanthal (**1**) and oleacein (**2**) the opposite trend was observed (Table 1 and Table S2). Moreover, the exact opposite trend was observed with regard to the lung cancer cell lines. Specifically, the H1437 cells growing faster than the H1299 cells seemed to be more resistant to treatment with oleocanthal (**1**) or oleacein (**2**) than the H1299 cell line. On the other hand, the H1437 cells were more sensitive to treatment with the other three OOPs (i.e., ligstroside aglycone (**4a,b**), oleuropein aglycone (**3a,b**) and oleomissional (**6a,b,c**)) in comparison to the other cell line of the same tissue origin. Finally, concerning the cervical cancer cell lines, it seemed that Hela, a highly proliferative cell line, is more resistant to OOPs treatment as compared to the ME-180 cancer cervical cells.

In summary, the above-commented results indicated that the EC50 values calculated in this study for each OOP tested (Table 1 and Figure 3) were cell type-specific and did not correlate with the doubling time of the cell lines (Table S2B).
