. 2020 Oct 19;10:552905. doi: 10.3389/fcimb.2020.552905

Table 5.

Cytotoxic action of СhBac3.4 modifications toward normal or tumor eukaryotic cells and resulting selectivity indices (SI).

	IC₅₀ ^a (μM) of cytotoxic action toward			SI_h/b ^b	SI_n/t ^c
	normal cells:	tumor cells:		$\frac{I C_{50}^{P B M C}}{G M I C}$ [ratio to ChBac3.4^d]	$\frac{I C_{50}^{P B M C}}{\sqrt{I C_{50}^{K 562} ∙ I C_{50}^{U 937}}}$ [ratio to ChBac3.4^d]
Peptides	human PBMC	K562	U937	$\frac{I C_{50}^{P B M C}}{G M I C}$ [ratio to ChBac3.4^d]
ChBac3.4-NH₂	18.6 ± 0.8	15.5 ± 0.3	8.1 ± 0.4	4.0 [=]	1.7 [=]
ChBac3.4-COOH	36.2 ± 6.9	24.4 ± 4.0	12.9 ± 0.3	6.0 [1.5]	2.0 [1.2]
ChBac3.4-1-NH₂	12.1 ± 0.8	8.4 ± 1.1	4.5 ± 1.6	2.1 [0.5]	2.0 [1.2]
ChBac3.4-1-COOH	33.7 ± 3.2	16.5 ± 1.3	9.8 ± 0.5	7.0 [1.7]	2.7 [1.6]*
RFR-ChBac3.4-1-NH₂	18.3 ± 4.1	20.0 ± 3.4	3.2 ± 0.4	3.5 [0.9]	2.3 [1.4]
ChBac3.4-2-COOH	20.2 ± 4.5	13.7 ± 2.3	4.1 ± 0.3	3.7 [0.9]	2.7 [1.6]*
ChBac3.4 (H-)	34.7 ± 7.3	25.0 ± 3.5	11.5 ± 0.5	8.9 [2.2]	2.0 [1.2]
ChBac3.4 (12-26)	43.3 ± 7.7	39.4 ± 2.3	17.0 ± 1.1	1.0 [0.2]	1.7 [1.0]
ChBac3.4 (1-19)-NH₂	>64	28.0 ± 6.5	>64	>4.7 [>1.2]	~1.5 [~0.9]
ChBac3.4 (1-14)-NH₂	>64	33.6 ± 4.1	>64	>3.7 [>0.9]	~1.4 [~0.8]
RFR-ChBac3.4 (1-14)-NH₂	>64	39.4 ± 6.6	>64	>17.3[>4.3]*	~1.3 [~0.8]

PBMC, peripheral blood mononuclear cells; K562, human erythroleukemia cells; U937, human histiocytic lymphoma cells.

Half maximal inhibitory concentrations (IC₅₀) of cytotoxic action were calculated using Sigma Plot Standard Curve Analysis based on data of three independent MTT-tests and are shown as mean ± standard deviation.

Selectivity index illustrating how much the peptide “prefers” damaging bacterial cells over normal human cells (SI_h/b). It was determined by dividing IC₅₀ toward human PBMC by the geometric mean of minimal inhibitory concentrations measured against different bacterial strains (GMIC, see Table 2 ).

Selectivity index demonstrating if toxic effects of the peptide toward tumor cells are higher than toward normal eukaryotic cells (SI_n/t). It was calculated as per the indciated formula, considering the geometric mean of ICs₅₀ toward both tested types of tumor cells.

^d To assess the improvement in either types of selectivity, the ratios of the corresponding SI of the peptide of interest to the corresponding SI of the native ChBac3.4-NH₂ are shown in square brackets. The best improvement results are marked with asterisks.