Biomedical subjects

Wim K Bleeker

Publications and source records attributed to Wim K Bleeker.

5 recordsLinked to original sources

PubMed2006

Effect of target dynamics on pharmacokinetics of a novel therapeutic antibody against the epidermal growth factor receptor: implications for the mechanisms of action.

The epidermal growth factor receptor (EGFR) is overexpressed on many solid tumors and represents an attractive target for antibody therapy. Here, we describe the effect of receptor-mediated antibody internalization on the pharmacokinetics and dose-effect relationship of a therapeutic monoclonal antibody (mAb) against EGFR (2F8). This mAb was previously found therapeutically active in mouse tumor models by two dose-dependent mechanisms of action: blockade of ligand binding and induction of antibody-dependent cell-mediated cytotoxicity. In vitro studies showed 2F8 to be rapidly internalized by EGFR-overexpressing cells. In vivo, accelerated 2F8 clearance was observed in cynomolgus monkeys at low doses but not at high doses. This enhanced clearance seemed to be receptor dependent and was included in a pharmacokinetic model designed to explain its nonlinearity. Receptor-mediated clearance was also found to affect in situ antibody concentrations in tumor tissue. Ex vivo analyses of xenograft tumors of 2F8-treated nude mice revealed that relatively high antibody plasma concentrations were required for maximum EGFR saturation in high-EGFR-expressing human A431 tumors, in contrast to lower-EGFR-expressing human xenograft tumors. In summary, receptor-mediated antibody internalization and degradation provides a saturable route of clearance that significantly affects pharmacokinetics, particularly at low antibody doses. EGFR saturation in normal tissues does not predict saturation in tumor tissue as local antibody concentrations in EGFR-overexpressing tumors may be more rapidly reduced by antibody internalization. Consequently, antibody saturation of the receptor may be affected, thereby affecting the local mechanism of action.

Animals↗

PubMed2004

Dual mode of action of a human anti-epidermal growth factor receptor monoclonal antibody for cancer therapy.

Epidermal growth factor receptor (EGF-R) overexpression is common in a large number of solid tumors and represents a negative prognostic indicator. Overexpression of EGF-R is strongly tumor associated, and this tyrosine kinase type receptor is considered an attractive target for Ab therapy. In this study, we describe the evaluation of mAb 2F8, a high avidity human mAb (IgG1kappa) directed against EGF-R, developed using human Ig transgenic mice. mAb 2F8 effectively blocked binding of EGF and TGF-alpha to the EGF-R. At saturating concentrations, 2F8 completely blocked EGF-R signaling and inhibited the in vitro proliferation of EGF-R-overexpressing A431 cells. At much lower concentrations, associated with low receptor occupancy, 2F8 induced efficient Ab-dependent cell-mediated cytotoxicity (ADCC) in vitro. In vivo studies showed potent antitumor effects in models with A431 tumor xenografts in athymic mice. Ex vivo analysis of the EGF-R status in tumor xenografts in 2F8-treated mice revealed that there are two therapeutic mechanisms. First, blocking of EGF-R signaling, which is most effective at complete receptor saturation and therefore requires a relatively high Ab dose. Second, at very low 2F8 receptor occupancy, we observed potent antitumor effects in mice, which are likely based on the engagement of immune effector mechanisms, in particular ADCC. Taken together, our findings indicate that ADCC represents an important effector mechanism of this Ab, which is effective at relatively low dose.

Animals↗

PubMed2004

Monomeric IgG in intravenous Ig preparations is a functional antagonist of FcgammaRII and FcgammaRIIIb.

Intravenous Ig preparations (IVIg), originally developed as a substitution therapy for patients with low plasma IgG, are nowadays frequently used in the treatment of various immune diseases. However, the mechanism of action of IVIg in these diseases remains elusive and is often referred to as "immunomodulatory." We hypothesized that monomeric IgG may act as a low-affinity FcgammaR antagonist and sought experimental evidence for this hypothesis. Human neutrophils as well FcgammaRIIa-transfected IIA1.6 cells were used as FcgammaR-positive cells and aggregated IgG (aIgG) or stable dimeric IgG as FcgammaR-specific agonists for these cells. We found that monomeric IgG purified from IVIg at concentrations similar to that of IgG in plasma, diminished the binding of stable dimeric IgG to FcgammaRIIa transfectants, reduced aIgG-induced influx of Ca(2+) ions into the cytosol of neutrophils, and attenuated the aIgG-induced release of elastase. Notably, monomeric IgG by itself did not elicit these responses, nor did it affect these processes in response to fMLP. Absorption of IgG from normal plasma revealed that plasma IgG exerted similar effects as monomeric IgG in IVIg. In addition, adding monomeric IgG to blood of healthy volunteers showed a dose-dependent decrease of aIgG-induced elastase release. Finally, we observed decreased aIgG-induced polymorphonuclear neutrophil responses in two hypogammaglobulinemic patients upon treatment with IVIg. We conclude that monomeric IgG at physiological levels acts as a low-affinity FcgammaR antagonist. Moreover, FcgammaR antagonism constitutes an immunomodulatory effect of IVIg.

Calcium↗

PubMed2004

Therapeutic antibody gene transfer: an active approach to passive immunity.

Advances in gene transfer approaches are enabling the possibility of applying therapeutic antibodies using DNA. In particular gene transfer in combination with electroporation is promising and can result in generating in vivo antibody concentrations in the low therapeutic range. However, several important problems need to be dealt with before antibody gene transfer can become a valuable supplement to the current therapies. As antibody production following gene transfer is difficult to control, the danger of inducing autoimmune conditions or uncontrollable side effects occurs in cases in which autologous antigens are targeted. It is suggested that the most promising area of application therefore appears to be infectious disease in which heterologous antigens are targeted and concerns for long-term antibody exposure are minimal. Finally, genes encoding fully human antibodies will enhance long-term expression and decrease problems linked to immunogenicity.

Antibodies↗

PubMed2003

Rat C-reactive protein activates the autologous complement system.

Activation of complement is a biological function of human C-reactive protein (hCRP), whereas rat CRP (rCRP) has been claimed to be unable to activate complement. As important biological functions of proteins are probably conserved among species, we re-evaluated, using various ligands, the capability of rCRP to activate complement. The activation of complement by hCRP and rCRP was investigated in solid- and fluid-phase systems. In the solid-phase system, purified CRP was fixed to enzyme-linked immunosorbent assay (ELISA) plates and incubated with human or rat recalcified plasma. Dose-dependent binding of human and rat C3 and C4 was observed to human and rat CRP, respectively. In the fluid-phase system, recalcified rat plasma, which contains about 500 mg/l of CRP, or human plasma supplemented with hCRP, were incubated with lyso-phosphatidylcholine. A dose-dependent activation of complement was observed upon incubation with this ligand, as reflected by the generation of activated C4 as well as of CRP-complement complexes. This activation was, in both cases, inhibited by preincubation of plasma with p-aminophosphorylcholine, a specific inhibitor of the interaction of CRP with its ligands, or by chelation of calcium ions. We conclude that rat CRP, similarly to human CRP, can activate autologous complement. These results support the notion that opsonization of ligands with complement is an important biological function of CRP.

Animals↗