Uses for Recombinant Protein Drugs - Biotechnology and Your Health: Pharmaceutical Applications - page 72

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cell production system, and produced the specific recombinant
proteins to stimulate production of red cells and several kinds of
white blood cells.
Red Blood Cells and Erythropoietin
The kidney normally manufactures erythropoietin, the growth
factor for the production of red blood cells. In fact, erythropoietin
was first isolated from the urine of patients with anemia, a con-
dition characterized by too few red blood cells. Red cells carry
oxygen to the body's tissues, and if too little oxygen is delivered
to them, certain kidney cells produce erythropoietin. Most of this
substance goes into the blood, where it circulates to the bone
marrow and other tissues and triggers increased production of red
cells from immature cells. Some erythropoietin spills into the
urine. The concentration of erythropoietin in the blood is very
low. The concentration is even lower in urine, but urine is easy,
safe, and cheap to collect, and it does not contain a large number
of other proteins.
The first successful scheme to purify erythropoietin from urine
started with 2,550 liters of urine, and through a series of steps to
remove other proteins based on what was known about erythro-
poietin, scientists produced only enough of the substance to conduct
some laboratory tests. This was not a practical way to get the growth
factor, so scientists engineered animal cells to produce recombinant
human erythropoietin (Procrit ® /Epogen ® and Aranesp ® ) to treat
people who have anemia. Anemic patients often feel very weak and
tired because their muscles do not receive enough oxygen. Red
blood cells are filled with hemoglobin, a protein that shuttles oxygen
from the lungs to the tissues and moves waste CO 2 from the tissues
to the lungs. Anemia occurs in patients whose kidneys have failed
(and thus do not produce erythropoietin), and in patients receiving
certain cancer drugs that slow the bone marrow's production of red
cells. The same form of erythropoietin is marketed to treat cancer