2β-(N-Substituted Piperazino)-5α-Androstane-3α,17β-Diols: Parallel Solid-Phase Synthesis and Antiproliferative Activity on Human Leukemia HL-60 Cells

An Aminosteroid Derivative Shows Higher In Vitro and In Vivo Potencies than Gold Standard Drugs in Androgen-Dependent Prostate Cancer Models

The aminosteroid derivative RM-581 blocks with high potency the growth of androgen-dependent (AR⁺) prostate cancer VCaP, 22Rv1, and LAPC-4 cells. Notably, RM-581 demonstrated superior antiproliferative activity in LAPC-4 cells compared to enzalutamide and abiraterone, two drugs that exhibited a synergistic effect in combination with RM-581. These findings suggest that RM-581 may have an action that is not directly associated with the hormonal pathway of androgens. Furthermore, RM-581 completely blocks tumor growth in LAPC-4 xenografts when given orally at 3, 10, and 30 mg/kg in non-castrated (intact) nude mice. During this study, an accumulation of RM-581 was observed in tumors compared to plasma (3.3-10 folds). Additionally, the level of fatty acids (FA) increased in the tumors and livers of mice treated with RM-581 but not in plasma. The increase was greater in unsaturated FA (21-28%) than in saturated FA (7-11%). The most affected FA were saturated palmitic acid (+16%), monounsaturated oleic acid (+34%), and di-unsaturated linoleic acid (+56%), i.e., the 3 most abundant FA, with a total of 55% of the 56 FA measured. For cholesterol levels, there was no significant difference in the tumor, liver, or plasma of mice treated or not with RM-581. Another important result was the innocuity of RM-581 in mice during a 28-day xenograft experiment and a 7-week dose-escalation study, suggesting a favorable safety window for this new promising drug candidate when given orally.

Novel 4-Azapregnene Derivatives as Potential Anticancer Agents: Synthesis, Antiproliferative Activity and Molecular Docking Studies

A series of novel 21E-arylidene-4-azapregn-5-ene steroids has been successfully designed, synthesized and structurally characterized, and their antiproliferative activity was evaluated in four different cell lines. Within this group, the 21E-(pyridin-3-yl)methylidene derivative exhibited significant cytotoxic activity in hormone-dependent cells LNCaP (IC₅₀ = 10.20 µM) and T47-D cells (IC₅₀ = 1.33 µM). In PC-3 androgen-independent cells, the steroid 21E-p-nitrophenylidene-4-azapregn-5-ene was the most potent of this series (IC₅₀ = 3.29 µM). Considering these results, the 21E-(pyridin-3-yl)methylidene derivative was chosen for further biological studies on T47-D and LNCaP cells, and it was shown that this azasteroid seems to lead T47-D cells to apoptotic death. Finally, molecular docking studies were performed to explore the affinity of these 4-azapregnene derivatives to several steroid targets, namely 5α-reductase type 2, estrogen receptor α, androgen receptor and CYP17A1. In general, compounds presented higher affinity to 5α-reductase type 2 and estrogen receptor α.

Turning a Quinoline-based Steroidal Anticancer Agent into Fluorescent Dye for its Tracking by Cell Imaging

RM-581 is an aminosteroid derivative comprised of a steroid core and a quinoline side chain showing potent cytotoxic activity on several types of cancer cells but for which the mechanism of action (MoA) remains to be fully elucidated. The opportunity to turn RM-581 into a fluorescent probe was explored because the addition of a N-dimethyl group was recently reported to induce fluorescence to quinoline derivatives. After the chemical synthesis of the N-dimethyl analogue of RM-581 (RM-581-Fluo), its fluorescent properties, as well as its cytotoxic activity in breast cancer MCF-7 cells, were confirmed. A cell imaging experiment in MCF-7 cells using confocal microscopy then revealed that RM-581-Fluo accumulated into the endoplasmic reticulum (ER) as highlighted by its colocalization with an ER-Tracker dye. This work provides a new tool for RM-581 MoA investigations as well as being a relevant example of a tailor-made quinolone-fluorescent version of a bioactive molecule.

