Antibody pharmacokinetics and pharmacodynamics

A phase 1 multidose study of SGN-30 immunotherapy in patients with refractory or recurrent CD30+ hematologic malignancies

Phase 1 testing of SGN-30, a chimeric monoclonal antibody for the treatment of CD30+ malignancies, was conducted in a multicenter study. To explore the safety profile and establish the maximum tolerated dose (MTD), 24 patients with refractory or relapsed Hodgkin lymphoma or CD30+ non-Hodgkin lymphoma received 6 weekly doses of intravenous SGN-30 at 4 dose levels (2, 4, 8, or 12 mg/kg). Serum concentrations of SGN-30 rose rapidly and were dose dependent. Adverse events were mild, with nausea, fatigue, and fever attributed to study treatment. One episode of hypersensitivity rash was reported. The MTD was not reached. Serious adverse events included herpes zoster (n = 2), influenza, and pneumonia. One patient with cutaneous anaplastic large cell lymphoma (8 mg/kg) achieved a complete response. Six patients, of whom 4 had Hodgkin lymphoma, achieved stable disease with durations ranging from 6 to 16 months. The pharmacokinetic profile of SGN-30 showed a biphasic disposition, and estimated half-lives ranging between 1 to 3 weeks. The 6 weekly infusions of SGN-30 resulted in approximately 2- to 3-fold accumulation in serum exposures consistently across the dose range. These results demonstrate that weekly administration of SGN-30 is safe and has modest clinical activity in patients with CD30+ tumors. This trial is registered at http://www.ClinicalTrials.gov as no. NCT00051597.

Development of a simple and rapid method for producing non-fucosylated oligomannose containing antibodies with increased effector function

Glycosylation in the Fc region of antibodies has been shown to play an important role in antibody function. In the current study, glycosylation of human monoclonal antibodies was metabolically modulated using a potent alpha-mannosidase I inhibitor, kifunensine, resulting in the production of antibodies with oligomannose-type N-glycans. Growing Chinese hamster ovary cells for 11 days in batch culture with a single treatment of kifunensine was sufficient to elicit this effect without any significant impact on cell viability or antibody production. Antibodies expressed in the presence of kifunensine at a concentration as low as 60 ng/mL contained mainly oligomannose-type glycans and demonstrated increased ADCC activity and affinity for FcgammaRIIIA, but reduced C1q binding. Although the kifunensine-mediated shift to oligomannose-type glycans could, in theory, result in rapid clearance of the antibody through increased mannose receptor binding, the serum levels of antibody in mice were not significantly altered up to 168 h following injection. The use of kifunensine provides a simple and rapid method for the production of antibodies with increased ADCC without the time-consuming need to re-engineer either the antibody molecule or the host cell line.

N-glycosylation as novel strategy to improve pharmacokinetic properties of bispecific single-chain diabodies

The therapeutic efficacy of recombinant antibodies such as single-chain Fv fragments and small bispecific or bifunctional molecules is often limited by rapid elimination from the circulation because of their small size. Here, we have investigated the effects of N-glycosylation on the activity and pharmacokinetics of a small bispecific single-chain diabody (scDb CEACD3) developed for the retargeting of cytotoxic T cells to CEA-expressing tumor cells. We could show that the introduction of N-glycosylation sequons into the flanking linker and a C-terminal extension results in the production of N-glycosylated molecules after expression in transfected HEK293 cells. N-Glycosylated scDb variants possessing 3, 6, or 9 N-glycosylation sites, respectively, retained antigen binding activity and bispecificity for target and effector cells as shown in a target cell-dependent IL-2 release assay, although activity was reduced approximately 3-5-fold compared with the unmodified scDb. All N-glycosylated scDb variants exhibited a prolonged circulation time compared with scDb, leading to a 2-3-fold increase of the area under curve (AUC). In comparison, conjugation of a branched 40-kDa PEG chain increased AUC by a factor of 10.6, while a chimeric anti-CEA IgG1 molecule had the longest circulation time with a 17-fold increase in AUC. Thus, N-glycosylation complements the repertoire of strategies to modulate pharmacokinetics of small recombinant antibody molecules by an approach that moderately prolongs circulation time.

Clinical pharmacokinetics of bevacizumab in patients with solid tumors

OBJECTIVE

To characterize the population pharmacokinetics of bevacizumab and the influence of demographic factors, disease severity, and concomitantly used chemotherapy agents on it's pharmacokinetic behavior.

PATIENTS AND METHODS

Data from eight clinical trials with bevacizumab administered by intravenous infusion were included. A total of 4,629 bevacizumab concentrations from 491 patients with solid tumors, who received bevacizumab doses ranging from 1 to 20 mg/kg at a dosing frequency ranging from weekly to every 3 weeks, were analyzed using a nonlinear mixed-effects modeling approach (NONMEM).

RESULTS

The best structural model was a two-compartment model with first-order elimination. In the final model, estimated clearance (CL) and central compartment volume of distribution (Vc) were 0.207 L/day and 2.39 L for a typical female. The terminal half-life estimate was approximately 20 days for both men and women. Body weight and gender were the most significant covariates to explain interpatient variability for CL and Vc. Clearance was 26% faster in men than in women. Patients with low serum albumin and high serum alkaline phosphatase had 19 and 23% faster CL, respectively, than a typical patient. Consistent with the long elimination half life, simulations showed that similar steady-state exposures can be maintained when the weekly mg/kg dose rate is maintained, therefore allowing administration of bevacizumab to coincide with the frequency of administration of the cytotoxic agents.

CONCLUSION

The PK parameters were consistent with those of other IgG molecules. The results support dosing bevacizumab on a once every 2 weeks or once every 3 weeks dosing schedule on a mg/kg basis.

A physiologically based pharmacokinetic (PBPK) model to characterize and predict the disposition of monoclonal antibody CC49 and its single chain Fv constructs

Optimization of the use of monoclonal antibodies (MAbs) as diagnostic tools and therapeutic agents in the treatment of cancer is aided by quantitative characterization of the transport and tissue disposition of these agents in whole animals. This characterization may be effectively achieved by the application of physiologically based pharmacokinetic (PBPK) models. The purpose of this study was to develop a PBPK model to characterize the biodistribution of the pancarcinoma MAb CC49 IgG in normal and neoplastic tissues of nude mice, and to further apply the model to predict the disposition of multivalent single chain Fv (scFv) constructs in mice. Since MAbs are macromolecules, their transport is membrane-limited and a two-pore formalism is employed to describe their extravasation. The influence of binding of IgG to the protective neonatal Fc receptor (FcRn) on its disposition is also accounted for in the model. The model successfully described (131)I-CC49 IgG concentrations in blood, tumor and various organs/tissues in mice. Sensitivity analysis revealed the rate of transcapillary transport to be a critical determinant of antibody penetration and localization in the tumor. The applicability of the model was tested by predicting the disposition of di- and tetravalent scFv constructs of CC49 in mice. The model gave reasonably good predictions of the disposition of the scFv constructs. Since the model employs physiological parameters, it can be used to scale-up mouse biodistribution data to predict antibody distribution in humans. Therefore, the clinical utility of the model was tested with data for (131)I-CC49 obtained in patients, by scaling up murine parameter values according to known empirical relationships. The model gave satisfactory predictions of CC49 disposition and tumor uptake in man.

