Synthesis of new steroidal isoxazoles: inhibitors of estrogen synthase

5-Amino-3-methyl-4-isoxazolecarboxylic acid hydrazide derivatives with in vitro immunomodulatory activities

Isoxazoles are an important class of compounds of potential therapeutic value. The aim of this study was to determine immunotropic effects of 5-amino-3-methyl-4-isoxazolecarboxylic acid hydrazide derivatives on spontaneous and mitogen-induced lymphocyte proliferation in young and old mice, cytokine production by peritoneal cells as well as possible mechanism of action in a model of Jurkat cells. Three-month-old and 13-month-old BALB/c mice were used as donors of the cells from a thymus, a spleen, mesenteric lymph nodes, and a peritoneal cavity. Spontaneous and concanavalin A or lipopolysaccharide (LPS)-induced cell proliferation was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric method. IL-1β and TNF-α production induced by LPS in macrophage-enriched peritoneal cell cultures was measured by enzyme-linked immunoassay. 5-amino-3-methyl-4-isoxazolecarboxylic acid hydrazide, 01K (4-phenyl-1-(5-amino-3-methylisoxazole-4-carbonyl)-thiosemicarbazide), and 06K (4-(4-chlorophenyl)-1-(5-amino-3-methylisoxazole-4-carbonyl)-thiosemicarbazide) exhibited regulatory activity in the proliferation tests. Prevailing stimulatory activity of the hydrazide and inhibitory activity of 01K and 06K was observed. Those effects were connected with different influence of the compounds on signaling proteins expression in Jurkat cells. The regulatory effects of the compounds on IL-1β production were more profound than those on TNF-α. Differences in the compound activity in young versus old mice were mainly restricted to 01K. Immunosuppressive isoxazole leflunomide and a stimulatory RM-11 (1,7-dimethyl-8-oxo-1,2H-isoxazole [5,4-e]triazepine) were applied as reference drugs.

Immunoregulatory effects of 4-(4-chlorophenyl)-1-(5-amino-3-methylisoxazole-4-carbonyl)-thiosemicarbazide (06K) in non-immunized and SRBC-immunized mice

OBJECTIVES

Immunoregulatory properties of 06K derivative (4-(4-chlorophenyl)-1-(5-amino-3-methylisoxazole-4-carbonyl)-thiosemicarbazide) in mouse in vivo models were investigated.

METHODS

Several in vivo models were used: humoral and cellular immune response, carrageenan inflammatory reaction and determination of lymphocyte subsets in non-immunized mice.

KEY FINDINGS

The compound administered before or after immunization with sheep erythrocytes (sheep red blood cell (SRBC)) elevated the number of plaque-forming cells (PFC), and this effect was stronger at lower doses. Although total haemagglutinin titres to SRBC decreased upon postimmunization treatment, IgG titre increased. In the model of delayed-type hypersensitivity (DTH) to ovalbumin (OVA), the compound, applied intraperitoneally before an eliciting dose of an antigen but not before immunization, inhibited the magnitude of a cutaneous reaction. Further, 06K significantly diminished carrageenan-induced foot pad inflammation when administered 1 h before carrageenan. The compound, administered intraperitoneally to naïve mice, elicited changes in weight, cell number in lymphoid organs and content of lymphocyte subsets, depending on the dose and number of applications. Phenotypic changes included increased turnover of thymocytes, changes in B-cell distribution in spleens and lymph nodes, increased percentage of CD8⁺ cells and regulatory CD4⁺ CD25⁺ Foxp3⁺ T cells.

CONCLUSIONS

Immunoregulatory properties of 06K involve mobilization of lymphopoiesis and generation of regulatory T cells.

