Duocarmycin-based antibody-drug conjugates as an emerging biotherapeutic entity for targeted cancer therapy: Pharmaceutical strategy and clinical progress

Synthesis and evaluation of KX-01 analogs with an exploration of linker attachment points for antibody-drug conjugates

KX-01 (tirbanibulin, Klisyri®) is a recently FDA-approved drug for treating actinic keratosis, with a distinct dual mechanism of action combining microtubule disruption and non-ATP-competitive Src inhibition. This unique mechanism and novel chemotype highlight KX-01's potential as a payload for antibody-drug conjugates. In this study, we synthesized and evaluated KX-01 derivatives to enhance anticancer potency and explore functional groups suitable for antibody conjugation. Notably, replacing the morpholine group with an N-benzoylpiperazine scaffold resulted in an analog with significantly improved in vitro antiproliferative activity, attributed to enhanced microtubule disruption and Src inhibition. Furthermore, introducing a phenol or aniline functionality as a common linker attachment point preserved substantial cytotoxicity. These results suggest the potential of KX-01 derivatives for future use as ADC payloads.

Antibody-Drug Conjugates (ADCs): current and future biopharmaceuticals

Antibody-drug conjugates (ADCs) represent a novel class of biopharmaceuticals comprising monoclonal antibodies covalently conjugated to cytotoxic agents via engineered chemical linkers. This combination enables targeted delivery of cytotoxic agents to tumor site through recognizing target antigens by antibody while minimizing off-target effects on healthy tissues. Clinically, ADCs overcome the limitations of traditional chemotherapy, which lacks target specificity, and enhance the therapeutic efficacy of monoclonal antibodies, providing higher efficacy and fewer toxicity anti-tumor biopharmaceuticals. ADCs have ushered in a new era of targeted cancer therapy, with 15 drugs currently approved for clinical use. Additionally, ADCs are being investigated as potential therapeutic candidates for autoimmune diseases, persistent bacterial infections, and other challenging indications. Despite their therapeutic benefits, the development and application of ADCs face significant challenges, including antibody immunogenicity, linker instability, and inadequate control over the release of cytotoxic agent. How can ADCs be designed to be safer and more efficient? What is the future development direction of ADCs? This review provides a comprehensive overview of ADCs, summarizing the structural and functional characteristics of the three core components, antibody, linker, and payload. Furthermore, we systematically assess the advancements and challenges associated with the 15 approved ADCs in cancer therapy, while also exploring the future directions and ongoing challenges. We hope that this work will provide valuable insights into the design and optimization of next-generation ADCs for wider clinical applications.

Design, synthesis and biological evaluation of camptothecin analogue FL118 as a payload for antibody-drug conjugates in targeted cancer therapy

FL118, a camptothecin derivative with dual mechanisms of action through topoisomerase I inhibition and proteasome-mediated degradation of anti-apoptotic proteins exhibits potent anti-tumor activity while remaining resistant to drug efflux transporters. This work describes the targeted delivery of FL118 to tumors via antibody-drug conjugates (ADCs) using the pH-sensitive CL2A linker. ADCs targeting Trop2, HER2, and EGFR exhibited potent in vitro cytotoxicity, with IC50 values as low as 0.025 nM in Trop2-positive FaDu cells. In vivo, Sac-CL2A-FL118 showed 130 % tumor growth inhibition (TGI) at 7 mg/kg in Trop2-expressing xenografts surpassing Trodelvy®. Pharmacokinetic evaluations revealed that FL118-ADCs exhibited a 2.6-fold increase in AUC and approximately 1.7-fold higher Cmax compared to Trodelvy®, confirming their favorable profiles and supporting their potential as a promising therapeutic approach.

Hepatocellular Carcinoma and Antibody Drug Conjugates: A Systematic Review

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths, primarily associated with liver cirrhosis from factors like hepatitis B virus (HBV), hepatitis C virus (HCV), alcohol abuse, metabolic syndrome, and genetic disorders. With the rising incidence of liver cancer, particularly in HBV-endemic regions, research into novel therapies like antibody-drug conjugates (ADCs) has gained momentum. ADCs target cancer cells by attaching cytotoxic drugs to antibodies, minimizing damage to healthy tissue. Recent clinical trials have demonstrated that ADCs targeting GPC3, such as GC33 and 32A9, show promising results in reducing tumor growth and improving patient outcomes in advanced HCC. These therapies offer a potential alternative to conventional chemotherapy, marking a significant advancement in precision oncology. This systematic review was implemented using various databases like PubMed, Google Scholar, Science Direct, EBSCO, and Public Library of Science (PLoS) using regular keywords and MeSH keywords. Eligibility criteria were restricted to free full texts in the English language, humans, and publications between 2019-2024. The exclusion criteria included languages other than English and publications before 2019. A total of 26 articles were identified, and 12 articles were selected after quality assessment.

Seco-Duocarmycin SA in Aggressive Glioblastoma Cell Lines

Glioblastoma multiforme (GBM) is among the most lethal primary brain tumors and is characterized by significant cellular heterogeneity and resistance to conventional therapies. This study investigates the efficacy of seco-duocarmycin SA (seco-DSA), a novel DNA alkylating agent. Initial investigations using a colony formation assay revealed that seco-DSA exhibits remarkable potential with IC50 values lower than its natural DSA counterpart. Cell viability assay indicated that LN18 cells showed a markedly greater sensitivity to DSA than T98G cells. Furthermore, seco-DSA achieved its full cytotoxic effect within 8 h of drug incubation in GBM cell lines. Although seco-DSA induced a concentration-dependent increase in apoptotic cell death, the extent of apoptosis did not fully account for the observed decrease in cell viability. Instead, seco-DSA treatment resulted in significant cell cycle arrest in S and G2/M phases. These findings suggest that seco-DSA's cytotoxicity in GBM cells is primarily due to its ability to disrupt cell cycle progression, though the precise mechanisms of action remain to be fully established, and further research is needed. Proteomic analysis of treated cells also indicates dysregulation of proteins involved in senescence, apoptosis, and DNA repair, alluding to seco-DSA-induced arrest as a major mechanism of GBM disruption. Data are available via ProteomeXchange with the dataset identifier "PXD061023". Our reports promote the future exploration of seco-DSA's therapeutic potential, representing a critical step toward developing a more targeted and effective treatment for GBM.

