Regulatory perspective for successful antibody-drug conjugate development Wen Jin Wu, M.D., Ph.D. Senior Investigator Division of Biotechnology Review and Research I Office of Biotechnology Products (OBP) Office of Pharmaceutical Quality (OPQ) CDER/FDA 1
Disclaimer: The information presented here reflects the views of the presenter and does not necessarily represent the views or policies of the U.S. Food and Drug Administration. 2
Schematic structure of antibody-drug conjugates (ADCs) mab Linker Drug mab IgG1, 2 or 4 Linkers 1. Cleavable peptide disulfide acid-labile hydrazone 2. Non-cleavable thioether Drugs 1. Tubulin inhibitors maytansinoides auristatins 2. DNA damaging agents Calicheamicin PBD dimer duocarmycins 3. Topoisomerase inhibitor SN-38 3
IND submission Milestones: FDA approved ADCs FDA approval 1993 7 years 2000 Gemtuzumab ozogamicin (Mylotarg) (accelerated approval) (withdrawn in 2010) Anti-CD33 (humanized IgG4) Hydrazone Calicheamicin 2006 6 years 2011 S Brentuximab vedotin (Adcetris) (accelerated approval ) Anti-CD30 Peptide MMAE (Chimeric IgG1) 2005 8 years 2013 N Ado-trastuzumab emtansine (Kadcyla) (T-DM1) Anti-HER2 (Humanized IgG1) Thioether DM1 4
ADC success depends on optimization of each component Monoclonal antibody/target Target specificity (tumor) o Drug delivery Target binding affinity o Unaltered compared to naked mab Internalization o Rapid process Target expression o High on tumor cell surface, low in normal tissues Source: Chari RV. Accounts of Chemical Research, 2008;41:98-107 Teicher BA. Current Cancer Drug Targets, 2009;9:982-1004 5
ADC success depends on optimization of each component cont. Linker Drug Stable in plasma and labile in target cells to release drug in the active form Stable upon storage High potency Linkable Water soluble Validated mechanism of action Source: Chari RV. Accounts of Chemical Research, 2008;41:98-107 Teicher BA. Current Cancer Drug Targets, 2009;9:982-1004 6
1) Internalization of the ADC complex and drug release following binding to antigen 2) Antibody-associated mechanisms ADCC CDC Signaling pathways Example: T-DM1, where antibody has demonstrated clinical activity Mechanisms of action of ADC 3) Bystander effect The ability of an ADC to produce cytotoxic effects on antigen positive, as well as on antigen-negative cells upon processing and releasing of the metabolized payload into the tumor microenvironment Example: brentuximab vedotin, which is capable of killing both CD30-positive and CD30-negative cells 7
Number of ADC INDs Increasing ADC IND submissions at FDA 50 40 30 20 10 0 Note: In 2015, 8 ADC INDs and 5 ADC pre-inds were submitted to FDA. 8
Number of antigens targeted by ADCs Target selections Antigen targeting frequency by ADC(s) There is a minimal overlap of antigens targeted by different ADCs 9
ADCs are giving new life to targets (Mullard A. Nature Review: Drug discovery. 2013:329-332.) mab-mediated internalization demonstrates the usefulness of the targets as a guidance system for payloads even though the naked mabs themselves fail to sufficiently kill cancer cells or become resistant by tumor. Relapsed or refractory Hodgkin s Lymphoma Brentuximab vedotin (anti-cd30 ADC) SGN-30 (a chimeric anti-cd30 mab) No. of patients 102 38 Dose 1.8 mg/kg 6 or 12 mg/kg The rate for the objective responses 75% 0% (Forero-Torres et al. British Journal of Hematology, 2009:146;171 179; Younes et al. Journal of Clinical Oncology, 2012:30:2183-2189) T-DM1 targets HER2 again to treat trastuzumab-resistant disease. 10
Number of ADCs Number of ADCs ADC component: monoclonal antibodies 60 50 40 30 20 10 0 IgG1 IgG2 IgG4 11
Number of products ADC component: linkers 40 Uncleavable thioether based 35 30 25 20 15 10 5 0 Disulfide based Enzyme cleavable dipeptides Acid labile Fewer products contain relatively unstable linkers with short half-lives such as disulfide-based linkers and hydrazones More products use linkers with improved stability in systemic circulation, e.g., peptide and non-cleavable thioether linkers 12
Cysteine or lysine ADC conjugation sites These random conjugation processes produce heterogeneous ADC products with different drug load distribution and drug/antibody ratio (DAR) Heterogeneity in overall charge of lysine conjugates can impact solubility, stability, and pharmacokinetics The conjugation process should be well controlled to ensure the lot-to-lot consistency Site-specific The site-specific conjugated ADCs have displayed homogeneous labeling 1) Engineered cysteines 2) Insertion of an unnatural amino acid 3) Bacterial transglutaminase Number of products 13
Number of products ADC component: payloads 45 40 35 30 25 20 15 10 5 0 Traditional chemotherapies Enzyme targeting agents DNA targeting agents More ADCs are armed with microtubule inhibitors. Microtubule targeting agents 14
