Sensitive assay design for detection of anti-drug antibodies to biotherapeutics that lack an immunoglobulin Fc domain

Method development for the detection of anti-drug antibodies against a therapeutic peptide: assay format selection

AIM

Monitoring immune responses to therapeutic peptides with endogenous counterparts is crucial for evaluating drug safety and efficacy. In this paper, we focused on the selection of an optimal assay format to develop a sensitive, robust, and drug-tolerant immunoassay for the detection of anti-drug antibody (ADA) against a therapeutic peptide.

RESULTS

We assessed distinct ADA assay formats for preclinical and clinical studies, such as direct binding with labeled protein A/G, direct binding with labeled multiple species-specific antibodies for detection, bridging and affinity capture elution (ACE) formats. The assay formats were evaluated based on multiple assay parameters including sensitivity, drug tolerance, individual matrix variability and inter-assay precision. Overall, direct binding assay with labeled protein A/G for detection, which utilized less labeled peptide drug and achieved desired sensitivity and drug tolerance, is appropriate for preclinical studies. Bridging assay is more suitable format to support clinical studies as bridging assay has less assay variability than ACE assay.

CONCLUSION

This study highlighted advantages and limitations of each ADA assay format for peptide drugs and evaluated the performance of different assay formats in the assay development process to aid in the selection of the best fit-for-purpose assay formats for preclinical and clinical phases.

Feasibility of a direct binding electrochemiluminescence assay to detect anti-drug antibodies against therapeutic peptides

The emergence of anti-drug antibodies (ADAs) poses significant impacts on the bioactivity and toxicity of biotherapeutics including proteins and peptides. Developing reliable assays to monitor the magnitudes of ADAs in blood samples is therefore considered a crucial task in animal and human studies throughout the development of biotherapeutics. Peptides represent a significant and fast-growing category of biotherapeutics for the management of a variety of indications. While peptides generally exhibit lower immunogenicity risks compared to biologics of larger sizes, drug developers are still required to conduct the risk-based immunogenicity assessment as mandated by the regulatory authorities. To address the need for efficient detection of ADAs against therapeutic peptides, we established a straightforward electrochemiluminescence immunoassay (ECLIA) based on direct binding strategy. Our assay demonstrates its applicability across various peptide therapeutics including marketed drugs and internal investigational compounds. Through stepwise tuning of the assay procedure, we identified several key factors such as buffer, detection reagent, plate type, and conjugation strategy that collectively contribute to the assay performance. Depending on the drug molecule and positive control antibody, the assay can achieve low single-digit to two-digit ng/ml sensitivity and ideal drug tolerance. In conclusion, this ECLIA platform presents a valuable and generic tool to expedite the development and validation of ADA assays for peptide-based therapeutics.

Successful Development of Nonclinical Anti-Drug Antibody Assays to Support Zinpentraxin Alfa Reproductive Toxicology Studies

Immunogenicity assessment is an essential part of biotherapeutic drug development. While the immune response in animals is not always representative of the human immune response, immunogenicity data obtained in animal models is still informative for the evaluation of drug exposure and safety. The most common assay format used for the detection of anti-drug antibodies (ADAs) in preclinical and clinical studies is the bridging format. The advantage of this method is that it can detect all antibody isotypes generated against the therapeutic. However, the method development can be time-consuming and labor-intensive, due to the need for labeling of the drug which is used both as capture and detection. Various generic ADA assays have been successfully implemented to overcome these disadvantages and to enable faster assay development timelines to support nonclinical toxicology studies. Here, we describe the challenges in the development of an assay to detect antibodies to zinpentraxin alfa, a recombinant human pentraxin-2, in rabbit and rat toxicology studies. Our initial efforts to develop a bridging assay failed, prompting us to develop a method adapted from generic assay formats to detect anti-zinpentraxin alfa antibodies in the serum of different species with minimal optimization. However, while the general assay format remained similar, assay reagents were adapted between the different species, resulting in the development of two distinct assays for the detection of ADAs in rat and rabbit. Here, we share the final development/validation data and the immunogenicity study results. Our work highlights the need for the evaluation of alternate assay formats when evaluating novel drug modalities.

