Magic in oncology

“Magic bullets”: monoclonal antibodies in oncology

Today malignant tumors occupy one of the first places in terms of morbidity and mortality. In the world every year 10 million new cases of cancer.

At the beginning of XX century. genius scientist Paul Ehrlich used the definition of “magic bullet”, referring to the drug, to be selectively destroyed and the cause of the disease.

Honors for basic immunology and modern technology enable a new class of anticancer drugs – monoclonal antibodies (MAT). These drugs have anti-tumor therapy more effective and less toxic. If traditional chemotherapy – a “carpet bombing”, in which affected and healthy cells, then immunotherapy AIT – a “pinpoint strikes” against the protein molecules in tumor cells.

In this review, we present an overview of the current successes and prospects of development of technology AIT in the treatment of cancer.
History and development of the technology of monoclonal antibodies

The first attempt to use antibodies to treat cancer was made Hericourt and Richet in 1895, extracts of osteogenic sarcoma in 50 patients, the results were very promising. Nevertheless, the problem remained of adverse reactions, nestandartiziruemosti sera and weak, short effect.

Treatment with antibodies was further developed in the 70 years of XX century. By this time it was shown that serum antitoxins formed are immunoglobulins, found that the producer of antibodies are plasma cells. Kohler and Milstein Researchers have developed technology to obtain a special cell lines, is a hybrid between the normal antibody-producing mouse spleen cells and mouse myeloma cells. Disparate cells form a dual hybrids that retain the capacity for cell division. So there Hybridoma, the structure of antibodies produced by it are absolutely identical. These antibodies are called monoclonal.
Antibody Humanization

In the 1980′s there have been several studies showing the presence of allergic reactions up to anaphylactic shock, the lack of effectiveness of mouse antibodies in the implementation of the mechanism of destruction of the target cell.

Obtaining human antibodies and antibody partly of human origin became possible after the cloning of immunoglobulin genes and the development of genetic engineering techniques. As in the lungs, and in the heavy chains of antibodies have the constant region and variable region which specifically binds to the antigen. A constant and variable region encoded by multiple independent genetic segments. Genetic engineering technologies allow the creation of hybrid antibodies are mouse / human, differing degrees of “humanization”. The earliest version of such hybrid antibodies are chimeric antibodies. In the chimeric antibody constant regions are of human origin, and variable obtained from the mouse. A typical example of chimeric antibodies – rituximab.

The second generation of hybrid antibody – humanized antibodies in which a mouse origin have only small antigen-binding sites of variable regions. Humanized antibodies have low immunogenicity. A typical example is a humanized antibody alemtuzumab.

Both the chimeric and humanized antibodies in the areas directly linking antigen, obtained from the immunized animals. In the last decade, developed methods of construction of fully human antibodies, bypassing the stage of immunization of man.

So, today, when the MAT are using genetic engineering methods, often bypassing the stage of immunization, the key in defining the term “monoclonal antibody” is precisely the similarity of antibodies, not only producing their monoclonality of B-cells.
Monoclonal antibodies in the treatment of cancer

In the therapy of tumors using two types of AIT:

* Simple, or unconjugated – MAT not associated with any cytotoxic substances;
* Conjugated – MAT, therapeutic effect which is due to attached to the antibody substances (radioactive particles, cytostatics or toxins).

Simple monoclonal antibodies

Most effectively used in oncology MAT – a simple mat. They have different exercise their influence on the malignant tumor. Some antibodies binding with the appropriate antigen, trigger the natural mechanisms of immune response to destroy tumor cells. Other MAT not interact properly with the human immune system. Their effect is realized through binding to antigens, providing a cell proliferation or tumor growth.

The mechanism of action of antibodies can consider the example of alemtuzumab (Campath) – a drug for treatment of chronic lymphocytic leukemia. Variable region connects with alemtuzumab CD52 antigen on the surface of lymphocytes, and constant regions – with Fc-receptors on the surface of cytotoxic cells, which destroy the target (ADCC – antibody-cell-mediated cytotoxicity). In addition, MabCampath activates the complement system, which leads to the formation of the complex, destroying the membrane of malignant cells (CDC – complement-dependent cytotoxicity). These two mechanisms, as well as induction of apoptosis are considered major in the action data of antibodies.

Rituximab (Rituxan, MabThera) was the first MAT, approved for use in oncology. Originally developed by Idec (now Biogen Idec), rituximab has been registered in the U.S. in 1997 for the treatment of B-cell non-Hodgkin’s lymphoma smoldering. In Russia, the drug is sold under the name MabThera.

