Synthesis, characterization and binding affinities of rhenium(I) thiosemicarbazone complexes for the estrogen receptor (α/β)

doi:10.1016/j.jinorgbio.2014.06.012

Journal of Inorganic Biochemistry

Volume 140, November 2014, Pages 53-63

https://doi.org/10.1016/j.jinorgbio.2014.06.012 Get rights and content

Abstract

The binding affinities towards estrogen receptors (ERs) α and β of a set of thiosemicarbazone ligands (HLⁿ) and their rhenium(I) carbonyl complexes [ReX(HLⁿ)(CO)₃] (X = Cl, Br) were determined by a competitive standard radiometric assay with [³H]-estradiol. The ability of the coordinated thiosemicarbazone ligands to undergo deprotonation and the lability of the Re single bond X bond were used as a synthetic strategy to obtain [Re(hpy)(Lⁿ)(CO)₃] (hpy = 3- or 4-hydroxypyridine). The inclusion of the additional hpy ligand endows the new thiosemicarbazonate complexes with an improved affinity towards the estrogen receptors and, consequently, the values of the inhibition constant (K_i) could be determined for some of them. In general, the values of K_i for both ER subtypes suggest an appreciable selectivity towards ERα.

Graphical abstract

The binding affinity towards estrogen receptors α and β of several thiosemicarbazone ligands (HLⁿ) and their complexes [ReX(HLⁿ)(CO)₃] was determined. These complexes can be transformed in the hydroxypyridine derivatives [Re(hpy)(Lⁿ)(CO)₃]. The affinity of these thiosemicarbazonato complexes is substantially improved and the values of K_i suggest selectivity towards the ERα.

Introduction

The estrogen receptors (ERs) are members of the steroid/thyroid hormone nuclear receptor superfamily and they bind estrogens with high affinity [1], [2]. Their function is the transcription of factors to modulate gene expression in a ligand-dependent manner. The two subtypes, ERα and ERβ (of which there are five isoforms), are products of different genes and differ in their tissue distribution, although the DNA-binding and ligand bond domains are highly conserved (97% and 61% amino acid identity, respectively) [2]. Both receptors play an important role in the growth of hormone-dependent breast cancer [3], [4]. Immunohistochemical analyses suggest that ERβ may have a dominant role in the healthy mammary gland, and its expression decreases in cancer and metastatic lymph node tissues [5], [6]. Overexpression of ERα is frequently observed in the early stage of breast cancer and this is accompanied by increased cell proliferation [7], [8], [9]. On the other hand, the discovery of the relationship between a high concentration of ERα and the sensitivity of the breast cancer to antiestrogenic molecules led to the possibility of designing drugs to predict the response to antihormonal therapy [3]. This regulation in cancer is the main reason why ER has become an active target for molecular imaging: noninvasive imaging technology offers great promise for the in vivo characterization of estrogen-dependent tumors [9]. Thus, the search for ER-targeted radiopharmaceuticals is an active research area because to date ER radiopharmaceuticals are not in routine clinical use [10], [11], [12].

Fortunately, the crystal structures of the ligand binding domain (LBD) of ERα and different agonist and antagonist ligands have been determined [13], [14], [15] and, although the analogous structure of ERβ is not known, the similar structural behavior of both LBDs against the partial agonist genistein [15] allows one to consider a similar ligand binding pocket with an accessible volume of approximately 450 Å in ERα and 390 Å in ERβ. Details of the interaction between 17β-estradiol [13] and 4-hydroxytamoxifen [14] (a metabolite of the prodrug tamoxifen) are shown in Fig. 1. These findings are the structural basis for the design of the selective ER modulators (SERMs). In short, the presence of a phenol group seems to be essential for the relevant binding affinity of a molecule as this group is able to form a strong hydrogen-bonding network involving Glu353, Arg394 and an ordered water molecule, while the side-chains of 4-hydroxy-tamoxifen and raloxifene [13] are responsible for the antiestrogenic properties.

