AMG 595, an Anti-EGFRvIII Antibody–Drug Conjugate, Induces Potent Antitumor Activity against EGFRvIII-Expressing Glioblastoma

Unlocking Natural Potential: Antibody-Drug Conjugates With Naturally Derived Payloads for Cancer Therapy

Natural compound-derived chemotherapies remain central to cancer treatment, however, they often cause off-target side effects that negatively impact patients' quality of life. In contrast, antibody-drug conjugates (ADCs) combine cytotoxic payloads with antibodies to specifically target cancer cells. Most approved and clinically investigated ADCs utilize naturally derived payloads, while those with conventional synthetic molecular payloads remain limited. This review focuses on approved ADCs that enhance the efficacy of naturally derived payloads by linking them with antibodies. We provide an overview of the core components of ADCs, their working mechanisms, and FDA-approved ADCs featuring naturally derived payloads, such as calicheamicin, camptothecin, dolastatin 10, maytansine, pyrrolbenzodiazepine (PBD), and the immunotoxin Pseudomonas exotoxin A. This review also explores recent clinical advancements aimed at broadening the therapeutic potential of ADCs, their applicability in treating heterogeneously composed tumors and their potential use beyond oncology. Additionally, this review highlights naturally derived payloads that are currently being clinically investigated but have not yet received approval. By summarizing the current landscape, this review provides insights into promising avenues for exploration and contributes to the refinement of treatment protocols for improved patient outcomes.

Genomic, epigenomic and transcriptomic landscape of glioblastoma

The mostly aggressive and extremely malignant type of central nervous system is Glioblastoma (GBM), which is characterized by an extremely short average survival time of lesser than 16 months. The primary cause of this phenomenon can be attributed to the extensively altered genome of GBM, which is characterized by the dysregulation of numerous critical signaling pathways and epigenetics regulations associated with proliferation, cellular growth, survival, and apoptosis. In light of this, different genetic alterations in critical signaling pathways and various epigenetics regulation mechanisms are associated with GBM and identified as distinguishing markers. Such GBM prognostic alterations are identified in PI3K/AKT, p53, RTK, RAS, RB, STAT3 and ZIP4 signaling pathways, metabolic pathway (IDH1/2), as well as alterations in epigenetic regulation genes (MGMT, CDKN2A-p16INK4aCDKN2B-p15INK4b). The exploration of innovative diagnostic and therapeutic approaches that specifically target these pathways is utmost importance to enhance the future medication for GBM. This study provides a comprehensive overview of dysregulated epigenetic mechanisms and signaling pathways due to mutations, methylation, and copy number alterations of in critical genes in GBM with prevalence and emphasizing their significance.

Understanding the immunosuppressive microenvironment of glioma: mechanistic insights and clinical perspectives

Glioblastoma (GBM), the predominant and primary malignant intracranial tumor, poses a formidable challenge due to its immunosuppressive microenvironment, thereby confounding conventional therapeutic interventions. Despite the established treatment regimen comprising surgical intervention, radiotherapy, temozolomide administration, and the exploration of emerging modalities such as immunotherapy and integration of medicine and engineering technology therapy, the efficacy of these approaches remains constrained, resulting in suboptimal prognostic outcomes. In recent years, intensive scrutiny of the inhibitory and immunosuppressive milieu within GBM has underscored the significance of cellular constituents of the GBM microenvironment and their interactions with malignant cells and neurons. Novel immune and targeted therapy strategies have emerged, offering promising avenues for advancing GBM treatment. One pivotal mechanism orchestrating immunosuppression in GBM involves the aggregation of myeloid-derived suppressor cells (MDSCs), glioma-associated macrophage/microglia (GAM), and regulatory T cells (Tregs). Among these, MDSCs, though constituting a minority (4-8%) of CD45+ cells in GBM, play a central component in fostering immune evasion and propelling tumor progression, angiogenesis, invasion, and metastasis. MDSCs deploy intricate immunosuppressive mechanisms that adapt to the dynamic tumor microenvironment (TME). Understanding the interplay between GBM and MDSCs provides a compelling basis for therapeutic interventions. This review seeks to elucidate the immune regulatory mechanisms inherent in the GBM microenvironment, explore existing therapeutic targets, and consolidate recent insights into MDSC induction and their contribution to GBM immunosuppression. Additionally, the review comprehensively surveys ongoing clinical trials and potential treatment strategies, envisioning a future where targeting MDSCs could reshape the immune landscape of GBM. Through the synergistic integration of immunotherapy with other therapeutic modalities, this approach can establish a multidisciplinary, multi-target paradigm, ultimately improving the prognosis and quality of life in patients with GBM.

Strategies to Improve Drug Delivery Across the Blood-Brain Barrier for Glioblastoma

PURPOSE OF REVIEW

Glioblastoma remains resistant to most conventional treatments. Despite scientific advances in the past three decades, there has been a dearth of effective new treatments. New approaches to drug delivery and clinical trial design are needed.

RECENT FINDINGS

We discuss how the blood-brain barrier and tumor microenvironment pose challenges for development of effective therapies for glioblastoma. Next, we discuss treatments in development that aim to overcome these barriers, including novel drug designs such as nanoparticles and antibody-drug conjugates, novel methods of drug delivery, including convection-enhanced and intra-arterial delivery, and novel methods to enhance drug penetration, such as blood-brain barrier disruption by focused ultrasound and laser interstitial thermal therapy. Lastly, we address future opportunities, positing combination therapy as the best strategy for effective treatment, neoadjuvant and window-of-opportunity approaches to simultaneously enhance therapeutic effectiveness with interrogation of on-treatment biologic endpoints, and adaptive platform and basket trials as imperative for future trial design. New approaches to GBM treatment should account for the blood-brain barrier and immunosuppression by improving drug delivery, combining treatments, and integrating novel clinical trial designs.

AGCM-22, a novel cetuximab-based EGFR-targeting antibody-drug-conjugate with highly selective anti-glioblastoma efficacy

The epidermal growth factor receptor (EGFR) has received significant attention as a potential target for glioblastoma (GBM) therapeutics in the past two decades. However, although cetuximab, an antibody that specifically targets EGFR, exhibits a high affinity for EGFR, it has not yet been applied in the treatment of GBM. Antibody-drug conjugates (ADCs) utilize tumor-targeting antibodies for the selective delivery of cytotoxic drugs, resulting in improved efficacy compared to conventional chemotherapy drugs. However, the effectiveness of cetuximab as a targeted antibody for ADCs in the treatment of GBM remains uncertain. In this study, we synthesized AGCM-22, an EGFR-targeted ADC derived from cetuximab, by conjugating it with the tubulin inhibitor monomethyl auristatin E (MMAE) using our Valine-Alanine Cathepsin B cleavable linker. In vitro experiments demonstrated that AGCM-22 effectively inhibited GBM cell proliferation through increased levels of apoptosis and autophagy-related cell death, whereas cetuximab alone had no anti-GBM effects. Additionally, both mouse and human orthotopic tumor models exhibited the selective tumor-targeting efficacy of AGCM-22, along with favorable metabolic properties and superior anti-GBM activity compared to temozolomide (TMZ). In summary, this study presents a novel ADC for GBM therapy that utilizes cetuximab as the tumor-targeting antibody, resulting in effective delivery of the cytotoxic drug payload.

Therapeutically targeting the unique disease landscape of pediatric high-grade gliomas

Pediatric high-grade gliomas (pHGG) are a rare yet devastating malignancy of the central nervous system's glial support cells, affecting children, adolescents, and young adults. Tumors of the central nervous system account for the leading cause of pediatric mortality of which high-grade gliomas present a significantly grim prognosis. While the past few decades have seen many pediatric cancers experiencing significant improvements in overall survival, the prospect of survival for patients diagnosed with pHGGs has conversely remained unchanged. This can be attributed in part to tumor heterogeneity and the existence of the blood-brain barrier. Advances in discovery research have substantiated the existence of unique subgroups of pHGGs displaying alternate responses to different therapeutics and varying degrees of overall survival. This highlights a necessity to approach discovery research and clinical management of the disease in an alternative subtype-dependent manner. This review covers traditional approaches to the therapeutic management of pHGGs, limitations of such methods and emerging alternatives. Novel mutations which predominate the pHGG landscape are highlighted and the therapeutic potential of targeting them in a subtype specific manner discussed. Collectively, this provides an insight into issues in need of transformative progress which arise during the management of pHGGs.

