Design, synthesis and biological evaluation of antiparasitic dinitroaniline-ether phospholipid hybrids.

A series of nine novel ether phospholipid-dinitroaniline hybrids were synthesized in an effort to deliver more potent antiparasitic agents with improved safety profile compared to miltefosine. The compounds were evaluated for their in vitro antiparasitic activity against L. infantum, L.donovani, L. amazonensis, L. major and L. tropica promastigotes, L. infantum and L. donovani intracellular amastigotes, Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the oligomethylene spacer between the dinitroaniline moiety and the phosphate group, the length of the side chain substituent on the dinitroaniline and the choline or homocholine head group were found to affect both the activity and toxicity of the hybrids. The early ADMET profile of the derivatives did not reveal major liabilities. Hybrid 3, bearing an 11-carbon oligomethylene spacer, a butyl side chain and a choline head group, was the most potent analogue of the series. It exhibited a broad spectrum antiparasitic profile against the promastigotes of New and Old World Leishmania spp., against intracellular amastigotes of two L. infantum strains and L. donovani, against T. brucei and against T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes. The early toxicity studies revealed that hybrid 3 showed a safe toxicological profile while its cytotoxicity concentration (CC50) against THP-1 macrophages being >100 µM. Computational analysis of binding sites and docking indicated that the interaction of hybrid 3 with trypanosomatid α-tubulin may contribute to its mechanism of action. Furthermore, compound 3 was found to interfere with the cell cycle in T. cruzi epimastigotes, while ultrastructural studies using SEM and TEM in T. cruzi showed that compound 3 affects cellular processes that result in changes in the Golgi complex, the mitochondria and the parasite's plasma membrane. The snapshot pharmacokinetic studies showed low levels of 3 after 24 h following oral administration of 100 mg/Kg, while, its homocholine congener compound 9 presented a better pharmacokinetic profile.

Design, Synthesis and Antiparasitic Evaluation of Click Phospholipids.

A library of seventeen novel ether phospholipid analogues, containing 5-membered heterocyclic rings (1,2,3-triazolyl, isoxazolyl, 1,3,4-oxadiazolyl and 1,2,4-oxadiazolyl) in the lipid portion were designed and synthesized aiming to identify optimised miltefosine analogues. The compounds were evaluated for their in vitro antiparasitic activity against Leishmania infantum and Leishmania donovani intracellular amastigotes, against Trypanosoma brucei brucei and against different developmental stages of Trypanosoma cruzi. The nature of the substituents of the heterocyclic ring (tail) and the oligomethylene spacer between the head group and the heterocyclic ring was found to affect the activity and toxicity of these compounds leading to a significantly improved understanding of their structure-activity relationships. The early ADMET profile of the new derivatives did not reveal major liabilities for the potent compounds. The 1,2,3-triazole derivative 27 substituted by a decyl tail, an undecyl spacer and a choline head group exhibited broad spectrum antiparasitic activity. It possessed low micromolar activity against the intracellular amastigotes of two L. infantum strains and T. cruzi Y strain epimastigotes, intracellular amastigotes and trypomastigotes, while its cytotoxicity concentration (CC50) against THP-1 macrophages ranged between 50 and 100 µM. Altogether, our work paves the way for the development of improved ether phospholipid derivatives to control neglected tropical diseases.

A simple open source bioinformatic methodology for initial exploration of GPCR ligands' agonistic/antagonistic properties.

Drug development is an arduous procedure, necessitating testing the interaction of a large number of potential candidates with potential interacting (macro)molecules. Therefore, any method which could provide an initial screening of potential candidate drugs might be of interest for the acceleration of the procedure, by highlighting interesting compounds, prior to in vitro and in vivo validation. In this line, we present a method which may identify potential hits, with agonistic and/or antagonistic properties on GPCR receptors, integrating the knowledge on signaling events triggered by receptor activation (GPCRs binding to Gα,ß,γ proteins, and activating Gα , exchanging GDP for GTP, leading to a decreased affinity of the Gα for the GPCR). We show that, by integrating GPCR-ligand and Gα -GDP or -GTP binding in docking simulation, which correctly predicts crystallographic data, we can discriminate agonists, partial agonists, and antagonists, through a linear function, based on the ΔG (Gibbs-free energy) of liganded-GPCR/Gα -GDP. We built our model using two Gαs (ß2-adrenergic and prostaglandin-D2 ), four Gαi (µ-opioid, dopamine-D3, adenosine-A1, rhodopsin), and one Gαo (serotonin) receptors and validated it with a series of ligands on a recently deorphanized Gαi receptor (OXER1). This approach could be a valuable tool for initial in silico validation and design of GPRC-interacting ligands.