Effective eradication of acute myeloid leukemia stem cells with FLT3-directed antibody-drug conjugates

Refractory disease and relapse are major challenges in acute myeloid leukemia (AML) therapy attributed to survival of leukemic stem cells (LSC). To target LSCs, antibody-drug conjugates (ADCs) provide an elegant solution, combining the specificity of antibodies with highly potent payloads. We aimed to investigate if FLT3-20D9h3-ADCs delivering either the DNA-alkylator duocarmycin (DUBA) or the microtubule-toxin monomethyl auristatin F (MMAF) can eradicate quiescent LSCs. We show here that DUBA more potently kills cell-cycle arrested AML cells compared to microtubule-targeting auristatins. Due to limited stability of 20D9h3-DUBA ADC in vivo, we analyzed both ADCs in advanced in vitro stem cell assays. 20D9h3-DUBA successfully eliminated leukemic progenitors in vitro in colony-forming unit and long-term culture initiating cell assays, both in patient cells and in patient-derived xenograft (PDX) cells. Further, it completely prevented engraftment of AML PDX leukemia-initiating cells in NSG mice. 20D9h3-MMAF had a similar effect in engraftment assays, but a less prominent effect in colony assays. Both ADCs did not affect healthy stem and progenitor cells at comparable doses providing the rationale for FLT3 as therapeutic LSC target. Collectively, we show that FLT3-directed ADCs with DUBA or MMAF have potent activity against AML LSCs and represent promising candidates for further clinical development.

Technical, preclinical, and clinical developments of Fc-glycan-specific antibody-drug conjugates

Antibody-drug conjugates (ADCs) have emerged as a powerful avenue in the therapeutic treatment of cancer. Site-specific antibody-drug conjugations represent the latest trend in the development of ADCs, addressing the limitations of traditional random conjugation technologies. This article summarizes the innovative development of Fc-glycan-specific ADCs (gsADCs), which utilize the conserved Fc N-glycan as the anchor point for site-specific conjugation. This approach offers significant strengths, including improved ADC homogeneity and overall hydrophilicity, enhanced pharmacokinetics and therapeutic index, and potentially reduced Fc receptor-mediated side effects. Currently dozens of gsADCs are in different preclinical and clinical development stages. Notably, JSKN003 and IBI343 have demonstrated promising results in phase 1 trials and are advancing into phase 3 studies. This review discusses the advantages of Fc-glycan-conjugation, various glycan-specific conjugation techniques, and the preclinical and clinical development of gsADCs. While challenges such as increased manufacturing cost for large-scale production need continuous innovation to overcome and there are different opinions regarding the pros and cons of reduced/diminished affinities to Fc gamma receptors, ongoing research and clinical progress underscore the potential of gsADCs to renovate ADC cancer therapy.

Key considerations based on pharmacokinetic/pharmacodynamic in the design of antibody-drug conjugates

Background

Antibody-drug conjugate (ADC) is an anticancer drug that links toxins to specifically targeted antibodies via linkers, offering the advantages of high target specificity and high cytotoxicity. However, complexity of its structural composition poses a greater difficulty for drug design studies.

Objectives

Pharmacokinetic/pharmacodynamic (PK/PD) based consideration of ADCs has increasingly become a hot research topic for optimal drug design in recent years, providing possible ideas for obtaining ADCs with desirable properties.

Methods

From the assessment of the ADC action process based on PK/PD, we introduce the main research strategies of ADCs. In addition, we investigated the strategies to solve the prominent problems of ADC in the clinic in recent years, and summarized and evaluated the specific ways to optimize various problems of ADC based on the PK/PD model from two perspectives of optimizing the structure and properties of the drugs themselves. Through the selection of target antigen, the optimization of the linker, the optimization of novel small molecule toxins as payload, the optimization of ADC, overcoming the multi-drug resistance of ADC, improving the ADC tumor penetration of ADC, surface modification of ADC and surface bystander effect of ADC provide a more comprehensive and accurate framework for designing new ADCs.

Results

We've expounded comprehensively on applying pharmacokinetics or pharmacodynamics while designing ADC to obtain higher efficacy and fewer side effects. From the ADC's PK/PD property while coming into play in vivo and the PK/PD study strategy, to specific ADC optimization methods and recommendations based on PK/PD, it has been study-approved that the PK/PD properties exert a subtle role in the development of ADC, whether in preclinical trials or clinical promotion.

Conclusion

The study of PK/PD unfolds the detailed mechanism of ADC action, making it easier to control related parameters in the process of designing ADC, limited efficacy and inevitable off-target toxicity remain a challenging bottleneck.

Senolytic Prodrugs: A Promising Approach to Enhancing Senescence-Targeting Intervention

Cellular senescence has emerged as a potential therapeutic target for aging and a wide range of age-related disorders. Despite the encouraging therapeutic impact of senolytic agents on improving lifespan and the outcomes of pharmacological intervention, the senolytic induced side effects pose barriers to clinical application. There is a pressing need for selective ablation of senescent cells (SnCs). The design of senolytic prodrugs has been demonstrated as a promising approach to addressing these issues. These prodrugs are generally designed via modification of senolytics with a cleavable galactose moiety to respond to the senescent biomarker - senescence-associated β-galactosidase (SA-β-gal) to restore their therapeutic effects. In this Concept, we summarize the developments by categorizing these prodrugs into two classes: 1) galactose-modified senolytic prodrugs, in which sensing unit galactose is either directly conjugated to the drug or via a self-immolative linker and 2) bioorthogonal activation of senolytic prodrugs. In the bioorthogonal prodrug design, galactose is incorporated into dihydrotetrazine to sense SA-β-gal for click activation. Notably, in addition to repurposed chemotherapeutics and small molecule inhibitors, PROTACs and photodynamic therapy have been introduced as new senolytics in the prodrug design. It is expected that the senolytic prodrugs would facilitate translating small-molecule senolytics into clinical use.

