Antibody-drug conjugates or ADCs are a class of biopharmaceutical drugs designed as a targeted therapy for treating cancer. [1] Unlike chemotherapy, ADCs are intended to target and kill tumor cells while sparing healthy cells. As of 2019, some 56 pharmaceutical companies were developing ADCs. [2]
ADCs are complex molecules composed of an antibody linked to a biologically active cytotoxic (anticancer) payload or drug. [3] Antibody-drug conjugates are an example of bioconjugates and immunoconjugates.
ADCs combine the targeting properties of monoclonal antibodies with the cancer-killing capabilities of cytotoxic drugs, designed to discriminate between healthy and diseased tissue. [4] [5]
An anticancer drug is coupled to an antibody that targets a specific tumor antigen (or protein) that, ideally, is only found in or on tumor cells. Antibodies attach themselves to the antigens on the surface of cancerous cells. The biochemical reaction that occurs upon attaching triggers a signal in the tumor cell, which then absorbs, or internalizes, the antibody together with the linked cytotoxin. After the ADC is internalized, the cytotoxin kills the cancer. [6] Their targeting ability was believed to limit side effects for cancer patients and give a wider therapeutic window than other chemotherapeutic agents, although this promise hasn’t yet been realized in the clinic.
ADC technologies have been featured in many publications, [7] [8] including scientific journals.
The idea of drugs that would target tumor cells and ignore others was conceived in 1900 by German Nobel laureate Paul Ehrlich; he described the drugs as a "magic bullet" due to their targeting properties. [2]
In 2001 Pfizer/Wyeth's drug Gemtuzumab ozogamicin (trade name: Mylotarg) was approved based on a study with a surrogate endpoint, through the accelerated approval process. In June 2010, after evidence accumulated showing no evidence of benefit and significant toxicity, the U.S. Food and Drug Administration (FDA) forced the company to withdraw it. [9] It was reintroduced into the US market in 2017. [10]
Brentuximab vedotin (trade name: Adcetris, marketed by Seattle Genetics and Millennium/Takeda) [11] was approved for relapsed HL and relapsed systemic anaplastic large-cell lymphoma (sALCL)) by the FDA on August 19, 2011 and received conditional marketing authorization from the European Medicines Agency in October 2012.
Trastuzumab emtansine (ado-trastuzumab emtansine or T-DM1, trade name: Kadcyla, marketed by Genentech and Roche) was approved in February 2013 for the treatment of people with HER2-positive metastatic breast cancer (mBC) who had received prior treatment with trastuzumab and a taxane chemotherapy. [12] [13]
The European Commission approved Inotuzumab ozogamicin [14] as a monotherapy for the treatment of adults with relapsed or refractory CD22-positive B-cell precursor acute lymphoblastic leukemia (ALL) on June 30, 2017 under the trade name Besponsa® (Pfizer/Wyeth), [15] followed on August 17, 2017 by the FDA. [16]
The first immunology antibody-drug conjugate (iADC), ABBV-3373, [17] showed an improvement in disease activity in a Phase 2a study of patients with rheumatoid arthritis [18] and a study with the second iADC, ABBV-154 [19] [20] to evaluate adverse events and change in disease activity in participants treated with subcutaneous injection of ABBV-154 is ongoing. [21]
In July 2018, Daiichi Sankyo Company, Limited and Glycotope GmbH have inked a pact regarding the combination of Glycotope's investigational tumor-associated TA-MUC1 antibody gatipotuzumab and Daiichi Sankyo's proprietary ADC technology for developing gatipotuzumab antibody drug conjugate. [22]
In 2019 AstraZeneca agreed to pay up to US$6.9 billion to jointly develop DS-8201 with Japan's Daiichi Sankyo. It is intended to replace Herceptin for treating breast cancer. DS8201 carries eight payloads, compared to the usual four. [2]
Thirteen ADCs have received market approval by the FDA – all for oncotherapies. Belantamab mafodotin is in the process of being withdrawn from US marketing.
