GC-MS Analysis and In Vitro Cytotoxic Effects of Ocimum gratissimum (Lamiaceae) Volatile Oil and Thymol on Cancer Cells

Background: Cancer is one of the most prominent causes of death worldwide. Ocimum gratissimum Linn. (Lamiaceae) leaves are used in many countries as a spice or medicine. Objectives: This study investigated the essential oil of the O. gratissimum leaves and its major constituent, thymol, for cytotoxic activity against breast (AU565) and cervical (HeLa) cancer cell lines. Methods: Preliminary screening was carried out using bench-top assay methods for cytotoxicity involving the use of tadpoles of Raniceps raninus (10-40 μg/mL) and brine shrimp of Artemia salina (10-1000 μg/mL) and growth inhibition using radicle of Sorghum bicolor seeds (1-30 mg/mL). Antiproliferation was verified by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Chromatographic separation of the oil resulted in fractions and sub-fractions, which were also subjected to biological testing. The components of the oil and active subfraction were further identified by gas chromatography-mass spectrometry (GC-MS). Results: Remarkable cytotoxic activities were seen against R. raninus tadpoles and A. salina nauplii. Growth inhibitory activity on S. bicolor seed radicles was produced concentration-dependent. The subfraction possessed greater cytotoxic activity on the cell lines than the oil, with inhibitory action of +85.07% and +29.20% against AU565 and HeLa cells, respectively. Thymol was the major constituent of the oil (22.49%) and increased to 94.31% in the subfraction.