## 3 Results
### Selectivity Index of S. triloba Acetone Extract for U2 OS and SKOV3 Cells  
The selectivity index of _S. triloba_ for U2 OS and SKOV3 cells was calculated in order to assess the extent to which _S. triloba_ selects for cancer cells over noncancerous ones. U2 OS cells treated with _S. triloba_ displayed the greatest SI (2.51) while SKOV3 cells treated with _S. triloba_ had a SI of 1.00. When compared with respective positive controls, the SI (1.167) of U2 OS cells treated with cisplatin was about 2-fold lower than the SI of those treated with _S. triloba_; on the other hand, SI (1.316) of cells treated with paclitaxel was slightly higher than the SI of those treated with _S. triloba_. The dose response curves of Hek-293 cells as well as the obtained IC\({}_{50}\) values are presented in Figure S4 and Table S2 respectively. All calculated SI values are summarized in Table S3. The Combination of S. triloba Acetone Extract and Pallitaxel Exhibits Strong Synergism in SKOV3 Cells  
Drug combination analysis using CompuSyn software facilitated the determination of dose-effect relationships for both _S. triloba_ acetone extract and paclitaxel independently, as well as in combination. This analysis aimed to determine whether the combined treatment produces synergistic, additive, or antagonistic effects. Dose-effect data for each treatment independently and in combination indicated a general reduction in SKOV3 cell viability with increasing treatment concentrations (Table 3). A dose-effect plot was generated and used to determine the potency of each treatment after linearization into the median effect plot. The least median effect dose (the dose that results in 50% effect) was observed for paclitaxel (0.221 ug/mL), followed by the combination treatment (13.8357 ug/mL), and _S. triloba_ (50.928 ug/mL) (Table 4 and Figure 3). By law of mass action, the median effect doses (Dm) were utilized to determine combination indices (CI) for the combined treatment. CI values less than, equal to, and greater than 1 are indicative of synergistic, additive, and antagonistic effects respectively [38; 39]. Synergism was observed at only one of the tested combined concentrations (19 ug/mL of _S. triloba_ + 0.787 ug/mL of paclitaxel), CI = 0.6415. An over 85% decrease in SKOV3 cell viability was observed for this combination (Table 5 and Figure 4A). The CompuSyn software further simulated dose reduction indices (DRI) at all experimental points tested. DRI values greater than 1 indicate that the dose of a specific drug can be reduced when used in combination. On the other hand, DRIs less than 1 are non-favourable for dose reduction [38; 39]. The combination treatment that exhibited synergy had a DRI above 1 for each of the single drug concentrations involved (Table 6 and Figure 4B). The detailed CompySyn report can be accessed in the Supplementary Material (File S1). \begin{table}
\begin{tabular}{l l l} \hline \hline
**Effect \({}^{*}\)** & **DRI S. _triloba_** & **DRI Paclitaxel** \\ \hline
0.01 & 0.9904 & 0.3907 \\ \hline
0.8833 & 28.3034 & 1.6498 \\ \hline
0.8571 & 10.7945 & 0.6729 \\ \hline
0.8345 & 4.4115 & 0.2891 \\ \hline
0.8105 & 1.8205 & 0.1251 \\ \hline
0.9 & 2.1655 & 0.1201 \\ \hline \hline \end{tabular} \({}^{*}\)Fraction of cells inhibited by treatment.  
\end{table} 
Table 6: Dose reduction index (DRI) values calculated at experimental points for SKOV3 cells. Figure 3: Dose-effect curve and median effect plot of the combination experiment in SKOV3 cells. Using dose and effect data obtained from the MTT assay, the CompuSyn software was used to plot the dose–effect curve (**A**); as a prerequisite for determining synergism or antagonism, the dose effect curve is utilized to determine the potency of each drug individually along with the drug combination. The dose–effect plots can be better visualized by linearization in the median effect plot (**B**); the antilog of the x-intercept of the median effect plot gives the median effect dose (Dm) which signifies the potency of each drug (the dose that results in 50% effect).