Monomethyl auristatin antibody and peptide drug conjugates for trimodal cancer chemo-radio-immunotherapy

Antibody-drug conjugates for targeted cancer therapy: Recent advances in potential payloads

Antibody-drug conjugates (ADCs) represent a promising cancer therapy modality which specifically delivers highly toxic payloads to cancer cells through antigen-specific monoclonal antibodies (mAbs). To date, 15 ADCs have been approved and more than 100 ADC candidates have advanced to clinical trials for the treatment of various cancers. Among these ADCs, microtubule-targeting and DNA-damaging agents are at the forefront of payload development. However, several challenges including toxicity and drug resistance limit the potential of this modality. To tackle these issues, multiple innovative payloads such as immunomodulators and proteolysis targeting chimeras (PROTACs) are incorporated into ADCs to enable multimodal cancer therapy. In this review, we describe the mechanism of ADCs, highlight the importance of ADC payloads and summarize recent progresses of conventional and unconventional ADC payloads, trying to provide an insight into payload diversification as a key step in future ADC development.

Design and synthesis of novel site-specific antibody-drug conjugates that target TROP2

The approval of Trodelvy® validates TROP2 as a druggable but challenging target for antibody-drug conjugates (ADCs) to treat metastatic triple-negative breast cancer (mTNBC). Here, based on the TROP2-targeted antibody sacituzumab, we designed and developed several site-specific ADC candidates, which employ MMAE (monomethyl auristatin E) as the toxin, via IgG glycoengineering or affinity-directed traceless conjugation. Systematic evaluation of these site-specific ADCs in homogeneity, hydrophilicity, stability, and antitumor efficiency was conducted. The results indicate that the site-specific ADCs gsADC 3b made from one-step glycoengineering exhibit good aggregation stability and in vivo efficacy, providing a new format of ADCs that target TROP2.

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.

Michael Acceptors as Anti-Cancer Compounds: Coincidence or Causality?

Michael acceptors represent a class of compounds with potential anti-cancer properties. They act by binding to nucleophilic sites in biological molecules, thereby disrupting cancer cell function and inducing cell death. This mode of action, as well as their ability to be modified and targeted, makes them a promising avenue for advancing cancer therapy. We are investigating the molecular mechanisms underlying Michael acceptors and their interactions with cancer cells, in particular their ability to interfere with cellular processes and induce apoptosis. The anti-cancer properties of Michael acceptors are not accidental but are due to their chemical structure and reactivity. The electrophilic nature of these compounds allows them to selectively target nucleophilic residues on disease-associated proteins, resulting in significant therapeutic benefits and minimal toxicity in various diseases. This opens up new perspectives for the development of more effective and precise cancer drugs. Nevertheless, further studies are essential to fully understand the impact of our discoveries and translate them into clinical practice.

Synthesis of site-specific Fab-drug conjugates using ADP-ribosyl cyclases

Targeted delivery of small-molecule drugs via covalent attachments to monoclonal antibodies has proved successful in clinic. For this purpose, full-length antibodies are mainly used as drug-carrying vehicles. Despite their flexible conjugation sites and versatile biological activities, intact immunoglobulins with conjugated drugs, which feature relatively large molecular weights, tend to have restricted tissue distribution and penetration and low fractions of payloads. Linking small-molecule therapeutics to other formats of antibody may lead to conjugates with optimal properties. Here, we designed and synthesized ADP-ribosyl cyclase-enabled fragment antigen-binding (Fab) drug conjugates (ARC-FDCs) by utilizing CD38 catalytic activity. Through rapidly forming a stable covalent bond with a nicotinamide adenine dinucleotide (NAD+ )-based drug linker at its active site, CD38 genetically fused with Fab mediates robust site-specific drug conjugations via enzymatic reactions. Generated ARC-FDCs with defined drug-to-Fab ratios display potent and antigen-dependent cytotoxicity against breast cancer cells. This work demonstrates a new strategy for developing site-specific FDCs. It may be applicable to different antibody scaffolds for therapeutic conjugations, leading to novel targeted agents.

