Validation of a flow cytometry-based assay to assess C5aR receptor occupancy on neutrophils and monocytes for use in drug development.

The C5a/C5a receptor (C5aR) pathway, a key component in the proinflammatory immune response, is an attractive therapeutic target since its dysregulation is implicated in a variety of autoimmune and inflammatory disorders. The objective of the present study was to validate a receptor occupancy (RO) assay for a human anti-C5aR monoclonal antibody drug candidate, NNC0215-0384 (NN0384). This flow cytometry-based assay measures the percentage (%), median fluorescence intensity (MFI), and molecules of equivalent soluble fluorochrome (MESF) of NN0384 binding to its target cells, neutrophils and monocytes, in whole blood from normal healthy donors and rheumatoid arthritis (RA) patients with clinically active disease. The validation parameters assessed included postcollection and postprocessing sample stability, intra- and interassay precision, an analyst-to-analyst comparison, a comparison of normal healthy donor and RA patient sample postcollection stability, and a laboratory-to-laboratory comparison and assay transfer. The cumulative results indicate that the assay was reproducible, met the clearly defined acceptance criteria for the validation parameters tested, and was transferable to another laboratory. In conclusion, this RO assay is suitable for use to accrue pharmacodynamic biomarker data in a multicenter, global clinical trial.

The peptidyl prolyl isomerase cyclophilin A localizes at the centrosome and the midbody and is required for cytokinesis.

Failed cytokinesis leads to tetraploidy, which is an important intermediate preceding aneuploidy and the onset of tumorigenesis. The centrosome is required for the completion of cytokinesis through the transport of important components to the midbody; however, the identity of molecular components and the mechanism involved remains poorly understood. In this study, we report that the peptidyl prolyl isomerase cyclophilin A (cypA) is a centrosome protein that undergoes cell cycle-dependent relocation to the midzone and midbody during cytokinesis in Jurkat cells implicating a role during division. Depletion of cypA does not disrupt mitotic spindle formation or progression through anaphase; however, it leads to cytokinesis defects through an inability to resolve intercellular bridges, culminating in delayed or failed cytokinesis. Defective cytokinesis is also evident by an increased prevalence of midbody-arrested cells. Expression of wild-type cypA reverses the cytokinesis defect in knockout cells, whereas an isomerase mutant does not, indicating that the isomerisation activity of cypA is required for cytokinesis. In contrast, wild-type cypA and the isomerase mutant localize to the centrosome and midbody, suggesting that localization to these structures is independent of isomerase activity. Depletion of cypA also generates tetraploid cells and supernumerary centrosomes. Finally, colony formation in soft agar is impaired in cypA-knockout cells, suggesting that cypA confers clonogenic advantage on tumor cells. Collectively, this data reveals a novel role for cypA isomerase activity in the completion of cytokinesis and the maintenance of genome stability.