Population pharmacokinetics and exposure-response relationship of trastuzumab and bevacizumab in early-stage breast cancer.

AIMS: To describe the sources of interindividual variability of bevacizumab and trastuzumab pharmacokinetics in early-stage breast cancer, and to study the relationship between exposure and both early clinical response and specific adverse events. PATIENTS AND METHODS: Patients (n = 86) received 6 cycles of docetaxel + trastuzumab. Early tumour response was assessed by determination of the maximum standard uptake value (SUVmax) variation (ΔSUVmax) after 1 cycle using [18F]-fluorodeoxyglucose (FDG) PET. Early poor responders (ΔSUVmax < 70%) also received bevacizumab from cycle 3 to cycle 6. Sources of interindividual variability in pharmacokinetics of both antibodies were studied by population compartment modelling. Exposure as assessed by area under the concentration-versus-time curve (AUC) was compared between responders and non-responders and between patients experiencing specific adverse events or not. RESULTS: A two-compartment model described the pharmacokinetics of both antibodies satisfactorily. Their central volume of distributions (Vc) increased with body surface area and their elimination half-lives were shorter (~14 days) than previously reported (~26-28 days). There was a time-dependent increase in trastuzumab Vc, positively correlated to baseline SUVmax. Bevacizumab elimination rate (k10) was positively correlated with ΔSUVmax measured at the end of the first cycle. Bevacizumab had no significantly influence on trastuzumab pharmacokinetics. No relationship between exposure and clinical response or occurrence of adverse events was found. CONCLUSION: Tumour uptake as assessed by SUVmax influences the pharmacokinetics of bevacizumab and trastuzumab. In early-stage breast cancer, elimination half-lives of these therapeutic monoclonal antibodies may be shorter than those previously reported in more advanced disease.

Realistic multi-cellular dosimetry for 177Lu-labelled antibodies: model and application.

Current preclinical dosimetric models often fail to take account of the complex nature of absorbed dose distribution typical of in vitro clonogenic experiments in targeted radionuclide therapy. For this reason, clonogenic survival is often expressed as a function of added activity rather than the absorbed dose delivered to cells/cell nuclei. We designed a multi-cellular dosimetry model that takes into account the realistic distributions of cells in the Petri dish, for the establishment of survival curves as a function of the absorbed dose. General-purpose software tools were used for the generation of realistic, randomised 3D cell culture geometries based on experimentally determined parameters (cell size, cell density, cluster density, average cluster size, cell cumulated activity). A mixture of Monte Carlo and analytical approaches was implemented in order to achieve as accurate as possible results while reducing calculation time. The model was here applied to clonogenic survival experiments carried out to compare the efficacy of Betalutin®, a novel 177Lu-labelled antibody radionuclide conjugate for the treatment of non-Hodgkin lymphoma, to that of 177Lu-labelled CD20-specific (rituximab) and non-specific antibodies (Erbitux) on lymphocyte B cells. The 3D cellular model developed allowed a better understanding of the radiative and non-radiative processes associated with cellular death. Our approach is generic and can also be applied to other radiopharmaceuticals and cell distributions.

[Anti-HER2 vaccines: The HER2 immunotargeting future?]. / Vaccination anti-HER2 : l'avenir du ciblage immunologique de HER2 ?

Breast cancer is a widely spread women's disease. In spite of progress in the field of surgery and adjuvant therapies, the risk of breast cancer metastatic relapses remains high especially in those overexpressing HER2. Different studies have shown cellular and/or humoral immune responses against HER2 in patients with HER2-overexpressing tumors. This immune response is associated with a lower tumor development at early stages of the disease. These observations, associated with the efficiency today demonstrated by a trastuzumab-based anti-HER2 immunotherapy, allowed to envisage various vaccinal strategies against HER2. These findings have so led to the hypothesis that the generation of an anti-HER2 immune response should protect patients from HER2-overexpressing tumor growth, and induction of a stable and strong immunity by cancer vaccines is expected to lead to establishment of immune memory, thereby preventing tumor recurrence. However, an immunological tolerance against HER2 antigen exists representing a barrier to effective vaccination against this oncoprotein. As a consequence, the current challenge for vaccines is to find the best conditions to break this immunological tolerance. In this review, we will discuss the different anti-HER2 vaccine strategies currently developed; considering the strategies having reached the clinical phases as well as those still in preclinical development. The used antigen can be composed of tumoral allogenic cells or autologous cells or be specific of HER2. It can be delivered by denditric cells or in a DNA, peptidic or proteic form. Another area of the research concerns the use of anti-idiotypic antibodies mimicking HER2.

