A Gyrolab Assay for the Quantitation of Free Complement Protein C5a in Human Plasma

Assay pH and critical reagent optimization in measuring concentrations of a monoclonal antibody and its target

Aim: To mitigate assay interference in the drug and target assays to support the development of monoclonal antibody REGN-Z. Results: Mild acidic assay conditions and capture and detection antibodies with different affinities and t_1/2 under different assay pHs were used to mitigate interference in the total drug and total target assays. A free target assay was also developed using a lower-affinity capture antibody with a much slower association and dissociation rate. The impact of sample incubation, dilution and storage on the accurate detection of the free target was also evaluated. Conclusion: The total drug, total and free target assays can accurately quantitate drug and target concentrations when tested with a subset of clinical study samples.

Development of a Meso Scale Discovery ligand-binding assay for measurement of free (drug-unbound) target in nonhuman primate serum

Aim: To quantify the free form of a protein as a target-engagement biomarker in nonhuman primate serum, a Meso Scale Discovery ligand-binding assay was developed and qualified. Results: The initial assay produced an unexpected artifact when used to measure the free target in study samples dosed with drug. By using incurred study samples dosed with high drug levels to test assay performance, we developed an alternative assay that does not suffer from drug interference. Conclusion: Our work demonstrated that an assay designed to measure free target may not necessarily deliver reliable quantitation. In our case, incurred study samples dosed with drug proved to be useful in developing an alternative free assay that does not suffer from drug interference.

A Novel Total Drug Assay for Quantification of Anti-C5 Therapeutic Monoclonal Antibody in the Presence of Abundant Target

SKY59 or RO7112689 is a humanized monoclonal antibody against complement protein C5 with pH-dependent C5-binding and neonatal Fc receptor-mediated recycling capabilities, which result in long-lasting neutralization of C5. We developed and validated a novel total drug assay for quantification of target-binding competent SKY59 in the presence of endogenous C5 in cynomolgus monkey plasma. The target-binding competent SKY59 was determined after complex formation by the addition of recombinant monkey C5 using goat anti-human IgG-heavy chain monkey-adsorbed polyclonal antibody as a capture antibody and rabbit anti-C5 monoclonal antibody (mAb) non-competing with SKY59 for detection. The total SKY59 assay was shown to be accurate and precise over the range of 0.05-3.2 μg/mL as well as be tolerant to more than 400 μg/mL of C5 (~ 3000-fold molar excess of target). We also developed and validated a total C5 assay, confirmed selectivity and parallelism, and verified the utility of recombinant monkey C5 for the total C5 assay as well as the total SKY59 assay. Furthermore, we used these validated methods to measure SKY59 and C5 concentrations in cynomolgus monkey plasma samples in a toxicology study. This total drug assay can be applied not only to other antibody therapeutics against shed/soluble targets when a non-competing reagent mAb is available but also for clinical studies when a reagent mAb specific for engineered Fc region on a therapeutic mAb is available.

Monitoring Ravulizumab effect on complement assays

Ravulizumab is a new C5 inhibitor therapeutic monoclonal antibody with a longer half-life than eculizumab. Monitoring complete complement blockade by eculizumab has allowed personalized therapy in specific settings. Similar action is expected with ravulizumab. Ravulizumab has 4 different amino acids from eculizumab, which allow greater affinity for the FcRn immunoglobulin receptor and change the affinity of the molecule for C5. Here we investigate if clinical lab tests traditionally used to monitor complement blockade for eculizumab are appropriate for monitoring complement blockade caused by ravulizumab. De-identified serum samples with known normal complement activity were spiked with increasing amounts of ravulizumab, from zero to 1000 μg/mL. Measurement of classical pathway function (CH50) and C5 function using a liposome method (Wako Diagnostics) showed >50% complement inhibition starting with 50 μg/mL of ravulizumab, but inhibition >95% of complement activity was not achieved, with residual measurements of 11% at 700 μg/mL. In contrast, measurement of alternative pathway function using an ELISA (AH50, Wieslab) showed alternative pathway function inhibition of 80% at 50 μg/mL of ravulizumab and > 95% at 200 μg/mL, which is consistent with expected therapeutic concentrations of ravulizumab >175 μg/mL. If replicated in patient sera, AH50 could be a suitable therapeutic monitoring tool.

Biosensing on the Centrifugal Microfluidic Lab-on-a-Disc Platform

Lab-on-a-Disc (LoaD) biosensors are increasingly a promising solution for many biosensing applications. In the search for a perfect match between point-of-care (PoC) microfluidic devices and biosensors, the LoaD platform has the potential to be reliable, sensitive, low-cost, and easy-to-use. The present global pandemic draws attention to the importance of rapid sample-to-answer PoC devices for minimising manual intervention and sample manipulation, thus increasing the safety of the health professional while minimising the chances of sample contamination. A biosensor is defined by its ability to measure an analyte by converting a biological binding event to tangible analytical data. With evolving manufacturing processes for both LoaDs and biosensors, it is becoming more feasible to embed biosensors within the platform and/or to pair the microfluidic cartridges with low-cost detection systems. This review considers the basics of the centrifugal microfluidics and describes recent developments in common biosensing methods and novel technologies for fluidic control and automation. Finally, an overview of current devices on the market is provided. This review will guide scientists who want to initiate research in LoaD PoC devices as well as providing valuable reference material to researchers active in the field.