Fig 1.
Schematic half antibody exchange and respective nBT062 model antibodies.
(A) Overview of in vivo IgG4 half antibody exchange mainly driven by the potential to form either interchain or intrachain disulfide bonds in the hinge region. A S228P mutation increases the sterical distance of the two cysteines preventing intrachain disulfide bonds. (B) Generated nBT062 model antibodies: Wild type (WT) nBT062, stable nBT062, half nBT062 and bispecific nBT062-natalizumab. Respective mutations are indicated.
Table 1.
Tumor control efficacy criteria.
Fig 2.
Analytical characterization of nBT062 model variants.
(A) Reducing and non-reducing SDS-PAGE analysis of indicated nBT062 variants. L = light chain, H = heavy chain, HL = half antibody, H2 = heavy chain dimer, H2L2 = intact antibody. Molecular weight and antibody explanations are representative for reducing and non-reducing conditions. (B) Indicated nBT062 model variants were separated by isoelectric focusing and blotted onto a PVDF membrane. Selective BT062 and natalizumab specificities were detected by anti-idiotypic antibodies visualized in green and red respectively. The bispecific nBT062-natalizumab fraction is showing two natalizumab exclusive bands.
Fig 3.
nBT062 model variants selectively bind to CD138+ cells in a dose-depended manner.
BaF3-hCD138 cells, positive for nBT062 antigen and negative for natalizumab antigen (A), and Jurkat cells, negative for nBT062 antigen and positive for natalizumab antigen (B), were incubated with different concentrations (5x10-7–2.82x10-12 M) of WT nBT062, stable nBT062, half nBT062 and bispecific nBT062-natalizumab antibodies. Data was obtained via flow cytometry using a secondary anti-human antibody for detection. Binding curves demonstrate one representative experiment out of three, each measured in triplicates. MFI = Median Fluorescence Intensity.
Table 2.
Antibody binding affinities towards BaF3-hCD138 (CD138+/CD49d-) and Jurkat (CD138-/CD49d+) cells calculated from binding curves of Fig 3.
Fig 4.
All nBT062 model variants are internalized in vitro.
(A) Schematic overview of measured binding/internalization status of fluorescent labeled antibodies. (B) Flow cytometric internalization analysis of WT nBT062, stable nBT062, half nBT062 and bispecific nBT062-natalizumab. CD49d was blocked by 50x excess of unlabeled natalizumab. Data represent median fluorescence intensity values of at least three separate experiments. Column colors represent antibody location as shown in (A). ****p<0.0001, ***p<0.001. (C) Fluorescence microscopy of BaF3-hCD138 (CD138+) cells (I-V) or BaF3 (CD138-) control cells (VI) incubated for 3h with indicated Dylight-448 labeled nBT062 model antibodies or natalizumab (green, a). Lysosomal-associated membrane protein-1 (LAMP-1) is shown in red (b), nucleus is shown in blue (c). Respective overlay pictures are demonstrated (d).
Table 3.
DM4-to-antibody ratios of wild type (WT), stable and half nBT062 and bispecific nBT062-natalizumab.
Table 4.
Binding avidity of unconjugated or DM4-conjugated WT nBT062, stable nBT062, half nBT062 and bispecific nBT062-natalizumab to CD138-positive cells measured by flow cytometry in three independent experiments.
Fig 5.
nBT062-DM4 model variants kill CD138+ NCI-H929 tumor cells in vitro.
NCI-H929 cells (CD138+/CD49d+) were incubated for 5 days with varying concentrations of WT nBT062-DM4, stable nBT062-DM4, half nBT062-DM4 and bispecific nBT062-natalizumab-DM4 antibodies. Natalizumab was used for CD49d blocking. Reciprocal IC50 values of each antibody-drug conjugate were normalized to WT nBT062-DM4 and one DM4 molecule per antibody. Results are shown from three separate experiments each measured in triplicates. *p<0.05, **p<0.01.
Fig 6.
Half-antibody exchange preventing mutations of nBT062-DM4 models improve the tumor growth inhibition in the presence of human IgG against CD138+ human mammary carcinoma xenografts in NMRI nude mice.
Mice bearing established xenograft tumors were treated with three once weekly i.v. injections (indicated by arrows) of WT nBT062-DM4, stable nBT062-DM4, half nBT062-DM4 and bispecific nBT062-natalizumab-DM4 either alone or in combination with a 10% intravenous immunoglobulin G (IVIg) preparation administered i.v. 10 ml/kg/week. PBS was used as vehicle control and IVIg was also tested as monotherapy. The nBT062-DM4 model variants were tested using doses of 4 mg/kg/week or 2 mg/kg/week.
Fig 7.
Half-antibody exchange preventing mutations of nBT062-DM4 models improve survival in the presence of human IgG against CD138+ human mammary carcinoma xenografts in NMRI nude mice.
Survival curves respective to tumor growth curves from Fig 6 are shown. Mice bearing established xenograft tumors were treated with three once weekly i.v. injections of WT nBT062-DM4, stable nBT062-DM4, half nBT062-DM4 and bispecific nBT062-natalizumab-DM4 either alone or in combination with a 10% intravenous immunoglobulin G (IVIg) preparation administered i.v. 10 ml/kg/week. PBS was used as vehicle control and IVIg was also tested as monotherapy. The nBT062-DM4 model variants were tested using doses of 4 mg/kg/week or 2 mg/kg/week.