Tumor-specific activation of an EGFR-targeting probody enhances therapeutic index

Hypoxia Induces Extensive Protein and Proteolytic Remodeling of the Cell Surface in Pancreatic Adenocarcinoma (PDAC) Cell Lines

The tumor microenvironment (TME) plays a crucial role in cancer progression. Hypoxia is a hallmark of the TME and induces a cascade of molecular events that affect cellular processes involved in metabolism, metastasis, and proteolysis. In pancreatic ductal adenocarcinoma (PDAC), tumor tissues are extremely hypoxic. Here, we leveraged mass spectrometry technologies to examine hypoxia-induced alterations in the abundance and proteolytic modifications to cell surface and secreted proteins. Across four PDAC cell lines, we discovered extensive proteolytic remodeling of cell surface proteins involved in cellular adhesion and motility. Looking outward at the surrounding secreted space, we identified hypoxia-regulated secreted and proteolytically shed proteins involved in regulating the humoral immune and inflammatory response, and an upregulation of proteins involved in metabolic processing and tissue development. Combining cell surface N-terminomics and secretomics to evaluate the cellular response to hypoxia enabled us to identify significantly altered candidate proteins which may serve as potential biomarkers and therapeutic targets in PDAC. Furthermore, this approach provides a blueprint for studying dysregulated extracellular proteolysis in other cancers and inflammatory diseases.

Engineered Proteins and Chemical Tools to Probe the Cell Surface Proteome

The cell surface proteome, or surfaceome, is the hub for cells to interact and communicate with the outside world. Many disease-associated changes are hard-wired within the surfaceome, yet approved drugs target less than 50 cell surface proteins. In the past decade, the proteomics community has made significant strides in developing new technologies tailored for studying the surfaceome in all its complexity. In this review, we first dive into the unique characteristics and functions of the surfaceome, emphasizing the necessity for specialized labeling, enrichment, and proteomic approaches. An overview of surfaceomics methods is provided, detailing techniques to measure changes in protein expression and how this leads to novel target discovery. Next, we highlight advances in proximity labeling proteomics (PLP), showcasing how various enzymatic and photoaffinity proximity labeling techniques can map protein-protein interactions and membrane protein complexes on the cell surface. We then review the role of extracellular post-translational modifications, focusing on cell surface glycosylation, proteolytic remodeling, and the secretome. Finally, we discuss methods for identifying tumor-specific peptide MHC complexes and how they have shaped therapeutic development. This emerging field of neo-protein epitopes is constantly evolving, where targets are identified at the proteome level and encompass defined disease-associated PTMs, complexes, and dysregulated cellular and tissue locations. Given the functional importance of the surfaceome for biology and therapy, we view surfaceomics as a critical piece of this quest for neo-epitope target discovery.

Protease-activated anti-Lewis Y antibody enhances selectivity and safety of glycan-targeting cancer therapy

Lewis Y carbohydrate antigen is overexpressed in various epithelial cancers, making it a potential therapeutic target. However, anti-Lewis Y antibodies have faced challenges due to gastrointestinal toxicity from Lewis Y antigen expression in normal tissues. To mitigate the toxicity, we engineered L-HKM4, a protease-activated anti-Lewis Y antibody, by modifying the N-terminal of HKM4 with an IgG1 hinge domain and a matrix metalloproteinase (MMP)-cleavable linker. This design ensures selective activation in the MMP2/9-rich gastric and colon tumor microenvironment, minimizing off-tumor effects. The results demonstrated that L-HKM4 binding to AGS gastric cancer cells decreased 104.6-fold compared to HKM4, accompanied by a 15.82-fold reduction in antibody-dependent cell-mediated cytotoxicity (ADCC) and no activity in complement-dependent cytotoxicity (CDC), all of binding and cytotoxicity were restored upon MMP2 activation. In mice, L-HKM4 showed minimal gastric tissue binding, confirming reduced on-target toxicity in vivo. In an AGS xenograft model, L-HKM4 achieved tumor-specific activation and inhibited tumor growth by 82 % (P < 0.001) compared to saline control. In conclusion, L-HKM4 enables tumor-specific activation while minimizing gastric toxicity, preserving strong tumor inhibition. This innovative approach overcomes key limitations of anti-Lewis Y therapies, making L-HKM4 a promising and safer treatment for gastrointestinal cancers.

Affibody-based HER2 prodrug shows conditional cytotoxic effect on HER2-positive cancer cells

Therapeutic affinity proteins offer a targeted mode of action due to their typically high affinity and specificity for disease-associated molecules. In cancer therapy, such target molecules are often overexpressed receptors on tumor cells. However, their presence in healthy tissues can lead to on-target, off-tumor toxicity, necessitating strategies to enhance tumor selectivity. Here, we present an affibody-based prodrug concept that exploits tumor-associated proteases for selective activation. As proof of concept, we designed, produced, and characterized HER2-specific prodrug candidates, each incorporating a distinct protease substrate for selective activation by tumor-associated proteases. Their activation by corresponding proteases and subsequent HER2 binding were assessed. The most promising prodrug candidate was conjugated to the cytotoxic agent DM1 and evaluated for cytotoxicity in HER2-positive cancer cells. The results demonstrated potent, HER2-dependent cell killing, with markedly reduced cytotoxicity in the absence of prodrug activation. These findings support the feasibility of affibody-based prodrugs as a strategy to enhance tumor selectivity and minimize off-tumor toxicity in targeted cancer therapy.

Preclinical Development of SGN-CD47M: Protease-Activated Antibody Technology Enables Selective Tumor Targeting of the Innate Immune Checkpoint Receptor CD47

CD47 is a cell-surface glycoprotein that is expressed on normal human tissues and plays a key role as a marker of self. Tumor cells have co-opted CD47 overexpression to evade immune surveillance, and thus blockade of CD47 is a highly active area of clinical exploration in oncology. However, clinical development of CD47-targeted agents has been complicated by its robust expression in normal tissues and the toxicities that arise from blocking this inhibitory signal. Furthermore, pro-phagocytic signals are not uniformly expressed in tumors, and antibody blockade alone is often not sufficient to drive antitumor activity. The inclusion of an IgG1 antibody backbone into therapeutic design has been shown to not only serve as an additional pro-phagocytic signal but also exacerbate toxicities in normal tissues. Therefore, a need persists for more selective therapeutic modalities targeting CD47. To address these challenges, we developed SGN-CD47M, a humanized anti-CD47 IgG1 mAb linked to novel masking peptides through linkers designed to be cleaved by active proteases enriched in the tumor microenvironment (TME). Masking technology has the potential to increase the amount of drug that reaches the TME while concomitantly reducing systemic toxicities. We demonstrate that SGN-CD47M is well tolerated in cynomolgus monkeys and displays a 20-fold improvement in tolerability to hematologic toxicities when compared with the unmasked antibody. SGN-CD47M also displays preferential activation in the TME that leads to robust single-agent antitumor activity. For these reasons, SGN-CD47M may have enhanced antitumor activity and improved tolerability relative to existing therapies that target the CD47-signal regulatory protein α interaction.

