Translational PK/PD framework for antibody-drug conjugates to inform drug discovery and development.

(171/200)ADCs represent a transformative class of medicine that combines the specificity of monoclonal antibodies with the potency of highly cytotoxic agents through linkers, aiming to enhance the therapeutic index of cytotoxic drugs. Given the complex molecular structures of ADCs, combining the molecular characteristics of small-molecule drugs and those of large-molecule biotherapeutics, there are several unique considerations when designing nonclinical-to-clinical PK/PD translation strategies.This complexity also demands a thorough understanding of the ADC's components-antibody, linker, and payload-to the overall toxicological, PK/PD, and efficacy profile. ADC development is a multidisciplinary endeavor requiring a strategic integration of nonclinical safety, pharmacology, and PK/PD modeling to translate from bench to bedside successfully.The ADC development underscores the necessity for a robust scientific foundation, leveraging advanced analytical and modeling tools to predict human responses and optimize therapeutic outcomes.This review aims to provide an ADC translational PK/PD framework by discussing unique aspects of ADC nonclinical to clinical PK translation, starting dose determination, and leveraging PK/PD modeling for human efficacious dose prediction and potential safety mitigation.

Characterization of Tissue Distribution, Catabolism, and Elimination of an Anti-Staphylococcus aureus THIOMAB Antibody-Antibiotic Conjugate in Rats.

Invasive Staphylococcus aureus infection is a leading cause of infectious disease-related deaths because S. aureus survives within host phagocytic cells, from which the bacteria are not adequately eliminated using current antibiotic treatments. Anti-S. aureus THIOMAB antibody-antibiotic conjugate (TAC), an anti-S. aureus antibody conjugated with antibiotic payload dmDNA31, was designed to deliver antibiotics into phagocytes, thereby killing intracellular S. aureus Herein, we present the distribution, metabolism/catabolism, and elimination properties for this modality. The tissue distribution of TAC and the release and elimination of its payload dmDNA31 were characterized in rats using multiple approaches. Intravenous injection of unconjugated [14C]dmDNA31 to rats resulted in a rapid clearance in both systemic circulation and tissues, with biliary secretion as the major route of elimination. Six major metabolites were identified. When [14C]dmDNA31 was conjugated to an antibody as TAC and administered to rat intravenously, a sustained exposure was observed in both systemic circulation and tissues. The dmDNA31 in blood and tissues mainly remained in conjugated form after administering TAC, although minimal deconjugation of dmDNA31 from TAC was also observed. Several TAC catabolites were identified, which were mainly eliminated through the biliary-fecal route, with dmDNA31 and deacetylated dmDNA31 as the most abundant catabolites. In summary, these studies provide a comprehensive characterization of the distribution, metabolism/catabolism, and elimination properties of TAC. These data fully support further clinical development of TAC for the invasive and difficult-to-treat S. aureus infection. SIGNIFICANCE STATEMENT: The present studies provide a comprehensive investigation of the absorption, distribution, metabolism/catabolism, and elimination of the first antibody-antibiotic conjugate developed for the treatment of an infectious disease. Although many antibody-drug conjugates are in development for various disease indications, only a limited amount of absorption, distribution, metabolism/catabolism, and elimination information is available in the literature. This study demonstrates the use of radiolabeling technology to delineate the absorption, distribution, metabolism/catabolism, and elimination properties of a complex modality and help address the key questions related to clinical pharmacological studies.

Antibody-mediated delivery of chimeric protein degraders which target estrogen receptor alpha (ERα).

Chimeric molecules which effect intracellular degradation of target proteins via E3 ligase-mediated ubiquitination (e.g., PROTACs) are currently of high interest in medicinal chemistry. However, these entities are relatively large compounds that often possess molecular characteristics which may compromise oral bioavailability, solubility, and/or in vivo pharmacokinetic properties. Accordingly, we explored whether conjugation of chimeric degraders to monoclonal antibodies using technologies originally developed for cytotoxic payloads might provide alternate delivery options for these novel agents. In this report we describe the construction of several degrader-antibody conjugates comprised of two distinct ERα-targeting degrader entities and three independent ADC linker modalities. We subsequently demonstrate the antigen-dependent delivery to MCF7-neo/HER2 cells of the degrader payloads that are incorporated into these conjugates. We also provide evidence for efficient intracellular degrader release from one of the employed linkers. In addition, preliminary data are described which suggest that reasonably favorable in vivo stability properties are associated with the linkers utilized to construct the degrader conjugates.

