Clinical chemistry of human FcRn transgenic mice.

Mice genetically engineered to express human FcRn are valuable models for the evaluation of therapeutic antibodies in the context of human FcRn in vivo. However, only limited clinical chemistry information on these mouse strains is available. Thus, we have compared 30 clinical chemical parameters of C57BL/6J wild-type mice, murine FcRn-knockout mice, and two human FcRn transgenic mouse strains expressing human FcRn in the absence of murine FcRn. Since FcRn-mediated recycling prevents albumin and IgG from intracellular degradation, significant differences for both proteins were observed in the murine FcRn-knockout mice. Mice lacking FcRn show lower IgG and albumin levels compared to wild-type mice. The most prominent differences in clinical chemical parameters can be explained by secondary effects of the altered albumin levels of murine FcRn-knockout mice on liver metabolism, as similar tendencies have been observed in analbuminemic Nagase rats and hypoalbuminemic human patients, showing an overall increased liver metabolism. Both human FcRn transgenic strains show clinical chemical parameters similar to those found for wild-type mice, with the exception of endogenous IgG levels, which are greatly reduced in these mice.

Development of tetravalent IgG1 dual targeting IGF-1R-EGFR antibodies with potent tumor inhibition.

In this study we present novel bispecific antibodies that simultaneously target the insulin-like growth factor receptor type I (IGF-1R) and epidermal growth factor receptor (EGFR). For this purpose disulfide stabilized scFv domains of the EGFR/ADCC antibody GA201 were fused via serine-glycine connectors to the C-terminus of the heavy (XGFR2) or light chain (XGFR4), or the N-termini of the light (XGFR5) or heavy chain (XGFR3) of the IGF-1R antibody R1507 as parental IgG1 antibody. The resulting bispecific IGF-1R-EGFR antibodies XGFR2, XGFR3 and XGFR4 were successfully generated with yields and stability comparable to conventional IgG1 antibodies. They effectively inhibited IGF-1R and EGFR phosphorylation and 3D proliferation of H322M and H460M2 tumor cells, induced strong down-modulation of IGF-1R as well as enhanced EGFR down-modulation compared to the parental EGFR antibody GA201 and were ADCC competent. The bispecific XGFR derivatives showed a strong format dependent influence of N- or C-terminal heavy and light chain scFv attachment on ADCC activity and an increase in receptor downregulation over the parental combination in vitro. XGFR2 and XGFR4 were selected for in vivo evaluation and showed potent anti-tumoral efficacy comparable to the combination of monospecific IGF-1R and EGFR antibodies in subcutaneous BxPC3 and H322M xenograft models. In summary, we have managed to overcome issues of stability and productivity of bispecific antibodies, discovered important antibody fusion protein design related differences on ADCC activity and receptor downmodulation and show that IGF-1R-EGFR antibodies represent an attractive therapeutic strategy to simultaneously target two key components de-regulated in multiple cancer types, with the ultimate goal to avoid the formation of resistance to therapy.

DuoMab: a novel CrossMab-based IgG-derived antibody format for enhanced antibody-dependent cell-mediated cytotoxicity.

High specificity accompanied with the ability to recruit immune cells has made recombinant therapeutic antibodies an integral part of drug development. Here we present a generic approach to generate two novel IgG-derived antibody formats that are based on a modification of the CrossMab technology. MoAbs harbor two heavy chains (HCs) resulting in one binding entity and one fragment crystallizable region (Fc), whereas DuoMabs are composed of four HCs harboring two binding entities and two Fc regions linked at a disulfide-bridged hinge. The latter bivalent format is characterized by avidity-enhanced target cell binding while simultaneously increasing the 'Fc-load' on the surface. DuoMabs were shown to be producible in high yield and purity and bind to surface cells with affinities comparable to IgGs. The increased Fc load directed at the surface of target cells by DuoMabs modulates their antibody-dependent cell-mediated cytotoxicity competency toward target cells, making them attractive for applications that require or are modulated by FcR interactions.

Effect of the new matrix metalloproteinase inhibitor RO-28-2653 on mitochondrial function.

Matrix metalloproteinases (MMPs) have recently become interesting as potential anticancer drugs. RO-28-2653 is a promising compound because of its antimetastatic and antiangiogenic activities. Due to the structural similarity of RO-28-2653 to mitochondriotoxic agents, speculation has arisen that this substance might impair mitochondrial function. We, therefore, investigated the effects of RO-28-2653 on mitochondrial enzymes and on the functional properties of isolated mitochondria and skinned muscle fibers from rat hearts. Results were compared to the action of amytal and 2,4-dinitrophenol (2,4-DNP), both of which are well documented mitochondriotoxic compounds. In contrast to 2,4-DNP, RO-28-2653 did not uncouple oxidative phosphorylation, although higher concentrations of the compound did impair mitochondrial function. Using malate/pyruvate as substrate, 50 microM of RO-28-2653 inhibited mitochondrial respiration in isolated mitochondria and skinned fibers by 23 and 11%, respectively while 2mM of amytal elicited almost complete inhibition of the mitochondrial respiration. RO-28-2653 (50 micro) inhibited succinate-dependent respiration in both systems by 43 and 24%, respectively while 2mM of amytal caused 41 and 23% inhibition, respectively. There was no change in the ADP/O ratios. RO-28-2653 (50 microM) did not significantly alter the activity of the respiratory chain complexes or succinate dehydrogenase, although citrate synthase (CS) was inhibited by upto 71%. This inhibition was non-competitive at a K(i) of 25+/-5 microM. Inhibitory effects in the presence of hydrophobic substances, such as BSA and Triton X-100, were significantly lower in both test systems. In conclusion, high concentrations of RO-28-2653 impair mitochondrial function, although compared to amytal and 2,4-DNP, this is rather low. The resultant impairment is less pronounced in the more complex skinned muscle fiber system, and is dependent on hydrophobic interactions.

