Anticancer and antiproliferative activity of natural brassinosteroids.

Brassinosteroids (BRs) are steroid plant hormones that are essential for many plant growth and developmental processes, including cell expansion, vascular differentiation and stress responses. Up to now the inhibitory effects of BRs on cell division of mammalian cells are unknown. To determine basic anticancer structure-activity relationships of natural BRs on human cells, several normal and cancer cell lines have been used. Several of the tested BRs were found to have high cytotoxic activity. Therefore, in our next series of experiments, we tested the effects of the most promising and readily available BR analogues with interesting anticancer properties, 28-homocastasterone (1) and 24-epibrassinolide (2), on the viability, proliferation, and cycling of hormone-sensitive/insensitive (MCF-7/MDA-MB-468) breast and (LNCaP/DU-145) prostate cancer cell lines to determine whether the discovered cytotoxic activity of BRs could be, at least partially, related to brassinosteroid-nuclear receptor interactions. Both BRs inhibited cell growth in a dose-dependent manner in the cancer cell lines. Flow cytometry analysis showed that BR treatment arrested MCF-7, MDA-MB-468 and LNCaP cells in G(1) phase of the cell cycle and induced apoptosis in MDA-MB-468, LNCaP, and slightly in the DU-145 cells. Our results provide the first evidence that natural BRs can inhibit the growth, at micromolar concentrations, of several human cancer cell lines without affecting the growth of normal cells. Therefore, these plant hormones are promising leads for potential anticancer drugs.

Platinum(II) complexes with steroidal esters of L-methionine and L-histidine: synthesis, characterization and cytotoxic activity.

Twelve steroidal platinum(II) complexes were synthesized by reaction of potassium tetrachloroplatinate with steroidal esters of L-methionine and L-histidine. The steroidal esters coordinated as bidentate ligands via S and N donor atoms of L-methionine and via two N donor atoms of L-histidine. Cholesterol, cholestanol, diosgenine, pregnenolone, dehydroepiandrosterone, testosterone, estrone, and estradiol were used as the steroidal compounds. The esters and complexes prepared were characterized by infrared, mass, and (1)H NMR spectroscopy and elemental analysis. Platinum complexes were tested for in vitro cytotoxicity against several cancer cell lines: T-lymphoblastic leukemia CEM, breast carcinoma MCF-7, lung carcinoma A-549, multiple myeloma RPMI 8226, and one normal cell line human fibroblast BJ.

Synthesis of lupane-type saponins bearing mannosyl and 3,6-branched trimannosyl residues and their evaluation as anticancer agents.

The saponins modified with mono- or trimannosyl residues can provide a convenient means of delivering drugs to certain human cells via interactions with mannose receptors. In the study reported therein, we developed a convenient approach for the synthesis of 3-O-mannoside and branched trimannoside derivatives of the saponin lupeol and of C-28 acyl esters of 3-O-acetyl-betulinic acid bearing the same mannosyl entities. Lupeol and 3-O-acetyl-betulinic acid were mannosylated with tetra-O-benzoyl- or tetra-O-acetyl-alpha-D-mannopyranosyl trichloroacetimidates. De-esterification followed by regioselective dimannosylation of the unprotected monosaccharide derivatives with 2equiv of tetra-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate selectively yielded O-3,O-6-linked trimannosides. The cytotoxic activity of selected lupane-type saponins (derivatives of lupeol, betulinic acid, and betulin) toward normal human fibroblasts and various cancer cell lines was also compared.

New analogues of the potent cytotoxic saponin OSW-1.

Saponin OSW-1 (5e-G2; 3 beta,16 beta,17 alpha-trihydroxycholest-5-en-22-one 16-O-{O-[2-O-(4-methoxybenzoyl)-beta-D-xylopyranosyl]-(1-->3)-2-O-acetyl-alpha-arabinopyranoside}) analogues: with modified side chain (5a/d-G2), 22-deoxo-23,24,25,26,27-pentanor- (14), 22-deoxo-23-oxa- (17), glycosylated with various monosaccharides (5e-G4/G6/G8), and OSW-1 structural isomer (10) were obtained. The analogues were synthesized using a previously published method for the synthesis of OSW-1. The structures of analogues were fully confirmed by spectroscopic methods, and the S-chirality at C-22 of the structural isomer was established by conformational analysis combined with the NMR spectrometry. The cytotoxicity of the analogues toward several types of malignant tumor cells was examined and compared with that of OSW-1. The results suggest that modification of the steroidal aglycone may lead to compounds with high cytotoxicity.

Batch immunoextraction method for efficient purification of aromatic cytokinins.

A range of benzylaminopurines naturally occur in plants and exhibit high biological activity. Others have been synthesized, such as 6-(2-hydroxy-3-methoxybenzylamino)purine riboside (2OH3MeOBAPR), which has shown interesting anti-cancer activity under in vitro conditions. In order to study the biological activity of this interesting compound in more detail, a rapid and highly efficient method for its purification from complex samples (e.g. blood and plant extracts) is needed. Therefore, we prepared monoclonal antibodies against 2OH3MeOBAPR. The antibody had undetectable cross-reactivity with all natural isoprenoid cytokinins, but relatively high cross-reactivity with aromatic cytokinins as well as some synthetic di- and tri-substituted 6-benzylaminopurines and the corresponding ribosides. The antibody also showed strong responses and specificity in enzyme-linked immunoassays (ELISAs). In addition, it was used to prepare, for the first time, an immunoaffinity sorbent with high specificity and capacity for aromatic cytokinins. A batch immunoextraction method was then developed and optimized for the purification of 2OH3MeOBAPR from murine blood samples. The high efficacy and simplicity of this method (in off-line combination with HPLC-MS) for the isolation of target analytes from biological material is demonstrated in this study.

Syntheses of new androstane brassinosteroids with 17beta-ester groups--butyrates, heptafluorobutyrates, and laurates.

New androstane brassinosteroids with 17beta-ester groups - butyrates, heptafluorobutyrates, and laurates (4-18) - were prepared. Brassinolide activity was evaluated using both the bean second internode bioassay and the rice lamina inclination test. Brassinosteroid 16 was found to be the most active by the bean second internode bioassay. This activity in the bean second internode bioassay corresponded with the field yield, while the RLIT bioassay does not.

Brassinosteroids: synthesis and activity of some fluoro analogues.

Three types of 5alpha-androstane and ergostane analogues of brassinolide, containing a fluorine atom in either the 3alpha or the 5alpha positions or in 3alpha and 5alpha positions, were prepared using standard operations (reaction of 3beta-alcohols with (diethylamino)sulfur trifluoride, cleavage of epoxide with HF in py or BF 3.Et 2O). The 5alpha-fluorine was found to affect chemical reactivity (e.g., electrophilic addition to the Delta (2)-double bond) as well as physical properties (e.g., NMR, chromatographic behavior) of the products. Cytotoxicity of the products was studied using human normal and cancer cell lines with 28-homocastasterone as positive control and their brassinolide type activity was established using the bean second-internode test with 24-epibrassinolide as standard. The equivalence of F and OH groups was observed in some of the active compounds. The anticancer and the brassinolide-type activity do not correlate with each other: ergostane derivatives were most active in the former test while androstane derivatives were best in the latter.