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Evaluation of assay interference and interpretation of CXCR4 receptor occupancy results in a preclinical study with MEDI 3185, a fully human antibody to CXCR 4
Author(s) -
Schwickart Martin,
Chavez Carlos,
Henderson Simon,
Vainshtein Inna,
Standifer Nathan,
DelNagro Christopher,
Mehrzai Freshta,
Schneider Amy,
Roskos Lorin,
Liang Meina
Publication year - 2016
Publication title -
cytometry part b: clinical cytometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.646
H-Index - 61
eISSN - 1552-4957
pISSN - 1552-4949
DOI - 10.1002/cyto.b.21327
Subject(s) - in vivo , flow cytometry , monoclonal antibody , receptor , chemistry , antibody , cxcr4 , in vitro , microbiology and biotechnology , biology , immunology , biochemistry , chemokine
Background Receptor occupancy (RO) assays provide a means to measure the direct interaction of therapeutics with their cell surface targets. Free receptor assays quantify cell‐surface receptors not bound by a therapeutic while total receptor assays quantify the amount of target on the cell surface. Methods We developed both a flow cytometry‐based free RO assay to detect free surface CXCR4, and a total surface CXCR4 assay. In an effort to evaluate potential displacement interference, we performed in vitro experiments to compare on‐cell affinity with the IC 50 values from in vitro and in vivo from the free CXCR4 assay. We determined free and total surface CXCR4 on circulating blood cells in cynomolgus monkeys dosed with MEDI3185, a fully human monoclonal antibody to CXCR4. Results We devised an approach to evaluate displacement interference during assay development and showed that our free assay demonstrated little to no displacement interference. After dosing cynomolgus monkeys with MEDI3185, we observed dose‐dependence in the magnitude and duration of receptor occupancy and found CXCR4 to increase on lymphocytes, monocytes, and granulocytes. In a multiple dose study, we observed time points where surface CXCR4 appeared fully occupied but MEDI3185 was not detectable in serum. These paradoxical results represented a type of assay interference, and by comparing pharmacokinetic, ADA and total CXCR4 results, the most likely reason for the free CXCR4 results was the emergence of neutralizing anti‐drug antibodies (ADA). The total CXCR4 assay was unaffected by ADA and provided a reliable marker of target modulation in both in vivo studies. © 2015 The Authors Cytometry Part B: Clinical Cytometry Published byWiley Periodicals, Inc.