The role of mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) modelling in translational research of biologics

Lack of predictability of clinical efficacy and safety is an important problem facing pharmaceutical research today. Translational PK-PD has the ability to integrate data generated from diverse test platforms during discovery and development in a mechanistic framework. Therefore, successful implementation of translational PK-PD modelling and simulation early in the development cycle could have a substantial impact on overall efficiency and success of pharmaceutical research. Three case studies are presented, which outline successful implementation of the translational PK-PD methodology in the rational development of biotherapeutics across various stages of discovery and development. Emerging developments within the field are also discussed.

Tumor necrosis factor antagonist mechanisms of action: a comprehensive review

During the past 30 years, elucidation of the pathogenesis of rheumatoid arthritis, Crohn's disease, psoriasis, psoriatic arthritis and ankylosing spondylitis at the cellular and molecular levels has revealed that these diseases share common mechanisms and are more closely related than was previously recognized. Research on the complex biology of tumor necrosis factor (TNF) has uncovered many mechanisms and pathways by which TNF may be involved in the pathogenesis of these diseases. There are 3 TNF antagonists currently available: adalimumab, a fully human monoclonal antibody; etanercept, a soluble receptor construct; and infliximab, a chimeric monoclonal antibody. Two other TNF antagonists, certolizumab and golimumab, are in clinical development. The remarkable efficacy of TNF antagonists in these diseases places TNF in the center of our understanding of the pathogenesis of many immune-mediated inflammatory diseases. The purpose of this review is to discuss the biology of TNF and related family members in the context of the potential mechanisms of action of TNF antagonists in a variety of immune-mediated inflammatory diseases. Possible mechanistic differences between TNF antagonists are addressed with regard to their efficacy and safety profiles.

Improved tumor imaging and therapy via i.v. IgG-mediated time-sequential modulation of neonatal Fc receptor

The long plasma half-life of IgG, while allowing for enhanced tumor uptake of tumor-targeted IgG conjugates, also results in increased background activity and normal-tissue toxicity. Therefore, successful therapeutic uses of conjugated antibodies have been limited to the highly sensitive and readily accessible hematopoietic tumors. We report a therapeutic strategy to beneficially alter the pharmacokinetics of IgG antibodies via pharmacological inhibition of the neonatal Fc receptor (FcRn) using high-dose IgG therapy. IgG-treated mice displayed enhanced blood and whole-body clearance of radioactivity, resulting in better tumor-to-blood image contrast and protection of normal tissue from radiation. Tumor uptake and the resultant therapeutic response was unaltered. Furthermore, we demonstrated the use of this approach for imaging of tumors in humans and discuss its potential applications in cancer imaging and therapy. The ability to reduce the serum persistence of conjugated IgG antibodies after their infusion can enhance their therapeutic index, resulting in improved therapeutic and diagnostic efficacy.

The future of antibody therapy

Antibodies have been used successfully as therapeutics for over 100 years. The successful development of therapeutic human(ized) monoclonal antibodies (mAbs) in the last 20 years has demonstrated the potency of mAbs but also revealed some of their limitations. Studies in animals and humans demonstrated that it is possible to overcome some of these limitations using mixtures of mAbs or polyclonal antibody (pAb) preparations. pAbs from human and animal plasma are efficacious and safe therapeutics for the treatment of many diseases. Novel technologies are being developed for the production of human pAbs in genetically engineered animals. Immunization of such animals should allow the production of effective and safe high-titer antibody preparations for the treatment of infectious diseases, cancer, and autoimmunity.

Immunotherapy targeting pathological tau conformers in a tangle mouse model reduces brain pathology with associated functional improvements

Immunotherapies for various neurodegenerative diseases have recently emerged as a promising approach for clearing pathological protein conformers in these disorders. This type of treatment has not been assessed in models that develop neuronal tau aggregates as observed in frontotemporal dementia and Alzheimer's disease. Here, we present that active immunization with a phosphorylated tau epitope, in P301L tangle model mice, reduces aggregated tau in the brain and slows progression of the tangle-related behavioral phenotype. Females had more tau pathology than males but were also more receptive to the immunotherapy. The tau antibodies generated in these animals recognized pathological tau on brain sections. Performance on behavioral assays that require extensive motor coordination correlated with tau pathology in corresponding brain areas, and antibody levels against the immunogen correlated inversely with tau pathology. Interestingly, age-dependent autoantibodies that recognized recombinant tau protein but not the immunogen were detected in the P301L mice. To confirm that anti-tau antibodies could enter the brain and bind to pathological tau, FITC-tagged antibodies purified from a P301L mouse, with a high antibody titer against the immunogen, were injected into the carotid artery of P301L mice. These antibodies were subsequently detected within the brain and colocalized with PHF1 and MC1 antibodies that recognize pathological tau. Currently, no treatment is available for clearing tau aggregates. Our present findings may lead to a novel therapy targeting one of the major hallmarks of Alzheimer's disease and frontotemporal dementia.

Recombinant therapeutic monoclonal antibodies: mechanisms of action in relation to structural and functional duality

Naked therapeutic recombinant monoclonal antibodies (mAbs) are bifunctional molecules. On the one hand, they recognize their antigen through the variable regions of the antigen binding portion (Fab). The recombinant mAb binding to a soluble or a membrane antigen may interfere with one or several functions of this antigen, leading to the therapeutic effect. On the other hand, since their crystalisable portion (Fc) is humanized (usually IgG1), they interact efficiently with human Fc-binding molecules, such as C1q and receptors for the Fc portion of IgG (FcgammaR). Thus, they initiate the classical pathway of complement and activate FcgammaR-expressing cells. The recruitment of these patient immune effector functions is essential in the therapeutic effect of several recombinant mAbs used in oncology. The aim of this review is to describe the main mechanisms of action of recombinant mAbs in relation to this structural and functional duality.