Regulatory requirements of ADCs 15
ADC regulation There is no specific Regulatory Guidance to Industry on ADC development FDA follows existing guidelines for small drugs and monoclonal antibodies to regulate ADC ADC review is a collaborative effort across product quality offices at FDA: o Office of Biotechnology Products (OBP)/OPQ primarily focuses on the manufacturing of the antibody component of the ADC and the control strategy for the antibody intermediate, as well as for the drug substance (DS) and drug product (DP) o Small molecule review groups in OPQ bear primary responsibility for review of the adequacy of the payload and linker, conjugation reaction and aspects of the control strategy 16
Characterization of mab intermediate and ADC Primary structure mab intermediate amino acid (aa) composition, N-terminal/Cterminal sequence analysis, peptide mapping ADC-specific drug attachment sites Conformational structure Posttranslational modifications size and charge variants, molecular weight e.g., sialic acid determination, monosaccharide content and oligosaccharide profile analysis drug load distribution and drug/antibody ratio (DAR) Impurities Biological activity product-related Impurities, e.g., dimers, aggregates and degradation products process-related Impurities, e.g., microbial contaminants, HCP, host cell DNA target specific binding and binding affinity, and effector function free drug and its related substance, residual solvents, heavy metals and unconjugated mab cytotoxicity The expectations for the characterization of unconjugated mab are the same whether or not it will be developed on its own or as part of an ADC Conjugation may impact on mab: 1) binding affinity and effector function, 2) primary 17 structure and posttranslational modifications, 3) size and charge variants.
ADC DS and/or DP release specifications Appearance, ph, osmolality, total protein Identity binding charge based peptide mapping Impurities drug free drug and its related substances residual solvents heavy metals Drug/antibody ratio Purity/Impurities mab monomer, fragments and aggregates charge variants unconjugated antibody Particulate matter (USP<788>) Safety Endotoxin bioburden/sterility Potency Binding cytotoxicity assay 18
Drug/antibody ratio (DAR) and drug load distribution 19
DAR and drug load distribution (cysteine-linked ADC) Fig. 2 A representative HIC chromatogram (Ouyang J. Antibody-Drug Conjugates, Methods Mol Biol 2013;1045:275-83.) 1. The hydrophobic interaction chromatography (HIC) method has been developed to determine the drug load distribution and DAR for cysteine-linked ADCs 2. Based on the drug load profiles, drug load distribution and DAR can be calculated 20
DAR and drug load distribution (lysine-linked ADC) (Basa L. Antibody-Drug Conjugate, Methods Mol Biol 2013;1045:285-293.) 1. MS-based method has been developed to determine the DAR and drug load distribution for lysine-linked ADCs 2. Drug load distribution (%) = (peak area of Ab with drug load n/sum of all peak areas x 100 (%) (n is number of drug load) 3. DAR = Ʃ (drug load distribution (%) of each Ab with drug load n (n)/100 21
Sites of attachment 1. Well controlled and robust chemical process leads to reproducible product 2. Peptide map fingerprint of drug-containing peptides shows consistency between processes at different scales and sites 3. Lot-to-lot the same lysines are modified at the same % occupancy (Fred Jacobson, CASSS CMC Strategy Forum Japan 2013) (Courtesy of Dr. Fred Jacobson) 22
DAR and drug load distribution: They are critical product quality attributes They determine the drug quantity to which the patient is exposed Various drug-loaded forms may differ in their PK/PD characteristics (Basa L. Antibody-Drug Conjugates, Methods Mol Biol 2013;1045:285-293) Question: Should Drug load distribution be included in the lot release specifications for a better quality control on ADCs? 23
ADC stability DS and DP stability studies Stability testing methods and acceptance criteria Test time/intervals Storage conditions: long term, accelerated and stressed Stability indicating assays ADC serum stability Linker stability 24
Issues identified in pre-ind meeting packages 1. The sponsor considered the small molecule of ADC as DS - The small molecule potion of ADC is considered as an intermediate, and antibody conjugated with small molecule via a linker is considered DS. 2. The mab potion of ADC was functioning to target cancer cells and was not considered as an active molecule in the ADC. Therefore, the sponsor thought the antibody component would not need further CMC characterization - The mab is a component of the mechanism of action of ADC. The expectations for characterization of the mab intermediate are the same whether the mab is used alone or as part of a conjugated structure. 3. The sponsor proposed to use non-gmp DM1 reagent in the GMP manufacturing of preclinical and clinical lots of ADC - DM1 is not a reagent. It is a drug substance intermediate. Therefore, DM1 should be manufactured under GMP. 25
