Table 1.
Different categories of the next generation protein therapeutics.
| Category | Example(s) | Salient Feature(s) |
|---|---|---|
| Engineered mAb | Altered Fc domain with increased affinity to FcγIIIa receptors | Increased effector function (e.g. Antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP)) |
| Altered Fc domain with decreased binding to Fcγ receptors and C1q | Decreased effector function | |
| Increased affinity of Fc domain with FcRn at pH 6.0 | Increased plasma half-life | |
| Addition of sialylated glycans in the Fc region | Enhanced anti-inflammatory properties | |
| Removal of recognized N-glycosylation sites in VH and VL | Prevents the formation of N-glycoforms | |
| N-glycosylation glyco-engineering | Decreased glycoforms | |
| Forced pyroglutamylation of the amino-terminal Gln residues | Decreased number of charge variants | |
| Deletion of carboxy-terminal Lys residues | Decreased number of charge variants | |
| IgG4 and IgG2 hinge engineering | Avoids ‘half’ IgGs and limits the scrambling of disulphide bonds | |
| Engineered variable domain to lower the isoelectric point | Decreased elimination of mAb | |
| Immunoconjugates | Antibody-Drug Conjugates: (1) cysteine or lysine based random conjugation of drugs on normal mAbs, or (2) site-specific conjugation of drugs on engineered antibodies. | Antibodies are used as targeted delivery agents for highly potent drug molecules. More than 50 in clinical trials. FDA approved drugs: Mylotarg®, Kadcyla®, Adcetris®. |
| Immunotoxins: Chimeric proteins containing antibody/fragment attached to a fragment of toxin (e.g. Resimmune, Moxetumomab pasudotox). | Antibody or fragments of it are used for targeted delivery of cytotoxic proteins derived from a bacteria or plant. | |
| Immunocytokines: recombinant antibody-cytokine fusion proteins (e.g. Teleukin, Darleukin, Fibromun). | Enhances the therapeutic index of cytokines by targeting them to the site of disease. | |
| Radioimmunoconjugates (RICs): Antibodies that are directly attached to radioactive isotopes. | Allows radiation therapy to be delivered directly to the surface of targeted cells. FDA approved drugs: Bexxar®, Zevalin®. | |
| Antibody-directed enzyme prodrug therapy (ADEPT): An antibody conjugated to an enzyme (e.g. A5CP, MFECP1). | Employs antibody-enzyme conjugates (AEC) to activate prodrugs selectively at the targeted cells. | |
| Bi/multi-specific | Asymmetric IgG like molecules: Triomab, CrossMAbs, Knobs-into-Holes, LUZ-Y, SEEDbody, Biclonic, and Fab-Exchanged antibody. | Retains the intact mAb structure, where each arm binds to a different antigen. FDA approved drug: Removab®. |
| Symmetric IgG like molecules: Dual-Targeting Ig, Two-in-one antibody, Crosslinked MAbs, mAb2, and CovX-body. | Antibodies whose each arm binds to two different antigens. Includes two antibodies cross-linked chemically, or Fc portion engineered to bind to a target. | |
| IgG Fusions: DVD-Ig, Ts2Ab, BsAb, TvAb, HERCULES, and IgG-like Bispecific. | Molecules bigger than normal mAb because of the added domains to achieve the bi/multi-specific binding. | |
| Fc Fusions: SCORPION, Fc-DART, Dual(ScFv)2-Fab, and ScFv/Fc Fusions. | Two to four ScFv molecules added to the Fc domain of IgG. | |
| Fab Fusions: F(ab)2, Tribody, Fab-Fv, Dock-and-Lock, Bis-Fab, Dual-Action, and Bivalent Bispecific. | Multiple combinations of Fab molecules with other Fab or ScFv molecules. | |
| ScFv and Diabody based: BiTE, DART, Tandab, COMBODY, Single-chain Diabody, HSA-ScFv fusion, and TCR-like antibodies. | Multiple combinations of ScFv/Diabody connected to each other, or non-IgG proteins. FDA approved drug: Blincyto®. | |
