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.

Biological Matrix Supply Chain Shortages: More Matrices Are Now Rare-the Case for Surrogate Matrices.

The COVID-19 pandemic has strained the biological matrix supply chain. An upsurge in demand driven by numerous COVID-19 therapeutic and vaccine development programs to combat the pandemic, along with logistical challenges sourcing and transporting matrix, has led to increased lead times for multiple matrices. Biological matrix shortages can potentially cause significant delays in drug development programs across the pharmaceutical and biotechnology industry. Given the current circumstances, discussion is warranted around what will likely be increased use of surrogate matrices in support of pharmacokinetic (PK), immunogenicity, and biomarker assays for regulatory filings. Regulatory authorities permit the use of surrogate matrix in bioanalytical methods in instances where matrix is rare or difficult to obtain, as long as the surrogate is appropriately selected and scientifically justified. Herein, the scientific justification and possible regulatory implications of employing surrogate matrix in PK, immunogenicity, and biomarker assays are discussed. In addition, the unique challenges that cell and gene therapy (C>) and other innovative therapeutic modalities place on matrix supply chains are outlined. Matrix suppliers and contract research organizations (CROs) are actively implementing mitigation strategies to alleviate the current strain on the matrix supply chain and better prepare the industry for any future unexpected strains. To maintain ethical standards, these mitigation strategies include projecting matrix needs with suppliers at least 6 months in advance and writing or updating study protocols to allow for additional matrix draws from study subjects and/or re-purposing of subject matrix from one drug development program to another.

Recommendations on qPCR/ddPCR assay validation by GCC.

Gene therapy, cell therapy and vaccine research have led to an increased use of qPCR/ddPCR in bioanalytical laboratories. CROs are progressively undertaking the development and validation of qPCR and ddPCR assays. Currently, however, there is limited regulatory guidance for the use of qPCR and a complete lack of any regulatory guidelines for the use of the newer ddPCR to support regulated bioanalysis. Hence, the Global CRO Council in Bioanalysis (GCC) has issued this White Paper to provide; 1) a consensus on the different validation parameters required to support qPCR/ddPCR assays; 2) a harmonized approach to their validation and 3) a consistent development of standard operating procedures (SOPs) for all the bioanalytical laboratories using these techniques.

Recommendations on ELISpot assay validation by the GCC.

Gene therapy, cell therapy and vaccine research have led to an increased need to perform cellular immunity testing in a regulated environment to ensure the safety and efficacy of these treatments. The most common method for the measurement of cellular immunity has been Enzyme-Linked Immunospot assays. However, there is a lack of regulatory guidance available discussing the recommendations for developing and validating these types of assays. Hence, the Global CRO Council has issued this white paper to provide a consensus on the different validation parameters required to support Enzyme-Linked Immunospot assays and a harmonized and consistent approach to Enzyme-Linked Immunospot validation among contract research organizations.

Evaluation of the Humoral Response to Adeno-Associated Virus-Based Gene Therapy Modalities Using Total Antibody Assays.

The number of viral vector-based gene therapies (GTx) continues to grow with two products (Zolgensma® and Luxturna®) approved in the USA as of March 2021. To date, the most commonly used vectors are adeno-associated virus-based (AAV). The pre-existing humoral immunity against AAV (anti-AAV antibodies) has been well described and is expected as a consequence of prior AAV exposure. Anti-AAV antibodies may present an immune barrier to successful AAV transduction and hence negatively impact clinical efficacy and may also result in adverse events (AEs) due to the formation of large immune complexes. Patients may be screened for the presence of anti-AAV antibodies, including neutralizing (NAb) and total binding antibodies (TAb) prior to treatment with the GTx. Recommendations for the development and validation of anti-AAV NAb detection methods have been presented elsewhere. This manuscript covers considerations related to anti-AAV TAb-detecting protocols, including the advantages of the use of TAb methods, selection of assay controls and reagents, and parameters critical to monitoring assay performance. This manuscript was authored by a group of scientists involved in GTx development representing eleven organizations. It is our intent to provide recommendations and guidance to industry sponsors, academic laboratories, and regulatory agencies working on AAV-based GTx viral vector modalities with the goal of achieving a more consistent approach to anti-AAV TAb assessment. Graphical abstract.

