Amanitins and their development as a payload for antibody-drug conjugates

Transforming toxins into treatments: the revolutionary role of α-amanitin in cancer therapy

Amanita phalloides is the primary species responsible for fatal mushroom poisoning, as its main toxin, α-amanitin, irreversibly and potently inhibits eukaryotic RNA polymerase II (RNAP II), leading to cell death. There is no specific antidote for α-amanitin, which hinders its clinical application. However, with the advancement of precision medicine in oncology, including the development of antibody-drug conjugates (ADCs), the potential value of various toxic small molecules has been explored. These ADCs ingeniously combine the targeting precision of antibodies with the cytotoxicity of small-molecule payloads to precisely kill tumor cells. We searched PubMed for studies in this area using these MeSH terms "Amanitins, Alpha-Amanitin, Therapeutic use, Immunotherapy, Immunoconjugates, Antibodies" and did not limit the time interval. Recent studies have conducted preclinical experiments on ADCs based on α-amanitin, showing promising therapeutic effects and good tolerance in primates. The current challenges include the not fully understood toxicological mechanism of α-amanitin and the lack of clinical studies to evaluate the therapeutic efficacy of ADCs developed based on α-amanitin. In this article, we will discuss the role and therapeutic efficacy of α-amanitin as an effective payload in ADCs for the treatment of various cancers, providing background information for the research and application strategies of current and future drugs.

Antibody-Drug Conjugates: A promising breakthrough in cancer therapy

Antibody-drug conjugates (ADCs) provide effective cancer treatment through the selective delivery of cytotoxic payloads to the cancer cells. They offer unparalleled precision and specificity in directing drugs to cancer cells while minimizing off-target effects. Despite several advantages, there is a requirement for innovations in the molecular design of ADC owing to drug resistance, cancer heterogeneity along the adverse effects of treatment. The review critically analyses ADC function mechanisms, unraveling the intricate interplay between antibodies, linkers, and payloads in facilitating targeted drug delivery to cancer cells. The article also highlights notable advancements in antibody engineering, which aid in creating highly selective and potent ADCs. Additionally, the review details significant progress in clinical ADC development with an in-depth examination of pivotal trials and approved formulations. Antibody Drug Conjugates (ADCs) are a ground-breaking approach to targeted drug delivery, especially in cancer treatment. They offer unparalleled precision and specificity in directing drugs to cancer cells while minimizing off-target effects. This review provides a comprehensive examination of the current state of ADC development, covering their design, mechanisms of action, and clinical applications. The article emphasizes the need for greater precision in drug delivery and explains why ADCs are necessary.

Diphenylphosphinylhydroxylamine (DPPH) Affords Late-Stage S-imination to access free-NH Sulfilimines and Sulfoximines

Sulfilimines, as potential aza-isosteres of sulfoxides, are valued as building blocks, auxiliaries, ligands, bioconjugation handles, and as precursors to versatile S(VI) scaffolds including sulfoximines and sulfondiimines. Here, we report a thioether imination methodology that exploits O-(diphenylphosphinyl)hydroxyl amine (DPPH). Under mild, metal-free, and biomolecule-compatible conditions, DPPH enables late-stage S-imination on peptides, natural products, and a clinically trialled drug, and shows both excellent chemoselectivity and broad functional group tolerance. This methodological report is extended to an efficient and high-yielding one-pot reaction for accessing free-NH sulfoximines with diverse substrates including ones of potential clinical importance. In the presence of a rhodium catalyst, sulfoxides are S-iminated in higher yields to afford free-NH sulfoximines. S-imination was validated on an oxidatively delicate amatoxin to give sulfilimine and sulfoximine congeners. Interestingly, these new sulfilimine and sulfoximine-amatoxins show cytotoxicity. This method is further extended to create sulfilimine and sulfoximine-Fulvestrant and buthionine analogues.

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

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

Exploring the next generation of antibody-drug conjugates

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

Novel Anti-B-cell Maturation Antigen Alpha-Amanitin Antibody-drug Conjugate HDP-101 Shows Superior Activity to Belantamab Mafodotin and Enhanced Efficacy in Deletion 17p Myeloma Models

B-cell maturation antigen (BCMA) plays a pathobiologic role in myeloma and is a validated target with five BCMA-specific therapeutics having been approved for relapsed/refractory disease. However, these drugs are not curative, and responses are inferior in patients with molecularly-defined high-risk disease, including those with deletion 17p (del17p) involving the tumor suppressor TP53, supporting the need for further drug development. Del17p has been associated with reduced copy number and gene expression of RNA polymerase II subunit alpha (POLR2A) in other tumor types. We therefore studied the possibility that HDP-101, an anti-BCMA antibody drug conjugate (ADC) with the POLR2A poison α-amanitin could be an attractive agent in myeloma, especially with del17p. HDP-101 reduced viability in myeloma cell lines representing different molecular disease subtypes, and overcame adhesion-mediated and both conventional and novel drug resistance. After confirming that del17p is associated with reduced POLR2A levels in publicly available myeloma patient databases, we engineered TP53 wild-type cells with a TP53 knockout (KO), POLR2A knockdown (KD), or both, the latter to mimic del17p. HDP-101 showed potent anti-myeloma activity against all tested cell lines, and exerted enhanced efficacy against POLR2A KD and dual TP53 KO/POLR2A KD cells. Mechanistic studies showed HDP-101 up-regulated the unfolded protein response, activated apoptosis, and induced immunogenic cell death. Notably, HDP-101 impacted CD138-positive but not-negative primary cells, showed potent efficacy against aldehyde dehydrogenase-positive clonogenic cells, and eradicated myeloma in an in vivo cell line-derived xenograft (CDX). Interestingly, in the CDX model, prior treatment with HDP-101 precluded subsequent engraftment on tumor cell line rechallenge in a manner that appeared to be dependent in part on natural killer cells and macrophages. Finally, HDP-101 was superior to the BCMA-targeted ADC belantamab mafodotin against cell lines and primary myeloma cells in vitro, and in an in vivo CDX. Together, the data support the rationale for translation of HDP-101 to the clinic, where it is now undergoing Phase I trials, and suggest that it could emerge as a more potent ADC for myeloma with especially interesting activity against the high-risk del17p myeloma subtype.

A Review of the Current FDA-Approved Antibody-Drug Conjugates: Landmark Clinical Trials and Indications

Despite considerable treatment progress, cancer remains among the leading causes of death worldwide. Antibody-drug conjugates (ADCs), a rapidly growing class of systemic therapy, show promise by combining the properties of conventional chemotherapy and targeted therapy. Antibody-drug conjugates have been shown to be more efficacious than traditional chemotherapy. To date, there are 13 ADCs approved by the United States Food and Drug Administration (FDA) for treating various hematological and solid organ cancers. There are several new promising ADCs that are being developed and are in clinical trials. This review provides an overview of the current FDA-approved ADCs, the landmark clinical trials that led to their approval, the common toxicities seen in the landmark trials, the challenges associated with ADCs, and the potential future directions.

