Jacques Gaudreault

Design, construction, and in vitro analyses of multivalent antibodies.

Some Abs are more efficacious after being cross-linked to form dimers or multimers, presumably as a result of binding to and clustering more surface target to either amplify or diversify cellular signaling. To improve the therapeutic potency of these types of Abs, we designed and generated Abs that express tandem Fab repeats with the aim of mimicking cross-linked Abs. The versatile design of the system enables the creation of a series of multivalent human IgG Ab forms including tetravalent IgG1, tetravalent F(ab′)2, and linear Fab multimers with either three or four consecutively linked Fabs. The multimerized Abs target the cell surface receptors HER2, death receptor 5, and CD20, and are more efficacious than their parent mAbs in triggering antitumor cellular responses, indicating they could be useful both as reagents for study as well as novel therapeutics.

Complexation of VEGF with Bevacizumab Decreases VEGF Clearance in Rats

Angiogenesis plays a critical role in several physiologic and pathologic processes, particularly in tumor growth, invasion, and metastasis (1). New blood vessels provide tumors with nutrients necessary for growth and also remove metabolic waste from the tumor (2). Several growth factors have been implicated in tumor angiogenesis, and one such factor is vascular endothelial growth factor (VEGF), which is a selective mitogen for endothelial cells. VEGF, a 43to 46-kD glycoprotein, induces proliferation and migration of vascular endothelial cells and functions as a vascular permeability factor through two receptors: flt-1 and KDR (3). There are also several isoforms of VEGF (VEGF206, VEGF189, VEGF165, VEGF121, and VEGF110), and in humans, recombinant humanized VEGF165 (rhVEGF) displays nonlinear pharmacokinetics, which is attributed to binding of the drug to endothelial cells (4). In numerous preclinical animal models, administration of an antibody-targeting VEGF has been found to be a potent suppressor of tumor growth and is being considered as a potential, novel anticancer therapy (5). Bevacizumab (AvastinTM, rhuMAb VEGF) is a recombinant humanized monoclonal antibody that binds all isoforms of VEGF and inhibits binding of VEGF to its receptors. The antibody was engineered by combining VEGF-binding residues from a murine-neutralizing antibody with the framework of a human immunoglobulin G (IgG1) (6). Bevacizumab is believed to be cleared through the FcRn system, a MHC class I-related receptor that has been shown to protect circulating IgG1s from catabolism and thereby contribute to the long terminal half-life of antibodies (7). Bevacizumab binds to primate VEGF and to rabbit VEGF (with lower affinity) but does not bind to rodent VEGF (8). The monoclonal antibody has been shown to inhibit tumor growth in a dosedependent manner in various animal models (9). Several clinical studies have also been conducted to characterize the pharmacokinetics, safety, and efficacy of bevacizumab in cancer subjects. In two phase II studies in cancer subjects, bevacizumab, in combination with 5-fluorouracil/leucovorin or carboplatin/paclitaxel, has been shown to be safe and has inhibited tumor growth (10,11). Results from clinical studies have also shown a rise in serum concentrations of endogenous VEGF over baseline after single and multiple intravenous (IV) administration(s) of bevacizumab at doses >1 mg/kg (12). This rise in concentrations was ∼3to 4-fold above baseline and seemed to return to baseline as the antibody cleared systemically. An increase in VEGF synthesis/distribution and/or decrease in VEGF clearance upon complexation with bevacizumab are possible causes for this phenomenon. The latter hypothesis was explored in a pharmacokinetic study conducted in rats where recombinant humanized VEGF165 (rhVEGF) was administered intravenously in the presence or absence of bevacizumab. Rats were selected because (i) bevacizumab does not bind rat VEGF, therefore diminishing any competition for binding of bevacizumab to the administered rhVEGF and (ii) serial sampling was possible in the same animal for measurement of drug concentrations. Results presented here confirm that complexation of VEGF with bevacizumab decreases the clearance of circulating VEGF.

Mixed‐effects modeling of the pharmacodynamic response to the calcimimetic agent R–568

The parathyroid cell calcium receptor is a novel drug target for affecting parathyroid hormone (PTH) secretion and for treating hyperparathyroidism. R–568 is a calcium receptor agonist that inhibits PTH secretion and increases calcitonin release in preclinical studies. The objective of this study was to evaluate the effect of R‐568 on PTH plasma concentrations in humans.

Concomitant administration of bevacizumab, irinotecan, 5-fluorouracil, and leucovorin: nonclinical safety and pharmacokinetics.

Bevacizumab (Avastin) is a humanized monoclonal antibody against vascular endothelial growth factor approved for use in combination with 5-fluorouracil (5-FU)-based chemotherapy for first-line treatment of metastatic colorectal cancer. The Saltz regimen (irinotecan/5-FU/leucovorin [LV]) is a first-line treatment for this indication. The objective of this study was to evaluate the safety of bevacizumab when administered concomitantly with the Saltz regimen to cynomolgus monkeys, and to determine if the pharmacokinetics of bevacizumab, irinotecan, SN38 (the active metabolite of irinotecan), or 5-FU were affected by combined administration. Male cynomolgus monkeys were intravenously administered the Saltz regimen (125 mg/m2 irinotecan, 500 mg/m2 5-FU, 20 mg/m2 LV) alone (n = 4) or concomitantly with 10 mg/kg bevacizumab (n = 5) on days 1 and 8. All animals survived to euthanasia on day 15. Adverse effects associated with the Saltz regimen included diarrhea and neutropenia. Macroscopically, two animals from each group had small thymus glands that correlated microscopically with lymphoid depletion. Myeloid hypoplasia and/or erythroid hyperplasia was observed in the sternal bone marrow of most animals. These effects were considered to be associated with the Saltz regimen; concomitant bevacizumab administration did not alter the severity of these findings. Irinotecan and 5-FU were observed to be rapidly eliminated (t 1/2 = 1 h and 0.5 h, respectively). Although the number of animals in each group was small and no statistical comparison between groups was performed, bevacizumab did not affect the disposition of either agent. These results indicate that bevacizumab can be safely administered in combination with the Saltz regimen without pharmacokinetic interaction.

A population pharmacokinetic model for bevacizumab

BV, a recombinant humanized IgG1 monoclonal antibody against vascular endothelial growth factor (VEGF) was demonstrated to improve survival in previously untreated metastatic colorectal cancer when added to standard chemotherapy. Pooled data (total 4629 BV concentration from 491 subjects) from 8 Phase I to Phase III clinical trials were analyzed using NONMEM and a two‐compartment structural model. Body weight and gender were the most significant covariates for both CL and Vc. The change in BV CL for extreme body weights (49 and 114 kg) was 30% around the typical value. After adjusting the weight, men had a 26% faster CL than females. In the final model, CL and Vc were 0.207 L/day and 2.66 L, respectively for the typical (female) patient. The inter‐patient variability (%CV) in CL and Vc was 26% and 17%, respectively. BV terminal half‐life was 19.9 and 19.3 days for a typical male and female patient. Low albumin and high alkaline phosphatase serum concentrations were associated with a faster CL (+19% and 23%, respectively). Concomitant administration of the combination irinotecan/5‐fluorouracil in patients with colon cancer did not influence BV CL. The effect of various dosing regimen on bevacizumab exposure will be explored using simulations.