Recommendations for the content and management of Certificates of Analysis for reference standards from the GCC for bioanalysis.

The 13th Global CRO Council (GCC) closed forum for bioanalysis was held in New Orleans, LA, USA on 5 April 2019. This GCC meeting was organized to discuss the contents of the 2019 ICH M10 Bioanalytical Method Validation Draft Guideline published in February 2019 and consolidate the feedback of the GCC members. While ICH M10 will cover requirements for reference standards, one of the biggest challenges facing the CRO community is the lack of consistency and completeness of Certificates of Analysis for reference standards used in regulated bioanalysis. Similar challenges exist with critical reagents (e.g., capture and detection antibodies) used for assays supporting biologics. The recommendations provided in this publication are the minimum requirements for the content that GCC members believe should be included in Certificates of Analysis for reference standards obtained from commercial vendors, sponsors and compendial suppliers, for use in regulated bioanalytical studies. In addition, recommendations for internal standards, metabolites and critical reagents are discussed.

ApoE and clusterin cooperatively suppress Abeta levels and deposition: evidence that ApoE regulates extracellular Abeta metabolism in vivo.

Apolipoprotein E (apoE) and clusterin can influence structure, toxicity, and accumulation of the amyloid-beta (Abeta) peptide in brain. Both molecules may also be involved in Abeta metabolism prior to its deposition. To assess this possibility, we compared PDAPP transgenic mice that develop age-dependent Abeta accumulation in the absence of apoE or clusterin as well as in the absence of both proteins. apoE(-/-) and clusterin(-/-) mice accumulated similar Abeta levels but much less fibrillar Abeta. In contrast, apoE(-/-)/clusterin(-/-) mice had both earlier onset and markedly increased Abeta and amyloid deposition. Both apoE(-/-) and apoE(-/-)/clusterin(-/-) mice had elevated CSF and brain interstitial fluid Abeta, as well as significant differences in the elimination half-life of interstitial fluid Abeta measured by in vivo microdialysis. These findings demonstrate additive effects of apoE and clusterin on influencing Abeta deposition and that apoE plays an important role in regulating extracellular CNS Abeta metabolism independent of Abeta synthesis.

In vivo assessment of brain interstitial fluid with microdialysis reveals plaque-associated changes in amyloid-beta metabolism and half-life.

Soluble amyloid-beta (Abeta) peptide converts to structures with high beta-sheet content in Alzheimer's disease (AD). Soluble Abeta is released by neurons into the brain interstitial fluid (ISF), in which it can convert into toxic aggregates. Because assessment of ISF Abeta levels may provide unique insights into Abeta metabolism and AD, an in vivo microdialysis technique was developed to measure it. Our Abeta microdialysis technique was validated ex vivo with human CSF and then in vivo in awake, freely moving mice. Using human amyloid precursor protein (APP) transgenic mice, we found that, before the onset of AD-like pathology, ISF Abeta in hippocampus and cortex correlated with levels of APP in those tissues. After the onset of Abeta deposition, significant changes in the ISF Abeta40/Abeta42 ratio developed without changes in Abeta1-x. These changes differed from changes seen in tissue lysates from the same animals. By rapidly inhibiting Abeta production, we found that ISF Abeta half-life was short ( approximately 2 hr) in young mice but was twofold longer in mice with Abeta deposits. This increase in half-life, without an increase in steady-state levels, suggests that inhibition of Abeta synthesis reveals a portion of the insoluble Abeta pool that is in dynamic equilibrium with ISF Abeta. This now measurable in vivo pool is a likely target for new diagnostic and therapeutic strategies.

Development of a novel radioimmunoassay to detect autoantibodies to amyloid beta peptides in the presence of a cross-reactive therapeutic antibody.

