Resistance to Antibody-Drug Conjugates

Antibody-Drug Conjugate Targets, Drugs and Linkers

Antibody-drug conjugates offer the possibility of directing powerful cytotoxic agents to a malignant tumor while sparing normal tissue. The challenge is to select an antibody target expressed exclusively or at highly elevated levels on the surface of tumor cells and either not all or at low levels on normal cells. The current review explores 78 targets that have been explored as antibody-drug conjugate targets. Some of these targets have been abandoned, 9 or more are the targets of FDA-approved drugs, and most remain active clinical interest. Antibody-drug conjugates require potent cytotoxic drug payloads, several of these small molecules are discussed, as are the linkers between the protein component and small molecule components of the conjugates. Finally, conclusions regarding the elements for the successful antibody-drug conjugate are discussed.

A branched small molecule-drug conjugate nanomedicine strategy for the targeted HCC chemotherapy

Off-target toxicity is one of the main challenges faced by anticancer chemotherapeutics. For tumor targeted and precision chemotherapy, we take the advantages of the ligand directed tumor active targeting of small molecule drug conjugates (SMDCs) and the passive tumor targeting of nanoparticles via the enhanced penetration and retention (EPR) effects, put forward a branched small molecule drug conjugate (BSMDC) nanomedicine design concept. In a proof of concept, we used pentaerythritol as the branched moiety, galactosamine (GalN) as the hepatocellular carcinoma (HCC) directing ligands, PTX as a payload, and a stearoyl moiety as the amphiphilic property adjusting group, designed and synthesized BSMDC 1 and prepared its NPs. In cellular level, the BSMDC 1 NPs targeted asialoglycoprotein receptor (ASGPR)-overexpressing HepG2 cells, were effectively taken up in the cells and released in tumor microenvironments, inhibited the HepG2 cell proliferation, arrested HepG2 cell in G2/M phase and induced tumor cell apoptosis. In HepG2 xenograft nude mice, the BSMDC 1 NPs were high specific to target the tumor and demonstrated a higher antitumor efficiency than BSMDC 1, having no apparent influences on mice body weights and major organs, supporting our BSMDC nanomedicine design concept. Therefore, this new strategy may find applications for cancer targeted and precision chemotherapy.

Patritumab Deruxtecan: Paving the Way for EGFR-TKI-Resistant NSCLC

HER3 is ubiquitously expressed in EGFR-mutant non-small cell lung cancer (NSCLC) irrespective of resistant mechanisms to EGFR tyrosine kinase inhibitors, thus garnering attention as a valuable therapeutic target. In this issue of Cancer Discovery, Jänne and colleagues highlight early clinical data supporting patritumab deruxtecan as a potentially appreciable agent for previously treated EGFR-mutant NSCLC.See related article by Jänne et al., p. 74.

Synthesis and preliminary evaluation of octreotate conjugates of bioactive synthetic amatoxins for targeting somatostatin receptor (sstr2) expressing cells

Targeted cancer therapy represents a paradigm-shifting approach that aims to deliver a toxic payload selectively to target-expressing cells thereby sparing normal tissues the off-target effects associated with traditional chemotherapeutics. Since most targeted constructs rely on standard microtubule inhibitors or DNA-reactive molecules as payloads, new toxins that inhibit other intracellular targets are needed to realize the full potential of targeted therapy. Among these new payloads, α-amanitin has gained attraction as a payload in targeted therapy. Here, we conjugate two synthetic amanitins at different sites to demonstrate their utility as payloads in peptide drug conjugates (PDCs). As an exemplary targeting agent, we chose octreotate, a well-studied somatostatin receptor (sstr2) peptide agonist for the conjugation to synthetic amatoxins via three tailor-built linkers. The linker chemistry permitted the evaluation of one non-cleavable and two cleavable self-immolative conjugates. The immolating linkers were chosen to take advantage of either the reducing potential of the intracellular environment or the high levels of lysosomal proteases in tumor cells to trigger toxin release. Cell-based assays on target-positive Ar42J cells revealed target-specific reduction in viability with up to 1000-fold enhancement in bioactivity compared to the untargeted amatoxins. Altogether, this preliminary study enabled the development of a highly modular synthetic platform for the construction of amanitin-based conjugates that can be readily extended to various targeting moieties.

Specific ablation of PDGFRβ-overexpressing pericytes with antibody-drug conjugate potently inhibits pathologic ocular neovascularization in mouse models

BACKGROUND

Crosstalk between pericytes and endothelial cells is critical for ocular neovascularization. Endothelial cells secrete platelet-derived growth factor (PDGF)-BB and recruit PDGF receptor β (PDGFRβ)-overexpressing pericytes, which in turn cover and stabilize neovessels, independent of vascular endothelial growth factor (VEGF). Therapeutic agents inhibiting PDGF-BB/PDGFRβ signaling were tested in clinical trials but failed to provide additional benefits over anti-VEGF agents. We tested whether an antibody-drug conjugate (ADC) - an engineered monoclonal antibody linked to a cytotoxic agent - could selectively ablate pericytes and suppress retinal and choroidal neovascularization.

METHODS

Immunoblotting, flow cytometry, cell viability test, and confocal microscopy were conducted to assess the internalization and cytotoxic effect of ADC targeting mPDGFRβ in an in vitro setting. Immunofluorescence staining of whole-mount retinas and retinal pigment epithelium-choroid-scleral complexes, electroretinography, and OptoMotry test were used to evaluate the effect and safety of ADC targeting mPDGFRβ in the mouse models of pathologic ocular neovascularization.

RESULTS

ADC targeting mPDGFRβ is effectively internalized into mouse brain vascular pericytes and showed significant cytotoxicity compared with the control ADC. We also show that specific ablation of PDGFRβ-overexpressing pericytes using an ADC potently inhibits pathologic ocular neovascularization in mouse models of oxygen-induced retinopathy and laser-induced choroidal neovascularization, while not provoking generalized retinal toxicity.

CONCLUSION

Our results suggest that removing PDGFRβ-expressing pericytes by an ADC targeting PDGFRβ could be a potential therapeutic strategy for pathologic ocular neovascularization.

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.

Barriers to achieving a cure in lymphoma

Lymphoma is a diverse disease with a variety of different subtypes, each characterized by unique pathophysiology, tumor microenvironment, and underlying signaling pathways leading to oncogenesis. With our increasing understanding of the molecular biology of lymphoma, there have been a number of novel targeted therapies and immunotherapy approaches that have been developed for the treatment of this complex disease. Despite rapid progress in the field, however, many patients still relapse largely due to the development of drug resistance to these therapies. A better understanding of the mechanisms underlying resistance is needed to develop more novel treatment strategies that circumvent these mechanisms and design better treatment algorithms that personalize therapies to patients and sequence these therapies in the most optimal manner. This review focuses on the recent advances in therapies in lymphoma, including targeted therapies, monoclonal antibodies, antibody-drug conjugates, cellular therapy, bispecific antibodies, and checkpoint inhibitors. We discuss the genetic and cellular principles of drug resistance that span across all the therapies, as well as some of the unique mechanisms of resistance that are specific to these individual classes of therapies and the strategies that have been developed to address these modes of resistance.