Physiologically-based pharmacokinetic (PBPK) model to predict IgG tissue kinetics in wild-type and FcRn-knockout mice

Although it is known that FcRn, the neonatal Fc-receptor, functions to protect immune gamma globulin (IgG) from elimination, the influence of FcRn on the tissue distribution of IgG has not been quantified. In the present work, a physiologically-based pharmacokinetic (PBPK) model has been developed to characterize and predict IgG disposition in plasma and in tissues. The model includes nine major compartments, connected in an anatomical manner, to represent tissues known to play a significant role in IgG disposition. Each tissue compartment was subdivided into vascular, endosomal and interstitial spaces. IgG transport between the blood and interstitial compartments may proceed by convection through paracellular pores in the vascular endothelium, or via FcRn-mediated transcytosis across vascular endosomal cells. The model was utilized to characterize plasma concentration-time data for 7E3, a monoclonal antiplatelet IgG1 antibody, in control and FcRn-knockout (KO) mice. These data showed that high dose intravenous immunoglobulin (IVIG), 1g/kg, increased 7E3 clearance in control mice from 5.2 +/- 0.3 to 14.4 +/- 1.4 ml/d/kg; however, IVIG failed to increase the clearance of 7E3 in KO mice (72.5 +/- 4.0 vs. 61.0 +/- 3.6 ml/d/kg). Based on model fitting to the 7E3 plasma concentration data, simulations were conducted to predict tissue concentrations of IgG in control and in KO mice, and the predictions were then tested by assessing 7E3 tissue distribution in KO mice and control mice. 7E3 was radiolabeled with Iodine-125 using chloramine T method, and (125)I-7E3 IgG was administered at a dose of 8 mg/kg to control and KO mice. At various time points, sub-groups of 3 mice were sacrificed, blood and tissue samples were collected, and radioactivity assessed by gamma counting. PBPK model performance was assessed by comparing model predictions with the observed data. The model accurately predicted 7E3 tissue concentrations, with mean predicted vs. observed AUC ratios of 1.04 +/- 0.2 and 0.86 +/- 0.3 in control and FcRn-KO mice. The PBPK model, which incorporates the influence of FcRn on IgG clearance and disposition, was found to provide accurate predictions of IgG tissue kinetics in control and FcRn-knockout mice.

Position independent and copy-number-related expression of the bovine neonatal Fc receptor α-chain in transgenic mice carrying a 102 kb BAC genomic fragment

We generated and characterized transgenic mice carrying a 102 kb bovine genomic fragment, encoding the neonatal Fc receptor alpha-chain (bFcRn). FcRn plays a crucial role in the maternal IgG transport and it also regulates the IgG and albumin homeostasis. Some of its functions and transcriptional regulation show species specific differences. The FcRn heterodimer is composed of the alpha-chain and beta-2-microglobulin (beta2 m). A bacterial artificial chromosome containing the bovine FcRn alpha-chain gene (bFCGRT) with its 44 kb 5' and 50 kb long 3' flanking sequences was microinjected into fertilized mouse oocytes. Two of the transgenic lines generated, showed copy number related and integration site independent bFcRn expression. The bFcRn alpha-chain forms a functional receptor with the mouse beta2-microglobulin and extends the half-life of the mouse IgG in transgenic mice. Our results underline the feasibility of creating BAC transgenic mouse models of economically important bovine genes.

Treatment parameters modulating regression of human melanoma xenografts by an antibody–drug conjugate (CR011-vcMMAE) targeting GPNMB

PURPOSE

To investigate the pharmacological properties of the CR011-vcMMAE fully human antibody-drug conjugate (ADC), such as dose titrations, quantitation of the time (days) to complete regression, pharmacokinetics, and schedule dependency. Our prior study characterized a fully human antibody to GPNMB covalently linked to monomethylauristatin E, CR011-vcMMAE, and further demonstrated cell surface staining of melanoma lines susceptible to the immunoconjugate's cytotoxicity (Clin Cancer Res 2005; 12(4): 1373-1382).

METHODS

The human SK-MEL-2 and SK-MEL-5 melanoma xenografts were used in athymic mice to assess anti-tumor efficacy. After s.c. implantation, tumors became established (60-100 mg), and treatment commenced by i.v. injection of the immunoconjugate or vinblastine or paclitaxel. Short-term anti-tumor effects (inhibition of tumor growth) and long-term effects (complete regression) were observed.

RESULTS

CR011-vcMMAE induced regression of established human SK-MEL-2 and SK-MEL-5 xenografts at doses from 1.25 to 80 mg/kg treatment when administered intravenously every 4 days (4 treatments); strikingly, regressions were not associated with re-growth during the observation period (200 days). The disappearance rate of implants was dose dependent (minimum time, 18.5 days). Detectable serum CR011-vcMMAE >or=1 microg/mL (approximately 0.01 microM) was observed for >30 days post-dose; CR011-vcMMAE showed an elimination half-life of 10.3 days. A low volume of distribution suggested that CR011-vcMMAE was confined to blood and interstitial fluid. CR011-vcMMAE could be delivered by either a single bolus dose or by intermittent dosing (i.e., every 1, 2, 4, 8, or 16 days) with no discernible differences in the proportion of tumor-free survivors, indicating a lack of schedule dependency. The antibody-drug conjugate produced complete regressions, but the equivalent doses of free monomethylauristatin E or unconjugated antibody did not show anti-tumor effects. In addition, decreases in plasma tumor-derived human interleukin-8 coincided with tumor nodule disappearance.

CONCLUSIONS

Short-term anti-tumor effects and long-term effects (complete regression) were observed with CR011-vcMMAE, but not with the reference agents. These results suggest that CR011-vcMMAE may provide therapeutic benefit in malignant melanoma.

Pharmacokinetics and safety of a fully human hepatocyte growth factor antibody, AMG 102, in cynomolgus monkeys

PURPOSE

AMG 102, a fully human monoclonal antibody that binds to hepatocyte growth factor (HGF), is a potential cancer therapeutic agent because of its ability to disrupt HGF/c-Met signaling pathways which have been implicated in most tumor types. To support a phase 1 study, the pharmacokinetic and safety profile of AMG 102 was assessed in cynomolgus monkeys.

MATERIALS AND METHODS

Serum concentration-time data from single- (i.v. and s.c.) and repeated-dose (i.v.) studies of up to 13 weeks were used for pharmacokinetic analysis. Safety was assessed in a single-dose safety pharmacology study with i.v. doses of 0 (vehicle), 25, 100, or 300 mg/kg and a 4-week toxicity study with once weekly i.v. doses of 0 (vehicle), 5, 25, or 100 mg/kg.

RESULTS

AMG 102 exhibited linear pharmacokinetics over a 600-fold dose range (0.5 to 300 mg/kg) with a mean terminal half-life of 5.6 days after i.v. dosing. Clearance and volume of distribution at steady state were 1.22 ml/h and 198.3 ml, respectively. Estimated bioavailability was 72% for s.c. administration. Antibody response to AMG 102 was observed in a small percentage of monkeys. No treatment-related cardiovascular, respiratory, or CNS changes were observed. Administration of AMG 102 for 4 weeks was well tolerated at doses up to 100 mg/kg. Potential treatment-related effects were limited to minimal/moderate gastric mucosa hemorrhage in the mid- and high-dose groups.

CONCLUSIONS

The nonclinical pharmacokinetic and safety profile of AMG 102 effectively supports clinical investigation.