An increasing need in the development of biotherapeutic agents is the ability to monitor a potential autoimmune response to the therapeutic target of interest. Unfortunately, the presence of high concentrations of therapeutic antibody can hinder such detection, because there is competition for binding in cases where epitopes are not structurally distinct. This situation was encountered in the development of LY2062430, a therapeutic mid-domain monoclonal anti-amyloid beta peptide (Aß) antibody undergoing clinical trials for the treatment of Alzheimer's disease. This communication reports the development and validation of a novel radioimmunoassay used to measure potential patient immune responses to Aß in the presence of LY2062430. This assay employs a radioiodinated analog of the human amyloid beta 1-40 peptide (Aß1-40) in which a single amino acid substitution of alanine for phenylalanine at position 19 (F19A) effectively eliminates binding by LY2062430. In contrast, F19A binding by monoclonal antibodies specific for the N- and C-termini of the human Aß1-40 peptide was shown to be unaltered. Additional experiments involving a polyclonal rabbit antibody raised against the midregion of Aß1-40 (residues 15-30) resulted in only a slight reduction in binding to the F19A tracer, suggesting that the modification does not affect distal epitopes in Aß1-40 and supporting the notion that this conservative substitution produces only subtle change in the overall peptide structure. The assay is therefore believed to detect most, if not all, patient antibodies to native Aß peptides. The assay was validated for use in clinical trials allowing detection of antibodies to Aß in human serum in the presence of therapeutic concentrations of LY2062430.

Aggregation of alpha-synuclein by DOPAL, the monoamine oxidase metabolite of dopamine.

Parkinson's disease (PD) is a neurodegenerative disease characterized by the selective loss of dopamine (DA) neurons and the presence of alpha-synuclein (AS) aggregates as Lewy bodies (LBs) in the remaining substantia nigra (SN) neurons. A continuing puzzle in studying PD pathogenesis is that although AS is expressed throughout the brain, LBs and selective dopaminergic cell loss lead to characteristic clinical signs of PD, suggesting that there is a link between AS aggregation and DA metabolism. One potential candidate for this link is the monoamine oxidase (MAO) metabolite of DA, 3,4-dihydroxyphenylacetaldehyde (DOPAL), as neither DA nor DA metabolites other than DOPAL are toxic to SN neurons at physiological concentrations. We tested DOPAL-induced AS aggregation in a cell-free system, in vitro in DA neuron cultures and in vivo with stereotactic injections into the SN of Sprague-Dawley rats by Western blots, fluorescent confocal microscopy and immunohistochemistry. We demonstrate that DOPAL in physiologically relevant concentrations, triggers AS aggregation in the cell-free system, and in cell cultures resulting in the formation of potentially toxic AS oligomers and aggregates. Furthermore, DOPAL injection into the SN of Sprague-Dawley rats resulted in DA neuron loss and the accumulation of high molecular weight oligomers of AS detected by Western blot. Our findings support the hypothesis that DA metabolism via DOPAL can cause both DA neuron loss and AS aggregation observed in PD.

The low density lipoprotein receptor regulates the level of central nervous system human and murine apolipoprotein E but does not modify amyloid plaque pathology in PDAPP mice.

Apolipoprotein E (apoE), a chaperone for the amyloid beta (Abeta) peptide, regulates the deposition and structure of Abeta that deposits in the brain in Alzheimer disease (AD). The primary apoE receptor that regulates levels of apoE in the brain is unknown. We report that the low density lipoprotein receptor (LDLR) regulates the cellular uptake and central nervous system levels of astrocyte-derived apoE. Cells lacking LDLR were unable to appreciably endocytose astrocyte-secreted apoE-containing lipoprotein particles. Moreover, cells overexpressing LDLR showed a dramatic increase in apoE endocytosis and degradation. We also found that LDLR knock-out (Ldlr-/-) mice had a significant, approximately 50% increase in the level of apoE in the cerebrospinal fluid and extracellular pools of the brain. However, when the PDAPP mouse model of AD was bred onto an Ldlr-/- background, we did not observe a significant change in brain Abeta levels either before or after the onset of Abeta deposition. Interestingly, human APOE3 or APOE4 (but not APOE2) knock-in mice bred on an Ldlr-/- background had a 210% and 380% increase, respectively, in the level of apoE in cerebrospinal fluid. These results demonstrate that central nervous system levels of both human and murine apoE are directly regulated by LDLR. Although the increase in murine apoE caused by LDLR deficiency was not sufficient to affect Abeta levels or deposition by 10 months of age in PDAPP mice, it remains a possibility that the increase in human apoE3 and apoE4 levels caused by LDLR deficiency will affect this process and could hold promise for therapeutic targets in AD.