Synthesis, NMR Characterization, and Antileukemic Activity of N-Nonanoylpiperazinyl-5α-Androstane-3α,17β-Diol A-Ring Derivatives

The combination of an androstane-3,17-diol nucleus and a 2β-N-alkylamidopiperazino sidechain is important for the anticancer activity of a new family of steroid derivatives. As the structure-activity relationship studies have so far been limited to the beta orientation of the substituent at position 2 of the steroid nucleus, a series of analogs (compounds 1–4) were synthesized to investigate the impact on biological activity of A-ring substitution. Nuclear magnetic resonance (NMR) analysis, especially using a series of 2D experiments, such as correlation spectroscopy (COSY), homonuclear Overhauser effect spectroscopy (NOESY), heteronuclear single-quantum correlation (HSQC), and heteronuclear multiple-bond correlation (HMBC) provided crucial information that was found essential in confirming the sidechain position and orientation of compounds 1–4. Assessment of their antiproliferative activity on leukemia HL-60 cells confirmed the best efficiency of the 2β-sidechain/3α-OH orientation (compound 1) compared to the other configurations tested (compounds 2–4).

Minor chemical modifications of the aminosteroid derivative RM-581 lead to major impact on its anticancer activity, metabolic stability and aqueous solubility

The aminosteroid (AM) RM-581 is built around a mestranol backbone and has recently emerged as this family's lead candidate, showing in vitro and in vivo potency over different types of cancer, including high fatality pancreatic cancer. To extend the structure-activity relationships (SAR) to other estrane analogs, we synthesized a focused series of RM-581 derivatives at position C3 or C2 of its steroidal core. These new AM derivatives were first tested on a large selection of prostate, breast, pancreatic and ovarian cancer cell lines. The impact of these modifications on metabolic stability (human liver microsomes) was also measured. A SAR study revealed a fine regulation of anticancer activity related to the nature of the substituent. Indeed, the addition of potential prodrug groups like acetate, sulfamate or phosphate (compounds 8, 9 and 10) at C3 of the phenolic counterpart provided better antiproliferative activities than RM-581 in breast and pancreatic cancer cell types while maintaining activity in other cancer cell lines. Also, the phosphate group was highly beneficial on water solubility. However, the bulkier carbamate prodrugs 6 (N,N-dimethyl) and 7 (N,N-diethyl) were less active. Otherwise, carbon homologation (CH₂) at C2 (compound 33) was beneficial to metabolic stability and, in the meantime, this AM conserved the same anticancer activity as RM-581. However, the replacement of the hydroxy or methoxy at C3 by a hydrogen or an acetyl (compound 17 or 21b) was detrimental for anticancer activity, pointing to a crucial molecular interaction of the aromatic oxygen atom at this position. Overall, this work provided a better knowledge of the structural requirements to maintain RM-581's anticancer activity, and also identified minor structural modifications to increase both metabolic stability and water solubility, three important parameters of pharmacological development.

Solvent-free synthesis of 6β-phenylamino-cholestan-3β,5α-diol and (25R)-6β-phenylaminospirostan-3β,5α-diol as potential antiproliferative agents

In this paper is described a synthetic route to 6β-phenylamino-cholestan-3β,5α-diol and (25R)-6β-phenylaminospirostan-3β,5α-diol, starting from cholesterol and diosgenin, respectively. The products were obtained in two steps by epoxidation followed by aminolysis, through an environmentally friendly and solvent-free method mediated by SZ (sulfated zirconia) as catalyst. The use of SZ allows chemo- and regioselective ring opening of the 5,6α-epoxide during the aminolysis reaction eliminating the required separation of the epoxide mixture. The products obtained were spectroscopically characterized by ¹H, PENDANT ¹³C NMR and HETCOR experiments, and complemented with FTIR-ATR and HRMS. The antiproliferative effect of the β-aminoalcohols was evaluated on MCF-7 cells after 48h of incubation, by MTT and CVS assays. These methodologies showed that both compounds have antiproliferative activity, being more active the cholesterol analogue. Additionally, the cell images obtained by Harris' Hematoxylin and Eosin (H&E) staining protocol, evidenced formation of apoptotic bodies due to the presence of the obtained β-aminoalcohols in a dose-dependent manner.