Discovery of targeted expression data for novel antibody-based and chimeric antigen receptor-based therapeutics in soft tissue sarcomas using RNA-sequencing: clinical implications

Recent failure of phase 3 trials and paucity of druggable oncogenic drivers hamper developmental therapeutics in sarcomas. Antibody-based therapeutics, like antibody-drug conjugates (ADCs) and chimeric antigen receptor (CAR)-based therapeutics, have emerged as promising strategies for anticancer drug delivery. The efficacy of these novel therapies is highly dependent on expression of the antibody target. We used RNA sequencing data from Cancer Genome Atlas (TCGA) to analyze expression of target antigens in sarcoma subtypes including dedifferentiated liposarcoma (DDLPS; n = 50), uterine leiomyosarcoma (ULMS; n = 27), leiomyosarcoma (STLMS; n = 53), undifferentiated pleomorphic sarcoma (UPS; n = 44), myxofibrosarcoma (MFS; n = 17), synovial sarcoma (SS; n = 10), and malignant peripheral nerve sheath tumor (MPNST; n = 5). We searched published literature and clinicaltrial.gov for ADC targets, bispecific antibodies, immunotoxins, radioimmunoconjugates, SPEAR T-cells, and CAR's that are in clinical trials. CD70 expression was significantly higher in DDLPS, UPS, and MFS than SS and STLMS. CDH3 expression was greater in LMS and ULMS than UPS (P < 0.001), MFS (P < 0.001), and DDLPS (P < 0.001). ERBB2 expression was low; however, it was overexpressed in MPNST when compared with UPS (P < 0.001), and MFS (P < 0.01). GPNMB was highly expressed in most sarcomas, with the exception of SS. LRRC15 also appeared to be a relevant target, especially in UPS. MSLN expression was relatively low except in SS and MPNST. PDGFRA was also highly expressed in most sarcomas with the exception of ULMS and STLMS. TNFRSF8 seems to be most appropriate in DDLPS, as well as MFS. AXL was expressed especially in MFS and STLMS. Sarcoma subtypes express multiple target genes relevant for ADCs, SPEAR T-cells and CAR's, warranting further clinical validation and evaluation.

Antibody-Drug Conjugates: Functional Principles and Applications in Oncology and Beyond

In the era of precision medicine, antibody-based therapeutics are rapidly enriched with emerging advances and new proof-of-concept formats. In this context, antibody-drug conjugates (ADCs) have evolved to merge the high selectivity and specificity of monoclonal antibodies (mAbs) with the cytotoxic potency of attached payloads. So far, ten ADCs have been approved by FDA for oncological indications and many others are currently being tested in clinical and preclinical level. This paper summarizes the essential components of ADCs, from their functional principles and structure up to their limitations and resistance mechanisms, focusing on all latest bioengineering breakthroughs such as bispecific mAbs, dual-drug platforms as well as novel linkers and conjugation chemistries. In continuation of our recent review on anticancer implication of ADC's technology, further insights regarding their potential usage outside of the oncological spectrum are also presented. Better understanding of immunoconjugates could maximize their efficacy and optimize their safety, extending their use in everyday clinical practice.

Generation of Antibody-Drug Conjugate Resistant Models

Simple Summary

Antibody-drug conjugates (ADCs) constitute new and effective therapies in cancer. However, resistance is frequently observed in treated patients after a given period of time. That resistance may be present from the beginning of the treatment (primary or de novo resistance) or raise after an initial response to the ADC (secondary resistance). Knowing the causes of those resistances is a necessity in the field as it may help in designing strategies to overcome them. Because of that, it is necessary to develop models that allow the identification of mechanisms of resistance. In this review, we present different approaches that have been used to model ADC resistance in the preclinical setting, and that include the use of established cell lines, patient-derived ex vivo cultures and xenografts primarily or secondarily resistant to the ADC.

Abstract

In the last 20 years, antibody-drug conjugates (ADCs) have been incorporated into the oncology clinic as treatments for several types of cancer. So far, the Food and Drug Administration (FDA) has approved 11 ADCs and other ADCs are in the late stages of clinical development. Despite the efficacy of this type of drug, the tumors of some patients may result in resistance to ADCs. Due to this, it is essential not only to comprehend resistance mechanisms but also to develop strategies to overcome resistance to ADCs. To reach these goals, the generation and use of preclinical models to study those mechanisms of resistance are critical. Some cells or patient tumors may result in primary resistance to the action of an ADC, even if they express the antigen against which the ADC is directed. Isolated primary tumoral cells, cell lines, or patient explants (patient-derived xenografts) with these characteristics can be used to study primary resistance. The most common method to generate models of secondary resistance is to treat cancer cell lines or tumors with an ADC. Two strategies, either continuous treatment with the ADC or intermittent treatment, have successfully been used to develop those resistance models.

Recent advances in trophoblast cell-surface antigen 2 targeted therapy for solid tumors

Trophoblast cell-surface antigen 2 (Trop 2) is a transmembrane glycoprotein that is highly expressed in various cancer types with relatively low or no baseline expression in most normal tissues. Its overexpression is associated with tumor growth and poor prognosis; Trop 2 is, therefore, an ideal therapeutic target for epithelial cancers. Several Trop 2 targeted therapeutics have recently been developed for the treatment of cancers, such as anti-Trop 2 antibodies and antibody-drug conjugates (ADCs), as well as Trop 2-specific cell therapy. In particular, the safety and clinical benefit of Trop 2-based ADCs have been demonstrated in clinical trials across multiple tumor types, including those with limited treatment options, such as triple-negative breast cancer, platinum-resistant urothelial cancer, and heavily pretreated non-small cell lung cancer. In this review, we elaborate on recent advances in Trop 2 targeted modalities and provide an overview of novel insights for future developments in this field.

Parallel Genomic Alterations of Antigen and Payload Targets Mediate Polyclonal Acquired Clinical Resistance to Sacituzumab Govitecan in Triple-Negative Breast Cancer

Sacituzumab govitecan (SG), the first antibody-drug conjugate (ADC) approved for triple-negative breast cancer, incorporates the anti-TROP2 antibody hRS7 conjugated to a topoisomerase-1 (TOP1) inhibitor payload. We sought to identify mechanisms of SG resistance through RNA and whole-exome sequencing of pretreatment and postprogression specimens. One patient exhibiting de novo progression lacked TROP2 expression, in contrast to robust TROP2 expression and focal genomic amplification of TACSTD2/TROP2 observed in a patient with a deep, prolonged response to SG. Analysis of acquired genomic resistance in this case revealed one phylogenetic branch harboring a canonical TOP1 ^E418K resistance mutation and subsequent frameshift TOP1 mutation, whereas a distinct branch exhibited a novel TACSTD2/TROP2 ^T256R missense mutation. Reconstitution experiments demonstrated that TROP2^T256R confers SG resistance via defective plasma membrane localization and reduced cell-surface binding by hRS7. These findings highlight parallel genomic alterations in both antibody and payload targets associated with resistance to SG. SIGNIFICANCE: These findings underscore TROP2 as a response determinant and reveal acquired SG resistance mechanisms involving the direct antibody and drug payload targets in distinct metastatic subclones of an individual patient. This study highlights the specificity of SG and illustrates how such mechanisms will inform therapeutic strategies to overcome ADC resistance.This article is highlighted in the In This Issue feature, p. 2355.