Combined cetuximab and trastuzumab are superior to gemcitabine in the treatment of human pancreatic carcinoma xenografts.

BACKGROUND: Pancreatic carcinoma remains a treatment-refractory cancer with a poor prognosis. Here, we compared anti-epidermal growth factor receptor (EGFR) and anti-HER2 monoclonal antibodies (2mAbs) injections with standard gemcitabine treatment on human pancreatic carcinoma xenografts. MATERIALS AND METHODS: Nude mice, bearing human pancreatic carcinoma xenografts, were treated with either combined anti-EGFR (cetuximab) and anti-HER2 (trastuzumab) or gemcitabine, and tumor growth was observed. RESULTS AND CONCLUSION: In first-line therapy, mice survival was significantly longer in the 2mAbs group compared with gemcitabine (P < 0.0001 for BxPC-3, P = 0.0679 for MiaPaCa-2 and P = 0.0019 for Capan-1) and with controls (P < 0.0001). In second-line therapy, tumor regressions were observed after replacing gemcitabine by 2mAbs treatment, resulting in significantly longer animal survival compared with mice receiving continuous gemcitabine injections (P = 0.008 for BxPC-3, P = 0.05 for MiaPaCa-2 and P < 0.001 for Capan-1). Therapeutic benefit of 2mAbs was observed despite K-Ras mutation. Interestingly, concerning the mechanism of action, coinjection of F(ab')(2) fragments from 2mAbs induced significant tumor growth inhibition, compared with controls (P = 0.001), indicating that the 2mAbs had an Fc fragment-independent direct action on tumor cells. This preclinical study demonstrated a significant improvement of survival and tumor regression in mice treated with anti-EGFR/anti-HER2 2mAbs in first- and second-line treatments, compared with gemcitabine, independently of the K-Ras status.

Isolation and characterisation of a human anti-idiotypic scFv used as a surrogate tumour antigen to elicit an anti-HER-2/neu humoral response in mice.

HER-2/neu is a tumour antigen that is overexpressed in human breast tumours. Among the vaccine strategies developed to overcome immune tolerance to self-proteins, vaccination with anti-idiotypic (anti-Id) antibodies has been described as a promising approach for treatment of several malignant diseases. To develop an active immunotherapy for cancer patients positive for HER-2/neu, we investigated immunisation with human anti-Id single-chain fragments (scFv) mimicking the conformation of HER-2/neu protein to induce a humoral response in mice. We selected by phage display two human anti-Id scFv (Ab2beta) directed against trastuzumab F(ab')2 fragments (Ab1), a humanised anti-HER-2/neu monoclonal antibody. Using competitive ELISA and Biacore biosensor analysis, we showed that anti-Id scFv 40 and scFv 69 could inhibit HER-2/neu binding to trastuzumab. Following vaccination of BALB/c mice with the soluble or phage-displayed scFv, Ab3 polyclonal antibodies, and among them Ab1' antibodies able to bind HER-2/neu, were detected in the sera of the immunised mice. These results demonstrate that the human anti-Id scFv could act as a surrogate antigen for HER-2/neu. The present study strongly suggests that the novel 30 kDa human mini-antibody could be used as an anti-idiotype-based vaccine formulation to induce an effective humoral response in patients bearing HER-2/neu-positive tumours.

Critical residues of epitopes recognized by several anti-p53 monoclonal antibodies correspond to key residues of p53 involved in interactions with the mdm2 protein.

