Biological
Response Modifiers
Biologic therapies for the
treatment of cancer are referred to as biologic response modifiers (BRM’s).
The United States Food and Drug Administration (FDA), the division of the U.S.
Department of Health and Human services charged with ensuring the safety and effectiveness
of new drugs before they can go on the market, has approved several BRM’s
for use in cancer treatment. These substances, which are naturally produced in
small quantities in the body, can now be produced in large quantities in the laboratory.
BRM’s stimulate the patient’s immune system to protect the body from
foreign substances such as tumor cells.
BRM’s include substances
such as monoclonal antibodies, tumor necrosis factor, and cytokines.
- Monoclonal antibodies
are proteins that target tumor associated antigens
– substances on the surface of the tumor cell that are different than
normal cells. Monoclonal antibodies can recognize and bind to tumor specific
antigens and help the body mount an immune response, thus interfering with
the cancer cell’s survival and ability to metastasize.
- Tumor necrosis factor
is a natural substance produced by one of the body’s types of white blood
cells (T lymphocytes) in response to the presence of tumor cells and infectious
agents. Tumor necrosis factor exerts a direct cytotoxic effect on tumor cells.
- Cytokines are naturally
occurring substances released from stimulated cells of the immune system.
Cytokines can strengthen the activities of the immune system, altering the
growth and metastatic ability of tumor cells. Cytokines include interferons,
interleukins, and colony-stimulating factors.
- Interferons are substances
produced by the body in response to biologic agents. Research has demonstrated
that interferons can inhibit the growth and division of cancer cells.
They also stimulate tumor-associated antigens on tumor cell surfaces,
making the tumor cell more apparent.
- Interleukins are
regulatory substances produced by lymphocytes and monocytes, two of the
five types of white blood cells. Interleukins demonstrate a wide range
of biologic effects that enhance the immune system response.
- Colony growth factors
are naturally occurring proteins that regulate the growth and development
of blood cells. Colony growth factors have played a major role in preventing
infection in cancer patients. For example, C-CSF (granulocyte colony stimulating
factor) increases the number of granulocytes or neutrophils, white blood
cells that are vital to fight infection. As a result, patients can better
tolerate standard treatment protocols and may be able to tolerate higher
doses of chemotherapeutic agents, which may improve outcomes. Erythropoetin
is another substance that is naturally produced by the kidneys in response
to decreased red cell production or hypoxia. Erythropoetin stimulates
the bone marrow to produce more red blood cells and to speed up red blood
cell maturation. Laboratory manufactured erythropoetin can be given to
patients experiencing anemia as a result of chemotherapy.
INSTANT
FEEDBACK:
Monoclonal
antibodies increase the immune response by targeting tumor specific antigens.
Additional biologic agents
and approaches such as vaccine therapy are based on the idea that there are tumor-associated
antigens on the cell surface of tumors not found on normal cells. Potentially,
the body’s immune system can be taught, through immunization, to recognize
these tumor-specific antigens, and to activate the immune system to prevent the
recurrence of cancer. Gene therapy is a technique in which new genetic material
is inserted into a patient’s cell to correct an inborn genetic error or to
introduce a new biologic function to the cell. Gene therapy may be useful in cancer
treatment to improve patient immune response.