Libraries of 2β-(N-substituted piperazino)-5α-androstane-3α, 17β-diols: chemical synthesis and cytotoxic effects on human leukemia HL-60 cells and on normal lymphocytes

Aminosteroid RM-581 Decreases Cell Proliferation of All Breast Cancer Molecular Subtypes, Alone and in Combination with Breast Cancer Treatments

Breast cancer (BC) is a heterogenous disease classified into four molecular subtypes (Luminal A, Luminal B, HER2 and triple-negative (TNBC)) depending on the expression of the estrogen receptor (ER), the progesterone receptor (PR) and the human epidermal receptor 2 (HER2). The development of effective treatments for BC, especially TNBC, remains a challenge. Aminosteroid derivative RM-581 has previously shown an antiproliferative effect in multiple cancers in vitro and in vivo. In this study, we evaluated its effect in BC cell lines representative of BC molecular subtypes, including metastatic TNBC. We found that RM-581 has an antiproliferative effect on all BC molecular subtypes, especially on Luminal A and TNBC, in 2D and 3D cultures. The combination of RM-581 and trastuzumab or trastuzumab-emtansine enhanced the anticancer effect of each drug for HER2-positive BC cell lines, and the combination of RM-581 and taxanes (docetaxel or paclitaxel) improved the antiproliferative effect of RM-581 in TNBC and metastatic TNBC cell lines. We also confirmed that RM-581 is an endoplasmic reticulum (EnR)-stress aggravator by inducing an increase in EnR-stress-induced apoptosis markers such as BIP/GRP78 and CHOP and disrupting lipid homeostasis. This study demonstrates that RM-581 could be effective for the treatment of BC, especially TNBC.

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.

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.

Induction of endoplasmic reticulum stress by aminosteroid derivative RM-581 leads to tumor regression in PANC-1 xenograft model

The high fatality and morbidity of pancreatic cancer have remained almost unchanged over the last decades and new clinical therapeutic tools are urgently needed. We determined the cytotoxic activity of aminosteroid derivatives RM-133 (androstane) and RM-581 (estrane) in three human pancreatic cancer cell lines (BxPC3, Hs766T and PANC-1). In PANC-1, a similar level of antiproliferative activity was observed for RM-581 and RM-133 (IC₅₀ = 3.9 and 4.3 μM, respectively), but RM-581 provided a higher selectivity index (SI = 12.8) for cancer cells over normal pancreatic cells than RM-133 (SI = 2.8). We also confirmed that RM-581 induces the same ER stress-apoptosis markers (BIP, CHOP and HERP) than RM-133 in PANC-1 cells, pointing out to a similar mechanism of action. Finally, these relevant in vitro results have been successfully translated in vivo by testing RM-581 using different doses (10-60 mg/kg/day) and modes of administration in PANC-1 xenograft models, which have led to tumor regression without any sign of toxicity in mice (animal weight, behavior and histology). Interestingly, RM-581 fully reduced the pancreatic tumor growth when administered orally in mice.

Implication of STARD5 and cholesterol homeostasis disturbance in the endoplasmic reticulum stress-related response induced by pro-apoptotic aminosteroid RM-133

The aminosteroid derivative RM-133 is an effective anticancer molecule for which proof of concept has been achieved in several mouse xenograph models (HL-60, MCF-7, PANC-1 and OVCAR-3). To promote this new family of molecules toward a clinical phase 1 trial, the mechanism of action governing the anticancer properties of the representative candidate RM-133 needs to be characterized. In vitro experiments were first used to determine that RM-133 causes apoptosis in cancer cells. Then, using proteomic and transcriptomic experiments, RM-133 cytotoxicity was proven to be achieved via the endoplasmic reticulum (ER)-related apoptosis, which characterizes RM-133 as an endoplasmic reticulum stress aggravator (ERSA) anticancer drug. Furthermore, an shRNA-genome-wide screening has permitted to identify the steroidogenic acute regulator-related lipid transfer protein 5 (STARD5) as a major player in the RM-133 ER-related apoptosis mechanism, which was validated by an in vitro binding experiment. Altogether, the results presented herein suggest that RM-133 provokes a disturbance of cholesterol homeostasis via the implication of STARD5, which delivers an ERSA molecule to the ER. These results will be a springboard for RM-133 in its path toward clinical use.

Antitumor effects of baicalin on ovarian cancer cells through induction of cell apoptosis and inhibition of cell migration in vitro

Baicalin, an active flavone isolated from Scutellaria baicalensis Georgi, has been demonstrated to induce various beneficial biochemical effects such as anti‑inflammatory, anti‑viral, and antitumor effects. However, the antitumor mechanism of baicalin is not well understood. In the present study, baicalin was demonstrated to inhibit the viability and migration of a widely used ovarian cancer cell line, A2780, in a dose‑dependent manner. MTT assays revealed that cell viability significantly decreased in ovarian cancer cells treated with baicalin compared with untreated cells, without effect on normal ovarian cells. Flow cytometric analysis indicated that baicalin suppressed cell proliferation by inducing apoptosis. The underlying mechanisms involved were indicated to be downregulation of the anti‑apoptotic protein B‑cell lymphoma 2 apoptosis regulator and activation of caspase‑3 and ‑9. In addition, wound healing and transwell assays revealed that cell migratory potential and expression of matrix metallopeptidase (MMP)‑2 and MMP‑9 were significantly inhibited when cells were exposed to baicalin, compared with untreated cells. The present study therefore suggested that baicalin has the potential to be used in novel anti‑cancer therapeutic formulations for treatment of ovarian cancer.