Drug | Trade name | Maker | Condition |
---|---|---|---|
Gemtuzumab ozogamicin | Mylotarg | Pfizer/Wyeth | relapsed acute myelogenous leukemia (AML) |
Brentuximab vedotin | Adcetris | Seattle Genetics, Millennium/Takeda | Hodgkin lymphoma (HL) and systemic anaplastic large-cell lymphoma (ALCL) |
Trastuzumab emtansine | Kadcyla | Genentech, Roche | HER2-positive metastatic breast cancer (mBC) following treatment with trastuzumab and a maytansinoid |
Inotuzumab ozogamicin | Besponsa | Pfizer/Wyeth | relapsed or refractory CD22-positive B-cell precursor acute lymphoblastic leukemia |
Polatuzumab vedotin | Polivy | Genentech, Roche | relapsed or refractory diffuse large B-cell lymphoma (DLBCL) [23] |
Enfortumab vedotin | Padcev | Astellas/Seattle Genetics | adult patients with locally advanced or metastatic urothelial cancer who have received a PD-1 or PD-L1 inhibitor, and a Pt-containing therapy [24] |
Trastuzumab deruxtecan | Enhertu | AstraZeneca/Daiichi Sankyo | adult patients with unresectable or metastatic HER2-positive breast cancer who have received two or more prior anti-HER2 based regimens [25] |
Sacituzumab govitecan | Trodelvy | Immunomedics | adult patients with metastatic triple-negative breast cancer (mTNBC) who have received at least two prior therapies for patients with relapsed or refractory metastatic disease [26] |
Belantamab mafodotin | Blenrep | GlaxoSmithKline | multiple myeloma patients whose disease has progressed despite prior treatment with an immunomodulatory agent, proteasome inhibitor and anti-CD38 antibody [27] |
Moxetumomab pasudotox | Lumoxiti | AstraZeneca | relapsed or refractory hairy cell leukemia (HCL) |
Loncastuximab tesirine | Zynlonta | ADC Therapeutics | relapsed or refractory large B-cell lymphoma (including diffuse large B-cell lymphoma (DLBCL) not otherwise specified, DLBCL arising from low-grade lymphoma, and high-grade B-cell lymphoma) after two or more lines of systemic therapy |
Tisotumab vedotin-tftv | Tivdak | Seagen Inc, Genmab | adult patients with recurrent or metastatic cervical cancer with disease progression on or after chemotherapy [28] |
Mirvetuximab soravtansine | Elahere | ImmunoGen | treatment of adult patients with folate receptor alpha (FRα)-positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer, who have received one to three prior systemic treatment regimens |
An antibody-drug conjugate consists of 3 components: [29] [30] Antibody - targets the cancer cell surface and may also elicit a therapeutic response. Payload - elicits the desired therapeutic response. Linker - attaches the payload to the antibody and should be stable in circulation only releasing the payload at the desired target. Multiple approaches to conjugation have been developed for attachment to the antibody and reviewed. [31] DAR is the drug to antibody ratio and indicates the level of loading of the payload on the ADC.
Many of the payloads for oncology ADCs (oADC) are natural product based [32] with some making covalent interactions with their target. [33] Payloads include the microtubulin inhibitors monomethyl auristatin A MMAE, [34] monomethyl auristatin F MMAF [35] and mertansine, [36] DNA binder calicheamicin [37] and topoisomerase 1 inhibitors SN-38 [38] and exatecan [39] resulting in a renaissance for natural product total synthesis. [40] Glucocorticoid Receptor Modulators (GRM) represent to most active payload class for iADCs.[ clarification needed ] Approaches releasing marketed GRM molecules like dexamethasone [41] [42] and budesonide [43] have been developed. Modified GRM molecules [44] [45] have also been developed that enable the attachment of the linker with the term ADCidified describing the medicinal chemistry process of payload optimization to facilitate linker attachment. [46] Alternatives to small molecule payloads have also been investigated, for example, siRNA. [47]
A stable link between the antibody and cytotoxic (anti-cancer) agent is a crucial aspect of an ADC. [48] A stable ADC linker ensures that less of the cytotoxic payload falls off before reaching a tumor cell, improving safety, and limiting dosages.
