16th GCC Closed Forum: ICH M10 implementation; NGS, qPCR/dPCR, flow cytometry validation; tissue biomarkers; IS response; immunogenicity harmonization; bioanalytical industry status.

The 16th GCC Closed Forum was held in Orlando, FL, USA, on 23 June 2023. Representatives from international bioanalytical Contract Research Organizations were in attendance in order to discuss scientific and regulatory issues specific to bioanalysis. The issues discussed at the meeting included: IS response, flow cytometry, changes to the bioanalytical industry, NGS assays, biomarker assay for tissues, dPCR validation, immunogenicity harmonization and ICH M10 implementation. Conclusions and consensus from discussions of these topics are included in this article.

Clinical Immunogenicity Risk Assessment Strategy for a Low Risk Monoclonal Antibody.

This article provides a theoretical case-study risk assessment report for a low-risk monoclonal antibody (mAb) therapeutic. In terms of risk, there are considerations around risks to safety, but also risks regarding effects on pharmacokinetics (PK), pharmacodynamics (PD), and efficacy. Much of the discussion in this document is around the risk of immunogenicity incidence. A higher incidence of immunogenicity would necessitate a detailed review of the PK, efficacy and safety in anti-drug antibody (ADA) positive and ADA negative subjects, in order to evaluate potential effects. The publication is intended to provide a framework of some the current thought processes around assessing immunogenicity risk and for building strategies to mitigate those risks. For this example, we have created a hypothetical antibody, ABC-123, targeting a membrane protein on antigen presenting cells, for the treatment of rheumatoid arthritis (RA). This hypothetical antibody therapeutic is provided as an example for the purposes of risk assessment for a low risk molecule, although any application of similar approach would be case by case.

Pharmacokinetics, Pharmacodynamics, Safety, and Tolerability of ASP2408, a Potent Selective T-Cell Costimulation Modulator After Single and Multiple Ascending Doses in Healthy Volunteers and RA Patients.

ASP2408 is a next-generation anti-cytotoxic T lymphocyte antigen-4 fusion protein engineered for improved CD86 binding affinity as a treatment for rheumatoid arthritis (RA). In 72 healthy subjects (n = 6/treatment), ASP2408 was administered as single ascending doses intravenously at 0.003 to 10.0 mg/kg or subcutaneously at 0.3 to 3.0 mg/kg. It showed decreased clearance and prolonged half-life with increasing doses, consistent with target-mediated disposition. The apparent bioavailability was 36.3%-56.7% across single subcutaneous doses. Sixteen RA patients (n = 8/treatment) on stable methotrexate received 3 × 3.0 mg/kg subcutaneously every 4 weeks or every 2 weeks. Similar to single-dose treatment, ASP2408 concentrations peaked 2 to 3 days postdose, with a median t1/2 of approximately 8 days. Using CD86 receptor occupancy (RO) as a mechanistic biomarker, ASP2408 demonstrated dose-dependent binding to its target. ASP2408 3.0 mg/kg subcutaneously every 4 weeks and every 2 weeks led to a mean %CD86 RO ≥ 74.7% and ≥ 81.5%, respectively, within each dosing interval. ASP2408 was well tolerated across studies with no evidence of dose-limiting toxicity or clinically significant changes in clinical laboratory test results, vital signs, or 12-lead electrocardiograms. ASP2408 elicited antidrug antibodies in the majority of patients, but with no clinical sequelae.

A Phase 1 Dose-Escalation Study of ASP2409, a Selective T-Cell Costimulation Inhibitor, in Stable Rheumatoid Arthritis Patients on Methotrexate Therapy.

ASP2409 represents a new class of CTLA4-Ig molecules with higher binding avidity and selectivity to CD86. This first-in-human study was to assess the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of ASP2409 in stable rheumatoid arthritis patients on methotrexate therapy with a randomized, double-blind, placebo-controlled dose-escalation study design. Patients were enrolled and randomized in each of 8 dose-escalation cohorts ranging from 0.001 to 3.0 mg/kg to receive either ASP2409 or placebo in a sequential manner. Escalation to higher dose levels occurred in the absence of dose-limiting toxicity. A total of 57 patients completed the study. ASP2409 showed nonlinear PK over the dose range of 0.01 to 3.0 mg/kg following a single intravenous administration, indicating target-mediated drug disposition. Area under the concentration-time curve (AUC) and maximum concentration (Cmax ) increased at a greater than dose-proportional rate. The half-life of ASP2409 increased dose dependently and ranged from 1.57 to 6.68 days. ASP2409 showed a dose-dependent increase in the extent and duration of CD86 receptor occupancy. There were no clinically relevant safety issues up to a single dose of 3.0 mg/kg. No maximum tolerated dose was reached. The incidence and duration of antidrug antibodies did not correlate with adverse events. ClinicalTrials.gov identifier: NCT02171143.