Nanobody-Targeted Conditional Antimicrobial Therapeutics

Conditional therapeutics that rely on disease microenvironment-specific triggers for activation are a promising strategy to improve therapeutic cargos. Among the investigated triggers, protease activity is used most often because of its dysregulation in several diseases. How to optimally fine-tune protease activation for different therapeutic cargos remains a challenge. Here, we designed nanobody-targeted conditional antimicrobial therapeutics to deliver a model therapeutic peptide and protein to the site of bacterial infection. We explored several parameters that influence proteolytic activation. We report the use of targeting nanobodies to enhance the activation of therapeutics that are otherwise activated inefficiently despite extensive optimization of the cleavable linker. Specifically, the pairing of Ly6G/C or ADAM10-targeting nanobodies with ADAM10-cleavable linkers improved activation via proximity-enabled reactivity. This study demonstrates a distinct role of active targeting in conditional therapeutic activation. More broadly, this optimization framework provides a guideline for the development of conditional therapeutics to treat various diseases in which protease activity is dysregulated.

Conditionally activated immunotoxins with prolonged half-life can enhance the anti-tumor activity

Immunotoxin has become a highly promising therapy for treating cancer and has achieved good results in preclinical trials targeting various cancers. However, there are still some issues that limit the development and application of immunotoxins, such as short half-life and toxic side effects on healthy tissues. In this study, we designed a tumor-conditional immunotoxin called NbHSA-uPA-A1-PE24. Anti-HSA nanobody (NbHSA) was fused to the N-terminus of A1-PE24 (immunotoxin targeting mesothelin) via a linker cleavable by tumor-associated proteases, urokinase-type plasminogen activator (uPA). NbHSA binds to HSA (human serum albumin) in the blood circulation, which not only prolongs the half-life of immunotoxins, but also creates a certain spatial barrier between A1 and mesothelin, thereby reducing the toxicity of NbHSA-uPA-A1-PE24 to healthy tissues expressing mesothelin. Moreover, uPA cleavable element rendered the immunotoxin conditional activation specifically in tumor microenvironment. In animal experiments, the half-life of the newly designed immunotoxins was increased dramatically. Noted, NbHSA-uPA-A1-PE24 has better enrichment at tumor, and shows robust anti-tumor effects in multiple preclinical models, such as pancreatic cancer and gastric cancer models. The results indicate that this strategy has greater potential and higher safety for application in tumor treatment, providing new ideas and strategies for the development of immunotoxins for cancer patients.

Virtual clinical trials via a QSP immuno-oncology model to simulate the response to a conditionally activated PD-L1 targeting antibody in NSCLC

Recently, immunotherapies for antitumoral response have adopted conditionally activated molecules with the objective of reducing systemic toxicity. Amongst these are conditionally activated antibodies, such as PROBODY® activatable therapeutics (Pb-Tx), engineered to be proteolytically activated by proteases found locally in the tumor microenvironment (TME). These PROBODY® therapeutics molecules have shown potential as PD-L1 checkpoint inhibitors in several cancer types, including both effectiveness and locality of action of the molecule as shown by several clinical trials and imaging studies. Here, we perform an exploratory study using our recently published quantitative systems pharmacology model, previously validated for triple-negative breast cancer (TNBC), to computationally predict the effectiveness and targeting specificity of a PROBODY® therapeutics drug compared to the non-modified antibody. We begin with the analysis of anti-PD-L1 immunotherapy in non-small cell lung cancer (NSCLC). As a first contribution, we have improved previous virtual patient selection methods using the omics data provided by the iAtlas database portal compared to methods previously published in literature. Furthermore, our results suggest that masking an antibody maintains its efficacy while improving the localization of active therapeutic in the TME. Additionally, we generalize the model by evaluating the dependence of the response to the tumor mutational burden, independently of cancer type, as well as to other key biomarkers, such as CD8/Treg Tcell and M1/M2 macrophage ratio. While our results are obtained from simulations on NSCLC, our findings are generalizable to other cancer types and suggest that an effective and highly selective conditionally activated PROBODY® therapeutics molecule is a feasible option.

A Competition-Based Strategy for the Isolation of an Anti-Idiotypic Blocking Module and Fine-Tuning for Conditional Activation of a Therapeutic Antibody

The masking of therapeutic antibodies by the installation of a blocking module that can be removed under certain physiological conditions, is becoming increasingly important to improve their safety and toxicity profile. To gain access to such masking units, we used chicken immunization in combination with yeast surface display and a competition-based FACS screening campaign to obtain anti-idiotypic single-chain Fv (scFv) fragments. This approach promotes the identification of functional masking units, since specificity and high affinity do not necessarily guarantee a paratope blocking effect. This strategy was used to isolate a scFv masking unit for the therapeutic antibody 6G11 (BI-1206), which is currently in clinical trials for the treatment of B-cell lymphoma to block the inhibitory Fcγ receptor IIB (CD32b). N-terminal fusion of the anti-idiotypic scFv to the 6G11 light chain successfully abolished binding to FcγRIIB in vitro. For conditional activation, a cleavable linker for the tumor-associated protease MMP-9 was implemented. To improve demasking efficiency, the affinity of the scFv mask was attenuated through rational design. The substitution of one key amino acid in the masking scFv reduced the affinity toward the 6G11 paratope by factor 10 but still mediated 9800-fold blocking of receptor binding. Proteolytic demasking allowed full recovery of therapeutic antibody function in vitro, supporting the concept of conditional antibody activation using this anti-idiotypic binding module.

Logic-gated and contextual control of immunotherapy for solid tumors: contrasting multi-specific T cell engagers and CAR-T cell therapies

CAR-T cell and T cell engager therapies have demonstrated transformational efficacy against hematological malignancies, but achieving efficacy in solid tumors has been more challenging, in large part because of on-target/off-tumor toxicities and sub-optimal T cell anti-tumor cytotoxic functions. Here, we discuss engineering solutions that exploit biological properties of solid tumors to overcome these challenges. Using logic gates as a framework, we categorize the numerous approaches that leverage two inputs instead of one to achieve better cancer selectivity or efficacy in solid tumors with dual-input CAR-Ts or multi-specific TCEs. In addition to the "OR gate" and "AND gate" approaches that leverage dual tumor antigen targeting, we also review "contextual AND gate" technologies whereby continuous cancer-selective inputs such a pH, hypoxia, target density, tumor proteases, and immune-suppressive cytokine gradients can be creatively incorporated in therapy designs. We also introduce the notion of "output directionality" to distinguish dual-input strategies that mechanistically impact cancer cell killing or T cell fitness. Finally, we contrast the feasibility and potential benefits of the various approaches using CAR-T and TCE therapeutics and discuss why the promising "IF/THEN" and "NOT" gate types pertain more specifically to CAR-T therapies, but can also succeed by integrating both technologies.