Antibody-drug conjugates in cancer therapy: innovations, challenges, and future directions

The emergence of antibody-drug conjugates (ADCs) as a potential therapeutic avenue in cancer treatment has garnered significant attention. By combining the selective specificity of monoclonal antibodies with the cytotoxicity of drug molecules, ADCs aim to increase the therapeutic index, selectively targeting cancer cells while minimizing systemic toxicity. Various ADCs have been licensed for clinical usage, with ongoing research paving the way for additional options. However, the manufacture of ADCs faces several challenges. These include identifying suitable target antigens, enhancing antibodies, linkers, and payloads, and managing resistance mechanisms and side effects. This review focuses on the strategies to overcome these hurdles, such as site-specific conjugation techniques, novel antibody formats, and combination therapy. Our focus lies on current advancements in antibody engineering, linker technology, and cytotoxic payloads while addressing the challenges associated with ADC development. Furthermore, we explore the future potential of personalized medicine, leveraging individual patients' molecular profiles, to propel ADC treatments forward. As our understanding of the molecular mechanisms driving cancer progression continues to expand, we anticipate the development of new ADCs that offer more effective and personalized therapeutic options for cancer patients.

Antibody-Drug Conjugates in Gynecologic Cancers

OPINION STATEMENT

Antibody-drug conjugates (ADCs) are a novel class of targeted cancer therapies with the ability to selectively deliver a cytotoxic drug to a tumor cell using a monoclonal antibody linked to a cytotoxic payload. The technology of ADCs allows for tumor-specificity, improved efficacy, and decreased toxicity compared to standard chemotherapy. Common toxicities associated with ADC use include ocular, pulmonary, hematologic, and neurologic toxicities. Several ADCs have been approved by the United States Food and Drug Administration (FDA) for the management of patients with recurrent or metastatic gynecologic cancers, a population with poor outcomes and limited effective treatment options. The first FDA-approved ADC for recurrent or metastatic cervical cancer was tisotumab vedotin, a tissue factor-targeting agent, after demonstrating response in the innovaTV 204 trial. Mirvetuximab soravtansine targets folate receptor alpha and is approved for use in patients with folate receptor alpha-positive, platinum-resistant, epithelial ovarian cancer based on results from the SORAYA trial. While there are no FDA-approved ADCs for the treatment of uterine cancer, trastuzumab deruxtecan, an anti-human epidermal growth factor receptor 2 (HER2) agent, is actively being investigated. In this review, we will describe the structure and mechanism of action of ADCs, discuss their toxicity profiles, review ADCs both approved and under investigation for the management of gynecologic cancers, and discuss mechanisms of ADC resistance.

Novel Immunotherapies and Combinations: The Future Landscape of Multiple Myeloma Treatment

In multiple myeloma impressive outcomes have improved with the introduction of new therapeutic approaches, mainly those including naked monoclonal antibodies such as daratumumab and isatuximab. However, moving to earlier lines of therapy with effective anti-myeloma drugs led to an increase in the number of patients who developed multi-refractoriness to them early on. Currently, triple- or multi-refractory MM represents an unmet medical need, and their management remains a complicated challenge. The recent approval of new immunotherapeutic approaches such as conjugated monoclonal antibodies, bispecific antibodies, and CAR T cells could be a turning point for these heavily pretreated patients. Nevertheless, several issues regarding their use are unsolved, such as how to select patients for each strategy or how to sequence these therapies within the MM therapeutic landscape. Here we provide an overview of the most recent data about approved conjugated monoclonal antibody belantamab, mafodotin, bispecific antibody teclistamab, and other promising compounds under development, mainly focusing on the ongoing clinical trials with monoclonal antibody combination approaches in advanced and earlier phases of MM treatment.

Antibody drug conjugates beyond cytotoxic payloads

For many years, antibody drug conjugates (ADC) have teased with the promise of targeted payload delivery to diseased cells, embracing the targeting of the antibody to which a cytotoxic payload is conjugated. During the past decade this promise has started to be realised with the approval of more than a dozen ADCs for the treatment of various cancers. Of these ADCs, brentuximab vedotin really laid the foundations of a template for a successful ADC with lysosomal payload release from a cleavable dipeptide linker, measured DAR by conjugation to the Cys-Cys interchain bonds of the antibody and a cytotoxic payload. Using this ADC design model oncology has now expanded their repertoire of payloads to include non-cytotoxic compounds. These new payload classes have their origins in prior medicinal chemistry programmes aiming to design selective oral small molecule drugs. While this may not have been achieved, the resulting compounds provide excellent starting points for ADC programmes with some compounds amenable to immediate linker attachment while for others extensive SAR and structural information offer invaluable design insights. Many of these new oncology payload classes are of interest to other therapeutic areas facilitating rapid access to drug-linkers for exploration as non-oncology ADCs. Other therapeutic areas have also pursued unique payload classes with glucocorticoid receptor modulators (GRM) being the most clinically advanced in immunology. Here, ADC payloads come full circle, as oncology is now investigating GRM payloads for the treatment of cancer. This chapter aims to cover all these new ADC approaches while describing the medicinal chemistry origins of the new non-cytotoxic payloads.

Immunotherapy of Multiple Myeloma: Current Status as Prologue to the Future

The landscape of therapeutic measures to treat multiple myeloma has undergone a seismic shift since the dawn of the current century. This has been driven largely by the introduction of new classes of small molecules, such as proteasome blockers (e.g., bortezomib) and immunomodulators (e.g., lenalidomide), as well as by immunotherapeutic agents starting with the anti-CD38 monoclonal antibody daratumumab in 2015. Recently, other immunotherapies have been added to the armamentarium of drugs available to fight this malignancy. These include the bispecifics teclistamab, talquetamab, and elranatamab, and the chimeric antigen receptor (CAR) T-cell products idecabtagene vicleucel (ide-cel) and ciltacabtagene autoleucel (cilta-cel). While the accumulated benefits of these newer agents have resulted in a more than doubling of the disease's five-year survival rate to nearly 60% and improved quality of life, the disease remains incurable, as patients become refractory to the drugs and experience relapse. This review covers the current scope of antimyeloma immunotherapeutic agents, both those in clinical use and in development. Included in the discussion are additional monoclonal antibodies (mAbs), antibody-drug conjugates (ADCs), bi- and multitargeted mAbs, and CAR T-cells and emerging natural killer (NK) cells, including products intended for "off-the-shelf" (allogeneic) applications. Emphasis is placed on the benefits of each along with the challenges that need to be surmounted if MM is to be cured.