The same hypothesis has been used for the design of radiopharmaceuticals based on ^99mTc, usually by obtaining its rhenium surrogate in the first stages [16], [17], [18]. Thus, two main approaches have been developed in research aimed at obtaining radiopharmaceuticals: (i) the bifunctional approach, in which a chelating group is joined by a spacer to a receptor-binding organic molecule (typically 17β-estradiol) [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29] and (ii) the integrated approach, in which the metal complex behaves as a receptor-specific molecule. In the first approach, although receptor binding assays indicated reasonably high ER affinity for this kind of compound, little or no ER-specific target tissue uptake ‘in vivo’ has been observed and this is attributed to the large size and/or the very high lipophilicity of these systems [19]. In the latter approach, the metal chelate is an essential part of the receptor binding motif because individual parts should not be active against the receptor and, ideally, the metal coordination arranges the different parts of the molecule to optimize binding to the receptor [13]. This means that the whole coordination sphere around the metal must be designed and its nature and topology must be compatible with biological media. From this point of view, the fragment fac-{M(CO)₃}⁺ (M = Tc, Re) has always been an ideal candidate due to its robustness and kinetic stability and, since the development by Alberto et al. [30] of synthetic pathways to obtain the organometallic precursor [^99mTc(H₂O)₃(CO)₃] in saline media, this research has continued to grow [31], [32].

In previous papers, we reported the synthesis and characterization of S,N-bidentate ligands derived from thiosemicarbazones (TSCs), which form stable six-coordinated rhenium(I) complexes [33], [34], [35], [36], and the resorcinol group, which is included in the TSC ligand as 2,4-dihydroxybenzaldehyde or 2,4-dihydroxyacetophenone. These systems show an interesting supramolecular association supported by hydrogen bonding through the 4-hydroxy group [37]. In the work reported here, we studied the relative binding affinities of related TSC Re(I) complexes and carried out modifications of the complexes to improve the ERα affinity.

Section snippets

Results and discussion

In previous work we found that TSCs are a very versatile ligands to explore the coordination of rhenium(I) [33], [35], [38], [39] and technetium(I) [40] centers. The stability of the S,N-chelate that links the TSC to the {M(CO)₃}⁺ center, besides the easy insertion of different groups at the azomethine carbon atom, allows the design of different molecules and the exploration of their potential properties as radiopharmaceuticals. The substituents at the azomethine carbon can be chosen to include

Conclusions

A group of rhenium(I) thiosemicarbazone derivatives were prepared and the values for the displacement of [³H]-17β-estradiol from the estrogen receptor subtypes (ERα and ERβ) were determined. The ability of a group of thiosemicarbazone ligands (whose affinity for the ER is negligible) to undergo deprotonation once coordinated to the fac-{ReX(CO)₃} fragment, along with the inherent lability of the Re single bond X bond, allowed the isolation of new complexes [Re(Lⁿ)(hpy)(CO)₃] in which the halogen is replaced

Materials and methods

All solvents used for synthesis were dried over appropriate drying agents, degassed using a vacuum line and distilled under an Ar atmosphere [52]. Ligands HL^5–7 were synthesized by condensation of the appropriate aldehyde with the corresponding thiosemicarbazide (Aldrich) following published procedures [37], [41], [42], [43]. Adducts [ReX(CO)₃(CH₃CN)₂] (X = Cl, Br) were synthesized following Farona and Kraus' published methods [53] from the corresponding [ReX(CO)₅](X = Cl, Br) [54]. Elemental

Abbreviations

BHA

butylated hydroxyanisole

estrogen receptor

ERα

estrogen receptor α subtype

ERβ

estrogen receptor β subtype

FBS

fetal bovine serum

3-hpy

3-hydroxypyridine

4-hpy

4-hydroxypyridine

LBD

ligand binding domain, in ER

MTT

([3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide])

NaOMe

sodium methoxide

PBS

phosphate buffered saline

SERMs

selective estrogen receptor modulators

TSC

thiosemicarbazone

Acknowledgments

This research was supported by the European Rural Development Fund and Spanish Ministry of Education and Science both through project CTQ2010-19386/BQU.

