Phytochemical Composition and In Vitro Anticancer Activities of the Marine Coastal Plant Heliotropium curassavicum L. Extract in Different Seasons

Heliotropium curassavicum L.(Family Boraginaceae) is a marine coastal wild herb species, reported to have multiple therapeutic activities including anti-gout, ant-rheumatism, anti-arteriosclerotic and anti-cancer. The aim of the current study is assessing the seasonal changes in the chemical composition and anticancer activities of H. curassavicum collected from Port Said Governorate. The GC-MS analysis was performed to screen the seasonal variation in the phytochemical constituents of the hexane extract of the plant.  GC-MS analysis of hexane extract of H. curassavicum identified the presence of thirty-two, fourteen, thirty-nine and forty-five compounds in winter, summer, autumn, and spring seasons, respectively. The extracts of H. curassavicum in all different seasons share three similar phytocompounds which were hexadecanoic acid, 9-octadecenoic acid (Z) in addition to 9,12-octadecadienoic acid (Z,Z). Erucic acid was the most common compound in autumn and spring, whereas the most prevalent compound in winter was eugenol, while summer extract was dominated by Z,Z. Quantitative phytochemical analysis revealed the seasonal variation in phytochemicals, where flavonoids and phenolic compounds were at a high level in the autumn and summer seasons, while alkaloid levels peaked during autumn and spring. The MTT assay demonstrated that the extract exhibited selective cytotoxic effects on cancer cell lines (HepG2 and MCF-7), with slight preference of autumn season. The underlying mechanism of cytotoxicity of IC₅₀ of the autumn extract against targeted MCF-7 cells resulted in cell cycle arrest at the S phase, accompanied by a significant rise in the proportion of apoptotic cells, as indicated by flowcytometric analyses cell cycle analysis and annexin-V assay. Apoptotic activities of the autumn plant extract were further confirmed by detecting the expression levels of some related genes in MCF-7 cell lines treated with the extract by qPCR, which showed increased expression of pro-apoptotic genes such as P53, BAX, and caspase-8, along with a decrease in the expression of the anti-apoptotic gene BCL-2 upon treatment. Therefore, the results highlight seasonal changes in the chemical composition of H. curassavicum extract, which are associated with differences in its anticancer activity.