Table 3.
Polar Face Substitutions of Positively Charged Residues
| peptide namea | net charge | peptide Mass | HC50 (μg/mL)b | HC50 (μM)b | HC50 fold improvementc | MICGM (μM)d | T.I.e | T.I. fold improvementf |
|---|---|---|---|---|---|---|---|---|
| with specificity determinants | ||||||||
| D87(Lys1-6 Arg-1) | +9 | 3033.7 | 12 | 4.0 | 1.0 | 0.8 | 5.0 | 1.0 |
| D84(Lys1-6 Lys-1) | +9 | 2865.6 | 155.5 | 54.3 | 13.6 | 0.5 | 108.6 | 21.7 |
| D85(Lys1-6 Orn-1) | +9 | 2781.5 | 406.5 | 146.1 | 36.5 | 0.5 | 292.2 | 58.4 |
| D86(Lys1-6 Dab-1) | +9 | 2697.3 | >2000 | >742 | >186 | 1.0 | >742 | >148 |
| D105(Lys1-6 Dap-1) | +9 | 2613.1 | >3000 | >1148 | >287 | 1.2 | >957 | >191 |
| D101(Lys1Ser26-5 Lys-1) | +8 | 2824.5 | 279 | 103.9 | 26.0 | 0.8 | 129.9 | 26.0 |
| D102(Lys1Ser26-5 Dab-1) | +8 | 2684.3 | >2000 | >708 | >177 | 0.7 | >1012 | >202 |
| without specificity determinants | fold decreasec | fold decreasef | ||||||
| D85(K13A/K16A)-(Lys1-6 Orn-1) | +7 | 2667.3 | 2.3 | 0.9 | −162.3 | 2.0 | 0.5 | −584.4 |
| D86(K13A/K16A)-(Lys1-6 Dab-1) | +7 | 2583.1 | 20.0 | 7.7 | >−96.4 | 0.9 | 8.6 | >−86.3 |
| D105(K13A/K16A)-(Lys1-6 Dap-1) | +7 | 2499.0 | 7.2 | 2.9 | >−395.9 | 1.3 | 2.2 | >−435.0 |
6 Lys-1 denotes 6 Lys residues on the polar face at positions 3,7,11,18, 22, and 26. 5 Lys-1 denotes 5 Lys residues on polar face at positions 3, 7,11,18, and 22 (position 26 is substituted by Ser).
Hemolytic activity, HC50, is the concentration of peptide that results in 50% hemolysis of human red blood cells after 18 h at 37°C.
Fold improvement in hemolytic activity, HC50, relative to the Arg-containing peptide. Fold decrease compares the same peptide with and without specificity determinants. That without specificity determinants shows a dramatic fold decrease in HC50.
MIC is minimal inhibitory concentration (μM) that inhibited growth of different strains in MH medium at 37°C after 24 h, with the MIC based on three sets of replicates; MICGM is the geometric mean of the MIC values from seven different strains of A. baumanii resistant to polymyxin B and colistin, antibiotics of last resort.
Therapeutic index (T.l.) was calculated from HC50 (μM)/MICGM (μM). Fold decrease compares the same peptide with and without specificity determinants. That without specificity determinants shows a dramatic fold decrease in the therapeutic index.
Fold improvement in the therapeutic index, relative to the Arg containing peptide.