ReviewKeynoteDual-acting therapeutic proteins for intraocular use
Introduction
Intravitreally administered antibody-based medicines targeting VEGF, which causes angiogenesis and neovascularisation, have revolutionised the treatment of neovascular retinal diseases 1, 2. Uncontrolled vascularisation and photoreceptor degeneration characterises several posterior blinding conditions, including wet age-related macular degeneration (wet-AMD), diabetic retinopathy (DR), and diabetic macular edema (DME) [3]. VEGF is not the only potential target for neovascularisation that can be used to treat chronic intraocular blinding disease [4]. Inflammation is also involved in causing blinding disease (e.g., posterior uveitis) [5]. Dual-targeting protein-based therapeutics, such as bispecific antibodies (bsAbs), that are capable of interacting with two target epitopes simultaneously 6, 7 have the potential to increase the efficacy of intraocular medicines.
The concept of bsAbs has long been known [8] and are envisaged to exploit spatiotemporal relationships that are not possible by using a combination or mixture of antibodies [9]. To date, clinical realisation has been achieved in oncology. Blinatumomab was approved in 2015 to treat acute lymphoblastic leukaemia and emicizumab was approved in 2018 to treat haemophilia A [10]. Catumaxomab was approved, but has now been withdrawn for commercial reasons. Blinatumomab is a bispecific T cell engager (BiTe) molecule comprising two antibody single-chain variable fragments (scFvs) in a molecule with an overall molecular weight of ∼55 kDa. One fragment of blinatumomab binds to CD19 on a malignant B cell and the other fragment binds to CD3 on a T cell to redirect and elicit a cytotoxic response 11, 12. Emicizumab is a full IgG antibody that binds to blood factors IXa and X to allow the coagulation cascade to continue in the absence of sufficient amounts of factor VIII [13].
Drug combination strategies are widely used in medicine, such as in oncology, and infection [14]. IVI is invasive and carries some risk; thus, intraocular combination strategies would need to be formulated as fixed-dose combinations to minimise the number of IVIs. Disadvantages of fixed-dose combinations include a lack of dosing flexibility and difficulties in identifying adverse reactions. The volume of an IVI is 50 μl, which is a very small volume for a combination of protein-based drugs at sufficient individual doses while minimising risks of protein misfolding and aggregation. Despite these limitations, and as described later, combinations have been evaluated, but have yet not progressed to clinical registration 14, 15, 16, 17, 18.
The key challenge in developing intraocular medicines is to ensure there is no ocular toxicity 19, 20, 21, 22. The eye is susceptible to inflammation, which can be caused by immunogenicity to the therapeutic protein and possible protein aggregation. The production of antidrug antibodies (ADAs) and inflammatory responses 19, 23 are damaging and sight-threatening and must be avoided because intraocular tissues are delicate and nonregenerative. The eye can be susceptible to endophthalmitis following injections [24]. Proteins that are modified, for example by poly(ethylene glycol) (PEG)-ylation, must be manufactured to the highest standard, as evidenced by the recent regulatory failure and withdrawal of Abicipar pegol [25]. The anti-VEGF PEGylated aptamer, pegaptanib sodium appeared to be well tolerated [26], although its use decreased after the clinical introduction of ranibizumab and aflibercept. Ocular tolerability and safety profiles should be thoroughly assessed. Preclinical and clinical studies must carefully designed [21] to minimise any adverse reactions related to the protein of interest [22]. Long-term studies moving from branded to biosimilar protein therapeutics must also be conducted [27]. In terms of bsAbs for development in retinal therapy, there are ongoing studies in preclinical stages with only one bsAb (i.e., faricimab) targeting VEGF and angiopoietin-2 (ANG-2) in full clinical development to treat DME 28, 29 and wet-AMD 30, 31, 32.