Antibody engineering and modification technologies

Antibody engineering has become a well-developed discipline, encompassing discovery methods, production strategies, and modification techniques that have brought forth clinically investigated and marketed therapeutics. The realization of the long-standing goal of production of fully human monoclonal antibodies has focused intensive research on the clinical employment of this potent drug category. However, antibodies are large macromolecules that pose numerous challenges in formulation, optimal pharmacokinetics, manufacturing, stability, and process development. While further improvements in discovery technologies, such as phage display, ribosome display, and transgenic animals continue to advance our capacity to rapidly screen and refine optimal binding molecules, antibody engineers have recently focused more of their efforts on improving protein production and stability, as well as engineering improved biological properties in the effector domains of monoclonal antibodies. A second long-standing goal of antibody engineering, the development of targeted drugs, has not been wholly realized, but this obvious application for antibodies is currently undergoing increasing exploration. Minimal binding proteins, such as Fab, scFv, and single variable domains are the preferred targeting elements for some investigational drugs, whereas non-immunoglobulin scaffold proteins have been explored as binding proteins in other designs. The necessity to utilize non-protein components in targeted drugs, such as polymers, linkers, and cytotoxics, has brought a convergence of the fields of bioconjugate chemistry and protein engineering in experimental antibody therapeutics.

Highly Concentrated Monoclonal Antibody Solutions: Direct Analysis of Physical Structure and Thermal Stability

Virtually all current analytical methods employed in the development of highly concentrated monoclonal antibody (MAb) formulations require dilution of the sample before acquiring data. Thus, there is an unmet need for methods to study proteins directly at high concentration, since extrapolation of stability indicating parameters obtained from dilute studies may not be representative of the high concentration solution. Only slight or no modifications of biophysical methods including fluorescence, UV absorbance, circular dichroism, and FTIR (ATR and transmittance) spectroscopies as well as differential scanning calorimetry (DSC) are described here that permit the direct study of immunoglobulins (and other proteins) at high concentrations. Although FTIR spectra show differences that are dependent upon sampling geometry, other spectroscopic data from two different recombinant MAbs suggests that structure of each antibody exists in a physically similar state in the concentration range of 0.1-190 mg/mL in 40 mM pH 6 citrate-phosphate buffer. Upon thermally stressing these proteins, spectroscopic techniques that probe tertiary structure demonstrate a decrease in the apparent thermal melting temperature of approximately 5-20 degrees C of both proteins with increasing concentration. In contrast, DSC thermograms and CD thermal experiments suggest a minor degree of stabilization (approximately 2 degrees C) for both antibodies although protein association could be responsible for these observations. Empirical phase diagrams produced from spectroscopic data also suggest (1) the existence of similar structural states at low temperatures independent of concentration and (2) a decrease in the temperature at which phase changes are observed with increasing concentration. The decrease in structural stability observed in these studies is probably the result of aggregation or self-association of the recombinant MAbs upon heating in crowded solutions and not due to a decrease in the intrinsic structural stability of the MAbs.

Antibody structure, instability, and formulation

The number of therapeutic monoclonal antibody in development has increased tremendously over the last several years and this trend continues. At present there are more than 23 approved antibodies on the US market and an estimated 200 or more are in development. Although antibodies share certain structural similarities, development of commercially viable antibody pharmaceuticals has not been straightforward because of their unique and somewhat unpredictable solution behavior. This article reviews the structure and function of antibodies and the mechanisms of physical and chemical instabilities. Various aspects of formulation development have been examined to identify the critical attributes for the stabilization of antibodies.

Clinical response to adalimumab: relationship to anti-adalimumab antibodies and serum adalimumab concentrations in rheumatoid arthritis

BACKGROUND

A substantial proportion of patients with rheumatoid arthritis (RA) do not respond, or lose initial response, to adalimumab treatment. One explanation for non-response is that patients develop anti-adalimumab antibodies.

OBJECTIVES

To evaluate the incidence of formation of antibody against adalimumab and the association with serum adalimumab concentrations and clinical response.

METHODS

In a cohort of 121 consecutive patients with RA treated with adalimumab, serum adalimumab concentrations and antibodies against adalimumab were measured together with clinical response variables before and up to 28 weeks after the start of treatment.

RESULTS

Anti-adalimumab antibodies were detected in 21 patients (17%) during 28 weeks of treatment. EULAR non-responders had antibodies significantly more often than good responders (34% vs 5%; p = 0.032). Patients with antibodies showed less improvement in disease activity (mean (SD) delta DAS28 0.65 (1.35)) than patients without antibodies (mean delta DAS28 1.70 (1.35)) (p = 0.001). Patients with antibodies during follow-up had lower serum adalimumab concentrations at 28 weeks than patients without antibodies (median 1.2 mg/l, range 0.0-5.6 vs median 11.0 mg/l, range 2.0-33.0, respectively; p<0.001). Good responders had higher serum adalimumab concentrations than moderate responders (p = 0.021) and non-responders (p = 0.001). Concomitant methotrexate use was lower in the group with anti-adalimumab antibodies (52%) than in the group without antibodies (84%) (p = 0.003).

CONCLUSIONS

Serum antibodies against adalimumab are associated with lower serum adalimumab concentrations and non-response to adalimumab treatment.

Antibody constructs in cancer therapy

Whereas over 85% of human cancers are solid tumors, of the 8 monoclonal antibodies (mAbs) currently approved for cancer therapy, 25% are directed at solid tumor surface antigens (Ags). This shortfall may be due to barriers to achieving adequate exposure in solid tumors. Advancements in tumor biology, protein engineering, and theoretical modeling of macromolecular transport are currently enabling identification of critical physical properties for antitumor Abs. It is now possible to structurally modify Abs or even replace full Abs with a plethora of Ab constructs. These constructs include Fab and Fab'(2) fragments, scFvs, multivalent scFvs (e.g., diabodies and tribodies), minibodies (e.g., scFv-CH3 dimers), bispecific Abs, and camel variable functional heavy chain domains. The purpose of the article is to provide investigators with a conceptual framework for exploiting the recent scientific advancements. The focus is on 2 properties that govern tumor exposure: 1) physical properties that enable penetration of and retention by tumors, and 2) favorable plasma pharmacokinetics. It is demonstrated that manipulating molecular size, charge, valence, and binding affinity can optimize these properties. These manipulations hold the key to promoting tumor exposure and to ultimately creating successful Ab therapies for solid tumors.

Quantitative structure-pharmacokinetic/pharmacodynamic relationships

Quantitative structure-activity relationships have long been considered a vital component of drug discovery and development, providing insight into the role of molecular properties in the biological activity of similar and unrelated compounds. Recognition that in vitro bioassay and/or pre-clinical activity are insufficient for anticipating which compounds are suitable leads for further development has shifted the focus toward integrated pharmacokinetic (PK) and pharmacodynamic (PD) processes. Over the last decade, considerable progress has been made in constructing empirical and mechanistic quantitative structure-PK relationships (QSPKR), as well as diverse mechanism-based pharmacodynamic models of drug effects. In this review, traditional and contemporary approaches to developing QSPKR models are discussed, along with selected examples of attempts to couple QSPKR and pharmacodynamic models to anticipate the intensity and time-course of the pharmacological effects of new or related compounds, or quantitative structure-pharmacodynamic relationships modeling. Such models are in accordance with the goals of systems biology and the ideal of designing drugs and delivery systems from first principles.

A mechanism-based binding model for the population pharmacokinetics and pharmacodynamics of omalizumab

AIM

Omalizumab, a humanized IgG monoclonal antibody that binds to human immunoglobulin E (IgE), interrupts the allergic cascade in asthmatic patients. The aim was to compare simultaneously drug exposure and IgE biomarker responses in Japanese and White patient populations.

