Determination of Real Time in Vivo Drug Receptor Occupancy for a Covalent Binding Drug as a Clinical Pharmacodynamic Biomarker by Immunocapture-LC-MS/MS.

We report a novel immunocapture (IC)-LC-MS/MS methodology to directly measure real time in vivo receptor occupancy (RO) for a covalent binding drug in blood lysate. A small molecule quencher was added immediately after sample collection to convert the free receptor to a quencher-bound receptor (QB-R) which was measured with the drug-bound receptor (DB-R) simultaneously by LC-MS/MS after immunocapture enrichment, followed by trypsin digestion. Addition of the quencher is necessary to prevent the free receptor from ex vivo binding with the drug. The real time RO was calculated based on the concentrations of DB-R and the free receptor (which is now QB-R) that were obtained from each sample. This strategy has been successfully applied to the measurement of the RO for Bruton's tyrosine kinase (BTK) in the blood lysate of monkeys after dosing with branebrutinib (BMS-986195), a covalent BTK inhibitor being evaluated to treat rheumatoid arthritis. A custom-made quencher, which is more reactive to BTK than branebrutinib, was added in excess amount to bind with all available free BTK to form quencher-bound BTK (QB-BTK) during blood sample collection. To measure a wide range of % BTK RO, including those of <5% or >95%, the required LLOQ at 0.125 nM for QB-BTK and 0.250 nM for drug-bound BTK (DB-BTK) in blood lysate were successfully achieved by using this IC-LC-MS/MS strategy. This proof-of-concept assay demonstrated its suitability with high throughput for real time in vivo BTK RO measurement as a pharmacodynamic (PD) biomarker for clinical drug development.

Evolution of fit-for-purpose biomarker validations: an LBA perspective.

Biomarker ligand-binding assays need to be validated for use on clinical studies in the drug development process. There is not one single guidance to cover all types of biomarker assays and their intended uses. Therefore, it is up to the scientist to piece together a validation strategy based on published papers and other sources. Shown here is a summary of what to take into consideration during a validation and how to apply it for use in the drug development process.

Recommendations for Selection and Characterization of Protein Biomarker Assay Calibrator Material.

As biomarkers continue to become an integral part of drug development and decision-making, there are increased expectations for reliable and quantitative assays. Protein biomarker assay results are directly influenced by the calibrator material. The selection of calibrator material presents many challenges that impact the relative accuracy and performance of the assay. There is an industry-wide challenge finding reliable and well-characterized calibrator material with good documentation. Several case studies are presented that demonstrate some of the challenges involved in selecting appropriate calibrators along with the resolutions that were ultimately applied. From these experiences, we present here a set of recommendations for selecting and characterizing calibrator material based on the intended purpose of the assay. Finally, we introduce a commutability approach, based on common clinical chemistry practices, which can be used to demonstrate inter-changeability with calibrator materials across multiple lots and technology platforms for all types of protein biomarker assays.

Development and Validation of Electrochemiluminescence Assays to Measure Free and Total sSLAMF7 in Human Serum in the Absence and Presence of Elotuzumab.

Elotuzumab is a first in class humanized IgG1 monoclonal antibody for the treatment of multiple myeloma (MM). Elotuzumab targets the glycoprotein signaling lymphocyte activation molecule family 7 (SLAMF7, also described as CS1 or CRACC) which is expressed on the surface of myeloma cells and a subset of immune cells, including natural killer cells. A soluble version of SLAMF7 (sSLAMF7) has also been reported in MM patients but has not been evaluated as a potential biomarker following therapeutic intervention. In order to measure serum levels of sSLAMF7, two immunoassays were developed to monitor changes in circulating sSLAMF7 before and after elotuzumab treatment. Free (drug-unbound) and total (drug-bound and unbound) electrochemiluminescence (ECL) ELISA assays were developed and validated following a fit for purpose (FFP) methodology. Both assays met analytical acceptance criteria for precision, drug interference, dilution linearity, spike recovery, parallelism, and stability. Both exhibited the range and sensitivity necessary to measure clinical samples with an LLOQ of 51.2 pg/mL and ULOQs of 160 (free) and 800 ng/mL (total). Previously described assays were unable to detect sSLAMF7 in healthy individuals. However, due to the increased sensitivity of these new assays, low but measurable sSLAMF7 levels were detected in all normal healthy sera evaluated and were significantly elevated in MM patients. Cohort statistics revealed a significant increase of circulating sSLAMF7 in MM patients versus normal controls and both significant decreases in free and increases in total levels of protein post-elotuzumab treatment.

