The advancements in recombinant protein technologies have enabled a plethora of bispecific antibody formats to achieve diverse mechanisms of action.

The ability of bispecific antibodies (bispecific antibodies) to target two different antigens, makes them versatile as therapeutic tools with novel functionalities. The various modes of action of bispecific antibodies are being explored in diverse therapeutic areas. Much of the clinical development pipeline is, however, focused on cancer therapeutics. However, its application in inflammation, infectious diseases and other disease areas is expanding and has shown great promise.

Clinical pipeline of bispecific antibodies

Bispecific Antibodies for Cancer therapy

The pathogenesis of cancer is multifactorial with varying degrees of heterogeneity, making most cancers highly complex and difficult to treat. The success of antibody therapeutics has opened new avenues for targeted therapies in cancer. Bispecific antibodies can be designed to target the pathogenesis of cancer in the following ways:

Cancer Immunotherapy

• It is now known that cancer cells have the ability to evade or suppress the immune response by various mechanisms. Immunotherapy, by boosting the immune response against tumor cells, has proven to be a revolutionary treatment strategy. In this regard, bispecific antibodies serve as an imperative therapeutic tool. A major class of bispecific antibodies for cancer therapy are immune cell engagers, designed to redirect immune cells to tumor cells by targeting an effector immune cell antigen and tumor cell antigen. One arm of the bispecific antibodies targets the tumor-specific antigen (for example, CD33 in acute myeloid leukaemia and HER2 in breast cancer), whilst the other arm targets T-cell (CD3 or CD4) or NK-cell (CD16). CD3-binding T-cell engagers are capable of activation independent of MHC restriction and TCR specificity, therefore bispecific antibodies without Fc are preferred to avoid Fc-mediated cytokine surge and toxicities. Several bispecific antibodies, mainly BiTes, along with DARTs and TandAbs are under development for the treatment of blood and solid malignancies. The BiTe molecule Blinatumomab (CD3 × CD19), is currently the only bispecific antibody in the market, for the treatment of Philadelphia chromosome-negative B cell acute lymphoblastic leukaemia (ALL). Some of the notable bispecific antibodies in clinical trials are CD3xCD20 for haematological malignancies, CD3xEpCAM for lung cancer, CD3 x gpA33 for colorectal cancer and CD3xHER2 for breast cancer, among numerous others. Another approach being investigated is the simultaneous targeting of two checkpoint inhibitors. Examples are PD1×CTLA4, PD-1×LAG3, PD-1×TIM3, and PD-L1×CTLA4 which are in early-stage clinical trials.

Directly targeting tumor cells

Bispecific antibodies targeting dual tumor-associated antigens (TAA) can be used to enhance the efficiency and destruction of tumor cells. This is achieved in different ways such as,

• Increased tumor selectivity over healthy cells. For instance, CD47×PDL-1 was seen to preferentially accumulate in PD-L1 positive solid tumors.
• Inhibiting two signalling pathways simultaneously to combat drug resistance because of monospecific mAbs. For instance, EGFR×MET bispecific antibodies are being developed for NSCLC treatment and HER2xHER3 (Zenocutuzumab) for breast cancer.
• Selective cytotoxic payload delivery using bispecific antibodies. Ab-drug conjugates are often internalized leading to tumor cell destruction. For example, preclinical evaluation of HER2xCD63 conjugated with duostatin-3 effectively targeted the lysosomal pathway in breast cancer cells.
• Biparatopic bispecific antibodies targeting two epitopes on the same antigen improve binding avidity. Several HER2xHER2 bispecific antibodies are being developed for breast cancer.

Inhibiting tumor angiogenesis

• Certain growth factors such as vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and angiopoietin (ANG) are secreted by tumor and endothelial cells which help in tumor angiogenesis. Targeting more than one angiogenetic factor increases therapeutic efficiency. Phase I trials are underway for different bispecific antibody formats in ANG2xVEGF and DLL4xVEGF against solid malignancies.