Evaluation of Double Self-Immolative Linker-Based Antibody-Drug Conjugate FDA022-BB05 with Enhanced Therapeutic Potential

Typical antibody-drug conjugates (ADCs) with valine-alanine linkage, often conjugated with the amino group in payloads, face challenges when interacting with hydroxyl group-containing payloads. Herein, we introduced a transformative Val-Ala-based double self-immolative linker-payload platform, reshaping ADCs by optimizing hydroxyl group-containing payload integration. Utilizing this platform, FDA022-BB05 was successfully conjugated with the hydroxyl group-containing payload DXd using trastuzumab (FDA022) as the monoclonal antibody (mAb). FDA022-BB05 demonstrated enhanced stability, effective cathepsin B sensitivity, reduced cell proliferation, increased bystander killing, and targeted delivery. Notably, acute toxicity evaluations in diverse preclinical models indicated favorable safety profiles and tolerability, with a broad therapeutic index in HER2-positive and -negative xenografts. Overall, these compelling findings support the promising therapeutic potential of FDA022-BB05, emphasizing the significance of diverse linker-payload platform strategies. This ADC is a valuable addition to targeted cancer therapy development, currently advancing through phase I clinical trials.

Present Scenario and Future Landscape of Payloads for ADCs: Focus on DNA-Interacting Agents

ADCs have emerged as a promising class of therapeutics, combining the targeting specificity of monoclonal antibodies with the cytotoxic potency of small-molecule drugs. Although the majority of approved ADCs are still based on microtubule binder payloads, the recent success of topoisomerase I inhibitors has revitalized interest in the identification of novel agents overcoming present limitations in the field including narrow therapeutic window and chemoresistance. The success of DNA binders as payload for ADCs has been very limited, up to now, due, among other factors, to high hydrophobicity and planar chemical structures resulting in most cases in ADCs with a strong tendency to aggregate, poor plasma stability, and limited therapeutic index. Some of these molecules, however, continue to be of interest due to their favorable properties in terms of cytotoxic potency even in chemoresistant settings, bystander and immunogenic cell death effects, and known combinability with approved drugs. We critically evaluated several clinically tested ADCs containing DNA binders, focusing on payload physicochemical properties, cytotoxic potency, and obtained clinical results. Our analysis suggests that further exploration of certain chemical classes, specifically anthracyclines and duocarmycins, based on the optimization of physicochemical parameters, reduction of cytotoxic potency, and careful design of targeting molecules is warranted. This approach will possibly result in a novel generation of payloads overcoming the limitations of clinically validated ADCs.

A Comprehensive Review of the Antitumor Properties and Mechanistic Insights of Duocarmycin Analogs

The duocarmycin family is a group of potent cytotoxic agents originally isolated from the bacterium Streptomyces. This discovery has spurred significant interest due to duocarmycins' unique chemical structures and powerful mechanism of action. This review comprehensively details the history of the duocarmycin family, the current understanding of their therapeutic potential, and the major clinical trials that have been conducted. Chemically, the duocarmycin family is characterized by a DNA-binding unit that confers specificity, a subunit-linking amide that positions the molecule within the DNA helix, and an alkylating unit that interacts with the DNA. This configuration allows them to bind selectively to the minor groove of DNA and alkylate adenine bases, a notable deviation from the more common guanine targeting performed by other alkylating agents. Duocarmycin's mechanism of action involves the formation of covalent adducts with DNA, leading to the disruption of the DNA architecture and subsequent inhibition of replication and transcription. Recent advancements in drug delivery systems, such as antibody-drug conjugates (ADCs), have further elevated the therapeutic prospects of duocarmycin analogs by providing a promising mechanism for enhancing intracellular concentrations and selective tumor delivery. Preclinical studies have highlighted the efficacy of duocarmycin derivatives in various in vitro models, providing a strong foundation for translational research. However, further biological research is required to fully understand the toxicology of duocarmycin family members before it can be clinically relevant. The major focus of this review is to cache the major biologically relevant findings of different duocarmycin analogs as well as their biological shortcomings to propose next steps in the field of cancer therapy with these potent therapeutics.

Pharmaceutical innovation and advanced biotechnology in the biotech-pharmaceutical industry for antibody-drug conjugate development

Antibody-drug conjugates (ADCs), from prototypes in the 1980s to first- and second-generation products in the 2000s, and now in their multiformats, have progressed tremendously to meet oncological challenges. Currently, 13 ADCs have been approved for medical practice, with over 200 candidates in clinical trials. Moreover, ADCs have evolved into different formats, including bispecific ADCs, probody-drug conjugates, pH-responsive ADCs, target-degrading ADCs, and immunostimulating ADCs. Technologies from biopharmaceutical industries have a crucial role in the clinical transition of these novel biotherapeutics. In this review, we highlight several features contributing to the prosperity of bioindustrial ADC development. Various proprietary technologies from biopharmaceutical companies are discussed. Such advances in biopharmaceutical industries are the backbone for the success of ADCs in development and clinical application.