Production and characterization of astrocyte-derived human apolipoprotein E isoforms from immortalized astrocytes and their interactions with amyloid-beta.

The apolipoprotein E (apoE) genotype is an important genetic risk factor for Alzheimer's disease (AD). In the central nervous system (CNS), most apoE is produced by astrocytes and is present in unique high-density lipoprotein (HDL)-like particles that have distinct properties from apoE derived from other sources. To develop an efficient system to produce astrocyte-derived apoE in large quantities, we produced and characterized immortalized cell lines from primary astrocyte cultures derived from human APOE knock-in mice. APOE2, APOE3, and APOE4 expressing cell lines were established that secrete apoE in HDL-like particles at similar levels, cholesterol composition, and size as those produced by primary astrocytes. In physiological buffers, astrocyte-secreted apoE3 and E4 associated equally well with amyloid-beta. Under the same conditions, only a small fraction of A beta formed sodium dodecyl sulfate (SDS)-stable complexes with apoE (E3 > E4). These immortalized astrocytes will be useful for studying mechanisms underlying the isoform-specific effects of apoE in the CNS.

Plaque-associated disruption of CSF and plasma amyloid-beta (Abeta) equilibrium in a mouse model of Alzheimer's disease.

To better understand amyloid-beta (Abeta) metabolism in vivo, we assessed the concentration of Abeta in the CSF and plasma of APP(V717F) (PDAPP) transgenic mice, a model that develops age-dependent Alzheimer's disease (AD)-like pathology. In 3-month-old mice, prior to the development of Abeta deposition in the brain, there was a highly significant correlation between Abeta levels in CSF and plasma. In 9-month-old-mice, an age at which some but not all mice have developed Abeta deposition, there was also a significant correlation between CSF and plasma Abeta; however, the correlation was not as strong as that present in young mice. In further exploring CSF and plasma Abeta levels in 9-month-old mice, levels of CSF Abeta were found to correlate highly with Abeta burden. Analysis of the CSF: plasma Abeta ratio revealed a selective two-fold increase in plaque versus non-plaque bearing mice, strongly suggesting a plaque-mediated sequestration of soluble Abeta in brain. Interestingly, in 9-month-old mice, a significant correlation between CNS and plasma Abeta was limited to mice lacking Abeta deposition. These findings suggest that there is a dynamic equilibrium between CNS and plasma Abeta, and that plaques create a new equilibrium because soluble CNS Abeta not only enters the plasma but also deposits onto amyloid plaques in the CNS.

Clusterin promotes amyloid plaque formation and is critical for neuritic toxicity in a mouse model of Alzheimer's disease.

Studies have shown that clusterin (also called apolipoprotein J) can influence the structure and toxicity of amyloid-beta (Abeta) in vitro. To determine whether endogenous clusterin plays a role in influencing Abeta deposition, structure, and toxicity in vivo, we bred PDAPP mice, a transgenic mouse model of Alzheimer's disease, to clusterin(-/-) mice. By 12 months of age, PDAPP, clusterin(-/-) mice had similar levels of brain Abeta deposition as did PDAPP, clusterin(+/+) mice. Although Abeta deposition was similar, PDAPP, clusterin(-/-) mice had significantly fewer fibrillar Abeta (amyloid) deposits than PDAPP mice expressing clusterin. In the absence of clusterin, neuritic dystrophy associated with the deposited amyloid was markedly reduced, resulting in a dissociation between fibrillar amyloid formation and neuritic dystrophy. These findings demonstrate that clusterin markedly influences Abeta structure and neuritic toxicity in vivo and is likely to play an important role in Alzheimer's disease pathogenesis.