Dissecting progressive stages of 5-fluorouracil resistance in vitro using RNA expression profiling

Resistance to anticancer drugs such as the widely used antimetabolite 5-fluorouracil (FU) is one of the most important obstacles to cancer chemotherapy. Using GeneChip arrays, we compared the expression profile of different stages of FU resistance in colon cancer cells after in vitro selection of low-, intermediate- and high-resistance phenotypes. Drug resistance was associated with significant changes in expression of 330 genes, mainly during early or intermediate stage. Functional annotation revealed a majority of genes involved in signal transduction, cell adhesion and cytoskeleton with subsequent alterations in apoptotic response, cell cycle control, drug transport, fluoropyrimidine metabolism and DNA repair. A set of 33 genes distinguished all resistant subclones from sensitive progenitor cells. In the early stage, downregulation of collagens and keratins, together with upregulation of profilin 2 and ICAM-2, suggested cytoskeletal changes and cell adhesion remodeling. Interestingly, 6 members of the S100 calcium-binding protein family were suppressed. Acquisition of the intermediate-resistance phenotype included upregulation of the well-known drug resistance gene ABCC6 (ATP-binding cassette subfamily C member 6). The very small number of genes affected during transition to high resistance included the primary FU target thymidylate synthase. Although limited to an in vitro model, our data suggest that resistance to FU cannot be explained by known mechanisms alone and substantially involves a wide molecular repertoire. This study emphasizes the understanding of resistance as a time-depending process: the cell is particularly challenged at the beginning of this process, while acquisition of the high-resistance phenotype seems to be less demanding.

Accessing single nucleotide polymorphisms in genomic DNA by direct multiplex polymerase chain reaction amplification on oligonucleotide microarrays

This study introduces a DNA microarray-based genotyping system for accessing single nucleotide polymorphisms (SNPs) directly from a genomic DNA sample. The described one-step approach combines multiplex amplification and allele-specific solid-phase PCR into an on-chip reaction platform. The multiplex amplification of genomic DNA and the genotyping reaction are both performed directly on the microarray in a single reaction. Oligonucleotides that interrogate single nucleotide positions within multiple genomic regions of interest are covalently tethered to a glass chip, allowing quick analysis of reaction products by fluorescence scanning. Due to a fourfold SNP detection approach employing simultaneous probing of sense and antisense strand information, genotypes can be automatically assigned and validated using a simple computer algorithm. We used the described procedure for parallel genotyping of 10 different polymorphisms in a single reaction and successfully analyzed more than 100 human DNA samples. More than 99% of genotype data were in agreement with data obtained in control experiments with allele-specific oligonucleotide hybridization and capillary sequencing. Our results suggest that this approach might constitute a powerful tool for the analysis of genetic variation.

Transcriptional activities of estrogen receptor alpha and beta in yeast properties of raloxifene

Raloxifene represents a potent compound for the prevention and treatment of osteoporosis and cardiovascular disease in postmenopausal women. Raloxifene exhibits targeted antiestrogenicity in breast and uterus, but acts as an agonist in bone and liver. This synthetic selective estrogen receptor modulator binds both estrogen receptors alpha and beta. The molecular mechanisms by which raloxifene exerts agonistic or antagonistic activity are still not resolved. Therefore, the binding behavior of raloxifene to estrogen receptors and its effects on DNA binding and transactivation were studied. The equilibrium binding affinity of raloxifene by displacing radiolabeled 17beta-estradiol exhibited a similar affinity behavior to that of its natural ligand. Using BIACORE technology with an immobilized estrogen response element, we showed that 17beta-estradiol and raloxifene increased the binding of estrogen receptor alpha to the DNA, suggesting a ligand-dependent dimerization. The influence of the ligands to the binding of estrogen receptor beta was lower. We may conclude that unliganded estrogen receptor alpha binds as a monomer whereas in the presence of 10(-8) M 17beta-estradiol or higher, homodimers are formed that interact with the estrogen response element. Transactivation studies in a yeast reporter system in a ligand-dependent manner resulted in a similar potency of raloxifene to estrogen receptor beta compared to the control testosterone. Subeffective doses of raloxifene combined with 17beta-estradiol did not shift the efficiency, whereas saturating concentrations of 17beta-estradiol combined with increasing concentrations of raloxifene altered the response induced by 17beta-estradiol. In this pure system, the antagonistic activity of raloxifene could not be detected as was expected by the results from ligand competition analysis.

Estrogenic activity of two standardized red clover extracts (Menoflavon) intended for large scale use in hormone replacement therapy

Isoflavones are the most potent estrogenic compounds in red clover extracts. Standardized extracts have been discussed as an alternative for hormone replacement therapy. Variation due to extraction procedure and natural seasonal variation and variations originating from agricultural conditions have prevented the large scale use of such phytochemicals. An improved extraction procedure and careful analysis of the raw material yielded in a highly standardized preparation (Menoflavon) with an average isoflavone content of approximately 9% (dry weight) determined by HPLC. The estrogenic activity has been further evaluated by a yeast two plasmid system using estrogen receptor alpha (ER alpha) and estrogen receptor beta (ER beta). An estrogenic activity corresponding to a transactivational capacity of ca. 18 microg 17 beta-estradiol per g red clover extract for ER alpha and ca. 78 microg 17 beta-estradiol per g red clover for ER beta was obtained. The difference is explained by the higher affinity of ER beta to isoflavones than that observed for ER alpha. Calculation of potency from isoflavone content measured by HPLC yielded a comparable potency to that experimentally determined by the bioassay. The high content of isoflavones as well as the higher transactivational potency for ER beta than ER alpha make these extracts interesting candidates for HRT.

Determination of estrogenic activity in beer by biological and chemical means

It has been suspected that beer drinking may change the hormonal status of men caused by phytoestrogens. Five different Austrian lager beers have been investigated for estrogenic activity by a yeast two-plasmid system harboring the human estrogen receptor alpha, after concentration by solid phase extraction. The beer concentrate was further fractionated by reversed phase HPLC, and then the fractions were characterized by the biological assay and GC-MS. The most potent fraction did not contain a known phytoestrogen. The total activity corresponded to an average of 43 ng of 17beta-estradiol/L of beer. It was concluded that the human health hazard of beer drinking originating from compounds activity on the estrogen receptor alpha is negligible.