Reversible Protection and Targeted Delivery of DNA Origami with a Disulfide-Containing Cationic Polymer

DNA nanostructures have considerable biomedical potential as intracellular delivery vehicles as they are highly homogeneous and can be functionalized with high spatial resolution. However, challenges like instability under physiological conditions, limited cellular uptake, and lysosomal degradation limit their use. This paper presents a bio-reducible, cationic polymer poly(cystaminebisacrylamide-1,6-diaminohexane) (PCD) as a reversible DNA origami protector. PCD displays a stronger DNA affinity than other cationic polymers. DNA nanostructures with PCD protection are shielded from low salt conditions and DNase I degradation and show a 40-fold increase in cell-association when linked to targeting antibodies. Confocal microscopy reveals a potential secondary cell uptake mechanism, directly delivering the nanostructures to the cytoplasm. Additionally, PCD can be removed by cleaving its backbone disulfides using the intracellular reductant, glutathione. Finally, the application of these constructs is demonstrated for targeted delivery of a cytotoxic agent to cancer cells, which efficiently decreases their viability. The PCD protective agent that is reported here is a simple and efficient method for the stabilization of DNA origami structures. With the ability to deprotect the DNA nanostructures upon entry of the intracellular space, the possibility for the use of DNA origami in pharmaceutical applications is enhanced.

Chemical Modification of Cytochrome C for Acid-Responsive Intracellular Apoptotic Protein Delivery for Cancer Eradication

Delivering bioactive proteins into cells without carriers presents significant challenges in biomedical applications due to limited cell membrane permeability and the need for targeted delivery. Here, we introduce a novel carrier-free method that addresses these challenges by chemically modifying proteins with an acid-responsive cell-penetrating peptide (CPP) for selective intracellular delivery within tumours. Cytochrome C, a protein known for inducing apoptosis, served as a model for intracellular delivery of therapeutic proteins for cancer treatment. The CPP was protected with 2,3-dimethyl maleic anhydride (DMA) and chemically conjugated onto the protein surface, creating an acid-responsive protein delivery system. In the acidic tumour microenvironment, DMA deprotects and exposes the positively charged CPP, enabling membrane penetration. Both in vitro and in vivo assays validated the pH-dependent shielding mechanism, demonstrating the modified cytochrome C could induce apoptosis in cancer cells in a pH-selective manner. These findings provide a promising new approach for carrier-free and tumour-targeted intracellular delivery of therapeutic proteins for a wide range of potential applications.

Chemical technology principles for selective bioconjugation of proteins and antibodies

Proteins are multifunctional large organic compounds that constitute an essential component of a living system. Hence, control over their bioconjugation impacts science at the chemistry-biology-medicine interface. A chemical toolbox for their precision engineering can boost healthcare and open a gateway for directed or precision therapeutics. Such a chemical toolbox remained elusive for a long time due to the complexity presented by the large pool of functional groups. The precise single-site modification of a protein requires a method to address a combination of selectivity attributes. This review focuses on guiding principles that can segregate them to simplify the task for a chemical method. Such a disintegration systematically employs a multi-step chemical transformation to deconvolute the selectivity challenges. It constitutes a disintegrate (DIN) theory that offers additional control parameters for tuning precision in protein bioconjugation. This review outlines the selectivity hurdles faced by chemical methods. It elaborates on the developments in the perspective of DIN theory to demonstrate simultaneous regulation of reactivity, chemoselectivity, site-selectivity, modularity, residue specificity, and protein specificity. It discusses the progress of such methods to construct protein and antibody conjugates for biologics, including antibody-fluorophore and antibody-drug conjugates (AFCs and ADCs). It also briefs how this knowledge can assist in developing small molecule-based covalent inhibitors. In the process, it highlights an opportunity for hypothesis-driven routes to accelerate discoveries of selective methods and establish new targetome in the precision engineering of proteins and antibodies.

Development of a MMAE-based antibody-drug conjugate targeting B7-H3 for glioblastoma

B7-H3 (immunoregulatory protein B7-homologue 3) is overexpressed in many cancer cells with limited expression in normal tissues, considered to be a promising target for tumor therapeutics. Clinical trials of antibody-drug conjugates (ADCs) against different targets for glioblastoma have been investigated and showed potent efficacies. In this study, we developed a homogeneous ADC 401-4 with a drug-to-antibody ratio (DAR) of 4, which was prepared by conjugation of Monomethyl auristatin E (MMAE) to a humanized anti-B7-H3 mAb 401, through a divinylsulfonamide-mediated disulfide re-bridging approach. In vitro studies, 401-4 displayed specific killing against B7-H3-expressing tumors and was more effective in cells with higher levels of B7-H3 for different glioblastoma cells. 401-4 was furthered labeled with Cy5.5 to yield a fluorescent conjugate 401-4-Cy5.5. The in vivo imaging studies showed that the conjugate accumulated in tumor regions and exhibited the ability to target-specific delivery. In addition, significant antitumor activities for 401-4 was observed against U87-derived tumor xenografts in a dose dependent manner.

