Dana L. Baker

Improved Potency of Hyperactive and Actin-resistant Human DNase I Variants for Treatment of Cystic Fibrosis and Systemic Lupus Erythematosus

The ability of recombinant human DNase I (DNase I) to degrade DNA to lower molecular weight fragments is the basis for its therapeutic use in cystic fibrosis (CF) patients and its potential use as a treatment for systemic lupus erythematosus (SLE). To increase the potency of human DNase I, we have generated and characterized three classes of mutants: (a) hyperactive variants, which have from one to six additional positively charged residues (+1 to +6) and digest DNA much more efficiently relative to wild type, (b) actin-resistant variants, which are no longer inhibited by G-actin, a potent inhibitor of DNase I, and (c) combination variants that are both hyperactive and actin-resistant. For DNA scission in CF sputum where the DNA concentration and length are large, we measured a ∼20-fold increase in potency relative to wild type for the +3 hyperactive variant Q9R/E13R/N74K or the actin-resistant variant A114F; the hyperactive and actin-resistant combination variant was ∼100-fold more potent than wild type DNase I. For digesting lower concentrations of DNA complexed to anti-DNA antibodies in human serum, we found a maximal enhancement of ∼400-fold over wild type for the +2 variant E13R/N74K. The +3 enzymes have ∼4000-fold enhancement for degrading moderate levels of exogenous DNA spiked into human serum, whereas the +6 enzyme has ∼30,000-fold increased activity for digesting the extremely low levels of endogenous DNA found in serum. The actin resistance property of the combination mutants further enhances the degree of potency in human serum. Thus, the human DNase I variants we have engineered for improved biochemical and pharmacodynamic properties have greater therapeutic potential for treatment of both CF and SLE.

Effect of antigen binding affinity and effector function on the pharmacokinetics and pharmacodynamics of anti-IgE monoclonal antibodies

Modulating the binding affinities to IgE or changing the FcγR binding properties of anti-IgE antibodies offers an opportunity to enhance the therapeutic potential of anti-IgE antibodies, but the influence of increased affinity to IgE or reduced Fc effector function on the pharmacological properties of anti-IgE therapies remains unclear. Our studies were designed to characterize the pharmacokinetics, pharmacodynamics and immune-complex distribution of two high-affinity anti-IgE monoclonal antibodies, high-affinity anti-IgE antibody (HAE) 1 and 2, in mice and monkeys. HAE1, also known as PRO98498, is structurally similar to omalizumab (Xolair®), a humanized anti-IgE IgG1 marketed for the treatment of asthma, but differs by 9 amino acid changes in the complementarity-determining region resulting in a 23-fold improvement in affinity. HAE2 is similar to HAE1, but its Fc region was altered to reduce binding to Fcγ receptors. As expected given the decreased binding to Fcγ receptors, systemic exposure to pre-formed HAE2:IgE complexes in mice was greater (six-fold) and distribution to the liver lower (four-fold) compared with HAE1:IgE complexes. In monkeys, systemic exposure to HAE1 was similar to that previously observed for omalizumab in this species, but required comparatively lower serum drug concentrations to suppress free IgE levels. HAE2 treatment resulted in greater exposure and greater increase of total IgE, relative to HAE1, because of decreased clearance of HAE2:IgE complexes. Overall, these data suggest that increased binding affinity to IgE may provide a more effective therapeutic for asthma patients, and that retaining FcγR binding of the anti-IgE antibody is important for elimination of anti-IgE:IgE complexes.

Evaluation of two commercial omalizumab/free IgE immunoassays: implications of use during therapy

Abstract Background: The anti-IgE monoclonal antibody, omalizumab, is approved in the US as add-on therapy for patients ≥12 years of age with moderate-to-severe persistent allergic asthma. Omalizumab is administered according to the US Food and Drug Administration approved dosing table included in the prescribing information. The dosing table was developed using Genentech’s free IgE assay and is designed to achieve free serum IgE levels of <50 ng/mL, known to be associated with clinical benefit. Lack of clinical benefit in a subset of patients on omalizumab has prompted demand for commercial free IgE assays to guide omalizumab dosing. To date, two commercial free IgE assays marketed by ViraCor-IBT (no longer offered) and BioTeZ have been available to physicians. Objective: This study compares the results generated from the two commercial free IgE assays with the free IgE levels generated by the Genentech assay. Methods: Two serum sample sets were prepared using 20 samples from patients with a wide range of IgE and omalizumab from an omalizumab clinical trial and 36 samples from omalizumab-naïve patients. Different amounts of omalizumab were added to the 36 omalizumab naïve samples based on measured total IgE levels to ensure that a good range of IgE and omalizumab was represented in the study samples. Samples were randomized for blinded analysis of free IgE levels using the Genentech, ViraCor-IBT and BioTeZ free serum IgE assays. Analysis of samples in the ViraCor-IBT assay were conducted by ViraCor-IBT and the analysis of samples using the Genentech and BioTeZ assay methods were conducted by a third party contract research organization. Results: The ViraCor-IBT and BioTeZ free IgE assays demonstrated significantly higher free IgE levels than the Genentech free IgE assay. Twenty-nine of 56 samples tested <50 ng/mL in the Genentech assay; of these, 12/29 (41%) and 20/29 (69%) tested >50 ng/mL in the BioTeZ and ViraCor-IBT assays, respectively. In the BioTeZ free IgE evaluations, 11/20 samples that were re-tested had inter-assay differences ranging from 40–190%. Conclusions: Free ligand (such as IgE) measurements are challenging and dependent on the method and reagents used. The Viracor-IBT and BioTeZ methods tend to over-estimate free serum IgE levels compared with the Genentech free IgE assay. Using these assays to monitor therapy and adjust omalizumab doses post treatment is considered off-label use and could lead to a potential risk for unnecessary treatment and/or risk to patient safety.