A Phase 1, Randomized, Single-Ascending-Dose Study To Investigate the Safety, Tolerability, and Pharmacokinetics of DSTA4637S, an Anti-Staphylococcus aureus Thiomab Antibody-Antibiotic Conjugate, in Healthy Volunteers.

Staphylococcus aureus causes serious bacterial infections with high morbidity and mortality, necessitating the discovery of new antibiotics. DSTA4637S is a novel antibody-antibiotic conjugate designed to target intracellular S. aureus that is not adequately eliminated by current standard-of-care antibiotics. DSTA4637S is composed of an anti-S. aureus Thiomab human immunoglobulin G1 (IgG1) monoclonal antibody linked to a novel rifamycin-class antibiotic (4-dimethylaminopiperidino-hydroxybenzoxazino rifamycin [dmDNA31]) via a protease-cleavable linker. Phagocytic cells ingest DSTA4637S-bound S. aureus, and intracellular cathepsins cleave the linker, releasing dmDNA31and killing intracellular S. aureus This first-in-human, randomized, double-blind, placebo-controlled, single-ascending-dose phase 1 trial analyzed the safety, pharmacokinetics, and immunogenicity of DSTA4637S in healthy volunteers. Thirty healthy male and female volunteers, 18-65 years old, were randomized into five cohorts receiving single intravenous (i.v.) doses of 5, 15, 50, 100, and 150 mg/kg of DSTA4637S or placebo (4 active:2 placebo). Subjects were followed for 85 days after dosing. No subject withdrew from the study, and no serious or severe adverse events occurred. One moderate infusion-related reaction (150 mg/kg DSTA4637S) occurred. No clinically meaningful or dose-related changes in laboratory parameters or vital signs occurred. Pharmacokinetics of plasma DSTA4637S conjugate and serum DSTA4637S total antibody were dose proportional. Systemic exposure of unconjugated dmDNA31 was low. No DSTA4637S-induced anti-drug antibody responses were observed. DSTA4637S was generally safe and well tolerated as a single i.v. dose in healthy volunteers. DSTA4637S has a favorable safety and pharmacokinetic profile that supports future development as a novel therapeutic for S. aureus infections. (This study has been registered at ClinicalTrials.gov under identifier NCT02596399.).

Antibody-Drug Conjugates Derived from Cytotoxic seco-CBI-Dimer Payloads Are Highly Efficacious in Xenograft Models and Form Protein Adducts In Vivo.

This work discloses the first examples of antibody-drug conjugates (ADCs) that are constructed from linker-drugs bearing dimeric seco-CBI payloads (duocarmycin analogs). Several homogeneous, CD22-targeting THIOMAB antibody-drug conjugates (TDCs) containing the dimeric seco-CBI entities are shown to be highly efficacious in the WSU-DLCL2 and BJAB mouse xenograft models. Surprisingly, the seco-CBI-containing conjugates are also observed to undergo significant biotransformation in vivo in mice, rats, and monkeys and thereby form 1:1 adducts with the Alpha-1-Microglobulin (A1M) plasma protein from these species. Variation of both the payload mAb attachment site and length of the linker-drug is shown to alter the rates of adduct formation. Subsequent experiments demonstrated that adduct formation attenuates the in vitro antiproliferation activity of the affected seco-CBI-dimer TDCs, but does not significantly impact the in vivo efficacy of the conjugates. In vitro assays employing phosphatase-treated whole blood suggest that A1M adduct formation is likely to occur if the seco-CBI-dimer TDCs are administered to humans. Importantly, protein adduct formation leads to the underestimation of total antibody (Tab) concentrations using an ELISA assay but does not affect Tab values determined via an orthogonal LC-MS/MS method. Several recommendations regarding bioanalysis of future in vivo studies involving related seco-CBI-containing ADCs are provided based on these collective findings.