Targeted Glioma Therapy-Clinical Trials and Future Directions

Glioblastoma multiforme (GBM) is the most common type of glioma, with a median survival of 14.6 months post-diagnosis. Understanding the molecular profile of such tumors allowed the development of specific targeted therapies toward GBM, with a major role attributed to tyrosine kinase receptor inhibitors and immune checkpoint inhibitors. Targeted therapeutics are drugs that work by specific binding to GBM-specific or overexpressed markers on the tumor cellular surface and therefore contain a recognition moiety linked to a cytotoxic agent, which produces an antiproliferative effect. In this review, we have summarized the available information on the targeted therapeutics used in clinical trials of GBM and summarized current obstacles and advances in targeted therapy concerning specific targets present in GBM tumor cells, outlined efficacy endpoints for major classes of investigational drugs, and discussed promising strategies towards an increase in drug efficacy in GBM.

Toxic warhead-armed antibody for targeted treatment of glioblastoma

Glioblastoma is a fatal intracranial tumor with a poor prognosis, exhibiting uninterrupted malignant progression, widespread invasion throughout the brain leading to the destruction of normal brain tissue and inevitable death. Monoclonal antibodies alone or conjugated with cytotoxic payloads to treat patients with different solid tumors showed effective. This treatment strategy is being explored for patients with glioblastoma (GBM) to obtain meaningful clinical responses and offer new drug options for the treatment of this devastating disease. In this review, we summarize clinical data (from pubmed.gov database and clinicaltrial.gov database) on the efficacy and toxicity of naked antibodies and antibody-drug conjugates (ADCs) against multiple targets on GBM, elucidate the mechanisms that ADCs act at the site of GBM lesions. Finally, we discuss the potential strategies for ADC therapies currently used to treat GBM patients.

Improving the efficacy of anti-EGFR drugs in GBM: Where we are going?

The therapies targeting mutations of driver genes in cancer have advanced into clinical trials for a variety of tumors. In glioblastoma (GBM), epidermal growth factor receptor (EGFR) is the most commonly mutated oncogene, and targeting EGFR has been widely investigated as a promising direction. However, the results of EGFR pathway inhibitors have not been satisfactory. Limited blood-brain barrier (BBB) permeability, drug resistance, and pathway compensation mechanisms contribute to the failure of anti-EGFR therapies. This review summarizes recent research advances in EGFR-targeted therapy for GBM and provides insight into the reasons for the unsatisfactory results of EGFR-targeted therapy. By combining the results of preclinical studies with those of clinical trials, we discuss that improved drug penetration across the BBB, the use of multi-target combinations, and the development of peptidomimetic drugs under the premise of precision medicine may be promising strategies to overcome drug resistance in GBM.

Antibody drug conjugates for glioblastoma: current progress towards clinical use

INTRODUCTION

Antibody drug conjugates (ADCs) are now a proven therapeutic class for many cancers, combining highly specific targeting with the potency of high effective payloads. This review summarizes the experience with ADCs in brain tumors and examines future paths for their use in these tumors.

AREAS COVERED

This review will cover all the key classes of ADCs which have been tested in primary brain tumors, including commentary on the major trials to date. The efficacy of these trials, as well as their limitations, will put in context of the overall landscape of drug development in brain tumors. Importantly, this review will summarize key learnings and insights from these trials that help provide the basis for rational ways in which these drugs can be effectively and appropriate developed for patients with primary brain tumors.

EXPERT OPINION

ADC development in brain tumors has occurred in two major phases to date. Key learnings from previous trials provide a strong rationale for the continued development of these drugs for primary brain tumors. However, the unique biology of these tumors requires development strategies specifically tailored to maximize their optimal development.

Understanding the activity of antibody-drug conjugates in primary and secondary brain tumours

Antibody-drug conjugates (ADCs), a class of targeted cancer therapeutics combining monoclonal antibodies with a cytotoxic payload via a chemical linker, have already been approved for the treatment of several cancer types, with extensive clinical development of novel constructs ongoing. Primary and secondary brain tumours are associated with high mortality and morbidity, necessitating novel treatment approaches. Pharmacotherapy of brain tumours can be limited by restricted drug delivery across the blood-brain or blood-tumour barrier, although data from phase II studies of the HER2-targeted ADC trastuzumab deruxtecan indicate clinically relevant intracranial activity in patients with brain metastases from HER2⁺ breast cancer. However, depatuxizumab mafodotin, an ADC targeting wild-type EGFR and EGFR variant III, did not provide a definitive overall survival benefit in patients with newly diagnosed or recurrent EGFR-amplified glioblastoma in phase II and III trials, despite objective radiological responses in some patients. In this Review, we summarize the available data on the central nervous system activity of ADCs from trials involving patients with primary and secondary brain tumours and discuss their clinical implications. Furthermore, we explore pharmacological determinants of intracranial activity and discuss the optimal design of clinical trials to facilitate development of ADCs for the treatment of gliomas and brain metastases.

Advances in antibody-based drugs and their delivery through the blood-brain barrier for targeted therapy and immunotherapy of gliomas

Gliomas are highly invasive and are the most common type of primary malignant brain tumor. The routine treatments for glioma include surgical resection, radiotherapy, and chemotherapy. However, glioma recurrence and patient survival remain unsatisfactory after employing these traditional treatment approaches. With the rapid development of molecular immunology, significant breakthroughs have been made in targeted glioma therapy and immunotherapy. Antibody-based therapy has excellent advantages in treating gliomas due to its high specificity and sensitivity. This article reviewed various targeted antibody drugs for gliomas, including anti-glioma surface marker antibodies, anti-angiogenesis antibodies, and anti-immunosuppressive signal antibodies. Notably, many antibodies have been validated clinically, such as bevacizumab, cetuximab, panitumumab, and anti-PD-1 antibodies. These antibodies can improve the targeting of glioma therapy, enhance anti-tumor immunity, reduce the proliferation and invasion of glioma, and thus prolong the survival time of patients. However, the existence of the blood-brain barrier (BBB) has caused significant difficulties in drug delivery for gliomas. Therefore, this paper also summarized drug delivery methods through the BBB, including receptor-mediated transportation, nano-based carriers, and some physical and chemical methods for drug delivery. With these exciting advancements, more antibody-based therapies will likely enter clinical practice and allow more successful control of malignant gliomas.

CDR3 Variants of the TXB2 Shuttle with Increased TfR1 Association Rate and Enhanced Brain Penetration

Since the delivery of biologic drugs to the brain is greatly hampered by the existence of the blood–brain barrier (BBB), brain shuttles are being developed to enhance therapeutic efficacy. As we have previously shown, efficient and selective brain delivery was achieved with TXB2, a cross-species reactive, anti-TfR1 VNAR antibody. To further explore the limits of brain penetration, we conducted restricted randomization of the CDR3 loop, followed by phage display to identify improved TXB2 variants. The variants were screened for brain penetration in mice using a 25 nmol/kg (1.875 mg/kg) dose and a single 18 h timepoint. A higher kinetic association rate to TfR1 correlated with improved brain penetration in vivo. The most potent variant, TXB4, showed a 3.6-fold improvement over TXB2, which had on average 14-fold higher brain levels when compared to an isotype control. Like TXB2, TXB4 retained brain specificity with parenchymal penetration and no accumulation in other organs. When fused with a neurotensin (NT) payload, it led to a rapid drop in body temperature upon transport across the BBB. We also showed that fusion of TXB4 to four therapeutic antibodies (anti-CD20, anti-EGFRvIII, anti-PD-L1 and anti-BACE1) improved their brain exposure between 14- to 30-fold. In summary, we enhanced the potency of parental TXB2 brain shuttle and gained a critical mechanistic understanding of brain delivery mediated by the VNAR anti-TfR1 antibody.