Uncovering therapeutic opportunities in the clinical development of antibody-drug conjugates

INTRODUCTION

Antibody-drug conjugates (ADCs) are a family of therapeutic agents that have demonstrated clinical activity in several indications.

MATERIAL AND METHODS

In this article, we performed a deep analysis of their clinical landscape matched with public genomic human datasets from tumour antigen targets (TATs), to identify empty areas for clinical development.

RESULTS

We observed that TATs used in haematological malignancies were more specific than the ones developed in solid cancers. Those included CD19, CD22, CD30, CD33 and CD79b. In solid tumours, we identified TATs, with approved ADCs, widely expressed in non-explored niche indications like Enfortumab vedotin (anti-Nectin4) in lung or cervical cancer; Tisotumab vedotin (anti-TF) in glioblastoma or pancreatic cancer; and Sacituzumab govitecan (anti-TROP2) in pancreatic, gastric, thyroid or endometrial cancer, among others. Similarly, niche indications for ADCs in clinical development included targets for CD71, PSMA, PTK7 or CD74, in tumours like breast, lung, stomach or colon. Some of these TATs were essential for the survival of tumour cells like CD71, PSMA and PTK7.

CONCLUSIONS

In summary, our study opens the door for further evaluation of ADCs in several indications not explored before.

Allomelanin-based biomimetic nanotherapeutics for orthotopic glioblastoma targeted photothermal immunotherapy

Immune checkpoint blockade (ICB) therapy has shown great potential in the treatment of malignant tumors, but its therapeutic effect on glioblastoma (GBM) is unsatisfactory because of the low immunogenicity and T cell infiltration, as well as the presence of blood-brain barrier (BBB) that blocks most of ICB agents to the GBM tissues. Herein, we developed a biomimetic nanoplatform of AMNP@CLP@CCM for GBM-targeted photothermal therapy (PTT) and ICB synergistic therapy by loading immune checkpoint inhibitor CLP002 into the allomelanin nanoparticles (AMNPs) and followed by coating cancer cell membranes (CCM). The resulting AMNP@CLP@CCM can successfully cross the BBB and deliver CLP002 to GBM tissues due to the homing effect of CCM. As a natural photothermal conversion agent, AMNPs are used for tumor PTT. The increased local temperature by PTT not only enhances BBB penetration but also upregulates the PD-L1 level on GBM cells. Importantly, PTT can effectively stimulate immunogenic cell death to induce tumor-associated antigen exposure and promote T lymphocyte infiltration, which can further amplify the antitumor immune responses of GBM cells to CLP002-mediated ICB therapy, resulting in significant growth inhibition of the orthotopic GBM. Therefore, AMNP@CLP@CCM has great potential for the treatment of orthotopic GBM by PTT and ICB synergistic therapy. STATEMENT OF SIGNIFICANCE: The effect of ICB therapy on GBM is limited by the low immunogenicity and insufficient T-cell infiltration. Here we developed a biomimetic nanoplatform of AMNP@CLP@CCM for GBM-targeted PTT and ICB synergistic therapy. In this nanoplatform, AMNPs are used as both photothermal conversion agents for PTT and nanocarriers for CLP002 delivery. PTT not only enhances BBB penetration but also upregulates the PD-L1 level on GBM cells by increasing local temperature. Additionally, PTT also induces tumor-associated antigen exposure and promotes T lymphocyte infiltration to amplify the antitumor immune responses of GBM cells to CLP002-mediated ICB therapy, resulting in significant growth inhibition of the orthotopic GBM. Thus, this nanoplatform holds great potential for orthotopic GBM treatment.

