Acetone extracts of selected plant species were evaluated for their in vitro cytotoxicity against a noncancerous African green monkey
kidney (Vero) cell line and an adenocarcinoma cervical cancer (HeLa) cell line. The plants studied were Origanum vulgare L.
(Oregano), Rosmarinus officinalis L. (Upright and ground cove rosemary), Lavandula spica L. (Lavender), Laurus nobilis L. (Bay
leaf), Thymus vulgaris L. (Thyme), Lavandula x intermedia L. (Margaret Roberts Lavender), Petroselinum crispum Mill. (Curly
leaved parsley), Foeniculum vulgareMill. (Fennel), and Capsicum annuum L. (Paprika). Antioxidant activity was determined using
a quantitative DPPH (1,1-diphenyl-2-picryl hydrazyl) assay. The rosemary species exhibited effective radical scavenging capacity
with 50% inhibitory concentration (IC50) of 3.48 ± 0.218 μg/mL and 10.84 ± 0.125 μg/mL and vitamin C equivalents of 0.351 g
and 1.09 g for McConnell’s Blue and Tuscan Blue, respectively. Cytotoxicity was measured using XTT (Sodium 3 -[1-(phenyl
amino-carbonyl)-3,4-tetrazolium]-bis-[4-methoxy-6-nitro] benzene sulfonic acid hydrate) colorimetric assay. Only L. nobilis and
O. vulgare exhibited pronounced effects on the HeLa cell line. Dose-dependent studies revealed IC50 of 34.46 ± 0.48 μg/mL and
126.3±1.00 μg/mL on theHeLa cells and on the Vero cells 124.1 μg/mL ± 18.26 and 163.8 μg/mL ± 2.95 for L. nobilis and O. vulgare,
respectively. Light (eosin and haematoxylin staining) and confocal microscopy (Hoechst 33342, acridine orange, and propidium
iodide staining) were used to evaluate the cytotoxic mechanism of action for L. nobilis and O. vulgare.