3.3.7. Cytotoxicity

Secondary metabolites from various plant species have become highly researched as alternative therapeutic agents for various diseases, including cancer. Interestingly, in the United States more than 60% of anticancer drugs approved from between 1983 and 1994 were of natural origin [64,65]. While their efficacy towards certain cancer types is encouraging, it is crucial that their toxicity towards normal healthy cells remain low to obtain the highest level of efficacy and specificity towards cancer cells. The toxicity of the ethanolic extract of *S. perfoliata* was investigated against cancerous and non-cancerous cells (Table 2). According to Kuete and Efferth [66], a plant extract is considered significantly toxic if it shows an IC50 value lower than 100 μg/mL when tested on normal cell lines in vitro, while IC50's between 100 and 300 μg/mL constitute moderate toxicity, those between 300 and 1000 μg/mL exhibit low toxicity, and those above 1000 μg/mL exhibit no in vitro toxicity. When investigating cancerous cell lines, plant extracts exhibiting IC50's lower than 20 μg/mL are considered to have significant anticancer activity, while moderate toxicity constitutes those values ranging between 20 and 50 μg/mL, low toxicity between 50 and 200 μg/mL, and no toxicity towards cancerous cells for values higher than 200 μg/mL. According to these thresholds, the ethanolic extract of *S. perfoliata* showed moderate toxicity towards the non-cancerous Vero and HaCat cells with IC50 values of 201.5 ± 3.32 and 134.3 ± 10.1 μg/mL, respectively. Low toxicity towards all the cancerous cell lines was noted with IC50 values of 103.15 ± 0.92, 133.25 ± 10.45, 64.27 ± 2.04 and 102.5 ± 0.99 μg/mL against UCT-MEL-1, A431, HepG2 and HeLa cells respectively (Table 2). Although the activity of the ethanolic extract was found to have low toxicity against HepG2 cells, the toxicity against this cell line was much higher than on the other cancerous cell lines. In a study by Loizzo et al. [67], the activity of the essential oil of *S. perfoliata* against amelanotic melanoma (C32) and renal cell adenocarcinoma (ACHN) was found to exhibit moderate toxicity with IC50 values of 95.58 and 100.90 μg/mL respectively, further supporting the cytotoxic effects of the *S. perfoliata*. The essential oil was, however, not toxic to human breast cancer (MCF-7) and human prostate cancer (LNCap) cells with IC50 values above 400 μg/mL.
