## 4 Discussion  
The objectives proposed in the present work were to evaluate the antiproliferativeativity on human colon cancer cell Caco-2 of the ethanolic extract from _Stokesia laevis_ plant species (codified Slae26), of five food-related polyphenols compounds (reference substances, ref.) selected based on precise criteria, and of Slae26 combinations with the five reference substances in a manner that ensured 1:1 mass rate (_w/w_) between the active compounds in the combined samples (GAE, ref.). The selection of the five polyphenols compounds, namely luteolin-7-O-glucoside (cinnaroside), luteolin-8-C-glucose (orientin), caffeic acid, gentisic acid, and p-amino benzoic acid (PABA), is supported by the following criteria: Luteolin monoglycosides are the major flavonoid compounds in _Stokesia laevis_ ethanolic extracts, and the main contributor on antiproliferative activity of Slae26 in the authors' works [33, 34], as also results from the literature data today [47, 48, 49, 50, 51]; caffeic acid is the foremost compound in human diet resulting from the metabolism of (iso)chlorogenic acid esters, also the subject of active transport in humans, therefore it can be considered the food-related bioactive compound with the largest and constant presence in the human intestine; moreover, studies proved its ability to protect the human peripheral blood lymphocytes against the cellular damages induced by gamma radiation (gamma radiation is used in radio-oncology to treat cancer patients), therefore the combination of a natural antiproliferative product with a natural radiation guardian is of interest for humans [52]; gentisic acid is a highly active antioxidant compound proven to enhance the activity of antioxidant enzymes in humans, at the same time acting as an inhibitor of lipid peroxidation in cell membranes, and is also demonstrated to effectively protect human erythrocytes against gamma radiation exposure [53, 54, 55]; benzoic acid is a natural phenolic acid with antibacterial activity [56] used as a preservative in food [57]; it also can be found in fermentation products such as Caciocavallo and mozzarella cheeses [58]. In this context, cytotoxicity MTS tests were designed to investigate both the effects of the five reference compounds applied on Caco-2 cells at the time when about 70% of the predicted \"sub-confluent\" cells had occurred, and the effects on Caco-2 cells viability of ethanol solvent in the test samples. Strong inhibitory effects of control (70%) ethanol solvent series on the viability of Caco-2 cells, more augmented than that of the test samples, made it impossible to draw a conclusion on the cytotoxicity of the reference compounds; yet, caffeic and gentisic acid diagrams' aspect at 24 h and 48 h both suggest their ability to protect intestinal cells against the cytotoxic effects of ethanol solvent. Antiproliferative MTS tests on the five reference compounds, applied on Caco-2 cells at the time when about 30% of the predicted \"sub-confluent\" cells had occurred, indicated certain antiproliferative effects of gentisic acid, caffeic acid, p-aminobenzoic acid (PABA) and luteolin-7-O-glucoside in the range of 10-25 \(\mu\)g/mL sample, after that the activity of the reference compounds series being substantially matching with that of the control solvent (70% ethanol) dilution series. The Slae26 test sample, in comparison with own control solvent (40% ethanol) dilution series, indicated certain inhibitory activity of the vegetal extract upon the viability of the human tumor cancer cell Caco-2 (IC\({}_{50}\) = 36 \(\mu\)g GAE/mL sample), and therefore is similar to that previously found for human breast cancer cell line BT20 (IC\({}_{50}\) = 42 \(\mu\)g GAE/mL sample) [33] and murine melanoma cell line B16 (IC\({}_{50}\) = 39 \(\mu\)g GAE/mL sample) [34].