Integrating molecular dynamics simulation with small- and wide-angle X-ray scattering to unravel the flexibility, antigen-blocking, and protease-restoring functions in a hindrance-based pro-antibody

Spatial hindrance-based pro-antibodies (pro-Abs) are engineered antibodies to reduce monoclonal antibodies' (mAbs) on-target toxicity using universal designed blocking segments that mask mAb antigen-binding sites through spatial hindrance. By linking through protease substrates and linkers, these blocking segments can be removed site-specifically. Although many types of blocking segments have been developed, such as coiled-coil and hinge-based Ab locks, the molecular structure of the pro-Ab, particularly the region showing how the blocking fragment blocks the mAb, has not been elucidated by X-ray crystallography or cryo-EM. To achieve maximal effect, a pro-Ab must have high antigen-blocking and protease-restoring efficiencies, but the unclear structure limits its further optimization. Here, we utilized molecular dynamics (MD) simulations to study the dynamic structures of a hinge-based Ab lock pro-Ab, pro-Nivolumab, and validated the simulated structures with small- and wide-angle X-ray scattering (SWAXS). The MD results were closely consistent with SWAXS data (χ2 best-fit = 1.845, χ2 allMD = 3.080). The further analysis shows a pronounced flexibility of the Ab lock (root-mean-square deviation = 10.90 Å), yet it still masks the important antigen-binding residues by 57.3%-88.4%, explaining its 250-folded antigen-blocking efficiency. The introduced protease accessible surface area method affirmed better protease efficiency for light chain (33.03 Å2) over heavy chain (5.06 Å2), which aligns with the experiments. Overall, we developed MD-SWAXS validation method to study the dynamics of flexible blocking segments and introduced methodologies to estimate their antigen-blocking and protease-restoring efficiencies, which would potentially be advancing the clinical applications of any spatial hindrance-based pro-Ab.

Rational design of environmentally responsive antibodies with pH-sensing synthetic amino acids

Antibodies are widely used as therapeutic agents to tackle various diseases. In the present study, to enhance their clinical values, we rationally designed pH-responsivity by exploiting the idiosyncratic protonation/deprotonation profiles of non-natural amino acids. 3-Nitro-L-tyrosine, 3-cyano-L-tyrosine, and 3, 5-halogenated-L-tyrosine, each with near neutral pKa, were thus incorporated into Fab fragments in place of tyrosines and other residues in the variable regions. Cell-based assays showed that these modifications achieved up to 140-fold tighter binding to antigens and several-fold tighter cytotoxicity to antigen-expressing cell at pH 6.0 than pH 7.4. The pH-dependent binding effect was retained in full-length antibodies. In silico structural analyses revealed electrostatic repulsion at neutral pH between antigens and antibodies or inside the antibody as the underlying mechanisms of the acid preference, and this finding increases the designability of pH-dependent antigen binding. The development of antibodies responsive to the microenvironments of diseased tissues will allow more disease-related antigens to be targeted in treatments, because of the reduced cross-reactivity toward healthy tissues.

The Roles of T cells in Immune Checkpoint Inhibitor-Induced Arthritis

Immune checkpoint inhibitor (ICI) therapy, a novel anti-tumor strategy, can specifically eliminate tumors by activating the immune system and inhibiting tumor immune escape. However, ICI therapy can lead to notable negative outcomes known as immune-related adverse events (irAEs). ICI-induced arthritis, also known as ICI arthritis, stands as the prevailing form of irAEs. The purpose of this review is to highlight the crucial functions of T cells in the progression of ICI arthritis. Under the influence of different signaling molecules, T cells could gather in large numbers within the synovial membrane of joints, releasing inflammatory substances and enzymes that harm healthy tissues, ultimately causing ICI arthritis. Moreover, considering the functions of T cells in triggering ICI arthritis, this review suggests several treatments to prevent ICI arthritis, including inhibiting the overstimulation of T cells at the synovial sac of joints, enhancing the precision of ICI medications, and directing ICI drugs specifically towards tumor tissues instead of joints. Collectively, T lymphocytes play a vital role in the onset of ICI arthritis, offering a hopeful perspective on treating ICI arthritis through the specific targeting of T cells within the affected joints.

New immune cell engagers for cancer immunotherapy

There have been major advances in the immunotherapy of cancer in recent years, including the development of T cell engagers - antibodies engineered to redirect T cells to recognize and kill cancer cells - for the treatment of haematological malignancies. However, the field still faces several challenges to develop agents that are consistently effective in a majority of patients and cancer types, such as optimizing drug dose, overcoming treatment resistance and improving efficacy in solid tumours. A new generation of T cell-targeted molecules was developed to tackle these issues that are potentially more effective and safer. In addition, agents designed to engage the antitumour activities of other immune cells, including natural killer cells and myeloid cells, are showing promise and have the potential to treat a broader range of cancers.

Cancer therapy with antibodies

The greatest challenge in cancer therapy is to eradicate cancer cells with minimal damage to normal cells. Targeted therapy has been developed to meet that challenge, showing a substantially increased therapeutic index compared with conventional cancer therapies. Antibodies are important members of the family of targeted therapeutic agents because of their extraordinarily high specificity to the target antigens. Therapeutic antibodies use a range of mechanisms that directly or indirectly kill the cancer cells. Early antibodies were developed to directly antagonize targets on cancer cells. This was followed by advancements in linker technologies that allowed the production of antibody-drug conjugates (ADCs) that guide cytotoxic payloads to the cancer cells. Improvement in our understanding of the biology of T cells led to the production of immune checkpoint-inhibiting antibodies that indirectly kill the cancer cells through activation of the T cells. Even more recently, bispecific antibodies were synthetically designed to redirect the T cells of a patient to kill the cancer cells. In this Review, we summarize the different approaches used by therapeutic antibodies to target cancer cells. We discuss their mechanisms of action, the structural basis for target specificity, clinical applications and the ongoing research to improve efficacy and reduce toxicity.

Homogeneous multi-payload antibody-drug conjugates

Many systemic cancer chemotherapies comprise a combination of drugs, yet all clinically used antibody-drug conjugates (ADCs) contain a single-drug payload. These combination regimens improve treatment outcomes by producing synergistic anticancer effects and slowing the development of drug-resistant cell populations. In an attempt to replicate these regimens and improve the efficacy of targeted therapy, the field of ADCs has moved towards developing techniques that allow for multiple unique payloads to be attached to a single antibody molecule with high homogeneity. However, the methods for generating such constructs-homogeneous multi-payload ADCs-are both numerous and complex owing to the plethora of reactive functional groups that make up the surface of an antibody. Here, by summarizing and comparing the methods of both single- and multi-payload ADC generation and their key preclinical and clinical results, we provide a timely overview of this relatively new area of research. The methods discussed range from branched linker installation to the incorporation of unnatural amino acids, with a generalized comparison tool of the most promising modification strategies also provided. Finally, the successes and challenges of this rapidly growing field are critically evaluated, and from this, future areas of research and development are proposed.

