A facile synthesis of C(2)-symmetric 17 beta-estradiol dimers

Synthesis and anticancer properties of a hybrid molecule with the testosterone and estradiol head-groups

This is the first report on a unique hybrid molecule made of estradiol and testosterone (TS). This distinctive hybrid molecule (1) was designed to interact with both the estrogen receptor (ER) and the androgen receptor (AR) found in hormone-dependent female and male cancer cells, and was synthesized using ethynylestradiol (17EE) as the estrogenic component and 7α-(4-azido-but-2-enyl)-4-androsten-17β-ol-3-one as the androgenic counterpart in a seven-step reaction with ∼ 26 % overall yield. We reasoned that the dual receptor binding ability could allow 1 to act as an antihormone. This was tested on hormone-dependent and hormone-independent breast cancer (BCa) and prostate cancer (PCa) cells. The antiproliferative activity was also assessed on colon and skin cancer cells. We found that 1 was active against MCF7 (ER + ) BCa cells (IC50 of 4.9 μM), had lower inhibitory potency on LNCaP (AR + ) PCa cells (IC50 > 5 μM) and no effect on PC3 and DU145 (AR-) PCa cells. This suggests that the estrogenic component of 1 can interact with the ER on MCF7 cells more effectively than the androgenic component with the AR on LNCaP PCa cells, possibly due to a suboptimal spacer or linkage site(s). Nonetheless, the hybrid 1 was active against colon (HT-29) and melanoma (M21) cancer cells (IC50 of 3.5 μM and 2.3 μM, respectively), and had low cross-reactivity with the drug- and androgen-metabolizing cytochrome P450 3A4 (CYP3A4, IC50 ≫ 5 µM). These findings demonstrate the anticancer potential of 1 and warrant further explorations on this new type of hybrids.

Triazole-based estradiol dimers prepared via CuAAC from 17α-ethinyl estradiol with five-atom linkers causing G2/M arrest and tubulin inhibition

Microtubule dynamic is exceptionally sensitive to modulation by small-molecule ligands. Our previous work presented the preparation of microtubule-targeting estradiol dimer (ED) with anticancer activity. In the present study, we explore the effect of selected linkers on the biological activity of the dimer. The linkers were designed as five-atom chains with carbon, nitrogen or oxygen in their centre. In addition, the central nitrogen was modified by a benzyl group with hydroxy or methoxy substituents and one derivative possessed an extended linker length. Thirteen new dimers were subjected to cytotoxicity assay and cell cycle profiling. Dimers containing linker with benzyl moiety substituted with one or more methoxy groups and longer branched ones were found inactive, whereas other structures had comparable efficacy as the original ED (e.g. D1 with IC₅₀ = 1.53 µM). Cell cycle analysis and immunofluorescence proved the interference of dimers with microtubule assembly and mitosis. The proposed in silico model and calculated binding free energy by the MM-PBSA method were closely correlated with in vitro tubulin assembly assay.

Testosterone and its dimers alter tRNA morphology

The morphology of tRNA was studied upon conjugation with testosterone and its aliphatic and aromatic dimers, using multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling. Structural analysis showed that testosterone binds tRNA through A62, A64, C60, C61, C63, G51, U50 and U59 bases. The binding affinity was testosterone dimer-aromatic>testosterone dimer-aliphatic>testosterone. The steroid loading efficacy was 35-45%. Transmission electron microscopy showed major changes in tRNA morphology upon testosterone interaction with an increase in the diameter of the tRNA aggregate, indicating encapsulation of testosterone by tRNA.

Synthesis of novel C2-symmetric testosterone dimers and evaluation of antiproliferative activity on androgen-dependent and -independent prostate cancer cell lines

A series of 7α-linked testosterone dimers were made and tested for biological activity on both androgen-dependent (LNCaP) and androgen-independent (DU-145 and PC3) prostate cancer cell lines. The synthesis proceeds through the formation of a trans-4-(17β-acetoxy-4-androsten-3-one-7α-yl)-but-2-enoic acid 4-hydroxy-alkyl ester intermediate of various length (7a-d) followed by the final dimerization step. The dimers showed interesting biological activity in comparison to the ω-hydroxyalkyl ester intermediates 7a-d. The most active dimer 8a (n=1) showed IC₅₀ of 3.8, 1.4 and 1.8μM, respectively on LNCaP, DU-145 and PC3 cancer cell lines. On these cell lines, this dimer is about 12, 70 and 47 times more powerful than cyproterone acetate (CPA) the reference antiandrogen. Furthermore, dimers 8b-d (n=2, 3, 4) were less active than 8a but showed selective activity on androgen-dependent LNCaP prostate cancer cells. This indicates possible application for the treatment of androgen-dependent prostate cancer.