Precision Medicine in Rheumatic Diseases: Unlocking the Potential of Antibody-Drug Conjugates

In the era of precision medicine, antibody-drug conjugates (ADCs) have emerged as a cutting-edge therapeutic strategy. These innovative compounds combine the precision of monoclonal antibodies with the potent cell-killing or immune-modulating abilities of attached drug payloads. This unique strategy not only reduces off-target toxicity but also enhances the therapeutic effectiveness of drugs. Beyond their well established role in oncology, ADCs are now showing promising potential in addressing the unmet needs in the therapeutics of rheumatic diseases. Rheumatic diseases, a diverse group of chronic autoimmune diseases with varying etiologies, clinical presentations, and prognoses, often demand prolonged pharmacological interventions, creating a pressing need for novel, efficient, and low-risk treatment options. ADCs, with their ability to precisely target the immune components, have emerged as a novel therapeutic strategy in this context. This review will provide an overview of the core components and mechanisms behind ADCs, a summary of the latest clinical trials of ADCs for the treatment of rheumatic diseases, and a discussion of the challenges and future prospects faced by the development of next-generation ADCs. SIGNIFICANCE STATEMENT: There is a lack of efficient and low-risk targeted therapeutics for rheumatic diseases. Antibody-drug conjugates, a class of cutting-edge therapeutic drugs, have emerged as a promising targeted therapeutic strategy for rheumatic disease. Although there is limited literature summarizing the progress of antibody-drug conjugates in the field of rheumatic disease, updating the advancements in this area provides novel insights into the development of novel antirheumatic drugs.

Implementation of antibody-drug conjugates in HER2-positive solid cancers: Recent advances and future directions

In recent decades, there has been a surge in the approval of monoclonal antibodies for treating a wide range of hematological and solid malignancies. These antibodies exhibit exceptional precision in targeting the surface antigens of tumors, heralding a groundbreaking approach to cancer therapy. Nevertheless, monoclonal antibodies alone do not show sufficient lethality against cancerous cells compared to chemotherapy. Consequently, a new class of anti-tumor medications, known as antibody-drug conjugates (ADCs), has been developed to bridge the divide between monoclonal antibodies and cytotoxic drugs, enhancing their therapeutic potential. ADCs are chemically synthesized by binding tumor-targeting monoclonal antibodies with cytotoxic payloads through linkers that are susceptible to cleavage by intracellular proteases. They combined the accurate targeting of monoclonal antibodies with the potent efficacy of cytotoxic chemotherapy drugs while circumventing systemic toxicity and boasting superior lethality over standalone targeted drugs. The human epidermal growth factor receptor (HER) family, which encompasses HER1 (also known as EGFR), HER2, HER3, and HER4, plays a key role in regulating cellular proliferation, survival, differentiation, and migration. HER2 overexpression in various tumors is one of the most frequently targeted antigens for ADC therapy in HER2-positive cancers. HER2-directed ADCs have emerged as highly promising treatment modalities for patients with HER2-positive cancers. This review focuses on three approved anti-HER2 ADCs (T-DM1, DS-8201a, and RC48) and reviews ongoing clinical trials and failed trials based on anti-HER2 ADCs. Finally, we address the notable challenges linked to ADC development and underscore potential future avenues for tackling these hurdles.

Duocarmycin SA Reduces Proliferation and Increases Apoptosis in Acute Myeloid Leukemia Cells In Vitro

Acute myeloid leukemia (AML) is a hematological malignancy that is characterized by an expansion of immature myeloid precursors. Despite therapeutic advances, the prognosis of AML patients remains poor and there is a need for the evaluation of promising therapeutic candidates to treat the disease. The objective of this study was to evaluate the efficacy of duocarmycin Stable A (DSA) in AML cells in vitro. We hypothesized that DSA would induce DNA damage in the form of DNA double-strand breaks (DSBs) and exert cytotoxic effects on AML cells within the picomolar range. Human AML cell lines Molm-14 and HL-60 were used to perform 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT), DNA DSBs, cell cycle, 5-ethynyl-2-deoxyuridine (EdU), colony formation unit (CFU), Annexin V, RNA sequencing and other assays described in this study. Our results showed that DSA induced DNA DSBs, induced cell cycle arrest at the G2M phase, reduced proliferation and increased apoptosis in AML cells. Additionally, RNA sequencing results showed that DSA regulates genes that are associated with cellular processes such as DNA repair, G2M checkpoint and apoptosis. These results suggest that DSA is efficacious in AML cells and is therefore a promising potential therapeutic candidate that can be further evaluated for the treatment of AML.

DNA Adducts in Cancer Chemotherapy

DNA adducting drugs, including alkylating agents and platinum-containing drugs, are prominent in cancer chemotherapy. Their mechanisms of action involve direct interaction with DNA, resulting in the formation of DNA addition products known as DNA adducts. While these adducts are well-accepted to induce cancer cell death, understanding of their specific chemotypes and their role in drug therapy response remain limited. This perspective aims to address this gap by investigating the metabolic activation and chemical characterization of DNA adducts formed by the U.S. FDA-approved drugs. Moreover, clinical studies on DNA adducts as potential biomarkers for predicting patient responses to drug efficacy are examined. The overarching goal is to engage the interest of medicinal chemists and stimulate further research into the use of DNA adducts as biomarkers for guiding personalized cancer treatment.

Comprehensive review on the elaboration of payloads derived from natural products for antibody-drug conjugates

Antibody-drug conjugates (ADCs) have arisen as a promising class of biotherapeutics for targeted cancer treatment, combining the specificity of monoclonal antibodies with the cytotoxicity of small-molecule drugs. The choice of an appropriate payload is crucial for the success development of ADCs, as it determines the therapeutic efficacy and safety profile. This review focuses on payloads derived from natural products, including cytotoxic agents, DNA-damaging agents, and immunomodulators. These offer several advantages such as diverse chemical structures, unique mechanism of actions, and potential for improved therapeutic index. Challenges and opportunities associated with their development were highlighted. This review underscores the significance of natural product payloads in the elaboration of ADCs, which serves as a valuable resource for researchers involved in developing and optimizing next-generation ADCs for cancer treatment.

Cancer-oocyte SAS1B protein is expressed at the cell surface of multiple solid tumors and targeted with antibody-drug conjugates

BACKGROUND

Sperm acrosomal SLLP1 binding (SAS1B) protein is found in oocytes, which is necessary for sperm-oocyte interaction, and also in uterine and pancreatic cancers. Anti-SAS1B antibody-drug conjugates (ADCs) arrested growth in these cancers. However, SAS1B expression in cancers and normal tissues has not been characterized. We hypothesized that SAS1B is expressed on the surface of other common solid cancer cells, but not on normal tissue cells, and might be selectively targeted therapeutically.