Advances and Limitations of Antibody Drug Conjugates for Cancer

The popularity of antibody drug conjugates (ADCs) has increased in recent years, mainly due to their unrivalled efficacy and specificity over chemotherapy agents. The success of the ADC is partly based on the stability and successful cleavage of selective linkers for the delivery of the payload. The current research focuses on overcoming intrinsic shortcomings that impact the successful development of ADCs. This review summarizes marketed and recently approved ADCs, compares the features of various linker designs and payloads commonly used for ADC conjugation, and outlines cancer specific ADCs that are currently in late-stage clinical trials for the treatment of cancer. In addition, it addresses the issues surrounding drug resistance and strategies to overcome resistance, the impact of a narrow therapeutic index on treatment outcomes, the impact of drug-antibody ratio (DAR) and hydrophobicity on ADC clearance and protein aggregation.

Impact of Endocytosis Mechanisms for the Receptors Targeted by the Currently Approved Antibody-Drug Conjugates (ADCs)-A Necessity for Future ADC Research and Development

Biologically-based therapies increasingly rely on the endocytic cycle of internalization and exocytosis of target receptors for cancer therapies. However, receptor trafficking pathways (endosomal sorting (recycling, lysosome localization) and lateral membrane movement) are often dysfunctional in cancer. Antibody-drug conjugates (ADCs) have revitalized the concept of targeted chemotherapy by coupling inhibitory antibodies to cytotoxic payloads. Significant advances in ADC technology and format, and target biology have hastened the FDA approval of nine ADCs (four since 2019). Although the links between aberrant endocytic machinery and cancer are emerging, the impact of dysregulated internalization processes of ADC targets and response rates or resistance have not been well studied. This is despite the reliance on ADC uptake and trafficking to lysosomes for linker cleavage and payload release. In this review, we describe what is known about all the target antigens for the currently approved ADCs. Specifically, internalization efficiency and relevant intracellular sorting activities are described for each receptor under normal processes, and when complexed to an ADC. In addition, we discuss aberrant endocytic processes that have been directly linked to preclinical ADC resistance mechanisms. The implications of endocytosis in regard to therapeutic effectiveness in the clinic are also described. Unexpectedly, information on endocytosis is scarce (absent for two receptors). Moreover, much of what is known about endocytosis is not in the context of receptor-ADC/antibody complexes. This review provides a deeper understanding of the pertinent principles of receptor endocytosis for the currently approved ADCs.

Antibody-drug conjugates, immune-checkpoint inhibitors, and their combination in breast cancer therapeutics

INTRODUCTION

Advanced breast cancer (aBC) remains incurable and the quest for more effective systemic anticancer agents continues. Promising results have led to the FDA approval of three antibody-drug conjugates (ADCs) and two immune checkpoint inhibitors (ICIs) to date for patients with aBC.

AREAS COVERED

With the anticipated emergence of newer ADCs and ICIs for patients with several subtypes of breast cancer, and given their potential synergy, their use in combination is of clinical interest. In this article, we review the use of ADCs and ICIs in patients with breast cancer, assess the scientific rationale for their combination, and provide an overview of ongoing trials and some early efficacy and safety results of such dual therapy.

EXPERT OPINION

Improvement in the medicinal chemistry of next-generation ADCs, their rational combination with ICIs and other agents, and the development of multiparametric immune biomarkers could help to significantly improve the outlook for patients with refractory aBC.

Contemporary Approaches for Site-Selective Dual Functionalization of Proteins

Site-selective protein functionalization serves as an invaluable tool for investigating protein structures and functions in complicated cellular environments and accomplishing semi-synthetic protein conjugates such as traceable therapeutics with improved features. Dual functionalization of proteins allows the incorporation of two different types of functionalities at distinct location(s), which greatly expands the features of native proteins. The attachment and crosstalk of a fluorescence donor and an acceptor dye provides fundamental insights into the folding and structural changes of proteins upon ligand binding in their native cellular environments. Moreover, the combination of drug molecules with different modes of action, imaging agents or stabilizing polymers provides new avenues to design precision protein therapeutics in a reproducible and well-characterizable fashion. This review aims to give a timely overview of the recent advancements and a future perspective of this relatively new research area. First, the chemical toolbox for dual functionalization of proteins is discussed and compared. The strengths and limitations of each strategy are summarized in order to enable readers to select the most appropriate method for their envisaged applications. Thereafter, representative applications of these dual-modified protein bioconjugates benefiting from the synergistic/additive properties of the two synthetic moieties are highlighted.

Structural changes of corneal epithelium in belantamab-associated superficial keratopathy using anterior segment optical coherence tomography

Purpose

To describe structural changes in corneal epithelium using anterior segment optical coherence tomography (AS-OCT) in two relapsed and refractory multiple myeloma (RRMM) patients with bilateral belantamab-associated superficial keratopathy (BASK).

Observations case 1

A 56-year-old male who was diagnosed with RRMM and initiated on belantamab mafodotin, presented on day 42 (three weeks after the second infusion) with decreased pinhole visual acuity from 20/20 and 20/25 to 20/70 and 20/50 in the right eye and left eye, respectively. Slit-lamp examination revealed moderate superficial keratopathy with microcystic-like epithelial changes (MECs) in the paracentral cornea in both eyes. AS-OCT demonstrated increased bilateral heterogeneous signal intensity and hyperreflective lesions as well as increased thickness in the paracentral corneal epithelium with uninvolved central cornea. Given bilateral MECs, the third infusion was withheld, and then given on day 62 after five weeks of drug-free interval. Although MECs had improved on day 82, pinhole visual acuity remained at 20/50 and 20/40 in the right eye and the left eye. AS-OCT showed that hyperreflective lesions mostly resolved and corneal epithelial thickness returned to baseline, despite a slightly increased persisting heterogeneous signal intensity in the peripheral corneal epithelium in both eyes.

Case 2

A 77-year-old male with RRMM was started on belantamab mafodotin infusions. His pinhole visual acuity decreased from 20/40 and 20/30 at baseline to 20/60 and 20/40 on day 41 (three weeks after the second infusion) in the right eye and left eye, respectively. Slit-lamp examination showed diffuse, moderate MECs in both eyes, which was more severe in the peripheral cornea. AS-OCT demonstrated increased bilateral heterogeneous signal intensity and hyperreflective lesions in the corneal epithelium, which are more severe in the right eye along with increased corneal epithelial thickness. Therefore, belantamab mafodotin was withheld.