Exploring the next generation of antibody-drug conjugates

Antibody-drug conjugates (ADCs) are a promising cancer treatment modality that enables the selective delivery of highly cytotoxic payloads to tumours. However, realizing the full potential of this platform necessitates innovative molecular designs to tackle several clinical challenges such as drug resistance, tumour heterogeneity and treatment-related adverse effects. Several emerging ADC formats exist, including bispecific ADCs, conditionally active ADCs (also known as probody-drug conjugates), immune-stimulating ADCs, protein-degrader ADCs and dual-drug ADCs, and each offers unique capabilities for tackling these various challenges. For example, probody-drug conjugates can enhance tumour specificity, whereas bispecific ADCs and dual-drug ADCs can address resistance and heterogeneity with enhanced activity. The incorporation of immune-stimulating and protein-degrader ADCs, which have distinct mechanisms of action, into existing treatment strategies could enable multimodal cancer treatment. Despite the promising outlook, the importance of patient stratification and biomarker identification cannot be overstated for these emerging ADCs, as these factors are crucial to identify patients who are most likely to derive benefit. As we continue to deepen our understanding of tumour biology and refine ADC design, we will edge closer to developing truly effective and safe ADCs for patients with treatment-refractory cancers. In this Review, we highlight advances in each ADC component (the monoclonal antibody, payload, linker and conjugation chemistry) and provide more-detailed discussions on selected examples of emerging novel ADCs of each format, enabled by engineering of one or more of these components.

Antibody-Drug Conjugates in Breast Cancer: A Comprehensive Review of How to Selectively Deliver Payloads

Antibody-drug conjugates (ADCs) have surfaced as a promising group of anticancer agents employing the precise targeting capacity of monoclonal antibodies to transport highly effective cytotoxic payloads. Compared to conventional chemotherapy, they aim to selectively eradicate cancer cells while minimizing off-target toxicity on healthy tissues. An increasing body of evidence has provided support for the efficacy of ADCs in treating breast cancer across various contexts and tumor subtypes, resulting in significant changes in clinical practice. Nevertheless, unlocking the full potential of these therapeutic agents demands innovative molecular designs to address complex clinical challenges, including drug resistance, tumor heterogeneity, and treatment-related adverse events. This thorough review provides an in-depth analysis of the clinical data on ADCs, offering crucial insights from pivotal clinical trials that assess the efficacy of ADCs in diverse breast cancer settings. This aids in providing a comprehensive understanding of the current state of ADCs in breast cancer therapy, while also providing valuable perspectives for the future.

Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

Antibody-epitope conjugates deliver immunogenic T-cell epitopes more efficiently when close to cell surfaces

Antibody-mediated delivery of immunogenic viral CD8+ T-cell epitopes to redirect virus-specific T cells toward cancer cells is a promising new therapeutic avenue to increase the immunogenicity of tumors. Multiple strategies for viral epitope delivery have been shown to be effective. So far, most of these have relied on a free C-terminus of the immunogenic epitope for extracellular delivery. Here, we demonstrate that antibody-epitope conjugates (AECs) with genetically fused epitopes to the N-terminus of the antibody can also sensitize tumors for attack by virus-specific CD8+ T cells. AECs carrying epitopes genetically fused at the N-terminus of the light chains of cetuximab and trastuzumab demonstrate an even more efficient delivery of the T-cell epitopes compared to AECs with the epitope fused to the C-terminus of the heavy chain. We demonstrate that this increased efficiency is not caused by the shift in location of the cleavage site from the N- to the C-terminus, but by its increased proximity to the cell surface. We hypothesize that this facilitates more efficient epitope delivery. These findings not only provide additional insights into the mechanism of action of AECs but also broaden the possibilities for genetically fused AECs as an avenue for the redirection of multiple virus-specific T cells toward tumors.

Eliciting the antitumor immune response with a conditionally activated PD-L1 targeting antibody analyzed with a quantitative systems pharmacology model

Conditionally activated molecules, such as Probody therapeutics (PbTx), have recently been investigated to improve antitumoral response while reducing systemic toxicity. PbTx are engineered to be proteolytically activated by proteases that are preferentially active locally in the tumor microenvironment (TME). Here, we perform an exploratory study using our recently published quantitative systems pharmacology model, previously validated for other drugs, to evaluate the effectiveness and targeting specificity of an anti-PD-L1 PbTx compared to the non-modified antibody. We have informed the model using the PbTx dynamics and pharmacokinetics published in the literature for anti-PD-L1 in patients with triple-negative breast cancer (TNBC). Our results suggest masking of the antibody slightly decreases its efficacy, while increasing the localization of active therapeutic component in the TME. We also perform a parameter optimization for the PbTx design and drug dosing regimens to maximize the response rate. Although our results are specific to the case of TNBC, our findings are generalizable to any conditionally activated PbTx molecule in solid tumors and suggest that design of a highly effective and selective PbTx is feasible.

Antibody-mediated delivery of viral epitopes to redirect EBV-specific CD8+ T-cell immunity towards cancer cells

Antibody-mediated delivery of immunogenic epitopes to redirect virus-specific CD8+ T-cells towards cancer cells is an emerging and promising new therapeutic strategy. These so-called antibody-epitope conjugates (AECs) rely on the proteolytic release of the epitopes close to the tumor surface for presentation by HLA class I molecules to eventually redirect and activate virus-specific CD8+ T-cells towards tumor cells. We fused the immunogenic EBV-BRLF1 epitope preceded by a protease cleavage site to the C-terminus of the heavy and/or light chains of cetuximab and trastuzumab. We evaluated these AECs and found that, even though all AECs were able to redirect the EBV-specific T-cells, AECs with an epitope fused to the C-terminus of the heavy chain resulted in higher levels of T-cell activation compared to AECs with the same epitope fused to the light chain of an antibody. We observed that all AECs were depending on the presence of the antibody target, that the level of T-cell activation correlated with expression levels of the antibody target, and that our AECs could efficiently deliver the BRLF1 epitope to cancer cell lines from different origins (breast, ovarian, lung, and cervical cancer and a multiple myeloma). Moreover, in vivo, the AECs efficiently reduced tumor burden and increased the overall survival, which was prolonged even further in combination with immune checkpoint blockade. We demonstrate the potential of these genetically fused AECs to redirect the potent EBV-specific T-cells towards cancer in vitro and in vivo.

Site-specific antibody masking enables conditional activation with different stimuli

Antibody therapeutics show great potential to treat a variety of diseases. Often, the dose that can be safely administered is limited by side effects that arise from the interaction with the target outside the diseased tissue. Conditionally-active antibodies provide an additional layer of selectivity to improve safety. Distinct external stimuli or internal cues enable different control strategies and applications. However, current antibody masking strategies have low transferability across stimuli. Here we propose a versatile approach to conditionally mask antibody derivatives and its application to a single chain variable fragment (scFv) against a receptor expressed on cancer stem cells in several tumours. Our strategy relies on the site-specific conjugation of a polymer to an engineered cysteine residue through a chemically-synthesised linker that can be cleaved in response to the target stimulus. We show that the masking efficiency depends on the conjugation site and the size of the mask. An optimised mask decreases antigen binding by up to 20-fold and affinity can be fully recovered upon activation by exposure to light at 365 nm or by incubation with matrix metalloproteinases overexpressed in solid tumours. This approach opens up the possibility to rapidly engineer antibodies activatable with any internal or external stimulus.