METHODS

SAS1B expression in human normal and cancer tissues was determined by immunohistochemistry, and complementary DNA (cDNA) libraries were employed to PCR amplify human SAS1B and its transcripts. Monoclonal antibodies (mAbs) to human SAS1B were generated using mouse hybridomas. SAS1B deletion constructs were developed to map SAS1B's epitope, enabling the creation of a blocking peptide. Indirect immunofluorescence (IIF) of human transfected normal and cancer cells was performed to assess SAS1B expression. SAS1B intracellular versus surface expression in normal and tumor tissues was evaluated by flow cytometry after staining with anti-SAS1B mAb, with specificity confirmed with the blocking peptide. Human cancer lines were treated with increasing mAb and ADC concentrations. ATP was quantitated as a measure of cell viability.

RESULTS

SAS1B expression was identified in a subset of human cancers and the cytoplasm of pancreatic islet cells. Two new SAS1B splice variants were deduced. Monoclonal antibodies were generated to SAS1B splice variant A. The epitope for mAbs SB2 and SB5 is between SAS1B amino acids 32-39. IIF demonstrated intracellular SAS1B expression in transfected kidney cells and on the cell surface of squamous cell lung carcinoma. Flow cytometry demonstrated intracellular SAS1B expression in all tumors and some normal cells. However, surface expression of SAS1B was identified only on cancer cells. SB2 ADC mediated dose-dependent cytotoxic killing of multiple human cancer lines.

CONCLUSION

SAS1B is a novel cancer-oocyte antigen with cell surface expression restricted to cancer cells. In vitro, it is an effective target for antibody-mediated cancer cell lysis. These findings support further exploration of SAS1B as a potential therapeutic cancer target in multiple human cancers, either with ADC or as a chimeric antigen receptor-T (CAR-T) cell target.

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.

Drug conjugates for the treatment of lung cancer: from drug discovery to clinical practice

A drug conjugate consists of a cytotoxic drug bound via a linker to a targeted ligand, allowing the targeted delivery of the drug to one or more tumor sites. This approach simultaneously reduces drug toxicity and increases efficacy, with a powerful combination of efficient killing and precise targeting. Antibody‒drug conjugates (ADCs) are the best-known type of drug conjugate, combining the specificity of antibodies with the cytotoxicity of chemotherapeutic drugs to reduce adverse reactions by preferentially targeting the payload to the tumor. The structure of ADCs has also provided inspiration for the development of additional drug conjugates. In recent years, drug conjugates such as ADCs, peptide‒drug conjugates (PDCs) and radionuclide drug conjugates (RDCs) have been approved by the Food and Drug Administration (FDA). The scope and application of drug conjugates have been expanding, including combination therapy and precise drug delivery, and a variety of new conjugation technology concepts have emerged. Additionally, new conjugation technology-based drugs have been developed in industry. In addition to chemotherapy, targeted therapy and immunotherapy, drug conjugate therapy has undergone continuous development and made significant progress in treating lung cancer in recent years, offering a promising strategy for the treatment of this disease. In this review, we discuss recent advances in the use of drug conjugates for lung cancer treatment, including structure-based drug design, mechanisms of action, clinical trials, and side effects. Furthermore, challenges, potential approaches and future prospects are presented.

Redefining bioactive small molecules from microbial metabolites as revolutionary anticancer agents

Cancer treatment remains a significant challenge due to issues such as acquired resistance to conventional therapies and the occurrence of adverse treatment-related toxicities. In recent years, researchers have turned their attention to the microbial world in search of novel and effective drugs to combat this devastating disease. Microbial derived secondary metabolites have proven to be a valuable source of biologically active compounds, which exhibit diverse functions and have demonstrated potential as treatments for various human diseases. The exploration of these compounds has provided valuable insights into their mechanisms of action against cancer cells. In-depth studies have been conducted on clinically established microbial metabolites, unraveling their anticancer properties, and shedding light on their therapeutic potential. This review aims to comprehensively examine the anticancer mechanisms of these established microbial metabolites. Additionally, it highlights the emerging therapies derived from these metabolites, offering a glimpse into the immense potential they hold for anticancer drug discovery. Furthermore, this review delves into approved treatments and major drug candidates currently undergoing clinical trials, focusing on specific molecular targets. It also addresses the challenges and issues encountered in the field of anticancer drug research and development. It also presents a comprehensive exposition of the contemporary panorama concerning microbial metabolites serving as a reservoir for anticancer agents, thereby illuminating their auspicious prospects and the prospect of forthcoming strides in the domain of cancer therapeutics.

Antibody-mimetic drug conjugate with efficient internalization activity using anti-HER2 VHH and duocarmycin

Antibody-mimetic drug conjugate (AMDC) is a cancer cell-targeted drug delivery system based on the non-covalent binding of mutated streptavidin and modified biotin, namely Cupid and Psyche. However, the development of AMDCs is hampered by difficulties in post-translational modification or poor internalization activity. Here, we report an expression, refolding, and purification method for AMDC using a variable heavy chain of heavy chain-only antibodies (VHHs). Monomeric anti-HER2 VHH fused to Cupid was expressed in Escherichia coli inclusion bodies. Solubilization and refolding at optimized reducing conditions and pH levels were selected to form a functional, tetrameric protein (anti-HER2 VHH-Cupid) that can be easily purified based on molecular weight. Anti-HER2 VHH-Cupid non-covalently creates a tight complex with Psyche linked to a potent DNA-alkylating agent, duocarmycin. This complex can be absorbed by the HER2-expressing human breast cancer cell line, KPL-4, and kills KPL-4 cells in vitro and in vivo. The production of a targeting protein with internalizing activity, combined with the non-covalent conjugation of a highly potent payload, renders AMDC a promising platform for developing cancer-targeted therapy.