Linkers are based on chemical motifs including disulfides, hydrazones or peptides (cleavable), or thioethers (noncleavable). Cleavable and noncleavable linkers were proved to be safe in preclinical and clinical trials. Brentuximab vedotin includes an enzyme-sensitive cleavable linker that delivers the antimicrotubule agent monomethyl auristatin E or MMAE, a synthetic antineoplastic agent, to human-specific CD30-positive malignant cells. MMAE inhibits cell division by blocking the polymerization of tubulin. Because of its high toxicity MMAE cannot be used as a single-agent chemotherapeutic drug. However, MMAE linked to an anti-CD30 monoclonal antibody (cAC10, a cell membrane protein of the tumor necrosis factor or TNF receptor) was stable in extracellular fluid. It is cleavable by cathepsin and safe for therapy. Trastuzumab emtansine is a combination of the microtubule-formation inhibitor mertansine (DM-1) and antibody trastuzumab that employs a stable, non-cleavable linker.
The availability of better and more stable linkers has changed the function of the chemical bond. The type of linker, cleavable or noncleavable, lends specific properties to the cytotoxic drug. For example, a non-cleavable linker keeps the drug within the cell. As a result, the entire antibody, linker and cytotoxic (anti-cancer) agent enter the targeted cancer cell where the antibody is degraded into an amino acid. The resulting complex – amino acid, linker and cytotoxic agent – is considered to be the active drug. In contrast, cleavable linkers are detached by enzymes in the cancer cell. The cytotoxic payload can then escape from the targeted cell and, in a process called "bystander killing", attack neighboring cells. [49]
Another type of cleavable linker, currently in development, adds an extra molecule between the cytotoxin and the cleavage site. This allows researchers to create ADCs with more flexibility without changing cleavage kinetics. Researchers are developing a new method of peptide cleavage based on Edman degradation, a method of sequencing amino acids in a peptide. [50] Also under development are site-specific conjugation (TDCs) [51] and novel conjugation techniques [52] [53] to further improve stability and therapeutic index, α emitting immunoconjugates, [54] antibody-conjugated nanoparticles [55] and antibody-oligonucleotide conjugates. [56]
As the antibody-drug conjugate field has matured, a more accurate definition of ADC is now Anything-Drug Conjugate. Alternatives for the antibody targeting component now include multiple smaller antibody fragments [57] like diabodies, [58] Fab, [59] scFV, [60] and bicyclic peptides. [61]
The first generation uses linking technologies that conjugate drugs non-selectively to cysteine or lysine residues in the antibody, resulting in a heterogeneous mixture. This approach leads to suboptimal safety and efficacy and complicates optimization of the biological, physical and pharmacological properties. [51] Site-specific incorporation of unnatural amino acids generates a site for controlled and stable attachment. This enables the production of homogeneous ADCs with the antibody precisely linked to the drug and controlled ratios of antibody to drug, allowing the selection of a best-in-class ADC. [51] An Escherichia coli -based open cell-free synthesis (OCFS) allows the synthesis of proteins containing site-specifically incorporated non-natural amino acids and has been optimized for predictable high-yield protein synthesis and folding. The absence of a cell wall allows the addition of non-natural factors to the system to manipulate transcription, translation and folding to provide precise protein expression modulation. [62]
The majority of ADCs under development or in clinical trials are for oncological and hematological indications. [63] This is primarily driven by the inventory of monoclonal antibodies, which target various types of cancer. However, some developers are looking to expand the application to other important disease areas. [64] [65] [66]
Trastuzumab, sold under the brand name Herceptin among others, is a monoclonal antibody used to treat breast cancer and stomach cancer. It is specifically used for cancer that is HER2 receptor positive. It may be used by itself or together with other chemotherapy medication. Trastuzumab is given by slow injection into a vein and injection just under the skin.
