Evaluation of a digital dispenser for direct curve dilutions in a vaccine potency assay

Automated ELISA for potency measurements of therapeutic antibodies and antibody fragments

Potency assays are essential for the development and quality control of biopharmaceutical drugs, but they are often a time limiting factor due to manual handling steps and consequently low analytical throughput. On the other hand, automation of potency assays can be challenging due to their complexity and the use of biological materials. ELISA (enzyme-linked immunosorbent assay) is widely used for potency determination and is a good candidate for automation as all ELISA types depend on the same basic steps: coating, blocking, sample incubation, detection, and signal measurement. Nevertheless, ELISA for relative potency measurements still require drug-specific development and assay validation thereby complicating automation efforts. To simplify potency testing by ELISA, we first developed a manual protocol generally applicable to different drugs and then adapted this protocol for automated measurements. We identified unexpected critical parameters which had to be adapted to transfer the manual ELISA to an automated liquid handling system and we demonstrated that gravimetric sample dilution is unnecessary with the automated protocol. Both manual and automated protocols were validated and compared using multiple biotherapeutics. The automated protocol showed similar or higher precision and accuracy when compared to the manual method.

Use of capillary-mediated vitrification to produce thermostable, single-use antibody conjugates as immunoassay reagents

The performance of enzyme-linked immunoassays is directly dependent on the storage, handling, and long-term stability of the critical reagents used in the assay. Currently, antibody reagents are routinely stored as concentrated, multi-use, frozen aliquots. This practice results in material waste, adds complexity to laboratory workflows, and can compromise reagents via cross-contamination and freeze-thaw damage. While refrigeration or freezing can slow down many degradation processes, the freezing process itself can have damaging effects, including introduction of aggregation and microheterogeneity. To address these challenges, we evaluated the application of capillary-mediated vitrification (CMV) as a tool for storing antibody reagents in a thermostable, single-use format. CMV is a novel biopreservation method that enables vitrification of biological materials without freezing. Using an anti-human IgG-alkaline phosphatase conjugate as a model system, we prepared CMV-stabilized aliquots which were stored in a single-use format at temperatures ranging from 25 to 55 °C for up to 3 months. Each stabilized aliquot contained enough antibody to perform a single assay run. We evaluated the assay performance and functional stability of the CMV-stabilized reagents using a plate-based ELISA. Assays run using the CMV stabilized reagents exhibited good linearity and precision that was comparable to results obtained with a frozen control. Throughout the stability study, the maximum signal and EC50s observed for ELISAs run using CMV-stabilized reagents were generally consistent with those obtained using a frozen control. These results indicate that the CMV process has the potential to improve both reagent stability and long-term assay performance, while also reducing reagent waste and simplifying assay workflows.

Evaluation of digital dispense-assisted broth microdilution antimicrobial susceptibility testing for Pseudomonas aeruginosa isolates

Antimicrobial susceptibility testing (AST) is essential for detecting resistance in Pseudomonas aeruginosa and other bacterial pathogens. Here we evaluated the performance of broth microdilution (BMD) panels created using a semi-automated liquid handler, the D300e Digital Dispenser (Tecan Group Ltd., CH) that relies on inkjet printing technology. Microtitre panels (96-well) containing nine twofold dilutions of 12 antimicrobials from five classes (β-lactams, β-lactam/β-lactamase inhibitors, aminoglycosides, fluoroquinolones, polymyxins) were prepared in parallel using the D300e Digital Dispenser and standard methods described by CLSI/ISO. To assess performance, panels were challenged with three well characterized quality control organisms and 100 clinical P. aeruginosa isolates. Traditional agreement and error measures were used for evaluation. Essential (EA) and categorical (CA) agreements were 92.7% and 98.0% respectively for P. aeruginosa isolates with evaluable on-scale results. The majority of minor errors that fell outside acceptable EA parameters (≥ ± 1 dilution, 1.9%) were seen with aztreonam (5%) and ceftazidime (4%), however all antimicrobials displayed acceptable performance in this situation. Differences in MIC were often log₂ dilution lower for D300e dispensed panels. Major and very major errors were noted for aztreonam (2.6%) and cefepime (1.7%) respectively. The variable performance of D300e panels suggests that further testing is required to confirm their diagnostic utility for P. aeruginosa.

Quantitation of Super Basic Peptides in Biological Matrices by a Generic Perfluoropentanoic Acid-Based Liquid Chromatography-Mass Spectrometry Method

Peptides represent a promising modality for the design of novel therapeutics that can potentially modulate traditionally non-druggable targets. Cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs) are two large families that are being explored extensively as drug delivery vehicles, imaging reagents, or therapeutic treatments for various diseases. Many CPPs and AMPs are cationic among which a significant portion is extremely basic and hydrophilic (e.g., nona-arginine). Despite their attractive therapeutic potential, it remains challenging to directly analyze and quantify these super cationic peptides from biological matrices due to their poor chromatographic behavior and MS response. Herein, we describe a generic method that combines solid phase extraction and LC-MS/MS for analysis of these peptides. As demonstrated, using a dozen strongly basic peptides, low μM concentration of perfluoropentanoic acid (PFPeA) in the mobile phase enabled excellent compound chromatographic retention, thus avoiding co-elution with solvent front ion suppressants. PFPeA also had a charge reduction effect that allowed the selection of parent/ion fragment pairs in the higher m/z region to further reduce potential low molecular weight interferences. When the method was coupled to the optimized sample extraction process, we routinely achieved low digit ng/ml sensitivity for peptides in plasma/tissue. The method allowed an efficient evaluation of plasma stability of CPPs/AMPs without fluorescence derivatization or other tagging methods. Importantly, using the widely studied HIV-TAT CPP as an example, the method enabled us to directly assess its pharmacokinetics and tissue distribution in preclinical animal models.