Tumor protease-activated theranostic nanoparticles for MRI-guided glioblastoma therapy

Rationale: As a cancer, Glioblastoma (GBM) is a highly lethal and difficult-to-treat. With the aim of improving therapies to GBM, we developed novel and target-specific theranostic nanoparticles (TNPs) that can be selectively cleaved by cathepsin B (Cat B) to release the potent toxin monomethyl auristatin E (MMAE). Methods: We synthesized TNPs composed of a ferumoxytol-based nanoparticle carrier and a peptide prodrug with a Cat-B-responsive linker and the tubulin inhibitor MMAE. We hypothesized that intratumoral Cat B can cleave our TNPs and release MMAE to kill GBM cells. The ferumoxytol core enables in vivo drug tracking with magnetic resonance imaging (MRI). We incubated U87-MG GBM cells with TNPs or ferumoxytol and evaluated the TNP content in the cells with transmission electron microscopy and Prussian blue staining. In addition, we stereotaxically implanted 6- to 8-week-old nude mice with U87-MG with U87-MG GBM cells that express a fusion protein of Green Fluorescence Protein and firefly Luciferase (U87-MG/GFP-fLuc). We then treated the animals with an intravenous dose of TNPs (25 mg/kg of ferumoxytol, 0.3 mg/kg of MMAE) or control. We also evaluated the combination of TNP treatment with radiation therapy. We performed MRI before and after TNP injection. We compared the results for tumor and normal brain tissue between the TNP and control groups. We also monitored tumor growth for a period of 21 days. Results: We successfully synthesized TNPs with a hydrodynamic size of 41 ± 5 nm and a zeta potential of 6 ± 3 mV. TNP-treated cells demonstrated a significantly higher iron content than ferumoxytol-treated cells (98 ± 1% vs. 3 ± 1% of cells were iron-positive, respectively). We also found significantly fewer live attached cells in the TNP-treated group (3.8 ± 2.0 px2) than in the ferumoxytol-treated group (80.0 ± 14.5 px2, p < 0001). In vivo MRI studies demonstrated a decline in the tumor signal after TNP (T2= 28 ms) but not control (T2= 32 ms) injections. When TNP injection was combined with radiation therapy, the tumor signals dropped further (T2 = 24 ms). The combination therapy of radiation therapy and TNPs extended the median survival from 14.5 days for the control group to 45 days for the combination therapy group. Conclusion: The new cleavable TNPs reported in this work accumulate in GBM, cause tumor cell death, and have synergistic effects with radiation therapy.

Chemoselective Methionine Labelling of Recombinant Trastuzumab Shows High In Vitro and In Vivo Tumour Targeting

A highly effective 2-step system for site-specific antibody modification and conjugation of the monoclonal antibody Herceptin (commercially available under Trastuzumab) in a cysteine-independent manner was used to generate labelled antibodies for in vivo imaging. The first step contains redox-activated chemical tagging (ReACT) of thioethers via engineered methionine residues to introduce specific alkyne moieties, thereby offering a novel easy way to fundamentally change the process of antibody bioconjugation. The second step involves modification of the introduced alkyne via azide-alkyne cycloaddition 'click' conjugation. The versatility of this 2-step approach is demonstrated here by the selective incorporation of a fluorescent dye but can also be applied to a wide variety of different conjugation partners depending on the desired application in a facile manner. Methionine-modified antibodies were characterised in vitro, and the diagnostic potential of the most promising variant was further analysed in an in vivo xenograft animal model using a fluorescence imaging modality. This study demonstrates how methionine-mediated antibody conjugation offers an orthogonal and versatile route to the generation of tailored antibody conjugates with in vivo applicability.

Drug conjugate-based anticancer therapy - Current status and perspectives

Drug conjugates are conjugates comprising a tumor-homing carrier tethered to a cytotoxic agent via a linker that are designed to deliver an ultra-toxic payload directly to the target cancer cells. This strategy has been successfully used to increase the therapeutic efficacy of cytotoxic agents and reduce their toxic side effects. Drug conjugates are being developed worldwide, with the potential to revolutionize current cancer treatment strategies. Antibody-drug conjugates (ADCs) have developed rapidly, and 14 of them have received market approval since the first approval event by the Food and Drug Administration in 2000. However, there are some limitations in the use of antibodies as carriers. Other classes of drug conjugates are emerging, such as targeted drugs conjugated with peptides (peptide-drug conjugates, PDCs) and polymers (polymer-drug conjugates, PolyDCs) with the remaining constructs similar to those of ADCs. These novel drug conjugates are gaining attention because they overcome the limitations of ADCs. This review summarizes the current state and advancements in knowledge regarding the design, constructs, and clinical efficacy of different drug conjugates.