METHODS

An instantaneous equilibrium drug-ligand binding and turnover population model was built from 202 Japanese patients. A posterior predictive evaluation for the steady-state distributions of omalizumab and IgE was then carried out against 531 White patients.

RESULTS

The mean parameters estimated from the Japanese patients were as follows: omalizumab clearance 7.32 +/- 0.153 ml h(-1), IgE clearance 71.0 +/- 4.68 ml h(-1) and the difference between that for omalizumab and the complex 5.86 +/- 0.920 ml h(-1), the volume of distribution for omalizumab and IgE 5900 +/- 107 ml, and that for the complex 3630 +/- 223 ml, the rate of IgE production 30.3 +/- 2.04 microg h(-1). Half-lives of IgG (23 days) and IgE (2.4 days) were close to previous reports. The dissociation constant for binding, 1.07 nM, was similar to in vitro values. Clearance and volume of distribution for omalizumab varied with bodyweight, whereas the clearance and rate of production of IgE were predicted accurately by baseline IgE. Overall, these covariates explained much of the interindividual variability.

CONCLUSIONS

The predictiveness of the Japanese model was confirmed by Monte-Carlo simulations for a White population, also providing evidence that the pharmacokinetics of omalizumab and IgE were similar in these two populations. Furthermore, the model enabled the estimation of not only omalizumab disposition parameters, but also the binding with and the rate of production, distribution and elimination of its target, IgE.

Pharmacokinetics of Cetuximab After Administration of Escalating Single Dosing and Weekly Fixed Dosing in Patients with Solid Tumors

PURPOSE

Previous studies of cetuximab pharmacokinetics did not fully characterize its elimination phase. The purpose of this trial was to evaluate the pharmacokinetics of cetuximab given as a single dose followed by weekly fixed repeated dosing in patients with solid tumors.

EXPERIMENTAL DESIGN

Patients were randomly assigned to treatment with a single 2-hour infusion of cetuximab at doses of 50, 100, 250, 400, or 500 mg/m2 followed 3 weeks later by weekly 1-hour infusions of cetuximab at a fixed dose of 250 mg/m2. Extended pharmacokinetic sampling was collected through 504 hours after the first drug administration. Trough samples were obtained before each fixed weekly dose. Single and multidose pharmacokinetic variables were correlated with clinical outcomes.

RESULTS

Forty patients were enrolled. Pharmacokinetic analysis confirmed previous reports of nonlinear pharmacokinetics for cetuximab. Modeling studies predicted a 90% saturation of clearance at a dose of 260 mg/m2. Analyses of weekly trough concentrations indicated a slight accumulation of drug concentrations following repeated weekly dosing. Correlative studies indicated a significant association between cetuximab clearance and both body surface area (P=0.002) and weight (P=0.002). The occurrence of rash was significantly associated with disease stability (P<0.002) but not with cetuximab pharmacokinetic variables.

CONCLUSIONS

Pharmacokinetic results support using body surface area or weight in calculating individual cetuximab doses. A weekly dose of 250 mg/m2 is predicted to nearly fully saturate cetuximab clearance and, by inference, epidermal growth factor receptors. The association between rash and disease stability supports further prospective studies of this relationship.

RANK ligand inhibition with denosumab for the management of osteoporosis

Receptor activator of nuclear factor-kappaB ligand (RANKL) is a cytokine member of the tumour necrosis factor family that is the principal final mediator of osteoclastic bone resorption. It plays a major role in the pathogenesis of postmenopausal osteoporosis, as well bone loss associated with rheumatoid arthritis, metastatic cancer, multiple myeloma, aromatase inhibitor therapy and androgen deprivation therapy. Denosumab (AMG 162) is an investigational fully human monoclonal antibody with a high affinity and specificity for RANKL. By inhibiting the action of RANKL, denosumab reduces the differentiation, activity and survival of osteoclasts, thereby slowing the rate of bone resorption. Denosumab has been shown to increase bone mineral density (BMD) and reduce bone turnover in postmenopausal women with low BMD. Denosumab is a potential treatment for osteoporosis and other skeletal disorders.

Structural basis for HIV-1 neutralization by a gp41 fusion intermediate-directed antibody

Elicitation of potent and broadly neutralizing antibodies is an important goal in designing an effective human immunodeficiency virus-1 (HIV-1) vaccine. The HIV-1 gp41 inner-core trimer represents a functionally and structurally conserved target for therapeutics. Here we report the 2.0-A-resolution crystal structure of the complex between the antigen-binding fragment of D5, an HIV-1 cross-neutralizing antibody, and 5-helix, a gp41 inner-core mimetic. Both binding and neutralization depend on residues in the D5 CDR H2 loop protruding into the conserved gp41 hydrophobic pocket, as well as a large pocket in D5 surrounding core gp41 residues. Kinetic analysis of D5 mutants with perturbed D5-gp41 interactions suggests that D5 persistence at the fusion intermediate is crucial for neutralization. Thus, our data validate the gp41 N-peptide trimer fusion intermediate as a target for neutralizing antibodies and provide a template for identification of more potent and broadly neutralizing molecules.

Pharmacokinetics of whole IgG equine antivenom: comparison between normal and envenomed rabbits

Pharmacokinetics of antivenoms has been mainly studied in normal animals, whereas very little is known on pharmacokinetics in envenomed animals. The aim of this study was to compare pharmacokinetic parameters of whole IgG equine antivenom in normal rabbits and in rabbits suffering a moderate envenoming by intramuscular injection of the venom of the viperid snake Bothriechis lateralis, which induces drastic microvascular alterations. Anti-Micrurus nigrocinctus antivenom was used, instead of polyvalent (Crotalinae) antivenom, to avoid the formation of toxin-antibody complexes which may alter antivenom pharmacokinetics. It was thus possible to study the effect of vascular alterations, i.e., edema and hemorrhage, induced by the venom on IgG antivenom distribution and elimination. An ELISA was utilized to quantify equine IgG antivenom concentration in rabbit serum. In addition, the amount of IgG antivenom extravasated in injected muscles was also determined. Results indicate that there were no significant differences, between control and envenomed rabbits, in any of the pharmacokinetic parameters investigated, thus suggesting that a moderate envenoming by this viperid species does not alter the pharmacokinetics of IgG antivenom. A significantly higher amount of antivenom IgG was observed in muscle from envenomed rabbits than in muscle from control animals. However, this corresponds to a low percentage of the administered antivenom and, therefore, this increased local extravasation does not have a significant impact in the overall antivenom pharmacokinetics.