In vitro activities of adamantylidene-substituted alkylphosphocholine TCAN26 against Trypanosoma cruzi: Antiproliferative and ultrastructural effects.

Phospholipids are the main component of membranes and are responsible for cell integrity. Alkylphospholipid analogues (APs) were first designed as antitumoral agents and were later tested against different cell types. Trypanosoma cruzi, the Chagas disease etiological agent, is sensitive to APs (edelfosine, miltefosine and ilmofosine) in vitro. We investigated the effect of synthetic ring substituted AP against epimastigotes, amastigotes and trypomastigotes. TCAN26, could inhibit the in vitro growth of epimastigotes and amastigotes with the 50% inhibitory concentrations (IC50) in the nanomolar range. Trypomastigotes lysis was also induced with 24-h treatment and a LC50 of 2.3 µM. Ultrastructural analysis by electron microscopy demonstrated that TCAN26 mainly affected the parasite's membranes leading to mitochondrial and Golgi cisternae swelling, membrane blebs, and autophagic figures in the different parasite developmental stages. While the Golgi of the parasites was significantly affected, the Golgi complex of the host cells remained normal suggesting a specific mechanism of action. In summary, our results suggest that TCAN 26 is a potent and selective inhibitor of T. cruzi growth probably due to disturbances of phospholipid biosynthesis.

Synergistic combination of alkylphosphocholines with peptaibols in targeting Leishmania infantum in vitro.

Anti-leishmanial treatment increasingly encounters therapeutic limitations due to drug toxicity and development of resistance. The effort for new therapeutic strategies led us to work on combinations of chemically different compounds that could yield enhanced leishmanicidal effect. Peptaibols are a special type of antimicrobial peptides that are able to form ion channels in cell membranes and potentially affect cell viability. We assayed the antileishmanial activity of two well studied helical peptaibols, the 16-residue antiamoebin and the 20-residue alamethicin-analogue suzukacillin, and we evaluated the biological effect of their combination with the alkylphosphocholine miltefosine and its synthetic analogue TC52. The peptaibols tested exhibited only moderate antileishmanial activity, however their combination with miltefosine had a super-additive effect against the intracellular parasite (combination index 0.83 and 0.43 for antiamoebin and suzukacillin respectively). Drug combinations altered the redox stage of promastigotes, rapidly dissipated mitochondrial membrane potential and induced concatenation of mitochondrial network promoting spheroidal morphology. These results evidenced a potent and specific antileishmanial effect of the peptaibols/miltefosine combinations, achieved with significantly lower concentrations of the compounds compared to monotherapy. Furthermore, they revealed the importance of exploring novel classes of bioactive compounds such as peptaibols and demonstrated for the first time that they can act in synergy with currently used antileishmanial drugs to improve the therapeutic outcome.

Ultraestructural study of effects of alkylphospholipid analogs against nematodes.

Alkylphospholipid analogs were initially developed as anticancer agents and were later found to antiparasitic activity. Miltefosine is the prototype alkylphosphocholine and is the first oral treatment against visceral leishmaniasis. Here we investigated the effects of miltefosine and two ring-substituted alkylphosphocholine derivatives, TCAN26 and TC70, on the viability, morphology, and ultrastructure of the life stages of Caenorhabditis elegans and infective larvae of the parasite Strongyloides venezuelensis. Miltefosine displayed activity against C. elegans adults at low concentrations and was more effective than TCAN26 and TC70. Miltefosine inhibited the hatching of eggs, leading to embryonic lethality, and showed larvicidal activity against C. elegans and S. venezuelensis larvae after 24 h. Mitelfosine also induced alterations in the reproductive system of hermaphrodites, causing vulvar prolapse and general effects in the body wall. Electron microscopy analysis showed that miltefosine induced selective embryonic lethality, leading to cell death. Our results suggest that alkylphospholipid analogs are a potential new alternative for anti-nematode chemotherapy.

Istaroxime Inhibits Motility and Down-Regulates Orai1 Expression, SOCE and FAK Phosphorylation in Prostate Cancer Cells.