Rituximab – a chimeric monoclonal antibody that has murine Variable and constant human region, specifically related to the CD20 antigen on B-lymphocytes and initiates immunological reactions that mediate lysis of B-cells. In 2006, the drug is registered for two indications: the treatment of CD20-positive diffuse large lymphoma (in combination with CHOP) and certain variants of rheumatoid arthritis.

To ensure the effectiveness of treatment before treatment is recommended to be screened at the level of expression of CD20-receptor.

Alemtuzumab (Mabkempas, MabCampath) – humanized monoclonal antibody to the antigen CD52, in which only small areas, direct contact with the antigen, are rat origin, and all the rest of the molecule – the human.

Antibodies to CD52 have been developed in England. After numerous studies, alemtuzumab was approved in 2001 for the treatment of chronic lymphocytic leukemia (CLL) – the most frequent type of leukemia in adults. In Russia, the drug is sold under the name MabCampath.

CD52 antigen is expressed on the membrane of most mature normal and tumor T-and B-lymphocytes with very high density – about 500 000 molecules per cell (compared to the antigen CD20, the density of expression of about 8000 molecules per cell). Molecules CD52 antigen cover about 5% of the cell surface of lymphocytes and are present in all cells of CLL patients with the disease. This explains the extremely high activity of alemtuzumab for CLL and T-cell lymphomas, as well as the lack of need to determine the level of expression of CD52 before treatment.

MabCampath is mainly used for treatment of patients with CLL refractory to conventional chemotherapy fludarabine, as well as first-line therapy for patients with extremely poor prognosis of the disease due to genetic disorders, such as deletions in the p53 gene.

MabCampath was effective and at T-prolimfotsitarnom leukemia (T-PLL). This is a rare but very aggressive disease, is usually resistant to chemotherapy. Good results were obtained when therapy MabCampath cutaneous T-cell lymphomas – a syndrome Cesar and granulosarcoid.

It is important to note that MabCampath does not have any effect on hematopoietic progenitor cells in bone marrow and does not prevent repopulation of hematopoietic system by normal lymphocytes after treatment.

In recent years MabCampath used to reduce the reaction “graft-versus-host disease in allogeneic transplantation of hematopoietic stem cells. Preliminary ex vivo purification of the transplant with Campath 8 times reduces the frequency of cases of acute reactions of “master”, which are the primary cause of death in patients after transplantation.

At present, examines the role of Campath in the treatment of certain autoimmune diseases (rheumatoid arthritis, multiple sclerosis).

The mechanism of action of some MAT (trastuzumab, bevacizumab, and tsetuksimab) is realized without immune mechanisms.

Developed by Genentech trastuzumab (Herceptin) was the first humanized antibody approved for the treatment of solid tumors in 1998 In Russia, the drug is sold under the brand name Herceptin.

Trastuzumab – recombinant humanized MAT against HER2/neu-retseptorov belonging to the epidermal growth factor receptor. Overexpression of HER2/neu in breast cancer tissue is found in 20-30% of patients and is accompanied by a sharp decrease in apoptosis, increased proliferation, a decrease in the number of estrogen receptors in the tumor, decrease the effectiveness of chemo-and endocrine. Herceptin blocks proliferation, induces apoptosis of target cells and has antiangiogenic activity. The drug is approved for use in monotherapy patients with expression of HER2/neu in conjunction with metastatic breast cancer, as well as in combination with cytotoxic agents in patients with previously untreated with chemotherapy. Before starting treatment with Herceptin should be screened for the expression level of HER2-receptor.

Bevacizumab (Avastin) is a recombinant humanized monoclonal antibody that binds selectively to the biologically active vascular endothelial growth factor (VEGF) and neutralize it, leading to a decrease in vascularization and inhibition of tumor growth.

In clinical studies have shown that Avastin has cytostatic and cytotoxic effects in many solid tumors, which was expressed in tumor regression, slowing tumor growth or increase time to progression. In addition, bevacizumab enhances the antitumor effect of some cytostatics. Bevacizumab has been registered in the U.S. in 2004 as first-line treatment of metastatic colorectal cancer (in combination with 5-fluorouracil). In Russia, the drug is sold under the brand name Avastin.

Currently under more than 130 clinical trials bevacizumab at 25 different types of malignant tumors, including breast cancer, colon, clear cell renal cell carcinoma, nonsmall cell lung cancer, melanoma.