Conclusions and Impotance

AS-OCT objectively demonstrated structural changes such as signal intensity and thickness alterations with hyperreflective lesions in the corneal epithelium related to BASK. AS-OCT might be useful for clinicians to monitor ocular surface adverse events in RRMM patients receiving belantamab mafodotin and to adjust therapeutic plans for the patients.

Antibody Drug Conjugates

Antibody drug conjugates (ADCs) are chemically engineered drugs consisting of monoclonal antibody (mAb) and cytotoxic compound attached chemically by a linker. Upon attachment to a specific target antigen, ADC enters into the cell and payload is released, which finally leads to cell killing. Payloads are broadly divided into tubulin-disrupting agents and DNA-damaging agents. Most of the current ADCs utilize humanized mAbs, and fully human mAbs are under investigation. ADC development process is accelerated by better designing and bio-engineering methods.

Antibody-Based Treatment Approaches in Multiple Myeloma

PURPOSE OF REVIEW

The field of multiple myeloma treatment has entered a new era with antibody-based approaches in clinical practice. In this review, we focus on the clinical approaches of utilizing antibody-based modality, specifically monoclonal antibodies, antibody-drug conjugates, and bispecific T-cell antibodies in the treatment of multiple myeloma.

RECENT FINDINGS

Three monoclonal antibodies (daratumumab, isatuximab, elotuzumab) and one anti-BCMA (B-cell maturation antigen) antibody-drug conjugate (belantamab mafodotin) have been approved by the FDA in the last 5 years for the treatment of multiple myeloma. There are many ongoing clinical trials using novel targets and constructs, including bispecific antibodies against BCMA, GPRC5D, and FCRH5. In addition to exploring efficacy, there are ongoing efforts to overcome the resistance to therapy. Antibody-based therapy has improved the outcomes of patients with multiple myeloma and has been incorporated in the standard of care. We expect to see novel targets and constructs that can achieve a deeper and more durable response while minimizing toxicity, as well as better strategies for toxicity management for existing agents. We also expect that antibody-based strategies will be used in earlier lines of therapy in the future.

Transforming targeted cancer therapy with PROTACs: A forward-looking perspective

Small-molecule targeted protein degraders have in recent years made a great impact on the strategies of many industry and academic cancer research endeavours. We seek here to provide a concise perspective on the opportunities and challenges that lie ahead for bifunctional degrader molecules, so-called 'Proteolysis Targeting Chimeras (PROTACs),' in the context of cancer therapy. We highlight high-profile studies that support the potential for PROTAC approaches to broaden drug target scope, address drug resistance, enhance target selectivity and provide tissue specificity, but also assess where the modality is yet to fully deliver in these contexts. Future opportunities presented by the unique bifunctional nature of these molecules are also discussed.

The clinical development of antibody-drug conjugates - lessons from leukaemia

Advances in our understanding of cancer biology have enabled drug development to progress towards better targeted therapies that are both more effective and safer owing to their lack of off-target toxicities. In this regard, antibody-drug conjugates (ADCs), which have the potential to combine the selectivity of therapeutic antibodies with the cytotoxicity of highly toxic small molecules, are a rapidly developing drug class. The complex and unique structure of an ADC, composed of a monoclonal antibody conjugated to a potent cytotoxic payload via a chemical linker, is designed to selectively target a specific tumour antigen. The success of an ADC is highly dependent on the specific properties of its components, all of which have implications for the stability, cytotoxicity, pharmacokinetics and antitumour activity of the ADC. The development of therapeutic ADCs, including gemtuzumab ozogamicin and inotuzumab ozogamicin, provided great knowledge of the refinements needed for the optimization of such agents. In this Review, we describe the key components of ADC structure and function and focus on the clinical development and subsequent utilization of two leukaemia-directed ADCs - gemtuzumab ozogamicin and inotuzumab ozogamicin - as well as on the mechanisms of resistance and predictors of response to these two agents.

Exatecan Antibody Drug Conjugates Based on a Hydrophilic Polysarcosine Drug-Linker Platform

We herein report the development and evaluation of a novel HER2-targeting antibody-drug conjugate (ADC) based on the topoisomerase I inhibitor payload exatecan, using our hydrophilic monodisperse polysarcosine (PSAR) drug-linker platform (PSARlink). In vitro and in vivo experiments were conducted in breast and gastric cancer models to characterize this original ADC and gain insight about the drug-linker structure-activity relationship. The inclusion of the PSAR hydrophobicity masking entity efficiently reduced the overall hydrophobicity of the conjugate and yielded an ADC sharing the same pharmacokinetic profile as the unconjugated antibody despite the high drug-load of the camptothecin-derived payload (drug-antibody ratio of 8). Tra-Exa-PSAR10 demonstrated strong anti-tumor activity at 1 mg/kg in an NCI-N87 xenograft model, outperforming the FDA-approved ADC DS-8201a (Enhertu), while being well tolerated in mice at a dose of 100 mg/kg. In vitro experiments showed that this exatecan-based ADC demonstrated higher bystander killing effect than DS-8201a and overcame resistance to T-DM1 (Kadcyla) in preclinical HER2+ breast and esophageal models, suggesting potential activity in heterogeneous and resistant tumors. In summary, the polysarcosine-based hydrophobicity masking approach allowsfor the generation of highly conjugated exatecan-based ADCs having excellent physicochemical properties, an improved pharmacokinetic profile, and potent in vivo anti-tumor activity.

Profile of Trastuzumab Deruxtecan in the Management of Patients with HER2-Positive Unresectable or Metastatic Breast Cancer: An Evidence-Based Review

Trastuzumab deruxtecan is a novel antibody–drug conjugate for the treatment of advanced solid tumors, including breast cancer, which overexpress or have amplification of the human epidermal growth factor receptor 2 (HER2). The novel structure of this exciting new agent means that it can deliver a highly potent cytotoxic agent to HER2-expressing tissues resulting in selective killing of cancer cells. In phase I and II trials, trastuzumab deruxtecan has shown impressive response rates in heavily pretreated populations, including patients who had received prior treatment with trastuzumab emtansine, another highly active antibody–drug conjugate. The most common side effects are gastrointestinal and hematological. Importantly, a high rate of interstitial lung disease was seen in early trials, but this appears manageable in most patients with corticosteroids. In light of its efficacy, this promising new drug may change the treatment paradigm of HER2-positive breast cancer.

What makes a good antibody-drug conjugate?

Introduction: Antibody-Drug Conjugates (ADCs) are becoming increasingly important weapons in the fight against cancer, as evidenced by the growing number of approved products. The complex nature of an ADC means that there is a vast array of choices to consider in the design of such drugs.Areas covered: We provide an overview of developments in each facet of ADC structure: the antibody, linker, and payload. Looking at the current clinical landscape, we discuss trends that have led to the evolution of ADC design.Expert opinion:Following a history of setbacks and high discontinuation rates, the understanding of the ADC field has grown. If developers can obtain a firm grasp of the structure-function relationship of their molecule, we expect the advances in ADC design to translate to improved clinical success. Moreover, the breadth of ADC applications will continue to expand to target new indications with novel targets and payloads.

