Stud . Doroshko Yu. M.,  stud. Borodina O.O., c.b.s. Lych I.V., stud. Shulzhenko V. S.

National University of Food Technologies

 

BIOENGINEERING STRUCTURES BASED ON ABZYMES

 

Medical abzymology achievements became the basis for developing new drugs. Catalytic antibodies (Ab) are defined as "new molecular tool" to explore rheumatologic and cardiac diseases, diseases of endocrine system, autoimmune diseases of the central nervous system (CNS), sepsis, HIV and other infectious and neoplastic lesions [1].

Beside various aspects of abzymes direct clinical usage, a particular interest to researchers, experts and healthcare provider causes an abzyme-based bioengineered structures with their further usage in fundamental and practical medicine.

There are two types of abzymes we know: natural and artificial.

Artificial abzymes - is hydrolyzed esters of dinitrophenol (DNP). During many diseases (autoimmune, viral and oncological) in human body are produced antibodies that hydrolyze peptides, proteins, DNA, RNA and polysaccharides. Such catalytically active antibodies called ‘natural’ [1].

We know that women hormonal and immune condition changes related to pregnancy, childbirth and lactation and may lead to autoimmune diseases development. Because of the autoimmune tolerance violation in women body appear highly specific auto-Ab and abzymes, determination of which may be useful for predicting the emergence of autoimmune diseases.

Catalytic Ab with therapeutic functions that will be further used in modern treatment regimens must meet two main criteria - to recognize and bind to a cell (or target molecule) and after specifically and selectively linked them, take adequate catalytic functions. 

In addition, there are active development process in a use of DNA-abzymes as molecular probes and diagnostic tools to treat patients with fungal airway disease [2]. It is possible that in the catalytic activity of auto-Ab (DNA abzymes for particular) are programmed an additional enzymatic Rh, implementation of which is related to a specific conditions of metabolism, such as the formation of autoimmune conflict, against infection or during pregnancy [2].

Another characteristic feature of abzymes allows to turn singlet oxygen into hydrogen peroxide. Researchers believe that immunoglobulins – a unique class of proteins that are capable of generating up to 500 molar equivalents of hydrogen peroxide from singlet oxygen without activity reduction due redox process of molecule that play catalyst role. It should be noted, that other proteins have ten times less activity; moreover, they are rapidly inactivates during redox reactions [3].

Next direction of abzymes usage, most dynamically developing one to date, associated with the creation of catalytic Ab, that are capable to bind and destroy narcotic drugs, circulating in the peripheral blood until the initialization their toxic effects on the nervous system and other systems and tissues [4].

Proved that catalytic antibodies can effectively neutralize toxic organophosphorus compound (toxic OPC). The resulting catalytic monoclonal Ab contribute to the rapid hydrolysis of stable toxic OPC. It makes possible to use catalytic Ab aiming to prevent and treat the most severe intoxication, caused by toxic OPC. This abzymes application is very promising in our time.

With unique catalytic and cytotoxic properties, DNA-abzymes can act as a powerful regulator of apoptosis and other mechanisms in systemic autoimmune and cancer diseases, while claiming the role of an additional tool in the diagnosis.

Therefore, it is possible to say that the perspective of abzymes usage for the tumors treatment is one of the important areas of catalytic Ab application that develops right now. In this case, abzymes chosen as activators of cytostatic drugs to minimize their overall toxic effect on the body [5]. Specifically, during breast cancer disease is used a bizarre Ab, one active center of which aims to integrate the receptor of tumor cells (concentration of those receptors in the tumor is significantly higher), while another Ab’s active center has catalytic function, which turns doxorubicin predecessor into its active cytostatic form [6]. During treatment, Ab selectively accumulated in the tumor and then show their catalytic activity. Thus, a concentration of active cytostatics rapidly increases in the tumor without a significant increase in activity of the drug in other organs and systems, which significantly reduces its overall toxic effect.