| Antibody mimetics/Novel scaffolds | Adhirons | A 100 amino-acid protein of plant origin, with four-strand antiparallel β-sheet core and a central helix. |
| AdNectin/Monobody | A 94 amino-acid protein inspired from the 10th domain of human fibronectin, which is a β-Sandwich of seven β-sheets. | |
| Affibody | A 58 amino-acid protein inspired from Z-domain of staphylococcal protein A, consisting of 3 α-helices. | |
| Affilin | A 176 amino-acid protein inspired from human γ-B-crystallin, which is a β-sheet. | |
| Affimer | A 98 amino-acid protein inspired from human protease inhibitor stefin-A. | |
| Affitin/Nanofitin | A 66 amino-acid protein inspired from DNA-binding protein Sac7d, which is a five-stranded incomplete β-barrel. | |
| Alphabody | 70–100 amino-acid artificial (de novo design) protein consisting triple antiparallel α-helices. | |
| Anticalin | A 160–180 amino-acid 8-stranded β-barrel protein inspired from human/insect lipocalins. | |
| Atrimer/Tetranectin | A 40 amino-acid protein with 5 flexible loops that is inspired from human C-type lectin domain. | |
| Avimer | A 43 amino-acid artificial protein inspired from human multimerized LDLR-A module. | |
| Centyrins | An 89 amino-acid β-Sheet protein inspired from Fn3 domains of human tenascin-C. | |
| DARPin | A 67 (+ multiples of 33) amino-acid artificial (consensus design) protein with α2/β2 repeats, inspired from human ankyrinrepeat proteins. | |
| Fynomer | A 63 amino-acid β-Sandwich protein inspired from SH3 domain of human Fyn tyrosine kinase. | |
| Kunitz domain | A 50–60 amino-acid, disulfide rich, protein consisting of α+β fold, which are inspired from the active domains of human protease inhibitors. FDA approved drug: Kalbitor®. | |
| Obody/OB-fold | A 111 amino-acid protein inspired from theOB-fold of the aspartyl tRNA synthetase that is usually a 5-stranded β-barrel. | |
| Pronectin | A 90–95 amino-acid protein with 2 β-sheets and 3 surface-exposed loops, which is inspired from the 14th extracellulardomain of human fibronectin-III. | |
| Repebody | An artificial (consensus design) 170 amino-acid protein with β-strand-turn-α-helix, which is inspired by the leucine-rich repeat (LRR) modules of the variable lymphocyte receptors (VLRs) from jawless vertebrates. | |
| Engineered ligands/receptors | Engineered soluble receptor that functions as a ‘ligand trap’ (e.g. TRAP-Fc, comprising ligand binding domains of EGFR and ErbB-4 fused to Fc domain). | Helps circumvent ligand multiplicity, where the targeted receptors often have multiple activating ligands. |
| ‘Receptor decoy’ strategy where binding domains of multiple receptors are expressed together to bind and inhibit multiple related ligands and their isoforms. | Helps block multiple ligand–receptor interactions driving independent pathways that synergizes by amplifying the same signal. FDA approved drugs: Eylea®, Zaltrap®. | |
| A ligand trap architecture consisting of receptors and their accessory proteins, which mimics multi-component receptor systems (e.g. IL-2 ‘superkine’). | Help exploit the avidity effects that drive the apparently high binding affinity of multimeric receptor complexes. FDA approved drug: Arcalyst®. | |
| Fc-fusion ligands: Therapeutics ligands (proteins) recombinantly fused with the Fc domain. | Provides enhanced exposure in vivo, leading to reduced dose and/or dosing frequency. FDA approved drug: Eloctate®, Alprolix®. | |
| Ligand-toxin conjugate | The ligand (e.g. cytokine) helps specifically deliver the toxin to the cells expressing the ligand specific receptors. FDA approved drug: Ontak®. |