Enzyme based Therapies

Enzymes are biologic catalysts exhibiting remarkable substrate specificity and high efficiency. They are found through out biological systems and are located both side of the cell membrane. Enzymes are mostly proteins (with few exceptions like RNA) that catalyze unique biochemical reactions by lowering the activation energy. Enzyme catalytic activities are essential for carrying out functions of life like cell division, protein synthesis, and metabolism. Highly coordinated biochemical reactions carried synchronized fashion leading to successful events with precision. Enzymes are usually regulated by phosphorylation, proteolytic modifications, binding to stimulatory and inhibitory co proteins and allosteric interactions.

To be precise the dynamisms of life depends on activities of the proteins. change in the perturbation of the dynamic, highly linked and synchronized bio systems due to deficiency of enzymes leads to diseased state. It also provides a therapeutic opportunity to restore the bioprocess imbalance by replacement of enzymes. Principles of enzyme-based therapies depend upon identifying the deficient or aberrant enzyme activity leading to clinical symptoms like shortage or excess accumulation of key substrates or end products. The major hurdles of enzyme therapy are development of immune reaction by the host and reduction in efficacy of the enzyme due to repeated administrations.

The advent of rDNA technology and PEGylation technology has raised many hopes to minimize the problems enzyme based therapy and there is an accelerated efforts world wise to develop novel therapeutics. Enzymes as drugs have two important features that distinguish them from all other types of drugs. First, enzymes often bind and act on their targets with great affinity and specificity. Second, enzymes are catalytic and convert multiple target molecules to the desired products. These two features make enzymes specific and potent drugs that can accomplish therapeutic biochemistry in the body that small molecules cannot. These characteristics have resulted in the development of many enzyme drugs for a wide range of disorders. Cystic fibrosis is a life threatening disease caused by a dysfunctional transmembrane regulator, CFTR protein, which modulates the transport of salt and water. This ion channel defect leads to poorly hydrated, thick mucus secretions to accumulate in the respiratory airways leading to choking and respiratory failure. More over the mucus being rich in DNA released by degenerating leukocytes is prone to bacterial infections of lungs leading to pneumonia.

Digestion of DNA by DNAse has been shown to reduce the sputum viscosity in CF patients and also reduces the risk of respiratory infections. L-asparginase is known to catalyze hydrolysis of L-asparginine to Aspartic acid and and ammonia by de aminatioin reaction. Leukemia cells lacking asparginine synthase depend upon exogenous source of asparginine for their requirement. Administration of asparginase will break down all the asparginine in the vicinity of leukemia cells leading to selective death of leukemia cells. Some of the hemolytic enzymes have changed the clinical situations in severe cardio vascular conditions like heart failure. Many enzymes have emerged as emergency medicines in handling clots found in delicate blood vessels of heart and brain. Sreptokinase is a 47-kDa protein obtained from ß –hemolytic streptococci whose binding to the clot exposes the plaminogen, which can be easily cleaved to form plasmin. Plasmin is known to mediate fibrinolysis. The immunological issues have led to the invention of Tissue plasminogen activator (tPA). tPA is a serine protease that catalyzes plasminogen to plasmin. The conversion is enhanced by the presence of fibrin. It is produced by human rDNA technology in Chinese hamster ovary cells, which are less immunogenic than streptokinase. TNkase (tenecteplase) is also similar to tPA with reduction in non intracranial bleeding complications. Urokinase, which is obtained from, cultured human kidney cells is less immunogenic and is known to act like streptokinase. Lysozyme has been used as a naturally occurring antibacterial agent in many foods and consumer products, because of its ability to break carbohydrate chains in the cell wall of bacteria. Lysozyme has also been shown to possess activity against HIV, as has RNase A and urinary RNase U, which selectively degrade viral RNA opening some exciting possibilities for the treatment of HIV infection. Other naturally occurring antimicrobial agents are the chitinases. As an element of the cell wall of various pathogenic organisms, including fungi, protozoa and helminths, chitin is a good target for antimicrobials. The cell walls of Streptococcus pneumonia, Bacillus anthracis and Clostridium perfringens have been targeted with the use of bacteriophage-derived lytic enzymes.



The use of lytic bacteriophages themselves as a treatment for infections is also being developed and could prove useful against new drug resistant bacterial strains. Advancements in biotechnology over the past ten years have allowed pharmaceutical companies to produce safer, cheaper enzymes with enhanced potency and specificity. Along with these advances, changes in orphan drug laws and new initiatives by the FDA have been effective in facilitating efforts to develop enzyme drugs. This synergy has a beneficial effect on the development of treatments for both rare and common diseases.The availability of endogenous enzymes and their variants has allowed the use of enzymes as replacement and therapeutic agents. The major advancement in the therapeutic frontiers includes MPS VI, Genetic diseases, Burn, debridement, Infectious diseases and Cancer. It is interesting to explore enzymes as novel therapeutic alternatives in the field of infectious diseases and prodrug activators. The pharmacokinetic alteration of enzyme is possible by PEGylation and glycosylation. All though gene therapy seems to be attractive approach to genetic disorders, enzyme therapy will continue to mange the patients with enzyme defects as rDNA technology will bring down the cost of enzyme therapies.

Table 1 Some Enzyme based therapy in practice and clinical studies 

Enzyme	Therapeutics
Pegademase	For enzyme replacement therapy for ADA in patients with SCID
Alglucerase injection	For replacement therapy in patients with Gaucher’s disease type I
Dornase α	To reduce mucous viscosity and enable the clearance of airway secretions in patients with Cystic Fibriosis
Imiglucerase	Replacement therapy in patients with types I,II, and III Gaucher’s disease
Pegaspargase	Treatment of acute lymphocytic leukemia
Sacrosidase	Treatment of congenital sucrase-isomaltase deficiency
Rasburicase	Treatment of malignancy-associated or chemotherapy-induced hyperuricemia
Agalsidase beta	Treatment of Fabry’s disease
Laronidase	Treatment of patients with MPS I
α-Galactosidase A	Long-term enzyme replacement therapy for the treatment of Fabry’s disease
Superoxide dismutase (recombinant human)	Prevention of reperfusion injury to donor organ tissue
Lipase, amylase and protease	Treatment of pancreatic insufficiency
Recombinant human porphobilinogen deaminase	Treatment of acute intermittent porphyria attacks
PEG-uricase	Control of the clinical consequences of hyperuricemia in patients with severe gout in whom conventional therapy is contraindicated or has been ineffective
Recombinant urate oxidase	Prophylaxis of chemotherapy-induced hyperuricemia
PEGylated arginine deiminase	Treatment of hepatocellular carcinoma
Phenylalanine ammonia-lyase	Treatment of hyperphenylalaninemia
Butyrylcholinesterase	Treatment of post-surgical apnea
Papain, trypsin and chymotrypsin	Treatment of multiple myeloma
Chondroitinase	Treatment of patients undergoing vitrectomy

Dr. Anantha Naik Nagappa,
Professor of Pharmacy,
Pharmacy Group,
Birla Institute of Technology and Science,
Pilani, 333031
Rajasthan
India
Phone: 091-1596-245074-ext - 413 (O) 091-1596-243417
Email: rnaik7@hotmail.com, anantha@bits-pilani.ac.in
Webpage: http://www.geocities.com/anantha1232000