Current Medicinal Chemistry, 2007, 14, 199-212 199 Medicinal Chemistry of Fetal Hemoglobin Inducers for Treatment of -Thalassemia Roberto Gambari *,1,2 and Eitan Fibach 3 1 ER-GenTech, Department of Biochemistry and Molecular Biology, Section of Molecular Biology, University of Ferrara, Ferrara, Italy 2 GenTech-for-Thal, Laboratory for the Development of Pharmacological and Pharmacogenomic Therapy of Thalassaemia, Biotechnology Centre, Ferrara, Italy 3 Department of Haematology, Hadassah - Hebrew University Medical Centre, Jerusalem, Israel Abstract: In this review we summarize the achievements of medicinal chemistry in the field of pharmacological approaches to the therapy of β-thalassemia using molecules able to stimulate the production of fetal hemoglobin (HbF). We first describe the molecular basis of the pathology and the biochemical rational of using HbF inducers for therapy; we then outlined the in vitro and in vivo experimental systems suitable for screening of such potential drugs, and finally we describe the different classes of compounds with emphasis on their advantages and disadvantages in the treatment. The results of these reviewed studies indicate that: (a) HbF inducers can be grouped in several classes based on their chemical structure and mechanism of action; (b) clinical trials with some of these inducers demonstrate that they are effective in ameliorating the symptoms of β-thalassemia; (c) a good correlation was found between HbF stimulation in vivo and in vitro indicating that in vitro testing might be predictive of the in vivo response; (d) combined use of different inducers might maximize the effect, both in vitro and in vivo. However, (e) the response to HbF inducers, evaluated in vitro and in vivo, is variable, and some patients might be refractory to HbF induction by certain inducers; in addition, (f) several considerations call for caution, including the fact that most of the inducers exhibit in vitro cytotoxicity, predicting side effects in vivo following prolonged treatments. Keywords: Fetal hemoglobin; β-thalassemia; Histone deacethylases; Hydroxyurea; DNA-binding drugs; Rapamycin. This paper is dedicated to the memory of Professor Panos Ioannou. INTRODUCTION acid). In addition, these clusters contain various sites that are responsible for the regulation of the expression of each gene [1]. The objective of this review is to summarize the achievements of medicinal chemistry in the field of pharmacological approaches to the therapy of β-thalassemia. We will shortly describe the molecular basis of the pathology and the experimental systems suitable for the screening of potential therapeutic compounds. Major emphasis will be dedicated to the description of the different classes of molecules employed in in vitro and in vivo preclinical studies, as well as recently performed clinical trials. The expression of the globin genes is regulated during ontogeny. In humans, globin production is characterized by two major "switches" [2]. Production of embryonic Hbs switches after the first two months of gestation into fetal Hb (HbF) (α 2 γ 2 ), and then again, before and immediately after birth, into adult Hb (HbA) (α 2 β 2 ). Since both HbA and HbF contain α chains, the switch from the former to the latter represents a decrease in the expression of the γ -globin genes, associated with an increase of β-globin gene expression. The prevalence of HbF during embryonic life is explained by its high affinity to oxygen, a property that allows it to remove oxygen from HbA in the maternal red blood cells (RBCs) through the placenta. 1. HEMOGLOBINS AND THEIR SWITCH DURING ONTOGENY Hemoglobin (Hb) is a tetramer of two α -like and two β- like globin polypeptide chains. In human, the genes for α - globins are clustered on chromosome 16, which contains one gene for ζ and two genes for α (α 1 and α 2 , the proteins of which are identical). The genes for β-like globins are clustered on chromosome 11, that contains genes for ε , β and δ, one gene for each, and two slightly different genes for γ ( G γ and A γ , the proteins of which differ in one amino Immediately after birth the newborn has 85-98% HbF, which gradually decreases to < 5% at the age of one year. In adult life HbA is the major Hb, a small < 5% is HbA2 (α 2 δ 2 ) and the rest (<5%) is HbF which is concentrated in a few RBC [3-5]. 2. -THALASSEMIAS In β-thalassemias, mutations affecting the β-globin gene or its regulatory regions cause absence (β 0 ) or reduced (β + ) synthesis of β-globin chains [1-4]. This is associated with a corresponding excess of the complementary α -globin. The *Address correspondence to this author at the Department of Biochemistry and Molecular Biology, Via L.Borsari n.46, 44100 Ferrara, Italy; Tel: +39- 532-424443; Fax: +39-532-424500; E-mail: gam@unife.it 0929-8673/07 $50.00+.00 © 2007 Bentham Science Publishers Ltd.