ELISA microplate: a viable immunocapture platform over magnetic beads for immunoaffinity-LC-MS/MS quantitation of protein therapeutics?

AIM: Evaluate the performance of ELISA microplates versus commonly used magnetic beads for biological sample cleanup and/or enrichment in immunoaffinity-LC-MS/MS to reduce tedious beads washing procedures and a relatively high assay cost. MATERIALS & METHODS: ELISA microplates were used as immunicapture platform and compared with magnetic beads for sample cleanup for LC-MS/MS quantitation of protein therapeutics. RESULTS: One unmodified and two surface-activated microplates provided comparable linear ranges and sensitivities for a therapeutic protein (mass 78 kDa) using a human serum sample of 100 µl with 1:1 dilution compared with Tosylactivated magnetic beads using 200 µl of human serum without sample dilution. The assays' precision and accuracy were all within acceptable ranges. No nonspecific binding or other selectivity issues were observed. CONCLUSION: The results suggested an ELISA microplate could be a viable immunocapture platform for immunoaffinity-LC-MS/MS quantitation of protein therapeutics.

Guanidinated protein internal standard for immunoaffinity-liquid chromatography/tandem mass spectrometry quantitation of protein therapeutics.

RATIONALE: A protein internal standard (IS) is essential and superior to a peptide IS to achieve reproducible results in the quantitation of protein therapeutics using immunoaffinity-liquid chromatography/tandem mass spectrometry (LC/MS/MS). Guanidination has been used as a protein post-modification technique for more than half a century. A decade ago, the modification was applied to lysine-ending peptides to enhance their MALDI responses and peptide sequencing coverage. However, rarely has tryptic digestion of guanidinated proteins been investigated, likely due to the early conclusion that trypsin did not hydrolyze peptide bonds involving homoarginine in guanidinated proteins. In this study, the opposite was observed. Guanidinated lysine residues of proteins did not hinder the access of trypsin allowing for proteolytic digestion. Based on this observation, a new concept of internal standard, named Guanidinated Protein Internal Standard (GP-IS), was proposed for LC/MS/MS quantitation of protein therapeutics. METHODS: The GP-IS is prepared by treating a portion of the therapeutic protein (analyte) with guanidine to convert arginine residues in the protein into homoarginine residues. After tryptic digestion, the GP-IS produces a series of homoarginine-ending peptides plus another series of arginine-ending peptides. One of the homoarginine-ending peptides, which corresponds to the analyte surrogate (lysine-ending) peptide, was chosen as a peptide internal standard (GP-PIS) for LC/MS/MS quantitation. RESULTS: Using this GP-IS approach, a sensitive and robust immunoaffinity-LC/MS/MS assay was developed and fully validated with a linearity range from 10 to 1000 ng/mL using 200 µL of human serum for the quantitation of an Astellas protein drug in clinical development. CONCLUSIONS: The proposed strategy allows LC/MS/MS to play an ever-increasing role in bioanalytical support for protein therapeutics development because of its capability of completely tracking all variations from the beginning to the end of sample analysis, easier preparation compared to isotope-labeled protein-IS, and greater flexibility for changing to alternate analyte surrogate peptides.

Permeabilization of the mitochondrial outer membrane by Bax/truncated Bid (tBid) proteins as sensitized by cardiolipin hydroperoxide translocation: mechanistic implications for the intrinsic pathway of oxidative apoptosis.

Cytochrome c (cyt c) release upon oxidation of cardiolipin (CL) in the mitochondrial inner membrane (IM) under oxidative stress occurs early in the intrinsic apoptotic pathway. We postulated that CL oxidation mobilizes not only cyt c but also CL itself in the form of hydroperoxide (CLOOH) species. Relatively hydrophilic CLOOHs could assist in apoptotic signaling by translocating to the outer membrane (OM), thus promoting recruitment of the pro-apoptotic proteins truncated Bid (tBid) and Bax for generation of cyt c-traversable pores. Initial testing of these possibilities showed that CLOOH-containing liposomes were permeabilized more readily by tBid plus Ca(2+) than CL-containing counterparts. Moreover, CLOOH translocated more rapidly from IM-mimetic to OM-mimetic liposomes than CL and permitted more extensive OM permeabilization. We found that tBid bound more avidly to CLOOH-containing membranes than to CL counterparts, and binding increased with increasing CLOOH content. Permeabilization of CLOOH-containing liposomes in the presence of tBid could be triggered by monomeric Bax, consistent with tBid/Bax cooperation in pore formation. Using CL-null mitochondria from a yeast mutant, we found that tBid binding and cyt c release were dramatically enhanced by transfer acquisition of CLOOH. Additionally, we observed a pre-apoptotic IM-to-OM transfer of oxidized CL in cardiomyocytes treated with the Complex III blocker, antimycin A. These findings provide new mechanistic insights into the role of CL oxidation in the intrinsic pathway of oxidative apoptosis.

