## 3 Results  
### Quantitative and LCMS-Based Screening of Phytoconstituents  
The quantitative determination of phenol products in the different extracts of _A. tetracantha_ was determined spectrophotometrically. Among these, methanol extract had higher phenol derivatives (277.35 \(\pm\) 10.4 mg GAE/g) followed by acetone extract (175.34 \(\pm\) 8.8 mg GAE/g). In the petroleum ether extract, the lowest recording of the phenol compounds was observed. Corroborating this, the flavonoid content was also higher in the methanol and acetone extracts (Table 2). The liquid chromatographic analysis coupled with the mass spectra indicated the presence of various phenolic acids and also complex flavonoid compounds in the methanol extract (Supplementary Material S1).  
Anti-Proliferative Activity of _A. tetracantha Methanol Extract_ and _Changes in the Cellular Redox Status_  
Figure 1a indicates the anti-proliferative potential of the extract in both Kato-III and AGS cells in a dose-dependent manner over 48 h (\(p\) < 0.01). However, the toxicity was lower in the non-cancerous human embryonic kidney cells, possibly indicating its selective anticancer properties (Figure 1a). The IC50 values of the extract in Kato-III cells was found to be 44.69 \(\pm\) 1.09 \(\mu\)g/mL and the same in AGS cells was 58.04 \(\pm\) 1.32 \(\mu\)g/mL; however, the cytotoxicity was significantly lower (\(p\) < 0.001) in non-cancerous HEK293 cells with an IC50 value of 109.75 \(\pm\) 1.85 \(\mu\)g/mL. Furthermore, the addition of reduced glutathione to the cells along with _A. tetracantha_ extracts induced a reduction in the toxic effect of the extract; furthermore, the addition of BSO, an inhibitor of glutathione biosynthesis, enhanced the cytotoxicity of the plant extract in cells (Supplementary Material S2a,b).  
Additionally, when the _A. tetracantha_ is exposed to the HEK293 cells at dose of 45 and 60 \(\mu\)g/mL (close to the IC50 doses in Kato-III and AGS cells), the observed % cell death was nearly 18% and 25%, respectively; this in turn confirms the significantly lower toxicity of _A. tetracantha_ in the cancerous cells (Supplementary Material S3). As indicated in Table 3, the cellular antioxidant levels and lipid peroxidation indicators in the cells (AGS and Kato-III) exposed to different concentrations of _A. tetracantha_ methanol extract were altered. The catalase activity was significantly increased in the different doses of _A. tetracantha_ methanol extract (\(p\) < 0.05); on the contrary, we observed a significant and dose-dependent reduction in reduced glutathione (GSH). Similarly, a corresponding increase in the lipid peroxidation products (TBARS and conjugated dienes) was observed after the different doses of _A. tetracantha_ methanol extract.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Parameters** & **Petroleum Ether** & **Chlororform Extract** & **Acetone Extract** & **Methanol Extract** \\ \hline Total phenols (TPC) & 72.35 \(\pm\) 4.3 & 92.22 \(\pm\) 4.1 1  & 175.34 \(\pm\) 8.8 1  & 277.35 \(\pm\) 10.4 1  \\ Total flavonoids (TP) & 11.05 \(\pm\) 1.5 & 13.19 \(\pm\) 2.6 1  & 29.67 \(\pm\) 3.4 1  & 48.06 \(\pm\) 3.8 1  \\ \hline \end{tabular}  
\end{table}
Table 2: The quantitative analysis of the predominant phytoconstituents of the different extracts of _A. tetracantha_ by spectrophotometric methods.  
Figure 1: Inhibitory potential of _A. tetracanthu_ on the proliferation of neoplastic cells of human gastric origin (**a**). qPCR-based detection of apoptotic gene expression in the different gastric neoplastic cells: Kato III (**b**) and AGS cells (**c**). The fold change in expression of each gene was calculated by the \(2^{-\Delta\Delta\text{CT}}\) method in comparison with the untreated control cells. (*** indicate \(p<0.001\)).