Biomimetic dual-responsive bioengineered nanotheranostics for intracellular cascade-synthesizing chemo-drugs and efficient oncotherapy

Intracellular-synthesized chemo-drugs based on the inherent characteristics of the tumor microenvironment (TME) have been extensively applied in oncotherapy. However, combining other therapeutic strategies to convert nontoxic small molecules into toxic small-molecule chemo-drugs in the TME is still a huge challenge. To address this issue, herein we have developed a biomimetic dual-responsive bioengineered nanotheranostics system via the supramolecular co-assembly of the nontoxic small-molecule 1,5-dihydroxynaphthalene (DHN) and small-molecule photosensitizer indocyanine green (ICG) followed by surface cloaking through red blood cell membranes (RBCs) for intracellular cascade-synthesizing chemo-drugs and efficient oncotherapy. Such nanotheranostics with a suitable diameter, core-shell structure, ultrahigh dual-drug payload rate, and excellent stability can efficiently accumulate in tumor regions and then internalize into tumor cells. Under the dual stimulations of near-infrared laser irradiation and acidic lysosomes, the nanotheranostics system exhibited exceptional instability under heat-primed membrane rupture and pH decrease, thereby achieving rapid disassembly and on-demand drug release. Furthermore, the released ICG can efficiently convert ³O₂ into ¹O₂. After that, the generated ¹O₂ can efficiently oxidize the released nontoxic DHN into the highly toxic chemo-drug juglone, thereby realizing intracellular cascade-synthesizing chemo-drugs and synergistic photodynamic-chemotherapy while reducing detrimental side effects on normal cells or tissues. Overall, it is envisioned that RBC-cloaked nanotheranostics with intracellular cascade-synthesizing chemo-drugs can provide a promising strategy for intracellular chemo-drug synthesis-based oncotherapy.

Targeting the complexity of ERBB2 biology in gastroesophageal carcinoma

ERBB2 is the most prominent therapeutic target in gastroesophageal adenocarcinoma (GEA). For two decades, trastuzumab was the only treatment available for GEA overexpressing ERBB2. Several drugs showing evidence of efficacy over or in complement to trastuzumab in breast cancer failed to show clinical benefit in GEA. This resistance to anti-ERBB2 therapy is peculiarly recurrent in GEA and is mostly due to tumor heterogeneity with the existence of low expressing ERBB2 tumor clones and loss of ERBB2 over time. The development of new ERBB2 testing strategies and the use of antibody-drug conjugates having a bystander effect are providing new tools to fight heterogeneity in ERBB2-positive GEA. Co-amplifications of tyrosine kinase receptors, alterations in mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K) signaling pathways and in proteins controlling cell cycle are well known to contribute resistance to anti-ERBB2 therapy, and they can be targeted by dual therapy. Recently described, NF1 mutations are responsible for Ras phosphorylation and activation and can also be targeted by MEK/ERK inhibition along with anti-ERBB2 therapy. Multiple lines of evidence suggest that immune mechanisms involving antibody-dependent cell-mediated cytotoxicity are preponderant over intracellular signaling in anti-ERBB2 therapy action. A better comprehension of these mechanisms could leverage immune action of anti-ERBB2 therapy and elucidate efficacy of combinations associating immunotherapy and anti-ERBB2 therapy, as suggested by the recent intermediate positive results of the KEYNOTE-811 trial.

Peptide-Drug Conjugates: A New Hope for Cancer Management

Cancer remains the leading cause of death worldwide despite advances in treatment options for patients. As such, safe and effective therapeutics are required. Short peptides provide advantages to be used in cancer management due to their unique properties, amazing versatility, and progress in biotechnology to overcome peptide limitations. Several appealing peptide-based therapeutic strategies have been developed. Here, we provide an overview of peptide conjugates, the better equivalents of antibody-drug conjugates, as the next generation of drugs for required precise targeting, enhanced cellular permeability, improved drug selectivity, and reduced toxicity for the efficient treatment of cancers. We discuss the basic components of drug conjugates and their release action, including the release of cytotoxins from the linker. We also present peptide-drug conjugates under different stages of clinical development as well as regulatory and other challenges.