BACKGROUND/AIMS: Istaroxime is a validated inotropic Na+/K+ ATPase inhibitor currently in development for the treatment of various cardiac conditions. Recent findings established that this steroidal drug exhibits potent apoptotic responses in prostate tumors in vitro and in vivo, by affecting key signaling orchestrating proliferation and apoptosis, such as c-Myc and caspase 3, Rho GTPases and actin cytoskeleton dynamics. In the present study we examined whether istaroxime is affecting cell motility and analyzed the underlying mechanism in prostate tumor cells. METHODS: Migration was assessed by transwell and wound healing assays, Orai1 and Stim1 abundance by RT-PCR and confocal immunofluorescence microscopy, Fura-2 fluorescence was utilized to determine intracellular Ca2+ and Western blotting for FAK/pFAK measurements. RESULTS: We observed strong inhibition of cell migration in istaroxime treated DU-145 prostate cancer cells. Istaroxime further decreased Orai1 and Stim1 transcript levels and downregulated Orai1 protein expression. Moreover, SOCE was significantly decreased upon istaroxime treatment. Furthermore, istaroxime strikingly diminished phosphorylated FAK levels. Interestingly, the efficacy of istaroxime on the inhibition of DU-145 cell migration was further enhanced by blocking Orai1 with 2-APB and FAK with the specific inhibitor PF-00562271. These results provide strong evidence that istaroxime prevents cell migration and motility of DU-145 prostate tumor cells, an effect at least partially attributed to Orai1 downregulation and FAK de-activation. CONCLUSION: Collectively our results indicate that this enzyme inhibitor, besides its pro-apoptotic action, affects motility of cancer cells, supporting its potential role as a strong candidate for further clinical cancer drug development.

Selective and differential interactions of BNN27, a novel C17-spiroepoxy steroid derivative, with TrkA receptors, regulating neuronal survival and differentiation.

Nerve growth factor (NGF) holds a pivotal role in brain development and maintenance, been also involved in the pathophysiology of neurodegenerative diseases. Here, we provide evidence that a novel C17-spiroepoxy steroid derivative, BNN27, specifically interacts with and activates the TrkA receptor of NGF, inducing phosphorylation of TrkA tyrosine residues and down-stream neuronal survival-related kinase signaling. Additionally, BNN27 potentiates the efficacy of low levels of NGF, by facilitating its binding to the TrkA receptors and differentially inducing fast return of internalized TrkA receptors into neuronal cell membranes. Furthermore, BNN27 synergizes with NGF in promoting axonal outgrowth, effectively rescues from apoptosis NGF-dependent and TrkA positive sympathetic and sensory neurons, in vitro, ex vivo and in vivo in NGF null mice. Interestingly, BNN27 does not possess the hyperalgesic properties of NGF. BNN27 represents a lead molecule for the development of neuroprotective TrkA receptor agonists, with potential therapeutic applications in neurodegenerative diseases and in brain trauma.

Adamantylidene-substituted alkylphosphocholine TCAN26 is more active against Sporothrix schenckii than miltefosine

Sporotrichosis is the most frequent subcutaneous mycosis in the world and its increasing incidence has led to the search for new therapeutic options for its treatment. In this study, we demonstrated that three structural analogues of miltefosine (TCAN26, TC19, and TC70) showed inhibitory activity against Sporothrix schenckii sensu stricto and that TCAN26 was more active in vitro than miltefosine against several isolates. Scanning electron microscopy showed that S. schenckii exposure to TCAN26 resulted in cells that were slightly more elongated than untreated cells. Transmission electron microscopy showed that TCAN26 treatment induced loss of the regular cytoplasmic electron-density and altered the cell envelope (disruption of the cell membrane and cell wall, and increased cell wall thickness). Additionally, TCAN26 concentrations required to kill S. schenckii cells were lower than concentrations that were cytotoxic in mammalian cells, and TCAN26 was more selective than miltefosine. Thus, the adamantylidene-substituted alkylphosphocholine TCAN26 is a promising molecule for the development of novel antifungal compounds, although further investigations are required to elucidate the mode of action of TCAN26 in S. schenckii cells.

Functional characterization and anti-cancer action of the clinical phase II cardiac Na+/K+ ATPase inhibitor istaroxime: in vitro and in vivo properties and cross talk with the membrane androgen receptor.

