How validated receptor occupancy flow cytometry assays can impact decisions and support drug development

Abstract

Because of the pressure of significant attrition in drug development, demonstration of target engagement after drug administration enables dose and regimen optimization, patient selection, and stratification from the earliest stages of drug development. The determination of receptor occupancy (RO) can support these efforts. Flow cytometry is one of the preferred technologies to be used based on the important advances in the technology over the last years enabling the simultaneous determination on target cells, of multi intra or surface cell parameters with adequate precision in a regulated environment. Nevertheless, compared to other platforms using the same antigen-antibody binding concept, the flow cytometry approach has faced several challenges, not only due to the technology per se and the diversity of receptor occupancy approaches, but also related to the nature of the matrix where the determination is performed. To illustrate these points, three case studies (antibody-drug conjugate and naked antibody) are provided here to highlight the importance of the choice of the right antibody pair to measure both receptor density (RD) and occupancy by the drug on cancer cells in blood and in bone marrow and the possibility to circumvent the lack of a critical reagent with an innovative approach. In addition, the use of RO data to determine the minimum anticipated biological effect level (MABEL) with translational data from preclinical to human studies, selection of starting dose for the first in man study will be discussed. In the last couple of years, the advent of molecular medicine and targeted therapy has opened up innovative areas of investigation, allowing not only the development of new highly specific drugs but also a concomitant progress for the discovery of new approaches. These approaches fit perfectly with the development of antibody-based therapeutics since the drug and its target are clearly identified and unique. Nevertheless, the clinical development of targeted therapies (naked antibodies, immunoconjugates, etc.) remains disappointing since the average response rate has generally been low in human, at around 15% of patients (1). A better characterization of drug mechanism of action and target engagement coupled with a better understanding of the relationship between drug pharmacokinetic and pharmacodynamics is needed (2). Robust data to support dose selection and optimization of regimen before pivotal trials are critical to substantially shorten the time to reach strategic points during the clinical development. The use of RO in early phases of the drug discovery process to demonstrate proof of mechanism of the drug could eventually reduce the development risks, including the Cytometry Part B (Clinical Cytometry) 90B: 150-158 (2016)

Clinical efficacy and management of monoclonal antibodies targeting CD38 and SLAMF7 in multiple myeloma

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Targeting CD38 with daratumumab is lethal to Waldenström macroglobulinaemia cells

“…Quantification of CD38 cell surface molecules was determined by using Quantibrite beads (BD Biosciences, San Jose, CA, USA), followed by analysis with QuantiCALC software (BD Biosciences); data are expressed as the specific antibody‐binding capacity (sABC), defined as the number of antibodies bound per cell. The utility of this approach has been previously described (Moulard & Ozoux, ) and its use in malignant B cells (treated with Dara) has also been reported (Matas‐Cespedes et al , ).…”

Prototyping Trastuzumab Docetaxel Immunoliposomes with a New FCM-Based Method to Quantify Optimal Antibody Density on Nanoparticles

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