Different propolis samples, phenolic content, and breast cancer cell lines: Variable cytotoxicity ranging from ineffective to potent.

Researchers have started focusing on investigating the anticarcinogenic effects of natural products with the slightest side effects possible, because current breast cancer treatment approaches are unable to achieve absolute success especially on aggressive subtypes. Propolis is among these products with its antimicrobial, antifungal, anti-inflammatory, and anticancer effects. Therefore, seven different samples were collected from different regions (Argentina, China, and Istanbul-Turkey) and applied on nonaggressive breast cancer cell line (BCCL) MCF-7 and aggressive cell lines SK-BR-3, and MDA-MB-231. Initially, the phenolic/flavonoid constituents of the propolis ethanol extracts were investigated by liquid chromatography-mass spectrometry-mass spectrometry (LS-MS/MS) and high-performance liquid chromatography (HPLC) analyses. Then, the anticarcinogenic effects of the propolis samples on MCF-7, SK-BR-3, MDA-MB-231 were evaluated by WST1 analysis and only selected ones on MCF-10A and hPdLF. According to the LS-MS/MS and HPLC analysis, Turkey originated propolis (Turkey3) were found to be richer than the other propolis samples in terms of phenolic/flavonoid compounds. Turkey propolis significantly inhibited cell proliferation in both nonaggressive and aggressive BCCL (P < 0.01). Therefore, Turkey3 propolis was selected for further evaluation using Annexin V-PI apoptosis detection assays. In addition, selected compounds among the propolis contents such as galangin, caffeic acid, apigenin, quercetin, and ferulic acid were applied to the MCF-7 cell line to detect cytotoxic and apoptotic effects. Galangin, caffeic acid, apigenin, and quercetin remarkably induced cell proliferation inhibition at all time intervals, whereas ferulic acid was found non efficient on the MCF-7 cell line. Annexin V-PI assay clarified that all cell proliferation inhibitions were markedly apoptotic. Our findings indicated that the inhibition effect of propolis on breast cancer cell proliferation was in a propolis type-, dose- and time-dependent fashion. Turkey3 propolis showed statistically significant cytotoxic effects on both the nonaggressive and aggressive BCCL. These findings were consistent with the effects of its rich phenolic and flavonoid contents, in terms of variety. © 2018 IUBMB Life, 71(5):619-631, 2019.