Evaluation of cytotoxic effects of capillene and 2,4-pentadiynylbenzene isolated from Artemisia campestris subsp. variabilis (Ten.) Greuter essential oil and identified by NMR studies

Artemisia is a vast genus of the Asteraceae family, comprising around five-hundred species, that has a large distribution in Europe, America, Asia, and Australia. Species of this genus have been reported to have several ethnopharmacological activities, and some of them are also largely used as food and spices. Artemisia campestris subsp. variabilis (Ten.) Greuter is a quite rare species endemic to Sicily, Sardinia, and Southern Italy. Seeking to delve deeper into the phytochemistry and pharmacological aspects of this species, in this work we investigated the essential oil (EO) obtained from the aerial parts of Sicilian accessions, hitherto unexplored, growing wild near Messina, Italy. The chemical composition of the EO, obtained by hydro-distillation method, was evaluated by GC and GC–MS. The most abundant constituent was capillene (36.45 %), principal representative of the alkynes class (50.69 %). However similar amount of hydrocarbon monoterpenes was identified (49.18 %), with β-pinene present at 35.31 %. The two alkyne compounds were confirmed by isolation and 1H NMR and 13C NMR spectroscopic characterization. The EO and its main constituents have been tested for possible cytotoxic activity against three human tumor cell lines (A375, MDA-MB 231, and CaCo2) and a human non-tumor cell line (HEK293) using the MTT assay. The EO showed remarkable cytotoxic activity against all cell lines tested with IC50 values ranging between 7.55 μg/mL and 23.05 μg/mL. 2,4-Pentadiynylbenzene exhibited potent cytotoxic activity with IC50 values ranging between 0.25 and 0.45 μg/mL for HEK293 and CaCo2 cells, respectively, while capillene showed very similar IC50 values ranging between 0.14 and 0.52 μg/mL for A375 and CaCo2 cells, respectively. The results demonstrated a remarkable cytotoxic activity against human tumor cell lines and suggest that A. campestris subsp. variabilis EO and could be regarded as a natural bioactive source and, in the future, further analyses could clarify the mechanism of action of the EO and its main constituents.