Cancer immunotherapy is the stimulation of the immune system to treat cancer, improving on the immune system's natural ability to fight the disease. It is an application of the fundamental research of cancer immunology and a growing subspecialty of oncology.
Gemtuzumab ozogamicin, sold under the brand name Mylotarg, is an antibody-drug conjugate that is used to treat acute myeloid leukemia.
Targeted therapy or molecularly targeted therapy is one of the major modalities of medical treatment (pharmacotherapy) for cancer, others being hormonal therapy and cytotoxic chemotherapy. As a form of molecular medicine, targeted therapy blocks the growth of cancer cells by interfering with specific targeted molecules needed for carcinogenesis and tumor growth, rather than by simply interfering with all rapidly dividing cells. Because most agents for targeted therapy are biopharmaceuticals, the term biologic therapy is sometimes synonymous with targeted therapy when used in the context of cancer therapy. However, the modalities can be combined; antibody-drug conjugates combine biologic and cytotoxic mechanisms into one targeted therapy.
Monoclonal antibody therapy is a form of immunotherapy that uses monoclonal antibodies (mAbs) to bind monospecifically to certain cells or proteins. The objective is that this treatment will stimulate the patient's immune system to attack those cells. Alternatively, in radioimmunotherapy a radioactive dose localizes a target cell line, delivering lethal chemical doses. Antibodies are used to bind to molecules involved in T-cell regulation to remove inhibitory pathways that block T-cell responses. This is known as immune checkpoint therapy.
Inotuzumab ozogamicin, sold under the brand name Besponsa, is an antibody-drug conjugate medication used to treat relapsed or refractory B-cell precursor acute lymphoblastic leukemia (ALL).
CD33 or Siglec-3 is a transmembrane receptor expressed on cells of myeloid lineage. It is usually considered myeloid-specific, but it can also be found on some lymphoid cells.
Photothermal therapy (PTT) refers to efforts to use electromagnetic radiation for the treatment of various medical conditions, including cancer. This approach is an extension of photodynamic therapy, in which a photosensitizer is excited with specific band light. This activation brings the sensitizer to an excited state where it then releases vibrational energy (heat), which is what kills the targeted cells.
Mertansine, also called DM1, is a thiol-containing maytansinoid that for therapeutic purposes is attached to a monoclonal antibody through reaction of the thiol group with a linker structure to create an antibody-drug conjugate (ADC).
Brentuximab vedotin, sold under the brand name Adcetris, is an antibody-drug conjugate medication used to treat relapsed or refractory Hodgkin lymphoma (HL) and systemic anaplastic large cell lymphoma (ALCL), a type of T cell non-Hodgkin lymphoma. It selectively targets tumor cells expressing the CD30 antigen, a defining marker of Hodgkin lymphoma and ALCL. The drug is being jointly marketed by Millennium Pharmaceuticals outside the US and by Seagen in the US.
Monomethyl auristatin E (MMAE) is a synthetic antineoplastic agent. Because of its toxicity, it cannot be used as a drug itself; instead, it is linked to a monoclonal antibody (MAB) which directs it to the cancer cells. In International Nonproprietary Names for MMAE-MAB-conjugates, the name vedotin refers to MMAE plus its linking structure to the antibody. It is a potent antimitotic drug derived from peptides occurring in marine shell-less mollusc Dolabella auricularia called dolastatins which show potent activity in preclinical studies, both in vitro and in vivo, against a range of lymphomas, leukemia and solid tumors. These drugs show potency of up to 200 times that of vinblastine, another antimitotic drug used for Hodgkin lymphoma as well as other types of cancer.