References (60)

G.M. Anstead et al.
Steroids
(1997)
L. Huang et al.
Steroids
(2010)
A.K. Shiau et al.
Cell
(1998)
L.G. Luyt et al.
Bioorg. Med. Chem.
(2003)
M.B. Skaddan et al.
Nucl. Med. Biol.
(2000)
T.W. Spradau et al.
Bioorg. Med. Chem. Lett.
(1998)
R. Carballo et al.
J. Organomet. Chem.
(2002)
A. Núñez-Montenegro et al.
Polyhedron
(2013)
A. Núñez-Montenegro et al.
Polyhedron
(2009)
A. Núñez-Montenegro et al.
Polyhedron
(2011)

A. Núñez-Montenegro et al.

Polyhedron

(2008)

R. Alberto et al.

Coord. Chem. Rev.

(1999)

E.S. Mull et al.

Bioorg. Med. Chem.

(2002)

R.N. Hanson et al.

Bioorg. Med. Chem.

(2012)

E.A. Ariazi et al.

Nuclear Receptors as Drug Targets

M. Robinson-Rechavi et al.

J. Cell Sci.

(2003)

E.V. Jensen et al.

Clinical

Cancer Res.

(2003)

B.S. Katzenellenbogen et al.

Breast Cancer Res.

(2000)

S.I. Hayashi et al.

Endocr. Relat. Cancer

(2003)

R.B. Clarke et al.

Cancer Res.

(1997)

J.A. Shaw et al.

J. Pathol.

(2002)

B.S. Katzenellenbogen et al.

Breast Cancer Res. Treat.

(1997)

P.W. Causey et al.

J. Med. Chem.

(2008)

S. Top et al.

ChemBioChem

(2004)

A.M. Brzozowski et al.

Nature

(1997)

A.C. Pike et al.

EMBO J.

(1999)

S. Liu

Chem. Soc. Rev.

(2004)

U. Abram et al.

J. Braz. Chem. Soc.

(2006)

M.D. Bartholomä et al.

Chem. Rev.

(2010)

J.B. Arterburn et al.

Angew. Chem. Int. Ed.

(2000)