Given that current anti-VEGF biologics require long-term monthly or bimonthly injections, there is a need to reduce the frequency of IVIs to treat chronic intra-ocular conditions. There has been near-exponential growth of IVIs since 2007 [33], but the need for repeated intravitreal administration is difficult for patients, and compliance often decreases after the first year of treatment 34, 35, 36. Minimising the cumulative number of IVIs is also important because of the potential for harmful effects to ocular tissues [37]. Chronic ocular hypertension has been associated with repeated intravitreal anti-VEGF injections [38]. Dual-acting biologics could be developed where one function is to display increased affinity to tissue in the posterior cavity to slow clearance from the vitreous (affinity targeting) and the other function would be to bind to a therapeutic target.
Here, we describe intraocular targets that could be considered for the development of dual-acting biologics and how bispecific molecules might be also used to increase duration of action. We also briefly describe different bispecific formats.
Section snippets
Targets to inhibit neovascularisation
VEGF is a proven clinical target for several different indications. Since its first discovery as an angiogenic factor during the late 1980s [39], several drugs have been developed as VEGF inhibitors in oncology. To date, three antibody-based therapies targeting VEGF for intraocular use have been approved [i.e., ranibizumab (Lucentis®), aflibercept (Eylea®), and brolucizumab (Beovu®)], and one non-antibody-based therapy [i.e., pegaptanib (Macugen®)]. Bevacizumab (Avastin®) is also widely used
Dual therapeutic targeting
Faricimab (Fig. 1a) is an IgG antibody with the ability to bind two therapeutic targets. It comprises one Fab with specificity for VEGF and another Fab with specificity for ANG-2, and is in Phase III trials for the treatment of wet-AMD [30] and DME [29]. By blocking two soluble targets, dual-acting antibodies could combine the activities of two pathway-modulating molecules into one for enhanced efficacy. Faricimab was developed as researchers began to look beyond anti-VEGF monotherapies because
Dual-action molecules designed for increased duration of action
There is a recognised need to increase the duration of action of intravitreally administered medicines 36, 102, 103, 104. There is often reduced compliance by patients after the first year of treatment 34, 69, especially patients who have not previously participated in a clinical trial 35, 36. Strategies to develop complex formulations of therapeutic proteins 105, 106, 107 have been considered, but these must address the challenges to maintain protein stability 108, 109, 110 and ocular
Bispecific molecular motifs include IgG and non-IgG formats
The IgG format (e.g., faricimab; Fig. 1a) is not the only molecular format that is being examined for use as a bispecific, dual-functional therapeutic protein for intraocular use. Fc-fusion (e.g., aflibercept) and Fab (e.g., ranibizumab) have elements of the IgG format. Non-IgG formats referred to earlier are brolucizumab, which is a scFv, and abicipar, which is a DARPin. These and other non-IgG formats 153, 154, 155 along with other molecules described in the patent literature 156, 157 might
Concluding remarks and future prospects
As with any therapeutic, target selection is a first crucial step for the development of dual-acting or bispecific biotherapeutics. Target selection is compounded by the need to select two different targets that together will bring clinical benefit. Bispecific therapeutics are clinically proven in oncology, where they can exploit spatial temporal relationships that are not possible using a combination of constituent drugs. The use of intravitreally administered drug combinations has been
Acknowledgments
M.C. is thankful for the PhD funding from University of East London. N.I. is grateful for PhD funding from Santen Pharmaceutical Co., Ltd. S.A., P.T.K., and S.B. are grateful for funding from the National Institute of Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, Moorfields Special Trustees, the Helen Hamlyn Trust (in memory of Paul Hamlyn), Medical Research Council, Fight for Sight, and the Michael and Ilse
Glossary
- Dual therapeutic bispecific antibodies (bsAbs)
- are molecules capable of binding to two different targets simultaneously.
- Affinity dual acting molecules
- are designed to contain therapeutic and vitreous tissue specific binding domains. The purpose of the binding domain specific to vitreous tissue is to delay ocular clearance of the molecule.