Orellanine: From Fungal Origin to a Potential Future Cancer Treatment

Fungal metabolites represent an underutilized resource in the development of novel anticancer drugs. This review will focus on the promising fungal nephrotoxin orellanine, found in mushrooms including Cortinarius orellanus (Fools webcap). Emphasis will be placed on its historical significance, structural features, and associated toxicomechanics. Chromatographic methods for analysis of the compound and its metabolites, its synthesis, and chemotherapeutic potential are also discussed. Although orellanine's exceptional selectivity for proximal tubular cells is well documented, the mechanics of its toxicity in kidney tissue remains disputed. Here, the most commonly proposed hypotheses are detailed in the context of the molecule's structure, the symptoms seen following ingestion, and its characteristic prolonged latency period. Chromatographic analysis of orellanine and its related substances remains challenging, while biological evaluation of the compound is complicated by uncertainty regarding the role of active metabolites. This has limited efforts to structurally refine the molecule; despite numerous established methods for its synthesis, there is minimal published material on how orellanine's structure might be optimized for therapeutic use. Despite these obstacles, orellanine has generated promising data in preclinical studies of metastatic clear cell renal cell carcinoma, leading to the early 2022 announcement of phase I/II trials in humans.

Dual-Warhead Conjugate Based on Fibroblast Growth Factor 2 Dimer Loaded with α-Amanitin and Monomethyl Auristatin E Exhibits Superior Cytotoxicity towards Cancer Cells Overproducing Fibroblast Growth Factor Receptor 1

Targeting fibroblast growth factor receptor 1 (FGFR1) is a promising therapeutic strategy for various cancers associated with alterations in the FGFR1 gene. In this study, we developed a highly cytotoxic bioconjugate based on fibroblast growth factor 2 (FGF2), which is a natural ligand of this receptor, and two potent cytotoxic drugs-α-amanitin and monomethyl auristatin E-with completely independent mechanistic modes of action. Utilizing recombinant DNA technology, we produced an FGF2 N- to C-end dimer that exhibited superior internalization capacity in FGFR1-positive cells. The drugs were site-specifically attached to the targeting protein using SnoopLigase- and evolved sortase A-mediated ligations. The resulting dimeric dual-warhead conjugate selectively binds to the FGFR1 and utilizes receptor-mediated endocytosis to enter the cells. Moreover, our results demonstrate that the developed conjugate exhibits about 10-fold higher cytotoxic potency against FGFR1-positive cell lines than an equimolar mixture of single-warhead conjugates. The diversified mode of action of the dual-warhead conjugate may help to overcome the potential acquired resistance of FGFR1-overproducing cancer cells to single cytotoxic drugs.

Development, efficacy and side effects of antibody‑drug conjugates for cancer therapy (Review)

Antibody-drug conjugates (ADCs) are anticancer drugs that combine cytotoxic small-molecule drugs (payloads) with monoclonal antibodies through a chemical linker and that transfer toxic payloads to tumor cells expressing target antigens. All ADCs are based on human IgG. In 2009, the Food and Drug Administration (FDA) approved gemtuzumab ozogamicin as the initial first-generation ADC. Since then, at least 100 ADC-related projects have been initiated, and 14 ADCs are currently being tested in clinical trials. The limited success of gemtuzumab ozogamicin has led to the development of optimization strategies for the next generation of drugs. Subsequently, experts have improved the first-generation ADCs and have developed second-generation ADCs such as ado-trastuzumab emtansine. Second-generation ADCs have higher specific antigen levels, more stable linkers and longer half-lives and show great potential to transform cancer treatment models. Since the first two generations of ADCs have served as a good foundation, the development of ADCs is accelerating, and third-generation ADCs, represented by trastuzumab deruxtecan, are ready for wide application. Third-generation ADCs are characterized by strong pharmacokinetics and high pharmaceutical activity, and their drug-to-antibody ratio mainly ranges from 2 to 4. In the past decade, the research prospects of ADCs have broadened, and an increasing number of specific antigen targets and mechanisms of cytotoxic drug release have been discovered and studied. To date, seven ADCs have been approved by the FDA for lymphoma, and three have been approved to treat breast cancer. The present review explores the function and development of ADCs and their clinical use in cancer treatment.

Antibody-Drug Conjugates in Gynecologic Cancer

The present article reviews the current evidence for antibody-drug conjugates (ADCs) in gynecologic cancer. ADCs consist of a highly selective monoclonal antibody for a tumor-associated antigen and a potent cytotoxic payload conjugated through a linker. Overall, the toxicity profiles of ADCs are manageable. Ocular toxicity is a known class effect of some ADCs and is managed with prophylactic corticosteroid and vasoconstrictor eye drops as well as dose interruptions/holds and dose modifications. In ovarian cancer, mirvetuximab soravtansine, an ADC targeting alpha-folate receptor (FRα), received US Food and Drug Administration (FDA) accelerated approval in November 2022 after data from the single-arm phase III SORAYA trial. A second ADC targeting FRα, STRO-002, received FDA fast track designation in August 2021. Multiple studies with upifitamab rilsodotin, an ADC comprising a NaPi2B-binding antibody, are underway. In cervical cancer, tisotumab vedotin, an ADC-targeting tissue factor, received FDA accelerated approval in September 2021 after the phase II innovaTV 204 trial. Tisotumab vedotin in combination with chemotherapy and other targeted agents is currently being evaluated. Although there are no currently approved ADCs for endometrial cancer, there are many under active evaluation, including mirvetuximab soravtansine. Trastuzumab-deruxtecan (T-DXd), an ADC targeting human epidermal growth factor receptor 2 (HER2), is currently approved for HER2-positive and HER2-low breast cancer and shows promise in endometrial cancer. Like all anticancer treatments, the decision for a patient to undergo therapy with an ADC is a personal choice that balances the potential benefits with the side effects and requires thorough and compassionate support of their physician and care team and shared decision making.