Effect of testosterone and its aliphatic and aromatic dimers on DNA morphology

Conjugation of DNA with testosterone and it aliphatic dimer (alip) and aromatic dimer (arom) was investigated in aqueous solution at pH 7.4. Multiple spectroscopic methods, transmission electron microscopy (TEM) and molecular modeling were used to characterize steroid-DNA binding and DNA morphology. Spectroscopic analysis showed that testosterone binds DNA via A7, A16, A17, T8, T15 and T18 nucleobases with overall binding constants K_test-DNA=1.8 (±0.4)×10⁴M^-1, K_{test-dimeralip-DNA}=5.7 (±0.7)×10⁴M^-1 and K_{test-dimer-arom-DNA}=7.3 (±0.9)×10⁴M^-1. The binding affinity increases in this order: testosterone dimer-aromatic>testosterone dimer-aliphatic>testosterone. The steroid loading efficacy was 40-50%. Transmission electron microscopy showed major changes in DNA morphology as testosterone-DNA interaction occurred with increase in the diameter of the DNA aggregate, indicating encapsulation of testosterone by DNA. Modeling showed the presence of several nucleobases attached to testosterone with the free binding energy of -4.93Kcal/mol.

Nonsteroidal bivalent estrogen ligands: an application of the bivalent concept to the estrogen receptor

The estrogen receptor (ER) is a hormone-regulated transcription factor that binds, as a dimer, to estrogens and to specific DNA sequences. To explore at a fundamental level the geometric and topological features of bivalent-ligand binding to the ER dimer, dimeric ER crystal structures were used to rationally design nonsteroidal bivalent estrogen ligands. Guided by this structure-based ligand design, we prepared two series of bivalent ligands (agonists and antagonists) tethered by flexible spacers of varying lengths (7-47 Å) and evaluated their ER-binding affinities for the two ER subtypes and their biological activities in cell lines. Bivalent ligands based on the agonist diethylstilbestrol (DES) proved to be poor candidates, but bivalent ligands based on the antagonist hydroxytamoxifen (OHT) were well suited for intensive study. Binding affinities of the OHT-based bivalent ligands were related to spacer length in a distinctive fashion, reaching two maximum values at 14 and 29 Å in both ER subtypes. These results demonstrate that the bivalent concept can operate in determining ER-ligand binding affinity and suggest that two distinct modes operate for the binding of bivalent estrogen ligands to the ER dimers, an intermolecular as well as an intramolecular mode. Our insights, particularly the possibility of intramolecular bivalent binding on a single ER monomer, may provide an alternative strategy for preparing more selective and active ER antagonists for endocrine therapy of breast cancer.

Atropodiastereoselectivity in solid state BINOL synthesis: leads from the estradiol platform

A novel functionalized steroidal BINOL scaffold is produced via a remarkable sequence of dehydrogenation, chlorination and atroposelective phenolic coupling steps. Its formation is straightforwardly obtained in a one-step synthesis under solid state conditions and in the absence of chiral additives.

Acylated mono-, bis- and tris- cinchona-based amines containing ferrocene or organic residues: synthesis, structure and in vitro antitumor activity on selected human cancer cell lines

A series of novel functionalized mono-, bis- and tris-(S)-{[(2S,4R,8R)-8-ethyl-quinuclidin-2-yl](6-methoxyquinolin-4-yl)}methanamines including ferrocene-containing derivatives was obtained by the reaction of the precursor amine with a variety of acylation agents. Their in vitro antitumor activity was investigated against human leukemia (HL-60), human neuroblastoma (SH-SY5Y), human hepatoma (HepG2) and human breast cancer (MCF-7) cells by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-assay and the 50% inhibitory concentration (IC₅₀) values were determined. Our data indicate that the precursor amine has no antitumor activity in vitro, but the bis-methanamines with ureido-, thioureido and amide-type linkers display attractive in vitro cytotoxicity and cytostatic effects on HL-60, HepG2, MCF-7 and SH-SY5Y cells. Besides ¹H- and ¹³C-NMR methods the structures of the new model compounds were also studied by DFT calculations.