Other perspective usage of abzymes is a new generation drugs development for site-directed anticancer chemotherapy programs, where instead of traditional bacterial enzymes activators (ADEPT, antibody-directed enzyme prodrug therapy), used abzymes that activates drug precursor (ADEPT) at the time of their delivery to the tissues and target organs. The foundation of this therapy is the use of antibodies conjugated with enzymes. This allows combining two important functions of antibodies, such as cell recognition and catalyst. ADEPT principle based on the specific interaction of tumor-binding antigen with the antibody and prodrug activating process by enzyme. This allows to avoid drug’s overall toxicity and allows to keep the reaction ongoing as closest to cancer cells as possible. The usage of non-human enzymes in human therapy increases the risk of immunogenicity and limits chances of potential therapeutic protein re-use. In this case, enzymes may be replaced by abzymes.

Humanization of antibodies by genetic engineering also allows resolving the immunogenicity issue. Currently, in the prodrug therapy following abzymes are used: 38C2, 33F12, 84G3 and 93F3, but the most studied are 38C2. This antibody detects aldolase activity and generated by reactive immunization.

Abzyme 38C2 activates prodrug form of such anticancer drugs as doxorubicin and camptothecin. 38C2 has the ability to inhibit a growth of primary and metastatic tumors, including Kaposi's sarcoma, melanoma and breast cancer. Antibodies, which used in abzyme’s prodrug therapy is an ADEPT strategy option, while abzymes that replaces enzymes in this therapy called bispecific (Figure 1). However, the usage of bispecific abzymes are not widely popular in clinical trials [6].

1

Fig.1 ADEPT strategy mechanism

New pharmacological structures, that composed of adapted to the human body abzymes, allows to more effectively and efficiently to apply prodrug-therapy methods in the complex treatment of a number of malignant tumors [6].

As a result, abzymes begins to be considered as potential ‘magic bullet’, which will allow to recognize and selectively destroy tumor cells without damaging the healthy ones [7]. The ‘magic bullets’ mechanism is based on a composing the target cell with a cytotoxic fragment. The combination of the target molecule with the cytotoxic molecule allows to selectively destroy cells that express the target molecule on its surface. In the cancer treatment as the target molecule is used the antigen, that is selectively expressed by tumor cells or blood vessels cells, which support tumor growth. The usage of catalytic antibodies during tumor diseases has number of advantages compared to ordinary enzymes, since human enzymes is limited due prodrug activation by endogenous enzymes in the blood and normal tissue of the patient. To overcome these limitations, researchers have suggested replacing the enzyme component with catalytic antibody.

Considering the data from latest academic publishing, it is safe to say that the potential usage of catalytic antibodies for selective chemotherapy convincing one, as both reaction are not catalyzed by human enzymes; low immunogenicity option due humanizing antibodies is also possible. Bifunctional antibody, which involved in this process, consists of two antibodies: targeted and catalytic. Immunoglobulin G (IgG) molecule is used as such bifunctional antibody [7]. As a result, the enzymatic component is replaced with catalytic antibody.

Therefore, can be said, that in the nearest future bioengineering catalytic antibodies with certain specificity and properties may become the basis for creating drugs that can recognize tumor target tissue and selectively destroy it, while leaving healthy cells intact.

 

References:

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4.                 Bosron W.F., Hurley T.D. Lessons from a bacterial cocaine esterase // Nat. Struct. Biol. –  2010. –  V. 9. ¹ 12.  –  P. 4–5.

5.                 Sinha S. C., Li L. S., Watanabe S. et al. Aldolase antibody ac­tivation of prodrugs of potent aldehyde containing cytotoxics for selective chemotherapy // 2004. – V. 10. ¹ 21. – P. 5467– 5472.

6.                  Abraham S., Guo F., Li L. S. ct at. Synthesis of the next-gener­ation therapeutic antibodies that combine cell targeting and an­tibody-catalyzed activation // Proc. Nati. Acad. Sci. USA. – 2007. – V. 104. ¹ 13 – P. 5584–5589.

7.                 Severine P. L., Raouia B.  N. Catalytic antibodies and their applications in biotechnology: state of the art // Biotechnol. Lett. – 2014. – V. 37. ¹ 20. – P. 69–81.