New strategies for the isolation and activity determination of naturally occurring type-4 glutathione peroxidase.

Type 4 glutathione peroxidase (GPx4) is a widely expressed mammalian selenoenzyme known to play a vital role in cytoprotection against lipid hydroperoxide (LOOH)-mediated oxidative stress and regulation of oxidative signaling cascades. Since prokaryotes are not equipped to express mammalian selenoproteins, preparation of recombinant GPx4 via commonly used bacterial transformation is not feasible. A published procedure for isolating the enzyme from rat testis employs affinity chromatography on bromosulfophthalein-glutathione-linked agarose as the penultimate step in purification. Since this resin is no longer commercially available and preparing it in satisfactory operational form is tedious, we have developed an alternative purification approach based on sequential anion exchange, size exclusion, and cation exchange chromatography. Final preparations were found to be essentially homogeneous in GPx4 (M(r) approximately 20 kDa), as demonstrated by SDS-PAGE with protein staining and immunoblotting. Specific enzymatic activity was determined using a novel thin-layer chromatographic approach in which the kinetics of phosphatidylcholine hydroperoxide loss or cholesterol-7alpha-hydroperoxide loss was monitored. A >400-fold purification of active enzyme has been attained. The relatively straightforward isolation procedure described should prove valuable for further functional studies on GPx4, e.g. how its ability to catalyze LOOH reduction compares with that of other LOOH detoxifying enzymes.

Secondary alkyl hydroperoxides as inhibitors and alternate substrates for lipoxygenase.

Lipoxygenase plays a central role in polyunsaturated fatty acid metabolism, inaugurating the biosynthesis of eicosanoids in animals and phytooxylipins in plants. Redox cycling of the non-heme iron cofactor represents a critical element of the catalytic mechanism. Paradoxically, the isolated enzyme contains Fe(II), but the catalytically active form contains Fe(III), and the natural oxidant for the iron is the hydroperoxide product of the catalyzed reaction. Controlling the redox state of lipoxygenase iron with small molecules, inhibitors or activators, could be a means to modulate the activity of the enzyme. The effects of secondary alkyl hydroperoxides and the corresponding alcohols on soybean lipoxygenase-1 reaction rates were investigated and found to be very different. Secondary alcohols were noncompetitive or linear mixed inhibitors with inhibition constants in the millimolar concentration range, with more hydrophobic compounds producing lower values. Secondary alkyl hydroperoxides were inhibitors of lipoxygenase-1 primarily at high substrate concentration. They were more effective inhibitors than the alcohols, with dissociation constants in the micromolar concentration range. The hydroperoxides bearing longer alkyl substituents were the more effective inhibitors. Oxidation of the iron in lipoxygenase-1 by 2-hydroperoxyalkanes was evident in electron paramagnetic resonance (EPR) measurements, but the enzyme was neither activated nor was it inactivated. Instead there was evidence for an entirely different reaction catalyzed by the enzyme, a homolytic dehydration of the hydroperoxide to produce the corresponding carbonyl compound.

Lipid transfer protein binding of unmodified natural lipids as assessed by surface plasmon resonance methodology.

A new approach for analyzing lipid-lipid transfer protein interactions is described. The transfer protein is genetically engineered for expression with a C-terminal biotinylated peptide extension (AviTag). This allows protein anchoring to a streptavidin-coated chip for surface plasmon resonance (SPR)-based assessment of lipid binding. Sterol carrier protein-2 (SCP-2), involved in the intracellular trafficking of cholesterol, fatty acids, and other lipids, was selected as the prototype. Biotinylated SCP-2 (bSCP-2) was expressed in Escherichia coli, purified to homogeneity by mutated streptavidin (SoftLink) affinity chromatography, and confirmed by mass spectrometry to contain one biotin group at the expected position. Intermembrane [(14)C]cholesterol transfer was strongly enhanced by bSCP-2, demonstrating that it was functional. Using bSCP-2 immobilized on a Biacore streptavidin chip, we determined on- and off-rate constants along with equilibrium dissociation constants for the following analytes: oleic acid, linoleic acid, cholesterol, and fluorophore (NBD)-derivatized cholesterol. The dissociation constant for NBD-cholesterol was similar to that determined by fluorescence titration for SCP-2 in solution, thereby validating the SPR approach. This method can be readily adapted to other transfer proteins and has several advantages over existing techniques for measuring lipid binding, including (i) the ability to study lipids in their natural states (i.e., without relatively large reporter groups) and (ii) the ability to measure on- and off- rate constants as well as equilibrium constants.