The effect of 5-amino-3-methyl-4-isoxazolecarboxylic acid hydrazide on lymphocyte subsets and humoral immune response in SRBC-immunized mice

5-Amino-3-methyl-4-isoxazolecarboxylic acid hydrazide is a non-cytotoxic synthetic isoxazole derivative with considerable immunomodulatory properties demonstrated in in vitro experiments. The aim of this study was to investigate the influence of this compound, depending on the dosage and schedule of treatment, on lymphocyte subsets in non-immunized mice and humoral immune response in SRBC (sheep red blood cells)-immunized mice. An analysis of lymphocyte subsets was carried out by flow cytometry, using specific monoclonal antibodies stained with fluorescein isothiocyanate (FITC) or phycoerythrin (PE). In the SRBC-immunized mice, the influence of the compound on the humoral response was determined, depending on the time of administration relative to the antigen. The number of plaque forming cells (PFC) was determined by a local hemolysis technique in an agar gel. Total and 2-mercaptoethanol resistant serum agglutination titers were defined by active hemagglutination test carried out on microplates. The investigated hydrazide was able to modulate the percentage and absolute number of T lymphocyte subsets in the thymus, and T and B lymphocytes in the peripheral lymphatic organs. It also enhanced humoral immune response in SRBC-immunized mice by increasing the number of cells producing hemolytic anti-SRBC antibodies (PFC) and by augmenting the level of total and 2-mercaptoethanol resistant hemagglutinin. The present study showed modulatory effects of 5-amino-3-methyl-4-isoxazolecarboxylic acid hydrazide on lymphocyte subsets and humoral immune response in mice. This compound could be potentially useful for the treatment of autoimmune diseases, infections or as an adjuvant for boosting the efficacy of vaccines.

N,N'-Bis(3β-acet-oxy-5α-cholest-6-yl-idene)hydrazine

The asymmetric unit of the title compound, C₅₈H₉₆N₂O₄, contains two crystallographically independent mol­ecules. All cyclohexane rings are in chair conformations, while the furan ring is in an envelope conformation in one mol­ecule and a twist conformation in the other. Two acetaldehyde and one isobutane groups are disordered over two orientations with refined site occupancies of 0.940 (4):0.060 (4) and 0.791 (7):0.209 (7), respectively. In the crystal, mol­ecules are stacked along the a axis through van der Waals inter­actions.

Synthesis and antitumor activity of new D-seco and D-homo androstane derivatives

Starting from 3beta-hydroxy-17-oxo-16,17-secoandrost-5-ene-16-nitrile (1), the new 16,17-secoandrostane derivatives 4-9 were synthesized. On the other hand, 3beta-hydroxy-17-oxa-D-homoandrost-5-ene-16-one (10) yielded the new d-homo derivatives 12, 13 and 15. In vitro antiproliferative activity of selected compounds against three tumor cell lines (human breast adenocarcinoma ER+, MCF-7, human breast adenocarcinoma ER-, MDA-MB-231, prostate cancer AR-, PC-3, and normal fetal lung fibroblasts, MRC-5) was evaluated. Compounds 3 and 12 showed strong antiproliferative activity against PC-3 cells, the IC(50) values being 2 microM and 0.55 microM, respectively. Compounds 6 (10 microM) and 14 (9 microM) showed moderate activity against MDA-MB-231 cells. The synthesized compounds 1-3, 5-8, 10 and 12-15 were not toxic to normal fetal lung fibroblasts cells, MRC-5.

Synthesis of New Pyrazole and Pyrimidine Steroidal Derivatives

The synthesis of steroidal heterocycles containing the pyrazole and pyrimidine ring fused to the 16,17-position of the steroid nucleus is reported. Androstenolone acetate (1) reacted with carbon disulfide, iodomethane and sodium hydride to furnish 3β-acetoxy-16-[bis(methylthio)methylene]-5-androst-5-en-17-one (2). The reactions of 2 with hydrazine hydrate and methylhydrazine afforded the 5’-methylthio- pyrazolo[4’,3’:16,17]androst-5-en-3β-ols 3a and 3b, respectively. Treatment of 2 with amidinium, guanidinium, and isothiuronium salts in the presence of sodium methoxide yielded the 6’-methoxy- pyrimido[5’,4’:16,17]androst-5-en-3β-ols (4a-4e).

