b -Thalassemia & Deferiprone

1. b-Thalassemia & Deferiprone Advanced Organic 2012 Gloria Phuong Le

2. Overview of b-Thalassemia: • Thalassemia(1): • The term is derived from Greek with thalassa (sea) and haima (blood) • Is a group of genetically anemia disorders in which b-subunit of hemoglobin are not synthesized in adequate amount. • Most thalassemias are inherited as recessive traits • Can be classified as: • Thalassemia Major • Thalassemia Intermedia • Thalassemia Minor (b-thalassemia carrier)

3. Epidemiology(1) • Beta-thalassemia is prevalent in • Mediterranean countries • The Middle East • Central Asia, India, Southern China, and the Far East as well as countries along the north coast of Africa and in South America.

4. Pathophysiology(2) • Genetic defects: • Lead to a variable quantitative but not qualitative reduction in b globin output ranging • b- globin chains that are usually structurally normal • Other factors that affect the degree of chain imbalance also affect the severity of the disease. • The co-inheritance of 2 or more a globin genes (quantitative trait loci) • Co-inheritance of other genetic variants mapping outside the globin clusters • Mutations in b chain that lead to lower affinity for a and b binding

5. Pathophysiology • Due to the lack of b- globin chains • The free a-globin chains are not able to form viable tetramers • This induces the destruction of the erythroid precursors • a-globin chains precipitate in the red cell precursors in the bone marrow forming inclusion bodies • The final effects of b-thalassemia are: • Ineffective erythropoiesis (red blood cells synthesis not effective) • Peripheral hemolysis (rupture or destruction of red blood cells) • As the spleen is a site of red blood cell removal, precipitate of red blood cells will result in splenectomy

6. Diagnosis(1) • Clinical diagnosis: • Severe microcytic anemia (small red blood cell) • Mild jaundice • Hepatosplenomegaly • Hematologic diagnosis: RBC indices show microcytic anemia • Peripheral blood smear: RBA morphologic changes, qualitative and quantitative Hb analysis • Molecular genetic analysis: mutations of the beta globin gene can be detected by PCR-based procedures • Can be prevented by genetic counseling and prenatal diagnosis

7. Management of thalassemia major • Thalassemia major is the most severe and requires blood transfusion • Blood transfusion(1): • Correction of anemia • Suppression of erythropoiesis • Inhibition of gastrointestinal iron absorption • RBC transfusion should not exceed 15-20 ml/kg/day • Along with the introduction of RBCs, iron is also introduced with the hemes in hemoglobin.

8. Blood transfusion complications • Regular blood transfusion increase macrophage-induced heme catabolism, which releases iron into the serum. As a result, iron-transport protein such as ferritin will be saturated (3) • As humans do not have an active mechanism for iron removal • Iron overload might result in patients subject to frequent blood transfusion

9. Assessment and treatment of Iron overload • Serum ferritin: • Iron storage and release • Ferritin level correlates to iron level • Measurement of ferritin is the easiest method to evaluate iron overload and efficacy of chelation therapy • Iron overload complications(4): • Because regular iron excretion is low, frequent transfusion will lead to • Inflammatory disorders • Liver disease • Malignancy • Without treatment, iron accumulates in the heart, liver, and joints and eventually will lead to organ failure and death

10. Metal-chelation therapy-An Introduction • Binding of metal ions for removal is one of the goal of medicinal inorganic chemistry(4) • Other goals include the introduction of metal ions to the biological system, manipulation and redistribution of metal ions within the system(4) • Metal-chelators play an important role in lead intoxication, mercury intoxication, and arsenic-containing syphilis therapies or arsenical industrial accidents

11. The challenges to drug design(4) • Deferoxamine (DFO) is a fungal siderophore • DFO is a hydroxamate-based hexadentate trivalent metal ion chelators • Used in the mid-1960s to treat iron overload • Hydroxamic acid=hydroxylamine+ carboxylic acid • Poor oral bioavailability (hydrophilic and peptidic nature) Must be administered via long subcutaneous infusions • Side effects include: auditory, ophthalmic, and neurotoxicities, as well as skin rashes Figure 2. Hydroxamicacid= hydroxylamine+ carboxylic acid Figure 1. DFO structure

12. Drug design(4) • We need to design an orally active agent with fewer side effects • Due to resonance structures (oxo forms), 3-hydroxy-4-pyridinone (3-HP) has considerably high affinity for Fe3+ at physiological pH (7.35~7.45) • Resonance forms of 3-hydroxy-4-pyridinone Pro-ligands in various protonation states • Deferiprone is designed from 3-hydroxy-4-pyridinone (pioneered by Hider’s lab) Figure 3. Resonance forms of 3-hydroxy-4-pyridinone Pro-ligands in Various Protonation States Figure 4. Deferiprone

13. Deferiprone-General features • Deferiprone has been used as an oral alternative to DFO since the late 1980s (4) • Because the drug is not effective in some patients and because of the concerns about side effects (agranulocytosis: a deficiency of granulocytes in the blood(3)), deferiprone is used as a second-line treatment after DFO • Effective in removal of cardiac iron and can be used in combination therapy with DFO in iron-overload thalassemia patients(4)

14. Pharmacokinetics • DFP has high specificity for the trivalent form of iron to form a 3:1 complex (5) and excreted via urination • Because the complex carries no net charge, it can penetrate membranes easily and helps the removal of potentially toxic iron from tissues (6) • Deferiprone can be used to treat Friedreich’ s ataxia, an inherited mitochondrial disease characterized by decreased production of mitochondrial iron chaperone, which leads to mitochondrial iron accumulation and related toxicity (7) • It has been found that Deferiprone can penetrate the blood-brain barrier better than its glucosylated analogue Figure 5. 3 Deferiprone: 1 Iron complex Figure 6. Glucosylated analogue of Deferiprone

15. Dosage and side effects • Typical dosage is 75 mg/kg/d in 3 divided doses, up to 100 mg/kg daily (6) • Common side effects(6): • Erosive arthritis • Neutropenia (low neutrophil levels in the blood) • Severe agranulocytosis

16. References 1. Galanello, R., and Origa, R. (2010) Beta-thalassemia, Orphanet J Rare Dis5, 11. 2. Thein, S. L. (2005) Pathophysiology of β Thalassemia— A Guide to Molecular Therapies, Hematology 31–37. 3. Liu, J., Obando, D., Schipanski, L. G., Groebler, L. K., Witting, P. K., Kalinowski, D. S., Richardson, D. R., and Codd, R. (2010) Conjugates of Desferrioxamine B (DFOB) with Derivatives of Adamantane or with Orally Available Chelators as Potential Agents for Treating Iron Overload, J. Med. Chem.53, 1370–1382. 4. Scott, L. E., and Orvig, C. (2009) Medicinal Inorganic Chemistry Approaches to Passivation and Removal of Aberrant Metal Ions in Disease, Chem. Rev.109, 4885–4910. 5. Galanello, R. (2007) Deferiprone in the treatment of transfusion-dependent thalassemia: a review and perspective., TherClin Risk Manag3, 795–805. 6. Neufeld, E. J. (2006) Oral chelators deferasirox and deferiprone for transfusional iron overload in thalassemia major: new data, new questions, Blood107, 3436–3441. 7. Roy, S., Preston, J. E., Hider, R. C., and Ma, Y. M. (2010) Glucosylated Deferiprone and Its Brain Uptake: Implications for Developing Glucosylated Hydroxypyridinone Analogues Intended to Cross the Blood−Brain Barrier, J. Med. Chem.53, 5886–5889.