Drug Combination in Cancer Treatment-From Cocktails to Conjugated Combinations

It is well recognized today that anticancer drugs often are most effective when used in combination. However, the establishment of chemotherapy as key modality in clinical oncology began with sporadic discoveries of chemicals that showed antiproliferative properties and which as a first attempt were used as single agents. In this review we describe the development of chemotherapy from its origins as a single drug treatment with cytotoxic agents to polydrug therapy that includes targeted drugs. We discuss the limitations of the first chemotherapeutic drugs as a motivation for the establishment of combined drug treatment as standard practice in spite of concerns about frequent severe, dose limiting toxicities. Next, we introduce the development of targeted treatment as a concept for advancement within the broader field of small-molecule drug combination therapy in cancer and its accelerating progress that was boosted by recent scientific and technological progresses. Finally, we describe an alternative strategy of drug combinations using drug-conjugates for selective delivery of cytotoxic drugs to tumor cells that potentiates future improvement of drug combinations in cancer treatment. Overall, in this review we outline the development of chemotherapy from a pharmacological perspective, from its early stages to modern concepts of using targeted therapies for combinational treatment.

Treating Prostate Cancer by Antibody-Drug Conjugates

Prostate cancer is the most frequent malignancy in the worldwide male population; it is also one of the most common among all the leading cancer-related death causes. In the last two decades, the therapeutic scenario of metastatic castration-resistant prostate cancer has been enriched by the use of chemotherapy and androgen receptor signaling inhibitors (ARSI) and, more recently, by immunotherapy and poly(ADP–ribose) polymerase (PARP) inhibitors. At the same time, several trials have shown the survival benefits related to the administration of novel ARSIs among patients with non-castration-resistant metastatic disease along with nonmetastatic castration-resistant cancer too. Consequently, the therapeutic course of this malignancy has been radically expanded, ensuring survival benefits never seen before. Among the more recently emerging agents, the so-called “antibody–drug conjugates” (ADCs) are noteworthy because of their clinical practice changing outcomes obtained in the management of other malignancies (including breast cancer). The ADCs are novel compounds consisting of cytotoxic agents (also known as the payload) linked to specific antibodies able to recognize antigens expressed over cancer cells’ surfaces. As for prostate cancer, researchers are focusing on STEAP1, TROP2, PSMA, CD46 and B7-H3 as optimal antigens which may be targeted by ADCs. In this paper, we review the pivotal trials that have currently changed the therapeutic approach to prostate cancer, both in the nonmetastatic castration-resistant and metastatic settings. Therefore, we focus on recently published and ongoing trials designed to investigate the clinical activity of ADCs against prostate malignancy, characterizing these agents. Lastly, we briefly discuss some ADCs-related issues with corresponding strategies to overwhelm them, along with future perspectives for these promising novel compounds.

The biology and rationale of targeting nectin-4 in urothelial carcinoma

Bladder cancer is the tenth most common cancer type worldwide. Urothelial carcinoma is the most common type of bladder cancer and accounts for 90% of bladder cancer cases in the USA and Europe. Novel approaches are needed to improve patient outcomes. Nectin-4 is a tumour-associated antigen found on the surface of most urothelial carcinoma cells. In the antibody-drug conjugate enfortumab vedotin, human anti-nectin-4 antibody is linked to the cytotoxic microtubule-disrupting agent monomethyl auristatin E. In ongoing phase I, II and III clinical trials, enfortumab vedotin has been evaluated as a monotherapy and in combination with a checkpoint inhibitor and/or chemotherapy in locally advanced and metastatic urothelial carcinoma. Encouraging data from the phase II study resulted in the FDA granting accelerated approval for enfortumab vedotin in December 2019 for patients with locally advanced or metastatic urothelial carcinoma who were previously treated with platinum and a checkpoint inhibitor therapy. Moreover, data from a phase I study led to the FDA granting breakthrough therapy designation to enfortumab vedotin combined with pembrolizumab as a first-line treatment in February 2020 for cisplatin-ineligible patients with locally advanced or metastatic urothelial carcinoma. Results of ongoing and future combination studies of enfortumab vedotin with immunotherapy and other novel agents are eagerly awaited.

Extracellular vesicles as modifiers of antibody-drug conjugate efficacy

Antibody-drug conjugates (ADCs) are a new class of anti-cancer drugs that consist of a monoclonal antibody, a highly potent small-molecule cytotoxic drug, and a chemical linker between the two. ADCs can selectively deliver cytotoxic drugs to cancer cells leading to a reduced systemic exposure and a wider therapeutic window. To date, nine ADCs have received marketing approval, and over 100 are being investigated in nearly 600 clinical trials. The target antigens of at least eight out of the nine approved anti-cancer ADCs and of 69 investigational ADCs are present on extracellular vesicles (EVs) (tiny particles produced by almost all types of cells) that may carry their contents into local and distant cells. Therefore, the EVs have a potential to mediate both the anti-cancer effects and the adverse effects of ADCs. In this overview, we discuss the mechanisms of action of ADCs and the resistance mechanisms to them, the EV-mediated resistance mechanisms to small molecule anti-cancer drugs and anti-cancer monoclonal antibodies, and the EVs as modifiers of ADC efficacy and safety.

Preclinical optimization of Ly6E-targeted ADCs for increased durability and efficacy of anti-tumor response

Early success with brentuximab vedotin in treating classical Hodgkin lymphoma spurred an influx of at least 20 monomethyl auristatin E (MMAE) antibody-drug conjugates (ADCs) into clinical trials. While three MMAE-ADCs have been approved, most of these conjugates are no longer being investigated in clinical trials. Some auristatin conjugates show limited or no efficacy at tolerated doses, but even for drugs driving initial remissions, tumor regrowth and metastasis often rapidly occur. Here we describe the development of second-generation therapeutic ADCs targeting Lymphocyte antigen 6E (Ly6E) where the tubulin polymerization inhibitor MMAE (Compound 1) is replaced with DNA-damaging agents intended to drive increased durability of response. Comparison of a seco-cyclopropyl benzoindol-4-one (CBI)-dimer (compound 2) to MMAE showed increased potency, activity across more cell lines, and resistance to efflux by P-glycoprotein, a drug transporter commonly upregulated in tumors. Both anti-Ly6E-CBI and -MMAE conjugates drove single-dose efficacy in xenograft and patient-derived xenograft models, but seco-CBI-dimer conjugates showed reduced tumor outgrowth following multiple weeks of treatment, suggesting that they are less susceptible to developing resistance. In parallel, we explored approaches to optimize the targeting antibody. In contrast to immunization with recombinant Ly6E or Ly6E DNA, immunization with virus-like particles generated a high-affinity anti-Ly6E antibody. Conjugates to this antibody improve efficacy versus a previous clinical candidate both in vitro and in vivo with multiple cytotoxics. Conjugation of compound 2 to the second-generation antibody results in a substantially improved ADC with promising preclinical efficacy.