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

An antibody-drug conjugate (ADC) is a unique therapeutic modality composed of a highly potent drug molecule conjugated to a monoclonal antibody. As the number of ADCs in various stages of nonclinical and clinical development has been increasing, pharmaceutical companies have been exploring diverse approaches to understanding the disposition of ADCs. To identify the key absorption, distribution, metabolism, and excretion (ADME) issues worth examining when developing an ADC and to find optimal scientifically based approaches to evaluate ADC ADME, the International Consortium for Innovation and Quality in Pharmaceutical Development launched an ADC ADME working group in early 2014. This white paper contains observations from the working group and provides an initial framework on issues and approaches to consider when evaluating the ADME of ADCs.

Translational pharmacokinetics and pharmacodynamics of monoclonal antibodies.

Monoclonal antibodies (mAbs) are an important therapeutic class with complex pharmacology and interdependent pharmacokinetic (PK) and pharmacodynamics (PD) properties. Understanding the PK and PD of mAbs and their biological and mechanistic underpinnings are crucial in enabling their design and selection, designing appropriate efficacy and toxicity studies, translating PK/PD parameters to humans, and optimizing dose and regimen to maximize success in the clinic. Significant progress has been made in this field however many critical questions still remain. This article gives a brief overview of the PK and PD of mAbs, factors that influence them, and areas of ongoing inquiry. Current tools and translational approaches to predict the PK/PD of mAbs in humans are also discussed.

Peripheral neuropathy with microtubule inhibitor containing antibody drug conjugates: Challenges and perspectives in translatability from nonclinical toxicology studies to the clinic.

Antibody drug conjugates (ADC) consist of potent cytotoxic drugs conjugated to antibodies via chemical linkers, which enables specific targeting of tumor cells while reducing systemic exposure to the cytotoxic drug and improving the therapeutic window. The valine citrulline monomethyl auristatin E (vcMMAE, conventional linker-drug) ADC platform has shown promising clinical activity in several cancers, but peripheral neuropathy (PN) is a frequent adverse event leading to treatment discontinuation and dose reduction. This was not predicted based on nonclinical toxicology studies in monkeys or rats treated with vcMMAE ADCs. We evaluated four hypotheses for the lack of translatability of PN with vcMMAE ADCs: 1) species differences in exposure; 2) insensitivity of animal models; 3) species differences in target biology and other vcMMAE ADC properties in peripheral nerves and 4) increased susceptibility of patient population. The result of this hypothesis-based approach identified opportunities to improve the predictivity of PN in our animal models by increasing duration of exposure and adding an expanded neurohistopathology assessment of peripheral nerves. The utility of a predictive animal model would be to provide possible mitigation strategies in the clinic with vcMMAE ADCs and help to screen the next generation microtubule inhibitor (MTI) ADCs for reduced PN.

Challenges and advances in the assessment of the disposition of antibody-drug conjugates.

Antibody-drug conjugates (ADCs) are a rapidly growing therapeutic platform for the treatment of cancer. ADCs consist of a cytotoxic small molecule drug linked to an antibody to provide targeted delivery of the cytotoxic agent to the tumor. Understanding the pharmacokinetics (PK) and pharmacodynamics (PD) of ADCs is crucial in their design to optimize dose and regimen, to maximize efficacy and to minimize toxicity in patients. Significant progress has been made in recent years in this area, however, many fundamental questions still remain. This review discusses factors to consider while assessing the disposition of ADCs, and the unique challenges associated with these therapeutics. Current tools that are available and strategies to enable appropriate assessment are also discussed.

Preclinical Pharmacokinetic Considerations for the Development of Antibody Drug Conjugates.

Antibody drug conjugates (ADCs) are an emerging new class of targeted therapeutics for cancer that use antibodies to deliver cytotoxic drugs to cancer cells. There are two FDA approved ADCs on the market and over 30 ADCs in the clinical pipeline against a number of different cancer types. The structure of an ADC is very complex with multiple components and considerable efforts are ongoing to determine the attributes necessary for clinical success. Understanding the pharmacokinetics of an ADC and how it impacts efficacy and toxicity is a critical part of optimizing ADC design and delivery i.e., dose and schedule. This review discusses the pharmacokinetic considerations for an ADC and tools and strategies that can be used to evaluate molecules at the preclinical stage.