Long-term multiple-dose pharmacokinetics of human monoclonal antibodies (MAbs) against human immunodeficiency virus type 1 envelope gp120 (MAb 2G12) and gp41 (MAbs 4E10 and 2F5)

While certain antibodies directed against the human immunodeficiency virus (HIV) envelope have the potential to suppress virus replication in vitro, the impact of neutralizing antibodies in vivo remains unclear. In a recent proof-of-concept study, the broadly neutralizing monoclonal antibodies 2G12, 4E10, and 2F5 exhibited inhibitory activities in vivo, as exemplified by a delay of the viral rebound following the interruption of antiretroviral therapy. Unexpectedly, the antiviral effect seen was most prominently due to 2G12 activity. To further investigate whether differential HIV-inhibitory activity was due to different pharmacokinetic properties of the antibodies, we performed a formal pharmacokinetic analysis with 14 patients. Repeated infusions at high dose levels were well tolerated by the patients and did not elicit an endogenous immune response against the monoclonal antibodies. The pharmacokinetic parameters of all three antibodies correlated with each other. Mean estimates were 0.047, 0.035, and 0.044 liter/kg for the central volume of distribution of 2G12, 4E10, and 2F5, respectively, and 0.0018, 0.0058, and 0.0077 liter/kg . day for the systemic clearance of 2G12, 4E10, and 2F5, respectively. Monoclonal antibody 2G12 had a significantly longer elimination half-life (21.8 +/- 7.2 days [P < 0.0001]) than monoclonal antibodies 4E10 (5.5 +/- 2.2 days) and 2F5 (4.3 +/- 1.1 days). The comprehensive pharmacokinetic data from this long-term multiple-dose phase II study were coherent with those from previous short-term phase I studies, as assessed by compartmental and noncompartmental techniques. The anti-HIV type 1 antibodies studied showed distribution and elimination kinetics similar to those seen for other human-like antibodies. Further studies examining tissue concentrations to explain the differential in vivo activity of the anti-gp120 antibody compared with those of the two anti-gp41 antibodies are warranted.

Immunoglobulin G has a role for systemic protein modulation in vivo: a new concept of protein homeostasis

The constant level of various proteins including albumin and cellular components in intravascular pool in vivo is strictly controlled by an unknown homeostatic mechanism, although there are fluctuations seen in pathologic conditions. Because the majority of the IgG in the serum is regarded as self-reactive natural autoantibodies, IgG may have a role to react with all proteins in vivo. It is hypothesized that like an immune system, a homeostatic mechanism for the protein pool also has a sensitive role to identify and memorize the extent and repertoire of both normal and pathogenic proteins on an individual basis, and IgG may be one of the major players in performing these functions. This hypothesis may explain the unresolved clinical observations as followed: (1) the marked increased IgG levels observed in self-limiting diseases presumed to come from immunological insults such as acute poststreptococcal glomerulonephritis and Kikuchi-Fujimoto disease, (2) an immediate reduction of all protein levels except immunoglobulins after intravenous immunoglobulin (IVIG) treatment in Kawasaki disease, (3) a unified explanation for the variety of immunomodulating effects exerted by IVIG, (4) the IgG-enzyme complexes observed in benign conditions such as macroamylasemia and hyperphosphatasemia, and (5) the marked decreased IgG level, which is correlated with the albumin level in minimal change nephrotic syndrome. IgG may be a 'watch-dog' for the disturbances of protein homeostasis in vivo. IgG may control the pathogenic proteins that appeared in disordered states, and it may help prevent the loss of proteins in case of nephrotic syndrome.

Pharmacokinetics of Intravenous Immunoglobulin: A Systematic Review

BACKGROUND

Intravenous immunoglobulin (IGIV) is used in the treatment of a wide variety of immune disorders. To our knowledge, no comprehensive or systematic review on the pharmacokinetics of IGIV has been published despite the availability of many published individual studies.

OBJECTIVE

To systematically review published studies of the pharmacokinetics of IGIV.

METHODOLOGY

We conducted a search of PubMed/MEDLINE from January 1966-September 2005 and EMBASE from January 1980-September 2005 for English-language articles on the pharmacokinetics of IGIV. This search was supplemented by a bibliographic review of all relevant articles.

RESULTS

Data elements extracted from these articles included study design, number of study subjects, indication for IGIV therapy, IGIV treatment regimen (formulation, dosage, and duration), pharmacokinetic parameters (clearance, volume of distribution, elimination rate constant, and half-life), analytic methodology, pharmacokinetic model, and blood sampling times. The United States Preventive Services Task Force rating scale was used to categorize the 50 pertinent citations identified in our literature search. According to the rating scale, 12 studies were level I (prospective, randomized, controlled studies), 3 were level II-1 (prospective, nonrandomized, controlled studies), 30 were level II-2 (prospective, nonrandomized, uncontrolled [cohort] studies), and 5 were level III (case reports or descriptive studies).

CONCLUSION

The pharmacokinetics of IGIV shows considerable intra- and interpopulation variability among patients with normal immunoglobulin levels, patients with primary immunodeficiency diseases, bone marrow transplant recipients, patients with immune deficiency due to chronic lymphocytic leukemia or multiple myeloma, very low birth weight neonates, neonates with suspected sepsis, high-risk infants in the neonatal intensive care unit, high-risk infants with cardiopulmonary disease, children with cryptogenic West or Lennox-Gastaut syndrome, women and infants with fetal alloimmune thrombocytopenia, and women with recurrent spontaneous abortions. Despite the large number of studies characterizing the pharmacokinetics of IGIV, major literature gaps include lack of information on IGIV clearance or area under the curve parameters and target serum immunoglobulin G concentrations. Further study is needed to rigorously characterize the pharmacokinetic properties of IGIV in a range of patient populations.

Target-mediated drug disposition and dynamics

Nonlinear pharmacokinetics and pharmacodynamics may result from several capacity-limited processes and often represent complicating factors in characterizing the pharmacological properties of drugs. Target-mediated drug disposition (TMDD) corresponds to a special case wherein a significant proportion of a drug (relative to dose) is bound with high affinity to a pharmacological target, such that this interaction is reflected in the pharmacokinetic properties of the drug. Dose-dependent effects on apparent pharmacokinetic parameters may manifest, including the steady-state volume of distribution and total systemic clearance. Although a few small molecular weight compounds have been identified to exhibit TMDD, the incidence of TMDD is likely to increase particularly among emerging biotechnology pharmaceuticals. The goal of this commentary is to describe the basic tenets of TMDD and discuss several mathematical modeling approaches for characterizing this phenomenon. Whereas traditional pharmacokinetic/pharmacodynamic models assume that the amount of the drug-target complex is negligible relative to the total amount of drug in the body, integrated mechanism-based models of TMDD incorporate the binding and stoichiometry of drug-target binding. These models may be utilized to infer the time-course of inaccessible system variables, such as the in vivo density of the drug-target complex, and provide a suitable platform for ascertaining the apparent pharmacodynamic implications of TMDD.

Potent antibody therapeutics by design

Antibodies constitute the most rapidly growing class of human therapeutics and the second largest class of drugs after vaccines. The generation of potent antibody therapeutics, which I review here, is an iterative design process that involves the generation and optimization of antibodies to improve their clinical potential.