Targeting cancer with antibody-drug conjugates: Promises and challenges

Antibody-drug conjugates (ADCs) are a rapidly expanding class of biotherapeutics that utilize antibodies to selectively deliver cytotoxic drugs to the tumor site. As of May 2021, the U.S. Food and Drug Administration (FDA) has approved ten ADCs, namely Adcetris®, Kadcyla®, Besponsa®, Mylotarg®, Polivy®, Padcev®, Enhertu®, Trodelvy®, Blenrep®, and Zynlonta™ as monotherapy or combinational therapy for breast cancer, urothelial cancer, myeloma, acute leukemia, and lymphoma. In addition, over 80 investigational ADCs are currently being evaluated in approximately 150 active clinical trials. Despite the growing interest in ADCs, challenges remain to expand their therapeutic index (with greater efficacy and less toxicity). Recent advances in the manufacturing technology for the antibody, payload, and linker combined with new bioconjugation platforms and state-of-the-art analytical techniques are helping to shape the future development of ADCs. This review highlights the current status of marketed ADCs and those under clinical investigation with a focus on translational strategies to improve product quality, safety, and efficacy.

The Evolving Landscape of Antibody-Drug Conjugates for Urothelial Carcinoma

Metastatic urothelial carcinoma (UC) carries a poor prognosis and a 5-year overall survival of less than 5%, despite standard of care therapy using cisplatin-based chemotherapy and immune checkpoint inhibitors. Thus, novel agents that improve survival and have an acceptable toxicity profile are urgently needed. Antibody-drug conjugates (ADCs) represent a promising new treatment option that utilizes the targeting ability of an antibody to deliver cytotoxic drugs directly to tumors. Many ADCs are currently being investigated for treatment of UC, with enfortumab vedotin being recently approved by the US Food and Drug Administration for treatment of metastatic UC with progressive disease after chemotherapy and/or immune checkpoint inhibitors. Overall, ADCs hold promise as a long-awaited treatment option for UC.

Antibody-Drug Conjugates: Patient and Treatment Selection

Antibody-drug conjugates (ADCs) are a promising drug platform designed to enhance the therapeutic index and minimize the toxicity of anticancer agents. ADCs have experienced substantial progress and technological growth over the past decades; however, several challenges to patient selection and treatment remain. Methods to optimally capture all patients who may benefit from a particular ADC are still largely unknown. Although target antigen expression remains a biomarker for patient selection, the impact of intratumor heterogeneity on antigen expression, as well as the dynamic changes in expression with treatment and disease progression, are important considerations in patient selection. Better understanding of these factors, as well as minimum levels of target antigen expression required to achieve therapeutic efficacy, will enable further optimization of selection strategies. Other important considerations include understanding mechanisms of primary and acquired resistance to ADCs. Ongoing efforts in the design of its constituent parts to possess the intrinsic ability to overcome these mechanisms, including use of the "bystander effect" to enhance efficacy in heterogeneous or low target antigen-expressing tumors, as well as modulation of the chemical and immunophenotypic properties of antibodies and linker molecules to improve payload sensitivity and therapeutic efficacy, are under way. These strategies may also lead to improved safety profiles. Similarly, combination strategies using ADCs with other cytotoxic or immunomodulatory agents are also under development. Great strides have been made in ADC technology. With further refinements, this therapeutic modality has the potential to make an important clinical impact on a wider range of tumor types.

Breast Cancer Heterogeneity and Response to Novel Therapeutics

Targeted cancer therapies against oncogenic drivers are actively being developed and tested in clinical trials. Targeting an oncogenic driver may only prove effective if the mutation is present in most tumoral cells. Therefore, highly heterogeneous tumors may be refractory to these therapies. This makes tumor heterogeneity a major challenge in cancer therapy. Although heterogeneity has traditionally been attributed to genetic diversity within cancer cell populations, it is now widely recognized that human cancers are heterogeneous in almost all distinguishable phenotypic characteristics. Understanding the genetic variability and also the non-genetic influences of tumor heterogeneity will provide novel insights into how to reverse therapeutic resistance and improve cancer therapy.

Considerations for setting occupational exposure limits for novel pharmaceutical modalities

In order to develop new and effective medicines, pharmaceutical companies must be modality agnostic. As science reveals an enhanced understanding of biological processes, new therapeutic modalities are becoming important in developing breakthrough therapies to treat both rare and common diseases. As these new modalities progress, concern and uncertainty arise regarding their safe handling by the researchers developing them, employees manufacturing them and nurses administering them. This manuscript reviews the available literature for emerging modalities (including oligonucleotides, monoclonal antibodies, fusion proteins and bispecific antibodies, antibody-drug conjugates, peptides, vaccines, genetically modified organisms, and several others) and provides considerations for occupational health and safety-oriented hazard identification and risk assessments to enable timely, consistent and well-informed hazard identification, hazard communication and risk-management decisions. This manuscript also points out instances where historical exposure control banding systems may not be applicable (e.g. oncolytic viruses, biologics) and where other occupational exposure limit systems are more applicable (e.g. Biosafety Levels, Biologic Control Categories).

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Review of toxicology and pharmacology information for novel therapeutic modalities.

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Identification of occupational hazards associated with novel therapeutic modalities.

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Occupational hazards and exposure risks differ across pharmaceutical modalities.

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Occupational exposure control banding systems are not one size fits all.

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Banding system variations offer benefits while enabling proper exposure controls.

Antibody-Drug Conjugates for Cancer Therapy

Antibody-drug conjugates (ADCs) are novel drugs that exploit the specificity of a monoclonal antibody (mAb) to reach target antigens expressed on cancer cells for the delivery of a potent cytotoxic payload. ADCs provide a unique opportunity to deliver drugs to tumor cells while minimizing toxicity to normal tissue, achieving wider therapeutic windows and enhanced pharmacokinetic/pharmacodynamic properties. To date, nine ADCs have been approved by the FDA and more than 80 ADCs are under clinical development worldwide. In this paper, we provide an overview of the biology and chemistry of each component of ADC design. We briefly discuss the clinical experience with approved ADCs and the various pathways involved in ADC resistance. We conclude with perspectives about the future development of the next generations of ADCs, including the role of molecular imaging in drug development.

Antibody-drug conjugates for previously treated aggressive lymphomas: focus on polatuzumab vedotin

INTRODUCTION

Antibody-drug conjugates (ADCs) are immunoconjugates and comprise a monoclonal antibody that is chemically attached to a cytotoxic drug (or payload) via a stable chemical linker. Since the approval of the first ADC in 2000, there are now nine different approved agents and over 100 ADCs in the drug-development pipeline.

