## 2 Results and Discussion
### Biological Activity
#### 2.5.2 Cytotoxic Activity  
The biological activities of plant-based materials, including anti-tumour activity, are often correlated with the type and concentration of their phenolic compounds in their chemical composition [5; 6]. From this perspective, each bee pollen sample was screened for their potential and in vitro cytotoxic activity against human cancer-derived cells, and a non-tumour cell line was used as a control. When evaluating cytotoxic activity, a lower 50% growth inhibition (GI\({}_{50}\)) value corresponds with higher cytotoxic activities, and values higher than 1000 ug/mL were considered to be inactive against the tested tumour cell lines. The GI of the cells was not significant (GI\({}_{50}\) > 1000) for all bee pollen extracts against AGS, CaCo, HeLa, and NCI tumour cell lines (Table 6). Among the bee pollen factions, BP1, BP6, and BP7 exhibited cytotoxicity effects exclusively against the MCF-7 cell line--breast adenocarcinoma. The cytotoxic GI\({}_{50}\) value of BP6 and BP7 against the MCF-7 tumour cell line was recorded as 814 \(\pm\) 10.0 ug/mL and 746 \(\pm\) 1.0 ug/mL, respectively. These values did not indicate any notable cytotoxic activity. However, BP1 showed effective cytotoxic activity against the same cell line with a value of 17 \(\pm\) 1.1 ug/mL. Even though BP6 and BP7 showed a higher concentration profile in terms of bioactive compounds when compared with BP1, a lower cytotoxic activity could be attributed to the presence of some specific bioactive compounds in the BP1 chemical composition. As shown in Table 3, the presence of various flavonoids (especially kaempfer, which was only determined to have a relatively high concentration in BP1) may be responsible for its anti-tumour activity. This was investigated previously by [PERSON] et al. [44]. In this study, it has been demonstrated that kaempfer is a chemopre compound that significantly inhibited triclosan and bisphenol A-induced breast cancer cell proliferation and anti-apoptosis effects; this occurred via the regulation of pro- and anti-apoptosis, production of reactive oxygen species, and stress response-related genes. Moreover, in a literature review with a similar perspective, the researchers discussed the issue, and presented ample evidence to support the efficacy of flavonoids on breast cancer [45], which \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Cell Lines**} & \multicolumn{6}{c}{**GI\({}_{50}\), ug/mL**} \\ \cline{2-7}  & **BP1** & **BP2** & **BP3** & **BP4** & **BP5** & **BP6** & **BP7** \\ \hline AGS & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ CaCo-2 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ HeLa & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ MCF-7 & \(17\pm 1\) & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ NCI-H460 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ hFOB & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 & \textgreater{}1000 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Cytotoxicity activity (GI\({}_{50}\) values, ug/mL) of BP samples (\(n\) = 3, mean \(\pm\) SD). is in alignment with our results. Moreover, [PERSON] et al. [46] showed that quercetin inhibited MCF-7 and MDA-MB-231 cells, as evaluated by apoptosis and cell cycle phase measurements. On the other hand, none of the tested bee pollen extracts showed toxic effects against a normal cell line (hFOB (human fetal osteoblastic)).