A novel approach to investigate the effect of methionine oxidation on pharmacokinetic properties of therapeutic antibodies.

Preserving the chemical and structural integrity of therapeutic antibodies during manufacturing and storage is a major challenge during pharmaceutical development. Oxidation of Fc methionines Met252 and Met428 is frequently observed, which leads to reduced affinity to FcRn and faster plasma clearance if present at high levels. Because oxidation occurs in both positions simultaneously, their individual contribution to the concomitant changes in pharmacokinetic properties has not been clearly established. A novel pH-gradient FcRn affinity chromatography method was applied to isolate three antibody oxidation variants from an oxidized IgG1 preparation based on their FcRn binding properties. Physico-chemical characterization revealed that the three oxidation variants differed predominantly in the number of oxMet252 per IgG (0, 1, or 2), but not significantly in the content of oxMet428. Corresponding to the increase in oxMet252 content, stepwise reduction of FcRn affinity in vitro, as well as faster clearance and shorter terminal half-life, in huFcRn-transgenic mice were observed. A single Met252 oxidation per antibody had no significant effect on pharmacokinetics (PK) compared with unmodified IgG. Importantly, only molecules with both heavy chains oxidized at Met252 exhibited significantly faster clearance. In contrast, Met428 oxidation had no apparent negative effect on PK and even led to somewhat improved FcRn binding and slower clearance. This minor effect, however, seemed to be abrogated by the dominant effect of Met252 oxidation. The novel approach of functional chromatographic separation of IgG oxidation variants followed by physico-chemical and biological characterization has yielded the first experimentally-backed explanation for the unaltered PK properties of antibody preparations containing relatively high Met252 and Met428 oxidation levels.

Analytical FcRn affinity chromatography for functional characterization of monoclonal antibodies.

The neonatal Fc receptor (FcRn) is important for the metabolic fate of IgG antibodies in vivo. Analysis of the interaction between FcRn and IgG in vitro might provide insight into the structural and functional integrity of therapeutic IgG that may affect pharmacokinetics (PK) in vivo. We developed a standardized pH gradient FcRn affinity liquid chromatography method with conditions closely resembling the physiological mechanism of interaction between IgG and FcRn. This method allows the separation of molecular IgG isoforms, degradation products and engineered molecules based on their affinity to FcRn. Human FcRn was immobilized on the column and a linear pH gradient from pH 5.5 to 8.8 was applied. FcRn chromatography was used in comparison to surface plasmon resonance to characterize different monoclonal IgG preparations, e.g., oxidized or aggregated species. Wild-type and engineered IgGs were compared in vitro by FcRn chromatography and in vivo by PK studies in huFcRn transgenic mice. Analytical FcRn chromatography allows differentiation of IgG samples and variants by peak pattern and retention time profile. The method can distinguish: 1) IgGs with different Fabs, 2) oxidized from native IgG, 3) aggregates from monomer and 4) antibodies with mutations in the Fc part from wild-type IgGs. Changes in the FcRn chromatographic behavior of mutant IgGs relative to the wild-type IgG correlate to changes in the PK profile in the FcRn transgenic mice. These results demonstrate that FcRn affinity chromatography is a useful new method for the assessment of IgG integrity.

PK modulation of haptenylated peptides via non-covalent antibody complexation.

We applied noncovalent complexes of digoxigenin (Dig) binding antibodies with digoxigeninylated peptide derivatives to modulate their pharmacokinetic properties. A peptide derivative which activates the Y2R receptor was selectively mono-digoxigeninylated by reacting a NHS-Dig derivative with an ε-amino group of lysine 2. This position tolerates modifications without destroying receptor binding and functionality of the peptide. Dig-peptide derivatives can be loaded onto Dig-binding IgGs in a simple and robust reaction, thereby generating peptide-IgG complexes in a defined two to one molar ratio. This indicates that each antibody arm becomes occupied by one haptenylated peptide. In vitro receptor binding and signaling assays showed that Dig-peptides as well as the peptide-antibody complexes retain better potency than the corresponding pegylated peptides. In vivo analyses revealed prolonged serum half-life of antibody-complexed peptides compared to unmodified peptides. Thus, complexes are of sufficient stability for PK modulation. We observed more prolonged weight reduction in a murine diet-induced obesity (DIO) model with antibody-complexed peptides compared to unmodified peptides. We conclude that antibody-hapten complexation can be applied to modulate the PK of haptenylated peptides and in consequence improve the therapeutic efficacy of therapeutic peptides.