Recombinant human
erythropoietin (rHuEPO) engineered in Chinese hamster ovary (CHO) cell cultures (
Epoetin alfa and
Epoetin beta) and its hyperglycosylated analogue
Darbepoetin alfa are known to be misused by athletes. The drugs can be detected by isoelectric focusing (IEF) and immunoblotting of urine samples, because "EPO" is in reality a mixture of
isoforms and the N-
glycans of the recombinant products differ from those of the endogenous
hormone. However, there is a plethora of novel
erythropoiesis stimulating agents (ESAs). Since the originator Epoetins alfa and beta are no longer protected by patent in the European Union, rHuEPO
biosimilars have entered the market. In addition, several companies in Asia, Africa and Latin America produce copied rHuEPOs for clinical purposes. While the amino acid sequence of all Epoetins is identical, the structure of their
glycans differs depending on the mode of production. Some products contain more acidic and others more basic EPO
isoforms.
Epoetin delta is special, as it was engineered by homologous recombination in human
fibrosarcoma cells (HT-1080), thus lacking
N-glycolylneuraminic acid like native human EPO. ESAs under development include EPO fusion
proteins, synthetic erythropoiesis stimulating
protein (SEP) and peptidic (
Hematide(),
CNTO 528) as well as non-peptidic EPO mimetics. Furthermore, preclinical respectively clinical trials have been performed with small orally active drugs that stimulate endogenous EPO production by activating the EPO promoter ("GATA-inhibitors": diazepane derivatives) or enhancer ("HIF-stabilizers":
2-oxoglutarate analogues). The prohibited direct EPO gene transfer may become a problem in sports only in the future.