A Bispecific Modeling Framework Enables the Prediction of Efficacy, Toxicity, and Optimal Molecular Design of Bispecific Antibodies Targeting MerTK.

Inhibiting MerTK on macrophages is a promising therapeutic strategy for augmenting anti-tumor immunity. However, blocking MerTK on retinal pigment epithelial cells (RPEs) results in retinal toxicity. Bispecific antibodies (bsAbs) containing an anti-MerTK therapeutic and anti-PD-L1 targeting arm were developed to reduce drug binding to MerTK on RPEs, since PD-L1 is overexpressed on macrophages but not RPEs. In this study, we present a modeling framework using in vitro receptor occupancy (RO) and pharmacokinetics (PK) data to predict efficacy, toxicity, and therapeutic index (TI) of anti-MerTK bsAbs. We first used simulations and in vitro RO data of anti-MerTK monospecific antibody (msAb) to estimate the required MerTK RO for in vivo efficacy and toxicity. Using these estimated RO thresholds, we employed our model to predict the efficacious and toxic doses for anti-MerTK bsAbs with varying affinities for MerTK. Our model predicted the highest TI for the anti-MerTK/PD-L1 bsAb with an attenuated MerTK binding arm, which was consistent with in vivo efficacy and toxicity observations. Subsequently, we used the model, in combination with sensitivity analysis and parameter scans, to suggest an optimal molecular design of anti-MerTK bsAb with the highest predicted TI in humans. Our prediction revealed that this optimized anti-MerTK bsAb should contain a MerTK therapeutic arm with relatively low affinity, along with a high affinity targeting arm that can bind to a low abundance target with slow turnover rate. Overall, these results demonstrated that our modeling framework can guide the rational design of bsAbs.

A Minimal PBPK/PD Model with Expansion-Enhanced Target-Mediated Drug Disposition to Support a First-in-Human Clinical Study Design for a FLT3L-Fc Molecule.

FLT3L-Fc is a half-life extended, effectorless Fc-fusion of the native human FLT3-ligand. In cynomolgus monkeys, treatment with FLT3L-Fc leads to a complex pharmacokinetic/pharmacodynamic (PK/PD) relationship, with observed nonlinear PK and expansion of different immune cell types across different dose levels. A minimal physiologically based PK/PD model with expansion-enhanced target-mediated drug disposition (TMDD) was developed to integrate the molecule's mechanism of action, as well as the complex preclinical and clinical PK/PD data, to support the preclinical-to-clinical translation of FLT3L-Fc. In addition to the preclinical PK data of FLT3L-Fc in cynomolgus monkeys, clinical PK and PD data from other FLT3-agonist molecules (GS-3583 and CDX-301) were used to inform the model and project the expansion profiles of conventional DC1s (cDC1s) and total DCs in peripheral blood. This work constitutes an essential part of our model-informed drug development (MIDD) strategy for clinical development of FLT3L-Fc by projecting PK/PD in healthy volunteers, determining the first-in-human (FIH) dose, and informing the efficacious dose in clinical settings. Model-generated results were incorporated in regulatory filings to support the rationale for the FIH dose selection.

Translational PK/PD and the first-in-human dose selection of a PD1/IL15: an engineered recombinant targeted cytokine for cancer immunotherapy.

Introduction: Interleukin 15 (IL-15) is a potential anticancer agent and numerous engineered IL-15 agonists are currently under clinical investigation. Selective targeting of IL-15 to specific lymphocytes may enhance therapeutic effects while helping to minimize toxicities. Methods: We designed and built a heterodimeric targeted cytokine (TaCk) that consists of an anti-programmed cell death 1 receptor antibody (anti-PD-1) and an engineered IL-15. This "PD1/IL15" selectively delivers IL-15 signaling to lymphocytes expressing PD-1. We then investigated the pharmacokinetic (PK) and pharmacodynamic (PD) effects of PD1/IL15 TaCk on immune cell subsets in cynomolgus monkeys after single and repeat intravenous dose administrations. We used these results to determine the first-in-human (FIH) dose and dosing frequency for early clinical trials. Results: The PD1/IL15 TaCk exhibited a nonlinear multiphasic PK profile, while the untargeted isotype control TaCk, containing an anti-respiratory syncytial virus antibody (RSV/IL15), showed linear and dose proportional PK. The PD1/IL15 TaCk also displayed a considerably prolonged PK (half-life range ∼1.0-4.1 days) compared to wild-type IL-15 (half-life ∼1.1 h), which led to an enhanced cell expansion PD response. The PD was dose-dependent, durable, and selective for PD-1+ lymphocytes. Notably, the dose- and time-dependent PK was attributed to dynamic TMDD resulting from test article-induced lymphocyte expansion upon repeat administration. The recommended first-in-human (FIH) dose of PD1/IL15 TaCk is 0.003 mg/kg, determined based on a minimum anticipated biological effect level (MABEL) approach utilizing a combination of in vitro and preclinical in vivo data. Conclusion: This work provides insight into the complex PK/PD relationship of PD1/IL15 TaCk in monkeys and informs the recommended starting dose and dosing frequency selection to support clinical evaluation of this novel targeted cytokine.