Elimination mechanisms of therapeutic monoclonal antibodies

Targeted therapies using monoclonal antibodies have achieved important therapeutic applications in the treatment of various human diseases. Understanding the factors that impact the pharmacokinetics of monoclonal antibodies is of high importance for effective therapy. Many factors related to the target antigen, antibody and patients can affect antibody elimination. Evaluation of these factors will facilitate the understanding of the processes involved in antibody elimination.

In vivobehaviour of antibody–drug conjugates for the targeted treatment of cancer

It is a commonly held belief that most treatments for disseminated cancers are only moderately effective because the agents lack cell-killing mechanisms that act specifically on cancer cells. In antibody-drug conjugates, such nonspecific cytotoxic agents are combined with exquisitely specific monoclonal antibodies that bind to tumour-associated antigens and, thus, get endowed with new pharmacological characteristics. Not only is their activity newly targeted towards tumours and tumour cells, which hopefully renders them more tumour-specific, but they also acquire much of the pharmacokinetic behaviour of the monoclonal antibody component. With the structural composition of a macromolecular protein (the antibody), a small chemical cytotoxic agent and a linker to chemically connect these two molecules, antibody-drug conjugates are some of the most complex pharmacological agents ever developed. Their development over the last 20 years or so owes much to sophisticated in vitro and in vivo preclinical testing. This review attempts to summarise and exemplify many of the factors that had to be considered during the development, with special emphasis on the in vivo pharmacology of these agents.

FcRn mediates elongated serum half-life of human IgG in cattle

IgG has the longest survival time in the circulation of the Ig classes and the lowest fractional catabolic rate. The neonatal Fc receptor (FcRn) plays an important role in regulating these processes. Recently, we have cloned the bovine neonatal Fc receptor (bFcRn) alpha chain and detected its expression in various epithelial cells which are mediating IgG secretion. However, its function in IgG homeostasis has not been investigated. In the current study, we analyzed the binding affinity of bovine and human IgGs to bFcRn using surface plasmon resonance and by in vitro radioreceptor binding assays. As human IgG binds stronger to the bFcRn, than bovine IgG at pH 6, we subsequently analyzed its catabolism in normal and transchromosomic calves that produce human Igs. Pharmacokinetic studies showed that human IgG had approximately 33 days serum half-life both in normal and transchromosomic calves, which is more than two times longer than its bovine counterpart. We also demonstrate FcRn expression in endothelial cells and in the kidney which are supposed to be involved in IgG metabolism. These data suggest that bFcRn is involved in IgG homeostasis in cattle and furthermore, that the transchromosomic calves producing human Igs can effectively protect their human IgGs which have implications for successful large-scale production of therapeutic antibodies.

Antiangiogenic chimeric anti-endoglin (CD105) antibody: pharmacokinetics and immunogenicity in nonhuman primates and effects of doxorubicin

We generated a human/mouse chimeric antibody c-SN6j of human IgG1 isotype from a murine anti-human endoglin (EDG) monoclonal antibody (mAb) SN6j that suppressed angiogenesis, tumor growth and metastasis in mice. We determined pharmacokinetics (PKs) and immunogenicity of c-SN6j in monkeys after multiple i.v. injections. A dose-escalation study was performed by administration of c-SN6j into six monkeys at the dose of 1 mg, 3 mg and 10 mg per kg body weight. In addition, both c-SN6j (3 mg/kg) and doxorubicin (0.275 mg/kg) were injected into two monkeys. c-SN6j and doxorubicin were injected twice a week for 3 weeks. We developed a unique and sensitive ELISA by sequentially targeting the common and idiotypic epitopes of c-SN6j-Fv to quantify plasma c-SN6j. Application of the ELISA showed that increasing the c-SN6j dose resulted in a proportional increase in the circulating c-SN6j after the first injection. In addition, the estimated area under the curve (AUC) for the first injection of c-SN6j is proportional to dose. We carried out detailed analyses of PKs of c-SN6j during and after the repeated injections. Our model of PKs fitted the empirical data well. Addition of doxorubicin modulated the PK parameters. We developed two ELISAs to separately determine the immune responses to the murine part and the human part of c-SN6j in monkeys. Interestingly, the murine part induced a weaker immune response than the human part. Doxorubicin potentiated the immune responses. Increasing the dose of c-SN6j increased plasma levels of c-SN6j but did not increase the immune responses to c-SN6j.

Pharmacokinetic and pharmacodynamic effects of high-dose monoclonal antibody therapy in a rat model of immune thrombocytopenia

Intravenous administration of pooled, polyvalent human immunoglobulin (IVIG) has been used for over 20 years as a therapy for immune thrombocytopenia (ITP). IVIG is available in limited quantities, and clinical preparations have been associated with the transfer of human pathogens. We have proposed that high-dose monoclonal antibody may be used in lieu of IVIG to achieve beneficial effects in the treatment of ITP. The current study investigates the effects of high-dose monoclonal antibody therapy in a rat model of ITP. Hybridoma cells secreting a murine monoclonal antiplatelet antibody (7E3) and murine monoclonal anti-methotrexate IgG (AMI) were grown in serum-free media. Next, 7E3, 8 mg kg(-1), was administered intravenously to rats following pretreatment with saline or AMI (1 g kg(-1) IV). AMI and 7E3 plasma concentrations were determined via enzyme-linked immunosorbent assay, and platelet count was determined with a Cell-Dyne hematology analyzer. Severe, transient thrombocytopenia was induced by 7E3. Platelet counts dropped to approximately 8% of initial values within 1 hour after 7E3 administration. AMI pretreatment dramatically affected 7E3-induced thrombocytopenia, significantly altering the time course of thrombocytopenia (P < .05) and significantly decreasing the severity of 7E3-induced thrombocytopenia (ie, following AMI pretreatment, nadir platelet count was greater than 8-fold that of the control group, P < .05). In addition, AMI pretreatment induced a 57% increase in 7E3 clearance (1.13 +/- 0.13 mL h(-1) kg(-1) vs 0.72 +/- 0.08 mL h(-1) kg(-1), P < .05). Consequently, high-dose monoclonal antibody therapy attenuated thrombocytopenia and produced a moderate increase in the clearance of antiplatelet antibodies in a rat model of ITP.

Enhancing exposure of protein therapeutics

Therapeutic proteins have made a major impact on medicine, with significant expansion in the past two decades. The medicinal attributes of these agents, particularly their efficacy and often their safety profile, make protein therapeutics attractive, despite the general necessity of invasive (parenteral) delivery. This perceived hurdle has been a primary component in limiting expansion of this class of drug therapies. Strategies that reduce the frequency of administration directly provide greater convenience to the patient, and potentially greater efficacy, that can yield a significant treatment advantage.:

Pharmacokinetics of a F(ab')2 scorpion antivenom in healthy human volunteers

This paper presents the first study of F(ab')2 scorpion antivenom pharmacokinetics in humans. We have studied the pharmacokinetics of an antiscorpion venom preparation (Alacramyn) in eight human healthy volunteers. The fabotherapic was administered as a 47.5 mg i.v. bolus. Blood samples were drawn at 0, 5, 15, 30, 45, 60, 90, 120, 180 and 360 min after antivenom administration. Subsequently, the volunteers made seven visits to the hospital. Four of them at 24 h intervals, one at day 10, and one at day 21. We measured antivenom plasmatic concentrations using a specific high sensitivity ELISA method for F(ab')2. The time course of F(ab')2 in serum of seven subjects was well described by a lineal combination of three exponential components; a four exponential component model was necessary to fit the eighth subject. The most significant antivenom pharmacokinetic parameters determined were: AUC(infinity)=596.9 (369.3, 891.2) mg h l(-1); V(c) = 3.1 (2.3, 4.3)l; V(ss) = 15.4 (12.8, 39.9)l; MRT = 250.0 (218.8, 310.2) h; CL = 96.6 (58.0, 139.2) ml h(-1); t(1/2,tau1) (also called t(1/2,alpha)) = 0.25 (0.13, 0.37) h; t(1/2,tau(z)) (corresponding to the slowest component) = 161.3 (141.0, 212.0) h.