An Enzymatically Cleavable Tripeptide Linker for Maximizing the Therapeutic Index of Antibody-Drug Conjugates

Valine-citrulline is a protease-cleavable linker commonly used in many drug delivery systems, including antibody-drug conjugates (ADC) for cancer therapy. However, its suboptimal in vivo stability can cause various adverse effects such as neutropenia and hepatotoxicity, leading to dose delays or treatment discontinuation. Here, we report that glutamic acid-glycine-citrulline (EGCit) linkers have the potential to solve this clinical issue without compromising the ability of traceless drug release and ADC therapeutic efficacy. We demonstrate that our EGCit ADC resists neutrophil protease-mediated degradation and spares differentiating human neutrophils. Notably, our anti-HER2 ADC shows almost no sign of blood and liver toxicity in healthy mice at 80 mg kg-1. In contrast, at the same dose level, the FDA-approved anti-HER2 ADCs Kadcyla and Enhertu show increased levels of serum alanine aminotransferase and aspartate aminotransferase and morphologic changes in liver tissues. Our EGCit conjugates also exert greater antitumor efficacy in multiple xenograft tumor models compared with Kadcyla and Enhertu. This linker technology could substantially broaden the therapeutic windows of ADCs and other drug delivery agents, providing clinical options with improved efficacy and safety.

Potential of antibody-drug conjugates (ADCs) for cancer therapy

The primary purpose of ADCs is to increase the efficacy of anticancer medications by minimizing systemic drug distribution and targeting specific cells. Antibody conjugates (ADCs) have changed the way cancer is treated. However, because only a tiny fraction of patients experienced long-term advantages, current cancer preclinical and clinical research has been focused on combination trials. The complex interaction of ADCs with the tumor and its microenvironment appear to be reliant on the efficacy of a certain ADC, all of which have significant therapeutic consequences. Several clinical trials in various tumor types are now underway to examine the potential ADC therapy, based on encouraging preclinical results. This review tackles the potential use of ADCs in cancer therapy, emphasizing the essential processes underlying their positive therapeutic impacts on solid and hematological malignancies. Additionally, opportunities are explored to understand the mechanisms of ADCs action, the mechanism of resistance against ADCs, and how to overcome potential resistance following ADCs administration. Recent clinical findings have aroused interest, leading to a large increase in the number of ADCs in clinical trials. The rationale behind ADCs, as well as their primary features and recent research breakthroughs, will be discussed. We then offer an approach for maximizing the potential value that ADCs can bring to cancer patients by highlighting key ideas and distinct strategies.

Brain Cancer Chemotherapy through a Delivery System across the Blood-Brain Barrier into the Brain Based on Receptor-Mediated Transcytosis Using Monoclonal Antibody Conjugates

Advances in pharmacotherapy have brought extraordinary benefits to humanity. However, unmet medical needs in patients remain, particularly in the treatment of central nervous system (CNS) diseases and cancers. CNS drug delivery into the brain across the endothelium is difficult due to the blood-brain barrier (BBB), which is composed mainly of tight junctions and efflux transporters, such as multiple drug resistance 1 (MDR1) (P-glycoprotein). On the other hand, the development of anti-cancer drugs is a challenging task due to their frequent off-target side effects and the complicated mechanisms of cancer pathogenesis and progression. Brain cancer treatment options are surgery, radiation therapy, and chemotherapy. It is difficult to remove all tumor cells, even by surgical removal after a craniotomy. Accordingly, innovative brain cancer drugs are needed. Currently, antibody (Ab) drugs that show high therapeutic effects are often used clinically. Furthermore, antibody-drug conjugates (ADCs), such as trastuzumab deruxtecan, an anti-HER2 (human epidermal receptor 2) ADC with low-molecular cancer drugs through the suitable linker, have been developed. In the case of trastuzumab deruxtecan, it is internalized into cancer cells across the membrane via receptor-mediated endocytosis. Moreover, it is reported that drug delivery into the brain across the BBB was carried out via receptor-mediated transcytosis (RMT), using anti-receptor Abs as a vector against the transferrin receptor (TfR) or insulin receptor (InsR). Thus, anti-TfR ADCs with cancer drugs are promising brain cancer agents due to their precise distribution and low side effects. In this review, I introduce the implementations and potential of brain cancer drug delivery into the brain across the BBB, based on RMT using ADCs.

Homogeneity of antibody-drug conjugates critically impacts the therapeutic efficacy in brain tumors

Glioblastoma multiforme (GBM) is the most aggressive and fatal disease of all brain tumor types. Most therapies rarely provide clinically meaningful outcomes in the treatment of GBM. Although antibody-drug conjugates (ADCs) are promising anticancer drugs, no ADCs have been clinically successful for GBM, primarily because of poor blood-brain barrier (BBB) penetration. Here, we report that ADC homogeneity and payload loading rate are critical parameters contributing to this discrepancy. Although both homogeneous and heterogeneous conjugates exhibit comparable in vitro potency and pharmacokinetic profiles, the former shows enhanced payload delivery to brain tumors. Our homogeneous ADCs provide improved antitumor effects and survival benefits in orthotopic brain tumor models. We also demonstrate that overly drug-loaded species in heterogeneous conjugates are particularly poor at crossing the BBB, leading to deteriorated overall brain tumor targeting. Our findings indicate the importance of homogeneous conjugation with optimal payload loading in generating effective ADCs for intractable brain tumors.

Most therapies rarely provide clinically meaningful improvements in glioblastoma multiforme (GBM) treatment. Anami et al. report that intravenous administration of homogeneous antibody-drug conjugates (ADCs) efficiently delivers payloads to brain tumors, leading to substantially improved tumor growth suppression. Their findings provide rational ADC design for effectively treating intractable brain tumors, including GBM.

Therapeutic Options in Neuro-Oncology

One of the biggest challenges in neuro-oncology is understanding the complexity of central nervous system tumors, such as gliomas, in order to develop suitable therapeutics. Conventional therapies in malignant gliomas reconcile surgery and radiotherapy with the use of chemotherapeutic options such as temozolomide, chloroethyl nitrosoureas and the combination therapy of procarbazine, lomustine and vincristine. With the unraveling of deregulated cancer cell signaling pathways, targeted therapies have been developed. The most affected signaling pathways in glioma cells involve tyrosine kinase receptors and their downstream pathways, such as the phosphatidylinositol 3-kinases (PI3K/AKT/mTOR) and mitogen-activated protein kinase pathways (MAPK). MAPK pathway inhibitors include farnesyl transferase inhibitors, Ras kinase inhibitors and mitogen-activated protein extracellular regulated kinase (MEK) inhibitors, while PI3K/AKT/mTOR pathway inhibitors are divided into pan-inhibitors, PI3K/mTOR dual inhibitors and AKT inhibitors. The relevance of the immune system in carcinogenesis has led to the development of immunotherapy, through vaccination, blocking of immune checkpoints, oncolytic viruses, and adoptive immunotherapy using chimeric antigen receptor T cells. In this article we provide a comprehensive review of the signaling pathways underlying malignant transformation, the therapies currently used in the treatment of malignant gliomas and further explore therapies under development, including several ongoing clinical trials.

PD1 Expression in EGFRvIII-Directed CAR T Cell Infusion Product for Glioblastoma Is Associated with Clinical Response

The epidermal growth factor receptor variant III (EGFRvIII) has been investigated as a therapeutic target for chimeric antigen receptor (CAR) T cell therapy in glioblastoma. Earlier research demonstrated that phenotypic and genotypic characteristics in T cells and CAR T product predicted therapeutic success in hematologic malignancies, to date no determinants for clinical response in solid tumors have been identified. We analyzed apheresis and infusion products from the first-in-human trial of EGFRvIII-directed CAR T for recurrent glioblastoma (NCT02209376) by flow cytometry. Clinical response was quantified via engraftment in peripheral circulation and progression-free survival (PFS), as determined by the time from CAR T infusion to first radiographic evidence of progression. The CD4⁺CAR T cell population in patient infusion products demonstrated PD1 expression which positively correlated with AUC engraftment and PFS. On immune checkpoint inhibitor analysis, CTLA-4, TIM3, and LAG3 did not exhibit significant associations with engraftment or PFS. The frequencies of PD1⁺GZMB⁺ and PD1⁺HLA-DR⁺ CAR T cells in the CD4⁺ infusion products were directly proportional to AUC and PFS. No significant associations were observed within the apheresis products. In summary, PD1 in CAR T infusion products predicted peripheral engraftment and PFS in recurrent glioblastoma.