Evaluation of multiple immunoassay formats for detection of anti-drug antibodies to zinpentraxin alfa

Zinpentraxin alfa (rhPTX-2; PRM-151) is currently being developed for the treatment of fibrotic diseases such as idiopathic pulmonary fibrosis and myelofibrosis. Notably, because it is administered chronically and has an endogenously expressed counterpart, clinical studies of zinpentraxin alpha must include immunogenicity assessments. Since the typical homogenous bridging ELISA assay does not adequately measure anti-drug antibodies (ADAs) against zinpentraxin alfa, additional assay formats have been developed to evaluate immunogenicity of this therapeutic. Here, we present the evaluation of four distinct assay formats that were used to measure zinpentraxin alpha ADA: step-wise bridging, direct binding, total ADA, and the semi-homogeneous formats, based on multiple parameters including assay sensitivity, precision, and drug tolerance. This paper presents the full details of method development for each of the aforementioned assay formats including evaluation of sample pre-treatment, determination of cut point, and assessment of assay performance by analyzing a subset of clinical samples. Overall, the semi-homogenous ADA assay format with no sample pre-treatment was selected for the measurement of zinpentraxin alpha immunogenicity as it provided the desired sensitivity, drug tolerance, and reproducibility. Our study emphasizes the importance of assay format evaluation during drug development and the necessity to select the most suitable assay format and sample pre-treatment method by which to evaluate therapeutic drug immunogenicity.

Feasibility of using PALSAR technology as a signal amplifier for antibody bridging assay

The immunogenicity testing of oligonucleotide drugs using an antibody bridging assay has been scarcely investigated. We developed a highly sensitive antibody bridging assay model and assessed it using probe alteration link self-assembly reactions (PALSAR) technology as a signal amplifier. Methods: The concentration of each probe was optimized, and the bridging assay model was compared with and without signal amplification. Cut-point and analytical sensitivity were determined, and accuracy, precision and drug tolerance were evaluated. Results: The PALSAR bridging assay achieved a net signal 21-36 times higher than that obtained with the conventional method. The analytical sensitivity achieved was 48.8 ng/ml, with adequate accuracy, precision and drug tolerance. Conclusion: PALSAR technology is feasible for developing an antibody bridging assay using oligonucleotides as capture and detection probes.

Development and Functional Characterization of a Versatile Radio-/Immunotheranostic Tool for Prostate Cancer Management

Simple Summary

In previous studies, we described a modular Chimeric Antigen Receptor (CAR) T cell platform which we termed UniCAR. In contrast to conventional CARs, the interaction of UniCAR T cells does not occur directly between the CAR T cell and the tumor cell but is mediated via bispecific adaptor molecules so-called target modules (TMs). Here we present the development and functional characterization of a novel IgG4-based TM, directed to the tumor-associated antigen (TAA) prostate stem cell antigen (PSCA), which is overexpressed in prostate cancer (PCa). We show that this anti-PSCA IgG4-TM cannot only be used for (i) redirection of UniCAR T cells to PCa cells but also for (ii) positron emission tomography (PET) imaging, and (iii) alpha particle-based endoradiotherapy. For radiolabeling, the anti-PSCA IgG4-TM was conjugated with the chelator DOTAGA. PET imaging was performed using the ⁶⁴Cu-labeled anti-PSCA IgG4-TM. According to PET imaging, the anti-PSCA IgG4-TM accumulates with high contrast in the PSCA-positive tumors of experimental mice without visible uptake in other organs. For endoradiotherapy the anti-PSCA IgG4-TM-DOTAGA conjugate was labeled with ²²⁵Ac³⁺. Targeted alpha therapy resulted in tumor control over 60 days after a single injection of the ²²⁵Ac-labeled TM. The favorable pharmacological profile of the anti-PSCA IgG4-TM, and its usage for (i) imaging, (ii) targeted alpha therapy, and (iii) UniCAR T cell immunotherapy underlines the promising radio-/immunotheranostic capabilities for the diagnostic imaging and treatment of PCa.

Abstract

Due to its overexpression on the surface of prostate cancer (PCa) cells, the prostate stem cell antigen (PSCA) is a potential target for PCa diagnosis and therapy. Here we describe the development and functional characterization of a novel IgG4-based anti-PSCA antibody (Ab) derivative (anti-PSCA IgG4-TM) that is conjugated with the chelator DOTAGA. The anti-PSCA IgG4-TM represents a multimodal immunotheranostic compound that can be used (i) as a target module (TM) for UniCAR T cell-based immunotherapy, (ii) for diagnostic positron emission tomography (PET) imaging, and (iii) targeted alpha therapy. Cross-linkage of UniCAR T cells and PSCA-positive tumor cells via the anti-PSCA IgG4-TM results in efficient tumor cell lysis both in vitro and in vivo. After radiolabeling with ⁶⁴Cu²⁺, the anti-PSCA IgG4-TM was successfully applied for high contrast PET imaging. In a PCa mouse model, it showed specific accumulation in PSCA-expressing tumors, while no uptake in other organs was observed. Additionally, the DOTAGA-conjugated anti-PSCA IgG4-TM was radiolabeled with ²²⁵Ac³⁺ and applied for targeted alpha therapy. A single injection of the ²²⁵Ac-labeled anti-PSCA IgG4-TM was able to significantly control tumor growth in experimental mice. Overall, the novel anti-PSCA IgG4-TM represents an attractive first member of a novel group of radio-/immunotheranostics that allows diagnostic imaging, endoradiotherapy, and CAR T cell immunotherapy.