Structural differences in diarylheptanoids analogues from Alnus viridis and Alnus glutinosa influence their activity and selectivity towards cancer cells

• Nine diarylheptanoids, including a new compound 4v, were isolated from the bark of Alnus viridis.
• Activity of A. viridis diarylheptanoids was compared to structural analogs from Alnus glutinosa.
• Presence of 3′ and 3″-OH groups had negative influence on cytotoxic activity.
• Carbonyl group at C-3 positively affected cytotoxicity of A. viridis diarylheptanoids.
• Small chemical structure differences had major effect on cell cycle, apoptosis and redox status.

Diarylheptanoids represent a group of plant secondary metabolites that possess multiple biological properties and are increasingly recognized for their therapeutic potential. A comparative study was performed on structurally analogous diarylheptanoids isolated from the bark of green (Alnus viridis) and black alder (Alnus glutinosa) to address their biological effects and determine structure-activity relationship. The structures and configurations of all compounds were elucidated by NMR, HR-ESI-MS, UV and IR. Diarylheptanoids actions were studied in human non-small cell lung carcinoma cells (NCI-H460) and normal keratinocytes (HaCaT). A. viridis compounds 3v, 5v, 8v and 9v that possess a carbonyl group at C-3 were considerably more potent than compounds without this group. A. viridis/A. glutinosa analogue pairs, 5v/5g and 9v/9g, which differ in the presence of 3′ and 3″-OH groups, were evaluated for anticancer activity and selectivity. 5v and 9v that do not possess 3′ and 3″-OH groups showed significantly higher cytotoxicity compared to analogues 5g and 9g. In addition, these two A. viridis compounds induced a more prominent apoptosis in both cell lines and an increase in subG0 cell cycle phase, compared to their A. glutinosa analogues. 5v and 9v treatment triggered intracellular superoxide anion accumulation and notably decreased mitochondrial transmembrane potential. In HaCaT cells, 9v and 9g with a 4,5 double bond caused a more prominent loss of mitochondrial transmembrane potential compared to 5v and 5g which possess a 5-methoxy group instead. Although green alder diarylheptanoids 5v and 9v displayed higher cytotoxicity, their analogues from black alder 5g and 9g could be more favorable for therapeutic use since they were more active in cancer cells than in normal keratinocytes. These results indicate that minor differences in the chemical structure can greatly influence the effect of diarylheptanoids on apoptosis and redox status and determine their selectivity towards cancer cells.

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