Current Approaches for Absorption, Distribution, Metabolism, and Excretion Characterization of Antibody-Drug Conjugates: An Industry White Paper

In Vivo Characterization of Platinum(II)-Based Linker Technology for the Development of Antibody-Drug Conjugates: Taking Advantage of Dual Labeling with 195mPt and 89Zr

Linker instability and impaired tumor targeting can affect the tolerability and efficacy of antibody-drug conjugates (ADCs). To improve these ADC characteristics, we recently described the use of a metal-organic linker, [ethylenediamineplatinum(II)]²⁺, herein called Lx Initial therapy studies in xenograft-bearing mice revealed that trastuzumab-Lx-auristatin F (AF) outperformed its maleimide benchmark trastuzumab-mal-AF and the Food and Drug Administration-approved ado-trastuzumab emtansine, both containing conventional linkers. In this study, we aimed to characterize Lx-based ADCs for in vivo stability and tumor targeting using ^195mPt and ⁸⁹Zr. Methods: The γ-emitter ^195mPt was used to produce the radiolabeled Lx [^195mPt]Lx⁸⁹Zr-Desferrioxamine (⁸⁹Zr-DFO) was conjugated to trastuzumab either via [^195mPt]Lx (to histidine residues) or conventionally (to lysine residues) in order to monitor the biodistribution of antibody, payload, and linker separately. Linker stability was determined by evaluating the following ADCs for biodistribution in NCI-N87 xenograft-bearing nude mice 72 h after injection: trastuzumab-[^195mPt]Lx-DFO-⁸⁹Zr, trastuzumab-[^195mPt]Lx-AF, and ⁸⁹Zr-DFO-(Lys)trastuzumab (control), all having drug-to-antibody ratios (DARs) of 2.2-2.5. To assess the influence of DAR on biodistribution, ⁸⁹Zr-DFO-(Lys)trastuzumab-Lx-AF with an AF-to-antibody ratio of 0, 2.6, or 5.2 was evaluated 96 h after injection. Results: Similar biodistributions were observed for trastuzumab-[^195mPt]Lx-DFO-⁸⁹Zr, trastuzumab-[^195mPt]Lx-AF, and ⁸⁹Zr-DFO-(Lys)trastuzumab irrespective of the isotope used for biodistribution assessment. The fact that Lx follows the antibody biodistribution indicates that the payload-Lx bond is stable in vivo. Uptake of the 3 conjugates, as percentage injected dose (%ID) per gram of tissue, was about 30 %ID/g in tumor tissue but less than 10 %ID/g in most healthy tissues. Trastuzumab-[^195mPt]Lx-AF (DAR 2.2) showed a tendency toward faster blood clearance and an elevated liver uptake, which increased significantly to 28.1 ± 4.2 %ID/g at a higher DAR of 5.2, as revealed from the biodistribution and PET imaging studies. Conclusion: As shown by ^195mPt/⁸⁹Zr labeling, ADCs containing the Lx linker are stable in vivo. In the case of trastuzumab-Lx-AF (DARs 2.2 and 2.6), an unimpaired biodistribution was demonstrated.

Pharmacokinetic Considerations for Antibody-Drug Conjugates against Cancer

Antibody-drug conjugates (ADCs) are ushering in the next era of targeted therapy against cancer. An ADC for cancer therapy consists of a potent cytotoxic payload that is attached to a tumour-targeted antibody by a chemical linker, usually with an average drug-to-antibody ratio (DAR) of 3.5-4. The theory is to deliver potent cytotoxic payloads directly to tumour cells while sparing healthy cells. However, practical application has proven to be more difficult. At present there are only two ADCs approved for clinical use. Nevertheless, in the last decade there has been an explosion of options for ADC engineering to optimize target selection, Fc receptor interactions, linker, payload and more. Evaluation of these strategies requires an understanding of the mechanistic underpinnings of ADC pharmacokinetics. Development of ADCs for use in cancer further requires an understanding of tumour properties and kinetics within the tumour environment, and how the presence of cancer as a disease will impact distribution and elimination. Key pharmacokinetic considerations for the successful design and clinical application of ADCs in oncology are explored in this review, with a focus on the mechanistic determinants of distribution and elimination.