Development and Fit-for-Purpose Validation of a Soluble Human Programmed Death-1 Protein Assay.

Programmed death-1 (PD-1) protein is a co-inhibitory receptor which negatively regulates immune cell activation and permits tumors to evade normal immune defense. Anti-PD-1 antibodies have been shown to restore immune cell activation and effector function-an exciting breakthrough in cancer immunotherapy. Recent reports have documented a soluble form of PD-1 (sPD-1) in the circulation of normal and disease state individuals. A clinical assay to quantify sPD-1 would contribute to the understanding of sPD-1-function and facilitate the development of anti-PD-1 drugs. Here, we report the development and validation of a sPD-1 protein assay. The assay validation followed the framework for full validation of a biotherapeutic pharmacokinetic assay. A purified recombinant human PD-1 protein was characterized extensively and was identified as the assay reference material which mimics the endogenous analyte in structure and function. The lower limit of quantitation (LLOQ) was determined to be 100 pg/mL, with a dynamic range spanning three logs to 10,000 pg/mL. The intra- and inter-assay imprecision were ≤15%, and the assay bias (percent deviation) was ≤10%. Potential matrix effects were investigated in sera from both normal healthy volunteers and selected cancer patients. Bulk-prepared frozen standards and pre-coated Streptavidin plates were used in the assay to ensure consistency in assay performance over time. This assay appears to specifically measure total sPD-1 protein since the human anti-PD-1 antibody, nivolumab, and the endogenous ligands of PD-1 protein, PDL-1 and PDL-2, do not interfere with the assay.

Characterization of novel CSF Tau and ptau biomarkers for Alzheimer's disease.

Cerebral spinal fluid (CSF) Aß42, tau and p181tau are widely accepted biomarkers of Alzheimer's disease (AD). Numerous studies show that CSF tau and p181tau levels are elevated in mild-to-moderate AD compared to age-matched controls. In addition, these increases might predict preclinical AD in cognitively normal elderly. Despite their importance as biomarkers, the molecular nature of CSF tau and ptau is not known. In the current study, reverse-phase high performance liquid chromatography was used to enrich and concentrate tau prior to western-blot analysis. Multiple N-terminal and mid-domain fragments of tau were detected in pooled CSF with apparent sizes ranging from <20 kDa to ~40 kDa. The pattern of tau fragments in AD and control samples were similar. In contrast, full-length tau and C-terminal-containing fragments were not detected. To quantify levels, five tau ELISAs and three ptau ELISAs were developed to detect different overlapping regions of the protein. The discriminatory potential of each assay was determined using 20 AD and 20 age-matched control CSF samples. Of the tau ELISAs, the two assays specific for tau containing N-terminal sequences, amino acids 9-198 (numbering based on tau 441) and 9-163, exhibited the most significant differences between AD and control samples. In contrast, CSF tau was not detected with an ELISA specific for a more C-terminal region (amino acids 159-335). Significant discrimination was also observed with ptau assays measuring amino acids 159-p181 and 159-p231. Interestingly, the discriminatory potential of p181 was reduced when measured in the context of tau species containing amino acids 9-p181. Taken together, these results demonstrate that tau in CSF occurs as a series of fragments and that discrimination of AD from control is dependent on the subset of tau species measured. These assays provide novel tools to investigate CSF tau and ptau as biomarkers for other neurodegenerative diseases.