The aim of this work was to study the reactivity of antibodies directed against the N-terminus of p53 protein. First, we analysed the cross-reactivity of anti-p53 antibodies from human, mouse and rabbit sera with peptides derived from human, mouse and Xenopus p53. Next, we characterized more precisely a series of monoclonal antibodies directed against the N-terminal part of p53 and produced by immunizing mice with either full length human or Xenopus p53. For each of these mAbs we localized the epitope recognized on human p53 by the Spot method of multiple peptide synthesis, defined critical residues on p53 involved in the interaction by alanine scanning replacement experiments and determined kinetic parameters using real-time interaction analysis. These antibodies could be divided into two groups according to their epitopic and kinetic characteristics and their cross-reactivity with murine p53. Our results indicate that critical residues involved in the interaction of some of these mAbs with p53 correspond to key residues on p53 involved in its interaction with the mdm2 protein. These antibodies could, therefore, represent powerful tools for the study of p53 regulation.

Affinity for the cognate monoclonal antibody of synthetic peptides derived from selection by phage display. Role of sequences flanking thebinding motif.

Randomized peptide sequences displayed at the surface of filamentous phages are often used to select antibody ligands. The selected sequences are generally further used in the form of synthetic peptides; however, as such, their affinity for the selecting antibody is extremely variable and factors influencing this affinity have not been fully deciphered. We have used an f88.4 phage-displayed peptide library to identify ligands of mAb 11E12, an antibody reactive to human cardiac troponin I. A majority of the sequences thus selected showed a (T/A/I/L) EP(K/R/H) motif, homologous to the Y-TEPH motif identified by multiple peptide synthesis as the critical motif recognized by mAb 11E12 in the peptide epitope. A set of 15-mer synthetic peptides derived from the phage-selected sequences was used in BIACORE to characterize their interaction with mAb 11E12. Most peptides exhibited affinities in the 7-26 nM range. These affinities represented, however, only 1.9-7. 5% of the affinity of the 15-mer peptide epitope. In circular dichroism experiments, the peptide epitope showed a propensity to have some stabilized conformation, whereas a low-affinity peptide selected by phage-display did not. To try to decipher the molecular basis of this difference in affinity, new peptides were prepared by grafting the N- or the C-terminal sequence of the peptide epitope to the Y-TEPK motif of a low-affinity peptide selected by phage-display. These hybrid peptides showed marked increases both in affinity (as assessed using BIACORE) and in inhibitory potency (as assessed in competition ELISA), compared with the parent sequence. Thus, the sequences flanking the motif, although not containing critical residues, convey some determinants necessary for high affinity. The affinity of a given peptide strongly depends on its capacity to maintain the antigenically reactive structure it has on the phage, implying that it is impossible to predict whether high- or low-affinity peptides will be obtained from phage display.

Affinity of recombinant antibody and antibody fragment binding to human thyroglobulin: potential applications in gene therapy.

Recombinant antibodies and antibody fragments are currently being produced. They can be used in vitro for the structural study of antigen-antibody interactions for instance, but their in vivo production may have applications for gene therapy of certain cancers and severe viral diseases and in developing new animal models of autoimmune disease. We report here these two types of applications using a recombinant antihuman thyroglobulin (hTg) antibody.

In-cell assembly of scFv from human thyroid-infiltrating B cells.

The construction of a large library of single-chain Fv (scFv) antibody fragments involves a random assortment of heavy and light chains. Although useful for the production of recombinant antibodies, this method is not adapted to the study of the autoantibody repertoire formed in vivo during autoimmune diseases. To attain this objective, we describe the use of the in-cell PCR together with Cre-recombination applied, to our knowledge, for the first time to human B cells to obtain in situ pairing of the variable (V) region genes of the immunoglobulin heavy (H) and light (L) chains. Our method is based on amplification and recombination of the VH and VL genes within CD19+ B cells isolated from human thyroid tissue. Nested primers were designed to amplify the known major human VH and VL gene families. After reverse transcription PCR and three rounds of PCR including recombination between VH and VL using the Cre-loxP system, we obtained a unique 800-bp band corresponding in size to scFv fragments. We provide evidence that recombination between VH and VL genes occurred inside the same cell. This in-cell amplification and association procedure is a potentially useful tool for the study of autoantibody gene families and the VH/VL pairing that occurs during the autoimmune process.

Analysis of the individual contributions of immunoglobulin heavy and light chains to the binding of antigen using cell transfection and plasmon resonance analysis.