Evaluation of IgE Antibodies to Omalizumab (Xolair®) and Their Potential Correlation to Anaphylaxis

ABSTRACTOmalizumab (Xolair®) is a recombinant humanized monoclonal antibody that selectively binds to human immunoglobulin E (IgE). Omalizumab is used to treat IgE-mediated diseases such as chronic idiopathic urticaria (CIU) and moderate to severe allergic asthma. In pre-marketing clinical trials in patients with asthma, anaphylaxis was reported in 3 of 3,507 (0.1%) patients. In post-marketing spontaneous reports, the frequency of anaphylaxis attributed to omalizumab use was estimated to be at least 0.2% of patients based on an estimated exposure of about 57,300 patients from June 2003 through December 2006. To better understand the risk of anaphylaxis in patients with allergic asthma receiving omalizumab, a post-marketing pharmacosurveillance study was initiated in 2009. As part of this study, an assay was developed to detect antibodies of IgE isotype to omalizumab. Serum samples from patients in the study were evaluated using this assay. Our results indicated that there was no observable correlation between either anaphylaxis or skin test reactivity and the presence of antibodies of IgE isotype to omalizumab. Here, we discuss the development of this assay as well as the results of the immunogenicity assessment.

When Assay Format Matters: a Case Study on the Evaluation of Three Assay Formats to Support a Clinical Pharmacokinetic Study

Data generated using various immunoassay methods are an integral part of the development of protein therapeutics. These assays are used in clinical and preclinical studies to establish the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics as well as to assess the immunogenicity properties of a therapeutic. PK assays measure therapeutic levels post-administration which is essential for understanding the effective dose and dose regimen for a therapeutic. Anti-OX40L is a fully humanized monoclonal antibody designed for the potential treatment of an autoimmune disease. The anti-OX40L human PK assay is required to be sensitive, robust, and precise. To address challenges due to assay sensitivity and reproducibility, as well as assay technology limitations, during development of the anti-OX40L human PK assay, three different assays, including an MSD-based electrochemiluminescence assay (ECLA), a fluorometric enzyme-linked immunosorbent assay (ELISA), and a colorimetric ELISA, were evaluated. The MSD-based assay was the most sensitive but posed risk of inter-well signal crosstalk. The fluorescence ELISA fell short on reproducibility. The colorimetric ELISA was ultimately chosen for supporting sample analysis. This paper presents characterization data obtained from each of these assay formats, challenges that were encountered in the development of the assay, and the rationale for selecting the ultimate assay format.

Response to Becher and Strohner comment regarding Baker DL et al. Evaluation of two commercial omalizumab/free IgE immunoassays: implications of use during therapy. CMRO 2014;30:913-22

We would like to reiterate that the purpose of this paper is to discourage the use of free IgE to adjust omalizumab dosing, which is considered off-label use of omalizumab. The manuscript is meant to demonstrate that measurement of free ligands (in this case IgE) is technically very challenging and different methods can produce very different results. This paper is not suggesting that the Genentech assay is the gold standard, rather that the Genentech free IgE assay is the clinically relevant assay in this context because it was used to generate the FDA approved omalizumab dosing table and the target free IgE levels. Regardless of the inconsistencies observed with the BioTeZ assay, both commercial assays tend to have over-recovery compared with the Genentech assay. Therefore, we felt compelled to warn against the use of commercial free IgE assays for off-label use as the two commercial assays produce very different results compared with the Genentech assay. The data was only to show how different the IgE results can be and the potential risk for unnecessary treatment and/or risk to patient safety.

A Multi-site In-depth Evaluation of the Quanterix Simoa from a User’s Perspective

An in-depth evaluation of the Quanterix© Simoa™ platform was undertaken by scientists from the AAPS Emerging Technologies Focus Group to determine the overall performance of the technology as well as provide guidance to future users. In order to test the platform in a non-GLP bioanalytical setting, a cross-site evaluation of the Quanterix IL-6 biomarker kit was performed. Parameters tested during this evaluation included sensitivity, accuracy and precision, and parallelism in human serum from normal individuals. The results demonstrated improved sensitivity compared to the claimed sensitivity of other commercially available IL-6 kits and showed excellent site-to-site reproducibility. Observed issues included difficulties with system reliability and a lack of parallelism and specificity in a subset of samples. Overall, these results demonstrate that while there are challenges to the Simoa platform this technology offers automation capabilities and excellent sensitivity that enhance bioanalysis especially of low-abundance analytes.