High-Throughput, Multispecies, Parallelized Plasma Stability Assay for the Determination and Characterization of Antibody-Drug Conjugate Aggregation and Drug Release

The stability of antibody-drug conjugates (ADCs) in circulation is critical for maximum efficacy and minimal toxicity. An ADC reaching the intended target intact can deliver the highest possible drug load to the tumor and reduce off-target toxicity from free drug in the blood. As such, assessment of ADC stability is a vital piece of data during development. However, traditional ADC stability assays can be manually intensive, low-throughput, and require large quantities of ADC material. Here, we introduce an automated, high-throughput plasma stability assay for screening drug release and aggregation over 144 h for up to 40 ADCs across five matrices simultaneously. The amount of ADC material during early drug development is often limited, so this assay was implemented in 384-well format to minimize material requirements to <100 μg of each ADC and 100 μL of plasma per species type. Drug release and aggregation output were modeled using nonlinear regression equations to calculate formation rates for each data type. A set of 15 ADCs with different antibodies and identical valine-citrulline-p-aminobenzylcarbamate-monomethylauristatin E linker-drug payloads was tested and formation rates were compared across ADCs and between species, revealing several noteworthy trends. In particular, a wide range in aggregation was found when altering only the antibody, suggesting a key role for plasma stability screening early in the development process to find and remove antibody candidates with the potential to create unstable ADCs. The assay presented here can be leveraged to provide stability data on new chemistry and antibody screening initiatives, select the best candidate for in vivo studies, and provide results that highlight stability issues inherent to particular ADC designs throughout all stages of ADC development.

Antibody Drug Conjugates Differentiate Uptake and DNA Alkylation of Pyrrolobenzodiazepines in Tumors from Organs of Xenograft Mice

Pyrrolobenzodiazepine (PBD)-dimer is a DNA minor groove alkylator, and its CD22 THIOMAB antibody drug conjugate (ADC) demonstrated, through a disulfide linker, an efficacy in tumor reduction for more than 7 weeks with minimal body weight loss in xenograft mice after a single 0.5-1 mg/kg i.v. dose. The DNA alkylation was investigated here in tumors and healthy organs of mice to understand the sustained efficacy and tolerability. The experimental procedures included the collection of tumors and organ tissues of xenograft mice treated with the ADC followed by DNA isolation/hydrolysis/quantitation and payload recovery from reversible DNA alkylation. PBD-dimer formed a considerable amount of adducts with tissue DNA, representing approximately 98% (at 24 hours), and 99% (at 96 hours) of the total PBD-dimer in tumors, and 78-89% in liver and lung tissues, suggesting highly efficient covalent binding of the released PBD-dimer to tissue DNA. The amount of PBD-DNA adducts in tumor tissues was approximately 24-fold (at 24 hours) and 70-fold (at 96 hours) greater than the corresponding amount of adducts in liver and lung tissues. In addition, the DNA alkylation levels increased 3-fold to 4-fold from 24 to 96 hours in tumors [41/106 base pairs (bp) at 96 hours] but remained at the same level (1/106 bp) in livers and lungs. These results support the typical target-mediated cumulative uptake of ADC into tumors and payload release that offers an explanation for its sustained antitumor efficacy. In addition, the low level of DNA alkylation in normal tissues is consistent with the tolerability observed in mice.

The third annual BRDS on research and development of nucleic acid-based nanomedicines

The completion of human genome project, decrease in the sequencing cost, and correlation of genome sequencing data with specific diseases led to the exponential rise in the nucleic acid-based therapeutic approaches. In the third annual Biopharmaceutical Research and Development Symposium (BRDS) held at the Center for Drug Discovery and Lozier Center for Pharmacy Sciences and Education at the University of Nebraska Medical Center (UNMC), we highlighted the remarkable features of the nucleic acid-based nanomedicines, their significance, NIH funding opportunities on nanomedicines and gene therapy research, challenges and opportunities in the clinical translation of nucleic acids into therapeutics, and the role of intellectual property (IP) in drug discovery and development.

Mechanisms of Resistance to Antibody-Drug Conjugates

Drug resistance limits the effectiveness of cancer therapies. Despite attempts to develop curative anticancer treatments, tumors evolve evasive mechanisms limiting durable responses. Hence, diverse therapies are used to attack cancer, including cytotoxic and targeted agents. Antibody-drug conjugates (ADC) are biotherapeutics designed to deliver potent cytotoxins to cancer cells via tumor-specific antigens. Little is known about the clinical manifestations of drug resistance to this class of therapy; however, recent preclinical studies reveal potential mechanisms of resistance. Because ADCs are a combination of antibody and small molecule cytotoxin, multifactorial modes of resistance are emerging that are inherent to the structure and function of the ADC. Decreased cell-surface antigen reduces antibody binding, whereas elevated drug transporters such as MDR1 and MRP1 reduce effectiveness of the payload. Inherent to the uniqueness of the ADC, other novel resistance mechanisms are emerging, including altered antibody trafficking, ADC processing, and intracellular drug release. Most importantly, the modular nature of the ADC allows components to be switched and replaced, enabling development of second-generation ADCs that overcome acquired resistance. This review is intended to highlight recent progress in our understanding of ADC resistance, including approaches to create preclinical ADC-refractory models and to characterize their emerging mechanisms of resistance. Mol Cancer Ther; 15(12); 2825-34. ©2016 AACR.