Advances in research based on antibody-cell conjugation

Antibody-cell conjugation (ACC) technology is a new research direction in medicine and biotechnology in recent years. The concept of ACC was proposed by Hsiao et al. and developed into a viable cell therapy technology, which refers to the cells with specific functions. Such as natural killer cells (NK cells), cytokine induced killer cells (CIK) and other immune cells and monoclonal antibodies through the linker together formed conjugate. ACC directly modifies specific antibodies on the cell surface through a simple and effective chemical coupling method to enable cells to have new functions. ACC has been developed for the treatment of various diseases, including cancers of the blood system and solid tumors. This paper reviews the current ACC construction methods, challenges and future development directions.

Design principles for engineering light-controlled antibodies

Engineered antibodies are essential tools for research and advanced pharmacy. In the development of therapeutics, antibodies are excellent candidates as they offer both target recognition and modulation. Thanks to the latest advances in biotechnology, light-activated antibody fragments can be constructed to control spontaneous antigen interaction with high spatiotemporal precision. To implement conditional antigen binding, several optogenetic and optochemical engineering concepts have recently been developed. Here, we highlight the various strategies and discuss the features of opto-conditional antibodies. Each concept offers intrinsic advantages beneficial to different applications. In summary, the novel design approaches constitute a complementary toolset to promote current and upcoming antibody technologies with ultimate precision.

Conditionally Active, pH-Sensitive Immunoregulatory Antibodies Targeting VISTA and CTLA-4 Lead an Emerging Class of Cancer Therapeutics

Immune checkpoints and other immunoregulatory targets can be difficult to precisely target due to expression on non-tumor immune cells critical to maintaining immune homeostasis in healthy tissues. On-target/off-tumor binding of therapeutics results in significant pharmacokinetic and pharmacodynamic problems. Target-mediated drug disposition (TMDD) significantly limits effective intratumoral drug levels and adversely affects anti-tumor efficacy. Target engagement outside the tumor environment may lead to severe immune-related adverse events (irAEs), resulting in a narrowing of the therapeutic window, sub-optimal dosing, or cessation of drug development altogether. Overcoming these challenges has become tractable through recent advances in antibody engineering and screening approaches. Here, we review the discovery and development of conditionally active antibodies with minimal binding to target at physiologic pH but high-affinity target binding at the low pH of the tumor microenvironment by focusing on the discovery and improved properties of pH-dependent mAbs targeting two T cell checkpoints, VISTA and CTLA-4.

Tumor Site-Specific Cleavage Improves the Antitumor Efficacy of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) play important roles in tumor therapy. However, traditional ADCs are limited by the extremely large molecular weight of the antibody molecules, which results in low permeability into solid tumors. The use of small ADCs may be expected to alleviate this problem, but this switch brings the new limitation of a greatly shortened blood circulation half-life. Here, we propose a new cleavable ADC design with excellent tumor tissue permeability and a long circulation half-life by fusing the small ADC Z_HER2-MMAE with the Fc domain of the antibody for circulation half-life extension, and inserting a digestion sequence between them to release the small ADC inside tumors for better tumor penetration. The experimental results showed that the designed molecule Fc-U-Z_HER2-MMAE has a significantly increased blood circulation half-life (7.1 h, 59-fold longer) compared to the small ADC Z_HER2-MMAE, and significantly improved drug accumulation ability at tumor sites compared to the conventional full-length antibody-coupled ADC Herceptin-MMAE. These combined effects led to Fc-U-Z_HER2-MMAE having significantly enhanced tumor treatment ability, as shown in mouse models of NCI-N87 gastric cancer and SK-OV-3 ovarian cancer, where Fc-U-Z_HER2-MMAE treatment achieved complete regression of tumors in all or a portion of animals with no obvious side effects and an MTD exceeding 90 mg/kg. These data demonstrate the therapeutic advantages of this cleavable ADC strategy, which could provide a new approach for ADC design.

Comparison of methods generating antibody-epitope conjugates for targeting cancer with virus-specific T cells

Therapeutic antibody-epitope conjugates (AECs) are promising new modalities to deliver immunogenic epitopes and redirect virus-specific T-cell activity to cancer cells. Nevertheless, many aspects of these antibody conjugates require optimization to increase their efficacy. Here we evaluated different strategies to conjugate an EBV epitope (YVL/A2) preceded by a protease cleavage site to the antibodies cetuximab and trastuzumab. Three approaches were taken: chemical conjugation (i.e. a thiol-maleimide reaction) to reduced cysteine side chains, heavy chain C-terminal enzymatic conjugation using sortase A, and genetic fusions, to the heavy chain (HC) C-terminus. All three conjugates were capable of T-cell activation and target-cell killing via proteolytic release of the EBV epitope and expression of the antibody target was a requirement for T-cell activation. Moreover, AECs generated with a second immunogenic epitope derived from CMV (NLV/A2) were able to deliver and redirect CMV specific T-cells, in which the amino sequence of the attached peptide appeared to influence the efficiency of epitope delivery. Therefore, screening of multiple protease cleavage sites and epitopes attached to the antibody is necessary. Taken together, our data demonstrated that multiple AECs could sensitize cancer cells to virus-specific T cells.

Functionally Masked Antibody to Uncouple Immune-Related Toxicities in Checkpoint Blockade Cancer Therapy

Of the existing immunotherapy drugs in oncology, monoclonal antibodies targeting the immune checkpoint axis are preferred because of the durable responses observed in selected patients. However, the associated immune-related adverse events (irAEs), causing uncommon fatal events, often require specialized management and medication discontinuation. The study aim was to investigate our hypothesis that masking checkpoint antibodies with tumor microenvironment (TME)-responsive polymer chains can mitigate irAEs and selectively target tumors by limiting systemic exposure to patients. We devised a broadly applicable strategy that functionalizes immune checkpoint-blocking antibodies with a mildly acidic pH-cleavable poly(ethylene glycol) (PEG) shell to prevent inflammatory side effects in normal tissues. Conjugation of pH-sensitive PEG to anti-CD47 antibodies (αCD47) minimized antibody-cell interactions by inhibiting their binding ability and functionality at physiological pH, leading to prevention of αCD47-induced anemia in tumor-bearing mice. When conjugated to anti-CTLA-4 and anti-PD-1 antibodies, double checkpoint blockade-induced colitis was also ameliorated. Notably, removal of the protective shell in response to an acidic TME restored the checkpoint antibody activities, accompanied by effective tumor regression and long-term survival in the mouse model. Our results support a feasible strategy for antibody-based therapies to uncouple toxicity from efficacy and show the translational potential for cancer immunotherapy.

Generation of an anti-idiotypic affibody-based masking domain for conditional activation of EGFR-targeting

Conditional activation of engineered affinity proteins by proteolytic processing is an interesting approach for a wide range of applications. We have generated an anti-idiotypic masking domain with specificity for the binding surface of an EGFR-targeting affibody molecule using an in-house developed staphylococcal display method. The masking domain could specifically abrogate EGFR-binding on cancer cells when fused to the EGFR-targeting affibody molecule via a linker comprising a protease cleavage site. EGFR-binding was restored by proteolytic cleavage of the linker region resulting in release of the masking domain. A saturation mutagenesis study provided detailed information on the interaction between the EGFR-targeting affibody molecule and the masking domain. Introducing an anti-idiotypic masking affibody domain is a viable approach for blocking EGFR-binding and allows for conditional activation by proteolytic processing. The results warrant further studies evaluating the therapeutic and diagnostic applicability both in vitro and in vivo.