Toxicology lots vs. lots to be used in the Phase 1 clinical study Issues: The toxicology lot and the clinical lot were manufactured by different processes. The original IND submission lacked sufficient data to demonstrate comparability of the toxicology and clinical lots. General considerations for monoclonal antibody products: 1.One lot each of the toxicology and clinical product may be sufficient to assess comparability at this stage of drug development 2.The focus of the comparability exercise is usually on an evaluation of quality attributes related to safety, such as impurities 3.The potency of the product should be considered in the comparability assessment 4.Generally, the phase I clinical product should have comparable or improved quality attributes (e.g., improved purity) relative to the toxicology product 5.Comparative stability data (real-time, accelerated, stress or forced degradation stability) are generally not required to demonstrate comparability of the non-clinical and phase I clinical products In the case of ADCs, comparability evaluation is focused on product impurities profiles, DAR and potency. Comparable DARs should be maintained between the toxicology lot and the clinical lot. 26
Example: Pitfalls encountered in setting DS and DP lot release specifications and stability study Potency assays: 1. Cytotoxicity assay or binding assay was not included as part of DS or DP lot release specifications. Both binding and cytotoxicity assays should be included for ADC lot release and stability study. 2. Potency of the DS was to be measured with an binding assay while the DP potency was determined using a cytotoxicity assay. It is recommended that a relevant potency assay, such as the cellbased cytotoxicity assay proposed to be used for DP testing, be incorporated into the DS release and stability testing program. 27
Example: Pitfalls in setting DS and DP lot release specifications and stability study cont. Potency assays: 3. The proposed specifications for DS and DP lot release for the antigen binding and the cytotoxicity assay were unusually broad, e.g., 50-200% of reference standard. This may not provide sufficient control over product potency to ensure consistent dosing. Furthermore, antibody-drug conjugates generally have a narrower therapeutic window than naked mabs due to their higher toxicity. Provide scientific justification for the values proposed. 28
Example: Pitfalls in setting DS and DP release specification and stability study cont. Charge variants: An assay to monitor charge isoforms was not included as part of DS and DP lot release and stability studies. A charge assay with quantitative acceptance criteria should be incorporated into DS and DP lot release specifications and stability study. Until quantitative acceptance criteria can be established, a semiquantitative criterion such as conforms to reference standard with a well-defined conformance description can be used. However, the quantitative results should still be reported at release and on stability. Caveat: Charge based assays may not be possible/meaningful after conjugation to lysine residues. 29
Example: Pitfalls in setting DS and DP release specifications and stability study cont. Unconjugated antibody testing was not included as part of DS and DP lot release Numerical acceptance criteria for unconjugated antibody were not set for lot release Quantitative acceptance criteria for DAR were not included for the release and stability study The acceptance criteria for free drug and its related species were not appropriately set Tighten your proposed acceptance criteria for free drug in the DS and DP specifications based on your actual manufacturing batch test data and provide the justifications for the acceptance criteria for the free drug species. For Phase 1, free drug related impurities in clinical lot should be qualified relative to data from toxicology studies. 30
Summary ADCs are a rapidly growing area in drug development, as reflected by a significant increase in IND submissions to the FDA. Advances in technology have optimized ADC development. Early communication with FDA regarding regulatory strategy is advisable. 31
Acknowledgement OBP Milos Dokmanovic Haoheng Yan Wendy Weinberg Marjorie Shapiro Kathleen Clouse ONDP Xiao-Hong Chen 32