Utilizing PK and PD Biomarkers to Guide the First-in-Human Starting Dose Selection of MTBT1466A: A Novel Humanized Monoclonal Anti-TGFß3 Antibody for the Treatment of Fibrotic Diseases.

MTBT1466A is a high-affinity TGFß3-specific humanized IgG1 monoclonal antibody with reduced Fc effector function, currently under investigation in clinical trials as a potential anti-fibrotic therapy. Here, we characterized the pharmacokinetics (PK) and pharmacodynamics (PD) of MTBT1466A in mice and monkeys and predicted the PK/PD of MTBT1466A in humans to guide the selection of the first-in-human (FIH) starting dose. MTBT1466A demonstrated a typical IgG1-like biphasic PK profile in monkeys, and the predicted human clearance of 2.69 mL/day/kg and t1/2 of 20.4 days are consistent with those expected for a human IgG1 antibody. In a mouse model of bleomycin-induced lung fibrosis, changes in expression of TGFß3-related genes, serpine1, fibronectin-1, and collagen 1A1 were used as PD biomarkers to determine the minimum pharmacologically active dose of 1 mg/kg. Unlike in the fibrosis mouse model, evidence of target engagement in healthy monkeys was only observed at higher doses. Using a PKPD-guided approach, the recommended FIH dose of 50 mg, IV, provided exposures that were shown to be safe and well tolerated in healthy volunteers. MTBT1466A PK in healthy volunteers was predicted reasonably well using a PK model with allometric scaling of PK parameters from monkey data. Taken together, this work provides insights into the PK/PD behavior of MTBT1466A in preclinical species, and supports the translatability of the preclinical data into the clinic.

Non-human primates in the PKPD evaluation of biologics: Needs and options to reduce, refine, and replace. A BioSafe White Paper.

Monoclonal antibodies (mAbs) deliver great benefits to patients with chronic and/or severe diseases thanks to their strong specificity to the therapeutic target. As a result of this specificity, non-human primates (NHP) are often the only preclinical species in which therapeutic antibodies cross-react with the target. Here, we highlight the value and limitations that NHP studies bring to the design of safe and efficient early clinical trials. Indeed, data generated in NHPs are integrated with in vitro information to predict the concentration/effect relationship in human, and therefore the doses to be tested in first-in-human trials. The similarities and differences in the systems defining the pharmacokinetics and pharmacodynamics (PKPD) of mAbs in NHP and human define the nature and the potential of the preclinical investigations performed in NHPs. Examples have been collated where the use of NHP was either pivotal to the design of the first-in-human trial or, inversely, led to the termination of a project prior to clinical development. The potential impact of immunogenicity on the results generated in NHPs is discussed. Strategies to optimize the use of NHPs for PKPD purposes include the addition of PD endpoints in safety assessment studies and the potential re-use of NHPs after non-terminal studies or cassette dosing several therapeutic agents of interest. Efforts are also made to reduce the use of NHPs in the industry through the use of in vitro systems, alternative in vivo models, and in silico approaches. In the case of prediction of ocular PK, the body of evidence gathered over the last two decades renders the use of NHPs obsolete. Expert perspectives, advantages, and pitfalls with these alternative approaches are shared in this review.

Effect of molecular size on interstitial pharmacokinetics and tissue catabolism of antibodies.