Prospects of Using Protein Engineering for Selective Drug Delivery into a Specific Compartment of Target Cells

A large number of proteins are successfully used to treat various diseases. These include natural polypeptide hormones, their synthetic analogues, antibodies, antibody mimetics, enzymes, and other drugs based on them. Many of them are demanded in clinical settings and commercially successful, mainly for cancer treatment. The targets for most of the aforementioned drugs are located at the cell surface. Meanwhile, the vast majority of therapeutic targets, which are usually regulatory macromolecules, are located inside the cell. Traditional low molecular weight drugs freely penetrate all cells, causing side effects in non-target cells. In addition, it is often difficult to elaborate a small molecule that can specifically affect protein interactions. Modern technologies make it possible to obtain proteins capable of interacting with almost any target. However, proteins, like other macromolecules, cannot, as a rule, freely penetrate into the desired cellular compartment. Recent studies allow us to design multifunctional proteins that solve these problems. This review considers the scope of application of such artificial constructs for the targeted delivery of both protein-based and traditional low molecular weight drugs, the obstacles met on the way of their transport to the specified intracellular compartment of the target cells after their systemic bloodstream administration, and the means to overcome those difficulties.

Overcoming the On-Target Toxicity in Antibody-Mediated Therapies via an Indirect Active Targeting Strategy

Antibody-based therapies could be led astray when target receptors are expressed on nontarget sites, and the on-target toxicity poses critical challenges to clinical applications. Here, a biomimetic indirect active targeting (INTACT) strategy is proposed based on receptor expression disparities between nontarget sites and the targets. By prebinding the antibodies using cell membrane vesicles with appropriate receptor expressions, the INTACT strategy could filter out the interactions on nontarget sites due to their inferior receptor expression, whereas ensure on-demand release at the targets by competitive binding. The strategy is verified on CD47 antibody, realizing drastic alleviation of its clinically concerned hematotoxicity on a series of animal models including humanized patient-derived xenograft platforms, accompanied by preferable therapeutic effects. Furthermore, the INTACT strategy proves extensive applicability for various systems including antibody, antibody-drug conjugate, and targeted delivery systems, providing a potential platform refining the specificity for frontier antibody-related therapies.

Strategies for Conditional Regulation of Proteins

Design of the next-generation of therapeutics, biosensors, and molecular tools for basic research requires that we bring protein activity under control. Each protein has unique properties, and therefore, it is critical to tailor the current techniques to develop new regulatory methods and regulate new proteins of interest (POIs). This perspective gives an overview of the widely used stimuli and synthetic and natural methods for conditional regulation of proteins.

Antibody engineering and its therapeutic applications

As a natural function, antibodies defend the host from infected cells and pathogens by recognizing their pathogenic determinants. Antibodies (Abs) gained wide acceptance with an enormous impact on human health and have predominantly captured the arena of bio-therapeutics and bio-diagnostics. The scope of Ab-based biologics is vast, and it is likely to solve many unmet clinical needs in future. The majority of attention is now devoted to developing innovative technologies for manufacturing and engineering Abs, better suited to satisfy human needs. The advent of Ab engineering technologies (AET) led to phenomenal developments leading to the generation of Abs-/Ab-derived molecules with desirable functional properties proportional to their expanding requirements. Evolution brought by AET, from the naturally occurring Ab forms to several advanced Ab formats and derivatives, was much needed as it is of great interest to the pharmaceutical industry. Thus, numerous advancements in AET have propelled success in therapeutic Ab development, along with the potential for ever-increasing improvements. Unique characteristics of Abs, such as its diversity, specificity, structural integrity and an array of possible applications, together inspire continuous innovation in the field. Overall, the AET could assist in conquer of several limitations of Abs in terms of their applicability in the field of therapeutics, diagnostics and research; AET has so far led to the production of next-generation Abs, which have revolutionized these arenas. Here in this review, we discuss the various distinguished engineering platforms for Ab development and the progress in modern therapeutics by the so-called "next-generation Abs."

Site-specific encoding of photoactivity and photoreactivity into antibody fragments

Design of biomolecules that perform two or more distinct functions in response to light remains challenging. Here, we have introduced concurrent photoactivity and photoreactivity into an epidermal growth factor receptor (EGFR)-targeting antibody fragment, 7D12. This was achieved by site-specific incorporation of photocaged tyrosine (pcY) for photoactivity and p-benzoyl-ʟ-phenylalanine (Bpa) for photoreactivity into 7D12. We identified a position for installing Bpa in 7D12 that has minimal effect on 7D12-EGFR binding affinity in the absence of light. Upon exposure to 365-nm light, this Bpa-containing 7D12 mutant forms a covalent bond with EGFR in an antigen-specific manner. We then developed a method for site-specific incorporation of pcY and Bpa at two distinct sites in 7D12. Finally, we demonstrated that in the absence of light, this pcY- and Bpa-containing mutant of 7D12 does not bind to EGFR, but irradiation with 365-nm light activates (1) specific binding and (2) covalent bond formation with EGFR.

A lesion-selective albumin-CTLA4Ig as a safe and effective treatment for collagen-induced arthritis

BACKGROUND

CTLA4Ig is a dimeric fusion protein of the extracellular domain of cytotoxic T-lymphocyte protein 4 (CTLA4) and an Fc (Ig) fragment of human IgG₁ that is approved for treating rheumatoid arthritis. However, CTLA4Ig may induce adverse effects. Developing a lesion-selective variant of CTLA4Ig may improve safety while maintaining the efficacy of the treatment.

METHODS

We linked albumin to the N-terminus of CTLA4Ig (termed Alb-CTLA4Ig) via a substrate sequence of matrix metalloproteinase (MMP). The binding activities and the biological activities of Alb-CTLA4Ig before and after MMP digestion were analyzed by a cell-based ELISA and an in vitro Jurkat T cell activation assay. The efficacy and safety of Alb-CTLA4Ig in treating joint inflammation were tested in mouse collagen-induced arthritis.

RESULTS

Alb-CTLA4Ig is stable and inactive under physiological conditions but can be fully activated by MMPs. The binding activity of nondigested Alb-CTLA4Ig was at least 10,000-fold weaker than that of MMP-digested Alb-CTLA4Ig. Nondigested Alb-CTLA4Ig was unable to inhibit Jurkat T cell activation, whereas MMP-digested Alb-CTLA4Ig was as potent as conventional CTLA4Ig in inhibiting the T cells. Alb-CTLA4Ig was converted to CTLA4Ig in the inflamed joints to treat mouse collagen-induced arthritis, showing similar efficacy to that of conventional CTLA4Ig. In contrast to conventional CTLA4Ig, Alb-CTLA4Ig did not inhibit the antimicrobial responses in the spleens of the treated mice.

CONCLUSIONS

Our study indicates that Alb-CTLA4Ig can be activated by MMPs to suppress tissue inflammation in situ. Thus, Alb-CTLA4Ig is a safe and effective treatment for collagen-induced arthritis in mice.