Sodium potassium pump (Na+/K+ ATPase) is a validated pharmacological target for the treatment of various cardiac conditions. Recent published data with Na+/K+ ATPase inhibitors suggest a potent anti-cancer action of these agents in multiple indications. In the present study, we focus on istaroxime, a Na+/K+ ATPase inhibitor that has shown favorable safety and efficacy properties in cardiac phase II clinical trials. Our experiments in 22 cancer cell lines and in prostate tumors in vivo proved the strong anti-cancer action of this compound. Istaroxime induced apoptosis, affected the key proliferative and apoptotic mediators c-Myc and caspase-3 and modified actin cystoskeleton dynamics and RhoA activity in prostate cancer cells. Interestingly, istaroxime was capable of binding to mAR, a membrane receptor mediating rapid, non-genomic actions of steroids in prostate and other cells. These results support a multi-level action of Na+/K+ ATPase inhibitors in cancer cells and collectively validate istaroxime as a strong re-purposing candidate for further cancer drug development.

Structural basis of multivalent galactose-based dendrimer recognition by human galectin-7.

Galectins are evolutionarily conserved and ubiquitously present animal lectins with a high affinity for ß-galactose-containing oligosaccharides. To date, 15 mammalian galectins have been identified. Their involvement in cell-cell and cell-matrix interactions has highlighted their importance in signal transduction and other intracellular processes. Human galectin-7 (hGal-7) is a 15 kDa proto type galectin that forms a dimer in solution and its involvement in the stimulation and development of tumour growth has been reported. Previously, we reported the crystal structure of hGal-7 and its complex with galactose and lactose which provided insight into its molecular recognition and detailed interactions. Here, we present newly obtained high-resolution structural data on carbohydrate-based dendrons in complex with hGal-7. Our crystallographic data reveal how multivalent ligands interact with and form cross-links with these galectin molecules. Understanding how these dendrimeric compounds interact with hGal-7 would help in the design of new tools to investigate the recognition of carbohydrates by lectins.

Design and synthesis of 21-alkynylaryl pregnenolone derivatives and evaluation of their anticancer activity.

A series of novel C21-alkynylaryl derivatives of pregnenolone were synthesized and screened for anticancer activity against a panel of seven human cancer cell lines (LNCaP, A549, MCF7, HeLa, A431, HepG2, HT29). The data revealed that these compounds can be potential antitumour agents against the specific cell models. Compound 6f bearing a 2-trifluoromethylphenyl group displayed improved cytotoxicity towards all cancer cell lines used. A431 cells were the most sensitive with derivatives 6e-6h bearing electron withdrawing substituents exhibiting high potency with IC50 values ranging between 2.18 and 0.54µM and drastic inhibition of the prosurvival PI3K-Akt/PKB pathway.

Na+/K+ ATPase inhibitors in cancer.

Sodium potassium pump (Na(+)/K(+) ATPase) is a transmembrane protein complex found in all higher eukaryotes acting as a key energy-consuming pump maintaining ionic and osmotic balance in cells. Recently recognized as an important transducer and/or integrator of various signals as well as a protein-protein interaction scaffold forming receptor complexes with signaling properties, the most prominent pharmacological role of Na(+)/K(+) ATPase inhibitors is the increase of myocardial contractility in pathologic conditions such as congestive heart failure. Consequently, modulators of Na(+)/K(+) ATPase such as digoxin have been approved by regulatory authorities and are widely used in the treatment of cardiac failure since 1975. Initiating from early observations of reduction of cancer incidence in cardiac patients taking digoxin, recent epidemiological and other studies have consolidated the anti-cancer potential of Na(+)/K(+) ATPase inhibitors in indications such as prostate, breast, lung cancer or leukemia. More importantly, a new series of pharmacologically optimized Na(+)/K(+) ATPase inhibitors has recently shown strong anti-cancer activities in multiple preclinical assays and have reached early clinical trials. Altogether, these results suggest that Na(+)/K(+) ATPase is an emerging cancer target that merits further investigation. In this review, we summarize key functional properties of the enzyme that are highly relevant for cancer cell selectivity, review the most prominent chemical classes of Na(+)/K(+) ATPase inhibitors and analyze their downstream effectors. Moreover, we discuss overall development prospects of these candidate drugs on their way to becoming new effective treatments of cancer in patients.

A steroidal Na+/K+ ATPase inhibitor triggers pro-apoptotic signaling and induces apoptosis in prostate and lung tumor cells.