Aromatase inhibitors: past, present and future

For the cellular physiology of sex steroid sensitive cells, the androgen/estrogen ratio may be more important than only one hormone action per se, in both sexes. This ratio is controlled in vertebrates by aromatase; its gene expression can be inhibited in different ways, and this is crucial for the treatment of estrogen-dependent diseases such as breast cancer, or gynecomastia in males for instance. To reach this goal, new steroidal and non-steroidal inhibitors are continuously being developed, and some of them are used as first or second line agents. Aromatase inhibition is also an essential tool for studying the role of estrogens in the adult, or during development. Aromatase inhibitors have shown in particular that estrogens are essential also in males for skeletal maturation and bone mineralization, development of masculine dendritic morphology in male brain linked to mating behaviour, and testicular function. Testosterone is often the prohormone converted in situ in active estrogens, at these levels. Several strategies can be used for aromatase inhibition. The first ones employed were blind screening or deductions from in vivo observations, which led for instance to the discovery of the role of aminoglutethimide in aromatase inhibition. Subsequently, in the years 1975-1990, the molecular modeling of compounds to mimic the substrate shape of the enzyme constituted the major idea. Hundreds of chemicals were synthesized by numerous authors, ranging from the well-known and very efficient 4-OHA to complicated imidazole or indane derivatives tested by sophisticated comparative molecular field analyses. Reticulum-bound active aromatase has not as yet been X-ray analyzed. Thus, aromatase inhibitors were also used more recently to probe and understand the active site conformation of the enzyme and its modelization was obtained from comparisons with bacterial-related cytochromes. We developed a mammalian model considerably closer to human aromatase in order to study the active site shape with new potent aromatase non-steroidal inhibitors. This model is equine aromatase. This enzyme was biochemically characterized, purified, and cloned by our group. It allowed testing, by site-directed mutagenesis, predictive hypotheses in human aromatase which contributed to designing of new inhibitors. The understanding of the functioning of an essential member of the cytochrome P450 family, which is necessary for cellular detoxification, was also facilitated. Inhibition of aromatase activity has also been carried out with antibodies directed to the catalytic site and at the gene level by knock-out or by control of factor-specific promoters. This may result in different mRNA synthesized by alternative splicing. We have also obtained specific inhibition of aromatase activity in human cells with antisense stable phosphorothioate oligodeoxynucleotides directed against aromatase mRNA tertiary structures. Besides known steroidal and non-steroidal inhibitors, the antiaromatase effects of compounds found in our daily environment such as dietary flavonoids or xenobiotic pollutants have also been described. Finally, we underline that all these aromatase inhibitors, or methods of aromatase inhibition, can modulate the estrogenic balance essential not only for female, but also for male physiology, including gonadal function.

Design and synthesis of new steroidal inhibitors of estrogen synthase (aromatase)

The estrogen synthase (aromatase) enzyme system is responsible for the biosynthesis of estrogen hormones in human females. Estrogens are vital for normal growth and development, but will promote the growth of certain breast cancers. Approximately 30-50% of breast cancers are considered to be hormone-dependent. Consequently regulation of estrogen biosynthesis has advanced as a potential therapeutic strategy. This has led to the development of active-site inhibitors, which may have potential for the control of breast cancer. We have recently prepared a number of new steroidal inhibitors that have been evaluated as aromatase inhibitors. These include steroidal A/B-ring isoxazoles and a series of A/B-ring pyrazoles with alkyl- and aryl-substituted nitrogen. In addition, we have developed new chemical procedures for the synthesis of 6beta-hydroxy steroids, which could be key intermediates in the preparation of C-19 inhibitors of aromatase activity.