- Neovascular ligands
- are non-membrane bound soluble targets that bind to cell surface receptors resulting in uncontrolled vascularisation. Multiple ligands are
Matthew Collins is studying for a PhD at the University of East London, working on a project to develop hybrid strategies to generate bispecific antibody mimetics. He earnt his MSc in clinical drug development from Queen Mary University of London in 2017.
References (175)
Drug delivery to retinal photoreceptors
Drug Discov. Today
(2019)Efficacy, safety, and pharmacokinetics of emicizumab prophylaxis given every 4 weeks in people with haemophilia A (HAVEN 4): a multicentre, open-label, non-randomised phase 3 study
Lancet Haematol.
(2019)Intravitreal combined aflibercept + anti-platelet-derived growth factor receptor β for neovascular age-related macular degeneration: results of the Phase 2 CAPELLA trial
Ophthalmology
(2020)The safety evaluation of long-acting ocular delivery systems
Drug Discov. Today
(2019)Simultaneous inhibition of angiopoietin-2 and vascular endothelial growth factor-A with faricimab in diabetic macular edema: BOULEVARD Phase 2 randomized trial
Ophthalmology
(2019)Phase I trial of anti-vascular endothelial growth factor/anti-angiopoietin 2 bispecific antibody RG7716 for neovascular age-related macular degeneration
Ophthalmol. Retina
(2017)The use of real-world evidence for evaluating anti–vascular endothelial growth factor treatment of neovascular age-related macular degeneration
Surv. Ophthalmol.
(2019)The acute and chronic effects of intravitreal anti-vascular endothelial growth factor injections on intraocular pressure: a review
Surv. Ophthalmol.
(2018)Novel VEGF decoy receptor fusion protein conbercept targeting multiple VEGF isoforms provide remarkable anti-angiogenesis effect in vivo
PLoS One
(2013)Novel interaction mechanism of a domain antibody-based inhibitor of human vascular endothelial growth factor with greater potency than ranibizumab and bevacizumab and improved capacity over aflibercept
J. Biol. Chem.
(2016)
Ranibizumab versus bevacizumab to treat neovascular age-related macular degeneration: one-year findings from the IVAN randomized trial
Ophthalmology
Alternative treatments to inhibit VEGF in age-related choroidal neovascularisation: 2-year findings of the IVAN randomised controlled trial
Lancet
HAWK and HARRIER: Phase 3, multicenter, randomized, double-masked trials of brolucizumab for neovascular age-related macular degeneration
Ophthalmology
Retinal arterial occlusive vasculitis following intravitreal brolucizumab administration
Am. J. Ophthalmol. Case Rep.
Severe vision loss secondary to retinal arteriolar occlusions after multiple intravitreal brolucizumab administrations
Am. J. Ophthalmol. Case Rep.
DARPins: a new generation of protein therapeutics
Drug Discov. Today
Phase 1 study of OPT-302 inhibition of vascular endothelial growth factors C and D for neovascular age-related macular degeneration
Ophthalmol. Retina
Seven-year outcomes in ranibizumab-treated patients in ANCHOR, MARINA, and HORIZON: a multicenter cohort study (SEVEN-UP)
Ophthalmology
Inhibition of platelet-derived growth factor B signaling enhances the efficacy of anti-vascular endothelial growth factor therapy in multiple models of ocular neovascularization
Am. J. Pathol.
Evidence for enhanced tissue factor expression in age-related macular degeneration
Lab. Investig. J. Tech. Methods Pathol.
Production and characterization of monoclonal anti-sphingosine-1-phosphate antibodies
J. Lipid Res.
Secukinumab in the treatment of noninfectious uveitis: results of three randomized, controlled clinical trials
Ophthalmology
VEGF and intraocular neovascularization: from discovery to therapy
Transl. Vis. Sci. Technol.
Current treatment limitations in age-related macular degeneration and future approaches based on cell therapy and tissue engineering
J. Ophthalmol.
New therapies of neovascular AMD beyond Anti-VEGF injections
Vision
The use of biologic therapies in uveitis
Clin. Rev. Allergy Immunol.
