Current Pharmaceutical Biotechnology - Volume 17, Issue 15, 2016

Monoclonal antibodies are currently the most attractive therapeutic modality in a broad range of disease areas, including infectious diseases, autoimmune diseases, and oncology. Fc engineering is one attractive application to maximize the value or overcome the drawbacks of monoclonal antibodies for therapeutic use. With the Fc region, antibodies bind to several types of receptors, such as Fc gamma receptors, a complement receptor, and a neonatal Fc receptor. Through this interaction with the receptors, antibodies demonstrate unique functions, such as antibody-dependent cellular cytotoxicity, antibody- dependent cellular phagocytosis, complement dependent cytotoxicity, agonistic activity, and endosomal recycling. Fc engineering technology is conducted mainly to maximize the receptor-mediated functions of antibodies. Moreover, Fc engineering of the two heavy chains to facilitate heterodimerization is indispensable for generating IgG-like bispecific antibodies that are asymmetric. Fc engineering is also conducted to avoid the undesired properties, such as cytokine release and protease-mediated cleavage of the hinge region, of wild-type antibodies, as well as providing additional functions. Thus, Fc engineering technology is an attractive approach for maximizing the potency and convenience of therapeutic antibodies. This review will cover a variety of Fc engineering technologies that improve the functions of therapeutic antibodies.

Monoclonal antibodies and Fc fusion proteins have been successful therapeutics in the field of cancer and immune disease. As their pharmacological activity is dependent on the Fc fragment governing their effector functions and long in vivo half-life, the extensive engineering of the Fc for altered binding of its natural ligands that enable these properties has delivered molecules optimized for their therapeutic effect. Recently, the IgG1 Fc region itself and its subunits monomeric Fc fragment, CH2 and monomeric CH3 domain, have been engineered into scaffolds with favorable biophysical properties and a high potential for de novo antigen recognition. A dimeric Fc fragment with an antigen binding site has proven suitable for evaluation in animal models and has already entered human trials. Such modified constant domains can easily be incorporated into an antibody or fused with antibody domains of a second specificity. The small size of the Fc and its subunits that enhances their tissue penetration, as well as the unique topology of their binding sites that allows novel modes of contact with the antigen, are attractive features that prompt their development into promising candidate therapeutics.

Bispecific antibodies with binding specificities for two different antigens have prompted a lot of interest into their development and application. Currently, more than ten bispecific antibodies have been clinically validated for the treatment of various diseases, including cancers and inflammatory diseases. Intensive studies in antibody engineering drive the generation of different bispecific antibody formats that differ in size and shape. However, the most prominent formats, such as IgG-single-chain (sc) Fv or dual-variable domain (DVD) IgG, deviating from the natural IgG structure, may lead to manufacturing difficulties or increase the potential risk of immunogenicity. Thus, the recent efforts focus on the development of bispecific antibodies by Fc heterodimerization that maintain the native structure of the antibody IgG molecule. This review summarizes the various techniques and methods to generate bispecific antibody molecules with Fc heterodimerization, and discusses perspectives of their application.

Advances in genetic and protein engineering and the ability to maintain proliferating mammalian cells in vitro, has allowed reverse engineering of antibodies, i.e. generation of antibodies having specificity for self-antigens. Thus, the lethal consequence of horror autotoxicus, anti-self-responses as envisaged by Paul Ehrlich (1854-1915), has been turned to advantage for treatment of multiple disease states. In order to reap these benefits, it is essential that, in addition to target specificity, the antibody is customised to deliver appropriate downstream biologic effector activities. Genetic engineering allows the development of any chosen isotype; however, The IgG class predominates in human serum and the majority of monoclonal antibody (mAb) therapeutics are based on the IgG format. This review focuses on the structure and function of the four human IgG isotypes (subclasses) and the biologic functions that their immune complexes activate through interactions with cellular Fc receptors (FcγR & FcRn) and/or the C1q component of complement. The long catabolic half-life (~21 days) of IgG contributes to its efficacy as a therapeutic. Each human IgG subclass exhibits a unique profile of biologic activities that are dependent on the glycoform profile of the IgG-Fc. Our current understanding of IgG structure/function relationships allows protein and glycosylation engineering of the IgG-Fc to enhance or eliminate biologic activities and the generation of therapeutics optimal for a given disease indication.

