Selenium as a chemoprotective anti-cancer agent: reality or wishful thinking?

It is generally accepted that selenium (Se) plays an important role in maintaining equilibrium of a healthy organism. It also participates in processes related to carcinogenesis such as inhibition of tumor formation and regression. Scientific data accumulated so far using experimental animal models and from clinical studies devoted to investigating the effects of Se confirm strong relationship or correlation between Se supplementation and tumor frequency of prostate, lungs, liver and colon. However, details of mechanisms of action of Se in modulation of carcinogenesis and cancer prevention are not yet fully elucidated. It is not clear yet whether Se deficiency itself is a cancer risk factor or whether it helps an already present cancer to progress. Additionally, the effects of other factors such as age, gender, life style, geographic location, comorbidities and use of drugs, are not clear. Despite the fact that some positive results were obtained with Se supplementation, it is necessary to verify these findings in more controlled experimental models including clinical studies. At the present time, data related to Se supplementation are not convincing enough as to allow general recommendation for using Se as an effective agent for chemoprevention of cancer. The goal of this minireview is to highlight present level of understanding of Se biological and prospects of its future clinical use. Information regarding Se, its effectiveness in various experimental models and in clinical tests, including combinations with other bioactive agents and anticancer drugs, is evaluated and summarized.

Ursolic acid: an anti-tumorigenic and chemopreventive activity. Minireview.

Ursolic acid, UA, as a pentacyclic triterpene is of interest to scientists in the area of oncology because of its cytotoxicity, induction of differentiation, anti-mutagenic, antiviral and anti-invasive activities. UA is capable of inducing apoptosis in tumor cells on one side and to prevent malignant transformation of normal cells on the other side. It also interferes with numerous enzymes, including the ones serving directly to DNA synthesis. The aim of this review is to summarize reports on UA biological properties and to show its main anti-tumor effects and chemopreventive properties in normal cells.

Potential carcinogenic and inhibitory activity of compounds isolated from Lilium candidum L.

This paper deals with determination of potential carcinogenic and inhibitory activity of 10 compounds isolated from the ethanolic extract of Lilium candidum L. perfonned by DC polarography. The series of investigated compounds consisted of two spirostanol saponins, two pyroline derivatives, jatropham and its glucoside, flavonol kaempferol, 2-fenylethyl-alpha-L-arabinopyranosyl-(1-->6)-beta-D-glucopyranoside, 2-phenylethylpalmitate and methylsuccinic acid. Carcinogenic, resp. mutagenic activity data for these compounds, with the exception of kaempferol, are not available in scientific literature. All tested compounds were reduced in N,N-dimethylformamide in one or two well defined steps. They also fonned a reversible complex with alpha-lipoic acid, a compound serving as an indicator of carcinogenic activity. The marginal diffuse current values of these complexes served as a criterion of a very low potential carcinogenicity. The inhibitory activity of isolates were studied in the presence of 12-O-tetradecanoylphorbol-13-acetate, a specific tumor promoter for an epidermal carcinogenesis, and in the presence of a polyaromatic substance 7,12-dimetylbenz(a)anthracene known as a carcinogen. The spirostanol saponins possessed the highest inhibitory activity (> 70%) and jatropham (66%). The inhibitory activity of jatropham glucoside was significantly lower (49%). Practically zero inhibitory activity was measured for the 2-phenylethylpalmitate and methylsuccinic acid.

Evaluation of potential carcinogenicity of steroidal alkaloids from Veratrum album L. by the DC polarography method.

The presented work is devoted to the study of polarographic reduction in the series of 13 alkaloids isolated from various parts of Veratrum album subsp. lobelianum. The used compounds were evaluated from the point of view of their potential carcinogenicity in anhydrous N,N-dimethylformamide (DMF) by the method of DC polarography. All compounds were reduced during an one two-electron irreversible step. Their potential carcinogenicity characterized by a parameter tg alpha value determined in the presence of alpha-lipoic acid ranged from the highest value 0.257 obtained for the solanidane skeleton containing rubijervine to the value 0.070 for jervine. The tg alpha value determined for rubijervine (0.257) is comparable with the tg alpha of naphto-(2',1',2,3)fluoranthene (0.270)-compound classified by IARC as possible carcinogen for human. The tg alpha values determined for other alkaloids were relatively low and they do not indicate any possible carcinogenic activity.

