Biological response-modifiers (biotherapy, immunotherapy)

Biological response modifiers (BRM) are substances that are able to trigger the immune system to fight again infections or indirectly affect tumors. Many of them can be found naturally in small amounts in the body but with the development of biotechnology BRMs can be produced in the laboratory in larger amounts. The use of BRMs spread quickly and they are essential in the treatment of certain cancers, autoimmune and inflammatory diseases and transplantation medicine. BRMs can act passively, for example, against cancerous cells by boosting the immune system, or they actively affect differentiation and cell division.

Although BRMs have several favorable effects, the unwanted side effects have been multiplied because of their direct pharmacological and immunological actions [Murthy 2010].

Most BRMs are endogenous effector peptides or proteins including cytokines, growth factors, certain enzymes, coagulation factors, hormones and monoclonal antibodies.

Examples of biological response modifiers

1.1. Cytokines

Cytokines are small cell-signaling protein molecules responsible for intercellular communication; they harmonize the immune system and activate immune cells. Because of their central role in the immune system, cytokines take part in different immunological, inflammatory and infectious diseases. Virtually all nucleated cells are able to secret cytokines but for example interleukins (IL-1, IL-6) and tumor necrosis factor alfa are produced by endothelial/epithelial cells and macrophages [Boyle 2005]. The most important therapeutic recombinant cytokines are listed in Table 3.

In the treatment of different types of cancer, interferon and IL-2 are often used cytokines.

They can directly kill tumor cells, stimulate the immune system and can combat side effects such as chemotherapy-induced thrombocytopenia [Weber 2004]. Interleukin plays a pivotal role in the immune system as it regulates the growth and function of different leukocytes. It can be used in the therapy of cancer, AIDS, or other immunodeficiencies and wound healing.

Table 3. Therapeutic recombinant cytokines

Generic name Brand name Indications

Aldesleukin /IL-2/ Proleukin Metastatic renal cell carcinoma, melanoma Denileukin diftitox (IL-2

and Diphteria toxin)

Ontak T-cell lymphoma

Interferon alfacon-1 Infergen Hepatitis C

Interferon alfa-n1 Wellferon Chronic hepatitis C

Interferon alfa-2a Roferon-A Hairy cell leukemia, AIDS-related Kaposi sarcoma, chronic myeloid leukemia

Interferon alfa-2b Intron-A Hairy cell leukemia, AIDS-related Kaposi sarcoma, chronic hepatitis B and C, melanoma

Interferon alfa-n3 Alferon-N Condyloma acuminate

Interferon beta-1b Betaseron Acute relapsing forms of multiple sclerosis Interferon beta-1a Avonex, Rebif Acute relapsing forms of multiple sclerosis Interferon gamma-1b Actimmune Chronic granulomatous osteoporosis Oprelvekin (IL-11) Neumega Chemotherapy-induced thrombocytopenia

1.2. Growth factors

Growth factors regulate cell growth, proliferation, and differentiation. Epidermal Growth Factor (EGF) as a drug can help wound healing [Fernandez 2009], Insulin-like Growth Factor (IGF) stimulates tissue growth and it can be used in the therapy of growth deficiencies [Wyatt 2011]. Platelet-Derived Growth Factor (PDGF) helps building collagen during tissue regeneration [Rosen 2006], while Colony Stimulating Factor (CSF) – as a hormone of the immune system – regulates differentiation, growth and activity of white blood cells and can be used in immunodeficiencies. Hematological growth factors in the market are listed in Table 4 [Rogers 2004].

Table 4. Hematological growth factors in the market

Generic name Brand name Effect Indication

Becaplermin (PDGF)

Regranex Inhibition of platelets Diabetic foot ulcers Darbepoetin alfa Aranesp Stimulates

Pegfilgrastim Neulasta Pegilated form of Filgrastim, granulocyte

Severe combined immunodeficiency (SCID) is the most serious hereditary immunodeficiency in which both B-cells and T-cells are impaired due to a defect in one of several possible genes. One autosomal recessive form of SCID (X-SCID) is caused by a defective enzyme, Adenosine DeAminase (ADA), necessary for the breakdown of purines.