Antibody-drug conjugates: beyond current approvals and potential future strategies

The recent approvals for antibody-drug conjugates (ADCs) in multiple malignancies in recent years have fuelled the ongoing development of this class of drugs. These novel agents combine the benefits of high specific targeting of oncogenic cell surface antigens with the additional cell kill from high potency cytotoxic payloads, thus achieving wider therapeutic windows. This review will summarise the clinical activity of ADCs in tumour types not covered elsewhere in this issue, such as gastrointestinal (GI) and genitourinary (GU) cancers and glioblastoma (GBM). In addition to the ongoing clinical testing of existing ADCs, there is substantial preclinical and early phase testing of newer ADCs or ADC incorporating strategies. This review will provide selected insights into such future development, focusing on the development of novel ADCs against new antigen targets in the tumour microenvironment (TME) and combination of ADCs with immuno-oncology (IO) agents.

Antibody-Based Formats to Target Glioblastoma: Overcoming Barriers to Protein Drug Delivery

Glioblastoma (GB) is recognized as the most aggressive form of primary brain cancer. Despite advances in treatment strategies that include surgery, radiation, and chemotherapy, the median survival time (∼15 months) of patients with GB has not significantly improved. The poor prognosis of GB is also associated with a very high chance of tumor recurrence (∼90%), and current treatment measures have failed to address the complications associated with this disease. However, targeted therapies enabled through antibody engineering have shown promise in countering GB when used in combination with conventional approaches. Here, we discuss the challenges in conventional as well as future GB therapeutics and highlight some of the known advantages of using targeted biologics to overcome these impediments. We also review a broad range of potential alternative routes that could be used clinically to administer anti-GB biologics to the brain through evasion of its natural barriers.

Visualizing Spatial and Stoichiometric Barriers to Bispecific T-cell Engager Efficacy

Bispecific T-cell engager (BiTE) molecules are biologic T cell-directing immunotherapies. Blinatumomab is approved for treatment of B-cell malignancies, but BiTE molecule development in solid tumors has been more challenging. Here, we employed intravital imaging to characterize exposure and pharmacodynamic response of an anti-muCD3/anti-huEGFRvIII mouse surrogate BiTE molecule in epidermal growth factor receptor variant III (EGFRvIII)-positive breast tumors implanted within immunocompetent mice. Our study revealed heterogeneous temporal and spatial dynamics of BiTE molecule extravasation into solid tumors, highlighting physical barriers to BiTE molecule function. We also discovered that high, homogeneous EGFRvIII expression on cancer cells was necessary for a BiTE molecule to efficiently clear tumors. Additionally, we found that resident tumor-infiltrating lymphocytes (TILs) were sufficient for optimal tumor killing only at high BiTE molecule dosage, whereas inclusion of peripheral T-cell recruitment was synergistic at moderate to low dosages. We report that deletion of stimulatory conventional type I DCs (cDC1) diminished BiTE molecule-induced T-cell activation and tumor clearance, suggesting that in situ antigen-presenting cell (APC) engagements modulate the extent of BiTE molecule efficacy. In summary, our work identified multiple requirements for optimal BiTE molecule efficacy in solid tumors, providing insights that could be harnessed for solid cancer immunotherapy development.

Antibody-drug conjugates: Resurgent anticancer agents with multi-targeted therapeutic potential

Antibody-drug conjugates (ADCs) constitute a relatively new group of anticancer agents, whose first appearance took place about two decades ago, but a renewed interest occurred in recent years, following the success of anti-cancer immunotherapy with monoclonal antibodies. Indeed, an ADC combines the selectivity of a monoclonal antibody with the cell killing properties of a chemotherapeutic agent (payload), joined together through an appropriate linker. The antibody moiety targets a specific cell surface antigen expressed by tumor cells and/or cells of the tumor microenvironment and acts as a carrier that delivers the cytotoxic payload within the tumor mass. Despite advantages in terms of selectivity and potency, the development of ADCs is not devoid of challenges, due to: i) low tumor selectivity when the target antigens are not exclusively expressed by cancer cells; ii) premature release of the cytotoxic drug into the bloodstream as a consequence of linker instability; iii) development of tumor resistance mechanisms to the payload. All these factors may result in lack of efficacy and/or in no safety improvement compared to unconjugated cytotoxic agents. Nevertheless, the development of antibodies engineered to remain inert until activated in the tumor (e.g., antibodies activated proteolytically after internalization or by the acidic conditions of the tumor microenvironment) together with the discovery of innovative targets and cytotoxic or immunomodulatory payloads, have allowed the design of next-generation ADCs that are expected to possess improved therapeutic properties. This review provides an overview of approved ADCs, with related advantages and limitations, and of novel targets exploited by ADCs that are presently under clinical investigation.

Antibody Drug Conjugates in Glioblastoma - Is There a Future for Them?

Glioblastoma (GBM) is an aggressive and fatal malignancy that despite decades of trials has limited therapeutic options. Antibody drug conjugates (ADCs) are composed of a monoclonal antibody which specifically recognizes a cellular surface antigen linked to a cytotoxic payload. ADCs have demonstrated superior efficacy and/or reduced toxicity in a range of haematological and solid tumors resulting in nine ADCs receiving regulatory approval. ADCs have also been explored in patients with brain tumours but with limited success to date. While earlier generations ADCs in glioma patients have had limited success and high toxicity, newer and improved ADCs characterised by low immunogenicity and more effective payloads have shown promise in a range of tumour types. These newer ADCs have also been tested in glioma patients, however, with mixed results. Factors affecting the effectiveness of ADCs to target the CNS include the blood brain barrier which acts as a physical and biochemical barrier, the pro-cancerogenic and immunosuppressive tumor microenvironment and tumour characteristics like tumour volume and antigen expression. In this paper we review the data regarding the ongoing the development of ADCs in glioma patients as well as potential strategies to overcome these barriers to maximise their therapeutic potential.

Glioblastoma pharmacotherapy: A multifaceted perspective of conventional and emerging treatments (Review)

Due to its localisation, rapid onset, high relapse rate and resistance to most currently available treatment methods, glioblastoma multiforme (GBM) is considered to be the deadliest type of all gliomas. Although surgical resection, chemotherapy and radiotherapy are among the therapeutic strategies used for the treatment of GBM, the survival rates achieved are not satisfactory, and there is an urgent need for novel effective therapeutic options. In addition to single-target therapy, multi-target therapies are currently under development. Furthermore, drugs are being optimised to improve their ability to cross the blood-brain barrier. In the present review, the main strategies applied for GBM treatment in terms of the most recent therapeutic agents and approaches that are currently under pre-clinical and clinical testing were discussed. In addition, the most recently reported experimental data following the testing of novel therapies, including stem cell therapy, immunotherapy, gene therapy, genomic correction and precision medicine, were reviewed, and their advantages and drawbacks were also summarised.

Novel Receptor Tyrosine Kinase Pathway Inhibitors for Targeted Radionuclide Therapy of Glioblastoma

Glioblastoma (GB) remains the most fatal brain tumor characterized by a high infiltration rate and treatment resistance. Overexpression and/or mutation of receptor tyrosine kinases is common in GB, which subsequently leads to the activation of many downstream pathways that have a critical impact on tumor progression and therapy resistance. Therefore, receptor tyrosine kinase inhibitors (RTKIs) have been investigated to improve the dismal prognosis of GB in an effort to evolve into a personalized targeted therapy strategy with a better treatment outcome. Numerous RTKIs have been approved in the clinic and several radiopharmaceuticals are part of (pre)clinical trials as a non-invasive method to identify patients who could benefit from RTKI. The latter opens up the scope for theranostic applications. In this review, the present status of RTKIs for the treatment, nuclear imaging and targeted radionuclide therapy of GB is presented. The focus will be on seven tyrosine kinase receptors, based on their central role in GB: EGFR, VEGFR, MET, PDGFR, FGFR, Eph receptor and IGF1R. Finally, by way of analyzing structural and physiological characteristics of the TKIs with promising clinical trial results, four small molecule RTKIs were selected based on their potential to become new therapeutic GB radiopharmaceuticals.