Antibody drug conjugates as targeted cancer therapy: past development, present challenges and future opportunities

Antibody drug conjugates (ADCs) are promising cancer therapeutics with minimal toxicity as compared to small cytotoxic molecules alone and have shown the evidence to overcome resistance against tumor and prevent relapse of cancer. The ADC has a potential to change the paradigm of cancer chemotherapeutic treatment. At present, 13 ADCs have been approved by USFDA for the treatment of various types of solid tumor and haematological malignancies. This review covers the three structural components of an ADC-antibody, linker, and cytotoxic payload-along with their respective structure, chemistry, mechanism of action, and influence on the activity of ADCs. It covers comprehensive insight on structural role of linker towards efficacy, stability & toxicity of ADCs, different types of linkers & various conjugation techniques. A brief overview of various analytical techniques used for the qualitative and quantitative analysis of ADC is summarized. The current challenges of ADCs, such as heterogeneity, bystander effect, protein aggregation, inefficient internalization or poor penetration into tumor cells, narrow therapeutic index, emergence of resistance, etc., are outlined along with recent advances and future opportunities for the development of more promising next-generation ADCs.

Antibody-Drug Conjugates for Multiple Myeloma: Just the Beginning, or the Beginning of the End?

Multiple myeloma is a malignancy of immunoglobulin-secreting plasma cells that is now often treated in the newly diagnosed and relapsed and/or refractory settings with monoclonal antibodies targeting lineage-specific markers used either alone or in rationally designed combination regimens. Among these are the anti-CD38 antibodies daratumumab and isatuximab, and the anti-Signaling lymphocytic activation molecule family member 7 antibody elotuzumab, all of which are used in their unconjugated formats. Single-chain variable fragments from antibodies also form a key element of the chimeric antigen receptors (CARs) in the B-cell maturation antigen (BCMA)-targeted CAR T-cell products idecabtagene vicleucel and ciltacabtagene autoleucel, which are approved in the advanced setting. Most recently, the bispecific anti-BCMA and T-cell-engaging antibody teclistamab has become available, again for patients with relapsed/refractory disease. Another format into which antibodies can be converted to exert anti-tumor efficacy is as antibody-drug conjugates (ADCs), and belantamab mafodotin, which also targets BCMA, represented the first such agent that gained a foothold in myeloma. Negative results from a recent Phase III study have prompted the initiation of a process for withdrawal of its marketing authorization. However, belantamab remains a drug with some promise, and many other ADCs targeting either BCMA or other plasma cell surface markers are in development and showing potential. This contribution will provide an overview of some of the current data supporting the possibility that ADCs will remain a part of our chemotherapeutic armamentarium against myeloma moving forward, and also highlight areas for future development.

Past, Present, and a Glance into the Future of Multiple Myeloma Treatment

Multiple myeloma (MM) is a challenging hematological cancer which typically grows in bone marrow. MM accounts for 10% of hematological malignancies and 1.8% of cancers. The recent treatment strategies have significantly improved progression-free survival for MM patients in the last decade; however, a relapse for most MM patients is inevitable. In this review we discuss current treatment, important pathways for proliferation, survival, immune suppression, and resistance that could be targeted for future treatments.

Payload diversification: a key step in the development of antibody-drug conjugates

Antibody-drug conjugates (ADCs) is a fast moving class of targeted biotherapeutics that currently combines the selectivity of monoclonal antibodies with the potency of a payload consisting of cytotoxic agents. For many years microtubule targeting and DNA-intercalating agents were at the forefront of ADC development. The recent approval and clinical success of trastuzumab deruxtecan (Enhertu^®) and sacituzumab govitecan (Trodelvy^®), two topoisomerase 1 inhibitor-based ADCs, has shown the potential of conjugating unconventional payloads with differentiated mechanisms of action. Among future developments in the ADC field, payload diversification is expected to play a key role as illustrated by a growing number of preclinical and clinical stage unconventional payload-conjugated ADCs. This review presents a comprehensive overview of validated, forgotten and newly developed payloads with different mechanisms of action.

Mechanism and treatment of α-amanitin poisoning

Amanita poisoning has a high mortality rate. The α-amanitin toxin in Amanita is the main lethal toxin. There is no specific detoxification drug for α-amanitin, and the clinical treatment mainly focuses on symptomatic and supportive therapy. The pathogenesis of α-amanitin mainly includes: α-amanitin can inhibit the activity of RNA polymeraseII in the nucleus, including the inhibition of the largest subunit of RNA polymeraseII, RNApb1, bridge helix, and trigger loop. In addition, α-amanitin acts in vivo through the enterohepatic circulation and transport system. α-Amanitin can cause the cell death. The existing mechanisms of cell damage mainly focus on apoptosis, oxidative stress, and autophagy. In addition to the pathogenic mechanism, α-amanitin also has a role in cancer treatment, which is the focus of current research. The mechanism of action of α-amanitin on the body is still being explored.

A review of recent advances on single use of antibody-drug conjugates or combination with tumor immunology therapy for gynecologic cancer

Immune checkpoint inhibitors have made significant progress in the treatment of various cancers. However, due to the low ICI responsive rate for the gynecologic cancer, ICI two-drug combination therapy tends to be a predominant way for clinical treatment. Antibody-drug conjugates, a promising therapeutic modality for cancer, have been approved by the FDA for breast cancer, lymphoma, multiple myeloma and gastric cancer. On September 2021, the FDA granted accelerated approval to tisotumab vedotin for patients with recurrent or metastatic cervical cancer. Currently, the role of therapy of ADCs on gynecologic tumors was also included in medication regimens. Now more than 30 ADCs targeting for 20 biomarkers are under clinical trials in the field, including monotherapy or combination with others for multiple lines of therapy. Some ADCs have been proved to enhance the antitumor immunity effect on both pre-clinical models and clinical trials. Therefore, combination of ADCs and ICIs are expected in clinical trials. In this review, we discuss current development of ADCs in gynecologic oncology and the combination effects of ICIs and ADCs.

Investigation of In Vitro and In Vivo Metabolism of α-Amanitin in Rats Using Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometric Method

The purpose of this study is to investigate the difference of in vitro-in vivo correlation of α-amanitin from clearance perspectives as well as to explore the possibility of extra-hepatic metabolism of α-amanitin. First, a liquid chromatography-quadrupole-time-of-flight-mass spectrometric (LC-qTOF-MS) method for α-amanitin in rat plasma was developed and applied to evaluate the in vitro liver microsomal metabolic stability using rat and human liver microsomes and the pharmacokinetics of α-amanitin in rat. The predicted hepatic clearance of α-amanitin in rat liver microsomes was quite low (5.05 mL/min/kg), whereas its in vivo clearance in rat (14.0 mL/min/kg) was close to the borderline between low and moderate clearance. To find out the difference between in vitro and in vivo metabolism, in vitro and in vivo metabolite identification was also conducted. No significant metabolites were identified from the in vivo rat plasma and the major circulating entity in rat plasma was α-amanitin itself. No reactive metabolites such as GSH-adducts were detected either. A glucuronide metabolite was newly identified from the in vitro liver microsomes samples with a trace level. A semi-mass balance study was also conducted to understand the in vivo elimination pathway of α-amanitin and it showed that most α-amanitin was mainly eliminated in urine as intact which implies some unknown transporters in kidney might play a role in the elimination of α-amanitin in rat in vivo. Further studies with transporters in the kidney would be warranted to figure out the in vivo clearance mechanism of α-amanitin.