Lack of ADA causes accumulation of dATP. This metabolite will inhibit the activity of ribonucleotide reductase, the enzyme that reduces ribonucleotides to generate deoxyribonucleotides. The effectiveness of the immune system depends upon lymphocyte proliferation and hence dNTP synthesis. Without functional ribonucleotide reductase, lymphocyte proliferation is inhibited and the immune system is compromised [Online Medelian inheritance]. ADA-deficiency in children can be treated by the delivery of the enzyme as a drug [Hersfield 1998].

The most diverse forms of chemical catalysts are produced by recombinant DNA

Table 5. Recombinant enzymes used as drugs

Generic name Brand name Effect Indication

Alteplase Activase Plasminogen activator Acute myocardial infarction, stroke, pulmonary embolism

Bivalirudin Angiomax Direct thrombin inhibitor Instable angina Dornase alfa Pulmozyme Hydrolyzes the DNA present

in sputum/mucus of patients with cystic fibrosis and reduces viscosity in the lungs

Cystic fibrosis

Eptifibatide Integrelin Inhibition of platelets Acute coronary syndromes Imiglucerase Carezyme Analogue of human

β-glucocerebrosidase

Type 1 Gaucher disease

Lepirudin Refludan Direct thrombin inhibitor Instable angina

Reteplase Retavase Thrombolytic drug Acute myocardial infarction Tenecteplase TNKase Thrombolytic drug Acute myocardial infarction Tirobifan Aggrastat Inhibition of platelets Acute coronary syndromes

1.4. Blood coagulation factors

Blood coagulation is a complex chemical process including several coagulation factors. Lack or deficiency of any of the coagulation cascade leads to severe anomaly. Hemophilia A is caused by a reduction in the amount or activity of factor VIII. People living with hemophilia require regular transfusions of clotting factors in order to maintain a normal blood clotting system. However, prior to 1992, there was no screening tool available to guarantee that donated blood products were HIV-free. Therefore, those hemophilia patients receiving untested and unscreened clotting factor prior to 1992 were at an extreme risk for contracting HIV via the very blood products that were saving their lives. Over 10,000 people living with hemophilia contracted HIV from the tainted blood supply [US Department of Health and Human Services]. Today not only recombinant factor VIII but IX and VII are also available for clinical use, thus making the treatment of Hemophilia B (factor IX) and factor VII deficiency safer [Pipe 2008, Table 6].

Table 6. Blood coagulation factors produced by recombinant DNA technology

Generic name Brand name Indication

Factor VII NovoSeven Hemophilia

Factor VIII Bioclate, Recombinate, Kogenate, Helixate, ReFacto

Hemophilia A

Factor IX BeneFIX Hemophilia B

1.5 Hormones

The use of hormones produced by recombinant DNA technology is not a rare event in everyday medical practice (Table 7). Before the widespread utilization of biotechnology, Human Growth Hormone (hGH, somatotropin) was extracted from the pituitary gland of human cadavers, and used for the treatment of childhood growth disorders such as dwarfism.

In some cases, this hormone from cadavers contained protein-associated infectious particles and caused Kreutzfeld-Jacob disease which is an incurable degenerative neurological disorder and invariably fatal. Today clean, recombinant hGH is available and has replaced the old, limited form which raised ethical issues as well. As hGH can strengthen bones and muscles, it is suitable for the treatment of severely underweight patients or those who suffer from certain nutrition disorders.

Before the production of recombinant human insulin, insulin was extracted from the pancreas of cows and pigs and often caused allergic reactions. Recombinant human insulin can be produced reliably, in large amounts without the risk of allergic side effects. Thanks to biotechnology, human insulin can be generated even in plants (Carthamus tinctorius, safflower) [From SemBiosys].

Assisted reproduction and in vitro fertilization would be out of the question without hormones produced by recombinant DNA technology.

Table 7. Some hormones used in the clinic and produced by recombinant DNA technology

Generic name Brand name Effect Indication

Choriogonadotropin

Follitropin alfa Follistim, Puregon Stimulates ovarian follicular growth

Ovulation problems Follitropin beta Gonal-F Stimulates ovarian follicular

growth for the glucose to enter into the cell

Glucagon GlucaGen Causes the liver to convert stored glycogen into glucose, increases blood glucose level

Hypoglycemia

Growth hormone releasing hormone

Geref Triggers the release of stored growth hormone

Childhood growth hormone deficiency Tireotropin Thyrogen Thyroid stimulating hormone Thyroid cancer

2. Potential side effects of therapies with recombinant biological response-modifiers