Advances in antibody engineering have enabled the construction of novel molecular formats in diverse shapes and sizes, providing new opportunities for biologic therapies and expanding the need to understand how various structural aspects affect their distribution properties. To assess the effect of antibody size on systemic pharmacokinetics (PK) and tissue distribution with or without neonatal Fc receptor (FcRn) binding, we evaluated a series of non-mouse-binding anti-glycoprotein D monoclonal antibody formats, including IgG [~150 kDa], one-armed IgG [~100 kDa], IgG-HAHQ (attenuated FcRn binding) [~150 kDa], F(ab')2 [~100 kDa], and F(ab) [~50 kDa]. Tissue-specific concentration-time profiles were corrected for blood content based on vascular volumes and normalized based on interstitial volumes to allow estimation of interstitial concentrations and interstitial:serum concentration ratios. Blood correction demonstrated that the contribution of circulating antibody on total uptake was greatest at early time points and for highly vascularized tissues. Tissue interstitial PK largely mirrored serum exposure profiles. Similar interstitial:serum ratios were obtained for the two FcRn-binding molecules, IgG and one-armed IgG, which reached pseudo-steady-state kinetics in most tissues. For non-FcRn-binding molecules, interstitial:serum ratios changed over time, suggesting that these molecules did not reach steady-state kinetics during the study. Furthermore, concentration-time profiles of both intact and catabolized molecule were measured by a dual tracer approach, enabling quantification of tissue catabolism and demonstrating that catabolism levels were highest for IgG-HAHQ. Overall, these data sets provide insight into factors affecting preclinical distribution and may be useful in estimating interstitial concentrations and/or catabolism in human tissues.

Nonclinical Pharmacokinetics, Pharmacodynamics, and Translational Model of RO7297089, A Novel Anti-BCMA/CD16A Bispecific Tetravalent Antibody for the Treatment of Multiple Myeloma.

RO7297089, an anti-B-cell maturation antigen (BCMA)/CD16A bispecific tetravalent antibody, is being developed as a multiple myeloma (MM) therapeutic. This study characterized nonclinical pharmacokinetics (PK), pharmacodynamics (PD), soluble BCMA (sBCMA), and soluble CD16 (sCD16) changes following administration of RO7297089 to support clinical trials. Unbound and total RO7297089 concentrations were measured in cynomolgus monkeys. RO7297089 exhibited a bi-phasic systemic concentration-time profile, similar to a typical human immunoglobulin 1 antibody. Target engagement by RO7297089 led to a robust increase (~100-fold) in total systemic sBCMA levels and relatively mild increase (~2-fold) in total sCD16 levels. To describe the relationship of nonclinical PK/PD data, we developed a target-mediated drug disposition (TMDD) model that includes the systemic target engagement of membrane BCMA (mBCMA), sBCMA, membrane CD16 (mCD16), and sCD16. We then used this model to simulate the PK/PD relationship of RO7297089 in MM patients by translating relevant PK parameters and target levels, based on the literature and newly generated data such as baseline sCD16A levels. Our model suggested that the impact of TMDD on RO7297089 exposure may be more significant in MM patients due to significantly higher expression levels of both mBCMA and sBCMA compared to healthy cynomolgus monkeys. Based on model simulations, we propose more frequent dosing of RO7297089 compared to regular monthly frequency in the clinic at the beginning of treatment to ensure sustained target engagement. This study demonstrates a translational research strategy for collecting relevant nonclinical data, establishing a TMDD model, and using simulations from this model to inform clinical dose regimens.

Nonclinical Pharmacokinetics and Pharmacodynamics Characterization of Anti-CD79b/CD3 T Cell-Dependent Bispecific Antibody Using a Surrogate Molecule: A Potential Therapeutic Agent for B Cell Malignancies.