Development of therapeutic antibodies for the treatment of diseases

Since the first monoclonal antibody drug, muromonab-CD3, was approved for marketing in 1986, 165 antibody drugs have been approved or are under regulatory review worldwide. With the approval of new drugs for treating a wide range of diseases, including cancer and autoimmune and metabolic disorders, the therapeutic antibody drug market has experienced explosive growth. Monoclonal antibodies have been sought after by many biopharmaceutical companies and scientific research institutes due to their high specificity, strong targeting abilities, low toxicity, side effects, and high development success rate. The related industries and markets are growing rapidly, and therapeutic antibodies are one of the most important research and development areas in the field of biology and medicine. In recent years, great progress has been made in the key technologies and theoretical innovations provided by therapeutic antibodies, including antibody-drug conjugates, antibody-conjugated nuclides, bispecific antibodies, nanobodies, and other antibody analogs. Additionally, therapeutic antibodies can be combined with technologies used in other fields to create new cross-fields, such as chimeric antigen receptor T cells (CAR-T), CAR-natural killer cells (CAR-NK), and other cell therapy. This review summarizes the latest approved or in regulatory review therapeutic antibodies that have been approved or that are under regulatory review worldwide, as well as clinical research on these approaches and their development, and outlines antibody discovery strategies that have emerged during the development of therapeutic antibodies, such as hybridoma technology, phage display, preparation of fully human antibody from transgenic mice, single B-cell antibody technology, and artificial intelligence-assisted antibody discovery.

Antibody-drug conjugates: What drives their progress?

Antibody-drug conjugates (ADCs) are on the brink of widespread use for the targeted treatment of cancer. ADCs manage the toxicity of drugs with unacceptable narrow therapeutic windows by guiding highly toxic compounds to the target cells, thereby sparing healthy cells. In this review, we describe approved ADCs and discuss their modes of action, together with medicinal chemical aspects, to evaluate the potential for improvement and to combat tumor-acquired resistance. A recent research focus has centered on the stimulation of immune responses to induce immunogenic cell death and the influence on the tumor microenvironment to enhance bystander effects.

Antibody-Drug Conjugates Containing Payloads from Marine Origin

Antibody-drug conjugates (ADCs) are an important class of therapeutics for the treatment of cancer. Structurally, an ADC comprises an antibody, which serves as the delivery system, a payload drug that is a potent cytotoxin that kills cancer cells, and a chemical linker that connects the payload with the antibody. Unlike conventional chemotherapy methods, an ADC couples the selective targeting and pharmacokinetic characteristics related to the antibody with the potent cytotoxicity of the payload. This results in high specificity and potency by reducing off-target toxicities in patients by limiting the exposure of healthy tissues to the cytotoxic drug. As a consequence of these outstanding features, significant research efforts have been devoted to the design, synthesis, and development of ADCs, and several ADCs have been approved for clinical use. The ADC field not only relies upon biology and biochemistry (antibody) but also upon organic chemistry (linker and payload). In the latter, total synthesis of natural and designed cytotoxic compounds, together with the development of novel synthetic strategies, have been key aspects of the consecution of clinical ADCs. In the case of payloads from marine origin, impressive structural architectures and biological properties are observed, thus making them prime targets for chemical synthesis and the development of ADCs. In this review, we explore the molecular and biological diversity of ADCs, with particular emphasis on those containing marine cytotoxic drugs as the payload.

Rationally Designed Amanitins Achieve Enhanced Cytotoxicity

For 70 years, α-amanitin, the most cytotoxic peptide in its class, has been without a synthetic rival; through synthesis, we address the structure-activity relationships to inform the design of new amatoxins and disclose analogues that are more cytotoxic than the natural product when evaluated on CHO, HEK293, and HeLa cells, whereas on liver-derived HepG2 cells, the same toxins show diminished cytotoxicity.

Worked to the bone: antibody-based conditioning as the future of transplant biology

Conditioning of the bone marrow prior to haematopoietic stem cell transplant is essential in eradicating the primary cause of disease, facilitating donor cell engraftment and avoiding transplant rejection via immunosuppression. Standard conditioning regimens, typically comprising chemotherapy and/or radiotherapy, have proven successful in bone marrow clearance but are also associated with severe toxicities and high incidence of treatment-related mortality. Antibody-based conditioning is a developing field which, thus far, has largely shown an improved toxicity profile in experimental models and improved transplant outcomes, compared to traditional conditioning. Most antibody-based conditioning therapies involve monoclonal/naked antibodies, such as alemtuzumab for graft-versus-host disease prophylaxis and rituximab for Epstein–Barr virus prophylaxis, which are both in Phase II trials for inclusion in conditioning regimens. Nevertheless, alternative immune-based therapies, including antibody–drug conjugates, radio-labelled antibodies and CAR-T cells, are showing promise in a conditioning setting. Here, we analyse the current status of antibody-based drugs in pre-transplant conditioning regimens and assess their potential in the future of transplant biology.

Selective delivery of clinically approved tubulin binding agents through covalent conjugation to an active targeting moiety

Abstract:

The efficacy and tolerability of tubulin binding agents are hampered by their low specificity for cancer cells, like most clinically used anticancer agents. To improve specificity, tubulin binding agents have been covalently conjugated to agents which target cancer cells to give actively targeted drug conjugates. These conjugates are designed to increase uptake of the drug by cancer cells, while having limited uptake by normal cells thereby improving efficacy and tolerability. Approaches used include attachment to small molecules, polysaccharides, peptides, proteins and antibodies that exploit the overexpression of receptors for these substances. Antibody targeted strategies have been the most successful to date with six such examples having gained clinical approval. Many other conjugate types, especially those targeting the folate receptor, have shown promising efficacy and toxicity profiles in pre-clinical models and in early-stage clinical studies. Presented herein is a discussion of the success or otherwise of the recent strategies used to form these actively targeted conjugates.