Recently we have reported potent anti-cancer actions of various steroidal Na(+)/K(+) ATPase inhibitors in multiple cell lines. Furthermore, the most powerful compound identified in this study, the 3-[(R)-3-pyrrolidinyl]oxime derivative (3-R-POD), was highly effective in various tumor cell lines in vitro, and exhibited significant tumor growth inhibition in prostate and lung xenografts in vivo. In the present study we have addressed the molecular mechanisms implicated in the anti-cancer actions of 3-R-POD. We report here that 3-R-POD induces strong apoptotic responses in A549 lung- and in DU145 prostate- cancer cells. These effects are accompanied by significant upregulation of caspase-3 activity. Focussing on A549 cells, we further demonstrate late downregulation of BCL-2- and upregulation of c-Fos- gene transcription. In addition, the steroidal Na(+)/K(+) ATPase inhibitor induced late de-phosphorylation of Focal Adhesion Kinase (FAK) and activation of p38 MAPK. Our findings suggest that the steroidal Na(+)/K(+) ATPase inhibitor 3-R-POD induces apoptosis, paralleled by altered BCL-2 and c-Fos gene transcription, inhibition of the pro-survival FAK signalling, up-regulation of the pro-apoptotic p38 MAPK pathway and stimulation of caspase-3 activity.

Steroidal cardiac Na+/K+ ATPase inhibitors exhibit strong anti-cancer potential in vitro and in prostate and lung cancer xenografts in vivo.

Sodium potassium pump (Na(+)/K(+)ATPase) is a validated pharmacological target for the treatment of congestive heart failure. Recent data with inotropic drugs such as digoxin & digitoxin (digitalis) suggest a potent anti-cancer action of these drugs and promote Na(+)/K(+)ATPase as a novel therapeutic target in cancer. However, digitalis have narrow therapeutic indices, are pro-arrhythmic and are considered non-developable drugs by the pharmaceutical industry. On the contrary, a series of recently-developed steroidal inhibitors showed better pharmacological properties and clinical activities in cardiac patients. Their anti-cancer activity however, remained unknown. In this study, we synthesized seventeen steroidal cardiac inhibitors and explored for the first time their anti-cancer activity in vitro and in vivo. Our results indicate potent anti-cancer actions of steroidal cardiac inhibitors in multiple cell lines from different tumor panels including multi-drug resistant cells. Furthermore, the most potent compound identified in our studies, the 3-[(R)-3- pyrrolidinyl]oxime derivative 3, showed outstanding potencies (as measured by GI50, TGI and LC50 values) in most cells in vitro, was selectively cytotoxic in cancer versus normal cells showing a therapeutic index of 31.7 and exhibited significant tumor growth inhibition in prostate and lung xenografts in vivo. Collectively, our results suggest that previously described cardiac Na(+)/K(+)ATPase inhibitors have potent anti-cancer actions and may thus constitute strong re-purposing candidates for further cancer drug development.

Neurosteroids and microneurotrophins signal through NGF receptors to induce prosurvival signaling in neuronal cells.

The neurosteroid dehydroepiandrosterone (DHEA) exerts a portion of its neuroprotective effects by directly interacting with the nerve growth factor (NGF) receptors TrkA and p75(NTR) to induce prosurvival signaling. DHEA is an intermediate in the biosynthesis of estrogens and androgens that affects the endocrine system and potentially increases the risk for developing estrogen- and androgen-dependent tumors. We have synthesized 17-spiro analogs of DHEA that lack estrogenic or androgenic properties and bind to and activate NGF receptors, thus exerting potent neuroprotective effects without the tumor risk. These synthetic DHEA derivatives may serve as lead molecules to develop small agonists of NGF receptors that can penetrate the blood-brain barrier (microneurotrophins) with potential applications in the treatment of neurodegenerative diseases. The neuroprotective properties of microneurotrophins are now being tested in various animal models of neurodegenerative diseases.

Inhibition of PrP(Sc) formation in scrapie infected N2a cells by 5,7,8-trimethyl-3,4-dihydro-2H-1,4-benzoxazine derivatives.