Unlocking the potential of antibody-drug conjugates for cancer therapy

Nine different antibody-drug conjugates (ADCs) are currently approved as cancer treatments, with dozens more in preclinical and clinical development. The primary goal of ADCs is to improve the therapeutic index of antineoplastic agents by restricting their systemic delivery to cells that express the target antigen of interest. Advances in synthetic biochemistry have ushered in a new generation of ADCs, which promise to improve upon the tissue specificity and cytotoxicity of their predecessors. Many of these drugs have impressive activity against treatment-refractory cancers, although hurdles impeding their broader use remain, including systemic toxicity, inadequate biomarkers for patient selection, acquired resistance and unknown benefit in combination with other cancer therapies. Emerging evidence indicates that the efficacy of a given ADC depends on the intricacies of how the antibody, linker and payload components interact with the tumour and its microenvironment, all of which have important clinical implications. In this Review, we discuss the current state of knowledge regarding the design, mechanism of action and clinical efficacy of ADCs as well as the apparent limitations of this treatment class. We then propose a path forward by highlighting several hypotheses and novel strategies to maximize the potential benefit that ADCs can provide to patients with cancer.

CAR T Cell-Based Immunotherapy for the Treatment of Glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumor in adults. Current treatment options typically consist of surgery followed by chemotherapy or more frequently radiotherapy, however, median patient survival remains at just over 1 year. Therefore, the need for novel curative therapies for GBM is vital. Characterization of GBM cells has contributed to identify several molecules as targets for immunotherapy-based treatments such as EGFR/EGFRvIII, IL13Rα2, B7-H3, and CSPG4. Cytotoxic T lymphocytes collected from a patient can be genetically modified to express a chimeric antigen receptor (CAR) specific for an identified tumor antigen (TA). These CAR T cells can then be re-administered to the patient to identify and eliminate cancer cells. The impressive clinical responses to TA-specific CAR T cell-based therapies in patients with hematological malignancies have generated a lot of interest in the application of this strategy with solid tumors including GBM. Several clinical trials are evaluating TA-specific CAR T cells to treat GBM. Unfortunately, the efficacy of CAR T cells against solid tumors has been limited due to several factors. These include the immunosuppressive tumor microenvironment, inadequate trafficking and infiltration of CAR T cells and their lack of persistence and activity. In particular, GBM has specific limitations to overcome including acquired resistance to therapy, limited diffusion across the blood brain barrier and risks of central nervous system toxicity. Here we review current CAR T cell-based approaches for the treatment of GBM and summarize the mechanisms being explored in pre-clinical, as well as clinical studies to improve their anti-tumor activity.

Advancements in folate receptor targeting for anti-cancer therapy: A small molecule-drug conjugate approach

Targeted delivery combined with controlled release of drugs has a crucial role in future of personalized medicine. The majority of cancer drugs are intended to interfere with one or more cellular events. Anticancer agents can also be toxic to healthy cells, as healthy cells may also need to proliferate and avoid apoptosis. The focus of this review covers the principles, advantages, drawbacks and summarize criteria that must be met for design of small molecule-drug conjugates (SMDCs) to achieve the desired therapeutic potency with minimal toxicity. SMDCs are composed of a targeting ligand, a releasable bridge, a spacer, and a therapeutic payload. We summarize the criteria for the effective design that influences the selection of tumor specific receptor and optimum elements in the design of SMDCs. We also discuss the criteria for selecting the optimal therapeutic drug payload, spacer and linker. The linker chemistries and cleavage strategies are also discussed. Finally, we review the folate receptor targeting SMDCs that are in preclinical development and in clinical trials.

Preclinical Assessment of AMG 596, a Bispecific T-cell Engager (BiTE) Immunotherapy Targeting the Tumor-specific Antigen EGFRvIII

AMG 596 is a bispecific T-cell engager (BiTE) immuno-oncology therapy in clinical development for treatment of glioblastoma multiforme (GBM), the most common primary brain tumor in adults with limited therapeutic options. AMG 596 is composed of two single-chain variable fragments that simultaneously bind to the tumor-specific antigen, EGFR variant III (EGFRvIII), on GBM cells and to CD3 on T cells, thereby activating T cells to proliferate and secrete cytotoxic substances that induce lysis of the bound tumor cell. T-cell-redirected lysis by AMG 596 is very potent; in vitro studies revealed EC₅₀ values in the low picomolar range, and in vivo studies showed that AMG 596 treatment significantly increased the overall survival of mice bearing EGFRvIII-expressing orthotopic tumors. In addition, AMG 596 activity is highly specific; no AMG 596-induced T-cell activity can be observed in assays with EGFRvIII-negative GBM cells, and no signs of toxicity and activity were observed in cynomolgus monkeys, which lack expression of EGFRvIII on normal tissues. With EGFRvIII-expressing GBM cells, we showed shedding of EGFRvIII-containing membrane vesicles, followed by vesicle uptake and EGFRvIII cell surface presentation by EGFRvIII noncoding GBM cells. Cell membrane presentation of EGFRvIII following microvesicle transfer allows engagement by AMG 596, resulting in T-cell activation and T-cell-dependent lysis of GBM cells. Together, these data show a compelling preclinical efficacy and safety profile of AMG 596, supporting its development as a novel immunotherapy for treatment of GBM.

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.

EGFR targeting for cancer therapy: Pharmacology and immunoconjugates with drugs and nanoparticles

The epidermal growth factor receptor (EGFR) belongs to the tyrosine kinase receptors family and is present in the epithelial cell membrane. Its endogenous activation occurs through the binding of different endogenous ligands, including the epidermal growth factor (EGF), leading to signaling cascades able to maintain normal cellular functions. Although involved in the development and maintenance of tissues in normal conditions, when EGFR is overexpressed, it stimulates the growth and progression of tumors, resulting in angiogenesis, invasion and metastasis, through some main cascades such as Ras/Raf/MAPK, PIK-3/AKT, PLC-PKC and STAT. Besides, considering the limitations of conventional chemotherapy that result in high toxicity and low tumor specificity, EGFR is currently considered an important target. As a result, several monoclonal antibodies are currently approved for use in cancer treatment, such as cetuximab (CTX), panitumumab, nimotuzumab, necitumumab and others are in clinical trials. Aiming to combine the chemotherapeutic agent toxicity and specific targeting to EGFR overexpressing tumor tissues, two main strategies will be discussed in this review: antibody-drug conjugates (ADCs) and antibody-nanoparticle conjugates (ANCs). Briefly, ADCs consist of antibodies covalently linked through a spacer to the cytotoxic drug. Upon administration, binding to EGFR and endocytosis, ADCs suffer chemical and enzymatic reactions leading to the release and accumulation of the drug. Instead, ANCs consist of nanotechnology-based formulations, such as lipid, polymeric and inorganic nanoparticles able to protect the drug against inactivation, allowing controlled release and also passive accumulation in tumor tissues by the enhanced permeability and retention effect (EPR). Furthermore, ANCs undergo active targeting through EGFR receptor-mediated endocytosis, leading to the formation of lysosomes and drug release into the cytosol. Herein, we will present and discuss some important aspects regarding EGFR structure, its role on internal signaling pathways and downregulation aspects. Then, considering that EGFR is a potential therapeutic target for cancer therapy, the monoclonal antibodies able to target this receptor will be presented and discussed. Finally, ADCs and ANCs state of the art will be reviewed and recent studies and clinical progresses will be highlighted. To the best of our knowledge, this is the first review paper to address specifically the EGFR target and its application on ADCs and ANCs.

Disentangling the therapeutic tactics in GBM: From bench to bedside and beyond

Glioblastoma multiforme (GBM) is one of the most common and malignant form of adult brain tumor with a high mortality rate and dismal prognosis. The present standard treatment comprising surgical resection followed by radiation and chemotherapy using temozolomide can broaden patient's survival to some extent. However, the advantages are not palliative due to the development of resistance to the drug and tumor recurrence following the multimodal treatment approaches due to both intra- and intertumoral heterogeneity of GBM. One of the major contributors to temozolomide resistance is O⁶ -methylguanine-DNA methyltransferase. Furthermore, deficiency of mismatch repair, base excision repair, and cytoprotective autophagy adds to temozolomide obstruction. Rising proof additionally showed that a small population of cells displaying certain stem cell markers, known as glioma stem cells, adds on to the resistance and tumor progression. Collectively, these findings necessitate the discovery of novel therapeutic avenues for treating glioblastoma. As of late, after understanding the pathophysiology and biology of GBM, some novel therapeutic discoveries, such as drug repurposing, targeted molecules, immunotherapies, antimitotic therapies, and microRNAs, have been developed as new potential treatments for glioblastoma. To help illustrate, "what are the mechanisms of resistance to temozolomide" and "what kind of alternative therapeutics can be suggested" with this fatal disease, a detailed history of these has been discussed in this review article, all with a hope to develop an effective treatment strategy for GBM.