Novel Thienoduocarmycin-Trastuzumab ADC Demonstrates Strong Antitumor Efficacy with Favorable Safety Profile in Preclinical Studies

New antibodies-drug conjugate (ADC) payloads overcoming chemoresistance and killing also poorly proliferating tumors at well-tolerated doses are much desired. Duocarmycins are a well-known class of highly potent cytotoxic agents, with DNA minor groove-binding and alkylation properties, active also in chemoresistant tumors. Although different duocarmycin derivatives have been used during the years as payloads for ADC production, unfavorable physicochemical properties impaired the production of ADCs with optimal features. Optimization of the toxin to balance reactivity and stability features and best linker selection allowed us to develop the novel duocarmycin-like payload-linker NMS-P945 suitable for conjugation to mAbs with reproducible drug-antibody ratio (DAR) >3.5. When conjugated to trastuzumab, it generated an ADC with good internalization properties, ability to induce bystander effect and immunogenic cell death. Moreover, it showed strong target-driven activity in cells and cytotoxic activity superior to trastuzumab deruxtecan tested, in parallel, in cell lines with HER2 expression. High in vivo efficacy with cured mice at well-tolerated doses in HER2-driven models was also observed. A developed pharmacokinetic/pharmacodynamic (PK/PD) model based on efficacy in mice and cynomolgus monkey PK data, predicted tumor regression in patients upon administration of 2 doses of trastuzumab-NMS-P945-ADC at 0.5 mg/kg. Thus, considering the superior physicochemical features for ADC production and preclinical results obtained with the model trastuzumab ADC, including bystander effect, immunogenic cell death and activity in chemoresistant tumors, NMS-P945 represents a highly effective, innovative payload for the creation of novel, next-generation ADCs.

Antibody-Drug Conjugates and Ocular Toxicity

Antibody-drug conjugates (ADCs) are a growing class of chemotherapeutic agents for the purpose of treating cancers that often have relapsed or failed first- and second-line treatments. ADCs are composed of extremely potent cytotoxins with a variety of side effects, one of the most significant being ocular toxicity. The available literature describes these toxicities as varying in severity and in incidence, although with disparate methods of evaluation and management. Some of the most common toxicities include microcyst-like epithelial keratopathy and dry eye. We discuss proposed mechanisms of ocular toxicity and describe the reports that mention these toxicities. We focus on ADCs with the most published literature and the most significant effects on ocular tissue. We propose areas for further investigation and possible ideas of future management. We provide a comprehensive look at the reports of ADCs in current literature to better inform clinicians on an expanding drug class.

Trends in the Development of Antibody-Drug Conjugates for Cancer Therapy

In cancer treatment, the first-generation, cytotoxic drugs, though effective against cancer cells, also harmed healthy ones. The second-generation targeted cancer cells precisely to inhibit their growth. Enter the third-generation, consisting of immuno-oncology drugs, designed to combat drug resistance and bolster the immune system's defenses. These advanced therapies operate by obstructing the uncontrolled growth and spread of cancer cells through the body, ultimately eliminating them effectively. Within the arsenal of cancer treatment, monoclonal antibodies offer several advantages, including inducing cancer cell apoptosis, precise targeting, prolonged presence in the body, and minimal side effects. A recent development in cancer therapy is Antibody-Drug Conjugates (ADCs), initially developed in the mid-20th century. The second generation of ADCs addressed this issue through innovative antibody modification techniques, such as DAR regulation, amino acid substitutions, incorporation of non-natural amino acids, and enzymatic drug attachment. Currently, a third generation of ADCs is in development. This study presents an overview of 12 available ADCs, reviews 71 recent research papers, and analyzes 128 clinical trial reports. The overarching objective is to gain insights into the prevailing trends in ADC research and development, with a particular focus on emerging frontiers like potential targets, linkers, and drug payloads within the realm of cancer treatment.

Antibody-Drug Conjugates in Solid Tumor Oncology: An Effectiveness Payday with a Targeted Payload

Antibody-drug conjugates (ADCs) are at the forefront of the drug development revolution occurring in oncology. Formed from three main components-an antibody, a linker molecule, and a cytotoxic agent ("payload"), ADCs have the unique ability to deliver cytotoxic agents to cells expressing a specific antigen, a great leap forward from traditional chemotherapeutic approaches that cause widespread effects without specificity. A variety of payloads can be used, including most frequently microtubular inhibitors (auristatins and maytansinoids), as well as topoisomerase inhibitors and alkylating agents. Finally, linkers play a critical role in the ADCs' effect, as cleavable moieties that serve as linkers impact site-specific activation as well as bystander killing effects, an upshot that is especially important in solid tumors that often express a variety of antigens. While ADCs were initially used in hematologic malignancies, their utility has been demonstrated in multiple solid tumor malignancies, including breast, gastrointestinal, lung, cervical, ovarian, and urothelial cancers. Currently, six ADCs are FDA-approved for the treatment of solid tumors: ado-trastuzumab emtansine and trastuzumab deruxtecan, both anti-HER2; enfortumab-vedotin, targeting nectin-4; sacituzuzmab govitecan, targeting Trop2; tisotumab vedotin, targeting tissue factor; and mirvetuximab soravtansine, targeting folate receptor-alpha. Although they demonstrate utility and tolerable safety profiles, ADCs may become ineffective as tumor cells undergo evolution to avoid expressing the specific antigen being targeted. Furthermore, the current cost of ADCs can be limiting their reach. Here, we review the structure and functions of ADCs, as well as ongoing clinical investigations into novel ADCs and their potential as treatments of solid malignancies.