Solid-phase synthesis of libraries of ethynylated aminosteroid derivatives as potential antileukemic agents

Steroids possessing an ethynyl group at position 17α (tertiary alcohols) are well known to be more stable than their non-ethynyl analogs (secondary alcohols). To facilitate the development of new drugs with better metabolic stability, we developed a new diethylsilyl acetylenic linker allowing us to rapidly synthesize libraries of ethynylated steroid derivatives using a solid-phase strategy. To illustrate its usefulness, this linker was used to expand the molecular diversity of a lead compound having a hydroxy acetylenic pattern and to potentially find new compounds with interesting cytotoxic activity against leukemia cell lines. Herein, we report the chemical synthesis and the characterization of three libraries of ethynylated aminosteroid derivatives using the diethylacetylenic linker. We discuss their antiproliferative activities obtained in 2 leukemia cell lines (HL-60 and Jurkat), which results provided new structure-activity relationships. We also identified a new promising aminosteroid derivative with an azetidine moiety (compound B1) inhibiting 60% and 75% of HL-60 and Jurkat cell proliferation, respectively, at 1 μM. More generally, these results validate the use of a diethylsilyl acetylenic linker for researchers interested in generating libraries of alcohol derivatives with better stability and drug profile.

Chemical synthesis, cytotoxicity, selectivity and bioavailability of 5α-androstane-3α,17β-diol derivatives

Aminosteroid derivatives represent a new family of compounds with promising antiproliferative activity over different cancer cell lines. Among all the aminosteroid derivatives synthesised in our laboratory, we have identified E-37P as one of the more potent when tested in vitro. Unfortunately, the pharmacokinetic properties of E-37P decrease its effectiveness when tested in vivo. To improve the bioavailability and increase the efficiency of aminosteroid E-37P, two series of analog compounds were synthesised by classic chemical synthesis, they were then characterized, and the concentration that inhibits 50% of cell proliferation (IC50) was determined on different cell lines. RM-133, a 5α-androstane-3α,17β-diol derivative with a quinoline nucleus at the end of the piperazine-proline side-chain at position 2β and an ethinyl at position 17α, showed very good antiproliferative activity among the five cancer cell lines studied (IC50=0.1, 0.1, 0.1, 2.0 and 1.1 μM for HL-60, MCF-7, T-47D, LNCaP and WEHI-3, respectively). Moreover, the plasmatic concentration of RM-133 at 3h, when injected subcutaneously in rats, was 2.3-fold higher than that of E-37P (151 vs 64.8 ng/mL). Furthermore, RM-133 weakly inhibited the two representative liver enzymes, CYP3A4 and CYP2D6, indicating a very low risk of drug-drug interactions. The cytotoxicity of RM-133 against normal cells was tested on peripheral blood lymphocytes (PBL) obtained from different donors and previously activated with phytohemagglutinin-L. PBL responded differently to treatment with RM-133, we observed a stimulation of cell proliferation and/or cytotoxicity in a dose-dependent manner. Based on these results, additional studies are currently underway to evaluate the selectivity of our lead compound against normal cell lines in a more detailed fashion.

Synthesis of steroidal and nonsteroidal vicinal heterocyclic alcohols, N-(1-cycloalkenyl)heterocycles and their antibacterial studies

A solvent free steroidal and nonsteroidal epoxide ring opening reaction by nitrogen containing heterocycles under microwave irradiation is described. Some of the epoxide ring opening compounds were converted to their corresponding N-(1-cycloalkenyl)heterocycles via an acid catalyzed dehydration reaction. The antimicrobial activities of the epoxide ring opening compounds and N-(1-cycloalkenyl)heterocyclic compounds were tested by agar diffusion assay. Compounds 6, 9-12, 24 and 27 showed moderate inhibition against the growth of pathogenic bacteria Escherichia coli, Pseudomonas syringae, Bacillus subtilis, Proteus vulgaris and Staphylococcus aureus.

Chemical synthesis, NMR analysis and evaluation on a cancer xenograft model (HL-60) of the aminosteroid derivative RM-133

The aminosteroid derivative RM-133 has been reported to be a promising pro-apoptotic agent showing activity on various cancer cell lines. Following the development of solid-phase synthesis that generated a series of libraries of aminosteroid derivatives, we now report the development of a convenient liquid phase chemical synthesis of RM-133, the most promising candidate, in order to obtain sufficient quantities to proceed with the first preclinical assays. A simple and convergent six-step synthesis was designed and allowed the preparation of a gram-quantity scale of RM-133. This aminosteroid derivative was also fully characterized by NMR experiments which revealed an interesting mixture of conformers. Finally, the in vivo potency of RM-133 was evaluated on a xenograft model in nude mice with HL-60 tumors, which has resulted in the blocking of tumor progression by 57%.