Advances in epidermal growth factor receptor specific immunotherapy: lessons to be learned from armed antibodies

The epidermal growth factor receptor (EGFR) has been recognized as an important therapeutic target in oncology. It is commonly overexpressed in a variety of solid tumors and is critically involved in cell survival, proliferation, metastasis, and angiogenesis. This multi-dimensional role of EGFR in the progression and aggressiveness of cancer, has evolved from conventional to more targeted therapeutic approaches. With the advent of hybridoma technology and phage display techniques, the first anti-EGFR monoclonal antibodies (mAbs) (Cetuximab and Panitumumab) were developed. Due to major limitations including host immune reactions and poor tumor penetration, these antibodies were modified and used as guiding mechanisms for the specific delivery of readily available chemotherapeutic agents or plants/bacterial toxins, giving rise to antibody-drug conjugates (ADCs) and immunotoxins (ITs), respectively. Continued refinement of ITs led to deimmunization strategies based on depletion of B and T-cell epitopes or substitution of non-human toxins leading to a growing repertoire of human enzymes capable of inducing cell death. Similarly, the modification of classical ADCs has resulted in the first, fully recombinant versions. In this review, we discuss significant advancements in EGFR-targeting immunoconjugates, including ITs and recombinant photoactivable ADCs, which serve as a blueprint for further developments in the evolving domain of cancer immunotherapy.

Epidermal growth factor receptor (EGFR) involvement in epithelial-derived cancers and its current antibody-based immunotherapies

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that is part of the family of tyrosine kinase receptors. The binding of EGFR to its cognate ligands leads to its autophosphorylation and subsequent activation of the signal transduction pathways involved in regulating cellular proliferation, differentiation, and survival. Accordingly, this receptor carries out both redundant and restricted functions in the germline development of mammals and in the maintenance of various adult tissues. Correspondingly, the loss of EGFR regulation results in many human diseases, with the most notable cancer. This receptor is overexpressed and/or mutated in multiple epithelial-derived tumors, and associated with poor prognosis and survival in cancer patients. Here, we discuss in detail the role of EGFR in specific epithelial-derived cancer pathologies; these include lung cancer, colorectal cancer, and squamous cell carcinomas. The development of multiple anticancer agents against EGFR diminished the progression and metastasis of tumors. Some of the most versatile therapeutic anti-EGFR agents include the monoclonal antibodies (mAbs), demonstrating success in clinical settings when used in combination with cytotoxic treatments, such as chemotherapy and/or radiation. We thus discuss the development and application of two of the most notable therapeutic mAbs, cetuximab, and panitumumab, currently utilized in various EGFR-related epithelial cancers.

ADCs, as Novel Revolutionary Weapons for Providing a Step Forward in Targeted Therapy of Malignancies

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Antibody drug conjugates (ADCs), as potent pharmaceutical trojan horses for cancer treatment, provide superior efficacy and specific targeting along with low risk of adverse reactions compared to traditional chemotherapeutics. In fact, the development of these agents combines the selective targeting capability of monoclonal antibody (mAb) with high cytotoxicity of chemotherapeutics for controlling the neoplastic mass growth. Different ADCs (more than 60 ADCs) in preclinical and clinical trials were introduced in this novel pharmaceutical field. Various design-based factors must be taken into account for improving the functionality of ADC technology, including selection of appropriate target antigen and high binding affinity of fragment (miniaturized ADCs) or full mAbs (preferentially use of humanized or fully human antibodies compared to murine and chimeric ones), use of bispecific antibodies for dual targeting effect, linker engineering and conjugation method efficacy to obtain more controlled drug to antibody ratio (DAR). Challenging issues affecting therapeutic efficacy and safety of ADCs, including bystander effect, on- and off-target toxicities, multi drug resistance (MDR) are also addressed. 4 FDA-approved ADCs in the market, including ADCETRIS ®, MYLOTARG®, BESPONSA ®, KADCYLA®. The goal of the current review is to evaluate the key parameters affecting ADCs development.

Development of a Novel EGFR-Targeting Antibody-Drug Conjugate for Pancreatic Cancer Therapy

BACKGROUND

Overexpression of epidermal growth factor receptor (EGFR) is common in pancreatic cancer and associated with the poor prognosis of this malignancy.

OBJECTIVE

To develop anti-EGFR antibody-drug conjugates (ADCs) for use in a novel EGFR-targeting approach to treat pancreatic cancer.

METHODS

A humanized anti-EGFR monoclonal antibody (RC68) was generated by mouse immunization and complementary-determining region grafting technology. Two RC68-based ADCs, RC68-MC-VC-PAB-MMAE and RC68-PY-VC-PAB-MMAE, were synthesized by conjugating monomethyl auristatin E (MMAE), a small-molecule cytotoxin, to RC68 through two distinct linkers (MC and PY). Internalization of the RC68-based ADCs was examined by flow cytometry. The in vitro and in vivo antitumor activities of RC68-based ADCs were evaluated in human pancreatic cancer cells and in a BXPC-3 xenograft nude mouse model, respectively.

RESULTS

The RC68-based ADCs bound to EGFR on the surface of tumor cells and were effectively internalized, resulting in the death of EGFR-positive cancer cell lines. The RC68-based ADCs (at 5 or 10 mg/kg) were more potent than gemcitabine hydrochloride (60 mg/kg) at inhibiting the growth of BXPC-3 xenografts. Moreover, RC68-PY-VC-PAB-MMAE was found to have superior stability in human plasma compared with RC68-MC-VC-PAB-MMAE.

CONCLUSION

A novel EGFR-targeting ADC, RC68-PY-VC-PAB-MMAE, shows promise as an effective, selective, and safe therapeutic agent for EGFR-positive pancreatic cancer.

Conjugation Site Analysis of Lysine-Conjugated ADCs

Lysine-conjugated antibody-drug conjugates (ADCs) are formed by attaching cytotoxic drugs to reactive lysine residues of monoclonal antibodies (mAbs) through chemical linkers. During production, the payloads are conjugated nonspecifically to lysine residues in mAbs, resulting in a heterogeneous mixture of ADCs with both different number and conjugation sites of drug payloads per mAb. On account of the drug conjugation sites and levels that both have significant influences on physical and pharmaceutical properties of ADCs, a reliable and straightforward approach for conjugation site analysis for ADCs is highly demanded. Herein, we used a lysine-conjugated ADC, Trastuzumab-MCC-DM1 (T-DM1), as a model ADC, and described an integrative strategy that combines the signature ion fingerprinting method for rapid and reliable filtering of DM1-conjugated peptides, and the normalized area quantitation approach for accurately gauging the conjugation levels for each identified site. This approach is believed to be readily applicable to other maytansinoid derivatives-modified ADCs, and more importantly, universally applicable to lysine-conjugated ADCs for both the recognition of conjugation sites and the measurement of conjugation levels.

EGFRvIII: An Oncogene with Ambiguous Role

Epidermal growth factor receptor variant III (EGFRvIII) seems to constitute the perfect therapeutic target for glioblastoma (GB), as it is specifically present on up to 28-30% of GB cells. In case of other tumor types, expression and possible role of this oncogene still remain controversial. In spite of EGFRvIII mechanism of action being crucial for the design of small active anticancer molecules and immunotherapies, i.e., CAR-T technology, it is yet to be precisely defined. EGFRvIII is known to be resistant to degradation, but it is still unclear whether it heterodimerizes with EGF-activated wild-type EGFR (EGFRWT) or homodimerizes (including covalent homodimerization). Constitutive kinase activity of this mutated receptor is relatively low, and some researchers even claim that a nuclear, but not a membrane function, is crucial for its activity. Based on the analyses of recurrent tumors that are often lacking EGFRvIII expression despite its initial presence in corresponding primary foci, this oncogene is suggested to play a marginal role during later stages of carcinogenesis, while even in primary tumors EGFRvIII expression is detected only in a small percentage of tumor cells, undermining the rationality of EGFRvIII-targeting therapies. On the other hand, EGFRvIII-positive cells are resistant to apoptosis, more invasive, and characterized with enhanced proliferation rate. Moreover, expression of this oncogenic receptor was also postulated to be a marker of cancer stem cells. Opinions regarding the role that EGFRvIII plays in tumorigenesis and for tumor aggressiveness are clearly contradictory and, therefore, it is crucial not only to determine its mechanism of action, but also to unambiguously define its role at early and advanced cancer stages.

