Receptor occupancy by flow cytometry

Dose escalation PET imaging for safety and effective therapy dose optimization of a bispecific antibody

Selecting the dose for efficacy and first-in-human studies of bispecific antibodies (BsAbs) is a challenging process. Herein, positron emission tomography (PET) imaging with ⁸⁹Zr-labeled IBI322, an anti-CD47/PD-L1 BsAb, was used to optimize the safety and effective therapy dose. By labeling with ⁸⁹Zr, we aimed to assess the pharmacokinetics (PK), safety, and target engagement of IBI322 with dose escalation dynamic PET imaging in humanized transgenic animal models bearing MC38 tumors (knock-in of hCD47 and hPDL1). ⁸⁹Zr-labeled IBI322 specifically accumulated in tumors with a tumor-to-muscle ratio of 12.37 ± 1.42 at 168 h (0.22 mg/kg) and the biodistribution of normal tissues from PET imaging could be used for preliminary safety prediction. According to the Pearson correlation analysis between the ELISA-quantified serum concentration and heart uptake (%ID/g) (r = 0.980), a modified Patlak model was proposed. The exploratory target-mediated 50% (0.38 mg/kg) and 90% (0.63 mg/kg) inhibitory mass doses were calculated with the current modified Patlak model. The preliminary pharmacodynamics (PD) study with 0.34 mg/kg revealed that the dose prediction was rational. In conclusion, dose escalation PET imaging with ⁸⁹Zr-labeled antibodies is promising for PK/PD modeling and safety prediction, and helpful for determining rational dosing for preclinical and clinical trials of BsAbs.

Digital Receptor Occupancy Assay in Quantifying On- and Off-Target Binding Affinities of Therapeutic Antibodies

While monoclonal antibodies are the fastest-growing class of therapeutic agents, we lack a method that can directly quantify the on- and off-target binding affinities of newly developed therapeutic antibodies in crude cell lysates. As a result, some therapeutic antibody candidates could have a moderate on-target binding affinity but a high off-target binding affinity, which not only gives a reduced efficacy but triggers unwanted side effects. Here, we report a single-molecule counting method that precisely quantifies antibody-bound receptors, free receptors, and unbound antibodies in crude cell lysates, termed digital receptor occupancy assay (DRO). Compared to the traditional flow cytometry-based binding assay, DRO assay enables direct and digital quantification of the three molecular species in solution without the additional antibodies for competitive binding. When characterizing the therapeutic antibody, cetuximab, using DRO assay, we found the on-target binding ratio to be 65% and the binding constant (K_d) to be 2.4 nM, while the off-target binding causes the binding constant to decrease by 0.3 nM. Other than cultured cells, the DRO assay can be performed on tumor mouse xenograft models. Thus, DRO is a simple and highly quantitative method for cell-based antibody binding analysis which can be broadly applied to screen and validate new therapeutic antibodies.

2018 White Paper on Recent Issues in Bioanalysis: focus on flow cytometry, gene therapy, cut points and key clarifications on BAV (Part 3 - LBA/cell-based assays: immunogenicity, biomarkers and PK assays)

The 2018 12^th Workshop on Recent Issues in Bioanalysis took place in Philadelphia, PA, USA on April 9-13, 2018 with an attendance of over 900 representatives from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations and regulatory agencies worldwide. WRIB was once again a 5-day full immersion in bioanalysis, biomarkers and immunogenicity. As usual, it was specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest including both small- and large-molecule bioanalysis involving LCMS, hybrid LBA/LCMS and LBA/cell-based assays approaches. This 2018 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2018 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 3) covers the recommendations for large molecule bioanalysis, biomarkers and immunogenicity using LBA and cell-based assays. Part 1 (LCMS for small molecules, peptides, oligonucleotides and small molecule biomarkers) and Part 2 (hybrid LBA/LCMS for biotherapeutics and regulatory agencies' inputs) are published in volume 10 of Bioanalysis, issues 22 and 23 (2018), respectively.

2016 White Paper on recent issues in bioanalysis: focus on biomarker assay validation (BAV): (Part 3 – LBA, biomarkers and immunogenicity)

The 2016 10th Workshop on Recent Issues in Bioanalysis (10th WRIB) took place in Orlando, Florida with participation of close to 700 professionals from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations, and regulatory agencies worldwide. WRIB was once again a weeklong event – A Full Immersion Week of Bioanalysis for PK, Biomarkers and Immunogenicity. As usual, it is specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest including both small and large molecules involving LCMS, hybrid LBA/LCMS, and LBA approaches, with the focus on PK, biomarkers and immunogenicity. This 2016 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. This White Paper is published in 3 parts due to length. This part (Part 3) discusses the recommendations for large molecule bioanalysis using LBA, biomarkers and immunogenicity. Parts 1 (small molecule bioanalysis using LCMS) and Part 2 (Hybrid LBA/LCMS and regulatory inputs from major global health authorities) have been published in the Bioanalysis journal, issues 22 and 23, respectively.

Robust Ki67 detection in human blood by flow cytometry for clinical studies

AIM

Ki67 is a prognostic and/or predictive biomarker in patients with malignancies. Flow cytometry is a powerful technology for single-cell multiparameter analysis.

RESULTS

We developed and validated a multicolor quantitative flow cytometry assay for detection of intracellular Ki67 expression in various immune cell subsets from human blood. The assay was optimized and showed excellent precisions. Assessment of the sample stability indicated that percentage changes from the fresh sample for the reportable results of interest were within 20%, up to 72 h after blood collection in the Cyto-Chex^® BCT tube.

CONCLUSION

The validated assay is sufficiently robust to analyze clinical samples. Easy access to peripheral blood enables continuous monitoring of Ki67 expression in blood as a biomarker, for example, for immunotherapy studies.