Tsetuksimab (Erbitux) – chimeric MAT blocking the activation of epidermal growth factor receptor (EGFR). In 2003, Erbitux was registered in the U.S. for the treatment of colon cancer (in combination with irinotecan), and in 2006 – to treat cancers of the head and neck. In Russia, the drug is sold under the name Erbitux.
Monoclonal antibodies as carriers of active substances

In recent years, AIT have been used to deliver cytotoxic agents directly to tumor cells, thus avoiding damage to healthy tissue, solves the problem associated with a weak anti-tumor effect of certain antibodies because of the inability to penetrate deep into the fabric of a solid tumor.

Depending on the active substance attached to the antibody, conjugated MAT divided into the following groups:

* Radioactive particles (this type of therapy is also called radioimmunoterapii);
* With cytostatics;
* With toxins (or immunotoxins).

Currently, for the treatment of tumors in the world, recorded only two monoclonal antibody linked to radioactive particles.

Tiuksetan Ibritumomab (Zevalin) – AIT against CD20, coupled with yttrium-90. The combined effect of the drug provides bou? Greater efficiency compared with treatment by a simple antibody to CD20. Zevalin was registered in 2002 for treatment of recurrent and refractory forms of follicular lymphoma. Currently undergoing clinical studies Zevalina as consolidation therapy in first-line treatment of follicular lymphoma, as well as large-B-lymphomas.

Zevalin is associated with malignant as well as with normal B-lymphocytes, therefore, to remove the healthy cells bearing the antigen CD20, from peripheral blood of patients receive a first dose of simple antibody. After the elimination of target cells from peripheral blood CD20 radiolabeled antibodies can specifically bind to tumor cells. This ensures a high bioavailability in the locations of foci of the tumor and prevents the spread of radioactivity in the body circulating lymphocytes.

90% of the effective energy of yttrium-90 – in the form in which it is used in the drug Zevalin – operates at a depth of 5 mm, resulting in all the possible harmful effects on healthy tissues is minimized. Yttrium-90 emits only ?-radiation, hence the application Zevalina not want to hospitalize or isolate the patient. Treatment Zevalinom with yttrium-90 can be safely conducted on an outpatient basis.

In Russia, the drug is in the process of registration.

Tozitumomab (Beksar) – MAT mouse to the antigen CD20, which is attached to a radioactive isotope of iodine-131. The drug received FDA approval in 2003 for the treatment of relapse of follicular lymphoma. Mode of Beksara includes two phases: the therapeutic dose and proper. Iodine-131 decays, releasing ?-and ?-radiation with a half life of 8 days. At the time of treatment required isolation of the patient and the special conditions of his stay in the hospital as a radioactive isotope iodine-131 excreted in urine. In Russia, the drug is not registered.

As for AIT, connected with the chemotherapeutic drugs currently registered and available drugs in this group no.

Immunotoxins are joining AIT bacterial (diphtheria toxin, Pseudomonas aeruginosa exotoxin) or plant toxins (ricin A or saporina). The results of the first clinical trials of immunotoxins have shown high promise of the method.

Only immunotoxins, currently registered for the treatment of malignant diseases, is gemtuzumab ozogamitsin (Milotarg) used in the treatment of acute myeloid leukemia in the elderly. Milotarg is a human antibody to the antigen CD33, which is present on the majority of leukemic cells, in combination with the toxin kalihimitsinom. In Russia, the drug is not registered.

Prospects for the development of technology, AIT in the treatment of cancer

Each year, AIT is increasingly used in the treatment of cancer. Antitumor antibodies are 50% of the market all sold drugs, AIT, for comparison: 37% of the market occupied by antibodies for correction of autoimmune / inflammatory disorders, 11% – MAT for the treatment of respiratory diseases and 2% – for cardiovascular. This gap will increase further because of the 400 studies being conducted now with the AIT, about 250 are research in oncology: for patients with breast cancer, ovarian cancer, colorectal cancer in patients with lymphoma and NSCLC.

However, despite the successes, AIT, this technology has its limitations. MAT – too large a molecule unable to penetrate deeply into the cell or tissue. They can not be used orally. AIT technology and production is still very expensive, which affects the cost of drugs.

And yet, AIT has several important properties: high selectivity with low toxicity and ability to activate the immune system to fight tumor cells.

Several biotechnology and pharmaceutical companies are now working on a MAT-next-generation technologies that combine the advantages of AIT and low-molecular drugs with high specificity and low toxicity, ability to influence the objects unrecognizable by modern AIT, including active sites of enzymes and receptors . Such MAT have higher stability, which allows for the possibility of oral, inhalation or topical application.

All over the world spend an enormous amount of testing MAT: 4 out of 10 drugs that are in the final stages of testing – a mat. New biotechnology today give more chances to extend the active years of life of cancer patients, and in the future lead to a victory over cancer.