BCMA-Targeted Biologic Therapies: The Next Standard of Care in Multiple Myeloma Therapy

With recent advances in myeloma therapy, patients can achieve long-term remissions, but eventually relapses will occur. Triple-class refractory myeloma (disease that is refractory to an immunomodulatory agent, a proteasome inhibitor, and an anti-CD38 monoclonal antibody) and penta-refractory myeloma (disease that is refractory to two proteasome inhibitors, two immunomodulatory agents, and an anti-CD38 antibody) are associated with a particularly poor prognosis, and novel treatments are desperately needed for these patients. Targeting B cell maturation antigen (BCMA), which is ubiquitously expressed on plasma cells, has emerged as a well-tolerated and highly efficacious strategy in patients with relapsed and refractory myeloma. Several mechanisms of targeting BCMA are currently under investigation, including antibody-drug conjugates, bispecific antibodies, and chimeric antigen receptor T cells and natural killer (NK) cells, all with unique side effect profiles. Early phase clinical trials showed unprecedented response rates in highly refractory myeloma patients, leading to the recent approvals of some of these agents. Still, many questions remain with regard to this target, including how best to target it, how to treat patients who have progressed on a BCMA-targeting therapy, and whether response rates will deepen if these agents are used in earlier lines of therapy. In this review, we examine the rationale for targeting BCMA and summarize the data for several agents across multiple classes of BCMA-targeting therapeutics, paying special attention to the diverse mechanisms and unique challenges of each therapeutic class.

Toxicokinetics of β-Amanitin in Mice and In Vitro Drug-Drug Interaction Potential

The toxicokinetics of β-amanitin, a toxic bicyclic octapeptide present abundantly in Amanitaceae mushrooms, was evaluated in mice after intravenous (iv) and oral administration. The area under plasma concentration curves (AUC) following iv injection increased in proportion to doses of 0.2, 0.4, and 0.8 mg/kg. β-amanitin disappeared rapidly from plasma with a half-life of 18.3−33.6 min, and 52.3% of the iv dose was recovered as a parent form. After oral administration, the AUC again increased in proportion with doses of 2, 5, and 10 mg/kg. Absolute bioavailability was 7.3−9.4%, which resulted in 72.4% of fecal recovery from orally administered β-amanitin. Tissue-to-plasma AUC ratios of orally administered β-amanitin were the highest in the intestine and stomach. It also readily distributed to kidney > spleen > lung > liver ≈ heart. Distribution to intestines, kidneys, and the liver is in agreement with previously reported target organs after acute amatoxin poisoning. In addition, β-amanitin weakly or negligibly inhibited major cytochrome P450 and 5′-diphospho-glucuronosyltransferase activities in human liver microsomes and suppressed drug transport functions in mammalian cells that overexpress transporters, suggesting the remote drug interaction potentials caused by β-amanitin exposure.

Emerging Role of Antibody-Drug Conjugates and Bispecific Antibodies for the Treatment of Multiple Myeloma

Multiple myeloma (MM) is characterized by malignant proliferation of malignant plasma cells; it is the second most common hematological malignancy associated with significant morbidity. Genetic intricacy, instability, and diverse clinical presentations remain a barrier to cure. The treatment of MM is modernized with the introduction of newer therapeutics agents, i.e., target-specific monoclonal antibodies. The currently available literature lacks the benefits of newer targeted therapy being developed with an aim to reduce side effects and increase effectiveness, compared to conventional chemotherapy regimens. This article aims to review literature about the current available monoclonal antibodies, antibody-drug conjugates, and bispecific antibodies for the treatment of MM.

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.

Advances with antibody-drug conjugates in breast cancer treatment

Antibody-drug conjugate-based therapy for treatment of cancer has attracted much attention because of its enhanced efficacy against numerous cancer types. Commonly, an ADC includes a mAb linked to a therapeutic payload. Antibody, linker and payload are the three main components of ADCs. The high specificity of antibodies is integrated with the strong potency of payloads in ADCs. ADCs with potential cytotoxic small molecules as payloads, generate antibody-mediated cancer therapy. Recently, ADCs with DNA-damaging agents have shown favor over microtubule-targeting agents as payloads. Although ADC resistance can be a barrier to effectiveness, several ADC therapies have been either approved or are in clinical trials for cancer treatment. The ADC-based treatments of breast cancers, particularly TNBC, MDR and metastatic breast cancers, have shown promise in recent years. This review discusses ADC drug designs, and developed for different types of breast cancer including TNBC, MDR and metastatic breast cancer.

Pharmacokinetics of α-amanitin in mice using liquid chromatography-high resolution mass spectrometry and in vitro drug-drug interaction potentials

The aim of this study was to determine pharmacokinetics of α-amanitin, a toxic bicyclic octapeptide isolated from the poisonous mushrooms, following intravenous (iv) or oral (po) administration in mice using a newly developed and validated liquid chromatography-high resolution mass spectrometry. The iv injected α-amanitin disappeared rapidly from the plasma with high a clearance rate (26.9-30.4 ml/min/kg) at 0.1, 0.2, or 0.4 mg/kg doses, which was consistent with a rapid and a major excretion of α-amanitin via the renal route (32.6%). After the po administration of α-amanitin at doses of 2, 5, or 10 mg/kg to mice, the absolute bioavailability of α-amanitin was 3.5-4.8%. Due to this low bioavailability, 72.5% of the po administered α-amanitin was recovered from the feces. When α-amanitin is administered po, the tissue to plasma area under the curve ratio was higher in stomach > large intestine > small intestine > lung ~ kidneys > liver but not detected in brain, heart, and spleen. The high distribution of α-amanitin to intestine, kidneys, and liver is in agreement with the previously reported major intoxicated organs following acute α-amanitin exposure. In addition, α-amanitin weakly or negligibly inhibited cytochrome P450 and 5'-diphospho-glucuronosyltransferase enzymes activity in human liver microsomes as well as major drug transport functions in mammalian cells overexpressing transporters. Data suggested remote drug interaction potential may be associated with α-amanitin exposure.

Copper(II)-mediated C-H sulphenylation or selenylation of tryptophan enabling macrocyclization of peptides

Cu(II)-mediated C-H sulphenylation or selenylation of Trp indole by a derivative of cysteine or selenocysteine enables access to the tryptathionine unit or its selenium congener. The mechanism of these protocols, which allow macrocyclization of Trp-containing peptides, has been studied.

Novel immunotherapies in multiple myeloma - chances and challenges

In this review article, we summarize the latest data on antibody-drug conjugates, bispecific T-cell-engaging antibodies, and chimeric antigen receptor T cells in the treatment of multiple myeloma. We discuss the pivotal questions to be addressed as these new immunotherapies become standard agents in the management of multiple myeloma. We also focus on the selection of patients for these therapies and speculate as to how best to individualize treatment approaches. We see these novel immunotherapies as representing a paradigm shift. However, despite the promising preliminary data, many open issues remain to be evaluated in future trials.