Bispecific antibodies: a mechanistic review of the pipeline
Nat. Rev. Drug Discov.
The making of bispecific antibodies
MAbs
Properties of the major component of a peptic digest of rabbit antibody
Science
Expanding the boundaries of biotherapeutics with bispecific antibodies
BioDrugs
Blinatumomab: a bispecific T cell engager (BiTE) antibody against CD19/CD3 for refractory acute lymphoid leukemia
J. Hematol. Oncol.
Blinatumomab, a bispecific B-cell and T-cell engaging antibody, in the treatment of B-cell malignancies
Hum. Vaccines Immunother.
Emicizumab for the treatment of haemophilia A: a narrative review
Blood Transfus.
Characteristics of drug combination therapy in oncology by analysing clinical trial data on ClinicalTrials.gov
Pac. Symp. Biocomput. Pac. Symp. Biocomput.
Regeneron Scraps Eylea Combination after Phase 2 Setbacks
Ocular Disease Therapeutics: Design and Delivery of Drugs for Diseases of the Eye
J. Med. Chem.
Choroidal neovascularization: newer molecules
Biotherapeutics and immunogenicity: ophthalmic perspective
Eye
Selected aspects of ocular toxicity studies with a focus on high-quality pathology reports: a pathology/toxicology consultant’s perspective
Toxicol. Pathol.
Immunogenicity testing of therapeutic antibodies in ocular fluids after intravitreal injection
Bioanalysis
Advancements in understanding immunogenicity of biotherapeutics in the intraocular space
AAPS J.
Endophthalmitis following intravitreal injections
Graefes. Arch. Clin. Exp. Ophthalmol.
Molecular Partners Provides Regulatory Update of European and Japanese Filings of Abicipar Pegol
Clinical experience with pegaptanib sodium
Clin. Ophthalmol. Auckl. N.Z.
Immunogenicity and efficacy after switching from original ranibizumab to a ranibizumab biosimilar: real-world data
Eye
Targeting key angiogenic pathways with a bispecific CrossMAb optimized for neovascular eye diseases
EMBO Mol. Med.
IVT injections: health policy implications
Rev. Ophthalmol.
Multi-country real-life experience of anti-vascular endothelial growth factor therapy for wet age-related macular degeneration
Br. J. Ophthalmol.
Cited by (0)
Matthew Collins is studying for a PhD at the University of East London, working on a project to develop hybrid strategies to generate bispecific antibody mimetics. He earnt his MSc in clinical drug development from Queen Mary University of London in 2017.
Sahar Awwad is a postdoctoral research fellow at UCL, School of Pharmacy and UCL, Institute of Ophthalmology. Her current research projects are widely based on (i) drug delivery; (ii) ocular pharmaceutics, pharmacokinetics and biodistribution studies; and (iii) protein production and modification; and she has extensive knowledge of protein characterisation, modification and conjugation. She has also developed the PK-Eye, an innovative two-compartment in vitro model of the human eye to aid in the evaluation of ocular formulations. This led to the formation of Optceutics Ltd, a spin-out company that utilises the PK-Eye with UK-US investment.
Hanieh Khalili was awarded a PhD in biotherapeutics in 2012 from University College of London, School of Pharmacy. She continued for additional 4 years as postdoctoral research fellow at UCL School of Pharmacy and Institute of Ophthalmology working on the development and formulation of novel antibody mimetics for ocular inflammation. She is currently a Senior Lecturer in Pharmaceutics at University of East London, School of Health, Sport and Bioscience. Her research focuses on the generation and formulation of bispecific antibody mimetics using recombinant-chemical approaches. Her expertise is to characterise and analyse the binding affinity and thermodynamic properties of modified proteins using protein–protein interaction assays, such as surface plasmon resonance and isothermal titration calorimetry.