Bispecific small molecule-antibody conjugate targeting prostate cancer.

Bispecific antibodies, which simultaneously target CD3 on T cells and tumor-associated antigens to recruit cytotoxic T cells to cancer cells, are a promising new approach to the treatment of hormone-refractory prostate cancer. Here we report a site-specific, semisynthetic method for the production of bispecific antibody-like therapeutics in which a derivative of the prostate-specific membrane antigen-binding small molecule DUPA was selectively conjugated to a mutant αCD3 Fab containing the unnatural amino acid, p-acetylphenylalanine, at a defined site. Homogeneous conjugates were generated in excellent yields and had good solubility. The efficacy of the conjugate was optimized by modifying the linker structure, relative binding orientation, and stoichiometry of the ligand. The optimized conjugate showed potent and selective in vitro activity (EC50 ~ 100 pM), good serum half-life, and potent in vivo activity in prophylactic and treatment xenograft mouse models. This semisynthetic approach is likely to be applicable to the generation of additional bispecific agents using drug-like ligands selective for other cell-surface receptors.

Neutralizing Antibody Sample Testing and Report Harmonization.

Immunogenicity testing and characterization is an important part of understanding the immune response to administration of a protein therapeutic. Neutralizing antibody (NAb) assays are used to characterize a positive anti-drug antibody (ADA) response. Harmonization of reporting of NAb assay performance and results enables efficient communication and expedient review by industry and health authorities. Herein, a cross-industry group of NAb assay experts have harmonized NAb assay reporting recommendations and provided a bioanalytical report (BAR) submission editable template developed to facilitate agency filings. This document addresses key bioanalytical reporting gaps and provides a report structure for documenting clinical NAb assay performance and results. This publication focuses on the content and presentation of the NAb sample analysis report including essential elements such as the method, critical reagents and equipment, data analysis, study samples, and results. The interpretation of immunogenicity data, including the evaluation of the impact of NAb on safety, exposure, and efficacy, is out of scope of this publication.

Anti-drug Antibody Sample Testing and Reporting Harmonization.

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

ARX788, a Site-specific Anti-HER2 Antibody-Drug Conjugate, Demonstrates Potent and Selective Activity in HER2-low and T-DM1-resistant Breast and Gastric Cancers.

First-generation antibody-drug conjugates (ADC) are heterogeneous mixtures that have shown clinical benefit, but generally exhibited safety issues and a narrow therapeutic window due, in part, to off-target toxicity caused by ADC instability. ARX788 is a next-generation, site-specific anti-HER2 ADC that utilizes a unique nonnatural amino acid-enabled conjugation technology and a noncleavable Amberstatin (AS269) drug-linker to generate a homogeneous ADC with a drug-to-antibody ratio of 1.9. ARX788 exhibits high serum stability in mice and a relatively long ADC half-life of 12.5 days. When compared in vitro against T-DM1 across a panel of cancer cell lines, ARX788 showed superior activity in the lower HER2-expressing cell lines and no activity in normal cardiomyocyte cells. Similarly, ARX788 significantly inhibited tumor growth, and generally outperformed T-DM1 in HER2-high and HER2-low expression xenograft models. Breast and gastric cancer patient-derived xenograft studies confirmed strong antitumor activity of ARX788 in HER2-positive and HER2-low expression tumors, as well as in a T-DM1-resistant model. The encouraging preclinical data support the further development of ARX788 for treatment of patients with HER2-positive breast and gastric cancer, including those who have developed T-DM1 resistance, and patients with HER2-low expression tumors who are currently ineligible to receive HER2-targeted therapy.

Recommendations for the development and validation of confirmatory anti-drug antibody assays.

Identification and characterization of anti-drug antibodies is a critical component of biopharmaceutical drug development. The tiered approach for immunogenicity testing consists of screening, confirmatory, and characterization assays. Herein, we provide recommendations for confirmatory assays by expanding upon published guidance and present common practices across the industry. The authors recommend scientific approaches for development and validation of confirmatory assays using competition methods in ligand-binding assays, along with statistical formulae for routine use and validation. The paper will assist in understanding the confirmatory assay, and carefully implementing validation criteria a priori, as well as during sample analysis. These approaches represent the authors' current knowledge and practices, with the aim that more uniform practices will be applied across the industry.

Comparison of bioanalytical methods for the quantitation of PEGylated human insulin.

PURPOSE: The quality of bioanalytical data is dependent upon selective, sensitive, and reproducible analytical methods. With evolving technologies available, bioanalytical scientists must assess which is most appropriate for their molecule through proper method validation. For an early stage PEGylated insulin program, the characteristics of four platforms, ELISA, ECL, Gyrolab, and LC-MS/MS, were evaluated using fit-for-purpose method development and validation, while also evaluating costs. METHOD: Methods selected for validation required acceptable performance based on satisfaction of a priori criteria prior to proceeding to subsequent stages of validation. LBA pre-validation included reagent selection, evaluation of matrix interference, and range determination. LC-MS/MS pre-validation included selection of a signature peptide; optimization of sample preparation, HPLC, and LC-MS/MS conditions; and calibration range determination. Pre-study validation tested accuracy and precision (mean bias criteria±30%; precision≤30%). Pharmacokinetic (PK) parameters were estimated for an in vivo study with WinNonlin noncompartmental analysis. Statistics were performed with JMP using ANOVA and Tukey-Kramer post hoc analysis. A cost analysis was performed for a 200-sample PK study using the methods from this study. RESULTS: All platforms, except Gyrolab, were taken through validation. However, a typical Gyrolab method was included for the cost analysis. Ranges for the ELISA, ECLA, and LC-MS/MS were 8.52-75, 2.09-125, and 100-1000 ng/mL, respectively, and accuracy and precision fell within a priori criteria. PK samples were analyzed in the 3 validated methods. PK profiles and parameters are similar for all methods, except LC-MS/MS, which differed at t=24h and with AUC0-24. Further investigation into this difference is warranted. The cost analysis identified the Gyrolab platform as the most expensive and ELISA as the least expensive, with method specific consumables attributing significantly to costs. CONCLUSIONS: ECLA had a larger dynamic range and sensitivity, allowing accurate assessment of PK parameters. Although this method was more expensive than the ELISA, it was the most appropriate for the early stage PEGylated insulin program. While this case study is specific to PEGylated human insulin, it highlights the importance of evaluating and selecting the most appropriate platform for bioanalysis during drug development.

Summary of confirmation cut point discussions.

A subgroup of AAPS NBC Immunogenicity Workshop attendees met to discuss the current recommendations in white papers and guidance documents, to describe and discuss current practices, and to resolve concerns as to the biologically and statistically appropriate approaches to determining a confirmatory cut point for immunogenicity assays. This is a summary of our discussions and recommendations.