Immunotherapy of Multiple Myeloma: Promise and Challenges

Whereas the treatment of MM was dependent solely on alkylating agents and corticosteroids during the prior three decades, the landscape of therapeutic measures to treat the disease began to expand enormously early in the current century. The introduction of new classes of small-molecule drugs, such as proteasome blockers (bortezomib and carfilzomib), immunomodulators (lenalidomide and pomalidomide), nuclear export inhibitors (selinexor), and histone deacetylase blockers (panobinostat), as well as the application of autologous stem cell transplantation (ASCT), resulted in a seismic shift in how the disease is treated. The picture changed dramatically once again starting with the 2015 FDA approval of two monoclonal antibodies (mAbs) - the anti-CD38 daratumumab and the anti-SLAMF7 elotuzumab. Daratumumab, in particular, has had a great impact on MM therapy and today is often included in various regimens to treat the disease, both in newly diagnosed cases and in the relapse/refractory setting. Recently, other immunotherapies have been added to the arsenal of drugs available to fight this malignancy. These include isatuximab (also anti-CD38) and, in the past year, the antibody-drug conjugate (ADC) belantamab mafodotin and the chimeric antigen receptor (CAR) T-cell product idecabtagene vicleucel (ide-cel). While the accumulated benefits of these newer agents have resulted in a doubling of the disease's five-year survival rate to more than 5 years and improved quality of life, the disease remains incurable. Almost without exception patients experience relapse and/or become refractory to the drugs used, making the search for innovative therapies all the more essential. This review covers the current scope of anti-myeloma immunotherapeutic agents, both those in clinical use and on the horizon, including naked mAbs, ADCs, bi- and multi-targeted mAbs, and CAR T-cells. Emphasis is placed on the benefits of each along with the challenges that need to be overcome if MM is to be considered curable in the future.

Iodine-Mediated Tryptathionine Formation Facilitates the Synthesis of Amanitins

Synthetic methods on the macrocyclization of peptides are of high interest since they facilitate the synthesis of various types of potentially bioactive compounds, e.g. addressing targets like protein-protein-interactions. Herein, we report on an efficient method to construct tryptathionine-cross-links in peptides between the amino acids Trp and Cys. This reaction not only is the basis for the total synthesis of the death cap toxin α-amanitin but also provides rapid access to various new amanitin analogues. This study for the first time presents a systematic compilation of structure-activity relations (SAR) of amatoxins with regard to RNA polymerase II inhibition and cytotoxicity with one amanitin derivative of superior RNAP II inhibition. The present approach paves the way for the synthesis of structurally diverse amatoxins as future payloads for antibody-toxin conjugates in cancer therapy.

Peptide Cyclization Mediated by Metal-Free S-Arylation: S-Protected Cysteine Sulfoxide as an Umpolung of the Cysteine Nucleophile

Covalent linking of side chains provides a method to produce cyclic or stapled peptides that are important in developing peptide-based drugs. A variety of crosslinking formats contribute to fixing the active conformer and prolonging its biological activity under physiological conditions. One format uses the cysteine thiol to participate in crosslinking through nucleophilic thiolate anions or thiyl radicals to form thioether and disulfide bonds. Removal of the S-protection from an S-protected Cys derivative generates the thiol, which functions as a nucleophile. S-Oxidation of a protected Cys allows the formation of a sulfoxide that operates as an umpolung electrophile. Herein, the applicability of S-p-methoxybenzyl Cys sulfoxide (Cys(MBzl)(O)) to the formation of a thioether linkage between tryptophan and Cys has been investigated. The reaction of peptides containing Cys(MBzl)(O) and Trp with trifluoromethanesulfonic acid (TFMSA) or methanesulfonic acid (MSA) in TFA in the presence of guanidine hydrochloride (Gn ⋅ HCl) proceeded to give cyclic or stapled peptides possessing the Cys-Trp thioether linkage. In this reaction, strong acids such as TFMSA or MSA are necessary to activate the sulfoxide. Additionally, Gn ⋅ HCl plays a critical role in producing an electrophilic Cys derivative that combines with the indole by aromatic electrophilic substitution. The findings led us to conclude that the less-electrophilic Cys(MBzl)(O) serves as an acid-activated umpolung of a Cys nucleophile and is useful for S-arylation-mediated peptide cyclization.

Emerging therapies for relapsed/refractory multiple myeloma: CAR-T and beyond

The pace of innovation of multiple myeloma therapy in recent years is remarkable with the advent of monoclonal antibodies and the approval of novel agents with new mechanisms of action. Emerging therapies are on the horizon for clinical approval with significant implications in extending patient survival and advancing closer to the goal of a cure, especially in areas of immunotherapy such as chimeric antigen receptor T cells, bispecific T cell engager antibodies, antibody drug conjugates, newer generations of monoclonal antibodies, and small molecule inhibitor and modulators. This review provides an update of current myeloma therapeutics in active preclinical and early clinical development and discusses the mechanism of action of several classes of novel therapeutics.

Mechanisms of Action of the New Antibodies in Use in Multiple Myeloma

Monoclonal antibodies (mAbs) directed against antigen-specific of multiple myeloma (MM) cells have Fc-dependent immune effector mechanisms, such as complement-dependent cytotoxicity (CDC), antibody-dependent cellular cytotoxicity (ADCC), and antibody-dependent cellular phagocytosis (ADCP), but the choice of the antigen is crucial for the development of effective immuno-therapy in MM. Recently new immunotherapeutic options in MM patients have been developed against different myeloma-related antigens as drug conjugate-antibody, bispecific T-cell engagers (BiTEs) and chimeric antigen receptor (CAR)-T cells. In this review, we will highlight the mechanism of action of immuno-therapy currently available in clinical practice to target CD38, SLAMF7, and BCMA, focusing on the biological role of the targets and on mechanisms of actions of the different immunotherapeutic approaches underlying their advantages and disadvantages with critical review of the literature data.

Toxic Effects of Amanitins: Repurposing Toxicities toward New Therapeutics

The consumption of mushrooms has become increasingly popular, partly due to their nutritional and medicinal properties. This has increased the risk of confusion during picking, and thus of intoxication. In France, about 1300 cases of intoxication are observed each year, with deaths being mostly attributed to Amanita phalloides poisoning. Among amatoxins, α- and β-amanitins are the most widely studied toxins. Hepatotoxicity is the hallmark of these compounds, leading to hepatocellular failure within three days of ingestion. The toxic mechanisms of action mainly include RNA polymerase II inhibition and oxidative stress generation, leading to hepatic cell apoptosis or necrosis depending on the doses ingested. Currently, there is no international consensus concerning Amanita phalloides poisoning management. However, antidotes with antioxidant properties remain the most effective therapeutics to date suggesting the predominant role of oxidative stress in the pathophysiology. The partially elucidated mechanisms of action may reveal a suitable target for the development of an antidote. The aim of this review is to present an overview of the knowledge on amanitins, including the latest advances that could allow the proposal of new innovative and effective therapeutics.

