The Biodistribution of a CD3 and EpCAM Bispecific T-Cell Engager Is Driven by the CD3 Arm

Design of Crosslinking Antibodies For T-Cell Activation: Experimental and Computational Analysis of PD-1/CD137 Bispecific Agents

Bispecific and multispecific agents have become increasingly utilized in cancer treatment and immunotherapy, yet their complex design parameters present a challenge in developing successful therapeutics. Bispecifics that crosslink receptors on two opposing cells can provide specific activation of a receptor only when these cells are in close spatial proximity, such as an immune cell and cancer cell in a tumor. These agents, including T cell activating bispecifics, can avoid off-tumor toxicity through activation only in the tumor microenvironment by utilizing a tumor target to cluster T-cell receptors for a selective costimulatory signal. Here, we investigate a panel of PD-1/CD137 targeted Humabody VH domains to determine the key factors for T cell activation, such as affinity, valency, expression level, domain orientation, and epitope location. Target expression is a dominant factor determining both specificity and potency of T cell activation. Given an intrinsic expression level, the affinity can be tuned to modulate the level of activation and IC50 and achieve specificity between low and high expression levels. Changing the epitope location and linker length showed minor improvements to activation at low expression levels, but increasing the valency for the target decreased activation at all expression levels. By combining non-overlapping epitopes for the target, we achieved higher receptor activation at low expression levels. A kinetic model was able to capture these trends, offering support for the mechanistic interpretation. This work provides a framework to quantify factors for T cell activation by cell-crosslinking bispecific agents and guiding principles for the design of new agents.

Heterodimerization of T cell engaging bispecific antibodies to enhance specificity against pancreatic ductal adenocarcinoma

BACKGROUND

EGFR and/or HER2 expression in pancreatic cancers is correlated with poor prognoses. We generated homodimeric (EGFRxEGFR or HER2xHER2) and heterodimeric (EGFRxHER2) T cell-engaging bispecific antibodies (T-BsAbs) to direct polyclonal T cells to these antigens on pancreatic tumors.

METHODS

EGFR and HER2 T-BsAbs were constructed using the 2 + 2 IgG-[L]-scFv T-BsAbs format bearing two anti-CD3 scFvs attached to the light chains of an IgG to engage T cells while retaining bivalent binding to tumor antigens with both Fab arms. A Fab arm exchange strategy was used to generate EGFRxHER2 heterodimeric T-BsAb carrying one Fab specific for EGFR and one for HER2. EGFR and HER2 T-BsAbs were also heterodimerized with a CD33 control T-BsAb to generate 'tumor-monovalent' EGFRxCD33 and HER2xCD33 T-BsAbs. T-BsAb avidity for tumor cells was studied by flow cytometry, cytotoxicity by T-cell mediated 51Chromium release, and in vivo efficacy against cell line-derived xenografts (CDX) or patient-derived xenografts (PDX). Tumor infiltration by T cells transduced with luciferase reporter was quantified by bioluminescence.

RESULTS

The EGFRxEGFR, HER2xHER2, and EGFRxHER2 T-BsAbs demonstrated high avidity and T cell-mediated cytotoxicity against human pancreatic ductal adenocarcinoma (PDAC) cell lines in vitro with EC50s in the picomolar range (0.17pM to 18pM). They were highly efficient in driving human polyclonal T cells into subcutaneous PDAC xenografts and mediated potent T cell-mediated anti-tumor effects. Both EGFRxCD33 and HER2xCD33 tumor-monovalent T-BsAbs displayed substantially reduced avidity by SPR when compared to homodimeric EGFRxEGFR or HER2xHER2 T-BsAbs (∼150-fold and ∼6000-fold respectively), tumor binding by FACS (8.0-fold and 63.6-fold), and T-cell mediated cytotoxicity (7.7-fold and 47.2-fold), while showing no efficacy against CDX or PDX. However, if either EGFR or HER2 was removed from SW1990 by CRISPR-mediated knockout, the in vivo efficacy of heterodimeric EGFRxHER2 T-BsAb was lost.

CONCLUSION

EGFR and HER2 were useful targets for driving T cell infiltration and tumor ablation. Two arm Fab binding to either one or both targets was critical for robust anti-tumor effect in vivo. By engaging both targets, EGFRxHER2 heterodimeric T-BsAb exhibited potent anti-tumor effects if CDX or PDX were EGFR+HER2+ double-positive with the potential to spare single-positive normal tissue.

Longitudinal evaluation of the biodistribution and cellular internalization of the bispecific CD3xTRP1 antibody in syngeneic mouse tumor models

BACKGROUND

CD3 bispecific antibodies (CD3-bsAbs) require binding of both a tumor-associated surface antigen and CD3 for their immunotherapeutic effect. Their efficacy is, therefore, influenced by the tumor uptake and the extracellular dose. To optimize their currently limited efficacy in solid tumors, increased understanding of their pharmacokinetics and in vivo internalization is needed.