AREAS COVERED

This review briefly describes the ADCs approved for treatment of lymphoma and their distinguishing factors in terms of target, linker and payload. The clinical implications of the use of ADCs are also considered. Here, we focus on polatuzumab vedotin, an ADC targeted to CD79b, which is approved for the treatment of patients with relapsed/refractory diffuse large B-cell lymphoma (R/R DLBCL) who have received at least one (EU approval) or two (US approval) prior therapies and are not eligible for bone marrow transplantation. The characteristics of polatuzumab vedotin are discussed and clinical data are presented. The future of polatuzumab vedotin clinical development, and ADCs in general, are also considered.

EXPERT OPINION

ADCs represent a significant advance in the treatment of lymphoma. Polatuzumab vedotin has shown clinical efficacy and a tolerable safety profile in both first-line and R/R DLBCL; future studies are planned to further investigate this ADC.

Recent advances of antibody drug conjugates for clinical applications

Antibody drug conjugates (ADCs) normally compose of a humanized antibody and small molecular drug via a chemical linker. After decades of preclinical and clinical studies, a series of ADCs have been widely used for treating specific tumor types in the clinic such as brentuximab vedotin (Adcetris®) for relapsed Hodgkin's lymphoma and systemic anaplastic large cell lymphoma, gemtuzumab ozogamicin (Mylotarg®) for acute myeloid leukemia, ado-trastuzumab emtansine (Kadcyla®) for HER2-positive metastatic breast cancer, inotuzumab ozogamicin (Besponsa®) and most recently polatuzumab vedotin-piiq (Polivy®) for B cell malignancies. More than eighty ADCs have been investigated in different clinical stages from approximately six hundred clinical trials to date. This review summarizes the key elements of ADCs and highlights recent advances of ADCs, as well as important lessons learned from clinical data, and future directions.

An Overview of Antibody Conjugated Polymeric Nanoparticles for Breast Cancer Therapy

Nanoparticles (NPs) are promising drug delivery systems (DDS) for identifying and treating cancer. Active targeting NPs can be generated by conjugation with ligands that bind overexpressed or mutant cell surface receptors on target cells that are poorly or not even expressed on normal cells. Receptor-mediated endocytosis of the NPs occurs and the drug is released inside the cell or in the surrounding tissue due to the bystander effect. Antibodies are the most frequently used ligands to actively target tumor cells. In this context, antibody-based therapies have been extensively used in HER2+ breast cancer. However, some patients inherently display resistance and in advanced stages, almost all eventually progress. Functionalized NPs through conjugation with antibodies appear to be a promising strategy to optimize targeted therapies due to properties related to biocompatibility, suitable delivery control and efficiency of functionalization. This review is focused on the different strategies to conjugate antibodies into polymeric NPs. Recent antibody conjugation approaches applied to the improvement of breast cancer therapy are highlighted in this review.

Antibody-Drug Conjugates: A Promising Novel Therapy for the Treatment of Ovarian Cancer

Antibody-drug conjugates (ADCs) represent a novel and promising therapeutic strategy for the treatment of cancer patients. ADCs target antigens highly expressed on the membrane surface of tumor cells to selectively deliver a cytotoxic drug. Ovarian tumors differentially express tumor-specific antigens, which can be used to guide ADCs. This strategy allows for optimizing tumor targeting while minimizing systemic toxicity compared to classical chemotherapeutic agents. ADCs can be improved by using a cleavable linker allowing the delivery of the toxic payload in surrounding cells not expressing the target protein, therefore acting on heterogeneous tumors with different cell populations. Currently, more than 15 ADCs are under preclinical investigation in ovarian cancer, and some of them have already been tested in early-phase clinical trials with promising results. In this review, we summarize the mechanism of action and the toxicity profile of ADCs and discuss the latest preclinical discoveries and forthcoming applications in ovarian cancer.

A real-time cell-binding assay reveals dynamic features of STxB-Gb3 cointernalization and STxB-mediated cargo delivery into cancer cells

The interaction between the Shiga toxin B-subunit (STxB) and its globotriaosylceramide receptor (Gb3) has a high potential for being exploited for targeted cancer therapy. The primary goal of this study was to evaluate the capacity of STxB to carry small molecules and proteins as cargo into cells. For this purpose, an assay was designed to provide real-time information about the StxB-Gb3 interaction as well as the dynamics and mechanism of the internalization process. The assay revealed the ability to distinguish the process of binding to the cell surface from internalization and presented the importance of receptor and STxB clustering for internalization. The overall setup demonstrated that the binding mechanism is complex, and the concept of affinity is difficult to apply. Hence, time-resolved methods, providing detailed information about the interaction of STxB with cells, are critical for the optimization of intracellular delivery.

Targeted Therapy With Immunoconjugates for Multiple Myeloma

The introduction of proteasome inhibitors (PI) and immunomodulatory drugs (IMiD) has markedly increased the survival of multiple myeloma (MM) patients. Also, the unconjugated monoclonal antibodies (mAb) daratumumab (anti-CD38) and elotuzumab (anti-SLAMF7) have revolutionized MM treatment given their clinical efficacy and safety, illustrating the potential of targeted immunotherapy as a powerful treatment strategy for MM. Nonetheless, most patients eventually develop PI-, IMiD-, and mAb-refractory disease because of the selection of resistant MM clones, which associates with a poor prognosis. Accordingly, these patients remain in urgent need of new therapies with novel mechanisms of action. In this respect, mAbs or mAb fragments can also be utilized as carriers of potent effector moieties to specifically target surface antigens on cells of interest. Such immunoconjugates have the potential to exert anti-MM activity in heavily pretreated patients due to their distinct and pleiotropic mechanisms of action. In addition, the fusion of highly cytotoxic compounds to mAbs decreases the off-target toxicity, thereby improving the therapeutic window. According to the effector moiety, immunoconjugates are classified into antibody-drug conjugates, immunotoxins, immunocytokines, or radioimmunoconjugates. This review will focus on the mechanisms of action, safety and efficacy of several promising immunoconjugates that are under investigation in preclinical and/or clinical MM studies. We will also include a discussion on combination therapy with immunoconjugates, resistance mechanisms, and future developments.

Patient Selection Strategies to Maximize Therapeutic Index of Antibody-Drug Conjugates: Prior Approaches and Future Directions

Antibody-drug conjugates (ADC) are targeted agents that have shown promise in treating cancer. A central challenge in development of ADCs is the relatively narrow therapeutic index observed in clinical studies. Patient selection strategies based on expression of the target in tumors have the potential to maximize benefit and provide the best chance of clinical success; however, implementation of biomarker-driven trials can be difficult both practically and scientifically. We conducted a survey of recent clinical experience from early-phase ADC trials completed between 2000 and 2019 to evaluate the different approaches to patient selection currently being used and assess whether there is evidence that target expression is associated with clinical activity. Our analysis of patient selection strategies indicates that optimal trial design for early-stage trials should be based on multiple factors, including prevalence and heterogeneity of target expression among intent-to-treat patients, as well as biological factors influencing expression of cell surface and soluble target. To ensure a high probability of success, early implementation of patient selection strategies centered around target expression are pivotal to development of ADCs. In this review, we propose a strategic approach that can be applied for optimization of trial design.