Protein-based therapeutics has become one of the most rapidly growing and successful drug class in the clinic. However, there are still a number of key challenges that need to be addressed before the full therapeutic potential of protein drugs can be realized. Of note, many biologically active proteins have very short in vivo half-lives, a fact that has greatly hindered their clinical applications. Consequently, several different strategies including polyethylene glycol modification and fusion with Fc or albumin have been developed and implemented to prolong the serum half-life of protein therapeutics. Here we will focus on the recent advances in the development of Fc-based antibody fragments and domains and their potential use as novel half-life-extending fusion partners for protein therapeutics.

Fc-based therapeutics including therapeutic full-size monoclonal antibodies (mAbs) and Fcfusion proteins represent fastest-growing market in biopharmaceutical industrial. However, one major challenge during development of Fc-based therapeutics is how to maintain their efficacy in clinic use. Many factors may lead to failure in final marketing. For example, the stability and aggregation resistance might not be high enough for bearing the disadvantages during fermentation, purification, formulation, storage, shipment and other steps in manufacture and sale. Low stability and high aggregation tendency lead to decreased bioactivity and increased risk of immunogenicity resulting in serious side effect. Because Fc is one of the major parts in monoclonal antibodies and Fc-fusion proteins, engineering of Fc to increase its stability and reduce or eliminate aggregation due to incorrect association are of great importance and could further extend the potential of Fc-based therapeutics. Lots of studies focus on Fc optimization for better physical and chemical characteristics and function by structured-based computer-aid rational design, high-throughput screening expression system selection and other methods. The identification of optimized Fc mutants increases the clinic potential of currently existed therapeutics mAbs and Fc-fusion proteins, and accelerates the development of new Fc-based therapeutics. Here we provide an overview of the related field, and discuss recent advances and future directions in optimization of Fc-based therapeutics with modified stability and aggregation resistance.

Background: Of the various biological activities ascribed to extracts from Casearia sylvestris (guaçatonga), its facilitatory activity, i.e., ability to increase skeletal muscle contractile amplitude, has promising therapeutic applications. In this work, we investigated the components responsible for the previously described neurofacilitation caused by C. sylvestris leaves. Methods: The methanolic fraction of C. sylvestris leaves was initially fractionated by column chromatography and partitioned in a MeOH:H2O gradient. The resulting fractions were analyzed by analytical HPLC and yielded fraction 5:5 (F55) that was subjected to solid phase extraction and preparative HPLC. Of the seven resulting subfractions, only F55-6 caused muscle facilitation. Subfractions F55-6 and F55-7 (similar in composition to F55-6 by TLC analysis, but inactive) were analyzed by 1H-NMR to identify their constituents. Results: This analysis identified a rutin-glycoside phytocomplex that caused neurofacilitation, a property that commercial rutin alone did not exhibit. Conclusion: F55-6 apparently caused neurofacilitation by the same mechanism (presynaptic action) as the methanolic fraction since its activity was also inhibited in tetrodotoxin-pretreated preparations.

Background: The natural products have increasing important for the development of anticancer agents. Colchicum baytopiorum C.D. Brickell (C. baytopiorum), an endemic species for Turkey, contains colchicine and its derivatives. Stimulation of apoptotic and autophagy-mediated cell deaths are effective strategy for anticancer therapies. Aim: The aim of the study is to determine the role of the extract on both apoptotic and autophagic cell death in HeLa cell line. Methods: The cell viability of C. baytopiorum (0.1 mg/ml) was determined by MTT assay. Active caspase-3 and t-Bid expressions were evaluated by immunohistochemical method. The mRNA expression of apoptotic regulatory genes (Bcl-xL, Bid, Bad, PUMA, NOXA, Caspase-3, -8, -9, Fas, FADD, TRADD, TRAF2, TNF, TNFR1), autophagic cell death related genes (Atg5-12, Beclin-1, DAPK), and also both autophagic and apoptotic cell death regulatory genes (Bif-1 and BNIP-3) were investigated by qRT-PCR. Results: We determined that the expressions of both apoptotic and autophagic regulatory genes were significantly increased in the treatment group compared to control group. Also, we showed that C. baytopiorum crude extract induces the cross-connection between apoptotic and autophagic cell deaths in HeLa cells. Conclusion: We suggested that this endemic plant extract seems to be a new promising therapeutic approach in cancer.