Glembatumumab vedotin is an antibody-drug conjugate (ADC) that targets cancer cells expressing transmembrane glycoprotein NMB (GPNMB).
Trastuzumab emtansine, sold under the brand name Kadcyla, is an antibody-drug conjugate consisting of the humanized monoclonal antibody trastuzumab (Herceptin) covalently linked to the cytotoxic agent DM1. Trastuzumab alone stops growth of cancer cells by binding to the HER2 receptor, whereas trastuzumab emtansine undergoes receptor-mediated internalization into cells, is catabolized in lysosomes where DM1-containing catabolites are released and subsequently bind tubulin to cause mitotic arrest and cell death. Trastuzumab binding to HER2 prevents homodimerization or heterodimerization (HER2/HER3) of the receptor, ultimately inhibiting the activation of MAPK and PI3K/AKT cellular signalling pathways. Because the monoclonal antibody targets HER2, and HER2 is only over-expressed in cancer cells, the conjugate delivers the cytotoxic agent DM1 specifically to tumor cells. The conjugate is abbreviated T-DM1.
The duocarmycins are members of a series of related natural products first isolated from Streptomyces bacteria in 1978. They are notable for their extreme cytotoxicity and thus represent a class of exceptionally potent antitumour antibiotics.
Seagen Inc. is an American biotechnology company focused on developing and commercializing innovative, empowered monoclonal antibody-based therapies for the treatment of cancer. The company, headquartered in Bothell, Washington, is the industry leader in antibody-drug conjugates or ADCs, a technology designed to harness the targeting ability of monoclonal antibodies to deliver cell-killing agents directly to cancer cells. Antibody-drug conjugates are intended to spare non-targeted cells and thus reduce many of the toxic effects of traditional chemotherapy, while potentially enhancing antitumor activity.
ImmunoGen, Inc. is a biotechnology company focused on the development of antibody-drug conjugate (ADC) therapeutics for the treatment of cancer. ImmunoGen was founded in 1981 and is headquartered in Waltham, Massachusetts.
Gold nanoparticles in chemotherapy and radiotherapy is the use of colloidal gold in therapeutic treatments, often for cancer or arthritis. Gold nanoparticle technology shows promise in the advancement of cancer treatments. Some of the properties that gold nanoparticles possess, such as small size, non-toxicity and non-immunogenicity make these molecules useful candidates for targeted drug delivery systems. With tumor-targeting delivery vectors becoming smaller, the ability to by-pass the natural barriers and obstacles of the body becomes more probable. To increase specificity and likelihood of drug delivery, tumor specific ligands may be grafted onto the particles along with the chemotherapeutic drug molecules, to allow these molecules to circulate throughout the tumor without being redistributed into the body.
Loncastuximab tesirine, sold under the brand name Zynlonta, is a monoclonal antibody conjugate medication used to treat large B-cell lymphoma and high-grade B-cell lymphoma. It is an antibody-drug conjugate (ADC) composed of a humanized antibody targeting the protein CD19.
Tisotumab vedotin, sold under the brand name Tivdak, is an antibody-drug conjugate used to treat cervical cancer. It is a combination of tisotumab, a monoclonal antibody against tissue factor, and monomethyl auristatin E (MMAE), a potent inhibitor of cell division. It is administered by infusion into a vein.
Passive antibody therapy, also called serum therapy, is a subtype of passive immunotherapy that administers antibodies to target and kill pathogens or cancer cells. It is designed to draw support from foreign antibodies that are donated from a person, extracted from animals, or made in the laboratory to elicit an immune response instead of relying on the innate immune system to fight disease. It has a long history from the 18th century for treating infectious diseases and is now a common cancer treatment. The mechanism of actions include: antagonistic and agonistic reaction, complement-dependent cytotoxicity (CDC), and antibody-dependent cellular cytotoxicity (ADCC).