Synthesis and functional analysis of novel bivalent estrogens

The steroid hormone estrogen plays a critical role in female development and homeostasis. Estrogen mediates its effects through binding and activation of specific estrogen receptors alpha (ERalpha) and beta (ERbeta), members of the steroid/nuclear receptor family of ligand-induced transcription factors. Due to their intimate roles in genomic and nongenomic signaling pathways, these hormones and their receptors have been also implicated in the pathologies of a variety of cancers and metabolic disorders, and have been the target of large therapeutic development efforts. The binding of estrogen to its respective receptors initiates a cascade of events that include receptor dimerization, nuclear localization, DNA binding and recruitment of co-regulatory protein complexes. In this manuscript, we investigate the potential for manipulating steroid receptor gene expression activity through the development of bivalent steroid hormones that are predicted to facilitate hormone receptor dimerization events. Data are presented for the development and testing of novel estrogen dimers, linked through their C-17 moiety, that can activate estrogen receptor alpha (ERalpha)-mediated transcription events with efficacy and potency equal to or greater than that of ERalpha's cognate ligand, 17beta-estradiol. These bivalent estrogen structures open the door to the development of a variety of steroid therapeutics that could dramatically impact future drug development in this area.

Steroidal bivalent ligands for the estrogen receptor: design, synthesis, characterization and binding affinities

Steroidal bivalent ligands for the estrogen receptor (ER) were designed using crystal structures of ERalpha dimers as a template. The syntheses of several 17alpha-ethynylestradiol-based bivalent ligands with varying linker compositions and lengths are described. The binding affinities of these bivalent ligands for ERalpha and ERbeta were determined. In the two series of bivalent ligands that we synthesized, there is a clear correlation between linker length and binding affinity, both of which reach a maximum at the same tether length. Further studies are underway to explore aspects of bivalent ligand and control compound binding to the ERs and their effects on ER dimer formation; these results will be reported in a subsequent publication.

Synthesis of unique 17beta-estradiol homo-dimers, estrogen receptors binding affinity evaluation and cytocidal activity on breast, intestinal and skin cancer cell lines

A rapid and efficient synthesis of a series of C2-symmetric 17beta-estradiol homo-dimers is described. The new molecules are linked at position 17alpha of the steroid nucleus with either an alkyl chain or a polyethylene glycol chain. They are made from estrone in only five chemical steps with an overall yield exceeding 30%. The biological activity of these compounds was evaluated in vitro on estrogen dependent and independent (ER+ and ER-) human breast tumor cell lines: MCF-7 and MDA-MB-231. Some of the dimers present selective cytotoxic activity against the ER+ cell line. However, they are not very cytotoxic when compared to the antiestrogen tamoxifen. Unfortunately, they show only weak affinity for the estrogen receptor alpha (ERalpha) and no affinity for the estrogen receptor beta (ERbeta). The new compounds were also tested on human intestinal (HT-29) cancer and on murine skin cancer (B16-F10) cell lines for further biological assessment. Interestingly, the dimers were found to be cytotoxic to the murine skin cancer cell line but were inactive towards the intestinal cancer cell line.

Steroids: reactions and partial synthesis

This article reviews the progress in the chemistry of the steroids that was published between January and December 2003. The reactions and partial synthesis of estrogens, androgens, pregnanes, cholic acid derivatives, cholestanes and vitamin D analogues are covered. There are 152 references.

Oxidative Coupling of 17β-Estradiol: Inventory of Oligomer Products and Configuration Assignment of Atropoisomeric C4-Linked Biphenyl-Type Dimers and Trimers

The oxidation chemistry of 17beta-estradiol (1) is of central relevance to the nongenomic effects of estrogens and offers valuable prospects in the search for novel steroidal scaffolds of academic and industrial interest. Herein, we report the results of a detailed investigation into the nature of the oligomer products formed by phenolic oxidation of 1. Of the oxidants tested, the peroxidase/H2O2 system proved to be the most effective in inducing conversion of 1 to a complex mixture of oligomer species. Repeated chromatographic fractionation followed by extensive 2D NMR and mass spectrometric analysis allowed identification of a series of phenolic coupling products comprising, besides the C2-symmetric dimers 2 and 3, a 2,4' dimer (4), two O-linked dimers (5, 6), and the novel trimers 7-9. All 4-linked biphenyl-type oligomers, i.e., 3 and 7-9, occurred as couples of atropoisomers, reflecting steric hindrance at biphenyl linkages. For all atropoisomers, absolute configuration was established by the exciton chirality method and the interconversion energy was determined by dynamic NMR. These results provide the first systematic inventory of oxidative coupling products of 1 and lay the foundation for future studies aimed to develop novel estrogen derivatives based on oligomeric scaffolds.