Embracing enzyme promiscuity with activity-based compressed biosensing

The development of protease-activatable drugs and diagnostics requires identifying substrates specific to individual proteases. However, this process becomes increasingly difficult as the number of target proteases increases because most substrates are promiscuously cleaved by multiple proteases. We introduce a method-substrate libraries for compressed sensing of enzymes (SLICE)-for selecting libraries of promiscuous substrates that classify protease mixtures (1) without deconvolution of compressed signals and (2) without highly specific substrates. SLICE ranks substrate libraries using a compression score (C), which quantifies substrate orthogonality and protease coverage. This metric is predictive of classification accuracy across 140 in silico (Pearson r = 0.71) and 55 in vitro libraries (r = 0.55). Using SLICE, we select a two-substrate library to classify 28 samples containing 11 enzymes in plasma (area under the receiver operating characteristic curve [AUROC] = 0.93). We envision that SLICE will enable the selection of libraries that capture information from hundreds of enzymes using fewer substrates for applications like activity-based sensors for imaging and diagnostics.

Turning adversity into opportunity: Small extracellular vesicles as nanocarriers for tumor-associated macrophages re-education

Currently, small extracellular vesicles (sEV) as a nanoscale drug delivery system, are undergoing biotechnological scaling and clinical validation. Nonetheless, preclinical pharmacokinetic studies revealed that sEV are predominantly uptaken by macrophages. Although this "sEV-macrophage" propensity represents a disadvantage in terms of sEV targeting and their bioavailability as nanocarriers, it also represents a strategic advantage for those therapies that involve macrophages. Such is the case of tumor-associated macrophages (TAMs), which can reprogram/repolarize their predominantly immunosuppressive and tumor-supportive phenotype toward an immunostimulatory and anti-tumor phenotype using sEV as nanocarriers of TAMs reprogramming molecules. In this design, sEV represents an advantageous delivery system, providing precision to the therapy by simultaneously matching their tropism to the therapeutic cell target. Here, we review the current knowledge of the role of TAMs in the tumoral microenvironment and the effect generated by the reprogramming of these phagocytic cells fate using sEV. Finally, we discuss how these vesicles can be engineered by different bioengineering techniques to improve their therapeutic cargo loading and preferential uptake by TAMs.

Turning antibodies off and on again using a covalently tethered blocking peptide

In their natural form, antibodies are always in an "on-state" and are capable of binding to their targets. This leads to undesirable interactions in a wide range of therapeutic, analytical, and synthetic applications. Modulating binding kinetics of antibodies to turn them from an "off-state" to an "on-state" with temporal and spatial control can address this. Here we demonstrate a method to modulate binding activity of antibodies in a predictable and reproducible way. We designed a blocking construct that uses both covalent and non-covalent interactions with the antibody. The construct consisted of a Protein L protein attached to a flexible linker ending in a blocking-peptide designed to interact with the antibody binding site. A mutant Protein L was developed to enable photo-triggered covalent crosslinking to the antibody at a specific location. The covalent bond anchored the linker and blocking peptide to the antibody light chain keeping the blocking peptide close to the antibody binding site. This effectively put the antibody into an "off-state". We demonstrate that protease-cleavable and photocleavable moieties in the tether enable controlled antibody activation to the "on-state" for anti-FLAG and cetuximab antibodies. Protein L can bind a range of antibodies used therapeutically and in research for wide applicability.

Engineering antibodies for conditional activity in the solid tumor microenvironment

Antibody-based therapeutics enjoy considerable clinical and commercial successes as cancer treatments. However, they can also cause serious toxicities due to recognition of tumor-associated antigens in noncancerous tissues, which can prevent antibody use in certain patient populations and therapeutic modalities. Here, we discuss recent efforts to develop advanced antibody therapeutics with activities restricted to the solid tumor microenvironment. With the intent of decreasing toxicities and expanding therapeutic windows, protein engineering strategies can render ligand binding sensitive to multiple tumor-specific characteristics. These triggers can be intrinsic to solid tumor microenvironments, such as low pH, high extracellular ATP, and the presence of specific proteases. Emerging strategies rely instead on exogenous triggers such as light and ultrasound to provide spatial and temporal control over antibody activation. These multilayered approaches to targeting diseased tissues are expected to usher in a new generation of precision therapeutics.

Therapeutic antibodies for precise cancer immunotherapy: current and future perspectives

Antibodies, as one of the most important components of host adaptive immune system, play an important role in defense of infectious disease, immune surveillance, and autoimmune disease. Due to the development of recombinant antibody technology, antibody therapeutics become the largest and rapidly expanding drug to provide major health benefits to patients, especially for the treatment of cancer patients. Many antibody-based therapeutic strategies have been developed including monoclonal antibodies, antibody-drug conjugates, bispecific and trispecific antibodies and pro-antibodies with promising results from both clinical and pre-clinical trials. However, the response rate and side-effect still vary between patients with undefined mechanisms. Here, we summarized the current and future perspectives of antibody-based cancer immunotherapeutic strategies for designing next-generation drugs.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

A Probody T Cell-Engaging Bispecific Antibody Targeting EGFR and CD3 Inhibits Colon Cancer Growth with Limited Toxicity

T cell-engaging bispecific antibodies (TCB) are highly potent therapeutics that can recruit and activate cytotoxic T cells to stimulate an antitumor immune response. However, the development of TCBs against solid tumors has been limited by significant on-target toxicity to normal tissues. Probody therapeutics have been developed as a novel class of recombinant, protease-activated antibody prodrugs that are "masked" to reduce antigen binding in healthy tissues but can become conditionally unmasked by proteases that are preferentially active in the tumor microenvironment (TME). Here, we describe the preclinical efficacy and safety of CI107, a Probody TCB targeting EGFR and CD3. In vitro, the protease-activated, unmasked CI107 effectively bound EGFR and CD3 expressed on the surface of cells and induced T-cell activation, cytokine release, and cytotoxicity toward tumor cells. In contrast, dually masked CI107 displayed a >500-fold reduction in antigen binding and >15,000-fold reduction in cytotoxic activity. In vivo, CI107 potently induced dose-dependent tumor regression of established colon cancer xenografts in mice engrafted with human peripheral blood mononuclear cells. Furthermore, the MTD of CI107 in cynomolgus monkeys was more than 60-fold higher than that of the unmasked TCB, and much lower levels of toxicity were observed in animals receiving CI107. Therefore, by localizing activity to the TME and thus limiting toxicity to normal tissues, this Probody TCB demonstrates the potential to expand clinical opportunities for TCBs as effective anticancer therapies for solid tumor indications.

SIGNIFICANCE

A conditionally active EGFR-CD3 T cell-engaging Probody therapeutic expands the safety window of bispecific antibodies while maintaining efficacy in preclinical solid tumor settings.