Whole genome and biomarker analysis of patients with recurrent glioblastoma on bevacizumab: A subset analysis of the CABARET trial

The CABARET trial (ACTRN12610000915055) reported no difference in overall survival (OS) between patients with recurrent glioblastoma (GBM) randomized to either bevacizumab monotherapy or bevacizumab plus carboplatin. However, a subset of patients showed durable responses and prolonged survival, with recorded survival times of over 30 months in five of 122 patients (4%). Patient selection for bevacizumab therapy would be enhanced if a predictive biomarker of response or survival could be identified; this biomarker sub-study attempted to identify novel biomarkers. Patients who opted to participate in this sub-study and who had adequate biospecimens for analysis (n = 54) were retrospectively evaluated for the expression of a series of tumor proteins. Immunohistochemistry (IHC) was used to measure the expression of 19 proteins previously implicated in cancer treatment response to bevacizumab. MGMT promoter methylation was also assessed. Tumor DNA from five patients with outlying survival duration ('poor' and 'exceptional' survivors) was subjected to whole genome sequencing (WGS). No single protein expression level, including VEGF-A, predicted OS in the cohort. WGS of poor and exceptional survivors identified a gain in Chromosome 19 that was exclusive to the exceptional survivors. Validation of this finding requires examination of a larger independent cohort.

Antibody-Drug Conjugate that Exhibits Synergistic Cytotoxicity with an Endosome-Disruptive Peptide

Antibody-drug conjugates are an important class of cancer therapeutics. These agents generally bind a specific cell surface receptor, undergo receptor-mediated endocytosis, and enter the endosomal-lysosomal system, where the environment in these organelles facilitates the release of a membrane-permeable cytotoxin. By using a membrane-impermeable cytotoxin, we describe here a method that allows the cytotoxicity of an antibody conjugate to be triggered by co-administration with an endosome-disruptive peptide that exhibits low toxicity. This approach was validated by conjugation of an anionic derivative of the tubulin-binding cytotoxin colchinol methyl ether to lysine residues of the HER2-targeting antibody trastuzumab (Herceptin) via a disulfide. When this antibody binds HER2 on SKBR3 breast cancer cells and undergoes endocytosis, the membrane-impermeable cytotoxin is released, but it becomes trapped in endosomes, resulting in relatively low cytotoxicity (IC50 > 1 μM). However, co-administration with an essentially nontoxic (IC50 > 10 μM) cholesterol-linked endosome-disruptive peptide promotes the release of this small molecule into the cytoplasm, conferring subnanomolar cytotoxic potency (IC50 = 0.11 ± 0.07 nM). Studies of a structurally related fluorophore conjugate revealed that the endosome-disruptive peptide does not substantially enhance cleavage of the disulfide (t 1/2 = 8 ± 2 h) within endosomes, suggesting that the mechanism of endosomal escape involves the efflux of some small molecules without facilitating substantial influx of reduced glutathione.

Production and Evaluation of an Avian IgY Immunotoxin against CD133+ for Treatment of Carcinogenic Stem Cells in Malignant Glioma: IgY Immunotoxin for the Treatment of Glioblastoma

Background

Glioblastoma is the most common malignant tumor of Central Nervous System. Despite the research in therapeutics, the prognosis is dismal. Malignant glioma stem cells (MGSCs) are a major cause of treatment failure and increasing tumor recurrence. In general, cancer stem cells (CSCs) express prominin-1 (CD133), considered as a potential therapeutic target. In this study, we produced an avian immunotoxin directed against the subpopulation of CD133+ CSCs within a malignant glioma. We used the avian IgY because it has various advantages as increased affinity to mammal antigens and inexpensive obtention of large amounts of specific antibodies (approximately 1 mg/per egg). The design, production, purification and use of IgY anti CD133 immunotoxin constitute an original goal of this research.

Methods

The immunodominant peptide of CD133 was designed to immunize hens; also, the extracellular domain of CD133 was cloned to probe the IgY antibodies. In parallel, a recombinant abrin A chain was produced in E. coli in order to join it to the Fc domain of the anti-CD133 IgY to conform the immunotoxin. This anti-CD133 IgY anti-tumor immunotoxin was tested in vitro and in vivo. Results. The cytotoxicity of the immunotoxin in vitro showed that IgY-abrin immunotoxin reduced 55% cell viability. After subcutaneous MGSCs implantation, the animals treated intraperitoneally or intratumorally with the IgY-abrin immunotoxin showed more than 50% decrease of tumor volume.

Conclusion

Results showed that the IgY-abrin immunotoxin had cytotoxic activity against CD133+ MGSCs and provides a novel approach for the immunotherapy of glioblastoma.

Monomethyl auristatin E-conjugated anti-EGFR antibody inhibits the growth of human EGFR-positive non-small cell lung cancer

PURPOSE

Epidermal growth factor receptor (EGFR) is highly expressed on non-small cell lung cancers (NSCLC) and a valuable therapeutic target. This study aimed at producing and characterizing monomethyl auristatin E (MMAE)-conjugated anti-EGFR antibody as a novel EGFR-targeting therapy for NSCLC.

METHODS

A humanized anti-EGFR monoclonal antibody (named RC68) was purified and conjugated with MMAE using a MC-VC-PAB or PY-VC-PAB linker. The in vitro and in vivo antitumor activity of RC68-MC-VC-PAB-MMAE and RC68-PY-VC-PAB-MMAE were characterized.

RESULTS

The RC68 was generated from RC68-expressing cells and had a purity of > 99.0%. The RC68 recognized EGFR on tumor cells, particularly for higher EGFR expressing H125, A431, HCC827 and H1975 cells. The RC68 was conjugated with an average of 4 MMAE molecules to generate RC68-MC-VC-PAB-MMAE and RC68-PY-VC-PAB-MMAE, respectively. The RC68-MC-VC-PAB-MMAE, RC68-PY-VC-PAB-MMAE and RC68 displayed similar binding affinity to EGFR on tumor cells, and RC68-MC-VC-PAB-MMAE and RC68-PY-VC-PAB-MMAE were effectively internalized by H125 cells. The RC68-MC-VC-PAB-MMAE and RC68-PY-VC-PAB-MMAE inhibited the growth of H125 cells in vitro with an IC₅₀ 7.37-8.04 ng/mL and implanted H125 tumors in vivo, but did not affect body weights of mice. The antitumor effect of RC68-MC-VC-PAB-MMAE was stronger than RC68-PY-VC-PAB-MMAE, which was also stronger than docetaxel in vivo.

CONCLUSIONS

These novel antibody-drug conjugates, particularly for RC68-MC-VC-PAB-MMAE, may be a potential candidate for treatment of EGFR + NSCLC.

Discovery of A Novel EGFR-Targeting Antibody-Drug Conjugate, SHR-A1307, for the Treatment of Solid Tumors Resistant or Refractory to Anti-EGFR Therapies

Although inhibiting EGFR-mediated signaling proved to be effective in treating certain types of cancers, a quickly evolved mechanism that either restores the EGFR signaling or activates an alternative pathway for driving the proliferation and survival of malignant cells limits the efficacy and utility of the approach via suppressing the EGFR functionality. Given the fact that overexpression of EGFR is commonly seen in many cancers, an EGFR-targeting antibody-drug conjugate (ADC) can selectively kill cancer cells independently of blocking EGFR-mediated signaling. Herein, we describe SHR-A1307, a novel anti-EGFR ADC, generated from an anti-EGFR antibody with prolonged half-life, and conjugated with a proprietary toxin payload that has increased index of EGFR targeting-dependent versus EGFR targeting-independent cytotoxicity. SHR-A1307 demonstrated strong and sustained antitumor activities in EGFR-positive tumors harboring different oncogenic mutations on EGFR, KRAS, or PIK3CA. Antitumor efficacy of SHR-A1307 correlated with EGFR expression levels in vitro and in vivo, regardless of the mutation status of EGFR signaling mediators and a resultant resistance to EGFR signaling inhibitors. Cynomolgus monkey toxicology study showed that SHR-A1307 is well tolerated with a wide therapeutic index. SHR-A1307 is a promising therapeutic option for EGFR-expressing cancers, including those resistant or refractory to the EGFR pathway inhibitors.