Bispecifics for non-cancer indications

Though most of the bispecific antibodies revolve around oncological indications, bispecific for non-cancer therapeutics are also being investigated. Few of the bispecific antibodies in the clinical pipeline are discussed below:

Inflammatory diseases

Currently, the bispecific antibodies for autoimmune and inflammatory diseases are being developed on the basis of the following mechanisms of action, namely,

• Dual ligand inactivation: Bispecific antibodies can bind and inhibit multiple ligands in the inflammation pathway. Bispecific antibodies that exemplify this mechanism of action include BAFFxB7RP1 for rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), NGFxTNF for osteoarthritis, IL-4xIL-13 (Romilkimab) for diffuse cutaneous systemic sclerosis and BAFFxIL-17A for Sjögren syndrome.
• PK modulating bispecifics: Here, Bispecific antibodies are designed to target cytokine on one arm and human serum albumin (HSA) on the other, to increase its in-vivo serum half-life. For example, IL-6 x HSA (Vobarilizumab) is in phase II development for RA and SLE. Another bispecific antibodies, TNFa x HSA (Ozoralizumab) is also under investigation for the treatment of RA.

Infectious diseases

• Bispecifics being designed for the treatment of infectious diseases such as hepatitis B virus, cytomegalovirus and HIV-1 infection, redirects T cells to infected cells. In apropos to HIV-1 infection, bispecific T-cell engagers such as CD3 x HIV-1 Env are directed specifically at gp120 envelope glycoprotein (Env). These bispecific antibodies are currently in phase I study in HIV-infected subjects on antiretroviral therapy.

Diabetes and Obesity

• Here the bispecific antibodies concept is based on the activation of receptor signalling by agonistic antibodies. To ameliorate obesity and diabetes, agonistic bispecific antibodies FGFR1 x KLB are being developed, which activate the fibroblast growth factor 21 (FGF21) pathway. These bispecific antibodies selectively target the liver, adipose and pancreatic cells, that are positive for both fibroblast growth factor receptor 1C(FGFR1C) and β-klotho (KLB).

Haemophilia

• In the case of Hemophilia A, a severe congenital coagulopathy, bispecific antibodies are architectured for the exact positioning of an enzyme and a substrate by mimicking a cofactor. Emicizumab, the marketed bispecific antibodies FIXa × FX, replaces a critical clotting factor FVIII. This factor when present binds to both activated coagulation factors IX and factor X facilitating the catalytic activity of FIXa.

Sepsis

• The bispecific antibodies Psl x PcrV, targeting Pseudomonas aeruginosa, directed against the type 3 secretion system (PcrV) and Psl exopolysaccharide, is being studied in phase II trials for the prevention of nosocomial pneumonia in patients undergoing mechanical ventilation.

Regenerative medicine

• In order to overcome the low homing efficiency of stem and progenitor cells to the site of ischaemia–reperfusion (IR) injury, bispecific antibodies-based redirection studies are under investigation. The bispecific targeted delivery of stem and progenitor cells can be utilized to improve the efficacy of tissue regeneration. For example, the bispecific antibodies SCA1 x PBMC, targeting stem cell antigen 1 (SCA1) and human peripheral blood mononuclear cells (PBMCs) reduced fibrosis, enhanced capillary density and restored cardiac function in preclinical animal studies.

Opthalmology

• Another bispecific antibodies Faricimab (VEGFA x ANG2), targeting redundancy of multiple angiogenesis factors, is being evaluated in two phase III studies of patients with diabetic macular oedema and was previously evaluated in three phase II studies in neovascular age-related macular degeneration.

Alzheimer’s

• An increase in amyloid-β (Aβ) peptide levels has been implied in the pathogenesis of Alzheimer’s disease. The bispecifics engaged in the treatment of Alzheimer’s have to cross the blood-brain barrier and then target Aβ or its precursor β-secretase 1 (BACE1). Preclinical studies on animal models have demonstrated that one binding arm targeting the transferrin receptor (TfR) enhanced brain delivery. The bispecific antibodies TfR×Aβ and TfR× BACE1 are currently under development and have shown promising results.

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