Natural products as a source of cytotoxic warheads in antibody-drug conjugates

Antibody-drug conjugates (ADCs) are one of the most rapidly expanding classes of oncology therapeutics. Till now, 11 ADCs have been approved by USFDA, with the first ADC approval of gemtuzumab ozogamicin (Mylotarg) in 2000. A large number of ADCs are being evaluated in different stages of clinical trials and pre-clinical studies. Interestingly, the cytotoxic warheads of the all approved ADCs, as well as clinical and preclinical candidates, belong to different classes of natural products viz. calicheamicins, auristatins, maytansinoids, camptothecin derivatives, pyrolidobenzodiazepines (PBDs), and duocarmycins, etc. Herein, a review of the natural product-based cytotoxic warheads, briefly discussing their source, modifications, and mechanism of action, has been conducted.

Antibody-Drug Conjugates in Breast Cancer: Ascent to Destiny and Beyond-A 2023 Review

Antibody-drug conjugates (ADCs) are revolutionizing cancer treatment, adding another important new class of systemic therapy. ADCs are a specially designed class of therapeutics that target cells expressing specific cancer antigens using directed antibody-drug delivery and release a cytotoxic chemotherapeutic payload. Over the past two decades, improvements in ADC design, development, and research, particularly in breast cancer, have led to several recent landmark publications. These advances have significantly changed various treatment paradigms and revamped traditional classifications of breast cancer with the introduction of a potential new subtype: "HER2-low". This review will focus on several ADCs developed for breast cancer treatment, including trastuzumab emtansine (T-DM1), trastuzumab deruxtecan (T-DXd), sacituzumab govitecan (SG) and other newer emerging agents. It will provide an overview of the role of ADCs in breast cancer and discuss the opportunities and challenges they present. Additionally, our review will discuss future research directions to improve the selection of targets, combination therapies, and aim to improve drug safety. Important first-line metastatic and adjuvant clinical trials are underway, which may expand the role of ADC therapy in breast cancer. We foresee ADCs driving a new era of breast cancer treatment, adding to the steady incremental survival advantage observed in recent years.

Comparison of Pyrrolobenzodiazepine Dimer Bis-imine versus Mono-imine: DNA Interstrand Cross-linking, Cytotoxicity, Antibody-Drug Conjugate Efficacy and Toxicity

Antibody-drug conjugates (ADC) delivering pyrrolobenzodiazepine (PBD) DNA cross-linkers are currently being evaluated in clinical trials, with encouraging results in Hodgkin and non-Hodgkin lymphomas. The first example of an ADC delivering a PBD DNA cross-linker (loncastuximab tesirine) has been recently approved by the FDA for the treatment of relapsed and refractory diffuse large B-cell lymphoma. There has also been considerable interest in mono-alkylating PBD analogs. We conducted a head-to-head comparison of a conventional PBD bis-imine and a novel PBD mono-imine. Key Mitsunobu chemistry allowed clean and convenient access to the mono-imine class. Extensive DNA-binding studies revealed that the mono-imine mediated a type of DNA interaction that is described as "pseudo cross-linking," as well as alkylation. The PBD mono-imine ADC demonstrated robust antitumor activity in mice bearing human tumor xenografts at doses 3-fold higher than those that were efficacious for the PBD bis-imine ADC. A single-dose toxicology study in rats demonstrated that the MTD of the PBD mono-alkylator ADC was approximately 3-fold higher than that of the ADC bearing a bis-imine payload, suggesting a comparable therapeutic index for this molecule. However, although both ADCs caused myelosuppression, renal toxicity was observed only for the bis-imine, indicating possible differences in toxicologic profiles that could influence tolerability and therapeutic index. These data show that mono-amine PBDs have physicochemical and pharmacotoxicologic properties distinct from their cross-linking analogs and support their potential utility as a novel class of ADC payload.

Amplification of the PLAG-family genes-PLAGL1 and PLAGL2-is a key feature of the novel tumor type CNS embryonal tumor with PLAGL amplification

Pediatric central nervous system (CNS) tumors represent the most common cause of cancer-related death in children aged 0-14 years. They differ from their adult counterparts, showing extensive clinical and molecular heterogeneity as well as a challenging histopathological spectrum that often impairs accurate diagnosis. Here, we use DNA methylation-based CNS tumor classification in combination with copy number, RNA-seq, and ChIP-seq analysis to characterize a newly identified CNS tumor type. In addition, we report histology, patient characteristics, and survival data in this tumor type. We describe a biologically distinct pediatric CNS tumor type (n = 31 cases) that is characterized by focal high-level amplification and resultant overexpression of either PLAGL1 or PLAGL2, and an absence of recurrent genetic alterations characteristic of other pediatric CNS tumor types. Both genes act as transcription factors for a regulatory subset of imprinted genes (IGs), components of the Wnt/β-Catenin pathway, and the potential drug targets RET and CYP2W1, which are also specifically overexpressed in this tumor type. A derived PLAGL-specific gene expression signature indicates dysregulation of imprinting control and differentiation/development. These tumors occurred throughout the neuroaxis including the cerebral hemispheres, cerebellum, and brainstem, and were predominantly composed of primitive embryonal-like cells lacking robust expression of markers of glial or neuronal differentiation (e.g., GFAP, OLIG2, and synaptophysin). Tumors with PLAGL1 amplification were typically diagnosed during adolescence (median age 10.5 years), whereas those with PLAGL2 amplification were diagnosed during early childhood (median age 2 years). The 10-year overall survival was 66% for PLAGL1-amplified tumors, 25% for PLAGL2-amplified tumors, 18% for male patients, and 82% for female patients. In summary, we describe a new type of biologically distinct CNS tumor characterized by PLAGL1/2 amplification that occurs predominantly in infants and toddlers (PLAGL2) or adolescents (PLAGL1) which we consider best classified as a CNS embryonal tumor and which is associated with intermediate survival. The cell of origin and optimal treatment strategies remain to be defined.