Quasi-equilibrium pharmacokinetic model for drugs exhibiting target-mediated drug disposition

PURPOSE

The aim of this study is to derive and evaluate an equilibrium model of a previously developed general pharmacokinetic model for drugs exhibiting target-mediated drug disposition (TMDD).

METHODS

A quasi-equilibrium solution to the system of ordinary differential equations that describe the kinetics of TMDD was obtained. Computer simulations of the equilibrium model were carried out to generate plasma concentration-time profiles resulting from a large range of intravenous bolus doses. Additionally, the final model was fitted to previously published pharmacokinetic profiles of leukemia inhibitory factor (LIF), a cytokine that seems to exhibit TMDD, following intravenous administration of 12.5, 25, 100, 250, 500, or 750 microg/kg in sheep.

RESULTS

Simulations show that pharmacokinetic profiles display steeper distribution phases for lower doses and similar terminal disposition phases, but with slight underestimation at early time points as theoretically expected. The final model well-described LIF pharmacokinetics, and the final parameters, which were estimated with relatively good precision, were in good agreement with literature values.

CONCLUSIONS

An equilibrium model of TMDD is developed that recapitulates the essential features of the full general model and eliminates the need for estimating drug-binding microconstants that are often difficult or impossible to identify from typical in vivo pharmacokinetic data.

Phase 1 safety and pharmacokinetic study of chimeric murine-human monoclonal antibody c alpha Stx2 administered intravenously to healthy adult volunteers

Hemolytic-uremic syndrome (HUS) is a serious complication of infection by Shiga toxin-producing Escherichia coli. Shiga toxin type 2 (Stx2) is responsible for the renal toxicity that can follow intestinal infection and hemorrhagic colitis due to E. coli. A chimeric mouse-human antibody, designated c alpha Stx2, that has neutralizing activity in a mouse model was produced and tested in healthy adult volunteers. In this phase I dose escalation study, c alpha Stx2 was generally well tolerated. Pharmacokinetic studies indicated that clearance was stable over the dose range of 1.0 to 10 mg/kg of body weight (0.249 +/- 0.023 ml/kg/h) but was higher for the 0.1-mg/kg dose (0.540 +/- 0.078 ml/kg/h), suggesting saturable elimination. A similar nonlinear trend was observed for the volume of distribution, where average values ranged from 0.064 +/- 0.015 liter/kg for the 1.0- to 10-mg/kg doses and 0.043 +/- 0.005 for the 0.01-mg/kg dose. The relatively small volume of distribution suggests that the antibody is limited to the vascular (plasma) compartment. The mean half-life was 165 +/- 66 h, with lowest values observed for the 0.1-mg/kg dose (56.2 +/- 9.7 h) and the highest values reported for the 10.0-mg/kg dose (206.4 +/- 12.4 h). Future studies are needed to confirm the safety of this c alpha Stx2, and innovative clinical trials will be required to measure its efficacy in preventing or treating HUS.

Trastuzumab and liposomal Doxorubicin in the treatment of mcf-7 xenograft tumor-bearing mice: combination does not affect drug serum levels

PURPOSE

We assessed the combination of doxorubicin or liposomal doxorubicin with trastuzumab for alterations in peak serum drug levels, as these agents are increasingly being paired in the treatment of aggressive breast cancer. We hypothesized that trastuzumab would exhibit a slower rate of elimination from the serum when in combination with liposomal doxorubicin based on the known effects of liposomal doxorubicin on phagocytic cells of the mononuclear phagocyte system (MPS), which are responsible in part for the uptake and degradation of antibodies.

METHODS

Doxorubicin and trastuzumab serum levels were assessed following injection of free doxorubicin, liposomal doxorubicin, or trastuzumab into female RAG2-M mice bearing subcutaneous MCF-7(HER-2) tumors. The effects of combination drug treatment on tumor growth were compared to single-agent treatment.

RESULTS

Peak serum trastuzumab levels were not altered as a result of addition of doxorubicin therapy, nor were doxorubicin levels altered over 24 h as a result of coadministration of trastuzumab. Liposomal doxorubicin administration did result in serum doxorubicin levels 200- to 1000-fold higher than with injection of free doxorubicin.

CONCLUSIONS

For the specific combination of trastuzumab with doxorubicin, either in free or liposomal form, coadministered in mice, there was no impact of one drug on the other in terms of peak serum drug levels or efficacy.

Approaches to optimize the use of monoclonal antibodies to epidermal growth factor receptor

Preclinical and clinical studies consistently demonstrate the antitumor activity of the various monoclonal antibodies (mAbs) that block ligand binding to the extracellular domain of the epidermal growth factor receptor (EGFR). However, the objective antitumor activities of these agents are disproportionately lower than would be expected based on the high rates of expression, overexpression, and aberrations of EGFR in human malignancies, particularly carcinomas. Several technologic and clinical approaches are being explored to optimize the potency of these antibodies, such as humanization of the murine parent molecules, and conjugation and widening of the specificity of the mAb. Also, combined therapy with the different types of EGFR-interacting or other targeted agents may lead to a heightened potential. This review highlights the results of current approaches for improvement of the therapeutic indices of these agents.

Mechanisms of Intravenous Immunoglobulin Action in Immune Thrombocytopenic Purpura

The use of high-dose intravenous gamma immunoglobulin (IVIG) for the treatment of immune thrombocytopenic purpura (ITP) was first reported more than two decades ago. After the therapeutic benefit of IVIG was established in ITP, it was then successfully used to treat many other autoimmune diseases. Although a complete definition of the mechanism of IVIG action is still lacking, extensive research suggests that IVIG may achieve its therapeutic effects through multiple mechanisms. IVIG exerts immunomodulatory effects that may include antiidiotypic neutralization of antiplatelet antibodies, stimulation of Fcgamma receptor IIB expression, and inhibition of Fcgamma receptor-mediated platelet destruction. Recent work suggests that a large fraction of the benefit provided by IVIG may be the result of competitive inhibition of neonatal Fc receptor (FcRn) and IVIG-induced acceleration of antiplatelet antibody elimination. This review provides an overview and critical discussion of mechanisms that may be responsible of IVIG effects in ITP.