Site-Specific, Stoichiometric-Controlled, PEGylated Conjugates of Fibroblast Growth Factor 2 (FGF2) with Hydrophilic Auristatin Y for Highly Selective Killing of Cancer Cells Overproducing Fibroblast Growth Factor Receptor 1 (FGFR1)

In spite of significant progress in the field of targeted anticancer therapy, the FDA has approved only five ADC-based drugs. Hence the search for new targeted anticancer agents is an unfulfilled necessity. Here, we present novel types of protein–drug conjugates (PDCs) that exhibit superior anticancer activities. Instead of a monoclonal antibody, we used fibroblast growth factor 2 (FGF2) as a targeting molecule. FGF2 is a natural ligand of fibroblast growth factor receptor 1 (FGFR1), a transmembrane receptor overproduced in various types of cancers. We synthesized site-specific and stoichiometric-controlled conjugates of FGF2 with a highly potent, hydrophilic derivative of auristatin called auristatin Y. To increase the hydrophilicity and hydrodynamic radius of conjugates, we employed PEG4 and PEG27 molecules as a spacer between the targeting molecule and the cytotoxic payload. All conjugates were selective to FGFR1-positive cell lines, effectively internalized via the FGFR1-dependent pathway, and exhibited a highly cytotoxic effect only on FGFR1-positive cancer cell lines.

DHA Affects Microtubule Dynamics Through Reduction of Phospho-TCTP Levels and Enhances the Antiproliferative Effect of T-DM1 in Trastuzumab-Resistant HER2-Positive Breast Cancer Cell Lines

Trastuzumab emtansine (T-DM1) is an anti-human epidermal growth factor receptor 2 (HER2) antibody-drug conjugated to the microtubule-targeting agent emtansine (DM1). T-DM1 is an effective agent in the treatment of patients with HER2-positive breast cancer whose disease has progressed on the first-line trastuzumab containing chemotherapy. However, both primary and acquired tumour resistance limit its efficacy. Increased levels of the phosphorylated form of Translationally Controlled Tumour Protein (phospho-TCTP) have been shown to be associated with a poor clinical response to trastuzumab therapy in HER2-positive breast cancer. Here we show that phospho-TCTP is essential for correct mitosis in human mammary epithelial cells. Reduction of phospho-TCTP levels by dihydroartemisinin (DHA) causes mitotic aberration and increases microtubule density in the trastuzumab-resistant breast cancer cells HCC1954 and HCC1569. Combinatorial studies show that T-DM1 when combined with DHA is more effective in killing breast cells compared to the effect induced by any single agent. In an orthotopic breast cancer xenograft model (HCC1954), the growth of the tumour cells resumes after having achieved a complete response to T-DM1 treatment. Conversely, DHA and T-DM1 treatment induces a severe and irreversible cytotoxic effect, even after treatment interruption, thus, improving the long-term efficacy of T-DM1. These results suggest that DHA increases the effect of T-DM1 as poison for microtubules and supports the clinical development of the combination of DHA and T-DM1 for the treatment of aggressive HER2-overexpressing breast cancer.

HER3 targeting with an antibody-drug conjugate bypasses resistance to anti-HER2 therapies

Despite impressive clinical benefit obtained with anti‐HER2‐targeted therapies, in advances stages, especially in the metastatic setting, HER2‐positive tumors remain incurable. Therefore, it is important to develop novel strategies to fight these tumors, especially when they become resistant to available therapies. We show here that the anti‐HER3 antibody–drug conjugate EV20/MMAF exerted potent anti‐tumoral properties against several models of primary resistance and secondary resistance to common anti‐HER2 available therapies, including trastuzumab, lapatinib, neratinib, and trastuzumab‐emtansine. HER3 was expressed in these HER2⁺ breast cancer cells and knockdown experiments demonstrated that HER3 expression was required for the action of EV20/MMAF. In mice injected with trastuzumab‐resistant HER2⁺ cells, a single dose of EV20/MMAF caused complete and long‐lasting tumor regression. Mechanistically, EV20/MMAF bound to cell surface HER3 and became internalized to the lysosomes. Treatment with EV20/MMAF caused cell cycle arrest in mitosis and promoted cell death through mitotic catastrophe. These findings encourage the clinical testing of EV20/MMAF for several indications in the HER2⁺ cancer clinic, including situations in which HER2⁺ tumors become refractory to approved anti‐HER2 therapies.

Construction of Bispecific Aptamer-Drug Conjugate by a Hybrid Chemical and Biological Approach

Bispecific aptamer-drug conjugates (BsApDC) may improve the efficacy of drugs by enhancing cellular internalization and targeted delivery. Nevertheless, the synthesis of single-molecular BsApDC has not yet been reported, and it could be thwarted by synthetic challenges. Herein we report a general approach to synthesize a BsApDC hybridized chemical and biological method. Primers incorporated with 5-Fluorouracil (5-FU), 10-Hydroxycamptothecin, and Maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl-monomethyl auristatin E(vcMMAE) were prepared by chemical synthesis, which were converted to corresponding ApDCs efficiently by enzymatic reaction. Biological studies revealed that BsApDC binds with target cells with enhanced internalization and better inhibitory activity, demonstrating the potential of BsApDCs for targeted tumor therapy.

Immune-Based Approaches for the Treatment of Pediatric Malignancies

Immune-based therapies have now been credentialed for pediatric cancers with the robust efficacy of chimeric antigen receptor (CAR) T cells for pediatric B cell acute lymphocytic leukemia (ALL), offering a chance of a cure for children with previously lethal disease and a potentially more targeted therapy to limit treatment-related morbidities. The developmental origins of most pediatric cancers make them ideal targets for immune-based therapies that capitalize on the differential expression of lineage-specific cell surface molecules such as antibodies, antibody-drug conjugates, or CAR T cells, while the efficacy of other therapies that depend on tumor immunogenicity such as immune checkpoint inhibitors has been limited to date. Here we review the current status of immune-based therapies for childhood cancers, discuss challenges to developing immunotherapeutics for these diseases, and outline future directions of pediatric immunotherapy discovery and development.

The role of antibody delivery formation in cancer therapy

Cancer has become one of the major threats to human survival. Because of antibodies specificity and low toxicity, it is the primary choice to diagnose and treat cancer. It is easy to be cleared from the blood circulation or distributing throughout the body and causes unnecessary side effects. It is necessary to delivery antibodies to the tumour region in a stable, safe and effective manner. In this review, we discuss the latest studies that aimed to delivery antibodies to tumour sites via several vector forms, such as liposomes, carbon nanomaterials, and gold nanomaterials. How to deliver antibodies to the target site is a difficulty for antibody therapy. This review summarises the antibody's therapeutic forms and carrier materials in recent years, and to explore how antibodies can be safely and stably delivered to the target site.