*2.2. The E*ff*ect of rHct-S3 on Cell Viability*

In order to determine the cytotoxic effect of rHct-S3, the panel of human cancer cell lines HT-29 (colorectal carcinoma), MDA-MB-231 (triple negative breast cancer), SK-MEL-28 (malignant melanoma), as well as normal mouse epidermal JB6 Cl41 cells and human embryonic kidney HEK 293 cells were treated by rHct-S3 at a concentration range 0.01 μM–10 μM for 24 h and cell viability was estimated by MTS assay. rHct-S3 had comparable effects on viability of cell lines with an IC50 of 8.6 μM for JB6 Cl41 cells (Figure 2a), 8.5 μM for HEK 293 (Figure 2b), 6.8 μM for HT-29 cells (Figure 2c), 7.3 μM for MDA-MB-231 cells (Figure 2d), and 8.3 μM for SK-MEL-28 cells (Figure 2e).

**Figure 2.** The effect of rHct-S3 on cell viability of (**a**) normal mouse epidermal cells JB6 Cl41, human (**b**) embryonic kidney HEK 293, (**c**) colorectal carcinoma HT-29, (**d**) breast cancer MDA-MB-231, and (**e**) melanoma SK-MEL-28 cell lines. The cytotoxic activity was determined by MTS assay after 24 h of treatment. The results are expressed as the percentage of inhibition that produced a reduction in absorbance by rHct-S3 treatment compared the non-treated cells. Results are expressed as the mean ± standard deviation (SD).