Current status on development of steroids as anticancer agents

Steroids are important biodynamic agents. Their affinities for various nuclear receptors have been an interesting feature to utilize them for drug development particularly for receptor mediated diseases. Steroid biochemistry and its crucial role in human physiology, has attained importance among the researchers. Recent years have seen an extensive focus on modification of steroids. The rational modifications of perhydrocyclopentanophenanthrene nucleus of steroids have yielded several important anticancer lead molecules. Exemestane, SR16157, fulvestrant and 2-methoxyestradiol are some of the successful leads emerged on steroidal pharmacophores. The present review is an update on some of the steroidal leads obtained during past 25 years. Various steroid based enzyme inhibitors, antiestrogens, cytotoxic conjugates and steroidal cytotoxic molecules of natural as well as synthetic origin have been highlighted. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

A new simple and high-yield synthesis of 5α-dihydrotestosterone (DHT), a potent androgen receptor agonist

We have devised an efficient procedure for the synthesis of 5α-dihydrotestosterone (DHT) (1) starting from 3β-hydroxy-5α-androstan-17-one, providing the product in unprecedented 82% yield. A reported method of using toxic Jones reagent is replaced by milder oxidizing agent (NMO/TPAP) in the synthesis of a key intermediate 17β-[(tert-butyldimethylsilyl)oxy]-5α-androstan-3-one (18). This new procedure is simple, does not require special apparatus/precautions or chromatographic purification in most of the steps.

Solid-phase chemical synthesis and in vitro biological evaluation of novel 2β-piperazino-(20R)-5α-pregnane-3α,20-diol N-derivatives as anti-leukemic agents

The steroid nucleus is an interesting scaffold for the development of new therapeutic agents. Within the goal of identifying anticancer agents, new pregnane derivatives were prepared by using a sequence of liquid and solid-phase reactions. After we dehydrated epi-allopregnanolone in one step with diethylaminosulfur trifluoride and generated a 2,3α-epoxide, the regio- and stereo-selective aminolysis of this epoxide enabled us to obtain a 2β-piperazino-pregnane, whose secondary amine was protected as N-Fmoc-derivative. Using the difference in reactivity between OHs 3 and 20, we linked the pregnane nucleus-selectively on the polystyrene diethylbutylsilane resin via the OH in position 20. We next achieved in parallel the coupling of an amino acid (1st level of diversity) and the coupling of a carboxylic acid (2nd level of diversity) to generate two libraries of pregnane derivatives. The compounds inhibited the HL-60 leukemia cell growth and the most potent were three compounds (PD, LPC-37 and LPC-48) with a l-proline as first level of diversity and a cyclohexyl-carbonyl, a naphthalene-2-carbonyl or a 3-acetylbenzoyl as second level of diversity. LPC-48 efficiently inhibited HL-60 cell proliferation with IC(50) value of 1.9 μM and exhibited a low toxicity on normal peripheral blood lymphocytes (IC(50)=31 μM). These results encouraged us to further evaluate the biological activity of these new aminosteroids by investigating their preliminary mechanism of action.

New diethylsilylacetylenic linker for parallel solid-phase synthesis of libraries of hydroxy acetylenic steroid derivatives with improved metabolic stability

Acetylenic tertiary alcohols are well-known to be compounds that are biologically more stable than their corresponding secondary alcohols. The linkage of an acetylenic compound to a polymer support and further introduction of molecular diversity was found to be an interesting way to generate libraries of hydroxy acetylenic derivatives and thus potentially improve their biological properties. For the first time, we describe the loading of an ethynyl steroid to a polystyrene-diethylsilane resin and its uses for the solid-phase synthesis of a model library of 21 steroid derivatives. Two levels of molecular diversity were introduced by successive addition of amino acids and carboxylic acids, and hydroxy acetylenic steroids were then released by an acidic treatment in high yield and purity without further purification step.

Synthesis, characterization and biological evaluation of some 16E-arylidene androstane derivatives as potential anticancer agents

A series of new 16E-arylidene androstane derivatives were synthesized and characterized. The new compounds were screened for their anticancer activities against the human cancer cell lines SW480, A549, HepG2 and HeLa in vitro using the MTT assay. The results of the in vitro study showed that a number of compounds have shown IC(50) values lower than 20 μM against the four cancer cell lines.