Potential carcinogenicity of homoisoflavanoids and flavonoids from Resina sanguinis draconis (Dracaena cinnabari Balf.).

Polarographic behavior of three homoisoflavanoids and four flavanoids isolated from the dragon's blood (Resina sanguinis draconis. Dracaena cinnabari Balf.), collected at Sokotra, was investigated in aprotic solution and an index of potential carcinogenicity tg alpha was determined. Generally, homoisoflavanoids and flavanoids were reduced in two two-electron steps, the first being reversible and the second one irreversible. The parameter tg alpha values indicated that the majority of these compounds possesses no or only marginal potential carcinogenic activity. However, it was demonstrated that some structural modifications in basic flavonoid structure lead to changed electrochemical properties and a substantial increase of derivative potential carcinogenicity.

Treatment of leukemia L1210 and P388 by arabinosylcytosine-polysaccharide conjugates.

Conjugates of 1-beta-D-arabinofuranosylcytosine (araC) with two polysaccharides such as polygalacturonic acid (PGA) and carboxymethylated yeast beta-D-glucan (CMG) were tested for their antileukemic activity in vitro on a L1210 cell line in suspension culture, in soft agar assay and in vivo on L1210, L1210/araC- and P388-leukemia-bearing mice. Both conjugates showed high activity in vitro in soft agar assay, compared with araC. Single administration of PGA-araC or CMG-araC increased the survival time 1.5 x or 1.7 x, respectively, compared with araC in vivo in L1210-leukemia-bearing mice. The conjugates were not active against araC-resistant leukemia line L1210/araC. The marked effect of both PGA-araC and CMG-araC against leukemia L1210 and P388 is probably due to the prolonged release of free araC from conjugates caused by hydrolysis.

Preparation, properties and antileukemic activity of arabinosylcytosine polysaccharide conjugates.

1. Conjugates of 1-beta-D-arabinofuranosylcytosine (araC) with polysaccharides containing carboxyl groups, such as polygalacturonic acid (PGA) and carboxymethylated yeast beta-D-glucan (CMG) were prepared. 2. Activation of the polysaccharidic carboxyl group by isobutylchloroformiate and formation of a peptide bond via 4-NH2 group of araC was used for a coupling reaction. 3. Elementary analysis, u.v. and i.r. spectra confirmed the structures of the conjugates. 4. The conjugates were most stable against the hydrolysis under the mild acid conditions. 5. It was also shown that under the physiological conditions trypsin catalyze the conjugate hydrolysis and the catalytic effect is higher than that of chymotrypsine. 6. It is suggested that trypsin or trypsin-like proteases could participate in the hydrolysis of the conjugates in vivo. PGA-araC and CMG-araC showed 1.5- or 2.5-times higher antileukemic activity than both free araC or polysaccharides.

Alkaloids from Roots of Strempeliopsis strempelioides - Structures of Strempeliopine and Strempeliopidine1.

From the roots of STREMPELIOPSIS STREMPELIOIDES K. Schum. (Apocynaceae), the following alkaloids were isolated: (+)-pleiocarpamine, (-)-aspidospermine, (+)-eburnamonine, (+)-tubotaiwine, (+)-haplocidine, (-)-vallesamidine, (+)-tubotaiwine N-oxide, (-)-strempeliopine ( 1A) and a bisindolic base (+)-strempeliopidine ( 2). Another bisindole alkaloid of composition C (38)H (46)N (4) was isolated in minute quantity. The structures were established on the basis of spectral and chemical evidence.