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When designing ligands HL11–HL14 (Scheme 2), we decided to include a 5-hydroxypyridine ring so that it may play a role in coordination to the metal together with the hydrazone chain. The substituents on C2 were chosen because they are susceptible to derivatization and/or able to interact with biomolecules [17]. HL14 is an exception as it contains another pyridine group.
Four acyl-hydrazones derived from 5-hydroxypicolinohydrazide and 4-hydroxybenzaldehyde (HL¹¹), 2-fluoro-4-hydroxybenzaldehyde (HL¹²), 2,4-dihydroxybenzaldehyde (HL¹³) or 2-pyridinecarboxaldehyde (HL¹⁴) and two hydrazones derived from 2-hydrazino pyridine and 4-dimethylaminobenzaldehyde (HL²¹) or 4-diethylamino-2-hydroxybenzaldehyde (HL²²) were synthesized and their X-ray structures determined. Twelve rhenium(I) complexes of formula [ReX(HLⁿ)(CO)₃] (X = Cl, Br) were obtained by treating these ligands with [ReX(CH₃CN)₂(CO)₃], and the structures of some representative compounds were determined by X-ray diffraction.
The coordination geometry around rhenium(I) can be described as octahedral, with three carbon atoms in a fac configuration, the halogen atom and two nitrogen atoms from the hydrazone chain and the pyridine group, respectively. The carbonyl group of the acyl-hydrazone ligands does not participate in coordination in any of complexes HL¹¹–HL¹⁴. The coordination mode of the ligands in all complexes could be established by comparing the IR and ¹H NMR spectra.
Formation of the hydrazonate complexes only proved possible with the derivatives of HL²². A study of the corresponding single crystal showed the presence of the dimer [Re₂(L²²)₂(CO)₆], in which the phenolate group of the ligand of the dimer partner coordinates to rhenium after deprotonation. This same group is used to bind to the rhenium atom of the dimer partner at the position released by the halide.
Chemical and biological studies of Re(I)/Tc(I) thiosemicarbazonate complexes relevant for the design of radiopharmaceuticals
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X-ray diffraction studies confirmed the spectroscopic results: the thiosemicarbazonate ligands are deprotonated at the N(2) and O(1) atoms and are coordinated to the fac-[Re(CO)3]+ core through the S(1), N(3) and O(1) atoms (Table 2). The ReS bond distances in complexes 2 and 4 are close to those found in other rhenium complexes with κ3-S,N,O tridentate ligands, such as the functionalized cysteine observed in NAQRII [21], NAZJUU [22], or slightly shorter than those observed in thiophosphoryl functionalized enaminoketones such as GIVZIW [23] and MOXX00 [24] and the pyridyl-cystamine derivative QAQJEY [25]. In the latter compound the functional group including the coordinating sulfur atom cannot undergo deprotonation.
Five thiosemicarbazones (H₂Lⁿ) derived from 4,6-diacetylresorcinol (n = 1–4) and salicylaldehyde (n = 5) have been synthesized and spectroscopically characterized. Single crystal X-ray diffraction studies on some of them show that the molecular structure is dominated by intramolecular hydrogen bonds involving the O(1)–H group of the resorcinol/salicylaldehyde group and the azomethinic nitrogen atom and sulfur atom of the thiosemicarbazone arm. All of the ligands react with fac-[ReBr(CO)₃(CH₃CN)₂] in the presence of NEt₃ to form the stable anionic complexes [NHEt₃][fac-[Re(Lⁿ)(CO)₃] (1–5). The thiosemicarbazonate ligand, as suggested by spectroscopic data and confirmed by X-ray diffraction, acts as a tridentate S,N,O system. The complexes are stable in solution for weeks, although other dimeric species were also detected by X-ray diffraction analysis. The reaction of fac-[^99mTc(CO)₃(H₂O)₃]⁺ with the appropriate ligand at 100 °C for 30 min yielded the complexes [fac-[^99mTc(Lⁿ)(CO)₃]⁻ (Tc1–Tc5). The radiochemical yield and purity were determined by HPLC and their chemical identity was ascertained by comparing their radiochromatogram with the chromatogram of the rhenium congeners (1–5). The results of biodistribution studies in mice on the five technetium compounds showed rapid blood clearance and fast liver uptake that slowly cleared into the intestines, a finding that indicates the hepatobiliary tract as the major excretory pathway. HPLC analysis of urine and blood serum samples from mice injected with the ^99mTc complexes confirmed their in vivo stability since the predominant radiochemical species had the same retention time as the corresponding injected compound.
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Some of them has been described recently [30,49–51]. An analogous core with a chlorine atom instead of a bromine atom has been reported earlier for a few complexes [50,52–57]. In turn, there are only two other crystal structures for rhenium(I) complexes in which the Re(CO)3INS core can be distinguished [58].
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Coordination compounds with tunable redox potentials, absorption and emission spectra, have attracted the worldwide attention due to their potential use in molecular devices [1–4]. Since the initial work of Wrigthon and Morse [5] on the luminescence properties of fac-[Re(CO)3(NN)Cl] compounds, NN = diimine ligands, much effort has been made to the derivatization of coordinated ligands for a wide range of applications such as photosensitization [6–8], luminescent sensors [9–13], photocatalysts [14–17], and light emitting devices [18–22]. Typically, the luminescence properties of the rhenium(I) complexes are associated with the metal-to-ligand charge-transfer excited state, MLCT, which can be tailored by changing the polypyridine ligands [23].
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Synthesis, characterization and binding affinities of rhenium(I) thiosemicarbazone complexes for the estrogen receptor (α/β)

Abstract

Graphical abstract

Introduction

Section snippets

Results and discussion

Conclusions

Materials and methods

Abbreviations

Acknowledgments

Steroids

Steroids

Cell

Bioorg. Med. Chem.

Nucl. Med. Biol.

Bioorg. Med. Chem. Lett.

J. Organomet. Chem.

Polyhedron

Polyhedron

Polyhedron

Polyhedron

Coord. Chem. Rev.

Bioorg. Med. Chem.

Bioorg. Med. Chem.

Nuclear Receptors as Drug Targets

J. Cell Sci.

Clinical

Cancer Res.

Breast Cancer Res.

Endocr. Relat. Cancer

Cancer Res.

J. Pathol.

Breast Cancer Res. Treat.

J. Med. Chem.

ChemBioChem

Nature

EMBO J.

Chem. Soc. Rev.

J. Braz. Chem. Soc.

Chem. Rev.

Angew. Chem. Int. Ed.