Antibody-Drug Conjugates-A Tutorial Review

Antibody-drug conjugates (ADCs) are a family of targeted therapeutic agents for the treatment of cancer. ADC development is a rapidly expanding field of research, with over 80 ADCs currently in clinical development and eleven ADCs (nine containing small-molecule payloads and two with biological toxins) approved for use by the FDA. Compared to traditional small-molecule approaches, ADCs offer enhanced targeting of cancer cells along with reduced toxic side effects, making them an attractive prospect in the field of oncology. To this end, this tutorial review aims to serve as a reference material for ADCs and give readers a comprehensive understanding of ADCs; it explores and explains each ADC component (monoclonal antibody, linker moiety and cytotoxic payload) individually, highlights several EMA- and FDA-approved ADCs by way of case studies and offers a brief future perspective on the field of ADC research.

CRISPR-based screens uncover determinants of immunotherapy response in multiple myeloma

Cancer cells commonly develop resistance to immunotherapy by loss of antigen expression. Combinatorial treatments that increase levels of the target antigen on the surface of cancer cells have the potential to restore efficacy to immunotherapy. Here, we use our CRISPR interference- and CRISPR activation-based functional genomics platform to systematically identify pathways controlling cell surface expression of the multiple myeloma immunotherapy antigen B-cell maturation antigen (BCMA). We discovered that pharmacologic inhibition of HDAC7 and the Sec61 complex increased cell surface BCMA, including in primary patient cells. Pharmacologic Sec61 inhibition enhanced the antimyeloma efficacy of a BCMA-targeted antibody-drug conjugate. A CRISPR interference chimeric antigen receptor T cells (CAR-T cells) coculture screen enabled us to identify both antigen-dependent and antigen-independent mechanisms controlling response of myeloma cells to BCMA-targeted CAR-T cells. Thus, our study shows the potential of CRISPR screens to uncover mechanisms controlling response of cancer cells to immunotherapy and to suggest potential combination therapies.

Enhancing the Pharmacokinetics and Antitumor Activity of an α-Amanitin-Based Small-Molecule Drug Conjugate via Conjugation with an Fc Domain

Herein we describe the design and biological evaluation of a novel antitumor therapeutic platform that combines the most favorable properties of small-molecule drug conjugates (SMDCs) and antibody drug conjugates (ADCs). Although the small size of SMDCs, compared to ADCs, is an appealing feature for their application in the treatment of solid tumors, SMDCs usually suffer from poor pharmacokinetics, which severely limits their therapeutic efficacy. To overcome this limitation, in this proof-of-concept study we grafted an α-amanitin-based SMDC that targets prostate cancer cells onto an immunoglobulin Fc domain via a two-step "program and arm" chemoenzymatic strategy. We demonstrated the superior pharmacokinetic properties and therapeutic efficacy of the resulting Fc-SMDC over the SMDC in a prostate cancer xenograft mouse model. This approach may provide a general strategy toward effective antitumor therapeutics combining small size with pharmacokinetic properties close to those of an ADC.

Scaling Amatoxin Synthesis with an Improved Route to (2S,3R,4R)-Dihydroxyisoleucine Exemplified by a Toxic, Clickable α-Amanitin Analogue

Here we report a scalable synthesis of the key amino acid residue, (2S,3R,4R)-4,5-dihydroxyisoleucine (DHIle) in α-amanitin, that in turn enables the scalable synthesis of an equipotent analogue, Asn^{(N-ethylazide)}-S,6'-dideoxy-α-amanitin, suitable for CuAAC conjugation to empower studies on therapeutic antibody-drug conjugates.

Natural Product Based Antibody Drug Conjugates: Clinical Status as of November 9, 2020

As of early November 2020, there are 10 approved antibody drug conjugates (ADCs) plus two others that are not usually listed. In addition, there are 70 ADCs at stages from phase I to phase III and 23 that are at the preclinical stage. The warheads of all of these drugs and drug candidates have their origins in natural product structures. The sources and modifications are discussed in general and then specifically commented on in each case with either the generic name if known and/or the ADC's ID names. Interestingly, almost all warheads listed are from microbial sources though initially a number were thought to have been from plants. The latest NCT numbers from Clintrials.gov of all phase I to phase III candidates are also given. Three unusual ADCs are also discussed, two of which (an antitumor agent and one directed against autoimmune diseases) are not usually listed as ADCs, with the third being an anti-infective.

Genetic Abnormalities in Multiple Myeloma: Prognostic and Therapeutic Implications

Some genetic abnormalities of multiple myeloma (MM) detected more than two decades ago remain major prognostic factors. In recent years, the introduction of cutting-edge genomic methodologies has enabled the extensive deciphering of genomic events in MM. Although none of the alterations newly discovered have significantly improved the stratification of the outcome of patients with MM, some of them, point mutations in particular, are promising targets for the development of personalized medicine. This review summarizes the main genetic abnormalities described in MM together with their prognostic impact, and the therapeutic approaches potentially aimed at abrogating the undesirable pathogenic effect of each alteration.

Belantamab Mafodotin to Treat Multiple Myeloma: A Comprehensive Review of Disease, Drug Efficacy and Side Effects

Multiple myeloma (MM) is a hematologic malignancy characterized by excessive clonal proliferation of plasma cells. The treatment of multiple myeloma presents a variety of unique challenges due to the complex molecular pathophysiology and incurable status of the disease at this time. Given that MM is the second most common blood cancer with a characteristic and unavoidable relapse/refractory state during the course of the disease, the development of new therapeutic modalities is crucial. Belantamab mafodotin (belamaf, GSK2857916) is a first-in-class therapeutic, indicated for patients who have previously attempted four other treatments, including an anti-CD38 monoclonal antibody, a proteosome inhibitor, and an immunomodulatory agent. In November 2017, the FDA designated belamaf as a breakthrough therapy for heavily pretreated patients with relapsed/refractory multiple myeloma. In August 2020, the FDA granted accelerated approval as a monotherapy for relapsed or treatment-refractory multiple myeloma. The drug was also approved in the EU for this indication in late August 2020. Of note, belamaf is associated with the following adverse events: decreased platelets, corneal disease, decreased or blurred vision, anemia, infusion-related reactions, pyrexia, and fetal risk, among others. Further studies are necessary to evaluate efficacy in comparison to other standard treatment modalities and as future drugs in this class are developed.