Antibody–drug conjugate bioanalysis using LB-LC–MS/MS hybrid assays: strategies, methodology and correlation to ligand-binding assays

Background: Antibody–drug conjugates (ADCs) are complex drug constructs with multiple species in the heterogeneous mixture that contribute to their efficacy and toxicity. The bioanalysis of ADCs involves multiple assays and analytical platforms. Methods: A series of ligand binding and LC–MS/MS (LB-LC–MS/MS) hybrid assays, through different combinations of anti-idiotype (anti-Id), anti-payload, or generic capture reagents, and cathepsin-B or trypsin enzyme digestion, were developed and evaluated for the analysis of conjugated-payload as well as for species traditionally measured by ligand-binding assays, total-antibody and conjugated-antibody. Results & conclusion: Hybrid assays are complementary or viable alternatives to ligand-binding assay for ADC bioanalysis and PK/PD modeling. The fit-for-purpose choice of analytes, assays and platforms and an integrated strategy from Discovery to Development for ADC PK and bioanalysis are recommended.

New Insights in Tissue Distribution, Metabolism, and Excretion of [3H]-Labeled Antibody Maytansinoid Conjugates in Female Tumor-Bearing Nude Rats

For antibody drug conjugates (ADCs), the fate of the cytotoxic payload in vivo needs to be well understood to mitigate toxicity risks and properly design the first in-patient studies. Therefore, a distribution, metabolism, and excretion (DME) study with a radiolabeled rat cross-reactive ADC ([(3)H]DM1-LNL897) targeting the P-cadherin receptor was conducted in female tumor-bearing nude rats. Although multiple components [total radioactivity, conjugated ADC, total ADC, emtansine (DM1) payload, and catabolites] needed to be monitored with different technologies (liquid scintillation counting, liquid chromatography/mass spectrometry, enzyme-linked immunosorbent assay, and size exclusion chromatography), the pharmacokinetic data were nearly superimposable with the various techniques. [(3)H]DM1-LNL897 was cleared with half-lives of 51-62 hours and LNL897-related radioactivity showed a minor extent of tissue distribution. The highest tissue concentrations of [(3)H]DM1-LNL897-related radioactivity were measured in tumor. Complimentary liquid extraction surface analysis coupled to micro-liquid chromatography-tandem mass spectrometry data proved that the lysine (LYS)-4(maleimidylmethyl) cyclohexane-1-carboxylate-DM1 (LYS-MCC-DM1) catabolite was the only detectable component distributed evenly in the tumor and liver tissue. The mass balance was complete with up to 13.8% ± 0.482% of the administered radioactivity remaining in carcass 168 hours postdose. LNL897-derived radioactivity was mainly excreted via feces (84.5% ± 3.12%) and through urine only to a minor extent (4.15% ± 0.462%). In serum, the major part of radioactivity could be attributed to ADC, while small molecule disposition products were the predominant species in excreta. We show that there is a difference in metabolite profiles depending on which derivatization methods for DM1 were applied. Besides previously published results on LYS-MCC-DM1 and MCC-DM1, maysine and a cysteine conjugate of DM1 could be identified in serum and excreta.

Antibody drug conjugates

Antibody drug conjugates (ADCs) have emerged as a viable option in targeted delivery of highly potent cytotoxic drugs in treatment of solid tumors. At the time of writing, only two ADCs have received regulatory approval with >40 others in clinical development. The first generation ADCs suffered from a lack of specificity in amino acid site-conjugations, yielding statistically heterogeneous stoichiometric ratios of drug molecules per antibody molecule. For the second generation ADCs, however, site-specific amino acid conjugation using enzymatic ligation, introduction of unnatural amino acids, and site-specific protein engineering hold promise to alleviate some of the current technical limitations. The rapid progress in technology platforms and antibody engineering has introduced novel linkers, site-specific conjugation chemistry, and new payload candidates that could possibly be exploited in the context of ADCs. A search using the Clinical Trial Database registry ( www.clinicaltrials.gov ), using the keyword 'antibody drug conjugate', yielded ~270 hits. The main focus of this article is to present a brief overview of the recent developments and current challenges related to ADC development.