Prion diseases are fatal, neurodegenerative diseases characterized by the structural conversion of the normal, cellular prion protein, PrP (C) into an abnormally structured, aggregated and partially protease-resistant isoform, termed PrP (Sc) . Although substantial research has been directed toward development of therapeutics targeting prions, there is still no curative treatment for the disease. Benzoxazines are bicyclic heterocyclic compounds possessing several pharmaceutically important properties, including neuroprotection and reactive oxygen species scavenging. In an effort to identify novel inhibitors of prion formation, several 5,7,8-trimethyl-1,4-benzoxazine derivatives were evaluated in vitro for their effectiveness on the expression levels of normal PrP (C) and its conversion to the abnormal isoforms of PrP (Sc) in a scrapie-infected cell culture model. The most potent compound was 2-(4-methoxyphenyl)-5,7,8-trimethyl-3,4-dihydro-2H-1,4-benzoxazine, with a diminishing effect on the formation of PrP (Sc) , thus establishing a class of compounds with a promising therapeutic use against prion diseases.

Neurosteroid dehydroepiandrosterone interacts with nerve growth factor (NGF) receptors, preventing neuronal apoptosis.

The neurosteroid dehydroepiandrosterone (DHEA), produced by neurons and glia, affects multiple processes in the brain, including neuronal survival and neurogenesis during development and in aging. We provide evidence that DHEA interacts with pro-survival TrkA and pro-death p75(NTR) membrane receptors of neurotrophin nerve growth factor (NGF), acting as a neurotrophic factor: (1) the anti-apoptotic effects of DHEA were reversed by siRNA against TrkA or by a specific TrkA inhibitor; (2) [(3)H]-DHEA binding assays showed that it bound to membranes isolated from HEK293 cells transfected with the cDNAs of TrkA and p75(NTR) receptors (K(D): 7.4 ± 1.75 nM and 5.6 ± 0.55 nM, respectively); (3) immobilized DHEA pulled down recombinant and naturally expressed TrkA and p75(NTR) receptors; (4) DHEA induced TrkA phosphorylation and NGF receptor-mediated signaling; Shc, Akt, and ERK1/2 kinases down-stream to TrkA receptors and TRAF6, RIP2, and RhoGDI interactors of p75(NTR) receptors; and (5) DHEA rescued from apoptosis TrkA receptor positive sensory neurons of dorsal root ganglia in NGF null embryos and compensated NGF in rescuing from apoptosis NGF receptor positive sympathetic neurons of embryonic superior cervical ganglia. Phylogenetic findings on the evolution of neurotrophins, their receptors, and CYP17, the enzyme responsible for DHEA biosynthesis, combined with our data support the hypothesis that DHEA served as a phylogenetically ancient neurotrophic factor.

Design and synthesis of new adamantyl-substituted antileishmanial ether phospholipids.

A series of new 2-[3-(2-alkyloxy-ethyl)-adamantan-1-yl]-ethoxy substituted ether phospholipids was synthesized and their antileishmanial activity was evaluated against Leishmania infantum amastigotes. The majority of the new analogues were significantly less cytotoxic than miltefosine while, antiparasitic activity depended on the length of the 2-alkyloxy substituent. The most potent compounds were {2-[[[3-(2-hexyloxy-ethyl)-adamant-1-yl]-ethoxy]hydroxyphosphinyloxy]ethyl}-Nu,Nu,Nu-trimethyl-ammonium inner salt (5b) and {2-[[[3-(2-octyloxy-ethyl)-adamant-1-yl]-ethoxy]hydroxyphosphinyloxy]ethyl}-Nu,Nu,Nu-trimethyl-ammonium inner salt (5c).

Novel dehydroepiandrosterone derivatives with antiapoptotic, neuroprotective activity.

DHEA analogues with modifications at positions C3 or C17 were synthesized and evaluated for neuroprotective activity against the neural-crest-derived PC12 cell model of serum deprivation-induced apoptosis. The most potent compounds were the spiro-epoxy derivatives 17beta-spiro[5-androstene-17,2'-oxiran]-3beta-ol (20), (20S)-3beta,21-dihydroxy-17beta,20-epoxy-5-pregnene (23), and (20R)-3beta,21-dihydroxy-17alpha,20-epoxy-5-pregnene (27) with IC(50) values of 0.19 +/- 0.01, 99.0 +/- 4.6, and 6.4 +/- 0.3 nM, respectively. Analogues 20, 23, and 27, up to the micromolar range of concentrations, were unable to activate estrogen receptor alpha and beta (ERalpha and ERbeta) or to interfere with ER-dependent gene expression significantly. In addition, they were unable to stimulate the growth of Ishikawa, MCF-7, and LNCaP cells. Our results suggest that the spiro-epoxyneurosteroid derivatives 20, 23, and 27 may prove to be lead molecules for the synthesis of novel neuroprotective agents.