Heliopsis longipes S.F. Blake (Asteraceae) extract causes cell cycle arrest and induces caspase dependent apoptosis against cancer cell lines

Heliopsis longipes is a common spice and a medicinal plant widely used in Mexico and South America due to its mouth anesthetic, analgesic, and anti-inflammatory properties related to its spilanthol content. Previous reports have demonstrated that N-alkylamides exhibit cytotoxic effect against different cancer cell lines; however, the anti-cancer potential of the species remains unknown. Therefore, we investigated the effects of H. longipes extract (HLE) and spilanthol on HeLa, K-562, MCF-7, and HaCaT cells. HLE displayed significative antiproliferative effects and increased the rate of cell apoptosis on all cancer cell lines tested. These effects were measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, cell counting by flow cytometry, cell cycle analysis, Annexin V-FITC/PI activation, and nuclear DAPI staining. Significant growth inhibition was found, with emphasis to K-562 and MCF-7 cells, exhibiting IC50 values of 87.14 and 134.25 μg/mL, respectively, without inducing substantial damage to HaCaT after 48 h of treatment. Spilanthol displayed a more pronounced inhibitory effect on cell lines, maintaining the selectivity index observed for the extract. Furthermore, real-time polymerase chain reaction revealed that HLE activated caspase 3 and caspase 8 after treatment for 48 h. Annexin V-FITC staining to detect early stage of apoptosis and DAPI staining of chromatin substantiated the cytotoxic effects. GC–MS analysis of the extract confirmed spilanthol as the major constituent present (63.94%), followed by other minor alkamides, which could also contribute to the biological effect observed. These results confirm the induction of apoptosis by Heliopsis longipes as well as the potential usefulness of the species and their alkamides as compounds to develop new anti-cancer agents.