40 Years of Duocarmycins: A Graphical Structure/Function Review of Their Chemical Evolution, from SAR to Prodrugs and ADCs

Synthetic analogues of the DNA-alkylating cytotoxins of the duocarmycin class have been extensively investigated in the past 40 years, driven by their high potency, their unusual mechanism of bioactivity, and the beautiful modularity of their structure-activity relationship (SAR). This Perspective analyzes how the molecular designs of synthetic duocarmycins have evolved: from (1) early SAR studies, through to modern applications for directed cancer therapy as (2) prodrugs and (3) antibody-drug conjugates in late-stage clinical development. Analyzing 583 primary research articles and patents from 1978 to 2022, we distill out a searchable A0-format "Minard map" poster of ca. 200 key structure/function-tuning steps tracing chemical developments across these three key areas. This structure-based overview showcases the ingenious approaches to tune and target bioactivity, that continue to drive development of the elegant and powerful duocarmycin platform.

Heterogeneity of triple-negative breast cancer: understanding the Daedalian labyrinth and how it could reveal new drug targets

INTRODUCTION

Triple-negative breast cancer (TNBC) is considered the most aggressive breast cancer subtype with the least favorable outcomes. However, recent research efforts have generated an enhanced knowledge of the biology of the disease and have provided a new, more comprehensive understanding of the multifaceted ecosystem that underpins TNBC.

AREAS COVERED

In this review, the authors illustrate the principal biological characteristics of TNBC, the molecular driver alterations, targetable genes, and the biomarkers of immune engagement that have been identified across the subgroups of TNBC. Accordingly, the authors summarize the landscape of the innovative and investigative biomarker-driven therapeutic options in TNBC that emerge from the unique biological basis of the disease.

EXPERT OPINION

The therapeutic setting of TNBC is rapidly evolving. An enriched understanding of the tumor spatial and temporal heterogeneity and the surrounding microenvironment of this complex disease can effectively support the development of novel and tailored opportunities of treatment.

Novel ADCs and Strategies to Overcome Resistance to Anti-HER2 ADCs

During recent years, a number of new compounds against HER2 have reached clinics, improving the prognosis and quality of life of HER2-positive breast cancer patients. Nonetheless, resistance to standard-of-care drugs has motivated the development of novel agents, such as new antibody-drug conjugates (ADCs). The latter are a group of drugs that benefit from the potency of cytotoxic agents whose action is specifically guided to the tumor by the target-specific antibody. Two anti-HER2 ADCs have reached the clinic: trastuzumab-emtansine and, more recently, trastuzumab-deruxtecan. In addition, several other HER2-targeted ADCs are in preclinical or clinical development, some of them with promising signs of activity. In the present review, the structure, mechanism of action, and potential resistance to all these ADCs will be described. Specific attention will be given to discussing novel strategies to circumvent resistance to ADCs.

Multiplexed Quantitative Analysis of Antibody-Drug Conjugates with Labile CBI-Dimer Payloads In Vivo Using Immunoaffinity LC-MS/MS

Quantitative analysis of antibody-drug conjugates (ADCs) involves cleavage of ADCs into smaller analytes representing different components and subsequent measurements from multiple assays for a more comprehensive pharmacokinetic (PK) assessment. Multiple PK analytes including the drug remaining conjugated to the antibody (or antibody-conjugated drug, acDrug) and total antibody can be accessed simultaneously using a multiplex assay by proteolytic digestion of an ADC, if the sites of conjugation are homogeneous for an ADC and the linker drug is stable to proteases. Herein, a multiplexed immunoaffinity liquid chromatography-mass spectrometry (LC-MS)/MS PK assay is described involving immunoaffinity enrichment, enzymatic conversion of prodrug, trypsin digestion, and LC-MS/MS as applied to next-generation ADCs constructed from linker drugs bearing dimeric cyclopropabenzindole (CBI) payloads (duocarmycin analogues). The cytotoxic payload is chemically labile, requiring extensive optimization in sample preparation steps to stabilize the drug without ex vivo modification and to convert the prodrug into a single active form of the drug. The qualification data for this assay format showed that this approach provides robust acDrug and total antibody data and can be extended to ADCs with different monoclonal antibody frameworks and linker chemistries. Applications of this multiplexed assay to support preclinical studies are presented.

Targeting the immune checkpoint B7-H3 for next-generation cancer immunotherapy

Immune checkpoint inhibitors (ICIs) for programmed death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) have become preferred treatment strategies for several advanced cancers. However, response rates for these treatments are limited, which encourages the search for new ICI candidates. Recent reports have underscored significant roles of B7 homolog 3 protein (B7-H3) in tumor immunity and disease progression. While its multifaceted roles are being elucidated, B7-H3 has already entered clinical trials as a therapeutic target. In this review, we overview the recent results of clinical trials evaluating the antitumor activity and safety of B7-H3 targeting drugs. On this basis, we also discuss the challenges and opportunities arising from the application of these drugs. Finally, we point out current gaps to address in the understanding of B7-H3 function and regulation in order to fully unleash the future clinical utility of B7-H3-based therapies for the treatment of cancer.

Antibody-Antineoplastic Conjugates in Gynecological Malignancies: Current Status and Future Perspectives

In the last decade, antibody-drug conjugates (ADCs), normally formed by a humanized antibody and a small drug via a chemical cleavable or non-cleavable linker, have emerged as a potential treatment strategy in cancer disease. They allow to get a selective delivery of the chemotherapeutic agents at the tumor level, and, consequently, to improve the antitumor efficacy and, especially to decrease chemotherapy-related toxicity. Currently, nine antibody-drug conjugate-based formulations have been already approved and more than 80 are under clinical trials for the treatment of several tumors, especially breast cancer, lymphomas, and multiple myeloma. To date, no ADCs have been approved for the treatment of gynecological formulations, but many formulations have been developed and have reached the clinical stage, especially for the treatment of ovarian cancer, an aggressive disease with a low five-year survival rate. This manuscript analyzes the ADCs formulations that are under clinical research in the treatment of gynecological carcinomas, specifically ovarian, endometrial, and cervical tumors.