METHODS

Here, were studied the pharmacokinetics and in vivo internalization of CD3xTRP1, a fully murine Fc-inert bsAb, in endogenous TRP1-expressing immunocompetent male C57BL/6J mice bearing TRP1-positive and negative tumors over time. Matching bsAbs lacking TRP1-binding or CD3-binding capacity served as controls. BsAbs were radiolabeled with 111In to investigate their pharmacokinetics, target binding, and biodistribution through SPECT/CT imaging and ex vivo biodistribution analyses. Co-injection of 111In- and 125I-labeled bsAb was performed to investigate the in vivo internalization by comparing tissue concentrations of cellular residing 111In versus effluxing 125I. Antitumor therapy effects were evaluated by monitoring tumor growth and immunohistochemistry.

RESULTS

SPECT/CT and biodistribution analyses showed that CD3xTRP1 specifically targeted TRP1-positive tumors and CD3-rich lymphoid organ and uptake peaked 24 hours pi (KPC3-TRP1: 37.7%ID/g±5.3%ID/g, spleen: 29.0%ID/g±3.9%ID/g). Studies with control bsAbs demonstrated that uptake of CD3xTRP1 in TRP1-positive tumors and CD3-rich tissues was primarily receptor-mediated. Together with CD3xTRP1 in the circulation being mainly unattached, this indicates that CD3+ T cells are generally not traffickers of CD3-bsAbs to the tumor. Additionally, target-mediated clearance by TRP1-expressing melanocytes was not observed. We further demonstrated rapid internalization of CD3xTRP1 in KPC3-TRP1 tumors (24 hours pi: 54.9%±2.3% internalized) and CD3-rich tissues (spleen, 24 hours pi: 79.7%±0.9% internalized). Therapeutic effects by CD3xTRP1 were observed for TRP1-positive tumors and consisted of high tumor influx of CD8+ T cells and neutrophils, which corresponded with increased necrosis and growth delay.

CONCLUSIONS

We show that CD3xTRP1 efficiently targets TRP1-positive tumors and CD3-rich tissues primarily through receptor-mediated targeting. We further demonstrate rapid receptor-mediated internalization of CD3xTRP1 in TRP1-positive tumors and CD3-rich tissues. Even though this significantly decreases the therapeutical available dose, CD3xTRP1 still induced effective antitumor T-cell responses and inhibited tumor growth. Together, our data on the pharmacokinetics and mechanism of action of CD3xTRP1 pave the way for further optimization of CD3-bsAb therapies.

Mechanism-based pharmacokinetic and pharmacodynamic modeling for bispecific antibodies: challenges and opportunities

INTRODUCTION

Unlike conventional antibodies, bispecific antibodies (bsAbs) are engineered antibody- or antibody fragment-based molecules that can simultaneously recognize two different epitopes or antigens. Over the past decade, there has been an explosion of bsAbs being developed across therapeutic areas. Development of bsAbs presents unique challenges and mechanism-based pharmacokinetic/pharmacodynamic (PK/PD) modeling has served as a powerful tool to optimize their development and realize their clinical utility.

AREAS COVERED

In this review, the guiding principles and case examples of how fit-for-purpose, mechanism-based PK/PD models have been applied to answer questions commonly encountered in bsAb development are presented. Such models characterize the key pharmacological elements of bsAbs, and they can be utilized for model-informed drug development. We also include the discussion of challenges, knowledge gaps and future direction for such models.

EXPERT OPINION

Mechanistic PK/PD modeling is a powerful tool to support the development of bsAbs. These models can be extrapolated to predict treatment outcomes based on mechanisms of action (MoA) and clinical observations to form positive learn-and-confirm cycles during drug development, due to their abilities to differentiate system- and drug-specific parameters. Meanwhile, the models should keep being adapted according to novel drug design and MoA, providing continuous opportunities for model-informed drug development.

Recent Trends in Diagnostic Biomarkers of Tumor Microenvironment

The tumor microenvironment (TME) play critical roles in tumor survival, progression, and metastasis and can be considered potential targets for molecular imaging of cancer. The targeting agents for imaging of TME components (e.g., fibroblasts, mesenchymal stromal cells, immune cells, extracellular matrix, blood vessels) provide a promising strategy to target these biomarkers for the early diagnosis of cancers. Moreover, various cancer types have similar tumor immune microenvironment (TIME) features that targeting those biomarkers and offer clinically translatable molecular imaging of cancers. In this review, we categorize and summarize the components in TME which have been targeted for molecular imaging. Moreover, this review updated the recent progress in targeted imaging of TIME biological molecules by various modalities for the early detection of cancer.