Therapeutic potential of nimotuzumab PEGylated-maytansine antibody drug conjugates against EGFR positive xenograft

Nimotuzumab is a humanized anti-epidermal growth factor receptor I (EGFR) monoclonal antibody. We have developed antibody drug conjugates (ADCs) with nimotuzumab conjugated to PEGylated-maytansine (PEG₆-DM1). We generated conjugates with low (nimotuzumab-PEG₆-DM1-Low: DAR = 3.5) and high (nimotuzumab-PEG₆-DM1-High: DAR = 7.3) drug to antibody ratios (DAR). Quality control was performed using UV spectrophotometry, size exclusion HPLC, bioanalyzer, biolayer interferometry (BLI), and flow cytometry in EGFR-positive DLD-1, MDA-MB-468 (high density EGFR), and HT-29 (very low EGFR density) cells. Control antibody drug conjugates were developed using a human anti-maltose binding protein (MBP) antibody. BLI showed that the binding of nimotuzumab-PEG₆-DM1-Low and nimotuzumab-PEG₆-DM1-High was slightly but significantly affected by conjugation of the drug (nimotuzumab K_D 0.89 ± 0.02 nM < nimotuzumab-PEG₆-DM1-Low K_D 1.94 ± 0.02 nM < nimotuzumab-PEG₆-DM1-High K_D 3.75 ± 0.03 nM). In vitro cytotoxicity was determined following incubation of cells with the immunoconjugates and IC₅₀ values were determined. Nimotuzumab-PEG₆-DM1-Low and nimotuzumab-PEG₆-DM1-High were used to treat EGFR positive KRAS mutant DLD-1 colorectal cancer xenograft. DLD-1 cells were transduced with a red fluorescent protein (iRFP702) to allow the use of near infrared imaging (NIR) for tumor response monitoring. In vitro potency correlated with the number of drugs on antibody, with nimotuzumab-PEG₆-DM1-High showing higher activity than nimotuzumab-PEG₆-DM1-Low. Three doses (15 mg/kg) of the ADCs prolonged the survival of DLD-1-iRFP-702 tumor bearing mice as monitored by NIR. Nimotuzumab-PEG₆-DM1-Low resulted in 4/6 complete cure while nimotuzumab-PEG₆-DM1-High resulted in 2/5 complete cure. The novel ADCs were very effective in a colorectal cancer model in vivo.

Preclinical Evaluation of 111In-Labeled PEGylated Maytansine Nimotuzumab Drug Conjugates in EGFR-Positive Cancer Models

Epidermal growth factor receptor I (EGFR) is overexpressed in most cancers of epithelial origin. Antibody drug conjugates (ADCs) with PEGylated-maytansine (PEG-DM1) show promise in vitro and in vivo. However, in vivo biodistribution data for ADCs with PEG-DM1 have not been reported. Development of methods to understand the real-time in vivo behavior of these ADCs is needed to move these compounds to the clinic. Methods: Here we have used noninvasive small-animal SPECT/CT imaging and ex vivo biodistribution to understand the in vivo behavior of PEG₆-DM1 ADCs. We developed nimotuzumab ADCs conjugated to PEG₆-DM1. We generated immunoconjugates with low (nimotuzumab-PEG₆-DM1-Low) and high (nimotuzumab-PEG₆-DM1-High) drug-to-antibody ratios. The drug-to-antibody of nimotuzumab-PEG₆-DM1-Low and nimotuzumab-PEG₆-DM1-High was 3.5 and 7.3, respectively. Quality control was performed using ultraviolet spectrophotometry, size-exclusion high-performance liquid chromatography, bioanalyzer, biolayer interferometry, and flow cytometry in EGFR-positive DLD-1 cells. These immunoconjugates were conjugated with DOTA and radiolabeled with ¹¹¹In. The in vitro binding and internalization rates of ¹¹¹In-nimotuzumab, ¹¹¹In-nimotuzumab-PEG₆-DM1-Low, and ¹¹¹In-nimotuzumab-PEG₆-DM1-High were characterized. Furthermore, the pharmacokinetics, biodistribution, and imaging characteristics were evaluated in normal and DLD-1 tumor-bearing mice. Results: Flow cytometry and biolayer interferometry showed a trend toward decreasing EGFR affinity with increasing number of PEG₆-DM1 on the antibody. Despite the lower overall cellular binding of the PEG₆-DM1 radioimmunoconjugates, internalization was higher for PEG₆-DM1 ADCs than for the non-PEGylated ADC in the following order: ¹¹¹In-nimotuzumab-PEG₆-DM1-High > ¹¹¹In-nimotuzumab-PEG₆-DM1-Low > ¹¹¹In-nimotuzumab. Nuclear uptake of ¹¹¹In-nimotuzumab-PEG₆-DM1-High was 4.4-fold higher than ¹¹¹In-nimotuzumab. Pharmacokinetics and biodistribution showed that ¹¹¹In-nimotuzumab-PEG₆-DM1-High had the slowest blood and whole-body clearance rate. Uptake in DLD-1 tumors of ¹¹¹In-nimotuzumab was similar to ¹¹¹In-nimotuzumab-PEG₆-DM1-Low but was significantly higher than for ¹¹¹In-nimotuzumab-PEG₆-DM1-High. Tumor-to-background ratios for ¹¹¹In-nimotuzumab and ¹¹¹In-nimotuzumab-PEG₆-DM1-Low were higher than for ¹¹¹In-nimotuzumab-PEG₆-DM1-High. Conclusion: The results show that conjugation of multiple PEG₆-DM1 reduces the affinity for EGFR in vitro. However, the reduced affinity is counteracted by the high internalization rate of constructs with PEG₆-DM1 ADCs in vitro. The decreased affinity resulted in low tumor uptake of ¹¹¹In-nimotuzumab-PEG₆-DM1-High, with a slow overall whole-body clearance rate. These data provide insights for evaluating the pharmacokinetics and normal -tissue toxicity and in determining dosing rate of PEGylated ADCs.

Prognostic implications of epidermal growth factor receptor variant III expression and nuclear translocation in Chinese human gliomas

Objective

To determine the prognostic implications and clinical significance of epidermal growth factor receptor variant III (EGFRvIII) expression and EGFRvIII nuclear translocation in Chinese human gliomas.

Methods

We retrospectively examined EGFRvIII expression and EGFRvIII nuclear translocation using immunohistochemistry in specimens of 240 Chinese patients with glioma, including 84 World Health Organization (WHO) II gliomas, 84 WHO III gliomas and 72 glioblastomas (WHO IV). Factors that correlated with EGFRvIII and EGFRvIII nuclear translocation expression were analyzed by the Chi-square test. Kaplan-Meier methodology and Cox regression were used for the survival analysis.

Results

Log-rank tests showed that patient age, Karnofsky performance scale (KPS) score, tumor grade, EGFRvIII expression, EGFRvIII nuclear translocation, 1p/19q codeletion, isocitrate dehydrogenase (IDH) mutation, Ki-67 labeling index and O6-methylguanine-DNA methyltransferase (MGMT) status (P<0.05) were significantly correlated with overall survival (OS) time. Multivariate Cox regression analysis revealed that patient age, tumor grade, EGFRvIII nuclear translocation, 1p/19q codeletion, and IDH mutation (P<0.05) were significantly correlated with OS. Patients with a high level of EGFRvIII nuclear translocation (≥7%) had both significantly shorter OS [hazard ratio (HR): 1.920, 95% confidence interval (95% CI): 1.228−3.003, P=0.004] and progression-free survival (PFS) times (HR: 1.661, 95% CI: 1.116−2.471, P=0.012) than those with a low level of EGFRvIII nuclear translocation (<7%).

Conclusions

A high level of EGFRvIII nuclear translocation in glioma is an independent factor indicating a poor prognosis, but EGFRvIII expression is not an independent clinical prognostic factor. The level of EGFRvIII nuclear translocation maybe a novel and crucial prognostic biomarker in glioma.