Genistein Derivatization – From a Dietary Supplement to a Pharmaceutical Agent

Field: Pharmacology, Toxicology and Pharmaceutics (Life Sciences)

IntroductionMany soy supplements in the market focus on estrogen and antioxidant properties of isoflavonoid, genistein.Due to the structural similarity to estrogen and binding to estrogen receptor, genistein is often referred to as a phyto-hormone or a dietary estrogen from soy.Target applications of isoflavone-enriched whole soy concentrates include natural hormonal replacement therapy and women's health products (Knight & Eden, 1996;Messina, 1995).However, beneficial effect of genistein on human health extends to the prevention of cancer, cardiovascular events, diabetes, and incidence of inflammatory diseases and management of some metabolic diseases (Birt et al., 2001, Kurzer, 2002;Rimbach et al., 2008;Węgrzyn et al., 2010).The view of genistein as a safe and healthy food supplement is not entirely clear, however.Although most studies show no risk of high consumption of soy-based products for human growth, development or reproduction, there are some data urging caution in genistein overdose.Genistein is implicated as a possible cause of infertility and liver disease in some animal species.Consumption of genistein-rich food and supplements during pregnancy have been suggested to increase the risk of infant leukemias (Hengstler et al., 2002).In addition, experimental data showing stimulatory effect of genistein on proliferation of some breast cancer cells lines raise the problem of safety of genistein supplementation in women with diagnosed breast cancer (Lavigne et al., 2008).Despite the controversies about safety and benefits of soy food supplementation, the pleiotropic activity of genistein, resulting from its interaction with numerous molecular targets, along with the possibility of chemical derivatization of a molecule place genistein among leading compounds for drug development.This chapter deals with two main issues: (1) describes the main molecular targets affected by genistein and indicates alterations in signaling pathways, revealed by global gene profiling analyses, and (2) delineates the relevant examples of genistein derivatives synthesized with aim to obtain compounds exhibiting improved pharmacological activity, increased affinity www.intechopen.comSoybean and Health 254 to molecular targets or altered mode of action as compared to the parent drug.The clinical utility of genistein-based pharmaceuticals is also discussed. Molecular targets affected by genisteinGenistein is known for its pleiotropic effects, mediated by alteration of the activity of key enzymes involved in cell signaling, and by changes of the expression of the genes involved in various physiological processes.To the large group of genistein targets new proteins discovered with use of potent computational methods have joined recently.The interplay between different signaling pathways is extensively studied; however, exact molecular mechanisms have not been clearly defined yet. Binding of genistein to different proteinsThe proteins affected directly by genistein belong to many families.Among them are nuclear receptors, tyrosine-specific protein kinases, topoisomerases, ABC transporters and transport proteins present in the bloodstream (Tab.1).Nuclear receptors are members of a large family of transcription factors activated by binding of a ligand and regulating gene expression underlying a plethora of physiological and pathological states.Genistein binds to and activates estrogen receptors, peroxisomeproliferators activated receptors, liver X receptors and estrogen related receptors.It was recognized very early that the chemical structure of genistein bears strong similarity to 17 -estradiol, and that genisten binds to estrogen receptors (ER) and to sex hormonebinding globulins (Klinge, 2000;Kuiper et al., 1998;Kurzer, 2002).A functional interaction of genistein with estrogen receptors, leading to stimulation of ER responsive genes was confirmed in experiments in vitro (Birt et al., 2001;Kostelac et al., 2003).There are two isoforms of estrogen receptor, ER and ER, differentially expressed in tissues and exhibiting different biological functions.The hydrophobic ligand-binding cavity displays 53% of similarity between two isoforms (Manas et al., 2004).This pocket contains 12helices and two -sheets, connected by several short straight fragments.Inside a ligand binding cavity the ligand molecule is oriented with hydrogen bonding at the ends and hydrophobic van der Waals contacts along the body of the hormone.In the ER functionally important polar amino acids in the binding pocket include: Glu-353, Arg-394, and His-524 (Tanenbaum et al., 1998).These aminoacids interact with 7 and 4' OH groups of genistein.Several other amino acid residues create hydrophobic bonds essential for stabilizing the nonpolar elements of the ligand ring structure.Genistein is regarded as an agonist of ER .Although ligand binding domain sequence and structure in ER is very similar to ER and stabilization of a ligand occurs due to analogous hydrogen bonding with the side chains of Glu-305, Arg-346 and His-475 (Fig. 1), genistein binds to this form with higher affinity than to ER (Manas et al., 2004).The position of the ligand in both receptor types is similar, but the volume of a cavity is smaller in ER, and genistein is bound more tightly in the cavity.Despite the higher affinity to ER than ER , genistein is only partial agonist of ER.The explanation may be derived from the different conformations of a ligand-bound state of ER and ER.Hormone-dependent activation of a receptor is a result of the movement of helix 12 from one position to another.The positional variability of this substructure appears to be a critical attribute of the ER receptors in their variable response to different ligands (Pike et al., 1999). www.intechopen.comGenistein Derivatization -From a Dietary Supplement to a Pharmaceutical Agent 255Recently it was shown that proteins constituting the family of estrogen related receptors (ERRs) are also able to bind genistein (Suetsugi et al., 2003).Although they display similarity to estrogen receptors, they do not bind estrogens.ERRs are referred to as orphan receptors, because no endogenous ligands required for their activity have been identified so far.The ligand-binding pockets of ERRs are very small (about half size of ER ) and partially filled with the aromatic bulky side chains of aminoacids forming the cavity, what is supposed to mimick the ligand-bound state inducing constitutive activity of the receptor.Surprisingly, genistein is a strong agonist of those receptors, augmenting their basal activity.Docking results showed that genistein, due to the small size of the cavity, is tightly packed and deeply docked into the ligand-binding site (Suetsugi et al., 2003) (Fig. 2).