We have cloned the Tg10 murine monoclonal antibody, which is specific for a human thyroglobulin (hTg) epitope targeted by autoantibodies in several thyroid pathologies. Transfection of COS-7 cells with plasmids expressing Tg10H and -kappa chains combined with surface plasmon resonance analysis (BIAcore) of culture supernatants showed that the entire cloned Tg10 antibody displays an affinity comparable to that of the parental antibody. This approach also permitted determination of the probable role of each chain to the recognition of the cognate epitope due to the ability of COS-7 cells to secrete independently each of the two constituting immunoglobulin chains. Tg10 heavy chain recognizes hTg in the absence of the light chain, but with a ten-fold lower affinity mainly due to an increase in kappaoff. In contrast, the light chain is unable to bind hTg on its own. This suggests that the latter is probably involved in stabilization rather than in initiating the formation of the antibody/antigen complex and that the specificity of Tg10 is mostly, if not exclusively, carried by the heavy chain. The potential applications of combined cell transfection and surface plasmon resonance to our understanding of antigen/antibody interactions are discussed.

Affinity and dose-dependent digoxin Na+K+ATPase dissociation by monoclonal digoxin-specific antibodies.

The effect of three monoclonal digoxin-specific antibodies and of polyclonal Digidot as reference on digoxin dissociation from rat brain Na+K+ATPase microsomes was studied to determine the role of the affinity constant (Ka) and dose of the antibody on the rate of digoxin dissociation from Na+K+ATPase. Stoichiometrical doses of 1C10, 6C9, 9F5 IgG, and Digidot (Ka = 6 10(9), 3.1 10(8), 2.5 10(7), and 8.5 10(9) M-1, respectively) resulted in digoxin dissociation related to Ka. When the IgG:digoxin molar ratio increased from 0.25 to 10, digoxin dissociation from Na+K+ATPase sites also increased according to the Hill equation, allowing comparative parameters among the three antibodies to be determined. 1C10 IgG was 2- and 10-fold more efficacious than 6C9 and 9F5, respectively. This in vitro model appears to be a useful predictive screening assay before in vivo experimentation.

Expression in Escherichia coli of soluble and M13 phage-displayed forms of a single-chain antibody fragment specific for digoxin: assessment in a novel drug immunoassay.

A high affinity anti-digoxin single-chain Fv antibody fragment (scFv) was cloned from the mouse 2C2 hybridoma cell line and was functionally expressed both in the Escherichia coli periplasm as a soluble molecule and at the surface of the filamentous M13 bacteriophage as a fusion protein with the gene III minor coat protein. The 2C2 scFv sequence significantly differs from that of all the other anti-digoxin antibodies previously described. The 2C2 scFv shares with its parental monoclonal antibody a high specificity for digoxin, a cross-reactivity with active digoxin metabolites, but none with inactive metabolites. M13 phages displaying the 2C2 scFv at their surface have a high apparent affinity constant for digoxin (6.6 x 10(8) M-1) and were directly used to set up a novel type of immunoenzymatic assay for monitoring digoxin in sera of patients treated for either congestive heart failure or cardiac arrythmias. We thus report for the first time that phages displaying scFv may constitute a large source of important new reagents in the field of immunodiagnosis.

Monoclonal digoxin-specific antibodies induce dose- and affinity-dependent plasma digoxin redistribution in rats.

The effect of three monoclonal digoxin-specific antibodies on total and free digoxin plasma disposition was studied in rats in order to determine the role of affinity constant (Ka) and dose. Thirty minutes after digoxin infusion, administration of a stoichiometrical dose of the ICIO, 6C9 and 9F5 IgG (Ka = 6 10(9), 3.1 10(8) and 2.5 10(7) M-1, respectively) resulted in a plasma digoxin increase linearly related to Ka. The mean free plasma digoxin was 0.6 +/- 0.4, 7.8 +/- 3.3 and 43 +/- 22% respectively after 1C10, 6C9, and 9F5 IgG infusion in comparison to 70 +/- 9% in the control group. When the IgG:digoxin ratio increased from 1 to 5, plasma digoxin Cmax and AUCT also increased as a function of both affinity (Ka) and dose (N), but not linearly. The product of NKa defined an immunoreactivity factor that was well fitted to the digoxin redistribution parameters (Cmax and AUCT) by a Hill equation.