Erythropoiesis Simulating Agents

Erythropoiesis Simulating Agents: New Ideas and Barriers to Drug Development
Presentation lecture by:Jeffrey R. Kanofsky, Loyola University

Objectives

* Physiology of erythropoietin
* Available Epoetins and how they differ
* Untoward Effects
o Thrombotic Complications
o Decreased Survival in Patients with Cancer
* New Agents
o Follow-on Epoetins
+ Regulatory Issues
o Modified Epoetins
o Erythropoietin-receptor agonists with no structural analogies to epoetins
o ESA agents that work by mechanisms other than direct binding to the erythropoietin receptor
* Conclusions

Physiology

* Erythropoietin cell surface receptor
o Member of Type I cytokine receptor family
o Glycoprotein with 484 amino acids and one N-linked glycan (60 kDa)
o Activate cytoplasmic protein tyrosine kinase JAK2
o Receptor is a dimer
+ Erythropoietin binding changes the conformation of the dimer

* Non-hematopoietic function of erythropoietin
o EPO receptors present on many other types of cells including brain, nerves, placenta and endothelial cells
+ The density of receptors appears to be considerably lower than on erythroid precursors
o EPO appears to be important for angiogenesis
o EPO receptors appear to be present on some cancers
+ The specificity of the assay for the EPO receptors has been questioned
* Most erythropoietin produced by interstitial cells of the kidney
o Low oxygen induced EPO gene expansion
+ Transcription activation
+ mRNA stabilization
o Hypoxia inducible factor-1 activation
+ Binds to hypoxia responsive element in the 3’ flanking region of the EPO gene
+ Forms a complex with p300 protein and hepatic nuclear factor 4
o Upstream kidney inducible elements needed for increased renal expression
Oxygen dependent hydroxylation of asparagine residue 803 also blocks binding to p300

Oxygen Mechanism Responsible for Oxygen-Dependent Degradation of HIF-

Hydroxylases
Available Agents
Epoetins
Modified Epoetins
Epoetins

* All have same 165 amino-acid sequence as natural human erythropoietin
* Identical protein tertiary structure not certain
* Different Epoetins differ somewhat in carbohydrates
* Carbohydrate needed for protein stability
o Unconjugated peptide chain has a very short life in circulation
* Epoetin alfa (Procrit, Epogen, Eprex outside the USA)
o Made in Chinese hamster ovary cells
o About 40% carbohydrate, similar to, but not identical to natural erythropoietin
+ Molecular weight about 30 kDa
o Half-life about 7 to 8 hours
* Epoetin beta (NeoRecormon, available in Europe)
o Same 165 amino acid sequence as epoetin alfa and natural erythropoietin
o Made in Chinese hamster ovary cells
o Carbohydrate composition differs somewhat from epoetin alfa
+ A greater proportion of more basic isoforms
o Terminal half-life is 20% longer than epoetin alfa
* Epoetin delta
o Made in human fibrosarcoma cell cultures (HT-1080)
o EPO gene activated by transformation of cells with cytomegalovirus promoter
o Does not have N-glycolyneuramic acid (humans are unable to synthesize this compound)
o Approved by European Agency for the Evaluation of Medicinal Agents (EMEA) in 2002 and marketed in some European countries
* Epoetin omega
o Made in baby hamster kidney cell cultures
o Clinically used in some Eastern European, Central American and Asian countries
Modified Epoetins
* Darbepoetin alfa (Aranesp)
Untoward Effects
* Background
o Epoetins developed in mid to late 1980s
o Risk of HIV infection from a transfusion on the order of 1:2,000
o Current risk 1:1,000,000
o Substantial reductions in risk for transmission for other viral diseases, such as hepatitis C

Effect of Epoetins on Thrombosis and Survival in Cancer Patients
Black Box Warning
* Cancer
Likely New Warnings
Follow-on Epoetins
Regulatory Issues
History of Legal Regulation
Justification for Differences in Regulation
Pure Red Cell Aplasia
* Clinical Features
Follow-On Epoetins
Drug Price Competition and Patent Restoration Act of 1984
(Hatch-Waxman Act)
* Requirements
Standards for Follow-on Biologics in Europe
Working Group on Follow-On Proteins at the FDA
Pathway for Biosimilars Act
New Agents: Modified Epoetins
Continuous Erythropoietin Receptor Activator
Promising Agents not yet in Clinical Trials
GATA Inhibitors
Hemopoietic Cell Phosphatase Inhibitors (SHP-1)
Synthetic Erythropoiesis Protein
Non-Peptide Erythropoietin Mimetics
Conclusions

Erythropoiesis Simulating Agents.ppt