Design of a Mestranol 2-N-Piperazino-Substituted Derivative Showing Potent and Selective in vitro and in vivo Activities in MCF-7 Breast Cancer Models

Anticancer structure-activity relationship studies on aminosteroid (5α-androstane) derivatives have emerged with a promising lead candidate: RM-133 (2β-[1-(quinoline-2-carbonyl)pyrrolidine-2-carbonyl]-N-piperazine-5α-androstane-3α,17β-diol), which possesses high in vitro and in vivo activities against several cancer cells, and selectivity over normal cells. However, the relatively weak metabolic stability of RM-133 has been a drawback to its progression toward clinical trials. We investigated the replacement of the androstane backbone by a more stable mestranol moiety. The resulting compound, called RM-581 ({4-[17α-ethynyl-17β-hydroxy-3-methoxyestra-1,3,5(10)-trien-2-yl]piperazin-1-yl}[(2S)-1-(quinolin-2-ylcarbonyl)pyrrolidin-2-yl]methanone), was synthesized efficiently in only five steps from commercially available estrone. In comparison with RM-133, RM-581 was found to be twice as metabolically stable, retains potent cytotoxic activity in breast cancer MCF-7 cell culture, and fully blocks tumor growth in a mouse xenograft model of breast cancer. Advantageously, the selectivity over normal cells has been increased with this estrane version of RM-133. In fact, RM-581 showed a better selectivity index (15.3 vs. 3.0) for breast cancer MCF-7 cells over normal breast MCF-10A cells, and was found to be nontoxic toward primary human kidney proximal tubule cells at doses reaching 50 μm.

Explorative study on the anticancer activity, selectivity and metabolic stability of related analogs of aminosteroid RM-133

RM-133 is a key representative of a new family of aminosteroids reported as potent anticancer agents. Although RM-133 produced interesting results in 4 mouse xenograft cancer models when injected subcutaneously, it needs to be improved to increase its in vivo potency. Thus, to obtain an analog of RM-133 with a better drug potential, a structure-activity relationship study was conducted by synthesizing eleven RM-133-related compounds and addressing their antiproliferative activity on 3 human cancer cells (HL-60, OVCAR-3 and PANC-1) and 3 human normal cell lines (primary ovary, pancreas and renal proximal tubule) as well as their metabolic stability in human liver microsomes. When the 2β-tertiary amine of RM-133 was transformed into a salt or moved to position 3β, the anticancer activity was lost. Modifying the orientation of the side chain of RM-133 increased anticancer activity and selectivity, but led to a drastic loss of stability. The protection of the 3α-hydroxyl of RM-133 by the formation of an ester or a carbamate stabilized the molecule against the phase I metabolic enzymes without affecting its anticancer activity. In comparison to RM-133, the 3-dimethylcarbamate derivative 3 is more selective for cancer cells over normal cells and is much more stable in liver microsomes. Those results support the use of a pro-drug strategy targeting the 3α-hydroxyl of RM-133 as an approach to improve its drug properties. The work presented will enable the development of an optimized anticancer drug of the aminosteroid family that is suitable for a future phase I clinical trial.

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.

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%.

Synthesis of sex hormone-derived modified steroids possessing antiproliferative activity

During recent years intensive research has been focused on the synthesis of structurally modified steroid hormones in order to obtain compounds with beneficial biological activity such as cell-growth inhibition. Experimental results have revealed that some steroidal derivatives possess direct cytostatic effect on cancer cells in a hormone receptor-independent manner. After a brief account on the most important biological function and characteristics of the naturally occurring sex hormones in physiological and pathological conditions, structural modifications of estrane and androstane scaffolds are discussed in detail. The review covers literature publications (from 2002 to 2012) relating to the synthesis and antiproliferative activity of semisynthetic sex hormone-derived molecules containing simple or heterocyclic substituents. The compounds reviewed are divided into three main categories according to their sterane framework and the nature of substitution. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Viability screen on pediatric low grade glioma cell lines unveils a novel anti-cancer drug of the steroid biosynthesis inhibitor family

Pediatric low grade gliomas are the most common central nervous system tumors and are still incurable among a subset of patients despite current treatment modalities. Steroid biosynthesis occurs in a wide variety of organs including the brain, to mediate an assortment of functions, including a proposed role in the growth of gliomas. Hence, targeting steroid biosynthesis and/or their signaling pathways, is anticipated as an effective approach for treating gliomas. In this study, we investigated whether our chemical library of steroid inhibitors can modulate the growth of pediatric low grade glioma cell lines (Res186, Res259, R286), and subsequently identified a potent inhibitor of 17β-hydroxysteroid dehydrogenase type 3, referred to as DK16, which functions by attenuating cell viability, proliferation, migration/invasion and anchorage independent growth and conversely induces apoptosis and cell cycle arrest in a dose and duration dependent manner. Further investigations into the mechanisms of how DK16 functions showed that this drug increased the BAX/BCL2 expression ratio, induced phosphatidylserine externalization, and mitochondrial membrane depolarizations culminating to the release and nuclear translocation of AIF. In addition, treatments of low grade glioma cell lines with DK16 increased the expression of pro-apoptotic mediators including CDK2 and CTSL1, and with the converse diminished expression of pro-survival and migratory/invasion genes like PRKCA, TERT, MAPK8, MMP1 and MMP2. Our findings collectively demonstrate the potent anti-neoplastic properties of DK16, a steroid biosynthesis inhibitor, on the growth of pediatric low grade gliomas.

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.