Table 3

Cytotoxic activity (IC50) in ng/ml of selected RFB4 (Fv)-PE38 mutants on six different CD22-positive cell lines

Cells were seeded at 5 × 104/well in 96-well plate 24 h before the assay. Immunotoxins were added to the plate, and cells were incubated at 37°C for 20 h and then were pulsed with [3H]leucine for 2 h. [3H]leucine incorporations were determined. Each assay was done in triplicate, and, except as noted below, at least three different assays were performed with each cell line. IC50 (expressed in ng/ml) is the toxin concentration that reduced incorporation of radioactivity by 50% compared with the cells that were not treated with the toxin. Mean values of three experiments ± SD are shown. SDs are not listed when the immunotoxins were tested only once. Below each IC50 is the significance in its difference from GSSY (WT) and GTHW when differences by Student’s t test were significant (P < 0.05).

JD38Ca46RajiDaudiNamalwaRamos
GSSY (WT) vs. GTHW2.3 ± 0.53.1 ± 0.25.1 ± 0.158.1 ± 2.310.6 ± 1.2252 ± 3
P < 0.01P < 0.05P < 0.01P < 0.01P < 0.01P < 0.01
GTHW vs. WT0.2 ± 0.091.4 ± 0.51 ± 0.141.7 ± 0.12.8 ± 0.432 ± 3
P < 0.01P < 0.05P < 0.01P < 0.01P < 0.01P < 0.01
GYNW vs. WT vs. GTHW0.6 ± 0.10.80.6 ± 0.072.1 ± 0.55.6 ± 3.3N.D.a
P < 0.01P < 0.01P < 0.01
P < 0.01P < 0.05
GTTW vs. WT vs. GTHW0.7 ± 0.031.7 ± 0.42.75 ± 0.32.0 ± 1.25.3 ± 0.2N.D.
P < 0.01P < 0.05P < 0.01P < 0.01P < 0.01
P < 0.01P < 0.01P < 0.01
GSTY vs. WT vs. GTHW1.124.18.5 ± 0.79.5N.D.
P < 0.01
GKNR vs. WT vs. GTHW561055 ± 725N.D.
P < 0.01
P < 0.01
  • a N.D., not determined.