Current landscape and future directions of bispecific antibodies in cancer immunotherapy

Recent advances in cancer immunotherapy using monoclonal antibodies have dramatically revolutionized the therapeutic strategy against advanced malignancies, inspiring the exploration of various types of therapeutic antibodies. Bispecific antibodies (BsAbs) are recombinant molecules containing two different antigens or epitopes identifying binding domains. Bispecific antibody-based tumor immunotherapy has gained broad potential in preclinical and clinical investigations in a variety of tumor types following regulatory approval of newly developed technologies involving bispecific and multispecific antibodies. Meanwhile, a series of challenges such as antibody immunogenicity, tumor heterogeneity, low response rate, treatment resistance, and systemic adverse effects hinder the application of BsAbs. In this review, we provide insights into the various architecture of BsAbs, focus on BsAbs' alternative different mechanisms of action and clinical progression, and discuss relevant approaches to overcome existing challenges in BsAbs clinical application.

Antibody-Drug Conjugates for Melanoma and Other Skin Malignancies

OPINION STATEMENT

While most skin malignancies are successfully treated with surgical excision, advanced and metastatic skin malignancies still often have poor long-term outcomes despite therapeutic advances. Antibody-drug conjugates (ADCs) serve as a potentially promising novel therapeutic approach to treat advanced skin cancers as they combine antibody-associated antigen specificity with cytotoxic anti-tumor effects, thereby maximizing efficacy and minimizing systemic toxicity. While no ADCs have gained regulatory approval for advanced skin cancers, several promising agents are undergoing preclinical and clinical investigation. In addition to identifying and validating skin cancer antigen targets, the key to maximizing therapeutic success is the careful development of each component of the ADC complex: antibodies, cytotoxic drugs, and linkers. It is the optimization of each of these components that will be integral in overcoming resistance, maximizing safety, and improving long-term clinical outcomes.

Antibody variable region engineering for improving cancer immunotherapy

The efficacy and specificity of conventional monoclonal antibody (mAb) drugs in the clinic require further improvement. Currently, the development and application of novel antibody formats for improving cancer immunotherapy have attracted much attention. Variable region-retaining antibody fragments, such as antigen-binding fragment (Fab), single-chain variable fragment (scFv), bispecific antibody, and bi/trispecific cell engagers, are engineered with humanization, multivalent antibody construction, affinity optimization and antibody masking for targeting tumor cells and killer cells to improve antibody-based therapy potency, efficacy and specificity. In this review, we summarize the application of antibody variable region engineering and discuss the future direction of antibody engineering for improving cancer therapies.

Rational Control of Protein-Protein Interactions with Protein-ATRP-Generated Protease-Sensitive Polymer Cages

Protease-protease interactions lie at the heart of the biological cascades that provide rapid molecular responses to living systems. Blood clotting cascades, apoptosis signaling networks, bacterial infection, and virus trafficking have all evolved to be activated and sustained by protease-protease interactions. Biomimetic strategies designed to target drugs to specific locations have generated proprotein drugs that can be activated by proteolytic cleavage to release native protein. We have previously demonstrated that the modification of enzymes with a custom-designed comb-shaped polymer nanoarmor can shield the enzyme surface and eliminate almost all protein-protein interactions. We now describe the synthesis and characterization of protease-sensitive comb-shaped nanoarmor cages using poly(ethylene glycol) [Sundy, J. S. Arthritis Rheum. 2008, 58(9), 2882-2891]methacrylate macromonomers where the PEG tines of the comb are connected to the backbone of the growing polymer chain by peptide linkers. Protease-induced cleavage of the tines of the comb releases a polymer-modified protein that can once again participate in protein-protein interactions. Atom transfer radical polymerization (ATRP) was used to copolymerize the macromonomer and carboxybetaine methacrylate from initiator-labeled chymotrypsin and trypsin enzymes, yielding proprotease conjugates that retained activity toward small peptide substrates but prevented activity against proteins. Native proteases triggered the release of the PEG side chains from the polymer backbone within 20 min, thereby increasing the activity of the conjugate toward larger protein substrates by 100%. Biomimetic cascade initiation of nanoarmored protease-sensitive protein-polymer conjugates may open the door to a new class of responsive targeted therapies.

Immune checkpoint inhibitors for PD-1/PD-L1 axis in combination with other immunotherapies and targeted therapies for non-small cell lung cancer

It has been widely acknowledged that the use of immune checkpoint inhibitors (ICI) is an effective therapeutic treatment in many late-stage cancers. However, not all patients could benefit from ICI therapy. Several biomarkers, such as high expression of PD-L1, high mutational burden, and higher number of tumor infiltration lymphocytes have shown to predict clinical benefit from immune checkpoint therapies. One approach using ICI in combination with other immunotherapies and targeted therapies is now being investigated to enhance the efficacy of ICI alone. In this review, we summarized the use of other promising immunotherapies and targeted therapies in combination with ICI in treatment of lung cancers. The results from multiple animals and clinical trials were reviewed. We also briefly discussed the possible outlooks for future treatment.

Nonclinical Efficacy and Safety of CX-2029, an Anti-CD71 Probody-Drug Conjugate

Probody therapeutics (Pb-Txs) are conditionally activated antibody-drug conjugates (ADCs) designed to remain inactive until proteolytically activated in the tumor microenvironment, enabling safer targeting of antigens expressed in both tumor and normal tissue. Previous attempts to target CD71, a highly expressed tumor antigen, have failed to establish an acceptable therapeutic window due to widespread normal tissue expression. This study evaluated whether a probody-drug conjugate targeting CD71 can demonstrate a favorable efficacy and tolerability profile in preclinical studies for the treatment of cancer. CX-2029, a Pb-Tx conjugated to maleimido-caproyl-valine-citrulline-p-aminobenzyloxycarbonyl-monomethyl auristatin E, was developed as a novel cancer therapeutic targeting CD71. Preclinical studies were performed to evaluate the efficacy and safety of this anti-CD71 PDC in patient-derived xenograft (PDX) mouse models and cynomolgus monkeys, respectively. CD71 expression was detected at high levels by IHC across a broad range of tumor and normal tissues. In vitro, the masked Pb-Tx form of the anti-CD71 PDC displayed a >50-fold reduced affinity for binding to CD71 on cells compared with protease-activated, unmasked anti-CD71 PDC. Potent in vivo tumor growth inhibition (stasis or regression) was observed in >80% of PDX models (28/34) at 3 or 6 mg/kg. Anti-CD71 PDC remained mostly masked (>80%) in circulation throughout dosing in cynomolgus monkeys at 2, 6, and 12 mg/kg and displayed a 10-fold improvement in tolerability compared with an anti-CD71 ADC, which was lethal. Preclinically, anti-CD71 PDC exhibits a highly efficacious and acceptable safety profile that demonstrates the utility of the Pb-Tx platform to target CD71, an otherwise undruggable target. These data support further clinical development of the anti-CD71 PDC CX-2029 as a novel cancer therapeutic.

Designing antibodies as therapeutics

Antibody therapeutics are a large and rapidly expanding drug class providing major health benefits. We provide a snapshot of current antibody therapeutics including their formats, common targets, therapeutic areas, and routes of administration. Our focus is on selected emerging directions in antibody design where progress may provide a broad benefit. These topics include enhancing antibodies for cancer, antibody delivery to organs such as the brain, gastrointestinal tract, and lungs, plus antibody developability challenges including immunogenicity risk assessment and mitigation and subcutaneous delivery. Machine learning has the potential, albeit as yet largely unrealized, for a transformative future impact on antibody discovery and engineering.