The T cell-dependent bispecific (TDB) antibody, anti-CD79b/CD3, targets CD79b and CD3 cell-surface receptors expressed on B cells and T cells, respectively. Since the anti-CD79b arm of this TDB binds only to human CD79b, a surrogate TDB that binds to cynomolgus monkey CD79b (cyCD79b) was used for preclinical characterization. To evaluate the impact of CD3 binding affinity on the TDB pharmacokinetics (PK), we utilized non-tumor-targeting bispecific anti-gD/CD3 antibodies composed of a low/high CD3 affinity arm along with a monospecific anti-gD arm as controls in monkeys and mice. An integrated PKPD model was developed to characterize PK and pharmacodynamics (PD). This study revealed the impact of CD3 binding affinity on anti-cyCD79b/CD3 PK. The surrogate anti-cyCD79b/CD3 TDB was highly effective in killing CD79b-expressing B cells and exhibited nonlinear PK in monkeys, consistent with target-mediated clearance. A dose-dependent decrease in B cell counts in peripheral blood was observed, as expected. Modeling indicated that anti-cyCD79b/CD3 TDB's rapid and target-mediated clearance may be attributed to faster internalization of CD79b, in addition to enhanced CD3 binding. The model yielded unbiased and precise curve fits. These findings highlight the complex interaction between TDBs and their targets and may be applicable to the development of other biotherapeutics.

Antibody Format and Serum Disposition Govern Ocular Pharmacokinetics of Intravenously Administered Protein Therapeutics.

Protein therapeutics have witnessed tremendous use and application in recent years in treatment of various diseases. Predicting efficacy and safety during drug discovery and translational development is a key factor for successful clinical development of these therapies. In general, drug related toxicities are predominantly driven by pharmacokinetic (PK) exposure at off-target sites. This work explores the ocular PK of intravenously administered protein therapeutics to understand impact of antibody format on off-site exposure. Species matched non-binding rabbit antibody proteins (rabFab and rabIgG) were intravenously administered to male New Zealand White rabbits at a single 1 mg bolus dose and exposure was measured up to 3 weeks. As anticipated based on absence of FcRn recycling, rabFab has relatively fast systemic PK (CL-943 mL/day and t1/2-1.93 days) compared to rabIgG (CL-18.5 mL/day and t1/2-8.93 days). Similarly, rabFab has lower absolute ocular exposure in ocular compartments (e.g., vitreous and aqueous humor) compared to rabIgG, despite higher relative exposures (measured as percent tissue partition in ocular tissues relative to serum, based on Cmax and AUC). In general, percent tissue partition based on AUC (in aqueous and vitreous humor) relative to serum exposure were 10.4 and 8.62 for rabFab respectively and 1.11 and 0.64 for rabIgG respectively. This work emphasizes size and format based ocular exposure of intravenously administered protein therapeutics. Findings from this work enable prediction of format based ocular exposure for systemically administered antibody based therapeutics and aid in selection of molecule format for clinical candidate to minimize ocular exposure.

Imaging Reveals Importance of Shape and Flexibility for Glomerular Filtration of Biologics.

Advances in antibody engineering have enabled the construction of novel molecular formats in diverse shapes and sizes, providing new opportunities for cancer immunotherapeutic drug discovery while also revealing limitations in knowledge of structure-activity relationships. The current understanding of renal filtration originates largely from data reported for dextrans, IgG, albumin, and selected globular proteins. For a one-armed IgG-based T-cell imaging agent, we observed higher renal signal than typically observed for bivalent IgGs, prompting us to explore the factors governing renal filtration of biologics. We constructed a small representative library of IgG-like formats with varied shapes and hinge flexibilities falling broadly into two categories: branched molecules including bivalent IgG and (scFv)2Fc, and nonbranched molecules including one-armed IgG, one-armed IgG with stacked Fab, and one-armed IgG with a rigid IgA2 hinge. Transmission electron microscopy revealed Y-shaped structures for the branched molecules and pseudo-linear structures for the nonbranched molecules. Single-photon emission CT imaging, autoradiography, and tissue harvest studies demonstrated higher renal uptake and catabolism for nonbranched molecules relative to branched molecules. Among the nonbranched molecules, the one-armed IgG with rigid IgA2 hinge molecule demonstrated higher kidney uptake and decreased systemic exposure relative to molecules with a more flexible hinge. Our results show that differences in shape and hinge flexibility drive the increased glomerular filtration of one-armed relative to bivalent antibodies and highlight the practical advantages of using imaging to assess renal filtration properties. These findings are particularly relevant for T-cell-dependent bispecific molecules, many of which have nonstandard antibody structures.