Characterization of an Anti-CD70 Half-Life Extended Bispecific T Cell Engager (HLE-BiTE) and Associated On-Target Toxicity in Cynomolgus Monkeys

Bispecific T cell Engager (BiTE®) molecules have great potential to treat cancer. Nevertheless, dependent on the targeted tumor antigen, the mechanism of action that drives efficacy may also contribute to on-target/off-tumor toxicities. In this study we characterize an anti-CD70 half-life extended BiTE molecule (termed N6P) which targets CD70, a TNF family protein detected in several cancers. Firstly, the therapeutic potential of N6P was demonstrated using in vitro cytotoxicity assays and an orthotopic xenograft mouse study resulting in potent killing of CD70+ cancer cells. Next, in vitro characterization demonstrated specificity for CD70 and equipotent activity against human and cynomolgus monkey CD70+ cells. To understand the potential for on-target toxicity, a tissue expression analysis was performed and indicated CD70 is primarily restricted to lymphocytes in normal healthy tissues and cells. Therefore, no on-target toxicity was expected to be associated with N6P. However, in a repeat-dose toxicology study using cynomolgus monkeys, adverse N6P-mediated inflammation was identified in multiple tissues frequently involving the mesothelium and epithelium. Follow-up immunohistochemistry analysis revealed CD70 expression in mesothelial and epithelial cells in some tissues with N6P-mediated injury, but not in control tissues or those without injury. Collectively the data indicates that for some target antigens such as CD70, BiTE molecules may exhibit activity in tissues with very low antigen expression or the antigen may be upregulated under stress enabling molecule activity. This work illustrates how a thorough understanding of expression and upregulation is needed to fully address putative liabilities associated with on-target/off-tumor activity of CD3 bispecific molecules.

Mesothelin/CD3 half-life extended bispecific T-cell engager molecule shows specific tumor uptake and distributes to mesothelin and CD3 expressing tissues

BiTE ® (bispecific T-cell engager) molecules exert antitumor activity by binding one arm to CD3 on cytotoxic T-cells and the other arm to a tumor-associated antigen. We generated a fully mouse cross-reactive mesothelin (MSLN)-targeted BiTE molecule that is genetically fused to a Fc-domain for half-life extension, and evaluated biodistribution and tumor targeting of a zirconium-89 (89Zr)-labeled MSLN HLE BiTE molecule in 4T1 breast cancer bearing syngeneic mice with positron emission tomography (PET). Biodistribution of 50 µg 89Zr-MLSN HLE BiTE was studied over time by PET imaging in BALB/c mice and revealed uptake in tumor and lymphoid tissues with an elimination half-life of 63.4 hours. Compared to a non-targeting 89Zr-control HLE BiTE, the 89Zr-MLSN HLE BiTE showed a 2-fold higher tumor uptake and higher uptake in lymphoid tissues. Uptake in the tumor colocalized with mesothelin expression, while uptake in the spleen colocalized with CD3 expression. Evaluation of the effect of protein doses on the biodistribution and tumor targeting of 89Zr-MSLN HLE BiTE revealed for all dose groups that uptake in the spleen was faster than in the tumor (day 1 vs day 5). The lowest dose of 10 µg 89Zr-MSLN HLE BiTE had higher spleen uptake and faster blood clearance compared to higher doses of 50 µg and 200 µg. 89Zr-MSLN HLE BiTE tumor uptake was similar at all doses. Conclusion: The MSLN HLE BiTE showed specific tumor uptake and both arms contributed to the biodistribution profile. These findings support the potential for clinical translation of HLE BiTE molecules.

Immune cell engagers in solid tumors: promises and challenges of the next generation immunotherapy

In the landscape of cancer immunotherapy, immune cell engagers (ICEs) are rapidly emerging as a feasible and easy-to-deliver alternative to adoptive cell therapy for the antitumor redirection of immune effector cells. Even if in hematological malignancies this class of new therapeutics already hit the clinic, the development of ICEs in solid tumors still represents a challenge. Considering that ICEs are a rapidly expanding biotechnology in cancer therapy, we designed this review as a primer for clinicians, focusing on the major obstacles for the clinical implementation and the most translatable approaches proposed to overcome the limitations in solid tumors.

Next Generation Imaging Techniques to Define Immune Topographies in Solid Tumors

In recent years, cancer immunotherapy experienced remarkable developments and it is nowadays considered a promising therapeutic frontier against many types of cancer, especially hematological malignancies. However, in most types of solid tumors, immunotherapy efficacy is modest, partly because of the limited accessibility of lymphocytes to the tumor core. This immune exclusion is mediated by a variety of physical, functional and dynamic barriers, which play a role in shaping the immune infiltrate in the tumor microenvironment. At present there is no unified and integrated understanding about the role played by different postulated models of immune exclusion in human solid tumors. Systematically mapping immune landscapes or "topographies" in cancers of different histology is of pivotal importance to characterize spatial and temporal distribution of lymphocytes in the tumor microenvironment, providing insights into mechanisms of immune exclusion. Spatially mapping immune cells also provides quantitative information, which could be informative in clinical settings, for example for the discovery of new biomarkers that could guide the design of patient-specific immunotherapies. In this review, we aim to summarize current standard and next generation approaches to define Cancer Immune Topographies based on published studies and propose future perspectives.